The Effect of Vitamin D Supplementation on Serum and Muscle Irisin Levels, and FNDC5 Expression in Diabetic Rats

Diabetes mellitus and metabolic disorders are a major burden on the healthcare system. Irisin is a novel myokine reported to have beneficial effects on glucose and lipid metabolism. Vitamin D deficiency has been implicated in the development of diabetes and hold a critical role in diabetes-related complications. In the present study, we examined the efficacy of vitamin D supplementation on serum irisin levels, skeletal muscle irisin levels, and the expression of the irisin precursor, FNDC5 (fibronectin-type III domain-containing 5) in type I diabetes mellitus rats. Thirty-six adult male Sprague-Dawley rats (150 - 250 g) were randomly divided into four groups: group I: healthy control rats with no treatment (n=8), group II: healthy control rats receiving sesame oil as a placebo (n=8), group III: diabetic rats receiving sesame oil as placebo (n=10), group IV: diabetic rats treated with 4300 IU/kg/week vitamin D (n=10). Diabetes was induced by intraperitoneal (IP) injection of streptozotocin. At the end of the vitamin D intervention blood and triceps muscle samples were collected. RNA was extracted from muscle and real-time PCR was performed to examine FNDC5 gene expression. Our study showed that the administration of vitamin D (4300 IU/kg/week) in a streptozotocin-diabetic rat model resulted in increased serum vitamin D levels, FNDC5 gene expression and muscle irisin levels. However, the levels of serum irisin were not significantly changed by the administration of vitamin D. In conclusion, we show that vitamin D supplementation enhances serum vitamin D levels, FDNC5 gene expression and muscle irisin levels in the streptozotocin-diabetic rat model. Our study highlights the potential therapeutic effect of vitamin D supplementation for diabetes mellitus.