Diss. (sammanfattning) Umeå : Umeå universitet, 2006. / Härtill 5 uppsatser.

Thesis (Ph.D.)--University of Alberta, 2009. / A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy, Faculty of Physical Education and Recreation. "(Nee: Martinuk)". Title from pdf file main screen (viewed on October 31, 2009). Includes bibliographical references.

Regeneration of adult skeletal muscle relies upon a population of quiescent myogenic progenitor cells, called satellite cells (SCs). Upon injury, SCs activate, proliferate, differentiate and fuse to make new myofibers or to repair damaged ones. SCs can also self-renew to repopulate the SC niche. The balance between differentiation and self-renewal is critical to maintain muscle homeostasis and changes in this equilibrium can lead to chronic muscle degeneration. For example, Duchenne’s muscular dystrophy (DMD) is characterized by rounds of muscle degeneration and regeneration leading to increased muscle wasting. One approach to treat DMD is transplantation of SCs. For this treatment to be viable, transplanted cells must contribute to repairing injured muscle and repopulating the SC niche. Here, we show that the transcription factor CCAAT/Enhancer Binding Protein beta (C/EBPβ) regulates SC function. C/EBPβ is down-regulated during differentiation and persistent expression of C/EBPβ inhibits differentiation and expression of the myogenic regulatory factors MyoD and Myogenin. C/EBPβ also promotes Pax7 expression by directly binding to and regulating Pax7 transcription. Using genetic tools to conditionally excise C/EBPβ expression in SCs, we found that C/EBPβ-null SCs lose quiescence and precociously differentiate at the expense of self-renewal. After a single injury, C/EBPβ-deficient SCs failed to self-renew, resulting in impaired muscle repair after a second injury. C/EBPβ-induced quiescence also requires upregulation of caveolin-1. Furthermore, pharmacological manipulation of C/EBPβ expression with the phosphodiesterase inhibitor, isobutylmethylxanthine (IBMX), increased the number of cells available for transplantation into dystrophic muscle and enhanced the expression of stem cell markers in a C/EBPβ-dependent fashion. IBMX treatment improved cell survival and migration, engraftment into the SC niche and repair of dystrophic muscle. Together, these results demonstrate that C/EBPβ is an important regulator of SC function and that pharmacological manipulation of C/EBPβ improves culture conditions for the expansion and selection of SCs available for cell therapy for the treatment of muscular dystrophies.

Óxido nítrico (NO) é uma molécula que exerce uma multiplicidade de funções fisiológicas importantes que vêm sendo estudadas em diversos tecidos. No entanto, o papel do NO em processos fisiológicos e patológicos no músculo estriado é pouco conhecido, apesar de algumas evidências apontarem para uma função de regulação redox e interação com células satélites progenitoras. Neste estudo avaliamos a participação do NO na regeneração muscular em um modelo de inflamação aguda in vivo. O trauma muscular foi induzido por um aparelho similar a uma prensa com impacto direto sobre o gastrocnêmio. Foram utilizados 40 ratos, Wistar, divididos em quatro grupos: (i) controle (CO); (ii) falso (sham) trauma; (iii) trauma; (iv) trauma com exposição ao nitro-L-arginina metil éster (L-NAME), um inibidor da sintase do óxido nítrico, em dois tempos experimentais: 24 horas e 7 dias após lesão. Vinte e quatro horas após o trauma, o músculo lesionado apresentava intensa vasodilatação e reação inflamatória na análise histológica, lipoperoxidação tecidual e estresse nitrosativo, aumento do mRNA das citocinas próinflamatórias (IL-1β, IL-6, iNOS), metaloproteinase-2, expressão proteica de iNOS e MMP-2, ativação do NF-κB e intensa atividade proliferativa. O tratamento com LNAME diminuiu significativamente os achados das alterações histológicas e moleculares em 24 horas após a lesão e, sete dias após o trauma, houve um aumento na expressão do TGF-β, na deposição de colágeno e proliferação celular. Entretanto, o grupo tratado com L-NAME apresentou uma maior expressão de TGF-β e de deposição de colágeno quando comparado ao grupo trauma e proliferação celular semelhante. Estes resultados indicam que a lesão muscular é associada com a ativação do sistema NO, o qual parece estar envolvido no equilíbrio entre os processos de regeneração e fibrose durante o reparo. / Nitric