scholarly journals Pharmacological Activation of PXR and CAR Downregulates Distinct Bile Acid-Metabolizing Intestinal Bacteria and Alters Bile Acid Homeostasis

2018 ◽  
Vol 168 (1) ◽  
pp. 40-60 ◽  
Author(s):  
Joseph L Dempsey ◽  
Dongfang Wang ◽  
Gunseli Siginir ◽  
Qiang Fei ◽  
Daniel Raftery ◽  
...  
Keyword(s):  
Bile Acid ◽  
Gut Microbiota ◽  
Gut Microbiome ◽  
Corn Oil ◽  
Constitutive Androstane Receptor ◽  
Intestinal Bacteria ◽  
Pregnane X Receptor ◽  
Bile Salt Hydrolase ◽  
Dependent Manner ◽  
Germ Free

AbstractThe gut microbiome regulates important host metabolic pathways including xenobiotic metabolism and intermediary metabolism, such as the conversion of primary bile acids (BAs) into secondary BAs. The nuclear receptors pregnane X receptor (PXR) and constitutive androstane receptor (CAR) are well-known regulators for xenobiotic biotransformation in liver. However, little is known regarding the potential effects of PXR and CAR on the composition and function of the gut microbiome. To test our hypothesis that activation of PXR and CAR regulates gut microbiota and secondary BA synthesis, 9-week-old male conventional and germ-free mice were orally gavaged with corn oil, PXR agonist PCN (75 mg/kg), or CAR agonist TCPOBOP (3 mg/kg) once daily for 4 days. PCN and TCPOBOP decreased two taxa in the Bifidobacterium genus, which corresponded with decreased gene abundance of the BA-deconjugating enzyme bile salt hydrolase. In liver and small intestinal content of germ-free mice, there was a TCPOBOP-mediated increase in total, primary, and conjugated BAs corresponding with increased Cyp7a1 mRNA. Bifidobacterium, Dorea, Peptociccaceae, Anaeroplasma, and Ruminococcus positively correlated with T-UDCA in LIC, but negatively correlated with T-CDCA in serum. In conclusion, PXR and CAR activation downregulates BA-metabolizing bacteria in the intestine and modulates BA homeostasis in a gut microbiota-dependent manner.

scholarly journals Gut Microbiome Critically Impacts PCB-induced Changes in Metabolic Fingerprints and the Hepatic Transcriptome in Mice

2020 ◽  
Vol 177 (1) ◽  
pp. 168-187 ◽  
Author(s):  
Joe Jongpyo Lim ◽  
Xueshu Li ◽  
Hans-Joachim Lehmler ◽  
Dongfang Wang ◽  
Haiwei Gu ◽  
...  
Keyword(s):  
Gut Microbiome ◽  
Target Genes ◽  
Metabolic Diseases ◽  
Corn Oil ◽  
Constitutive Androstane Receptor ◽  
Pregnane X Receptor ◽  
Dependent Manner ◽  
Integrated Network ◽  
Hepatic Transcriptome ◽  
Pcb Exposure

Abstract Polychlorinated biphenyls (PCBs) are ubiquitously detected and have been linked to metabolic diseases. Gut microbiome is recognized as a critical regulator of disease susceptibility; however, little is known how PCBs and gut microbiome interact to modulate hepatic xenobiotic and intermediary metabolism. We hypothesized the gut microbiome regulates PCB-mediated changes in the metabolic fingerprints and hepatic transcriptome. Ninety-day-old female conventional and germ-free mice were orally exposed to the Fox River Mixture (synthetic PCB mixture, 6 or 30 mg/kg) or corn oil (vehicle control, 10 ml/kg), once daily for 3 consecutive days. RNA-seq was conducted in liver, and endogenous metabolites were measured in liver and serum by LC-MS. Prototypical target genes of aryl hydrocarbon receptor, pregnane X receptor, and constitutive androstane receptor were more readily upregulated by PCBs in conventional conditions, indicating PCBs, to the hepatic transcriptome, act partly through the gut microbiome. In a gut microbiome-dependent manner, xenobiotic, and steroid metabolism pathways were upregulated, whereas response to misfolded proteins-related pathways was downregulated by PCBs. At the high PCB dose, NADP, and arginine appear to interact with drug-metabolizing enzymes (ie, Cyp1–3 family), which are highly correlated with Ruminiclostridium and Roseburia, providing a novel explanation of gut-liver interaction from PCB-exposure. Utilizing the Library of Integrated Network-based Cellular Signatures L1000 database, therapeutics targeting anti-inflammatory and endoplasmic reticulum stress pathways are predicted to be remedies that can mitigate PCB toxicity. Our findings demonstrate that habitation of the gut microbiota drives PCB-mediated hepatic responses. Our study adds knowledge of physiological response differences from PCB exposure and considerations for further investigations for gut microbiome-dependent therapeutics.

