Metformin and exenatide upregulate hepatocyte nuclear factor-4α, sex hormone binding globulin levels and improve hepatic triglyceride deposition in polycystic ovary syndrome with insulin resistance rats

OBJECTIVE

To explore the efficacy and underlying mechanisms of metformin and exenatide in reversing reproductive and metabolic disturbances in letrozole combined with high-fat diet-induced polycystic ovary syndrome (PCOS) rats.

METHODS

Rats with PCOS and insulin resistance (IR) were induced by intra-gastric instillation of letrozole combined with a high-fat diet and verified by histological screening of vaginal exfoliated cells. After metformin and exenatide supplementation, body weight, chow intake and ovarian morphology were observed. Serum biochemical profiles were analyzed using ELISA, while the levels of key anabolism-related proteins, including sex hormone binding globulin (SHBG), hepatocyte nuclear factor-4α (HNF-4α), PI3K, and AKT, were determined using western blotting.

RESULTS

The estrus cycle and ovarian morphology of rats with PCOS and IR were significantly recovered following metformin and exenatide treatment, with decreased body weight and chow intake. Furthermore, PCOS-induced changes in metabolic disorders including IR and hepatic triglyceride (TG) deposition, and hyperandrogenemia were reversed by treatment with both drugs. Specifically, the levels of HNF-4α and SHBG in liver tissue of rats with PCOS and IR were upregulated significantly.

CONCLUSIONS

Both metformin and exenatide could recover the estrous cycle and ovarian morphology, reduce body weight and high-fat chow intake, and improve glycolipid metabolism disorders and hyperandrogenemia in PCOS with IR rat models. Interestingly, our findings also highlight the potential of both therapeutic agents for improving IR by regulating the liver PI3K/AKT pathway, reducing the deposition of hepatic TG, as well as upregulating the levels of SHBG and HNF-4α in PCOS with IR rat liver tissue.

Metformin inhibits pancreatic cancer metastasis caused by SMAD4 deficiency and consequent HNF4G upregulation

Pancreatic ductal adenocarcinoma (PDAC) has poor prognosis due to limited therapeutic options. This study examines the roles of genome-wide association study identified PDAC-associated genes as therapeutic targets. We have identified HNF4G gene whose silencing most effectively repressed PDAC cell invasiveness. HNF4G overexpression is induced by the deficiency of transcriptional factor and tumor suppressor SMAD4. Increased HNF4G are correlated with SMAD4 deficiency in PDAC tumor samples and associated with metastasis and poor survival time in xenograft animal model and in patients with PDAC (log-rank P = 0.036; HR = 1.60, 95% CI = 1.03-2.47). We have found that Metformin suppresses HNF4G activity via AMPK-mediated phosphorylation-coupled ubiquitination degradation and inhibits in vitro invasion and in vivo metastasis of PDAC cells with SMAD4 deficiency. Furthermore, Metformin treatment significantly improve clinical outcomes and survival in patients with SMAD4-deficient PDAC (log-rank P = 0.022; HR = 0.31, 95% CI = 0.14-0.68) but not in patients with SMAD4-normal PDAC. Pathway analysis shows that HNF4G may act in PDAC through the cell-cell junction pathway. These results indicate that SMAD4 deficiency-induced overexpression of HNF4G plays a critical oncogenic role in PDAC progression and metastasis but may form a druggable target for Metformin treatment.

Hepatocyte nuclear factor 4α (HNF4α) in coordination with retinoic acid receptors increases all-trans-retinoic acid-dependent CYP26A1 gene expression in HepG2 human hepatocytes

CYP26A1 expression is very highly induced by retinoic acid (RA) in the liver, compared to most other tissues, suggesting that a liver-enriched factor may be required for its physiological transcriptional response. HNF4α is a highly conserved liver-specific/enriched member of nuclear receptor superfamily. In this study, we hypothesized that HNF4α and RARs may cooperate in an RA-dependent manner to induce a high level of CYP26A1 expression in liver cells. Partial inhibition of endogenous HNF4α by siRNA reduced the level of RA-induced CYP26A1 mRNA in HepG2 cells. Cotransfection of HNF4α, with or without RARs, demonstrated RA-dependent activation of a human CYP26A1 promoter-luciferase construct. Analysis of a 2.5-kbp putative CYP26A1 promoter sequence identified five potential HNF4α DNA response elements: H1 located in a proximal region overlapping with an RAR element-1 (RARE1 or R1); H2 and H3 in the distal region, close to RARE2 (R2) and RARE3 (R3); and H4 and H5 in intermediary regions. In EMSA and ChIP analyses HNF4α and RARs binding in the proximal and distal CYP26A1 promoter regions was significantly higher in RA-treated cells. Mutational analysis of the individual HNF4α DNA-response elements identified H1 as the major site for HNF4α binding because mutation of H1 inhibited the promoter activity by ~90%, followed by H2 mutation with less than 40% inhibition. Our results indicate that HNF4α coordinates with RARs in an RA-dependent manner to strongly induce CYP26A1 gene expression in the liver, which may explain the high level of response to RA observed in vivo.

