Roux-en-Y gastric bypass surgery (RYGB) can achieve long-term remission of type 2 diabetes. However, the specific molecular mechanism through which this occurs has remained largely elusive. Bile acid signaling through the nuclear hormone receptor farnesoid X receptor (FXR) exerts beneficial effects after sleeve gastrectomy (VSG), which has similar effects to RYGB. Therefore, we investigated whether FXR signaling is necessary to mediate glycemic control after RYGB.
RYGB or sham surgery was performed in high-fat diet-induced obese FXR−/− (knockout) and FXR+/+ (wild type) littermates. Sham-operated mice were fed ad libitum (S-AL) or by weight matching (S-WM) to RYGB mice via caloric restriction. Body weight, body composition, food intake, energy expenditure, glucose tolerance tests, insulin tolerance tests, and homeostatic model assessment of insulin resistance were performed.
RYGB surgery decreases body weight and fat mass in WT and FXR-KO mice. RYGB surgery has similar effects on food intake and energy expenditure independent of genotype. In addition, body weight-independent improvements in glucose control were attenuated in FXR −/− relative to FXR +/+ mice after RYGB. Furthermore, pharmacologic blockade of the glucagon-like peptide-1 receptor (GLP-1R) blunts the glucoregulatory effects of RYGB in FXR +/+ but not in FXR −/− mice at 4 weeks after surgery.
These results suggest that FXR signaling is not required for the weight loss up to 16 weeks after RYGB. Although most of the improvements in glucose homeostasis are secondary to RYGB-induced weight loss in wild type mice, FXR signaling contributes to glycemic control after RYGB in a body weight-independent manner, which might be mediated by an FXR-GLP-1 axis during the early postoperative period.