Mechanism of action of the bile acid receptor TGR5 in obesity

G protein-coupled receptors (GPCRs) are a large family of membrane protein receptors, and Takeda G protein-coupled receptor 5 (TGR5) is a member of this family. As a membrane receptor, TGR5 is widely distributed in different parts of the human body and plays a vital role in regulating metabolism, including the processes of energy consumption, weight loss and blood glucose homeostasis. Recent studies have shown that TGR5 plays an important role in glucose and lipid metabolism disorders such as fatty liver, obesity and diabetes. With the global obesity situation becoming more and more serious, a comprehensive explanation of the mechanism of TGR5 and filling the gaps in knowledge concerning clinical ligand drugs are urgently needed. In this review, we mainly explain the anti-obesity mechanism of TGR5 to promote the further study of this target, and show the electron microscope structure of TGR5 and review recent studies on TGR5 ligands to illustrate the specific binding between TGR5 receptor binding sites and ligands, which can effectively provide new ideas for ligand research and promote drug research.

Activation of TGR5 Attenuates Renal Fibrosis after Renal Ischemia Reperfusion Injury / 中山大学学报(医学科学版)

ObjectiveTo investigate the role of bile acid receptor TGR5 activation in renal fibrosis induced by unilateral ischemia reperfusion injury and contralateral nephrectomy （uIRIx） model. MethodsIn vivo： C57BL/6J mice were randomly divided into Sham group， uIRIx group and uIRIx+ lithcholic acid （LCA） group with 6 mice in each group. Kidney fibrosis was induced by uIRIx model， kidney function was evaluated by blood and urine biochemical indexes， and the degree of kidney injury was evaluated by HE staining. Masson staining and immunohistochemistry were used to evaluate the degree of renal fibrosis， and Western Blotting was used to detect the expression of related index proteins of renal cortical fibrosis. Sham group and uIRIx group were set in TGR5+/+ mice and TGR5-/- mice respectively， with 6 mice in each group. The degree of renal fibrosis in each group was detected by Western Blotting. In vitro： TGF-β1 was administered to induce pro-fibrosis response in human renal tubular epithelial cell line （HK2 cells）， LCA was used for drug intervention， cytoskeleton was labeled with phalloidin-FITC staining and the expression of fibrosis related indicator protein in HK2 cells was detected by Western Blotting. ResultsIn vivo： Compared with the Sham group， plasma creatinine level （P=0.007） and urinary albumin/creatinine ratio （P=0.041） in uIRIx group were significantly increased， renal cortical protein TGR5 expression （P=0.002） was decreased， Fibronectin expression （P=0.020） and COL1A1 expression （P<0.001） were increased. At the same time， the kidney structure was damaged and collagen deposition was aggravated. LCA intervention effectively improved the kidney function and alleviated the degree of kidney injury and fibrosis. TGR5 gene knockout increased uIRIx-induced Fibronectin expression （P<0.001） and COL1A1 expression （P=0.001） compared with TGR5+/+ mice. In vitro： TGF-β1 induced morphological changes of HK2 cells， cytoskeletal depolymerization and recombination， and promoted the up-regulation of fibrosis index protein. LCA effectively inhibited the morphological changes and skeletal depolymerization induced by TGF-β1， and down-regulated the expression of fibrosis related indicator proteins. ConclusionsLCA alleviated renal fibrosis induced by uIRIx model， and knockout of TGR5 gene aggravated uIRIx induced renal fibrosis； In HK2 cells， LCA alleviated fibrogenic reaction induced by TGF-β1. This indicates that activation of TGR5 alleviates renal fibrosis induced by uIRIx.

Effect and Mechanism of "Liver-Soothing and Spleen-Invigorating" Therapies Against Liver Injury in Rats： An Exploration Based on TGR5 and Intestinal Mucosal Barrier Function / 中国实验方剂学杂志

