The gene for hepatocyte nuclear factor (HNF)-4alpha is activated by glucocorticoids and glucagon, and repressed by insulin in rat liver

The human glucocorticoid receptor variant rs6190 promotes blood cholesterol and atherosclerosis

Elevated cholesterol poses a significant cardiovascular risk, particularly in older women. The glucocorticoid receptor (GR), a crucial nuclear transcription factor that regulates the metabolism of virtually all major nutrients, harbors a still undefined role in cholesterol regulation. Here, we report that a coding single nucleotide polymorphism (SNP) in the gene encoding the GR, rs6190, associated with increased cholesterol levels in women according to UK Biobank and All Of Us datasets. In SNP-genocopying transgenic mice, we found that the rs6190 SNP enhanced hepatic GR activity to transactivate Pcsk9 and Bhlhe40, negative regulators of low-density lipoprotein (LDL) and high-density lipoprotein (HDL) receptors in liver respectively. Accordingly, in mice the rs6190 SNP was sufficient to elevate circulating cholesterol levels across all lipoprotein fractions and the risk and severity of atherosclerotic lesions on the pro-atherogenic hAPOE*2/*2 background. The SNP effect on atherosclerosis was blocked by in vivo knockdown of Pcsk9 and Bhlhe40 in liver. Remarkably, we found that this mechanism was conserved in human hepatocyte-like cells using CRISPR-engineered, SNP-genocopying human induced pluripotent stem cells (hiPSCs). Taken together, our study leverages a non-rare human variant to uncover a novel GR-dependent mechanism contributing to atherogenic risk, particularly in women.

Amino Acid Catabolism: An Overlooked Area of Metabolism

Amino acids have been extensively studied in nutrition, mainly as key elements for maintaining optimal protein synthesis in the body as well as precursors of various nitrogen-containing compounds. However, it is now known that amino acid catabolism is an important element for the metabolic control of different biological processes, although it is still a developing field to have a deeper understanding of its biological implications. The mechanisms involved in the regulation of amino acid catabolism now include the contribution of the gut microbiota to amino acid oxidation and metabolite generation in the intestine, the molecular mechanisms of transcriptional control, and the participation of specific miRNAs involved in the regulation of amino acid degrading enzymes. In addition, molecules derived from amino acid catabolism play a role in metabolism as they are used in the epigenetic regulation of many genes. Thus, this review aims to examine the mechanisms of amino acid catabolism and to support the idea that this process is associated with the immune response, abnormalities during obesity, in particular insulin resistance, and the regulation of thermogenesis.

Hepatocyte Nuclear Factor 4-α (HNF4α) controls the insulin resistance-induced pancreatic β-cell mass expansion

BACKGROUND

Regardless of the etiology, any type of DM presents a reduction of insulin-secreting cell mass, so it is important to investigate pathways that induce the increase of this cell mass.

AIM

Based on the fact that (1) HNF4α is crucial for β-cell proliferation, (2) DEX-induced IR promotes β-cell mass expansion, and (3) the stimulation of β-cell mass expansion may be an important target for DM therapies, we aimed to investigate whether DEX-induced proliferation of β pancreatic cells is dependent on HNF4α.

METHODS

We used WildType (WT) and Knockout (KO) mice for HNF4-α, treated or not with 100 mg/Kg/day of DEX, for 5 consecutive days. One day after the last injection of DEX the IR was confirmed by ipITT and the mice were euthanized for pancreas removal.

RESULTS

In comparison to WT, KO mice presented increased glucose tolerance, lower fasting glucose and increased glucose-stimulates insulin secretion (GSIS). DEX induced IR in both KO and WT mice. In addition, DEX-induced β-cell mass expansion and an increase in the Ki67 immunostaining were observed only in WT mice, evidencing that IR-induced β-cell mass expansion is dependent on HNF4α. Also, we observed that DEX-treatment, in an HNF4α-dependent way, promoted an increase in PDX1, PAX4 and NGN3 gene expression.

CONCLUSIONS

Our results strongly suggest that DEX-induced IR promotes β-cell mass expansion through processes of proliferation and neogenesis that depend on the HNF4α activity, pointing to HNF4α as a possible therapeutic target in DM treatment.

Liver bioengineering: Recent trends/advances in decellularization and cell sheet technologies towards translation into the clinic

Development of novel technologies provides the best tissue constructs engineering and maximizes their therapeutic effects in regenerative therapy, especially for liver dysfunctions. Among the currently investigated approaches of tissue engineering, scaffold-based and scaffold-free tissues are widely suggested for liver regeneration. Analogs of liver acellular extracellular matrix (ECM) are utilized in native scaffolds to increase the self-repair and healing ability of organs. Native ECM analog could improve liver repairing through providing the supportive framework for cells and signaling molecules, exerting normal biomechanical, biochemical, and physiological signal complexes. Recently, innovative cell sheet technology is introduced as an alternative for conventional tissue engineering with the advantage of fewer scaffold restrictions and cell culture on a Thermo-Responsive Polymer Surface. These sheets release the layered cells through a temperature-controlled procedure without enzymatic digestion, while preserving the cell-ECM contacts and adhesive molecules on cell-cell junctions. In addition, several novelties have been introduced into the cell sheet and decellularization technologies to aid cell growth, instruct differentiation/angiogenesis, and promote cell migration. In this review, recent trends, advancements, and issues linked to translation into clinical practice are dissected and compared regarding the decellularization and cell sheet technologies for liver tissue engineering.

