Farnesoid X Receptor Knockout Mice Research Articles

FXR deletion in hepatocytes does not affect the severity of alcoholic liver disease in mice

Emerging evidence has shown that FXR activation ameliorates the development of alcoholic liver diseases (ALD) while whole-body deficiency of FXR in mice leads to more severe ALD. However, it’s unknown whether the enhanced susceptibility to ALD development in FXR−/− mice is due to deficiency of hepatic FXR or increased toxicity secondary to increased bile acid (BA) levels. Hepatocyte-specific FXR knockout mice (FXRhep−/−) present similar BA levels compared to wild-type mice, and are therefore a useful model to study a direct role of hepatic FXR in ALD development. FXRhep−/− mice were subject to an ALD model with chronic plus binge drinking of alcohol to determine the effects of hepatic FXR deficiency on ALD development. The FXRhep−/− mice showed an altered expression of genes involved in BA and lipid homeostasis with alcohol treatment. Despite a slightly increased trend in hepatic lipid deposition and collagen accumulation in FXRhep−/− mice, there were no significant differences in the severity of steatosis, inflammation, or fibrosis between WT and FXRhep−/− mice. Therefore, these findings indicate that FXR deficiency in hepatocytes might only play a minor role in ALD development. Deficiency of FXR in other non-hepatic tissues and/or increased BA levels resultant from whole-body FXR deficiency might be responsible for more severe ALD development.

Effects of FXR Deficiency in Acute Phase Response After Bacterial Infection

Farnesoid X receptor (FXR) is a ligand‐activated nuclear receptor and a transcription factor, regulating bile acid synthesis and transport. FXR is highly expressed in the liver, and more recently FXR has been shown to play a key role in modulating inflammation. Studies have shown that FXR, when activated, acts as a protective agent against liver inflammation and potentially liver diseases such as nonalcoholic steatohepatitis, a part of fatty liver disease. Furthermore, FXR may regulate acute phase proteins, which are secreted as a result of acute phase response (APR)—a systemic reaction that is important for innate immunity and is caused by infection, trauma, or tissue injury. However, the exact mechanism is not well‐established. Thus, the purpose of this study was to investigate the role of FXR in the regulation of the hepatic APR using a bacterial infection model. To understand the mechanism and the effects, hepatocyte‐specific FXR knockout mice (FXRhep −/−) and wild‐type control mice (WT) were injected with Escherichia coli (E. coli) intraperitoneally. Serum, liver, and spleen were isolated 24 hrs following bacterial exposure, and in vivo bacterial counts were determined in whole blood, liver, and spleen. Gene expression of inflammatory cytokines (Tnfα, Il‐1β, Il‐6,) and acute phase proteins (LCN2, Mcp‐1, and Saa3) were measured using quantitative PCR (qPCR) in both liver and spleen. Compared to WT mice, FXRhep −/− mice had significantly increased bacterial load in the liver and spleen following the E.coli treatment, suggesting that they were more susceptible to bacterial infection; however, there was no significant increase in bacterial load in the blood. Serum activities of ALT and AST in FXRhep −/− mice were also elevated, indicating increased liver damage after E.coli treatment. In addition, following the E.coli treatment, gene expression showed a diminished induction of acute phase proteins, Mcp‐1 and Saa3, along with cytokines IL‐1β, IL‐6, and Tnfα in FXRhep −/− mice compared to WT mice. Furthermore, this infection resulted in high levels of LCN2 induction for both the WT and FXRhep −/− mice. In conclusion, the study demonstrates that FXR might be a putative regulator of hepatic acute phase proteins.Support or Funding InformationR25ES020721, R01GM104037 and ASPET SURF Intern ProgramThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

ZFP36L1 is a post‐transcriptional regulator of lipid metabolism.

