O músculo esquelético é um tecido que tem a capacidade de se regenerar após lesão, seja ela patológica ou induzida. Para tanto, células musculares progenitoras, presentes no músculo adulto, atuam fundindo-se entre si, ou com as fibras musculares danificadas, para formar novas fibras. A via da macroautofagia, implicada na degradação e reciclagem de proteínas e organelas danificadas via lisossomo, é essencial para a manutenção da massa muscular, mas já foi também implicada na diferenciação e funcionamento de células progenitoras do músculo. Além disso, essa via está desregulada em diversas doenças neuromusculares, o que destaca seu papel nesse tecido. Nesse estudo, a regulação da autofagia foi investigada em diferentes situações de formação e degradação do músculo. Para estudar o processo de diferenciação muscular in vitro utilizamos um modelo de células musculares imortalizadas normais, e de paciente com miopatia ligada ao X com autofagia excessiva (XMEA). A análise dos genes e proteínas p62, BNIP3, BECLIN1, VPS34, ATG12 e LC3, além de alvos de mTOR, mostrou um padrão similar de expressão em mioblastos indiferenciados e miotubos diferenciados a partir de células controle e nas derivadas de paciente XMEA. Estes resultados sugerem que a desregulação da via autofágica relacionada à doença provavelmente surge em estágios mais avançados, como se observa em doenças de acúmulo lisossomal. A investigação da diferenciação muscular nessas células mostrou um aumento na capacidade de fusão de mioblastos XMEA, que não foi relacionado a mudanças na expressão de genes envolvidos na miogênese. Isso indica que o defeito primário relacionado a XMEA, como a deficiência da ATPase vacuolar, pode interferir no processo de diferenciação muscular. Para estudar o músculo em condições patológicas, utilizamos modelos animais para distrofias musculares que possuem distintos graus de afecção do músculo, como o DMDmdx, modelo para distrofia muscular de Duchenne, o SJL/J, modelo para distrofia muscular de cinturas tipo 2B e o Largemyd, modelo para distrofia muscular congênita 1D. Observamos que não há alterações globais na expressão de genes e proteínas da autofagia. Adicionalmente, cada modelo murino teve alterações pontuais, destacando a ausência de correlação entre o grau de degeneração do músculo e as alterações observadas na via autofágica. Por outro lado, quando uma lesão muscular é induzida em músculo normal, houve uma diminuição da expressão de todos os genes estudados, Bnip3, Beclin1, Vps34, Atg12, Lc3 e Gabarapl1, com possível acúmulo das proteínas autofágicas p62 e Beclin1. Com a recuperação do músculo, após cinco dias da lesão, a maior parte dos genes estudados teve sua expressão normalizada. Tais resultados indicam que a lesão aguda se relaciona a uma resposta drástica e recuperação rápida na via da autofagia. Em conjunto, nossos resultados mostram que a via da autofagia é diferencialmente afetada a depender do estímulo dado ao músculo, seja ele de regeneração e formação de novas células musculares ou de degeneração. Dessa forma, este estudo pode ter implicações para o desenvolvimento de terapias que tenham como alvo a via autofágica, já que indica que o momento da intervenção terapêutica pode ser importante, assim como o estímulo que levou a alterações no tecido muscular / The skeletal muscle is a tissue that has the ability to regenerate upon lesion, whether it occurs pathologically or induced. Therefore, progenitor muscle cells, present in the adult muscle, act by fusing with each other or with damaged fibers in order to recover the tissue. The macroautophagy pathway, related to degradation and recycling of proteins and damaged organelles via lysosome, is essential for the maintenance of muscle mass, and it was also implicated in the differentiation and functioning of muscle progenitor cells. Besides that, this pathway is deregulated in several neuromuscular disorders, highlighting its important role in this tissue. In this study, the autophagic regulation was investigated in distinct contexts of muscle formation and degradation. To study the muscle differentiation process in vitro, we used a model of immortalized muscle cells from both a normal control and a patient with X-linked myopathy with excessive autophagy (XMEA). The genes and proteins p62, BNIP3, BECLIN1, VPS34, ATG12, LC3 and mTOR targets showed a similar pattern of expression in both undifferentiated myoblasts and differentiated myotubes, from both control cells and XMEA patient-derived cells. This