TW. TGR5 in inflammation and cardiovascular disease. Biochem Soc Trans

Abstract TGR5 (Takeda G-protein-coupled receptor 5) [also known as GPBAR1 (G-protein-coupled bile acid receptor 1), M-BAR (membrane-type receptor for bile acids) or GPR131 (G-protein-coupled receptor 131)] is a Gprotein-coupled receptor that was discovered as a bile acid receptor. TGR5 has specific roles in several tissues, among which are the regulation of energy expenditure, GLP-1 (glucagon-like peptide 1) secretion and gall bladder filling. An accumulating body of evidence now demonstrates that TGR5 also acts in a number of processes important in inflammation. Most striking in this context are several observations that TGR5 signalling curbs the inflammatory response of macrophages via interfering with NF-κB (nuclear factor κB) activity. In line with this, recent animal studies also suggest that TGR5 could be exploited as a potential target for intervention in a number of inflammation-driven diseases, including atherosclerosis. In the present paper, I review our current understanding of TGR5 with a strong focus on its potential as target for intervention in inflammation-driven diseases

TGR5 in inflammation and cardiovascular disease

TGR5 (Takeda G-protein-coupled receptor 5) [also known as GPBAR1 (G-protein-coupled bile acid receptor 1), M-BAR (membrane-type receptor for bile acids) or GPR131 (G-protein-coupled receptor 131)] is a G-protein-coupled receptor that was discovered as a bile acid receptor. TGR5 has specific roles in several tissues, among which are the regulation of energy expenditure, GLP-1 (glucagon-like peptide 1) secretion and gall bladder filling. An accumulating body of evidence now demonstrates that TGR5 also acts in a number of processes important in inflammation. Most striking in this context are several observations that TGR5 signalling curbs the inflammatory response of macrophages via interfering with NF-κB (nuclear factor κB) activity. In line with this, recent animal studies also suggest that TGR5 could be exploited as a potential target for intervention in a number of inflammation-driven diseases, including atherosclerosis. In the present paper, I review our current understanding of TGR5 with a strong focus on its potential as target for intervention in inflammation-driven disease

NR4A nuclear orphan receptors: protective in vascular disease?

PURPOSE OF REVIEW: The nuclear orphan receptors Nur77 (NR4A1), Nurr1 (NR4A2) and NOR-1 (NR4A3) are known to be involved in T-cell apoptosis, brain development, and the hypothalamic-pituitary-adrenal axis. Here, we review our current understanding of the NR4A nuclear receptors in processes that are relevant to vascular disease. RECENT FINDINGS: NR4A nuclear receptors have recently been described to play a role in metabolism by regulating gluconeogenesis, lipolysis, energy expenditure, and adipogenesis. The function of NR4A nuclear receptors has also extensively been investigated in cells crucial in vascular lesion formation, such as macrophages, endothelial cells and smooth muscle cells. SUMMARY: The involvement of NR4A nuclear receptors in both metabolism and in processes in the vessel wall supports a substantial role for NR4A nuclear receptors in the development of vascular diseas

Lithocholic acid controls adaptive immune responses by inhibition of Th1 activation through the Vitamin D receptor.

Bile acids are established signaling molecules next to their role in the intestinal emulsification and uptake of lipids. We here aimed to identify a potential interaction between bile acids and CD4+ Th cells, which are central in adaptive immune responses. We screened distinct bile acid species for their potency to affect T cell function. Primary human and mouse CD4+ Th cells as well as Jurkat T cells were used to gain insight into the mechanism underlying these effects. We found that unconjugated lithocholic acid (LCA) impedes Th1 activation as measured by i) decreased production of the Th1 cytokines IFNγ and TNFαα, ii) decreased expression of the Th1 genes T-box protein expressed in T cells (T-bet), Stat-1 and Stat4, and iii) decreased STAT1α/β phosphorylation. Importantly, we observed that LCA impairs Th1 activation at physiological relevant concentrations. Profiling of MAPK signaling pathways in Jurkat T cells uncovered an inhibition of ERK-1/2 phosphorylation upon LCA exposure, which could provide an explanation for the impaired Th1 activation. LCA induces these effects via Vitamin D receptor (VDR) signaling since VDR RNA silencing abrogated these effects. These data reveal for the first time that LCA controls adaptive immunity via inhibition of Th1 activation. Many factors influence LCA levels, including bile acid-based drugs and gut microbiota. Our data may suggest that these factors also impact on adaptive immunity via a yet unrecognized LCA-Th cell axis

LCA inhibits IFNγ gene expression in Jurkat T cells

<p><b>(A)</b> Cell viability of Jurkat T cells measured by flowcytometry analysis and expressed as percentage of control in response to incubation with unconjugated bile acids and <b>(B)</b> taurine-conjugated bile acids for 24 hours. <b>(C)</b> IFNγ mRNA expression of PMA/Ionomycin (P/I)-activated Jurkat T cells treated for 24 hours with 10 μM of different bile acid species. LCA, lithocholic acid; CDCA, chenodeoxycholic acid; CA, cholic acid; DCA, deoxycholic acid; TLCA, taurolithocholic acid; TDCA, taurodeoxycholic acid; TCDCA, taurochenodeoxycholic acid; TCA, taurocholic acid; AU, Arbitrary units. Results represent the mean ± SEM. *Statistically significant, P<0.05. Experiments were performed in triplicates and repeated at least twice.</p

LCA inhibits CD4⁺ Th cell activation.

<p><b>(A)</b><i>IFN</i>γ mRNA expression and <b>(B)</b> <i>TNF</i>α mRNA expression in Jurkat T cells in response to 10 μM LCA treatment (light grey lines) or vehicle (dark grey lines) with P/I activation (triangles) or in resting Jurkat T cells (squares). <b>(C)</b> <i>IFN</i>γ and <b>(D)</b> <i>TNF</i>α mRNA expression in P/I-activated Jurkat T cells in response to increasing concentrations of LCA. <b>(E)</b> Secreted TNFα protein levels of Jurkat T cells in the supernatant in response to 10 μM LCA treatment (light grey lines) or vehicle (dark grey lines) with P/I activation (triangles) or in resting Jurkat T cells (squares). <b>(F)</b> mRNA expression of <i>IFN</i>γ, <i>IL-6</i>, <i>CD40L</i>, <i>TNF</i>α in primary mouse CD4⁺ Th cells activated with P/I and treated with 10 μμM LCA (light grey bars) or vehicle (dark grey bars). <b>(G)</b> mRNA expression of <i>IFN</i>γ, <i>IL-6</i>, <i>CD40L</i>, <i>TNF</i>α in primary human CD4⁺ Th cells stimulated with Dynabeads T-activator (T-act) and treated with 10 μM LCA (light grey bars) or vehicle (dark grey bars). P/I, PMA/ionomycin; LCA, lithocholic acid; AU, Arbitrary units. Results represent the mean ± SEM. *Statistically significant, P<0.05. Experiments were performed in triplicates and repeated at least twice.</p

Probing the Binding Site of Bile Acids in TGR5

TGR5 is a G-protein-coupled receptor (GPCR) mediating cellular responses to bile acids (BAs). Although some efforts have been devoted to generate homology models of TGR5 and draw structure-activity relationships of BAs, none of these studies has hitherto described how BAs bind to TGR5. Here, we present an integrated computational, chemical, and biological approach that has been instrumental to determine the binding mode of BAs to TGR5. As a result, key residues have been identified that are involved in mediating the binding of BAs to the receptor. Collectively, these results provide new hints to design potent and selective TGR5 agonists