Les cellules souches musculaires adultes, appelées cellules satellites, sont les principaux acteurs de la régénération musculaire et constituent donc un enjeu médical majeur, notamment pour le traitement des dystrophies musculaires. Dans certaines dystrophies, ainsi que dans le vieillissement musculaire, un stress oxydant important associé à une perturbation de l'homéostasie protéique ont été décrits. L'objectif de cette thèse est de déterminer le rôle d'un des seuls systèmes de réparation des protéines oxydées, les enzymes méthionine sulfoxyde réductases ou Msr, dans la fonction des cellules satellites au cours du processus de régénération ainsi que leur rôle dans la protection des fibres musculaires au cours du vieillissement. Nos résultats montrent qu'en absence de Msr, l'augmentation des niveaux d'espèces réactives de l'oxygène et l'accumulation de protéines oxydées entraînent des défauts de prolifération associés à la sénescence des myoblastes primaires en culture. Dans la fibre, nous avons observé une diminution de l'activité des Msr avec l'âge, ce qui pourrait contribuer à l'accumulation de dommages irréversibles présents dans les fibres musculaires âgées. Cette thèse constitue la première étude des protéines Msr dans le muscle squelettique. Nos résultats ont permis d'établir le rôle de la protéine MsrA dans la régulation des cellules souches musculaires au cours du processus de régénération et révèlent qu'une modulation de ce système pourrait représenter une cible thérapeutique intéressante, en complément des thérapies cellulaires déjà utilisées, pour le traitement de désordres musculaires tels que les dystrophies. / Muscle regeneration and the muscle adult stem cells, also known as satellite cells, that are engaged in this process are a major biomedical issue, mainly for the treatment of muscular dystrophies. In some muscular dystrophies as for muscle ageing, an important oxidative stress state and an altered protein homeostasis have been described. The objective of this thesis is to determine the importance of methionine sulfoxide reductase (Msr) enzymes, one of the few enzymatic systems involved in the reduction of protein oxidation, in satellite cells function during regeneration as well as their role in skeletal muscle fibres protection during muscle ageing. Our results show that in the absence of Msr enzymes, cultured primary myoblasts revealed increased reactive oxygen species content and accumulation of oxidised proteins that result in decreased myoblasts proliferative capacities associated to a senescence state. Regarding the study of muscle fibres, we found a decrease in Msr activity during ageing, which could contribute to the accumulation of irreversible damages observed in aged muscle fibres. This thesis is the first study of Msr proteins in skeletal muscle tissue. Our results demonstrate the importance of MsrA enzymes in the regulation of satellite cells function during muscle regeneration and suggest that it could represent an interesting therapeutic target in complement of the cell therapies already used for the treatment of muscle disorders such as muscular dystrophies.

Pw1/Peg3 est un gène d’empreinte parental exprimé par l’allèle paternel. Il est exprimé dans l’ensemble des populations de cellules souches, y compris les cellules satellites du tissu musculaire. Nous avons découvert que la perte constitutive de Pw1/Peg3 entraîne une perte de la masse musculaire, résultat d’une diminution du nombre de fibres musculaires. Le nombre de fibres réduit est présent dès la naissance. De plus, les souris double KO ont un nombre de fibres encore inférieur, suggérant que l’allèle maternel est fonctionnel pendant le développement pré-natal, et des analyses de souris hybrides C57BL6J/CAST/Ei révèlent une expression bi-allélique de Pw1/Peg3 d’environ 10%. Pw1/Peg3 est également fortement exprimé après blessure du muscle squelettique. Chez les souris Pw1/Peg3 KO, nous avons observé que les cellules satellites montrent une réduction de leur capacité d’auto-renouvèlement à la suite d’une blessure. Pw1/Peg3 est également exprimé dans une sous-population de cellules souches interstitielles, les PICS. Afin de déterminer le rôle spécifique de Pw1/Peg3 dans les cellules satellites nous avons croisé notre allèle conditionnel Pw1/Peg3 avec la lignée Pax7-Cre-ER. Ces souris ont un phénotype présentant un défaut de régénération prononcé, montrant ainsi un rôle clair et direct de Pw1/Peg3 dans la fonction régénératrice des cellules satellites. En résumé, l’ensemble de ces données montre un rôle de Pw1/Peg3 dans le développement fœtal et la détermination du nombre de