Time course of IL-15 expression after acute resistance exercise in trained rats: effect of diabetes and skeletal muscle phenotype.

Type 1 diabetes is associated with skeletal muscle atrophy. Skeletal muscle is an endocrine organ producing myokines such as interleukin-15 (IL-15) and interleukin-6 (IL-6) in response to contraction. These factors may mediate the effects of exercise on skeletal muscle metabolism and anabolic pathways. Lack of correlation between muscle IL-15 mRNA and protein levels after exercise training has been observed, while regulatory effects of IL-6 on IL-15 expression have also been suggested. This study determined post-exercise changes in muscle IL-15 and IL-6 mRNA expression and IL-15 protein levels in healthy and streptozotocin-induced diabetic rats in both the fast flexor hallucis longus (FHL) and slow soleus muscles. Resistance training preserved FHL muscle weight in diabetic rats and increased IL-15 protein levels in both the soleus and FHL muscles. However, the temporal pattern of this response was distinct in normal and diabetic rats. Moreover, discordance between post-exercise muscle IL-15 mRNA and protein expression was observed in our study, and diabetes suppressed post-exercise increases in FHL muscle IL-6 mRNA expression. Our study indicates that training, skeletal muscle phenotype, and metabolic status all influence the temporal pattern of post-exercise changes in IL-15 expression. Muscle IL-15 protein levels increase following training, suggesting this may be an adaptation contributing to increased capacity for secretion of this myokine that is not depressed by the diabetic state.