The Wnt/β-catenin signaling pathway in liver biology and disease

Liver zonation: Novel aspects of its regulation and its impact on homeostasis

Liver zonation, the spatial separation of the immense spectrum of different metabolic pathways along the liver sinusoids, is fundamental for proper functioning of this organ. Recent progress in elucidating localization and interactions of different metabolic pathways by using “omics” techniques and novel approaches to couple them with refined spatial resolution and in characterizing novel master regulators of zonation by using transgenic mice has created the basis for a deeper understanding of core mechanisms of zonation and their impact on liver physiology, pathology and metabolic diseases. This review summarizes the fascinating technical achievements for investigating liver zonation and the elucidation of an emerging network of master regulators of zonation that keep the plethora of interrelated and sometimes opposing functions of the liver in balance with nutritional supply and specific requirements of the entire body. In addition, a brief overview is given on newly described zonated functions and novel details on how diverse the segmentation of metabolic zonation may be. From these facts and developments a few fundamental principles are inferred which seem to rule zonation of liver parenchyma. In addition, we identify important questions that still need to be answered as well as interesting fields of research such as the connection of zonation with circadian rhythm and gender dimorphism which need to be pushed further, in order to improve our understanding of metabolic zonation. Finally, an outlook is given on how disturbance of liver zonation and its regulation may impact on liver pathology and the development of metabolic diseases.

BMP and activin membrane-bound inhibitor (BAMBI) inhibits the adipogenesis of porcine preadipocytes through Wnt/β-catenin signaling pathway

The process of differentiation from preadipocytes to adipocytes contributes to adipose tissue expansion in obesity. Blocking adipogenesis may be conducive to the etiology of obesity-related diseases. BMP and activin membrane-bound inhibitor (BAMBI) is a transmembrane protein, which was identified as a target of β-catenin in colorectal and hepatocellular tumor cells. However, whether BAMBI affects adipogenesis by Wnt/β-catenin signaling remains to be explored. In this study, we distinguish BAMBI as an inhibitor of preadipocytes differentiation. We found that BAMBI was downregulated during preadipocytes differentiation. Knockdown of BAMBI increased adipogenesis and blocked Wnt/β-catenin signaling by repressing β-catenin accumulation. In BAMBI overexpression cells, lipid accumulation was reduced by promoting nuclear translocation of β-catenin. Lithium chloride (LiCl) is an activator of Wnt/β-catenin signaling, which is an inhibitor of glycogen synthetase kinase-3 (GSK-3), maintaining the stability of β-catenin in cytosolic. We showed BAMBI strengthened the anti-adipogenic effects of LiCl. In addition, the results indicated that BAMBI was upregulated by β-catenin. These observations illuminated that BAMBI inhibits adipogenesis by a feedback loop (BAMBI→β-catenin nuclear translocation→BAMBI), which forms with Wnt/β-catenin signaling.

Promoter methylation of SFRP3 is frequent in hepatocellular carcinoma

Oncogenic activation of the Wnt/β-catenin signaling pathway is common in human cancers. The secreted frizzled-related proteins (SFRPs) function as negative regulators of Wnt signaling and have important implications in carcinogenesis. Because there have been no reports about the role of SFRP3 in hepatocellular carcinoma (HCC), we investigated the level of methylation and transcription of SFRP3. Four HCC cell lines, 60 HCCs, 23 cirrhosis livers, 37 chronic hepatitis livers, and 30 control livers were prescreened for SFRP3 promoter methylation by methylation-specific polymerase chain reaction (MS-PCR) and bisulfite sequencing. SFRP3 promoter methylation was observed in 100%, 60%, 39.1%, 16.2%, and 0% in HCC cell lines, primary HCCs, cirrhosis livers, chronic hepatitis livers, and control livers, respectively. Demethylation treatment with 5-aza-2′-deoxycytidine in HCC cells restored or increased the SFRP3 mRNA expression. We next used quantitative MS-PCR (QMSP) to analyze the methylation level of SFRP3 in 60 HCCs and their corresponding nontumor tissues. Methylation of SFRP3 promoter region in HCCs increased significantly compared with control tissues. There is a positive correlation between promoter hypermethylation and SFRP3 mRNA downregulation. Our data suggest that promoter hypermethylation of SFRP3 is a common event in HCCs and plays an important role in regulation of SFRP3 mRNA expression.