ObjectiveTo explore the effects of different treatment methods of "soothing liver， invigorating spleen， soothing liver and invigorating spleen， soothing liver first and then soothing liver and invigorating spleen， as well as invigorating spleen first and then soothing liver and invigorating spleen" on liver depression combined with liver injury in rats and their action mechanisms. MethodA six-week rat model of liver depression combined with liver injury was established by restraint stress and subcutaneous injection of carbon tetrachloride （CCl4， 5.89 g·kg-1， once every three days）. At the same time， the drugs were given by gavage. Forty-eight male SD rats of clean grade were randomly divided into eight groups， namely the normal group， model group， bicyclol （0.2 g·kg-1） group， Sinisan （4.32 g·kg-1） group， Liu Junzitang （9.26 g·kg-1） group， Chaishao Liu Junzitang A （Chai A， soothing liver and invigorating spleen，13.57 g·kg-1） group， Chaishao Liu Junzitang B （Chai B， soothing liver first and then soothing liver and invigorating spleen， 13.57 g·kg-1） group， and Chaishao Liu Junzitang C （Chai C， invigorating spleen first and then soothing liver and invigorating spleen， 13.57 g·kg-1） group， with six rats in each group. The pathological changes in liver and colon tissues of each group were observed under light microscope and electron microscope. The serum biochemical indexes of the liver were detected using an automatic biochemical analyzer. The relative mRNA expression levels of Takeda G protein-coupled receptor 5 （TGR5） and intestinal mucosal zona occluden-1 （ZO-1）， Occludin， and Claudin-1 in the liver and colon were detected by reverse-transcription polymerase chain reaction （RT-PCR）. The positive expression rate of proliferating cell nuclear antigen （PCNA） in the colon was detected by immunohistochemistry. ResultCompared with normal group， the model group exhibited significantly elevated serum alkaline phosphatase （ALP）， alanine aminotransferase （ALT）， aspartate aminotransferase （AST）， total bilirubin （TBIL）， and direct bilirubin （DBIL） （P<0.01）， lowered TGR5 mRNA expression in liver tissue， up-regulated TGR5 mRNA expression in the colon tissue （P<0.05，P<0.01）， and down-regulated ZO-1， Occludin， and tight junction protein-1 (Claudin-1) mRNA expression and PCNA in the colon tissue （P<0.01）. Compared with the model group， bicyclol and Chai C remarkably decreased the levels of serum ALP， ALT， AST， TBIL， and DBIL （P<0.05，P<0.01）， while Liu Junzitang， Chai A， Chai B， and Chai C significantly up-regulated the TGR5 mRNA expression in the liver and down-regulated its expression in the colon （P<0.01）. Bicyclol， Chai A， Chai B， and Chai C enhanced the ZO-1 and Claudin-1 mRNA expression in the colon （P<0.05，P<0.01）. Bicyclol， Sinisan， and Chai C increased PCNA expression （P<0.01）. The comparison with the Chai C group showed that the TGR5 mRNA expression in the liver and ZO-1 mRNA expression in the colon of the bicyclol and Sinisan groups were lower， whereas the TGR5 mRNA expression in the colon was higher （P<0.01）. However， the PCNA expression in the colon of the Liu Junzitang and Chai B groups declined significantly （P<0.05）. ConclusionIn the presence of liver injury， invigorating spleen first helps to relieve the liver injury， and the efficacy of "spleen-invigorating" therapy in increasing the intestinal mucosal tight junction proteins and improving the gastrointestinal function is related to its activation of TGR5 to improve the intestinal mucosal barrier function， promote the renewal of intestinal stem cells， and drive the regeneration after injury.

Analysis of the hypoglycemic effect of sleeve gastrectomy on obese and diabetic rats and exploration of its mechanism / 中华内分泌外科杂志

Objective:To investigate the effect of sleeve gastrectomy on blood glucose in obese rats with diabetes mellitus.Methods:Thirty-two 12 week old Goto Kakizaki (GK) diabetic rats were randomly divided into 4 groups: sham operation group (A) , sleeve stomach operation group (B) , sleeve stomach operation+external bile drainage group (C) and sleeve stomach operation + external bile drainage + oleanolic acid group (D) . The changes of fasting blood glucose and blood bile acid were compared before and after operation. The expression level of GLP-1 in serum of each group was detected by ELISA, and the difference of protein expression of bile acid G protein coupled receptor (TGR5) was detected by Western blot.Results:The blood glucose level of group A had no significant change after operation. But blood glucose level in group B and group D was significantly lower than that before operation. Blood glucose in group C was lower than that before operation, but there was no significant difference in comparison. Serum total bile acid level in group A had no significant difference before and after operation. Bile acid level in group B was significantly higher than that before operation, while bile acid level in group C and group D was significantly lower than that before operation. There was no significant difference in the level of serum GLP-1 in group A before and after operation. The level of serum GLP-1 in group B and group D was significantly higher than that before operation. The level of serum GLP-1 in group C was lower than that before operation, but there was no significant difference. The expression of TGR5 protein in terminal ileum in group B and group D was higher than that in group A, but the expression in group C was similar with that in group A.Conclusions:Sleeve gastrectomy has definite hypoglycemic effect on T2DM rats. Bile acid and its related receptor TGR5 should play an important role in the mechanism of sleeve gastrectomy in treatment of diabetes.

