Macrophages are classified mainly into two subtypes, M1 and M2, which exhibit distinct phenotypes, based on their microenvironment. We have recently demonstrated that Gpr137b is abundantly expressed in RAW264 macrophages, "Gpr137b is an orphan G-protein-coupled receptor associated with M2 macrophage polarization" (Islam et al., in press) [1]. Although recent studies have suggested that G-protein-coupled receptors (GPCRs) are associated with M1/M2 macrophage polarization ("G-protein-coupled bile acid receptor 1 (GPBAR1, TGR5) agonists reduce the production of proinflammatory cytokines and stabilize the alternative macrophage phenotype" (Hogenauer et al., 2014) [2], "Leukotriene B4 promotes neovascularization and macrophage recruitment in murine wet-type AMD models" (Sasaki et al., 2018) [3]), available information about GPCR-mediated macrophage polarization is still limited. This prompted us to generate Gpr137b-knockout (KO) RAW264 clones using the CRISPR/Cas9 genome editing system to elucidate the function of Gpr137b in interleukin (IL)-4-induced M2 macrophage polarization (Islam et al., in press) [1]. Here we present the datasets of a microarray analysis to identify Gpr137b-dependent IL-4-responsive genes in RAW264 cells. The raw microarray data are available in the Gene Expression Omnibus database (https://www.ncbi.nlm.nih.gov/geo/) under the accession number GSE117578, https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE117578.

The G-protein-coupled bile acid receptor TGR5 agonists were widely developed in type 2 diabetes and gastrointestinal disorders, but were also full of challenges, due to the systemic on-targeted side effects, especially the gallbladder-filling effects. Here, to circumvent these risks, several TGR5 agonists with soft-drug designation had been designed and synthesized with the properties of rapid metabolized after drug effect. Among them, compound 19 showed negligible systemic exposure and favorable gallbladder safety on a 3-day continuous administration, providing a novel strategy for developing TGR5 agonists.

Keywords: Carboxylic ester; GLP-1; Gallbladder-filling effects; Rapid metabolism; Soft drug; TGR5.

OBJECTIVE

Bile acids have been implicated as important regulators of glucose metabolism via activation of FXR and GPBAR1. We have previously shown that FGF19 can modulate glucose handling by suppressing the activity of hypothalamic AGRP/NPY neurons. As bile acids stimulate the release of FGF19/FGF15 into the circulation, we pursued the potential of bile acids to improve glucose tolerance via a gut-brain axis involving FXR and FGF15/FGF19 within enterocytes and FGF receptors on hypothalamic AGRP/NPY neurons.

METHODS

A 5-day gavage of taurocholic acid, mirroring our previous protocol of a 5-day FGF19 treatment, was performed. Oral glucose tolerance tests in mice with genetic manipulations of FGF signaling and melanocortin signaling were used to define a gut-brain axis responsive to bile acids.

RESULTS

The taurocholic acid gavage led to increased serum concentrations of taurocholic acid as well as increases of FGF15 mRNA in the ileum and improved oral glucose tolerance in obese (ob/ob) mice. In contrast, lithocholic acid, an FXR antagonist but a potent agonist for GPBAR1, did not improve glucose tolerance. The positive response to taurocholic acid is dependent upon an intact melanocortinergic system as obese MC4R-null mice or ob/ob mice without AGRP did not show improvements in glucose tolerance after taurocholate gavage. We also tested the FGF receptor isoform necessary for the bile acid response, using AGRP:Fgfr1-/- and AGRP:Fgfr2-/- mice. While the absence of FGFR1 in AGRP/NPY neurons did not alter glucose tolerance after taurocholate gavage, manipulations of Fgfr2 caused bidirectional changes depending upon the experimental model. We hypothesized the existence of an endogenous hypothalamic FGF, most likely FGF17, that acted as a chronic activator of AGRP/NPY neurons. We developed two short peptides based on FGF8 and FGF17 that should antagonize FGF17 action. Both of these peptides improved glucose homeostasis after a 4-day course of central and peripheral injections. Significantly, daily average blood glucose from continuous glucose monitoring was reduced in all tested animals but glucose concentrations remained in the euglycemia range.