Gut microbiota regulate Alzheimer’s disease pathologies and cognitive disorders via PUFA-associated neuroinflammation

Gut ◽  
2022 ◽  
pp. gutjnl-2021-326269
Author(s):  
Chun Chen ◽  
Jianming Liao ◽  
Yiyuan Xia ◽  
Xia Liu ◽  
Rheinallt Jones ◽  
...  
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Gut Microbiota ◽  
Gut Microbiome ◽  
Amyloid Β ◽  
Microglia Activation ◽  
Oxidative Enzymes ◽  
Dependent Manner ◽  
Germ Free ◽  
Healthy Donors

ObjectiveThis study is to investigate the role of gut dysbiosis in triggering inflammation in the brain and its contribution to Alzheimer’s disease (AD) pathogenesis.DesignWe analysed the gut microbiota composition of 3×Tg mice in an age-dependent manner. We generated germ-free 3×Tg mice and recolonisation of germ-free 3×Tg mice with fecal samples from both patients with AD and age-matched healthy donors.ResultsMicrobial 16S rRNA sequencing revealed Bacteroides enrichment. We found a prominent reduction of cerebral amyloid-β plaques and neurofibrillary tangles pathology in germ-free 3×Tg mice as compared with specific-pathogen-free mice. And hippocampal RNAseq showed that inflammatory pathway and insulin/IGF-1 signalling in 3×Tg mice brain are aberrantly altered in the absence of gut microbiota. Poly-unsaturated fatty acid metabolites identified by metabolomic analysis, and their oxidative enzymes were selectively elevated, corresponding with microglia activation and inflammation. AD patients’ gut microbiome exacerbated AD pathologies in 3×Tg mice, associated with C/EBPβ/asparagine endopeptidase pathway activation and cognitive dysfunctions compared with healthy donors’ microbiota transplants.ConclusionsThese findings support that a complex gut microbiome is required for behavioural defects, microglia activation and AD pathologies, the gut microbiome contributes to pathologies in an AD mouse model and that dysbiosis of the human microbiome might be a risk factor for AD.

scholarly journals Understanding the Physiological Functions of the Host Xenobiotic-sensing Nuclear Receptors PXR and CAR on the Gut Microbiome using Genetically Modified Mice

2020 ◽  
Author(s):  
Mallory Little ◽  
Moumita Dutta ◽  
Hao Li ◽  
Adam Matson ◽  
Xiaojian Shi ◽  
...  
Keyword(s):  
Nuclear Receptors ◽  
Gut Microbiome ◽  
Constitutive Androstane Receptor ◽  
Immune Surveillance ◽  
Specific Effect ◽  
Pregnane X Receptor ◽  
Bile Salt Hydrolase ◽  
Physiological Functions ◽  
Species Specific ◽  
Host Immune Surveillance