Study on anti-inflammatory effect of taurolithocholic acid based on network pharmacology and its mechanism / 中国药理学通报

Aim To explore the anti-inflammatory effect of taurolithocholic acid (TLCA) through network pharmacology-based analyses, to verify with in vitro macrophage study and to reveal the possible mechanisms. Methods The potential targets of TLCA were acquired from public database, and then the protein-protein interaction (PPI) networks against inflammation were constructed and visualized by using Cytoscape. Gene ontology (GO) analyses and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment were performed. The binding activity of TLCA and its target (TGR5) was evaluated through molecular docking analysis. Lastly, the results of the network analysis were confirmed by lipopolysaccharide and interferon-γ induced RAW264.7 cells. Results There were 87 anti-inflammatory potential targets were screened. GO analysis revealed gene functions were mainly involved in regulation of inflammatory response, membrane raft and protein tyrosine kinase. The results of KEGG pathway analysis suggested that PI3K-Akt signaling pathway, human cytomegalovirus infection might be the critical pathways of TLCA against inflammation. The results of in vitro experiments showed that TLCA decreased the LPS and IFN-γ induced inflammatory response in RAW 264.7 macrophages. Furthermore, the expression of TGR5 protein increased after TLCA treatment. Conclusions The potential therapeutic targets of TLCA against inflammation are revealed through network pharmacology analysis. Our results indicate that TLCA might regulate key inflammatory markers through the membrane receptor TGR5.

Taurochenodeoxycholic acid mediates cAMP-PKA-CREB signaling pathway / 中国天然药物

Taurochenodeoxycholic acid (TCDCA) is one of the main effective components of bile acid, playing critical roles in apoptosis and immune responses through the TGR5 receptor. In this study, we reveal the interaction between TCDCA and TGR5 receptor in TGR5-knockdown H1299 cells and the regulation of inflammation via the cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA)-cAMP response element binding (CREB) signal pathway in NR8383 macrophages. In TGR5-knockdown H1299 cells, TCDCA significantly activated cAMP level via TGR5 receptor, indicating TCDCA can bind to TGR5; in NR8383 macrophages TCDCA increased cAMP content compared to treatment with the adenylate cyclase (AC) inhibitor SQ22536. Moreover, activated cAMP can significantly enhance gene expression and protein levels of its downstream proteins PKA and CREB compared with groups of inhibitors. Additionally, TCDCA decreased tumour necrosis factor-α (TNF-α), interleukin-1β (IL-1β), IL-6, IL-8 and IL-12 through nuclear factor kappa light chain enhancer of activated B cells (NF-κB) activity. PKA and CREB are primary regulators of anti-inflammatory and immune response. Our results thus demonstrate TCDCA plays an essential anti-inflammatory role via the signaling pathway of cAMP-PKA-CREB induced by TGR5 receptor.

Research progress of signaling transduction pathway mediated by tgr5 / 中国药理学通报

GPCBAR1, also known as TGR5 receptor, is one member of the GPCRs family. TGR5, a pattern recognition receptor located on cell membrane, is widely expressed in human beings and animals, playing numerous significant roles in anti-inflammation and immune regulation, energy metabolism, glucose metabolism and anti-cancer. Many signaling pathways are induced by TGR5 upon activated. AKT, NF-kB, ERK, STAT3, cAMP signaling pathways, methods and results of TGR5-mediated signaling pathways and t(ie development of new drugs via TGR5-mediated signaling pathways were reviewed in this paper.

Expressions of Bile Acid Receptor FXR and TGR5 in Patients with Ulcerative Colitis / 胃肠病学

Background:The incidence of ulcerative colitis (UC)in developed countries is higher than that in developing countries,which may be related with westernized lifestyle,especially high animal protein and low complex carbohydrate diet. With the increased high fat and meat intake,synthesis and secretion of bile acid in liver is also increased,which may have an impact on the occurrence of UC. Aims:To investigate the expressions of farnesoid X receptor (FXR)and G protein-coupled bile acid receptor 5 (TGR5)in patients with UC. Methods:Thirty patients with active UC from January 2013 to June 2016 at the Affiliated Jiangning Hospital of Nanjing Medical University were enrolled,and 30 healthy subjects were served as controls. Expressions of FXR and TGR5 were determined by immunohistochemistry. Results:Compared with control group,expression of FXR was significantly decreased in UC patients (4. 63 ± 2. 07 vs. 6. 91 ± 2. 62,P =0. 00),however,no significant difference in expression of TGR5 was found between the two groups (6. 70 ± 2. 90 vs. 6. 11 ± 2. 44,P = 0. 40). Expression of FXR was significantly increased in right hemicolon colitis than in left hemicolon colitis (P < 0. 05). Conclusions:There is a significant decrease in FXR in active UC patients,indicating that FXR may have some role in the pathogenesis of UC,however,TGR5 may have no obvious effect in the pathogenesis of UC.

