Jérôme Feige

Nestlé Institute of Health Sciences – Nestlé Research (Lausanne, Switzerland)

School of Life Sciences, Ecole Polytechnique (Lausanne, Switzerland)

Targeting Muscle Stem Cells during Aging: from Mechanisms to the Doscovery & clinical Validation of Nutritional Activators

Invité par Rémi Mounier et Julien Gondin

Abstract
The regenerative capacity of skeletal muscle relies on the activity of Muscle Stem Cells (MuSCs), a population of resident stem cells that enables myofiber repair following intense exercise or injuries, and contributes to tissue homeostasis and turnover. Aging and muscle diseases impair MuSC function, leading to altered regenerative capacity and progressive loss of skeletal muscle mass and strength.
In a first project, we generated a novel StemRep dual color Pax7 and Myf5 in vivo reporter mouse model to investigate MuSC heterogeneity. High levels of Pax7 protein and low levels of Myf5 delineate a deeply quiescent MuSC subpopulation with higher asymmetric division and distinct dynamics of activation, proliferation, and commitment. Aging primarily reduces the Myf5Low MuSCs and skews the stem cell pool towards Myf5High cells with lower quiescence and self-renewal capacity. Altogether, we establish the StemRep model as a versatile tool to study MuSC heterogeneity and broaden our understanding of the function of Myf5 in regulating MuSC quiescence and self-renewal in homeostatic, regenerating, and aged muscles.
In a second project, we used a high-content imaging screen of natural molecules to identify nicotinamide (NAM) and pyridoxine (PN) as potent bioactive nutrients from vitamin B metabolism that synergistically stimulate MuSC activity, while having a history of safe human use. In human clinical cohorts or preclinical models, endogenous levels of NAM and bioactive PN decline during aging and inter-independently associate with muscle mass and walking speed. Oral treatment with a combination of NAM/PN accelerates muscle repair in vivo by stimulating MuSCs and enhances recovery of muscle strength. In a human randomized placebo-controlled clinical trial using eccentric contraction-induced muscle regeneration in healthy volunteers, oral NAM/PN supplementation was well tolerated and stimulated the myogenic activity of MuSCs detected via increased number of MyoD and Myogenin positive cells in muscle biopsies during recovery. Collectively, our results establish NAM/PN as a promising nutritional intervention that stimulates MuSCs, enhances muscle repair, and alleviates muscle decline during aging, and opens new opportunities to enhance muscle recovery and manage regenerative capacity in muscle disorders through nutrition.

Trigonelline is an NAD+ precursor that improves muscle function during aging and is reduced in human sarcopenia. Membrez, Migliavacca , Christen,… JT Treebak,… Koopman, Lynch G, Sorrentino V and Feige JN. Nature Metabolism, 2024, Mar 6(3):433-447.

Apelin stimulation of the vascular skeletal muscle stem cell niche enhances endogenous repair in dystrophic mice. Le Moal E, Liu Y, Collerette-Tremblay, , …, Feige JN, Auger-Messier M, Dumont NA, Bentzinger CF. Science Transl Med., 2024 Mar 20;16(739)

The mitochondrial calcium uniporter (MCU) promotes muscle energy metabolism and mobility by regulating mitochondrial redox state. Weiser A, Hermant A, …, Sorrentino V, Feige JN & De Marchi U. Redox Biology, 2023, 64:102759

Evidence for inefficient contraction and abnormal mitochondrial activity in sarcopenia using magnetic resonance spectroscopy. Stephenson MC, Ho, …, Feige JN, Merchant RA, Tay SKH. J Cachexia Sarcopenia Muscle. 2023, 14(3):1482-1494

An Engineered Multicellular Stem Cell Niche for the 3D Derivation of Human Myogenic Progenitors from iPSCs. Mashinchian O, De Franceschi F,… G, Dumont NA, Lutolf MP, Feige JN*, Bentzinger CF* EMBO J, 2022, 41(14):e110655. *: co-senior author

Mitochondrial oxidative capacity and NAD+ biosynthesis are reduced in human sarcopenia across ethnicities. Migliavacca, E., Tay, S.K.H., Patel, H.P., …Karnani, N., Feige, JN. Nature Communications, 2019, 10(1), 5808

Aging Disrupts Muscle Stem Cell Function by Impairing Matricellular WISP1 Signals Secretion from Fibro-Adipogenic Progenitors. Lukjanenko L, Karaz S, Stuelsatz P, …, Rudnicki MA, Bentzinger CF, Feige JN. Cell Stem Cell, 2019, S1934-5909(18)30604-0.

The exerkine apelin reverses age-associated sarcopenia. Vinel C, Lukjanenko L,…, Feige JN, Vellas, Valet P, Dray C. Nature Medicine 2018, 24(9):1360-1371.

Loss of Fibronectin from the Aged Stem Cell Niche Affects the Regenerative Capacity of Skeletal Muscle in Mice. Lukjanenko L, Jung MJ, Hegde N, … , von Maltzahn J, Feige JN*, Bentzinger CF*. Nature Medicine 2016, 22(8):897-905. *: co-senior author

Pr Emeritus Stefan Dimitrov

Institute of molecular biology (Sofia, Bulgaria)

Institut of Advanced Biosciences (Grenoble Alpes University, France)

Epigenetics Meets Immunity and Inflammation

Invité par Laurent Schaeffer et Edwige Belotti

Abstract
The function of chromatin is largely dependent of its underlying structure. Linker histone H1 is a key player in both nucleosome and chromatin fiber 3D organization. Yet, how does H1 achieve this was the major challenge that has defied the epigenetic community for decades. Here, I will initially describe at higher resolution the conformational transitions of both the nucleosome and the chromatin filament induced by the binding of histone H1 and the resulting condensed structures. Some data on the elasticity of native mitotic chromosomes will be also presented.

The DNA templated processes (gene expression, DNA repair, DNA replication, mitosis, etc.) requires unfolding of the condensed H1-bound chromatin and then refolding in order to preserve nucleus homeostasis. Histone variants are key epigenetic factors, deeply involved in chromatin dynamics. The second part of the talk will be focused on the histone variant H2A.Z. H2A.Z is an essential protein, which is implicated in the vast majority of nuclear processes. Yet, how H2A.Z exhibits such pleiotropic functions remains unclear. We have addressed this question by using mouse genetics and a large cohort of molecular and cellular biology and epigenetic approaches. Depletion of H2A.Z in the stem cells of the basal layer of the skin epidermis leads to the activation of the three main cytosolic DNA sensor pathways, namely cGAS/STING, AIM2 inflammasome, and Toll-like receptor sensors, suggesting the presence of self-DNA in the cytoplasm. We provide evidence that such DNA originates, upon depletion of H2A.Z, from the accumulation of mitotic defects, micronuclei, R-loops, stalled replication forks, de-repression of distinct DNA repeats and structurally altered mitochondria. These changes instigate a profound innate immune response, leading to the activation of the interferon-responsive genes and a strong inflammation phenotype. Our data identify H2A.Z as a major epigenetic mediator of genome integrity, and its deficiency affects overall genome organization and nuclear homeostasis.

During the last years, our lab was very much interested in the etiology of epigenetic and rare diseases. At the end of the talk, some of our data on both Rett syndrome, a very severe neurodevelopmental disease, and Rahman syndrome, a newly identified rare disease casually linked with mutations in the linker histone H1, will be also presented.

1. Graies, M. et al., submitted
2. Nucleosome dyad determines the H1 C-terminus collapse on distinct DNA arms – Louro, J.A. et al., Structure 2023, Feb 2;31(2):201-212
3. MeCP2 is a microsatellite binding protein that protects CA repeats from nucleosome invasion – Ibrahim A. et al., Science 2021, Jun 25;372(6549) :eabd5581.
4. Structure of an H1-Bound 6-Nucleosome Array Reveals an Untwisted Two-Start Chromatin Fiber Conformation – Garcia-Saez I. et al., Mol. Cell, 2018 Dec 6;72(5):902-915.e7.
5. Structure and Dynamics of a 197 bp Nucleosome in complex with Linker Histone H1 – Bednar J. et al. , Mol Cell. 2017, May 4;66(3):384-397.e8.
6. Molecular basis and specificity of H2A.Z-H2B recognition and deposition by the histone chaperone YL1 – Latrick, CM et. al. Nat Struct Mol Biol. 2016 Apr;23(4):309-16.
7. ANP32E is a histone chaperone that removes H2A.Z from chromatin – Obri, A. et al. Nature. 2014 Jan 30;505(7485):648-53

Dr Carsten Bönnemann

National Institute of neurological Disorders and Stroke (NIH, USA)

Childhood ALS and the Missing 6th Sense: Novel SPT and PIEZO2 Associated Syndromes

Invité par Laurent Schaeffer et Carole Vuillerot

Short Biography
Carsten Bönnemann graduated from Medical School at the University of Freiburg in Germany. He trained in pediatrics in Hamburg and Göttingen (where he was awarded the Habilitation in pediatrics), and in neurology/child neurology at Massachusetts General Hospital/Harvard Medical School in Boston. He did postdoctoral research in genetics and neuromuscular specialty training at Boston Children’s Hospital/Harvard Medical School. From 2002 he was Co-Director of the Neuromuscular Program and Director of the Pediatric Neurogenetics Clinic at Children’s Hospital of Philadelphia/University of Pensylvania School of Medicine, where he continues to be on faculty as Adjunct Full Professor of Neurology. In 2010 he joined the NIH as tenured Senior Investigator and Chief of the Neuromuscular and Neurogenetics Disorders of Childhood Section in the Neurogenetics Branch of the National Institute of Neurological Disorders and Stroke. Clinical, genomic and translational work in the Section centers in particular around early onset neuromuscular disorders such as the congenital myopathies and congenital muscular dystrophies and on the development of molecular and gene directed treatment approaches to these conditions, including first-in-human intrathecal and intravenous AAV mediated gene transfer trials. Dr. Bönnemann was a Pew Fellow in the Biomedical Sciences, he received the 2010 Derek Denny-Brown Neurological Scholar Award and the 2023 Jacoby Award from the American Neurological Association, in 2022 the Legacy Award of the Muscular Dystrophy Association USA and in 2023 the International Duchenne-Erb Price of the German DGM. He has been elected to the American Association of Physicians (AAP) and is Co-Editor-in-Chief of the Journal of Neuromuscular Diseases (JND).

Chesler AT *, M Szczot, D Bharucha-Goebel, M Ceko, S Donkervoort, C Laubacher, L Hotchkiss, AR Foley, K Alter, C Zampieri, C Stanley, AM Innes, JK Mah, CM Grossmann, N Bradley, D Nguyen, CE Le Pichon, CG Bönnemann*. The role of PIEZO2 in human mechanosensation. N Engl J Med 375:1355-64 (2016) PMID: 27653382 * Co-corresponding

Szczot M, Liljencrantz J, Ghitani N, Barik A, Lam R, Thompson JH, Bharucha-Goebel D, Saade D, Necaise A, Donkervoort S, Foley AR, Gordon T, Case L, Bushnell MC, Bönnemann CG, Chesler AT PIEZO2 mediates injury-induced tactile pain in mice and humans. Sci Transl Med. 2018 Oct 10;10(462) PMID: 30305456

P. Mohassel, S. Donkervoort*, M. Nalls*, M.A. Lone*, K. Gable*, S.D. Gupta*, A.R. Foley, Y. Hu, J.A. Morales Saute, A.L. Moreira, F. Kok, A. Introna, G. Logroscino, C. Grunseich, A.R. Nickolls, N. Pourshafie, S.B. Neuhaus, D. Saade, A. Gangfuβ, H. Kolbel, Z. Piccus, C.E. Le Pichon, C. Fiorillo, C.V. Ly, A. Topf, L. Brady, S. Specht, A. Zidell, H. Pedro, E. Mittelmann, F.P. Thomas, K.R. Chao, C.G. Konersman, M.T. Cho, T. Brandt, V. Straub, A.M. Connolly, U. Schara, A. Roos, M. Tarnopolsky, A. Hoke, R.H. Brown, C-H Lee, T. Hornemann, T.M. Dunn*, C.G. Bönnemann* Childhood amyotrophic lateral sclerosis caused by excess sphingolipid synthesis. Nature Medicine, 2021 May 31. doi: 10.1038/s41591-021-01346-1. PMID: 34059824. (* co-senior)

Bönnemann CG, Belluscio BA, Braun S, Morris C, Singh T, Muntoni F. Dystrophin Immunity after Gene Therapy for Duchenne’s Muscular Dystrophy. N Engl J Med. 2023 Jun 15;388(24):2294-2296. doi: 10.1056/NEJMc2212912. PMID: 37314712.

Lorenzo Giordani

Centre de recherche en myologie, Sorbonne Universités, Paris, France

Multimodal single cell profiling of Duchenne Muscular Dystrophy

Invité par Rémi MOUNIER

Abstract
Duchenne muscular dystrophy (DMD) is one of the most severe pediatric degenerative myopathies. In the initial phase of the disease, muscle is exposed to continuous cycles of degeneration and regeneration; over time, regenerative potential is exhausted, and necrosis prevails. As of today, the cellular and molecular determinants responsible for this functional exhaustion remain largely uncharacterized.
Adult tissue repair requires the activation of resident stem cells that can both self-renew and generate differentiated progeny. To establish and maintain their properties, stem cells require constant interactions with their microenvironment and their neighboring cells that altogether constitute the niche. The stem cell and its niche form as a whole the minimum functional unit of adult tissue repair. Any given perturbation affecting either the stem cell or the molecular/cellular components of the niche will invariantly impact repair potential. Therefore, in DMD the changes hindering the correct execution of the repair process must therefore occur either in the stem cell or in its niche.
Here we present a multi-omic Spatial strategy to elucidate the determinants interfering with regeneration in the dystrophic muscle and study the niche-stem cell interactions. By leveraging multi-modal data integration (Spatial transcriptomics, snRNAseq and snATACseq), we assessed changes in cell-type compositions, their spatial relationships and dependencies on other cell types, and the evolution of their respective crosstalk. Through our approach, we highlight the changes that occur in the transcriptome and muscle epigenome during disease progression in those regions associated with injury, regeneration, and degeneration. In conclusion, our study delivers an integrative molecular map of dystrophic muscle and lays the groundwork for future studies aimed at the identification of novel biomarkers and potential therapeutic approaches to promote muscle regeneration.

Spatially resolved transcriptomics reveals innervation-responsive functional cluster in skeletal muscle. D’Ercole C., D’Angelo P., Ruggieri V., Proietti D., Sanchez Riera C., Macone A., Bonvissuto D., Sette C., Madaro L. #, Giordani L. #. – Cell Reports 2022

High-dimensional single-cell cartography reveals novel skeletal muscle resident cell populations. Giordani L, He GJ, Negroni E, Sakai H, Law JY, Siu MM, Wan R, Tajbakhsh S, Cheung TH, Grand FL. – Molecular Cell 2019

Dynamics of cellular states of fibro-adipogenic progenitors during myogenesis and muscular dystrophy. Malecova B, Gatto S, Etxaniz U, Passafaro M, Cortez A, Nicoletti C, Giordani L, Torcinaro A,Bardi MD, Bicciato S, Santa FD, Madaro L, Puri PL.- Nature Comm. 2018

Denervation-activated STAT3–IL-6 signalling in fibro-adipogenic progenitors promotes myofibres atrophy and fibrosis. Madaro L, Passafaro M, Sala D, Etxaniz U, Lugarini F, Proietti D, Alfonsi MV, Nicoletti C, Gatto S, Bardi MD, Rojas-García R, Giordani L, Marinelli S, Pagliarini V, Sette C, Sacco A, Puri PL. Nat Cell Biol. 2018.

Muscle-specific microRNAs as biomarkers of Duchenne Muscular Dystrophy progression and response to therapies. Giordani L*, Sandoná M*, Rotini A, Puri PL, Consalvi S, Saccone V. – Rare Dis. 2014.

Charlotte Rivière

Institut Lumière Matière (ILM), Villeurbanne, France

Probing cancer cell response upon mechanical or chemical stimuli

Invitée par Patrick LOMONTE

Abstract
There are number of evidences indicating that both tumour micro-environment and mechanics are playing an important role in the malignant transformation of cells and resistance to treatment. We try to take into account these important issues (micro-environment and mechanics) by developing original techniques enabling to precisely control cell micro-environment, including the applied mechanical stress.
In particular, we have developed agarose-based microsystems that enable a precise control of cell micro-environment in terms of mechanics (stiffness, stress) and transport of molecules (through a porous matrix). Combined with multipositions time-lapse microscropy and image analysis, we are able to decipher cell response in-situ in such confined situation, at the single cell level and over space and time.
In this seminar, I will first present our agarose-based microsystems, before describing results obtained for 2D or 3D confinement, as well as how these systems can be used to assess transport and therapeutic efficacy of novel nano-therapeutics in a more physiological environment than the classical 2D in vitro assay used. As such, it could be a valuable tool to assess the interplay between mechanics and biochemical signaling in the progression of cancer.

Rivière C et al., Plaque de Micropuits En Hydrogel Biocompatible (Biocompatible Hydrogel Microwell Plate). Patent 2018:FR3079524A1

A. Prunet et al., A new agarose-based microsystem to investigate cell response to prolonged confinement, Lab on a Chip. 20:4016–4030 (2020)

S. Goodarzi et al., Quantifying nanotherapeutic penetration using a hydrogel-based microsystem as a new 3D in vitro platform, Lab on a Chip. 21:2495–2510 (2021)

P. Bregigeon et al., Integrated platform for culture, observation and parallelized electroporation of spheroids, Lab on a Chip, 22, 2489-2501 (2022)

M. Mouelhi et al., Mitosis sets nuclear homeostasis of cancer cells under confinement. BioRxiv, 2023.05. 11.540326

Jaime de Juan Sanz

Institut du cerveau, Paris, France

Metabolic control of long-term memory across species

Invité par Julien COURCHET

Abstract
While the strong link between nutrition and cognitive function has been appreciated since the days of the early Greek philosophers, the mechanisms bridging metabolism to neural function remain largely unknown. In the last decades, many studies have connected mitochondrial dysfunction and neurological disease, showing that impaired metabolic states in neurons subsequently cause brain dysfunction. However, a major unsolved question has arised: given that dysfunctional neuronal metabolism impairs brain function, can the opposite perturbation, i.e. increasing neurometabolism, boost brain function? In this talk I will show our efforts on tackling this issue in insects and mammals, exploring how scaling up synapse metabolism can boost higher-order brain functions. Using novel genetic perturbations to accelerate mitochondrial metabolism in firing neurons, we find that metabolic enhancement in neurons of memory centers of flies and rodents can significantly improve long-term memory in both species. These findings suggest that metabolism is a key factor in modulating brain efficiency and cognitive abilities, offering new perspectives on the potential for metabolic interventions in cognition.

Cuhadar*, Calzado-Reyes* et al. (2024). Activity-driven synaptic translocation of LGI1 controls excitatory neurotransmission. Cell Reports. In press

Amrapali Vishwanath et al. (2024). Mitochondrial Ca2+ efflux controls neuronal metabolism and long-term memory across species. BioRxiv, 2024.02.01.578153

Ashrafi*, de Juan-Sanz* et al (2020). Molecular Tuning of the Axonal Mitochondrial Ca2+ Uniporter Ensures Metabolic Flexibility of Neurotransmission. Neuron. 105(4), 678-687

Sylvie Mazoyer

Centre de Recherches en Neurosciences de Lyon (CRNL), Lyon, France

Splicing: when « minor » means « of the most importance »

Invitée par Julien COURCHET

Abstract
Splicing is a well-known process that consists in the removal from pre-messenger RNAs of intronic sequences recognized thanks to their consensus splice-sites by a large ribonucleoproteic complex, the spliceosome. The spliceosome is composed of 5 small nuclear RNAs (snRNAs) linked to proteins, called small nuclear ribonucleoproteins (snRNPs), and a large number of additional protein factors and complexes. There are two types of spliceosomes and two types of introns in most organisms, a fact mostly known by splicing specialists: the major introns, the “classical ones”, and the minor introns, so-called as they represent <1% of the total number of introns in most species. Their number differ widely though, with the champion being the slime mold with >20.000 minor introns, versus only 19 in Drosophila and none in C. elegans and S. cerevisiae. In humans, mice and zebrafish, ~850 minor introns are found in ~750 genes among which – a largely ignored fact – some genes that play major roles in diseases such as PTEN, STK11, BRAF (cancer), and XPO7, CUL1, SETD1A as well as all the CACNA and SCN genes (neurological and mental disorders).

The aim of our research project is to unravel the role played by minor intron splicing in gene expression regulation and to understand what goes wrong when this mechanism is impaired, as happens in patients with mutations in U4atac, a component of the minor spliceosome. Indeed, several severe overlapping developmental syndromes (associating microcephaly, intellectual disability, growth retardation, immunodeficiency, bone dysplasia, …) are due to biallelic mutations in RNU4ATAC, the gene for U4atac.

I will present our most recent results, that provide the first pathophysiological mechanism for explaining RNU4ATACassociated syndromes, and reveal an unexpected link between minor and major splicing.

Khatri D*, Putoux A*, Cologne A, Kaltenbach S, Besson A, Bertiaux E, Guguin J, Fendler A, Dupont MA, Benoit-Pilven C, Qebibo L, Ahmed-Elie S, Audebert S, Blanc P, Rambaud T, Castelle M, Cornen G, Grotto S, Guët A, Guibaud L, Michot C, Odent S, Ruaud L, Sacaze E, Hamel V, Bordonné R, Leutenegger AL, Edery P, Burglen L, Attie-Bitach T, Mazoyer S*, Delous M*. Deficiency of the minor spliceosome component U4atac snRNA secondarily results in ciliary defects in human and zebrafish. PNAS, 2023, 120(9):e2102569120.

Benoit-Pilven C*, Besson A*, Putoux A, Benetollo C, Saccaro C, Guguin J, Sala G, Cologne A, Delous M, Lesca G, Padgett RA, Leutenegger AL, Lacroix V, Edery P*, Mazoyer S*. Clinical interpretation of variants identified in RNU4ATAC, a non-coding spliceosomal gene. PLoS ONE, 2020, 15(7):e0235655.

Cologne A, Benoit-Pilven C, Besson A, Putoux A, Campan-Fournier A, Bober MB, de Die-Smulders CEM, Paulussen ADC, Pinson L, Toutain A, Roifman C, Leutenegger AL*, Mazoyer S*, Edery P*, Lacroix V*. New insights into minor splicing – A transcriptomic analysis of cells derived from TALS patients. RNA, 2019, 25(9), 1130-1149.

Jocelyn Laporte

Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Strasbourg, France

Pathophysiology and therapeutic approaches for centronuclear myopathies

Invité par Vincent GACHE

Abstract
Centronuclear and myotubular myopathies (CNM) are severe congenital myopathies linked to muscle weakness and often respiratory distress. A main histopathological hallmark is the centralized localization of nuclei in muscle fibers. There is an urgent unmet need for therapy. Most CNM are caused by mutations in either the lipid phosphatase myotubularin (MTM1), the membrane remodeling protein amphiphysin (BIN1), or the mechanoenzyme dynamin (DNM2)(Gomez-Oca 2021).

We found MTM1, BIN1 and DNM2 interact and function together in skeletal muscle. Moreover, modulation of their levels in mouse models of CNM ameliorate the motor defects and histopathology, highlighting the concept of cross-therapy, where modulation of one CNM gene can rescue defects linked to mutations in the other genes (Lionello 2019; Giraud 2023). Adeno-associated virus (AAV), antisense oligonucleotides or drugs can be used to modulate the function of the CNM proteins. In addition, we repurposed tamoxifen, previously used in breast cancer, to ameliorate different genetic forms of CNM in mouse models (Gineste 2023).

Overall, the CNM pathway is a key pathway for controlling organelle positioning and function in muscle, and a therapeutic target amenable to clinical development.

Gineste C, Simon A, Braun M, Reiss D, Laporte J. Tamoxifen improves muscle structure and function of Bin1- and Dnm2-related centronuclear myopathies. Brain. 2023 Jul 3;146(7):3029-3048. doi: 10.1093/brain/awac489

Giraud Q, Spiegelhalter C, Messaddeq N, Laporte J. MTM1 overexpression prevents and reverts BIN1-related centronuclear myopathy. Brain. 2023 Oct 3;146(10):4158-4173. doi: 10.1093/brain/awad251

Gómez-Oca R, Cowling BS, Laporte J. Common Pathogenic Mechanisms in Centronuclear and Myotubular Myopathies and Latest Treatment Advances. Int J Mol Sci. 2021 Oct 21;22(21):11377. doi: 10.3390/ijms222111377

Lionello VM, Nicot AS, Sartori M, Kretz C, Kessler P, Buono S, Djerroud S, Messaddeq N, Koebel P, Prokic I, Herault Y, Romero NB, Laporte J, Cowling BS. Amphiphysin 2 (BIN1) modulation rescues MTM1 centronuclear myopathy and prevents focal adhesion defects. Sci Transl Med. 2019 Mar 20;11(484). doi: 10.1126/scitranslmed.aav1866

Chiara Lanzuolo

National Reasearch Council, Milan, Italie

Chromatin dynamics of human diseases captured by chromatin solubility

Invitée par Isabella SCIONTI

Abstract
Chromatin within the cell nucleus acquires a complex structure fundamental for genome function. The tridimensional organization of the genome abides tight rules that ensure proper genome usage and cell identity maintenance and has emerged as a hallmark of healthy cells.
We developed a new high-throughput sequencing technique, the Sequential Analysis of MacroMolecule accessibilitY (SAMMY-seq) to study different levels of chromatin solubility. We presented our improved versions of the protocol, to recover simultaneously euchromatin and heterochromatin. We applied SAMMY-seq on different cell populations highlighting a cell-specific organization of the chromatin. Moreover, tailored bioinformatic analysis allowed the A and B compartments determination, through the identification of discrete domains.
Primary prostate cancer (PCa) has a multifocal random growth and highly variable clinical course confusing the PCa diagnostic screenings. A reliable prognostic molecular signatures for the stratification of primary prostate cancers is still unavailable. We analyzed the epigenome of 17 chemo-naïve patients with putative PCa by SAMMY-seq on prostate biopsies. Transcriptome analysis (RNA-seq) was performed in parallel to confirm the functional effects of epigenome alterations. We identified two subgroups of cancer samples with different degrees of chromatin 3D architecture alterations, namely LDD (Low Degree of Decompartmentalization) and HDD (High Degree of Decompartmentalization). Gene expression analysis revealed a protective, antitumoral activity of the HDD subtype associated to changes in chromatin compartments and transcriptional repression. To discriminate HDD and LDD subtypes we derived a 21-genes transcriptional signature with prognostic relevance on prostate cancer patients confirmed across multiple cohorts. Our data highlight for the first time the impact of chromatin 3D conformation on early-stages primary prostate cancer. We propose a transcriptional signature derived from chromatin compartments driven stratification of patients as a novel prognostic tool to be adopted for prostate tumors at the time of diagnosis.

Frittoli E., Palamidessi A., Iannelli F., Zanardi F., Villa S., Barzaghi L., Abdo H., Cancila V., Beznuskenko G.V., della Chiara G., Pagani M., Malinverno C., Bhattacharya D., Pisati F., Yu W., Galimberti V., Bonizzi G., Martini E., Mironov A., Gioia U., Ascione F., Li Q., Havas K., Magni S., Lavagnino Z., Pennacchio F.A., Maiuri P., Caponi S., Mattarelli M., Martino S., d’Adda di Fagagna F., Rossi C., Lucioni M., Tancredi R., Pedrazzoli P., Vecchione A., Petrini C., Ferrari F., Lanzuolo C., Bertalot G., Nader G., Foiani M., Piel M., Cerbino R., Giavazzi F., Tripodo C. and Scita G. “Tissue fluidification promotes a cGAS/STING-mediated cytosolic DNA response in invasive breast cancer”, Nature Materials 2022 Dec 29.

Pegoli G., Milan M., Manti P.G., Bianchi A, Lucini F., Santarelli P., Bearzi C., Rizzi R. and Lanzuolo C “Role of Cdkn2a in the Emery–Dreifuss Muscular Dystrophy Cardiac Phenotype” – Biomolecules 2021, Apr 6.

Sebestyén E, Marullo F, Lucini F, Bianchi A, Petrini C, Valsoni S, Olivieri I, Antonelli L, Gregoretti F, Oliva G, Ferrari F and Lanzuolo C “SAMMY-seq reveals early alteration of heterochromatin and deregulation of bivalent genes in Hutchinson-Gilford Progeria Syndrome” – Nat Commun 2020, Dec 8.

Bianchi A, Mozzetta C, Pegoli G, Lucini F, Valsoni S, Rosti V, Petrini C, Cortesi A, Antonelli L, Gregoretti F, Oliva G, De Bardi M, Rizzi R, Bodega B, Pasini D, Ferrari F, Bearzi C and Lanzuolo C “Dysfunctional polycomb transcriptional repression contributes to Lamin A/C dependent muscular dystrophy.” J Clin Invest; 2020 Jan 30.

Marullo F., Cesarini E., Antonelli L., Gregoretti F., Oliva G. and Lanzuolo C  » Nucleoplasmic Lamin A/C and Polycomb group of proteins: an evolutionarily conserved interplay  » – Nucleus. 2016 Mar 1: 1-9.

Cesarini E, Mozzetta C, Marullo F, Gregoretti F, Gargiulo A, Columbaro M., Cortesi A, Antonelli L, Di Pelino S, Squarzoni S, Palacios D, Zippo A, Bodega B, Oliva G and Lanzuolo C “Lamin A/C sustains PcG proteins architecture maintaining transcriptional repression at target genes” – J Cell Biol. 2015 Nov 9;211(3):533-51.

Letizia Marvaldi

Université de Turin, Italie

Importin Alpha 3 governs the crosstalk between extrinsic and intrinsic signals in peripheral nerve regeneration

Invitée par Julien COURCHET

Abstract
Sensory neurons have the capacity to grow long distances and high morphological plasticity during development. Upon injury this plasticity is reactivated and causes neuropathic pain due to axonal misguidance and excessive branching. Axonal outgrowth upon injury is regulated by the importin alpha 3 (IMPa3). To understand how neuronal growth causes pain, we study IMPa3’s role in the retrograde signaling. Extrinsic factors such as neurotrophins are released at the injury site of the sciatic nerve and elicit retrograde signalling that is carried by IMPa3 back into the nucleus, where it initiates regeneration-specific transcription. Our in vitro data shows that loss of IMPa3 has severe consequences on neuronal morphology such as impaired neuronal outgrowth. Our in vivo post-injury RNAseq data shows a clear regeneration-specific signature, yielding many functionally interesting candidate genes downstream of IMPa3. Using an in vitro model for axotomy, we now validate these genes, demonstrating that down-regulation of COMP, an extracellular matrix protein, can rescue neurite-outgrowth deficiency in IMPa3 deficient neurons. We are aiming to identify the regeneration-specific transcription factors that drive the expression of our validated candidate genes such as COMP. These transcription factors are putative regulators of regeneration and can thus be used in a therapeutic approach to promote regeneration in the peripheral nervous system and suppress neuropathic pain.

S Alber, P Di Matteo, MD Zdradzinski, I Dalla Costa, KF Medzihradszky, R Kawaguchi, A Di Pizio, P Freund, N Panayotis, L Marvaldi, E Doron-Mandel, N Okladnikov, I Rishal, R Nevo, G Coppola, SJ Lee, PK Sahoo, AL Burlingame, JL Twiss, M Fainzilber. PTBP1 regulates injury responses and sensory pathways in adult peripheral neurons. Sci Adv. 2023 Jul 28;9(30):eadi0286. doi: 10.1126/sciadv.adi0286. Epub 2023 Jul 28.

N. Panayotis, P. Freund, L. Marvaldi, T. Shalit, A. Brandis, T Mehlman, M. Tsoory, M. Fainzilber. β-Sitosterol Reduces Anxiety and Synergizes with Established Anxiolytic Drugs in mice. Cell Reports Medicine doi: 10.1016/j.xcrm.2021.100281 (2021).

L. Marvaldi, N. Panayotis, S. Alber°, S.-Y. Dagan°, N. Okladinikov, I. Koppel, A. Di Pizio, D.-A. Song, Y. Tzur, M. Terenzio, I. Rishal, D. Gordon, F. Rother, E. Hartmann, M. Bader, and M. Fainzilber. Importin α3 regulates chronic pain pathways in peripheral sensory neurons. Science 369, (6505):842-846 (2020). This work has been highlighted in a perspective piece in Science 369, (6505) 774-775 (2020) and in Nature Chemical Biology 1037 (2020) and recommended by Ji R: Faculty Opinions Recommendation 22 Sep 2020; 10.3410/f.738498141.793578282.

B.-C. Tamin-Yecheskel°, M. Fraiberg°, K. Kokabi°, S. Freud, O. Shatz, L. Marvaldi, N. Subic, O. Brenner, M. Tsoory, R. Eilam-Altstadter, I. Biton, A. Savidor, G. Heimer, C. Behrendes, B Ben-Zeev, Z. Elazar. Novel mouse model simulating spastic paraplegia type 49 reveals defects in autophagosomal consumption. Autophagy 10.1080/15548627.2020.1852724 (2020).

M. Terenzio, S. Koley, N. Samra, I. Rishal, Q. Zhao, P. K. Sahoo, A. Urisman, L. Marvaldi, J. A. Oses-Prieto, C. Forester, C. Gomes, A. L. Kalinski, A. Di Pizio, E. Doron-Mandel, R. B.-T. Perry, I. Koppel, J. L. Twiss, A. L. Burlingame, M. Fainzilber, Locally translated mTOR controls axonal local translation in nerve injury. Science. 359, 1416–1421 (2018).

L. Marvaldi, S. Thongrong, A. Kozłowska, R. Irschick, C. O. Pritz, B. Bäumer, G. Ronchi, S. Geuna, B. Hausott, L. Klimaschewski, Enhanced axon outgrowth and improved long-distance axon regeneration in sprouty2 deficient mice. Dev. Neurobiol. 75, 217–231 (2015).

Olivier Dorchies

Université de Genève, Suisse

20 years of pharmacotherapy for Duchenne Muscular Dystrophy: From mouse models to patients… and back

Invité par Laurent SCHAEFFER

Abstract
Duchenne muscular dystrophy (DMD) is a rare genetic disease due to the absence of dystrophin from striated muscles. Affected boys suffer from progressive muscle wasting. Despite improved medical care, most patients die before their 30s due to cardiac and respiratory failure. For almost 40 years, DMD has been the focus of intense preclinical research, using a variety of dystrophic mouse models that all lack functional dystrophin: the main lines are mdx, mdx5Cv, and more recently D2.mdx. Hundreds of reports have been published that demonstrate impressive efficacy of diverse therapeutic interventions in dystrophic mice, leading to huge hope in families afflicted with DMD. However, most of these promising therapies show little efficacy, if any, in subsequent clinical trials in DMD patients. At present, lack of preclinical to clinical translation is a major obstacle to the development of efficacious therapy for DMD. It is largely accepted that the poor clinical translation results from a much milder phenotype, disease progression and life expectancy in dystrophic mice compared to patients.

We will give an overview of our contribution to pharmacotherapy for DMD over the last 20 years. Emphasis will be made on tamoxifen, including the long preclinical path and the outcome of the ensuing clinical trial TAMDMD. Then, we will present our current work for developing more reliable models of DMD towards more predictable outcomes in clinical trials. To this aim, we are exploring the roles of the susceptibility gene Ltbp4: Ltbp4DEL mutation is naturally present in the DBA/2J genetic background and is thought to enhancefibrosis and atrophy in D2.mdx mice, as in DMD patients. However, no effect was observed after transfer of Ltbp4DEL into mdx5Cv mice in the C57BL/6J background. These findings question the roles of Ltbp4 in DMD and its value to aggravate the phenotype of mice.

In parallel, we have developed the FU-5Cv dystrophic line, which allows to downregulate utrophin (a dystrophin homologue upregulated in dystrophic muscle) in skeletal muscle only. This model showed impaired muscle function and force, enhanced fibrosis and muscle wasting, and a shorter lifespan. All these outcomes reveal an aggravated dystrophic phenotype and make the FU-5Cv mouse line a better DMD-like model. Finally, we will introduce manipulation of the utrophin promoter to reduce utrophin overexpression in muscles of dystrophic mice while sparing expression in other tissues and at the neuromuscular junction.