CONCLUSIONS

We have defined a gut-brain axis that regulates glucose metabolism mediated by antagonistic fibroblast growth factors. From the intestine, bile acids stimulate FGF15 secretion, leading to activation of the FGF receptors in hypothalamic AGRP/NPY neurons. FGF receptor intracellular signaling subsequently silences AGRP/NPY neurons, leading to improvements of glucose tolerance that are likely mediated by the autonomic nervous system. Finally, short peptides that antagonize homodimeric FGF receptor signaling within the hypothalamus have beneficial effects on glucose homeostasis without inducing hypoglycemia. These peptides could provide a new mode of regulating glucose metabolism.

Once known exclusively for their role in nutrients absorption, bile acids have emerged as signaling molecules, generated from cholesterol breakdown, acting on several immune cells by activating a variety of receptors including the G protein-coupled bile acid receptor 1 (GPABR1 or TGR5), the Farnesoid-X-receptor (FXR) and, as recently discovered, the retinoid-related orphan receptors (ROR)γt. GPBAR1, FXR, and RORγt are highly expressed in cells of the innate and adaptive immune system (i.e., dendritic cells (DCs), macrophages, innate lymphoid 3 cells (ILC3s), and T helper 17 (Th17) lymphocytes) and plays an important role in regulating intestinal and liver immunity, highlighting a role for various bile acid species in regulating immune responses to intestinal microbial antigens. While primary bile acids are generated from the cholesterol breakdown secondary bile acids, the GPBAR1 ligands, and oxo-bile acids derivatives, the RORγt ligands, are generated by the intestinal microbiota, highlighting the potential of these bile acids in mediating the chemical communication between the intestinal microbiota and the host. Changes in intestinal microbiota, dysbiosis, alter the composition of the bile acid pool, promoting the activation of the immune system and development of chronic inflammation. In this review, we focus on the molecular mechanisms by which an altered bile acid signaling promotes intestinal inflammation.

Keywords: FXR; GPBAR1; RORγt; bile acids; intestinal immunity; intestinal microiota.

Background: DNA methylation is an important part of epigenetic modification, and its abnormality is closely related to esophageal adenocarcinoma (EAC). This study was aimed at using bioinformatics analysis to identify methylation-driven genes (MDGs) in EAC patients and establish a risk model as a biological indicator of EAC prognosis.

Method: Downloaded EAC DNA methylation, transcriptome, and related clinical data from TCGA database. MethylMix was used to identify MDGs. R package clusterProfiler and the ConsensusPathDB online database were used to analyze the rich functions and pathways of these MDGs. The prognostic risk model was established by univariate Cox regression, Lasso regression, and multivariate Cox regression analysis. Finally each MDG in the model were carried out through the survival R package.

Results: A total of 273 MDGs were identified, which were enriched in transcriptional regulation and embryonic organ morphogenesis. Cox regression analysis established a risk model consisting of GPBAR1, OLFM4, FOXI2, and CASP10. In addition, further survival analysis revealed that OLFM4 and its two related sites were significantly related to the EAC patients' survival.

Conclusion: In summary, this study used bioinformatics methods to identify EAC MDGs and established a reliable risk prognosis model. It provided potential biomarkers for the early treatment and prognosis evaluation of EAC.

Next to their involvement in digestion, bile acids have been defined as signaling molecules. They have been demonstrated to control many physiological functions among which lipid homeostasis, glucose and energy metabolisms. Bile acids are ligands of several receptors and multiple studies using transgenic mouse models defined the major roles of their respective nuclear and membrane receptors namely the Farnesoid-X-Receptor (FXRα) and the G-protein-coupled bile acid receptor 1(GPBAR1; TGR5). Here we review the reports highlighting the impacts of bile acids on testicular physiology and on male reproductive functions. The studies on mouse models open perspectives to better understand the deleterious effects of bile acids on testicular pathophysiologies and fertility disorders. Additional studies are needed to corroborate these correlations in humans.