Resetting the transcription factor network reverses terminal chronic hepatic failure

The cause of organ failure is enigmatic for many degenerative diseases, including end-stage liver disease. Here, using a CCl4-induced rat model of irreversible and fatal hepatic failure, which also exhibits terminal changes in the extracellular matrix, we demonstrated that chronic injury stably reprograms the critical balance of transcription factors and that diseased and dedifferentiated cells can be returned to normal function by re-expression of critical transcription factors, a process similar to the type of reprogramming that induces somatic cells to become pluripotent or to change their cell lineage. Forced re-expression of the transcription factor HNF4α induced expression of the other hepatocyte-expressed transcription factors; restored functionality in terminally diseased hepatocytes isolated from CCl4-treated rats; and rapidly reversed fatal liver failure in CCl4-treated animals by restoring diseased hepatocytes rather than replacing them with new hepatocytes or stem cells. Together, the results of our study indicate that disruption of the transcription factor network and cellular dedifferentiation likely mediate terminal liver failure and suggest reinstatement of this network has therapeutic potential for correcting organ failure without cell replacement.

Decreased expression of hepatocyte nuclear factor 4α (Hnf4α)/microRNA-122 (miR-122) axis in hepatitis B virus-associated hepatocellular carcinoma enhances potential oncogenic GALNT10 protein activity

MicroRNA-122 (miR-122), a mammalian liver-specific miRNA, has been reported to play crucial roles in the control of diverse aspects of hepatic function and dysfunction, including viral infection and hepatocarcinogenesis. In this study, we explored the clinical significance, transcriptional regulation, and direct target of miR-122 in hepatitis B virus (HBV)-associated hepatocellular carcinoma. Reduced expression of miR-122 in patients with HBV-associated hepatocellular carcinoma was correlated with venous invasion and poor prognosis. Furthermore, UDP-N-acetyl-α-D-galactosamine:polypeptide N-acetylgalactosaminyltransferase-10 (GALNT10) was identified as a bona fide target of miR-122 in hepatoma cells. Ectopic expression and knockdown studies showed that GALNT10 indeed promotes proliferation and apoptosis resistance of hepatoma cells in a glycosyltransferase-dependent manner. Critically, adverse correlation between miR-122 and GALNT10, a poor prognosticator of clinical outcome, was demonstrated in hepatoma patients. Hepatocyte nuclear factor 4α (Hnf4α), a liver-enriched transcription factor that activates miR-122 gene transcription, was suppressed in HBV-infected hepatoma cells. Chromatin immunoprecipitation assay showed significantly reduced association of Hnf4α with the miR-122 promoter in HBV-infected hepatoma cells. Moreover, GALNT10 was found to intensify O-glycosylation following signal activation of the epidermal growth factor receptor. In addition, in a therapeutic perspective, we proved that GALNT10 silencing increases sensitivity to sorafenib and doxorubicin challenge. In summary, our results reveal a novel Hnf4α/miR-122/GALNT10 regulatory pathway that facilitates EGF miR-122 activation and hepatoma growth in HBV-associated hepatocarcinogenesis.

