Treadmill exercise promotes interleukin 15 expression in skeletal muscle and interleukin 15 receptor alpha expression in adipose tissue of high-fat diet rats.

Interleukin 15 (IL-15) has recently been proposed as a myokine involved in regulating lipid metabolism. We investigated the effect of exercise training on IL-15 content in skeletal muscle and expression of IL-15 receptor (IL-15R) in adipose tissue of obese rats. After 12 weeks of a high-fat diet, obese rats underwent treadmill running at 26 m/min (60 min each, 5 days/week for 8 weeks). High-fat diet induced obesity, with increased body weight, body fat, and lipid profile. The level of IL-15 immunoreactivity (IL-15-ir) in plasma and gastrocnemius muscle was lower in obese than control rats, and the mRNA level of IL-15 in gastrocnemius muscle was markedly decreased. The mRNA and protein levels of IL-15R in adipose tissue were markedly lower in obese rats. Compared with sedentary obese rats, treadmill running showed decreased body weight and elevated mRNA expression of IL-15 in muscle and elevated IL-15-ir level in plasma and muscle. The mRNA and protein level of IL-15R were increased in adipose tissue in treadmill running obese rats. Our results showed that exercise training improve obesity and reversed the downregulation of the IL-15 in muscle and IL-15R in adipose tissue induced by high-fat diet.