Transcriptional Regulation of the Angptl8 Gene by Hepatocyte Nuclear Factor-1 in the Murine Liver

Brief refeeding times (~60 min) enhanced hepatic Angptl8 expression in fasted mice. We cloned the mouse Angptl8 promoter region to characterise this rapid refeeding-induced increase in hepatic Angptl8 expression. Deletion of the −309/−60 promoter region significantly attenuated basal promoter activity in hepatocytes. A computational motif search revealed a potential binding motif for hepatocyte nuclear factor 1α/1β (HNF-1α/β) at −84/−68 bp of the promoter. Mutation of the HNF-1 binding site significantly decreased the promoter activity in hepatocytes, and the promoter carrying the mutated HNF-1 site was not transactivated by co-transfection of HNF-1 in a non-hepatic cell line. Silencing Hnf-1 in hepatoma cells and mouse primary hepatocytes reduced Angptl8 protein levels. Electrophoretic mobility-shift assays confirmed direct binding of Hnf-1 to its Angptl8 promoter binding motif. Hnf-1α expression levels increased after short-term refeeding, paralleling the enhanced in vivo expression of the Angptl8 protein. Chromatin immunoprecipitation (ChIP) confirmed the recruitment of endogenous Hnf-1 to the Angptl8 promoter region. Insulin-treated primary hepatocytes showed increased expression of Angptl8 protein, but knockdown of Hnf-1 completely abolished this enhancement. HNF-1 appears to play essential roles in the rapid refeeding-induced increases in Angptl8 expression. HNF-1α may therefore represent a primary medical target for ANGPTL8-related metabolic abnormalities. The study revealed the transcriptional regulation of the mouse hepatic Angptl8 gene by HNF-1.

Establishing a model of primary bovine hepatocytes with responsive growth hormone receptor expression

The liver becomes resistant to growth hormone before parturition in dairy cows (uncoupling of the somatotropic axis). However, the mechanism of growth hormone insensitivity has not been fully described. The aim of the present study was to improve a previous model of adult bovine hepatocytes in a sandwich culture system to ensure growth hormone receptor (GHR) expression. First, we modified the protocol for hepatocyte retrieval and tested the effect of short (18 min) and long (up to 30 min) warm ischemia on hepatocyte viability. Second, we used medium additives that affect GHR expression in vivo-insulin (INS), dexamethasone (DEX), both (INS+DEX), or no hormone additives (CTRL)-to ensure the functionality of hepatocytes, as measured by lactate dehydrogenase activity and urea concentration in the medium. We also used reverse transcriptase PCR of hepatocytes to evaluate expression of albumin (ALB), hepatocyte nuclear factor 4α (HNF4A), nuclear factor-κ-B-inhibitor α (NFKBIA), cytosolic phosphoenolpyruvate carboxykinase (PCK1), and vimentin (VIM) mRNA. Moreover, we analyzed the expression of GHRtot (GHR), GHR1A, insulin-like growth factor-1 (IGF1), and IGF binding protein-2 (IGFBP2) in response to exposure to media with the different compositions. Modification of the protocol (changes in rinsing and perfusion times, buffer composition, and the volume and standardization of collagenase) led to increased cell counts and cell viability. Short warm ischemia with the modified protocol significantly increased cell count (4.7 × 10⁷ ± 1.9 × 10⁷ vs. 3.5 × 10⁶ ± 1.5 × 10⁶ vital cells/g of liver) and viability (79.1 ± 8.4 vs. 37.1 ± 8.9%). Therefore, we gathered hepatocytes from the liver after short warm ischemia with the modified protocol. For these hepatocytes, lactate dehydrogenase activity was lower in media with INS and with DEX than in media with INS+DEX or CTRL; urea concentrations were highest at d 4 for INS+DEX. As well, HNF4A and ALB were more highly expressed in hepatocytes cultured with INS and INS+DEX than in those cultured with DEX or CTRL, and the substitution of DEX suppressed VIM and NFKBIA expression but increased PCK1 expression. The expression of GHR, GHR1A, and IGF1 was suppressed by dexamethasone (DEX and INS+DEX), whereas INS distinctly increased GHR, GHR1A, and IGF1 mRNA expression. Hepatocytes in a sandwich culture showed influenceable GHR expression; this study provides a model that can be used in studies examining factors that influence the expression and signal transduction of GHR in dairy cows.

Glucocorticoid receptor regulates organic cation transporter 1 (OCT1, SLC22A1) expression via HNF4α upregulation in primary human hepatocytes

BACKGROUND

Organic cation transporter 1 (OCT1, SLC22A1) is a membrane transporter that is important for therapeutic effect of the antidiabetic drug metformin. Its liver-specific expression in hepatocytes is strongly controlled by hepatocyte nuclear factor-4α (HNF4α). HNF4α expression and transcriptional activity have been demonstrated to be augmented by glucocorticoid receptor (GR) in human hepatocytes and rodent livers.

METHODS

It was examined whether GR activation indirectly induces OCT1 gene expression via HNF4α up-regulation in primary human hepatocytes. We also examined which other transcription factors are involved in OCT1 gene expression and whether they are regulated by dexamethasone using qRT-PCR and gene reporter assays.

RESULTS

We found that dexamethasone significantly up-regulates OCT1 mRNA and protein in normal primary human hepatocytes, but not in hepatocyte-derived tumor cell lines HepG2 and MZ-Hep1. Consistently, we observed that HNF4α is induced by dexamethasone in primary human hepatocytes, but not in hepatocyte tumor-derived cell lines. Viral transduction of MZ-Hep1 cells with the expression constructs for HNF4α, CCAAT/enhancer binding proteins β (C/EBPβ) and peroxisome proliferator-activated receptor-γ coactivator 1α (PGC1α) demonstrated significant roles of the transcription factors in OCT1 gene regulation. We found that expression of OCT1 mRNA in human livers significantly correlates with C/EBPβ and HNF4α mRNAs expression and that C/EBPβ co-transfection stimulates OCT1 gene reporter construct in HepG2 cells. Nevertheless, neither C/EBPβ nor PGC1α were upregulated in human hepatocytes by dexamethasone.

CONCLUSION

We can conclude that GR-induced expression of HNF4α may contribute to indirect OCT1 gene up-regulation by dexamethasone in primary human hepatocytes, but not in hepatocyte-derived tumor cell lines.