In vitro reprogramming of pancreatic alpha cells towards a beta cell phenotype following ectopic HNF4α expression

There is currently a shortage of organ donors available for pancreatic beta cell transplantation into diabetic patients. An alternative source of beta cells is pre-existing pancreatic cells. While we know that beta cells can arise directly from alpha cells during pancreatic regeneration we do not understand the molecular basis for the switch in phenotype. The aim of the present study was to investigate if hepatocyte nuclear factor 4 alpha (HNF4α), a transcription factor essential for a normal beta cell phenotype, could induce the reprogramming of alpha cells towards potential beta cells. We utilised an in vitro model of pancreatic alpha cells, the murine αTC1-9 cell line. We initially characterised the αTC1-9 cell line before and following adenovirus-mediated ectopic expression of HNF4α. We analysed the phenotype at transcript and protein level and assessed its glucose-responsiveness. Ectopic HNF4α expression in the αTC1-9 cell line induced a change in morphology (1.7-fold increase in size), suppressed glucagon expression, induced key beta cell-specific markers (insulin, C-peptide, glucokinase, GLUT2 and Pax4) and pancreatic polypeptide (PP) and enabled the cells to secrete insulin in a glucose-regulated manner. In conclusion, HNF4α reprograms alpha cells to beta-like cells.

Hepatocyte nuclear factor 4A expression discriminates gastric involvement by metastatic breast carcinomas from primary gastric adenocarcinomas

Breast carcinomas sometimes metastasize to the stomach, and the histopathologic distinction of such metastases from primary gastric adenocarcinomas is often difficult. We characterized the clinicopathologic features of 21 breast carcinomas that had metastasized to the stomach and examined the use of a panel of antibodies, including hepatocyte nuclear factor 4A, for distinguishing the metastases from primary gastric diffuse-type adenocarcinomas. Histologically, all the metastatic breast carcinomas showed a poorly differentiated and/or signet ring cell morphology. Although most metastatic breast and primary gastric carcinomas contained signet ring cell components, the cases that were predominantly or exclusively composed of univacuolated-type signet ring cells were limited to metastatic breast carcinomas. Immunohistochemically, hepatocyte nuclear factor 4A was expressed in all 33 primary gastric carcinomas that were examined but was never expressed in metastatic breast carcinomas. Previously reported markers for breast and gastric carcinomas also showed a high specificity, but their sensitivities were quite variable. Estrogen receptor α, progesterone receptor, mammaglobin, and gross cystic disease fluid protein 15 were expressed in 76%, 33%, 52%, and 62%, respectively, of the metastatic breast carcinomas, whereas none of the primary gastric carcinomas expressed these antigens. CDX2, MUC5AC, MUC6, and CK20 were expressed in 36%, 85%, 27%, and 55%, respectively, of the primary gastric carcinomas. All the metastatic breast carcinomas were negative for these antibodies except for 1 case that expressed MUC5AC. Overall, the use of immunohistochemistry efficiently discriminated metastatic breast carcinomas from primary gastric carcinomas. In particular, the present study identified hepatocyte nuclear factor 4A as an excellent marker for differentiating the 2 lesions.

Species-specific differences in the expression of the HNF1A, HNF1B and HNF4A genes

Background

The HNF1A, HNF1B and HNF4A genes are part of an autoregulatory network in mammalian pancreas, liver, kidney and gut. The layout of this network appears to be similar in rodents and humans, but inactivation of HNF1A, HNF1B or HNF4A genes in animal models cause divergent phenotypes to those seen in man. We hypothesised that some differences may arise from variation in the expression profile of alternatively processed isoforms between species.

Methodology/Principal Findings

We measured the expression of the major isoforms of the HNF1A, HNF1B and HNF4A genes in human and rodent pancreas, islet, liver and kidney by isoform-specific quantitative real-time PCR and compared their expression by the comparative Ct (ΔΔCt) method. We found major changes in the expression profiles of the HNF genes between humans and rodents. The principal difference lies in the expression of the HNF1A gene, which exists as three isoforms in man, but as a single isoform only in rodents. More subtle changes were to the balance of HNF1B and HNF4A isoforms between species; the repressor isoform HNF1B(C) comprised only 6% in human islets compared with 24–26% in rodents (p = 0.006) whereas HNF4A9 comprised 22% of HNF4A expression in human pancreas but only 11% in rodents (p = 0.001).

Conclusions/Significance

The differences we note in the isoform-specific expression of the human and rodent HNF1A, HNF1B and HNF4A genes may impact on the absolute activity of these genes, and therefore on the activity of the pancreatic transcription factor network as a whole. We conclude that alterations to expression of HNF isoforms may underlie some of the phenotypic variation caused by mutations in these genes.

Control of ACAT2 liver expression by HNF4{alpha}: lesson from MODY1 patients

OBJECTIVE

ACAT2 is thought to be responsible for cholesteryl ester production in chylomicron and VLDL assembly. Recently, we identified HNF1alpha as an important regulator of the human ACAT2 promoter. Thus, we hypothesized that MODY3 (HNF1alpha gene mutations) and possibly MODY1 (HNF4alpha, upstream regulator of HNF1alpha, gene mutations) subjects may have lower VLDL esterified cholesterol.

