Activation of farnesoid X receptor attenuates hepatic injury in a murine model of alcoholic liver disease

Alcoholic liver disease (ALD) is a common cause of advanced liver disease, and considered as a major risk factor of morbidity and mortality worldwide. Hepatic cholestasis is a pathophysiological feature observed in all stages of ALD. The farnesoid X receptor (FXR) is a member of the nuclear hormone receptor superfamily, and plays an essential role in the regulation of bile acid, lipid and glucose homeostasis. However, the role of FXR in the pathogenesis and progression of ALD remains largely unknown. Mice were fed Lieber-DeCarli ethanol diet or an isocaloric control diet. We used a specific agonist of FXR WAY-362450 to study the effect of pharmacological activation of FXR in alcoholic liver disease. In this study, we demonstrated that FXR activity was impaired by chronic ethanol ingestion in a murine model of ALD. Activation of FXR by specific agonist WAY-362450 protected mice from the development of ALD. We also found that WAY-362450 treatment rescued FXR activity, suppressed ethanol-induced Cyp2e1 up-regulation and attenuated oxidative stress in liver. Our results highlight a key role of FXR in the modulation of ALD development, and propose specific FXR agonists for the treatment of ALD patients.     

Pyrrole[2,3-d]azepino compounds as agonists of the farnesoid X receptor (FXR)

Pyrrole[2,3-d]azepines have been identified as potent agonists of the farnesoid X receptor (FXR). Based on the planar X-ray crystal structure of WAY-362450 1 in the ligand binding domain and molecular modeling studies, non-planar reduced compounds were designed which led to agonists that exhibit high aqueous solubility and retain moderate in vitro potency.     

Activation of farnesoid X receptor (FXR) protects against fructose-induced liver steatosis via inflammatory inhibition and ADRP reduction

Fructose is a key dietary factor in the development of nonalcoholic fatty liver disease (NAFLD). Here we investigated whether WAY-362450 (WAY), a potent synthetic and orally active FXR agonist, protects against fructose-induced steatosis and the underlying mechanisms. C57BL/6J mice, fed 30% fructose for 8 weeks, were treated with or without WAY, 30 mg/kg, for 20 days. The elevation of serum and hepatic triglyceride in mice fed 30% fructose was reversed by WAY treatment. Histologically, WAY significantly reduced triglyceride accumulation in liver, attenuated microphage infiltration and protected the junction integrity in intestine. Moreover, WAY remarkably decreased portal endotoxin level, and lowered serum TNFα concentration. In lipopolysaccharide (LPS)-induced NAFLD model, WAY attenuated serum TNFα level. Moreover, WAY suppressed LPS-induced expression of hepatic lipid droplet protein adipose differentiation-related protein (ADRP), down-regulation of it in mice fed 30% fructose. Furthermore, WAY repressed lipid accumulation and ADRP expression in a dose-dependent manner in palmitic acid (PA)-treated HepG2 and Huh7 cells. WAY suppressed TNFα-induced ADRP up-regulation via competing with AP-1 for ADRP promoter binding region. Together, our findings suggest that WAY, an FXR agonist, attenuates liver steatosis through multiple mechanisms critically involved in the development of hepatosteatosis, and represents a candidate for NAFLD treatment.     

Activation of farnesoid X receptor prevents atherosclerotic lesion formation in LDLR−/− and apoE−/− mice

The role of farnesoid X receptor (FXR) in the development of atherosclerosis has been unclear. Here, LDL receptor (LDLR^−/−) or apolipoprotein E (apoE^−/−) female or male mice were fed a Western diet and treated with a potent synthetic FXR agonist, WAY-362450. Activation of FXR blocked diet-induced hypertriglyceridemia and elevations of non-HDL cholesterol and produced a near complete inhibition of aortic lesion formation. WAY-362450 also induced small heterodimer partner (SHP) expression and repressed cholesterol 7α-hydroxylase (CYP7A1) and sterol 12 α-hydroxylase (CYP8B1) expression. To determine if SHP was essential for these protective activities, LDLR^−/−SHP^−/− and apoE^−/−SHP^−/− mice were similarly treated with WAY-362450. Surprisingly, a notable sex difference was observed in these mice. In male LDLR^−/−SHP^−/− or apoE^−/−SHP^−/− mice, WAY-362450 still repressed CYP7A1 and CYP8B1 expression by 10-fold and still strongly reduced non-HDL cholesterol levels and aortic lesion area. In contrast, in the female LDLR^−/−SHP^−/− or apoE^−/−SHP^−/− mice, WAY-362450 only slightly repressed CYP7A1 and CYP8B1 expression and did not reduce non-HDL cholesterol or aortic lesion size. WAY-362450 inhibition of hypertriglyceridemia remained intact in LDLR^−/− or apoE^−/− mice lacking SHP of both sexes. These results suggest that activation of FXR protects against atherosclerosis in the mouse, and this protective effect correlates with repression of bile acid synthetic genes, with mechanistic differences between male and female mice.     