Hepatogenic and neurogenic differentiation of bone marrow mesenchymal stem cells from abattoir-derived bovine fetuses

Background

Mesenchymal stem cells (MSC) are multipotent progenitor cells characterized by their ability to both self-renew and differentiate into tissues of mesodermal origin. The plasticity or transdifferentiation potential of MSC is not limited to mesodermal derivatives, since under appropriate cell culture conditions and stimulation by bioactive factors, MSC have also been differentiated into endodermal (hepatocytes) and neuroectodermal (neurons) cells. The potential of MSC for hepatogenic and neurogenic differentiation has been well documented in different animal models; however, few reports are currently available on large animal models. In the present study we sought to characterize the hepatogenic and neurogenic differentiation and multipotent potential of bovine MSC (bMSC) isolated from bone marrow (BM) of abattoir-derived fetuses.

Results

Plastic-adherent bMSC isolated from fetal BM maintained a fibroblast-like morphology under monolayer culture conditions. Flow cytometric analysis demonstrated that bMSC populations were positive for MSC markers CD29 and CD73 and pluripotency markers OCT4 and NANOG; whereas, were negative for hematopoietic markers CD34 and CD45. Levels of mRNA of hepatic genes α-fetoprotein (AFP), albumin (ALB), alpha1 antitrypsin (α1AT), connexin 32 (CNX32), tyrosine aminotransferase (TAT) and cytochrome P450 (CYP3A4) were up-regulated in bMSC during a 28-Day period of hepatogenic differentiation. Functional analyses in differentiated bMSC cultures evidenced an increase (P < 0.05) in albumin and urea production and glycogen storage. bMSC cultured under neurogenic conditions expressed NESTIN and MAP2 proteins at 24 h of culture; whereas, at 144 h also expressed TRKA and PrP^C. Levels of MAP2 and TRKA mRNA were up-regulated at the end of the differentiation period. Conversely, bMSC expressed lower levels of NANOG mRNA during both hepatogenic and neurogenic differentiation processes.

Conclusion

The expression patterns of linage-specific markers and the production of functional metabolites support the potential for hepatogenic and neurogenic differentiation of bMSC isolated from BM of abattoir-derived fetuses. The simplicity of isolation and the potential to differentiate into a wide variety of cell lineages lays the foundation for bMSC as an interesting alternative for investigation in MSC biology and eventual applications for regenerative therapy in veterinary medicine.

Tungstate reduces the expression of gluconeogenic enzymes in STZ rats

Aims

Oral administration of sodium tungstate has shown hyperglycemia-reducing activity in several animal models of diabetes. We present new insights into the mechanism of action of tungstate.

Methods

We studied protein expression and phosphorylation in the liver of STZ rats, a type I diabetes model, treated with sodium tungstate in the drinking water (2 mg/ml) and in primary cultured-hepatocytes, through Western blot and Real Time PCR analysis.

Results

Tungstate treatment reduces the expression of gluconeogenic enzymes (PEPCK, G6Pase, and FBPase) and also regulates transcription factors accountable for the control of hepatic metabolism (c-jun, c-fos and PGC1α). Moreover, ERK, p90rsk and GSK3, upstream kinases regulating the expression of c-jun and c-fos, are phosphorylated in response to tungstate. Interestingly, PKB/Akt phosphorylation is not altered by the treatment. Several of these observations were reproduced in isolated rat hepatocytes cultured in the absence of insulin, thereby indicating that those effects of tungstate are insulin-independent.

Conclusions

Here we show that treatment with tungstate restores the phosphorylation state of various signaling proteins and changes the expression pattern of metabolic enzymes.

Nutritional status affects fluvastatin-induced hepatotoxicity and myopathy in rats

Rats that consumed a high-fat and high-sucrose diet (HF diet) developed hepatic steatosis. Treatment of HF diet-fed rats with fluvastatin (8 mg/kg) was lethal, followed by an elevation in levels of plasma aspartate aminotransferase and creatine kinase activities and skeletal muscle toxicity. This study was conducted to determine whether nutritional status affects statin-induced adverse effects in rats. Fluvastatin treatment of rats fed the HF diet led to an increase in systemic exposure, suggesting altered metabolism and elimination. In fact, although hepatic multidrug resistance-associated protein (Mrp) 2 and multidrug resistance (Mdr) 1b protein levels were not significantly changed by fluvastatin treatment for 8 days of rats fed a HF diet, the organic anion-transporting protein (Oatp) 1, Mrp3, CYP1A, CYP2C, UDP-glucuronosyltransferase (UGT) 1A1, and UGT1A5 protein levels were moderately decreased and the Oatp2, CYP3A, and UGT2B1 protein levels were markedly suppressed. No significant difference in the baseline level of Oatp1, Oatp2, Mrp2, Mrp3, Mdr1b, CYP1A, CYP2C, CYP3A, UGT1A1, UGT1A5, or UGT2B1 protein was found between the standard diet- and HF diet-fed groups. In addition, the mRNA levels of Oatp2, CYP2C11, and CYP3A1/2 were markedly decreased in HF diet-fed and fluvastatin-treated rats. There was no significant difference in the glucuronidation activities against fluvastatin among the four groups. In liver cell nuclei, levels of constitutive androstane receptor, pregnane X receptor, and hepatocyte nuclear factor 4α proteins were decreased in fluvastatin-treated HF diet-fed rats, which correlated with the decrease in Oatp2, CYP2C, and CYP3A. Taken together, these results indicate that nutritional status may influence adverse effects of fluvastatin by increasing systemic exposure through modulation of hepatic uptake and elimination.

Roles of hepatocyte nuclear factors (HNF) in the regulation of reproduction in teleosts

Hepatocyte nuclear factor (HNF) families are composed of liver-enriched transcription factors and upstream regulators of many liver-specific genes. HNF are involved in liver-specific gene expression, metabolism, development, cell growth and many cellular functions in the body. HNF genes can be activated or influenced by several hormones and insulin-like growth factors (IGF), and different combinations of the four HNF factors form a network in controlling the expression of liver-specific or liver-enriched genes. The functions of these factors and their interactions within the gonads of bony fishes, however, are not well understood, and the related literature is scant. Recently, several members of the HNF families have been detected in teleost gonads together with their downstream genes (IGF-I and IGF-II), suggesting that these HNF could be upregulated in vitro by steroid hormones. Thus, the hormone-HNF-IGF-gonad interaction may be an alternative axis in the reproductive mechanism that acts in concert with the conventional hypothalamus-pituitary-gonad pathway. This may help the early development and maturation of the gonad or gamete, sexual maturity or reversion and spawning-regulating mechanisms among fishes to be understood.

