Flavie Strappazzon

Fondation Santa Luccia, Rome, Italie

Targeting mitophagy as a strategy for therapeutic intervention in diseases

Invited by 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

Invited by 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

Invited by Héléne 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

Invited by 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, Switzerland

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

Invited by 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

Université Aix Marseille

The axonal cytoskeleton at the nanoscale

Invited by 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

Invited by Fabien Le Grand

Abstract
Muscle cells are characterized by the presence of multiple nuclei evenly spaced under the plasma membrane. Whether this particular arrangement is required for muscle function is still under debate. Nonetheless, several muscular diseases are characterized by abnormal nuclear positioning, such as centronuclear myopathies, titinopathies and desminopathies or due to mutations of nuclear envelope proteins known to be involved in nuclear movement in other systems. We have, since several years, investigated the mechanisms controlling three of the four different and successive nuclear movements occurring during myofiber formation through live imaging. By screening the effect of different molecular motors deletion, we have identified several microtubule-associated motors implicated at different levels on nuclear movement and positioning. We have established the connection between the nucleus and the cytoskeleton to be decisive for proper nuclear positioning. In particular, Nesprin-1, a protein mutated in congenital muscular dystrophy, is required for the reorganization of the microtubule cytoskeleton during the differentiation of muscle cells and the subsequent nuclear movements. We are now investigating the implication of nuclear deformations and nuclear envelope composition on muscle differentiation. Our research uses in vitro systems that recapitulate in vivo observations and allow the study of mutations found in muscular diseases on nuclear positioning in muscle cells.

Sabine Fanny Bensamoun

Université de Sorbonne

Caractérisation in vitro/in vivo du tissu musculaire

Invited by 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

Invited by 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

Invited by 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, University of Montreal

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

Invited by 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, Italy

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

Invited by 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

Invited by 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

Invited by 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

Invited by 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

Invited by 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

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

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