fibres musculaires par son action dans l’auto-renouvellement des cellules satellites du tissu musculaire. / Pw1/Peg3 is a parentally imprinted gene expressed from the paternal allele. It is expressed in all adult progenitor/stem cell populations examined to date including muscle satellite cells. We examined the impact of loss-of-function of Pw1/Peg3 in skeletal muscle, a tissue that greatly contributes to body mass. We found that constitutive loss of Pw1/Peg3 results in reduced muscle mass resulting from a decrease in muscle fiber number. The reduced fiber number is present at birth. Mice lacking both the paternal and maternal alleles display a lower fiber number as compared to mice carrying the paternal deletion, suggesting that the maternal allele is functional during prenatal development. Hybrid analyses (C57BL6J and Cast/Ei) of muscle tissue reveal a bi-allelic expression of Pw1/Peg3 around 10%. Pw1/Peg3 is strongly up-regulated in response to muscle injury. Using the constitutive Pw1/Peg3 knock out mouse, we observed that satellite cells display a reduced self-renewal capacity following muscle injury. Pw1/Peg3 is expressed in satellite cells as well as a subset of muscle interstitial cells (PICs). To determine the specific role of Pw1/Peg3 in satellite cells, we crossed our conditional Pw1/Peg3 allele with the Pax7-CreER line. Interestingly, these mice displayed a more pronounced phenotype of impaired regeneration revealing a clear and direct role for Pw1/Peg3 in satellite cells. Taken together, our data show that Pw1/Peg3 plays a role during fetal development in the determination of muscle fiber number that is gene-dosage dependent and plays a specific role in muscle satellite cell self-renewal.

Muscle stem cells self-renew to maintain the long-term capacity for skeletal muscles to regenerate. However, the homeostatic regulation of muscle stem cell self-renewal is poorly understood. By utilizing high-throughput screening and transcriptomic approaches, we identify the critical function of dystrophin, the epidermal growth factor receptor (EGFR), and fibronectin in the establishment of cell polarity and in determining symmetric and asymmetric modes of muscle stem cell self-renewal. These findings reveal an orchestrated network of paracrine signaling that regulate muscle stem cell homeostasis during regeneration and have profound implications for the pathogenesis and development of therapies for Duchenne muscular dystrophy.

MLK3 est une ser/thr MAP3K qui active la voie de signalisation des MAPKs dans différents types cellulaires. GSK3β interagit et active MLK3 en la phosphorylant sur le residue ser 792. Cependant, le rôle de MLK3 ainsi que l’interaction entre MLK3 et GSK3β n’ont pas été précédemment étudiés dans le muscle squelettique. La croissance post-natale du muscle et la régénération musculaire chez l’adulte sont dépendantes de l’accrétion de myonoyaux, un processus médié par les cellules satellites qui prolifèrent, se différencient puis fusionnent aux fibres préexistantes. Durant ma thèse, j’ai démontré que GSK3β agit en amont de MLK3 pour induire la prolifération des cellules satellites, et cela par l’activation de la voie de signalisation MLK3-p38γ MAPK. In vivo, les muscles de souris déficientes injectés par la CTX montrent une diminution du nombre de cellules satellites prolifératrices Pax7+/ki67+, ainsi qu’une accélération du processus de régénération. En conclusion, mes résultats évoquent un nouveau rôle de MLK3 dans le muscle squelettique pouvant servir pour vaincre les dystrophies musculaire. / MLK3 is a Ser/Thr MAP3K, which activates MAPKs signalling pathways in different cell types. The Ser/Thr kinase GSK3-β directly phosphorylate Ser 792 residue and activate MLK3. Since neither the role of MLK3, nor GSK3-β -MLK3 interaction have been previously investigated in muscle, the aim of my thesis was to elucidate their contribution in the regulation of muscle mass and physiology.Skeletal muscle post-natal growth and adult regeneration relies on satellite cell-mediated myonuclear accretion, during which, activated satellite cells, proliferate, differentiate and fuse with preexisting myotubes.I have demonstrated that in skeletal muscle, GSK3-β acts upstream of MLK3 to induce satellite cells proliferation through the induction of MLK3-p38γ MAPK signalling. Similarly, in vivo CTX-induced TA damage in MLK3 KO mice resulted in decreased number of proliferating Pax7+/ki67+ satellite cells, with a rapid muscle regeneration ability.These data suggest provide a yet unknown role of MLK3 in skeletal muscle tissue that could help in curing age-related muscle dystrophies.