METHODS AND RESULTS

Serum analysis and lipoprotein separation using size-exclusion chromatography were performed in controls and MODY1 and MODY3 subjects. In vitro analyses included mutagenesis and cotransfections in HuH7 cells. Finally, the relevance in vivo of these findings was tested by ChIP assays in human liver. Whereas patients with MODY3 had normal lipoprotein composition, those with MODY1 had lower levels of VLDL and LDL esterified cholesterol, as well as of VLDL triglyceride. Mutagenesis revealed one important HNF4 binding site in the human ACAT2 promoter. ChIP assays and protein-to-protein interaction studies showed that HNF4alpha, directly or indirectly (via HNF1alpha), can bind to the ACAT2 promoter.

CONCLUSIONS

We identified HNF4alpha as an important regulator of the hepatocyte-specific expression of the human ACAT2 promoter. Our results suggest that the lower levels of esterified cholesterol in VLDL- and LDL-particles in patients with MODY1 may-at least in part-be attributable to lower ACAT2 activity in these patients.

Expression of CYP3A23/1, CYP3A2, PXR, CAR and HNF4alpha in large-for-gestational-age neonatal rats

BACKGROUND

The available information about hepatic drug-metabolizing enzymes in the large-for-gestational-age (LGA) neonate is limited.

OBJECTIVE

To determine whether LGA status alters expression of the cytochrome p450 enzymes, CYP3A23/1 and CYP3A2, and nuclear receptors PXR, CAR and HNF4alpha.

METHODS

Appropriate-for-gestational-age (AGA) and LGA pups from 10 litters of rats (n=15 pups/group) were used. Hepatic expression levels of CYP3A23/1, CYP3A2, pregnane X receptor (PXR), constitutive androstane receptor (CAR), and HNF4alpha mRNA were detected by quantitative real-time RT-PCR. Protein expression was determined immunohistochemically and expression levels were evaluated using staining intensity scores and percentage of positive hepatocytes.

RESULTS

The mean body weights of AGA and LGA rat pups were 6.20 +/- 0.49 and 7.77 +/- 0.70 g (mean +/- SD), respectively (P < 0.001). Liver weight/body weight ratios trended higher in the LGA group (5.18 +/- 0.50%, mean +/- SD) than in the AGA group (4.90 +/- 0.01%, mean +/- SD), but the difference was not significant. CYP3A2 mRNA levels were higher in LGA than in AGA pups (P < 0.05), but there were no group differences in CYP3A23/1 mRNA levels. HNF4alpha levels were also higher in the LGA group (P < 0.05), but PXR and CAR mRNA levels did not differ between the groups. The staining intensity and frequency of CYP3A23/1-positive and HNF4alpha-positive hepatocytes differed between LGA and AGA pups, whereas no significant differences in CYP3A2 or CAR protein expression were observed between groups.

CONCLUSIONS

LGA status affects the hepatic expression of CYP3A23/1, CYP3A2, and HNF4alpha, suggesting that further research on this issue is warranted.

Expression of HNF4alpha variants in pancreatic islets and Ins-1 beta cells

BACKGROUND

Hepatocyte nuclear factor (HNF4alpha) is a nuclear receptor essential for endodermal differentiation and cell functions in the adult pancreas, liver, and other tissues. Mutations in the HNF4A gene cause MODY1. Up to nine protein variants arise from two developmentally regulated promoters. Because some variants lack the N-terminal activation function 1 (AF-1) and/or C-terminal inhibitory F domain, defining their tissue-specific regulation and function is important for understanding pancreatic beta cell behaviour.

METHODS

Expression of HNF4alpha variants in islets, rat Ins-1 insulinoma cells, and human Hep3B hepatocellular carcinoma cells was assessed using a long-range reverse transcription-polymerase chain reaction (RT-PCR) strategy capable of recognizing each combination of mRNA termini. Protein expression was verified by immuno-blotting with terminus-specific antibodies and DNA-binding assays.

