Liver Receptor Homolog-1 Regulates Bile Acid Homeostasis but Is Not Essential for Feedback Regulation of Bile Acid Synthesis

Abstract Liver receptor homolog 1 (LRH-1), an orphan nuclear receptor, is highly expressed in liver and intestine, where it is implicated in the regulation of cholesterol, bile acid, and steroid hormone homeostasis. Among the proposed LRH-1 target genes in liver are those encoding cholesterol 7α-hydroxylase (CYP7A1) and sterol 12α-hydroxylase (CYP8B1), which catalyze key steps in bile acid synthesis. In vitro studies suggest that LRH-1 may be involved both in stimulating basal CYP7A1 and CYP8B1 transcription and in repressing their expression as part of the nuclear bile acid receptor [farnesoid X receptor (FXR)]-small heterodimer partner signaling cascade, which culminates in small heterodimer partner binding to LRH-1 to repress gene transcription. However, in vivo analysis of LRH-1 actions has been hampered by the embryonic lethality of Lrh-1 knockout mice. To overcome this obstacle, mice were generated in which Lrh-1 was selectively disrupted in either hepatocytes or intestinal epithelium. LRH-1 deficiency in either tissue changed mRNA levels of genes involved in cholesterol and bile acid homeostasis. Surprisingly, LRH-1 deficiency in hepatocytes had no significant effect on basal Cyp7a1 expression or its repression by FXR. Whereas Cyp8b1 repression by FXR was also intact in mice deficient for LRH-1 in hepatocytes, basal CYP8B1 mRNA levels were significantly decreased, and there were corresponding changes in the composition of the bile acid pool. Taken together, these data reveal a broad role for LRH-1 in regulating bile acid homeostasis but demonstrate that LRH-1 is either not involved in the feedback regulation of bile acid synthesis or is compensated for by other factors.

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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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microRNA-192 suppresses the expression of the farnesoid X receptor

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.00297.2015 ◽

2016 ◽

Vol 310 (11) ◽

pp. G1044-G1051 ◽

Cited By ~ 12

Author(s):

Regina Krattinger ◽

Adrian Boström ◽

Helgi B. Schiöth ◽

Wolfgang E. Thasler ◽

Jessica Mwinyi ◽

...

Keyword(s):

Bile Acid ◽

Colon Carcinoma ◽

Growth Regulation ◽

Target Genes ◽

Farnesoid X Receptor ◽

Luciferase Reporter ◽

Mrna Levels ◽

Protective Effects ◽

Colonic Adenocarcinoma

Farnesoid X receptor (FXR, NR1H4) plays an important role in the regulation of bile acid homeostasis in liver and intestine and may exert protective effects against certain forms of cancer such as colon carcinoma. However, the role of FXR in cell growth regulation, apoptosis, and carcinogenesis is still controversial. Similar to FXR, microRNA-192 (miR-192) is mainly expressed in the liver and colon and plays an important role in the pathogenesis of colon carcinoma. In this study, we investigated the extent to which FXR is regulated by miR-192. Two in silico-predicted binding sites for miR-192-3p within the NR1H4-3′ untranslated region (UTR) were examined in vitro by luciferase reporter assays. Wild-type and mutated forms of the NR1H4-3′UTR were subcloned into a pmirGLO vector and cotransfected into Huh-7 cells with miR-192-3p. To study the effects of miR-192 on the expression of FXR, FXR target genes and cell proliferation, Huh-7 and Caco-2 cells were transfected with miR-192-5p and -3p mimics or antagomirs. In addition, the correlation between FXR and miR-192 expression was studied by linear regression analyses in colonic adenocarcinoma tissue from 27 patients. MiR-192-3p bound specifically to the NR1H4-3′UTR and significantly decreased luciferase activity. Transfection with miR-192 led to significant decreases in NR1H4 mRNA and protein levels as well as the mRNA levels of the FXR-inducible bile acid transporters OSTα-OSTβ and OATP1B3. Significant inverse correlations were detected in colonic adenocarcinoma between NR1H4 mRNA and miR-192-3p expression. In summary, microRNA-192 suppresses the expression of FXR and FXR target genes in vitro and in vivo.