In vitro hepatic differentiation of human bone marrow mesenchymal stem cells under differential exposure to liver-specific factors

Recent findings demonstrated that stem cells could be harvested from a patient and used to repair his or her own damaged liver. Additionally, stem cells may be manipulated in vitro to induce hepatic differentiation. The current study aims to determine the differentiation efficacy of various liver-specific factors (hepatocyte growth factor, Insulin-Transferrin-Selenium, dexamethasone, and nicotinamide) used for stem cell differentiation into hepatocyte-like cells. Human mesenchymal stem cells were exposed to different media containing these compounds added individually or in various combinations. Hepatic differentiation was assessed via quantitative reverse transcription-polymerase chain reaction and immunocytochemical staining for stemness or liver-specific genes and proteins, including albumin, cytokeratins 18 and 19, HepPar-1, alpha-fetoprotein, and nestin. In addition, functional tests for glycogen storage, urea production, glucose, and albumin synthesis were also performed. The expression profiles of albumin, alpha-fetoprotein, and cytokeratin 19 demonstrated that when hepatocyte growth factor, nicotinamide, or dexamethasone were added individually, incomplete hepatocyte differentiation was achieved; the obtained cell populations contained progenitors that expressed both hepatic (albumin) and biliary (cytokeratin 19) markers, as well as alpha-fetoprotein. Hepatocyte growth factor and nicotinamide were the factors with the most hepatogenic potential. When all factors were added to the culture, cells exhibited features that closely resembled human adult hepatocytes as determined by their gene expression patterns (albumin, HepPar-1, and alpha-fetoprotein, but not cytokeratin 19) and functional testing. These cells with hepatic function may become important tools for liver transplant procedures, liver development studies, and pharmacologic research.

Characterization of glucocorticoid receptor and hepatocyte nuclear factor 4alpha (HNF4alpha) binding to the hnf4alpha gene in the liver

Hepatocyte nuclear factor 4alpha (HNF4alpha) plays a crucial role in hepatocyte differentiation, liver organogenesis and regulation of liver functions. In mouse liver, HNF4alpha is expressed from two promoters, P1 and P2, the latter being very weakly active and only in the embryo. Previously, using transfection assays we identified an enhancer upstream of P1 that mediates both HNF4alpha transactivation and glucocorticoid induction and showed that HNF4alpha1, originated from P1, represses activity of the P2 promoter, possibly through its indirect recruitment to the promoter. However, glucocorticoid receptor (GR) binding to the enhancer was not shown and HNF4alpha binding to P2, first reported in isolated human hepatocytes, was not confirmed in mouse liver. Here, to analyse glucocorticoid inducibility and auto-regulation of the hnf4alpha gene in the liver, we accurately mapped and quantitatively assessed GR and HNF4alpha binding to enhancer and HNF4alpha recruitment to the P2 promoter using chromatin immunoprecipitation (ChIP) and real-time PCR. We proved that GR binds to enhancer from embryonic day (E) 17.5 onward and HNF4alpha even earlier. We showed that HNF4alpha binds to P2 independently of the activation function (AF) 1 domain in adult liver. We mapped the binding region between -400 and -200 bp upstream of the transcription start site. Although Sp1 binds within this region in vitro, we did not find evidence of a role of this factor in HNF4alpha recruitment. Our results suggest that, in the liver, HNF4alpha expression may be induced by glucocorticoids around birth and positive auto-regulation of the gene may take place early in development. They support a model of P2 repression involving HNF4alpha recruitment to promoter, possibly through interaction with several promoter-bound factors.

Down-regulation of hepatic HNF4alpha gene expression during hyperinsulinemia via SREBPs

Mutations in the coding region of hepatocyte nuclear factor 4alpha (HNF4alpha), and its upstream promoter (P2) that drives expression in the pancreas, are known to lead to maturity-onset diabetes of the young 1 (MODY1). HNF4alpha also controls gluconeogenesis and lipid metabolism in the liver, where the proximal promoter (P1) predominates. However, very little is known about the role of hepatic HNF4alpha in diabetes. Here, we examine the expression of hepatic HNF4alpha in two diabetic mouse models, db/db mice (type 2, insulin resistant) and streptozotocin-treated mice (type 1, insulin deficient). We found that the level of HNF4alpha protein and mRNA was decreased in the liver of db/db mice but increased in streptozotocin-treated mice. Because insulin increases the activity of sterol regulatory element-binding proteins (SREBP)-1c and -2, we also examined the effect of SREBPs on hepatic HNF4alpha gene expression and found that, like insulin, ectopic expression of SREBPs decreases the level of hepatic HNF4alpha protein and mRNA both in vitro in primary hepatocytes and in vivo in the liver of C57BL/6 mice. Finally, we use gel shift, chromatin immunoprecipitation, small interfering RNA, and reporter gene analysis to show that SREBP2 binds the human HNF4alpha P1 promoter and negatively regulates its expression. These data indicate that hyperinsulinemia down-regulates HNF4alpha in the liver through the up-regulation of SREBPs, thereby establishing a link between these two critical transcription factor pathways that regulate lipid and glucose metabolism in the liver. These findings also provide new insights into diabetes-associated complications such as fatty liver disease.

