Combined deletion of Fxr and Shp in mice induces Cyp17a1 and results in juvenile onset cholestasis

Hepatocyte nuclear receptor SHP suppresses inflammation and fibrosis in a mouse model of nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is a burgeoning health problem worldwide, ranging from nonalcoholic fatty liver (NAFL, steatosis without hepatocellular injury) to the more aggressive nonalcoholic steatohepatitis (NASH, steatosis with ballooning, inflammation, or fibrosis). Although many studies have greatly contributed to the elucidation of NAFLD pathogenesis, the disease progression from NAFL to NASH remains incompletely understood. Nuclear receptor small heterodimer partner (Nr0b2, SHP) is a transcriptional regulator critical for the regulation of bile acid, glucose, and lipid metabolism. Here, we show that SHP levels are decreased in the livers of patients with NASH and in diet-induced mouse NASH. Exposing primary mouse hepatocytes to palmitic acid and lipopolysaccharide in vitro, we demonstrated that the suppression of Shp expression in hepatocytes is due to c-Jun N-terminal kinase (JNK) activation, which stimulates c-Jun-mediated transcriptional repression of Shp Interestingly, in vivo induction of hepatocyte-specific SHP in steatotic mouse liver ameliorated NASH progression by attenuating liver inflammation and fibrosis, but not steatosis. Moreover, a key mechanism linking the anti-inflammatory role of hepatocyte-specific SHP expression to inflammation involved SHP-induced suppression of NF-κB p65-mediated induction of chemokine (C-C motif) ligand 2 (CCL2), which activates macrophage proinflammatory polarization and migration. In summary, our results indicate that a JNK/SHP/NF-κB/CCL2 regulatory network controls communications between hepatocytes and macrophages and contributes to the disease progression from NAFL to NASH. Our findings may benefit the development of new management or prevention strategies for NASH.

Effects of corilagin on alleviating cholestasis via farnesoid X receptor-associated pathways in vitro and in vivo

BACKGROUND AND PURPOSE

The aim of this study was to investigate the ameliorative effects of corilagin on intrahepatic cholestasis induced by regulating liver farnesoid X receptor (FXR)-associated pathways in vitro and in vivo.

EXPERIMENTAL APPROACH

Cellular and animal models were treated with different concentrations of corilagin. In the cellular experiments, FXR expression was up-regulated by either lentiviral transduction or GW4064 treatment and down-regulated by either siRNA technology or treatment with guggulsterones. Real-time PCR and Western blotting were employed to detect the mRNA and protein levels of FXR, SHP1, SHP2, UGT2B4, BSEP, CYP7A1, CYP7B1, NTCP, MRP2 and SULT2A1. Immunohistochemistry was used to examine the expression of BSEP in liver tissues. Rat liver function and pathological changes in hepatic tissue were assessed using biochemical tests and haematoxylin and eosin staining.

RESULTS

Corilagin increased the mRNA and protein levels of FXR, SHP1, SHP2, UGT2B4, BSEP, MRP2 and SULT2A1, and decreased those of CYP7A1, CYP7B1 and NTCP. After either up- or down-regulating FXR using different methods, corilagin could still increase the mRNA and protein levels of FXR, SHP1, SHP2, UGT2B4, BSEP, MRP2 and SULT2A1 and decrease the protein levels of CYP7A1, CYP7B1 and NTCP, especially when administered at a high concentration. Corilagin also exerted a notable effect on the pathological manifestations of intrahepatic cholestasis, BSEP staining in liver tissues and liver function.

CONCLUSIONS AND IMPLICATIONS

Corilagin exerts a protective effect in hepatocytes and can prevent the deleterious activities of intrahepatic cholestasis by stimulating FXR-associated pathways.

Small heterodimer partner deletion prevents hepatic steatosis and when combined with farnesoid X receptor loss protects against type 2 diabetes in mice

Nuclear receptors farnesoid X receptor (FXR) and small heterodimer partner (SHP) are important regulators of bile acid, lipid, and glucose homeostasis. Here, we show that global Fxr ^-/- Shp^-/- double knockout (DKO) mice are refractory to weight gain, glucose intolerance, and hepatic steatosis when challenged with high-fat diet. DKO mice display an inherently increased capacity to burn fat and suppress de novo hepatic lipid synthesis. Moreover, DKO mice were also very active and that correlated well with the observed increase in phosphoenolpyruvate carboxykinase expression, type IA fibers, and mitochondrial function in skeletal muscle. Mechanistically, we demonstrate that liver-specific Shp deletion protects against fatty liver development by suppressing expression of peroxisome proliferator-activated receptor gamma 2 and lipid-droplet protein fat-specific protein 27 beta.

CONCLUSION

These data suggest that Fxr and Shp inactivation may be beneficial to combat diet-induced obesity and uncover that hepatic SHP is necessary to promote fatty liver disease. (Hepatology 2017;66:1854-1865).

TSPYL Family Regulates CYP17A1 and CYP3A4 Expression: Potential Mechanism Contributing to Abiraterone Response in Metastatic Castration-Resistant Prostate Cancer

The testis‐specific Y‐encoded‐like protein (TSPYL) gene family includes TSPYL1 to TSPYL6. We previously reported that TSPYL5 regulates cytochrome P450 (CYP) 19A1 expression. Here we show that TSPYLs, especially TSPYL 1, 2, and 4, can regulate the expression of many CYP genes, including CYP17A1, a key enzyme in androgen biosynthesis, and CYP3A4, an enzyme that catalyzes the metabolism of abiraterone, a CYP17 inhibitor. Furthermore, a common TSPYL1 single nucleotide polymorphism (SNP), rs3828743 (G/A) (Pro62Ser), abolishes TSPYL1's ability to suppress CYP3A4 expression, resulting in reduced abiraterone concentrations and increased cell proliferation. Data from a prospective clinical trial of 87 metastatic castration‐resistant prostate cancer patients treated with abiraterone acetate/prednisone showed that the variant SNP genotype (A) was significantly associated with worse response and progression‐free survival. In summary, TSPYL genes are novel CYP gene transcription regulators, and genetic alteration within these genes significantly influences response to drug therapy through transcriptional regulation of CYP450 genes.

