Repeated resistance exercise training induces different changes in mRNA expression of MAFbx and MuRF-1 in human skeletal muscle

1 Åstrand Laboratory, Swedish School of Sport and Health Sciences; 2 Department of Physiology and Pharmacology; and 3 Department of Laboratory Medicine, Division of Clinical Physiology, Karolinska University Hospital, Karolinska Institutet, Stockholm, Sweden Submitted 1 August 2007 ; accepted in final form 18 October 2007 The gain in muscle mass as a result of resistance training is dependent on changes in both anabolic and catabolic reactions. A frequency of two to three exercise sessions per 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 h, and 2 h after exercise. Exercise led to severalfold increases in phosphorylation of mTOR at Ser 2448 , p70 S6 kinase (p70 S6k ) at Ser 424 /Thr 421 and Thr 389 , and ribosomal protein S6, which persisted for up to 2 h of recovery on both occasions. There was a tendency toward a larger effect of the second exercise on p70 S6k 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 downregulated 30% 48 h 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. atrogin-1; protein translation; p70 S6 kinase Address for reprint requests and other correspondence: E. Blomstrand, Åstrand Laboratory, Swedish School of Sport and Health Sciences, Box 5626, Stockholm, S-114 86, Sweden (e-mail: eva.blomstrand{at}gih.se )