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.
Alex’s Notes: It seems that almost every fitness enthusiast uses whey protein at least peri-workout. The idea is to provide a rapid stream of amino acids to stimulate protein synthesis after the catabolic training session. This is accomplished via multiple pathways, not the least of which is the mTOR pathway. Yet, another aspect of protein synthesis is inhibition of breakdown. Muscle protein degradation is mediated primarily (80-90%) by the ubiquitin proteasome system (UPS), and more specifically by MAFbx and MuRF-1. These enzymes are generally overexpressed in muscle wasting diseases. The study at hand aimed to see the gene expression effects of whey protein during an 8-week resistance training routine.
32 male mice were randomly put into one of four groups: Control sedentary (CS), control exercised (CE), whey protein sedentary (WS), and whey protein exercised (WE). The composition of the diets was identical except for the whey protein groups used whey instead of casein. Body weight gain and muscle weight was similar in all groups except the CS group, which was notably lower. This isn’t surprising given that exercise promotes growth and both whey and casein are powerful protein sources. That said, the similarity of the WS group to the exercising groups is intriguing. The whey protein groups also had better feeding efficiency, as judged by a lower food intake despite similar gains.
As for gene expression, mTOR was reduced with exercise but whey protein prevented this decline. Notably, the CE group was significantly lower than all other groups. Moreover, although MuRF-1 was reduced by exercise but not whey protein, MAFbx was only decreased by whey protein independent of exercise.
So what does all this mean? Resistance training is catabolic and reduces the important muscle synthesis pathway of mTOR. Only whey protein prevents this suppression. Whey protein, compared to casein, is also the only thing to reduce a marker of protein breakdown – MAFbx – and this happens regardless of training. Thus, whether sedentary or exercising, whey seems to confer some benefits with gene expression over its dairy counterpart (casein).