Consumption of Soy Protein Isolate Reduces Hepatic SREBP-1c and Lipogenic Gene Expression in Wild-Type Mice,but Not in FXR-Deficient Mice

We examined to determine whether hepatic gene expression is affected in mice in which blood lipid levels remain unchanged fed soy protein isolate (SPI) for a short time. We also examined SPI-mediated effects in farnesoid X receptor (FXR)-deficient mice. Compared with casein, SPI affected the expression of various hepatic genes related to lipid metabolism in the wild-type mice. No effects of SPI were observed in the FXR-deficient mice, suggesting the importance of FXR. Hepatic peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) gene expression was reduced by SPI, and this might be associated with a decrease in FXR expression. Decreased FXR led to decreased expression of its target, the bile-salt export pump necessary for bile acid secretion and dietary lipid absorption. The earliest response to SPI was a decrease in hepatic sterol regulatory element-binding protein (SREBP)-1c mRNA, on day 3. SPI activated hepatic adenosine monophosphate-activated protein kinase (AMPK), which can lead to a reduction in SREBP-1c mRNA. These data indicate the importance of SREBP-1c and PGC-1α/FXR in SPI-mediated alterations in hepatic gene expression.     

The nuclear receptor FXR is expressed in pancreatic β-cells and protects human islets from lipotoxicity

Farnesoid X receptor (FXR) is highly expressed in liver and intestine where it controls bile acid (BA), lipid and glucose homeostasis. Here we show that FXR is expressed and functional, as assessed by target gene expression analysis, in human islets and β-cell lines. FXR is predominantly cytosolic-localized in the islets of lean mice, but nuclear in obese mice. Compared to FXR+/+ mice, FXR−/− mice display a normal architecture and β-cell mass but the expression of certain islet-specific genes is altered. Moreover, glucose-stimulated insulin secretion (GSIS) is impaired in the islets of FXR−/− mice. Finally, FXR activation protects human islets from lipotoxicity and ameliorates their secretory index.     

Cryptochinones from Cryptocarya chinensis act as farnesoid X receptor agonists

Cryptochinones A–D are tetrahydroflavanones isolated from the leaves of Cryptocarya chinensis, an evergreen tree whose extracts are believed to have a variety of health benefits. The origin of their possible bioactivity is unclear. The farnesoid X receptor (FXR) is a member of nuclear receptor superfamily that has been widely targeted for developing treatments for chronic liver disease and for hyperglycemia. We studied whether cryptochinones A–D, which are structurally similar to known FXR ligands, may act at this target. Indeed, in mammalian one-hybrid and transient transfection reporter assays, cryptochinones A–D transactivated FXR to modulate promoter action including GAL4, SHP, CYP7A1, and PLTP promoters in dose-dependent manner, while they exhibited similar agonistic activity as chenodeoxycholic acid (CDCA), an endogenous FXR agonist. Through molecular modeling docking studies we evaluated their ability to bind to the FXR ligand binding pocket. Our results indicate that cryptochinones A–D can behave as FXR agonists.     