Abstract Background: Pharmacological activation of the host xenobiotic-sensing nuclear receptors pregnane X receptor (PXR) and constitutive androstane receptor (CAR) is well-known to increase drug metabolism and reduce inflammation. Little is known regarding the physiological functions of PXR and CAR on the gut microbiome, which is an important regulator for the host immune surveillance and bile acid (BA) metabolism. We examined the gut microbiome composition and BA metabolites in high vs. low PXR/CAR-expressing mice, and in mice that are deficient in PXR, CAR, or both, at two developmental ages. We also utilized humanized PXR transgenic (hPXR-TG) mice to compare the species-specific effect of PXR on the gut microbiome. Results: We discovered bivalent hormetic functions of PXR and CAR in modulating the richness of the gut microbiome and inflammatory biomarkers: the high PXR/CAR expressers had higher microbial richness, pro-inflammatory bacteria (distinct taxa in Helicobacteraceae and Helicobacter), and fecal pro-inflammatory cytokines, suggesting higher immune surveillance to prevent the colonization of harmful bacteria. Interestingly, the absence of PXR or CAR also increased the microbial richness, and absence of both receptors synergistically increased the microbial richness. PXR and CAR deficiency increased the pro-inflammatory bacteria (Helicobacteraceae and Helicobacter). Most notably, deficiency in both PXR and CAR markedly increased the relative abundance of Lactobacillus, which is capable of bile salt hydrolase (BSH) activity. This corresponded to a decrease in major primary taurine-conjugated bile acids (BAs) in feces, which may lead to higher internal burden of taurine and unconjugated BAs, both of which are linked to inflammation, oxidative stress, and cytotoxicity. hPXR-TG mice had a distinct microbial profile as compared to wild-type mice, including a higher representation of Prevotella. hPXR-TG mice also had higher 12-OH BAs but lower 6-OH BAs, suggesting PXR’s species-specific role in modulating host hepatic BA synthesis. Conclusions: This study is the first to show that the host PXR and CAR profoundly influence the composition of the gut microbiome and its BA metabolites, with a bivalent hormetic relationship between PXR/CAR levels and microbial richness, unveiling the involvement of PXR/CAR-microbiome interactions in host immune surveillance and BA metabolism.

scholarly journals Early Exposure to Gut Microbiome Reduces Hepatocellular Carcinoma Risks in Mice

2020 ◽  
Vol 2020 ◽  
pp. 1-6
Author(s):  
Yang-Ming Lee ◽  
Wei-Chun Chang ◽  
Fu-Ju Lei ◽  
Chew-Teng Kor ◽  
Hsueh-Chou Lai ◽  
...  
Keyword(s):  
Hepatocellular Carcinoma ◽  
Gut Microbiota ◽  
Gut Microbiome ◽  
Liver Tumors ◽  
Male Mice ◽  
Germ Free ◽  
Housing Environment ◽  
Male Sex ◽  
Group 10 ◽  
Group 5

Aims. Liver cancer is a multietiological disease that has multiple factors contributing to the hepatocarcinogenic process, e.g., hepatitis viruses, carcinogens, male sex, or metabolic factors. Notably, emerging evidence reported that gut microbiota is crucial to the pathogenesis of hepatocellular carcinoma (HCC) via activation of innate immunity. However, the effect of time to gut microbiota exposure after birth is unknown. Using a germ-free animal housing environment, instead of antibiotics, we examined the effects of various time-to-exposure (TTE) to gut microbiota durations on HCC risk. Methods. HBV or carcinogen-mediated spontaneous HCC models were implemented in this study. The HCC incidence rates in mice either kept germ-free (GF; that is, with no exposure to gut microbiota) or exposed to gut microbiota after being moved to a specific pathogen-free (SPF) housing environment and with various time-to-exposure (TTE) durations, namely, 5 weeks after birth, 10 weeks after birth, or since conception (that is, 5-week TTE group, 10-week TTE group, and SPF group, respectively), were recorded. The mice were sacrificed at 30 or 40 weeks after birth, and macro-/microscopic observations and pathological diagnosis were performed. Results. The incidence of liver tumors among the male mice was higher than that among the female mice in the carcinogen-induced HCC mice sacrificed at 40 weeks after birth (with P=0.011, 0.035, 0.0003, and 0.012, respectively, in the GF group, 5-week TTE group, 10-week TTE group, and SPF group). Similarly, in the HBV-HCC model, the incidence of liver tumors among the male mice was significantly higher than that among the female mice (with P=0.013, 0.020, 0.012, and 0.002, respectively, in the GF group, 5-week TTE group, 10-week TTE group, and SPF group). These results suggest that gut microbiota exposure is irrelevant to the male sex preference of HCC. Surprisingly, when comparing carcinogen-induced HCC male mice in the 10-week TTE group (90%; n=10), 5-week TTE group (56%; n=9), and SPF group (30%; n=10) (P=0.020), we found that the incidence of liver tumors was higher in the mice with later exposure to gut microbiome. Similarly, when comparing HBV-HCC male mice in the 10-week TTE group (100%; n=11), 5-week TTE group (70%; n=10), and SPF group (33%; n=9) (P=0.080), we also found that the incidence of liver tumors was higher in the mice with later exposure to gut microbiome. Conclusions. Early (prepubertal) exposure to gut microbiome reduces the risk of HCC development, indicating a potentially important factor for cancer surveillance. Exploring the mechanisms by which such exposure affects HCC risk might lead to novel cancer vaccines.

