Aim: To determine whether our novel approach of diazoxide-induced stem cell preconditioning might be extrapolated to human skeletal myoblasts to support their survival under lethal oxidant stress.
Methods & results: Using an in vitro model of H(2)O(2) treatment of human skeletal myoblasts, we report the ability of diazoxide-preconditioned human skeletal myoblasts to express cytokines and growth factors, which act in an autocrine and paracrine fashion to promote their own survival. Preconditioning of skeletal myoblasts was cytoprotective and significantly reduced their apoptotic index (p < 0.05). IL-11 gene and protein expression was significantly increased in preconditioned skeletal myoblasts. Transfection of skeletal myoblasts with IL-11-specific siRNA incurred their death under oxidant stress. The cytoprotective effect of diazoxide preconditioning was blocked by Erk1/2 inhibitor PD98059 (20-100 µM), which abrogated STAT-3 phosphorylation, thus confirming a possible involvement of Erk1/2/STAT3 signaling downstream of IL-11 in cell survival. We also investigated the time course of subcellular changes and signaling pathway of skeletal myoblasts apoptosis under oxidant stress before and after preconditioning. Apoptosis was induced in skeletal myoblasts with 100-500 µM H(2)O(2) for time points ranging from 1 to 24 h. Release of lactate dehydrogenase, disruption of the mitochondrial membrane potential and cytochrome-c translocation into cytoplasm were the earliest signs of apoptosis. Total Akt protein remained unchanged whereas marked reduction in pAkt was observed in the native skeletal myoblasts. Terminal dUTP nick end-labeling and annexin-V positivity were significantly increased after 4 h. Ultra-structure studies showed condensed chromatin, shriveled nuclei and swollen mitochondria.
Conclusion: These data suggest that skeletal myoblasts undergo apoptosis under oxidant stress in a time-dependent manner and preconditioning of skeletal myoblasts significantly prevented their apoptosis via IL-11/STAT3 signaling.