oxide (NO) is a molecule that carries a variety of important physiological functions that have been studied in various tissues. However, the role of NO in physiological and pathological processes in striated muscle is poorly known, although some evidence suggests a role of redox regulation and interaction with progenitor satellite cells. We evaluated the role of NO in muscle regeneration in a model of acute inflammation in vivo. The muscle trauma was induced by a device similar to a press with a direct impact on the gastrocnemius. A total of 40 rats were divided into four groups: (i) control (CO), (ii) sham trauma, (iii) trauma, (iv) trauma + L-NAME, an inhibitor of nitric oxide synthase in two experimental phases: 24 hours and 7 days after injury. Twenty-four hours after the trauma, the injured muscle showed intense vasodilatation and inflammation in the histological analysis, tissue lipid peroxidation and nitrosative stress, activation of NF-κB, increased mRNA of pro-inflammatory, (IL- 1β, IL-6, iNOS), metalloproteinase-2 and HGF, and increased total cell proliferation. The administration of the L-NAME significantly reduced iNOS, MMP-2 and activation of NF-κB reduced the histological and molecular findings 24 hours after injury, and 7 days after injury, there was an increase in the expression of TGF-β, collagen deposition, and total cell proliferation. However, the L-NAME group showed increased expression and collagen deposition when compared to the trauma and similar total cell proliferation. These results indicate that muscle injury is associated with activation of the NO, which seems to be involved in the balance between the processes of regeneration and fibrosis during the repair.

Óxido nítrico (NO) é uma molécula que exerce uma multiplicidade de funções fisiológicas importantes que vêm sendo estudadas em diversos tecidos. No entanto, o papel do NO em processos fisiológicos e patológicos no músculo estriado é pouco conhecido, apesar de algumas evidências apontarem para uma função de regulação redox e interação com células satélites progenitoras. Neste estudo avaliamos a participação do NO na regeneração muscular em um modelo de inflamação aguda in vivo. O trauma muscular foi induzido por um aparelho similar a uma prensa com impacto direto sobre o gastrocnêmio. Foram utilizados 40 ratos, Wistar, divididos em quatro grupos: (i) controle (CO); (ii) falso (sham) trauma; (iii) trauma; (iv) trauma com exposição ao nitro-L-arginina metil éster (L-NAME), um inibidor da sintase do óxido nítrico, em dois tempos experimentais: 24 horas e 7 dias após lesão. Vinte e quatro horas após o trauma, o músculo lesionado apresentava intensa vasodilatação e reação inflamatória na análise histológica, lipoperoxidação tecidual e estresse nitrosativo, aumento do mRNA das citocinas próinflamatórias (IL-1β, IL-6, iNOS), metaloproteinase-2, expressão proteica de iNOS e MMP-2, ativação do NF-κB e intensa atividade proliferativa. O tratamento com LNAME diminuiu significativamente os achados das alterações histológicas e moleculares em 24 horas após a lesão e, sete dias após o trauma, houve um aumento na expressão do TGF-β, na deposição de colágeno e proliferação celular. Entretanto, o grupo tratado com L-NAME apresentou uma maior expressão de TGF-β e de deposição de colágeno quando comparado ao grupo trauma e proliferação celular semelhante. Estes resultados indicam que a lesão muscular é associada com a ativação do sistema NO, o qual parece estar envolvido no equilíbrio entre os processos de regeneração e fibrose durante o reparo. / Nitric oxide (NO) is a molecule that carries a variety of important physiological functions that have been studied in various tissues. However, the role of NO in physiological and pathological processes in striated muscle is poorly known, although some evidence suggests a role of redox regulation and interaction with progenitor satellite cells. We evaluated the role of NO in muscle regeneration in a model of acute inflammation in vivo. The muscle trauma was induced by a device similar to a press with a direct impact on the gastrocnemius. A total of 40 rats were divided into four groups: (i) control (CO), (ii) sham trauma, (iii) trauma, (iv) trauma + L-NAME, an inhibitor of nitric oxide synthase in two experimental phases: 24 hours and 7 days after injury. Twenty-four hours after the trauma, the injured muscle showed intense vasodilatation and inflammation