Dose-related liver injury of Geniposide associated with the alteration in bile acid synthesis and transportation

Fructus Gardenia (FG), containing the major active constituent Geniposide, is widely used in China for medicinal purposes. Currently, clinical reports of FG toxicity have not been published, however, animal studies have shown FG or Geniposide can cause hepatotoxicity in rats. We investigated Geniposide-induced hepatic injury in male Sprague-Dawley rats after 3-day intragastric administration of 100 mg/kg or 300 mg/kg Geniposide. Changes in hepatic histomorphology, serum liver enzyme, serum and hepatic bile acid profiles, and hepatic bile acid synthesis and transportation gene expression were measured. The 300 mg/kg Geniposide caused liver injury evidenced by pathological changes and increases in serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP) and γ-glutamytransferase (γ-GT). While liver, but not sera, total bile acids (TBAs) were increased 75% by this dose, dominated by increases in taurine-conjugated bile acids (t-CBAs). The 300 mg/kg Geniposide also down-regulated expression of Farnesoid X receptor (FXR), small heterodimer partner (SHP) and bile salt export pump (BSEP). In conclusion, 300 mg/kg Geniposide can induce liver injury with associated changes in bile acid regulating genes, leading to an accumulation of taurine conjugates in the rat liver. Taurocholic acid (TCA), taurochenodeoxycholic acid (TCDCA) as well as tauro-α-muricholic acid (T-α-MCA) are potential markers for Geniposide-induced hepatic damage.

Hepatic FXR/SHP axis modulates systemic glucose and fatty acid homeostasis in aged mice

The nuclear receptors farnesoid X receptor (FXR; NR1H4) and small heterodimer partner (SHP; NR0B2) play crucial roles in bile acid homeostasis. Global double knockout of FXR and SHP signaling (DKO) causes severe cholestasis and liver injury at early ages. Here, we report an unexpected beneficial impact on glucose and fatty acid metabolism in aged DKO mice, which show suppressed body weight gain and adiposity when maintained on normal chow. This phenotype was not observed in single Fxr or Shp knockouts. Liver-specific Fxr/Shp double knockout mice fully phenocopied the DKO mice, with lower hepatic triglyceride accumulation, improved glucose/insulin tolerance, and accelerated fatty acid use. In both DKO and liver-specific Fxr/Shp double knockout livers, these metabolic phenotypes were associated with altered expression of fatty acid metabolism and autophagy-machinery genes. Loss of the hepatic FXR/SHP axis reprogrammed white and brown adipose tissue gene expression to boost fatty acid usage.

CONCLUSION

Combined deletion of the hepatic FXR/SHP axis improves glucose/fatty acid homeostasis in aged mice, reversing the aging phenotype of body weight gain, increased adiposity, and glucose/insulin tolerance, suggesting a central role of this axis in whole-body energy homeostasis. (Hepatology 2017;66:498-509).

Sphingosine Kinases/Sphingosine 1-Phosphate Signaling in Hepatic Lipid Metabolism

The ever-increasing prevalence of metabolic diseases such as dyslipidemia and diabetes in the western world continues to be of great public health concern. Biologically active sphingolipids, such as sphingosine 1-phosphate (S1P) and ceramide, are important regulators of lipid metabolism. S1P not only directly functions as an active intracellular mediator, but also activates multiple signaling pathways via five transmembrane G-protein coupled receptors (GPCRs), S1PR1-5. S1P is exclusively formed by sphingosine kinases (SphKs). Two isoforms of SphKs, SphK1 and SphK2, have been identified. Recent identification of the conjugated bile acid-induced activation of S1PR2 as a key regulator of SphK2 opened new directions for both the sphingolipid and bile acid research fields. The role of SphKs/S1P-mediated signaling pathways in health and various human diseases has been extensively reviewed elsewhere. This review focuses on recent findings related to SphKs/S1P-medaited signaling pathways in regulating hepatic lipid metabolism.

Four Major Factors Contributing to Intrahepatic Stones

Intrahepatic stone is prevalent in Asian countries; though the incidence declines in recent years, the number of patients is still in a large quantity. Because of multiple complications, high recurrence rates, serious systemic damage, and a lack of extremely effective procedure for the management, it is more important to find out the etiology and pathogenesis of intrahepatic stones to prevent the disease from happening and developing rather than curing. A number of factors contribute to the development of the disease, such as cholestasis, infection, and anatomic abnormity of bile duct and bile metabolic defect. The four factors and possible pathogenesis will be discussed in detail in the review.

Bile acid excess induces cardiomyopathy and metabolic dysfunctions in the heart

Cardiac dysfunction in patients with liver cirrhosis is strongly associated with increased serum bile acid concentrations. Here we show that excess bile acids decrease fatty acid oxidation in cardiomyocytes and can cause heart dysfunction, a cardiac syndrome that we term cholecardia. Farnesoid X receptor; Small Heterodimer Partner double knockout mice, a model for bile acid overload, display cardiac hypertrophy, bradycardia, and exercise intolerance. In addition, double knockout mice exhibit an impaired cardiac response to catecholamine challenge. Consistent with this decreased cardiac function, we show that elevated serum bile acids reduce cardiac fatty acid oxidation both in vivo and ex vivo. We find that increased bile acid levels suppress expression of proliferator-activated receptor-γ coactivator 1α, a key regulator of fatty acid metabolism, and that proliferator-activated receptor-γ coactivator 1α overexpression in cardiac cells was able to rescue the bile acid-mediated reduction in fatty acid oxidation genes. Importantly, intestinal bile acid sequestration with cholestyramine was sufficient to reverse the observed heart dysfunction in the double knockout mice.

CONCLUSIONS

Decreased proliferator-activated receptor-γ coactivator 1α expression contributes to the metabolic dysfunction in cholecardia so that reducing serum bile acid concentrations may be beneficial against the metabolic and pathological changes in the heart. (Hepatology 2017;65:189-201).

Precise diagnosis and treatment of hepatolithiasis

Hepatolithiasis is a complex condition and the lesion is extensive. It is necessary to introduce the notion of precise surgery during the diagnosis and treatment of hepatolithiasis because the commonly used clinical methods have their limitations. A variety of technical means should be comprehensively applied to improve the levels of precise diagnosis and treatment, and individualized treatment strategy should be used. In addition, surgeons must attach great importance to the latest achievements of precise medicine, biomedical and intelligent technology.

Expression of MRP3 and MRP4 in pyloric ligation induced hepatic injury in rats

AIM: To detect the expression of drug-resistant related protein (MRP) 3 and MRP4 genes in pyloric ligation induced hepatic injury in rats.

METHODS: A rat model of pyloric ligation induced liver injury was first developed. Serum indexes were determined, and HE staining was used to observe pathological changes. Real-time quantitative PCR (qRT-PCR) was used to detect the expression of MRP3 and MRP4 in pyloric ligation induced liver injury.

RESULTS: Serum alanine transaminase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), BILD2, and SBIL3 were significantly increased in model rats compared with normal rats (P < 0.01 or P < 0.05). Macroscopically, model rats showed liver congestion and peritoneal effusion. Microscopically, obvious hepatocyte fatty change, edema, liver cell necrosis, and liver cell apoptosis were noted in model rats. The expression of MRP3 was 3.5 times higher in the model group than in the normal group, while the expression of MRP4 was 0.05 times lower in the model group than in the normal group.

