GPBAR1 (TGR5 or M-BAR) is a G protein–coupled receptor for secondary bile acids that is highly expressed in monocytes/macrophages. In this study, we aimed to determine the role of GPBAR1 in mediating leukocyte trafficking in chemically induced models of colitis and investigate the therapeutic potential of BAR501, a small molecule agonist for GPBAR1. These studies demonstrated that GPBAR1 gene ablation enhanced the recruitment of classically activated macrophages in the colonic lamina propria and worsened the severity of inflammation. In contrast, GPBAR1 activation by BAR501 reversed intestinal inflammation in the trinitrobenzenesulfonic acid and oxazolone models by reducing the trafficking of Ly6C⁺ monocytes from blood to intestinal mucosa. Exposure to BAR501 shifted intestinal macrophages from a classically activated (CD11b⁺, CCR7⁺, F4/80⁻) to an alternatively activated (CD11b⁺, CCR7⁻, F4/80⁺) phenotype, reduced the expression of inflammatory genes (TNF-α, IFN-γ, IL-1β, IL-6, and CCL2 mRNAs), and attenuated the wasting syndrome and severity of colitis (≈70% reduction in the Colitis Disease Activity Index). The protective effect was lost in Gpbar1^−/− mice. Exposure to BAR501 increased the colonic expression of IL-10 and TGF-β mRNAs and the percentage of CD4⁺/Foxp3⁺ cells. The beneficial effects of BAR501 were lost in Il-10^−/− mice. In a macrophage cell line, regulation of IL-10 by BAR501 was GPBAR1 dependent and was mediated by the recruitment of CREB to its responsive element in the IL-10 promoter. In conclusion, GPBAR1 is expressed in circulating monocytes and colonic macrophages, and its activation promotes a IL-10–dependent shift toward an alternatively activated phenotype. The targeting of GPBAR1 may offer therapeutic options in inflammatory bowel diseases.

GPBAR1, also known as TGR5, is a G protein-coupled receptor activated by bile acids. Hepatic innate immune cells are involved in the immunopathogenesis of human liver diseases and in several murine hepatitis models. Here, by using genetic and pharmacological approaches, we provide evidence that GPBAR1 ligation attenuates the inflammation in rodent models of hepatitis. Hepatitis was induced by concanavalin A (Con A) or α-galactosyl-ceramide (α-GalCer). 6b-Ethyl-3a,7b-dihydroxy-5b-cholan-24-ol (BAR501), a selective agonist of GPBAR1, was administrated by o.s. In the mouse models of hepatitis, the genetic ablation of Gpabar1 worsened the severity of liver injury and resulted in a type I NKT cells phenotype that was biased toward a NKT1, a proinflammatory, IFN-γ producing, NKT cells subtype. Further on, NKT cells from GPBAR1-/- mice were sufficient to cause a severe hepatitis when transferred to naïve mice. In contrast, GPBAR1 agonism rescued wild-type mice from acute liver damage and redirects the NKT cells polarization toward a NKT10, a regulatory, IL-10 secreting, type I NKT cell subset. In addition, GPBAR1 agonism significantly expanded the subset of IL-10 secreting type II NKT cells. RNAseq analysis of both NKT cells type confirmed that IL-10 is a major target for GPABR1. Accordingly, IL-10 gene ablation abrogated protection afforded by GPBAR1 agonism in the Con A model. Present results illustrate a role for GPBAR1 in regulating liver NKT ecology. Because NKT cells are an essential component of liver immune system, our data provide a compelling evidence for a GPBAR1-IL-10 axis in regulating of liver immunity.

Background. In addition to strain taxonomy, the ability of probiotics to confer beneficial effects on the host rely on a number of additional factors including epigenetic modulation of bacterial genes leading to metabolic variability and might impact on probiotic functionality. Aims. To investigate metabolism and functionality of two different batches of a probiotic blend commercialized under the same name in Europe in models of intestinal inflammation. Methods. Boxes of VSL#3, a probiotic mixture used in the treatment of pouchitis, were obtained from pharmacies in UK subjected to metabolomic analysis and their functionality tested in mice rendered colitis by treatment with DSS or TNBS. Results. VSL#3-A (lot DM538), but not VSL#3-B (lot 507132), attenuated “clinical” signs of colitis in the DSS and TNBS models. In both models, VSL#3-A, but not VSL#3-B, reduced macroscopic scores, intestinal permeability and expression of TNFα, IL-1β and IL-6 mRNAs, while increased the expression of TGFβ and IL-10, occludin and zonula occludens-1 (ZO-1) mRNAs and shifted colonic macrophages from a M1 to M2 phenotype (P<0.05 versus TNBS). In contrast, VSL#3-B, failed to reduce inflammation and worsened intestinal permeability in the DSS model (P<0.001 versus VSL#3-A). A metabolomic analysis of the two formulations allowed the identification of two specific patterns, with at least 3 folds enrichment in the concentrations of four metabolites, including 1-3 dihydroxyacetone (DHA), an intermediate in the fructose metabolism, in VSL#3-B supernatants. Feeding mice with DHA, increased intestinal permeability. Conclusions. Two batches of a commercially available probiotic show divergent metabolic activities. DHA, a product of probiotic metabolism, increases intestinal permeability, highlighting the complex interactions between food, microbiota, probiotics and intestinal inflammation.

Gpbar1 is a bile acid activated receptor for secondary bile acids. Here we have investigated the mechanistic role of Gpbar1 in the regulation of adipose tissues functionality in a murine model of steatohepatitis (NASH). Feeding wild type and Gpbar1^−/− mice with a high fat diet-fructose (HFD-F) lead to development of NASH-like features. Treating HFD-F mice with 6β-ethyl-3a,7b-dihydroxy-5b-cholan-24-ol (BAR501), a selective Gpbar1-ligand, reversed insulin resistance and histologic features of NASH, increased the weight of epWAT and BAT functionality and promoted energy expenditure and the browning of epWAT as assessed by measuring expression of Ucp1 and Pgc-1α. The beneficial effects of BAR501 were lost in Gpbar1^−/− mice. In vitro, BAR501 promoted the browning of 3T3-L1 cells a pre-adipocyte cell line and recruitment of CREB to the promoter of Pgc-1α. In conclusion, Gpbar1 agonism ameliorates liver histology in a rodent model of NASH and promotes the browning of white adipose tissue.