Les mouvements nucléaires sont importants pour une multitude de fonctions cellulaires et sont induits par des forces produites par des protéines moteurs et le cytosquelette. Lors de la formation et régénération de myofibres, les noyaux migrent du centre à la périphérie de la cellule pour son bon fonctionnement. De plus, certaines maladies musculaires sont caractérisées par une accumulation de noyaux centraux. En utilisant une approche théorique et empirique, nous démontrons que le mouvement de noyaux vers la périphérie des myofibres est induit par des forces centripètes autour des noyaux ainsi que par des changements locaux de rigidité nucléaire. Ces forces centripètes sont générées par la contraction de myofibrilles et par leur réticulation autour des noyaux. Les changements de rigidité nucléaire relèvent d’une asymétrie de la distribution de la lamin A/C. En débutant par BIN1, gène muté dans les myopathies centro-nucléés (CNM), nous avons identifié la cascade moléculaire à l’origine du mouvement des noyaux. Nous montrons que l’Amphiphysin 2 (BIN1) est indispensable pour le recrutement de N-WASP, activateur du complexe Arp2/3 afin de promouvoir la polymérisation de l’actine. Cette cascade est nécessaire au mouvement des noyaux vers la périphérie et pour la formation de triades transversales. Cet enchainement est perturbé chez certains patients portant des mutations de BIN1 car cela affecte la bonne localisation de l’Amphiphysin 2. Bien que provenant de la même cascade, le mouvement des noyaux vers la périphérie et la formation transversale de triades sont des processus indépendants. Un complexe de Arp2/3 contenant Arpc5L avec la γ-actine organisent la desmine et donc la réticulation des myofibrilles important pour le mouvement nucléaire. En revanche, un complexe de Arp2/3 contenant Arpc5 avec la β-actine est nécessaires à la formation de triades transversales. / Nuclear movements are important for multiple cellular functions and are driven by forces originating from motor proteins and cytoskeleton. During skeletal myofiber formation or regeneration, nuclei move from the center to the periphery of the myofiber for proper muscle function. Furthermore, centrally located nuclei are found in different muscle disorders. Using theoretical and experimental approaches, we demonstrate that nuclear movement to the periphery of myofibers is mediated by centripetal forces around the nucleus in combination with local changes of nuclear stiffness. The centripetal forces are generated by myofibril contraction, cross-linking and zipping around the nucleus. Local changes of nuclear stiffness are achieved by asymmetric distribution of lamin A/C. Beginning with BIN1, gene mutated in centronuclear myopathies (CNMs); we identified the molecular cascade involved in nuclear movement to the periphery. We show that Amphipysin 2 (BIN1) is important for N-WASP recruitment which itself activates the Arp2/3 complex to induce actin polymerization. This cascade is important for nuclear movement to the periphery and transversal triad formation. This pathway is perturbed in certain patients harboring BIN1 mutations as it leads to mis-localized amphiphysin 2. Despite originating from the same pathway, peripheral nuclear movement and transversal triad formation are independent processes. An Arp2/3 complex containing Arpc5L together with γ-actin organize desmin to cross-link and zip myofibrils for nuclear movement whereas an Arp2/3 complex containing Arpc5 together with β-actin is required for transversal triad formation.