CONCLUSION: Pyloric ligation induces liver injury via mechanisms possibly associated with regulating MRP3 and MRP4 expression.

Gut Microbiota and Nonalcoholic Fatty Liver Disease: Insights on Mechanism and Application of Metabolomics

Gut microbiota are intricately involved in the development of obesity-related metabolic diseases such as nonalcoholic fatty liver disease (NAFLD), type 2 diabetes, and insulin resistance. In the current review, we discuss the role of gut microbiota in the development of NAFLD by focusing on the mechanisms of gut microbiota-mediated host energy metabolism, insulin resistance, regulation of bile acids and choline metabolism, as well as gut microbiota-targeted therapy. We also discuss the application of a metabolomic approach to characterize gut microbial metabotypes in NAFLD.

Fibroblast Growth Factor Signaling Controls Liver Size in Mice With Humanized Livers

BACKGROUND & AIMS

The ratio of liver size to body weight (hepatostat) is tightly controlled, but little is known about how the physiologic functions of the liver help determine its size. Livers of mice repopulated with human hepatocytes (humanized livers) grow to larger than normal; the human hepatocytes do not recognize the fibroblast growth factor (FGF)-15 produced by mouse intestine. This results in up-regulation of bile acid synthesis in the human hepatocytes and enlargement of the bile acid pool. We investigated whether abnormal bile acid signaling affects the hepatostat in mice.

METHODS

We crossed Fah(-/-), Rag2(-/-), Il2r(-/-) mice with nonobese diabetic mice to create FRGN mice, whose livers can be fully repopulated with human hepatocytes. We inserted the gene for human FGF19 (ortholog to mouse Fgf15), including regulatory sequences, into the FRGN mice to create FRGN19(+) mice. Livers of FRGN19(+) mice and their FRGN littermates were fully repopulated with human hepatocytes. Liver tissues were collected and bile acid pool sizes and RNA sequences were analyzed and compared with those of mice without humanized livers (controls).

RESULTS

Livers were larger in FRGN mice with humanized livers (13% of body weight), compared with control FRGN mice; they also had much larger bile acid pools and aberrant bile acid signaling. Livers from FRGN19(+) normalized to 7.8% of body weight, and their bile acid pool and signaling more closely resembled that of control FRGN19(+) mice. RNA sequence analysis showed activation of the Hippo pathway, and immunohistochemical and transcription analyses revealed increased hepatocyte proliferation, but not apoptosis, in the enlarged humanized livers of FRGN mice. Cell sorting experiments showed that although healthy human liver does not produce FGF19, nonparenchymal cells from cholestatic livers produce FGF19.

CONCLUSIONS

In mice with humanized livers, expression of an FGF19 transgene corrects bile acid signaling defects, resulting in normalization of bile acid synthesis, the bile acid pool, and liver size. These findings indicate that liver size is, in part, regulated by the size of the bile acid pool that the liver must circulate.

Farnesoid X receptor-induced lysine-specific histone demethylase reduces hepatic bile acid levels and protects the liver against bile acid toxicity

Bile acids (BAs) function as endocrine signaling molecules that activate multiple nuclear and membrane receptor signaling pathways to control fed-state metabolism. Since the detergent-like property of BAs causes liver damage at high concentrations, hepatic BA levels must be tightly regulated. Bile acid homeostasis is regulated largely at the level of transcription by nuclear receptors, particularly the primary BA receptor, farnesoid X receptor, and small heterodimer partner, which inhibits BA synthesis by recruiting repressive histone-modifying enzymes. Although histone modifiers have been shown to regulate BA-responsive genes, their in vivo functions remain unclear. Here, we show that lysine-specific histone demethylase1 (LSD1) is directly induced by BA-activated farnesoid X receptor, is recruited to the BA synthetic genes Cyp7a1 and Cyp8b1 and the BA uptake transporter gene Ntcp, and removes a gene-activation marker, trimethylated histone H3 lysine-4, leading to gene repression. Recruitment of LSD1 was dependent on small heterodimer partner, and LSD1-mediated demethylation of trimethylated histone H3 lysine-4 was required for additional repressive histone modifications, acetylated histone 3 on lysine 9 and 14 deacetylation, and acetylated histone 3 on lysine 9 methylation. A BA overload, feeding 0.5% cholic acid chow for 6 days, resulted in adaptive responses of altered expression of hepatic genes involved in BA synthesis, transport, and detoxification/conjugation. In contrast, adenovirus-mediated downregulation of hepatic LSD1 blunted these responses, which led to substantial increases in liver and serum BA levels, serum alanine aminotransferase and aspartate aminotransferase levels, and hepatic inflammation.

CONCLUSION

This study identifies LSD1 as a novel histone-modifying enzyme in the orchestrated regulation mediated by the farnesoid X receptor and small heterodimer partner that reduces hepatic BA levels and protects the liver against BA toxicity.

Bile Acid Metabolism and Signaling in Cholestasis, Inflammation, and Cancer

Bile acids are synthesized from cholesterol in the liver. Some cytochrome P450 (CYP) enzymes play key roles in bile acid synthesis. Bile acids are physiological detergent molecules, so are highly cytotoxic. They undergo enterohepatic circulation and play important roles in generating bile flow and facilitating biliary secretion of endogenous metabolites and xenobiotics and intestinal absorption of dietary fats and lipid-soluble vitamins. Bile acid synthesis, transport, and pool size are therefore tightly regulated under physiological conditions. In cholestasis, impaired bile flow leads to accumulation of bile acids in the liver, causing hepatocyte and biliary injury and inflammation. Chronic cholestasis is associated with fibrosis, cirrhosis, and eventually liver failure. Chronic cholestasis also increases the risk of developing hepatocellular or cholangiocellular carcinomas. Extensive research in the last two decades has shown that bile acids act as signaling molecules that regulate various cellular processes. The bile acid-activated nuclear receptors are ligand-activated transcriptional factors that play critical roles in the regulation of bile acid, drug, and xenobiotic metabolism. In cholestasis, these bile acid-activated receptors regulate a network of genes involved in bile acid synthesis, conjugation, transport, and metabolism to alleviate bile acid-induced inflammation and injury. Additionally, bile acids are known to regulate cell growth and proliferation, and altered bile acid levels in diseased conditions have been implicated in liver injury/regeneration and tumorigenesis. We will cover the mechanisms that regulate bile acid homeostasis and detoxification during cholestasis, and the roles of bile acids in the initiation and regulation of hepatic inflammation, regeneration, and carcinogenesis.