Bile acids are detergents and important signaling molecules that activate the nuclear receptor FXR to control key metabolic processes, including feedback mechanisms to maintain bile acid homeostasis. FXR agonists are currently promising therapeutic agents to treat non‐alcoholic steatohepatitis (NASH), a significant risk factor for cardiovascular disease. FXR is the central rheostat of bile acid metabolism, and activation of FXR decreases the mRNA levels of several bile acid synthetic genes, including the expression of the gene encoding the rate‐limiting enzyme of bile acid synthesis, Cyp7a1. We show that Cyp7a1 mRNA levels were rapidly reduced after pharmacologic FXR activation in wild‐type, but not Fxr−/− or liver‐specific Fxr knockout mice (FxrL‐KO). The rapid decrease in Cyp7a1 mRNA suggested a previously unidentified post‐transcriptional mechanism. To identify the molecular mechanism, we used FXR ChIP‐Seq and RNA‐Seq to identify the RNA binding protein Zfp36l1 as a novel FXR target gene. We showed that FXR activation using synthetic and endogenous agonists increases ZFP36L1 mRNA and protein levels in wild‐type, but not Fxr−/− mice. Further, the increased ZFP36L1 mRNA and protein was observed as early as 30 minutes after FXR activation. ZFP36L1 is a bona‐fide RNA binding protein that promotes degradation of mRNA targets by binding to AU‐rich elements (AREs) in the 3′ UTR. We generated in vivo and in vitro gain‐of‐function models and we used reporter assays to show that ZFP36L1 targets the Cyp7a1 UTR. In mice, hepatic overexpression of ZFP36L1 decreased Cyp7a1 mRNA and protein and decreased bile acid levels. To complement our gain‐of‐function studies, we generated liver‐specific Zfp36l1 knockout mice (Zfp36l1L‐KO) and we show that loss of Zfp36l1 resulted in elevated Cyp7a1 mRNA and protein, and increased bile acid levels. Given that bile acids are important metabolites that control lipid absorption and signaling, we investigated whether loss of hepatic Zfp36l1 resulted in more broad metabolic dysfunction. Western diet fed Zfp36l1L‐KO mice had reduced body weight gain, specifically in adipose tissue depots compared to littermate Zfp36l1flox‐flox mice. In addition, Zfp36l1L‐KO mice also had reduced hepatic steatosis, without any differences in energy expenditure compared to littermate Zfp36l1flox‐flox mice. The differences in adiposity and steatosis were attributed to reduced lipid absorption, as Zfp36l1L‐KO mice have increased fecal caloric content and reduced triglyceride absorption as determined by an intragastric fat tolerance test. The decreased lipid absorption is consistent with an altered bile acid metabolism. Thus, we have identified a novel pathway that controls Cyp7a1 and bile acid metabolism but may also have wider implications in diseases such as obesity and hepatosteatosis, which are both significant risk factors for cardiovascular disease.Support or Funding InformationNIH grants HL118161 and HL136543 to E.J.T., and AHA grant SDG18440015 and NIH grants HL122677 and DK102559 to T.Q.de A.V.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

GW4064 attenuates lipopolysaccharide‑induced hepatic inflammation and apoptosis through inhibition of the Toll‑like receptor 4‑mediated p38 mitogen‑activated protein kinase signaling pathway in mice.

Liver injury is associated with devastating consequences caused by inflammation and apoptosis. The farnesoid X receptor (FXR) is a nuclear receptor that has an essential role in hepatoprotection by maintaining the homeostasis of liver metabolism. The present study investigated the capacity of the FXR agonist GW4064 to protect the livers of mice from lipo-polysaccharide (LPS)-induced inflammation and apoptosis. Male C57BL/6J [wild-type (WT)] and FXR knockout (KO) mice were intraperitoneally injected with LPS or saline. LPS-treated mice were intraperitoneally injected with vehicle or GW4064 (20 mg/kg) twice and then sacrificed. Activation of FXR by GW4064 alleviated hepatic inflammation in the LPS-induced murine liver injury model as reflected by reduced serum levels of aspartate aminotransferase and pro-inflammatory cytokine mRNA expression, including tumor necrosis factor-α, as well as interleukin-6 and -1β in WT mice. In addition, Toll-like receptor 4 (TLR4), p38 mitogen-activated protein kinase (MAPK), B-cell lymphoma-2-associated X protein and cytochrome c protein levels were decreased in WT mice receiving LPS with simultaneous GW4064 administration compared with those receiving LPS alone, while this was not observed in FXR KO mice. These results indicated that in WT mice, administration of GW4064 ameliorated LPS-mediated liver injury by upregulation of FXR expression, which was in part mediated by the TLR4/p38 MAPK pathway.

Hepatic inflammation caused by dysregulated bile acid synthesis is reversible by butyrate supplementation.

