Résumé :
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Satellite cells are the unique cell population able to incorporate myofibres in order to insure muscular growth and hypertrophy mechanisms. Decrease of their number or alteration of their capacities to proliferate and differentiate may strongly affect the myofibre survival and myonuclei utrnover following muscular dystrophy. Unfortunately, the effect of atrophy on the number of satellite cells and myonuclei is a subject of controversy in relation with the methods used to their count. The goal of this study was to determine what would be the behaviour and the role of the satellite cells during the atrophic stage and the relaoding period. Hindlimb adult mice were unloaded by the tail suspension method and reloaded with normal activity during variable period from 2 days to 2 months. After this time, fibres of EDL and soleus muscles of one hindlimb were isolated by mechanical dissociation in 4 mice. The muscles of the opposite leg were frozen for cross sections. At selected dates, the number of myonuclei (DAPI staining) and the number of satellite cells (Pax7 and MyoD immunostainings) were microscopically evaluated on the isolated fibres. On HE stained cross sections, the diameter of the fibres was calculated. Preliminary results indicated that the EDL muscle was not affected by hindlimb suspension: the fast fibres which composed this muscle didn't present any atrophy and the number myonuclei and satellite cells was stable whatever the post-suspension date. In the soleus muscle, only slow fibres showed an important decrease of their diameter (less 30% compared to control soleus), fast fibres were not affected by the atrophy like EDL fibres. For the slow fibres, it is notable that myonuclei population stayed constant although satellite cell pool decreased during atrophic period and grew during the early relaoding period. These preliminary results throw again the debate on myonuclei lose during atrophy and give information about satellite cells behaviour during reloading, especially in relation with myofibre type.
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