RESUMO
PURPOSE: The aim of this study was to investigate the molecular mechanism of autophagy and apoptosis induced by cyclic mechanical stretch and the potential role of autophagy in stretch-induced apoptosis of myoblasts. METHODS: Loading model of L6 myoblasts was established in vitro. The cells were then subjected to cyclic mechanical stretch involving 3 s of 15% stretch alternating with 3 s of relaxation. The cells were collected after mechanical stretch for 6 h, 12 h and 24 h, respectively. Control cells were cultured on the same plates without mechanical strain. Apoptosis of myoblasts was assessed by Hoechst 33258 staining and Annexin V binding and propidium iodide staining. Autophagy was determined by MDC staining and transmission electron microscopy(TEM). The level of proteins associated with apoptosis and autophagy was detected by Western blot. The data were analyzed with SPSS 17.0 software package. RESULTS: The results of Hoechst 33258 staining and Annexin V binding and propidium iodide staining indicated that mechanical stretch notably induced apoptosis of myoblasts. Caspase inhibitor z-VAD-fmk effectively abrogated apoptosis of myoblasts, indicating mechanical stretch induced caspase-dependent apoptosis. In addition, the results of TEM, MDC staining and Western blot proved that mechanical stretch elicited autophagy of myoblasts. Inhibition of autophagy using 3-MA enhanced caspase-dependent apoptosis induced by mechanical stretch. CONCLUSIONS: Cyclic mechanical stretch induced apoptosis and autophagy of myoblasts time-dependently. Protective autophagy, acting as the compensatory mechanism, inhibited caspase-dependent apoptosis induced by mechanical stretch.