Hypoxic Training Increases the Concentration of Serum Irisin and Reduces Weight in Diet-induced Obese Rats

Abstract

Irisin promotes browning of white fat, improves energy metabolism, and-weight loss. In this study, we investigated the effects of different oxygen concentrations during hypoxic training on the serum irisin and the PGC-1(peroxisome proliferator-activated receptor gamma coactivator 1-alpha)-FNDC5(fibronectin type III domain containing 5)-UCPl(uncoupling protein 1) signaling pathway in the skeletal muscle of obese rats. Male Sprague-Dawley Obese rats (n=80) were randomly divided into 8 groups as follows: the control group (group A, n=10); the endurance exercise group (AE group, n=10), which involved animal treadmill training at slope 0{degrees}, 20 m/min, 40 min/d, and 5 d/w; the 16.3% hypoxia exposure group (group B, n=10), 13.3% hypoxia exposure group (group C, n=10), and 11.3% hypoxia exposure group (group D, n=10), which were exposed to a low oxygen environment with oxygen concentrations of 16.3%, 13.3%, and 11.3%, respectively, for 12 h/d; and the 16.3% hypoxic training group (BE group, n=10), 13.3% hypoxic training group (CE group, n=10), and 11.3% hypoxic training group (DE group, n=10) with animal treadmill training during hypoxia exposure. After 8 weeks, the serum irisin concentrations in the AE, BE, CE, and DE groups were significantly higher than that in the A group (p<0.05). Hypoxia exposure and hypoxic training at the three different concentrations significantly increased PGC-1 and FNDC5 gene expression in the skeletal muscle. The PGC-1 and FNDC5 protein contents were significantly higher in the skeletal muscle of the obese rats in the C, AE, and DE groups than those in group A (p<0.05). UCP1 protein expression was significantly higher in groups C, CE, D, and DE than in group A (p<0.05). To conclude, training at oxygen concentrations of 13.3% and 11.3% significantly increased the serum irisin level, and 11.3% hypoxic training enhanced the effects of the PGC-l-Irisin-UCP1 signaling pathway in skeletal muscle.