Submitted by Nadir Basilio (nadirsb@uninove.br) on 2018-07-18T21:12:26Z No. of bitstreams: 1 Carla Bernardo Soldera.pdf: 1125219 bytes, checksum: a9bf43bd0d44898b4a48ec77b3f45001 (MD5) / Made available in DSpace on 2018-07-18T21:12:26Z (GMT). No. of bitstreams: 1 Carla Bernardo Soldera.pdf: 1125219 bytes, checksum: a9bf43bd0d44898b4a48ec77b3f45001 (MD5) Previous issue date: 2017-12-15 / Peripheral nerve lesions (LNP) do not clinically present a risk of death to the individual but may result in motor and sensory disturbances altering the function of the affected limb. Phototherapy using low level laser has demonstrated positive effects for the nervous and muscle repair process after different types of injury and little is known about the effects of light emitting diode (LED) therapy. Objective: To analyze the effects of LED on the nervous and muscular repair of Wistar rats after sciatic nerve crush injury. Methodology: 85 Wistar rats, weighing 200-250g, in 5 groups: Control: without any procedure; Injury: carried out only the crushing of the Left Sciatic Nerve (LSN); Injury + LEDn: LSN crushing and LED irradiation in the area corresponding to the nerve injury; Injury + LEDmm: LSN and LED crushing in Tibial Anterior muscle; Injury + LEDn + LEDmm: NSE crushing and LED irradiation in the area corresponding to nerve injury and muscle. The application of the LED in the nervous region was performed with the following parameters: wavelength of 808nm, beam area 1 cm2, average power 40Mw, power density 0.04 W/cm2, energy density 0.8 J/cm2, energy per point 0.8J , total of points 4, time per point 20sec, total time 80sec, energy per point 3.2J and in muscle region was used wavelength of 808nm, beam area 1 cm2, average power 40Mw, power density 0.04 W/ cm2, density of energy 0.4 J/ cm2, energy per point 0.4J, total of points 8, time per point 10sec, total time 80sec, energy per point 3.2J. At the end of the experimental periods, the gait analysis and the mechanical hyperalgesia test were performed. At the end of the experimental periods, gait analysis was performed using the Sciatic Function Index (IFC), as well as the analysis of mechanical hyperalgesia using the von Frey test using the pressure analgesimeter with transducer. After the euthanasia of the animals, the tibial muscles, left and right, were removed and weighed in a semi-analytical balance to determine the degree of muscular atrophy and the muscle mass ratio was calculated. Result: After the IFC, within 7 days, all groups treated with LED showed an improvement in gait compared to the lesion group. The group LEDn was the one that presented the best result compared to the control group. After 14 days, the group LEDn and LEDnm presented similar values to the control group. Regarding the muscular atrophy index, in the 7-day period, all the groups treated with LED showed a decrease of the index in relation to the Control group. In 14 days, the LED groups showed an increase in relation to the Injury group. At 21 and 28 days, the injured groups showed a decrease in relation to the Control group. Only the LEDnm group showed a decrease compared to the Injury group. Regarding mechanical hyperalgesia, the results showed that in 7 days, the LEDn group was the one that presented the best result compared to the control group. At 14 days, the LEDn and LEDm groups showed an increase in the threshold, requiring a greater pressure to promote an allergic response compared to the control group, making them more resistant to the stimuli. At 28 days, all lesioned and treated groups showed an increase in hyperalgesia in relation to the control group. Conclusion: We can conclude that LED increased gait functionality assessed by IFC after 1 and 2 weeks post LNP, especially when it was used in the nerve region associated or not to the muscle region, induced an increase in muscle mass in relation to the animals that did not receive treatment in the period of 2 weeks post LNP and in the 2 week period post LNP provided an increase in the pain threshold