Down-regulation of hepatic nuclear factor 4alpha on expression of human hepatic stimulator substance via its action on the proximal promoter in HepG2 cells

hHSS (human hepatic stimulator substance) stimulates hepatocyte growth. To understand the mechanism controlling hHSS expression, we analysed the proximal promoter activity and identified two regulatory regions (-212/-192 and -152/-132) that were important for transcription in HepG2 cells. Using the luciferase reporter assay, gel-shift experiments and ChIP (chromatin immunoprecipitation), we found that the transcription factors HNF4alpha (hepatocyte nuclear factor 4alpha) and Sp1 (stimulating protein-1) were essential for hHSS promoter activity and could directly bind to regions -209/-204 and -152/-145 respectively. We also confirmed that activation and repression of hHSS transcription induced by Sp1 and HNF4alpha resulted from binding of these factors to these two cis-elements respectively. Overexpression of HNF4alpha led to a dramatic repression of the promoter activity and, in contrast, the activity was markedly elevated by overexpression of Sp1. Furthermore, overexpression of HNF4alpha1, one of the HNF4alpha isoforms, resulted in a dramatic suppression of the promoter activity. Moreover, repression of HNF4alpha expression by siRNA (small interfering RNA) remarkably enhanced the hHSS mRNA level. It has been reported previously that expression of HNF4alpha is functionally regulated by dexamethasone. To further confirm the transcriptional control of HNF4alpha on hHSS, we tested the effect of dexamethasone on hHSS transcription in HepG2 cells. In the present study we have demonstrated that the expression of the hHSS gene was down-regulated at the transcriptional level by dexamethasone in HepG2 cells. A deletion and decoy assay revealed that binding of HNF4alpha to nucleotides -209/-204 was responsible for the suppression of hHSS promoter activity by dexamethasone. Increases in the HNF4alpha-binding activity and expression were simultaneously observed in an electrophoretic mobility-shift assay and Western blot analysis. These results suggested that Sp1 activates hHSS basal expression, but HNF4alpha inhibits hHSS gene expression.

Effect of berberine on expression of hepatocyte nuclear factor-4alpha in rats with fructose-induced insulin resistance

The effects of berberine on the expression of hepatocyte nuclear factor-4alpha (HNF-4alpha) in liver of rats with fructose-induced insulin resistance and the molecular mechanism of berberine preventing insulin resistance were investigated. The experimental animals were divided into two groups of 16 animals each. The control group received a control routine diet containing 60% carbohydrate, and the study group a high-fructose diet containing 60% fructose as the sole source of carbohydrate. At the end of 6 weeks these were each subdivided into two groups. One was administered with berberine [187.5 mg/(kg x d) in 5 g/L carboxymethyl cellulose] by intragastric intubation and the other group was treated with a vehicle (5 g/L carboxymethyl cellulose). The rats were fed on the same dietary regimen for the next 4 weeks. After the experimental period of 10 weeks, plasma glucose, insulin and triglyceride levels were measured. HOMA insulin resistance index (HOMA-IR) was assayed. Immunohistochemistry, semiquantitative RT-PCR and western blot were used to detect the expression of HNF-4alpha in liver. Compared with control diet, fructose feeding induced hyperinsulinemia, HOMA-IR and increased triglyceride (all P<0.01). Berberine prevented the rise in plasma insulin (P<0.01), HOMA-IR (P<0.01) and triglyceride (P<0.05) in the fructose-fed rats. No change in plasma glucose was seen among these groups. The mRNA and protein expression of HNF-4alpha was decreased in the fructose-fed rats, but berberine could promote its expression. It was concluded that berberine could prevent fructose-induced insulin resistance in rats possibly by promoting the expression HNF-4alpha in liver.

Dexamethasone exposure of neonatal rats modulates biliary lipid secretion and hepatic expression of genes controlling bile acid metabolism in adulthood without interfering with primary bile acid kinetics

Literature suggests that glucocorticoid (GC) exposure during early life may have long-term consequences into adult life. GCs are known to influence hepatic bile acid synthesis and their transport within the enterohepatic circulation. This study addresses effects of early postnatal exposure to GC on hepatic expression of key genes in bile acid metabolism and bile acid kinetics in adult rats. Male rats were treated with either dexamethasone (DEX) or saline at days 1-3 d after birth. Liver tissue and blood were collected from 2 d to 50 wk of age. Bile acid kinetics were determined at week 8. DEX acutely induced hepatic mRNA levels of cholesterol 7alpha-hydroxylase (Cyp7a1), cholesterol 27-hydroxylase (Cyp27), and in particular sterol 12alpha-hydroxylase (Cyp8b1), whereas expression of the bile acid transporters bile salt export pump (Bsep) and sodium taurocholate cotransporting polypeptide (Ntcp) was moderately affected. Neonatal DEX administration led to increased bilary lipid secretion, decreased Cyp8B1 mRNA expression and a 3-fold higher Cyp7a1/Cyp8b1 mRNA ratio in rats at week 8 compared with age-matched controls without alterations in bile acid kinetics. Therefore, neonatal DEX administration causes altered gene expressions later in life that are not translated into quantitative changes in bile acid kinetics.

Expression of hepatic UDP-glucuronosyltransferase 1A1 and 1A6 correlated with increased expression of the nuclear constitutive androstane receptor and peroxisome proliferator-activated receptor alpha in male rats fed a high-fat and high-sucrose diet

Rats that consumed a high-fat and high-sucrose (HF1) diet or a high-fat (HF2) diet developed hepatic steatosis. The alteration in nutritional status affected hepatic cytochrome P450 and UDP-glucuronosyltransferase (UGT) levels. Messenger RNA and protein levels of UGT1A1 and UGT1A6 in the liver but not the jejunum were increased in male rats fed the HF1 diet. These protein levels did not increase in HF2-fed male rats or HF1-fed female rats. In contrast, the CYP1A2 protein level was decreased in the HF1 but not HF2 diet group, whereas CYP2E1 and CYP4A protein levels were elevated in the HF2 but not HF1 diet group. No significant difference in the organic anion transporter polypeptide (Oatp) 1, Oatp2, multidrug resistance-associated protein (Mrp) 2, or Mrp3 protein levels was found between the standard and HF1 diet groups of male rats. Consumption of the HF1 diet affected the in vivo metabolism of acetaminophen (APAP) such that the area under the APAP-glucuronide plasma concentration-time curve was elevated 2.1-fold in male rats but not female rats. In liver cell nuclei of male rats but not female rats, constitutive androstane receptor (CAR) and proliferator-activated receptor alpha (PPARalpha) protein levels were significantly enhanced by intake of the HF1 diet. Additionally, administration of the PPARalpha agonist clofibrate to male rats up-regulated UGT1A1 and UGT1A6 and down-regulated CYP1A2 in the liver. Taken together, these results indicate that nutritional status may gender-specifically influence the expression and activation of CAR and PPARalpha in liver cell nuclei, and this effect appears to be associated with alterations in UGT1A1 and UGT1A6 expression.

