Mechanism of tissue-specific farnesoid X receptor in suppressing the expression of genes in bile-acid synthesis in mice

The relationship between BA (bile acid) secretion (measured by GC–MS) and the expression of genes (measured by reverse transcription real-time PCR) involved in liver BA transport and metabolism was investigated at 20 and 32 weeks during rat hepatocarcinogenesis. A progressive loss of mRNA for transporters (more marked for Ntcp, Bsep and Mrp2 than for Oatp1/Oatp1a1, Oatp2/Oatp1a4 and Oatp4/Oatp1b2) was found. The mRNA levels of Cyp7a1 and the nuclear receptors FXR (farnesoid X receptor), SHP (small heterodimer partner) and FTF (α-fetoprotein transcription factor) were not modified, whereas those of Cyp8b1 were enhanced and those of Cyp27 were reduced. Biliary secretion of CA (cholic acid) remained unchanged, whereas that of CDCA (chenodeoxycholic acid) and other non-C12-hydroxylated BAs was diminished. The re-appearance of ‘flat-BAs’ (mainly allo-BAs at 20 weeks and Δ4-unsaturated-BAs at 32 weeks) probably reflects the progressive decrease observed in the expression of 3-oxo-Δ4-steroid 5β-reductase, together with the maintenance of steroid 5α-reductase type I. A significant correlation between the 5α-reductase/5β-reductase ratio and bile output of ‘flat-BAs’ was found. In conclusion, during rat hepatocarcinogenesis, the expression of transporters/enzymes responsible for BA homoeostasis is changed due to mechanisms other than those controlled by FXR/SHP/FTF. These modifications result in the re-appearance of ‘flat-BAs’, together with an increased CA/CDCA ratio in bile.

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Farnesoid X receptor induces Takeda G-protein receptor 5 cross-talk to regulate bile acid synthesis and hepatic metabolism

Journal of Biological Chemistry ◽

10.1074/jbc.m117.784322 ◽

2017 ◽

Vol 292 (26) ◽

pp. 11055-11069 ◽

Cited By ~ 81

Author(s):

Preeti Pathak ◽

Hailiang Liu ◽

Shannon Boehme ◽

Cen Xie ◽

Kristopher W. Krausz ◽

...

Keyword(s):

Bile Acid ◽

G Protein ◽

Cross Talk ◽

Hepatic Metabolism ◽

Acid Synthesis ◽

Bile Acid Synthesis ◽

Farnesoid X Receptor ◽

Protein Receptor

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Recent advances in understanding bile acid homeostasis

F1000Research ◽

10.12688/f1000research.12449.1 ◽

2017 ◽

Vol 6 ◽

pp. 2029 ◽

Cited By ~ 52

Author(s):

John YL Chiang

Keyword(s):

Bile Acid ◽

Bile Acids ◽

Acid Synthesis ◽

Bile Acid Synthesis ◽

Farnesoid X Receptor ◽

Recent Advances ◽

Bile Acid Pool Size ◽

Bile Acid Receptor ◽

Acid Toxicity ◽

G Protein Coupled

Bile acids are derived from cholesterol to facilitate intestinal nutrient absorption and biliary secretion of cholesterol. Recent studies have identified bile acids as signaling molecules that activate nuclear farnesoid X receptor (FXR) and membrane G protein-coupled bile acid receptor-1 (Gpbar-1, also known as TGR5) to maintain metabolic homeostasis and protect liver and other tissues and cells from bile acid toxicity. Bile acid homeostasis is regulated by a complex mechanism of feedback and feedforward regulation that is not completely understood. This review will cover recent advances in bile acid signaling and emerging concepts about the classic and alternative bile acid synthesis pathway, bile acid composition and bile acid pool size, and intestinal bile acid signaling and gut microbiome in regulation of bile acid homeostasis.

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Bile acid diarrhoea: pathophysiology, diagnosis and management

Frontline Gastroenterology ◽

10.1136/flgastro-2020-101436 ◽

2020 ◽

pp. flgastro-2020-101436

Author(s):

Alexia Farrugia ◽

Ramesh Arasaradnam

Keyword(s):

