Effects Of CL316,243 On Skeletal Muscle Metabolism: Role Of Sex And Estrogen Receptor Beta

PURPOSE: CL316,243 (CL), a beta 3 adrenergic receptor (B3AR) agonist has ‘exercise mimetic’ effects in adipose tissue (AT). We demonstrated that male (M) and female (F) mice benefit metabolically from CL treatment, which also induced AT fatty acid synthase (FAS) expression. Further, CL had a lean mass preserving effect, which may involve its effects on skeletal muscle (SM). Estrogen receptor beta (ERβ) is present in SM, yet its role in mediating SM-specific effects of CL is not known. We aimed to compare the effects of CL on SM markers of fat oxidation and protein synthesis, and investigated the role played by genomic ERβ activity. METHODS: High-fat diet-fed M and F wild-type (WT) and ERβ DNA binding domain knockout (KO) mice were administered CL (1 mg/kg) daily for 2 weeks. Systemic physiological assessments of body composition (EchoMRI) and bioenergetics (metabolic chambers) were performed, alongside assessment of quadricep SM protein markers of fat oxidation and protein synthesis (Western blot). Statistical analyses were performed using 2 × 3 analysis of variance for main effects of genotype (G), treatment (T) and sex (S), as well as interactions (int) (SPSS V24). RESULTS: CL significantly increased relative lean mass in both sexes, independent of genotype (12.4% increase; T, P = 0.012). There was a SxTxG int (P = 0.04) for systemic fat oxidation (respiratory quotient (RQ)) such that, in F/WT, CL tended to reduce RQ, whereas in F/KO, CL increased RQ. M/KO mice tended to have a higher RQ, whereas CL increased RQ in both genotypes, resulting in greater CL-induced fat oxidation in F/WT compared M/KO (post-hoc, P = 0.039). F also had higher SM UCP2 (S, P = 0.004) and FAS (S, P = 0.037) content in both genotypes; KO had higher SM UCP2 expression in both sexes (G, P = 0.022); CL-mediated increase in UCP2 was not significant (P = 0.094). Coinciding with RQ sex differences, CL increased SM fat oxidation (assessed via fasted pACC) in F and reduced it in M (SxT int, P = 0.015). Finally, CL robustly increased FAS across sexes and genotypes (T, P < 0.001). No differences in expression of fasted state markers SM anabolism were observed. CONCLUSION: We demonstrate for the first time that CL increases SM FAS content, there are sex-divergent effects of CL on SM metabolism, and that loss of ERβ genomic activity may affect some sex-specific SM responses to CL.