Dysregulated bile acid (BA) synthesis or reduced farnesoid X receptor (FXR) levels are found in patients having metabolic diseases, autoimmune hepatitis, and liver cirrhosis or cancer. The objective of this study was to establish the relationship between butyrate and dysregulated BA synthesis-induced hepatitis as well as the effect of butyrate in reversing the liver pathology. Wild-type (WT) and FXR knockout (KO) male mice were placed on a control (CD) or western diet (WD) for 15 months. In the presence or absence of butyrate supplementation, feces obtained from 15-month-old WD-fed FXR KO mice, which had severe hepatitis and liver tumors, were transplanted to 7-month-old WD-fed FXR KO for 3 months. Hepatic phenotypes, microbiota profile, and BA composition were analyzed. Butyrate-generating bacteria and colonic butyrate concentration were reduced due to FXR inactivation and further reduced by WD intake. In addition, WD-fed FXR KO male mice had the highest concentration of hepatic β-muricholic acid (β-MCA) and bacteria-generated deoxycholic acid (DCA) accompanied by serious hepatitis. Moreover, dysregulated BA and reduced SCFA signaling co-existed in both human liver cancers and WD-fed FXR KO mice. Microbiota transplantation using butyrate-deficient feces derived from 15-month-old WD-fed FXR KO mice increased hepatic lymphocyte numbers as well as hepatic β-MCA and DCA concentrations. Furthermore, butyrate supplementation reduced hepatic β-MCA as well as DCA and eliminated hepatic lymphocyte infiltration. In conclusion, reduced butyrate contributes to the development of hepatitis in the FXR KO mouse model. In addition, butyrate reverses dysregulated BA synthesis and its associated hepatitis. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Chicken bile powder protects against α-naphthylisothiocyanate-induced cholestatic liver injury in mice.

This study explored the effects of chicken bile powder (CBP), a 2000-year-old Chinese medicine, on α-naphthyl isothiocyanate (ANIT)-induced intrahepatic cholestasis in mice. CBP treatment for 14 days significantly ameliorated ANIT-induced changes in serum alanine aminotransferase, aspartate aminotransferase, bile acids, bilirubin, γ-glutamyl transpeptidase, alkaline phosphatase, and liver tissue morphology. Serum metabolomics showed changes in 24 metabolites in ANIT-exposed mice; 16 of these metabolites were reversed by CBP treatment via two main pathways (bile acid biosynthesis and arachidonic acid metabolism). Additionally, CBP administration markedly increased fecal and biliary bile acid excretion, and reduced total and hydrophobic bile acid levels in the livers of cholestatic mice. Moreover, CBP increased liver expression of bile acid efflux transporters and metabolic enzymes. It also attenuated ANIT-induced increases in hepatic nuclear factor-κB-mediated inflammatory signaling, and increased liver expression of the nuclear farnesoid X receptor (FXR) in cholestatic mice. CBP also activated FXR in vitro in HEK293T cells expressing mouse Na+-taurocholate cotransporting polypeptide. It did not ameliorate the ANIT-induced liver injuries in FXR-knockout mice. These results suggested that CBP provided protection from cholestatic liver injury by restoring bile acid homeostasis and reducing inflammation in a FXR-dependent manner.

Altenusin, a Nonsteroidal Microbial Metabolite, Attenuates Nonalcoholic Fatty Liver Disease by Activating the Farnesoid X Receptor.

Nonalcoholic fatty liver disease (NAFLD) is a prevalent chronic liver disease. The incidence of NAFLD has increased steadily due to its close association with the global epidemic of obesity and type 2 diabetes. However, there is no effective pharmacological therapy approved for NAFLD. Farnesoid X receptor (FXR), a member of the nuclear receptor subfamily, plays important roles in maintaining the homeostasis of bile acids, glucose, and lipids. FXR agonists have shown promise for the treatment of NAFLD. In this study, we report altenusin (2076A), a natural nonsteroidal fungal metabolite, as a novel selective agonist of FXR with an EC50 value of 3.2 ± 0.2 μM. Administration of 2076A protected mice from high-fat diet (HFD)-induced obesity by reducing the body weight and fat mass by 22.9% and 50.0%, respectively. Administration of 2076A also decreased the blood glucose level from 178.3 ± 12.4 mg/dl to 116.2 ± 4.1 mg/dl and the serum insulin level from 1.4 ± 0.6 ng/dl to 0.4 ± 0.1 ng/dl. Moreover, 2076A treatment nearly reversed HFD-induced hepatic lipid droplet accumulation and macrovesicular steatosis. These metabolic effects were abolished in FXR knockout mice. Mechanistically, the metabolic benefits of 2076A might have been accounted for by the increased insulin sensitivity and suppression of genes that are involved in hepatic gluconeogenesis and lipogenesis. In summary, we have uncovered a new class of nonsteroidal FXR agonist that shows promise in treating NAFLD and the associated metabolic syndrome.