fact suggests that autophagic deregulation might arise in later stages of the disease, in a pattern observed in disorders with protein accumulation. The investigation of muscle differentiation in the studied cells showed an enhancement of the myoblast fusion capacity in XMEA cells, which was not related to changes in the expression of myogenic genes. This observation indicates that the primary defect related to the XMEA pathology, as the deficiency of the vacuolar ATPase, might interfere in the process of muscle differentiation. In order to evaluate muscle in pathological conditions, we studied animal models for muscular dystrophies that have distinct patterns of muscle affection, such as the DMDmdx, model for the Duchenne muscular dystrophy, the SJL/J, model for the limb-girdle muscle dystrophy type 2B and the Largemyd, model for the congenital muscular dystrophy type 1D. We did not find any global alterations in the expression of autophagic genes and proteins. Additionally, each animal model had discrete changes, highlighting the absence of correlation between the pattern of muscle degeneration and alterations in the autophagy pathway. On the other hand, when a lesion is induced in normal muscle, there is a decrease in the expression of all studied genes, such as Bnip3, Beclin1, Vps34, Atg12, Lc3 and Gabarapl1, with a possible accumulation of the autophagic proteins p62 and Beclin1. With muscle recovery, five days after lesion, most of the studied genes had their expression returning to normal levels. These results indicate that the acute lesion is related to a drastic response and rapid recovery of the autophagic pathway. Together, our results show that autophagy is differentially affected depending on the stimulus given to the muscle, either of regeneration and formation of new muscle cells or degeneration. In that sense, this study may have implications for the development of therapies that target autophagy, since it indicates that the time point of therapeutic interventions may be important, as well as the stimulus that led to alterations in the skeletal muscle tissue

La forme des mitochondries change continuellement grâce aux actions combinées d'événements de fission et de fusion rendant le réseau mitochondrial très dynamique. Les processus mitochondriaux de fission et de fusion sont finement régulés par des GTPases de la famille des dynamines qui sont bien conservées entre les espèces. Chez C. elegans, la fission est régulée par DRP-1, la fusion de la membrane interne par EAT-3, homologue d’OPA1, et la fusion de la membrane externe par FZO-1, homologue de MFN1. Dans les cellules musculaires du nématode sauvage, les mitochondries tubulaires et circulaires sont dans des proportions égales et organisées le long du sarcomère. Cependant, durant la dégénérescence musculaire dystrophine-dépendante, une fragmentation du réseau mitochondrial dans les cellules musculaires apparaît. Or le rôle des acteurs de la dynamique mitochondriale dans les mécanismes moléculaires menant à la dégénérescence musculaire dystrophine-dépendante reste encore incompris. Nous avons trouvé que: (i) la dégénérescence musculaire dystrophine-dépendante s'accompagnait d'une augmentation drastique de la fragmentation mitochondriale qui peut être sauvée par des manipulations génétiques de la dynamique mitochondriale (ii) la perte de fonction du gène de fission drp-1 ou la surexpression des gènes de fusion eat-3 et fzo-1 provoquent une réduction de la dégénérescence musculaire et une mobilité améliorée des mutants dystrophiques (iii) les fonctions de DRP-1 dans l'apoptose et d’autres acteurs de l’apoptose sont importants pour la mort des cellules musculaires déficientes en dystrophine (iv) L’implication de DRP-1 dans l’apoptose est également importante pour la dégénérescence musculaire liée au vieillissement. En conclusion, nos résultats pointent vers un mécanisme impliquant la dynamique mitochondriale pour impacter la dégénérescence musculaire via l’apoptose chez Caenorhabditis elegans / Mitochondrial shape is continually changing thanks to the combined actions of fission and fusion events making the mitochondrial network very dynamic. The mitochondrial fission and fusion processes are finely regulated by GTPases of the family of dynamins that are well conserved between species. In C. elegans, fission is regulated by DRP-1, fusion of the inner membrane by EAT-3, homologue of OPA1, and fusion of the outer membrane by FZO-1, homologue of MFN1. In the muscle cells of wild