MAFG is a transcriptional repressor of bile acid synthesis and metabolism (ChIP-seq)
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ABSTRACT: Specific bile acids are potent signaling molecules that modulate metabolic pathways affecting lipid, glucose and bile acid homeostasis, and the microbiota. Bile acids are synthesized from cholesterol in the liver, and the key enzymes involved in bile acid synthesis (Cyp7a1, Cyp8b1) are regulated transcriptionally by the nuclear receptor FXR. We have identified an FXR-regulated pathway upstream of a transcriptional repressor that controls multiple bile acid metabolism genes. We identify MafG as an FXR target gene and show that hepatic MAFG overexpression represses genes of the bile acid synthetic pathway and modifies the biliary bile acid composition. In contrast, loss-of-function studies using MafG(+/-) mice causes de-repression of the same genes with concordant changes in biliary bile acid levels. Finally, we identify functional MafG response elements in bile acid metabolism genes using ChIP-seq analysis. Our studies identify a molecular mechanism for the complex feedback regulation of bile acid synthesis controlled by FXR.
Project description:Specific bile acids are potent signaling molecules that modulate metabolic pathways affecting lipid, glucose and bile acid homeostasis, and the microbiota. Bile acids are synthesized from cholesterol in the liver, and the key enzymes involved in bile acid synthesis (Cyp7a1, Cyp8b1) are regulated transcriptionally by the nuclear receptor FXR. We have identified an FXR-regulated pathway upstream of a transcriptional repressor that controls multiple bile acid metabolism genes. We identify MafG as an FXR target gene and show that hepatic MAFG overexpression represses genes of the bile acid synthetic pathway and modifies the biliary bile acid composition. In contrast, loss-of-function studies using MafG(+/-) mice causes de-repression of the same genes with concordant changes in biliary bile acid levels. Finally, we identify functional MafG response elements in bile acid metabolism genes using ChIP-seq analysis. Our studies identify a molecular mechanism for the complex feedback regulation of bile acid synthesis controlled by FXR
Project description:Bile acids are multifunctional signaling molecules that play significant roles in maintaining microbial homeostasis. N6-methyladenine (m6A), the most abundant epitranscriptomic modification, mediates various biological processes by modulating RNA metabolism. However, the precise regulatory mechanisms of m6A methylation in bile acid metabolism, and its downstream effects on microbiota remain unclear. In this study, liver-specific Mettl14 knockout (Mettl14-LKO) reshaped bile acid profile and expression levels of protein related to bile acid metabolism, namely CYP7A1, FXR, and BSEP. M6A-seq data revealed m6A methylated peaks on CYP7A1. Mettl14-LKO significantly elevated expression of m6A “reader” IGF2BP3. Knockdown of IGF2BP3 inhibited CYP7A1 expression by decreasing mRNA stability. Mechanistically, Mettl14-LKO promoted bile acid synthesis by upregulating CYP7A1 expression in an m6A-IGF2BP3-dependent manner. Interestingly, Mettl14-LKO reduced bile acid content in ileum due to decreased BSEP level in liver. Noteworthy, we discovered for the first time that Mettl14 knockout in the liver altered fecal microbiota composition. Specifically, it changed the abundance of Cyanobacteria and Patescibacteria at phylum level, and Lachnochostridium, Candidatus-Saccharimonas, and Roseburia at genera level. Remarkably, Roseburia was negatively correlated with the bile acid levels and CYP7A1 expression. Our findings provide new insights into the role of METTL14 in regulating bile acid homeostasis and its impact on fecal microbiota. Roseburia emerges as a potential target for addressing metabolic diseases linked to disrupted METTL14 signaling.
Project description:Bile acids are not only physiological detergents facilitating nutrient absorption, but also signaling molecules regulating metabolic homeostasis. We reported recently that transgenic expression of CYP7A1 in mice stimulated bile acid synthesis and prevented Western diet-induced obesity, insulin resistance and hepatic steatosis. The aim of this experiment is to determine the impact of induction of hepatic bile acid synthesis on liver metabolism by determining hepatic gene expression profile in CYP7A1 transgenic mice. CYP7A1 transgenic mice and wild type control mice were fed either standard chow diet or high fat high cholesterol Western diet for 4 month. Hepatic gene expressions were measured by microarray analysis. Our results indicate that hepatic bile acid synthesis is closely linked to cholesterogenesis and lipogenesis, and maintaining bile acid homeostasis is improtant in hepatic metabolic homeostasis.