Western Diet–Induced Dysbiosis in Farnesoid X Receptor Knockout Mice Causes Persistent Hepatic Inflammation after Antibiotic Treatment

Patients who have liver cirrhosis and liver cancer also have reduced farnesoid X receptor (FXR). The current study analyzes the effect of diet through microbiota that affect hepatic inflammation in FXR knockout (KO) mice. Wild-type and FXR KO mice were on a control (CD) or Western diet (WD) for 10 months. In addition, both CD- and WD-fed FXR KO male mice, which had hepatic lymphocyte and neutrophil infiltration, were treated by vancomycin, polymyxin B, and Abx (ampicillin, neomycin, metronidazole, and vancomycin). Mice were subjected to morphological analysis as well as gut microbiota and bile acid profiling. Male WD-fed FXR KO mice had the most severe steatohepatitis. FXR KO also had reduced Firmicutes and increased Proteobacteria, which could be reversed by Abx. In addition, Abx eliminated hepatic neutrophils and lymphocytes in CD-fed, but not WD-fed, FXR KO mice. Proteobacteria and Bacteroidetes persisted in WD-fed FXR KO mice even after Abx treatment. Only polymyxin B could reduce hepatic lymphocytes in WD-fed FXR KO mice. The reduced hepatic inflammation by antibiotics was accompanied by decreased free and conjugated secondary bile acids as well as changes in gut microbiota. Our data revealed that Lactococcus, Lactobacillus, and Coprococcus protect the liver from inflammation.

Farnesoid X receptor agonist GW4064 ameliorates lipopolysaccharide-induced ileocolitis through TLR4/MyD88 pathway related mitochondrial dysfunction in mice

Inflammatory bowel disease (IBD) is a complex and relapsing inflammatory condition of the gastro intestinal tract characterized by diarrhoea and abdominal pain. Farnesoid X receptor (FXR) plays an important role in enteroprotection and mucosal injury by regulating inflammatory responses and barrier function in the intestinal tract. Here we show the mechanisms of FXR agonist, GW4064, inhibits mucosal injury in ileum caused by lipopolysaccharides (LPS). Ileum injury was induced by intraperitoneal injection of LPS in Wild-type (WT) and FXR knockout (KO) mice. GW4064 alleviates LPS-mediated tight junction dysfunction as well as macrophage infiltration in WT mice, but not in FXR KO mice. Interesting, GW4064 suppresses NACHT, LRR and PYD domains-containing protein 3 (NALP3) inflammasome mediates tumor necrosis factor-alpha (TNF-α), interleukin (IL)-6 and IL-1β, as well as mitochondrial respiratory complexes mRNA expression in WT and FXR KO mice treated with LPS. This results demonstrated that central roles of FXR in coordinating regulation of both inflammation and mitochondrial dysfunction. We propose that GW4064 is promising therapeutic agent for treatment of ileocolitis.

Gender Differences in Bile Acids and Microbiota in Relationship with Gender Dissimilarity in Steatosis Induced by Diet and FXR Inactivation

This study aims to uncover how specific bacteria and bile acids (BAs) contribute to steatosis induced by diet and farnesoid X receptor (FXR) deficiency in both genders. A control diet (CD) and Western diet (WD), which contains high fat and carbohydrate, were used to feed wild type (WT) and FXR knockout (KO) mice followed by phenotyping characterization as well as BA and microbiota profiling. Our data revealed that male WD-fed FXR KO mice had the most severe steatosis and highest hepatic and serum lipids as well as insulin resistance among the eight studied groups. Gender differences in WD-induced steatosis, insulin sensitivity, and predicted microbiota functions were all FXR-dependent. FXR deficiency enriched Desulfovibrionaceae, Deferribacteraceae, and Helicobacteraceae, which were accompanied by increased hepatic taurine-conjugated cholic acid and β-muricholic acid as well as hepatic and serum lipids. Additionally, distinct microbiota profiles were found in WD-fed WT mice harboring simple steatosis and CD-fed FXR KO mice, in which the steatosis had a potential to develop into liver cancer. Together, the presented data revealed FXR-dependent concomitant relationships between gut microbiota, BAs, and metabolic diseases in both genders. Gender differences in BAs and microbiota may account for gender dissimilarity in metabolism and metabolic diseases.

Targeting the Gut Microbiota-FXR Signaling Axis for Glycemic Control: Does a Dietary Supplement Work Magic?

