Farnesoid X Receptor Target Genes Research Articles

Aspirin Caused Intestinal Damage through FXR and ET-1 Signaling Pathways.

Aspirin is a non-steroidal, anti-inflammatory drug often used long term. However, long-term or large doses will cause gastrointestinal adverse reactions. To explore the mechanism of intestinal damage, we used non-targeted metabolomics; farnesoid X receptor (FXR) knockout mice, which were compared with wild-type mice; FXR agonists obeticholic acid (OCA) and chenodeoxycholic acid (CDCA); and endothelin-producing inhibitor estradiol to explore the mechanisms of acute and chronic intestinal injuries induced by aspirin from the perspective of molecular biology. Changes were found in the bile acids taurocholate acid (TCA) and tauro-β-muricholic acid (T-β-MCA) in the duodenum, and we detected a significant inhibition of FXR target genes. After additional administration of the FXR agonists OCA and CDCA, duodenal villus damage and inflammation were effectively improved. The results in the FXR knockout mice and wild-type mice showed that the overexpression of endothelin 1 (ET-1) was independent of FXR regulation after aspirin exposure, whereas CDCA was able to restore the activation of ET-1, which was induced by aspirin in wild-type mice in an FXR-dependent manner. The inhibition of ET-1 production could also effectively protect against small bowel damage. Therefore, the study revealed the key roles of the FXR and ET-1 pathways in acute and chronic aspirin-induced intestinal injuries, as well as strategies on alleviating aspirin-induced gastrointestinal injury by activating FXR and inhibiting ET-1 overexpression.

Discovery of novel and selective farnesoid X receptor antagonists through structure-based virtual screening, preliminary structure-activity relationship study, and biological evaluation

Farnesoid X receptor (FXR) is a bile acids receptor and plays a crucial role in regulating bile acids, lipids, and glucose metabolism. Previous research suggests that inhibiting FXR activation can be beneficial in reducing cholesterol and low-density lipoprotein cholesterol (LDL-C) levels, offering potential treatment options for metabolic syndrome with lipid disorders. Herein, we report p-acetylaminobenzene sulfonate derivatives as a novel scaffold of FXR antagonists by multistage screening. Among these derivatives, compound F44-A13 exhibited a half-maximal inhibitory concentration of 1.1 μM. Furthermore, compound F44-A13 demonstrated effective inhibition of FXR activation in cellular assays and exhibited high selectivity over eleven other nuclear receptors. Besides, compound F44-A13 significantly suppressed the regulation of FXR target genes Shp, Besp, and Cyp7a1, while reducing cholesterol levels in human hepatoma HepG2 cells. Pharmacological studies conducted on C57BL/6 mice further confirmed that compound F44-A13 had beneficial effects in reducing cholesterol, triglycerides, and LDL-C levels. These findings highlight that F44-A13 is a highly selective FXR antagonist that might serve as a useful molecule for further FXR studies as well as the development of FXR antagonists for the potential treatment of metabolic diseases with lipid disorders.

Elevated expression of LCN13 through FXR activation ameliorates hepatocellular lipid accumulation and inflammation

BackgroundLipocalin 13 (LCN13) is a member of the lipocalin family that consists of numerous secretory proteins. LCN13 high-expression has been reported to possess anti-obesity and anti-diabetic effects. Although metabolic dysfunction-associated steatotic liver diseases (MASLD) including metabolic dysfunction-associated steatohepatitis (MASH) are frequently associated with obesity and insulin resistance, the functional role of endogenous LCN13 and the therapeutic effect of LCN13 in MASH and related metabolic deterioration have not been evaluated. MethodsWe employed a methionine-choline deficient diet model and MASH cell models to investigate the role of LCN13 in MASH development. We sought to explore the effects of LCN13 on lipid metabolism and inflammation in hepatocytes under PA/OA exposure using Western blotting, real-time RT-PCR, enzyme-linked immunosorbent assay, hematoxylin and eosin staining, oil red O staining. Using RNA sequencing, chromatin immunoprecipitation assay, and luciferase reporter assays to elucidate whether farnesoid X receptor (FXR) regulates human LCN13 transcription as a transcription factor. ResultsOur study found that LCN13 was down-regulated in MASH patients, MASH mouse and cell models. LCN13 overexpression in hepatocyte cells significantly inhibited lipid accumulation and inflammation in vitro. Conversely, LCN13 downregulation significantly exacerbated lipid accumulation and inflammatory responses in vivo and in vitro. Mechanistically, we provided the first evidence that LCN13 was transcriptionally activated by FXR, representing a novel direct target gene of FXR. And the key promoter region of LCN13 binds to FXR was also elucidated. We further revealed that LCN13 overexpression via FXR activation ameliorates hepatocellular lipid accumulation and inflammation in vivo and in vitro. Furthermore, LCN13-down-regulated mice exhibited aggravated MASH phenotypes, including increased hepatic lipid accumulation and inflammation. ConclusionOur findings provide new insight regarding the protective role of LCN13 in MASH development and suggest an innovative therapeutic strategy for treating MASH or related metabolic disorders.