Project description:Bile acids are not only physiological detergents facilitating nutrient absorption, but also signaling molecules regulating metabolic homeostasis. We reported recently that transgenic expression of CYP7A1 in mice stimulated bile acid synthesis and prevented Western diet-induced obesity, insulin resistance and hepatic steatosis. The aim of this experiment is to determine the impact of induction of hepatic bile acid synthesis on liver metabolism by determining hepatic gene expression profile in CYP7A1 transgenic mice. CYP7A1 transgenic mice and wild type control mice were fed either standard chow diet or high fat high cholesterol Western diet for 4 month. Hepatic gene expressions were measured by microarray analysis. Our results indicate that hepatic bile acid synthesis is closely linked to cholesterogenesis and lipogenesis, and maintaining bile acid homeostasis is improtant in hepatic metabolic homeostasis. Male aged matched (~ 12-14 weeks) CYP7A1 transgenic mice and their wild type control littermates were fed a standard chow diet or a high fat (42%) high cholesterol (0.2%) diet (Harlan Teklad #88137) for 4 month Four groups (4 mice/group) are included in the experiments: Group 1: WT _ Chow Group 2: CYP7A1-tg + chow Group 3: WT + Western diet Group 4: CYP7A1-tg _ Western diet Total liver mRNA was isolated with a RNeasy kit (Qiagen) and used for microarray analysis.
Project description:Insulin regulation of hepatic gene expression is critical for controlling metabolism and preventing diabetes, atherosclerosis and NAFLD; yet, how insulin regulates gene expression in the spatial context of the liver lobule is largely unexplored. Here, we find that insulin regulates bile acid metabolism by segregating CYP8B1, the enzyme that catalyzes the 12α-hydroxylation of bile acids, from the other enzymes required for bile acid synthesis. When insulin signaling is disrupted, Cyp8b1 and the other bile acid synthesis genes become co-localized within the same zone, and 12α-hydroxylated bile acids, which drive atherosclerosis and NAFLD, are increased. Novel zone-specific genetic manipulations of Cyp8b1 that mimic the effects of insulin result in a more benign bile salt profile. Mechanistically, the zonal effects of insulin are not due to gradients of insulin concentration or signaling, but through insulin crosstalk with positional Wnt signals: Wnt and insulin act together to determine the complement of transcription factors active in the pericentral hepatocytes and thereby regulate Cyp8b1 zonation. Taken together, these data show that by repatterning gene expression in the liver lobule, insulin can transcriptionally regulate the outputs of a metabolic pathway. The spatial dimension of transcriptional regulation represents a novel lens with which to view the control of metabolism that may ultimately lead us to more precise therapies.
Project description:Biliary reverse cholesterol transport (RCT) plays a crucial role in cholesterol clearance and regulation of atherogenesis. San-wei-tan-xiang capsule (SWTX), a traditional Chinese medicine, has shown potential in inhibiting atherogenesis by increasing high-density lipoprotein (HDL) cholesterol levels and promoting macrophage-mediated cholesterol efflux. However, the specific role of HDL-driven cholesterol metabolism in the anti-atherogenic effects of SWTX remains unclear. In this study, liquid chromatography coupled with tandem mass spectrometry was used to analyze the circulating metabolic profile, and RNA sequencing was performed on liver samples from ApoE−/− mice fed a cholesterol-enriched diet. We found that SWTX treatment induced significantly differential expression of metabolites and genes involved in cholesterol and lipid metabolism, as well as bile secretion pathways, which are critical for HDL-driven biliary RCT. Furthermore, alterations in L-carnitine and choline metabolism induced by SWTX treatment was involved in the atheroprotective effects of SWTX. Notably, SWTX treatment led to a significant increase in the expression of cholesterol 7α-hydroxylase (CYP7A1), a key enzyme involved in bile acid synthesis during atherogenesis. Additionally, the expression of CYP7A1 and CYP7A1-mediated bile acid secretion were enhanced by the addition of choline in hepatic cells, suggesting that SWTX-induced elevation of choline metabolic products may contribute to the upregulation of CYP7A1 and CYP7A1-mediated biliary RCT. Overall, SWTX demonstrated its ability to attenuate atherosclerotic plaque formation, which can be attributed to alterations in carnitine and choline metabolism, as well as the modulation of CYP7A1-mediated HDL-driven biliary RCT.