Safety and efficacy of tamoxifen in boys with Duchenne muscular dystrophy (TAMDMD): a multicentre, randomised, double-blind, placebo-controlled, phase 3 trial. Henzi BC, Schimdt S, Nagy S, Rubino-Nacht D, Schaedelin S, Putananickal N, Amthor H, Childs A-M, Deconinck N, de Groot I, Horrocks I, Houwen-van Opstal S, Laugel V, Lopez Lobato M, Madruga Garrido M, Nascimento Osorio A, Schara-Schmidt U, Spinty S, von Moers A, Lawrence F, Hafner P, Dorchies OM, Fischer D. Lancet Neurol.22(10):890-899 (2023). doi: 10.1016/S1474-4422(23)00285-5

Multi-omics comparisons of different forms of centronuclear myopathies and the effects of several therapeutic strategies. Djeddi S, Reiss D, Menuet A, Freismuth S, de Carvalho Neves J, Djerroud S, Massana-Muñoz X, Sosson AS, Kretz C, Raffelsberger W, Keime C, Dorchies OM, Thompson J, Laporte J. Mol Ther, 29(8):2514-2534 (2021). doi: 10.1016/j.ymthe.2021.04.033

Le tamoxifène dans l’arsenal thérapeutique des maladies neuromusculaires ? . Dorchies OM, Brignol TN. Cah Myol. 19, 25-27 (2019).

Repurposing the selective oestrogen receptor modulator tamoxifen for the treatment of Duchenne muscular dystrophy. Gayi E, Neff LA, Ismail HM, Ruegg UT, Scapozza L, Dorchies OM. Chimia (Aarau). 72(4), 238-240 (2018). doi: 10.2533/chimia.2018.238

The potential and benefits of repurposing existing drugs to treat rare muscular dystrophies. Ismail HM, Dorchies OM, Scapozza L. Exp Opin Orphan Drugs. 6(4), 259-271 (2018). doi.org/10.1080/21678707.2018.

Tamoxifen prolongs survival and alleviates symptoms in mice with fatal X-linked myotubular myopathy. Gayi E, Neff LA, Massana Muñoz X, Ismail HM, Sierra M, Mercier T, Décosterd LA, Laporte J, Cowling BS, Dorchies OM, Scapozza L. Nat Commun. 9(1), 4848 (2018). doi: 10.1038/s41467-018-07058-4

The anticancer drug tamoxifen counteracts the pathology in a mouse model of duchenne muscular dystrophy. Dorchies OM, Reutenauer-Patte J, Dahmane E, Ismail HM, Petermann O, Patthey- Vuadens O, Comyn SA, Gayi E, Piacenza T, Handa RJ, Décosterd LA, Ruegg UT. Am J Pathol. 182(2):485-504 (2013). doi: 10.1016/j.ajpath.2012.10.018

Yan Burelle

Université des sciences d’Ottawa, Canada

Mitochondrial Quality Control in Muscle Stem Cells: A Determinant of Fate Decision and Tissue Repair Capacity

Invité par Rémi MOUNIER

Abstract
Maintenance of optimal mitochondrial function plays a crucial role in the regulation of muscle stem cell (MuSC) behavior, but the underlying maintenance mechanisms remain ill defined. Our lab aims to delineate the importance of mitophagy as a mitochondrial quality control regulator in MuSCs and the role this process plays in maintaining optimal muscle regenerative capacity. In this seminar I will summarize results from our recent unpublished work in which we characterized the dynamics and regulation of mitophagy in MuSCs under various physiological myogenic states and identified an important role for both Ubiquitin- and Receptor-dependent mitophagy in the regulation of MuSC fate decision and muscle regeneration.

Cairns G, Thumiah-Mootoo M, Abassi MR, Racine J, Larionov N , Prola A, Khacho M , Burelle Y PINK1 Deficiency Alters Muscle Stem Cell Fate Decision and Muscle Regenerative Capacity. BioRxiv 2023.06.23.546123; doi: https://doi.org/10.1101/2023.06.23.546123

Baker N, Wade S, Triolo M, Girgis J, Chwastek D, Larrigan S, Feige P, Fujita R, Crist C, Rudnicki MA, Burelle Y, Khacho M.The mitochondrial protein OPA1 regulates the quiescent state of adult muscle stem cells. Cell Stem Cell. 2022 Sep 1;29(9):1315-
1332.e9.

Cairns G, Thumiah-Mootoo M, Burelle Y, Khacho Mitophagy: A New Player in Stem Cell Biology. M.Biology (Basel). 2020 Dec 19;9(12):481. doi: 10.3390/biology9120481.

Pr Masaaki Komatsu

Dpt of Physiology, Juntendo University School of Medecine, Tokyo, Japon

Selective autophagy of phase-separated p62: from molecular mechanism to pathophysiology

Invité par Flavie STRAPPAZZON et Carole KRETZ-REMY

Anna Raffaello

Université de Padoue, Italie

The pleiotropic role of mitochondrial calcium signalling in skeletal muscle

Invitée par Rémi MOUNIER

Abstract
The second messenger Ca2+ regulates a broad repertoire of cellular processes. Upon physiological stimuli, skeletal muscle mitochondria rapidly and efficiently accumulate Ca2+ into their matrix via an electrogenic pathway, that relies on the driving force of a steep electrochemical gradient. A large mt peak occurs dynamically in parallel to agonist-induced cyt increases, thanks to the activity of the Mitochondrial Calcium Uniporter (MCU), the highly selective channel responsible for mitochondrial Ca2+ accumulation. MCU positively regulates myofiber size in physiological conditions and counteracts pathological loss of skeletal muscle mass. Furthermore, skeletal muscle-specific MCU deletion inhibits mitochondrial Ca2+ uptake, impairs muscle force and exercise performance. The crucial role of mitochondrial Ca2+ is not limited to muscle fibers. Indeed, we found that MCUb, that is part of MCU complex and negatively regulates the entry of Ca2+ into mitochondria, is highly expressed in macrophages during skeletal muscle regeneration. In vitro and in vivo experiments demonstrated that MCUb absence affects macrophages skewing from a M1 to M2 profile. Coherently with the M2 pro-regenerative role, we found that regenerating muscles of MCUb KO mice, show a decrease in the expression level of myogenic regulatory transcription factors and an alteration in the reconstitution of muscle architecture after damage. In addition, co-culture experiments demonstrated that macrophage-conditioned medium from M2 MCUb KO macrophages drastically decreases satellite cell differentiation. We are currently studying the role of mitochondrial Ca2+ on satellite cells homeostasis. Our preliminary results show that the expression of the pore-forming subunit MCU does not change between quiescent and activated cells, while we observed a trend of increase of the dominant-negative subunit MCUb and of the gatekeeper MICU2, and a trend of decrease of the positive modulator of the channel MICU1 upon activation. Moreover, to understand whether satellite cells proliferation and differentiation is sensitive to mitochondrial Ca2+ homeostasis, we are generating a mouse model where MCU expression is blunted specifically in satellite cells. We will soon characterize its muscle regeneration capacity, calcium homeostasis and perform transcriptomic analysis.

Feno S, Munari F, Reane DV, Gissi R, Hoang DH, Castegna A, Chazaud B, Viola A, Rizzuto R, Raffaello A. The dominant-negative mitochondrial calcium uniporter subunit MCUb drives macrophage polarization during skeletal muscle regeneration. Sci Signal. 2021 Nov 2;14(707):eabf3838. doi: 10.1126/scisignal.abf3838.

Butera G, Vecellio Reane D, Canato M, Pietrangelo L, Boncompagni S, Protasi F, Rizzuto R, Reggiani C, Raffaello A. Parvalbumin affects skeletal muscle trophism through modulation of mitochondrial calcium uptake. Cell Reports. 2021 May 4;35(5):109087. doi: 10.1016/j.celrep.2021.109087.

Vecellio Reane D, Vallese F, Checchetto V, Acquasaliente L, Butera G, De Filippis V, Szabò I, Zanotti G, Rizzuto R, Raffaello A. A MICU1 Splice Variant Confers High Sensitivity to the Mitochondrial Ca2+ Uptake Machinery of Skeletal Muscle. Molecular Cell. 2016 Nov 17;64(4):760-773. doi: 10.1016/j.molcel.2016.10.001.

Logan CV, Szabadkai G, Sharpe JA, Parry DA, Torelli S, Childs AM, Kriek M, Phadke R, Johnson CA, Roberts NY, Bonthron DT, Pysden KA, Whyte T, Munteanu I, Foley AR, Wheway G, Szymanska K, Natarajan S, Abdelhamed ZA, Morgan JE, Roper H, Santen GW, Niks EH, van der Pol WL, Lindhout D, Raffaello A, De Stefani D, den Dunnen JT, Sun Y, Ginjaar I, Sewry CA, Hurles M, Rizzuto R; UK10K Consortium, Duchen MR, Muntoni F, Sheridan E (2014). Loss-of-function mutations in MICU1 cause a brain and muscle disorder linked to primary alterations in mitochondrial calcium signaling. Nature Genetics. 46, 188-193.

Raffaello A*, De Stefani D*, Sabbadin D, Teardo E, Merli G, Picard A, Checchetto V, Moro S, Szabò I, Rizzuto R (2013). The mitochondrial calcium uniporter is a multimer that can include a dominant-negative pore-forming subunit. EMBO Journal. 32, 2362-2376. * Equal contributors

Rizzuto R, De Stefani D, Raffaello A, Mammucari C (2012). Mitochondria as sensors and regulators of calcium signaling. Nature Reviews Molecular Cell Biology. 13, 566-578.

De Stefani D*, Raffaello A*, Teardo E, Szabò I, Rizzuto R (2011). A forty-kilodalton protein of the inner membrane is the mitochondrial calcium uniporter. Nature. 476, 336-340. * Equal contributors

Raffaello A, Milan G, Masiero E, Carnio S, Lee D, Lanfranchi G, Goldberg AL, Sandri M (2010). JunB transcription factor maintains skeletal muscle mass and promotes hypertrophy. The Journal of Cell Biology. 191, 101-113.

Virginie Hamel

Université de Genève, Suisse

Expansion microscopy for Structural Cell Biology: from centriole architecture to retinopathies and associated gene therapies

Invitée par Caroline BRUN

Abstract
Ultrastructure expansion microscopy can be useful for structural cell biology, placing specific emphasis on centrioles and their inner scaffold structure. This discovery has significantly contributed to our comprehension of the molecular mechanisms underlying retinitis pigmentosa RP28 photoreceptor degeneration, thus paving the path for the development of a gene augmentation therapy strategy.

Nanoscopy of organelles and tissues with iterative Ultarstructure expansion microscopy (iU-ExM). Louvel V, Hasse R, Mercey O, Laporte M.H, Soldati-Favre D, Hamel V** and Guichard P**. bioRxiv doi: https://doi.org/10.1101/2022.11.14.516383

The connecting cilium inner scaffold provides a structural foundation to maintain photoreceptor integrity. Mercey O, Kostic C, Bertiaux E, Giroud A, Morrison C., Sadian Y, Chang N, Arsenijevic Y, Guichard P** and Hamel V**. PLOS Biology, June 2022. https://doi.org/10.1371/journal.pbio.3001649

WDR90 is a centriolar microtubule wall protein important for centriole architecture integrity. Steib E., Gambarotto D., Laporte MH, Olieric N., Zheng C., Borgers S., Olieric V., Le Guennec M., Koll F., Tassin AM, Steinmetz MO, Guichard P** and Hamel V**. eLife. September 2020. https://doi.org/10.7554/eLife.57205

Imaging cellular ultrastructures using expansion microscopy (U-ExM). Gambarotto D.##, Zwettler F. U. ##, Cernohorska M., Fortun D., Borgers S., Heine J., Schloetel J. G., Reuss M., Unser M., Boyden E.S., Sauer M**, Hamel V** and P. Guichard**. Nature Methods. January 2019. https://doi.org/10.1038/s41592-018-0238-1

Gabrielle Kardon

University of Utah, USA

Cellular dynamics of muscle regeneration

Invitée par Bénédicte CHAZAUD

Abstract
The function of many organs, including skeletal muscle, depends on its three-dimensional structure. Muscle regeneration therefore requires not only reestablishment of myofibers, but restoration of tissue architecture. Resident muscle stem cells (SCs) are essential for regeneration, but how SCs regenerate muscle architecture is largely unknown. Using genetic labeling of SCs and whole mount imaging to reconstruct in three dimensions muscle regeneration, we address this problem. I will present unpublished data revealing new insights into the cellular events of regeneration.

Dr Karoline Pytka

Jagiellonian University Medical College, Cracovie, Pologne

Beyond traditional therapies : Functionally selective compounds for fast antidepressant-like and procognitive effects

Invitée par Julien COURCHET

Abstract
Functional selectivity, a phenomenon where a ligand favors activation of specific signaling pathways over others, emerges as an innovative approach to neuropsychiatric challenges, especially depression and related cognitive impairments. This seminar will illuminate the complex interplay of the serotonin 5-HT1A receptor with multiple signaling pathways, resulting in diverse behavioral impacts. A detailed exploration of the cellular profiles of biased 5-HT1A receptor agonists such as NLX-101, NLX-204, and F13714 will be undertaken, along with a discussion on their pharmacological effects observed in rodents. Additionally, the seminar will delve into the unique pharmacological properties of HBK-15, a multimodal compound, which exhibits both rapid antidepressant-like and procognitive benefits in rodents.

Sałaciak, K. & Pytka, K. Biased agonism in drug discovery: Is there a future for biased 5-HT1A receptor agonists in the treatment of neuropsychiatric diseases? Pharmacol Therapeut 227:107872 (2021)

Sniecikowska, J. et al. Discovery of Novel pERK1/2- or β Arrestin-Preferring 5 HT1A Receptor-Biased Agonists: Diversified Therapeutic-like versus Side Effect Profile. J Med Chem 63, 10946–10971 (2020).

Pytka, K. et al. HBK-15, a multimodal compound, induces procognitive effects through modulating hippocampal LTP and enhancing theta-gamma coupling in mice. (2023) doi:10.21203/rs.3.rs-3126208/v1.

Keir Menzies

Ottawa University, Canada

Unravelling the PARamount role of NAD+-metabolism and PARylation in skeletal muscle and satellite cell health

Invité par Bénédicte CHAZAUD et Julien GONDIN

Abstract
Poly-ADP-Ribose Polymerases (PARPs) are a family of proteins that consume nicotinamide adenine dinucleotide (NAD+; a form of Vitamin B3) to modify proteins in a process called Poly-ADPribosylation or PARylation. Specifically, PARPs covalently attach NAD+-derived ADP-ribose groups to proteins that can then be removed by PAR glycohydrolase (PARG). PARylation signalling was identified as a cellular response to genotoxic stressors with its primary role in the DNA repair process, but has now been associated with glycolysis, chromatin modulation, differentiation, methylation and replication.
Our previous work demonstrated that NAD+ availability is critical for maintaining muscle health. In particular, we showed that reduced MuSC function in aged mice is associated with reduced NAD+ levels and treatment with the NAD+ precursor nicotinamide riboside rejuvenated MuSCs and improved their capacity for muscle regeneration. We have also shown that NAD+-levels are limited in the muscle of mouse models of muscular dystrophy as a result of elevated PARylation signalling.
Given the surge in use and development of pharmaceuticals that alter NAD+-homeostasis and PARylation status, we set out to examine the physiological relevance of these changes in muscle during health, disease and regeneration.

Meta-analysis of NAD(P)(H) quantification results exhibits variability across mammalian tissues. Azouaoui D, Choinière MR, Khan M, Sayfi S, Jaffer S, Yousef S, Patten DA, Green AE, Menzies KJ. Sci Rep. 2023 Feb 11;13(1):2464. doi: 10.1038/s41598-023-29607-8.

GCN5 maintains muscle integrity by acetylating YY1 to promote dystrophin expression. Addicks GC, Zhang H, Ryu D, Vasam G, Green AE, Marshall PL, Patel S, Kang BE, Kim D, Katsyuba E, Williams EG, Renaud JM, Auwerx J, Menzies KJ. J Cell Biol. 2022 Feb 7;221(2):e202104022. doi: 10.1083/jcb.202104022. Epub 2022 Jan 13

NAD+ repletion improves muscle function in muscular dystrophy and counters global PARylation. Ryu D, Zhang H, Ropelle ER, Sorrentino V, Mázala DA, Mouchiroud L, Marshall PL, Campbell MD, Ali AS, Knowels GM, Bellemin S, Iyer SR, Wang X, Gariani K, Sauve AA, Cantó C, Conley KE, Walter L, Lovering RM, Chin ER, Jasmin BJ, Marcinek DJ, Menzies KJ, Auwerx J. Sci Transl Med. 2016 Oct 19;8(361):361ra139. doi: 10.1126/scitranslmed.aaf5504

NAD⁺ repletion improves mitochondrial and stem cell function and enhances life span in mice. Zhang H, Ryu D, Wu Y, Gariani K, Wang X, Luan P, D’Amico D, Ropelle ER, Lutolf MP, Aebersold R, Schoonjans K, Menzies KJ, Auwerx J. Science. 2016 Jun 17;352(6292):1436-43. doi: 10.1126/science.aaf2693. Epub 2016 Apr 28

Pr Véronique Paquis

IRCAN, Nice, France

CHCHD10-related neurodegeneration : from gene to therapeutic approach

Invitée par Rémi MOUNIER et Lola LESSARD

Abstract
The identification of a point mutation (p.Ser59Leu) in the CHCHD10 gene was the first genetic evidence that mitochondrial dysfunction can trigger motor neuron disease (MND). The generation of different cell models has allowed us to understand some of the steps involved in neuronal death, including the central role of the disassembly of the MItochondrial contact site and Cristae Organizing System (MICOS) complex, which leads to the destructuring of mitochondrial cristae. CHCHD10-associated diseases have a broad clinical spectrum and Chchd10S59L/+ mice recapitulate all phenotypes presented by patients with mitochondrial myopathy, cardiomyopathy and, typical MND features. Recent data show that these animals also provide a model for the frontotemporal dementia, seen in patients.
Dissecting the cellular pathways disrupted by the expression of mutant CHCHD10 alleles contributes to the development of new therapeutic approaches. Using a yeast-based high-throughput drug screen to search for FDA-approved molecules that rescue the deleterious effects of MICOS disassembly, we identified nifuroxazide (NFX), an antibacterial molecule. NFX rescues the mitochondrial network fragmentation and cristae abnormalities found in CHCHD10S59L/+ patient fibroblasts. This molecule also decreases caspase-dependent death of human motor neurons derived from iPSCs carrying the p.Ser59Leu variant. The positive effects of NFX on mitochondrial settings in CHCHD10S59L/+ cells depend on KIF5B, a protein involved in mitochondrial transport, linking cristae organization and transport machinery. Our results identify NFX and selected structural analogues as potential therapeutic molecules for disorders associated with MICOS disassembly, including amyotrophic lateral sclerosis-like motor neuron disease.

Pr Smita Saxena

Dpt of Neurology, Bern University Hospital, Suisse

Understanding circuit-mediated vulnerability in SCA1

Invitée par Hélène PUCCIO

Abstract
Spinocerebellar ataxia type 1 (SCA1) is a fatal neurodegenerative disease caused by a polyglutamine (PolyQ) expansion in the Ataxin-1 protein, which is involved in regulation of transcription. ATXN1 protein is expressed throughout the central nervous system, but the expression of the mutated protein mainly affects the Purkinje cells (PCs), the sole output of the cerebellar cortex. At a circuit level there are early functional alterations involving the climbing fiber, the major excitatory inputs onto PCs, leading to impaired activation of proteins involved in synaptic transmission, but little is known about the excitation inhibition (E/I) balance of the cerebellar circuit in the context of SCA1. We show with in vivo imaging in behaving mice that there is a selective overactivation of the molecular layer interneurons (MLIs) in Sca1154/2Q that could contribute or determine the degeneration of the PCs in SCA1. Moreover, hyperconnectivity between MLIs and PCs using excitatory DREADD mimics most SCA1-specific pathological hallmarks including motor incoordination. Finally, using DREADDs we modulate the functionality of the MLIs to restore PCs functionality and ameliorate motor impairments. Our results, identify early network changes within the cerebellum of presymptomatic Sca1154/2Qmice and reveal that the modulation of synaptic component within the cerebellar cortex at any disease stage can ameliorate the motor symptoms of the pathology.

Early molecular layer interneuron hyperactivity triggers Purkinje neuron degeneration in SCA1. Neuron. 2023; 111: 2523-2543

Aberrant Cerebellar Circuitry in the Spinocerebellar Ataxias. – Front. Neurosci. 2020; 14: 707

Cerebellar Development and Circuit Maturation: A Common Framework for Spinocerebellar Ataxias – Front Neurosci. 2020 Apr 2;14:293

Impaired mTORC1-Dependent Expression of Homer-3 Influences SCA1 Pathophysiology – Neuron. 2016 Jan 6;89(1):129-46.

Xavier Nicol

Institut de la Vision, Paris, France

Subcellular second messenger networks drive distinct repellent-induced axon behaviors

Invité par Julien COURCHET

Abstract
Second messengers, including cAMP, cGMP and Ca2+ are often placed in an integrating position to combine the extracellular cues that orient growing axons in the developing brain. This view suggests that axon repellents share the same set of cellular messenger signals and that axon attractants evoke opposite cAMP, cGMP and Ca2+ changes. Investigating the confinement of these second messengers in cellular nanodomains, we instead demonstrate that two repellent cues, ephrin-A5 and Slit1, induce spatially segregated signals. These guidance molecules activate subcellular-specific second messenger crosstalks, each signaling network controlling distinct axonal morphology changes in vitro and pathfinding decisions in vivo.

Subcellular second messenger networks drive distinct repellent-induced axon behaviors S Baudet, Y Zagar, F Roche, C Gomez Bravo, S Couvet, J Bécret, M Belle, O Ros, X Nicol. BioRxiv 2023.02.02.526245

Ludo Van Den Bosch

University of Leuven & Group Leader VIB, Leuven, Belgique

Therapeutic effects of HDAC6 inhibition in peripheral neuropathies and amyotrophic lateral sclerosis (ALS)

Invité par Laurent SCHAEFFER

Abstract
Ludo research focuses on the cause, mechanism and treatment options for neurodegenerative diseases. In particular, he studies amyotrophic lateral sclerosis (ALS, Lou Gehrig’s disease) and its relation to frontotemporal dementia, as well as Charcot-Marie-Tooth disease (an axonal peripheral neuropathy). To this end, he performs genetic studies, study in vitro models and fruit fly, fish, mouse and rat models, and has an intensive clinical research program. He aims to translate results from genetic and animal studies to biomarker aspects and treatment strategies. His group has contributed significantly to the development of in vitro motor neuron models (including iPSC-derived motor neurons). The fish model for ALS that he developed, has found its way to many other groups, and allowed genetic screens for the identification of modifiers. These research activities have resulted in many papers in top journals.

HDAC6 inhibitors reverse axonal loss in a mouse model of mutant HSPB1-induced Charcot-Marie-Tooth disease. Nature Medicine, 17 (8), 968-974. van Outryve d’Ydewalle, C., Krishnan, J., Chiheb, D., Van Damme, P., Irobi, J., Kozikowski, A.P., Vanden Berghe, P., Timmerman, V., Robberecht, W., Van Den Bosch, L. (2011).

HDAC6 inhibition reverses axonal transport defects in motor neurons derived from FUS-ALS patients. Nature Communications. Guo, W., Naujock, M., Fumagalli, L., Vandoorne, T., Baatsen, P., Boon, R., Ordovás, L., PATEL, S., Welters, M., Vanwelden, T., Geens, N., Tricot, T., Benoy, V., Steyaert, J., Lefebvre-Omar, C., Boesmans, W., Jarpe, M., Sterneckert, J., Wegner, F., Petri, S., Bohl, D., Vanden Berghe, P., Robberecht, W., Van Damme, P., Verfaillie, C., Van Den Bosch, L. (2017).

HDAC6 inhibition reverses axonal transport defects in motor neurons derived from FUS-ALS patients. Nature Communications, 8 (1), Art.No. ARTN 861. Guo, W., Naujock, M., Fumagalli, L., Vandoorne, T., Baatsen, P., Boon, R., Ordovás, L., PATEL, S., Welters, M., Vanwelden, T., Geens, N., Tricot, T., Benoy, V., Steyaert, J., Lefebvre-Omar, C., Boesmans, W., Jarpe, M., Sterneckert, J., Wegner, F., Petri, S., Bohl, D., Vanden Berghe, P., Robberecht, W., Van Damme, P., Verfaillie, C., Van Den Bosch, L. (2017).

HDAC6 is a therapeutic target in mutant GARS-induced Charcot-Marie-Tooth disease. Brain, 141 (3), 673-687 Benoy, V., Van Helleputte, L., Prior, R.C., d’Ydewalle, C., Haeck, W., Geens, N., Scheveneels, W., Schevenels, B., Vanden Berghe, P., Van Damme, P., Robberecht, W., Van Den Bosch, L. (2018).

Inhibition of histone deacetylase 6 (HDAC6) protects against vincristine-induced peripheral neuropathies and inhibits tumor growth. Neurobiology of Disease, 111, Art.No. S0969-9961(17)30267-X, 59-69. Van Helleputte, L., Kater, M., Cook, D.P., Eykens, C., Rossaert, E., Haeck, W., Jaspers, T., Geens, N., Vanden Berghe, P., Gysemans, C., Mathieu, C., Robberecht, W., Van Damme, P., Cavaletti, G., Jarpe, M., Van Den Bosch, L. (2018).

Human motor units in microfluidic devices are impaired by FUS mutations and improved by HDAC6 inhibition. bioRxiv Dittlau, K.S., Krasnow, E., Fumagalli, L., Vandoorne, T., Baatsen, P., Kerstens, A., Giacomazzi, G., Pavie, B., Sampaolesi, M., Van Damme, P., Van Den Bosch, L. (2020).

HDAC6 inhibition restores TDP-43 pathology and axonal transport defects in human motor neurons with TARDBP mutations. EMBO JOURNAL, 40 (7), Art.No. ARTN e106177. doi: 10.15252/embj.2020106177 Open Access. Fazal, R., Boeynaems, S., Swijsen, A., De Decker, M., Fumagalli, L., Moisse, M., Vanneste, J., Guo, W., Boon, R., Vercruysse, T., Eggermont, K., Swinnen, B., Beckers, J., Pakravan, D., Vandoorne, T., Vanden Berghe, P., Verfaillie, C., Van den Bosch, L., Van Damme, P. with Van den Bosch, L. (corresp. author), Van Damme, P. (corresp. author) (2021).

FUS-ALS hiPSC-derived astrocytes impair human motor units through both gain-of-toxicity and loss-of-support mechanisms. Katarina Stoklund Dittlau, Lisanne Terrie, Pieter Baatsen,4 Axelle Kerstens, Lim De Swert, Rekin’s Janky, Nikky Corthout, Pegah Masrori, Philip Van Damme, Poul Hyttel, Morten Meyer, Lieven Thorrez, Kristine Freude and Van Den Bosch Ludo.(2023)

Pr Bert Blaauw

University of Padova, Italie

Dissecting the connection between fiber type and mTORC1

Invité par Julien GONDIN

Abstract

Dr. Frank Lezoualc’h

Institut des Maladies Métaboliques et Cardiovasculaires (I2MC), Toulouse, France

Novel cylic AMP signalosome in cardiac remodeling and heart failure

Invité par Rémi MOUNIER

Abstract
The compartmentation of signaling processes is accomplished by the assembly of protein complexes called signalosomes. These signaling platforms colocalize enzymes, substrates, and anchoring proteins into specific subcellular compartments. Exchange protein directly activated by cAMP 1 (EPAC1) is an effector of the second messenger, 3′,5′-cyclic adenosine monophosphate (cAMP) that is associated with multiple roles in several pathologies including cardiac diseases. Both EPAC1 intracellular localization and molecular partners are key players in the regulation of cell fate, which may have important therapeutic potential. Here, we summarize the recent findings on EPAC1 structure, regulation, and pharmacology. We discuss the importance of EPAC1 subcellular distribution in its biological action, paying special attention to its mechanism of action leading to cardiomyocyte death in stress conditions.

Lezoualc’h F, Badimon L, Baker H, Bernard M, Czibik G, de Boer RA, D’Humières T, Kergoat M, Kowala M, Rieusset J, Vilahur G, Détrait M, Watson C, Derumeaux GA. Diabetic cardiomyopathy: the need for adjusting experimental models to meet clinical reality. Cardiovasc Res. 2023 May 22;119(5):1130-1145.

Laudette M, Sainte-Marie Y, Cousin G, Bergonnier D, Belhabib I, Brun S, Formoso K, Laib L, Tortosa F, Bergoglio C, Marcheix B, Borén J, Lairez O, Fauconnier J, Lucas A, Mialet-Perez J, Moro C, Lezoualc’h F. (2021) Cyclic AMP-binding protein Epac1 acts as a metabolic sensor to promote cardiomyocyte lipotoxicity. Cell Death Dis. 2021 Sep 1;12(9):824.

Laudette M, Coluccia A, Sainte-Marie Y, Solari A, Fazal L, Sicard P, Silvestri R, Mialet-Perez J, Pons S, Ghaleh B, Blondeau JP, Lezoualc’h F. (2019) Identification of a pharmacological inhibitor of Epac1 that protects the heart against acute and chronic models of cardiac stress. Cardiovasc Res. 115:1766-1777.

Fazal L, Laudette M, Paula-Gomes S, Pons S, Conte C, Tortosa F, Sicard P, Sainte-Marie Y, Bisserier M, Lairez O, Lucas A, Roy J, Ghaleh B, Fauconnier J, Mialet-Perez J, Lezoualc’h F. (2017) Multifunctional Mitochondrial Epac1 Controls Myocardial Cell Death. Circ Res. 120:645-657

Bisserier M, Berthouze-Duquesnes M, Breckler M, Tortosa F, Fazal L, de Régibus A, Laurent AC, Varin A, Lucas A, Branchereau M, Marck P, Schickel JN, Deloménie C, Cazorla O, Soulas-Sprauel P, Crozatier B, Morel E, Heymes C, Lezoualc’h F. (2015) Carabin protects against cardiac hypertrophy by blocking calcineurin, Ras, and Ca2+/calmodulin-dependent protein kinase II signaling. Circulation 131:390-400.

Joana Esteves de Lima

Institut Mondor de Recherche Biomédicale , Créteil, France

H3.3 incorporation in muscle-specific gene loci safeguards myogenic cell identity

Invitée par Rémi MOUNIER

Abstract
Chromatin architecture impacts on gene expression and defines cell lineage specification. Although epigenetic processes in myogenesis start to be unveiled, the role of the histone variant H3.3, which is implicated in epigenetic memory, is poorly understood. By combining studies using a HIRA-KO myoblast cell line and the Pax7CreErt2;Hirafl/fl mouse model we showed that myoblasts and skeletal muscle stem cells lacking HIRA lose Pax7, Myf5 and Myod1 expression, consistent with the loss of PAX7-positive cells and impaired muscle regeneration. Mechanistically, in the absence of HIRA, H3.3 enrichment in regulatory regions of myogenic genes is decreased and correlates with the loss of the transcriptional permissive histone mark H3K27ac. Moreover, loss of myogenic identity in HIRA mutant cells is associated with the atypical expression of alternative lineage genes which is linked with the increased enrichment of H3K4me3 at promoters. Consistently, HIRA is required for myogenic development, with decreased muscle progenitor cells and muscle size in Pax3Cre;Hirafl/fl embryos. In order to investigate gene expression and motif accessibility at the single cell level, we performed multiome analysis (scRNA-seq coupled with scATAC-seq) and observed distinct clusters of muscle stem cells that respond differently in the context of HIRA loss-of-function. Taken together, our data demonstrate that nucleosome incorporation of H3.3 by HIRA safeguards myogenic gene expression and represses that of alternative lineage genes.

Dr France Pietri-Rouxel

Institut de Myologie, Paris, France

GDF5: A potential treatment for (neuro)-muscular diseases

Invitée par Laurent SCHAEFFER

Abstract
Among factors involved in muscle homeostasis, emerging relevance is observed for Growth Differentiation Factor 5 (GDF5) which we have shown to prevent age-related muscle mass loss and force decline.
Indeed, we demonstrated that GDF5 overexpression in muscle during ageing induces muscle mass gain and improves neuromuscular connectivity and endplate morphology. In addition, we presented the characterization of the cellular and molecular effects of GDF5 in muscle during aging and showed its “rejuvenating signature”. Based on this proof of concept, we defined a cutting-edge therapeutic approach describing how the treatment with the recombinant GDF5 protein is able to counteract the age-related skeletal muscle wasting in mice and might have a strong curative potential on sarcopenia.

GDF5, because of its functions in muscle regeneration, could also be a good candidate for preserving muscle mass in neuromuscular diseases as Duchenne muscular dystrophy (DMD). DMD is a lethal disorder characterized by the lack of dystrophin, which is essential for muscle fibers integrity as its absence results in muscle necrosis followed by cyclic degeneration and regeneration. Initially, regeneration in DMD disease is supported by the proliferation and differentiation of muscle precursor cells, as satellite cells (SCs). However, they progressively exhausted, rendering muscle repair inefficient and leading to muscular dysfunction. Among the therapeutic strategies developed for DMD, clinical trials with AAV administration of microdystrophins (AAV-microDys) are underway and the first data indicate the potential of gene therapy as treatment to respond to unmet need for DMD.

However, these approaches target the degenerating muscle, so their long-term success heavily depends on maintaining muscle mass for as long as possible. We investigated the role of GDF5 in DMD progression using mdx mice and showed that its over-expression modulates regeneration process and induces hyperplasia. Of relevance, we propose to investigate the benefits of a combination of GDF5 with AAV-microdystrophin in improving gene therapy by preserving myofibers integrity and increasing muscle mass.

Valentina Taglietti, Kaouthar Kef, Iwona Bronisz Budzyńska1, Busra Mirciloglu, Mathilde Rodrigues, Nastasia Cardone, Fanny Coulpier, Baptiste Periou, Christel Gentil, Melissa Goddard, François Jérôme Authier, France Pietri Rouxel, Edoardo Malfatti, Peggy Lafuste, Laurent Tiret and Frederic Relaix Effects of lipid based Multiple Micronutrients Supplement on the birth outcome of underweight pre-eclamptic women: A randomized clinical trial. Acta Neuropathologica Communications 2022 10:60 https://doi.org/10.1186/s40478-022-01355-2

Amélie Vergnol, Massiré Traoré, France Pietri-Rouxel* and Sestina Falcone* New Insights in CaVβ Subunits: Role in the Regulation of Gene Expression and Cellular Homeostasis Front. Cell Dev. Biol., 06 April 2022 DOI: 10.3389/fcell.2022.880441 (*authors with equal contribution(s) to the work).