Introdução: As miopatias congênitas são doenças musculares genéticas caracterizadas por hipotonia e fraqueza muscular de início precoce na infância. Histologicamente são caracterizadas por alterações estruturais no músculo esquelético (corpos nemalínicos, cores ou centralização nuclear), no entanto, existem casos com alterações leves e inespecíficas, alterações mínimas, tais como, desproporção no tamanho das fibras e desarranjo na arquitetura interna das fibras (falhas focais na atividade oxidativa). Quanto ao aspecto molecular, vários genes já foram identificados em associação com os diversos subtipos, porém com grande sobreposição de achados histológicos e clínicos. Objetivo: Caracterização clínica, histológica e molecular de pacientes Brasileiros com miopatia nemalínica e com miopatia congênita com achados histológicos mínimos. Métodos: Avaliação clínica e histológica (revisão dos achados das biopsias musculares) de pacientes com diagnóstico de miopatia congênita nemalínica e com alterações mínimas, provenientes de dois centros de investigação em doenças neuromusculares da cidade de São Paulo (HC-FMUSP e UNIFESP). O estudo molecular foi realizado através de sequenciamento Sanger para os genes ACTA1, TPM3, MYH7 e SEPN1 e/ou sequenciamento de nova geração para painel de genes musculares e/ou exoma. Resultados: Foram avaliados 23 pacientes com miopatia nemalínica (20 famílias) e 22 pacientes com alterações mínimas (20 famílias). O diagnóstico molecular foi concluído em sete famílias com miopatia nemalínica, sendo quatro com variantes missense, em heterozigose, no gene ACTA1 já associadas previamente a miopatia nemalínica, e três famílias, com variantes não conhecidas, em heterozigose, no gene NEB com alta predição de patogenicidade. Na coorte de miopatias congênitas com alterações mínimas o diagnóstico molecular foi concluído em nove famílias, sendo uma com variante conhecida no gene CHRNE, descrita em miastenia congênita; duas famílias com variantes no gene TPM3, sendo uma inédita, em homozigose, e outra, em heterozigose, já conhecida; duas famílias com variantes novas, em heterozigose, no RYR1, uma no gene TTN e três famílias com variantes já conhecidas no gene no MYH7 com fenótipo de miopatia distal de Laing. A despeito da realização de sequenciamento de exoma, sete famílias ainda permanecem sem gene candidato. Conclusões: Os achados clínicos, histológicos e moleculares dos pacientes da coorte de miopatia nemalínica seguem aos padrões descritos da literatura. O estudo dos pacientes com miopatia congênita com alterações mínimas se revelou complexo e variável, tanto no fenótipo quanto no genótipo. As mutações novas no gene NEB, RYR1, TTN, TPM3 e MYH7 confirmam a importância e patogenicidade destes genes nas miopatias congênitas e ampliam o seu espectro de alterações. Diante da quantidade de genes candidatos e do tamanho de alguns genes envolvidos com essas miopatias, técnicas de sequenciamento de nova geração são de grande valor / Introduction: Congenital myopathy are a group of genetic muscle diseases characterized by hypotonia and weakness in early childhood. They are characterized by structural abnormalities in muscle biopsy (nemaline bodies, central-cores or nuclear centralization). However, it can present within mild and unspecific findings like fiber type disproportion and abnormalities on oxidative staining (minimal changes). Regarding the molecular aspects, there are many genes associated with the congenital myopathies with an important overlapping between the histological and phenotypical findings. Objectives: Clinical, histological and molecular characterization of Brazilian patients with nemaline myopathy and congenital myopathy with minimal changes. Methods: Clinical and histological evaluation (review of muscle biopsy) of patients with nemaline myopathy and congenital myopathy with minimal changes from two centers of neuromuscular diseases (HC-FMUSP e UNIFESP). The molecular study was performed using Sanger sequencing for ACTA1, TPM3, SEPN1 and MYH7 genes and/or neuromuscular panel and/or exome. Results: Twenty-three patients with nemaline myopathy (20 families) and 22 patients with congenital myopathy with minimal changes (20 families) were evaluated. The molecular diagnose were concluded in seven families with nemaline myopathy, with four families having missense, heterozygous and pathogenic ACTA1 variants and three families having unknown heterozygous and pathogenic variants in NEB gene. In the congenital myopathy with minimal findings group, the diagnose was concluded in 9 families. One presenting with a pathogenic variant in CHRNE gene previously described in congenital myasthenia, two families with pathogenic variants in TPM3, one novel homozygous and one heterozygous previously reported. Two families presented with novel and pathogenic RYR1 variants, one with novel and pathogenic TTN variants and 3 families presented with heterozygous variants in MYH7 myopathy with Laing distal myopathy phenotype. Despite the NGS realization, 7 families remain without a gene candidate. Conclusions: The clinical, histological and molecular findings of nemaline myopathy cohort follow the literature pattern. In contrast, the study for minimal change patients appear complex and variable, either on phenotype or on genotype. The new gene mutations for NEB, RYR1, TTN, TPM3 and MYH7 reinforce relevance and pathogenicity of these genes in the congenital myopathies and expand the mutation spectrum. In light of diversity of candidate genes and the size of some genes involved with these myopathies, next generation sequencing techniques have been proved essential

Introduction: Idiopathic inflammatory myopathies (myositis, IIM) are heterogeneous group of rare autoimmune systemic diseases, characterized particularly by proximal skeletal muscle weakness. Heretogeneity of myositis is based on different pathogenetic mechanisms which may be reflected by variable imunophenotypic response in individual subtypes. Objectives: The aim of this work was to explore the associations and influence of soluble factors of immune system in patient's sera on phenotypic characteristics and subtypes of IIM, to describe their expression in inflammed muscle tissue and study their eventual role in pathogenesis by analysis of effect on immune and muscle cells in vitro. Results: We have described prevalence and characteristics of joint involvement in myositis patients and its significant association with anti-Jo-1 autoantibody. Further we confirmed the relation of anti-HMGCR antibody to immune mediated necrotizing myopathy, its tight relation to statins and recent increase in incidence. We showed inverse association of IFNα serum levels with muscle activity detected on MRI. Clinical activity positively correlated with IFN type-I pathway activation in patients with dermatomyositis. We also show positive correlation of resistin levels and clinical activity and correlation of activity...