Serum amyloid A-induced IL-6 production by rheumatoid synoviocytes

In this study, we investigated the role of serum amyloid A protein (SAA) in the production of interleukin-6 (IL-6) using rheumatoid arthritis fibroblast-like synoviocytes (RA-FLS). Recombinant SAA stimulation induced the production of pro-inflammatory cytokine, IL-6, from RA-FLS. The signaling events induced by SAA included the activation of the mitogen-activated protein kineases, p38 and JNK1/2 and the activation of nuclear factor-kappa B (NF-kappaB). Inhibitor studies have shown SAA-induced IL-6 production to be down-regulated by NF-kappaB inhibition and partially inhibited by p38 or JNK inhibitors. Our findings demonstrate that SAA is a significant inducer of IL-6, which is critically involved in RA pathogenesis.     

脆性X相关蛋白Ⅰ的研究进展

脆性X相关基因I(FXR1)发现于1995年,位于3号染色体3q28。其产物脆性X相关蛋白1(FXR1P)与脆性X智障蛋白1 (FMR1P)、脆性X相关蛋白2(FXR2P)形成一个RNA结合蛋白家族。目前认为这三种蛋白能输送mRNA分子并调控其翻译过程。FXR1的翻译产物(FXR1P)分子中存在两个KH结构域和一个RGG结构域,这两种结构域与FXR1P分子的RNA结合作用有关。FXR1P的表达具有较高的组织特意性,在横纹肌中表达最高。合适的动物模型对于一种蛋白的功能研究具有十分重要的意义,目前,FXR1敲除的各种动物模型如小鼠、斑马鱼、非洲爪蟾的近亲Xenopus tropicalis已经在不同的实验室建立。本文主要介绍了FXR1P的结构特点、功能及其实验动物模型。     

Transient impairment of the adaptive response to fasting in FXR-deficient mice

The farnesoid X receptor (FXR) has been suggested to play a role in gluconeogenesis. To determine whether FXR modulates the response to fasting in vivo, FXR-deficient (FXR^−/−) and wild-type mice were submitted to fasting for 48 h. Our results demonstrate that FXR modulates the kinetics of alterations of glucose homeostasis during fasting, with FXR^−/− mice displaying an early, accelerated hypoglycaemia response. Basal hepatic glucose production rate was lower in FXR^−/− mice, together with a decrease in hepatic glycogen content. Moreover, hepatic PEPCK gene expression was transiently lower in FXR^−/−mice after 6 h of fasting and was decreased in FXR^−/−hepatocytes. FXR therefore plays an unexpected role in the control of fuel availability upon fasting.     

Cytokines and serum amyloid A in the pathogenesis of hepatitis C virus infection

Expression of the acute phase protein serum amyloid A (SAA) is dependent on the release of the pro-inflammatory cytokines IL-1, IL-6 and TNF-α during infection and inflammation. Hepatitis C virus (HCV) upregulates SAA-inducing cytokines. In line with this, a segment of chronically infected individuals display increased circulating levels of SAA. SAA has even been proposed to be a potential biomarker to evaluate treatment efficiency and the course of disease. SAA possesses antiviral activity against HCV via direct interaction with the viral particle, but might also divert infectivity through its function as an apolipoprotein. On the other hand, SAA shares inflammatory and angiogenic activity with chemotactic cytokines by activating the G protein-coupled receptor, formyl peptide receptor 2. These latter properties might promote chronic inflammation and hepatic injury. Indeed, up to 80 % of infected individuals develop chronic disease because they cannot completely clear the infection, due to diversion of the immune response. In this review, we summarize the interconnection between SAA and cytokines in the context of HCV infection and highlight the dual role SAA could play in this disease. Nevertheless, more research is needed to establish whether the balance between those opposing activities can be tilted in favor of the host defense.     

Prion infection correlates with hypersensitivity of P2X7 nucleotide receptor in a mouse microglial cell line

We recently established mouse microglial cells persistently infected with mouse-adapted scrapie ME7 (ScMG20/ME7) for in vitro study of prion pathogenesis. Here, we found that ScMG20/ME7 cells were hypersensitive to P2X7 receptor agonists, as demonstrated by sustained Ca(2+) influx, membrane pore formation, cell death, and interleukin-1beta release. P2X7 mRNA expression was upregulated in these cells, and also in scrapie-infected mice brains. Treatment with pentosan polysulfate eliminated the infectivity and disease-related forms of prion protein from ScMG20/ME7 cell cultures, however, hypersensitivity of P2X7 receptors remained. These results suggest that prion infections may strongly affect the P2X7 receptor system in mouse microglial cells.     