Antoine de Zélicourt, Abdallah Fayssoil, Mbarka Dakouane-Giudicelli, Isley De Jesus, Ahmed Karoui, Faouzi Zarrouki, Florence Lefebvre, Arnaud Mansart, Jean-Marie Launay, Jerome Piquereau, Mariana G. Tarragó, Marcel Bonay, Anne Forand, Sophie Moog, France Piétri-Rouxel, Claudia C.S. Chini, Mathias Mericskay, Eduardo N. Chini, Ana Maria Gomez, José-Manuel Cancela* and Sabine de la Porte* The CD38-NADase is a new major contributor to EMBO Molecular Medicine 2022 e12860 doi: 10.15252/emmm.202012860

Boulinguiez A, Duhem C, Mayeuf-Louchart A, Pourcet B, Sebti Y, Kondratska K, Montel V, Delhaye S, Thorel Q, Beauchamp J, Hebras A, Gimenez M, Couvelaere M, Zecchin M, Ferri L, Prevarskaya N, Forand A, Gentil C, Ohana J, Piétri-Rouxel F, Bastide B, Staels B, Duez H, Lancel S. NR1D1 controls skeletal muscle calcium homeostasis through myoregulin repression. JCI Insight. 2022 Sep 8;7(17):e153584. doi: 10.1172/jci.insight.153584.PMID: 35917173

Amédée Mollard, Cécile Peccate, Anne Forand, Julie Chassagne, Laura Julien, Thibaut Marais, Marc Bitoun, France Piétri-Rouxel, Sofia Benkhelifa-Ziyyat#* and Stéphanie Lorain# Muscle regeneration affects Adeno-Associated Virus-mediated transduction Scientific Report Mollard A, Peccate C, Forand A, Chassagne J, Julien L, Meunier P, Guesmia Z, Marais T, Bitoun M, Piétri-Rouxel F, Benkhelifa-Ziyyat S, Lorain S.Sci Rep. 2022 Jun 11;12(1):9674. doi: 10.1038/s41598-022-13405-9. PMID: 35690627

Francisco Jaque-Fernandez, Gonzalo Jorquera, Jennifer Troc-Gajardo, France Pietri-Rouxel, Christel Gentil, Sonja Buvinic, Bruno Allard, Enrique Jaimovich, Vincent Jacquemond, and Mariana Casas. Pannexin-1 and CaV1.1 show reciprocal interaction during excitation-contraction and excitation-transcription coupling in skeletal muscle The Journal of General Physiology 2021 0ctober doi 10.1085/jgp.202012635

Gargaun E, Falcone S, Solé G, Durigneux J, Urtizberea A, Cuisset JM, Benkhelifa-Ziyyat S, Julien L, Boland A, Sandron F, Meyer V, Deleuze JF, Salgado D, Desvignes JP, Béroud C, Chessel A, Blesius A, Krahn M, Levy N, Leturcq F, Pietri-Rouxel F. The lncRNA 44s2 Study Applicability to the Design of 45-55 Exon Skipping Therapeutic Strategy for DMD. Biomedicines. 2021 Feb 20;9(2):219. doi: 10.3390/biomedicines9020219. PMID: 33672764

Forand A, Muchir A, Mougenot N, Sevoz-Couche C, Peccate C, Lemaitre M, Izabelle C, Wood M, Lorain S, Piétri-Rouxel F. Combined Treatment with Peptide-Conjugated Phosphorodiamidate Morpholino Oligomer-PPMO and AAV-U7 Rescues the Severe DMD Phenotype in Mice. Mol Ther Methods Clin Dev. 2020 Mar 17; 17:695-708. Doi: 10.1016/j.omtm.2020.03.011. eCollection 2020 Jun 12.PMID: 32346547

Traoré M, Gentil C, Benedetto C, Hogrel JY, De la Grange P, Cadot B, Benkhelifa-Ziyyat S, Julien L, Lemaitre M, Ferry A, Piétri-Rouxel F*, Falcone S* (*authors with equal contribution(s) to the work). An embryonic CaVβ1 isoform promotes muscle mass maintenance via GDF5 signaling in adult mouse. Sci Transl Med. 2019 Nov 6; 11(517):eaaw1131. Doi: 10.1126/scitranslmed.aaw1131. PMID: 31694926
Guilbaud M, Gentil C, Peccate C, Gargaun E, Holtzmann I, Gruszczynski C, Falcone S, Mamchaoui K, Ben Yaou R, Leturcq F, Jeanson-Leh L, Piétri-Rouxel F. miR-708-5p and miR-34c-5p are involved in nNOS regulation in dystrophic context. Skeletal Muscle. 2018 Apr 27;8(1):15. Doi: 10.1186/s13395-018-0161-2. PMID: 29703249

Dr Jean-Sébastien Sylvestre

Université de Paris PARCC, Paris, France

Immunotherapies for myocardial infarction

Invité par Bénédicte Chazaud

Abstract
Despite improved in the management, patients with ischemic heart failure still suffer from high morbidity and mortality, and there is an urgent need to develop therapeutic approaches that promote recovery of cardiac function after myocardial infarction with a favorable safety profile and improved efficacy. Immune responses play important roles in the development of post-infarction adverse events, and numerous preclinical data confirm the critical role of the immune system in regulating cardiac repair and remodeling in this setting. We will discuss the development of different immunotherapy approaches targeting the lymphocyte populations to improve cardiac function after myocardial infarction.

Zouggari Y, Ait-Oufella H, Bonnin P, Simon T, Sage AP, Guérin G, Vilar J, Caligiuri G, Tsiantoulas D, Laurans L, Dumeau E, Kotti K, Bruneval K, Charo IF, Binder CJ, Danchin N, Tedgui A, Tedder TF, Silvestre JS*/Mallat Z*. B lymphocytes trigger Ccl7-dependent mobilization of monocytes and promote adverse ventricular remodeling after acute myocardial infarction. Nature Medicine. 2013.Oct;19(10):1273-80. *equal contribution.

Sun Y, Pinto C, Camus S, Duval V, Alayrac P, Zlatanova I, Loyer X, Vilar J, Lemitre M, Levoye A, Nus M, Ait-Oufella H, Mallat Z, Silvestre JS. Splenic Marginal Zone B Lymphocytes Regulate Cardiac Remodeling After Acute Myocardial Infarction in Mice. J Am Coll Cardiol. 2022 Feb 22;79(7):632-647.

Santos-Zas I, Lemarié J, Zlatanova I, Cachanado M, Seghezzi JC, Benamer H, Goube P, Vandestienne M, Cohen R, Ezzo M, Duval V, Zhang Y, Su JB, Bizé A, Sambin L, Bonnin P, Branchereau M, Heymes C, Tanchot C, Vilar J, Delacroix C, Hulot JS, Cochain C, Bruneval P, Danchin N, Tedgui A, Mallat Z, Simon T, Ghaleh B, Silvestre JS, Ait-Oufella H. Cytotoxic CD8+ T cells promote granzyme B-dependent adverse post-ischemic cardiac remodeling. Nat Commun. 2021 Mar 5;12(1):1483.

Robert Knight

king’s College of London, United-Kingdom

Heterogeneity within the muscle stem cell population reflects a Notch-driven response to macrophages

Invité par Bénédicte Chazaud

Abstract
Muscle stem cells (muSCs) are crucial for muscle repair, but are increasingly understood to represent a heterogenous population with different regenerative potentials and responses to regulatory signals. To investigate how heterogeneity affects muSC function in vivo we have used zebrafish as a model of tissue regeneration and explored the importance of Notch activity and macrophage function. We show that Notch activity is found in a subset of muSCs that do not show large contributions to focal injury. This response is amplified in an absence of Notch signalling and after ablation of macrophages. In contrast, a population of pax7-expressing muSCs require Notch activity for their expansion after injury and are negatively regulated by macrophages. Manipulation of Notch in macrophages reveals a macrophage-dependent activation of Notch differentially regulates these two muSC populations to ensure robustness in response to tissue injury.

Sultan, S.H.A., C. Dyer, and Knight, R. D. Notch Signaling Regulates Muscle Stem Cell Homeostasis and Regeneration in a Teleost Fish. Frontiers in Cell and Developmental Biology, 2021. 9(2501). doi.org/10.3389/fcell.2021.726281

Haroon M, Klein-Nulend J, Bakker A. D., Jin J, Seddiqi H, Offringa C, de Wit G. M. J., Le Grand F, Giordani L, Liu K. J., Knight R. D., Jaspers R. T. Myofiber stretch induces tensile and shear deformation of muscle stem cells in their native niche. Biophys J. 2021 Jul 6;120(13):2665-2678. doi:10.1016/j.bpj.2021.05.021

Mitchell, C., Caroff, L., Vigilante, A., Solis-Lemus, J.-A., Reyes-Aldasoro, C. C., de Chaumont, F., Dufour, Al, Dallongeville, S., Olivo-Marin, J.-C., Knight, R. D. ‘Cell Tracking Profiler: a user-driven analysis framework for evaluating 4D live cell imaging datasets’. Journal of Cell Science (2020) 133(22): jcs241422.doi:10.1242/jcs.241422

Claire Chazaud

Institut de Génétique, Reproduction & Développement (iGReD), Clermont-Ferrand, France

Differentiation of the pluripotent stem cells of the mammalian embryo: the emergence of the Epiblast

Invitée par Rémi MOUNIER

Abstract
Our goal is to decipher the mechanisms of cell differentiation in the preimplantation mouse embryo. We are focusing on Primitive Endoderm versus Epiblast specification during blastocyst development and in the past years we have shown the interplay between different transcription factors such as Nanog for the Epiblast and Gata6, Sox17, Gata4 for the Primitive Endoderm. These findings have an important impact in stem cell biology, as embryonic stem cells (ES) are derived from blastocysts.

I will present our latest results that reveal a stochastic mechanism to differentiate Epiblast cells.

Allègre N*, Chauveau S*, Dennis C, Renaud Y, Meistermann D, Valverde Estrella L, Pouchin P, Cohen-Tannoudji M, David L and Chazaud C (2022). NANOG initiates epiblast fate through the coordination of pluripotency genes expression. Nature Communications 13, 3550 -.*equal contribution

Azami T*, Bassalert C*, Allègre N, Valverde Estrella L, Pouchin P, Ema M and Chazaud C (2019). Regulation of ERK signalling pathway in the developing mouse blastocyst. Development 146: dev177139. *equal contribution

Tosenberger A, Gonze D, Bessonnard S, Cohen-Tannoudji M, Chazaud C and Dupont G (2017). A multiscale model of early cell lineage specification including cell division. Nature Partner Journal Systems Biology and Applications 3:16. doi: 10.1038/s41540-017-0017-0

Igor Medina

INMED, Université d’Aix-Marseille, France

Impaired KCC2 leads for neuranal network dysfunction and neurodevelopmental pathologies

Invité par Julien COURCHET

Abstract
My research activity during last decade is dedicated to study the structure, function and physiological importance of KCC2, a neuron – restricted K+,Cl- co-transporter. KCC2 plays a critical role in setting neuronal i and control of the inhibitory strength of GABA and glycine neurotransmission. The dysfunction of KCC2 leads to i misbalance, change of the inhibitory action of GABA and formation of different types of epilepsies. A number of recent studies also assign an important role for modified i neuronal in etiology of multiple neurodevelopmental diseases (NDD), including autism spectrum disorders (ASDs), schizophrenia, Rett syndrome. However yet, none of studies have established a direct causal link between perturbed Cl- homeostasis and pathology.
To better understand the role of Cl- in formation of NDD we are seeking for rare mutation in KCC2 associated with diseases and explore functional consequences of these mutation using different in-vitro and animal models. For example, we have found that mouse harboring functionally important mutations in KCC2 has modified neuronal i resulting in changes of neuronal circuits and associated with abnormal social behavior. Thus, KCC2 dysfunction itself can conduct to NDD. Respectively, upregulation of KCC2 constitutes an attractive therapeutic target.

Friedel P, Kahle KT, Zhang J, Hertz NT, Pisella LI, Buhler E, Schaller F, Duan J, Khanna AR, Bishop PN, Shokat KM & Medina I (2015). WNK1-regulated inhibitory phosphorylation of the KCC2 cotransporter maintains the depolarizing action of GABA in immature neurons. Sci Signal 8, 23–26.
Friedel P, Ludwig A, Pellegrino C, Agez M, Jawhari A, Rivera C & Medina I (2017). A Novel View on the Role of Intracellular Tails in Surface Delivery of the Potassium-Chloride Cotransporter KCC2. eNeuro 2, 1–19.
Medina I, Friedel P, Rivera C, Kahle KT, Kourdougli N, Uvarov P & Pellegrino C (2014). Current view on the functional regulation of the neuronal K+-Cl− cotransporter KCC2. Front Cell Neurosci 8, 1–18.
Pisella LI, Gaiarsa J-L, Diabira D, Zhang J, Khalilov I, Duan J, Kahle KT & Medina I (2019). Impaired regulation of KCC2 phosphorylation leads to neuronal network dysfunction and neurodevelopmental pathology. Sci Signal 12, 0300.

Angelica Harbauer

Max Planck-Institute of Neurobiology, Munich, Germany

Mitochondrial health maintenance in neurons

Invitée par Julien COURCHET

Abstract
Neurons with their elaborate and extended morphology must employ homeostatic mechanisms that allow neuronal mitochondria to exist far away from the cell body while still retaining a functional proteome. This process, called “Mitostasis”, is most likely a finely tuned concert of mitochondrial transport, local protein synthesis and local degradation by proteasomal and autophagic mechanisms.

However, the processes that allow transport mRNAs encoding for mitochondrial proteins are only partially understood. Using the transcript of PTEN-induced kinase 1 (PINK1) as a model substrate we have discovered that this RNA associates with mitochondria specifically in neurons and uses mitochondria as a means of transport into axons and dendrites. This is a neuron specific mechanism driven by selective expression of an mRNA anchoring complex at the outer mitochondrial membrane. Loss of this complex impairs local PINK1 function in the removal of damaged organelles (mitophagy) and hence mitostasis. Modulation of this pathway may therefore prove beneficial in the treatment of mitostatic diseases including Parkinson’s disease.

Flavie Strappazzon

Fondation Santa Luccia, Rome, Italie

Targeting mitophagy as a strategy for therapeutic intervention in diseases

Invitée par Julien COURCHET

Abstract
Mitophagy is a form of autophagy (a self-protective mechanism of living cells or organisms under various stressful conditions) that selectively degrades damaged mitochondria. During this process, double membrane autophagosomes enclose entire mitochondria and then fuse with lysosomes for degradation. It is now clear that many human pathologies present alterations in mitophagy. Maintaining a healthy mitochondrial pool by modulating mitophagy is therefore of particular importance in neurodegenerative and other related diseases. Our laboratory explores the molecular components of mitophagy as novel pharmacological targets for drug development and therapeutic intervention for neuodegenerative and other diseases. In particular, I will present our latest findings on the central role of microRNA-218 in the control of mitophagy and therefore as a promising new target for human diseases. In addition, I will unveil, one of the main mitophagic receptors, as a novel protective factor in the context of multiple sclerosis, an autoimmune disease of the central nervous system.

Strappazzon F, Di Rita A, Peschiaroli A, Leoncini PP, Locatelli F, Melino G, Cecconi F. HUWE1 controls MCL1 stability to unleash AMBRA1-induced mitophagy. Cell Death Differ. 2020 Apr;27(4):1155-1168. doi: 10.1038/s41418-019-0404-8. Epub 2019 Aug 21

D’Acunzo P, Strappazzon F, Caruana I, Meneghetti G, Di Rita A, Simula L, Weber G, Del Bufalo F, Dalla Valle L, Campello S, Locatelli F, Cecconi F. Reversible induction of mitophagy by an optogenetic bimodular system. Nat Commun. 2019 Apr 4;10(1):1533.

Di Rita A, Peschiaroli A, D Acunzo P, Strobbe D, Hu Z, Gruber J, Nygaard M, Lambrughi M, Melino G, Papaleo E, Dengjel J, El Alaoui S, Campanella M, Dötsch V, Rogov VV, Strappazzon F, Cecconi F. HUWE1 E3 ligase promotes PINK1/PARKIN-independent mitophagy by regulating AMBRA1 activation via IKKα. Nat Commun. 2018 Sep 14;9(1):3755.

Stephan KROGER

Department of Physiological Genomics, Biomedical Center, Ludwig-Maximilians-University, Germany

Muscles have feelings too: muscle spindle function in normal and dystrophic muscle

Invité par Laurent SCHAEFFER

Abstract
Coordinated movements, including locomotion, and their control, require proprioceptive information, i.e. information about muscle tone as well as position and movement of the extremities in space. Muscle spindles are the primary proprioceptive sensory receptors and are present in almost all skeletal muscles. In many neuromuscular diseases, movement is impaired, although the mechanism remains elusive. For example, in muscular dystrophies (MD), patients often experience sudden spontaneous falls, balance problems, as well as gait and posture abnormalities, suggesting the possibility of an impaired muscle spindle function. To investigate, if proprioception is affected in dystrophic muscles, we analyzed muscle spindle number, morphology and function in wildtype mice and in murine models for two distinct types of muscular dystrophy with very different disease etiology, i.e. dystrophin- (DMDmdx) and dysferlin-deficient mice. The total number and the overall structure of muscle spindles in soleus muscles of the dystrophic mice appeared unchanged, demonstrating that intrafusal fibers are less affected by the degeneration compared to extrafusal fibers. Immunohistochemical analyses of wildtype muscle spindles revealed a concentration of dystrophin and -dystroglycan in intrafusal fibers outside the region of contact to the sensory neuron. Utrophin was substantially upregulated in dystrophin-deficient mice, suggesting a potential compensatory activity of utrophin in DMDmdx mice. Single-unit extracellular recordings of sensory afferents from muscle spindles of the extensor digitorum longus muscle revealed that muscle spindles from both dystrophic mouse strains have an increased resting discharge and a higher action potential firing rate during sinusoidal vibrations. In contrast, the response to ramp-and-hold stretches appeared mostly unaltered compared to the respective wildtype mice. These results show alterations in muscle spindle afferent responses in dystrophic mouse muscles, which might cause an increased muscle tone, and might contribute to the unstable gait and frequent falls observed in patients with muscular dystrophy.

Pascale BOMONT

Equipe AVENIR-INSERM, INM-INSERM U1051, Hopital St Eloi, Montpellier

Exploring neurofilament biology and autophagy in neuromuscular diseases:from Giant Axonal Neuropathy to Charcot-Marie-Tooth diseases

Invitée par Hélène Puccio

Abstract
Our group is interested in inherited neuromuscular diseases, and in particular in axonal forms of Charcot-Marie-Tooth diseases. Our focus is on a severe related form, called Giant Axonal Neuropathy (GAN), which causes rapid loss of sensori-motor capacities in the periphery and subsequently spreads widely to the central nervous system. Our group identified the GAN gene and its defective protein, the Gigaxonin-E3 ligase and developed diagnostic tools to discriminate GAN from related CMTs. Furthermore, we modelized GAN in patient’s cells, mouse and zebrafish to investigate the pathological dysfunctions and translate our research into therapeutic products. In particular, I will present our findings on the pivotal role of Gigaxonin-E3 ligase in controlling key biological processes: Neurofilament and more generally Intermediate Filament organization, autophagy induction, and Sonic Hedgehog mediated neuron specification. In addition, achievements in generating relevant therapeutic methodologies for GAN will be discussed. Considering the evolving landscape of CMTs, which now highlights central nervous system involvement and common functional modalities with GAN, we would like to propose GAN as a key CMT form to understand the complexity of CMT biology. Finally, I will present the new scientific directions we are undertaking, expanding from GAN to other CMT diseases, with neurofilaments at the center of our focus.

Mechanisms & functions
1. Sonic Hedgehog repression underlies gigaxonin mutation-induced motor deficits in giant axonal neuropathy. Arribat Y*, Mysiak KS*, Lescouzères L, Boizot A, Ruiz M, Rossel M, Bomont P.
J Clin Invest. 2019 Dec 2;129(12):5312-5326
2. Gigaxonin E3 ligase governs ATG16L1 turnover to control autophagosome production.
Scrivo A, Codogno P, Bomont P.
Nat Commun. 2019 Feb 15;10(1):780.
3. Giant axonal neuropathy-associated gigaxonin mutations impair intermediate filament protein degradation. Mahammad S, et al.
J Clin Invest. 2013 May;123(5):1964-75.

Diagnosis
4. The instability of the BTB-KELCH protein Gigaxonin causes Giant Axonal Neuropathy and constitutes a new penetrant and specific diagnostic test. Boizot A, Talmat-Amar Y, Morrogh D, Kuntz NL, Halbert C, Chabrol B, Houlden H, Stojkovic T, Schulman BA, Rautenstrauss B, Bomont P.
Acta Neuropathol Commun. 2014 Apr 24;2:47.

Clinics & genetics
5. Giant Axonal Neuropathy.
Kuhlenbäumer G, Timmerman V, Bomont P.
In: Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJH, Stephens K, Amemiya A, editors. GeneReviews® . Seattle (WA): University of Washington, Seattle; 1993-2020.
6. The gene encoding gigaxonin, a new member of the cytoskeletal BTB/kelch repeat family, is mutated in giant axonal neuropathy.
Bomont P, Cavalier L, Blondeau F, Ben Hamida C, Belal S, Tazir M, Demir E, Topaloglu H, Korinthenberg R, Tüysüz B, Landrieu P, Hentati F, Koenig M.
Nat Genet. 2000 Nov;26(3):370-4.

Thomas LAUMONIER

Cell Therapy & Musculoskeletal Disorders Lab, Department of Orthopedic Surgery, Genève

Cellular and molecular heterogeneity of human skeletal muscle stem cells

Invité par Isabella SCIONTI

Abstract
Satellite cells (SC) are Pax7+ tissue resident muscle stem cells, essential for muscle regeneration. SC are therefore considered as a potential stem cell source to treat skeletal muscle diseases. Nevertheless, as other primary muscle stem cells, SC are difficult to expand in vitro without dramatically reducing their regenerative potential. We have recently demonstrated that human myogenic reserve cells (RC) are quiescent myogenic stem cells with properties required for their use in cell therapy i.e. they survive, they form new myofibers and they generate new Pax7+ cells in vivo. Moreover, as compare to other muscle stem cells, RC hold the advantage to be generated in vitro in number compatible with possible therapeutic applications. We also showed that RC is an heterogenous population with a Pax7Hi and a Pax7Lo population. To study their cellular and molecular heterogeneity, we combined intracellular flow cytometry to isolate a pure population of Pax7Hi and Pax7Lo fixed-permeabilized human RC with high sensitivity RNAseq to analyze their transcriptional profile. Additionally, we study their metabolic and bioenergetic profile as metabolism is considered to be an active player in the regulation of cell state. Significant transcriptional changes were observed between Pax7Hi and Pax7Lo RC subpopulations with 399 modified genes. Pax7, Spry1 and Hes1 were upregulated in Pax7Hi subpopulation as genes involved in apoptosis, cell cycle regulation and oxidative stress. Our findings suggest that the Pax7Hi RC subpopulation adopt a more stem-like state and may constitute an appropriate stem cell source for potential therapeutic applications.

Katrien De Bock

Laboratory of Exercise and Health, ETH Zurich, Suisse

Metabolic crosstalk between the endothelium and macrophages during recovery from hindlimb ischemia

Invité par Rémi MOUNIER

Abstract
Angiogenesis, the formation of new blood vessels from existing ones, is initiated by the secretion of growth factors – the vascular endothelial growth factor VEGF is the best described one – from a hypoxic environment. To grow under low oxygen conditions, ECs have unique metabolic characteristics. Indeed, even though they are located next to the blood stream – and therefore have access to the highest oxygen levels – ECs are highly glycolytic. However, when they need to sprout into avascular areas and form new vessels, they upregulate glycolysis even further to fuel migration and proliferation. Suppression of glycolysis via inhibition of the glycolytic regulator PFKFB3 (phosphofructokinase-2/fructose-2,6-bisphosphatase isoform 3) in endothelial cells prevents blood vessel growth in the retina of the mouse pup and also in various models of pathological angiogenesis. While we now know that ECs are metabolically preconditioned to rapidly form new vessels, it remains an outstanding question whether this also holds true in muscle and whether endothelial metabolism can become a target for the treatment of peripheral artery disease.

We recently could show that EC specific loss of PFKFB3 reduced revascularization of the mouse ischemic hindlimb and impaired muscle regeneration. This was caused by the reduced ability of macrophages to adopt a proangiogenic and proregenerative phenotype. Mechanistically, we found that endothelial cells metabolically communicate with macrophages to drive M2-like polarization of macrophages during recovery from ischemia. In summary, we have identified angiocrine metabolic properties of ECs during muscle regeneration from ischemia.

Recent Publications:
PHD1 controls muscle mTORC1 in a hydroxylation-independent manner by stabilizing leucyl tRNA synthetase.
D’Hulst G, Soro-Arnaiz I, Masschelein E, Veys K, Fitzgerald G, Smeuninx B, Kim S, Deldicque L, Blaauw B, Carmeliet P, Breen L, Koivunen P, Zhao SM, De Bock K.
Nat Commun. 2020 Jan 10;11(1):174. doi: 10.1038/s41467-019-13889-6.

Differentiation but not ALS mutations in FUS rewires motor neuron metabolism.
Vandoorne T, Veys K, Guo W, Sicart A, Vints K, Swijsen A, Moisse M, Eelen G, Gounko NV, Fumagalli L, Fazal R, Germeys C, Quaegebeur A, Fendt SM, Carmeliet P, Verfaillie C, Van Damme P, Ghesquière B, De Bock K, Van Den Bosch L.
Nat Commun. 2019 Sep 12;10(1):4147. doi: 10.1038/s41467-019-12099-4.

Partial and transient reduction of glycolysis by PFKFB3 blockade reduces pathological angiogenesis.
Schoors S, De Bock K, Cantelmo AR, Georgiadou M, Ghesquière B, Cauwenberghs S, Kuchnio A, Wong BW, Quaegebeur A, Goveia J, Bifari F, Wang X, Blanco R, Tembuyser B, Cornelissen I, Bouché A, Vinckier S, Diaz-Moralli S, Gerhardt H, Telang S, Cascante M, Chesney J, Dewerchin M, Carmeliet P.
Cell Metab. 2014 Jan 7;19(1):37-48. doi: 10.1016/j.cmet.2013.11.008. Epub 2013 Dec 12.

Role of PFKFB3-driven glycolysis in vessel sprouting.
De Bock K, Georgiadou M, Schoors S, Kuchnio A, Wong BW, Cantelmo AR, Quaegebeur A, Ghesquière B, Cauwenberghs S, Eelen G, Phng LK, Betz I, Tembuyser B, Brepoels K, Welti J, Geudens I, Segura I, Cruys B, Bifari F, Decimo I, Blanco R, Wyns S, Vangindertael J, Rocha S, Collins RT, Munck S, Daelemans D, Imamura H, Devlieger R, Rider M, Van Veldhoven PP, Schuit F, Bartrons R, Hofkens J, Fraisl P, Telang S, Deberardinis RJ, Schoonjans L, Vinckier S, Chesney J, Gerhardt H, Dewerchin M, Carmeliet P.
Cell. 2013 Aug 1;154(3):651-63. doi: 10.1016/j.cell.2013.06.037.

Christophe LETERRIER

Aix Marseille Université

The axonal cytoskeleton at the nanoscale

Invité par Julien COURCHET

Abstract
The intricate morphology and molecular identity of axons is maintained for decades, but also continuously adapts to changes in the environment and activity of neurons. Axons fulfill these paradoxical demands thanks to a unique cytoskeletal organization that ensures the coordinated transport, anchoring and mobility of axonal components (1). In our lab, we use super-resolution microscopy to map the nanoscale architecture actin-based structures within the axon. In the axon initial segment, a key compartment for the maintenance of neuronal polarity, we resolved a highly organized assembly encompassing the periodic actin/spectrin scaffold and its partners: ankyrin, myosins (2). We have also visualized new actin structures along the axon shaft: rings, hotspots and trails, and are now exploring their molecular organization and functions (3). For this, we develop a combination of versatile labeling, correlative live-cell/super-resolution/electron microscopy and quantitative analysis that allow for high-content, nanoscale interrogation of the axonal architecture (4).

1. Leterrier, C., Dubey, P., Roy, s. (2017). The nano-architecture of the axonal cytoskeleton. Nature Reviews Neurosciences 18(12), 713 – 726.
2. Leterrier, C., Potier, J., Caillol, G., Debarnot, C., Rueda-Boroni, F., Dargent, B. (2015). Nanoscale Architecture of the Axon Initial Segment Reveals an Organized and Robust Scaffold Cell Reports 13(12), 2781 – 2793.
3. Ganguly, A., Tang, Y., Wang, L., Ladt, K., Loi, J., Dargent, B., Leterrier, C., Roy, s. (2015). A dynamic formin-dependent deep F-actin network in axons. The Journal of Cell Biology 104(51), 20576 – 417.
4. Vassilopoulos, S., Gibaud, S., Jimenez, A., Caillol, G., Leterrier, C. (2019). Ultrastructure of the axonal periodic scaffold reveals a braid-like organization of actin rings. Nature Communications 10(1), 5803.

Bruno CADOT

Université de Sorbonne

Nuclear dynamics and myogenic differentiation

Invité par Fabien Le Grand

Abstract

Les cellules musculaires sont caractérisées par la présence de plusieurs noyaux régulièrement espacés sous la membrane plasmique. La question de savoir si cet arrangement particulier est nécessaire pour la fonction musculaire est encore en discussion. Néanmoins, plusieurs maladies musculaires sont caractérisées par un positionnement nucléaire anormal, telles que les myopathies centronucléaires, les titinopathies et les desminopathies ou dues à des mutations de protéines d’enveloppe nucléaire connues pour être impliquées dans le mouvement nucléaire dans d’autres systèmes. Depuis plusieurs années, nous étudions les mécanismes contrôlant trois des quatre mouvements nucléaires successifs et différents se produisant lors de la formation de myofibres par live imaging. En criblant l’effet de la suppression de différents moteurs moléculaires, nous avons identifié plusieurs moteurs associés aux microtubules impliqués à différents niveaux sur le mouvement et le positionnement nucléaires. Nous avons établi la connexion entre le noyau et le cytosquelette comme étant décisive pour un bon positionnement nucléaire. En particulier, la Nesprin-1, une protéine mutée dans une dystrophie musculaire congénitale, est nécessaire à la réorganisation du cytosquelette des microtubules lors de la différenciation des cellules musculaires et des mouvements nucléaires ultérieurs. Nous étudions actuellement l’implication des déformations nucléaires et la composition de l’enveloppe nucléaire sur la différenciation musculaire. Notre recherche utilise des systèmes in vitro qui récapitulent les observations in vivo et permettent l’étude des mutations trouvées dans les maladies musculaires sur le positionnement nucléaire dans les cellules musculaires.

Sabine Fanny BENSAMOUN

Université de Sorbonne

Caractérisation in vitro/ in vivo du tissu musculaire

Invité par Vincent Gache

Alexandre REYMOND

Director, Center for Integrative Genomics,
University of Lausanne, Genopode building, CH-1015 Lausanne, Switzerland

Genome architecture and diseases: the 16p11.2 paradigm

Invité par Julien Courchet

Abstract

Copy number changes in 16p11.2 contribute significantly to neuropsychiatric traits. Besides the 600 kb BP4-BP5 (breakpoint) CNV found in 1% of individuals with autism spectrum disorders and schizophrenia and whose rearrangement causes reciprocal defects in head size and body weight, a second distal 220kb BP2-BP3 CNV is a likewise potent driver of neuropsychiatric, anatomical and metabolic pathologies. These two CNVs-prone regions at 16p11.2 are reciprocally engaged in complex chromatin looping and concomitant expression changes, as well as genetic interaction between genes mapping within both intervals, intimating a functional relationship between genes in these regions that might be relevant to pathomechanism.
These recurrent pathogenic deletions and duplications are mediated by a complex set of highly identical and directly oriented segmental duplications. This disease-predisposing architecture results from recent, Homo sapiens-specific duplications (i.e. absent in Neandertal and Denisova) of a segment including the BOLA2 gene, the latest among a series of genomic changes that dramatically restructured the region during hominid evolution. Our results show that BOLA2 participates in iron homeostasis and a lower dosage is associated with anemia. These data highlight a potential adaptive role of the human-specific expansion of BOLA2 in improving iron metabolism.
Finally, we combined phenotyping of carriers of rare copy variant at 16p11.2, Mendelian randomization and animal modeling to identify the causative gene in a Genome-wide association studies (GWAS) locus for age at menarche. Our interdisciplinary approach allowed overcoming the GWAS recurrent inability to link a susceptibility locus with causal gene(s).

Robert KNIGHT

King’s College London, Craniofacial Development & Stem Cell Biology

In vivo dissection of macrophage function during tissue regeneration

Invité par Bénédicte Chazaud

Abstract

Regeneration of tissue is intimately linked to function of the immune system. Although it is widely agreed that inflammatory cells are important for effective repair of a wide variety of tissue types, inappropriate or over-activation of inflammation will promote fibrosis and impair regeneration. Specifically, muscle repair requires macrophage function, but changes to macrophage function can prevent regeneration, implying that macrophages have a dynamic and highly regulated role in this process. To dissect the role of macrophages and inflammatory signalling during repair of muscle we have adopted an in vivo imaging approach to visualise cell behaviour during regeneration. We describe how macrophage responses to injury in zebrafish are regulated by NF-kB activity through a TNF-mediated regulation of recruitment. We explore how macrophages are required for modulating muscle stem cell (muSC) responses to injury and the molecules involved in this interaction and propose a model for how muSC proliferation, differentiation and migration are affected by inflammatory cells.
If you wish to meet Robert, please contact Bénédicte Chazaud (benedicte.chazaud@inserm.fr).

Nicolas Dumont

Centre de recherche du CHU Ste-Justine,Université de Montréal

A novel approach targeting inflammation and muscle stem cells simultaneously to mitigate Duchenne Muscular Dystrophy

Invité par Rémi Mounier

Abstract

Duchenne muscular dystrophy (DMD) is a severe childhood muscle disease characterized by the absence of dystrophin, a structural protein critical for muscle fiber stability. Different factors contribute to the progression of the disease such as myofiber fragility, chronic inflammation, fibroadipose tissue deposition, and muscle stem cell dysfunction. So far, glucocorticoids remain the only drugs that are able to delay the progression of the disease; however, they also directly stimulate protein catabolism and long-term muscle wasting. Therefore, the therapeutic potential of glucocorticoids is mitigated by their harmful side effects. Our research project investigates the therapeutic potential of a novel class of bioactive lipids that have potent anti-inflammatory capacities and can simultaneously target muscle stem cells. Our findings indicate that these novel mediators improve myogenesis, muscle growth and function in dystrophic mice to a higher level than glucocorticoids. Thus, our findings suggest that this new therapeutic approach is a significant improvement compared to the standard-of-care treatment for DMD.

Giovanna De Chiara

Institute of Translational Pharmacology, National Research Council,Italie

Herpes Simplex Virus -1 (HSV-1) and Alzheimer’s disease: more than a hypothesis

Invité par Patrick Lomonte

Abstract
HSV is a DNA virus causing life-long latent infection in humans with multiple reactivations. Starting from the pioneering studies showing evidence of HSV-1 genome in Alzheimer’s disease (AD) brains, a growing body of epidemiological and experimental reports have proposed a possible connection between AD risk and HSV-1 recurrent infections. However, a cause-effect relationship between virus reactivations and this disorder has yet to be definitely proved. For this reason, we investigated a mouse model of recurrent HSV-1 infection for the appearance over time of AD markers, including brain accumulation of amyloid-β and hyperphosphorylated tau proteins, oxidative damages and neuroinflammation. Biochemical analysis of mouse brains revealed that multiple HSV-1 reactivations induced all these hallmarks. Specific oxidative damages were: increased levels of 4-hydroxynonenal (HNE, marker of lipid peroxidation), protein nytrosylation and carboxylation; alteration in the level of 13 HNE-modified proteins involved in important intracellular processes, suggesting that their oxidation may affect brain physiology. Finally, behavioral tests evidenced cognitive deficits that increased with multiple virus reactivations. Overall, our data suggest that recurrent HSV-1 infections concur to AD neurodegeneration also through oxidative damages.

Baptiste LACOSTE

The University of Ottawa Brain and Mind Research Institute

Vascular contribution to a neurodevelopmental disorder

Invité par Julien Courchet

Abstract

While the neuronal underpinnings of autism spectrum disorders (ASD) are being unraveled, vascular contributions to these conditions remain elusive. We investigated postnatal cerebrovascular development in a mouse model of the 16p11.2 deletion ASD syndrome, and discovered that 16p11.2 hemizygosity was causally linked to structural and functional abnormalities of brain vascular networks. Cortical vascular density was reduced at postnatal day (P) 14 in 16p11.2df/+ mice, while baseline cerebral blood flow, neurovascular coupling, and cerebrovascular reactivity were altered at P50. Both developmental and functional vascular deficits were endothelium-dependent. Moreover, network-forming defects were identified in vitro using either 16p11.2df/+ primary mouse brain endothelial cells or human endothelial cells derived from 16p11.2 deletion carriers. We also found that mice with endothelium-specific 16p11.2 haploinsufficiency displayed ASD-associated behavioral traits,including locomotor hyperactivity and increased marble burying. By establishing vascular cells as substantial contributors to 16p11.2 deletion syndrome, our findings open new doors for ASD research.

Jyoti Jaiswal

Children’s National Medical Center, Georges Washington University, Washington DC

Beyond the energy needs –
what can diseases tell us about the role of mitochondria in muscle repair

Invité par Benedicte Chazaud

Abstract

Skeletal muscle relies on mitochondria to produce energy needed for its contractility. Muscle mitochondria are also signaling hubs that regulate structural and functional changes in the muscle in response to physical activity. However, all the mechanical load and activity can cause sarcolemmal tear which impacts on muscle function in many muscle diseases. We have identified that a novel role of mitochondria in the muscle is to facilitate repair of such sarcolemmal injuries and defect in this contributes to muscle diseases. Therefore, to develop therapies that can improve sarcolemmal integrity in muscular dystrophies, there is an unmet need to better understand the underlying mechanism. I will discuss our effort that led to the identification of this new role of mitochondria, and what we have learned since about this mechanism by way of muscle diseases linked to mitochondrial deficiency in handling calcium, membrane potential, and its dynamics.
If you wish to meet Jyoti Jaiswal, please contact Bénédicte Chazaud (benedicte.chazaud@inserm.fr).