in the histological analysis, tissue lipid peroxidation and nitrosative stress, activation of NF-κB, increased mRNA of pro-inflammatory, (IL- 1β, IL-6, iNOS), metalloproteinase-2 and HGF, and increased total cell proliferation. The administration of the L-NAME significantly reduced iNOS, MMP-2 and activation of NF-κB reduced the histological and molecular findings 24 hours after injury, and 7 days after injury, there was an increase in the expression of TGF-β, collagen deposition, and total cell proliferation. However, the L-NAME group showed increased expression and collagen deposition when compared to the trauma and similar total cell proliferation. These results indicate that muscle injury is associated with activation of the NO, which seems to be involved in the balance between the processes of regeneration and fibrosis during the repair.

Le déclin de la masse musculaire au cours du vieillissement physiologique, appelé sarcopénie, est un phénomène progressif dont les conséquences sur la santé peuvent être désastreuses. Les cellules souches assurant l’homéostasie musculaire, appelées cellules satellites, perdent progressivement leur capacité́ à régénérer le tissu endommagé. Les mécanismes précis de ce processus dégénératif sont encore mal connus et semblent impliquer des altérations des marques épigénétiques qui régulent l’expression des gènes des cellules satellites.Cette thèse a porté sur les mécanismes conduisant à cette incapacité progressive des cellules satellites à fabriquer de nouvelles fibres musculaires avec l’âge. Les travaux ont été menés autour de deux axes : le rôle d’UTX dans le contrôle de l’expression des gènes musculaires et plus particulièrement leur épissage ; les conséquences des altérations du niveau de triméthylation de la lysine 27 de l’histone H3 (H3K27me3) régulé par UTX dans les cellules satellites de souris dites « gériatriques ».Nous avons ainsi démontré qu’UTX était nécessaire à différentes étapes du processus de différenciation en permettant d’une part d’activer la transcription des gènes et d’autre part de réguler leurs épissages alternatifs en régulant plusieurs facteurs d’épissage.Chez les individus âgés, l’expression d’UTX est altérée avec pour conséquence une modification du profil épigénétique des cellules satellites et une perturbation de leur programme d’expression génique. Enfin, des résultats préliminaires suggèrent qu’UTX participe aussi au « syndrome inflammatoire chronique » observé chez les souris âgées, en régulant l’expression de facteurs pro et anti-inflammatoires comme l’IL-6. Ces travaux ont permis de mettre en évidence le rôle d’UTX à différents niveaux de régulation de l’expression des gènes dans les cellules musculaires et d’expliquer en partie les défauts de régénération liés à l’âge. / The decline in muscle mass during physiological aging, called sarcopenia, is a progressive phenomenon whose consequences on health can be disastrous. Muscle stem cells, also called satellite cells, ensure muscle homeostasis. They gradually lose the ability to regenerate damaged tissue with age. The precise mechanisms of this degenerative process are still poorly understood but it seems to imply alterations of the epigenetic marks regulating gene expression in satellite cells.This thesis has focused on the mechanisms leading to this progressive incapacity of the satellite cells to make new muscle fibers with age. The work is divided in two major parts: the role of UTX on the expression of muscle genes and more particularly their splicing and the consequences of the alterations in the trimethylation level of histone H3 lysine 27 (H3K27me3) regulated by UTX in the satellite cells of so-called "geriatric" mice.We have thus demonstrated that UTX is necessary at different stages of the differentiation process to activate gene transcription and alternative splicing.In elderly individuals, the expression of UTX is altered, resulting in modifications of the epigenetic profile of the satellite cells and a disruption of their gene expression program. Finally, preliminary results suggest that UTX also participates in the "chronic inflammatory syndrome" observed in elderly mice, regulating the expression of pro-inflammatory factors such as IL-6.This work allowed us to highlight the role of UTX at different levels of regulation of gene expression in muscle cells, explaining at least in part the defects of regeneration related to aging.