Pigment epithelium-derived factor (PEDF) blocks the interleukin-6 signaling to C-reactive protein expression in Hep3B cells by suppressing Rac-1 activation

There is a growing body of evidence to show that that C-reactive protein (CRP), an acute phase reactant, is one of the most valuable predictors of future cardiovascular events. Since CRP proteins directly contribute to the development and progression of atherosclerosis as well, reduction of CRP levels may be a novel therapeutic target for the treatment of cardiovascular disease. In this study, we examined whether pigment epithelium-derived factor (PEDF) could block the interleukin-6-induced CRP expression in cultured human hepatoma cells and the way that it might achieve this effect. PEDF inhibited the IL-6-induced CRP expression in Hep3B cells at both mRNA and proteins levels. PEDF suppressed the intracellular reactive oxygen species generation in IL-6-exposed Hep3B cells. Anti-oxidants mimicked the effects of PEDF. PEDF was also found to inhibit the IL-6-elicited Rac-1 activation, whereas dominant-negative Rac-1 dose-dependently decreased the CRP mRNA levels. PEDF blocked the IL-6-induced STAT3 phosphorylations and NF-kappaB p65 activity in Hep3B cells. Our present study suggests that PEDF could be one of the potent suppressors of CRP production by the liver and may play a protective role against atherosclerosis.     

Differential binding modes of the bromodomains of CREB-binding protein (CBP) and p300 with acetylated MyoD

We investigated whether blocking of monocyte chemoattractant-1 (MCP-1) function would inhibit recruitment of tumor-associated macrophages (TAMs) and prevent tumor angiogenesis and tumor growth of human malignant melanoma. B16-F1 melanoma cells were implanted onto the back of C57BL/6 mice (Day 0). At Day 7, a dominant negative MCP-1 mutant (7ND) gene was transfected in the thigh muscle to make overexpressed 7ND protein secreted into systemic circulation. 7ND treatment inhibited TAM recruitment and partially reduced tumor angiogenesis and tumor growth. Also, 7ND treatment attenuated inductions of tumor necrosis factor-α (TNFα), interleukin-1α (IL-1α), and vascular endothelial growth factor (VEGF) in the stroma and tumor. Melanoma cells expressed not only MCP-1 but also its receptor CCR2. Accordingly, it was suggested that MCP-1 would enhance tumor angiogenesis and early tumor growth in the early stages by inducing TNFα, IL-1α, and VEGF through TAM recruitment and probably the direct autocrine/paracrine effects on melanoma cells.     

Effects of coumestrol on lipid and glucose metabolism as a farnesoid X receptor ligand

In the course of an effort to identify novel agonists of the farnesoid X receptor (FXR), coumestrol was determined to be one such ligand. Reporter and in vitro coactivator interaction assays revealed that coumestrol bound and activated FXR. Treatment of Hep G2 cells with coumestrol stimulated the expression of FXR target genes, thereby regulating the expression of target genes of the liver X receptor and hepatocyte nuclear factor-4α. Through these actions, coumestrol is expected to exert beneficial effects on lipid and glucose metabolism.     

Regulation of human class I alcohol dehydrogenases by bile acids

Class I alcohol dehydrogenases (ADH1s) are the rate-limiting enzymes for ethanol and vitamin A (retinol) metabolism in the liver. Because previous studies have shown that human ADH1 enzymes may participate in bile acid metabolism, we investigated whether the bile acid-activated nuclear receptor farnesoid X receptor (FXR) regulates ADH1 genes. In human hepatocytes, both the endogenous FXR ligand chenodeoxycholic acid and synthetic FXR-specific agonist GW4064 increased ADH1 mRNA, protein, and activity. Moreover, overexpression of a constitutively active form of FXR induced ADH1A and ADH1B expression, whereas silencing of FXR abolished the effects of FXR agonists on ADH1 expression and activity. Transient transfection studies and electrophoretic mobility shift assays revealed functional FXR response elements in the ADH1A and ADH1B proximal promoters, thus indicating that both genes are direct targets of FXR. These findings provide the first evidence for direct connection of bile acid signaling and alcohol metabolism.