Improved Satellite Cell Proliferation Induced by L-Carnosine Benefits Muscle Growth of Pigs in Part through Activation of the Akt/mTOR/S6K Signaling Pathway

(1) Background: L-carnosine (beta-alanyl-L-histidine), a natural dipeptide, exists at relatively high concentrations in skeletal muscles, and has been shown to protect cells from adverse conditions due to its antioxidant, anti-aging, anti-glycation, and buffering properties. Satellite cells (SCs), residing on the myofiber surface, are crucial for muscle post-growth and regeneration. However, the effects of L-carnosine on muscle development of pigs in vivo, on proliferation and growth of SCs in vitro, and the relationship between SCs and muscle development have not yet been investigated. (2) Methods: The objective of this study was to assess the effect of dietary L-carnosine on growth performance and longissimus dorsi muscle development of pigs in vivo, and to elaborate its molecular mechanisms in vitro using L-carnosine-treated SCs. (3) Results: It was shown that L-carnosine supplementation (0.2 and 2 mM) increased (p < 0.05) SC proliferation and cell percentage in the synthesis (S) phase and decreased cell percentage in the resting (G0)/first gap (G1)/phase. Moreover, average daily gain (ADG) of pigs fed diets containing 0.1% of L-carnosine was higher (p < 0.05) than that of pigs fed diets without L-carnosine, and the longissimus dorsi muscle weight of pigs assigned to the L-carnosine treatments was 7.95% higher compared to control pigs. Both in the longissimus dorsi muscle and cultured SCs of pigs, the Akt/mTOR/S6K signaling pathway was activated (p < 0.05), suggesting that L-carnosine improved muscle growth and SC proliferation of pigs. (4) Conclusions: Considering the important role of SCs in post-natal muscle growth, there is evidence that L-carnosine may improve muscle growth of pigs through promoting SC proliferation via activating the Akt/mTOR/S6K signaling pathway.