Introdução: As miopatias congênitas são doenças musculares genéticas caracterizadas por hipotonia e fraqueza muscular de início precoce na infância. Histologicamente são caracterizadas por alterações estruturais no músculo esquelético (corpos nemalínicos, cores ou centralização nuclear), no entanto, existem casos com alterações leves e inespecíficas, alterações mínimas, tais como, desproporção no tamanho das fibras e desarranjo na arquitetura interna das fibras (falhas focais na atividade oxidativa). Quanto ao aspecto molecular, vários genes já foram identificados em associação com os diversos subtipos, porém com grande sobreposição de achados histológicos e clínicos. Objetivo: Caracterização clínica, histológica e molecular de pacientes Brasileiros com miopatia nemalínica e com miopatia congênita com achados histológicos mínimos. Métodos: Avaliação clínica e histológica (revisão dos achados das biopsias musculares) de pacientes com diagnóstico de miopatia congênita nemalínica e com alterações mínimas, provenientes de dois centros de investigação em doenças neuromusculares da cidade de São Paulo (HC-FMUSP e UNIFESP). O estudo molecular foi realizado através de sequenciamento Sanger para os genes ACTA1, TPM3, MYH7 e SEPN1 e/ou sequenciamento de nova geração para painel de genes musculares e/ou exoma. Resultados: Foram avaliados 23 pacientes com miopatia nemalínica (20 famílias) e 22 pacientes com alterações mínimas (20 famílias). O diagnóstico molecular foi concluído em sete famílias com miopatia nemalínica, sendo quatro com variantes missense, em heterozigose, no gene ACTA1 já associadas previamente a miopatia nemalínica, e três famílias, com variantes não conhecidas, em heterozigose, no gene NEB com alta predição de patogenicidade. Na coorte de miopatias congênitas com alterações mínimas o diagnóstico molecular foi concluído em nove famílias, sendo uma com variante conhecida no gene CHRNE, descrita em miastenia congênita; duas famílias com variantes no gene TPM3, sendo uma inédita, em homozigose, e outra, em heterozigose, já conhecida; duas famílias com variantes novas, em heterozigose, no RYR1, uma no gene TTN e três famílias com variantes já conhecidas no gene no MYH7 com fenótipo de miopatia distal de Laing. A despeito da realização de sequenciamento de exoma, sete famílias ainda permanecem sem gene candidato. Conclusões: Os achados clínicos, histológicos e moleculares dos pacientes da coorte de miopatia nemalínica seguem aos padrões descritos da literatura. O estudo dos pacientes com miopatia congênita com alterações mínimas se revelou complexo e variável, tanto no fenótipo quanto no genótipo. As mutações novas no gene NEB, RYR1, TTN, TPM3 e MYH7 confirmam a importância e patogenicidade destes genes nas miopatias congênitas e ampliam o seu espectro de alterações. Diante da quantidade de genes candidatos e do tamanho de alguns genes envolvidos com essas miopatias, técnicas de sequenciamento de nova geração são de grande valor / Introduction: Congenital myopathy are a group of genetic muscle diseases characterized by hypotonia and weakness in early childhood. They are characterized by structural abnormalities in muscle biopsy (nemaline bodies, central-cores or nuclear centralization). However, it can present within mild and unspecific findings like fiber type disproportion and abnormalities on oxidative staining (minimal changes). Regarding the molecular aspects, there are many genes associated with the congenital myopathies with an important overlapping between the histological and phenotypical findings. Objectives: Clinical, histological and molecular characterization of Brazilian patients with nemaline myopathy and congenital myopathy with minimal changes. Methods: Clinical and histological evaluation (review of muscle biopsy) of patients with nemaline myopathy and congenital myopathy with minimal changes from two centers of neuromuscular diseases (HC-FMUSP e UNIFESP). The molecular study was performed using Sanger sequencing for ACTA1, TPM3, SEPN1 and MYH7 genes and/or neuromuscular panel and/or exome. Results: Twenty-three patients with nemaline myopathy (20 families) and 22 patients with congenital myopathy with minimal changes (20 families) were evaluated. The molecular diagnose were concluded in seven families with nemaline myopathy, with four families having missense, heterozygous and pathogenic ACTA1 variants and three families having unknown heterozygous and pathogenic variants in NEB gene. In the congenital myopathy with minimal findings group, the diagnose was concluded in 9 families. One presenting with a pathogenic variant in CHRNE gene previously described in congenital myasthenia, two families with pathogenic variants in TPM3, one novel homozygous and one heterozygous previously reported. Two families presented with novel and pathogenic RYR1 variants, one with novel and pathogenic TTN variants and 3 families presented with heterozygous variants in MYH7 myopathy with Laing distal myopathy phenotype. Despite the NGS realization, 7 families remain without a gene candidate. Conclusions: The clinical, histological and molecular findings of nemaline myopathy cohort follow the literature pattern. In contrast, the study for minimal change patients appear complex and variable, either on phenotype or on genotype. The new gene mutations for NEB, RYR1, TTN, TPM3 and MYH7 reinforce relevance and pathogenicity of these genes in the congenital myopathies and expand the mutation spectrum. In light of diversity of candidate genes and the size of some genes involved with these myopathies, next generation sequencing techniques have been proved essential