Bile acids are signaling molecules with important endocrine functions. Some of these, including the induction of energy expenditure in brown adipose tissue and skeletal muscle as well as the stimulation of glucagon-like peptide-1 (GLP-1) production in enteroendocrine L-cells, are mediated by the G-protein-coupled bile acid receptor 1 (GPBAR1). Therefore, we investigated in a cohort of white subjects at increased risk for type 2 diabetes mellitus whether a genetic variation within the GPBAR1 gene contributes to prediabetic phenotypes, such as disproportionate fat distribution, insulin resistance, or beta-cell dysfunction. We genotyped 1576 subjects (1043 women, 533 men) for the single nucleotide polymorphism rs3731859 in the GPBAR1 gene. All subjects underwent an oral glucose tolerance test; a subset additionally had a hyperinsulinemic-euglycemic clamp. Regional fat distribution, ectopic hepatic and intramyocellular lipids were determined by magnetic resonance techniques. Peak aerobic capacity, a surrogate parameter for oxidative capacity of skeletal muscle, was measured by an incremental exercise test on a motorized treadmill. Total GLP-1 and gastric inhibitory peptide levels were determined by radioimmunoassay. After appropriate adjustment and Bonferroni correction for multiple comparisons, rs3731859 was not significantly associated with regional or ectopic fat distribution, peak aerobic capacity, levels of incretins, insulin sensitivity, or indices of insulin secretion. Nominal associations were found between rs3731859 and body mass index, waist circumference, fasting GLP-1 levels, and intramyocellular lipids in the soleus muscle (P = .02, P = .02, P = .05, and P = .03, respectively). Our data suggest that a common genetic variation within the GPBAR1 gene may not play a major role in the development of prediabetic phenotypes in our white population.

As a cellular bile acid sensor, farnesoid X receptor (FXR) and the membrane G-coupled receptor (GPBAR1) participate in maintaining bile acid, lipid, and glucose homeostasis. To date, several selective and dual agonists have been developed as promising pharmacological approach to metabolic disorders, with most of them possessing an acidic conjugable function that might compromise their pharmacokinetic distribution. Here, guided by docking calculations, nonacidic 6-ethyl cholane derivatives have been prepared. In vitro pharmacological characterization resulted in the identification of bile acid receptor modulators with improved pharmacokinetic properties.

Bile acids (BAs) as important endogenous ligands can activate farnesoid X receptor (FXR) and G-protein-coupled bile acid receptor 1 (GPBAR1, also known as TGR5) signaling to regulate glycolipid metabolism. In this study, a simple, reliable and sensitive analysis method for simultaneous determination of four BAs from rat feces based on high-performance liquid chromatography with evaporative light scattering detector (HPLC-ELSD) was developed. Chromatographic analysis was performed with the mobile phases of acetonitrile and 0.2% formic acid. All the standard curves exhibited good linearity (R2 ≥ 0.99). The relative standard deviations of precision, stability and repeatability varied from 1.27 to 3.96%, 2.20 to 3.89% and 3.00 to 4.31%, respectively. The validated method was successfully applied to investigate the variation of four BAs in feces from T2DM rats after oral administration of Sanhuang Xiexin Tang (SXT). Data showed that SXT could remarkably increase the contents of conjunct BAs and decrease the contents of free BAs, which might contribute to ameliorate the symptoms of T2DM rats.

Bile acids are steroidal acids found in bile. Primary bile acids are steroids produced via the liver, specifically in peroxisomes.[1][2][3] There, the acids conjugate/connect to hydrophilic amino acids, namely glycine/taurine (i.e., conjugated bile acids called glycocholic and taurocholic acids, respectively); alongside sodium/potassium, they are termed bile salts.[4][5] Secondary bile acids, however, are made via colonic bacteria. Of the organic compounds found in bile, bile acids constitute the large majority.[6][7] Right after being synthesized, bile acids are secreted into bile and concentrated for storage in the gallbladder. Eating then stimulates cholecystokinin release, which causes gallbladder contraction--releasing its bile acids into the duodenum through the sphincter of Oddi.[8][9] The more bile acid that gets secreted, the faster that bile flows. The primary purpose of bile acids is to facilitate the digestion of fat via its surfactant properties, which emulsify fats into micelles.[10] Hormonally, bile acids are also ligands for the farnesoid X receptor (FXR) and GPBAR1 (TGR5).[11] In sum, the three main functions of bile acids are to (1) emulsify fat, (2) excrete cholesterol, and (3) have an antimicrobial effect.[1]

