Nutritional status modifies pregnane X receptor regulated transcriptome

Abstract Pregnane X receptor (PXR) regulates glucose and lipid metabolism, but little is known of the nutritional regulation of PXR function. We investigated the genome wide effects of the nutritional status on the PXR mediated gene regulation in the liver. Mice were treated with a PXR ligand pregnenolone 16α-carbonitrile (PCN) for 4 days and subsequently either fasted for 5 hours or after 4-hour fast treated with intragastric glucose 1 hour before sample collection. Gene expression microarray study indicated that PCN both induced and repressed much higher number of genes in the glucose fed mice and the induction of multiple well-established PXR target genes was potentiated by glucose. A subset of genes, including bile acid synthesis gene Cyp8b1, responded in an opposite direction during fasting and after glucose feeding. PXR knockout abolished these effects. In agreement with the Cyp8b1 regulation, PCN also modified the bile acid composition in the glucose fed mice. Contribution of glucose, insulin and glucagon on the observed nutritional effects was investigated in primary hepatocytes. However, only mild impact on PXR function was observed. These results show that nutritional status modifies the PXR regulated transcriptome both qualitatively and quantitatively and reveal a complex crosstalk between PXR and energy homeostasis.

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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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Rifampicin, not vitamin E, suppresses parenteral nutrition-associated liver disease development through the pregnane X receptor pathway in piglets

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.00193.2019 ◽

2020 ◽

Vol 318 (1) ◽

pp. G41-G52 ◽

Cited By ~ 1

Author(s):

Gregory Guthrie ◽

Barbara Stoll ◽

Shaji Chacko ◽

Charlotte Lauridsen ◽

Jogchum Plat ◽

...

Keyword(s):

Liver Disease ◽

Bile Acid ◽

Vitamin E ◽

Parenteral Nutrition ◽

Pregnane X Receptor ◽

Acid Synthesis ◽

Bile Acid Synthesis ◽

Bile Acid Metabolism ◽

Neonatal Piglets ◽

Hyocholic Acid

Infants receiving long-term parenteral nutrition (PN) develop PN-associated liver disease (PNALD). We previously (Ng K et al. JPEN J Parenter Enteral Nutr 40: 656–671, 2016. doi: 10.1177/0148607114567900 .) showed that PN containing soy-based lipid supplemented with vitamin E (α-tocopherol) prevents the development of PNALD. We hypothesize that this occurs via vitamin E activation of pregnane X receptor (PXR)-mediated pathways involved in bile acid metabolism. Neonatal piglets received PN for 14 days containing Intralipid (IL; soy-based lipid emulsion), IL supplemented with 12.6 mg·kg−1·day−1 vitamin E (VITE), or IL with 10 mg·kg−1·day−1 Rifadin IV (RIF), a PXR agonist. Pigs treated with IL and VITE, but not RIF, developed cholestasis and hyperbilirubinemia, markers of liver disease. The hepatic PXR target genes CYP3A29 and UGT1A6 increased during RIF treatment. RIF also modestly increased metabolism of chenodeoxycholic acid to the more hydrophilic bile acid hyocholic acid. Serum fibroblast growth factor (FGF)-19, a key regulator in suppressing hepatic bile acid synthesis, significantly increased in the RIF group. We conclude rifampicin modified markers of PNALD development by increased metabolism of bile acids and potentially suppressed bile acid synthesis. Vitamin E was ineffective at high lipid doses in preventing PNALD. NEW & NOTEWORTHY Intravenous vitamin E and rifampicin were administered to neonatal piglets receiving parenteral nutrition to determine their efficacy in reducing the progression of parenteral nutrition-associated liver disease (PNALD). Rifampicin increased serum FGF-19 concentrations and synthesis of the bile acid hyocholic acid which led to a reduction of PNALD parameters at 2 wk of administration. This result has potential clinical implications for the use of rifampicin as a safe and inexpensive treatment for short-term development of PNALD.

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Effects of Vitamin K2 on the Expression of Genes Involved in Bile Acid Synthesis and Glucose Homeostasis in Mice with Humanized PXR

Nutrients ◽

10.3390/nu10080982 ◽

2018 ◽

Vol 10 (8) ◽

pp. 982 ◽

Cited By ~ 9

Author(s):

Halima Sultana ◽

Kimika Watanabe ◽

Md Rana ◽

Rie Takashima ◽

Ai Ohashi ◽

...