Project description:Obstruction of bile flow results in bacterial proliferation and mucosal injury in the small intestine that can lead to the translocation of bacteria across the epithelial barrier and systemic infection. These adverse effects of biliary obstruction can be inhibited by administration of bile acids. Here we show that the farnesoid X receptor (FXR), a nuclear receptor for bile acids, induces genes involved in enteroprotection and inhibits bacterial overgrowth and mucosal injury in ileum caused by bile duct ligation. Mice lacking FXR have increased ileal levels of bacteria and a compromised epithelial barrier. These findings reveal a central role for FXR in protecting the distal small intestine from bacterial invasion and suggest that FXR agonists may prevent epithelial deterioration and bacterial translocation in patients with impaired bile flow. In this report we have examined the role of FXR in the ileum. We demonstrate that it plays a crucial role in preventing bacterial overgrowth and maintaining the integrity of the intestinal epithelium
Project description:Through the combined use of glutamine synthase / GLUL immunostaining, and CTNNB1 genotyping, we previously analyzed nearly 200 hepatocellular carcinomas (HCC). Little was reported on HCC with mutant B-catenin excepted their low genomic instability, their lack of association with hepatitis B virus and their well-differentiated pattern. We have demonstrated that HCC with mutant B-catenin exhibit specific features such as an homogeneous well differentiated pattern with a mixture of microtrabecular and acinar architecture, the absence of steatosis and the presence of frequent extra-cellular cholestasis. The aim of our study was to characterize the bile components in HCC with mutant B-catenin. To this end, we carried out transcriptome profiling of five typical B-catenin activated HCCs and we analysed the composition of the bile accumulated in these tumors. The transcriptional analysis of these tumors showed overexpression of genes belonging both to the synthesis (CYP7A1, CYP27A1 and CYP7B1) and transport (ABCG2/BCRP, ABCC2/MRP2, ABCB11/BSEP, OATP8/SLC01B3) of bile acids. However, the composition of bile in these tumors is not significantly modified. The large amount of bilirubin in these tumors follows the increase in biliverdin pigment reflecting the characteristic green color of these tumors and biliary acids content is not profoundly altered. Surprisingly, the main change affects the non-tumoral counterparts of HCC with mutant B-catenin which display an unexpected high content in biliary acids. These observations suggest that increased bile acids level due to an underlying pathology may play a role in the emergence of HCC with mutant B-catenin.
Project description:The nuclear receptor FXR acts as an intracellular bile salt sensor that regulates synthesis and transport of bile salts within their enterohepatic circulation. In addition, FXR is involved in control of a variety of crucial metabolic pathways. Four FXR splice variants are known, i.e. FXRα1-4. Although these isoforms show differences in spatial and temporal expression patterns as well as in transcriptional activity, the physiological relevance hereof has remained elusive. We have evaluated specific roles of hepatic FXRα2 and FXRα4 by stably expressing these isoforms using liver-specific self-complementary adeno-associated viral vectors in total body FXR knock-out mice. The hepatic gene expression profile of the FXR knock-out mice was largely normalized by both isoforms. Yet, differential effects were also apparent; FXRα2 was more effective in reducing elevated HDL levels and transrepressed hepatic expression of Cyp8B1, the regulator of cholate synthesis. The latter coincided with a switch in hydrophobicity of the bile salt pool. Furthermore, FXRα2-transduction caused an increased neutral sterol excretion compared to FXRα4 without affecting intestinal cholesterol absorption. Our data show, for the first time, that hepatic FXRα2 and FXRα4 differentially modulate bile salt and lipoprotein metabolism in mice.
Project description:Cholesterol 7alpha-hydroxylase (CYP7A1) is the rate limiting enzyme of bile acid biosynthetic pathway to convert cholesterol to bile acids, which is a major output pathway for cholesterol catabolism. In this study, we aimed to assess the potential regulatory mechanisms of microRNA-185 (miR-185) involved in cholesterol and bile acid homeostasis. This study provides convincing evidences about the critical role of miR-185 in FoxO1 modulation at both posttranscriptional and posttranslational levels, which account for the effects on CYP7A1 gene and its mediated cholesterol-bile acid metabolism. These results suggest an important role of miR-185 as a novel atherosclerosis-protective target for drug discovery.