RESULTS

Mouse islets and both cell lines express HNF4alpha9, which lacks both AF-1 and the F domain. Islets also expressed the HNF4alpha P1 promoter variants HNF4alpha1/alpha2, and Hep3B cells expressed HNF4alpha3. When ectopically expressed in COS-7 cells, HNF4alpha1, alpha3, alpha7, and alpha9 each stimulated an HNF4alpha-dependent promoter. Variants containing exon 1B (HNF4alpha4 - alpha6) were not detected. Lack of canonical splicing signals and species conservation argues against exon 1B usage.

CONCLUSIONS

This is the first report of HNF4alpha9 expression in any tissue. Our findings extend our understanding of HNF4alpha gene transcription and function. This knowledge may be useful in efforts to recover or establish regulated insulin secretion.

Hepatocyte nuclear factor-4 mediates apolipoprotein A-IV transcriptional regulation by fatty acid in newborn swine enterocytes

Hepatocyte nuclear factor-4alpha (HNF-4alpha) regulates transcription of several genes involved in lipid metabolism, including that of apolipoprotein (apo) A-IV, which is tightly regulated by lipid absorption and enhances enterocyte chylomicron secretion. Studies were performed to define the role of HNF-4alpha in the regulation of apo A-IV gene transcription by dietary fatty acid in neonatal swine small intestine. HNF-4alpha mRNA was expressed in liver > intestine > kidney in suckling, weanling, and weaned pigs. Jejunal HNF-4alpha mRNA and protein and apo A-IV and swine microsomal triglyceride transfer protein (MTP) large subunit mRNA expression were induced in parallel in 2-day-old swine by a 24-h high-fat intraduodenal infusion. In IPEC-1 cells, incubation with oleic acid (OA) resulted in coordinate induction of both HNF-4alpha, apo A-IV, and MTP mRNA, similar to that observed in vivo. When HNF-4alpha expression was driven by doxycycline by using the TET-On system in the absence of OA to observe the effect of HNF-4alpha directly on apo A-IV and MTP mRNA levels in the absence of other factors that might be concomitantly induced by fatty acid absorption, apo A-IV and MTP expression were increased. In luciferase reporter gene assays in IPEC-1 cells using apo A-IV/C-III intergenic region constructs, TET-On-regulated HNF-4alpha expression without OA increased luciferase activity, and incubation with OA did not further increase activity. These data suggest that acute induction of the apo A-IV and MTP genes by dietary lipid in newborn intestine occurs, at least in part, via ligand-independent transactivation by HNF-4alpha that is itself induced by a lipid-mediated mechanism.

Expression of constitutive androstane receptor, hepatic nuclear factor 4 alpha, and P450 oxidoreductase genes determines interindividual variability in basal expression and activity of a broad scope of xenobiotic metabolism genes in the human liver

Identification of genetic variation predictive of clearance rate of a wide variety of prescription drugs could lead to cost-effective personalized medicine. Here we identify regulatory genes whose variable expression level among individuals may have widespread effects upon clearance rate of a variety of drugs. Twenty liver samples with variable CYP3A activity were profiled for expression level and activity of xenobiotic metabolism genes as well as genes involved in the regulation thereof. Regulatory genes whose expression level accounted for the highest degree of collinearity among expression levels of xenobiotic metabolism genes were identified as possible master regulators of drug clearance rate. Significant linear correlations (p < 0.05) were identified among mRNA levels of CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, MRP2, OATP2, P450 oxidoreductase (POR), and UDP-glucuronosyltranferase 1A1, suggesting that these xenobiotic metabolism genes are coregulated at the transcriptional level. Using partial regression analysis, constitutive androstane receptor (CAR) and hepatic nuclear factor 4 alpha (HNF4 alpha) were identified as the nuclear receptors whose expression levels are most strongly associated with expression of coregulated xenobiotic metabolism genes. POR expression level, which is also associated with CAR and HNF4 alpha expression level, was found to be strongly associated with the activity of many cytochromes P450. Thus, interindividual variation in the expression level of CAR, HNF4 alpha, and POR probably determines variation in expression and activity of a broad scope of xenobiotic metabolism genes and, accordingly, clearance rate of a variety of xenobiotics. Identification of polymorphisms in these candidate master regulator genes that account for their variable expression among individuals may yield readily detectable biomarkers that could serve as predictors of xenobiotic clearance rate.