O músculo estriado esquelético apresenta em sua constituição células satélites (CS) que se encontram em estado quiescente localizadas entre o sarcolema e a lâmina basal das fibras musculares. As CS podem ser ativadas, diferenciando em mioblastos, contribuindo para regeneração e/ou crescimento do tecido muscular. Os Fusos neuromusculares são mecanorreceptores localizados no interior dos músculos esqueléticos considerados a unidade contrátil reguladora, monitorando a velocidade e duração do alongamento do músculo. Está composto de fibras intrafusais (FIF), circundadas por uma bainha de tecido conjuntivo e encontra-se paralelo às fibras extrafusais. A desnervação promove alterações no músculo esquelético, tanto em CS, quanto nos fusos neuromusculares. Este trabalho analisou quantitativamente as FIF e a proliferação de CS em músculos esquelético de ratos desnervados por longo período. Foram utilizados ratos Wistar. Os animais foram divididos em grupos desnervados e controle. Os músculos Sóleo e Extensor longo dos dedos (EDL) foram desnervados experimentalmente. Após os períodos de 0, 12, 16, 19, 30 e 38 semanas, os músculos foram dissecados, removidos e preparados histológicamente. A porcentagem de CS em músculos imediatamente após desnervação aumenta em relação ao músculo normal e depois decresce em ambos os músculos. Durante o progresso do tempo de desnervação ocorreu um aumento no número de FIF, se comparado com o grupo normal. O número de CS diminui significantemente entre os períodos de desnervação, em ambos os grupos. Nos músculos estudados quanto menor a porcentagem de CS maior é o número de FIF e, aumentando o tempo de desnervação, diminui o número de CS. Em relação às FIF, no grupo controle com o aumento do tempo, o número de fibras não se altera. Já para o grupo experimental, com o aumento do tempo de desnervação, diminui o número de CS e aumenta o número de FIF significantemente. Concluimos então que nos músculos desnervados por longo período ocorre diminuição na porcentagem de células satélites e aumento no número de FIF. Finalmente nossos resultados sugerem que entre 16ª e 19ª semana pós-desnervação encontra-se o melhor período para reinervação de um músculo desnervados. / The skeletal muscle consists of satellite cells (SC) which are in a quiescent state located between the sarcolemma and basal lamina of the muscle fibers. The SC can get activated, differentiating into myoblasts, contributing to regeneration and/or growth of muscle tissue. The neuromuscular spindles are mechanoreceptors located within the skeletal muscle and are considered as contractile regulatory unit, monitoring the speed and duration of muscle stretching. It is composed of Intrafusal muscle fibers (FIF), surrounded by a sheath and is parallel to extrafusal fibers. Denervation cause changes in skeletal muscles both in the CS and neuromuscular spindles. This study analyzed quantitatively the FIF and the proliferation of CS in rat skeletal muscle, denervated for long period. We used Wistar rats to perform this study. The animals were divided into control and denervated groups. The soleus and extensor digitorum longus (EDL) were denervated experimentally. After periods of 0, 12, 16, 19, 30 and 38 weeks, the muscles were dissected, removed and were prepared for histological analysis. The percentage of SC in muscles immediately after denervation, increases in relation to normal muscle and later decreases in both the groups. During the process of denervation, there was an increase in FIF when compared with normal group. The number of SC reduces significantly between the periods of denervation in both the groups. In the muscles studied, the smaller the percentage of SC, higher is the number of FIF and increase in the duration of denervation, reduces the number of SC. As for FIF, with the increase in time in control group, the number of fibres was unaltered. However, in the experimental group, with increase in the time of denervation, the number of SC decreases while there is increase in the number of FIF significantly. We thus conclude that in denervated mucles for long period, there is decrease in the percentage of satellite cells and increase in FIF. Finally our results suggest that the period between 16th and 19th week of post denervation is the best time for reinnervation of denervated muscle.