Investigating SHP and PCSK9 Interactions in Cholesterol-Mediated Cardiovascular Diseases: A Research Protocol

Introduction: Improper cholesterol metabolism results in accumulation of low-density lipoproteins (LDL). High levels of LDL cholesterol deposits in blood vessels, forming plaques and contributing to various cardiovascular diseases (CVD). The nuclear farnesoid X receptor (FXR) regulates the transcription of genes involved in cholesterol metabolism and is a therapeutic target for cholesterol dysregulation. Studies conducted on immortalized human hepatocytes demonstrate FXR signaling-induced downregulation of proprotein convertase subtilisin/kexin type 9 (PCSK9) expression. PCSK9 is an LDL receptor-degrading enzyme whose upregulation is implicated in cholesterol-mediated diseases. Specifically, the FXR target gene SHP (small heterodimer partner) is a transcriptional regulator that has been implicated in an inverse relationship with PCSK9 expression. The biomolecular mechanism mediating this relationship has not been explored, meriting investigation into a potential novel axis of cholesterol metabolism. We hypothesize that SHP is a direct repressor of PCSK9 transcription. Methods: To investigate, we will knock out SHP expression in the liver hepatocyte cell line AML12 using small interfering RNAs (siRNAs). To confirm SHP knockout on transcriptomic and proteomic levels, reverse transcription quantitative PCR (RT-qPCR) and Western blotting will be performed. To assess SHP binding to the promoter region of PCSK9, an electrophoretic mobility supershift (EMSA) assay will be performed on unstimulated or chenodeoxycolic acid (CDCA)-stimulated AML12 cells that have undergone SHP or control knockouts. Western blotting will quantitate PCSK9 protein expression following SHP knockout in CDCA-stimulated and unstimulated conditions. Results: Results from EMSA are expected to demonstrate SHP binding to the promoter region of PCSK9 in a transcription factor complex to repress transcription. SHP knockout models are expected to show upregulated PCSK9 expression at transcriptomic and proteomic levels. Discussion: If successful, our study presents a novel perspective on cholesterol metabolism by characterizing the inhibitory effect of SHP on PCSK9 expression. This underlines the critical role of FXR signaling in PCSK9 regulation, and knockout models and assay techniques provide valuable evidence of this regulatory role. Conclusion: This study will establish an enhanced understanding of the SHP/PCSK9 pathway within broader pathways of cholesterol metabolism. Further research may explore therapies targeting the SHP/PCSK9 pathway to manage CVD downstream of cholesterol dysregulation.

FXR controls insulin content by regulating Foxa2-mediated insulin transcription

Farnesoid X receptor (FXR) is a nuclear ligand-activated receptor of bile acids that plays a role in the modulation of insulin content. However, the underlying molecular mechanisms remain unclear. Forkhead box a2 (Foxa2) is an important nuclear transcription factor in pancreatic β-cells and is involved in β-cell function. We aimed to explore the signaling mechanism downstream of FXR to regulate insulin content and underscore its association with Foxa2 and insulin gene (Ins) transcription. All experiments were conducted on FXR transgenic mice, INS-1 823/13 cells, and diabetic Goto-Kakizaki (GK) rats undergoing sham or Roux-en-Y gastric bypass (RYGB) surgery. Islets from FXR knockout mice and INS-1823/13 cells with FXR knockdown exhibited substantially lower insulin levels than that of controls. This was accompanied by decreased Foxa2 expression and Ins transcription. Conversely, FXR overexpression increased insulin content, concomitant with enhanced Foxa2 expression and Ins transcription in INS-1 823/13 cells. Moreover, FXR knockdown reduced FXR recruitment and H3K27 trimethylation in the Foxa2 promoter. Importantly, Foxa2 overexpression abrogated the adverse effects of FXR knockdown on Ins transcription and insulin content in INS-1 823/13 cells. Notably, RYGB surgery led to improved insulin content in diabetic GK rats, which was accompanied by upregulated FXR and Foxa2 expression and Ins transcription. Collectively, these data suggest that Foxa2 serves as the target gene of FXR in β-cells and mediates FXR-enhanced Ins transcription. Additionally, the upregulated FXR/Foxa2 signaling cascade could contribute to the enhanced insulin content in diabetic GK rats after RYGB.

