Caspase-3-mediated cyclic stretch-induced myoblast apoptosis via a Fas/FasL-independent signaling pathway during myogenesis.

Skeletal muscle cells are exposed to mechanical stretch during embryogenesis. Increased stretch may contribute to cell death, and the molecular regulation by stretch remains incompletely understood. The aim of this study was to investigate the effects of cyclic stretch on cell death and apoptosis in myoblast using a Flexercell Strain Unit. Apoptosis was studied by annexin V binding and PI staining, DNA size analysis, electron microphotograph, and caspase assays. Fas/FasL expression was determined by Western blot. When myoblasts were cultured on a flexible membrane and subjected to cyclic strain stress, apoptosis was observed in a time-dependent manner. We also determined that stretch induced cleavage of caspase-3 and increased caspase-3 activity. Caspase-3 inhibition reduced stretch-induced apoptosis. Protein levels of Fas and FasL remained unchanged. Our findings implicated that stretch-induced cell death is an apoptotic event, and that the activation of caspase cascades is required in stretch-induced cell apoptosis. Furthermore, we had provided evidence that caspase-3 mediated cyclic stretch-induced myoblast apoptosis. Mechanical forces induced activation of caspase-3 via signaling pathways independent of Fas/FasL system.