Bile acid promotes liver regeneration via farnesoid X receptor signaling pathways in rats

Bile acids, which are synthesized from cholesterol in the hepatocytes of the liver, are amphipathic molecules with a steroid backbone. Studies have shown that bile acid exhibits important effects on liver regeneration. However, the mechanism underlying these effects remains unclear. The aim of the present study was to investigate the effect of bile acid and the farnesoid X receptor (FXR) on hepatic regeneration and lipid metabolism. Rats were fed with 0.2% bile acid or glucose for 7 days and then subjected to a 50 or 70% hepatectomy. Hepatic regeneration rate, serum and liver levels of bile acid, and expression of FXR and Caveolin‑1, were detected at 24, 48 or 72 h following hepatectomy. The expression of proliferating cell nuclear antigen (PCNA) in the liver was measured using immunohistochemistry at the end of the study. Hepatocytes isolated from rats were treated with bile acid, glucose, FXR agonist and FXR antagonist, separately or in combination. Lipid metabolism, the expression of members of the FXR signaling pathway and energy metabolism‑related factors were measured using ELISA kits or western blotting. Bile acid significantly increased the hepatic regeneration rate and the expression of FXR, Caveolin‑1 and PCNA. Levels of total cholesterol and high density lipoprotein were increased in bile acid‑ or FXR agonist‑treated hepatocytes in vitro. Levels of triglyceride, low density lipoprotein and free fatty acid were decreased. In addition, bile acid and FXR agonists increased the expression of bile salt export pump and small heterodimer partner, and downregulated the expression of apical sodium‑dependent bile acid transporter, Na+/taurocholate cotransporting polypeptide and cholesterol 7α‑hydroxylase. These results suggested that physiological concentrations of bile acid may promote liver regeneration via FXR signaling pathways, and may be associated with energy metabolism.

Bridging cell surface receptor with nuclear receptors in control of bile acid homeostasis

Bile acids (BAs) are traditionally considered as "physiological detergents" for emulsifying hydrophobic lipids and vitamins due to their amphipathic nature. But accumulating clinical and experimental evidence shows an association between disrupted BA homeostasis and various liver disease conditions including hepatitis infection, diabetes and cancer. Consequently, BA homeostasis regulation has become a field of heavy interest and investigation. After identification of the Farnesoid X Receptor (FXR) as an endogenous receptor for BAs, several nuclear receptors (SHP, HNF4α, and LRH-1) were also found to be important in regulation of BA homeostasis. Some post-translational modifications of these nuclear receptors have been demonstrated, but their physiological significance is still elusive. Gut secrets FGF15/19 that can activate hepatic FGFR4 and its downstream signaling cascade, leading to repressed hepatic BA biosynthesis. However, the link between the activated kinases and these nuclear receptors is not fully elucidated. Here, we review the recent literature on signal crosstalk in BA homeostasis.

The Hippo signaling pathway in liver regeneration and tumorigenesis

The Hippo signaling pathway is an evolutionarily conserved signaling module that plays critical roles in liver size control and tumorigenesis. The Hippo pathway consists of a core kinase cascade in which the mammalian Ste20-like kinases (Mst1/2, orthologs of Drosophila Hippo) and their cofactor Salvador (Sav1) form a complex to phosphorylate and activate the large tumor suppressor (Lats1/2). Lats1/2 kinases in turn phosphorylate and inhibit the transcription co-activators, the Yes-associated protein (YAP) and the transcriptional co-activator with PDZ-binding motif (TAZ), two major downstream effectors of the Hippo pathway. Losses of the Hippo pathway components induce aberrant hepatomegaly and tumorigenesis, in which YAP coordinates regulation of cell proliferation and apoptosis and plays an essential role. This review summarizes the current findings of the regulation of Hippo signaling in liver regeneration and tumorigenesis, focusing on how the loss of tumor suppressor components of the Hippo pathway results in liver cancers and discussing the molecular mechanisms that regulate the expression and activation of its downstream effector YAP in liver tumorigenesis.

FXR and liver carcinogenesis

Farnesoid X receptor (FXR) is a member of the nuclear receptor family and a ligand-modulated transcription factor. In the liver, FXR has been considered a multi-functional cell protector and a tumor suppressor. FXR can suppress liver carcinogenesis via different mechanisms: 1) FXR maintains the normal liver metabolism of bile acids, glucose and lipids; 2) FXR promotes liver regeneration and repair after injury; 3) FXR protects liver cells from death and enhances cell survival; 4) FXR suppresses hepatic inflammation, thereby preventing inflammatory damage; and 5) FXR can directly increase the expression of some tumor-suppressor genes and repress the transcription of several oncogenes. However, inflammation and epigenetic silencing are known to decrease FXR expression during tumorigenesis. The reactivation of FXR function in the liver may be a potential therapeutic approach for patients with liver cancer.

Hepatic expression of detoxification enzymes is decreased in human obstructive cholestasis due to gallstone biliary obstruction

BACKGROUND & AIMS

Levels of bile acid metabolic enzymes and membrane transporters have been reported to change in cholestasis. These alterations (e.g. CYP7A1 repression and MRP4 induction) are thought to be adaptive responses that attenuate cholestatic liver injury. However, the molecular mechanisms of these adaptive responses in human obstructive cholestasis due to gallstone biliary obstruction remain unclear.

METHODS

We collected liver samples from cholestatic patients with biliary obstruction due to gallstones and from control patients without liver disease (n = 22 per group). The expression levels of bile acid synthetic and detoxification enzymes, membrane transporters, and the related nuclear receptors and transcriptional factors were measured.

RESULTS

The levels of bile acid synthetic enzymes, CYP7B1 and CYP8B1, and the detoxification enzyme CYP2B6 were increased in cholestatic livers by 2.4-fold, 2.8-fold, and 1.9-fold, respectively (p<0.05). Conversely, the expression levels of liver detoxification enzymes, UGT2B4/7, SULT2A1, GSTA1-4, and GSTM1-4, were reduced by approximately 50% (p<0.05) in human obstructive cholestasis. The levels of membrane transporters, OSTβ and OCT1, were increased 10.4-fold and 1.8-fold, respectively, (p<0.05), whereas those of OSTα, ABCG2 and ABCG8 were all decreased by approximately 40%, (p<0.05) in human cholestatic livers. Hepatic nuclear receptors, VDR, HNF4α, RXRα and RARα, were induced (approximately 2.0-fold, (p<0.05) whereas FXR levels were markedly reduced to 44% of control, (p<0.05) in human obstructive cholestasis. There was a significantly positive correlation between the reduction in FXR mRNA and UGT2B4/7, SULT2A1, GSTA1, ABCG2/8 mRNA levels in livers of obstructive cholestatic patients (p<0.05).

