Genetic evidence that HNF-1alpha-dependent transcriptional control of HNF-4alpha is essential for human pancreatic beta cell function

Feeding during hibernation shifts gene expression toward active season levels in brown bears (Ursus arctos)

Hibernation in bears involves a suite of metabolical and physiological changes, including the onset of insulin resistance, that are driven in part by sweeping changes in gene expression in multiple tissues. Feeding bears glucose during hibernation partially restores active season physiological phenotypes, including partial resensitization to insulin, but the molecular mechanisms underlying this transition remain poorly understood. Here, we analyze tissue-level gene expression in adipose, liver, and muscle to identify genes that respond to midhibernation glucose feeding and thus potentially drive postfeeding metabolical and physiological shifts. We show that midhibernation feeding stimulates differential expression in all analyzed tissues of hibernating bears and that a subset of these genes responds specifically by shifting expression toward levels typical of the active season. Inferences of upstream regulatory molecules potentially driving these postfeeding responses implicate peroxisome proliferator-activated receptor gamma (PPARG) and other known regulators of insulin sensitivity, providing new insight into high-level regulatory mechanisms involved in shifting metabolic phenotypes between hibernation and active states.

HNF1A Mutations and Beta Cell Dysfunction in Diabetes

Understanding the genetic factors of diabetes is essential for addressing the global increase in type 2 diabetes. HNF1A mutations cause a monogenic form of diabetes called maturity-onset diabetes of the young (MODY), and HNF1A single-nucleotide polymorphisms are associated with the development of type 2 diabetes. Numerous studies have been conducted, mainly using genetically modified mice, to explore the molecular basis for the development of diabetes caused by HNF1A mutations, and to reveal the roles of HNF1A in multiple organs, including insulin secretion from pancreatic beta cells, lipid metabolism and protein synthesis in the liver, and urinary glucose reabsorption in the kidneys. Recent studies using human stem cells that mimic MODY have provided new insights into beta cell dysfunction. In this article, we discuss the involvement of HNF1A in beta cell dysfunction by reviewing previous studies using genetically modified mice and recent findings in human stem cell-derived beta cells.

Role of Actionable Genes in Pursuing a True Approach of Precision Medicine in Monogenic Diabetes

Monogenic diabetes is a genetic disorder caused by one or more variations in a single gene. It encompasses a broad spectrum of heterogeneous conditions, including neonatal diabetes, maturity onset diabetes of the young (MODY) and syndromic diabetes, affecting 1-5% of patients with diabetes. Some of these variants are harbored by genes whose altered function can be tackled by specific actions ("actionable genes"). In suspected patients, molecular diagnosis allows the implementation of effective approaches of precision medicine so as to allow individual interventions aimed to prevent, mitigate or delay clinical outcomes. This review will almost exclusively concentrate on the clinical strategy that can be specifically pursued in carriers of mutations in "actionable genes", including ABCC8, KCNJ11, GCK, HNF1A, HNF4A, HNF1B, PPARG, GATA4 and GATA6. For each of them we will provide a short background on what is known about gene function and dysfunction. Then, we will discuss how the identification of their mutations in individuals with this form of diabetes, can be used in daily clinical practice to implement specific monitoring and treatments. We hope this article will help clinical diabetologists carefully consider who of their patients deserves timely genetic testing for monogenic diabetes.

Disruption of Tumor Suppressors HNF4α/HNF1α Causes Tumorigenesis in Liver

The hepatocyte nuclear factor-4α (HNF4α) and hepatocyte nuclear factor-1α (HNF1α) are transcription factors that influence the development and maintenance of homeostasis in a variety of tissues, including the liver. As such, disruptions in their transcriptional networks can herald a number of pathologies, such as tumorigenesis. Largely considered tumor suppressants in liver cancer, these transcription factors regulate key events of inflammation, epithelial-mesenchymal transition, metabolic reprogramming, and the differentiation status of the cell. High-throughput analysis of cancer cell genomes has identified a number of hotspot mutations in HNF1α and HNF4α in liver cancer. Such results also showcase HNF1α and HNF4α as important therapeutic targets helping us step into the era of personalized medicine. In this review, we update current findings on the roles of HNF1α and HNF4α in liver cancer development and progression. It covers the molecular mechanisms of HNF1α and HNF4α dysregulation and also highlights the potential of HNF4α as a therapeutic target in liver cancer.