Saikosaponins regulate bile acid excretion in mice liver and ileum by activating farnesoid X receptor and bile acid transporter.

Radix Bupleuri exerts effective hepatoprotective and cholagogic effects through its Saikosaponins (SSs) component. Therefore, we attempted to determine the mechanism of saikosaponins used to promote bile excretion by studying their effects on intrahepatic bile flow, focusing on the synthesis, transport, excretion, and metabolism of bile acids. C57BL/6N mice were continuously gavaged with saikosaponin a (SSa), saikosaponin b2 (SSb2 ), or saikosaponin D (SSd) (200 mg/kg) for 14 days. Liver and serum biochemical indices were determined using Enzyme-linked immunosorbent assay (ELISA) kits. In addition, an ultra-performance liquid chromatography-mass spectrometer (UPLC-MS) was used to measure the levels of the 16 bile acids in the liver, gallbladder, and cecal contents. Furthermore, SSs pharmacokinetics and docking between SSs and farnesoid X receptor (FXR)-related proteins were analyzed to investigate the underlying molecular mechanisms. Administration of SSs and Radix Bupleuri alcohol extract (ESS) did not cause significant changes in alanine aminotransferase (ALT), aspartate aminotransferase (AST), or alkaline phosphatase (ALP) levels. Saikosaponin-regulated changes in bile acid (BA) levels in the liver, gallbladder, and cecum were closely related to genes involved in BA synthesis, transport, and excretion in the liver. Pharmacokinetic studies indicated that SSs were characterized by rapid elimination (t1/2 as 0.68-2.47 h), absorption (Tmax as 0.47-0.78 h), and double peaks in the drug-time curves of SSa and SSb2 . A molecular docking study revealed that SSa, SSb2 , and SSd docked well with the 16 protein FXR molecules and target genes (<-5.2 kcal/mol). Collectively, saikosaponins may maintain BA homeostasis in mice by regulating FXR-related genes and transporters in the liver and intestine.

Farnesoid X receptor is inhibited after ileum transposition in diabetic rats: its hypoglycemic effect

Background: Aim to investigate bile acid profile changes and the Farnesoid X receptor (FXR) status after ileotransposition (IT), and reveal its possible hypoglycemic mechanism. Methods: Twenty male diabetic rats were randomly assigned into the IT group and the sham IT (SH) group. Bile acid profiles were measured using an ultra-performance liquid chromatography-tandem mass spectrometry. Glucose metabolism was monitored after oral administration of FXR inhibitor and agonist. And the expression of key FXR target genes were measured. Results: The levels of β-muricholic acid (P = 0.047), tauro-α-muricholic acid and tauro-β-muricholic acid (P < 0.001) in plasma in the IT group were higher than those in the SH group, and the levels of taurocholic acid (P = 0.049) and turoursodeoxycholic acid (P = 0.030) were lower than those in the SH group. After inhibition of intestinal FXR, the glucose metabolism in the SH group was improved. When FXR agonist was given, the blood glucose level was increased in both groups. After sacrifice, the levels of glycoursodeoxycholic acid, tauro-α-muricholic acid and tauro-β-muricholic acid in liver and ileum tissues were higher than those in the SH group (P < 0.05), the level of α- muricholic acid (P < 0.001) in liver tissues were lower than that in the SH group. Moreover, the expression of CYP7A1 mRNA (P < 0.001) and FGF15 mRNA (P = 0.001) in the IT group was significantly higher, and the expression of PEPCK mRNA (P = 0.004), SREPB1c mRNA (P = 0.005) and SRB1 mRNA (P = 0.001) were significantly lower than that in the SH group. Conclusions: We demonstrate a remarkable heterogeneity of BA profiles after IT, FXR activation might has a detrimental effect on glucose metabolism.

