The farnesoid X receptor (FXR) is a nuclear receptor that plays key roles in hepatoprotection by maintaining the homeostasis of liver metabolism. FXR null mice display strong hepatic inflammation and develop spontaneous liver tumors. In this report, we demonstrate that FXR is a negative modulator of nuclear factor B (

Gpbar1 (TGR5), a membrane-bound bile acid receptor, is well known for its roles in regulation of energy homeostasis and glucose metabolism. TGR5 also displays strong attenuation of macrophage reactivity in vitro, but the physiological roles of TGR5 in inflammatory response and its mechanism is unknown. Here we demonstrate that TGR5 is a negative modulator of nuclear factor κB (NF-κB)-mediated inflammation. TGR5 activation suppresses the phosphorylation of IκBα, the translocation of p65, NF-κB DNA binding activity and its transcription activity. Furthermore, TGR5 activation enhances the interaction of IκBα and β-arrestin2. Suppression of NF-κB transcription activity and its target gene expression by TGR5 agonist are specifically abolished by expression of anti-β-arrestin2 small interfering RNA. These results show that TGR5 suppresses NF-κB pathway by mediation of the interaction between IκBα and β-arrestin2. In a lipopolysaccharide (LPS)-induced inflammation model, TGR5−/− mice show more severe liver necroses and inflammation compared with wild-type (WT) mice. Activation of TGR5 by its agonist ligand inhibits the expression of inflammatory mediators in response to NF-κB activation induced by LPS in WT but not TGR5−/− mouse liver. Conclusion These findings identify TGR5 as a negative mediator of inflammation that may serve as an attractive therapeutic tool for immune and inflammatory liver diseases.

Vertical sleeve gastrectomy (VSG) is one of the most commonly performed clinical bariatric surgeries used for the remission of obesity and diabetes. However, the precise molecular mechanism by which VSG exerts its beneficial effects remains elusive. Here we report that the membrane-bound G protein-coupled bile acid receptor, GPBAR-1 (also known as TGR5), is required to mediate the effects of anti-obesity, anti-hyperglycemia, and improvements of fatty liver of VSG in mice. In the absence of TGR5, the beneficial metabolic effects of VSG in mice are lost. Moreover, we found that expression of TGR5 was significantly increased after VSG, and VSG alters both BA levels and composition in mice, resulting in enhancement of TGR5 signaling in the ileum and brown adipose tissues, concomitant with improved glucose control and increased energy expenditure. Conclusion Our study elucidates a novel underlying mechanism by which VSG achieves its postoperative therapeutic effects through enhanced TGR5 signaling.

Elucidating the mechanism of liver regeneration could lead to life-saving therapy for a large number of patients, especially elderly patients, after segmental liver transplantation or resection of liver tumors. The forkhead box m1b (Foxm1b) transcription factor is required for normal liver regeneration. Here we report that Foxm1b is the first direct farnesoid X receptor (

GPBAR1/TGR5 is a novel plasma membrane-bound G protein–coupled bile acid (BA) receptor. BAs are known to induce the expression of inflammatory cytokines in the liver with unknown mechanism. Here we show that without other external stimuli, TGR5 activation alone induced the expression of interleukin 1β (IL-1β) and tumor necrosis factor-α (TNF-α) in murine macrophage cell line RAW264.7 or murine Kupffer cells. The TGR5-mediated increase of pro-inflammatory cytokine expression was suppressed by JNK inhibition. Moreover, the induced pro-inflammatory cytokine expression in mouse liver by 1% cholic acid (CA) diet was blunted in JNK−/− mice. TGR5 activation by its ligands enhanced the phosphorylation levels, DNA-binding and trans-activities of c-Jun and ATF2 transcription factors. Finally, the induced pro-inflammatory cytokine expression in Kupffer cells by TGR5 activation correlated with the suppression of Cholesterol 7α-hydroxylase (Cyp7a1) expression in murine hepatocytes. These results suggest that TGR5 mediates the BA-induced pro-inflammatory cytokine production in murine Kupffer cells through JNK-dependent pathway. This novel role of TGR5 may correlate to the suppression of Cyp7a1 expression in hepatocytes and contribute to the delicate BA feedback regulation.