compared to the control group, requiring a nociceptive stimulus of greater intensity to generate the pain stimulus indicating a better recovery. / As lesões nervosas periféricas (LNP) não apresentam clinicamente um risco de morte ao indivíduo, porém podem resultar em distúrbios motores e sensoriais alterando a funcionalidade do membro afetado. A fototerapia utilizando laser de baixa potência (LBP) tem demonstrado efeitos positivos para o processo de reparo nervoso e muscular após diferentes tipos de lesão e pouco se conhece a respeito dos efeitos da terapia com diodo emissor de luz (LED, do inglês light emitting diode). Objetivo: Analisar os efeitos do LED sobre o reparo nervoso e muscular de ratos Wistar pós lesão por esmagamento do nervo ciático. Metodologia: foram utilizados 85 ratos Wistar, pesando 200-250g, em 5 grupos: Controle: sem nenhum procedimento; Lesão: realizado apenas o esmagamento do Nervo Ciático Esquerdo (NCE); Lesão+LEDn: esmagamento do NCE e irradiação LED na área correspondente à lesão nervosa; Lesão+LEDm: esmagamento do NCE e LED no músculo Tibial Anterior; Lesão+LEDnm: esmagamento do NCE e irradiação LED na área correspondente à lesão nervosa e músculo. A aplicação do LED em região nervosa foi realizada com os seguintes parâmetros: comprimento de onda de 808nm, área do feixe 1cm2, potência média 40Mw, densidade de potência 0.04W/ cm2, densidade de energia 0.8 J/cm2, energia por ponto 0.8J, total de pontos 4, tempo por ponto 20seg, tempo total 80seg, energia por ponto 3.2J e em região muscular foi utilizado comprimento de onda de 808nm, área do feixe 1cm2, potência média 40Mw, densidade de potência 0.04W/ cm2, densidade de energia 0.4 J/cm2, energia por ponto 0.4J, total de pontos 8, tempo por ponto 10seg, tempo total 80seg, energia por ponto 3.2J. Ao término dos períodos experimentais, foi realizada a análise de marcha utilizando o Índice Funcional Ciático (IFC), bem como a análise da hiperalgesia mecânica através do teste de von Frey utilizando o analgesímetro de pressão com transdutor. Após a eutanásia dos animais os músculos Tibial Anterior direito e esquerdo foram removidos e pesados em uma balança semi-analítica para determinação do grau de atrofia muscular sendo calculada a relação de massa muscular. Resultado: Após a realização do IFC, no período de 7 dias, todos os grupos tratados com LED apresentaram uma melhora da marcha em relação ao grupo Lesão. O grupo LEDn foi o que apresentou o melhor resultado comparado ao grupo controle. Após 14 dias, o grupo LEDn e LEDnm apresentaram valores semelhantes ao grupo controle. Já em relação ao índice de atrofia muscular, no período de 7 dias, todos os grupos tratados com LED demonstraram uma diminuição do índice em relação ao grupo Controle. Em 14 dias, os grupos LED demonstraram um aumento em relação ao grupo Lesão. Em 21 e 28 dias, os grupos lesionados demonstraram uma diminuição em relação ao grupo Controle. Apenas o grupo LEDnm apresentou uma diminuição em relação ao grupo Lesão. No que diz respeito a hiperalgesia mecânica, os resultados obtidos demonstraram que em 7 dias, o grupo LEDn foi o que apresentou o melhor resultado comparado ao grupo controle. Em 14 dias, os grupos LEDn e LEDm apresentaram um aumento no limiar sendo necessário uma pressão maior para promover uma resposta álgica comparados ao grupo controle, tornando-os mais resistentes aos estímulos. Em 28 dias todos os grupos lesionados e tratados apresentaram um aumento da hiperalgesia em relação ao grupo controle. Conclusão: O LED aumentou a funcionalidade da marcha avaliada pelo IFC após 1 e 2 semanas pós LNP, especialmente quando foi usado na região nervosa associada ou não à região muscular, induziu um aumento na massa muscular em relação aos animais que não receberam tratamento no período de 2 semanas pós LNP e proporcionou um aumento no limiar álgico comparado ao grupo controle no período de 2 semanas pós LNP, sendo necessário um estímulo nociceptivo de maior intensidade para gerar o estímulo doloroso indicando uma melhor recuperação.