Activation of TGR5 reduces high glucose-induced cardiomyocyte hyper-trophy by inhibiting CaN/NFAT3 signaling / 中国病理生理杂志

AIM: To investigate the role of G-protein-coupled bile acid receptor 1 ( GPBR1; also known as TGR5) activation in high glucose-induced cardiomyocyte hypertrophy and calcineurin (CaN)/nuclear factor of activated T-cells 3 (NFAT3) signaling.METHODS:Primarily cultured mouse cardiomyocytes were used in the study .The cell surface areas of the cardiomyocytes were measured by an image analysis system .The cell protein content was detected by BCA meth-od.The expression of TGR5, CaN and NFAT3 at mRNA and protein levels was determined by RT-PCR and Western blot . RESULTS:The mouse cardiomyocytes were successfully cultured .High glucose significantly induced the increases in the cell surface area, the cell protein content and the expression of CaN and NFAT 3 (P<0.05) in the cardiomyocytes.TGR5 activation or a CaN antagonist cyclosporin A inhibited high glucose-induced cardiomyocyte hypertrophy and the expression of CaN and NFAT3 (P<0.05).These effects of TGR5 activation were abolished by TGR5 gene interference (P<0.05). CONCLUSION:TGR5 activation reduces high glucose-induced cardiomyocyte hypertrophy by inhibiting CaN /NFAT3 sig-naling.

Regulatory effects of the bile acid membrane receptor TGR5 on FN and TGF-β1 in rat glomerular mesangial cells cultured under high glucose condition / 中国药理学通报

Aim To investigate the expression of G protein-coupled receptor TGR5 and its effects on FN and TGF-β1 expression cultured under high glucose condition in rat glomerular mesangial cells , and then to explore the role of TGR5 in diabetic nephropathy. Methods INT-777 and TGR5 plasmid were used to activate TGR5 under high glucose(HG,30 mmol·L - 1 glucose ) condition, and anti-TGR5 small interfering RNA(TGR5 siRNA) was used to knock down TGR5. The protein expression of FN and TGF-β1 in rat me-sangial cells was detected by Western blot. Results TGR5 could be detected in rat glomerular mesangial cells. Both FN and TGF-β1 protein levels could be in-creased by high glucose compared with control group(P < 0. 05),and be inhibited by activiation of TGR5(P <0. 05). On the other hand,knockdown of TGR5 could increase FN and TGF-β1 protein to abnormal levels(P< 0. 01,P < 0. 05). Conclusion TGR5 suppresses HG-induced FN and TGF-β1 expression in rat glomer-ular mesangial cells,suggesting a protective role in the process of diabetic nephropathy.

TGR5 is a novel regulative factor in metabolism / 基础医学与临床

G protein-coupled bile acid receptor 1(TGR5) is a specific membrane receptor of bile acids , playing an important role in the bile acid signaling network .Its activation has been proved to increase the glycemic control , regulate of blood lipid balance , enhance energy expenditure , exert anti-inflammatory actions and so on .It suggests that TGR5 may play an important role in metabolic diseases .

Progress of TGR5 receptors in liver metabolism and immune / 中华肝胆外科杂志

TGR5,expressing in many tissue cells,is a kind of bile acid membrane receptor and participates in a variety of metabolic and immune diseases.Activated TGR5 can keep the metabolism system in a steady state by mediating the metabolism of bile acid,lipid,and blood sugar,reducing insulin resistance and increasing the body's energy consumption; TGR5 could regulate the immune responses of mononuclear cell and Kupffer cell in the liver.For example,it can regulate the adaptive immune response by inhibiting the expression and release of inflammatory cytokines in Kupffer cells,and regulating the differentiation and maturation of dendritic cells.This review mainly focused on the function of TGR5 in liver metabolism and immune and further explored the related mechanism,as well as its clinical significance in related liver diseases.