Tris(1,3-dichloro-2-propyl) phosphate is a metabolism-disrupting chemical in male mice

Tris(1,3-dichloro-2-propyl) phosphate (TDCPP) is an organophosphate flame retardant. The primary TDCPP metabolite, bis(1,3-dichloro-2-propyl) phosphate (BDCPP), is detectable in the urine of over 90 % of Americans. Epidemiological studies show sex-specific associations between urinary BDCPP levels and metabolic syndrome, which is an established risk factor for type 2 diabetes, heart disease, and stroke. We used a mouse model to determine whether TDCPP exposure disrupts glucose homeostasis. Six-week old male and female C57BL/6J mice were given ad libitum access to diets containing vehicle (0.1 % DMSO) and TDCPP resulting in the following treatment groups: 0 mg/kg/day, 0.02 mg/kg/day, 1 mg/kg/day, or 100 mg/kg/day. After being on the experimental diet for five weeks without interruption, body composition was analyzed, glucose and insulin tolerance tests were performed, and fasting glucose and insulin levels were quantified. TDCPP at 100 mg/kg/day caused male sex-specific adiposity, fasting hyperglycemia, and insulin resistance. TDCPP-induced modulation of nuclear receptor activation was investigated using an in vitro screen to identify potential mechanisms of metabolic disruption. TDCPP activated farnesoid X receptor (FXR) and pregnane X receptor (PXR), and inhibited the androgen receptor (AR). PXR target genes, but not FXR target genes, were upregulated in livers from mice exposed to 100 mg TDCPP/kg/day. Interestingly, PXR target genes were differentially expressed in livers from both males and females. It remains to be determined whether TDCPP-induced metabolic disruption occurs via modulation of nuclear receptor activity. Taken together, these studies build upon the association of TDCPP exposure and metabolic syndrome in humans by identifying sex-specific effects of TDCPP on glucose homeostasis in mice.

Transcription Factor FXR Activates DHRS9 to Inhibit the Cell Oxidative Phosphorylation and Suppress Colon Cancer Progression.

Colon cancer is a common gastrointestinal malignancy. It has been discovered that Farnesoid X receptor (FXR) plays an imperative regulatory role in multitype cancers in recent years. However, its regulatory mechanism in colon cancer has not been clearly explored. This study intended to explore the molecular regulatory mechanism of FXR and its downstream genes on the malignant progression of colon cancer. The mRNA and protein expression of FXR in colon cancer cells were measured by quantitative real-time polymerase chain reaction and Western blot. The effects of FXR on the biological function of colon cancer cells were measured by Cell Counting Kit-8, colony formation, and transwell assays. The downstream target gene of FXR was predicted by bioinformatics analysis and found to be associated with cellular oxidative phosphorylation. The binding relationship between FXR and its downstream gene dehydrogenase/reductase member 9 (DHRS9) was verified through luciferase reporter assay and chromatin immunoprecipitation assay. The changes of oxidative phosphorylation were detected by Western blot and oxygen consumption rate determination. The effect of FXR/DHRS9 axis on the malignant progression of colon cancer cells was further confirmed by rescue experiments. FXR was underexpressed in colon cancer tissues and cells, and overexpressing FXR could repress the malignant behaviors of colon cancer cells. Besides, DHRS9 was a downstream gene of FXR, and FXR/DHRS9 inhibited the deterioration of colon cancer through inhibiting oxidative phosphorylation. Moreover, promoting FXR expression in colon cancer cells could partially reverse the biological function changes caused by silencing DHRS9 expression. FXR inhibited the oxidative phosphorylation and inhibited the malignant progression of colon cancer cells via targeting DHRS9.

Identification of a novel farnesoid X receptor agonist, kaempferol-7-O-rhamnoside, a compound ameliorating drug-induced liver injury based on virtual screening and in vitro validation

Farnesoid X receptor (FXR), a bile acid receptor, plays an essential role in maintaining bile acid and liver homeostasis and has been recognized as an essential target for drug-induced liver injury (DILI). This study aimed to identify potential FXR agonists by virtual screening, molecular dynamics (MD) simulation, and biological assays. First, an in-house Traditional Chinese medicine compound database was screened using a virtual approach based on molecular docking to reveal potential FXR agonists. Secondly, MD was applied to analyze the process of agonist binding. Finally, the acetaminophen (APAP)-induced L02 cells model evaluated the pharmacodynamic activity of agonists treating DILI. Virtual screening results showed that kaempferol-7-O-rhamnoside was confirmed as the FXR agonist. MD results showed that kaempferol-7-O-rhamnoside could stably bind the FXR. In addition, in vitro cell-based assay showed that kaempferol-7-O-rhamnoside could promote the expression of the FXR gene and inhibit the Cyp7a1 gene expression in APAP-induced cells, significantly reducing the activities of AST, AKP and ROS, and enhancing the expression of GSH. The current study confirmed that kaempferol-7-O-rhamnoside might improve liver function by promoting proliferation, ameliorating oxidative stress, and regulating FXR target genes as observed in vitro. Therefore, in this study, discovering the FXR agonist, kaempferol-7-O-rhamnoside, provides valuable guidance for developing novel drugs against DILI.

