Creatine and low-dose lithium supplementation separately alter energy expenditure, body mass, and adipose metabolism for the promotion of thermogenesis.

Nutraceutical approaches to promote adipose tissue thermogenesis may help to prevent obesity onset. Creatine is a critical regulator of adipose metabolic function and low-dose lithium supplementation has been shown to promote adipose thermogenesis. In the present study, we sought to directly compare the two supplements for their effects on adipose metabolism and thermogenesis. We show that both supplements increase daily energy expenditure (EE) and reduce body mass in male Sprague-Dawley rats. Lithium increased brown adipose tissue (BAT) mitochondrial and lipolytic proteins that are associated with thermogenesis, while creatine increased BAT UCP1 and mitochondrial respiration. The BAT thermogenic findings were not observed in females. White adipose tissue and skeletal muscle markers of thermogenesis were unaltered with the supplements. Together, the data show that low-dose lithium and creatine have diverging effects on markers of BAT thermogenesis and that each increase daily EE and lower body mass in a sex-dependent manner.

Characterizing the effects of muscle-specific GSK3α/ß 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 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 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 versus 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 that an increase in absolute and specific 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.NEW & NOTEWORTHY Here we show that partial GSK3 knockdown has minimal effects on whole body metabolism and muscle contractility in female mice. This is partly inconsistent with previous results found in male mice, which reveal a potential influence of biological sex.

Effect of acute and chronic autophagy deficiency on skeletal muscle apoptotic signaling, morphology, and function.

Autophagy is a catabolic process that targets and degrades cytoplasmic materials. In skeletal muscle, autophagy is required for the control of mass under catabolic conditions, but is also basally active in the maintenance of myofiber homeostasis. In this study, we found that some specific autophagic markers (LC3-I, LC3-II, SQSTM1) were basally lower in glycolytic muscle compared to oxidative muscle of autophagy competent mice. In contrast, basal autophagic flux was higher in glycolytic muscle. In addition, we used several skeletal muscle-specific Atg7 transgenic mouse models to investigate the effect of acute (iAtg7-/-) and chronic (cAtg7-/-) autophagy deficiency on skeletal muscle morphology, contractility, and apoptotic signaling. While acute autophagy ablation (iAtg7-/-) resulted in increased centralized nuclei in glycolytic muscle, it did not alter contractile properties or measures of apoptosis and proteolysis. In contrast, with chronic autophagy deficiency (cAtg7-/-) there was an increased proportion of centralized nuclei, as well as reduced force and altered twitch kinetics in glycolytic muscle. Glycolytic muscle of cAtg7-/- mice also displayed an increased level of the pro-apoptotic protein BAX, as well as calpain and proteasomal enzymatic activity. Collectively, our data demonstrate cumulative damage from chronic skeletal muscle-specific autophagy deficiency with associated apoptotic and proteasomal upregulation. These findings point towards the importance of investigating different muscle/fiber types when studying skeletal muscle autophagy, and the critical role of autophagy in the maintenance of myofiber function, integrity, and cellular health.