Introduction: Idiopathic inflammatory myopathies (myositis, IIM) are heterogeneous group of rare autoimmune systemic diseases, characterized particularly by proximal skeletal muscle weakness. Heretogeneity of myositis is based on different pathogenetic mechanisms which may be reflected by variable imunophenotypic response in individual subtypes. Objectives: The aim of this work was to explore the associations and influence of soluble factors of immune system in patient's sera on phenotypic characteristics and subtypes of IIM, to describe their expression in inflammed muscle tissue and study their eventual role in pathogenesis by analysis of effect on immune and muscle cells in vitro. Results: We have described prevalence and characteristics of joint involvement in myositis patients and its significant association with anti-Jo-1 autoantibody. Further we confirmed the relation of anti-HMGCR antibody to immune mediated necrotizing myopathy, its tight relation to statins and recent increase in incidence. We showed inverse association of IFNα serum levels with muscle activity detected on MRI. Clinical activity positively correlated with IFN type-I pathway activation in patients with dermatomyositis. We also show positive correlation of resistin levels and clinical activity and correlation of activity...

La dystrophine est une protéine filamenteuse qui contribue à la structuration des cellules musculaires en créant un lien entre le cytosquelette et le sarcolemme. Avec l’actine du cytosquelette et les lipides membranaires, la dystrophine représente l’un des éléments d’un complexe macromoléculaire, localisé sous la membrane plasmique, dont le rôle est la prévention des dommages qui pourraient être induits à force de contractions-relâchements répétés. De tels dommages, notamment des ruptures du sarcolemme, sont observés chez des personnes atteintes de myopathies de Duchenne (DMD) et de Becker (BMD), des maladies causées par des mutations qui altèrent l’expression ou la fonction de la dystrophine. Ces myopathies sont actuellement incurables et une connaissance approfondie de la relation structure-fonction de la dystrophine et de ses interactions avec ses partenaires s’avère absolument nécessaire à la mise au point de nouvelles stratégies de thérapies géniques. Cette protéine se compose de quatre domaines fonctionnels, dont un domaine central filamentaire, constitué de 24 répétitions successives d’un même motif structural, un faisceau de trois hélices alpha ou « coiled-coil ». Or, il a été récemment montré que la structure de ce domaine central n’est pas strictement linéaire et que certaines régions inter-répétitions (linker) forment des coudes, délimitant ainsi des sous-domaines d’interaction spécifiques. Cette thèse a pour objectif de comprendre l’origine de cette diversité de conformations inter-répétition dans un domaine structuralement homogène, et d’explorer comment elle permet à certaines régions de se différencier afin d’interagir avec l’actine et/ou les lipides membranaires. / Dystrophin is a filamentous protein involved in muscular cells structure which links the cytoskeleton to the sarcolemma. Together with cytoskeletal actin and membrane lipids, dystrophin is a part of a macromolecular complex, located under the sarcolemma, which prevents damages induced during repeated muscle contractions and relaxations. Such damages, including sarcolemma disruption, are found in people with Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD), diseases caused by mutations altering dystrophin expression or function. There is currently no treatment to cure these myopathies, and a deep understanding of the structure-function of the dystrophin and its interactions with its partners is necessary to the development of gene therapy strategies. Structuraly, this protein is composed of four functionnal domains, including a long filamentous central domain, composed of 24 successive coiled-coil repeats. It was recently showed that the central domain is not rod shaped and some inter-repeats regions (linker) are kinked, delimiting specific interaction sub-domains. This thesis aims to bring knowledge about the basis of the conformationnal diversity of linkers in a structuraly homogenous domain in human dystrophin. We explore how dystrophin delimits some regions that interact with f-actin and/or membrane lipids.