Decreased GLUT2 and glucose uptake contribute to insulin secretion defects in MODY3/HNF1A hiPSC-derived mutant β cells

Heterozygous HNF1A gene mutations can cause maturity onset diabetes of the young 3 (MODY3), characterized by insulin secretion defects. However, specific mechanisms of MODY3 in humans remain unclear due to lack of access to diseased human pancreatic cells. Here, we utilize MODY3 patient-derived human induced pluripotent stem cells (hiPSCs) to study the effect(s) of a causal HNF1A^+/H126D mutation on pancreatic function. Molecular dynamics simulations predict that the H126D mutation could compromise DNA binding and gene target transcription. Genome-wide RNA-Seq and ChIP-Seq analyses on MODY3 hiPSC-derived endocrine progenitors reveal numerous HNF1A gene targets affected by the mutation. We find decreased glucose transporter GLUT2 expression, which is associated with reduced glucose uptake and ATP production in the MODY3 hiPSC-derived β-like cells. Overall, our findings reveal the importance of HNF1A in regulating GLUT2 and several genes involved in insulin secretion that can account for the insulin secretory defect clinically observed in MODY3 patients.

Heterozygous HNF1A mutations can give rise to maturity onset diabetes of the young 3 (MODY3), characterized by insulin secretion defects. Here the authors show that MODY3-related HNF1A mutation in patient hiPSCderived pancreatic cells decreases glucose transporter GLUT2 expression due to compromised DNA binding.

Neonatal diabetes mutations disrupt a chromatin pioneering function that activates the human insulin gene

Despite the central role of chromosomal context in gene transcription, human noncoding DNA variants are generally studied outside of their genomic location. This limits our understanding of disease-causing regulatory variants. INS promoter mutations cause recessive neonatal diabetes. We show that all INS promoter point mutations in 60 patients disrupt a CC dinucleotide, whereas none affect other elements important for episomal promoter function. To model CC mutations, we humanized an ∼3.1-kb region of the mouse Ins2 gene. This recapitulated developmental chromatin states and cell-specific transcription. A CC mutant allele, however, abrogated active chromatin formation during pancreas development. A search for transcription factors acting through this element revealed that another neonatal diabetes gene product, GLIS3, has a pioneer-like ability to derepress INS chromatin, which is hampered by the CC mutation. Our in vivo analysis, therefore, connects two human genetic defects in an essential mechanism for developmental activation of the INS gene.

Associations of novel variants in PIK3C3, INSR and MAP3K4 of the ATM pathway genes with pancreatic cancer risk

The ATM serine/threonine kinase (ATM) pathway plays important roles in pancreatic cancer (PanC) development and progression, but the roles of genetic variants of the genes in this pathway in the etiology of PanC are unknown. In the present study, we assessed associations between 31,499 single nucleotide polymorphisms (SNPs) in 198 ATM pathway-related genes and PanC risk using genotyping data from two previously published PanC genome-wide association studies (GWASs) of 15,423 subjects of European ancestry. In multivariable logistic regression analysis, we identified three novel independent SNPs to be significantly associated with PanC risk [PIK3C3 rs76692125 G>A: odds ratio (OR)=1.26, 95% confidence interval (CI)=1.12-1.43 and P=2.07×10^-4, INSR rs11668724 G>A: OR=0.89, 95% CI=0.84-0.94 and P=4.21×10^-5 and MAP3K4 rs13207108 C>T: OR=0.83, 95% CI=0.75-0.92, P=2.26×10^-4]. The combined analysis of these three SNPs exhibited an increased PanC risk in a dose-response manner as the number of unfavorable genotypes increased (P _trend<0.0001). The risk-associated rs76692125 A allele was correlated with decreased PIK3C3 mRNA expression levels, while the protective-associated rs11668724 A allele was correlated with increased INSR mRNA expression levels, but additional mechanistic studies of these SNPs are warranted. Once validated, these SNPs may serve as biomarkers for PanC risk in populations of European ancestry.

Association Analysis of the HNF4A Common Genetic Variants with Type 2 Diabetes Mellitus Risk

Type 2 diabetes mellitus (T2DM) is a complex disease that involves a wide range of genetic and environmental factors. The hepatocyte nuclear factor (HNF4A) carries out hepatic gluconeogenesis regulation and insulin secretion crucially, and the corresponding gene was shown to be linked to T2DM in several studies. The aim of the present study was to evaluate the association between HNF4A genetic variants (rs1884613 and rs1884614) and T2DM risk in a group of Iranian patients. This case-control study included 100 patients with T2DM and 100 control subjects. Genotyping of two single nucleotide polymorphisms (SNPs) (rs1884613 and rs1884614) of HNF4A was performed using the sequencing method. There was no statistically significant difference for allele and genotype distribution of the HNF4A common variants (rs1884613 and rs1884614) between subjects with and without T2DM (P=0.9 and P=0.9, respectively). Regarding diabetic complications, although the presence of mentioned polymorphisms increased the odds of developing ophthalmic complications and reduction of the odds of renal complications among diabetic patients, the mentioned risk was non- significant and cannot be generalized to the whole population.  It seems that rs1884613 and rs1884614 polymorphisms are not associated with T2DM or its renal and ophthalmic complications. To investigate the precise influence of these polymorphisms, prospective cohorts with larger sample sizes are required.

