Hypoxic Exercise Training Promotes apelin/APJ Expression in Skeletal Muscles of High Fat Diet-Induced Obese Mice

Apelin, an endogenous ligand of the G-protein-coupled receptor APJ, is a novel myokine and may play a key role in regulating energy metabolism. The purpose of the present study was to investigate the effects of hypoxic exposure, exercise, and hypoxic exercise training on the expression of apelin and APJ in skeletal muscle of obese mice. Sixty two-months old C57BL/6J mice were randomly divided into two groups: Ten in normal diet group (N) and 50 in the high fat diet (HFD) groups. After two months of feeding, the HFD mice, whose body weight was 20% higher than the average weight of the N group, were selected as obese mice and further allocated into four groups: Control (C), Exercise (E), Hypoxia (H), and Exercise plus Hypoxia (E+H), at 8-9 mice/group. Besides body weight, measured variables in skeletal muscle were protein/mRNA levels of apelin/APJ, AMPKα-Thr172 phosphorylation, hypoxia inducible factor-1α (HIF-1α), mRNA levels of peroxisome proliferator-activated receptor α (PPARα), estrogen-related receptor (ERRα), and nuclear respiratory factor 1 (NRF1). Obese mice had significantly lower mRNA and protein expressions of apelin/ APJ in skeletal muscles than the normal body weight mice. After four weeks of interventions, hypoxic exercise training decreased body weight and increased mRNA and protein expressions of apelin and APJ, mRNA expression of ERRα, and protein expression of HIF-1α. These results indicate that changes of body weight may be associated with the levels of apelin/APJ expressions in skeletal muscle.