Expression of the hepatic specific V1 messenger ribonucleic acid of the human growth hormone receptor gene is regulated by hepatic nuclear factor (HNF)-4alpha2 and HNF-4alpha8

Human (h) GH plays an essential role in growth and metabolism, and its effectiveness is modulated by the availability of its specific receptor [hGH receptor (hGHR)] on target cells. The hGHR gene has a complex 5'-regulatory region containing multiple first exons. Seven are clustered within two small regions: V2,V3,V9 (module A) and V1,V4,V7,V8 (module B). Module A-derived mRNAs are ubiquitously expressed whereas those from module B are only found in postnatal liver, suggesting developmental- and liver-specific regulation of module B hGHR gene expression. To characterize the elements regulating module B activity, we studied a 1.8-kb promoter of the highest expressing exon in liver, V1. This promoter was repressed in transfection assays; however, either 5'- or 3'-deletions relieved this, suggesting the presence of multiple negative regulatory elements. Six putative hepatic nuclear factor 4 (HNF-4) response elements were identified. We determined that HNF-4alpha is developmentally regulated in the human liver: HNF-4alpha2 and HNF-4alpha8 are expressed in fetal hepatocytes but only HNF-4alpha2 is expressed in postnatal liver. Transient transfection assays demonstrated that HNF-4alpha2 and HNF-4alpha8 have a similar dual effect on V1 transcription: activation via site 1 in the proximal promoter and repression through site 6, approximately 1.7 kb upstream. EMSA/electrophoretic mobility supershift assays and chromatin immunoprecipitation analyses confirmed these two sites are bound by HNF-4alpha. Based on these data, we speculate there are multiple regions working together to repress the expression of V1 hGHR transcripts in tissues other than the normal postnatal liver, and that HNF-4alpha is a good candidate for regulating V1 hGHR expression in the human hepatocyte.

Steroid hormones (17β-estradiol and hydrocortisone) upregulate hepatocyte nuclear factor (HNF)-3β and insulin-like growth factors I and II expression in the gonads of tilapia (Oreochromis mossambicus) in vitro

Hepatocyte nuclear factors (HNF-1alpha, -1beta and -3beta) and insulin-like growth factors (IGF-I and -II), which are involved in liver-specific gene expression, metabolism, development and cell growth, have been found in the gonads of tilapia (Oreochromis mossambicus). However, the functions of these factors and how they interact within the gonads of bony fish are not understood. In the present study, we provided experimental evidence that the expression of HNF-3beta in the gonads of tilapia, but not HNF-1alpha and -1beta, was affected in vitro by 17beta-estradiol and hydrocortisone. Immunohistochemical staining confirmed that tilapia HNF-3beta was mainly found in the nuclei of hepatocytes, the follicular granulosa cells of the ovaries, and the interstitial cells of the testes of adult tilapia. Further data were gathered at various steroid concentrations (0.1, 1, 10, 100, and 1000 nM) over various culture intervals (6, 12, 18, 24, 30, and 36 h) and subjected to semi-quantitative RT-PCR analysis. The expression of downstream genes (IGF-I and -II) followed the same temporal patterns as HNF-3beta, albeit at decreased levels for 30 and 36 h culture intervals. Both hormones upregulated HNF-3beta mRNA expression at concentrations of 0.1-10 nM, and reached optimal physiological concentrations for induction of IGFs at 1-10 nM. The identity of the PCR fragments was concurrently verified by sequencing and PCR-Southern hybridization. We inferred that HNF-3beta and IGFs may play a regulatory role in tilapia gonads during oocyte maturation and spermatogenesis.

Transcriptional regulation by insulin: from the receptor to the gene

Insulin, after binding to its receptor, regulates many cellular processes and the expression of several genes. For a subset of genes, insulin exerts a negative effect on transcription; for others, the effect is positive. Insulin controls gene transcription by modifying the binding of transcription factors on insulin-response elements or by regulating their transcriptional activities. Different insulin-signaling cascades have been characterized as mediating the insulin effect on gene transcription. In this review, we analyze recent data on the molecular mechanisms, mostly in the liver, through which insulin exerts its effect. We first focus on the key transcription factors (viz. Foxo, sterol-response-element-binding protein family (SREBP), and Sp1) involved in the regulation of gene transcription by insulin. We then present current information on the way insulin downregulates and upregulates gene transcription, using as examples of downregulation phosphoenolpyruvate carboxykinase (PEPCK) and insulin-like growth factor binding protein 1 (IGFBP-1) genes and of upregulation the fatty acid synthase and malic enzyme genes. The last part of the paper focuses on the signaling cascades activated by insulin in the liver, leading to the modulation of gene transcription.

Dietary inulin alleviates hepatic steatosis and xenobiotics-induced liver injury in rats fed a high-fat and high-sucrose diet: association with the suppression of hepatic cytochrome P450 and hepatocyte nuclear factor 4alpha expression

Inulin enzymatically synthesized from sucrose is a dietary component that completely escapes glucide digestion. Supplementing inulin to a high-fat and high-sucrose diet (HF) ameliorated hypertriglycemia and hepatic steatosis in 8-week-fed rats by suppressing elevated levels of serum triacylglycerols, fatty acids, and glucose, and the accumulation of hepatic triacylglycerols and fatty acids. Inulin intake prevented phenobarbital (PB)- and dexamethasone-induced liver injuries in the HF group. No significant alteration in the baseline expression of CYP2B, CYP2C11, CYP3A, and NADPH-cytochrome P450 (P450) reductase mRNAs and proteins was found. In contrast, baseline and PB-treated expressions of CYP2E1 mRNA were reduced in HF-fed rats. The induction of P450s in response to PB was affected by the nutritional status of the rats; mRNA levels of CYP2B1 and CYP3A1 after PB treatment, as assessed by quantitative real-time polymerase chain reaction analysis were reduced in the inulin-supplemented HF (HF+I) group, compared with those in the HF group. Western blot analysis detected the corresponding changes of CYP2B and CYP3A proteins. These alterations were correlated with changes in hepatic thiobarbituric acid-reactive substances. Furthermore, no significant difference in the expression of nuclear receptors constitutive androstane receptor, pregnane X receptor, and retinoid X receptor alpha and coactivator peroxisome proliferator-activated receptor-gamma coactivator 1alpha proteins was found in the hepatic nucleus between the HF and HF+I groups, but the expression of hepatocyte nuclear factor alpha (HNF4alpha) protein was significantly reduced in the HF+I group. Taken together, these results indicate that inulin intake ameliorates PB-induced liver injury, associated with a decline in lipid accumulation and PB-induced expression of CYP2B and CYP3A, which may be related by a reduction in the nuclear expression of HNF4alpha.