Óxido nítrico (NO) é uma molécula que exerce uma multiplicidade de funções fisiológicas importantes que vêm sendo estudadas em diversos tecidos. No entanto, o papel do NO em processos fisiológicos e patológicos no músculo estriado é pouco conhecido, apesar de algumas evidências apontarem para uma função de regulação redox e interação com células satélites progenitoras. Neste estudo avaliamos a participação do NO na regeneração muscular em um modelo de inflamação aguda in vivo. O trauma muscular foi induzido por um aparelho similar a uma prensa com impacto direto sobre o gastrocnêmio. Foram utilizados 40 ratos, Wistar, divididos em quatro grupos: (i) controle (CO); (ii) falso (sham) trauma; (iii) trauma; (iv) trauma com exposição ao nitro-L-arginina metil éster (L-NAME), um inibidor da sintase do óxido nítrico, em dois tempos experimentais: 24 horas e 7 dias após lesão. Vinte e quatro horas após o trauma, o músculo lesionado apresentava intensa vasodilatação e reação inflamatória na análise histológica, lipoperoxidação tecidual e estresse nitrosativo, aumento do mRNA das citocinas próinflamatórias (IL-1β, IL-6, iNOS), metaloproteinase-2, expressão proteica de iNOS e MMP-2, ativação do NF-κB e intensa atividade proliferativa. O tratamento com LNAME diminuiu significativamente os achados das alterações histológicas e moleculares em 24 horas após a lesão e, sete dias após o trauma, houve um aumento na expressão do TGF-β, na deposição de colágeno e proliferação celular. Entretanto, o grupo tratado com L-NAME apresentou uma maior expressão de TGF-β e de deposição de colágeno quando comparado ao grupo trauma e proliferação celular semelhante. Estes resultados indicam que a lesão muscular é associada com a ativação do sistema NO, o qual parece estar envolvido no equilíbrio entre os processos de regeneração e fibrose durante o reparo. / Nitric oxide (NO) is a molecule that carries a variety of important physiological functions that have been studied in various tissues. However, the role of NO in physiological and pathological processes in striated muscle is poorly known, although some evidence suggests a role of redox regulation and interaction with progenitor satellite cells. We evaluated the role of NO in muscle regeneration in a model of acute inflammation in vivo. The muscle trauma was induced by a device similar to a press with a direct impact on the gastrocnemius. A total of 40 rats were divided into four groups: (i) control (CO), (ii) sham trauma, (iii) trauma, (iv) trauma + L-NAME, an inhibitor of nitric oxide synthase in two experimental phases: 24 hours and 7 days after injury. Twenty-four hours after the trauma, the injured muscle showed intense vasodilatation and inflammation in the histological analysis, tissue lipid peroxidation and nitrosative stress, activation of NF-κB, increased mRNA of pro-inflammatory, (IL- 1β, IL-6, iNOS), metalloproteinase-2 and HGF, and increased total cell proliferation. The administration of the L-NAME significantly reduced iNOS, MMP-2 and activation of NF-κB reduced the histological and molecular findings 24 hours after injury, and 7 days after injury, there was an increase in the expression of TGF-β, collagen deposition, and total cell proliferation. However, the L-NAME group showed increased expression and collagen deposition when compared to the trauma and similar total cell proliferation. These results indicate that muscle injury is associated with activation of the NO, which seems to be involved in the balance between the processes of regeneration and fibrosis during the repair.