Glucose-dependent organs such as the brain are sustained through periods of fasting by glucose production in the liver, called hepatic gluconeogenesis. Normally, rising blood glucose levels homeostatically suppress gluconeogenesis. In obesity-related type 2 diabetes, however, insulin resistance and elevated glucagon inhibit the suppression of gluconeogenesis, contributing to hyperglycemia. Therapeutic intervention to suppress hepatic gluconeogenesis is therefore clinically important for controlling glucose in type 2 diabetes. Recent studies have suggested that the bile acid−farnesoid X receptor (FXR) signaling axis is a potential therapeutic target for metabolic disorders, including hyperglycemia caused by elevated hepatic gluconeogenesis (1,2). Bile acids are synthesized in the liver from cholesterol as conjugates of taurine (in mice) or glycine (in humans) and delivered to the gut to facilitate solubilization of dietary lipids and vitamins. Bile acids and their metabolites also function as endogenous ligands of FXR, a ligand-activated transcription factor highly expressed in the liver and the intestine. Bile acid−FXR signaling provides negative feedback control of bile acid production and transport to maintain bile acid homeostasis (3). Moreover, the bile acid−FXR signaling axis has been shown to regulate fat and glucose metabolism (4–7). Comparative analysis of global, liver-specific, and intestine-specific FXR knockout mice revealed a complex signaling network, wherein activation of the liver FXR and intestinal FXR result in distinct metabolic outcomes in diet-induced or genetic obesity models (6,8–12). In particular, several recent studies indicate that selective inhibition of intestinal FXR improves metabolic phenotypes in obese animals (9 …

Farnesoid X Receptor Activation Promotes Hepatic Amino Acid Catabolism and Ammonium Clearance in Mice

The nuclear receptor subfamily 1 group H member 4 (NR1H4 or farnesoid X receptor [FXR]) regulates bile acid synthesis, transport, and catabolism. FXR also regulates postprandial lipid and glucose metabolism. We performed quantitative proteomic analyses of liver tissues from mice to evaluate these functions and investigate whether FXR regulates amino acid metabolism. To study the role of FXR in mouse liver, we used mice with a disruption of Nr1h4 (FXR-knockout mice) and compared them with floxed control mice. Mice were gavaged with the FXR agonist obeticholic acid or vehicle for 11 days. Proteome analyses, as well as targeted metabolomics and chromatin immunoprecipitation, were performed on the livers of these mice. Primary rat hepatocytes were used to validate the role of FXR in amino acid catabolism by gene expression and metabolomics studies. Finally, control mice and mice with liver-specific disruption of Nr1h4 (liver FXR-knockout mice) were re-fed with a high-protein diet after 6 hours fasting and gavaged a 15NH4Cl tracer. Gene expression and the metabolome were studied in the livers and plasma from these mice. In livers of control mice and primary rat hepatocytes, activation of FXR with obeticholic acid increased expression of proteins that regulate amino acid degradation, ureagenesis, and glutamine synthesis. We found FXR to bind to regulatory sites of genes encoding these proteins in control livers. Liver tissues from FXR-knockout mice had reduced expression of urea cycle proteins, and accumulated precursors of ureagenesis, compared with control mice. In liver FXR-knockout mice on a high-protein diet, the plasma concentration of newly formed urea was significantly decreased compared with controls. In addition, liver FXR-knockout mice had reduced hepatic expression of enzymes that regulate ammonium detoxification compared with controls. In contrast, obeticholic acid increased expression of genes encoding enzymes involved in ureagenesis compared with vehicle in C57Bl/6 mice. In livers of mice,FXR regulates amino acid catabolism and detoxification of ammonium via ureagenesis and glutamine synthesis. Failure of the urea cycle and hyperammonemia are common in patients with acute and chronic liver diseases; compounds that activate FXR might promote ammonium clearance in these patients.

Orally Administered Berberine Modulates Hepatic Lipid Metabolism by Altering Microbial Bile Acid Metabolism and the Intestinal FXR Signaling Pathway.

