IL-15 expression in skeletal muscle by resistance exercise training in type 2 diabetic rats

Abstract

Introduction: Interleukin-15 (IL-15) is reported as a myokine that potentially regulates body composition and glucose metabolism. We investigated the effect of 8 weeks of resistance exercise training on endogenous IL-15 expression in skeletal muscle and glucose tolerance with concomitant changes of body composition in type 2 diabetic rats.Methods: 6 week-old Male ZDF (Zucker diabetic fatty) and ZLC (ZDF Lean Control) rats were randomly divided into 4 groups: sedentary ZDF (Con-ZDF), exercised ZDF (Ex-ZDF), sedentary ZLC (Con-ZLC), and exercised ZLC (Ex-ZLC). Ex-ZDF and Ex-ZLC rats were trained (once every 3 days for 8 weeks) to climb a 1.1-m vertical (80° incline) ladder with weights secured to their tail for progressive workload resistance exercise (the training was started at 50% or 70% of maximal weight of the last trial). Body weight, grip strength and intraperitoneal glucose tolerance test (IPGTT) were evaluated at every week. Body composition was analyzed by PET-CT (Positron Emission Tomography – Computed Tomography) and expression of IL-15 was measured using ELISA in extracted soleus muscle and tibialis anterior muscle.Results: After 8 weeks of resistance training, substantial reduction of the body weight was observed in Ex-ZDF compared to Con-ZDF. Grip strength was also significantly increased in Ex-ZDF compared to Con-ZDF after 8 weeks of regular strength exercise indicating the efficacy of resistance training. Glucose tolerance (IPGTT) was significantly improved in Ex-ZDF (p<0.05) compared to Con-ZDF showing more delayed drop in blood glucose level between 90 min and 120 min. Concurrently, the expression of IL-15 was significantly increased (p<0.01) after training especially in soleus muscle of Ex-ZDF compared to Con-ZDF and also there was a tendency of increase in IL-15 expression in tibialis anterior muscle in Ex-ZDF as well. Accordingly, PET-CT scan showed that muscle quality tended to be higher in Ex-ZDF than Con-ZDF while no significant difference between Con-ZLC and Ex-ZLC.Discussion: 8 weeks of progressive resistance exercise significantly improved glucose tolerance with the concomitant increase of IL-15 expression in hind-limb muscles suggesting that increased level of IL-15 in skeletal muscle by resistance exercise might be a potential mediator in glucose regulation of type 2 diabetes. Further study is needed to elucidate the mechanisms by which how increased IL-15 expression in skeletal muscle by resistance exercise exerts a favorable influence on impaired glucose metabolism in type 2 diabetes mellitus. Introduction: Interleukin-15 (IL-15) is reported as a myokine that potentially regulates body composition and glucose metabolism. We investigated the effect of 8 weeks of resistance exercise training on endogenous IL-15 expression in skeletal muscle and glucose tolerance with concomitant changes of body composition in type 2 diabetic rats. Methods: 6 week-old Male ZDF (Zucker diabetic fatty) and ZLC (ZDF Lean Control) rats were randomly divided into 4 groups: sedentary ZDF (Con-ZDF), exercised ZDF (Ex-ZDF), sedentary ZLC (Con-ZLC), and exercised ZLC (Ex-ZLC). Ex-ZDF and Ex-ZLC rats were trained (once every 3 days for 8 weeks) to climb a 1.1-m vertical (80° incline) ladder with weights secured to their tail for progressive workload resistance exercise (the training was started at 50% or 70% of maximal weight of the last trial). Body weight, grip strength and intraperitoneal glucose tolerance test (IPGTT) were evaluated at every week. Body composition was analyzed by PET-CT (Positron Emission Tomography – Computed Tomography) and expression of IL-15 was measured using ELISA in extracted soleus muscle and tibialis anterior muscle. Results: After 8 weeks of resistance training, substantial reduction of the body weight was observed in Ex-ZDF compared to Con-ZDF. Grip strength was also significantly increased in Ex-ZDF compared to Con-ZDF after 8 weeks of regular strength exercise indicating the efficacy of resistance training. Glucose tolerance (IPGTT) was significantly improved in Ex-ZDF (p<0.05) compared to Con-ZDF showing more delayed drop in blood glucose level between 90 min and 120 min. Concurrently, the expression of IL-15 was significantly increased (p<0.01) after training especially in soleus muscle of Ex-ZDF compared to Con-ZDF and also there was a tendency of increase in IL-15 expression in tibialis anterior muscle in Ex-ZDF as well. Accordingly, PET-CT scan showed that muscle quality tended to be higher in Ex-ZDF than Con-ZDF while no significant difference between Con-ZLC and Ex-ZLC. Discussion: 8 weeks of progressive resistance exercise significantly improved glucose tolerance with the concomitant increase of IL-15 expression in hind-limb muscles suggesting that increased level of IL-15 in skeletal muscle by resistance exercise might be a potential mediator in glucose regulation of type 2 diabetes. Further study is needed to elucidate the mechanisms by which how increased IL-15 expression in skeletal muscle by resistance exercise exerts a favorable influence on impaired glucose metabolism in type 2 diabetes mellitus.