CONCLUSIONS

The levels of hepatic detoxification enzymes were significantly decreased in human obstructive cholestasis, and these decreases were positively associated with a marked reduction of FXR levels. These findings are consistent with impaired detoxification ability in human obstructive cholestasis.

Hepatic farnesoid X-receptor isoforms α2 and α4 differentially modulate bile salt and lipoprotein metabolism in mice

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.

Intestinal farnesoid X receptor signaling promotes nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a major worldwide health problem. Recent studies suggest that the gut microbiota influences NAFLD pathogenesis. Here, a murine model of high-fat diet-induced (HFD-induced) NAFLD was used, and the effects of alterations in the gut microbiota on NAFLD were determined. Mice treated with antibiotics or tempol exhibited altered bile acid composition, with a notable increase in conjugated bile acid metabolites that inhibited intestinal farnesoid X receptor (FXR) signaling. Compared with control mice, animals with intestine-specific Fxr disruption had reduced hepatic triglyceride accumulation in response to a HFD. The decrease in hepatic triglyceride accumulation was mainly due to fewer circulating ceramides, which was in part the result of lower expression of ceramide synthesis genes. The reduction of ceramide levels in the ileum and serum in tempol- or antibiotic-treated mice fed a HFD resulted in downregulation of hepatic SREBP1C and decreased de novo lipogenesis. Administration of C16:0 ceramide to antibiotic-treated mice fed a HFD reversed hepatic steatosis. These studies demonstrate that inhibition of an intestinal FXR/ceramide axis mediates gut microbiota-associated NAFLD development, linking the microbiome, nuclear receptor signaling, and NAFLD. This work suggests that inhibition of intestinal FXR is a potential therapeutic target for NAFLD treatment.

Cysteine sulfinic acid decarboxylase regulation: A role for farnesoid X receptor and small heterodimer partner in murine hepatic taurine metabolism

AIM

Bile acid synthesis is regulated by nuclear receptors including farnesoid X receptor (FXR) and small heterodimer partner (SHP), and by fibroblast growth factor 15/19 (FGF15/19). We hypothesized that hepatic cysteine sulfinic acid decarboxylase (CSAD) (a key enzyme in taurine synthesis) is regulated by bile acids (BA). The aim of this study was to investigate CSAD regulation by BA dependent regulatory mechanisms.

METHODS

Mice were fed a control diet or a diet supplemented with either 0.5% cholate or 2% cholestyramine. To study BA dependent pathways, we utilized GW4064 (FXR agonist), FGF19 or T-0901317 (liver X receptor [LXR] agonist) and Shp-/- mice. Tissue mRNA was determined by quantitative reverse transcription polymerase chain reaction. Amino acids were measured by high-performance liquid chromatography.

RESULTS

Mice supplemented with dietary cholate exhibited reduced hepatic CSAD mRNA while those receiving cholestyramine exhibited increased mRNA. Activation of FXR suppressed CSAD mRNA expression whereas CSAD expression was increased in Shp-/- mice. Hepatic hypotaurine concentration (the product of CSAD) was higher in Shp-/- mice with a corresponding increase in serum taurine conjugated BA. FGF19 administration suppressed hepatic cholesterol 7-α-hydroxylase (CYP7A1) mRNA but did not change CSAD mRNA expression. LXR activation induced CYP7A1 mRNA yet failed to induce CSAD mRNA expression.

CONCLUSION

BA regulate CSAD mRNA expression in a feedback fashion via mechanisms involving SHP and FXR but not FGF15/19 or LXR. These findings implicate BA as regulators of CSAD mRNA via mechanisms shared with CYP7A1.

Cytoplasmic tyrosine phosphatase Shp2 coordinates hepatic regulation of bile acid and FGF15/19 signaling to repress bile acid synthesis

Bile acid (BA) biosynthesis is tightly controlled by intrahepatic negative feedback signaling elicited by BA binding to farnesoid X receptor (FXR) and also by enterohepatic communication involving ileal BA reabsorption and FGF15/19 secretion. However, how these pathways are coordinated is poorly understood. We show here that nonreceptor tyrosine phosphatase Shp2 is a critical player that couples and regulates the intrahepatic and enterohepatic signals for repression of BA synthesis. Ablating Shp2 in hepatocytes suppressed signal relay from FGFR4, receptor for FGF15/19, and attenuated BA activation of FXR signaling, resulting in elevation of systemic BA levels and chronic hepatobiliary disorders in mice. Acting immediately downstream of FGFR4, Shp2 associates with FRS2α and promotes the receptor activation and signal relay to several pathways. These results elucidate a molecular mechanism for the control of BA homeostasis by Shp2 through the orchestration of multiple signals in hepatocytes.

Gene expression profile in chronic mouse liver injury caused by long-term exposure to CeCl3

Numerous studies have demonstrated lanthanide (Ln) accumulation in the liver, and the corresponding damage; however, very little work has been done to evaluate the relationship between Ln-induced liver injury and its gene expression profile in mice. In this study, liver injury and gene-expressed profiles in male mice induced by oral administration of CeCl3 (2 mg/kg) via gavage for 90 consecutive days were investigated. The results showed that cerium accumulation, liver inflammation, and hepatocyte necrosis were observed. CeCl3 exposure significantly decreased the counts of white blood cells, lymphocyte, and platelet, the reticulocyte count (Ret) and neutrophilic granulocyte percentages as well as A/G ratio, whereas markedly increased the activities of alkaline phosphatase, lactate dehydrogenase, and cholinesterase, and the concentrations of triglycerides and total cholesterol. Furthermore, microarray results of liver showed that the differential expression of 675 known function genes involved in immune/inflammation response, apoptosis, metabolic process, cell cycle, cell proliferation, cytoskeleton, oxidative stress, signal transduction, transcription, translation, and transportation in CeCl3 exposed livers, respectively. Specifically, the significant downregulation of Nt5e led to inflammation, overexpressed Cyp4a12a and great suppression of Cdkn1a resulted in hepatocyte apoptosis, marked elevation of Cel, and Cyp7b1 expression caused the metabolic disorders in mouse liver after long-term CeCl3 exposure. Therefore, these genes may be in great relation to liver damages induced by exposure to CeCl3 .

Regulation of bile acid homeostasis by the intestinal Diet1-FGF15/19 axis

PURPOSE OF REVIEW

Hepatic bile acid synthesis is controlled, in part, by a complex enterohepatic feedback regulatory mechanism. In this review, we focus on the role of the intestinal FGF15/19 hormone in modulating bile acid levels, and additional metabolic effects on glucose metabolism, nonalcoholic liver disease (NAFLD), and liver regeneration. We also highlight the newly identified intestinal protein, Diet1, which is a modulator of FGF15/19 levels.