Alban DE KERCHOV D’EXAERDE

ULB Neuroscience Institute, Lab of Neurophysiology, Bruxelles

Neuronal populations and genes involved in drug addiction

Invité par Laurent Schaeffer

Abstract

Motivational processes are under the critical influence of the ventral part of basal ganglia, comprising several interconnected nuclei (as striatum, globus pallidus and ventral tegmental area (VTA)). Addictive drugs increase extracellular DA levels in the ventral striatum, Nucleus Accumbens (NAc), and share this ability despite varied pharmacological properties and mechanisms of action. A major goal in the field of drug addiction has been to uncover the molecular mechanisms underlying addiction-associated neuroadaptations. It has been hypothesized that one such mechanism is the regulation of gene expression7, and there have been numerous studies that have documented altered expression of genes in the NAc. We discovered that Maged1 (Melanoma antigen genes d1) has a mandatory role in behaviours related to drug addiction in BG. Mice lacking Maged1 are insensitive to the behavioural effects of cocaine as assessed by locomotor sensitization, conditioned place preference (CPP), and drug self-administration. Electrophysiological experiments in brain slices and conditional KO mice demonstrated that Maged1 is critical for cortico-accumbal neurotransmission. Further, expression of Maged1 in the prefrontal cortex and amygdala, but not in dopaminergic or striatal neurons, is required for cocaine-induced extracellular DA release in the NAc as well as cocaine-mediated behavioural sensitization and acute cocaine effect respectively. This work identifies Maged1 as a critical molecule involved in cellular processes in BG and behavioural models of addiction.
I initially learned molecular biology and biochemistry during my PhD to decipher the role plasma membrane H+-ATPase in yeast and plant (P.I. Pr André Goffeau). Next, I learned molecular neurobiology, mouse transgenesis, single cell PCR by working on the physiology of nAChRs in NMJ and in catecholaminergic neurons during my postdoctoral fellowship at Pasteur Institute in Paris (P.I. Pr Jean-Pierre Changeux). For the past 16 years, my main interest is the study of the roles of neuronal populations and genes in pathophysiology of Basal Ganglia (BG), mainly in neuropsychiatric models and in the striatum. Our program is based on our ability to target and manipulate genetically and specifically the two populations of Striatal Projecting Neurons (SPN) to evaluate their contributions or the contribution of specific genes in SPNs in various behaviors. My group was the first to demonstrate in vivo that the SPNs of the indirect pathway of BG has an inhibitory effect on locomotion and drug preference and are necessary for drug sensitization and cataleptic effect of antipsychotic by a proper genetic targeting of this population. I am currently Research Director at FRS-FNRS in Belgium at Brussels and President-Elect of the Belgian Society of Neuroscience.

Virginie MOURNETAS

ISTEM Paris

Duchenne muscular dystrophy, a developmental disease

Invitée par Laurent Schaeffer

Abstract

Duchenne muscular dystrophy (DMD) is a recessive X-linked monogenic myopathy. Mutations in the dystrophin gene result in a progressive, yet severe muscle wasting as death occurs around 30. DMD boys are currently diagnosed around 4 – an age at which muscles have already suffered. Moreover, no treatment can currently stop this disease and efficacy of developing human therapies aiming at restoring the expression of dystrophin stays too low.
Our group has identified Dp412e, an embryonic isoform of dystrophin, leading us to investigate DMD during skeletal muscle development by modelling it with human induced pluripotent stem cells (hiPSCs). Our multi-omics study of the differentiation dynamics strongly argues for an early developmental manifestation of DMD whose onset is triggered before the entry into the skeletal muscle compartment, where mitochondria play an initial role and fibrosis is an intrinsic cell feature of skeletal muscle cells. It also demonstrates that hiPSCs 1) recapitulate key developmental steps, enabling the identification of early disease markers; 2) are suitable for studying skeletal myogenesis in human, in both healthy and disease contexts; and 3) are compatible with high-throughput experiments, thus increasing the capability of drug screening.

Luc BERTRAND

Université catholique de Louvain, Brussels

AMPK in cardiac pathologies, not just a metabolic sensor !

Abstract
The AMP-activated protein kinase (AMPK) has been firstly discovered to be activated under metabolic stress conditions such as myocardial ischemia. Its protective action during an ischemic episode has been demonstrated by several research groups. By targeting metabolism, AMPK helps the heart to survive under such deleterious conditions. However, AMPK action extends beyond metabolism and acute stress conditions. Indeed, it has been more recently shown that AMPK acts as protector of the heart in several chronic diseases such heart failure, diabetic cardiomyopathy and cardiac hypertrophy by acting in cardiomyocytes but also on the other cell types such as fibroblasts. Very recently, our group discovered a connection between AMPK and a particular post-translational modification called O-GlcNAcylation, this interplay acting a major role in the development of cardiac hypertrophy. The lecture will focus on the different protective roles of cardiac AMPK.

Saadi Khochbin

Institute for Advanced Biosciences, La Tronche, France

Les séminaires du Chromatin Club – Metabolism-driven epigenetics

Invité par Armelle Corpet / Patrick Lomonte

Annonce de séminaire

Frédéric RELAIX

INSERM – IMRB U955-E10, F-94010 Créteil, France

PAX3 controls the adaptive response of skeletal muscle stem cells to environmental stress

Invité par Rémi Mounier

Abstract
We have identified a molecular link between the Aryl hydrocarbon Receptor (AhR) environmental stress pathway and Pax3/Pax7 developmental genes during craniofacial development. Since Pax3/7 are key regulators of muscle stem cells (muscle satellite cells), we investigated the cellular and molecular impact of chronic 2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD) exposure on skeletal muscle and satellite cells in the adult. We combined in vivo and ex vivo approaches, in order to analyse the impact of chronic exposure to TCDD in several muscles such as tibialis anterior and biceps brachii. While all MuSCs express the transcription factor PAX7, we show that a muscle-specific subset also express PAX3 and exhibit resistance to environmental stress. Upon systemic TCDD treatment, PAX3-negative MuSCs display impaired survival, atypical activation and sporadic differentiation through the xenobiotic Aryl Hydrocarbon Receptor. We further show PAX3-positive MuSCs become sensitized to environmental stress when PAX3 function is impaired and that PAX3-mediated induction of mTORC1-dependent G(alert) is required for protection. Our study therefore identifies a functional heterogeneity of MuSCs in response to environmental stress controlled by PAX3.

Annonce de séminaire

Nicolas RENIER

ICM – Institut du Cerveau et de la Moelle Epinière Paris – FRANCE

A framework for the study of behaviour and plasticity in the adult brain using light sheet microscopy

Invité par Julien Courchet

Abstract
There has been over the past 6 years a convergence in the fields of optics, biochemistry and computing leading to dramatic improvements in light sheet microscopy, tissue clearing protocols and image analysis algorithms. The convergence of these different fields has the potential to streamline brain studies by accelerating data acquisition speed and reliability over the current whole brain analysis pipelines based on serial sectioning methods. We previously developed the iDISCO+ protocol for immunostaining and imaging intact adult mouse brains. As a companion tool, we also developed and distribute ClearMap, an open source environment to segment objects and map them onto reference atlases optimized for large 3D datasets. We used this pipeline as a discovery tool to find brain regions active in correlation with various behaviors by mapping neuronal activity landscapes derived from Fos expression. Here, I will present recent unpublished projects made possible by our upcoming brain mapping pipeline ClearMap 2, expanding the repertoire of applications derived from intact whole brain preparations. We hope that ongoing developments in light sheet microscopy and image analysis pipelines will facilitate our understanding of individual variations in brain activity, connectivity and structure.

Annonce de séminaire

Emmanuel COMPE

Institut de Génétique et de Biologie Moléculaire et Cellulaire Illkirch, Strasbourg

TFIIH and TFIIE mutations: when transcriptional deficiencies lead to neurological disorders

Invité par Ambra Giglia-Mari

Abstract
Trichothiodystrophy (TTD) is an autosomal recessive disorder mainly related to mutations in the DNA repair/transcription factor TFIIH. In addition to the typical dry and brittle hair, individuals with TTD develop neurological defects, including microcephaly and hypomyelination. Using a TTD transgenic mouse model, we previously observed a spatial and selective deregulation of thyroid hormone target genes in the brain, suggesting that transcriptional failures contribute to TTD phenotypes.
Remarkably, mutations within TFIIE, another general transcription factor, have been recently associated with TTD. Such observation prompted us to accurately dissect the partnerships occurring between TFIIE and TFIIH during transcription. Our work revealed an unexpected dynamic process during which TFIIE act as key factors to recruit and position the kinase module of TFIIH within the preinitiation complex. Strikingly, TTD-related mutations in either TFIIH or TFIIE similarly disrupt this early transcriptional process, which could explain why alterations in different transcription factors can lead to the same clinical syndrome.

Annonce de séminaire

Laurent BARTHOLIN

CRCL, Lyon

The obnoxious faces of TGFbeta in pancreatic cancer

Invité par Rémi Mounier

Abstract
The Transforming growth factor beta (TGFB) is a pleiotropic secreted factor with many roles during embryonic and adult life. In cancer, it behaves either as a tumor suppressor or a tumor promoter. To understand this functional duality, our lab have been using as a model Pancreatic Ductal Adenocarcinoma (PDAC), one of the most aggressive tumor, which is expected to become the second cancer-related cause of death by 2030 (after lung cancer). Our work is focused on the oncogenic properties of TGFB with the final goal to specifically target them by developing innovating therapeutics. During this presentation, I will present our work to understand the TGFB oncogenic effects at the molecular (a “new” oncogenic signaling pathway), cellular (effect on differentiation of pancreatic acinar cells), organ (interaction between PDAC cells and nerves invading the tumor) and whole body levels (interaction with muscle).

Fabien LE GRAND

Centre de Recherche en Myologie, Paris

Signaling pathways in muscle tissue regeneration

Invité par Laurent Schaeffer

Abstract
The development and repair of complex metazoan tissues are coordinated by a startlingly small number of evolutionarily conserved signaling pathways. These signals can act in parallel but often function as an integrated hyper-network. Our research aims at understanding the signaling nodes defining this molecular circuitry and the biological significance of pathway cross-talk, using skeletal muscle as a fitting model. Regeneration of the adult muscle tissue relies on a pool of quiescent muscle stem cells located in a niche around the myofibers: the satellite cells (MuSCs). We previously demonstrated that numerous WNT molecules are secreted in the local milieu during muscle regeneration and showed that MuSC self-renewal is in part controlled by non-canonical Wnt7a/PCP (1). To elucidate the roles of the canonical Wnt/ß-catenin pathway in MuSCs, we generated mice with inducible MuSC-specific mutations (2, 3). Mechanistically, we observed that Wnt/ß-catenin signaling orchestrate the cytoplasmic relocalisation of the H3K9 methyltransferase SETDB1 during differentiation (4). We further investigated how Wnt/ß-catenin signaling is connected to Bone morphogenetic protein (BMP) and Transforming growth factor beta (TGF-ß) pathways. Recent work in our lab consisted in dissecting the impact on these pathways on MuSC return to the niche and fusion, respectively. Nevertheless, our understanding of the cells that compose skeletal muscle tissue is limited and molecular definitions of the principal cell types are lacking. This hinders our capacity to decipher signal integration and reciprocity between cells. We thus used a novel combined approach of single-cell RNA-sequencing and mass cytometry and precisely mapped 10 different cell types in adult mouse skeletal muscle, including two previously unidentified populations (5). This cartography yields crucial insights into muscle-resident cell type identities and will be exploited to build a muscle connectome.

Bert Blaauw

Venetian Insitute of Molecular Medicine

The role of mTORC1 signaling in adult skeletal muscle

Invité par Laurent Schaeffer

Abstract
It is well established that mTORC1 signaling is key modulator of skeletal muscle mass and function. Surprisingly, despite the fact that skeletal muscle undergoes major changes in size and contractility in numerous diseases, no genetic loss-of-function model has been generated to determine the effect of inducible deletion of mTORC1 in adult skeletal muscle. Here we generated inducible, muscle-specific Raptor and mTOR k.o. mice. Interestingly, we do not observe a change in muscle size or contractile properties one month after deletion. However, treating these mice with the mTOR-inhibitor rapamycin is sufficient to induce a very rapid and marked myopathy, suggesting that little residual mTOR signaling can maintain muscle homeostasis in adult muscle. Prolonging deletion of Raptor to 7 months, however, leads to a very marked phenotype characterized by muscle dysfunction, regeneration, glycogen accumulation and mitochondrial dysfunction and block in autophagy. Unexpectedly, one of the best markers of reduced mTOR signaling in muscle fibers is the appearance of denervated fibers. Both muscle-specific deletion of mTOR or Raptor, or the use of rapamycin, was sufficient to induce the appearance of numerous NCAM-positive fibers, muscle fibrillation, and neuromuscular junction fragmentation. Taken together, these results link one of the most important anabolic pathways in skeletal muscle fibers to the maintenance of the NMJ.

Hélène PUCCIO

Department of Translational Medecine and Neurogenetics, IGBMC, Strasbourg

Advances in Friedreich Ataxia: understanding the function of frataxin and developing therapeutic approaches

Invité par Laurent Schaeffer

Abstract
Friedreich’s ataxia (FA), the most common autosomal recessive ataxia, is characterized by a sensory and spinocerebellar ataxia, hypertrophic cardiomyopathy and increase incidence of diabetes. FA is caused by reduced levels of frataxin (FXN), an essential mitochondrial protein involved in the biosynthesis of iron-sulfur (Fe-S) clusters. Fe-S clusters are ancient and essential cofactors that participate in a number of cellular processes ranging from mitochondrial respiration to DNA metabolism. In eukaryotes, de novo Fe-S biogenesis takes place within mitochondria and relies on proteins that are highly conserved from bacteria to humans. Impaired mitochondrial oxidative phosphorylation, bioenergetics imbalance, deficit of Fe-S cluster enzymes and mitochondrial iron overload occur in individuals with FA. To date, no treatment exists for stopping or slowing FA disease.
Over the past years, we have generated cellular and mouse models that reproduce important progressive pathological and biochemical features of the human disease, including cardiac hypertrophy, mixed cerebellar and sensory ataxia, Fe-S enzyme deficiency, and intramitochondrial iron accumulation. These models have enabled us to demonstrate that Fe-S deficit is a primary event of the disease leading to iron metabolism deregulation through the activation of the iron-regulatory protein, IRP1. These models are excellent models for deciphering the physiopathology of the disease and for testing pre-clinical therapeutic protocols. The latest advances in understanding the pathophysiology will be discussed, with a particular emphasis on new neurological models that are being developed as well as therapeutic approaches.

Juliette GODIN

Institut de Génétique et Biologie Moléculaire et Cellulaire, Strasbourg

Pleiotropic activities of the (atypical ?) kinesin KIF21B during cortical development

Invité par Julien Courchet

Abstract
Cortical development progresses through concurrent steps, including neural proliferation, migration and differentiation, that rely on dynamic cell shape remodeling which largely depends on the tight regulation of the microtubules (MT) cytoskeleton. Mutations in tubulin, MT associated proteins or motors have been linked to several neurodevelopmental disorders including malformation of cortical development (MCDs), affecting 2,5% of the world population. Here we identified KIF21B gene as a major locus of human neurodevelopmental disorder. We identified 4 de novo variants in KIF21B gene in patients with intellectual disabilities associated with several brain malformations, including microcephaly, corpus callosum agenesis or facial dimorphism. In support of the pathogenic potential of the discovered alleles, expression of KIF21B variant in mice using in utero electroporation or in zebrafish embryos recapitulated key neurodevelopmental phenotypes, namely migration and microcephaly. In addition, longitudinal neuroanatomical analysis of Kif21b KO model showed strong morphological defects starting prenatally and worsening with time. Finally, we demonstrated that Kif21b regulates migration of projection neurons through the tight control of locomotion and neural shape. Although its motility is dispensable, the regulatory function cytoskeleton dynamics is essential for neuronal migration. Altogether, our data represent an important step to delineate the mechanisms involving KIF21B-mediated MT dynamics and trafficking in the context of brain development.

Annonce de séminaire

Belinda COWLING

Institut de Génétique et Biologie Moléculaire et Cellulaire, Strasbourg

Myostatin – A novel biomarker for Dnm2 therapy in Myotubular Myopathy mice

Invité par Vincent Gache

Abstract
Centronuclear myopathies (CNM) are non-dystrophic muscle diseases for which no effective therapy is currently available. The most severe form, myotubular myopathy (X-linked CNM), is caused by myotubularin 1 (MTM1) loss-of-function mutations, while the main autosomal dominant form is due to dynamin2 (DNM2) mutations. We have shown that antisense oligonucleotide (ASO) mediated DNM2 knockdown can efficiently correct muscle defects due to loss of MTM1 in mice, providing an attractive therapeutic strategy for this disease. We are now investigating blood-based biomarkers that can be used to monitor disease state and rescue in myotubular myopathy mice. Myostatin is a protein produced and released by myocytes, which acts in an autocrine function to inhibit muscle growth and differentiation. Our results suggest myostatin pathway is ‘turned down’ at the mRNA level in muscle biopsies, leading to low levels of circulating and endogenous muscle myostatin in plasma. We have generated preliminary data suggesting ASO-mediated DNM2 reduction results in an increase in circulating myostatin. With clinical trials for myotubular myopathy currently in progress, identification of novel blood-based biomarkers such as myostatin may allow for monitoring of treatment efficacy in patients.

Annonce de séminaire

Huating WANG

The Chinese University of Hong Kong, Hong Kong, China

Functional investigation of LncRNAs and enhancers in skeletal muscle stem cells

Invité par Bénédicte Chazaud

Abstract
Previously, the majority of the human genome was thought to be « junk » DNA with no functional purpose. Over the past decade, evidence from numerous high-throughput genomic platforms reveals that even though less than 2% of the mammalian genome encodes proteins, a significant fraction can be transcribed into different complex families of non-coding RNAs (ncRNAs). Growing evidence supports that ncRNAs have fundamental roles as regulators of genomic output. Among various types of ncRNAs, microRNAs have dominated the current literature. Other groups, however, such as long ncRNAs (lncRNAs, >200nt), have been largely under explored.
Huating Wang’s lab is currently interested in studying the functional roles of long non-coding RNAs (lncRNAs and enhancers) in regulating gene expression in skeletal muscle stem cells and muscle regeneration.

Annonce de séminaire

Yasushi Okamura

Graduate School of Medicine, Osaka University Suita

Coupling from electric signal to lipid signal; voltage-sensing phosphoinositide phosphatase

Invité par Vincent Jacquemond

Résumé

Biological membranes have dual roles in cell signaling: insulator for electrical signal by transfer of ion across membrane as well as the place for metabolism for production of lipid mediators such as arachidonic acids or phosphophositides. These two signals interact with each other through changes of ion concentration, mainly intracellular calcium ions, by the concerted activities of ion channels, transporters and GPCRs. There is a rare case where single membrane proteins directly link between electrical signal and lipid-mediated cell signaling. Voltage-sensing phosphatase consists of the ion channel like voltage sensor and PTEN-like phosphoinositide enzyme. In VSP, single voltage sensor regulates the downstream enzyme and the phosphoinositide phosphatase activity is activated by membrane depolarization leading to depletion of mainly PI(4,5)P2. Substrate specificity of VSP is more broad than PTEN; VSP shows both of 3-phosphatase activity and 5-phosphatase activity unlike PTEN which shows the rigid selectivity toward 3-phosphate of the inositol ring of PI(3,4,5)P3 and PI(3,4)P2. However, the key question how transmembrane voltage sensor regulates the cytoplasmic enzyme has remained unanswered, mainly because a method of detecting structural change in the cytoplasmic region has been limited. We have recently applied a method of genetical incorporation of fluorescent unnatural amino acid, Anap, to the cytoplasmic region of Ci-VSP (sea squirt Ciona intestinalis VSP) which was expressed in Xenopus oocyte. This method enables detection of fine structural change reported by fluorescence intensitiy without perturbing the local protein structure. Voltage-dependent fluorescence change of Anap showed two bidirectional changes along the voltage, decrease at low membrane depolarization and increase at higher depolarization, suggesting that the structure of the cytoplasmic region takes multiple conformations. By applying the method to different constructs of Ci-VSP with altered enzyme activity, we obtained evidence that the enzyme takes at least two activated states with distinct magnitude of enzyme activity. Given that voltage sensor of Ci-VSP takes multiple states during activation, it will be intriguing to see in the future how individual enzyme states correlate with states of the voltage sensor.

Annonce de séminaire

Edgar Gomes

Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal

Mechanisms of nuclear positioning during myofiber formation

Invité par Bénédicte Chazaud

Résumé

Connecting the nucleus to the cytoskeleton is relevant for multiple cellular processes and disruption of these connections result in multiple pathologies. Nuclear positioning within cell cytoplasm requires de connection between nucleus and the cytoskeleton. We are interesting to understand the processes involved in these connections and the role for nuclear positioning in cell function. We study cell migration and skeletal myofiber formation which required the connection between the nucleus and the cytoskeleton and precise nuclear positioning. We use different molecular and cellular approaches in combination with time-lapse imaging analysis to address these questions.

Annonce de séminaire

Rashmi KOTHARY

Centre for Neuromuscular Disease University of Ottawa

Spinal Muscular Atrophy: a multi-organ disease

Invité par Patrick Lomonte

Abstract

Spinal Muscular Atrophy was characterized in the late 1800s but it was almost 100 years later that the genetic cause was identified as a mutation in the human SMN1 gene. While humans do have two genes that code for SMN, SMN2 only produces 10% protein when compared to SMN1. Early work with mouse models was complicated by the fact that mice only have the one Smn gene which when mutated results in preimplantation lethality. This problem was solved by the development of a mouse model incorporating human SMN2 gene, which was for years the only viable mouse model. Now, there are over a hundred mouse models available that have served to inform our understanding of pathogenesis in SMA.
Classically, SMA is described as a motor neuron disease; however, SMN is expressed ubiquitously throughout the body. In fact, SMA is emerging to be a multi-organ disease with SMN depletion having impacts on many tissues in the body. Subcutaneous administration of available treatments may address these affected organs better than intrathecal administration. Also, systemic gene therapies that are currently under development may help repair function in these other organs.
Dr. Kothary will present on the work in his laboratory on the multi-organ nature of SMA. Defects in various tissues will be discussed.

Annonce de séminaire

Laure STROCHLIC

Institut de Myologie – Centre de Recherche en Myologie, Sorbonne Université, INSERM AIM UMRS974, Paris

Regulation of neuromuscular connectivity by Wnt signaling from signaling molecules to therapeutic strategies

Invité par Rémi Mounier

Résumé

The development and maintenance of the neuromuscular connectivity relies on a temporally fine-tuned balance of distinct bi-directional communication between motor neurons and their muscle targets. Disruption of this communication leads to structural and functional defects that affect the motor function and causes severe neuromuscular pathologies. Wnt signaling participates in various developmental mechanisms such as migration, axonal guidance or synaptogenesis. But how the Wnt signaling network could regulate neuromuscular connectivity and how it could affect motor function is unknown. In this presentation, I will provide data using Wnts gain or loss of function studies in cell culture or in mice showing that distinct branches of Wnt signaling, acting in part via the muscle-specific kinase MuSK regulate several key aspects of the formation and maintenance of the neuromuscular synapse including pre and postsynaptic differentiation/stabilization, retrograde control of motor axon outgrowth and synapse-specific gene expression. I will also present evidence showing that the pharmacological modulation of Wnt signaling in a pathological context could be used as a therapeutic strategy to counteract neuromuscular junction (NMJ)- associated disorders. Overall, our results provide novel insights into the mechanisms by which synaptic diffusible cues act to prevent NMJ dysfunction, muscle weakness and disease.

Dans cette présentation, je fournirai des données, utilisant des approches expérimentales in vitro et in vivo chez la souris, qui montrent le rôle émergent de la signalisation Wnt dans la régulation de la connectivité neuromusculaire dans un contexte physiologique et pathologique.

Annonce de séminaire

Helge AMTHOR

Université de Versailles – Paris Saclay Laboratoire U1179 UVSQ – INSERM

BMP signaling controls limb muscle development and maintenance

Invité par Laurent Schaeffer

Résumé
Bone morphogenetic proteins (BMPs) regulate the activity of skeletal muscle precursors as well as the trophic state of differentiated muscle. Here, the role of BMP signaling was explored at different stages of limb muscle development by overexpressing an inhibitory Smad protein (Smad6) to abrogate the BMP signaling cascade at cell autonomous level. Overexpression of Smad6 in limb muscle precursors during development (crossing Rosa26-Lox-Stop-Lox-Smad6-IRES-GFP mice, termed RS6, with Lbx1^Cre/+ transgenic mice) disturbed limb muscle myogenesis: early myogenic markers Pax3 and MyoD were strongly downregulated, fetal limb muscles were smaller, consisted of fewer myofibers and displayed a disturbed muscle patterning. Overexpression of Smad6 in postnatal muscle precursors (using RS6: Pax7^CreERT2/+ mice) caused decreased cell proliferation resulting in smaller myofibers containing less myonuclei and in decreased generation of satellite cells. Overexpression of Smad6 in differentiated muscle resulted in a different phenotype (using RS6:HSA-Cre mice): limb muscles were only modestly smaller, however, consisted of fewer but larger myofibers with increased myonuclear number. Overexpression of the BMP antagonist Noggin in adult muscle (loss-of-function) resulted in muscle fiber atrophy, whereas overexpression of the BMP receptor Alk3 (gain-of-function) caused muscle fiber hypertrophy. These latter effects were likely muscle precursor independent, as overexpression of Smad6 in differentiated fibers (using RS6:Pax7^CreERT2/+ mice) had no effect on satellite cell number and muscle size in the adult. In conclusion, the role of BMP signaling in skeletal muscle is stage and context specific.

Annonce de séminaire

Vanina ROMANELLO

Venetian Institute of Molecular Medicine, Padova

The role of the myokine FGF21 in skeletal muscle homeostasis

Invité par Rémi Mounier

Résumé
Skeletal muscle is a major site of metabolic activity and the most abundant tissue in the human body accounting for almost 40% of the total body mass. It is a plastic tissue that adapts to changes in exercise, nutrition and hormones, which also induces the release of myokines and myometabolites. These muscle-secreted factors have autocrine, paracrine and endocrine effects, explaining how muscles regulate metabolic homeostasis in other tissues. These systemic effects help to explain why physical activity, and thereby muscle recruitment, elicits several beneficial effects in many different diseases. Indeed, exercise preserves and ameliorates mitochondrial function and muscle metabolism, thereby affecting the release of myokines and metabolites that systemically counteract organ deterioration. We have recently proposed an interplay between the myokine Fgf21 and the mitochondrial quality control pathways that greatly contributes to a pro-senescence metabolic shift. However, even though the myokine field is exponentially increasing, little is known about their role in muscle homeostasis.

Annonce de séminaire

Athanassia SOTIROPOULOS

Institut Cochin, Paris

Role of Srf transcription factor and F-actin scaffold in muscle stem cell fusion

Invité par Rémi Mounier

Résumé
Our team is interested on how signaling pathways control of adult skeletal muscle plasticity. In the past years, we focused our attention on Srf transcription factor which is one of the three master genes that controls myogenesis in Caenorhabditis elegans, together with MyoD and HAND. We investigated the role of Srf in two cellular compartments of mouse skeletal muscle (myofibers and adult muscle stem cells) upon different perturbation of muscle homeostasis (hypertrophy, atrophy, regeneration). In the present seminar, I will summarize our findings concerning the role of Srf in myofibers to control muscle mass and I will present recent data identifying Srf as a master regulator of muscle stem cell fusion and demonstrating the implication of F-actin architecture in this process.

Seminar announcement

Cécile MARTINAT

INSERM/UEVE UMR861, I-STEM, AFM

Human pluripotent stem cells for the study and treatment of neuromuscular diseases : myth or reality ?

Résumé
Neuromuscular diseases correspond to a vast group of diseases that perturbs the function of the skeletal muscles by affecting motoneurons, muscles and/or NMJs. To date, no efficient curative treatments have been identified for NMD. Progresses towards identification of new treatment have been hampered by the incomprehension of disease pathogenesis, particularly in early phases, as well as the availability of relevant screening tools. Disease-specific human pluripotent stem cells, from embryonic origin or derived from reprogramming somatic cells, offer the unique opportunity to have access to a large spectrum of disease-specific cell models. Due to their ability of self-renewal and differentiation into various tissues affected in each pathological condition, the development of these human disease-specific pluripotent stem cells provide new insights in pathological mechanisms implicated in human diseases for which, accessing homogenous affected tissues is often challenging. Validating this concept, we previously demonstrated that human pluripotent stem cells and derivatives which, express the causal mutation implicated in the Myotonic Dystrophy type 1 (DM1), offer pertinent disease-cell models, applicable for a wide systemic analysis ranging from mechanistic studies to therapeutic screening. Thus, we identified, through a genome-wide analysis, two early developmental molecular involved both in myogenesis as well as in neurite formation and establishment of neuromuscular connections. These neuropathological mechanisms may bear clinical significance as related to the functional alteration of neuromuscular connections associated with DM1. In parallel to these functional pathological studies, we also demonstrated the pertinence of this new disease-specific cell model to identify new therapeutic strategies. Thus, our results identified the possibility to repurposing metformin, the most commonly prescribed drug for type 2 diabetes, for DM1 leading to a phase 2 clinical trial that is actually ongoing.
We are now extending our approach to another incurable neuromuscular disease, spinal muscular atrophy (SMA). This disease, considered as the leading genetic cause of infant death, is due to mutations or deletions in the « Survival of Motor Neuron » gene, SMN1, which results in low levels of the expressed SMN protein. Despite this ubiquitous SMN expression, the pathology is characterized by degeneration of spinal Motor neurons whereas other neuronal types are relatively preserved suggesting that spinal motor neurons specific features control this differential sensitivity. Based on our recent development allowing the efficient and robust conversion of human pluripotent stem cells into affected spinal motor neurons and non- affected cranial motor neurons, our objective is to deepen the mechanisms involved in the specific degeneration of spinal motor neurons in SMA as well as the mis communication of these neurons with their muscular target.

Annonce de séminaire

Christoph Hoefer, M. Sc.

Senior Business Development Manager ; Life Sciences Solutions, Cell Biology, ThermoFisherScientific

Séminaire Technique : Travailler avec des iPSC (induced Pluripotente Stem Cell)

Résumé
Les cellules souches pluripotentes humaines (iPSC) sont des outils puissants pour la recherche en biologie du développement, la médecine régénérative et l’étude des pathologies humaines. Les données obtenues à partir de modèles physiologiques in vitro amélioreront grandement notre compréhension des processus biologiques. Dans cette présentation, j’aborderai les principaux défis rencontrés dans la mise en place des cellules souches pluripotentes au sein d’un laboratoire et les améliorations récentes apportées à la construction de modèles pour les maladies humaines, telles que la reprogrammation, l’expansion, la transfection, la préservation et la différenciation efficace de iPSC, ainsi que les options de modifications génomiques.

Annonce de séminaire

Nicolas PLACE

Institute of sport Sciences, University of Lausanne

Skeletal muscle adaptations to exercise : a translational approach

Invité par Julien Gondin

Résumé
The amount of force skeletal muscles can produce depends on their contractile history. For instance, repeated contractions generally lead to reduced muscle force generating capacity, namely muscle fatigue. Although muscle fatigue has been the focus of many works in the last 100 years, the underlying mechanisms remain elusive. In this presentation, special emphasis will be given to the role of Ca²⁺ handling as a key regulator of (i) muscle weakness and (ii) beneficial adaptations observed after high intensity interval training. In particular, the potential role of the sarcoplasmic reticulum Ca²⁺ release channel, the ryanodine receptor type 1, will be discussed.

Annonce de séminaire

Julien OCHALA

Faculty of Life Sciences & Medicine, King’s College, London

Actinopathies : From Mutations to Treatment

Invité par Laurent SCHAEFFER

Résumé
Actinopathies are genetically and clinically heterogeneous disorders mainly characterized by generalized muscle weakness. The understanding of this group of disorders has advanced in recent years through the identification of the causative mutations in the gene encoding one of the major proteins of the basic contractile unit of skeletal muscle, i.e., actin. In the present seminar, I will present (i) how these gene mutations lead to generalized muscle weakness and (ii) the advances regarding potential therapies.

Annonce de séminaire

Norbert WEISS

Institute of Organic Chemistry and Biochemistry, Prague

Trafficking of T-type calcium channels in health and disease

Invité par Vincent JACQUEMOND

Résumé
T-type calcium channels are key contributors to neuronal physiology where they shape electrical activity of nerve cells and contribute to the release of neurotransmitters. Alteration of T-type channel expression has been causally linked to a number of pathological conditions including neuropathic pain and absence seizure activity. Although a number of signaling pathways regulating the activity of T-type calcium channels have been reported, the molecular machinery and signaling molecules controlling the trafficking and expression of the channel protein at the plasma membrane remain largely unknown. I will present some of the basic mechanisms recently identified controlling the physiological trafficking of T-type channels, and illustrate how metabolic defects or congenital mutations can disturb this trafficking machinery and eventually leading to disease conditions.

Annonce de séminaire

Justin FALLON

Brown University, Providence, RI

MuSK as a BMP co-receptor

Invité par Laurent Schaeffer

Chantal Thibert

Institute for Advanced Biosciences, Université Grenoble Alpes

The tumor suppressor LKB1 controls cell fate through pyruvate-alanine transamination

Invité par Julien Courchet

Résumé
The tumor suppressor LKB1 (also named STK11) codes for a serine/threonine kinase. LKB1 acts as a key regulator of cell polarity as well as energy metabolism partly through the activation of the AMP-activated protein kinase (AMPK), a sensor that adapts energy supply to the nutrient demands of cells facing situations of metabolic stress.
To determine if Lkb1 exerts a coordinated regulation of energy metabolism and cell polarity, we deleted the Lkb1 gene in polarized cells and explored the metabolic consequences. In particular, we generated spatio-temporal ablation of Lkb1 in a subpopulation of mouse embryonic multipotent neural crest cells (NCC) that originate from the neural tube and give rise to a broad range of derivatives including most of the face, the melanocytes, the peripheral nerves and the enteric nervous system (ENS). Mutant mice exhibited craniofacial malformations, hypopigmentation, intestinal pseudo-obstruction and hindlimb paralysis. Further phenotypic characterization revealed that LKB1 is required for the differentiation and maintenance of two NCC-derivatives, Schwann cells and the ENS. Using a model of neural crest stem cell line, we demonstrated that Lkb1 is key for neural crest-derived glial commitment. Mechanistically, Lkb1 loss led to an increase of alanine and glutamate levels and inhibition of pyruvate-alanine transamination rescued glial differentiation of Lkb1-null NCC, in a mTOR dependent manner. Furthermore, AICAR, an analogue of AMP, rescued glial differentiation of Lkb1-deficient NCC and corrected the Schwann cells and ENS phenotypes of Lkb1 mutant mice.
Altogether, these findings highlight the central role of Lkb1 during neural crest cell lineage and uncovered a link between Lkb1-mediated pyruvate-alanine cycling and glial commitment. These results provide also new insights for the understanding of metabolic events that contribute to the formation of LKB1-deficient malignancies.

Annonce de séminaire

Michalis Averof

Institut de Génomique Fonctionnelle de Lyon (IGFL).

Live imaging of regenerating legs: cell dynamics and progenitors

Invité par Rémi Mounier

Résumé
Regeneration is a complex and dynamic process, mobilising diverse cell types and remodelling tissues over a long time period. Compared with embryonic development, it is less genetically tractable and less accessible for direct observation. I will describe our recent efforts to establish a small crustacean, Parhyale hawaiensis, as an experimental model for studying regeneration. Using transgenic markers and live imaging we are starting to describe the cell behaviours and progenitors that underpin limb regeneration. We find that crustacean limb regeneration relies lineage-committed progenitor cells: muscles derive from satellite-like stem cells, whereas epidermis regenerates from existing epidermal cells.

Annonce de séminaire

Kei Sakamoto

Institut des Nestlé Institute of Health Sciences SA, Lausanne.

Key signaling players in the control of hepatic gluconeogenesis — AMPK or other AMPK-related/AMP-regulated enzymes ?

Invité par Rémi Mounier

Résumé
Hepatic glucose production is a key physiologic process that ensures energy balance for glucose-dependent organs/cells such as brain. The inability of insulin to suppress hepatic glucose output is a major aetiological factor in the hyperglycaemia of type 2 diabetes. LKB1, originally identified as a tumor suppressor protein, is currently thought as a critical regulator of cellular metabolism and growth by controlling the activity of AMP-activated protein kinase (AMPK) and also 12 other kinases that are closely related to AMPK. Among those AMPK-related kinases, we have recently identified that Salt-Inducible Kinase (SIK) plays an important role as a gluconeogenic gatekeeper in the liver.
Metformin exerts its major effect via inhibition of hepatic glucose production. This is thought to be mediated through decreased hepatic energy charge (i.e. increasing AMP/ATP ratio) via inhibition of mitochondrial respiration. The long-standing belief that 5’-adenosine monophosphate (AMP)-activated protein kinase (AMPK) mediates the anti-hyperglycaemic action of metformin has recently been challenged in experiments using mice lacking hepatic AMPK. I will discuss our recent data demonstrating AMP-mediated allosteric inhibition of an enzyme involved in gluconeogenesis plays a key role in acute glucose-lowering effect of metformin.

