Résumé :
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Ubiquitous calpains (µ- and m-calpain) are proteases of which enzymatic and structural properties are well characterized. Their implication in the early stages of myogenesis and more particularly in the fusion and migration of myoblasts seems well established. In the aim of improving myoblasts transplantation therapy, our study focuses on the role of the different actors of the proteolytic neutral calcium dependant system during adhesion and migration of murin (C2C12) and human (LHCN-M2) myoblasts. The adhesion of both cell lines is similar and rapid. In presence of calpain inhibitor, this phenomenon is delayed and reduced by about 55%. The characteristics of the migration phenomenon (cell morphology, velocity and migration area) have been analysed using video-microscopy. The morphology of both migrating cell lines as well as their migration velocity are similar. During this migration process, the global proteolytic activity of calpains has been measured on living cells using a fluorescent substrate (t-Boc-LM-CMAC). The calpain activity is higher in C2C12 cells than in LHCN-M2 myoblasts. The addition of a specific inhibitor decreases dramatically the velocity of myoblasts migration as well as the migration area of myoblasts. The impact of this inhibition has been observed on the actin cytoskeleton known to be the motor of migration. The stress fibres are disorganised, the cells have a rounded morphology and failed to form membrane protrusion. In conclusion, calpain activity seems to play a pivotal role for migration process and dispersion of human myoblasts. At the molecular level, these results suggest the implication of calpains in the organisation of stress fibres probably by a limited proteolysis of proteins involved in the organisation of the actin cytoskeleton.
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