Insulin controls hepatic bile acid metabolism by the spatial repatterning of gene expression
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ABSTRACT: 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: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:Cardiovascular diseases, especially atherosclerosis and its complications, are a leading cause of death. Inhibition of the non-canonical IkB kinases TBK1 and IKKe with amlexanox restores insulin sensitivity and glucose homeostasis in diabetic mice and human subjects. Here we report that amlexanox improves diet-induced hypertriglyceridemia and hypercholesterolemia in Western diet (WD)-fed Ldlr-/- mice, and protects against atherogenesis. Amlexanox ameliorates dyslipidemia, inflammation and vascular dysfunction through synergistic actions that involve upregulation of bile acid synthesis to increase cholesterol excretion. Transcriptomic profiling demonstrates an elevated expression of key bile acid synthesis genes. Furthermore, we found that amlexanox attenuates monocytosis, eosinophilia and vascular dysfunction during WD-induced atherosclerosis. These findings demonstrate the potential of amlexanox as a new therapy for hypercholesterolemia and atherosclerosis.
Project description:Chronic jet lag induces spontaneous hepatocellular carcinoma (HCC) in wild-type mice following a pathophysiological pathway very similar to that observed in obese humans. This process initiates with non-alcoholic fatty liver disease (NAFLD), progresses to steatohepatitis and fibrosis before HCC detection, and is driven by persistent genome-wide gene deregulation that induces global liver metabolic dysfunction. Nuclear receptor-controlled cholesterol/bile acid and xenobiotic metabolism are found among top deregulated pathways. Ablation of the bile acid receptor FXR dramatically increases intrahepatic bile acid levels and jet-lag-induced HCC, while loss of CAR, a well-known liver tumor promoter, inhibits NAFLD-induced hepatocarcinogenesis. Circadian disruption activates CAR by promoting cholestasis, peripheral clock disruption, and sympathetic dysfunction. Thus, FXR and CAR are clock-controlled therapeutic targets for spontaneous HCC
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.
Project description:Dyslipidemia and inflammation play key roles in the pathogenesis of both nonalcoholic fatty liver disease (NAFLD) and atherosclerosis. NAFLD, particularly its severe form nonalcoholic steatohepatitis (NASH) is associated with increased cardiovascular disease (CVD) risk. HDL (high density lipoprotein- also a CVD risk) are decreased in NAFLD but whether HDL function is abnormal in NAFLD is unknown. Furthermore, it is unknown whether dyslipidemia contributes to reduced HDL function in NAFLD and whether hepatic inflammation further impairs HDL function in patients with NASH. Therefore, the aim of this study was to investigate HDL function and to examine the effect of dyslipidemia and inflammation on HDL metabolism in patients with biopsy-proven simple steatosis (SS) and NASH. RESULTS: Compared to controls, SS and NASH subjects had significantly higher levels of plasma triglyceride, insulin, and were more insulin resistant (HOMA, P<0.05) with no differences in total cholesterol, HDL cholesterol, ApoB100 and ApoAI levels. NAFLD patients had increased production and degradation rates of both HDLc and ApoAI that resulted in their levels remaining stable. The degradation rates also were increased of other HDL proteins, including ApoAII, ApoAIV, vitamin D-binding protein, and complement 3 (all P<0.05). NAFLD patients had increased activities of LCAT and CETP, indicating altered HDL lipidation. NAFLD induced alterations in HDL metabolism were associated with reduced anti-oxidant but increased pro-inflammatory activity of HDL. However, no differences were observed in either HDL function or the kinetics of HDLc and HDL proteins between SS and NASH subjects.
Project description:Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease with increased risk in patients with metabolic syndrome. There are no FDA approved treatments, but farnesoid X receptor (FXR) agonists have shown promising results in clinical studies for NAFLD management. In addition to FXR, fibroblast growth factor receptor FGFR4 is a key mediator of hepatic bile acid synthesis. Using N-acetylgalactosamine-conjugated siRNA, we knocked down FGFR4 specifically in the liver of mice on chow or high-fat diet (HFD) and in mouse primary hepatocytes to determine the role of FGFR4 in metabolic processes and hepatic steatosis. Liver-specific FGFR4 silencing increased bile acid production and lowered serum cholesterol. Additionally, we found that HFD-induced liver steatosis and insulin resistance improved following FGFR4 knockdown. These improvements were associated with activation of the FXR-FGF15 axis in intestinal cells, but not in hepatocytes. We conclude that targeting FGFR4 in the liver to activate the intestinal FXR-FGF15 axis may be a promising strategy for the treatment of NAFLD and metabolic dysfunction.
Project description:Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease with increased risk in patients with metabolic syndrome. There are no FDA approved treatments, but farnesoid X receptor (FXR) agonists have shown promising results in clinical studies for NAFLD management. In addition to FXR, fibroblast growth factor receptor FGFR4 is a key mediator of hepatic bile acid synthesis. Using N-acetylgalactosamine-conjugated siRNA, we knocked down FGFR4 specifically in the liver of mice on chow or high-fat diet (HFD) and in mouse primary hepatocytes to determine the role of FGFR4 in metabolic processes and hepatic steatosis. Liver-specific FGFR4 silencing increased bile acid production and lowered serum cholesterol. Additionally, we found that HFD-induced liver steatosis and insulin resistance improved following FGFR4 knockdown. These improvements were associated with activation of the FXR-FGF15 axis in intestinal cells, but not in hepatocytes. We conclude that targeting FGFR4 in the liver to activate the intestinal FXR-FGF15 axis may be a promising strategy for the treatment of NAFLD and metabolic dysfunction.
Project description:The farnesoid X receptor (FXR) is a nuclear receptor activated by bile acids and regulates bile acid metabolism, glucose and cholesterol homeostasis. From mouse studies we know that the novel FXR agonist obeticholic acid (OCA) regulates expression of many genes in the liver, but there is currently no data on the effects of OCA on human liver gene expression. This is especially relevant since the novel FXR agonist OCA is currently tested in clinical trials for the treatment of several diseases, such as nonalcoholic steatohepatitis (NASH), nonalcoholic fatty liver disease (NAFLD) and Type 2 Diabetes. In this study we investigate the effect of OCA treatment on gene expression profiles and localization of FXR to the genome in relevant liver samples. ChIP-Seq for FXR in Liver tissue from 2 male mice treated with OCA/INT-747 (10mg/kg/day) and 2 male mice treated with vehicle (1% methyl cellulose).