Correlation of changes of (non)exfoliated endometrial organelles and expressions of Musashi-1 and β-catenin with endometriosis in menstrual period

This study aims to investigate the correlation of structural changes of endometrial organelles and expressions of Musashi-1 (Msi-1) and β-catenin with the endometriosis (EMs) in the menstrual period. The structural changes of exfoliated and nonexfoliated endometrial organelles in the experimental group and the control group were observed by the transmission electron microscopy (TEM) on the first and fifth day of menstruation. (1) TEM: compared with the control group, the exfoliated endometrial organelles in the experimental group on the first day were rich, with irregular nucleus, the bi-nucleolus could be seen, with rich chromatin; while the shapes of epithelial secretory cells in the nonexfoliated endometrial gland were irregular, with abundant organelles, the basal film varied in width, with abnormal curvature, and a lot of intercellular collagen fibers could be seen. (2) The expressions of Msi-1 and β-catenin in the exfoliated and nonexfoliated endometrium of the experimental group were higher than those of the control group and exhibited positively correlation, while no correlation could be found within the control group. (1) The organelles' structural changes might cause the changes of endometrial cellular functions. (2) Msi-1 might participate in the formation of EMs through activating the Wnt/β-catenin signaling pathway.

Maternal Western-style high fat diet induces sex-specific physiological and molecular changes in two-week-old mouse offspring

Maternal diet is associated with the development of metabolism-related and other non-communicable diseases in offspring. Underlying mechanisms, functional profiles, and molecular markers are only starting to be revealed. Here, we explored the physiological and molecular impact of maternal Western-style diet on the liver of male and female offspring. C57BL/6 dams were exposed to either a low fat/low cholesterol diet (LFD) or a Western-style high fat/high cholesterol diet (WSD) for six weeks before mating, as well as during gestation and lactation. Dams and offspring were sacrificed at postnatal day 14, and body, liver, and blood parameters were assessed. The impact of maternal WSD on the pups’ liver gene expression was characterised by whole-transcriptome microarray analysis. Exclusively male offspring had significantly higher body weight upon maternal WSD. In offspring of both sexes of WSD dams, liver and blood parameters, as well as hepatic gene expression profiles were changed. In total, 686 and 604 genes were differentially expressed in liver (p≤0.01) of males and females, respectively. Only 10% of these significantly changed genes overlapped in both sexes. In males, in particular alterations of gene expression with respect to developmental functions and processes were observed, such as Wnt/beta-catenin signalling. In females, mainly genes important for lipid metabolism, including cholesterol synthesis, were changed. We conclude that maternal WSD affects physiological parameters and induces substantial changes in the molecular profile of the liver in two-week-old pups. Remarkably, the observed biological responses of the offspring reveal pronounced sex-specificity.

Caudatin inhibits human hepatoma cell growth and metastasis through modulation of the Wnt/β-catenin pathway

In the present study, we investigated the antitumor activity of caudatin in the human hepatoma cell line SMMC‑7721 by analysis of cell viability, cell cycle distribution, apoptosis and metastasis. The results showed that caudatin impaired the cell viability and inhibited the growth of SMMC-7721 cells in a time- and dose-dependent manner and resulted in cell cycle arrest in the G2 phase. In addition, SMMC-7721 cells, treated with caudatin exhibited typical characteristics of apoptosis. Furthermore, caudatin treatment resulted in a decrease in β-catenin and GSK3β in SMMC-7721 cells, with a concomitant reduction in metastatic capability and expression of Wnt signaling pathway targeted genes including cox-2, mmp-2 and mmp-9. Our findings revealed that caudatin inhibits human hepatoma cell growth and metastasis by targeting the GSK3β/β-catenin pathway and suppressing VEGF production.

Transcript profiling identifies iqgap2(-/-) mouse as a model for advanced human hepatocellular carcinoma

