Impact of Exercise on Apelin/APJ Expression in Skeletal Muscle and Adipose Tissue in Normal and Obese Male Albino Rats; Possible Interaction with Serum IL-6 and TNFcc

Background: Apelin is a recently discovered adipokine that contributes to glucose and obesity related conditions. Until now, its responses to muscle exercise are largely unknown. We aim to investigate the impact of regular swimming exercise on Apelin/APJ expression in Visceral Adipose Tissue (VAT) and skeletal muscle of High Fat Diet (HFD)-induced obesity rats. Methods: A total of 40 male albino rats (160-180gm) were divided into the following groups each containing 10 rats. Group 1: Control group (fed commercial rat chew diet). Group 2: Obese group (fed HFD containing 20% protein, 35% carbohydrate, and 45% fat for 12 weeks.) Each group was randomly subdivided to the following subgroups: Subgroup A: Non exercising group. Subgroup B: Exercising group enrolled in a 4 week regular swimming exercise protocol. Body weight, glycemic parameters, lipid profile, and serum TNF-α IL-6 levels were assessed at baseline and after 4 weeks of exercise. VAT and skeletal muscle samples were taken for the determination of gene expression of Apelin/APJ receptor. Results: HFD-induced obese rats showed impairment in lipid profile with rise in insulin resistance together with a significant rise in circulating levels of inflammatory markers, TNFa and IL-6. Swimming exercise improved lipid profile, and increased insulin sensitivity and body weight reduction were observed. Parallel measurements of apelin/APJ expression in skeletal muscle and VAT of control and obese rats showed an increased APJ expression in VAT but not in skeletal muscle of obese rats. Interestingly, at the end of the swimming exercise protocol, an increase of APJ expression was observed in skeletal muscle but not in VAT of control rats. In addition, swimming exercise down-regulated Apelin/APJ receptor expression in VAT, and upregulated it in skeletal muscle. Conclusion: Our results indicate that Apelin/APJ upregulation in muscle tissue and down-regulation in VAT may be one of the mechanisms by which swimming exercise combat obesity and related disorders.