scholarly journals IgA dysfunction induced by the early-lifetime disruption of gut microbiota aggravates diet–induced metabolic syndrome in mice

2021 ◽  
Author(s):  
Jielong Guo ◽  
Xue Han ◽  
Yilin You ◽  
Weidong Huang ◽  
Zhan Jicheng
Keyword(s):  
Metabolic Syndrome ◽  
Gut Microbiota ◽  
Early Life ◽  
Low Dose ◽  
Dependent Manner ◽  
Wild Type ◽  
Bacterial Composition ◽  
Germ Free ◽  
Iga Response ◽  
Intestinal Iga

Abstract BackgroundLow-dose antibiotic contamination in animal food is still a severe food safety problem worldwide. Penicillin is one of the main classes of antibiotics being detected in food. Previous studies have shown that transient exposure of low-dose penicillin (LDP) during early life resulted in metabolic syndrome (MetS) in mice. However, the underlying mechanism(s) and efficient approaches to counteracting this are largely unknown.MethodsWild-type (WT) or secretory IgA (SIgA)-deficient (Pigr-/-) C57BL/6 mice were exposed to LDP or not from several days before birth to 30 d of age. Five times of FMT or probiotics (a mixture of Lactobacillus bulgaricus and L. rhamnosus GG) treatments were applied to parts of these LDP-treated mice from 12 d to 28 d of life. Bacterial composition from different regions (mucosa and lumen) of the colon and ileum were analyzed through 16S rDNA sequencing. Intestinal IgA response was analyzed. Multiple parameters related to MetS were also determined. In addition, germ-free animals and in vitro tissue culture were also used to determine the correlations between LDP, gut microbiota (GM) and intestinal IgA response.ResultsLDP disturbed the intestinal bacterial composition, especially for ileal mucosa, the main inductive and effective sites of IgA response, in 30-d-old mice. The alteration of early GM resulted in a persistent inhibition of the intestinal IgA response, leading to a constant reduction of fecal and caecal SIgA levels throughout the 25-week experiment, which is early life-dependent, as transfer of LDP-GM to 30 d germ-free mice only resulted in a transient reduction in fecal SIgA. LDP-induced reduction in SIgA led to a decrease in IgA+ bacteria and a dysbiosis in the ileal mucosal samples of 25 week wild-type but not Pigr-/- mice. Moreover, LDP also resulted in increases in ileal bacterial encroachment and adipose inflammation, along with an enhancement of diet-induced MetS in an intestinal SIgA-dependent manner. Furthermore, several times of FMT or probiotic treatments during LDP treatment are efficient to fully (for FMT) or partially (for probiotics) counteract the LDP-effect on both GM and metabolism.ConclusionsEarly-life LDP-induced enhancement of diet-induced MetS is mediated by intestinal SIgA, which could be (partially) restored by FMT or probiotics treatment.

Molecular Physiology of Bile Acid Signaling in Health, Disease and Aging

2020 ◽  
Author(s):  
Alessia Perino ◽  
Hadrien Demagny ◽  
Laura Alejandra Velazquez-Villegas ◽  
Kristina Schoonjans
Keyword(s):  
Bile Acid ◽  
Gut Microbiota ◽  
Bile Acids ◽  
Gut Microbiome ◽  
Signaling Molecules ◽  
Therapeutic Strategies ◽  
Fine Tuning ◽  
Physiological Effects ◽  
Adaptive Responses ◽  
Molecular Physiology