Keyword(s):

Bile Acid ◽

Drug Metabolism ◽

Oral Treatment ◽

Pregnane X Receptor ◽

Acid Synthesis ◽

Bile Acid Synthesis ◽

Vitamin K2 ◽

Mrna Levels ◽

Humanized Mouse Model ◽

Physiological Conditions

Pregnane X receptor (PXR) is a nuclear receptor activated by various compounds, including prescribed drugs and dietary ingredients. Ligand-specific activation of PXR alters drug metabolism and affects many other physiological conditions. Species-specific ligand preference is a considerable challenge for studies of PXR function. To increase translational value of the results of mouse studies, humanized mouse model expressing human PXR (hPXR) has been developed. Menaquinone-4 (MK-4), one of vitamin K2 analogs prescribed in osteoporosis, is a PXR ligand. We hypothesized that MK-4 could modulate the physiological conditions endogenously influenced by PXR, including those that have not been yet properly elucidated. In the present study, we investigated the effects of a single oral treatment with MK-4 on hepatic gene expression in wild-type and hPXR mice by using quantitative RT-PCR and DNA microarray. MK-4 administration altered mRNA levels of genes involved in drug metabolism (Abca3, Cyp2s1, Sult1b1), bile acid synthesis (Cyp7a1, Cyp8b1), and energy homeostasis (Aldoc, Slc2a5). Similar mRNA changes of CYP7A1 and CYP8B1 were observed in human hepatocarcinoma HepG2 cells treated with MK-4. These results suggest that MK-4 may modulate bile acid synthesis. To our knowledge, this is the first report showing the effect of MK-4 in hPXR mice.

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Mechanism of rifampicin and pregnane X receptor inhibition of human cholesterol 7α-hydroxylase gene transcription

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.00258.2004 ◽

2005 ◽

Vol 288 (1) ◽

pp. G74-G84 ◽

Cited By ~ 129

Author(s):

Tiangang Li ◽

John Y. L. Chiang

Keyword(s):

Bile Acid ◽

Mrna Expression ◽

Gene Transcription ◽

Pregnane X Receptor ◽

Acid Synthesis ◽

Bile Acid Synthesis ◽

Protective Mechanism ◽

Peroxisome Proliferator ◽

Peroxisome Proliferator Activated Receptor ◽

Human Primary Hepatocytes

Bile acids, steroids, and drugs activate steroid and xenobiotic receptor pregnane X receptor (PXR; NR1I2), which induces human cytochrome P4503A4 (CYP3A4) in drug metabolism and cholesterol 7α-hydroxylase (CYP7A1) in bile acid synthesis in the liver. Rifampicin, a human PXR agonist, inhibits bile acid synthesis and has been used to treat cholestatic diseases. The objective of this study is to elucidate the mechanism by which PXR inhibits CYP7A1 gene transcription. The mRNA expression levels of CYP7A1 and several nuclear receptors known to regulate the CYP7A1 gene were assayed in human primary hepatocytes by quantitative real-time PCR (Q-PCR). Rifampicin reduced CYP7A1 and small heterodimer partner (SHP; NR02B) mRNA expression suggesting that SHP was not involved in PXR inhibition of CYP7A1. Rifampicin inhibited CYP7A1 reporter activity and a PXR binding site was localized to the bile acid response element-I. Mammalian two-hybrid assays revealed that PXR interacted with hepatic nuclear factor 4α (HNF4α, NR2A1) and rifampicin was required. Coimmunoprecipitation assay confirmed PXR interaction with HNF4α. PXR also interacted with peroxisome proliferator-activated receptor γ coactivator (PGC-1α), which interacted with HNF4α and induced CYP7A1 gene transcription. Rifampicin enhanced PXR interaction with HNF4α and reduced PGC-1α interaction with HNF4α. Chromatin immunoprecipitation assay showed that PXR, HNF4α, and PGC-1α bound to CYP7A1 chromatin, and rifampicin dissociated PGC-1α from chromatin. These results suggest that activation of PXR by rifampicin promotes PXR interaction with HNF4α and blocks PGC-1α activation with HNF4α and results in inhibition of CYP7A1 gene transcription. Rifampicin inhibition of bile acid synthesis may be a protective mechanism against drug and bile acid-induced cholestasis.