Previous studies suggest that the lipid-lowering effect of berberine (BBR) involves actions on the low-density lipoprotein receptor and the AMP-activated protein kinase signaling pathways. However, the implication of these mechanisms is unclear because of the low bioavailability of BBR. Because the main action site of BBR is the gut and intestinal farnesoid X receptor (FXR) plays a pivotal role in the regulation of lipid metabolism, we hypothesized that the effects of BBR on intestinal FXR signaling pathway might account for its pharmacological effectiveness. Using wild type (WT) and intestine-specific FXR knockout (FXRint-/-) mice, we found that BBR prevented the development of high-fat-diet-induced obesity and ameliorated triglyceride accumulation in livers of WT, but not FXRint-/- mice. BBR increased conjugated bile acids in serum and their excretion in feces. Furthermore, BBR inhibited bile salt hydrolase (BSH) activity in gut microbiota, and significantly increased the levels of tauro-conjugated bile acids, especially tauro-cholic acid(TCA), in the intestine. Both BBR and TCA treatment activated the intestinal FXR pathway and reduced the expression of fatty-acid translocase Cd36 in the liver. These results indicate that BBR may exert its lipid-lowering effect primarily in the gut by modulating the turnover of bile acids and subsequently the ileal FXR signaling pathway. In summary, we provide the first evidence to suggest a new mechanism of BBR action in the intestine that involves, sequentially, inhibiting BSH, elevating TCA, and activating FXR, which lead to the suppression of hepatic expression of Cd36 that results in reduced uptake of long-chain fatty acids in the liver.

The role of bile salts in liver regeneration.

A growing body of evidence has demonstrated that bile salts are important for liver regeneration following partial hepatectomy. The relative bile salt overload after partial liver resection causes activation of bile salt receptors in non-parenchymal (viz. the plasma membrane receptor TGR5) and parenchymal (viz. the intracellular receptor FXR) cells in the liver, thus, providing signals to the regenerative process. Impaired bile salt signaling in mice with genetic deficiency of Tgr5 or Fxr results in delayed liver regeneration after partial hepatectomy, and is accompanied by mortality in case of Fxr knock-out mice. Conversely, compensatory liver re-growth in hepatectomized mice can be stimulated by feeding of bile salts or alisol B 23-acetate, a natural triterpenoid agonist of Fxr. A large number of animal studies underscore the importance of strict maintenance of bile salt homeostasis for proper progression of liver regeneration. Both ileal and hepatic Fxr play a key role in regulation of bile salt homeostasis and, thus, preventing hepatotoxicity caused by excessive levels of bile salts. They further contribute to liver regeneration by induction of mitogenic factors. Agents that target bile salt receptors hold promise as drugs to stimulate liver regeneration in selected patients.

Obeticholic acid, a synthetic bile acid agonist of the farnesoid X receptor, attenuates experimental autoimmune encephalomyelitis

Bile acids are ligands for the nuclear hormone receptor, farnesoid X receptor (FXR). The bile acid-FXR interaction regulates bile acid synthesis, transport, and cholesterol metabolism. Recently, bile acid-FXR regulation has been reported to play an integral role in both hepatic and intestinal inflammation, and in atherosclerosis. In this study, we found that FXR knockout mice had more disease severity in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). Obeticholic acid (6α-ethyl-chenodeoxycholic acid, 6-ECDCA), a synthetic FXR agonist, is an orally available drug that is currently in clinical trials for the treatment of inflammatory diseases such as alcoholic hepatitis, nonalcoholic steatohepatitis, and primary biliary cirrhosis. When we treated mice exhibiting established EAE with 6-ECDCA, or the natural FXR ligand chenodeoxycholic acid (CDCA), clinical disease was ameliorated by (i) suppressing lymphocyte activation and proinflammatory cytokine production; (ii) reducing CD4(+) T cells and CD19(+) B cell populations and their expression of negative checkpoint regulators programmed cell death protein 1 (PD1), programmed death-ligand 1 (PD-L1), and B and T lymphocyte attenuator (BTLA); (iii) increasing CD8(+) T cells and PD1, PDl-1, and BTLA expression; and (iv) reducing VLA-4 expression in both the T- and B-cell populations. Moreover, adoptive transfer of 6-ECDCA- or CDCA-treated donor cells failed to transfer disease in naive recipients. Thus, we show that FXR functions as a negative regulator in neuroinflammation and we highlight that FXR agonists represent a potential previously unidentified therapy for MS.

FXR Primes the Liver for Intestinal FGF15 Signaling by Transient Induction of β-Klotho.

