Estrogen receptor (ERb), one of the two major estrogen receptors, acts via genomic and non-genomic signaling pathways to affect many metabolic functions, including mitochondrial biogenesis and respiration. This study assessed the effect of ERb classical genomic activity on adipocyte-specific and systemic metabolic responses to wheel running exercise in a rodent model of menopause. Female mice lacking the ERb DNA-binding domain (ERbDBDKO, N = 20) and wild-type (WT, N = 21) littermate controls were fed high-fat diet (HFD), ovariectomized (OVX), and randomized to control (no running wheel) and exercise (running wheel access) groups and were followed for eight weeks. Wheel running did not confer protection against metabolic dysfunction associated with HFD+OVX in either ERbDBDKO or WT mice, despite increased energy expenditure. Unexpectedly, in the ERbDBDKO group, wheel running increased fasting insulin and surrogate measures of insulin resistance, and modestly increased adipose tissue inflammatory gene expression (P<0.05). These changes were not accompanied by significant changes in adipocyte mitochondrial respiration. It was demonstrated for the first time, that female WT OVX mice do experience exercise-induced browning of white adipose tissue, indicated by a robust increase in uncoupling protein 1 (UCP1) (P<0.05). However, KO mice were completely resistant to this effect, indicating that full ERb genomic activity is required for exercise-induced browning. The inability to upregulate UCP1 with exercise following OVX may have resulted in the increased insulin resistance observed in KO mice, a hypothesis requiring further investigation.
Laura M Clart, Rebecca J. Welly, Eric D Queathem, R. Scott Rector, Jaume Padilla, Christopher P Baines, Jill A Kanaley, Dennis B Lubahn, and Victoria J Vieira-Potter
Jay W Porter, Joe L Rowles III, Justin A Fletcher, Terese M Zidon, Nathan C Winn, Leighton T McCabe, Young-Min Park, James W Perfield II, John P Thyfault, R Scott Rector, Jaume Padilla, and Victoria J Vieira-Potter
Exercise enhances insulin sensitivity; it also improves adipocyte metabolism and reduces adipose tissue inflammation through poorly defined mechanisms. Fibroblast growth factor 21 (FGF21) is a pleiotropic hormone-like protein whose insulin-sensitizing properties are predominantly mediated via receptor signaling in adipose tissue (AT). Recently, FGF21 has also been demonstrated to have anti-inflammatory properties. Meanwhile, an association between exercise and increased circulating FGF21 levels has been reported in some, but not all studies. Thus, the role that FGF21 plays in mediating the positive metabolic effects of exercise in AT are unclear. In this study, FGF21-knockout (KO) mice were used to directly assess the role of FGF21 in mediating the metabolic and anti-inflammatory effects of exercise on white AT (WAT) and brown AT (BAT). Male FGF21KO and wild-type mice were provided running wheels or remained sedentary for 8 weeks (n = 9–15/group) and compared for adiposity, insulin sensitivity (i.e., HOMA-IR, Adipo-IR) and AT inflammation and metabolic function (e.g., mitochondrial enzyme activity, subunit content). Adiposity and Adipo-IR were increased in FGF21KO mice and decreased by EX. The BAT of FGF21KO animals had reduced mitochondrial content and decreased relative mass, both normalized by EX. WAT and BAT inflammation was elevated in FGF21KO mice, reduced in both genotypes by EX. EX increased WAT Pgc1alpha gene expression, citrate synthase activity, COX I content and total AMPK content in WT but not FGF21KO mice. Collectively, these findings reveal a previously unappreciated anti-inflammatory role for FGF21 in WAT and BAT, but do not support that FGF21 is necessary for EX-mediated anti-inflammatory effects.