Seasonal changes of myostatin expression and its relation to body Mass acclimation in the Djungarian hamster, Phodopus sungorus.

The Djungarian hamster is an animal that is prominent for distinct seasonal adaptations. Cued by shortening day length in autumn they spontaneously exhibit reductions in food intake, body mass (BM), fat mass and also in lean mass (LM). The mechanisms behind the seasonal regulation of body composition are only partly resolved. Although most studies focused on the participation of body fat in seasonal body weight regulation, we addressed the influence of LM, moreover of muscle mass (MM) on seasonal BM changes. Therefore, we analyzed body composition, MM and the expression of myostatin, a hormone negatively regulating muscle growth and differentiation, in Djungarian hamsters in response to naturally changing photoperiod in winter compared to long photoperiod (LP). Winter-acclimated hamsters upregulated myostatin mRNA when compared with hamsters adapted to natural and artificial LP, whereas MM remained unchanged when compared with natural LP. Moreover, in natural short photoperiod, individual myostatin expression levels were negatively correlated with MM. These results suggest that myostatin is under seasonal control in order to regulate MM and hence contributes to the overall LM and therefore BM changes in seasonal mammals.