Makisterone A attenuates experimental cholestasis by activating the farnesoid X receptor

Cholestasis is the accumulation of bile acids in the liver due to impaired bile formation, secretion, and excretion caused by infections, drugs, metabolic or genetic diseases. Ursodeoxycholic acid is the only drug approved by the Food and Drug Administration for the treatment of primary biliary cholangitis, but nearly 40% of patients do not adequately respond to this drug and 5–10% show intolerance. The farnesoid X receptor (FXR) plays a key role in bile acid metabolism. Here, by using HERB, a high-throughput experimental and reference-oriented database of herbal medicines, and molecular docking, we identified makisterone A (MakA) as a compound that could target FXR. We showed that MakA enhanced FXR activity in liver cells and expression levels of FXR target genes in vitro. Importantly, MakA intervention alleviated cholestatic liver injury and dysregulation of hepatic bile acid metabolism induced by α-naphthylisothiocyanate and, 5-diethoxycarbonyl-1,4-dihydrocollidine in mice. The ability of MakA to improve liver injury in a mouse model suggests that this drug may be used for clinical treatment of cholestasis.

Regulation of the Nuclear Bile Acid Receptor, Farnesoid X Receptor, by the Omega‐3 Polyunsaturated Fatty Acid, Alpha‐Linolenic Acid, in Colonic Epithelial Cells

Introduction and AimsThe intestinal epithelium forms the interface between the body and the luminal contents, facilitating fluid and electrolyte transport, while also acting as a barrier to harmful pathogens. Dysregulation of barrier and transport function is associated with the pathogenesis of a number of conditions, including chronic diarrhoeal and inflammatory bowel diseases (IBD). Previous studies from ours, and other laboratories, have identified the nuclear bile acid receptor, farnesoid x receptor (FXR), as an excellent target for the development of new anti‐diarrhoeal and anti‐inflammatory therapeutics. Polyunsaturated fatty acids (PUFAs), such as alpha‐linolenic acid (ALA), are a group of bioactive phytochemicals, which have been shown in other systems to modulate FXR activity. PUFAs are also thought to be ligands for another group of nuclear receptors, known as the peroxisome proliferator‐activated receptors (PPARs), which have been recently shown to modulate FXR expression. Here, we set out to investigate a possible role for ALA in regulating farnesoid x receptor signalling in colonic epithelial cells.MethodsT84 human colonic epithelial cells were cultured as polarised monolayers on permeable supports and treated bilaterally with alpha‐linolenic acid (ALA) (100 µM) for 1 – 24 hours, in the presence or absence of the FXR agonist, GW4064 (5 µM), or the PPARg antagonist, GW9662 (20 µM). Levels of FXR, FGF19, an index of FXR activation, and ANGPTL4, a PPAR target gene, were measured by qRT‐PCR, western blotting, or ELISA.ResultsTreatment of T84 cells with ALA increased FXR expression in a time dependent fashion. Maximal effects of ALA occurred after 6 hrs when increases in FXR mRNA and protein were 8.65 ± 0.80 fold (n = 4; p &lt; 0.01) and 4.44 ± 0.85 fold (n = 4) of untreated controls, respectively. Moreover, treatment of the cells with ALA potentiated GW4064‐induced expression of the FXR target gene, FGF‐19, at both mRNA and protein levels by 2.66 ± 0.56 (n = 4) and 5.52 ± 1.52 (n = 6), respectively. The effects of ALA on FXR expression and activity were mimicked by the PPARg agonist, rosiglitazone (1 mM). Treatment with ALA also significantly increased mRNA expression of the PPAR target gene, ANGPTL4, by 56.69 ± 5.7 (n = 4; p &lt; 0.01), while the PPARg antagonist, GW9662 (20 µM; 1 hr), inhibited ALA‐induced FXR mRNA expression by 0.44 ± 0.12 fold (n =4) and protein by 0.23 ± 0.06 fold (n = 3).ConclusionThe dietary PUFA, ALA, regulates colonic epithelial FXR expression through mechanisms that involve activation of PPARγ. By virtue of their ability to upregulate FXR expression and activity, PUFAs, such as ALA, have excellent potential for development as FXR‐targeted nutraceuticals for the treatment and prevention of intestinal disease.