nematode, tubular and circular mitochondria are in equal proportions and organized along the sarcomere. However, during dystrophin-dependent muscle degeneration, fragmentation of the mitochondrial network in muscle cells occurs. But the role of the actors of mitochondrial dynamics in the molecular mechanisms leading to dystrophin-dependent muscle degeneration is still misunderstood. We found that: (i) dystrophin-dependent muscle degeneration was accompanied by a drastic increase in mitochondrial fragmentation that can be saved by genetic manipulation of mitochondrial dynamics (ii) loss of function of the fission gene drp-1 or overexpression of the eat-3 and fzo-1 fusion genes causes a reduction in muscle degeneration and improved mobility of dystrophic mutants (iii) DRP-1 functions in apoptosis and other are important for the death of dystrophin-deficient muscle cells (iv) The involvement of DRP-1 in apoptosis is also important for age-dépendant muscle degeneration. In conclusion, our results point toward a mechanism involving mitochondrial dynamics to impact muscle degeneration via apoptosis in Caenorhabditis elegans

La Dystrophie Musculaire de Duchenne (DMD) est la plus fréquente et la plus sévère des maladies dégénératives du muscle. Elle se caractérise par une dégénérescence progressive des fibres musculaires due à l’absence de dystrophine fonctionnelle dans les muscles. Actuellement, le rôle physiologique de la dystrophine n’est pas clairement établi et il n’existe pas encore de traitement curatif pour cette maladie. La difficulté de mettre en évidence la fonction de la dystrophine et la physiopathologie de la DMD est en partie expliquée par la complexité moléculaire et cellulaire du muscle des modèles vertébrés utilisés dans les études actuelles. Notre équipe de recherche a développé un modèle de DMD chez le nématode Caenorhabditis elegans. Dans ce modèle, la mutation du gène de la dystrophine, provoque une dégénérescence progressive des muscles conduisant à une paralysie des animaux adultes. Nous utilisons ce modèle afin d’étudier la fonction de la dystrophine et les mécanismes impliqués dans la dégénérescence musculaire chez le nématode. Ce travail de thèse porte sur deux nouveaux acteurs de la dégénérescence musculaire dépendante de la dystrophine : la protéine DYC‐1 et son principal partenaire ZYX‐1. Ce travail présente la caractérisation de ces deux protéines et étudie leurs fonctions dans le muscle. Par ailleurs, ce travail de thèse présente les premiers résultats d’un projet de microscopie électronique ayant pour but de caractériser en détail les évènements subcellulaires du processus dégénératif au cours du cycle de vie du nématode dystrophique. À plus long terme, les études chez le nématode permettront de proposer de nouvelles hypothèses quant aux mécanismes moléculaires et cellulaires de la dégénérescence musculaire / Duchenne Muscular Dystrophy (DMD) is the most prevalent and one of the most severe muscular dystrophy. DMD is due to the absence of functional dystrophin in cardiac and skeletal muscle cells, this lack leads to a progressive muscle degeneration of contractile fibres. Currently, the physiological role of dystrophin is not yet clearly established and curative treatments for DMD are not yet available. The lack of knowledge about dystrophin function and DMD physiopathology can be partly attributed to the complexity of vertebrate muscle, and the absence of a simple model that emulates the human pathology. Our research team developed a model of muscle degeneration in the nematode Caenorhabditis elegans. In this model, the mutation of the dystrophin gene produces a progressive muscle degeneration leading to the paralysis of the adult worms. We use this model for investigating the role of dystrophin and the mechanisms of muscle degeneration in C. elegans. This PhD work concerns two new actors of dystrophin‐dependant muscle degeneration: The DYC‐1 protein and its main interactor ZYX‐1. This study aims to characterise these proteins and to study their muscle functions. Moreover, this PhD work presents preliminary results of an in depth characterisation of subcellular processes of muscle degeneration in dystrophic worms by electron microscopy. Our aim is to visualise first events and to observe the progression of degeneration until the death of muscle cell. These molecular and cellular approaches aims to get new insights in the mechanisms underlying muscle degeneration in order to propose new hypotheses for the understanding of DMD