Annonce de séminaire

Colin Crist

Department of Human Genetics, McGill University – Québec, Canada.

Translational Control of Muscle Stem Cells

Invité par Rémi Mounier

Abstract
Regeneration of adult tissues depends on somatic stem cells that remain quiescent, yet are primed to enter a differentiation program. The molecular pathways that prevent activation of these cells are not well understood. Using mouse skeletal muscle stem cells as a model, we show that accumulating transcripts specifying the myogenic program are not translated in quiescent satellite cells, but are repressed by the action of microRNAs and RNA binding proteins. Furthermore, the reversible nature of microRNA dependent silencing mechanisms may underlie the rapid activation of satellite cells that are poised to enter the myogenic program. We also show that a general repression of translation, mediated by the phosphorylation of translation initiation factor eIF2 at serine 51 (P-eIF2α), is required to maintain the quiescent state. Skeletal muscle stem cells unable to phosphorylate eIF2 exit quiescence, activate the myogenic program and differentiate, but do not self-renew. P-eIF2α ensures in part the robust translational silencing of accumulating mRNAs that is needed to prevent the activation of muscle stem cells. Additionally, P-eIF2α dependent translation of mRNAs regulated by upstream open reading frames (uORFs) contributes to the molecular signature of stemness. Finally, we show that addition of small molecule inhibitors of eIF2α dephosphorylation to muscle stem cell cultures permits their ex vivo expansion and engraftment into a preclinical mouse model of Duchenne muscular dystrophy.

Annonce de séminaire

Michael A Rudnicki

Center of Ottawa Hospital Research Institute, Ottawa, Ontario, Canada

Molecular regulation of muscle stem cell asymmetric division

Invité par Bénédicte Chazaud

Abstract
We discovered that a subset of satellite cells in skeletal muscle are self-renewing stem cells that give rise to myogenic progenitors through asymmetric apical-basal cell divisions. The regulation of asymmetric stem cell division is a key control point that impacts the efficacy of the entire regenerative program. Stem cell polarity is established by the PAR complex, comprised of PAR3/PAR6/aPKC, to regulate self-renewal and expansion. Duchenne Muscular Dystrophy (DMD) is coaused by a lack of dystrophin which is expressed in muscle fibers where it plays a role in ensuring structural integrity. We have made the seminal finding that dystrophin regulates the establishment of PAR-mediated polarity in satellite cells. In the absence of dystrophin, the polarity effector Par1b is dysregulated, leading to the failure of Par3 to become localized to the cortex associated with the basal lamina. Importantly, this results in an abnormal increase in centrosome number, a 10-fold reduction in the numbers of satellite stem cells undergoing asymmetric divisions, and a marked decrease in the generation of myogenin-expressing progenitors. Accordingly, our data suggests that the failure of regenerative myogenesis to keep pace with disease progression in DMD is not due to muscle stem cell exhaustion, but rather is due to a cell-autonomous deficiency in asymmetric division.

Annonce de séminaire

F. Jeffrey Dilworth

Center of Ottawa Hospital Research Institute, Ottawa, Ontario, Canada

Epigenetic control of stem cell fate decisions in muscle repair

Invité par Bénédicte Chazaud

Abstract
During muscle regeneration, the conversion of muscle stem cells to terminally differentiated myofibers requires multiple cell fate transitions. Each of these transitions necessitates an alteration in the set of genes being expressed within the cell. In this presentation, our studies on the role of transcription factors and epigenetic enzymes in dictating changes in muscle gene expression will be highlighted. In particular, I will focus on the role for the antagonism between various transcription factors and epigenetic enzymes in controlling the commitment of muscle stem cells towards alternate cell fates.

Annonce de séminaire

Fabien Le Grand

Center of Research in Myology, Université Pierre et Marie Curie Paris – France.

Control of muscle stem cell fate by Wnt signaling pathway(s)

Invité par Bénédicte Chazaud

Abstract
Regeneration of the adult skeletal muscle tissue relies on a pool of quiescent muscle stem cells located in a niche around the myofibers: the satellite cells (MuSCs). Upon activation following injury or repeated exercise, MuSCs leave quiescence to proliferate and then differentiate to form new muscle fibers while a sub-population exit the cell cycle to self-renew and replenish the stem cell niche. In the course of this process, signals from the microenvironment instruct cycling MuSCs and control myogenesis. We previously demonstrated that numerous Wnt molecules are secreted in the local milieu during regeneration and showed that MuSC self-renewal is in part controlled by non-canonical Wnt7a/PCP signals sent by the regenerating myofibers. To elucidate the roles of the canonical Wnt/ß-catenin pathway in MuSCs, we generated mice with inducible MuSC-specific ß-catenin Loss-Of-Function or Gain-Of-Function. Strikingly, we observed that induction of either ß-catenin LOF or GOF mutations in MuSCs leads to the impairment of skeletal muscle regeneration following injury. By using a mouse model of conditional APC gene deletion in MuSCs we further demonstrated that the massive activation of canonical Wnt signaling in MuSC following APC loss results in defective cell cycle progression and apoptosis. Mechanistically, we observed that Wnt/ß-catenin signaling orchestrates the cytoplasmic relocalization of the histone 3 lysine 9 methyltransferase Setdb1 during differentiation. We further showed that Setdb1 is required for MuSCs amplification and suppresses myoblast terminal differentiation. Genome-wide analyses showed a Wnt3a-dependant release of Setdb1 from the promoter of selected target genes upon myoblast terminal differentiation. Taken together, our results demonstrate that both canonical and non-canonical Wnt pathways are necessary for MuSC function. Lastly, I will discuss the potential cross-talks between these two faces of an important signaling.

Annonce de séminaire

Stefan Dimitrov

Institut Albert Bonniot, Centre de Recherche UGA – INSERM U1209 / CNRS UMR 5309, Grenoble, France.

Epigenetic strategies : nucleosome remodeling, histone modifications and histone variants.

Invité par Laurent Schaeffer

Abstract
Chromatin impedes the binding of protein factors to the underlying DNA sequences. The cell uses three main “epigenetic tools” to overcome the chromatin barrier, namely, chromatin remodelers, histone variants and histone post-translational modifications. We will give specific examples of how either one of these “epigenetic tools” functions.
Chromatin remodelers are sophisticated nano-machines, which are able to alter histone-DNA interactions and to mobilize nucleosomes. Neither the mechanism of their action nor the conformation of the remodeled nucleosomes are, however, yet well understood. We have studied the mechanism of RSC-induced chromatin remodeling by using high resolution microscopy and state of the art biochemistry techniques. The data illustrates how RSC remodels the nucleosome in vitro and shed light on its in vivo function. The crystal structure of the CENP-A nucleosome was recently solved. Intriguingly, in contrast to the canonical nucleosome (where 147 bp of DNA are wrapped around the histone octamer), only the central 121 bp were visible, suggesting flexible CENP-A nucleosomal ends. Why the CENP-A nucleosome exhibits flexible DNA ends is totally unknown. Our data show that the flexible DNA ends of the CENP-A nucleosome are required for mitotic fidelity.
The Aurora family of oncogenic kinase consists of two major members, Aurora A and Aurora B. Both kinases exhibit very high homology. They show, however, quite distinct localization and function. Histone H3 is specifically phosphorylated, presumably by the oncogenic kinase Aurora B, at serine 10 at the onset of mitosis. Here we will present data on the distinct function of the two Aurora kinases and the mechanism of phosphorylation of histone H3 by Aurora B.

Annonce de séminaire

Stéphane Vassilopoulos

Institut de Myologie, UMRS 974 UPMC-Inserm / FRE 3617 CNRS, G. H. Pitié-Salpétrière, Paris – France.

The endocytic machinery in healthy and diseased muscle

Invité par Laurent Schaeffer

Abstract
Costameres represent specialized focal adhesion sites of muscle fibres, located between the plasma membrane and sarcomeres, the contractile units of muscle. When disrupted, they directly contribute to the development of several distinct myopathies.
We have shown that the ubiquitous clathrin heavy chain (CHC), well characterized for its role in intracellular membrane traffic and endocytosis from the plasma membrane (PM), forms large plaques connected to α-actinin and actin filaments. Depletion of CHC leads to defective costamere formation and maintenance both in vitro and in vivo and induces sarcomere disorganization and a loss of contractile force due to the detachment of sarcomeres from the PM. At costameres, CHC is co-expressed with dynamin 2 (DNM2), another key protein of the intracellular membrane trafficking machinery which is mutated in autosomal dominant centronuclear myopathy (CNM). We analyzed the role of DNM2 and several actin binding proteins on clathrin plaque function at costameres in vitro by using either siRNA depletion combined to high resolution electron microscopy or in vivo by intravital microscopy. We also focused on the possible link between costamere and CNM pathophysiology. Using myoblasts from DNM2-mutated patients and using myoblasts and muscles from a knock-in mouse model of DNM2-related myopathy, we analyzed structure of costameres by biochemical and immunocytochemical approaches, as well as their ultrastructure.
Our results demonstrate a crucial role for the endocytic machinery and the cytoskeleton. Their contribution to the formation and maintenance of the contractile apparatus highlight an unconventional role for clathrin flat lattices in skeletal muscle which may be relevant to pathophysiology of several neuromuscular disorders.

Annonce de séminaire

Sandrine Humbert

GIN – Inserm U1216 – University Grenoble Alpes, Grenoble, France.

Huntingtin regulates cortical development: consequences for Huntington’s disease

Invité par Julien Courchet

Abstract
The bulk of interest in the huntingtin protein has centered on the fact that, when mutated, huntingtin causes Huntington’s disease (HD), a devastating neurodegenerative disorder. The mutation causing HD is an abnormal polyglutamine stretch in huntingtin. Given the adult onset and dysfunction and death of adult neurons characterizing HD, most studies have focused on the toxic effects elicited by mutant huntingtin in post-mitotic neurons. However, the protein is ubiquitous and expressed in the developing embryo where it plays an essential role as revealed by the early embryonic lethality at day 7.5 of the complete knockout of the huntingtin gene in mouse. Anyway, the roles of the wild-type protein during development have been overlooked. I will discuss how huntingtin regulates several steps of mouse embryonic corticogenesis. I will also show the consequences of the presence of an abnormal polyglutamine expansion in huntingtin during cortical neurogenesis and consider the viewing of HD as a developmental disorder.

Annonce de séminaire

Jan Tuckermann

Institute of Comparative Molecular Endocrinology Ulm University, Ulm, Germany.

Modes of GR action revised – Novel mechanisms of corticosteroids in inflammation and bone integrity

Invited by Bénédicte Chazaud

Abstract
The Tuckerman Laboratory made major contributions to the molecular mechanisms of corticosteroids in beneficial and side effects of steroid therapy. With the help of conditional and function-selective knockout mice for the glucocorticoid receptor (GR) the lab identified critical cell types and novel mechanisms for anti-inflammatory activities of glucocorticoids in different inflammatory disease models. Furthermore we made the discovery that in a model of lung inflammation the anti-inflammatory action of glucocorticoids is not dependent on the inhibition of pro-inflammatory mediators, but rather requires cooperation with pro-inflammatory signaling pathways (e.g. p38) to induce anti-inflammatory acting genes and alternative polarization of macrophages.

Annonce de séminaire  

Dr. Francesco Zorzato

Department of Biomedicine, Basel University

Pathophysiology of ryanodinopathies

Invited by Bruno Allard

Abstract
Type 1 ryanodine receptor (RyR1) is preferentially expressed in skeletal muscle, and mutations in the gene have been associated with malignant hyperthermia, a pharmacogenetic disease, and with several congenital myopathies, including central core disease, multiminicore disease, centronuclear myopathy, congenital fibre type disproportion. Experimental data have indicated that RyR1 is also expressed in some areas of the central nervous system, in some cell types of the immune system and in smooth muscle cells. These results imply that mutations in the gene encoding RyR1 will not only affect skeletal muscles, but other tissues that express this calcium channel as well, thereby broadening the clinical spectrum of disorders due to RyR1 dysfunctions.
The RyR1 is of fundamental importance for the development of muscle force and a decrease in its content may be causally linked to the profound muscle weakness seen in patients with some forms of congenital myopathies linked to recessive RYR1 mutations. The protein composition of the junctional sarcoplasmic reticulum membrane encompassing the excitation-contraction coupling molecular complex (ECCMC) is extremely complicated. Polymorphic variants of the junctional sarcoplasmic reticulum protein JP45 have been shown to segregate in Malignant Hyperthermia Susceptible subjects of Malignant Hyperthermia families in the UK. Thus, some ECCMC accessory proteins may play a role not only in regulating excitation-contraction coupling but also as modifiers of the ryanodinopathies phenotype.

Annonce de séminaire

Vendredi 29 janvier à 14:00 – Bâtiment l’Herbier

Pura Muñoz-Cànoves

ICREA Research Professor at Universitat Pompeu Fabra, Barcelona.

Tissue regenerative decline with aging: focus on muscle stem cells

Invited by Bénédicte Chazaud

Abstract
Our group aims to understand the mechanisms regulating stem cell homeostasis and regenerative functions. Research is specially centered on stem cells of skeletal muscle (i.e., satellite cells). Recently, we have focused on two areas: 1) the functional decline of satellite cells with aging; and 2) the physiopathology of muscular dystrophies, with a specific interest in the contribution of inflammation and fibrosis to dystrophy progression. Concerning the first area, work from different laboratories has demonstrated that both environmental and cell- autonomous signals alter satellite cell regenerative potential with aging. I will discuss our latest results showing that satellite cells in their homeostatic quiescent state are equipped with quality control mechanisms to preserve their fitness, and how age-associate alterations in these protective mechanisms lead to stem cell loss of function and regenerative capacity.

Annonce de séminaire

Marc HAMMARLUND

Yale University, New Haven, USA

How C. elegans neurons sense and respond to injury

Invité par Jean-Louis Bessereau

Abstract
The nervous system has an extraordinary capacity to repair damage by regenerating axons and synaptic connections. I will discuss the molecular and cellular basis of axon regeneration in C. elegans, and describe how regenerated synapses and circuits differ from those generated during development. Finally, I will present new data on a novel ncRNA pathway that controls regeneration.

Luc BERTRAND

Université catholique de Louvain, Brussels

AMPK in cardiac pathologies, not just a metabolic sensor !

Abstract
The AMP-activated protein kinase (AMPK) has been firstly discovered to be activated under metabolic stress conditions such as myocardial ischemia. Its protective action during an ischemic episode has been demonstrated by several research groups. By targeting metabolism, AMPK helps the heart to survive under such deleterious conditions. However, AMPK action extends beyond metabolism and acute stress conditions. Indeed, it has been more recently shown that AMPK acts as protector of the heart in several chronic diseases such heart failure, diabetic cardiomyopathy and cardiac hypertrophy by acting in cardiomyocytes but also on the other cell types such as fibroblasts. Very recently, our group discovered a connection between AMPK and a particular post-translational modification called O-GlcNAcylation, this interplay acting a major role in the development of cardiac hypertrophy. The lecture will focus on the different protective roles of cardiac AMPK.

Michisuke Yuzaki

Keio University School of Medicine, Tokyo

Bridge over troubled synapses — a new synthetic synapse organizer

Invité par Jean-Louis Bessereau

Abstract
Synaptic organizers regulate formation, elimination and maintenance of synaptic connections throughout life. Although excitatory and inhibitory synaptic imbalance underlies certain neuropsychiatric and neurological disorders, no tools are currently available to directly modulate the balance. Recently, a new class of synaptic organizers, termed extracellular scaffolding proteins (ESPs), are reported to acutely and potently modulate specific synapses by directly binding to certain pre- and postsynaptic membrane proteins. Here, to expand the repertoire of ESPs with a variety of pre- and postsynaptic specificities, we developed a new synthetic ESP, Cbln1–neuronal pentraxin 1 (NP1) chimera (CPTX), by exploiting the structure of NP1 and Cbln1. Unlike original Cbln1, CPTX induced excitatory synapses by recruiting AMPA glutamate receptors in vitro. Furthermore, CPTX restored excitatory synapses and synaptic plasticity in vivo, as well as spatial and contextual memories in Alzheimer’s disease model mice. In this talk, I would like to discuss a possible toolkit of ESPs with a variety of pre- and postsynaptic specificities to modify neuronal circuits.

Saadi Khochbin

Institute for Advanced Biosciences, La Tronche, France

Les séminaires du Chromatin Club – Metabolism-driven epigenetics

Invité par Armelle Corpet / Patrick Lomonte

Annonce de séminaire

Frédéric RELAIX

INSERM – IMRB U955-E10, F-94010 Créteil, France

PAX3 controls the adaptive response of skeletal muscle stem cells to environmental stress

Invité par Rémi Mounier

Abstract
We have identified a molecular link between the Aryl hydrocarbon Receptor (AhR) environmental stress pathway and Pax3/Pax7 developmental genes during craniofacial development. Since Pax3/7 are key regulators of muscle stem cells (muscle satellite cells), we investigated the cellular and molecular impact of chronic 2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD) exposure on skeletal muscle and satellite cells in the adult. We combined in vivo and ex vivo approaches, in order to analyse the impact of chronic exposure to TCDD in several muscles such as tibialis anterior and biceps brachii. While all MuSCs express the transcription factor PAX7, we show that a muscle-specific subset also express PAX3 and exhibit resistance to environmental stress. Upon systemic TCDD treatment, PAX3-negative MuSCs display impaired survival, atypical activation and sporadic differentiation through the xenobiotic Aryl Hydrocarbon Receptor. We further show PAX3-positive MuSCs become sensitized to environmental stress when PAX3 function is impaired and that PAX3-mediated induction of mTORC1-dependent G(alert) is required for protection. Our study therefore identifies a functional heterogeneity of MuSCs in response to environmental stress controlled by PAX3.

Annonce de séminaire

Nicolas RENIER

ICM – Institut du Cerveau et de la Moelle Epinière Paris – FRANCE

A framework for the study of behaviour and plasticity in the adult brain using light sheet microscopy

Invité par Julien Courchet

Abstract
There has been over the past 6 years a convergence in the fields of optics, biochemistry and computing leading to dramatic improvements in light sheet microscopy, tissue clearing protocols and image analysis algorithms. The convergence of these different fields has the potential to streamline brain studies by accelerating data acquisition speed and reliability over the current whole brain analysis pipelines based on serial sectioning methods. We previously developed the iDISCO+ protocol for immunostaining and imaging intact adult mouse brains. As a companion tool, we also developed and distribute ClearMap, an open source environment to segment objects and map them onto reference atlases optimized for large 3D datasets. We used this pipeline as a discovery tool to find brain regions active in correlation with various behaviors by mapping neuronal activity landscapes derived from Fos expression. Here, I will present recent unpublished projects made possible by our upcoming brain mapping pipeline ClearMap 2, expanding the repertoire of applications derived from intact whole brain preparations. We hope that ongoing developments in light sheet microscopy and image analysis pipelines will facilitate our understanding of individual variations in brain activity, connectivity and structure.

Annonce de séminaire

Hugues NURY

Institut de Biologie Structurale, Grenoble

Structures and transitions of the serotonin 5-HT3 receptor

Invité par Thomas Boulin

Abstract
The serotonin 5-HT3 receptor is a pentameric ligand-gated ion channel. It belongs to a large family of receptors that transduce signals across the plasma membrane​: upon binding of neurotransmitter molecules to extracellular sites, the receptors undergo complex conformational transitions, which result in transient opening of a pore permeable ​to ions. 5-HT3 receptors are therapeutic targets for emesis and nausea, irritable bowel syndrome and depression. I will present structures of the 5-HT3 receptor obtained by crystallography or cryo-electron microscopy. The structures, obtained in complex with inhibitors or agonists, represent snapshots in different states: inhibited, pre-active, active. Together with molecular dynamics simulations and functional recordings, they reveal the molecular mechanism of the fast neurotransmission mediated by 5HT3 receptors.

Annonce de séminaire

Emmanuel COMPE

Institut de Génétique et de Biologie Moléculaire et Cellulaire Illkirch, Strasbourg

TFIIH and TFIIE mutations: when transcriptional deficiencies lead to neurological disorders

Invité par Ambra Giglia-Mari

Abstract
Trichothiodystrophy (TTD) is an autosomal recessive disorder mainly related to mutations in the DNA repair/transcription factor TFIIH. In addition to the typical dry and brittle hair, individuals with TTD develop neurological defects, including microcephaly and hypomyelination. Using a TTD transgenic mouse model, we previously observed a spatial and selective deregulation of thyroid hormone target genes in the brain, suggesting that transcriptional failures contribute to TTD phenotypes.
Remarkably, mutations within TFIIE, another general transcription factor, have been recently associated with TTD. Such observation prompted us to accurately dissect the partnerships occurring between TFIIE and TFIIH during transcription. Our work revealed an unexpected dynamic process during which TFIIE act as key factors to recruit and position the kinase module of TFIIH within the preinitiation complex. Strikingly, TTD-related mutations in either TFIIH or TFIIE similarly disrupt this early transcriptional process, which could explain why alterations in different transcription factors can lead to the same clinical syndrome.

Annonce de séminaire

Laurent BARTHOLIN

CRCL, Lyon

The obnoxious faces of TGFbeta in pancreatic cancer

Invité par Rémi Mounier

Abstract
The Transforming growth factor beta (TGFB) is a pleiotropic secreted factor with many roles during embryonic and adult life. In cancer, it behaves either as a tumor suppressor or a tumor promoter. To understand this functional duality, our lab have been using as a model Pancreatic Ductal Adenocarcinoma (PDAC), one of the most aggressive tumor, which is expected to become the second cancer-related cause of death by 2030 (after lung cancer). Our work is focused on the oncogenic properties of TGFB with the final goal to specifically target them by developing innovating therapeutics. During this presentation, I will present our work to understand the TGFB oncogenic effects at the molecular (a “new” oncogenic signaling pathway), cellular (effect on differentiation of pancreatic acinar cells), organ (interaction between PDAC cells and nerves invading the tumor) and whole body levels (interaction with muscle).

Fabien LE GRAND

Centre de Recherche en Myologie, Paris

Signaling pathways in muscle tissue regeneration

Invité par Laurent Schaeffer

Abstract
The development and repair of complex metazoan tissues are coordinated by a startlingly small number of evolutionarily conserved signaling pathways. These signals can act in parallel but often function as an integrated hyper-network. Our research aims at understanding the signaling nodes defining this molecular circuitry and the biological significance of pathway cross-talk, using skeletal muscle as a fitting model. Regeneration of the adult muscle tissue relies on a pool of quiescent muscle stem cells located in a niche around the myofibers: the satellite cells (MuSCs). We previously demonstrated that numerous WNT molecules are secreted in the local milieu during muscle regeneration and showed that MuSC self-renewal is in part controlled by non-canonical Wnt7a/PCP (1). To elucidate the roles of the canonical Wnt/ß-catenin pathway in MuSCs, we generated mice with inducible MuSC-specific mutations (2, 3). Mechanistically, we observed that Wnt/ß-catenin signaling orchestrate the cytoplasmic relocalisation of the H3K9 methyltransferase SETDB1 during differentiation (4). We further investigated how Wnt/ß-catenin signaling is connected to Bone morphogenetic protein (BMP) and Transforming growth factor beta (TGF-ß) pathways. Recent work in our lab consisted in dissecting the impact on these pathways on MuSC return to the niche and fusion, respectively. Nevertheless, our understanding of the cells that compose skeletal muscle tissue is limited and molecular definitions of the principal cell types are lacking. This hinders our capacity to decipher signal integration and reciprocity between cells. We thus used a novel combined approach of single-cell RNA-sequencing and mass cytometry and precisely mapped 10 different cell types in adult mouse skeletal muscle, including two previously unidentified populations (5). This cartography yields crucial insights into muscle-resident cell type identities and will be exploited to build a muscle connectome.

Bert Blaauw

Venetian Insitute of Molecular Medicine

The role of mTORC1 signaling in adult skeletal muscle

Invité par Laurent Schaeffer

Abstract
It is well established that mTORC1 signaling is key modulator of skeletal muscle mass and function. Surprisingly, despite the fact that skeletal muscle undergoes major changes in size and contractility in numerous diseases, no genetic loss-of-function model has been generated to determine the effect of inducible deletion of mTORC1 in adult skeletal muscle. Here we generated inducible, muscle-specific Raptor and mTOR k.o. mice. Interestingly, we do not observe a change in muscle size or contractile properties one month after deletion. However, treating these mice with the mTOR-inhibitor rapamycin is sufficient to induce a very rapid and marked myopathy, suggesting that little residual mTOR signaling can maintain muscle homeostasis in adult muscle. Prolonging deletion of Raptor to 7 months, however, leads to a very marked phenotype characterized by muscle dysfunction, regeneration, glycogen accumulation and mitochondrial dysfunction and block in autophagy. Unexpectedly, one of the best markers of reduced mTOR signaling in muscle fibers is the appearance of denervated fibers. Both muscle-specific deletion of mTOR or Raptor, or the use of rapamycin, was sufficient to induce the appearance of numerous NCAM-positive fibers, muscle fibrillation, and neuromuscular junction fragmentation. Taken together, these results link one of the most important anabolic pathways in skeletal muscle fibers to the maintenance of the NMJ.

Hélène PUCCIO

Department of Translational Medecine and Neurogenetics, IGBMC, Strasbourg

Advances in Friedreich Ataxia: understanding the function of frataxin and developing therapeutic approaches

Invité par Laurent Schaeffer

Abstract
Friedreich’s ataxia (FA), the most common autosomal recessive ataxia, is characterized by a sensory and spinocerebellar ataxia, hypertrophic cardiomyopathy and increase incidence of diabetes. FA is caused by reduced levels of frataxin (FXN), an essential mitochondrial protein involved in the biosynthesis of iron-sulfur (Fe-S) clusters. Fe-S clusters are ancient and essential cofactors that participate in a number of cellular processes ranging from mitochondrial respiration to DNA metabolism. In eukaryotes, de novo Fe-S biogenesis takes place within mitochondria and relies on proteins that are highly conserved from bacteria to humans. Impaired mitochondrial oxidative phosphorylation, bioenergetics imbalance, deficit of Fe-S cluster enzymes and mitochondrial iron overload occur in individuals with FA. To date, no treatment exists for stopping or slowing FA disease.
Over the past years, we have generated cellular and mouse models that reproduce important progressive pathological and biochemical features of the human disease, including cardiac hypertrophy, mixed cerebellar and sensory ataxia, Fe-S enzyme deficiency, and intramitochondrial iron accumulation. These models have enabled us to demonstrate that Fe-S deficit is a primary event of the disease leading to iron metabolism deregulation through the activation of the iron-regulatory protein, IRP1. These models are excellent models for deciphering the physiopathology of the disease and for testing pre-clinical therapeutic protocols. The latest advances in understanding the pathophysiology will be discussed, with a particular emphasis on new neurological models that are being developed as well as therapeutic approaches.

Juliette GODIN

Institut de Génétique et Biologie Moléculaire et Cellulaire, Strasbourg

Pleiotropic activities of the (atypical ?) kinesin KIF21B during cortical development

Invité par Julien Courchet

Abstract
Cortical development progresses through concurrent steps, including neural proliferation, migration and differentiation, that rely on dynamic cell shape remodeling which largely depends on the tight regulation of the microtubules (MT) cytoskeleton. Mutations in tubulin, MT associated proteins or motors have been linked to several neurodevelopmental disorders including malformation of cortical development (MCDs), affecting 2,5% of the world population. Here we identified KIF21B gene as a major locus of human neurodevelopmental disorder. We identified 4 de novo variants in KIF21B gene in patients with intellectual disabilities associated with several brain malformations, including microcephaly, corpus callosum agenesis or facial dimorphism. In support of the pathogenic potential of the discovered alleles, expression of KIF21B variant in mice using in utero electroporation or in zebrafish embryos recapitulated key neurodevelopmental phenotypes, namely migration and microcephaly. In addition, longitudinal neuroanatomical analysis of Kif21b KO model showed strong morphological defects starting prenatally and worsening with time. Finally, we demonstrated that Kif21b regulates migration of projection neurons through the tight control of locomotion and neural shape. Although its motility is dispensable, the regulatory function cytoskeleton dynamics is essential for neuronal migration. Altogether, our data represent an important step to delineate the mechanisms involving KIF21B-mediated MT dynamics and trafficking in the context of brain development.

Annonce de séminaire

Belinda COWLING

Institut de Génétique et Biologie Moléculaire et Cellulaire, Strasbourg

Myostatin – A novel biomarker for Dnm2 therapy in Myotubular Myopathy mice

Invité par Vincent Gache

Abstract
Centronuclear myopathies (CNM) are non-dystrophic muscle diseases for which no effective therapy is currently available. The most severe form, myotubular myopathy (X-linked CNM), is caused by myotubularin 1 (MTM1) loss-of-function mutations, while the main autosomal dominant form is due to dynamin2 (DNM2) mutations. We have shown that antisense oligonucleotide (ASO) mediated DNM2 knockdown can efficiently correct muscle defects due to loss of MTM1 in mice, providing an attractive therapeutic strategy for this disease. We are now investigating blood-based biomarkers that can be used to monitor disease state and rescue in myotubular myopathy mice. Myostatin is a protein produced and released by myocytes, which acts in an autocrine function to inhibit muscle growth and differentiation. Our results suggest myostatin pathway is ‘turned down’ at the mRNA level in muscle biopsies, leading to low levels of circulating and endogenous muscle myostatin in plasma. We have generated preliminary data suggesting ASO-mediated DNM2 reduction results in an increase in circulating myostatin. With clinical trials for myotubular myopathy currently in progress, identification of novel blood-based biomarkers such as myostatin may allow for monitoring of treatment efficacy in patients.

Annonce de séminaire

Luisa COCHELLA

Research Institute of Molecular Pathology (IMP), Vienna, Austria

Roles of micro RNAs in animal development: lessons from C.elegans

Invité par Florence Solari

Abstract
One of the main goals of developmental biology is to understand how the different cell types that constitute a multicellular organism are specified during its development. Luisa Cochella is a young PI (awarded for both ERC starting Grant and EMBO Young investigator program) who is currently exploring the different mechanisms of gene expression regulation that control this process. Her lab investigates how the transcriptional history of a cell influences its fate as well as how post- transcriptional mechanisms contribute to the diversification of the genetic programs that control cell fate. Luisa is more specifically interested in both neuronal and muscle differentiation

Annonce de séminaire

Huating WANG

The Chinese University of Hong Kong, Hong Kong, China

Functional investigation of LncRNAs and enhancers in skeletal muscle stem cells

Invité par Bénédicte Chazaud

Abstract
Previously, the majority of the human genome was thought to be « junk » DNA with no functional purpose. Over the past decade, evidence from numerous high-throughput genomic platforms reveals that even though less than 2% of the mammalian genome encodes proteins, a significant fraction can be transcribed into different complex families of non-coding RNAs (ncRNAs). Growing evidence supports that ncRNAs have fundamental roles as regulators of genomic output. Among various types of ncRNAs, microRNAs have dominated the current literature. Other groups, however, such as long ncRNAs (lncRNAs, >200nt), have been largely under explored.
Huating Wang’s lab is currently interested in studying the functional roles of long non-coding RNAs (lncRNAs and enhancers) in regulating gene expression in skeletal muscle stem cells and muscle regeneration.

Annonce de séminaire

Sonia Garel

Institut de Biologie de l’École Normale Supérieure, Paris

Microglia and prenatal inflammation in early cortical wiring

Invité par Jean-Louis Bessereau

Abstract

Prenatal inflammation and dysfunction of microglia, the brain resident macrophages, have both been associated with the etiology of several neuropsychiatric disorders, including schizophrenia and autism spectrum disorders. Consistently, microglia were shown to regulate neurogenesis, synaptic remodeling and maturation at postnatal stages. However, microglia invade the brain during mid-embryogenesis and could thus exert earlier prenatal and perinatal roles during normal and pathological brain wiring. Here we show that embryonic microglia, which display a transient uneven distribution, regulate the wiring of forebrain circuits. By taking advantage of multiple mouse models, including cell-depletion approaches, we found that perturbing microglia activity affects the development of neocortical inhibitory interneurons, which constitute main actors in neuropsychiatric diseases. In particular, absence, prenatal inflammation or functional perturbation of microglia affects the timely positioning of specific subsets of interneurons as well as their subsequent functional integration in the neocortex. We furthermore found that responses of microglia to environmental signals, including the ones from the microbiome, are sexually dimorphic in males and females. This remarkable finding has major implications for our comprehension of sexual biases in the occurrence of microglia-related diseases, such as the prevalence in males of neurodevelopmental disorders. Our work reveals key roles for immune cells during the normal assembly of cortical circuits and provides novel insights onto how microglia dysfunction or immune risks lead to pathological brain wiring.

Annonce de séminaire

Yasushi Okamura

Graduate School of Medicine, Osaka University Suita

Coupling from electric signal to lipid signal; voltage-sensing phosphoinositide phosphatase

Invité par Vincent Jacquemond

Résumé

Biological membranes have dual roles in cell signaling: insulator for electrical signal by transfer of ion across membrane as well as the place for metabolism for production of lipid mediators such as arachidonic acids or phosphophositides. These two signals interact with each other through changes of ion concentration, mainly intracellular calcium ions, by the concerted activities of ion channels, transporters and GPCRs. There is a rare case where single membrane proteins directly link between electrical signal and lipid-mediated cell signaling. Voltage-sensing phosphatase consists of the ion channel like voltage sensor and PTEN-like phosphoinositide enzyme. In VSP, single voltage sensor regulates the downstream enzyme and the phosphoinositide phosphatase activity is activated by membrane depolarization leading to depletion of mainly PI(4,5)P2. Substrate specificity of VSP is more broad than PTEN; VSP shows both of 3-phosphatase activity and 5-phosphatase activity unlike PTEN which shows the rigid selectivity toward 3-phosphate of the inositol ring of PI(3,4,5)P3 and PI(3,4)P2. However, the key question how transmembrane voltage sensor regulates the cytoplasmic enzyme has remained unanswered, mainly because a method of detecting structural change in the cytoplasmic region has been limited. We have recently applied a method of genetical incorporation of fluorescent unnatural amino acid, Anap, to the cytoplasmic region of Ci-VSP (sea squirt Ciona intestinalis VSP) which was expressed in Xenopus oocyte. This method enables detection of fine structural change reported by fluorescence intensitiy without perturbing the local protein structure. Voltage-dependent fluorescence change of Anap showed two bidirectional changes along the voltage, decrease at low membrane depolarization and increase at higher depolarization, suggesting that the structure of the cytoplasmic region takes multiple conformations. By applying the method to different constructs of Ci-VSP with altered enzyme activity, we obtained evidence that the enzyme takes at least two activated states with distinct magnitude of enzyme activity. Given that voltage sensor of Ci-VSP takes multiple states during activation, it will be intriguing to see in the future how individual enzyme states correlate with states of the voltage sensor.

Annonce de séminaire

Edgar Gomes

Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal

Mechanisms of nuclear positioning during myofiber formation

Invité par Bénédicte Chazaud

Résumé

Connecting the nucleus to the cytoskeleton is relevant for multiple cellular processes and disruption of these connections result in multiple pathologies. Nuclear positioning within cell cytoplasm requires de connection between nucleus and the cytoskeleton. We are interesting to understand the processes involved in these connections and the role for nuclear positioning in cell function. We study cell migration and skeletal myofiber formation which required the connection between the nucleus and the cytoskeleton and precise nuclear positioning. We use different molecular and cellular approaches in combination with time-lapse imaging analysis to address these questions.

Annonce de séminaire

Rashmi KOTHARY

Centre for Neuromuscular Disease University of Ottawa

Spinal Muscular Atrophy: a multi-organ disease

Invité par Patrick Lomonte

Abstract

Spinal Muscular Atrophy was characterized in the late 1800s but it was almost 100 years later that the genetic cause was identified as a mutation in the human SMN1 gene. While humans do have two genes that code for SMN, SMN2 only produces 10% protein when compared to SMN1. Early work with mouse models was complicated by the fact that mice only have the one Smn gene which when mutated results in preimplantation lethality. This problem was solved by the development of a mouse model incorporating human SMN2 gene, which was for years the only viable mouse model. Now, there are over a hundred mouse models available that have served to inform our understanding of pathogenesis in SMA.
Classically, SMA is described as a motor neuron disease; however, SMN is expressed ubiquitously throughout the body. In fact, SMA is emerging to be a multi-organ disease with SMN depletion having impacts on many tissues in the body. Subcutaneous administration of available treatments may address these affected organs better than intrathecal administration. Also, systemic gene therapies that are currently under development may help repair function in these other organs.
Dr. Kothary will present on the work in his laboratory on the multi-organ nature of SMA. Defects in various tissues will be discussed.

