Abstract
Eccentric (ECC) contractions are used to maintain skeletal muscle mass and strength in healthy subjects and patients. Here we investigated the effects of ECC training induced by electrical stimulation (ES) on muscle wasting in colon 26 (C-26) tumor-bearing mice. Mice were divided into four groups: control (CNT), CNT + ECC, C-26, and C-26 + ECC. Cancer cachexia was induced by a subcutaneous injection of C-26 cells and developed for four weeks. In experiment 1, muscle protein synthesis rate and mammalian target of rapamycin complex (mTORC) 1 signaling were investigated six hours after one bout of ECC-ES (2 s contraction given every 6 s, 20°/s, 4 sets of 5 contractions). In experiment 2, ECC-ES training, a total of 14 sessions, was performed every other day starting one day after C-26 injection. Compared to the CNT mice, the gastrocnemius muscle weight was significantly decreased in the tumor-bearing mice. This change was accompanied by a reduction in protein synthesis rate and a marked increase in the expression levels of genes including regulated in development and DNA damage responses (REDD) 1, forkhead box protein O1 (FoxO1), muscle-specific E3 ubiquitin ligases atrogin-1, and muscle ring finger 1 (MuRF-1) mRNA. ECC-ES increased the protein synthesis rate and the phosphorylation levels of p70S6K (Thr389) and rpS6 (Ser240/244), markers for mTORC1 signaling, and reversed an upregulation of MuRF-1 mRNA in muscles from C-26 mice. Our findings suggest that ECC-ES training reduces skeletal muscle atrophy in C-26 tumor-bearing mice through activation of mTORC1 signaling and the inhibition of ubiquitin-proteasome pathway. Thus, ECC-ES training might be used to effectively ameliorate muscle wasting in patients with cancer cachexia.