As células-satélite musculares vêm sendo muito estudadas em diferentes pesquisas, especialmente com o objetivo de aumentar a compreensão do mecanismo de sua ação na regeneração muscular e as respectivas implicações nas diferentes miopatias, visando identificar possíveis alvos terapêuticos. Dois modelos para distrofias, os camundongos Largemy d e Lama2dy2j/J possuem um padrão de degeneração intenso e bastante semelhante, mas com diferenças na expressão de genes envolvidos na cascata de regeneração. Por isso, estes constituem interessantes modelos para o estudo de possíveis diferenças no mecanismo de ativação e atuação das células-satélite no músculo distrófico. Assim, os objetivos específicos deste projeto consistiram em: 1) isolar e caracterizar por citometria de fluxo as populações de células-satélite dos modelos Largemy d e Lama2dy2j/J em comparação com o normal C57Black6, quanto a expressão de marcadores de miogênese e de células-tronco pluripotentes; e 2) estudar e comparar o perfil de expressão gênica destas populações de células satélites através de microarray de expressão. Na caracterização fenotípica das células isoladas do músculo normal, aquelas que aderem mais precocemente (PP1) e mais tardiamente (PP2) mostram um padrão fenotípico semelhante entre si e com características mais próximas às miogênicas. Já a população de células de adesão bem mais tardia (PP6) apresentou um padrão de marcação misto, mantendo as características miogênicas, mas apresentando tambem padrão de células-tronco mesenquimais, sugerindo o fenótipo de células mais imaturas. Nos músculos distróficos, identificamos diferenças na constituição do pool de células presentes inicialmente no músculo, onde na linhagem Lama2dy2j/J há indícios de uma população em estágio proliferativo, enquanto que na linhagem Largemy d há presença de células com maior imaturidade. Os resultados da analise de expressão gênica nas populações caracterizadas se mostraram concordantes com os fenótipos celulares avaliados por citometria. Identificamos a hipo-expressão de genes ligados à regeneração e remodelamento muscular em ambos modelos distróficos. Considerando os genes diferentemente expressos somente em cada um dos modelos, os resultados sugerem ativação de proliferação celular e inibição da diferenciação na linhagem Lama2dy2j/J e distúrbios na miogênese na linhagem Largemy d. Assim, pudemos identificar vias importantes alteradas em cada um dos modelos que explicam parte das diferenças encontradas nos trabalhos anteriores / Muscle satellite cells have been widely studied, especially to understand their mechanism of action in muscle regeneration and correspondent implications in the different dystrophic processes, aiming the identification of potential therapeutic targets. Two mice models for muscular dystrophies, Largemyd and Lama2dy2j/J, have a pattern of an intense and very similar degeneration, but with differences in the expression of genes involved in the regeneration cascade. Therefore, they are interesting models to study possible differences in the mechanism of activation and action of satellite cells in the dystrophic muscle. The main objectives of this project are: 1) to isolate and characterize by flow cytometry, populations of satellite cells from Largemyd and Lama2dy2j/J models, as compared to normal C57Black6, evaluating the presence of myogenic and pluripotent stem cells markers; and 2) to study and compare gene expression profiles of these populations of satellite cells using microarray technique. In the phenotypic characterization of cells harvested from normal muscle, both faster (PP1) and slower (PP2) populations to adhere in culture flasks show similar phenotypic characteristics, which were closer to myogenic phenotype. On the other hand, the population of cells with very delayed adhesion ability (PP6) presented a mixed pattern, maintaining the myogenic characteristics, but associated to positive mesenchymal stem cell´s markers, suggesting a phenotype of more immature cells. In dystrophic muscles, we could identify differences in the constitution of the first pool of cells present in the Lama2dy2j/J muscle where there is evidence of a population in proliferative stage, while in the Largemyd strain, we found more immature cells. Gene expression profile in the characterized