During aging there is a decline in (MuSCs) and muscle regeneration, though the underlying reason is unknown. Interestingly, mitochondrial fragmentation is a common feature in aging, however, how this impacts MuSC function and maintenance has not been investigated. To address the effect of mitochondrial fragmentation in MuSCs, we generated a knockout mouse model using the Pax7CreERT2 inducible system to target deletion of the mitochondrial fusion protein Opa1 specifically within MuSCs (Opa1-KO). Analysis of MuSC function following muscle injury revealed a defect in the regenerative potential of Opa1-KO MuSCs. Moreover, following injury there was a substantial decrease in the number of MuSC in Opa1-KO animals with a concomitant increase in the number of committing cells, illustrating that loss of Opa1 drives MuSC towards commitment at the expense of self-renewal. Furthermore, loss of Opa1 in MuSCs alters the quiescence state, priming MuSCs for activation, as indicated by a reduction in quiescence-related genes, increased EdU incorporation, and enhanced cell cycle kinetics. To address the impact of mitochondrial dysfunction on muscle stem cell capacity, we generated a model of chronic Opa1 loss. Analysis of muscle stem cell function 3 months after Opa1 ablation revealed mitochondrial dysfunction and a defect in proliferation upon activation, leading to failed muscle regeneration. These data are the first to demonstrate a novel role for mitochondrial structure in the regulation of MuSC maintenance and regenerative capacity.

No description available.

Les macrophages peuvent transiter entre les états pro et anti-inflammatoires, un processus appelé de polarisation. Les molécules sécrétées par les macrophages sont capables d'induire différents profils métaboliques. Les analyses transcriptomiques de macrophages pro et anti-inflammatoires humains ont identifié nouvelles molécules avec un peptide sécrétoire. Parmi ces candidates, les sélénoprotéines étaient l’une des plus exprimés dans les macrophages anti-inflammatoires. Ainsi, nous évaluons l’impact des sélénoprotéines sur la polarisation des macrophages, secondaires à l’inflammation et leur implication au cours de la régénération musculaire. Une fois établi que les cytokines stimulent les transitions des macrophages, nous avons utilisé IFN-gamma et IL10 pour explorer ces différents profils inflammatoires in vitro. Les macrophages dérivés de la moelle osseuse de WT et de sélénoprotéines KO ont été polarisés avec les deux cytokines pour obtenir un phénotype pro et anti-inflammatoire, respectivement. Nos résultats ont montré que, en absence de sélénoprotéines, les macrophages réduisaient leur capacité à migrer d'un état d'activation à l’autre par rapport au contrôle, soulignant ainsi l'importance de ces molécules pour contrôler les états d’alternance des macrophages. Le modèle de lésion en réponse à la cardiotoxine a été utilisé pour examiner, in vivo, la capacité des macrophages à modifier leur phénotype au cours de la régénération du muscle squelettique. Trois jours après une lésion, la population pro est remplacé par une anti-inflammatoire, comme l'a déjà montré l'analyse par cytométrie en flux. Cependant, les modèles de macrophages pro-inflammatoires sélénoprotéines KO étaient présent trois fois plus nombreux relativement à la population anti-inflammatoire, indiquant que ces macrophages n’ont pas acquis le phénotype anti-inflammatoire. De plus, nous évaluons la fonction des macrophages en absence de sélénoprotéines. Suite à la polarisation avec les cytokines, décrites ci-dessus, les expériences ont démontré que les macrophages anti-inflammatoires WT favorisaient la fusion des myoblastes, alors que les sélénoprotéines KO n'étaient pas en mesure de maintenir cette fusion. En conclusion, les sélénoprotéines modulent la polarisation des macrophages, impliquant leur capacité à acquérir différents phénotypes in vitro et in vivo, ainsi que leurs effets sur la fusion des myoblastes / Macrophages can go through transitions between pro and anti-inflammatory states, one process called polarization skewing. Molecules secreted by macrophages are able to induce different metabolic profiles. Transcriptomic analyses of human pro and anti-inflammatory macrophages identified new molecules with a secretory peptide. Selenoproteins were one of the most expressed in anti-inflammatory macrophages. Thus, we evaluate the respective roles of selenoproteins on macrophage