Type 2 Diabetes-Associated Genetic Polymorphisms as Potential Disease Predictors

Diabetes is a major cause of mortality worldwide. There are several types of diabetes, with type 2 diabetes mellitus (T2DM) being the most common. Many factors, including environmental and genetic factors, are involved in the etiology of the disease. Numerous studies have reported the role of genetic polymorphisms in the initiation and development of T2DM. While genome-wide association studies have identified around more than 200 susceptibility loci, it remains unclear whether these loci are correlated with the pathophysiology of the disease. The present review aimed to elucidate the potential genetic mechanisms underlying T2DM. We found that some genetic polymorphisms were related to T2DM, either in the form of single-nucleotide polymorphisms or direct amino acid changes in proteins. These polymorphisms are potential predictors for the management of T2DM.

Monogenic Forms of Diabetes Mellitus

In addition to the common types of diabetes mellitus, two major monogenic diabetes forms exist. Maturity-onset diabetes of the young (MODY) represents a heterogenous group of monogenic, autosomal dominant diseases. MODY accounts for 1-2% of all diabetes cases, and it is not just underdiagnosed but often misdiagnosed to type 1 or type 2 diabetes. More than a dozen MODY genes have been identified to date, and their molecular classification is of great importance in the correct treatment decision and in the judgment of the prognosis. The most prevalent subtypes are HNF1A, GCK, and HNF4A. Genetic testing for MODY has changed recently due to the technological advancements, as contrary to the sequential testing performed in the past, nowadays all MODY genes can be tested simultaneously by next-generation sequencing. The other major group of monogenic diabetes is neonatal diabetes mellitus which can be transient or permanent, and often the diabetes is a part of a syndrome. It is a severe monogenic disease appearing in the first 6 months of life. The hyperglycemia usually requires insulin. There are two forms, permanent neonatal diabetes mellitus (PNDM) and transient neonatal diabetes mellitus (TNDM). In TNDM, the diabetes usually reverts within several months but might relapse later in life. The incidence of NDM is 1:100,000-1:400,000 live births, and PNDM accounts for half of the cases. Most commonly, neonatal diabetes is caused by mutations in KCNJ11 and ABCC8 genes encoding the ATP-dependent potassium channel of the β cell. Neonatal diabetes has experienced a quick and successful transition into the clinical practice since the discovery of the molecular background. In case of both genetic diabetes groups, recent guidelines recommend genetic testing.

Pancreatic atrophy caused by dietary selenium deficiency induces hypoinsulinemic hyperglycemia via global down-regulation of selenoprotein encoding genes in broilers

This study was envisaged to comprehensively profile genes in selected tissues along with a few biochemical indicators and integrate resulting information with dietary selenium (Se) deficiency symptoms in broilers. A total of 120 one-day-old Cobb male broilers were equally divided into two groups and fed a Se deficient corn-soybean-based basal diet supplemented with 0.3 mg/kg sodium selenite (Control, Se adequate) or without selenite (Se deficiency) for five weeks. Effects of Se deficiency on mRNA abundance of twenty-three selenoprotein encoding genes and seventeen insulin signaling related genes were studied at day 35 in pancreas, liver and muscle along with plasma biochemical constituents and enzyme activities. Compared to healthy birds in control diet, Se deficient diet induced deficiency symptoms in 90% birds and classic nutritional pancreatic atrophy, depressed growth performance of broilers, and decreased (P < 0.01 to P < 0.05) total antioxidant capacity and activities of superoxide dismutase and glutathione peroxidase in plasma and three other tissues. Se deficiency resulted in 58% higher mortality than control birds. Dietary Se deficiency down-regulated (P < 0.01-0.05) eighteen selenoprotein encoding genes in pancreas, fourteen genes in muscle and nine genes in liver, and up-regulated (P < 0.05) Txnrd1 and Selx in liver. Meanwhile, six, thirteen and five insulin signaling related genes were down-regulated (P < 0.01-0.05) in pancreas, muscle and liver, respectively, and three genes were up-regulated (P < 0.01) in liver. The decrease (P < 0.05) in levels of plasma insulin, total triglyceride and total cholesterol, and concurrent elevated (P < 0.05) levels of plasma glucose and inflammatory cytokines accompanied the global down-regulation of selenoprotein encoding- and insulin signaling related- genes in Se deficient birds. It was concluded that dietary Se deficiency induces nutritional pancreatic atrophy and metabolic disorder of glucose and lipid in broilers via down-regulation of selenoprotein encoding- and insulin signaling related- genes, indicating potential roles of these genes in metabolic regulation.