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ENDOCRINOLOGY IN PREGNANCY: Metabolic impact of bile acids in gestation

Acta Endocrinologica ◽

10.1530/eje-20-1101 ◽

2021 ◽

Vol 184 (3) ◽

pp. R69-R83

Author(s):

Hei Man Fan ◽

Alice L Mitchell ◽

Catherine Williamson

Keyword(s):

Bile Acid ◽

Bile Acids ◽

Acid Synthesis ◽

Bile Acid Synthesis ◽

Maternal Serum ◽

Farnesoid X Receptor ◽

Acid Uptake ◽

Glucose And Lipid Metabolism ◽

Bile Acid Uptake ◽

In Pregnancy

Bile acids are lipid-solubilising molecules that also regulate metabolic processes. Farnesoid X receptor (FXR) and Takeda G-protein coupled receptor 5 (TGR5) are two bile acid receptors with key metabolic roles. FXR regulates bile acid synthesis in the liver and influences bile acid uptake in the intestine. TGR5 is mainly involved in regulation of signalling pathways in response to bile acid uptake in the gut and therefore prandial response. Both FXR and TGR5 have potential as therapeutic targets for disorders of glucose and/or lipid homeostasis. Gestation is also known to cause small increases in bile acid concentrations, but physiological hypercholanaemia of pregnancy is usually not sufficient to cause any clinically relevant effects. This review focuses on how gestation alters bile acid homeostasis, which can become pathological if the elevation of maternal serum bile acids is more marked than physiological hypercholanaemia, and on the influence of FXR and TGR5 function in pregnancy on glucose and lipid metabolism. This will be discussed with reference to two gestational disorders: intrahepatic cholestasis of pregnancy (ICP), a disease where bile acids are pathologically elevated, and gestational diabetes mellitus (GDM), characterised by hyperglycaemia during pregnancy.

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

Molecular Endocrinology ◽

10.1210/me.2007-0565 ◽

2008 ◽

Vol 22 (6) ◽

pp. 1345-1356 ◽

Cited By ~ 101

Author(s):

Youn-Kyoung Lee ◽

Daniel R. Schmidt ◽

Carolyn L. Cummins ◽

Mihwa Choi ◽

Li Peng ◽

...

Keyword(s):

Bile Acid ◽

Target Genes ◽

Feedback Regulation ◽

Acid Synthesis ◽

Bile Acid Synthesis ◽

Farnesoid X Receptor ◽

Mrna Levels ◽

Orphan Nuclear Receptor ◽

Small Heterodimer Partner

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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Nuclear factor-E2-related factor 2 is a major determinant of bile acid homeostasis in the liver and intestine

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.00263.2011 ◽

2012 ◽

Vol 302 (9) ◽

pp. G925-G936 ◽

Cited By ~ 28

Author(s):

Jittima Weerachayaphorn ◽

Albert Mennone ◽

Carol J. Soroka ◽

Kathy Harry ◽

Lee R. Hagey ◽

...

Keyword(s):

Bile Acid ◽

Liver Injury ◽

Mrna Expression ◽

Pregnane X Receptor ◽

Acid Synthesis ◽

Bile Acid Synthesis ◽

Related Factor ◽

Nuclear Factor ◽

Wild Type ◽

Duct Ligation

The transcription factor nuclear factor-E2-related factor 2 (Nrf2) is a key regulator for induction of hepatic detoxification and antioxidant mechanisms, as well as for certain hepatobiliary transporters. To examine the role of Nrf2 in bile acid homeostasis and cholestasis, we assessed the determinants of bile secretion and bile acid synthesis and transport before and after bile duct ligation (BDL) in Nrf2−/− mice. Our findings indicate reduced rates of biliary bile acid and GSH excretion, higher levels of intrahepatic bile acids, and decreased expression of regulators of bile acid synthesis, Cyp7a1 and Cyp8b1, in Nrf2−/− compared with wild-type control mice. The mRNA expression of the bile acid transporters bile salt export pump ( Bsep) and organic solute transporter ( Ostα) were increased in the face of impaired expression of the multidrug resistance-associated proteins Mrp3 and Mrp4. Deletion of Nrf2 also decreased ileal apical sodium-dependent bile acid transporter ( Asbt) expression, leading to reduced bile acid reabsorption and increased loss of bile acid in feces. Finally, when cholestasis is induced by BDL, liver injury was not different from that in wild-type BDL mice. These Nrf2−/− mice also had increased pregnane X receptor ( Pxr) and Cyp3a11 mRNA expression in association with enhanced hepatic bile acid hydroxylation. In conclusion, this study finds that Nrf2 plays a major role in the regulation of bile acid homeostasis in the liver and intestine. Deletion of Nrf2 results in a cholestatic phenotype but does not augment liver injury following BDL.

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