L-Arginine Enhances Protein Synthesis by Phosphorylating mTOR (Thr 2446) in a Nitric Oxide-Dependent Manner in C2C12 Cells.

Muscle atrophy may arise from many factors such as inactivity, malnutrition, and inflammation. In the present study, we investigated the stimulatory effect of nitric oxide (NO) on muscle protein synthesis. Primarily, C2C12 cells were supplied with extra L-arginine (L-Arg) in the culture media. L-Arg supplementation increased the activity of inducible nitric oxide synthase (iNOS), the rate of protein synthesis, and the phosphorylation of mTOR (Thr 2446) and p70S6K (Thr 389). L-NAME, an NOS inhibitor, decreased NO concentrations within cells and abolished the stimulatory effect of L-Arg on protein synthesis and the phosphorylation of mTOR and p70S6K. In contrast, SNP (sodium nitroprusside), an NO donor, increased NO concentrations, enhanced protein synthesis, and upregulated mTOR and p70S6K phosphorylation, regardless of L-NAME treatment. Blocking mTOR with rapamycin abolished the stimulatory effect of both L-Arg and SNP on protein synthesis and p70S6K phosphorylation. These results indicate that L-Arg stimulates protein synthesis via the activation of the mTOR (Thr 2446)/p70S6K signaling pathway in an NO-dependent manner.