Pancreatic and duodenal homeobox gene 1 (Pdx1) down-regulates hepatic transcription factor 1 alpha (HNF1α) expression during reprogramming of human hepatic cells into insulin-producing cells

Ectopic expression of Pdx1 triggers rapid hepatocyte dedifferentiation by down-regulating liver-enriched transcription factors and liver-specific functional genes such as hepatic nuclear factor-1α (HNF1α), albumin, and AAT. However, the links between Pdx1 over-expression and hepatic gene down-regulation are incompletely understood. HNF1α and HNF4α are important transcription factors that establish and maintain the hepatocyte phenotype. The human HNF4α gene contains two promoters (P1 and P2) that drive expression of P1-(HNF4α 1-6) or P2-(HNF4α 7-9)-derived isoforms, which are used in different tissues and at different times during development. We hypothesized that the relative expression of HNF1α and HNF4α following ectopic Pdx1 expression may promote hepatic cell dedifferentiation and transdifferentiation toward pancreatic beta-cells. We produced lentiviruses expressing Pdx1, Pdx1-VP16, and Ngn3, along with dual-color reporter genes to indicate hepatic and pancreatic beta-cell phenotype changes. Using these PTF alone or in combinations, we demonstrated that Pdx1 not only activates specific beta-cell genes but down-regulates HNF1α. Pdx1-mediated reduction of HNF1α is accompanied by altered expression of its major activator, HNF4α isoforms, down-regulating hepatic genes ALB and AAT. Pdx1 up-regulates HNF4α via the P2 promoter. These P2-driven isoforms compete with P1-driven isoforms to suppress target gene transcription. In Huh7 cells, the AF-1 activation domain is more important for transactivation, whereas in INS1 cells, the F inhibitory domain is more important. The loss and gain of functional activity strongly suggests that Pdx1 plays a central role in reprogramming hepatocytes into beta-cells by suppressing the hepatic phenotype.

Hepatocyte nuclear factor 4 alpha polymorphisms and the metabolic syndrome in French-Canadian youth

Objectives

Hepatocyte nuclear factor 4 alpha (HNF4α) is a transcription factor involved in the regulation of serum glucose and lipid levels. Several HNF4A gene variants have been associated with the risk of developing type 2 diabetes mellitus. However, no study has yet explored its association with insulin resistance and the cardiometabolic risk in children. We aimed to investigate the relationship between HNF4A genetic variants and the presence of metabolic syndrome (MetS) and metabolic parameters in a pediatric population.

Design and Methods

Our study included 1,749 French-Canadians aged 9, 13 and 16 years and evaluated 24 HNF4A polymorphisms that were previously identified by sequencing.

Results

Analyses revealed that, after correction for multiple testing, one SNP (rs736824; P<0.022) and two haplotypes (P1 promoter haplotype rs6130608-rs2425637; P<0.032 and intronic haplotype rs736824-rs745975-rs3212183; P<0.025) were associated with the risk of MetS. Additionally, a significant association was found between rs3212172 and apolipoprotein B levels (coefficient: -0.14 ± 0.05; P<0.022). These polymorphisms are located in HNF4A P1 promoter or in intronic regions.

Conclusions

Our study demonstrates that HNF4α genetic variants are associated with the MetS and metabolic parameters in French Canadian children and adolescents. This study, the first exploring the relation between HNF4A genetic variants and MetS and metabolic variables in a pediatric cohort, suggests that HNF4α could represent an early marker for the risk of developing type 2 diabetes mellitus.

