L-Arginine/nitric oxide regulates skeletal muscle development via muscle fibre-specific nitric oxide/mTOR pathway in chickens

L-Arginine(L-Arg), the precursor of nitric oxide(NO), plays an important role in muscle function. Fast-twitch glycolytic fibres are more susceptible to age-related atrophy than slow-twitch oxidative fibres.The effect of L-Arg/NO on protein metabolism of fast-and slow-twitch muscle fibres was evaluated in chickens. In Exp. 1, 48 chicks at 1 day old were divided into 4 groups of 12 birds and subjected to 4 treatments: basal diet without supplementation or supplemented with 1% L-Arg, and water supplemented with or without L-nitro-arginine methyl ester(L-NAME, 18.5 mM). In Exp. 2, 48 chicks were divided into 4 groups of 12 birds fed with the basal diet and subjected to the following treatments: tap water(control), tap water supplemented with L-NAME(18.5 m M), or molsidomine(MS, 0.1 mM), or 18.5 mM L-NAME + 0.1 mM MS(NAMS). The regulatory effect of L-Arg/NO was further investigated in vitro with myoblasts obtained from chicken embryo pectoralis major(PM) and biceps femoris(BF).In vivo, dietary L-Arg supplementation increased breast(+14.94%, P < 0.05) and thigh muscle mass(+23.40%, P < 0.05); whereas, MS treatment had no detectable influence. However, L-NAME treatment blocked the beneficial influence of L-Arg on muscle development. L-Arg decreased(P < 0.05) protein synthesis rate, phosphorylated mTOR and ribosomal protein S6 kinase beta-1(p70S6K) levels in breast muscle, which was recovered by L-NAME treatment. In vitro, L-Arg or sodium nitroprusside(SNP)reduced protein synthesis rate, suppressed phosphorylated m TOR/p70S6K and decreased atrogin-1 and muscle RING finger 1(MuRF1) in myoblasts from PM muscle(P < 0.05). L-NAME abolished the inhibitory effect of L-Arg on protein synthesis and the m TOR/p70S6K pathway. However, myoblasts from BF muscle showed the weak influence. Moreover, blocking the mTOR/p70S6K pathway with rapamycin suppressed protein synthesis of the 2 types of myoblasts; whereas, the protein expression of atrogin-1 and MuRF1 levels were restricted only in myoblasts from PM muscle. In conclusion, L-Arg/NO/mTOR/p70S6K pathway enhances protein accumulation and muscle development in fast-twitch glycolytic muscle in chickens. L-Arg/NO regulates protein turnover in a muscle fibre specific way, which highlights the potential clinical application in fast-twitch glycolytic muscle fibres.