polarization parameters in inflammation and their implication in regenerative processes. Once established that cytokines largely spur macrophage transitions we used IFN-gamma and IL10 to explore these different inflammatory profiles in vitro. Bone marrow derived macrophages from WT and selenoproteins KO models were polarized with both cytokines to obtain a pro and anti-inflammatory phenotype, respectively. Our results showed that without selenoproteins, macrophages had impairment of their capacity to switch from one activation state to another as compared with the control, emphasizing the importance of these molecules to control macrophage transitional states. The cardiotoxin injury model was use to in vivo examine the macrophages capability to switch their phenotype during skeletal muscle regeneration. Three days after an injury pro is replaced by anti-inflammatory population, as has already been shown by flow cytometry analysis. However, macrophages from selenoproteins KO presented three-fold increase of pro-inflammatory macrophages while anti-inflammatory population decreased, indicating that they did not acquire an anti-inflammatory phenotype. In addition, we evaluate the macrophage function in absence of selenoproteins. After polarization with cytokines, experiments demonstrated that WT anti-inflammatory macrophages promoted myoblast fusion, whereas selenoproteins KO were not able to sustain their fusion. In conclusion, selenoproteins modulate macrophage polarization implicating their ability to acquire different phenotypes in vitro and in vivo as well as their effects on myoblast fusion

No description available.

Le muscle strié squelettique est un tissu richement vascularisé. Au delà de l'apport en oxygène et en nutriments, de nouvelles fonctions des vaisseaux ont été récemment identifiées, par le biais des interactions établies entre les cellules du vaisseau (cellules endothéliales) et les cellules du muscle, en particulier les cellules souches musculaires (cellules satellites). Celles-ci interagissent étroitement avec les cellules endothéliales pour leur expansion et leur différenciation, puis avec les cellules péri-endothéliales pour leur auto-renouvellement et leur retour à la quiescence. Les vaisseaux participent ainsi au contrôle de l’homéostasie du muscle squelettique. Grâce à ces interactions, les cellules vasculaires jouent donc un rôle central dans le remodelage tissulaire après un phénomène destructif, survenant par exemple au cours d’un trauma ou d’une myopathie. Pour étudier, les mécanismes de la plasticité vasculaire au cours du remodelage tissulaire, deux situations paradigmatiques de muscle en régénération chez l’enfant : la dermatomyosite juvénile (DMJ) et la dystrophie musculaire de Duchenne (DMD) ont été étudiées. Il existe, dans ces deux pathologies une souffrance musculaire associée à des cycles de nécrose/régénération. Elles se différencient par leur plasticité vasculaire et par leur évolution. En effet, la DMJ, la myopathie inflammatoire la plus fréquente de l’enfant est caractérisée par une vasculopathie avec perte en capillaires. L’évolution peut être favorable avec restitution ad integrum du muscle. La DMD est une myopathie génétique conduisant à une dégradation progressive de la force musculaire associée à une néovascularisation compensatrice. Le volet clinique/histologique incluant une analyse multiparamétrique des critères évolutifs cliniques et de réponse thérapeutique couplée à une réévaluation des données histologiques de la DMJ (analyse morphométrique des muscles DMJ) a permis de montrer qu’il existait des sous groupes phénotypiques homogènes de sévérité différente dans la DMJ. Le degré de sévérité clinique est relié à la gravité de la vasculopathie musculaire Par ailleurs, des marqueurs cliniques et histologiques simples permettant de repérer au diagnostic les patients nécessitant une escalade thérapeutique rapide (CMAS>34, atteinte gastrointestinale, fibrose endomysiale musculaire au diagnostic) ont été identifiés. Le volet cellulaire a permis l’identification in vitro des interactions cellulaires spécifiques et différentielles des myoblastes issues de patients DMD et DMJ sur les cellules endothéliales normales par l’analyse de leur rôle sur la prolifération, migration et différenciation des cellules vasculaires. Dans la DMD, les myoblastes entrainent une réponse angiogénique importante mais non efficace (néovascularisation anarchique). Dans la DMJ, les