The bile acid (BA)-sensing nuclear receptor, farnesoid X receptor (FXR), regulates postprandial metabolic responses, including inhibition of BA synthesis, by inducing the intestinal hormone, fibroblast growth factor (FGF)15 (FGF19 in human). In this study, we tested a novel hypothesis that FXR not only induces intestinal FGF15 but also primes the liver for effectively responding to the signal by transcriptional induction of the obligate coreceptor for FGF15, β-Klotho (βKL). Activation of FXR by a synthetic agonist, GW4064, in mice increased occupancy of FXR and its DNA-binding partner, retinoid X receptor-α, at FGF15-signaling component genes, particularly βKL, and induced expression of these genes. Interestingly, mRNA levels of Fgfr4, the FGF15 receptor, were not increased by GW4064, but protein levels increased as a result of βKL-dependent increased protein stability. Both FGF receptor 4 and βKL protein levels were substantially decreased in FXR-knockout (KO) mice, and FGF19 signaling, monitored by phosphorylated ERK, was blunted in FXR-KO mice, FXR-KO mouse hepatocytes, and FXR-down-regulated human hepatocytes. Overexpression of βKL in FXR-lacking hepatocytes partially restored FGF19 signaling and inhibition by FGF19 of Cyp7a1, which encodes the rate-limiting BA biosynthetic enzyme. In mice, transient inductions of intestinal Fgf15 and hepatic βKL were temporally correlated after GW4064 treatment, and pretreatment of hepatocytes with GW4064 before FGF19 treatment enhanced FGF19 signaling, which was abolished by transcriptional inhibition or βKL down-regulation. This study identifies FXR as a gut-liver metabolic coordinator for FGF15/19 action that orchestrates transient induction of hepatic βKL and intestinal Fgf15/19 in a temporally correlated manner.

Cyclosporin A induced toxicity in mouse liver slices is only slightly aggravated by Fxr-deficiency and co-occurs with upregulation of pro-inflammatory genes and downregulation of genes involved in mitochondrial functions.

BackgroundThe transcription factor farnesoid X receptor (FXR) governs bile acid and energy homeostasis, is involved in inflammation, and has protective functions in the liver. In the present study we investigated the effect of Fxr deficiency in mouse precision cut liver slices (PCLS) exposed to a model hepatotoxicant cyclosporin A (CsA). It was anticipated that Fxr deficiency could aggravate toxicity of CsA in PCLS and pinpoint to novel genes/processes regulated by FXR.MethodsTo test this hypothesis, PCLS obtained from livers of wild type mice (WT-PCLS) and Fxr-knockout mice (FXRKO-PCLS) were treated with 40 μM CsA for 24 h and 48 h. ATP and histological assays were applied to assess the viability of PCLS. DNA microarrays combined with bioinformatics analysis were used to identify genes and processes that were affected by CsA in WT-PCLS and/or FXRKO-PCLS. In addition, WT-PCLS and FXRKO-PCLS were exposed to the endogenous FXR ligand chenodeoxycholic acid (CDCA) and subjected to q-PCR to determine whether subsets of known FXR-targets and the identified genes were regulated upon FXR activation in an FXR-dependent manner.ResultsNo difference in viability was observed between WT-PCLS and FXRKO-PCLS upon CsA treatment. Transcriptomics data analysis revealed that CsA significantly upregulated stress-response and inflammation and significantly downregulated processes involved in lipid and glucose metabolism in WT-PCLS and FXRKO-PCLS. However, only in FXRKO-PCLS, CsA upregulated additional pro-inflammatory genes and downregulated genes related to mitochondrial functions. Furthermore, only in WT-PCLS, CDCA upregulated a subset of known FXR-target genes as well as the regulator of inflammation and mitochondrial functions peroxisome proliferator- activated receptor delta (Ppar delta).ConclusionsAlthough FXR governs energy metabolism, no major differences in response to CsA could be observed between WT-PCLS and FXRKO-PCLS in regulation of processes involved in lipid and glucose metabolism. This finding indicates that CsA does not directly affect FXR functions in relation to the above mentioned processes. However, the more pronounced induction of pro-inflammatory genes and the downregulation of genes involved in mitochondrial functions only in FXRKO-PCLS suggest that FXR deficiency aggravates CsA-induced inflammation and impairs mitochondrial functions. Therefore, FXR can exert its hepatoprotective functions by controlling inflammation and mitochondrial functions, possibly involving an FXR-PPAR delta cross-talk.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-2054-7) contains supplementary material, which is available to authorized users.

Deletion of mouse FXR gene disturbs multiple neurotransmitter systems and alters neurobehavior.