RECENT FINDINGS

Low FGF19 levels are associated with bile acid diarrhea and NAFLD. In contrast, high FGF19 levels are associated with diabetes remission following Roux-en-Y gastric bypass surgery, suggesting new therapeutic approaches against type 2 diabetes. The effect of FGF15/19 on liver plasticity is a double-edged sword: whereas elevated FGF15/19 levels improve survival of mice after partial hepatectomy, FGF19 mitogenic activity is associated with liver carcinoma. Finally, a recent study has identified Diet1, an intestinal factor that influences FGF15/19 levels in mouse intestine and human enterocytes. Diet1 represents the first factor shown to influence FGF15/19 levels at a post-transcriptional level.

SUMMARY

The biological effects of FGF15/19 make it an attractive target for treating metabolic dysregulation underlying conditions such as fatty liver and type 2 diabetes. Further elucidation of the role of Diet1 in FGF15/19 secretion may provide a control point for the pharmacological modulation of FGF15/19 levels.

Bile acids activate YAP to promote liver carcinogenesis

Elevated bile acid levels increase hepatocellular carcinoma by unknown mechanisms. Here, we show that mice with a severe defect in bile acid homeostasis due to the loss of the nuclear receptors FXR and SHP have enlarged livers, progenitor cell proliferation, and Yes-associated protein (YAP) activation and develop spontaneous liver tumorigenesis. This phenotype mirrors mice with loss of hippo kinases or overexpression of their downstream target, YAP. Bile acids act as upstream regulators of YAP via a pathway dependent on the induction of the scaffold protein IQGAP1. Patients with diverse biliary dysfunctions exhibit enhanced IQGAP1 and nuclear YAP expression. Our findings reveal an unexpected mechanism for bile acid regulation of liver growth and tumorigenesis via the Hippo pathway.

Nuclear receptor control of enterohepatic circulation

Enterohepatic circulation is responsible for the capture of bile acids and other steroids produced or metabolized in the liver and secreted to the intestine, for reabsorption back into the circulation and transport back to the liver. Bile acids are secreted from the liver in the form of mixed micelles that also contain phosphatidylcholines and cholesterol that facilitate the uptake of fats and vitamins from the diet due to the surfactant properties of bile acids and lipids. Bile acids are synthesized in the liver from cholesterol by a cascade of enzymes that carry out oxidation and conjugation reactions, and transported to the bile duct and gall bladder where they are stored before being released into the intestine. Bile flow from the gall bladder to the small intestine is triggered by food intake in accordance with its role in lipid and vitamin absorption from the diet. Bile acids are further metabolized by gut bacteria and are transported back to the circulation. Metabolites produced in the liver are termed primary bile acids or primary conjugated bile salts, while the metabolites generated by bacterial are called secondary bile acids. About 95% of bile acids are reabsorbed in the proximal and distal ileum into the hepatic portal vein and then into the liver sinusoids, where they are efficiently transported into the liver with little remaining in circulation. Each bile acid is reabsorbed about 20 times on average before being eliminated. Enterohepatic circulation is under tight regulation by nuclear receptor signaling, notably by the farnesoid X receptor (FXR).

Bile acid signal-induced phosphorylation of small heterodimer partner by protein kinase Cζ is critical for epigenomic regulation of liver metabolic genes

Bile acids (BAs) are recently recognized key signaling molecules that control integrative metabolism and energy expenditure. BAs activate multiple signaling pathways, including those of nuclear receptors, primarily farnesoid X receptor (FXR), membrane BA receptors, and FXR-induced FGF19 to regulate the fed-state metabolism. Small heterodimer partner (SHP) has been implicated as a key mediator of these BA signaling pathways by recruitment of chromatin modifying proteins, but the key question of how SHP transduces BA signaling into repressive histone modifications at liver metabolic genes remains unknown. Here we show that protein kinase Cζ (PKCζ) is activated by BA or FGF19 and phosphorylates SHP at Thr-55 and that Thr-55 phosphorylation is critical for the epigenomic coordinator functions of SHP. PKCζ is coimmunopreciptitated with SHP and both are recruited to SHP target genes after bile acid or FGF19 treatment. Activated phosphorylated PKCζ and phosphorylated SHP are predominantly located in the nucleus after FGF19 treatment. Phosphorylation at Thr-55 is required for subsequent methylation at Arg-57, a naturally occurring mutation site in metabolic syndrome patients. Thr-55 phosphorylation increases interaction of SHP with chromatin modifiers and their occupancy at selective BA-responsive genes. This molecular cascade leads to repressive modifications of histones at metabolic target genes, and consequently, decreased BA pools and hepatic triglyceride levels. Remarkably, mutation of Thr-55 attenuates these SHP-mediated epigenomic and metabolic effects. This study identifies PKCζ as a novel key upstream regulator of BA-regulated SHP function, revealing the role of Thr-55 phosphorylation in epigenomic regulation of liver metabolism.

Comparative proteomics study on liver mitochondria of primary biliary cirrhosis mouse model

Background

Primary biliary cirrhosis (PBC) is a liver specific chronic disease with unclear pathogenesis, especially for the early stage molecular events. The mitochondrion is a multi-functional organelle associated with various diseases including PBC. The purpose of this study was to discover the alterations in the mitochondria proteome using an early stage PBC mouse model for revealing the possible pathogenesis mechanisms in the early stages of PBC.

Methods

Mouse model of early stage of PBC was constructed by consecutive administration of poly I:C. Mitochondria of mouse models and controls were purified and comparative proteomics was performed by iTRAQ technology. Then, differentially expressed proteins were validated by western blotting.

Results

In total 354 proteins that satisfied the criteria for comparative proteomics study were identified. Of them, nine proteins were downregulated and 20 were up-regulated in liver mitochondria of PBC mouse model. Most differentially expressed proteins are associated with oxidation-reduction and lipid metabolism, and some are involved in the biosynthesis of steroid hormone and primary bile acid. Interestingly, four proteins (HCDH, CPT I, DECR, ECHDC2) involved in the fatty acid beta-oxidation were all upregulated.

Conclusions

iTRAQ is a powerful tool for comparative proteomics study of PBC mouse model and differentially expressed proteins in mitochondria proteome of PBC mouse model provide insights for the pathogenesis mechanism at early stage of PBC.