Les maladies neuromusculaires sont des maladies souvent très sévères et très handicapantes, et un fardeau pour les patients, leurs familles, ainsi que pour le système de santé. Le but de ce projet était de mettre au point et de valider une approche de capture de séquence et de séquençage haut débit pour identifier les mutations en cause chez les patients atteints de maladies neuromusculaires et également trouver les nouveaux gènes qui sont impliqués dans une sous-classe de myopathies, les myopathies centronucléaires. Nous avons montré que l’approche de capture de séquence et de séquençage haut débit peux être utile dans le domaine des maladies neuromusculaires car elle est moins coûteuse que les approches conventionnelles « gène par gène » mise en oeuvre dans les laboratoires de diagnostics génétiques.Cette stratégie devrait élargir les spectres cliniques connus et identifier de nouvelles maladies alléliques (des mutations dans un gène causant différentes maladies). De plus, cela sera utile pour l’élargissement des connaissances sur les corrélations génotypes-phénotypes qui sont nécessaires à une prise en charge plus adaptée et au développement de stratégies thérapeutiques. / Neuromuscular disorders (NMD) are genetic diseases affecting muscles, nerves and neuromuscular junctions. They are rare and often severe with different age of onset from childhood to adulthood with significant burden to the patients, their families and public health system. For testing the possibility of using massively parallel sequencing as a routine technique in molecular diagnosis of neuromuscular disorders, the first aim of my PhD project was to use massively parallel sequencing technique in patients with different NMDs for disease-causing mutation detection. The second aim of my PhD project was to find novel gene(s) implicated in centronuclear myopathies (CNM). CNM are inherited neuromuscular disorders and a type of congenital myopathies, characterized mainly by presence of central and one or more internalized nuclei in muscle fibers with different severities and age of onset, using massively parallel sequencing. About 20% of CNM patients don’t have any mutations in four implicated genes. Disease- causing mutation(s)/ gene(s) in these patients need to be identified. We could show that next generation sequencing is a robust technique for gene identification if a homogenous cohort of patients is available and also is useful to use as a routine technique in molecular diagnosis as it istime and cost effective technique.

