Arsenic induces apoptosis in myoblasts through a reactive oxygen species-induced endoplasmic reticulum stress and mitochondrial dysfunction pathway

A pool of myoblasts available for myogenesis is important for skeletal muscle size. The decreased number of skeletal muscle fibers could be due to the decreased myoblast proliferation or cytotoxicity. Identification of toxicants that regulate myoblast apoptosis is important in skeletal muscle development or regeneration. Here, we investigate the cytotoxic effect and its possible mechanisms of arsenic trioxide (As2O3) on myoblasts. C2C12 myoblasts underwent apoptosis in response to As2O3 (1-10 mu M), accompanied by increased Bax/Bcl-2 ratio, decreased mitochondria membrane potential, increased cytochrome c release, increased caspase-3/-9 activity, and increased poly (ADP-ribose) polymerase (PARP) cleavage. Moreover, As2O3 triggered the endoplasmic reticulum (ER) stress indentified through several key molecules of the unfolded protein response, including glucose-regulated protein (GRP)-78, GRP-94, PERK, eIF2 alpha, ATF6, and caspase-12. Pretreatment with antioxidant N-acetylcysteine (NAC, 0.5 mM) dramatically suppressed the increases in reactive oxygen species (ROS), lipid peroxidation, ER stress, caspase cascade activity, and apoptosis in As2O3 (10 mu M)-treated myoblasts. Furthermore, As2O3 (10 mu M) effectively decreased the phosphorylation of Akt, which could be reversed by NAC. Over-expression of constitutive activation of Akt (c.a. Akt) also significantly attenuated As2O3-induced myoblast apoptosis. Taken together, these results suggest that As2O3 may exert its cytotoxicity on myoblasts by inducing apoptosis through a ROS-induced mitochondrial dysfunction, ER stress, and Akt inactivation signaling pathway.