Tumour suppressor p53 down-regulates the expression of the human hepatocyte nuclear factor 4alpha (HNF4alpha) gene

The liver is exposed to a wide variety of toxic agents, many of which damage DNA and result in increased levels of the tumour suppressor protein p53. We have previously shown that p53 inhibits the transactivation function of HNF (hepatocyte nuclear factor) 4alpha1, a nuclear receptor known to be critical for early development and liver differentiation. In the present study we demonstrate that p53 also down-regulates expression of the human HNF4alpha gene via the proximal P1 promoter. Overexpression of wild-type p53 down-regulated endogenous levels of both HNF4alpha protein and mRNA in Hep3B cells. This decrease was also observed when HepG2 cells were exposed to UV irradiation or doxorubicin, both of which increased endogenous p53 protein levels. Ectopically expressed p53, but not a mutant p53 defective in DNA binding (R249S), down-regulated HNF4alpha P1 promoter activity. Chromatin immunoprecipitation also showed that endogenous p53 bound the HNF4alpha P1 promoter in vivo after doxorubicin treatment. The mechanism by which p53 down-regulates the P1 promoter appears to be multifaceted. The down-regulation was partially recovered by inhibition of HDAC activity and appears to involve the positive regulator HNF6alpha. p53 bound HNF6alpha in vivo and in vitro and prevented HNF6alpha from binding DNA in vitro. p53 also repressed stimulation of the P1 promoter by HNF6alpha in vivo. However, since the R249S p53 mutant also bound HNF6alpha, binding HNF6alpha is apparently not sufficient for the repression. Implications of the p53-mediated repression of HNF4alpha expression in response to cellular stress are discussed.

Apolipoprotein A-IV is regulated by nutritional and metabolic stress: involvement of glucocorticoids, HNF-4 alpha, and PGC-1 alpha

Apolipoprotein A-IV (apoA-IV) is a 46 kDa glycoprotein that associates with triglyceride-rich and high density lipoproteins. Blood levels of apoA-IV generally correlate with triglyceride levels and are increased in diabetic patients. This study investigated the mechanisms regulating the in vivo expression of apoA-IV in the liver and intestine of mice in response to changes in nutritional status. Fasting markedly increased liver and ileal apoA-IV mRNA and plasma protein concentrations. This induction was associated with increased serum glucocorticoid levels and was abolished by adrenalectomy. Treatment with dexamethasone increased apoA-IV expression in adrenalectomized mice. Marked increases of apoA-IV expression were also observed in two murine models of diabetes. Reporter gene analysis of the murine and human apoA-IV/C-III promoters revealed a conserved cooperative activation by the hepatic nuclear factor-4 alpha (HNF-4 alpha) and the peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1 alpha) but no evidence of a direct regulatory role for the glucocorticoid receptor. Consistent with these in vitro data, induction of apoA-IV in response to fasting was accompanied by increases in HNF-4 alpha and PGC-1 alpha expression and was abolished in liver-specific HNF-4 alpha-deficient mice. Together, these results indicate that the induction of apoA-IV expression in fasting and diabetes likely involves PGC-1 alpha-mediated coactivation of HNF-4 alpha in addition to glucocorticoid-dependent actions.

Expression of endoderm stem cell markers: evidence for the presence of adult stem cells in human thyroid glands

OBJECTIVE

Adult stem cells have been detected in several human tissues. The object of this study was to investigate whether they also occur in the human thyroid gland.

DESIGN

The expression of the stem cell marker Oct- 4 and the early endodermal markers GATA-4 and HNF4alpha was analyzed in histologic slides and cultured cells derived from goiters, in the FRTL5 cell line, and the HTh74, HTC, C643, and XTC133 thyroid carcinoma cell lines.

MAIN OUTCOME

Stem cell markers were detectable in all primary cultures whereas in the differentiated FRTL5 cell line no expression was observed. Expression of stem cell marker mRNA was not affected by thyrotropin (TSH) stimulation and did not decrease when cells underwent several passages. Immunostaining of cultured cells and of histologic slides of goitrous tissues showed only single cells that were immunoreactive for Oct-4, GATA-4, and HNF4a. Expression of Oct-4 but not of endodermal marker GATA-4 was also detectable in some thyroid carcinoma cell lines. Fluorescence-activated cell sorter (FACS) analysis demonstrated cell populations that were positive for either Oct-4, GATA-4, or HNF4alpha but negative for thyroglobulin. When these putative, FACS-sorted stem cell populations were further analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR), expression of all stem cell markers and of Pax8 but not of thyroglobulin mRNA was detectable.