Annonce de séminaire

Laure STROCHLIC

Institut de Myologie – Centre de Recherche en Myologie, Sorbonne Université, INSERM AIM UMRS974, Paris

Regulation of neuromuscular connectivity by Wnt signaling from signaling molecules to therapeutic strategies

Invité par Rémi Mounier

Résumé

The development and maintenance of the neuromuscular connectivity relies on a temporally fine-tuned balance of distinct bi-directional communication between motor neurons and their muscle targets. Disruption of this communication leads to structural and functional defects that affect the motor function and causes severe neuromuscular pathologies. Wnt signaling participates in various developmental mechanisms such as migration, axonal guidance or synaptogenesis. But how the Wnt signaling network could regulate neuromuscular connectivity and how it could affect motor function is unknown. In this presentation, I will provide data using Wnts gain or loss of function studies in cell culture or in mice showing that distinct branches of Wnt signaling, acting in part via the muscle-specific kinase MuSK regulate several key aspects of the formation and maintenance of the neuromuscular synapse including pre and postsynaptic differentiation/stabilization, retrograde control of motor axon outgrowth and synapse-specific gene expression. I will also present evidence showing that the pharmacological modulation of Wnt signaling in a pathological context could be used as a therapeutic strategy to counteract neuromuscular junction (NMJ)- associated disorders. Overall, our results provide novel insights into the mechanisms by which synaptic diffusible cues act to prevent NMJ dysfunction, muscle weakness and disease.

Dans cette présentation, je fournirai des données, utilisant des approches expérimentales in vitro et in vivo chez la souris, qui montrent le rôle émergent de la signalisation Wnt dans la régulation de la connectivité neuromusculaire dans un contexte physiologique et pathologique.

Annonce de séminaire

Helge AMTHOR

Université de Versailles – Paris Saclay Laboratoire U1179 UVSQ – INSERM

BMP signaling controls limb muscle development and maintenance

Invité par Laurent Schaeffer

Résumé
Bone morphogenetic proteins (BMPs) regulate the activity of skeletal muscle precursors as well as the trophic state of differentiated muscle. Here, the role of BMP signaling was explored at different stages of limb muscle development by overexpressing an inhibitory Smad protein (Smad6) to abrogate the BMP signaling cascade at cell autonomous level. Overexpression of Smad6 in limb muscle precursors during development (crossing Rosa26-Lox-Stop-Lox-Smad6-IRES-GFP mice, termed RS6, with Lbx1^Cre/+ transgenic mice) disturbed limb muscle myogenesis: early myogenic markers Pax3 and MyoD were strongly downregulated, fetal limb muscles were smaller, consisted of fewer myofibers and displayed a disturbed muscle patterning. Overexpression of Smad6 in postnatal muscle precursors (using RS6: Pax7^CreERT2/+ mice) caused decreased cell proliferation resulting in smaller myofibers containing less myonuclei and in decreased generation of satellite cells. Overexpression of Smad6 in differentiated muscle resulted in a different phenotype (using RS6:HSA-Cre mice): limb muscles were only modestly smaller, however, consisted of fewer but larger myofibers with increased myonuclear number. Overexpression of the BMP antagonist Noggin in adult muscle (loss-of-function) resulted in muscle fiber atrophy, whereas overexpression of the BMP receptor Alk3 (gain-of-function) caused muscle fiber hypertrophy. These latter effects were likely muscle precursor independent, as overexpression of Smad6 in differentiated fibers (using RS6:Pax7^CreERT2/+ mice) had no effect on satellite cell number and muscle size in the adult. In conclusion, the role of BMP signaling in skeletal muscle is stage and context specific.

Annonce de séminaire

Vanina ROMANELLO

Venetian Institute of Molecular Medicine, Padova

The role of the myokine FGF21 in skeletal muscle homeostasis

Invité par Rémi Mounier

Résumé
Skeletal muscle is a major site of metabolic activity and the most abundant tissue in the human body accounting for almost 40% of the total body mass. It is a plastic tissue that adapts to changes in exercise, nutrition and hormones, which also induces the release of myokines and myometabolites. These muscle-secreted factors have autocrine, paracrine and endocrine effects, explaining how muscles regulate metabolic homeostasis in other tissues. These systemic effects help to explain why physical activity, and thereby muscle recruitment, elicits several beneficial effects in many different diseases. Indeed, exercise preserves and ameliorates mitochondrial function and muscle metabolism, thereby affecting the release of myokines and metabolites that systemically counteract organ deterioration. We have recently proposed an interplay between the myokine Fgf21 and the mitochondrial quality control pathways that greatly contributes to a pro-senescence metabolic shift. However, even though the myokine field is exponentially increasing, little is known about their role in muscle homeostasis.

Annonce de séminaire

Robert J. Johnston

Johns Hopkins University, Baltimore, USA

Stochastic gene expression and nuclear architecture in fly eyes and human retinal organoids

Invité par Thomas Boulin

Résumé
A central challenge in developmental neurobiology is to understand how the myriad types of neurons in the human nervous system are generated. Stochastic gene expression mechanisms are crucial to differentiate neuronal subtypes and expand function. During stochastic fate specification, individual neurons randomly choose between different fates, resulting in unique patterns but consistent proportions of cell types among genetically identical organisms. My lab studies the stochastic mechanisms that specify the color-detecting photoreceptors in the fly and human retina. Fruit flies have a well-characterized retina and an abundance of genetic tools that enable molecular analyses of gene regulatory mechanisms. To overcome the challenges associated with human studies, we have developed a human retinal organoid system that recapitulates retinal development and photoreceptor specification. With these systems, we are interrogating how DNA elements, trans factors, and chromatin architecture control random on/off gene expression. Our molecular approaches are complemented by quantitative genetics to determine how natural variation in the genome impacts gene expression and photoreceptor specification. Finally, we conduct behavioral and functional assays to measure differences in color perception when photoreceptor fates are altered. By studying highly divergent organisms from multiple angles, we aim to define the unifying principles underlying stochastic fate specification during nervous system development.

Annonce de séminaire

Athanassia SOTIROPOULOS

Institut Cochin, Paris

Role of Srf transcription factor and F-actin scaffold in muscle stem cell fusion

Invité par Rémi Mounier

Résumé
Our team is interested on how signaling pathways control of adult skeletal muscle plasticity. In the past years, we focused our attention on Srf transcription factor which is one of the three master genes that controls myogenesis in Caenorhabditis elegans, together with MyoD and HAND. We investigated the role of Srf in two cellular compartments of mouse skeletal muscle (myofibers and adult muscle stem cells) upon different perturbation of muscle homeostasis (hypertrophy, atrophy, regeneration). In the present seminar, I will summarize our findings concerning the role of Srf in myofibers to control muscle mass and I will present recent data identifying Srf as a master regulator of muscle stem cell fusion and demonstrating the implication of F-actin architecture in this process.

Seminar announcement

Cécile MARTINAT

INSERM/UEVE UMR861, I-STEM, AFM

Human pluripotent stem cells for the study and treatment of neuromuscular diseases : myth or reality ?

Résumé
Neuromuscular diseases correspond to a vast group of diseases that perturbs the function of the skeletal muscles by affecting motoneurons, muscles and/or NMJs. To date, no efficient curative treatments have been identified for NMD. Progresses towards identification of new treatment have been hampered by the incomprehension of disease pathogenesis, particularly in early phases, as well as the availability of relevant screening tools. Disease-specific human pluripotent stem cells, from embryonic origin or derived from reprogramming somatic cells, offer the unique opportunity to have access to a large spectrum of disease-specific cell models. Due to their ability of self-renewal and differentiation into various tissues affected in each pathological condition, the development of these human disease-specific pluripotent stem cells provide new insights in pathological mechanisms implicated in human diseases for which, accessing homogenous affected tissues is often challenging. Validating this concept, we previously demonstrated that human pluripotent stem cells and derivatives which, express the causal mutation implicated in the Myotonic Dystrophy type 1 (DM1), offer pertinent disease-cell models, applicable for a wide systemic analysis ranging from mechanistic studies to therapeutic screening. Thus, we identified, through a genome-wide analysis, two early developmental molecular involved both in myogenesis as well as in neurite formation and establishment of neuromuscular connections. These neuropathological mechanisms may bear clinical significance as related to the functional alteration of neuromuscular connections associated with DM1. In parallel to these functional pathological studies, we also demonstrated the pertinence of this new disease-specific cell model to identify new therapeutic strategies. Thus, our results identified the possibility to repurposing metformin, the most commonly prescribed drug for type 2 diabetes, for DM1 leading to a phase 2 clinical trial that is actually ongoing.
We are now extending our approach to another incurable neuromuscular disease, spinal muscular atrophy (SMA). This disease, considered as the leading genetic cause of infant death, is due to mutations or deletions in the « Survival of Motor Neuron » gene, SMN1, which results in low levels of the expressed SMN protein. Despite this ubiquitous SMN expression, the pathology is characterized by degeneration of spinal Motor neurons whereas other neuronal types are relatively preserved suggesting that spinal motor neurons specific features control this differential sensitivity. Based on our recent development allowing the efficient and robust conversion of human pluripotent stem cells into affected spinal motor neurons and non- affected cranial motor neurons, our objective is to deepen the mechanisms involved in the specific degeneration of spinal motor neurons in SMA as well as the mis communication of these neurons with their muscular target.

Annonce de séminaire

Christoph Hoefer, M. Sc.

Senior Business Development Manager ; Life Sciences Solutions, Cell Biology, ThermoFisherScientific

Séminaire Technique : Travailler avec des iPSC (induced Pluripotente Stem Cell)

Résumé
Les cellules souches pluripotentes humaines (iPSC) sont des outils puissants pour la recherche en biologie du développement, la médecine régénérative et l’étude des pathologies humaines. Les données obtenues à partir de modèles physiologiques in vitro amélioreront grandement notre compréhension des processus biologiques. Dans cette présentation, j’aborderai les principaux défis rencontrés dans la mise en place des cellules souches pluripotentes au sein d’un laboratoire et les améliorations récentes apportées à la construction de modèles pour les maladies humaines, telles que la reprogrammation, l’expansion, la transfection, la préservation et la différenciation efficace de iPSC, ainsi que les options de modifications génomiques.

Annonce de séminaire

Nicolas PLACE

Institute of sport Sciences, University of Lausanne

Skeletal muscle adaptations to exercise : a translational approach

Invité par Julien Gondin

Résumé
The amount of force skeletal muscles can produce depends on their contractile history. For instance, repeated contractions generally lead to reduced muscle force generating capacity, namely muscle fatigue. Although muscle fatigue has been the focus of many works in the last 100 years, the underlying mechanisms remain elusive. In this presentation, special emphasis will be given to the role of Ca²⁺ handling as a key regulator of (i) muscle weakness and (ii) beneficial adaptations observed after high intensity interval training. In particular, the potential role of the sarcoplasmic reticulum Ca²⁺ release channel, the ryanodine receptor type 1, will be discussed.

Annonce de séminaire

Julien OCHALA

Faculty of Life Sciences & Medicine, King’s College, London

Actinopathies : From Mutations to Treatment

Invité par Laurent SCHAEFFER

Résumé
Actinopathies are genetically and clinically heterogeneous disorders mainly characterized by generalized muscle weakness. The understanding of this group of disorders has advanced in recent years through the identification of the causative mutations in the gene encoding one of the major proteins of the basic contractile unit of skeletal muscle, i.e., actin. In the present seminar, I will present (i) how these gene mutations lead to generalized muscle weakness and (ii) the advances regarding potential therapies.

Annonce de séminaire

Norbert WEISS

Institute of Organic Chemistry and Biochemistry, Prague

Trafficking of T-type calcium channels in health and disease

Invité par Vincent JACQUEMOND

Résumé
T-type calcium channels are key contributors to neuronal physiology where they shape electrical activity of nerve cells and contribute to the release of neurotransmitters. Alteration of T-type channel expression has been causally linked to a number of pathological conditions including neuropathic pain and absence seizure activity. Although a number of signaling pathways regulating the activity of T-type calcium channels have been reported, the molecular machinery and signaling molecules controlling the trafficking and expression of the channel protein at the plasma membrane remain largely unknown. I will present some of the basic mechanisms recently identified controlling the physiological trafficking of T-type channels, and illustrate how metabolic defects or congenital mutations can disturb this trafficking machinery and eventually leading to disease conditions.

Annonce de séminaire

Isabelle JANOUEIX

Institut Curie – Inserm U8330, Paris

Understanding neuroblastoma biology through the analysis of its genetic and epigenetic landscapes

Invité par Valérie Castellani

Résumé
Neuroblastoma is an embryonal neoplasm arising from the peripheral nervous system that accounts for 15% of cancer deaths in childhood. It is an enigmatic tumor presenting with a great genetic and clinical heterogeneity, both in terms of presentation and outcome.
The characterization of the genetic alterations observed in neuroblastoma led to the identification of major players of neuroblastoma oncogenesis that has considerably improved our understanding of the biology of this pediatric cancer. More recently, the analysis of the super-enhancer landscape allowed to decipher the core regulatory circuitries controlling the gene expression program of neuroblastoma. Distinct transcription factor networks predicate different tumor identities, corresponding to sympathetic noradrenergic or mesenchymal/neural-crest cell like identities. Cells of mesenchymal identity are more resistant to chemotherapeutic agents. Moreover, some neuroblastoma cells exhibit plasticity and are able to shift between the NCC-like and noradrenergic identities.
The understanding of cell identity, heterogeneity and plasticity in neuroblastoma has strong implications with respect to the development of new therapeutic strategies to eradicate tumor cells in neuroblastoma patients.

Annonce de séminaire

Justin FALLON

Brown University, Providence, RI

MuSK as a BMP co-receptor

Invité par Laurent Schaeffer

Chantal Thibert

Institute for Advanced Biosciences, Université Grenoble Alpes

The tumor suppressor LKB1 controls cell fate through pyruvate-alanine transamination

Invité par Julien Courchet

Résumé
The tumor suppressor LKB1 (also named STK11) codes for a serine/threonine kinase. LKB1 acts as a key regulator of cell polarity as well as energy metabolism partly through the activation of the AMP-activated protein kinase (AMPK), a sensor that adapts energy supply to the nutrient demands of cells facing situations of metabolic stress.
To determine if Lkb1 exerts a coordinated regulation of energy metabolism and cell polarity, we deleted the Lkb1 gene in polarized cells and explored the metabolic consequences. In particular, we generated spatio-temporal ablation of Lkb1 in a subpopulation of mouse embryonic multipotent neural crest cells (NCC) that originate from the neural tube and give rise to a broad range of derivatives including most of the face, the melanocytes, the peripheral nerves and the enteric nervous system (ENS). Mutant mice exhibited craniofacial malformations, hypopigmentation, intestinal pseudo-obstruction and hindlimb paralysis. Further phenotypic characterization revealed that LKB1 is required for the differentiation and maintenance of two NCC-derivatives, Schwann cells and the ENS. Using a model of neural crest stem cell line, we demonstrated that Lkb1 is key for neural crest-derived glial commitment. Mechanistically, Lkb1 loss led to an increase of alanine and glutamate levels and inhibition of pyruvate-alanine transamination rescued glial differentiation of Lkb1-null NCC, in a mTOR dependent manner. Furthermore, AICAR, an analogue of AMP, rescued glial differentiation of Lkb1-deficient NCC and corrected the Schwann cells and ENS phenotypes of Lkb1 mutant mice.
Altogether, these findings highlight the central role of Lkb1 during neural crest cell lineage and uncovered a link between Lkb1-mediated pyruvate-alanine cycling and glial commitment. These results provide also new insights for the understanding of metabolic events that contribute to the formation of LKB1-deficient malignancies.

Annonce de séminaire

Michalis Averof

Institut de Génomique Fonctionnelle de Lyon (IGFL).

Live imaging of regenerating legs: cell dynamics and progenitors

Invité par Rémi Mounier

Résumé
Regeneration is a complex and dynamic process, mobilising diverse cell types and remodelling tissues over a long time period. Compared with embryonic development, it is less genetically tractable and less accessible for direct observation. I will describe our recent efforts to establish a small crustacean, Parhyale hawaiensis, as an experimental model for studying regeneration. Using transgenic markers and live imaging we are starting to describe the cell behaviours and progenitors that underpin limb regeneration. We find that crustacean limb regeneration relies lineage-committed progenitor cells: muscles derive from satellite-like stem cells, whereas epidermis regenerates from existing epidermal cells.

Annonce de séminaire

Damaris Lorenzo

University of North Carolina at Chapel Hill

Ankyrin-B and beta-II spectrin in axonal transport and brain connectivity

Invité par Thomas Boulin

Résumé
The formation, targeting, and maintenance of axon and dendrites are critical for proper brain development and synaptic function. Deficits in synapse establishment and maturation can lead to neurodevelopmental, neurodegenerative, and psychiatric disorders. The neuronal cytoskeleton regulates the architecture and dynamics of synaptic processes by providing structural support and the tracks for motor protein-based synaptic transport. The latter is particularly important for the establishment of long axonal projections, which requires coordinated long-range organelle transport. The membrane associated adaptor ankyrin-B (AnkB) promotes fast axonal transport and elongation by coupling dynactin to multiple organelles through binding to phosphatidylinositol 3-phosphate lipids in these cargos. Additionally, AnkB directly binds βII-spectrin, which, in turn, controls the formation of a ring-shaped membrane periodic skeleton (MPS) in axons and mature dendrites. Interestingly, βII-spectrin also associates with molecular motors. I will show that AnkB and βII-spectrin are key elements in independent and overlapping pathways responsible for the transport of synaptic cargo and other organelles, and are essential for establishing proper brain structural and functional connectivity.

Annonce de séminaire

Andre Brown

MRC London Institute of Medical Sciences – Imperial College, London

Syntax in C. elegans locomotion

Invité par Thomas Boulin

Résumé
Behaviour is a striking phenotype and often one of the first things we notice about an animal. Broadly speaking, we are interested in understanding how genes affect behaviour, but despite rapid advances in technology for sequencing and engineering genomes, it is still a challenge to associate particular genes with heritable behavioural differences because behaviour is time consuming to measure and difficult to quantify. We are using automated imaging to record the behaviour of freely moving nematode worms and developing new analysis methods to extract relevant features. I will discuss unsupervised methods to quantify behavioural repertoires, and how making connections to language processing and data compression can give insight into the structure of behaviour. Finally I will show how these new representations can advance the study of behavioural genetics and phenotypic drug screening.

Annonce de séminaire

Hélène CASTEL

Normandie Rouen University / Inserm 1239 – Équipe Astrocyte and Vascular Niche

Cancer and Cancer treatments on cognition: A major translational impact of the preclinical research

Invité par Virginie DESESTRET

Résumé
Co-head Cancer and Neurosciences axis Northwest canceropole, Cancer and cognition platform; ICCTF member (editing of preclinical research guidelines).
The emergence of a new field in oncology addressing cognitive deficits in cancer patients is justified by the existence of deficits in memory, concentration and attention, as well as executive functions before, during and after treatments, symptoms often referring to the “chemofog” or “cancerfog”. Our work mainly involves research and clinical groups of Normandie developing programs in patients and animal models, to improve our understanding of the impact of cancer and its treatments on cognitive functions. Two main examples of these translational studies we participated on can be exposed:
The first Cog-Age clinical study (Pr F. Joly, Baclesse Caen) showed that cognitive decline can be detected 6 months after chemotherapy in breast cancer elderly patients. In a mirror study, chemotherapy administration in young and elderly mice resulted in a change in behavioral flexibility and alteration of neuron precursor proliferation in the hippocampal dentate gyrus. We were thus able to conclude that age-related cognitive decline is accentuated by chemotherapy, providing basis for questioning the place of adjuvant chemotherapy in this elderly patient population. The second clinical study COG-ANGIO (Pr Joly) demonstrated that antiangiogenics exert a direct negative impact on cognitive functions and fatigue in kidney cancer patients. In mice, the anti-angiogenic mTOR inhibitor everolimus did not alter cognitive functions but led to weight loss and modification of cell metabolism in brain regions involved in sleep/wake cycle or food intake, likely connected to fatigue. On the other hand, immunoneutralizing VEGF (Genentech-Roche, MTA) impaired spatial learning performance and neuronal activity of CA3 hippocampus neurons. These data suggest that a careful and systematic evaluation of targeted cancer therapies on cognitive functions in preclinical models may constitute a strategy of prevention by selection of treatments exhibiting minimum brain co-morbidities.
Together, this translational program is developed within the National Cancer and Cognition Platform (CNO/Ligue Nationale contre le cancer), with the aim to collaborate in a structured way with French oncology groups, research teams as well as pharmaceutical industry, by providing preclinical models and guidance on standard operating procedures for ancillary or future studies in identified population at risk.

Annonce de séminaire

Kei Sakamoto

Institut des Nestlé Institute of Health Sciences SA, Lausanne.

Key signaling players in the control of hepatic gluconeogenesis — AMPK or other AMPK-related/AMP-regulated enzymes ?

Invité par Rémi Mounier

Résumé
Hepatic glucose production is a key physiologic process that ensures energy balance for glucose-dependent organs/cells such as brain. The inability of insulin to suppress hepatic glucose output is a major aetiological factor in the hyperglycaemia of type 2 diabetes. LKB1, originally identified as a tumor suppressor protein, is currently thought as a critical regulator of cellular metabolism and growth by controlling the activity of AMP-activated protein kinase (AMPK) and also 12 other kinases that are closely related to AMPK. Among those AMPK-related kinases, we have recently identified that Salt-Inducible Kinase (SIK) plays an important role as a gluconeogenic gatekeeper in the liver.
Metformin exerts its major effect via inhibition of hepatic glucose production. This is thought to be mediated through decreased hepatic energy charge (i.e. increasing AMP/ATP ratio) via inhibition of mitochondrial respiration. The long-standing belief that 5’-adenosine monophosphate (AMP)-activated protein kinase (AMPK) mediates the anti-hyperglycaemic action of metformin has recently been challenged in experiments using mice lacking hepatic AMPK. I will discuss our recent data demonstrating AMP-mediated allosteric inhibition of an enzyme involved in gluconeogenesis plays a key role in acute glucose-lowering effect of metformin.

Annonce de séminaire

Alexandre Pattyn

Institut des Neurosciences de Montpellier, INSERM U1051. France.

Heterogeneous precursor populations underlie developmental plasticity of the dorsal root ganglia

Invité par Valérie Castellani

Résumé
Although a variety of primary sensory neurons are implicated in the detection and transmission of different sensory modalities, how they arise during development remains poorly understood. The process of neuronal specification is the acquisition of definitive phenotypic characteristics for a given subclass of neurons during embryonic development. This acquisition can be divided into several interdependent and sequential phases, from the time point when progenitor cells exit the cell cycle toward the newly formed and perfectly differentiated neuron. Using mouse genetics, Alexandre demonstrated that transcriptions factors of Maf and Zeb families control the specification and differentiation of specific sensory neuron sub-types. His work contributed to uncover the complex developmental sequence ensuring the formation of the peripheral sensory system and to highlight the progenitor diversity that underlies the developmental plasticity of sensory neuron generation.

Annonce de séminaire

Georgia Rapti

The Rockefeller University, Shaham lab, New York, USA.

It takes two to tango with elegance: Glia and pioneer neurons orchestrate C. elegans brain assembly

Invité par Jean-Louis Bessereau

Résumé
Brain assembly is hypothesized to begin when pioneer axons extend over non-neuronal cells, forming tracts guiding follower axons. Yet, the identities of the pioneer-neurons and of their guidance-substrates and their interactions, are not well understood. Here, using time-lapse embryonic imaging, genetics, protein-interaction, and functional studies, we uncover the early events of C. elegans brain assembly. We demonstrate that C. elegans possesses radial-glia-like cells key for assembly initiation. Glia guide pioneer and follower axons using distinct signals. Pioneer neurons we identify, with unique growth properties, anatomy, and innervation, cooperate with glia to guide follower axons. We identified a CHIN-1/Chimaerin- KPC-1/Furin double mutant that severely disrupts assembly, unlike previously known mutants. CHIN-1/Chimaerin and KPC-1/Furin cooperate non-canonically in glia and pioneer neurons for guidance-cue trafficking. We exploit this genetic bottleneck to define a guidance-gene network governing assembly, with specific glia and pioneer-neuron contributions. Our studies reveal previously-unknown roles for glia in pioneer-axon guidance, and suggest conserved principles of brain formation.

Annonce de séminaire

Sophie Creuzet

Institut des Neurosciences Paris-Saclay, CNRS UMR 9197, Gif-sur-Yvette. France.

Neural crest in forebrain development: from embryology to pathophysiology

Invité par Valérie Castellani

Abstract
In my group, we study the neural crest, a unique cell population that emerges from the primitive neural field and which has a multi-systemic and structural contribution to vertebrate development. Over the last decade, I have been dedicating myself to the cellular and molecular background of the observation I made in 2004, that the cephalic neural crest (CNC), exerts an autonomous and prominent control on forebrain development. This notion has broken the traditional view of how the brain develops. By using exquisite grafting experiments in combination with focal spatially and temporally controlled transgenesis, we have discovered the unexpected and potent “paracrine role that the CNC exerts on forebrain growth and patterning early in development and documented this mechanism at the level of cell interaction, signalling and gene expression. We are now following this exiting line of research, which revisits fundamental concepts in Neurosciences. This notion provides also a conceptual renewal, which is biomedically relevant. The mechanisms identified so far in our model are conserved across tetrapodes, but some social behavioural features are specific to amniotes. Our ongoing project and future directions are to explore the aetiology of neural disorders and behavioural impairments in Humans and in the light of CNC dysfunctions.

Annonce de séminaire

Colin Crist

Department of Human Genetics, McGill University – Québec, Canada.

Translational Control of Muscle Stem Cells

Invité par Rémi Mounier

Abstract
Regeneration of adult tissues depends on somatic stem cells that remain quiescent, yet are primed to enter a differentiation program. The molecular pathways that prevent activation of these cells are not well understood. Using mouse skeletal muscle stem cells as a model, we show that accumulating transcripts specifying the myogenic program are not translated in quiescent satellite cells, but are repressed by the action of microRNAs and RNA binding proteins. Furthermore, the reversible nature of microRNA dependent silencing mechanisms may underlie the rapid activation of satellite cells that are poised to enter the myogenic program. We also show that a general repression of translation, mediated by the phosphorylation of translation initiation factor eIF2 at serine 51 (P-eIF2α), is required to maintain the quiescent state. Skeletal muscle stem cells unable to phosphorylate eIF2 exit quiescence, activate the myogenic program and differentiate, but do not self-renew. P-eIF2α ensures in part the robust translational silencing of accumulating mRNAs that is needed to prevent the activation of muscle stem cells. Additionally, P-eIF2α dependent translation of mRNAs regulated by upstream open reading frames (uORFs) contributes to the molecular signature of stemness. Finally, we show that addition of small molecule inhibitors of eIF2α dephosphorylation to muscle stem cell cultures permits their ex vivo expansion and engraftment into a preclinical mouse model of Duchenne muscular dystrophy.

Annonce de séminaire

Michael A Rudnicki

Center of Ottawa Hospital Research Institute, Ottawa, Ontario, Canada

Molecular regulation of muscle stem cell asymmetric division

Invité par Bénédicte Chazaud

Abstract
We discovered that a subset of satellite cells in skeletal muscle are self-renewing stem cells that give rise to myogenic progenitors through asymmetric apical-basal cell divisions. The regulation of asymmetric stem cell division is a key control point that impacts the efficacy of the entire regenerative program. Stem cell polarity is established by the PAR complex, comprised of PAR3/PAR6/aPKC, to regulate self-renewal and expansion. Duchenne Muscular Dystrophy (DMD) is coaused by a lack of dystrophin which is expressed in muscle fibers where it plays a role in ensuring structural integrity. We have made the seminal finding that dystrophin regulates the establishment of PAR-mediated polarity in satellite cells. In the absence of dystrophin, the polarity effector Par1b is dysregulated, leading to the failure of Par3 to become localized to the cortex associated with the basal lamina. Importantly, this results in an abnormal increase in centrosome number, a 10-fold reduction in the numbers of satellite stem cells undergoing asymmetric divisions, and a marked decrease in the generation of myogenin-expressing progenitors. Accordingly, our data suggests that the failure of regenerative myogenesis to keep pace with disease progression in DMD is not due to muscle stem cell exhaustion, but rather is due to a cell-autonomous deficiency in asymmetric division.

Annonce de séminaire

F. Jeffrey Dilworth

Center of Ottawa Hospital Research Institute, Ottawa, Ontario, Canada

Epigenetic control of stem cell fate decisions in muscle repair

Invité par Bénédicte Chazaud

Abstract
During muscle regeneration, the conversion of muscle stem cells to terminally differentiated myofibers requires multiple cell fate transitions. Each of these transitions necessitates an alteration in the set of genes being expressed within the cell. In this presentation, our studies on the role of transcription factors and epigenetic enzymes in dictating changes in muscle gene expression will be highlighted. In particular, I will focus on the role for the antagonism between various transcription factors and epigenetic enzymes in controlling the commitment of muscle stem cells towards alternate cell fates.

Annonce de séminaire

Fabien Le Grand

Center of Research in Myology, Université Pierre et Marie Curie Paris – France.

Control of muscle stem cell fate by Wnt signaling pathway(s)

Invité par Bénédicte Chazaud

Abstract
Regeneration of the adult skeletal muscle tissue relies on a pool of quiescent muscle stem cells located in a niche around the myofibers: the satellite cells (MuSCs). Upon activation following injury or repeated exercise, MuSCs leave quiescence to proliferate and then differentiate to form new muscle fibers while a sub-population exit the cell cycle to self-renew and replenish the stem cell niche. In the course of this process, signals from the microenvironment instruct cycling MuSCs and control myogenesis. We previously demonstrated that numerous Wnt molecules are secreted in the local milieu during regeneration and showed that MuSC self-renewal is in part controlled by non-canonical Wnt7a/PCP signals sent by the regenerating myofibers. To elucidate the roles of the canonical Wnt/ß-catenin pathway in MuSCs, we generated mice with inducible MuSC-specific ß-catenin Loss-Of-Function or Gain-Of-Function. Strikingly, we observed that induction of either ß-catenin LOF or GOF mutations in MuSCs leads to the impairment of skeletal muscle regeneration following injury. By using a mouse model of conditional APC gene deletion in MuSCs we further demonstrated that the massive activation of canonical Wnt signaling in MuSC following APC loss results in defective cell cycle progression and apoptosis. Mechanistically, we observed that Wnt/ß-catenin signaling orchestrates the cytoplasmic relocalization of the histone 3 lysine 9 methyltransferase Setdb1 during differentiation. We further showed that Setdb1 is required for MuSCs amplification and suppresses myoblast terminal differentiation. Genome-wide analyses showed a Wnt3a-dependant release of Setdb1 from the promoter of selected target genes upon myoblast terminal differentiation. Taken together, our results demonstrate that both canonical and non-canonical Wnt pathways are necessary for MuSC function. Lastly, I will discuss the potential cross-talks between these two faces of an important signaling.

Annonce de séminaire

Stefan Dimitrov

Institut Albert Bonniot, Centre de Recherche UGA – INSERM U1209 / CNRS UMR 5309, Grenoble, France.

Epigenetic strategies : nucleosome remodeling, histone modifications and histone variants.

Invité par Laurent Schaeffer

Abstract
Chromatin impedes the binding of protein factors to the underlying DNA sequences. The cell uses three main “epigenetic tools” to overcome the chromatin barrier, namely, chromatin remodelers, histone variants and histone post-translational modifications. We will give specific examples of how either one of these “epigenetic tools” functions.
Chromatin remodelers are sophisticated nano-machines, which are able to alter histone-DNA interactions and to mobilize nucleosomes. Neither the mechanism of their action nor the conformation of the remodeled nucleosomes are, however, yet well understood. We have studied the mechanism of RSC-induced chromatin remodeling by using high resolution microscopy and state of the art biochemistry techniques. The data illustrates how RSC remodels the nucleosome in vitro and shed light on its in vivo function. The crystal structure of the CENP-A nucleosome was recently solved. Intriguingly, in contrast to the canonical nucleosome (where 147 bp of DNA are wrapped around the histone octamer), only the central 121 bp were visible, suggesting flexible CENP-A nucleosomal ends. Why the CENP-A nucleosome exhibits flexible DNA ends is totally unknown. Our data show that the flexible DNA ends of the CENP-A nucleosome are required for mitotic fidelity.
The Aurora family of oncogenic kinase consists of two major members, Aurora A and Aurora B. Both kinases exhibit very high homology. They show, however, quite distinct localization and function. Histone H3 is specifically phosphorylated, presumably by the oncogenic kinase Aurora B, at serine 10 at the onset of mitosis. Here we will present data on the distinct function of the two Aurora kinases and the mechanism of phosphorylation of histone H3 by Aurora B.

Annonce de séminaire

Stéphane Vassilopoulos

Institut de Myologie, UMRS 974 UPMC-Inserm / FRE 3617 CNRS, G. H. Pitié-Salpétrière, Paris – France.

The endocytic machinery in healthy and diseased muscle

Invité par Laurent Schaeffer

Abstract
Costameres represent specialized focal adhesion sites of muscle fibres, located between the plasma membrane and sarcomeres, the contractile units of muscle. When disrupted, they directly contribute to the development of several distinct myopathies.
We have shown that the ubiquitous clathrin heavy chain (CHC), well characterized for its role in intracellular membrane traffic and endocytosis from the plasma membrane (PM), forms large plaques connected to α-actinin and actin filaments. Depletion of CHC leads to defective costamere formation and maintenance both in vitro and in vivo and induces sarcomere disorganization and a loss of contractile force due to the detachment of sarcomeres from the PM. At costameres, CHC is co-expressed with dynamin 2 (DNM2), another key protein of the intracellular membrane trafficking machinery which is mutated in autosomal dominant centronuclear myopathy (CNM). We analyzed the role of DNM2 and several actin binding proteins on clathrin plaque function at costameres in vitro by using either siRNA depletion combined to high resolution electron microscopy or in vivo by intravital microscopy. We also focused on the possible link between costamere and CNM pathophysiology. Using myoblasts from DNM2-mutated patients and using myoblasts and muscles from a knock-in mouse model of DNM2-related myopathy, we analyzed structure of costameres by biochemical and immunocytochemical approaches, as well as their ultrastructure.
Our results demonstrate a crucial role for the endocytic machinery and the cytoskeleton. Their contribution to the formation and maintenance of the contractile apparatus highlight an unconventional role for clathrin flat lattices in skeletal muscle which may be relevant to pathophysiology of several neuromuscular disorders.

Annonce de séminaire

Sandrine Humbert

GIN – Inserm U1216 – University Grenoble Alpes, Grenoble, France.

Huntingtin regulates cortical development: consequences for Huntington’s disease

Invité par Julien Courchet

Abstract
The bulk of interest in the huntingtin protein has centered on the fact that, when mutated, huntingtin causes Huntington’s disease (HD), a devastating neurodegenerative disorder. The mutation causing HD is an abnormal polyglutamine stretch in huntingtin. Given the adult onset and dysfunction and death of adult neurons characterizing HD, most studies have focused on the toxic effects elicited by mutant huntingtin in post-mitotic neurons. However, the protein is ubiquitous and expressed in the developing embryo where it plays an essential role as revealed by the early embryonic lethality at day 7.5 of the complete knockout of the huntingtin gene in mouse. Anyway, the roles of the wild-type protein during development have been overlooked. I will discuss how huntingtin regulates several steps of mouse embryonic corticogenesis. I will also show the consequences of the presence of an abnormal polyglutamine expansion in huntingtin during cortical neurogenesis and consider the viewing of HD as a developmental disorder.

Annonce de séminaire

Jan Tuckermann

Institute of Comparative Molecular Endocrinology Ulm University, Ulm, Germany.

Modes of GR action revised – Novel mechanisms of corticosteroids in inflammation and bone integrity

Invited by Bénédicte Chazaud

Abstract
The Tuckerman Laboratory made major contributions to the molecular mechanisms of corticosteroids in beneficial and side effects of steroid therapy. With the help of conditional and function-selective knockout mice for the glucocorticoid receptor (GR) the lab identified critical cell types and novel mechanisms for anti-inflammatory activities of glucocorticoids in different inflammatory disease models. Furthermore we made the discovery that in a model of lung inflammation the anti-inflammatory action of glucocorticoids is not dependent on the inhibition of pro-inflammatory mediators, but rather requires cooperation with pro-inflammatory signaling pathways (e.g. p38) to induce anti-inflammatory acting genes and alternative polarization of macrophages.

