Arginine and Lysine Promote Skeletal Muscle Hypertrophy by Regulating the mTOR Signaling Pathway in Bovine Myocytes

The objective of this study was to assess the effects of additional arginine (ARG) and lysine (LYS) on the regulatory factors associated with myogenic differentiation of bovine satellite cells and hypertrophy of myotubes. Bovine satellite cells were isolated from 3-mo-old Holstein bull calves (n=3) and subjected to a process of myogenic differentiation while exposed to varying doses of ARG or LYS. The experimental groups were as follows: (1) ARG dose-dependent (ARG: 0 [control], 60, and 120μM) with the presence of basal LYS (800μM) and (2) LYS dose-dependent (LYS: 0 [control], 50, and 100μM) with basal ARG (400μM) for the duration of 48 or 96 h. As a result of their alteration of myogenic regulatory factors (MRF), ARG and LYS might promote myogenic differentiation. Myoblast determination protein 1 (MyoD) and myogenin (MyoG) gene expression and protein abundance levels were elevated (P<0.01) in myocytes treated with ARG or LYS compared to the untreated group. Additionally, supplementation with ARG or LYS phosphorated the proteins associated with the mechanistic target of rapamycin (mTOR) signaling pathway in a dose-dependent manner without affecting insulin-like growth factor 1 (IGF-1). These findings suggest that ARG and LYS may promote myofiber hypertrophy by directly modulating the mTOR signaling pathway. Furthermore, our observations indicate that the supplementation of ARG or LYS may have the potential to induce a transformation of muscle fiber types toward oxidative muscle fibers, as evidenced by the altered (P<0.01) expression of myosin heavy chain (MHC) isoforms,specifically MHC I and MHC IIA. Taken together, our findings provide evidence that ARG and LYS have the capacity to enhance myotube hypertrophy through the regulation of MRF and mTOR signaling pathways.