Farnesoid X receptor (FXR) is a nuclear hormone receptor involved in bile acid synthesis and homeostasis. Dysfunction of FXR is involved in cholestasis and atherosclerosis. FXR is prevalent in liver, gallbladder, and intestine, but it is not yet clear whether it modulates neurobehavior. In the current study, we tested the hypothesis that mouse FXR deficiency affects a specific subset of neurotransmitters and results in an unique behavioral phenotype. The FXR knockout mice showed less depressive-like and anxiety-related behavior, but increased motor activity. They had impaired memory and reduced motor coordination. There were changes of glutamatergic, GABAergic, serotoninergic, and norepinephrinergic neurotransmission in either hippocampus or cerebellum. FXR deletion decreased the amount of the GABA synthesis enzyme GAD65 in hippocampus but increased GABA transporter GAT1 in cerebral cortex. FXR deletion increased serum concentrations of many bile acids, including taurodehydrocholic acid, taurocholic acid, deoxycholic acid (DCA), glycocholic acid (GCA), tauro-α-muricholic acid, tauro-ω-muricholic acid, and hyodeoxycholic acid (HDCA). There were also changes in brain concentrations of taurocholic acid, taurodehydrocholic acid, tauro-ω-muricholic acid, tauro-β-muricholic acid, deoxycholic acid, and lithocholic acid (LCA). Taken together, the results from studies with FXR knockout mice suggest that FXR contributes to the homeostasis of multiple neurotransmitter systems in different brain regions and modulates neurobehavior. The effect appears to be at least partially mediated by bile acids that are known to cross the blood-brain barrier (BBB) inducing potential neurotoxicity.

Role of FXR in β-cells of lean and obese mice.

We have recently shown that the bile acid (BA) taurochenodeoxycholate (TCDC) acutely stimulates insulin secretion via activation of the farnesoid X receptor (FXR). Aims of the current investigation were to discriminate between nongenomic (≤1 h) and genomic effects (24-48 h) of BAs on β-cells and to evaluate whether FXR can modulate the adverse effects of a high-fat diet (HFD). TCDC (500 nM) as well as glycine-conjugated and unconjugated CDC (chenodeoxycholate) increased insulin secretion in acute incubations but did not evoke additional effects after 1-2 days of preincubation. The BAs did not stimulate β-cells of FXR-knockout (KO) mice and activation of the G protein-coupled BA receptor TGR5 was ineffective, suggesting that FXR is the sole BA receptor in β-cells activated by TCDC and its analogues. As opposed to lean mice, obese FXR-KO mice did not show HFD-induced glucose intolerance and increased fasting glucose. The beneficial impact of FXR-KO on glucose metabolism cannot be explained by an adaptive compensation of insulin secretion or β-cell mass. Interestingly, in contrast to its effect on islets from lean mice, the FXR agonist GW4064 was ineffective in stimulating insulin secretion of islets from wild type mice fed a HFD or isolated islets kept in a glucolipotoxic medium. Additional feeding of CDC restored the effect of GW4064. CDC prevented HFD-induced impairment of glucose tolerance and in vitro effects of glucolipotoxicity. The data show that the FXR is the most important BA receptor in β-cells and that FXR signaling in β-cells is impaired by overnutrition, which alters activatability of the FXR.

Ménage-à-trois of bariatric surgery, bile acids and the gut microbiome.

Bariatric surgeries have emerged as highly effective treatments for obesity associated type-2 diabetes mellitus. Evidently, the desired therapeutic endpoints such as rates of weight loss, lower levels of glycated hemoglobin and remission of diabetes are achieved more rapidly and last longer following bariatric surgery, as opposed to drug therapies alone. In light of these findings, it has been suspected that in addition to causing weight loss dependent glucose intolerance, bariatric surgery induces other physiological changes that contribute to the alleviation of diabetes. However, the putative post-surgical neuro-hormonal pathways that underpin the therapeutic benefits of bariatric surgery remain undefined. In a recent report, Ryan and colleagues shed new light on the potential mechanisms that determine the salutary effects of bariatric surgery in mice. The authors demonstrated that the improved glucose tolerance and weight loss in mice after vertical sleeve gastrectomy (VSG) surgery were likely to be caused by post-surgical changes in circulating bile acids and farnesoid-X receptor (FXR) signaling, both of which were also mechanistically linked to changes in the microbial ecology of the gut. The authors arrived at this conclusion from a comparison of genome-wide, metabolic consequences of VSG surgery in obese wild type (WT) and FXR knockout mice. Gene expression in the distal small intestines of WT and FXR knockout mice revealed that the pathways regulating bile acid composition, nutrient metabolism and anti-oxidant defense were differentially altered by VSG surgery in WT and FXR(-/-) mice. Based on these data Ryan et al, hypothesized that bile acid homeostasis and FXR signaling were mechanistically linked to the gut microbiota that played a role in modulating post-surgical changes in total body mass and glucose tolerance. The authors' data provide a plausible explanation for putative weight loss-independent benefits of bariatric surgery and its relationship with metabolism of bile acids.