Transcriptional Control of Trpm6 by the Nuclear Receptor FXR.

Farnesoid x receptor (FXR) is a nuclear bile acid receptor that belongs to the nuclear receptor superfamily. It plays an essential role in bile acid biosynthesis, lipid and glucose metabolism, liver regeneration, and vertical sleeve gastrectomy. A loss of the FXR gene or dysregulations of FXR-mediated gene expression are associated with the development of progressive familial intrahepatic cholestasis, tumorigenesis, inflammation, and diabetes mellitus. Magnesium ion (Mg2+) is essential for mammalian physiology. Over 600 enzymes are dependent on Mg2+ for their activity. Here, we show that the Trpm6 gene encoding a Mg2+ channel is a direct FXR target gene in the intestinal epithelial cells of mice. FXR expressed in the intestinal epithelial cells is absolutely required for sustaining a basal expression of intestinal Trpm6 that can be robustly induced by the treatment of GW4064, a synthetic FXR agonist. Analysis of FXR ChIP-seq data revealed that intron regions of Trpm6 contain two prominent FXR binding peaks. Among them, the proximal peak from the transcription start site contains a functional inverted repeat 1 (IR1) response element that directly binds to the FXR-RXRα heterodimer. Based on these results, we proposed that an intestinal FXR-TRPM6 axis may link a bile acid signaling to Mg2+ homeostasis.

Intestinal farnesoid X receptor signaling controls hepatic fatty acid oxidation

In addition to maintaining bile acid, cholesterol and glucose homeostasis, farnesoid X receptor (FXR) also regulates fatty acid β-oxidation (FAO). To explore the different roles of hepatic and intestinal FXR in liver FAO, FAO-associated metabolites, including acylcarnitines and fatty acids, and FXR target gene mRNAs were profiled using an integrated metabolomic and transcriptomic analysis in control (Fxrfl/fl), liver-specific Fxr-null (FxrΔHep) and intestine-specific Fxr-null (FxrΔIE) mice, treated either with the FXR agonist obeticholic acid (OCA) or vehicle (VEH). Activation of FXR by OCA treatment significantly increased fatty acyl-CoA hydrolysis (Acot1) and decreased FAO-associated mRNAs in Fxrfl/fl mice, resulting in reduced levels of total acylcarnitines and relative accumulation of long/medium chain acylcarnitines and fatty acids in liver. FxrΔHep mice responded to OCA treatment in a manner similar to Fxrfl/fl mice while FxrΔIE mice responded differently, thus illustrating that intestinal FXR plays a critical role in the regulation of hepatic FAO. A significant negative-correlation between intestinal FXR-FGF15 and hepatic CREB-PGC1A pathways was observed after both VEH and OCA treatment, suggesting that OCA-induced activation of the intestinal FXR-FGF15 axis downregulates hepatic PGC1α signaling via inactivation of hepatic CREB, thus repressing FAO. This mechanism was confirmed in experiments based on human recombinant FGF19 treatment and intestinal Fgf15-null mice. This study revealed an important role for the intestinal FXR-FGF15 pathway in hepatic FAO repression.

Bile acid-induced tissue factor activity in hepatocytes correlates with activation of farnesoid X receptor