Annonce de séminaire

Dr. Pierre-Jean Corringer

Pasteur Institute, Channel-receptor Unit, CNRS UMR 3571, 25 rue du Docteur Roux, 75015 Paris, France.

Pentameric ligand-gated ion channels functioning at the atomic resolution

Invited by Maëlle Jospin

Abstract
Pentameric channel-receptors, including nicotinic acetylcholine, glycine and GABAA receptors, play a key role in fast excitatory and inhibitory transmission in the nervous system and are the target of numerous therapeutic and addictive drugs. They carry several neurotransmitter binding sites which govern the opening of a transmembrane ion channel. Extensively expressed in animals, they were found in several bacteria, especially the homolog from the cyanobacteria Gloeobacter violaceus (GLIC) which functions as a proton-gated ion channel. The simplified architecture of this archaic homologue, as well as its prokaryotic origin, allowed solving its X-ray structure in several conformations. Those static structures suggest that channel opening occurs through symmetrical quaternary twist and “blooming” motions, together with tertiary deformation. We further engineered multiple fluorescent reporters on the structure, allowing investigating the dynamics of the allosteric reorganizations and showing that activation involves a key pre-active conformation. Finally, the GLIC system was exploited to solve the structure of human receptors through the generation of functional chimeras. Overall, our work gives insights into the mechanism of gating and pharmacological regulation of this important family of neurotransmitter receptors.

Dr. Yishi Jin

UC San Diego.

Mechanisms regulating synapse maintenance and neural activity

Invited by Jean-Louis Bessereau

Abstract
Synapses are organized subcellular structures that transmit information within the nervous system and to other parts of our body. Our studies use C. elegans have uncovered multiple pathways controlling synapse formation, maintenance and function. Using a genetic model mimicking the physiological state of seizures, our recent work have identified novel regulatory themes affecting presynaptic release machinery. We also discovered that a novel immunoglobulin superfamily (IgSF) transmembrane protein mediates synapse and non-neuronal tissue interaction in synapse maintenance. These findings have implications to our understanding of circuit malfunction under disease conditions.

Annonce de séminaire

Dr. Francesco Zorzato

Department of Biomedicine, Basel University

Pathophysiology of ryanodinopathies

Invited by Bruno Allard

Abstract
Type 1 ryanodine receptor (RyR1) is preferentially expressed in skeletal muscle, and mutations in the gene have been associated with malignant hyperthermia, a pharmacogenetic disease, and with several congenital myopathies, including central core disease, multiminicore disease, centronuclear myopathy, congenital fibre type disproportion. Experimental data have indicated that RyR1 is also expressed in some areas of the central nervous system, in some cell types of the immune system and in smooth muscle cells. These results imply that mutations in the gene encoding RyR1 will not only affect skeletal muscles, but other tissues that express this calcium channel as well, thereby broadening the clinical spectrum of disorders due to RyR1 dysfunctions.
The RyR1 is of fundamental importance for the development of muscle force and a decrease in its content may be causally linked to the profound muscle weakness seen in patients with some forms of congenital myopathies linked to recessive RYR1 mutations. The protein composition of the junctional sarcoplasmic reticulum membrane encompassing the excitation-contraction coupling molecular complex (ECCMC) is extremely complicated. Polymorphic variants of the junctional sarcoplasmic reticulum protein JP45 have been shown to segregate in Malignant Hyperthermia Susceptible subjects of Malignant Hyperthermia families in the UK. Thus, some ECCMC accessory proteins may play a role not only in regulating excitation-contraction coupling but also as modifiers of the ryanodinopathies phenotype.

Annonce de séminaire

Dr. Jean-Marc Goaillard

UNIS – Aix Marseille Université

Biophysical networks underlying electrical phenotype of dopaminergic neurons

Invited by Thomas Boulin

Abstract
Any type of neurons can be easily identified based on its electrophysiological activity, such as its pattern of spontaneous activity, the shape of its action potential, its dendritic integration, etc. How is stability of such electrical phenotype achieved, what are its molecular principles, and what is the degree of robustness of electrical phenotype in the face of different perturbations are questions only very partially answered. We studied these questions on dopaminergic neurons of the substantia nigra pars compacta. Our work involved characterizing the electrical phenotype of these neurons and measuring its post-natal development and its stability at mature stages. We also characterized the specific relationships of electrophysiological parameters underlying the electrical phenotype. In order to determine how complex electrical phenotype is achieved, we then investigated the networks of co-regulation of ion channels at the genetic and at the protein levels. Our results suggest that ion channel gene expression and protein interactions display a modular structure that may be involved in stabilizing phenotype. We also show that electrical phenotype also presents such a modular structure. Our ultimate goal is to provide a systems-level approach to robustness of electrical phenotype.

Annonce de séminaire

Dr. Michele Zoli

Friday Avril 29th at 14:00 – Amphithéâtre de la délégation du CNRS

Dr. Shiva Tyagarajan

Inst. of Pharmacology and Toxicology, University of Zurich.

Interrupting neuronal communication from a GABAergic viewpoint

Invited by Jean-Louis Bessereau

Abstract
In the brain distinct population of inhibitory GABAergic interneurons innervate principal glutamatergic neurons to regulate various aspects of brain function. At the postsynaptic compartment, specific GABAAR subunits are segregated to different neuronal compartments to recieve specific inputs from different interneurons. The correct interpretation of the incoming signal requires functional coupling between the presynaptic neurotransmitter GABA, postsynaptic GABAARs, and downstream signaling by postsynaptic density proteins. The main postsynaptic density protein at inhibitory synapse is gephyrin. In the past decade we have identified diverse signaling cascades that converge on gephyrin scaffold to regulate its scaffolding property, and in turn GABAergic neurotransmission. These studies have shed light into mechanisms that underlie dynamic changes in inhibitory neurotransmission, and how excitation shapes inhibition.

Annonce de séminaire

Vendredi 29 janvier à 14:00 – Bâtiment l’Herbier

Pura Muñoz-Cànoves

ICREA Research Professor at Universitat Pompeu Fabra, Barcelona.

Tissue regenerative decline with aging: focus on muscle stem cells

Invited by Bénédicte Chazaud

Abstract
Our group aims to understand the mechanisms regulating stem cell homeostasis and regenerative functions. Research is specially centered on stem cells of skeletal muscle (i.e., satellite cells). Recently, we have focused on two areas: 1) the functional decline of satellite cells with aging; and 2) the physiopathology of muscular dystrophies, with a specific interest in the contribution of inflammation and fibrosis to dystrophy progression. Concerning the first area, work from different laboratories has demonstrated that both environmental and cell- autonomous signals alter satellite cell regenerative potential with aging. I will discuss our latest results showing that satellite cells in their homeostatic quiescent state are equipped with quality control mechanisms to preserve their fitness, and how age-associate alterations in these protective mechanisms lead to stem cell loss of function and regenerative capacity.

Annonce de séminaire

Marc HAMMARLUND

Yale University, New Haven, USA

How C. elegans neurons sense and respond to injury

Invité par Jean-Louis Bessereau

Abstract
The nervous system has an extraordinary capacity to repair damage by regenerating axons and synaptic connections. I will discuss the molecular and cellular basis of axon regeneration in C. elegans, and describe how regenerated synapses and circuits differ from those generated during development. Finally, I will present new data on a novel ncRNA pathway that controls regeneration.

Luc BERTRAND

Université catholique de Louvain, Brussels

AMPK in cardiac pathologies, not just a metabolic sensor !

Abstract
The AMP-activated protein kinase (AMPK) has been firstly discovered to be activated under metabolic stress conditions such as myocardial ischemia. Its protective action during an ischemic episode has been demonstrated by several research groups. By targeting metabolism, AMPK helps the heart to survive under such deleterious conditions. However, AMPK action extends beyond metabolism and acute stress conditions. Indeed, it has been more recently shown that AMPK acts as protector of the heart in several chronic diseases such heart failure, diabetic cardiomyopathy and cardiac hypertrophy by acting in cardiomyocytes but also on the other cell types such as fibroblasts. Very recently, our group discovered a connection between AMPK and a particular post-translational modification called O-GlcNAcylation, this interplay acting a major role in the development of cardiac hypertrophy. The lecture will focus on the different protective roles of cardiac AMPK.

Michisuke Yuzaki

Keio University School of Medicine, Tokyo

Bridge over troubled synapses — a new synthetic synapse organizer

Invité par Jean-Louis Bessereau

Abstract
Synaptic organizers regulate formation, elimination and maintenance of synaptic connections throughout life. Although excitatory and inhibitory synaptic imbalance underlies certain neuropsychiatric and neurological disorders, no tools are currently available to directly modulate the balance. Recently, a new class of synaptic organizers, termed extracellular scaffolding proteins (ESPs), are reported to acutely and potently modulate specific synapses by directly binding to certain pre- and postsynaptic membrane proteins. Here, to expand the repertoire of ESPs with a variety of pre- and postsynaptic specificities, we developed a new synthetic ESP, Cbln1–neuronal pentraxin 1 (NP1) chimera (CPTX), by exploiting the structure of NP1 and Cbln1. Unlike original Cbln1, CPTX induced excitatory synapses by recruiting AMPA glutamate receptors in vitro. Furthermore, CPTX restored excitatory synapses and synaptic plasticity in vivo, as well as spatial and contextual memories in Alzheimer’s disease model mice. In this talk, I would like to discuss a possible toolkit of ESPs with a variety of pre- and postsynaptic specificities to modify neuronal circuits.

Saadi Khochbin

Institute for Advanced Biosciences, La Tronche, France

Les séminaires du Chromatin Club – Metabolism-driven epigenetics

Invité par Armelle Corpet / Patrick Lomonte

Annonce de séminaire

Frédéric RELAIX

INSERM – IMRB U955-E10, F-94010 Créteil, France

PAX3 controls the adaptive response of skeletal muscle stem cells to environmental stress

Invité par Rémi Mounier

Abstract
We have identified a molecular link between the Aryl hydrocarbon Receptor (AhR) environmental stress pathway and Pax3/Pax7 developmental genes during craniofacial development. Since Pax3/7 are key regulators of muscle stem cells (muscle satellite cells), we investigated the cellular and molecular impact of chronic 2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD) exposure on skeletal muscle and satellite cells in the adult. We combined in vivo and ex vivo approaches, in order to analyse the impact of chronic exposure to TCDD in several muscles such as tibialis anterior and biceps brachii. While all MuSCs express the transcription factor PAX7, we show that a muscle-specific subset also express PAX3 and exhibit resistance to environmental stress. Upon systemic TCDD treatment, PAX3-negative MuSCs display impaired survival, atypical activation and sporadic differentiation through the xenobiotic Aryl Hydrocarbon Receptor. We further show PAX3-positive MuSCs become sensitized to environmental stress when PAX3 function is impaired and that PAX3-mediated induction of mTORC1-dependent G(alert) is required for protection. Our study therefore identifies a functional heterogeneity of MuSCs in response to environmental stress controlled by PAX3.

Annonce de séminaire

Nicolas RENIER

ICM – Institut du Cerveau et de la Moelle Epinière Paris – FRANCE

A framework for the study of behaviour and plasticity in the adult brain using light sheet microscopy

Invité par Julien Courchet

Abstract
There has been over the past 6 years a convergence in the fields of optics, biochemistry and computing leading to dramatic improvements in light sheet microscopy, tissue clearing protocols and image analysis algorithms. The convergence of these different fields has the potential to streamline brain studies by accelerating data acquisition speed and reliability over the current whole brain analysis pipelines based on serial sectioning methods. We previously developed the iDISCO+ protocol for immunostaining and imaging intact adult mouse brains. As a companion tool, we also developed and distribute ClearMap, an open source environment to segment objects and map them onto reference atlases optimized for large 3D datasets. We used this pipeline as a discovery tool to find brain regions active in correlation with various behaviors by mapping neuronal activity landscapes derived from Fos expression. Here, I will present recent unpublished projects made possible by our upcoming brain mapping pipeline ClearMap 2, expanding the repertoire of applications derived from intact whole brain preparations. We hope that ongoing developments in light sheet microscopy and image analysis pipelines will facilitate our understanding of individual variations in brain activity, connectivity and structure.

Annonce de séminaire

Hugues NURY

Institut de Biologie Structurale, Grenoble

Structures and transitions of the serotonin 5-HT3 receptor

Invité par Thomas Boulin

Abstract
The serotonin 5-HT3 receptor is a pentameric ligand-gated ion channel. It belongs to a large family of receptors that transduce signals across the plasma membrane​: upon binding of neurotransmitter molecules to extracellular sites, the receptors undergo complex conformational transitions, which result in transient opening of a pore permeable ​to ions. 5-HT3 receptors are therapeutic targets for emesis and nausea, irritable bowel syndrome and depression. I will present structures of the 5-HT3 receptor obtained by crystallography or cryo-electron microscopy. The structures, obtained in complex with inhibitors or agonists, represent snapshots in different states: inhibited, pre-active, active. Together with molecular dynamics simulations and functional recordings, they reveal the molecular mechanism of the fast neurotransmission mediated by 5HT3 receptors.

Annonce de séminaire

Emmanuel COMPE

Institut de Génétique et de Biologie Moléculaire et Cellulaire Illkirch, Strasbourg

TFIIH and TFIIE mutations: when transcriptional deficiencies lead to neurological disorders

Invité par Ambra Giglia-Mari

Abstract
Trichothiodystrophy (TTD) is an autosomal recessive disorder mainly related to mutations in the DNA repair/transcription factor TFIIH. In addition to the typical dry and brittle hair, individuals with TTD develop neurological defects, including microcephaly and hypomyelination. Using a TTD transgenic mouse model, we previously observed a spatial and selective deregulation of thyroid hormone target genes in the brain, suggesting that transcriptional failures contribute to TTD phenotypes.
Remarkably, mutations within TFIIE, another general transcription factor, have been recently associated with TTD. Such observation prompted us to accurately dissect the partnerships occurring between TFIIE and TFIIH during transcription. Our work revealed an unexpected dynamic process during which TFIIE act as key factors to recruit and position the kinase module of TFIIH within the preinitiation complex. Strikingly, TTD-related mutations in either TFIIH or TFIIE similarly disrupt this early transcriptional process, which could explain why alterations in different transcription factors can lead to the same clinical syndrome.

Annonce de séminaire

Laurent BARTHOLIN

CRCL, Lyon

The obnoxious faces of TGFbeta in pancreatic cancer

Invité par Rémi Mounier

Abstract
The Transforming growth factor beta (TGFB) is a pleiotropic secreted factor with many roles during embryonic and adult life. In cancer, it behaves either as a tumor suppressor or a tumor promoter. To understand this functional duality, our lab have been using as a model Pancreatic Ductal Adenocarcinoma (PDAC), one of the most aggressive tumor, which is expected to become the second cancer-related cause of death by 2030 (after lung cancer). Our work is focused on the oncogenic properties of TGFB with the final goal to specifically target them by developing innovating therapeutics. During this presentation, I will present our work to understand the TGFB oncogenic effects at the molecular (a “new” oncogenic signaling pathway), cellular (effect on differentiation of pancreatic acinar cells), organ (interaction between PDAC cells and nerves invading the tumor) and whole body levels (interaction with muscle).

Fabien LE GRAND

Centre de Recherche en Myologie, Paris

Signaling pathways in muscle tissue regeneration

Invité par Laurent Schaeffer

Abstract
The development and repair of complex metazoan tissues are coordinated by a startlingly small number of evolutionarily conserved signaling pathways. These signals can act in parallel but often function as an integrated hyper-network. Our research aims at understanding the signaling nodes defining this molecular circuitry and the biological significance of pathway cross-talk, using skeletal muscle as a fitting model. Regeneration of the adult muscle tissue relies on a pool of quiescent muscle stem cells located in a niche around the myofibers: the satellite cells (MuSCs). We previously demonstrated that numerous WNT molecules are secreted in the local milieu during muscle regeneration and showed that MuSC self-renewal is in part controlled by non-canonical Wnt7a/PCP (1). To elucidate the roles of the canonical Wnt/ß-catenin pathway in MuSCs, we generated mice with inducible MuSC-specific mutations (2, 3). Mechanistically, we observed that Wnt/ß-catenin signaling orchestrate the cytoplasmic relocalisation of the H3K9 methyltransferase SETDB1 during differentiation (4). We further investigated how Wnt/ß-catenin signaling is connected to Bone morphogenetic protein (BMP) and Transforming growth factor beta (TGF-ß) pathways. Recent work in our lab consisted in dissecting the impact on these pathways on MuSC return to the niche and fusion, respectively. Nevertheless, our understanding of the cells that compose skeletal muscle tissue is limited and molecular definitions of the principal cell types are lacking. This hinders our capacity to decipher signal integration and reciprocity between cells. We thus used a novel combined approach of single-cell RNA-sequencing and mass cytometry and precisely mapped 10 different cell types in adult mouse skeletal muscle, including two previously unidentified populations (5). This cartography yields crucial insights into muscle-resident cell type identities and will be exploited to build a muscle connectome.

Bert Blaauw

Venetian Insitute of Molecular Medicine

The role of mTORC1 signaling in adult skeletal muscle

Invité par Laurent Schaeffer

Abstract
It is well established that mTORC1 signaling is key modulator of skeletal muscle mass and function. Surprisingly, despite the fact that skeletal muscle undergoes major changes in size and contractility in numerous diseases, no genetic loss-of-function model has been generated to determine the effect of inducible deletion of mTORC1 in adult skeletal muscle. Here we generated inducible, muscle-specific Raptor and mTOR k.o. mice. Interestingly, we do not observe a change in muscle size or contractile properties one month after deletion. However, treating these mice with the mTOR-inhibitor rapamycin is sufficient to induce a very rapid and marked myopathy, suggesting that little residual mTOR signaling can maintain muscle homeostasis in adult muscle. Prolonging deletion of Raptor to 7 months, however, leads to a very marked phenotype characterized by muscle dysfunction, regeneration, glycogen accumulation and mitochondrial dysfunction and block in autophagy. Unexpectedly, one of the best markers of reduced mTOR signaling in muscle fibers is the appearance of denervated fibers. Both muscle-specific deletion of mTOR or Raptor, or the use of rapamycin, was sufficient to induce the appearance of numerous NCAM-positive fibers, muscle fibrillation, and neuromuscular junction fragmentation. Taken together, these results link one of the most important anabolic pathways in skeletal muscle fibers to the maintenance of the NMJ.

Hélène PUCCIO

Department of Translational Medecine and Neurogenetics, IGBMC, Strasbourg

Advances in Friedreich Ataxia: understanding the function of frataxin and developing therapeutic approaches

Invité par Laurent Schaeffer

Abstract
Friedreich’s ataxia (FA), the most common autosomal recessive ataxia, is characterized by a sensory and spinocerebellar ataxia, hypertrophic cardiomyopathy and increase incidence of diabetes. FA is caused by reduced levels of frataxin (FXN), an essential mitochondrial protein involved in the biosynthesis of iron-sulfur (Fe-S) clusters. Fe-S clusters are ancient and essential cofactors that participate in a number of cellular processes ranging from mitochondrial respiration to DNA metabolism. In eukaryotes, de novo Fe-S biogenesis takes place within mitochondria and relies on proteins that are highly conserved from bacteria to humans. Impaired mitochondrial oxidative phosphorylation, bioenergetics imbalance, deficit of Fe-S cluster enzymes and mitochondrial iron overload occur in individuals with FA. To date, no treatment exists for stopping or slowing FA disease.
Over the past years, we have generated cellular and mouse models that reproduce important progressive pathological and biochemical features of the human disease, including cardiac hypertrophy, mixed cerebellar and sensory ataxia, Fe-S enzyme deficiency, and intramitochondrial iron accumulation. These models have enabled us to demonstrate that Fe-S deficit is a primary event of the disease leading to iron metabolism deregulation through the activation of the iron-regulatory protein, IRP1. These models are excellent models for deciphering the physiopathology of the disease and for testing pre-clinical therapeutic protocols. The latest advances in understanding the pathophysiology will be discussed, with a particular emphasis on new neurological models that are being developed as well as therapeutic approaches.

Juliette GODIN

Institut de Génétique et Biologie Moléculaire et Cellulaire, Strasbourg

Pleiotropic activities of the (atypical ?) kinesin KIF21B during cortical development

Invité par Julien Courchet

Abstract
Cortical development progresses through concurrent steps, including neural proliferation, migration and differentiation, that rely on dynamic cell shape remodeling which largely depends on the tight regulation of the microtubules (MT) cytoskeleton. Mutations in tubulin, MT associated proteins or motors have been linked to several neurodevelopmental disorders including malformation of cortical development (MCDs), affecting 2,5% of the world population. Here we identified KIF21B gene as a major locus of human neurodevelopmental disorder. We identified 4 de novo variants in KIF21B gene in patients with intellectual disabilities associated with several brain malformations, including microcephaly, corpus callosum agenesis or facial dimorphism. In support of the pathogenic potential of the discovered alleles, expression of KIF21B variant in mice using in utero electroporation or in zebrafish embryos recapitulated key neurodevelopmental phenotypes, namely migration and microcephaly. In addition, longitudinal neuroanatomical analysis of Kif21b KO model showed strong morphological defects starting prenatally and worsening with time. Finally, we demonstrated that Kif21b regulates migration of projection neurons through the tight control of locomotion and neural shape. Although its motility is dispensable, the regulatory function cytoskeleton dynamics is essential for neuronal migration. Altogether, our data represent an important step to delineate the mechanisms involving KIF21B-mediated MT dynamics and trafficking in the context of brain development.

Annonce de séminaire

Belinda COWLING

Institut de Génétique et Biologie Moléculaire et Cellulaire, Strasbourg

Myostatin – A novel biomarker for Dnm2 therapy in Myotubular Myopathy mice

Invité par Vincent Gache

Abstract
Centronuclear myopathies (CNM) are non-dystrophic muscle diseases for which no effective therapy is currently available. The most severe form, myotubular myopathy (X-linked CNM), is caused by myotubularin 1 (MTM1) loss-of-function mutations, while the main autosomal dominant form is due to dynamin2 (DNM2) mutations. We have shown that antisense oligonucleotide (ASO) mediated DNM2 knockdown can efficiently correct muscle defects due to loss of MTM1 in mice, providing an attractive therapeutic strategy for this disease. We are now investigating blood-based biomarkers that can be used to monitor disease state and rescue in myotubular myopathy mice. Myostatin is a protein produced and released by myocytes, which acts in an autocrine function to inhibit muscle growth and differentiation. Our results suggest myostatin pathway is ‘turned down’ at the mRNA level in muscle biopsies, leading to low levels of circulating and endogenous muscle myostatin in plasma. We have generated preliminary data suggesting ASO-mediated DNM2 reduction results in an increase in circulating myostatin. With clinical trials for myotubular myopathy currently in progress, identification of novel blood-based biomarkers such as myostatin may allow for monitoring of treatment efficacy in patients.

Annonce de séminaire

Luisa COCHELLA

Research Institute of Molecular Pathology (IMP), Vienna, Austria

Roles of micro RNAs in animal development: lessons from C.elegans

Invité par Florence Solari

Abstract
One of the main goals of developmental biology is to understand how the different cell types that constitute a multicellular organism are specified during its development. Luisa Cochella is a young PI (awarded for both ERC starting Grant and EMBO Young investigator program) who is currently exploring the different mechanisms of gene expression regulation that control this process. Her lab investigates how the transcriptional history of a cell influences its fate as well as how post- transcriptional mechanisms contribute to the diversification of the genetic programs that control cell fate. Luisa is more specifically interested in both neuronal and muscle differentiation

Annonce de séminaire

Huating WANG

The Chinese University of Hong Kong, Hong Kong, China

Functional investigation of LncRNAs and enhancers in skeletal muscle stem cells

Invité par Bénédicte Chazaud

Abstract
Previously, the majority of the human genome was thought to be « junk » DNA with no functional purpose. Over the past decade, evidence from numerous high-throughput genomic platforms reveals that even though less than 2% of the mammalian genome encodes proteins, a significant fraction can be transcribed into different complex families of non-coding RNAs (ncRNAs). Growing evidence supports that ncRNAs have fundamental roles as regulators of genomic output. Among various types of ncRNAs, microRNAs have dominated the current literature. Other groups, however, such as long ncRNAs (lncRNAs, >200nt), have been largely under explored.
Huating Wang’s lab is currently interested in studying the functional roles of long non-coding RNAs (lncRNAs and enhancers) in regulating gene expression in skeletal muscle stem cells and muscle regeneration.

Annonce de séminaire

Sonia Garel

Institut de Biologie de l’École Normale Supérieure, Paris

Microglia and prenatal inflammation in early cortical wiring

Invité par Jean-Louis Bessereau

Abstract

Prenatal inflammation and dysfunction of microglia, the brain resident macrophages, have both been associated with the etiology of several neuropsychiatric disorders, including schizophrenia and autism spectrum disorders. Consistently, microglia were shown to regulate neurogenesis, synaptic remodeling and maturation at postnatal stages. However, microglia invade the brain during mid-embryogenesis and could thus exert earlier prenatal and perinatal roles during normal and pathological brain wiring. Here we show that embryonic microglia, which display a transient uneven distribution, regulate the wiring of forebrain circuits. By taking advantage of multiple mouse models, including cell-depletion approaches, we found that perturbing microglia activity affects the development of neocortical inhibitory interneurons, which constitute main actors in neuropsychiatric diseases. In particular, absence, prenatal inflammation or functional perturbation of microglia affects the timely positioning of specific subsets of interneurons as well as their subsequent functional integration in the neocortex. We furthermore found that responses of microglia to environmental signals, including the ones from the microbiome, are sexually dimorphic in males and females. This remarkable finding has major implications for our comprehension of sexual biases in the occurrence of microglia-related diseases, such as the prevalence in males of neurodevelopmental disorders. Our work reveals key roles for immune cells during the normal assembly of cortical circuits and provides novel insights onto how microglia dysfunction or immune risks lead to pathological brain wiring.

Annonce de séminaire

Yasushi Okamura

Graduate School of Medicine, Osaka University Suita

Coupling from electric signal to lipid signal; voltage-sensing phosphoinositide phosphatase

Invité par Vincent Jacquemond

Résumé

Biological membranes have dual roles in cell signaling: insulator for electrical signal by transfer of ion across membrane as well as the place for metabolism for production of lipid mediators such as arachidonic acids or phosphophositides. These two signals interact with each other through changes of ion concentration, mainly intracellular calcium ions, by the concerted activities of ion channels, transporters and GPCRs. There is a rare case where single membrane proteins directly link between electrical signal and lipid-mediated cell signaling. Voltage-sensing phosphatase consists of the ion channel like voltage sensor and PTEN-like phosphoinositide enzyme. In VSP, single voltage sensor regulates the downstream enzyme and the phosphoinositide phosphatase activity is activated by membrane depolarization leading to depletion of mainly PI(4,5)P2. Substrate specificity of VSP is more broad than PTEN; VSP shows both of 3-phosphatase activity and 5-phosphatase activity unlike PTEN which shows the rigid selectivity toward 3-phosphate of the inositol ring of PI(3,4,5)P3 and PI(3,4)P2. However, the key question how transmembrane voltage sensor regulates the cytoplasmic enzyme has remained unanswered, mainly because a method of detecting structural change in the cytoplasmic region has been limited. We have recently applied a method of genetical incorporation of fluorescent unnatural amino acid, Anap, to the cytoplasmic region of Ci-VSP (sea squirt Ciona intestinalis VSP) which was expressed in Xenopus oocyte. This method enables detection of fine structural change reported by fluorescence intensitiy without perturbing the local protein structure. Voltage-dependent fluorescence change of Anap showed two bidirectional changes along the voltage, decrease at low membrane depolarization and increase at higher depolarization, suggesting that the structure of the cytoplasmic region takes multiple conformations. By applying the method to different constructs of Ci-VSP with altered enzyme activity, we obtained evidence that the enzyme takes at least two activated states with distinct magnitude of enzyme activity. Given that voltage sensor of Ci-VSP takes multiple states during activation, it will be intriguing to see in the future how individual enzyme states correlate with states of the voltage sensor.

Annonce de séminaire

Edgar Gomes

Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal

Mechanisms of nuclear positioning during myofiber formation

Invité par Bénédicte Chazaud

Résumé

Connecting the nucleus to the cytoskeleton is relevant for multiple cellular processes and disruption of these connections result in multiple pathologies. Nuclear positioning within cell cytoplasm requires de connection between nucleus and the cytoskeleton. We are interesting to understand the processes involved in these connections and the role for nuclear positioning in cell function. We study cell migration and skeletal myofiber formation which required the connection between the nucleus and the cytoskeleton and precise nuclear positioning. We use different molecular and cellular approaches in combination with time-lapse imaging analysis to address these questions.

Annonce de séminaire

Rashmi KOTHARY

Centre for Neuromuscular Disease University of Ottawa

Spinal Muscular Atrophy: a multi-organ disease

Invité par Patrick Lomonte

Abstract

Spinal Muscular Atrophy was characterized in the late 1800s but it was almost 100 years later that the genetic cause was identified as a mutation in the human SMN1 gene. While humans do have two genes that code for SMN, SMN2 only produces 10% protein when compared to SMN1. Early work with mouse models was complicated by the fact that mice only have the one Smn gene which when mutated results in preimplantation lethality. This problem was solved by the development of a mouse model incorporating human SMN2 gene, which was for years the only viable mouse model. Now, there are over a hundred mouse models available that have served to inform our understanding of pathogenesis in SMA.
Classically, SMA is described as a motor neuron disease; however, SMN is expressed ubiquitously throughout the body. In fact, SMA is emerging to be a multi-organ disease with SMN depletion having impacts on many tissues in the body. Subcutaneous administration of available treatments may address these affected organs better than intrathecal administration. Also, systemic gene therapies that are currently under development may help repair function in these other organs.
Dr. Kothary will present on the work in his laboratory on the multi-organ nature of SMA. Defects in various tissues will be discussed.

Annonce de séminaire

Laure STROCHLIC

Institut de Myologie – Centre de Recherche en Myologie, Sorbonne Université, INSERM AIM UMRS974, Paris

Regulation of neuromuscular connectivity by Wnt signaling from signaling molecules to therapeutic strategies

Invité par Rémi Mounier

Résumé

The development and maintenance of the neuromuscular connectivity relies on a temporally fine-tuned balance of distinct bi-directional communication between motor neurons and their muscle targets. Disruption of this communication leads to structural and functional defects that affect the motor function and causes severe neuromuscular pathologies. Wnt signaling participates in various developmental mechanisms such as migration, axonal guidance or synaptogenesis. But how the Wnt signaling network could regulate neuromuscular connectivity and how it could affect motor function is unknown. In this presentation, I will provide data using Wnts gain or loss of function studies in cell culture or in mice showing that distinct branches of Wnt signaling, acting in part via the muscle-specific kinase MuSK regulate several key aspects of the formation and maintenance of the neuromuscular synapse including pre and postsynaptic differentiation/stabilization, retrograde control of motor axon outgrowth and synapse-specific gene expression. I will also present evidence showing that the pharmacological modulation of Wnt signaling in a pathological context could be used as a therapeutic strategy to counteract neuromuscular junction (NMJ)- associated disorders. Overall, our results provide novel insights into the mechanisms by which synaptic diffusible cues act to prevent NMJ dysfunction, muscle weakness and disease.

Dans cette présentation, je fournirai des données, utilisant des approches expérimentales in vitro et in vivo chez la souris, qui montrent le rôle émergent de la signalisation Wnt dans la régulation de la connectivité neuromusculaire dans un contexte physiologique et pathologique.

Annonce de séminaire

Helge AMTHOR

Université de Versailles – Paris Saclay Laboratoire U1179 UVSQ – INSERM

BMP signaling controls limb muscle development and maintenance

Invité par Laurent Schaeffer

Résumé
Bone morphogenetic proteins (BMPs) regulate the activity of skeletal muscle precursors as well as the trophic state of differentiated muscle. Here, the role of BMP signaling was explored at different stages of limb muscle development by overexpressing an inhibitory Smad protein (Smad6) to abrogate the BMP signaling cascade at cell autonomous level. Overexpression of Smad6 in limb muscle precursors during development (crossing Rosa26-Lox-Stop-Lox-Smad6-IRES-GFP mice, termed RS6, with Lbx1^Cre/+ transgenic mice) disturbed limb muscle myogenesis: early myogenic markers Pax3 and MyoD were strongly downregulated, fetal limb muscles were smaller, consisted of fewer myofibers and displayed a disturbed muscle patterning. Overexpression of Smad6 in postnatal muscle precursors (using RS6: Pax7^CreERT2/+ mice) caused decreased cell proliferation resulting in smaller myofibers containing less myonuclei and in decreased generation of satellite cells. Overexpression of Smad6 in differentiated muscle resulted in a different phenotype (using RS6:HSA-Cre mice): limb muscles were only modestly smaller, however, consisted of fewer but larger myofibers with increased myonuclear number. Overexpression of the BMP antagonist Noggin in adult muscle (loss-of-function) resulted in muscle fiber atrophy, whereas overexpression of the BMP receptor Alk3 (gain-of-function) caused muscle fiber hypertrophy. These latter effects were likely muscle precursor independent, as overexpression of Smad6 in differentiated fibers (using RS6:Pax7^CreERT2/+ mice) had no effect on satellite cell number and muscle size in the adult. In conclusion, the role of BMP signaling in skeletal muscle is stage and context specific.

Annonce de séminaire

Vanina ROMANELLO

Venetian Institute of Molecular Medicine, Padova

The role of the myokine FGF21 in skeletal muscle homeostasis

Invité par Rémi Mounier

Résumé
Skeletal muscle is a major site of metabolic activity and the most abundant tissue in the human body accounting for almost 40% of the total body mass. It is a plastic tissue that adapts to changes in exercise, nutrition and hormones, which also induces the release of myokines and myometabolites. These muscle-secreted factors have autocrine, paracrine and endocrine effects, explaining how muscles regulate metabolic homeostasis in other tissues. These systemic effects help to explain why physical activity, and thereby muscle recruitment, elicits several beneficial effects in many different diseases. Indeed, exercise preserves and ameliorates mitochondrial function and muscle metabolism, thereby affecting the release of myokines and metabolites that systemically counteract organ deterioration. We have recently proposed an interplay between the myokine Fgf21 and the mitochondrial quality control pathways that greatly contributes to a pro-senescence metabolic shift. However, even though the myokine field is exponentially increasing, little is known about their role in muscle homeostasis.

Annonce de séminaire

Robert J. Johnston

Johns Hopkins University, Baltimore, USA

Stochastic gene expression and nuclear architecture in fly eyes and human retinal organoids

Invité par Thomas Boulin

Résumé
A central challenge in developmental neurobiology is to understand how the myriad types of neurons in the human nervous system are generated. Stochastic gene expression mechanisms are crucial to differentiate neuronal subtypes and expand function. During stochastic fate specification, individual neurons randomly choose between different fates, resulting in unique patterns but consistent proportions of cell types among genetically identical organisms. My lab studies the stochastic mechanisms that specify the color-detecting photoreceptors in the fly and human retina. Fruit flies have a well-characterized retina and an abundance of genetic tools that enable molecular analyses of gene regulatory mechanisms. To overcome the challenges associated with human studies, we have developed a human retinal organoid system that recapitulates retinal development and photoreceptor specification. With these systems, we are interrogating how DNA elements, trans factors, and chromatin architecture control random on/off gene expression. Our molecular approaches are complemented by quantitative genetics to determine how natural variation in the genome impacts gene expression and photoreceptor specification. Finally, we conduct behavioral and functional assays to measure differences in color perception when photoreceptor fates are altered. By studying highly divergent organisms from multiple angles, we aim to define the unifying principles underlying stochastic fate specification during nervous system development.

Annonce de séminaire

Athanassia SOTIROPOULOS

Institut Cochin, Paris

Role of Srf transcription factor and F-actin scaffold in muscle stem cell fusion

Invité par Rémi Mounier

Résumé
Our team is interested on how signaling pathways control of adult skeletal muscle plasticity. In the past years, we focused our attention on Srf transcription factor which is one of the three master genes that controls myogenesis in Caenorhabditis elegans, together with MyoD and HAND. We investigated the role of Srf in two cellular compartments of mouse skeletal muscle (myofibers and adult muscle stem cells) upon different perturbation of muscle homeostasis (hypertrophy, atrophy, regeneration). In the present seminar, I will summarize our findings concerning the role of Srf in myofibers to control muscle mass and I will present recent data identifying Srf as a master regulator of muscle stem cell fusion and demonstrating the implication of F-actin architecture in this process.