Les myopathies inflammatoires (MI) représentent un groupe hétérogène de maladies caractérisépar une faiblesse musculaire chronique et symétrique associée à une augmentation du taux sérique decréatine phosphokinase (CPK). Les MI sont actuellement subdivisées en 5 entitées : les dermatomyosites,les myopathies nécrosantes auto-immunes, la myosite à inclusion, la polymyosite et les myosites dechevauchement. A ce jour, le diagnostic des MI repose sur l’association de signes cliniques, decaractéristiques anatomopathologiques sur la biopsie musculaire et la présence d’auto-anticorps (aAc). Eneffet, la découverte d’aAc spécifiques et/ou associés aux myosites (MSA/MAA) a considérablementamélioré le diagnostic et le pronostic de la maladie. Cependant, un nombre non négligeable de patientsatteints de MI sont séronégatifs pour les MSA/MAA connus. Par ailleurs, la biopsie musculaire nécessaireau diagnostic est parfois guidée par imagerie par résonance magnétique (IRM), bien qu’il n’ait pas étéprouvé que les données d’imagerie soient corrélées aux signes histologiques. Enfin, le traitement des MIrepose sur l’utilisation d’immunosuppresseurs systémiques, une approche non spécifique de laphysiopathologie de la maladie. Les modèles animaux de MI les plus utilisés sont induits et nonspontanés : ils reposent principalement sur l’immunisation d’animaux contre des protéines telles que lamyosine, la protéine C ou l’histidyl-tRNA synthétase.Les souris NOD (non obese diabetic) sont le modèle classique d’étude du diabète de type 1.Lorsque ces souris sont invalidées pour la voie de costimulation lymphocytaire ICOS/ICOSL, les souris nedéveloppent plus de diabète mais présentent alors une atteinte musculaire. Dans ce travail, nous avonsétudié le phénotype et caractérisé l’atteinte musculaire des souris NOD Icos-/- et NOD Icosl-/-. Nous avonsainsi établi le 1er modèle murin spontané de MI, dont la physiopathologie est médiée par leslymphocytes T CD4+ et la sécrétion d’IFN-γ. Par ailleurs, ces souris présentent un déficit en lymphocytes Trégulateurs. Nous avons également identifié 4 auto-antigènes (aAg) candidats cibles d’aAc chez ces souris.La recherche des aAc correspondants aux aAg orthologues dans le sérum des patients atteints de MI apermis d’identifier, pour l’un d’entre eux, une minorité d’individus séropositifs grâce au développementd’un nouveau test ALBIA (addressable laser bead immunoassay). Il pourrait donc s’agir d’un nouveaubiomarqueur. Dans la perspective de nouvelles évaluations thérapeutiques, nous avons établi desdonnées préliminaires montrant que l’interleukine 2 à faibles doses permet de retarder l’apparition de lamaladie. Enfin, nous avons mis à profit ce modèle et démontré la corrélation entre les données généréespar IRM et par analyse histologique de l’inflammation, confortant le rôle de cette technique d’imagerie àla fois pour le diagnostic et le suivi des MI. / Inflammatory Myopathies (IM) are a heterogeneous group of diseases characterized bychronic and symmetrical muscle weakness associated to increased creatine phosphokinase (CPK)levels, according to entity concerned. Currently, IM are divided into 5 main entities:dematomyositis, immune-mediated necrotizing myopathies, inclusion body myositis, polymyositisand overlap myositis. Nowadays, IM diagnosis is based on clinical signs associated to pathologicfeatures on muscle biopsy and presence of auto-antibodies (aAb). Indeed, the discovery of myositisspecific and/or associated auto-antibodies (MSA/MAA) had considerably improve disease diagnosisand prognosis. However, substantial proportion of IM patients do not display any knownMSA/MAA. Furthermore, diagnosis requires muscle biopsy. This biopsy is sometimes guided bymagnetic resonance imaging (MRI), even though correlation between MRI findings and pathologicalfeatures is not established. Lastly, therapeutics used in IM treatment are systemicimmunosuppressive agents, i.e. not specific to IM pathophysiology. Animal models of IM are mainlybased on active immunization against different proteins as myosin, C protein orhistidyl-tRNA synthetase, while spontaneous models are required to identify pathophysiologicalmechanisms that new therapeutics should target.NOD (non obese diabetic) mice are the main model of type 1 diabetes. When invalidatedfor ICOS/ICOSL costimulation pathway, these mice do not develop diabetes but present musculardisorders. In this work, we study Icos-/- and Icosl-/- NOD mice phenotype and characterize theremuscle lesion. Thus, we have established this model as the first paradigm of IM. Pathophysiologicalstudy in these mice demonstrated that disease is CD4+ T cell dependent and associated to IFN-γproduction. Furthermore, we shown a quantitative defect in regulatory T cells. We have alsoidentified 4 candidate autoantigens (aAg) in Icos-/- and Icosl-/- NOD mice. Searching forcorresponding aAb against ortholog proteins in patients with IM, we identified for one of them, alow percentage of seropositive individuals using a new ALBIA (addressable laser beadimmunoassay). It could be identified as a new biomarker. In order to evaluate new therapies, weestablished preliminary data showing that low dose interleukin 2 therapy allow to delay diseaseonset. Lastly, we took advantage of this new model to demonstrate the correlation betweenMRI findings and histological inflammation features, confirming the valuable role of MRI for thediagnosis and monitoring of IM.