It is broadly accepted that genetically engineered animal models do not always recapitulate human pathobiology. Therefore identifying best-fit mouse models of human cancers that truly reflect the corresponding human disease is of vital importance in elucidating molecular mechanisms of tumorigenesis and developing preventive and therapeutic approaches. A new hepatocellular carcinoma (HCC) mouse model lacking a novel putative tumor suppressor IQGAP2 has been generated by our laboratory. The aim of this study was to obtain the molecular signature of Iqgap2^−/− HCC tumors and establish the relevance of this model to human disease. Here we report a comprehensive transcriptome analysis of Iqgap2^−/− livers and a cross-species comparison of human and Iqgap2^−/− HCC tumors using Significance Analysis of Microarray (SAM) and unsupervised hierarchical clustering analysis. We identified the Wnt/β-catenin signaling pathway as the top canonical pathway dysregulated in Iqgap2^−/− livers. We also demonstrated that Iqgap2^−/− hepatic tumors shared genetic signatures with HCC tumors from patients with advanced disease as evidenced by a 78% mouse-to-human microarray data set concordance rate with 117 out of 151 identified ortholog genes having similar expression profiles across the two species. Collectively, these results indicate that the Iqgap2 knockout mouse model closely recapitulates human HCC at the molecular level and supports its further application for the study of this disease.

Repair problems in podocytes: Wnt, Notch, and glomerulosclerosis

Wnt/Ctnnb1 and Notch signaling play key roles in kidney development and epithelial cell specification. Recent reports have suggested that these pathways are reactivated in response to injury and in different disease conditions. Studies using genetically modified animal models showed that sustained activation of Notch and Wnt signaling in podocytes are causally related to albuminuria and glomerulosclerosis development. Here, we discuss the role and regulation of Wnt/Ctnnb1 and Notch signaling in podocytes.

Frequent concomitant epigenetic silencing of SOX1 and secreted frizzled-related proteins (SFRPs) in human hepatocellular carcinoma

BACKGROUND AND AIM

Except for genetic mutations, epigenetic changes are also involved in the development of human cancers. Recently, we have identified SOX1, SRY (sex determining region Y)-box 1, is hypermethylated in cervical cancer and ovarian cancer. Therefore, we investigated whether promoter hypermethylation of SOX1 is common in hepatocellular carcinoma (HCC).

METHODS

We used methylation-specific polymerase chain reaction (MS-PCR) and bisulfite sequencing to analyze the methyaltion level of the SOX1 promoter in seven HCC cell lines, 54 clinical HCCs, 42 cirrhotic livers, 21 livers with chronic hepatitis, and 15 control livers. Then, we employed quantitative MS-PCR (QMSP) to validate in an independent set of samples (60 paired HCCs and 30 control livers). Finally, we used luciferase reporter and colony formation assay to check the effect of SOX1 in HCC.

RESULTS

Promoter methylation of SOX1 was significantly frequent in HCC cell lines and clinical HCCs, cirrhotic livers, but not in control livers (P < 0.0001). There is a significant correlation between downregulation of SOX1 expression and promoter methylation. QMSP results confirmed that promoter hypermethylation of SOX1 is significantly more frequent in HCCs than control livers (P < 0.0001). The frequency of SOX1 methylation in patients with secreted frizzled-related proteins (SFRPs) methylation is significantly higher than in patients without SFRPs methylation (P < 0.0001). Furthermore, ectopic expression of SOX1 could suppress T-cell factor-dependent transcriptional activity and colony formation number in HCCs.

CONCLUSIONS

Concomitant epigenetic silencing of SOX1 and SFRPs through promoter hypermethylation is frequent in HCCs, and this might contribute to abnormal activation of canonical Wnt signal pathway.

The epigenetic effects of a high prenatal folate intake in male mouse fetuses exposed in utero to arsenic

Inorganic arsenic (iAs) is a complete transplacental carcinogen in mice. Previous studies have demonstrated that in utero exposure to iAs promotes cancer in adult mouse offspring, possibly acting through epigenetic mechanisms. Humans and rodents enzymatically convert iAs to its methylated metabolites. This reaction requires S-adenosylmethionine (SAM) as methyl group donor. SAM is also required for DNA methylation. Supplementation with folate, a major dietary source of methyl groups for SAM synthesis, has been shown to modify iAs metabolism and the adverse effects of iAs exposure. However, effects of gestational folate supplementation on iAs metabolism and fetal DNA methylation have never been thoroughly examined. In the present study, pregnant CD1 mice were fed control (i.e. normal folate, or 2.2 mg/kg) or high folate diet (11 mg/kg) from gestational day (GD) 5 to 18 and drank water with 0 or 85 ppm of As (as arsenite) from GD8 to 18. The exposure to iAs significantly decreased body weight of GD18 fetuses and increased both SAM and S-adenosylhomocysteine (SAH) concentrations in fetal livers. High folate intake lowered the burden of total arsenic in maternal livers but did not prevent the effects of iAs exposure on fetal weight or hepatic SAM and SAH concentrations. In fact, combined folate-iAs exposure caused further significant body weight reduction. Notably, iAs exposure alone had little effect on DNA methylation in fetal livers. In contrast, the combined folate-iAs exposure changed the CpG island methylation in 2,931 genes, including genes known to be imprinted. Most of these genes were associated with neurodevelopment, cancer, cell cycle, and signaling networks. The canonical Wnt-signaling pathway, which regulates fetal development, was among the most affected biological pathways. Taken together, our results suggest that a combined in utero exposure to iAs and a high folate intake may adversely influence DNA methylation profiles and weight of fetuses, compromising fetal development and possibly increasing the risk for early-onset of disease in offspring.