Over the last two decades, bile acids (BAs) have become established as important signaling molecules that enable fine-tuned inter-tissue communication from the liver, their site of production, over the intestine, where they are modified by the gut microbiota, to virtually any organ, where they exert their pleiotropic physiological effects. The chemical variety of BAs, to a large extent determined by the gut microbiome, also allows for a complex fine-tuning of adaptive responses in our body. This review provides an overview of the mechanisms by which BA receptors coordinate several aspects of physiology and highlights new therapeutic strategies for diseases underlying pathological BA signaling.

scholarly journals Gut Microbiome: Profound Implications for Diet and Disease

Nutrients ◽  
2019 ◽  
Vol 11 (7) ◽  
pp. 1613 ◽  
Author(s):  
Ronald Hills ◽  
Benjamin Pontefract ◽  
Hillary Mishcon ◽  
Cody Black ◽  
Steven Sutton ◽  
...  
Keyword(s):  
Gut Microbiota ◽  
Gut Microbiome ◽  
Bacterial Species ◽  
Intestinal Bacteria ◽  
Short Chain Fatty Acids ◽  
E Coli ◽  
Beneficial Effects ◽  
Microbial Profile ◽  
Irritable Bowel ◽  
Prebiotic Fiber

The gut microbiome plays an important role in human health and influences the development of chronic diseases ranging from metabolic disease to gastrointestinal disorders and colorectal cancer. Of increasing prevalence in Western societies, these conditions carry a high burden of care. Dietary patterns and environmental factors have a profound effect on shaping gut microbiota in real time. Diverse populations of intestinal bacteria mediate their beneficial effects through the fermentation of dietary fiber to produce short-chain fatty acids, endogenous signals with important roles in lipid homeostasis and reducing inflammation. Recent progress shows that an individual’s starting microbial profile is a key determinant in predicting their response to intervention with live probiotics. The gut microbiota is complex and challenging to characterize. Enterotypes have been proposed using metrics such as alpha species diversity, the ratio of Firmicutes to Bacteroidetes phyla, and the relative abundance of beneficial genera (e.g., Bifidobacterium, Akkermansia) versus facultative anaerobes (E. coli), pro-inflammatory Ruminococcus, or nonbacterial microbes. Microbiota composition and relative populations of bacterial species are linked to physiologic health along different axes. We review the role of diet quality, carbohydrate intake, fermentable FODMAPs, and prebiotic fiber in maintaining healthy gut flora. The implications are discussed for various conditions including obesity, diabetes, irritable bowel syndrome, inflammatory bowel disease, depression, and cardiovascular disease.

scholarly journals Resveratrol Attenuates Trimethylamine- N -Oxide (TMAO)-Induced Atherosclerosis by Regulating TMAO Synthesis and Bile Acid Metabolism via Remodeling of the Gut Microbiota

mBio ◽  
2016 ◽  
Vol 7 (2) ◽  
Author(s):  
Ming-liang Chen ◽  
Long Yi ◽  
Yong Zhang ◽  
Xi Zhou ◽  
Li Ran ◽  
...  
Keyword(s):  
Bile Acid ◽  
Growth Factor ◽  
Gut Microbiota ◽  
Fibroblast Growth Factor ◽  
Farnesoid X Receptor ◽  
Fecal Excretion ◽  
Bile Acid Metabolism ◽  
Bile Salt Hydrolase ◽  
Fibroblast Growth ◽  
As Effects

