MOTS‐c protein expression increases following aerobic exercise training and remains elevated during detraining

Abstract

Mitochondrial open reading frame of the 12S rRNA‐c (MOTS‐c) is a mitochondrial‐derived peptide that is released into the circulation following intense physical activity and, purportedly, has systemic impacts on energy metabolism and insulin sensitivity. Exogenous administration of MOTS‐c in rodent models enhances physical activity / endurance and reduces fat mass in aged mice through the regulation of, in part, the glycolysis / pentose phosphate pathway and amino acid metabolism. Considering that mitochondrial volume and mitochondrial DNA copy number increase following chronic aerobic exercise training, we hypothesized that MOTS‐c expression also would be elevated in exercise‐trained skeletal muscle. MOTS‐c protein expression from phenotypically mixed plantaris muscles of adult female Sprague Dawley rats were compared from six conditions: sedentary (SED; n=11), voluntary exercise training for four (EX4; n=9), six (EX6; n=6), or eight weeks (EX8; n=8), and detraining after four (DETR4) or six (DETR6) weeks, which followed four or six weeks of exercise training, respectively. Total running distances were ~551±61, 371±94, 560±71, 321±44, and 519±27 km for EX4, EX6, EX8, DETR4 and DETR6, respectively. DETR4 rat running distance was significantly lower than EX4, EX8, and DETR6 rats (p<0.01). Total muscle protein homogenate was isolated from mid‐belly muscle chunks and separated using 15% SDS‐PAGE gels (10 μg/sample). Following transfer, membranes were incubated with a custom rabbit anti‐rat MOTS‐c polyclonal antibody, developed, scanned, stripped and re‐probed for GAPDH as a loading control. MOTS‐c protein was significantly elevated from SED (set at 100%) to 188±61, 158±37, 212±27, 168±29, 223±36% in EX4, EX6, EX8, DETR4 and DETR6, respectively (p<0.05). Furthermore, preliminary findings indicate that MOTS‐c is present exclusively within the cytoplasm of skeletal muscle and not compartmentalized within the nuclei or mitochondria. Given that long‐term aerobic exercise augments mitochondrial volume within skeletal muscle, our data suggest that the observed increase in MOTS‐c protein in the present study parallels this mitochondrial adaptation to aerobic physical activity. Taken together, these findings indicate that a more aerobically‐trained individual would have an enhanced MOTS‐c presence within skeletal muscle and, therefore, a greater potential to regulate energy and insulin sensitivity when MOTS‐c is released systemically; additionally, the potential benefits of MOTS‐c are sustained during a period of physical inactivity (e.g., detraining) following exercise training.