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Changes in the expression of genes related to bile acid synthesis and transport by the rat liver during hepatocarcinogenesis

Clinical Science ◽

10.1042/cs20050035 ◽

2005 ◽

Vol 109 (2) ◽

pp. 199-207 ◽

Cited By ~ 9

Author(s):

Maria J. Monte ◽

Maria Fernandez-Tagarro ◽

Rocio I. R. Macias ◽

Felipe Jimenez ◽

Francisco Gonzalez-San Martin ◽

...

Keyword(s):

Bile Acid ◽

Acid Synthesis ◽

Bile Acid Synthesis ◽

Farnesoid X Receptor ◽

Type I ◽

Mrna Levels ◽

Expression Of Genes ◽

Bile Output ◽

The Relationship ◽

Bile Acid Secretion

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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Faculty Opinions recommendation of Liver receptor homolog-1 regulates bile acid homeostasis but is not essential for feedback regulation of bile acid synthesis.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1104641.560698 ◽

2008 ◽

Author(s):

Guorong Xu

Keyword(s):

Bile Acid ◽

Feedback Regulation ◽

Acid Synthesis ◽

Bile Acid Synthesis

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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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3P-0771 Bile acid precursors are endogenous ligands for FXR and mediate the negative feedback regulation of bile acid synthesis

Atherosclerosis Supplements ◽

10.1016/s1567-5688(03)90989-5 ◽

2003 ◽

Vol 4 (2) ◽

pp. 231

Author(s):

T. Nishimaki-Mogami ◽

T. Fujino ◽

M. Une ◽

Y. Sato ◽

M. Tohkin ◽

...

Keyword(s):

Bile Acid ◽

Negative Feedback ◽

Feedback Regulation ◽

Acid Synthesis ◽

Bile Acid Synthesis ◽

Negative Feedback Regulation ◽

Endogenous Ligands

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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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Dietary cholesterol stimulates CYP7A1 in rats because farnesoid X receptor is not activated

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.00397.2003 ◽

2004 ◽

Vol 286 (5) ◽

pp. G730-G735 ◽

Cited By ~ 25

Author(s):

Guorong Xu ◽

Lu-xing Pan ◽

Hai Li ◽

Quan Shang ◽

Akira Honda ◽

...

Keyword(s):

Bile Acid ◽

Target Genes ◽

Dietary Cholesterol ◽

Farnesoid X Receptor ◽

Mrna Levels ◽

Sprague Dawley ◽

Bile Acid Pool ◽

Acid Pool ◽

Sprague Dawley Rats ◽

Bile Acid Pool Size

Cholesterol feeding upregulates CYP7A1 in rats but downregulates CYP7A1 in rabbits. To clarify the mechanism responsible for the upregulation of CYP7A1 in cholesterol-fed rats, the effects of dietary cholesterol (Ch) and cholic acid (CA) on the activation of the nuclear receptors, liver X-receptor (LXR-α) and farsenoid X-receptor (FXR), which positively and negatively regulate CYP7A1, were investigated in rats. Studies were carried out in four groups ( n = 12/group) of male Sprague-Dawley rats fed regular chow (control), 2% Ch, 2% Ch + 1% CA, and 1% CA alone for 1 wk. Changes in mRNA expression of short heterodimer partner (SHP) and bile salt export pump (BSEP), target genes for FXR, were determined to indicate FXR activation, whereas the expression of ABCA1 and lipoprotein lipase (LPL), target genes for LXR-α, reflected activation. CYP7A1 mRNA and activity increased twofold and 70%, respectively, in rats fed Ch alone when the bile acid pool size was stable but decreased 43 and 49%, respectively, after CA was added to the Ch diet, which expanded the bile acid pool 3.4-fold. SHP and BSEP mRNA levels did not change after feeding Ch but increased 88 and 37% in rats fed Ch + CA. This indicated that FXR was activated by the expanded bile acid pool. When Ch or Ch + CA were fed, hepatic concentrations of oxysterols, ligands for LXR-α increased to activate LXR-α, as evidenced by increased mRNA levels of ABCA1 and LPL. Feeding CA alone enlarged the bile acid pool threefold and increased the expression of both SHP and BSEP. These results suggest that LXR-α was activated in rats fed both Ch or Ch + CA, whereas CYP7A1 mRNA and activity were induced only in Ch-fed rats where the bile acid pool was not enlarged such that FXR was not activated. In rats fed Ch + CA, the bile acid pool expanded, which activated FXR to offset the stimulatory effects of LXR-α on CYP7A1.

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