myoblastes participent efficacement à la reconstruction vasculaire notamment via la sécrétion de facteurs proangiogéniques. Ces résultats ont été renforcés par analyse transcriptomique effectuée à partir de cellules endothéliales et satellites isolées de muscles de patients confirmant le rôle central de la vasculopathie associée à un contexte inflammatoire spécifique lié à l’interféron dans la physiopathologie de la DMJ et montrant dans la DMD une dérégulation de l’homéostasie normale des interactions vaisseau-muscle avec mise en jeu d’un remodelage tissulaire non efficace. Ces données permettent d'identifier de nouvelles fonctions des cellules vasculaires dans le remodelage du muscle strié squelettique au cours des pathologies musculaires de l'enfant, et devraient ouvrir la voie à de nouvelles approches thérapeutiques. / Skeletal muscle is highly vascularised. Beyond oxygen and nutriment supply, new functions for vessels have been recently identified, through the interactions that vessel cells (endothelial cells) establish with muscle cells, particularly with muscle stem cells (satellite cells). These latter closely interact with endothelial cells for their expansion and their differentiation, then with periendothelial cells for their self-renewal and return to quiescence. During skeletal muscle regeneration endothelial cells reciprocally interact with myogenic cells by direct contact or by releasing soluble factors to promote both myogenesis and angiogenesis processes. Skeletal muscle regeneration typically occurs as a result of a trauma or disease, such as congenital or myopathies. To better understand the role of vessel plasticity in tissue remodeling, we took advantage of two muscular disorders that could be considered as paradigmatic situations of regenerating skeletal muscle in the child: Juvenile Dermatomyositis (JDM), the most frequent inflammatory myopathy and Duchenne Muscular Dystrophy (DMD), the most common type of muscular dystrophy. Although these two muscular disorders share, at the tissue level, similar mechanisms of necrosis-inflammation, they differ regarding the vessel domain. In JDM patients, microvascular changes consist in a destruction of endothelial cells assessed by focal capillary loss. This capillary bed destruction is transient. The tissue remodeling is efficient and muscle may progressively recover its function. By contrast, in DMD, despite an increase of vessels density in an attempt to improve the muscle perfusion, the muscle function progressively alters with age. We identified clinical and pathological markers of severity and predictive factors for poor clinical outcome in JDM by computing a comprehensive initial and follow-up clinical data set with deltoid muscle biopsy alterations controlled by age-based analysis of the deltoid muscle capillarization. We demonstrated that JDM can be divided into two distinctive clinical subgroups. The severe clinical presentation and outcome are linked to vasculopathy. Furthermore, a set of simple predictors (CMAS<34, gastrointestinal involvement, muscle endomysial fibrosis at disease onset) allow early recognition of patients needing rapid therapeutic escalation with more potent drugs. We studied in vitro the specific cell interactions between myogenic cells issued from JDM and DMD patients and normal endothelial cells to explore whether myogenic cells participate to the vessel remodeling observed in the two pathologies. We demonstrated that MPCs possessed angiogenic properties depending on the pathological environment. In DMD, MPCs promoted the development of establishment of an anarchic, although strong, EC stimulation, leading to the formation of weakly functional vessels. In JDM, MPCs enhanced the vessel reconstruction via the secretion of proangiogenic factors. This functional analysis was supported by the transcriptomic analysis consistent with a central vasculopathy in JDM including a strong and specific response to an inflammatory environment. On the contrary, DMD cells presented an unbalanced homeostasis with deregulation of several processes including muscle and vessel development with attempts to recover neuromuscular system by MPCs. To summarize, our data should allow the definition of new functions of vessel cells in skeletal muscle remodelling during muscle pathologies of the child that will open the way to explore new therapeutic options and to gain further insights in the pathogenesis of these diseases.