Whey protein modifies gene expression related to protein metabolism affecting muscle weight in resistance-exercised rats.

OBJECTIVE The aim of this study was to evaluate the effects of resistance exercise on the mRNA expression of muscle mammalian target of rapamycin (mTOR), muscle-specific RING finger-1 (MuRF-1), and muscle atrophy F-box (MAFbx) in the presence or absence of whey protein ingestion. We hypothesized that resistance exercise in combination with whey protein ingestion alters the gene expression of proteins related to muscle protein synthesis (mTOR) and/or degradation (MuRF-1 and MAFbx), thus affecting muscle weight gain in rats. METHODS Thirty-two male Fischer rats were randomly assigned to the following four experimental groups (n = 8/group): Control sedentary, control exercised, whey protein sedentary, and whey protein exercised. Exercise consisted of inducing the animals to perform sets of jumps for 8 wk. Body weight gain, muscle weights, food intake, and feeding efficiency were evaluated. Gene expressions were analyzed by quantitative real-time reverse transcription polymerase chain reaction. Statistical evaluation was performed using a two-way analysis of variance with a Tukey post hoc test. RESULTS Whey protein exercised rats exhibited higher body and muscle weight gain compared with control-exercised rats (P = 0.032). The expression of mTOR was reduced by exercise but increased when whey protein was consumed as a dietary protein (P = 0.005). MuRF-1 expression was reduced by exercise (P < 0.001), whereas MAFbx was reduced only by whey protein ingestion (P = 0.008) independent of exercise. CONCLUSIONS A reduction in MAFbx gene transcription induced by whey protein and the interaction between exercise and whey protein ingestion on mTOR gene expression contributed significantly to differences in body and muscle weight gain.