Les myopathies auto-immunes (MAI), classiquement appelées myosites ou myopathies inflammatoires idiopathiques, représentent un groupe de maladies définies par des caractéristiques cliniques, histopathologiques et biologiques. Une des caractéristiques les plus notables est la présence d’auto-anticorps (aAc) chez environ 60% des patients. Les MAI regroupent : les dermatomyosites, les polymyosites, les myosites à inclusion, les myosites de chevauchement incluant le syndrome des anti-synthétases et les myopathies nécrosantes auto-immunes (MNAI). Les MNAI ont été récemment individualisées parmi les MAI comme des maladies graves fréquemment associées à la présence d’aAc dirigés contre la Signal Recognition Particle (SRP) ou la 3-Hydroxy-3-MéthylGlutaryl-CoA Réductase (HMGCR). La localisation de SRP et HMGCR étant intracellulaire, le rôle des aAc dans la physiopathologie des MNAI reste mal compris. La pathogénicité des aAc anti-SRP et anti-HMGCR envers des cellules musculaires cultivées in vitro a récemment été mise en évidence mais leurs effets in vivo demeurent inconnus.Au cours de cette thèse, j’ai étudié le rôle physiopathologique des aAc anti-SRP et anti-HMGCR in vivo chez la souris. Le transfert passif d’IgG de patients atteints de MNAI, positifs pour les aAc anti-SRP ou anti-HMGCR, à la souris sauvage entraîne un déficit musculaire. Ce déficit était prolongé chez la souris immunodéficiente Rag2-/-, et limité chez la souris déficiente pour la fraction C3 du complément. Chez les souris recevant les IgG anti-SRP+, le déficit musculaire était important et accompagné de quelques signes de nécrose myocytaire. Les IgG anti-HMGCR+ induisaient une faiblesse musculaire moindre, et des signes histopathologiques rares ou absents. Ces résultats sont en accord avec l’observation chez l’homme d’une maladie plus grave chez les patients anti-SRP+ par rapport aux patients anti-HMGCR+. La supplémentation en complément humain des souris augmentait le déficit musculaire induit par les IgG anti-HMGCR+ et de façon moindre pour les IgG anti-SRP+. En collaboration avec l’INSERM UMRS974, nous avons montré que les cibles SRP et HMGCR peuvent être détectées à la surface des fibres musculaires in vitro, suggérant qu’elles puissent être accessibles aux aAc in vivo.Ces résultats démontrent pour la première fois le rôle pathogène des aAc anti-SRP et anti-HMGCR in vivo et l’implication du complément, contribuant à une avancée dans la compréhension de la physiopathologie des MNAI. / Autoimmune myopathies (AIM), classically called myositis or idiopathic inflammatory myopathies, represent a group of diseases characterized by clinical, histopathologic and biologic properties. One of the most notable properties is the presence of autoantibodies (aAb) in approximately 60% of patients. AIM includes five principal entities: dermatomyositis, polymyositis, inclusion body myositis, overlap myositis including the anti-synthetase syndrome and immune-mediated necrotizing myopathies (IMNM). IMNM have recently been individualized among AIM as severe diseases frequently associated with aAb directed against Signal Recognition Particle (SRP) or 3-Hydroxy-3-MethylGlutaryl-CoA Reductase (HMGCR). Since SRP and HMGCR have an intracellular localization, the role of anti-SRP and anti-HMGCR aAb in the pathophysiology of IMNM remains unclear. Anti-SRP and anti-HMGCR aAb were recently shown to be pathogenic to muscle cells in vitro but in vivo effects remain unknown.During this thesis, I studied the pathophysiological role of anti-SRP and anti-HMGCR aAb in vivo in mice. Passive transfer of IgG purified from plasma of IMNM patients positive for anti-SRP and anti-HMGCR aAb to wild-type mice elicited a muscle weakness. Immune-deficient Rag2-/- mice presented a prolonged muscle deficit, whereas complement component C3 deficient mice had limited signs. Mice injected with anti-SRP+ IgG displayed a strong muscle weakness with mild myocytic necrosis. The muscle deficit was milder and histopathologic findings were not always present in mice receiving anti-HMGCR+ IgG. This is in accordance with clinical findings in anti-SRP+ patients which present a more severe disease than anti-HMGCR+ patients. When supplemented with human complement, mice receiving anti-HMGCR+ IgG showed a more severe muscle deficit. This supplementation increased the deficit induced by anti-SRP IgG in a milder way. In collaboration with INSERM UMRS974, we showed that the targets SRP and HMGCR can be detected on the surface of myofibres in vitro, suggesting that they could be accessible to aAb in vivo.Together, these results demonstrate for the first time the pathogenic role of anti-SRP and anti-HMGCR aAb in vivo and the implication of complement, contributing to a progress in the comprehension of MNAI pathophysiology.

