Characterizing the effects of muscle-specific GSK3a/b reduction on murine muscle contractility and metabolism in female mice.

Dysregulation of skeletal muscle morphology and metabolism is associated with chronic diseases such as obesity and type 2 diabetes. The enzyme glycogen synthase kinase 3 (GSK3) is highly involved in skeletal muscle physiology and metabolism, acting as a negative regulator of muscle size, strength, adaptive thermogenesis, and glucose homeostasis. Correspondingly, we have shown that partial gene expression knockdown (~40%) of gsk3 specifically in skeletal muscle increases lean mass, reduces fat mass, and activates muscle-based adaptive thermogenesis via sarco(endo)plasmic reticulum Ca2+ (SERCA) uncoupling in male mice. However, the effects of partial GSK3 knockdown in female mice have yet to be investigated. Here, we examined the effects of muscle-specific GSK3 knockdown on body composition, muscle size and strength, and whole-body metabolism in female C57BL/6J mice. Our results show that GSK3 content is higher in the female soleus vs. the male soleus; however, there were no differences in the extensor digitorum longus (EDL). Furthermore, muscle-specific GSK3 knockdown did not alter body composition in female mice, nor did it alter daily energy expenditure, glucose/insulin tolerance, mitochondrial respiration, or the expression of the SERCA uncouplers sarcolipin and neuronatin. We also did not find any differences in soleus muscle size, strength, or fatigue resistance. In the EDL, we found an increase in cross-sectional area associated with an increase in absolute force production but there were no differences in fatigability. Therefore, our study highlights sex-differences in the response to genetic reduction of gsk3 , with most of the effects previously observed in male mice being absent in females.