Bile acids (BA) have been found to promote coagulation by increasing tissue factor (TF) activity. The contribution of elevated BA levels and cholestasis to TF decryption within the liver parenchyma and the role of farnesoid X receptor (FXR) in this process remain unclear. We investigated the effects of BA on TF activity and thrombin generation in hepatocytes and correlated these effects with activation of FXR-dependent signaling and apoptosis. HepG2 cells and primary hepatocytes were incubated with chenodeoxycholic acid (CDCA), glycochenodeoxycholic acid (GCDCA), ursodeoxycholic acid (UCDA), or the synthetic FXR agonist GW4064 for 24 h. MTT tests demonstrated cell viability throughout experiments. TF activity was tested via factor Xa generation and thrombin generation was measured by calibrated automated thrombography. Increased TF activity alongside enhanced thrombin generation was observed with CDCA and GW4064 but not with GCDCA and UDCA. TF activity was substantially reduced when FXR activation was blocked with the antagonist DY 268. Quantitative polymerase chain reaction revealed upregulation of FXR target genes only by CDCA and GW4064. Western blot analysis and fluorescence microscopy showed no TF overexpression arguing for TF decryption. Caspase 3 activity measurements and flow cytometric analysis of Annexin V binding showed no signs of apoptosis. Long-term exposure of hepatocytes to nontoxic BA may cause intracellular FXR overstimulation, triggering TF decryption irrespective of the amphiphilic properties of BA. The effect of BA on TF activation correlates with the molecule's ability to enter the cells and activate FXR. TF decryption occurs independently of apoptotic mechanisms.The potential of various bile acids to induce procoagulant tissue factor (TF) activity in viable HepG2 cells and primary human hepatocytes was investigated. Increased TF activity correlated with the molecules' ability to enter the cells and activate the farnesoid X receptor (FXR) suggesting a crucial role of FXR in bile acid-mediated TF activity within the liver parenchyma.

Bile Salt and FGF19 Signaling in the Early Phase of Human Liver Regeneration.

The involvement of bile salt–fibroblast growth factor 19 (FGF19) signaling in human liver regeneration (LR) is not well studied. Therefore, we studied aspects of bile salt–FGF19 signaling shortly after liver resection in patients. We compared plasma bile salt and FGF19 levels in arterial, portal and hepatic venous blood, calculated venous‐arterial differences (ΔVA), and determined hepatic transcript levels on two intra‐operative time points: before (< 1 hour) and immediately after (> 2‐3 hours) liver resection (i.e., following surgery). Postoperative bile salt and FGF19 levels were assessed on days 1, 2, and 3. LR was studied by computed tomography (CT)–liver volumetry. Following surgery, the liver, arterial, and portal bile salt levels were elevated (P < 0.05). Furthermore, an increased amount of bile salts was released in portal blood and extracted by the remnant liver (P < 0.05). Postoperatively, bile salt levels were elevated from day 1 onward (P < 0.001). For FGF19, intra‐operative or postoperative changes of ΔVA or plasma levels were not observed. The bile salt–homeostatic regulator farnesoid X receptor (FXR) was markedly up‐regulated following surgery (P < 0.001). Cell‐cycle re‐entry priming factors (interleukin 6 [IL‐6], signal transducer and activator of transcription 3 [STAT3], and cJUN) were up‐regulated following surgery and were positively correlated with FXR expression (P < 0.05). Postoperative hyperbilirubinemia was preceded by postsurgery low FXR and high Na+/Taurocholate cotransporting polypeptide (NTCP) expression in the remnant liver coupled with higher liver bile salt content (P < 0.05). Finally, bile salt levels on postoperative day 1 were an independent predictor of LR (P < 0.05). Conclusion: Systemic, portal, and liver bile salt levels are rapidly elevated after liver resection. Postoperative bile salts were positively associated with liver volume gain. In the studied time frame, FGF19 levels remained unaltered, suggesting that FGF19 plays a minor role in human LR. These findings indicate a more relevant role of bile salts in human LR.

Suppressing the intestinal farnesoid X receptor/sphingomyelin phosphodiesterase 3 axis decreases atherosclerosis.

Intestinal farnesoid X receptor (FXR) signaling is involved in the development of obesity, fatty liver disease, and type 2 diabetes. However, the role of intestinal FXR in atherosclerosis and its potential as a target for clinical treatment have not been explored. The serum levels of fibroblast growth factor 19 (FGF19), which is encoded by an FXR target gene, were much higher in patients with hypercholesterolemia than in control subjects and were positively related to circulating ceramide levels, indicating a link between intestinal FXR, ceramide metabolism, and atherosclerosis. Among ApoE-/- mice fed a high-cholesterol diet (HCD), intestinal FXR deficiency (in FxrΔIE ApoE-/- mice) or direct FXR inhibition (via treatment with the FXR antagonist glycoursodeoxycholic acid [GUDCA]) decreased atherosclerosis and reduced the levels of circulating ceramides and cholesterol. Sphingomyelin phosphodiesterase 3 (SMPD3), which is involved in ceramide synthesis in the intestine, was identified as an FXR target gene. SMPD3 overexpression or C16:0 ceramide supplementation eliminated the improvements in atherosclerosis in FxrΔIE ApoE-/- mice. Administration of GUDCA or GW4869, an SMPD3 inhibitor, elicited therapeutic effects on established atherosclerosis in ApoE-/- mice by decreasing circulating ceramide levels. This study identified an intestinal FXR/SMPD3 axis that is a potential target for atherosclerosis therapy.