Les arthrogryposes multiples congénitales (AMC), limitations articulaires multiples survenant au cours du développement et présentes à la naissance, sont un ensemble hétérogène de maladies dont le dénominateur commun est une diminution des mouvements fœtaux. Dans la majorité des cas, l'AMC est liée à un mécanisme impliquant le système neuromusculaire. Les causes sont dans un grand nombre de cas d'origine génétique. La connaissance de cette cause permet de proposer un conseil génétique avec une évaluation précise du risque de récurrence et éventuellement un diagnostic anténatal. La connaissance du mécanisme sous-jacent participe à l'évaluation du pronostic et permet d'élargir les connaissances sur la mise en place du système neuromusculaire. Mes travaux de thèse ont porté sur ces deux aspects. Dans un premier temps, j'ai étudié l'expression du récepteur de la ryanodine RyR1 dans le muscle squelettique fœtal humain. Les mutations de RYR1 sont responsables de myopathies congénitales. Dans les formes sévères précoces, une AMC peut être occasionnellement associée. L'expression de RyR1 est détectée dès 14 semaines d'aménorrhée dans le muscle fœtal humain. Ce résultat confirme l'expression précoce de RyR1 chez l'homme et permet d'expliquer la possibilité de limitations articulaires. Dans un second temps, j'ai étudié une famille consanguine avec trois enfants atteints d'arthrogrypose distale à la recherche de la cause génétique sous-jacente. L'analyse pangénomique m'a permis de lier pour la première fois le gène ECEL1, codant une endopeptidase, à une pathologie humaine. La recherche de mutations d'ECEL1 dans une cohorte de 20 patients a permis d'identifier cinq autres familles. Toutes les mutations sont transmises sur un mode autosomique récessif et conduisent à une perte de fonction de la protéine. L'ensemble des patients présentent un phénotype clinique et IRM semblable et distinct des autres tableaux d'arthrogrypose distale. Au total, ces travaux confirment l'expression précoce de RyR1 chez l'homme et identifient le gène ECEL1 comme une cause récurrente d'un type particulier d'arthrogrypose distale autosomique récessive. / Arthrogryposis multiplex congenita (AMC) is a heterogeneous group of disorders characterised by multiple joint contractures at birth due to diminished foetal movements. In most cases, the underlying mechanism involves the neuromuscular system. Genetic causes are frequent. Identifying the genetic cause is paramount for precise recurrent risk assessment, genetic counselling and prenatal diagnosis. Elucidating the underlying mechanism allows for prognostic evaluation and expands our knowledge on the development of the human neuromuscular system. My thesis focused on these two aspects. First I studied the expression of the ryanodine receptor 1 in human foetal skeletal muscle. RYR1 mutations cause congenital myopathies. AMC can occasionally be associated with severe forms of RYR1 related congenital myopathies. RyR1 is expressed at 14 weeks of gestational age in human skeletal muscle. Thus it confirms the early expression of RyR1 in human and can account for the occurrence of joint contractures. Second, in order to identify an underlying genetic cause, I studied a consanguineous family with three affected children showing a distal arthrogryposis phenotype. The genome wide linkage study allowed me to link for the first time the endopeptidase coding gene ECEL1 to a human disease. Five other families were shown to carry ECEL1 mutations after screening a cohort of 20 families with distal arthrogryposis. All mutations were recessive and predicted to lead to a loss of function of the protein. All patients showed a recognisable clinical and MRI phenotype that differed to that of currently known distal arthrogryposes. Altogether, these results confirm the early expression of RyR1 in human and identify ECEL1 as a recurrent cause of a distinct type of distal arthrogryposis.