Intestinal metaplasia (IM) increases the risk of gastric cancer. Our previous results indicated that bile acids (BAs) reflux promotes gastric IM development through kruppel-like factor 4 (KLF4) and caudal-type homeobox 2 (CDX2) activation. However, the underlying mechanisms remain largely elusive. Herein, we verified that secondary BAs responsive G-protein-coupled bile acid receptor 1 (GPBAR1, also known as TGR5) was increased significantly in IM specimens. Moreover, TGR5 contributed to deoxycholic acid (DCA)-induced metaplastic phenotype through positively regulating KLF4 and CDX2 at transcriptional level. Then we employed PCR array and identified hepatocyte nuclear factor 4α (HNF4α) as a candidate mediator. Mechanically, DCA treatment could induce HNF4α expression through TGR5 and following ERK1/2 pathway activation. Furthermore, HNF4α mediated the effects of DCA treatment through directly regulating KLF4 and CDX2. Finally, high TGR5 levels were correlated with high HNF4α, KLF4, and CDX2 levels in IM tissues. These findings highlight the TGR5-ERK1/2-HNF4α axis during IM development in patients with BAs reflux, which may help to understand the mechanism underlying IM development and provide prospective strategies for IM treatment.

Background: Ovarian cancer (OC) is the most lethal malignancy of all female cancers and lacks an effective prognostic biomarker. Serous ovarian cancer (SOC) is the most common OC histologic type. The expression and function of bile acid receptor, G-protein-coupled bile acid receptor-1 (GPBAR1), in tumor progression remains controversial, and its clinical significance in SOC is unclear.

Materials and methods: In our study, we detected the expression of GPBAR1 in SOCs and normal ovarian tissues with quantitative real-time polymerase chain reaction and immunohistochemistry to detect its expression pattern. Moreover, the prognostic significance of GPBAR1 was investigated with univariate and multivariate analyses. The function of GPBAR1 in regulating SOC proliferation was studied and the underlying mechanism was investigated with experiments in vitro.

Results: GPBAR1 was overexpressed in SOCs compared with the normal ovarian tissues. In the 166 SOCs, subsets with low and high GPBAR1 accounted for 57.23% and 42.77%, respectively. Moreover, our results suggested that GPBAR1 expression was significantly associated with poor prognosis and can be considered as an independent prognostic biomarker. With experiments in vitro, we suggested that GPBAR1 promoted SOC proliferation by increasing Smad4 ubiquitination, which required the involvement of GPBAR1-induced ERK phosphorylation.

Conclusions: GPBAR1 was overexpressed in SOC and predicted the poor prognosis of SOC. We showed that GPBAR1 promoted SOC proliferation by activating ERK and ubiquitining Smad4. Our results suggested that GPBAR1 was a supplement to better classify SOC on the basis of the molecular profile and that GPBAR1 may be a potential drug target of SOC.

<em>GPBAR1</em> agonists have been identified as potential leads for the treatment of diseases related to colon inflammation such as Crohn's and ulcerative colitis. In this paper, we report the discovery of a small library of hyodeoxycholane analogues, decorated at C-6 with different substituents, as potent and selective <em>GPBAR1</em> agonists. <i>In vitro</i> pharmacological assays showed that compound <b>6</b> selectively activates <em>GPBAR1</em> (EC₅₀ = 0.3 μM) and reduces the production of pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α) in THP1 cells. The binding mode of compound <b>6</b> in <em>GPBAR1</em> was elucidated by docking calculations. Moreover, compound <b>6</b> protects against TNBS-induced colitis in <em>Gpbar1</em>^+/+ rodent model, representing an intriguing lead for the treatment of these inflammatory disorders.