ABSTRACT The gut microbiota is found to be strongly associated with atherosclerosis (AS). Resveratrol (RSV) is a natural phytoalexin with anti-AS effects; however, its mechanisms of action remain unclear. Therefore, we sought to determine whether the anti-AS effects of RSV were related to changes in the gut microbiota. We found that RSV attenuated trimethylamine- N -oxide (TMAO)-induced AS in ApoE −/− mice. Meanwhile, RSV decreased TMAO levels by inhibiting commensal microbial trimethylamine (TMA) production via gut microbiota remodeling in mice. Moreover, RSV increased levels of the genera Lactobacillus and Bifidobacterium , which increased the bile salt hydrolase activity, thereby enhancing bile acid (BA) deconjugation and fecal excretion in C57BL/6J and ApoE −/− mice. This was associated with a decrease in ileal BA content, repression of the enterohepatic farnesoid X receptor (FXR)-fibroblast growth factor 15 (FGF15) axis, and increased cholesterol 7a-hydroxylase (CYP7A1) expression and hepatic BA neosynthesis. An FXR antagonist had the same effect on FGF15 and CYP7A1 expression as RSV, while an FXR agonist abolished RSV-induced alterations in FGF15 and CYP7A1 expression. In mice treated with antibiotics, RSV neither decreased TMAO levels nor increased hepatic BA synthesis. Additionally, RSV-induced inhibition of TMAO-caused AS was also markedly abolished by antibiotics. In conclusion, RSV attenuated TMAO-induced AS by decreasing TMAO levels and increasing hepatic BA neosynthesis via gut microbiota remodeling, and the BA neosynthesis was partially mediated through the enterohepatic FXR-FGF15 axis. IMPORTANCE Recently, trimethylamine- N -oxide (TMAO) has been identified as a novel and independent risk factor for promoting atherosclerosis (AS) partially through inhibiting hepatic bile acid (BA) synthesis. The gut microbiota plays a key role in the pathophysiology of TMAO-induced AS. Resveratrol (RSV) is a natural phytoalexin with prebiotic benefits. A growing body of evidence supports the hypothesis that phenolic phytochemicals with poor bioavailability are possibly acting primarily through remodeling of the gut microbiota. The current study showed that RSV attenuated TMAO-induced AS by decreasing TMAO levels and increasing hepatic BA neosynthesis via gut microbiota remodeling. And RSV-induced hepatic BA neosynthesis was partially mediated through downregulating the enterohepatic farnesoid X receptor-fibroblast growth factor 15 axis. These results offer new insights into the mechanisms responsible for RSV’s anti-AS effects and indicate that the gut microbiota may become an interesting target for pharmacological or dietary interventions to decrease the risk of developing cardiovascular diseases.

scholarly journals Effects of Gut Microbiota and Ingredient-Ingredient Interaction on the Pharmacokinetic Properties of Rotundic Acid and Pedunculoside

Planta Medica ◽  
2019 ◽  
Vol 85 (09/10) ◽  
pp. 729-737 ◽  
Author(s):  
Bao Yang ◽  
Hui Li ◽  
Qingfeng Ruan ◽  
Shenxin Xuan ◽  
Xiaojing Chen ◽  
...  
Keyword(s):  
Gut Microbiota ◽  
Oral Administration ◽  
Systemic Exposure ◽  
Lipid Lowering ◽  
Maximum Plasma ◽  
Dependent Manner ◽  
Monomer Mixture ◽  
Germ Free ◽  
Pharmacokinetic Interactions ◽  
Rotundic Acid

AbstractRotundic acid and pedunculoside are the most abundant constituents in Ilicis Rotundae Cortex, and possess lipid-lowering activity. In this study, we evaluated the pharmacokinetic interactions of rotundic acid with pedunculoside and other ingredients from Ilicis Rotundae Cortex with rotundic acid and pedunculoside, and preliminarily investigated the effects of gut microbiota on their pharmacokinetics using a pseudo-germ-free rat model. After a single oral administration of each monomer, a monomer mixture, and Ilicis Rotundae Cortex extract to the conventional and pseudo-germ-free rats, rotundic acid and pedunculoside were quantified in plasma by an UPLC/Q-TOF-MS/MS method. The systemic exposure (maximum plasma concentration and area under concentration-time curve) of two analytes in conventional rats were increased in an approximately dose-dependent manner. Oral administration of rotundic acid and pedunculoside in the forms of a monomer mixture and Ilicis Rotundae Cortex extract to the conventional rats significantly decreased the systemic exposure compared with the monomer groups, which demonstrated the existence of significant pharmacokinetic interactions. The pseudo-germ-free rats were prepared by nonabsorbable antibiotic treatment, and the systemic exposure of two analytes were significantly decreased and most of the “time to reach the maximum” values were delayed in comparison to conventional rats, therefore gut microbiota might serve as an efficient absorption promoter. These results provide a scientific basis for the clinical application of the two bioactive constituents and Ilicis Rotundae Cortex.

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

2009 ◽  
Vol 296 (5) ◽  
pp. G1119-G1129 ◽  
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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