Bile Acid ◽

Enterohepatic Circulation ◽

Acid Synthesis ◽

Bile Acid Synthesis ◽

Feedback Loops ◽

Farnesoid X Receptor ◽

Delay In Diagnosis ◽

Negative Feedback Loops ◽

Irritable Bowel ◽

Fibroblast Growth Factor 19

The actual incidence of bile acid diarrhoea (BAD) is unknown, however, there is increasing evidence that it is misdiagnosed in up to 30% with diarrhoea-predominant patients with irritable bowel syndrome. Besides this, it may also occur following cholecystectomy, infectious diarrhoea and pelvic chemoradiotherapy.BAD may result from either hepatic overproduction of bile acids or their malabsorption in the terminal ileum. It can result in symptoms such as bowel frequency, urgency, nocturnal defecation, excessive flatulence, abdominal pain and incontinence of stool. Bile acid synthesis is regulated by negative feedback loops related to the enterohepatic circulation, which are dependent on the farnesoid X receptor and fibroblast growth factor 19. Interruption of these feedback loops is thought to cause bile acid overproduction leading to BAD. This process may occur idiopathically or following a specific trigger such as cholecystectomy. There may also be an interplay with the gut microbiota, which has been reported to be significantly different in patients with severe BAD.Patients with suspected BAD are investigated in various ways including radionucleotide imaging such as SeHCAT scans (though this is not available worldwide) and blood tests. However, other methods such as bile acid measurement in stool (either spot test or 48 hours samples) and urine tests have been explored. Importantly, delay in diagnosis and treatment of BAD greatly affects patient’s quality of life and may double the overall cost of diagnosis.

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Knockdown of ATP8B1 expression leads to specific downregulation of the bile acid sensor FXR in HepG2 cells: effect of the FXR agonist GW4064

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.90371.2008 ◽

2009 ◽

Vol 296 (5) ◽

pp. G1119-G1129 ◽

Cited By ~ 21

Author(s):

Pilar Martínez-Fernández ◽

Loreto Hierro ◽

Paloma Jara ◽

Luis Alvarez

Keyword(s):

Bile Acid ◽

Hepg2 Cells ◽

Target Genes ◽

Constitutive Androstane Receptor ◽

Pregnane X Receptor ◽

Acid Synthesis ◽

Bile Acid Synthesis ◽

Bile Secretion ◽

Farnesoid X Receptor ◽

Mrna Levels

Farnesoid X receptor (FXR) is a bile acid-sensing nuclear receptor that controls bile acid homeostasis. It has been suggested that downregulation of FXR contributes to the pathogenesis of an inherited disorder of bile secretion caused by mutations in ATP8B1. We have investigated the relationship between ATP8B1 knockdown and FXR downregulation in the human hepatoblastoma cell line HepG2. Transfection of HepG2 cells with ATP8B1 small interfering RNA (siRNA) duplexes led to a 60% reduction in the endogenous levels of ATP8B1 mRNA and protein and a concomitant decrease in FXR mRNA and protein content, as well as in FXR phosphorylation. This decrease was accompanied by a marked reduction in mRNA levels of a subset of FXR targets, such as bile salt export pump ( ABCB11), small heterodimer partner, and uridine 5′-diphosphate-glucuronosyltransferase. ATP8B1 inhibition specifically targeted FXR since mRNA expression of other prominent nuclear receptors, such as pregnane X receptor and constitutive androstane receptor, or liver-enriched transcription factors, such as hepatocyte nuclear factor 1α ( HNF-1α) and HNF-4α, was not altered. The expression of other key genes involved in bile acid synthesis, detoxification, and transport also remained unchanged upon ATP8B1 knockdown. Supporting the specificity of the effect, siRNA-mediated silencing of ABCB11, whose defect is associated with another inherited disorder of bile secretion, did not affect FXR expression. Treatment with the synthetic FXR agonist GW4064 was able to partially neutralize ATP8B1 siRNA-mediated FXR downregulation and fully counteract inhibition of FXR target genes. Collectively these findings indicate that ATP8B1 knockdown specifically downregulates FXR, and this action can be circumvented by treatment with FXR agonists.

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Peroxisome Proliferator-Activated Receptor-γ Prevents Cholesterol Gallstone Formation in C57bl Mice by Regulating Bile Acid Synthesis and Enterohepatic Circulation

BioMed Research International ◽

10.1155/2018/7475626 ◽

2018 ◽

Vol 2018 ◽

pp. 1-12

Author(s):

Gang Wang ◽

Tao Han ◽

ShiJia Wang ◽

Min Chen ◽

Yueming Sun ◽

...