A series of non-steroidal GPBAR1 (TGR5) agonists was developed from a hit in a high-throughput screening campaign. Lead identification efforts produced biphenyl-4-carboxylic acid derivative (R)-22, which displayed a robust secretion of PYY after oral administration in a degree that can be correlated with the unbound plasma concentration. Further optimisation work focusing on reduction of the lipophilicity provided the 1-phenylpiperidine-4-carboxylic acid derivative (R)-29 (RO5527239), which showed an improved secretion of PYY and GLP-1, translating into a significant reduction of postprandial blood glucose excursion in an oral glucose tolerance test in DIO mice.

Introduction: Previous studies in patients with irritable bowel syndrome (IBS) showed immune activation, secretion, and barrier dysfunction in duodenal, jejunal, or colorectal mucosa. This study aimed to measure ileal mucosal expression of genes and proteins associated with mucosal functions.

Methods: We measured by reverse transcription polymerase chain reaction messenger RNA (mRNA) expression of 78 genes (reflecting tight junction proteins, chemokines, innate immunity, ion channels, and transmitters) and 5 proteins (barrier, bile acid receptor, and ion exchanger) in terminal ileal mucosa from 11 patients with IBS-diarrhea (IBS-D), 17 patients with IBS-constipation (IBS-C), and 14 healthy controls. Fold changes in mRNA were calculated using 2(-Δ, ΔCT) formula. Group differences were measured using analysis of variance. Protein ratios relative to healthy controls were based on Western blot analysis. Nominal P values (P < 0.05) are reported.

Results: In ileal mucosal biopsies, significant differences of mRNA expression in IBS-D relative to IBS-C were upregulation of barrier proteins (TJP1, FN1, CLDN1, and CLDN12), repair function (TFF1), and cellular functions. In ileal mucosal biopsies, mRNA expression in IBS-C relative to healthy controls was reduced GPBAR1 receptor, myosin light chain kinase (MYLK in barrier function), and innate immunity (TLR3), but increased mRNA expression of cadherin cell adhesion mechanisms (CTNNB1) and transport genes SLC9A1 (Na-H exchanger [NHE1]) and INADL (indirect effect on ion transport).

Discussion: These data support a role of ileal mucosal dysfunction in IBS, including barrier dysfunction in IBS-D and alterations in absorption/secretion mechanisms in IBS-C.

Trial registration: ClinicalTrials.gov NCT02163213.

Obesity is dramatically increasing worldwide. Ginsenosides extracted from ginseng have been reported against obesity and the associated metabolic disorders. As a subtype of ginsenoside, ginsenoside Ro is a critical constituent of ginseng. However, its specific effects on obesity remains unknown. G protein-coupled bile acid receptor 5 (TGR5, also known as GPBAR1) is a bile acid membrane receptor, widely expressed in human tissues contributing to various metabolic processes to confer the regulations of glucose and lipid homeostasis.TGR5 has displayed potentials as a therapeutic target for the treatment of metabolic disorders. Here, we explore the anti-obesity effect of ginsenoside Ro with TGR5 activation screened by a library of natural products. Our results showed that the ginsenoside Ro (90mg/kg) treatment ameliorated body weight and lipid accumulation in multiple metabolic organs of high fat diet-induced obese (DIO) mice without affecting food intake, and improved oral glucose tolerance tests (OGTT), intraperitoneal insulin tolerance tests (IPITT), and fasting serum glucose. We also found that triglyceride (TG) and total cholesterol (TC) in serum and liver were significantly decreased after ginsenoside Ro treatment. Then we used Tgr5 knockout mice to explore the role of Tgr5 in the anti-obesity effect of ginsenoside Ro.Our results further demonstrated that ginsenoside Ro promoted glucagon-like peptide-1 (GLP-1) secretion and energy expenditure in wild type DIO mice. However, the stimulation of ginsenoside Ro on GLP-1 secretion and energy expenditure were restrained in the Tgr5 knockout mice.In conclusion, our findings demonstrated that ginsenoside Ro ameliorates obesity and insulin resistance in DIO mice via activating TGR5. Significance Statement Obesityis dramatically increasing worldwide and it contributes to multiple metabolic diseases. TGR5 is a potential therapeutic target for the treatment of metabolic disorders. Ginsenoside Ro, as aoleanane-type ginsenoside, ameliorates obesity and insulin resistance, promotes GLP-1 secretion, increases energy expenditure via activating TGR5. Ginsenoside Ro could be a potential leading compound for treating obesity and its associated metabolic diseases.

