Effect of Muscle Contraction Under Caloric Restriction on Irisin and FGF21 Secretion in Mice.

Combining diet and physical activity is known to be more effective for health than either intervention alone. Recent research has shown that skeletal muscle secretes myokines in response to exercise, which contribute to the adaptation of other organs to exercise. Therefore, we hypothesized that muscle adaptation by calorie restriction (CR) might enhance myokine responses to exercise. It is known that the myokine fibroblast growth factor-21 (FGF-21) secreted by skeletal muscle during exercise activates adipose tissue browning. We have already reported that irisin, a myokine that contributes to the metabolic activation of adipose tissue and weight loss, is secreted in response to muscle contraction by electrical stimulation (ES). Thus, we investigated the secretion of FGF21 and irisin upon the combination of ES with CR in this study. Mice were divided into four groups: control mice (Con), calorie restriction mice (CR), acute muscle contraction mice (ES), and acute muscle contraction after calorie restriction mice (CRES). After 1 week of acclimation, we subjected the mice to 60 % calorie restriction. After 2 weeks of CR, we performed ES. The results showed that the irisin expression level in serum was significantly increased by the combination of ES and CR, and an interaction between CR and ES was confirmed. FGF21 expression in serum was significantly decreased by CR. In conclusion, we confirm that irisin is a myokine whose secretion is increased synergistically by CR and muscle contraction. Keywords Muscle " Calorie restriction " Myokine " Irisin " FGF21.