Effect of Treadmill Exercise on Interleukin-15 Expression and Glucose Tolerance in Zucker Diabetic Fatty Rats

Background: Interleukin-15 (IL-15), a well-known myokine, is highly expressed in skeletal muscle and is involved in muscle-fat crosstalk. Recently, a role of skeletal muscle-derived IL-15 in the improvement of glucose homeostasis and insulin sensitivity has been proposed. However, little is known regarding the influence of endurance training on IL-15 expression in type 2 diabetic skeletal muscles. We investigated the effect of endurance exercise training on glucose tolerance and IL-15 expression in skeletal muscles using type 2 diabetic animal models. Methods: Male Zucker diabetic fatty (ZDF) and ZDF lean control (ZLC) rats were randomly divided into three groups: sedentary ZLC, sedentary ZDF (ZDF-Con), and exercised ZDF (ZDF-Ex). The ZDF-Ex rats were forced to run a motor-driven treadmill for 60 minutes once a day 5 times per week for 12 weeks. Intraperitoneal glucose tolerance test (IPGTT) was performed after 12 weeks. Expression of IL-15 was measured using ELISA in extracted soleus (SOL) and gastrocnemius medial muscles. Results: After 12 weeks of treadmill training, reduction of body weight was observed in ZDF-Ex compared to ZDF-Con rats. Glucose tolerance using IPGTT in diabetic rats was significantly improved in ZDF-Ex rats. Furthermore, the expression of IL-15 was significantly increased (P<0.01) only in the SOL of ZDF-Ex rats compared to ZDF-Con. Additionally, IL-15 expression in SOL muscles was negatively correlated with change of body weight (R=-0.424, P=0.04). Conclusion: The present study results suggest that 12 weeks of progressive endurance training significantly improved glucose tolerance with concomitant increase of IL-15 expression in SOL muscles of type 2 diabetic rats.