Metformin-mediated Bambi expression in hepatic stellate cells induces prosurvival Wnt/β-catenin signaling

AMP-activated protein kinase (AMPK) regulates lipid, cholesterol, and glucose metabolism in specialized metabolic tissues, such as muscle, liver, and adipose tissue. Agents that activate AMPK, such as metformin and 5-aminoimidazole-4-carboxamide-1-beta-4-ribofuranoside (AICAR), have beneficial effects on liver glucose and lipid metabolism. In addition, AMPK activation in proliferating hepatic stellate cells (HSC) induces growth arrest and inhibits hepatic fibrosis. As metformin and AICAR act in different ways to achieve their effects, our aim was to examine the effects of AMPK activation in quiescent HSCs with these two agents on HSC function. We found that phospho-AMPK levels were markedly upregulated by both AICAR and metformin in quiescent HSCs. However, although AICAR treatment induced cell death, cells treated with metformin did not differ from untreated controls. AICAR-mediated HSC cell death was paralleled by loss of expression of the TGF-β decoy receptor Bambi, whereas metformin increased Bambi expression. Transfection of siRNA-Bambi into HSCs also induced cell death, mimicking the effects of AICAR, whereas overexpression of Bambi partially rescued AICAR-treated cells. As Bambi has previously been shown to promote cell survival through Wnt/β-catenin signaling, a reporter incorporating binding sites for a downstream target of this pathway was transfected into HSCs and was induced. We conclude that although AICAR and metformin both activate AMPK in quiescent HSCs, AICAR rapidly induced cell death, whereas metformin-treated cells remained viable. The finding that metformin increases Bambi expression and activates Wnt/β-catenin signaling provides a possible mechanistic explanation for this observation. These results suggest that AICAR and metformin may confer disease-specific therapeutic benefits.

MicroRNA-194 is a target of transcription factor 1 (Tcf1, HNF1α) in adult liver and controls expression of frizzled-6

Transcription factor 1 (Tcf1; hepatocyte nuclear factor 1α [HNF1α]) is critical for hepatocyte development and function. Whether Tcf1 also regulates hepatic microRNAs (miRNAs) has not been investigated yet. Here we analyzed Tcf1-dependent miRNA expression in adult mice in which this transcription factor had been genetically deleted (Tcf1(-/-) ) using miRNA microarray analysis. The miR-192/-194 cluster was markedly down-regulated in liver of Tcf1(-/-) mice. MiR-192/-194 levels were also decreased in two other tissues that express Tcf1, kidney and small intestine, although to a lesser extent than in liver. In order to identify targets of miR-192/-194 in vivo we combined Affymetrix gene analysis of liver in which miR-192/-194 had been silenced or overexpressed, respectively, and tested regulated messenger RNAs (mRNAs) with multiple binding sites for these miRNAs. This approach revealed frizzled-6 (Fzd6) as a robust endogenous target of miR-194. MiR-194 also targets human FZD6 and expression of miR-194 and Fzd6 are inversely correlated in a mouse model of hepatocellular carcinoma (Dgcr8(flox/flox) p53(flox/flox) × Alb-Cre).

CONCLUSION

Our results support a role of miR-194 in liver tumorigenesis through its endogenous target Fzd6. These results may have important implications for Tcf1-mediated liver proliferation.