Keyword(s):

Bile Acid ◽

Enterohepatic Circulation ◽

Cholesterol Gallstone ◽

Gallstone Formation ◽

Acid Synthesis ◽

Bile Acid Synthesis ◽

Chow Diet ◽

Peroxisome Proliferator ◽

Peroxisome Proliferator Activated Receptor ◽

Expression Of Genes

To investigate the role of the peroxisome proliferator-activated receptor-γ (PPARγ) in the progression of cholesterol gallstone disease (CGD), C57bl/6J mice were randomized to the following groups (n=7/group): L (lithogenic diet, LGD), LM (LGD+pioglitazone), CM (chow diet+pioglitazone), and NC (normal control, chow diet). Gallbladder stones were observed by microscopy. Histological gallbladder changes were assessed. Bile acids (BA) and cholesterol were measured in the serum, bile, and feces. Proteins and mRNA expression of genes involved in BA metabolism and enterohepatic circulation were assessed by western blotting and real-time RT-PCR. PPARγ activation was performed in LO2 cell by lentivirus transfection and in Caco2 cell by PPARγ agonist treatment. Downregulation of farnesoid X receptor (FXR) by small interference RNA (siRNA) was performed in L02 cells and Caco2 cells, respectively. Results showed that pharmacological activation of PPARγ by pioglitazone prevents cholesterol gallstone formation by increasing biliary BA synthesis and enterohepatic circulation. Activated PPARγ induced the expression of genes involved in enterohepatic circulation and bile acid synthesis (like PCG1α, BSEP, MRP2, MRP3, MRP4, NTCP, CYP7A1, CYP27A1, ASBT, OSTα, and OSTβ). Downregulation of FXR repressed expression of partial genes involved in BA enterohepatic circulation. These findings suggest a new function of PPARγ in preventing CGD by handling BA synthesis and transport through a FXR dependent or independent pathway.

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Tu1262 Obeticholic Acid, a Farnesoid X Receptor Agonist, Reduces Bile Acid Synthesis in Patients With Primary Bile Acid Diarrhea

Gastroenterology ◽

10.1016/s0016-5085(14)62881-x ◽

2014 ◽

Vol 146 (5) ◽

pp. S-797 ◽

Cited By ~ 1

Author(s):

Claire Vassie ◽

Jonathan D. Nolan ◽

Ian M. Johnston ◽

David Shapiro ◽

Julian R. Walters

Keyword(s):

Bile Acid ◽

Receptor Agonist ◽

Acid Synthesis ◽

Bile Acid Synthesis ◽

Farnesoid X Receptor ◽

Obeticholic Acid ◽

Primary Bile Acid

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β-Klotho and FGF-15/19 inhibit the apical sodium-dependent bile acid transporter in enterocytes and cholangiocytes

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.90343.2008 ◽

2008 ◽

Vol 295 (5) ◽

pp. G996-G1003 ◽

Cited By ~ 56

Author(s):

Jyoti Sinha ◽

Frank Chen ◽

Tamir Miloh ◽

Robert C. Burns ◽

Zhisheng Yu ◽

...

Keyword(s):

Bile Acid ◽

Culture Media ◽

Retinoic Acid Receptor ◽

Cancer Cell Line ◽

Acid Synthesis ◽

Colon Cancer Cell Line ◽

Bile Acid Synthesis ◽

Dominant Negative ◽

Farnesoid X Receptor ◽

Site Directed Mutagenesis

β-Klotho, a newly described membrane protein, regulates bile acid synthesis. Fibroblast growth factor-15 (FGF-15) and FGF receptor-4 (FGFR4) knockout mice share a similar phenotype with β-Klotho-deficient mice. FGF-15 secretion by the intestine regulates hepatic bile acid biosynthesis. The effects of β-Klotho and FGF-15 on the ileal apical sodium bile transporter (ASBT) are unknown. β-Klotho siRNA treatment of the mouse colon cancer cell line, CT-26, and the human intrahepatic biliary epithelial cells (HIBEC) resulted in upregulation of endogenous ASBT expression that was associated with reduced expression of the farnesoid X receptor (FXR) and the short heterodimer partner (SHP). Silencing β-Klotho activated the ASBT promoter in CT-26, Mz-ChA-1 (human cholangiocarcinoma), and HIBEC cells. Site-directed mutagenesis of liver receptor homolog-1 (mouse) or retinoic acid receptor/retinoid X receptor (RAR/RXR) (human) cis-elements attenuated the basal activity of the ASBT promoter and abrogated its response to β-Klotho silencing. siSHP, siFXR, or dominant-negative FXR treatment also eliminated the β-Klotho response. FGF-15 secretion into cell culture media by CT-26 cells was diminished after siFGF-15 or siβ-Klotho treatment and enhanced by chenodeoxycholic acid. Exogenous FGF-19 repressed ASBT protein expression in mouse ileum, gallbladder, and in HIBEC and repressed ASBT promoter activity in Caco-2, HIBEC, and Mz-ChA-1 cells. Promoter repression was dependent on the expression of FGFR4. These results indicate that both β-Klotho and FGF-15/19 repress ASBT in enterocytes and cholangiocytes. These novel signaling pathways need to be considered in analyzing bile acid homeostasis.

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