populations showed consistent concordance with the cellular phenotypes assessed by flow citometry. In both dystrophic models, we identified down-regulated genes related to regeneration and remodeling of the muscle. Considering only the genes differently expressed in each dystrophic model, data suggest the activation of cell proliferation and inhibition of differentiation pathways in Lama2dy2j/J strain and altered myogenesis in the Largemyd model. Thus, we identified important altered pathways in each of the dystrophic models that could explain most of the differences in gene expression profile in the muscle, described in our previous work

La croissance musculaire postnatale chez la souris s’effectue principalement par une hypertrophie et un allongement des fibresmusculaires. L’augmentation de l’aire des fibres est contrôlée par plusieurs voies de signalisation telle que la voie Notch, qui est impliquée dans l’activation des cellules satellites (CS) en début de croissance musculaire postnatale chez la souris. La O-fucosylation, médiée par la protéine O-fucosyltransférase 1 (POFUT1), des répétitions EGF-like de la partie extracellulaire des récepteurs NOTCH joue un rôle déterminant dans la modulation des interactions récepteur-ligand (R-L), nécessaires à l’activation de la voie Notch.Les souris Pofut1cax/cax sont hypomorphes pour le gène Pofut1 et nosrésultats montrent, en plus de malformations squelettiques, unehypertrophie musculaire post-natale, pas d’hyperplasie et une réduction du pool de CS. Pour comprendre l’origine de cette hypertrophie, des cultures primaires de myoblastes dérivés de CS (MDCS) de muscles squelettiques ont été réalisées dans des conditions de prolifération ou de différenciation. Les MDCS Pofut1cax/cax présentent une activité réduite de la signalisation Notch, due à une moins bonne interaction R-L provoquée par une O-fucosylation amoindrie des répétitions EGF-like. Il en résulte une diminution de l’expression de Pax7, marqueur de l’état indifférencié, et une dérégulation de l’expression des facteurs régulateurs de lamyogenèse (Myod, Myf5 et Myogénine). La conséquence ultime est laréduction de la proportion en progéniteurs Pax7+/MyoD- au profit decellules Pax7-/MyoD+ engagées dans la différenciation. Ces observations sont en accord avec la différentiation précoce des MDCS Pofut1cax/cax. Nos résultats indiquent que cette hypertrophie musculaire post-natale chez les souris Pofut1cax/cax est due à une propension plus importante des CS activées à se différencier et à fusionner avec des fibres pré-existantes plutôt que retourner à l’état de quiescence. / Postnatal muscle growth in mice mainly occurs by hypertrophy and by anincrease of myofibres length. This increase in myofibres area is controlled by multiple signaling pathways such as Notch signaling, which is involved in activation of satellite cells (SC) at the beginning of postnatal muscle growth in mice. The O-fucosylation of EGF-like repeats within the extracellular domain of NOTCH receptors, mediated by protein O-fucosyltransferase 1 (POFUT1), plays a key role in the modulation of receptor-ligand interactions (R-L), necessary for activation of Notch signaling. Pofut1cax/cax mice are hypomorphic for the Pofut1 gene. In addition to skeletal defects, our results show postnatal muscular hypertrophy, no hyperplasia and a reduced pool of SC. To understand the origin of this hypertrophy, primary cultures of myoblasts derived from SC (SCDM) from skeletal muscles were studied in proliferating and differentiating conditions. Pofut1cax/cax SCDM showed a reduced Notch signaling due to aless efficient R-L interactions provoked by a low O-fucosylation of EGF-like repeats. This results in decreased expression of Pax7, a marker of undifferentiated state, and a change in the expression of myogenic regulatory factors (Myod, Myf5 and Myogenin). Subsequently, the proportion of Pax7+/MyoD- progenitors decreased while the proportion of Pax7-/MyoD+ cells committed in differentiation increased. These findings corroborate early differentiation of Pofut1cax/cax SCDM.Our results indicate that this postnatal muscle hypertrophy in Pofut1cax/caxmice is due to the fact that activated satellite cells are more prone todifferentiate and fuse with pre-existing myofibres that returning toquiescence.