CONCLUSIONS

These data provide evidence for the presence of adult stem and precursor cells of endodermal origin in the human thyroid gland.

Treatment of surgically induced acute liver failure by transplantation of HNF4-overexpressing embryonic stem cells

OBJECTIVE

Tissue-specific stem cells from differentiating embryonic stem (ES) cells are both pluripotent and genetically flexible. Recent observations indicate that ES cells can differentiate into hepatocytes. Therefore, cell-based therapy can potentially be a therapeutic alternative to liver transplantation. In this study the treatment of acute liver failure in rats by transplantation of hepatocyte nuclear factor 4 (HNF4)-overexpressing ES cells was investigated.

METHODS

The HNF4 was transfected into ES cells and ES cell clones overexpressing HNF4 were selected. The levels of markers of hepatocyte differentiation, including albumin, transthyretin, glucose-6-phosphates (G-6-P) and SAPK/ERK kinase-1 (SEK1) mRNA, were tested in spontaneously differentiated HNF4-overexpressing ES cells by reverse transcription-polymerase chain reaction (RT-PCR). The ultrastructure of the spontaneously differentiated HNF4-overexpressing ES cells was examined by electron microscopy. To induce acute liver failure, Sprague-Dawley rats were subjected to 90% hepatectomy and given 5% oral dextrose. The rats were divided into three groups. The rats in the treatment group (n = 12) received intraliver injection of 2 x 10(7) undifferentiated HNF4-overexpressing ES cells from the same clone, the rats in control group 1 (n = 12) received 2 x 10(7) undifferentiated ES cells, and the rats in control group 2 (n = 12) received the same volume of media without any cells.

RESULTS

All rats in control group 1 and control group 2 died within 72 h, while 33% of rats that received undifferentiated HNF4-overexpressing ES cells transplantation survived more than 1 month. Spontaneously differentiated HNF4-overexpressing ES cells only expressed transthyretin mRNA. The cells were rich in mitochondrion and catalase-containing peroxisomes in ultrastructure.

CONCLUSIONS

Transplantation of ES cells could be a potential treatment in supporting life during acute liver insufficiency and could be a bridge to orthotopic liver transplantation.

Functional inhibitory cross-talk between constitutive androstane receptor and hepatic nuclear factor-4 in hepatic lipid/glucose metabolism is mediated by competition for binding to the DR1 motif and to the common coactivators, GRIP-1 and PGC-1alpha

The role of the constitutive androstane receptor (CAR) in xenobiotic metabolism by inducing expression of cytochromes P450 is well known, but CAR has also been implicated in the down-regulation of key genes involved in bile acid synthesis, gluconeogenesis, and fatty acid beta-oxidation by largely unknown mechanisms. Because a key hepatic factor, hepatic nuclear factor-4 (HNF-4), is crucial for the expression of many of these genes, we examined whether CAR could suppress HNF-4 transactivation. Expression of CAR inhibited HNF-4 transactivation of CYP7A1, a key gene in bile acid synthesis, in HepG2 cells, and mutation of the DNA binding domain of CAR impaired this inhibition. Gel shift assays revealed that CAR competes with HNF-4 for binding to the DR1 motif in the CYP7A1 promoter. TCPOBOP, a CAR agonist that increases the interaction of CAR with coactivators, potentiated CAR inhibition of HNF-4 transactivation. Furthermore, inhibition by CAR was reversed by expression of increasing amounts of GRIP-1 or PGC-1alpha, indicating that CAR competes with HNF-4 for these coactivators. Treatment of mice with phenobarbital or TCPOBOP resulted in decreased hepatic mRNA levels of the reported genes down-regulated by CAR, including Cyp7a1 and Pepck. In vivo recruitment of endogenous CAR to the promoters of Cyp7a1 and Pepck was detected in mouse liver after phenobarbital treatment, whereas association of HNF-4 and coactivators, GRIP-1, p300, and PGC-1alpha, with these promoters was significantly decreased. Our data suggest that CAR inhibits HNF-4 activity by competing with HNF-4 for binding to the DR1 motif and to the common coactivators, GRIP-1 and PGC-1alpha, which may be a general mechanism by which CAR down-regulates key genes in hepatic lipid and glucose metabolism.

