Biphasic regulation of myogenesis by ALDH2, aldosterone, and oxidative stress.

Aldehyde dehydrogenase 2 (ALDH2) is a mitochondrial enzyme that metabolizes 4-hydroxynonenal (4-HNE), a lipoperoxidation-derived aldehyde that promotes oxidative stress. ALDH2 is therefore considered part of the antioxidant defense. On the other hand, the hormone aldosterone enhances the production of reactive oxygen species (ROS) in many cell types. During skeletal muscle development (myogenesis), myoblasts fuse to form multinucleated cells, called myotubes. In the present study, we investigated the potential of ALDH2 to regulate ROS production in C2C12 cells and its effects on myotube formation during early (0-3 days) and late (4-9 days) stages. Western blot results indicate that these cells actually express ALDH2. Interestingly, incubating cells (1.5-24h) with the pro-oxidant compounds H2O2, 4-HNE, aldosterone, and daidzin (ALDH2 antagonist) enhanced ROS production. In contrast, two ALDH2 agonists (Alda-1 and AD-5591) prevented, with similar potency, the 4-HNE- and aldosterone-induced oxidative stress. We next demonstrated that incubating cells with H2O2 (0.5-5 µM) induces a biphasic regulation of myotube formation, with early inhibition and late stimulation. This H2O2-induced biphasic regulation was also reproduced by aldosterone, daidzin, and another ALDH2 antagonist (CVT-10216). Consistent with their effects on oxidative stress, the ALDH2 agonists Alda-1 and AD-5591 eliminated the regulation of myoblast fusion by H2O2 and aldosterone. Additional data suggest that aldosterone acts through the mineralocorticoid receptor, and both calpain and p38-MAPK are also implicated. These findings indicate that ALDH2 is essential for regulating oxidative stress in myogenic cells and is involved in a signaling pathway that governs myoblast fusion through biphasic and opposing mechanisms.