Inhibitory effect of blueberry polyphenolic compounds on oleic acid-induced hepatic steatosis in vitro

Nonalcoholic fatty liver disease (NAFLD) is one of the most common chronic liver diseases worldwide and is closely associated with metabolic syndromes, such as obesity, diabetes, and insulin resistance. Nonalcoholic fatty liver (NAFL), also called simple steatosis, is the initial phase of NAFLD, which is accompanied the characteristic pathological overaccumulation of lipids without inflammation. To prevent NAFLD from reaching the NAFL stage through dietary therapy, in the present work, wild Chinese blueberries (Vacciniun spp.) were selected for their well-known benefits in inhibiting metabolic syndrome. After being purified from wild Chinese blueberries, polyphenol-rich extracts were subsequently separated into three fractions, namely, anthocyanin-rich fraction, phenolic acid-rich fraction, and ethyl acetate extract. The inhibition of oleic acid (OA)-induced triglyceride (TG) deposition in HepG 2 cells was referred to as the potential activity of preventing NAFL. Biochemical indicators, such as cytotoxicity, TG level, levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST), and intracellular reactive oxygen species, were used to evaluate the analogous pathological stage of NAFLD. The results show that OA ≤ 1.0 mM exhibits a dose-dependent induction of TG accumulation, and no inflammation was observed based on the changes in ALT and AST levels. Therefore, 1.0 mM OA was used to simulate an in vitro fatty liver. Blueberry polyphenol-rich extract efficiently inhibited OA-induced TG accumulation in HepG2 cells, and the phenolic acid-rich fraction performed efficiently. Seven phenolic acids were subsequently identified using a high-performance liquid chromatography assay, and the main types were caffeic, chlorogenic, ferulic, p-coumaric, and cinnamic acids. These phenolic acid standards also displayed good efficiency in inhibiting TG accumulation in HepG2 cells. These results imply that wild Chinese blueberries have a potential preventive effect on NAFLD in its early stage, and phenolic acids are the most efficient component.

Maternal hepatic growth response to pregnancy in the mouse

Pregnancy is characterized by physiological adjustments in the maternal compartment. In this investigation, the influence of pregnancy on maternal liver was examined in CD-1 mice. Dramatic changes were observed in the size of the maternal liver during pregnancy. Livers doubled in weight from the non-pregnant state to day 18 of pregnancy. The pregnancy-induced hepatomegaly was a physiological event of liver growth confirmed by DNA content increase and detection of hepatocyte hyperplasia and hypertrophy. Growth of the liver was initiated following implantation and peaked at parturition. The expression and/or activities of key genes known to regulate liver regeneration, a phenomenon of liver growth compensatory to liver mass loss, were investigated. The results showed that pregnancy-dependent liver growth was associated with interleukin (IL)-6, tumor necrosis factor α, c-Jun and IL-1β, but independent of hepatocyte growth factor, fibroblast growth factor 1, tumor necrosis factor receptor 1, constitutive androstane receptor and pregnane X receptor. Furthermore, maternal liver growth was associated with the activation of hepatic signal transducer and activator of transcription 3, β-catenin and epidermal growth factor receptor, but pregnancy did not activate hepatic c-Met. The findings suggest that the molecular mechanisms regulating pregnancy-induced liver growth and injury-induced liver regeneration exhibit overlapping features but are not identical. In summary, the liver of the mouse adapts to the demands of pregnancy via a dramatic growth response driven by hepatocyte proliferation and size increase.

Gene expression patterns in livers of Hispanic patients infected with hepatitis C virus

We report a gene expression study aimed at the identification of genes differentially expressed in the livers of Hispanic patients infected with hepatitis C virus (HCV). Six uninfected controls were compared with 14 HCV(+) patients in which the liver biopsies were obtained at the time of diagnosis. Among the latter, five patients were also analyzed 4 weeks after the onset of standard anti-HCV therapy (pegylated interferon-α + ribavirin). We identified many genes up- or down-regulated by the infection with HCV in the human livers. When these genes were subjected to pathway analysis, several prominent pathways were revealed including many interferon (IFN)-inducible pathways as well as immune cell trafficking, inflammation, anti-microbial responses, and even cancer. We detected expression of many genes that have previously been associated with HCV infection, as well as several novel genes including CD47. The genes induced by HCV infection showed large expression changes, whereas the genes induced by the IFN-α combination therapy were relatively few (including MX2, ORMDL3, GPAM, KOPX18, TMEM56, and HBP1) and they reflected relatively small expression changes. This is the first study to identify changes in gene expression in livers of HCV(+) Hispanic patients and the first to identify genes induced by anti-HCV combination therapy in the human liver.