Functional activity of human hepatoma cells transfected with adenovirus-mediated hepatocyte nuclear factor (HNF)-4 gene

Fulminant hepatic failure (FHF) is still associated with high mortality despite recent advances in medical management. There is need of an effective and safe bioartificial liver (BAL) support to help keep patients with FHF alive until an organ becomes available for transplantation or the native liver recovers. The aim of this study was to establish highly functional liver cells by means of transfecting hepatocyte nuclear factor (HNF)-4 gene for the development of BAL. We constructed adenovirus vector carrying rat HNF-4 cDNA, and transfected to hepatoma-derived cell lines, HepG2 and HuH-7, to enforce expression of the exogenous HNF-4 gene. We analyzed expression of HNF-4, HNF-1, and liver-specific genes in cells infected by the adenovirus vector expressing HNF-4. Adenovirus-mediated HNF-4 gene transfer resulted in increases in expressions of HNF-4, HNF-1, and liver-specific genes such as apolipoproteins, alpha1-antitrypsin (alpha1-AT), phosphoenolpyruvate carboxy-kinase, cytochrome P450 families, and glutamine synthetase in transfected hepatoma cells. Cells overexpressing HNF-4 removed ammonia from medium supplemented with NH4Cl to a greater extent than control cells. These findings demonstrated that transfected cell lines restored differentiated gene expressions and liver-specific function by the overproduction of HNF-4. HNF-4-overexpressing hepatocyte cell lines are useful for bioreactor of BAL systems.

Novel Method to Examine Hepatocyte-Specific Gene Expression in a Functional Coculture System

To mimic native tissue function, coculture systems are an extremely useful model. In many cases, differentiated functions can be maintained only through the interactions of various cell types. Therefore, methods for examining the interactions between cocultured cells are necessary. The assessment of cell-to-cell cross-talk at the level of gene expression is one such method to examine interactions between different cell types. However, it is generally difficult to determine the gene expression of specific cell types in coculture without first separating cell populations. To overcome these obstacles, we have established a novel method to determine gene expression levels of a targeted cell population in coculture, using species-specific primers. With this approach, we were able to determine hepatocyte-specific gene expression of Fao cells (a rat hepatocyte cell line) in culture with human umbilical vein endothelial cells (HUVECs). Expression of both albumin and apolipoprotein A-I (apoA-I) increased time dependently for 10 days and maintained significantly higher expression in the coculture system as compared with isolated Fao cells. This indicates that hepatocyte function increased gradually in our coculture system and could be maintained long-term, suggesting that the construction of mature cell-to-cell communication between the two cell lines required a considerable amount of time. The expression of HNF-4 and HNF-1alpha, which are liver-enriched transcription factors, did not differ between the monolayer and cocultured Fao cells, suggesting that expression of HNF-4 and HNF-1alpha was not responsible for the increased expression albumin and apoA-I. Our findings suggest that this novel method for the detection of gene expression of targeted cell populations can be a useful tool in determining the molecular mechanisms that regulate communication between different cell types.

[Expression of HNF4alpha and HNF6 mRNA during the process of mouse liver development]

OBJECTIVE

To investigate the function of HNF4a and HNF6 during liver development.

METHODS

The expression levels of HNF4alpha and HNF6 at E8, 9, 13, 15, 17, P1 and in adult mouse liver were detected by RT-PCR and in situ hybridization.

RESULTS

RT-PCR results showed that HNF4alpha first expressed at E9, the time of liver bud formation, and lasted through all gestation and existed in adult liver. In situ hybridization showed that the expression of HNF4alpha was detected at the cells of liver cords during various stages of mouse liver development, and there were still a few HNF4alpha positive hepatocytes in adult liver. The cells of bile duct plate and biliary epithelial cells, endothelial cells, hematopoietic cells of liver were negative for HNF4alpha. The expression of HNF6 mRNA was detected in the liver at E9, the time of liver formation onset. Then, HNF6 mRNA disappeared transiently at E13, but it appeared again at E15. Its expression lasted until adult. In situ hybridization studies showed that most liver cord cells were positive for HNF6 at E9 and E15. At E17 and P1, the expression levels of liver cord cells declined, and HNF6 strongly expressed in the cells of bile duct plate and biliary epithelial cells.

CONCLUSION

HNF4alpha could modulate the formation of liver bud, trigger the differentiation of hepatic stem cell towards hepatocytes, and keep the shape of hepatocytes. HNF6 might play a role at the onset of liver development, in the differentiation of hepatic stem cell towards biliary epithelial cells, and in maintaining the morphological characteristic of biliary epithelial cells.