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.

Nuclear factor 1 family members interact with hepatocyte nuclear factor 1alpha to synergistically activate L-type pyruvate kinase gene transcription

Transcription of hepatic L-type pyruvate kinase (L-PK) gene is cell type-specific and is under the control of various nutritional conditions. The L-PK gene contains multiple cis-regulatory elements located within a 170-bp upstream region necessary for these regulations. These elements can synergistically stimulate L-PK gene transcription, although their mechanisms are largely unknown. Because nuclear factor (NF) 1 family members bind to specific cis-regulatory elements known as L-IIA and L-IIB and hepatocyte nuclear factor (HNF) 1alpha binds to the adjacent element L-I, we examined the functional and physical interactions between these two transcription factors. Reporter gene assay showed that these two factors synergistically activated the L-PK promoter containing the 5'-flanking region up to -189. Although two NF1-binding sites are required for the maximum synergistic effect of NF1 family members with HNF1alpha, significant functional interaction between the two factors was observed in the L-PK promoter containing two mutated NF1-binding sites and also in the promoter containing only the HNF1alpha-binding site, raising the possibility that NF1 proteins function as HNF1alpha co-activators. Chromatin immunoprecipitation assay revealed that both NF1 proteins and HNF1alpha bound to the promoter region of the L-PK gene in vivo. In vitro binding assay confirmed that NF1 proteins directly interacted mainly with the homeodomain of HNF1alpha via their DNA-binding domains. This interaction enhanced HNF1alpha binding to the L-I element and was also observed in rat liver by co-immunoprecipitation assay. Thus, we conclude that cooperative interaction between NF1 family members and HNF1alpha plays an important role in hepatic L-PK transcription.

Gonadal dysfunction in systemic diseases

Gonadal function is significantly affected in many acute and chronic systemic diseases. As the function of the testes and the ovaries is determined by the integrity of the hypothalamic-pituitary-gonadal axis, it is obvious that a systemic disease may affect one or more levels of the axis in such a manner that the gonadal dysfunction may have various clinical and laboratory manifestations. In this brief review, the most common disturbances seen in the main systemic diseases will be discussed.

An mRNA amplification procedure with directional cDNA cloning and strand-specific cRNA synthesis for comprehensive gene expression analysis

We developed an integrated system suitable for comprehensive gene expression studies including construction and analysis of cDNA microarrays starting from a small amount of mRNA. We amplified total mRNA first as cDNA mixtures by polymerase chain reaction and then as strand-specific cRNA mixtures by in vitro transcription. These amplified cDNA and cRNA enabled determination of mRNA levels by hybridization analyses such as Southern, Northern, reverse-Northern macroarray, and cDNA microarray analyses, as well as construction of the cDNA library with a unidirectional cDNA insert. By using strand-specific cRNA derived from rat primary-cultured hepatocytes, we detected putative antisense transcripts for the metallothionein gene. cDNA microarray analysis for genes regulated by glucocorticoids and glucagon in the hepatocytes revealed that a number of genes involved in signal transduction and transcriptional regulation were up- or down-regulated. The present system is widely applicable to gene expression analysis with limited amounts of RNA samples.

Phenobarbital responsiveness as a uniquely sensitive indicator of hepatocyte differentiation status: requirement of dexamethasone and extracellular matrix in establishing the functional integrity of cultured primary rat hepatocytes

We used a serum-free, highly defined primary hepatocyte culture model to investigate the mechanisms whereby dexamethasone (Dex) and extracellular matrix (ECM) coordinate cell differentiation and transcriptional responsiveness to the inducer, phenobarbital (PB). Low nanomolar levels of Dex and dilute concentrations of ECM overlay were essential in the maintenance of normal hepatocyte physiology, as assessed by cell morphology, LDH release, expression of the hepatic nuclear factors C/EBPalpha, -beta, -gamma, HNF-1alpha, -1beta, -4alpha, and RXRalpha, expression of prototypical hepatic marker genes, including albumin and transferrin, and ultimately, cellular capacity to respond to PB. The loss of hepatocyte integrity produced by deficiency of these components correlated with the activation of several stress signaling pathways including the MAPK, SAPK/JNK, and c-Jun signaling pathways, with resulting nuclear recruitment of the activated protein-1 (AP-1) complex. In Dex-deficient cultures, normal cellular function, including the PB induction response, was largely restored in a dose-dependent manner by reintroduction of nanomolar additions of the hormone, in the presence of ECM. Our results demonstrate critical and cooperative roles for Dex and ECM in establishing hepatocyte integrity and in the coordination of an array of liver-specific functions. These studies further establish the PB gene induction response as an exceptionally sensitive indicator of hepatocyte differentiation status.

