SMRT regulation of nuclear receptors orchestrates bile acid homeostasis.

Nuclear receptors are key effectors of metabolic programs; however, the contribution of co-regulatory complexes in maintaining metabolic homeostasis is not fully understood. Here, we show that modulation of the constitutive androstane receptor (CAR) by the co-repressor silencing mediator of retinoic acid and thyroid hormone receptors (SMRT) is required for bile acid (BA) homeostasis. Transcriptional changes in the livers of mice harboring a targeted disruption in one of the nuclear receptor-interacting domains (RIDs), SMRTmRID1 mice, revealed increased expression of CAR target genes involved in BA export. Consistent with this, SMRTmRID1 mice challenged with a high-fat diet showed increased BAs in serum and urine with commensurate decreases in the liver and intestines. Notably, the reduction in intestinal BAs led to decreased activity of the BA receptor farnesoid X receptor (FXR). This reduction in FXR activity compromised the integrity of the intestinal barrier, increased bacterial burden, and augmented intestinal inflammation. Moreover, SMRTmRID1 mice were susceptible to intestinal damage, with higher mortality rates in acute colitis and colitis-associated cancer models. Treatment with a synthetic FXR agonist (XL335) rescued SMRTmRID1 mice during acute colitis. Collectively, these studies highlight the importance of SMRT in maintaining BA homeostasis through direct and indirect regulation of hepatic CAR and intestinal FXR activity, respectively, and point to potential therapeutic routes for combating intestinal pathologies associated with a high-fat diet.