FXR signaling in the enterohepatic system

Enterohepatic circulation serves to capture bile acids and other steroid metabolites produced in the liver and secreted to the intestine, for reabsorption back into the circulation and reuptake to the liver. This process is under tight regulation by nuclear receptor signaling. Bile acids, produced from cholesterol, can alter gene expression in the liver and small intestine via activating the nuclear receptors farnesoid X receptor (FXR; NR1H4), pregnane X receptor (PXR; NR1I2), vitamin D receptor (VDR; NR1I1), G protein coupled receptor TGR5, and other cell signaling pathways (JNK1/2, AKT and ERK1/2). Among these controls, FXR is known to be a major bile acid-responsive ligand-activated transcription factor and a crucial control element for maintaining bile acid homeostasis. FXR has a high affinity for several major endogenous bile acids, notably cholic acid, deoxycholic acid, chenodeoxycholic acid, and lithocholic acid. By responding to excess bile acids, FXR is a bridge between the liver and small intestine to control bile acid levels and regulate bile acid synthesis and enterohepatic flow. FXR is highly expressed in the liver and gut, relative to other tissues, and contributes to the maintenance of cholesterol/bile acid homeostasis by regulating a variety of metabolic enzymes and transporters. FXR activation also affects lipid and glucose metabolism, and can influence drug metabolism.

Farnesoid X receptor inhibits gankyrin in mouse livers and prevents development of liver cancer

One of the early events in the development of liver cancer is a neutralization of tumor suppressor proteins Rb, p53, hepatocyte nuclear factor 4α (HNF4α), and CCAAT/enhancer binding protein (C/EBP) α. The elimination of these proteins is mediated by a small subunit of proteasome, gankyrin, which is activated by cancer. The aim of this study was to determine the mechanisms that repress gankyrin in quiescent livers and mechanisms of activation of gankyrin in liver cancer. We found that farnesoid X receptor (FXR) inhibits expression of gankyrin in quiescent livers by silencing the gankyrin promoter through HDAC1-C/EBPβ complexes. C/EBPβ is a key transcription factor that delivers HDAC1 to gankyrin promoter and causes epigenetic silencing of the promoter. We show that down-regulation of C/EBPβ in mouse hepatoma cells and in mouse livers reduces C/EBPβ-HDAC1 complexes and activates the gankyrin promoter. Deletion of FXR signaling in mice leads to de-repression of the gankyrin promoter and to spontaneous development of liver cancer at 12 months of age. Diethylnitrosoamine (DEN)-mediated liver cancer in wild-type mice also involves the reduction of FXR and activation of gankyrin. Examination of liver cancer in old mice and liver cancer in human patients revealed that FXR is reduced, while gankyrin is elevated during spontaneous development of liver cancer. Searching for animal models with altered levels of FXR, we found that long-lived Little mice have high levels of FXR and do not develop liver cancer with age and after DEN injections due to failure to activate gankyrin and eliminate Rb, p53, HNF4α and C/EBPα proteins.

CONCLUSION

FXR prevents liver cancer by inhibiting the gankyrin promoter via C/EBPβ-HDAC1 complexes, leading to subsequent protection of tumor suppressor proteins from degradation.

Glucocorticoids promote hepatic cholestasis in mice by inhibiting the transcriptional activity of the farnesoid X receptor

BACKGROUND & AIMS

Glucocorticoids have potent anti-inflammatory effects, but also can cause insulin resistance, osteoporosis, and muscle wasting, preventing their long-term use. Glucocorticoids also have been associated with the development of hepatic cholestasis and gallstone disease, but little is known about their pathogenic mechanisms.

METHODS

We analyzed levels of bile acids (BAs) and glucocorticoids in serum samples from patients with Cushing disease and obese individuals (body mass index, >30). C57BL/6 mice were injected with dexamethasone and db/db obese mice were injected with glucocorticoid receptor (GR) antagonists or small hairpin RNAs. We analyzed farnesoid X receptor (FXR) signaling in HepG2 cells and cells from mice using immunoprecipitation, luciferase reporter, and glutathione-s-transferase and chromatin immunoprecipitation assays. We analyzed BA metabolism in FXR-/- mice and mice with reduced levels of the transcription factor C-terminal binding protein (CtBP).

RESULTS

Serum levels of BAs were higher in patients with Cushing disease or obesity than in individuals with normal levels of glucocorticoids. Administration of dexamethasone promoted cholestasis and overproduction of BAs in C57BL/6 mice, but not in FXR-/- mice. GR antagonists, or injection of an adenoviral small hairpin RNA against GR, reduced features of hepatic cholestasis in db/db mice. The GR interacted with FXR to reduce its transcriptional activity by recruiting CtBP co-repressor complexes. Mice with reduced levels of CtBP were resistant to induction of hepatic cholestasis by dexamethasone.

CONCLUSIONS

Glucocorticoids promote hepatic cholestasis in mice by recruiting CtBP co-repressor complexes to FXR and thereby blocking the transcriptional activity.

Specific bile acids inhibit hepatic fatty acid uptake in mice

Bile acids are known to play important roles as detergents in the absorption of hydrophobic nutrients and as signaling molecules in the regulation of metabolism. We tested the novel hypothesis that naturally occurring bile acids interfere with protein-mediated hepatic long chain free fatty acid (LCFA) uptake. To this end, stable cell lines expressing fatty acid transporters as well as primary hepatocytes from mouse and human livers were incubated with primary and secondary bile acids to determine their effects on LCFA uptake rates. We identified ursodeoxycholic acid (UDCA) and deoxycholic acid (DCA) as the two most potent inhibitors of the liver-specific fatty acid transport protein 5 (FATP5). Both UDCA and DCA were able to inhibit LCFA uptake by primary hepatocytes in a FATP5-dependent manner. Subsequently, mice were treated with these secondary bile acids in vivo to assess their ability to inhibit diet-induced hepatic triglyceride accumulation. Administration of DCA in vivo via injection or as part of a high-fat diet significantly inhibited hepatic fatty acid uptake and reduced liver triglycerides by more than 50%.

CONCLUSION

The data demonstrate a novel role for specific bile acids, and the secondary bile acid DCA in particular, in the regulation of hepatic LCFA uptake. The results illuminate a previously unappreciated means by which specific bile acids, such as UDCA and DCA, can impact hepatic triglyceride metabolism and may lead to novel approaches to combat obesity-associated fatty liver disease.

