Submitted on August 1, 2007
Accepted on October 18, 2007
Repeated resistance exercise training induces different changes in mRNA expression of MAFbx and MuRF-1 in human skeletal muscle
Henrik Mascher1, Jorgen Tannerstedt2, Thibault Elfegoun2, Bjorn T. Ekblom2, Thomas Gustafsson3, and Eva Blomstrand4*
1 Astrand Laboratory, Swedish School of Sport and Health Sciences, Stockholm, Sweden; Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden
2 Astrand Laboratory, Swedish School of Sport and Health Sciences, Stockholm, Sweden
3 Department of Laboratory Medicine, Karolinska Institutet, S-141 86 Stockholm, Sweden
4 Astrand Laboratory, Swedish School of Sport and Health Sciences, Stockholm, Sweden; Dept of Physiology and Pharmacology, Karolinska Institutet, Stockholm, 171 77, Sweden
* To whom correspondence should be addressed. E-mail: eva.blomstrand{at}gih.se.
The gain in muscle mass as a result of resistance training is dependent on changes in both anabolic and catabolic reactions. A frequency of 2-3 exercise sessions a week is considered optimal for muscle gain in untrained individuals. Our hypothesis was that a second exercise session would enlarge the anabolic response and/or decrease the catabolic response. Eight male subjects performed resistance exercise on two occasions separated by 2 days. Muscle biopsies were taken from the vastus lateralis before and 15 min, 1 and 2 h after exercise. Exercise led to several-fold increases in phosphorylation of mTOR at Ser2448, p70S6 kinase (p70S6k) at Ser424/Thr421 and Thr389 and ribosomal protein S6, which persisted up to 2 h of recovery on both occasions. There was a tendency to a larger effect of the second exercise on p70S6k and S6, but the difference did not reach statistical significance. The mRNA expression of MuRF-1, which increased after exercise, was 30% lower after the second exercise session than after the first one. MAFbx expression was not altered after exercise, but down-regulated 30% 48h later, whereas myostatin expression was reduced by 45% after the first exercise and remained low until after the second exercise session. The results indicate that 1) changes in expression of genes involved in protein degradation are attenuated as a response to repetitive resistance training with minor additional increases in enzymes regulating protein synthesis and 2) the two ubiquitin-ligases, MuRF-1 and MAFbx, are differently affected by the exercise as well as by repeated exercise.