Keywords: GLP1; bile acids; g protein-coupled receptors (GPCRS); obesity.

The activation of the Takeda G-protein receptor 5 (TGR5, also known as the G protein-coupled bile acid receptor 1, GPBAR1) in enteroendocrine L-cells results in secretion of the anti-diabetic hormone Glucagon-Like Peptide 1 (GLP-1) into systemic circulation. Consequently, recent research has focused on identification and development of TGR5 agonists as type 2 diabetes therapeutics. However, the clinical application of TGR5 agonists has been hampered by side effects of these compounds that primarily result from their absorption into circulation. Here we describe an in vitro screening protocol to evaluate the TGR5 agonism, GLP-1 secretion, and gut-restricted properties of small molecules. The protocol involves differentiating gut epithelial and endocrine cells together in transwells to assess both the pharmacodynamics of TGR5 agonists and the toxicity of compounds to the intestinal monolayer. As a proof of concept, we demonstrate the use of the protocol in evaluating properties of naturally occurring bile acid metabolites that are potent TGR5 agonists. This protocol is adapted from Chaudhari et al. (2021).

Keywords: Diabetes; Enteroendocrine cells; GLP-1; Gut-restriction; Intestinal permeability; TGR5.

Emerging evidence has shown that bile acids play important roles in renal physiology and diseases by activating two major receptors, the nuclear farnesoid X receptor (FXR) and the membrane G protein-coupled bile acid receptor-1 (Gpbar1; also known as TGR5). Both FXR and TGR5 have been identified in human and rodent kidneys, where they are deeply involved in renal water handling. In mice, FXR- or TGR5-related gene deficiency has been associated with reduced aquaporin-2 expression accompanied with impaired urinary concentration ability. In this mini-review, we briefly discuss the current understanding of FXR/TGR5 signaling in the kidneys, with a special focus on the regulation of aquaporin-2 expression by bile acids in the collecting ducts and its potential significance in disease conditions.

The cysteinyl leukotrienes (CysLTs), i.e. LTC₄, LTD₄ and LTE₄, are a family of proinflammatory agents synthesized from the arachidonic acid. In target cells, these lipid mediators bind to the cysteinyl leukotriene receptors (CysLTR), a family of seven transmembrane G-protein coupled receptors. The CysLT₁R is a validated target for treatment of pulmonary diseases and several selective antagonists for this receptor, including montelukast, zafirlukast and pranlukast, have shown effective in the management of asthma. Nevertheless, others CysLT₁R antagonists, such as the alpha-pentyl-3-[2-quinolinylmethoxy] benzyl alcohol (REV5901), have been extensively characterized without reaching sufficient priority for clinical development. Since drug reposition is an efficient approach for maximizing investment in drug discovery, we have investigated whether CysLT₁R antagonists might exert off-target effects. In the report we demonstrate that REV5901 interacts with GPBAR1, a well characterized cell membrane receptor for secondary bile acids. REV5901 transactivates GPBAR1 in GPBAR1-transfected cells with an EC₅₀ of 2.5 µM and accommodates the GPBAR1 binding site as shown by in silico analysis. Exposure of macrophages to REV5901 abrogates the inflammatory response elicited by bacterial endotoxin in a GPBAR1-dependent manner. In vivo, in contrast to montelukast, REV5901 attenuates inflammation and immune dysfunction in rodent models of colitis. The beneficial effects exerted by REV5901 in these models were abrogated by GPBAR1 gene ablation, confirming that REV5901, a shelved CysLT₁R antagonist, is a GPBAR1 ligand. These data ground the basis for the development of novel hybrid ligands designed for simultaneous modulation of CysTL₁R and GPBAR1.