Farnesoid X receptor via Notch1 directs asymmetric cell division of Sox9+ cells to prevent the development of liver cancer in a mouse model

BackgroundAsymmetrical cell division (ACD) maintains the proper number of stem cells to ensure self-renewal. The rate of symmetric division increases as more cancer stem cells (CSCs) become malignant; however, the signaling pathway network involved in CSC division remains elusive. FXR (Farnesoid X receptor), a ligand-activated transcription factor, has several anti-tumor effects and has been shown to target CSCs. Here, we aimed at evaluating the role of FXR in the regulation of the cell division of CSCs.MethodsThe FXR target gene and downstream molecular mechanisms were confirmed by qRT-PCR, Western blot, luciferase reporter assay, EMAS, Chip, and IF analyses. Pulse-chase BrdU labeling and paired-cell experiments were used to detect the cell division of liver CSCs. Gain- and loss-of-function experiments in Huh7 cells and mouse models were performed to support findings and elucidate the function and underlying mechanisms of FXR-Notch1 in liver CSC division.ResultsWe demonstrated that activation of Notch1 was significantly elevated in the livers of hepatocellular carcinoma (HCC) in Farnesoid X receptor-knockout (FXR-KO) mice and that FXR expression negatively correlated with Notch1 level during chronic liver injury. Activation of FXR induced the asymmetric divisions of Sox9+ liver CSCs and ameliorated liver injury. Mechanistically, FXR directs Sox9+ liver CSCs from symmetry to asymmetry via inhibition of Notch1 expression and activity. Deletion of FXR signaling or over-expression of Notch1 greatly increased Notch1 expression and activity along with ACD reduction. FXR inhibited Notch1 expression by directly binding to its promoter FXRE. FXR also positively regulated Numb expression, contributing to a feedback circuit, which decreased Notch1 activity and directed ACD.ConclusionOur findings suggest that FXR represses Notch1 expression and directs ACD of Sox9+ cells to prevent the development of liver cancer.

Isotschimgine alleviates nonalcoholic steatohepatitis and fibrosis via FXR agonism in mice.

Farnesoid X receptor (FXR) agonist obeticholic acid (OCA) has emerged as a potential therapy for nonalcoholic fatty liver disease (NAFLD). However, the side effects of OCA may limit its application in clinics. We identified previously that isotschimgine (ITG) is a non-steroidal FXR selective agonist and has potent therapeutic effects on NAFLD in mice. Here, we aimed to evaluate the therapeutic effects of ITG on nonalcoholic steatohepatitis (NASH) and fibrosis in mice. We used methionine and choline deficient (MCD) diet-induced NASH mice, bile duct ligation (BDL), and carbon tetrachloride (CCl4 )-treated hepatic fibrosis mice to investigate the effects of ITG on NASH, fibrosis, and cholestatic liver injury. Our results showed that ITG improved steatosis and inflammation in the liver of MCD diet-fed mice, as well as alleviated fibrosis and inflammation in the liver of CCl4 -treated mice. Furthermore, ITG attenuated serum bile acid levels, and reduced vacuolization, inflammatory infiltration, hepatic parenchymal necrosis, and collagen accumulation in the liver of BDL mice. Mechanistically, ITG increased the expression of FXR target genes. These data suggest that ITG is an FXR agonist and may be developed as a novel therapy for NASH, hepatic fibrosis, or primary biliary cholangitis.

Discovery of Orally Active and Nonsteroidal Farnesoid X Receptor (FXR) Antagonist with Propensity for Accumulation and Responsiveness in Ileum.

We describe the discovery of analog 15 (FLG249), which is an orally active and nonsteroidal farnesoid X receptor (FXR) antagonist in mice with unique profiles, such as a propensity for ileum distribution and the significant control in the expression level of three FXR target genes in mouse ileum. Key design features incorporated in 15 were the introduction of metabolically stable groups in potent and metabolically labile antagonist 9. Our pursuit ultimately identified FXR antagonist 15, which has enabled its assessment in a drug discovery program.