Eight-week dietary methionine restriction does not impair resistance exercise-induced mTORC1 signalling activation in rats

Essential amino acids (EAA) and resistance exercise (RE) are well-known approaches to activate muscle protein synthesis. Methionine is an EAA that stimulates mechanistic/mammalian target of rapamycin complex 1 (mTORC1) signalling. It is believed that the lack of a single EAA could blunt protein synthesis. However, to our knowledge, no study has investigated the effects of methionine-restricted diet (MR) on RE-induced anabolic and catabolic signalling in skeletal muscle. Therefore, in this study, we aimed to investigate the effects of MR on RE-induced muscle protein synthesis and breakdown-related signalling. Male Sprague-Dawley rats were randomly divided into Control and MR group, and rats in the MR group were fed the experimental diets for 8 weeks. After the dietary intervention, RE was performed. p70S6K phosphorylation exhibited a significant main effect of RE and MR, with higher values observed across both conditions. FoxO3a Ser253 phosphorylation showed a significant main effects of both RE and MR, with lower values observed across conditions, while MuRF-1 protein expression showed a significant main effect of MR, with lower values observed in the MR condition. Furthermore, muscle protein synthesis demonstrated a significant main effect of MR, with higher values observed across MR conditions. These results suggested that the MR for 8 weeks neither attenuate RE-induced muscle anabolic response nor enhance catabolic response in rat skeletal muscle.