Hepatocyte nuclear factor-4 is a novel downstream target of insulin via FKHR as a signal-regulated transcriptional inhibitor

Previous studies have shown that FKHR, a member of the forkhead family of transcription factors, acts as a DNA binding-independent cofactor of nuclear receptors, including estrogen, retinoid, and thyroid hormone receptors, in addition to the original function as a DNA binding transcription factor that redistributes from the nucleus to the cytoplasm by insulin-induced phosphorylation. Here, we demonstrated the physical interaction of FKHR with hepatocyte nuclear factor (HNF)-4, a member of steroid/thyroid nuclear receptor superfamily, and the repression of HNF-4 transactivation by FKHR. FKHR interacted with the DNA binding domain of HNF-4 and inhibited HNF-4 binding to the cognate DNA. Furthermore, the binding affinity of HNF-4 with phosphorylated FKHR significantly decreased in comparison to that with unphosphorylated FKHR. Therefore, a phosphorylation of FKHR by insulin followed by its dissociation from HNF-4 and the redistribution of FKHR from the nucleus to the cytoplasm would expect to induce the transcriptional activation of HNF-4 by facilitating to the access of HNF-4 to its DNA element. Indeed, most intriguingly, insulin stimulation reversed the repression of HNF-4 transcriptional activity by phosphorylation-sensitive (wild-type) FKHR, but not by phosphorylation-deficient FKHR. These results suggest that insulin regulates the transcriptional activity of HNF-4 via FKHR as a signal-regulated transcriptional inhibitor.

Hepatocyte nuclear factors-1alpha, -1beta, and -3beta expressed in the gonad of tilapia (Oreochromis mossambicus)

Hepatocyte nuclear factors (HNFs) are upstream regulators of many liver-specific genes and are involved in many cellular functions in the body, but their existence, expression, and function in gonads are still poorly understood. Here we report on the first cloning of partial cDNAs of HNF-1alpha and -1beta and full HNF-3beta cDNA from a tilapia (Oreochromis mossambicus) liver cDNA library. The deduced amino acid sequence of tilapia HNF-3beta has a 90 to 96% identity with those of other fishes (dwarf gourami, medaka, and zebrafish), 74% with mammals (human, rat, and mouse), and 82% with Xenopus. RT-PCR detected IGF-I and -II and HNF-1alpha, -1beta, and -3beta in both liver and gonads and the identity of the PCR fragments was confirmed by PCR hybridization. Immunoprecipitation and Western blotting also detected all three HNF proteins in both liver and gonads. Expression of HNFs in the gonads of the tilapia suggests that multi-HNFs may form a cascade to regulate gonadal physiology in the bony fish.

Nitric oxide-induced apoptosis in pancreatic beta cells is mediated by the endoplasmic reticulum stress pathway

Excessive nitric oxide (NO) production in cytokine-activated beta cells has been implicated in beta cell disruption in type 1 diabetes. beta cells are very vulnerable to NO-induced apoptosis. However, the mechanism underlying this phenomenon is unclear. Low concentrations of NO that lead to apoptosis apparently do not cause severe DNA damage in mouse MIN6 beta cells. CHOP, a C/EBP homologous protein that is induced by endoplasmic reticulum (ER) stress and plays a role in growth arrest and cell death, was induced by a NO donor, S-nitroso-N-acetyl-D,L-penicillamine (SNAP). SNAP increased cytosolic Ca(2+), and only agents depleting ER Ca(2+) induced CHOP expression and led to apoptosis, suggesting that NO depletes ER Ca(2+). Overexpression of calreticulin increased the Ca(2+) content of ER and afforded protection to cells against NO-mediated apoptosis. Furthermore, pancreatic islets from CHOP knockout mice showed resistance to NO. We conclude that NO depletes ER Ca(2+), causes ER stress, and leads to apoptosis. Thus, ER Ca(2+) stores are a new target of NO, and the ER stress pathway is a major mechanism of NO-mediated beta cell apoptosis.

An enhancer element 6 kb upstream of the mouse HNF4alpha1 promoter is activated by glucocorticoids and liver-enriched transcription factors

We have characterized a 700 bp enhancer element around -6 kb relative to the HNF4alpha1 transcription start. This element increases activity and confers glucocorticoid induction to a heterologous as well as the homologous promoters in differentiated hepatoma cells and is transactivated by HNF4alpha1, HNF4alpha7, HNF1alpha and HNF1beta in dedifferentiated hepatoma cells. A 240 bp sub-region conserves basal and hormone-induced enhancer activity. It contains HNF1, HNF4, HNF3 and C/EBP binding sites as shown by DNase I footprinting and electrophoretic mobility shift assays using nuclear extracts and/or recombinant HNF1alpha and HNF4alpha1. Mutation analyses showed that the HNF1 site is essential for HNF1alpha transactivation and is required for full basal enhancer activity, as is the C/EBP site. Glucocorticoid response element consensus sites which overlap the C/EBP, HNF4 and HNF3 sites are crucial for optimal hormonal induction. We present a model that accounts for weak expression of HNF4alpha1 in the embryonic liver and strong expression in the newborn/adult liver via the binding sites identified in the enhancer.

Coinduction of endothelial nitric oxide synthase and arginine recycling enzymes in aorta of diabetic rats

Decreased availability of arginine and impaired production of NO (nitric oxide) have been implicated in the development of endothelial dysfunction. Citrulline formed by the NOS reaction is recycled to arginine by the citrulline-NO cycle, which is composed of NOS, argininosuccinate synthetase (AS), and argininosuccinate lyase. Therefore, we investigated the alterations of these enzymes in the aorta of streptozotocin (STZ)-induced diabetic rats. eNOS and AS mRNAs were increased by three- to fourfold 1-2 weeks after STZ treatment and decreased at 4 weeks. AL mRNA was weakly induced. Induction of eNOS and AS proteins was also observed. Cationic amino acid transporter (CAT)-1 mRNA remained little changed, and CAT-2 mRNA was not detected. The plasma nitrogen oxide levels were increased 1-2 weeks after STZ treatment and decreased at 4 weeks. Transforming growth factor-beta1 (TGF-beta1) mRNA in the aorta was also induced. TGF-beta1 induced eNOS and AS mRNAs in human umbilical vein endothelial cells but inhibited the proliferation of HUVEC. These results indicate that eNOS and AS are coinduced in the aorta in early stages of STZ-induced diabetic rats and that the induction is mediated by TGF-beta1. The results also suggest that TGF-beta1 works antiatherogenically at early stages of diabetes by increasing NO production, whereas prolonged elevation of TGF-beta1 functions atherogenically by inhibiting endothelial cell growth.