Progress in understanding the role of FXR in promoting liver regeneration

The regenerative capacity of the liver is well known, and it can regenerate itself by a compensatory regrowth in response to partial hepatectomy or injury. Farnesoid X receptor (FXR) is a member of the nuclear hormone receptor superfamily of ligand-activated transcription factors. Bile acids are FXR physiological ligands. As a metabolic regulator, FXR plays key roles in regulating metabolism of bile acids, lipids and glucose. Recently, activation of intercellular signal transduction has been shown to play an important role in liver regeneration by binding of bile acids to their receptor FXR. Bile acid/FXR signaling pathway is required for normal liver regeneration. Furthermore, FXR promotes liver repair after injury, and activation of FXR is able to alleviate age-related defective liver regeneration. These novel findings suggest that FXR-mediated bile acid signaling is an important component of normal liver regeneration and highlight the potential use of FXR ligands to promote liver regeneration after segmental liver transplantation or resection of liver tumors. This review summarizes the recent progress in understanding the role of FXR in promoting liver regeneration.

Genomic analysis of hepatic farnesoid X receptor binding sites reveals altered binding in obesity and direct gene repression by farnesoid X receptor in mice

The nuclear bile acid receptor, farnesoid X receptor (FXR), is an important transcriptional regulator of liver metabolism. Despite recent advances in understanding its functions, how FXR regulates genomic targets and whether the transcriptional regulation by FXR is altered in obesity remain largely unknown. Here, we analyzed hepatic genome-wide binding sites of FXR in healthy and dietary obese mice by chromatin immunoprecipitation sequencing (ChIP-seq) analysis. A total of 15,263 and 5,272 FXR binding sites were identified in livers of healthy and obese mice, respectively, after a short 1-hour treatment with the synthetic FXR agonist, GW4064. Of these sites, 7,440 and 2,344 were detected uniquely in healthy and obese mice. FXR-binding sites were localized mostly in intergenic and intron regions at an inverted repeat 1 motif in both groups, but also clustered within 1 kilobase of transcription start sites. FXR-binding sites were detected near previously unknown target genes with novel functions, including diverse cellular signaling pathways, apoptosis, autophagy, hypoxia, inflammation, RNA processing, metabolism of amino acids, and transcriptional regulators. Further analyses of randomly selected genes from both healthy and obese mice suggested that more FXR-binding sites are likely functionally inactive in obesity. Surprisingly, occupancies of FXR, retinoid X receptor alpha, RNA polymerase II, and epigenetic gene activation and repression histone marks, and messenger RNA levels of genes examined, suggested that direct gene repression by agonist-activated FXR is common.

CONCLUSION

Comparison of genomic FXR-binding sites in healthy and obese mice suggested that FXR transcriptional signaling is altered in dietary obese mice, which may underlie aberrant metabolism and liver function in obesity.

Dissecting modes of action of non-genotoxic carcinogens in primary mouse hepatocytes

Under REACH, the European Community Regulation on chemicals, the testing strategy for carcinogenicity is based on in vitro and in vivo genotoxicity assays. Given that non-genotoxic carcinogens are negative for genotoxicity and chronic bioassays are no longer regularly performed, this class of carcinogens will go undetected. Therefore, test systems detecting non-genotoxic carcinogens, or even better their modes of action, are required. Here, we investigated whether gene expression profiling in primary hepatocytes can be used to distinguish different modes of action of non-genotoxic carcinogens. For this, primary mouse hepatocytes were exposed to 16 non-genotoxic carcinogens with diverse modes of action. Upon profiling, pathway analysis was performed to obtain insight into the biological relevance of the observed changes in gene expression. Subsequently, both a supervised and an unsupervised comparison approach were applied to recognize the modes of action at the transcriptomic level. These analyses resulted in the detection of three of eight compound classes, that is, peroxisome proliferators, metalloids and skin tumor promotors. In conclusion, gene expression profiles in primary hepatocytes, at least in rodent hepatocytes, appear to be useful to detect some, certainly not all, modes of action of non-genotoxic carcinogens.

Hepatocarcinogenesis in FXR-/- mice mimics human HCC progression that operates through HNF1α regulation of FXR expression

Farnesoid X receptor (FXR) (nuclear receptor subfamily 1, group H, member 4) is a member of nuclear hormone receptor superfamily, which plays essential roles in metabolism of bile acids, lipid, and glucose. We previously showed spontaneously hepatocarcinogenesis in aged FXR(-/-) mice, but its relevance to human hepatocellular carcinoma (HCC) is unclear. Here, we report a systematical analysis of hepatocarcinogenesis in FXR(-/-) mice and FXR expression in human liver cancer. In this study, liver tissues obtained from FXR(-/-) and wild-type mice at different ages were compared by microarray gene profiling, histological staining, chemical analysis, and quantitative real-time PCR. Primary hepatic stellate cells and primary hepatocytes isolated from FXR(-/-) and wild-type mice were also analyzed and compared. The results showed that the altered genes in FXR(-/-) livers were mainly related to metabolism, inflammation, and fibrosis, which suggest that hepatocarcinogenesis in FXR(-/-) mice recapitulated the progression of human liver cancer. Indeed, FXR expression in human HCC was down-regulated compared with normal liver tissues. Furthermore, the proinflammatory cytokines, which were up-regulated in human HCC microenvironment, decreased FXR expression by inhibiting the transactivity of hepatic nuclear factor 1α on FXR gene promoter. Our study thereby demonstrates that the down-regulation of FXR has an important role in human hepatocarcinogenesis and FXR(-/-) mice provide a unique animal model for HCC study.

Farnesoid x receptor agonists: what they are and how they might be used in treating liver disease

The farnesoid X receptor (FXR) is a nuclear receptor expressed in the liver, small intestine, kidneys, and adrenals. In mouse liver, FXR is bound to thousands of genomic DNA binding sites. Conformational changes induced by bile acid binding to pre-bound FXR leads to increased expression of a variety of genes. These changes lead to decreased intracellular bile acid concentrations through multiple mechanisms including decreased bile acid synthesis from cholesterol, decreased hepatocellular uptake and increased secretion into bile. Activated FXR also modulates the expression of genes responsible for lipid and glucose metabolism. One of the other genes induced by activated FXR is a small heterodimeric partner (SHP), a protein that represses expression of specific genes. The effects of pharmacologically modulating FXR activation in humans is only beginning to be explored with the hopes of favorably altering lipid and glucose metabolism to address the vascular and metabolic complications of obesity and diabetes.

Nuclear receptors as new perspective for the management of liver diseases

Nuclear receptors (NRs) are ligand-activated transcription factors that act as sensors for a broad range of natural and synthetic ligands and regulate several key hepatic functions including bile acid homeostasis, bile secretion, lipid and glucose metabolism, as well as drug deposition. Moreover, NRs control hepatic inflammation, regeneration, fibrosis, and tumor formation. Therefore, NRs are key for understanding the pathogenesis and pathophysiology of a wide range of hepatic disorders. Finally, targeting NRs and their alterations offers exciting new perspectives for the treatment of liver diseases.