Seminar announcement

Cécile MARTINAT

INSERM/UEVE UMR861, I-STEM, AFM

Human pluripotent stem cells for the study and treatment of neuromuscular diseases : myth or reality ?

Résumé
Neuromuscular diseases correspond to a vast group of diseases that perturbs the function of the skeletal muscles by affecting motoneurons, muscles and/or NMJs. To date, no efficient curative treatments have been identified for NMD. Progresses towards identification of new treatment have been hampered by the incomprehension of disease pathogenesis, particularly in early phases, as well as the availability of relevant screening tools. Disease-specific human pluripotent stem cells, from embryonic origin or derived from reprogramming somatic cells, offer the unique opportunity to have access to a large spectrum of disease-specific cell models. Due to their ability of self-renewal and differentiation into various tissues affected in each pathological condition, the development of these human disease-specific pluripotent stem cells provide new insights in pathological mechanisms implicated in human diseases for which, accessing homogenous affected tissues is often challenging. Validating this concept, we previously demonstrated that human pluripotent stem cells and derivatives which, express the causal mutation implicated in the Myotonic Dystrophy type 1 (DM1), offer pertinent disease-cell models, applicable for a wide systemic analysis ranging from mechanistic studies to therapeutic screening. Thus, we identified, through a genome-wide analysis, two early developmental molecular involved both in myogenesis as well as in neurite formation and establishment of neuromuscular connections. These neuropathological mechanisms may bear clinical significance as related to the functional alteration of neuromuscular connections associated with DM1. In parallel to these functional pathological studies, we also demonstrated the pertinence of this new disease-specific cell model to identify new therapeutic strategies. Thus, our results identified the possibility to repurposing metformin, the most commonly prescribed drug for type 2 diabetes, for DM1 leading to a phase 2 clinical trial that is actually ongoing.
We are now extending our approach to another incurable neuromuscular disease, spinal muscular atrophy (SMA). This disease, considered as the leading genetic cause of infant death, is due to mutations or deletions in the « Survival of Motor Neuron » gene, SMN1, which results in low levels of the expressed SMN protein. Despite this ubiquitous SMN expression, the pathology is characterized by degeneration of spinal Motor neurons whereas other neuronal types are relatively preserved suggesting that spinal motor neurons specific features control this differential sensitivity. Based on our recent development allowing the efficient and robust conversion of human pluripotent stem cells into affected spinal motor neurons and non- affected cranial motor neurons, our objective is to deepen the mechanisms involved in the specific degeneration of spinal motor neurons in SMA as well as the mis communication of these neurons with their muscular target.

Annonce de séminaire

Christoph Hoefer, M. Sc.

Senior Business Development Manager ; Life Sciences Solutions, Cell Biology, ThermoFisherScientific

Séminaire Technique : Travailler avec des iPSC (induced Pluripotente Stem Cell)

Résumé
Les cellules souches pluripotentes humaines (iPSC) sont des outils puissants pour la recherche en biologie du développement, la médecine régénérative et l’étude des pathologies humaines. Les données obtenues à partir de modèles physiologiques in vitro amélioreront grandement notre compréhension des processus biologiques. Dans cette présentation, j’aborderai les principaux défis rencontrés dans la mise en place des cellules souches pluripotentes au sein d’un laboratoire et les améliorations récentes apportées à la construction de modèles pour les maladies humaines, telles que la reprogrammation, l’expansion, la transfection, la préservation et la différenciation efficace de iPSC, ainsi que les options de modifications génomiques.

Annonce de séminaire

Nicolas PLACE

Institute of sport Sciences, University of Lausanne

Skeletal muscle adaptations to exercise : a translational approach

Invité par Julien Gondin

Résumé
The amount of force skeletal muscles can produce depends on their contractile history. For instance, repeated contractions generally lead to reduced muscle force generating capacity, namely muscle fatigue. Although muscle fatigue has been the focus of many works in the last 100 years, the underlying mechanisms remain elusive. In this presentation, special emphasis will be given to the role of Ca²⁺ handling as a key regulator of (i) muscle weakness and (ii) beneficial adaptations observed after high intensity interval training. In particular, the potential role of the sarcoplasmic reticulum Ca²⁺ release channel, the ryanodine receptor type 1, will be discussed.

Annonce de séminaire

Julien OCHALA

Faculty of Life Sciences & Medicine, King’s College, London

Actinopathies : From Mutations to Treatment

Invité par Laurent SCHAEFFER

Résumé
Actinopathies are genetically and clinically heterogeneous disorders mainly characterized by generalized muscle weakness. The understanding of this group of disorders has advanced in recent years through the identification of the causative mutations in the gene encoding one of the major proteins of the basic contractile unit of skeletal muscle, i.e., actin. In the present seminar, I will present (i) how these gene mutations lead to generalized muscle weakness and (ii) the advances regarding potential therapies.

Annonce de séminaire

Norbert WEISS

Institute of Organic Chemistry and Biochemistry, Prague

Trafficking of T-type calcium channels in health and disease

Invité par Vincent JACQUEMOND

Résumé
T-type calcium channels are key contributors to neuronal physiology where they shape electrical activity of nerve cells and contribute to the release of neurotransmitters. Alteration of T-type channel expression has been causally linked to a number of pathological conditions including neuropathic pain and absence seizure activity. Although a number of signaling pathways regulating the activity of T-type calcium channels have been reported, the molecular machinery and signaling molecules controlling the trafficking and expression of the channel protein at the plasma membrane remain largely unknown. I will present some of the basic mechanisms recently identified controlling the physiological trafficking of T-type channels, and illustrate how metabolic defects or congenital mutations can disturb this trafficking machinery and eventually leading to disease conditions.

Annonce de séminaire

Isabelle JANOUEIX

Institut Curie – Inserm U8330, Paris

Understanding neuroblastoma biology through the analysis of its genetic and epigenetic landscapes

Invité par Valérie Castellani

Résumé
Neuroblastoma is an embryonal neoplasm arising from the peripheral nervous system that accounts for 15% of cancer deaths in childhood. It is an enigmatic tumor presenting with a great genetic and clinical heterogeneity, both in terms of presentation and outcome.
The characterization of the genetic alterations observed in neuroblastoma led to the identification of major players of neuroblastoma oncogenesis that has considerably improved our understanding of the biology of this pediatric cancer. More recently, the analysis of the super-enhancer landscape allowed to decipher the core regulatory circuitries controlling the gene expression program of neuroblastoma. Distinct transcription factor networks predicate different tumor identities, corresponding to sympathetic noradrenergic or mesenchymal/neural-crest cell like identities. Cells of mesenchymal identity are more resistant to chemotherapeutic agents. Moreover, some neuroblastoma cells exhibit plasticity and are able to shift between the NCC-like and noradrenergic identities.
The understanding of cell identity, heterogeneity and plasticity in neuroblastoma has strong implications with respect to the development of new therapeutic strategies to eradicate tumor cells in neuroblastoma patients.

Annonce de séminaire

Justin FALLON

Brown University, Providence, RI

MuSK as a BMP co-receptor

Invité par Laurent Schaeffer

Chantal Thibert

Institute for Advanced Biosciences, Université Grenoble Alpes

The tumor suppressor LKB1 controls cell fate through pyruvate-alanine transamination

Invité par Julien Courchet

Résumé
The tumor suppressor LKB1 (also named STK11) codes for a serine/threonine kinase. LKB1 acts as a key regulator of cell polarity as well as energy metabolism partly through the activation of the AMP-activated protein kinase (AMPK), a sensor that adapts energy supply to the nutrient demands of cells facing situations of metabolic stress.
To determine if Lkb1 exerts a coordinated regulation of energy metabolism and cell polarity, we deleted the Lkb1 gene in polarized cells and explored the metabolic consequences. In particular, we generated spatio-temporal ablation of Lkb1 in a subpopulation of mouse embryonic multipotent neural crest cells (NCC) that originate from the neural tube and give rise to a broad range of derivatives including most of the face, the melanocytes, the peripheral nerves and the enteric nervous system (ENS). Mutant mice exhibited craniofacial malformations, hypopigmentation, intestinal pseudo-obstruction and hindlimb paralysis. Further phenotypic characterization revealed that LKB1 is required for the differentiation and maintenance of two NCC-derivatives, Schwann cells and the ENS. Using a model of neural crest stem cell line, we demonstrated that Lkb1 is key for neural crest-derived glial commitment. Mechanistically, Lkb1 loss led to an increase of alanine and glutamate levels and inhibition of pyruvate-alanine transamination rescued glial differentiation of Lkb1-null NCC, in a mTOR dependent manner. Furthermore, AICAR, an analogue of AMP, rescued glial differentiation of Lkb1-deficient NCC and corrected the Schwann cells and ENS phenotypes of Lkb1 mutant mice.
Altogether, these findings highlight the central role of Lkb1 during neural crest cell lineage and uncovered a link between Lkb1-mediated pyruvate-alanine cycling and glial commitment. These results provide also new insights for the understanding of metabolic events that contribute to the formation of LKB1-deficient malignancies.

Annonce de séminaire

Michalis Averof

Institut de Génomique Fonctionnelle de Lyon (IGFL).

Live imaging of regenerating legs: cell dynamics and progenitors

Invité par Rémi Mounier

Résumé
Regeneration is a complex and dynamic process, mobilising diverse cell types and remodelling tissues over a long time period. Compared with embryonic development, it is less genetically tractable and less accessible for direct observation. I will describe our recent efforts to establish a small crustacean, Parhyale hawaiensis, as an experimental model for studying regeneration. Using transgenic markers and live imaging we are starting to describe the cell behaviours and progenitors that underpin limb regeneration. We find that crustacean limb regeneration relies lineage-committed progenitor cells: muscles derive from satellite-like stem cells, whereas epidermis regenerates from existing epidermal cells.

Annonce de séminaire

Damaris Lorenzo

University of North Carolina at Chapel Hill

Ankyrin-B and beta-II spectrin in axonal transport and brain connectivity

Invité par Thomas Boulin

Résumé
The formation, targeting, and maintenance of axon and dendrites are critical for proper brain development and synaptic function. Deficits in synapse establishment and maturation can lead to neurodevelopmental, neurodegenerative, and psychiatric disorders. The neuronal cytoskeleton regulates the architecture and dynamics of synaptic processes by providing structural support and the tracks for motor protein-based synaptic transport. The latter is particularly important for the establishment of long axonal projections, which requires coordinated long-range organelle transport. The membrane associated adaptor ankyrin-B (AnkB) promotes fast axonal transport and elongation by coupling dynactin to multiple organelles through binding to phosphatidylinositol 3-phosphate lipids in these cargos. Additionally, AnkB directly binds βII-spectrin, which, in turn, controls the formation of a ring-shaped membrane periodic skeleton (MPS) in axons and mature dendrites. Interestingly, βII-spectrin also associates with molecular motors. I will show that AnkB and βII-spectrin are key elements in independent and overlapping pathways responsible for the transport of synaptic cargo and other organelles, and are essential for establishing proper brain structural and functional connectivity.

Annonce de séminaire

Andre Brown

MRC London Institute of Medical Sciences – Imperial College, London

Syntax in C. elegans locomotion

Invité par Thomas Boulin

Résumé
Behaviour is a striking phenotype and often one of the first things we notice about an animal. Broadly speaking, we are interested in understanding how genes affect behaviour, but despite rapid advances in technology for sequencing and engineering genomes, it is still a challenge to associate particular genes with heritable behavioural differences because behaviour is time consuming to measure and difficult to quantify. We are using automated imaging to record the behaviour of freely moving nematode worms and developing new analysis methods to extract relevant features. I will discuss unsupervised methods to quantify behavioural repertoires, and how making connections to language processing and data compression can give insight into the structure of behaviour. Finally I will show how these new representations can advance the study of behavioural genetics and phenotypic drug screening.

Annonce de séminaire

Hélène CASTEL

Normandie Rouen University / Inserm 1239 – Équipe Astrocyte and Vascular Niche

Cancer and Cancer treatments on cognition: A major translational impact of the preclinical research

Invité par Virginie DESESTRET

Résumé
Co-head Cancer and Neurosciences axis Northwest canceropole, Cancer and cognition platform; ICCTF member (editing of preclinical research guidelines).
The emergence of a new field in oncology addressing cognitive deficits in cancer patients is justified by the existence of deficits in memory, concentration and attention, as well as executive functions before, during and after treatments, symptoms often referring to the “chemofog” or “cancerfog”. Our work mainly involves research and clinical groups of Normandie developing programs in patients and animal models, to improve our understanding of the impact of cancer and its treatments on cognitive functions. Two main examples of these translational studies we participated on can be exposed:
The first Cog-Age clinical study (Pr F. Joly, Baclesse Caen) showed that cognitive decline can be detected 6 months after chemotherapy in breast cancer elderly patients. In a mirror study, chemotherapy administration in young and elderly mice resulted in a change in behavioral flexibility and alteration of neuron precursor proliferation in the hippocampal dentate gyrus. We were thus able to conclude that age-related cognitive decline is accentuated by chemotherapy, providing basis for questioning the place of adjuvant chemotherapy in this elderly patient population. The second clinical study COG-ANGIO (Pr Joly) demonstrated that antiangiogenics exert a direct negative impact on cognitive functions and fatigue in kidney cancer patients. In mice, the anti-angiogenic mTOR inhibitor everolimus did not alter cognitive functions but led to weight loss and modification of cell metabolism in brain regions involved in sleep/wake cycle or food intake, likely connected to fatigue. On the other hand, immunoneutralizing VEGF (Genentech-Roche, MTA) impaired spatial learning performance and neuronal activity of CA3 hippocampus neurons. These data suggest that a careful and systematic evaluation of targeted cancer therapies on cognitive functions in preclinical models may constitute a strategy of prevention by selection of treatments exhibiting minimum brain co-morbidities.
Together, this translational program is developed within the National Cancer and Cognition Platform (CNO/Ligue Nationale contre le cancer), with the aim to collaborate in a structured way with French oncology groups, research teams as well as pharmaceutical industry, by providing preclinical models and guidance on standard operating procedures for ancillary or future studies in identified population at risk.

Annonce de séminaire

Kei Sakamoto

Institut des Nestlé Institute of Health Sciences SA, Lausanne.

Key signaling players in the control of hepatic gluconeogenesis — AMPK or other AMPK-related/AMP-regulated enzymes ?

Invité par Rémi Mounier

Résumé
Hepatic glucose production is a key physiologic process that ensures energy balance for glucose-dependent organs/cells such as brain. The inability of insulin to suppress hepatic glucose output is a major aetiological factor in the hyperglycaemia of type 2 diabetes. LKB1, originally identified as a tumor suppressor protein, is currently thought as a critical regulator of cellular metabolism and growth by controlling the activity of AMP-activated protein kinase (AMPK) and also 12 other kinases that are closely related to AMPK. Among those AMPK-related kinases, we have recently identified that Salt-Inducible Kinase (SIK) plays an important role as a gluconeogenic gatekeeper in the liver.
Metformin exerts its major effect via inhibition of hepatic glucose production. This is thought to be mediated through decreased hepatic energy charge (i.e. increasing AMP/ATP ratio) via inhibition of mitochondrial respiration. The long-standing belief that 5’-adenosine monophosphate (AMP)-activated protein kinase (AMPK) mediates the anti-hyperglycaemic action of metformin has recently been challenged in experiments using mice lacking hepatic AMPK. I will discuss our recent data demonstrating AMP-mediated allosteric inhibition of an enzyme involved in gluconeogenesis plays a key role in acute glucose-lowering effect of metformin.

Annonce de séminaire

Alexandre Pattyn

Institut des Neurosciences de Montpellier, INSERM U1051. France.

Heterogeneous precursor populations underlie developmental plasticity of the dorsal root ganglia

Invité par Valérie Castellani

Résumé
Although a variety of primary sensory neurons are implicated in the detection and transmission of different sensory modalities, how they arise during development remains poorly understood. The process of neuronal specification is the acquisition of definitive phenotypic characteristics for a given subclass of neurons during embryonic development. This acquisition can be divided into several interdependent and sequential phases, from the time point when progenitor cells exit the cell cycle toward the newly formed and perfectly differentiated neuron. Using mouse genetics, Alexandre demonstrated that transcriptions factors of Maf and Zeb families control the specification and differentiation of specific sensory neuron sub-types. His work contributed to uncover the complex developmental sequence ensuring the formation of the peripheral sensory system and to highlight the progenitor diversity that underlies the developmental plasticity of sensory neuron generation.

Annonce de séminaire

Georgia Rapti

The Rockefeller University, Shaham lab, New York, USA.

It takes two to tango with elegance: Glia and pioneer neurons orchestrate C. elegans brain assembly

Invité par Jean-Louis Bessereau

Résumé
Brain assembly is hypothesized to begin when pioneer axons extend over non-neuronal cells, forming tracts guiding follower axons. Yet, the identities of the pioneer-neurons and of their guidance-substrates and their interactions, are not well understood. Here, using time-lapse embryonic imaging, genetics, protein-interaction, and functional studies, we uncover the early events of C. elegans brain assembly. We demonstrate that C. elegans possesses radial-glia-like cells key for assembly initiation. Glia guide pioneer and follower axons using distinct signals. Pioneer neurons we identify, with unique growth properties, anatomy, and innervation, cooperate with glia to guide follower axons. We identified a CHIN-1/Chimaerin- KPC-1/Furin double mutant that severely disrupts assembly, unlike previously known mutants. CHIN-1/Chimaerin and KPC-1/Furin cooperate non-canonically in glia and pioneer neurons for guidance-cue trafficking. We exploit this genetic bottleneck to define a guidance-gene network governing assembly, with specific glia and pioneer-neuron contributions. Our studies reveal previously-unknown roles for glia in pioneer-axon guidance, and suggest conserved principles of brain formation.

Annonce de séminaire

Sophie Creuzet

Institut des Neurosciences Paris-Saclay, CNRS UMR 9197, Gif-sur-Yvette. France.

Neural crest in forebrain development: from embryology to pathophysiology

Invité par Valérie Castellani

Abstract
In my group, we study the neural crest, a unique cell population that emerges from the primitive neural field and which has a multi-systemic and structural contribution to vertebrate development. Over the last decade, I have been dedicating myself to the cellular and molecular background of the observation I made in 2004, that the cephalic neural crest (CNC), exerts an autonomous and prominent control on forebrain development. This notion has broken the traditional view of how the brain develops. By using exquisite grafting experiments in combination with focal spatially and temporally controlled transgenesis, we have discovered the unexpected and potent “paracrine role that the CNC exerts on forebrain growth and patterning early in development and documented this mechanism at the level of cell interaction, signalling and gene expression. We are now following this exiting line of research, which revisits fundamental concepts in Neurosciences. This notion provides also a conceptual renewal, which is biomedically relevant. The mechanisms identified so far in our model are conserved across tetrapodes, but some social behavioural features are specific to amniotes. Our ongoing project and future directions are to explore the aetiology of neural disorders and behavioural impairments in Humans and in the light of CNC dysfunctions.

Annonce de séminaire

Colin Crist

Department of Human Genetics, McGill University – Québec, Canada.

Translational Control of Muscle Stem Cells

Invité par Rémi Mounier

Abstract
Regeneration of adult tissues depends on somatic stem cells that remain quiescent, yet are primed to enter a differentiation program. The molecular pathways that prevent activation of these cells are not well understood. Using mouse skeletal muscle stem cells as a model, we show that accumulating transcripts specifying the myogenic program are not translated in quiescent satellite cells, but are repressed by the action of microRNAs and RNA binding proteins. Furthermore, the reversible nature of microRNA dependent silencing mechanisms may underlie the rapid activation of satellite cells that are poised to enter the myogenic program. We also show that a general repression of translation, mediated by the phosphorylation of translation initiation factor eIF2 at serine 51 (P-eIF2α), is required to maintain the quiescent state. Skeletal muscle stem cells unable to phosphorylate eIF2 exit quiescence, activate the myogenic program and differentiate, but do not self-renew. P-eIF2α ensures in part the robust translational silencing of accumulating mRNAs that is needed to prevent the activation of muscle stem cells. Additionally, P-eIF2α dependent translation of mRNAs regulated by upstream open reading frames (uORFs) contributes to the molecular signature of stemness. Finally, we show that addition of small molecule inhibitors of eIF2α dephosphorylation to muscle stem cell cultures permits their ex vivo expansion and engraftment into a preclinical mouse model of Duchenne muscular dystrophy.

Annonce de séminaire

Michael A Rudnicki

Center of Ottawa Hospital Research Institute, Ottawa, Ontario, Canada

Molecular regulation of muscle stem cell asymmetric division

Invité par Bénédicte Chazaud

Abstract
We discovered that a subset of satellite cells in skeletal muscle are self-renewing stem cells that give rise to myogenic progenitors through asymmetric apical-basal cell divisions. The regulation of asymmetric stem cell division is a key control point that impacts the efficacy of the entire regenerative program. Stem cell polarity is established by the PAR complex, comprised of PAR3/PAR6/aPKC, to regulate self-renewal and expansion. Duchenne Muscular Dystrophy (DMD) is coaused by a lack of dystrophin which is expressed in muscle fibers where it plays a role in ensuring structural integrity. We have made the seminal finding that dystrophin regulates the establishment of PAR-mediated polarity in satellite cells. In the absence of dystrophin, the polarity effector Par1b is dysregulated, leading to the failure of Par3 to become localized to the cortex associated with the basal lamina. Importantly, this results in an abnormal increase in centrosome number, a 10-fold reduction in the numbers of satellite stem cells undergoing asymmetric divisions, and a marked decrease in the generation of myogenin-expressing progenitors. Accordingly, our data suggests that the failure of regenerative myogenesis to keep pace with disease progression in DMD is not due to muscle stem cell exhaustion, but rather is due to a cell-autonomous deficiency in asymmetric division.

Annonce de séminaire

F. Jeffrey Dilworth

Center of Ottawa Hospital Research Institute, Ottawa, Ontario, Canada

Epigenetic control of stem cell fate decisions in muscle repair

Invité par Bénédicte Chazaud

Abstract
During muscle regeneration, the conversion of muscle stem cells to terminally differentiated myofibers requires multiple cell fate transitions. Each of these transitions necessitates an alteration in the set of genes being expressed within the cell. In this presentation, our studies on the role of transcription factors and epigenetic enzymes in dictating changes in muscle gene expression will be highlighted. In particular, I will focus on the role for the antagonism between various transcription factors and epigenetic enzymes in controlling the commitment of muscle stem cells towards alternate cell fates.

Annonce de séminaire

Fabien Le Grand

Center of Research in Myology, Université Pierre et Marie Curie Paris – France.

Control of muscle stem cell fate by Wnt signaling pathway(s)

Invité par Bénédicte Chazaud

Abstract
Regeneration of the adult skeletal muscle tissue relies on a pool of quiescent muscle stem cells located in a niche around the myofibers: the satellite cells (MuSCs). Upon activation following injury or repeated exercise, MuSCs leave quiescence to proliferate and then differentiate to form new muscle fibers while a sub-population exit the cell cycle to self-renew and replenish the stem cell niche. In the course of this process, signals from the microenvironment instruct cycling MuSCs and control myogenesis. We previously demonstrated that numerous Wnt molecules are secreted in the local milieu during regeneration and showed that MuSC self-renewal is in part controlled by non-canonical Wnt7a/PCP signals sent by the regenerating myofibers. To elucidate the roles of the canonical Wnt/ß-catenin pathway in MuSCs, we generated mice with inducible MuSC-specific ß-catenin Loss-Of-Function or Gain-Of-Function. Strikingly, we observed that induction of either ß-catenin LOF or GOF mutations in MuSCs leads to the impairment of skeletal muscle regeneration following injury. By using a mouse model of conditional APC gene deletion in MuSCs we further demonstrated that the massive activation of canonical Wnt signaling in MuSC following APC loss results in defective cell cycle progression and apoptosis. Mechanistically, we observed that Wnt/ß-catenin signaling orchestrates the cytoplasmic relocalization of the histone 3 lysine 9 methyltransferase Setdb1 during differentiation. We further showed that Setdb1 is required for MuSCs amplification and suppresses myoblast terminal differentiation. Genome-wide analyses showed a Wnt3a-dependant release of Setdb1 from the promoter of selected target genes upon myoblast terminal differentiation. Taken together, our results demonstrate that both canonical and non-canonical Wnt pathways are necessary for MuSC function. Lastly, I will discuss the potential cross-talks between these two faces of an important signaling.

Annonce de séminaire

Stefan Dimitrov

Institut Albert Bonniot, Centre de Recherche UGA – INSERM U1209 / CNRS UMR 5309, Grenoble, France.

Epigenetic strategies : nucleosome remodeling, histone modifications and histone variants.

Invité par Laurent Schaeffer

Abstract
Chromatin impedes the binding of protein factors to the underlying DNA sequences. The cell uses three main “epigenetic tools” to overcome the chromatin barrier, namely, chromatin remodelers, histone variants and histone post-translational modifications. We will give specific examples of how either one of these “epigenetic tools” functions.
Chromatin remodelers are sophisticated nano-machines, which are able to alter histone-DNA interactions and to mobilize nucleosomes. Neither the mechanism of their action nor the conformation of the remodeled nucleosomes are, however, yet well understood. We have studied the mechanism of RSC-induced chromatin remodeling by using high resolution microscopy and state of the art biochemistry techniques. The data illustrates how RSC remodels the nucleosome in vitro and shed light on its in vivo function. The crystal structure of the CENP-A nucleosome was recently solved. Intriguingly, in contrast to the canonical nucleosome (where 147 bp of DNA are wrapped around the histone octamer), only the central 121 bp were visible, suggesting flexible CENP-A nucleosomal ends. Why the CENP-A nucleosome exhibits flexible DNA ends is totally unknown. Our data show that the flexible DNA ends of the CENP-A nucleosome are required for mitotic fidelity.
The Aurora family of oncogenic kinase consists of two major members, Aurora A and Aurora B. Both kinases exhibit very high homology. They show, however, quite distinct localization and function. Histone H3 is specifically phosphorylated, presumably by the oncogenic kinase Aurora B, at serine 10 at the onset of mitosis. Here we will present data on the distinct function of the two Aurora kinases and the mechanism of phosphorylation of histone H3 by Aurora B.

Annonce de séminaire

Stéphane Vassilopoulos

Institut de Myologie, UMRS 974 UPMC-Inserm / FRE 3617 CNRS, G. H. Pitié-Salpétrière, Paris – France.

The endocytic machinery in healthy and diseased muscle

Invité par Laurent Schaeffer

Abstract
Costameres represent specialized focal adhesion sites of muscle fibres, located between the plasma membrane and sarcomeres, the contractile units of muscle. When disrupted, they directly contribute to the development of several distinct myopathies.
We have shown that the ubiquitous clathrin heavy chain (CHC), well characterized for its role in intracellular membrane traffic and endocytosis from the plasma membrane (PM), forms large plaques connected to α-actinin and actin filaments. Depletion of CHC leads to defective costamere formation and maintenance both in vitro and in vivo and induces sarcomere disorganization and a loss of contractile force due to the detachment of sarcomeres from the PM. At costameres, CHC is co-expressed with dynamin 2 (DNM2), another key protein of the intracellular membrane trafficking machinery which is mutated in autosomal dominant centronuclear myopathy (CNM). We analyzed the role of DNM2 and several actin binding proteins on clathrin plaque function at costameres in vitro by using either siRNA depletion combined to high resolution electron microscopy or in vivo by intravital microscopy. We also focused on the possible link between costamere and CNM pathophysiology. Using myoblasts from DNM2-mutated patients and using myoblasts and muscles from a knock-in mouse model of DNM2-related myopathy, we analyzed structure of costameres by biochemical and immunocytochemical approaches, as well as their ultrastructure.
Our results demonstrate a crucial role for the endocytic machinery and the cytoskeleton. Their contribution to the formation and maintenance of the contractile apparatus highlight an unconventional role for clathrin flat lattices in skeletal muscle which may be relevant to pathophysiology of several neuromuscular disorders.

Annonce de séminaire

Sandrine Humbert

GIN – Inserm U1216 – University Grenoble Alpes, Grenoble, France.

Huntingtin regulates cortical development: consequences for Huntington’s disease

Invité par Julien Courchet

Abstract
The bulk of interest in the huntingtin protein has centered on the fact that, when mutated, huntingtin causes Huntington’s disease (HD), a devastating neurodegenerative disorder. The mutation causing HD is an abnormal polyglutamine stretch in huntingtin. Given the adult onset and dysfunction and death of adult neurons characterizing HD, most studies have focused on the toxic effects elicited by mutant huntingtin in post-mitotic neurons. However, the protein is ubiquitous and expressed in the developing embryo where it plays an essential role as revealed by the early embryonic lethality at day 7.5 of the complete knockout of the huntingtin gene in mouse. Anyway, the roles of the wild-type protein during development have been overlooked. I will discuss how huntingtin regulates several steps of mouse embryonic corticogenesis. I will also show the consequences of the presence of an abnormal polyglutamine expansion in huntingtin during cortical neurogenesis and consider the viewing of HD as a developmental disorder.

Annonce de séminaire

Jan Tuckermann

Institute of Comparative Molecular Endocrinology Ulm University, Ulm, Germany.

Modes of GR action revised – Novel mechanisms of corticosteroids in inflammation and bone integrity

Invited by Bénédicte Chazaud

Abstract
The Tuckerman Laboratory made major contributions to the molecular mechanisms of corticosteroids in beneficial and side effects of steroid therapy. With the help of conditional and function-selective knockout mice for the glucocorticoid receptor (GR) the lab identified critical cell types and novel mechanisms for anti-inflammatory activities of glucocorticoids in different inflammatory disease models. Furthermore we made the discovery that in a model of lung inflammation the anti-inflammatory action of glucocorticoids is not dependent on the inhibition of pro-inflammatory mediators, but rather requires cooperation with pro-inflammatory signaling pathways (e.g. p38) to induce anti-inflammatory acting genes and alternative polarization of macrophages.

Annonce de séminaire

Dr. Pierre-Jean Corringer

Pasteur Institute, Channel-receptor Unit, CNRS UMR 3571, 25 rue du Docteur Roux, 75015 Paris, France.

Pentameric ligand-gated ion channels functioning at the atomic resolution

Invited by Maëlle Jospin

Abstract
Pentameric channel-receptors, including nicotinic acetylcholine, glycine and GABAA receptors, play a key role in fast excitatory and inhibitory transmission in the nervous system and are the target of numerous therapeutic and addictive drugs. They carry several neurotransmitter binding sites which govern the opening of a transmembrane ion channel. Extensively expressed in animals, they were found in several bacteria, especially the homolog from the cyanobacteria Gloeobacter violaceus (GLIC) which functions as a proton-gated ion channel. The simplified architecture of this archaic homologue, as well as its prokaryotic origin, allowed solving its X-ray structure in several conformations. Those static structures suggest that channel opening occurs through symmetrical quaternary twist and “blooming” motions, together with tertiary deformation. We further engineered multiple fluorescent reporters on the structure, allowing investigating the dynamics of the allosteric reorganizations and showing that activation involves a key pre-active conformation. Finally, the GLIC system was exploited to solve the structure of human receptors through the generation of functional chimeras. Overall, our work gives insights into the mechanism of gating and pharmacological regulation of this important family of neurotransmitter receptors.

Dr. Yishi Jin

UC San Diego.

Mechanisms regulating synapse maintenance and neural activity

Invited by Jean-Louis Bessereau

Abstract
Synapses are organized subcellular structures that transmit information within the nervous system and to other parts of our body. Our studies use C. elegans have uncovered multiple pathways controlling synapse formation, maintenance and function. Using a genetic model mimicking the physiological state of seizures, our recent work have identified novel regulatory themes affecting presynaptic release machinery. We also discovered that a novel immunoglobulin superfamily (IgSF) transmembrane protein mediates synapse and non-neuronal tissue interaction in synapse maintenance. These findings have implications to our understanding of circuit malfunction under disease conditions.

Annonce de séminaire

Dr. Francesco Zorzato

Department of Biomedicine, Basel University

Pathophysiology of ryanodinopathies

Invited by Bruno Allard

Abstract
Type 1 ryanodine receptor (RyR1) is preferentially expressed in skeletal muscle, and mutations in the gene have been associated with malignant hyperthermia, a pharmacogenetic disease, and with several congenital myopathies, including central core disease, multiminicore disease, centronuclear myopathy, congenital fibre type disproportion. Experimental data have indicated that RyR1 is also expressed in some areas of the central nervous system, in some cell types of the immune system and in smooth muscle cells. These results imply that mutations in the gene encoding RyR1 will not only affect skeletal muscles, but other tissues that express this calcium channel as well, thereby broadening the clinical spectrum of disorders due to RyR1 dysfunctions.
The RyR1 is of fundamental importance for the development of muscle force and a decrease in its content may be causally linked to the profound muscle weakness seen in patients with some forms of congenital myopathies linked to recessive RYR1 mutations. The protein composition of the junctional sarcoplasmic reticulum membrane encompassing the excitation-contraction coupling molecular complex (ECCMC) is extremely complicated. Polymorphic variants of the junctional sarcoplasmic reticulum protein JP45 have been shown to segregate in Malignant Hyperthermia Susceptible subjects of Malignant Hyperthermia families in the UK. Thus, some ECCMC accessory proteins may play a role not only in regulating excitation-contraction coupling but also as modifiers of the ryanodinopathies phenotype.

Annonce de séminaire

Dr. Jean-Marc Goaillard

UNIS – Aix Marseille Université

Biophysical networks underlying electrical phenotype of dopaminergic neurons

Invited by Thomas Boulin

Abstract
Any type of neurons can be easily identified based on its electrophysiological activity, such as its pattern of spontaneous activity, the shape of its action potential, its dendritic integration, etc. How is stability of such electrical phenotype achieved, what are its molecular principles, and what is the degree of robustness of electrical phenotype in the face of different perturbations are questions only very partially answered. We studied these questions on dopaminergic neurons of the substantia nigra pars compacta. Our work involved characterizing the electrical phenotype of these neurons and measuring its post-natal development and its stability at mature stages. We also characterized the specific relationships of electrophysiological parameters underlying the electrical phenotype. In order to determine how complex electrical phenotype is achieved, we then investigated the networks of co-regulation of ion channels at the genetic and at the protein levels. Our results suggest that ion channel gene expression and protein interactions display a modular structure that may be involved in stabilizing phenotype. We also show that electrical phenotype also presents such a modular structure. Our ultimate goal is to provide a systems-level approach to robustness of electrical phenotype.

Annonce de séminaire

Dr. Michele Zoli

Friday Avril 29th at 14:00 – Amphithéâtre de la délégation du CNRS

Dr. Shiva Tyagarajan

Inst. of Pharmacology and Toxicology, University of Zurich.

Interrupting neuronal communication from a GABAergic viewpoint

Invited by Jean-Louis Bessereau

Abstract
In the brain distinct population of inhibitory GABAergic interneurons innervate principal glutamatergic neurons to regulate various aspects of brain function. At the postsynaptic compartment, specific GABAAR subunits are segregated to different neuronal compartments to recieve specific inputs from different interneurons. The correct interpretation of the incoming signal requires functional coupling between the presynaptic neurotransmitter GABA, postsynaptic GABAARs, and downstream signaling by postsynaptic density proteins. The main postsynaptic density protein at inhibitory synapse is gephyrin. In the past decade we have identified diverse signaling cascades that converge on gephyrin scaffold to regulate its scaffolding property, and in turn GABAergic neurotransmission. These studies have shed light into mechanisms that underlie dynamic changes in inhibitory neurotransmission, and how excitation shapes inhibition.

Annonce de séminaire

Vendredi 29 janvier à 14:00 – Bâtiment l’Herbier

Pura Muñoz-Cànoves

ICREA Research Professor at Universitat Pompeu Fabra, Barcelona.

Tissue regenerative decline with aging: focus on muscle stem cells

Invited by Bénédicte Chazaud

Abstract
Our group aims to understand the mechanisms regulating stem cell homeostasis and regenerative functions. Research is specially centered on stem cells of skeletal muscle (i.e., satellite cells). Recently, we have focused on two areas: 1) the functional decline of satellite cells with aging; and 2) the physiopathology of muscular dystrophies, with a specific interest in the contribution of inflammation and fibrosis to dystrophy progression. Concerning the first area, work from different laboratories has demonstrated that both environmental and cell- autonomous signals alter satellite cell regenerative potential with aging. I will discuss our latest results showing that satellite cells in their homeostatic quiescent state are equipped with quality control mechanisms to preserve their fitness, and how age-associate alterations in these protective mechanisms lead to stem cell loss of function and regenerative capacity.

Annonce de séminaire