Résumé :
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Communication n° 428. Skeletal muscle can undergo apoptosis as a post-mitotic tissue both in response to specific physiological stimuli or in pathological processes. Acquisition of an apoptosis-resistant status is part of differentiation program of skeletal muscle cells. Whereas intracellular redox state and mitochondrial activity are closely related to apoptosis in most cell types, their relative role in apoptotic signaling in muscle cells is unclear. The responsiveness of myoblasts and myotubes to the induction of apoptosis involving mitochondrial pathways was studied, as well as the role of ROS generation in this process. For this purpose, L6 myoblasts and myotubes were treated with staurosporine, and oxidative stress parameters (intracellular ROS generation, GSH levels), caspases activation and NF-kappa-B activation were analyzed. Staurosporine induced apoptotic parameters (caspase-3 and 9) as well as NFKB activity in a dose-dependent manner. It also increased intracellular ROS and reduced GSH levels. However, for all the parameters tested, myotubes had a dramatically lower sensitivity in their responsiveness than myotubes. Massive oxidative stress elicited by hydrogen peroxide could also induce caspase-3 activation, at least in myoblasts. To investigate the role of ROS in the response of apoptotic activation to staurosporine, vitamin C and E, two ROS scavengers, were used. ROS generation in response to staurosporine could be blocked by vitamin C and E treatment, but this did not modify the induction of caspases either in myoblasts or in myotubes. NFkB induction by staurosporine was unaltered in myoblasts treated with the antioxidants and slightly enhanced in myotubes This indicated that staurosporine-dependent induction of apoptosis is not dependent on ROS generation in muscle cells. In this sense, depletion of GSH by the use of BSO, also did not affect apoptotic activation by staurosporine. It is concluded that oxidative stress is not required for activation of apoptosis in skeletal muscle cells and it does not appear to be involved in the differential sensitivity of myoblasts and myotubes to the apoptotic stimuli.
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