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

Abstract

20Irisin promotes browning of white fat, improves energy metabolism, and weight loss. In 21 this study, we investigated the effects of different oxygen concentrations during hypoxic 22 training on the serum irisin and the PGC-1α(peroxisome proliferator-activated receptor gamma 23 coactivator 1-alpha)-FNDC5(fibronectin type III domain containing 5)-UCP1(uncoupling 24 protein 1) signaling pathway in the skeletal muscle of obese rats. Male Sprague-Dawley 25 Obese rats (n=80) were randomly divided into 8 groups as follows: the control group (group A, 26 n=10); the endurance exercise group (AE group, n=10), which involved animal treadmill 27 training at slope 0°, 20 m/min, 40 min/d, and 5 d/w; the 16.3% hypoxia exposure group (group 28 B, n=10), 13.3% hypoxia exposure group (group C, n=10), and 11.3% hypoxia exposure group 29 (group D, n=10), which were exposed to a low oxygen environment with oxygen concentrations 30 of 16.3%, 13.3%, and 11.3%, respectively, for 12 h/d; and the 16.3% hypoxic training group 31 (BE group, n=10), 13.3% hypoxic training group (CE group, n=10), and 11.3% hypoxic training 32 group (DE group, n=10) with animal treadmill training during hypoxia exposure. After 8 weeks, 33 the serum irisin concentrations in the AE, BE, CE, and DE groups were significantly higher 34 than that in the A group (p<0.05). Hypoxia exposure and hypoxic training at the three different 35 concentrations significantly increased PGC-1α and FNDC5 gene expression in the skeletal 36 muscle. The PGC-1α and FNDC5 protein contents were significantly higher in the skeletal 37 muscle of the obese rats in the C, AE, and DE groups than those in group A (p<0.05). UCP1 38 protein expression was significantly higher in groups C, CE, D, and DE than in group A 39 (p<0.05).To conclude, training at oxygen concentrations of 13.3% and 11.3% significantly 3 40 increased the serum irisin level, and 11.3% hypoxic training enhanced the effects of the PGC-41 1α-Irisin-UCP1 signaling pathway in skeletal muscle. Introduction 43Obesity has become a global public health problem, and the rates of obese and overweight 44 individuals of different genders and age groups continue to increase [1]. Therefore, safe weight-45 control methods and effective weight-loss action targets are a focus of research. As a new 46 myokine[2] and adipokine [3], irisin causes browning of white fat and promote energy 47 metabolism. Thus, irisin has great potential for the prevention and treatment of metabolic 48 diseases and obesity. Numerous studies have found that exercise can stimulate skeletal muscle 49 to release irisin into the blood circulation and that it has obvious benign effects on obese or 50 diabetic patients of different ages [4][5][6][7][8]. Currently, the relationship between irisin and various 51 chronic diseases related to energy metabolism disorders is gradually being revealed, and new 52 functions of irisin are constantly being discovered[9, 10]. Long-term endurance training or 53 short-term sprint training can both promote an increase in the irisin lev...

Moderate intensity exercise in hypoxia increases IGF-1 bioavailability and serum irisin in individuals with type 1 diabetes

“…Similarly, significantly higher serum irisin levels in response to the 8-week Ex training in a Hyp environment compared with Ex training alone in obese rats have been reported. 37 Interestingly, serum irisin level decreased post-Ex in CG but not in the T1D group, where its levels remained elevated. These different responses of circulating irisin to Ex protocols in both groups suggest either impaired secretion of irisin or irisin resistance in T1D group.…”

“…[34][35][36] Hypoxic Ex training significantly increased serum irisin concentrations in diet-induced obese rats. 37 A study by Hall et al demonstrated that 40 min of continuous Ex at moderate intensity (50% lactate threshold: LAT), as well as high intensity (120% LAT) intermittent (4 × 5 min intermittent with 5 min rest) Ex during Hyp, improved glycaemia and had beneficial effects on the concentrations of selected markers of vascular function in patients with T1D. 34 Furthermore, Ex with Hyp contributed to reducing serum levels of proinflammatory cytokine tumour necrosis factor alpha (TNF-α), 34,38 and increased the activity of erythrocytes NO synthase levels in patients with T1D, 38 potentially leading to beneficial changes in skeletal muscle oxygen capacity.…”