Clinical application of transcriptional activators of bile salt transporters

Hepatobiliary bile salt (BS) transporters are critical determinants of BS homeostasis controlling intracellular concentrations of BSs and their enterohepatic circulation. Genetic or acquired dysfunction of specific transport systems causes intrahepatic and systemic retention of potentially cytotoxic BSs, which, in high concentrations, may disturb integrity of cell membranes and subcellular organelles resulting in cell death, inflammation and fibrosis. Transcriptional regulation of canalicular BS efflux through bile salt export pump (BSEP), basolateral elimination through organic solute transporters alpha and beta (OSTα/OSTβ) as well as inhibition of hepatocellular BS uptake through basolateral Na(+)-taurocholate cotransporting polypeptide (NTCP) represent critical steps in protection from hepatocellular BS overload and can be targeted therapeutically. In this article, we review the potential clinical implications of the major BS transporters BSEP, OSTα/OSTβ and NTCP in the pathogenesis of hereditary and acquired cholestatic syndromes, provide an overview on transcriptional control of these transporters by the key regulatory nuclear receptors and discuss the potential therapeutic role of novel transcriptional activators of BS transporters in cholestasis.

Pulsatile exposure to simulated reflux leads to changes in gene expression in a 3D model of oesophageal mucosa

Oesophageal exposure to duodenogastroesophageal refluxate is implicated in the development of Barrett's metaplasia (BM), with increased risk of progression to oesophageal adenocarcinoma. The literature proposes that reflux exposure activates NF-κB, driving the aberrant expression of intestine-specific caudal-related homeobox (CDX) genes. However, early events in the pathogenesis of BM from normal epithelium are poorly understood. To investigate this, our study subjected a 3D model of the normal human oesophageal mucosa to repeated, pulsatile exposure to specific bile components and examined changes in gene expression. Initial 2D experiments with a range of bile salts observed that taurochenodeoxycholate (TCDC) impacted upon NF-κB activation without causing cell death. Informed by this, the 3D oesophageal model was repeatedly exposed to TCDC in the presence and absence of acid, and the epithelial cells underwent gene expression profiling. We identified ~300 differentially expressed genes following each treatment, with a large and significant overlap between treatments. Enrichment analysis (Broad GSEA, DAVID and Metacore™; GeneGo Inc) identified multiple gene sets related to cell signalling, inflammation, proliferation, differentiation and cell adhesion. Specifically NF-κB activation, Wnt signalling, cell adhesion and targets for the transcription factors PTF1A and HNF4α were highlighted. Our data suggest that HNF4α isoform switching may be an early event in Barrett's pathogenesis. CDX1/2 targets were, however, not enriched, suggesting that although CDX1/2 activation reportedly plays a role in BM development, it may not be an initial event. Our findings highlight new areas for investigation in the earliest stages of BM pathogenesis of oesophageal diseases and new potential therapeutic targets.

Evaluation of a target region capture sequencing platform using monogenic diabetes as a study-model

BACKGROUND

Monogenic diabetes is a genetic disease often caused by mutations in genes involved in beta-cell function. Correct sub-categorization of the disease is a prerequisite for appropriate treatment and genetic counseling. Target-region capture sequencing is a combination of genomic region enrichment and next generation sequencing which might be used as an efficient way to diagnose various genetic disorders. We aimed to develop a target-region capture sequencing platform to screen 117 selected candidate genes involved in metabolism for mutations and to evaluate its performance using monogenic diabetes as a study-model.

RESULTS

The performance of the assay was evaluated in 70 patients carrying known disease causing mutations previously identified in HNF4A, GCK, HNF1A, HNF1B, INS, or KCNJ11. Target regions with a less than 20-fold sequencing depth were either introns or UTRs. When only considering translated regions, the coverage was 100% with a 50-fold minimum depth. Among the 70 analyzed samples, 63 small size single nucleotide polymorphisms and indels as well as 7 large deletions and duplications were identified as being the pathogenic variants. The mutations identified by the present technique were identical with those previously identified through Sanger sequencing and Multiplex Ligation-dependent Probe Amplification.

CONCLUSIONS

We hereby demonstrated that the established platform as an accurate and high-throughput gene testing method which might be useful in the clinical diagnosis of monogenic diabetes.

Hepatocyte nuclear factor 4-alpha involvement in liver and intestinal inflammatory networks

Hepatocyte nuclear factor 4-alpha (HNF4-α) is a nuclear receptor regulating metabolism, cell junctions, differentiation and proliferation in liver and intestinal epithelial cells. Mutations within the HNF4A gene are associated with human diseases such as maturity-onset diabetes of the young. Recently, HNF4A has also been described as a susceptibility gene for ulcerative colitis in genome-wide association studies. In addition, specific HNF4A genetic variants have been identified in pediatric cohorts of Crohn’s disease. Results obtained from knockout mice supported that HNF4-α can protect the intestinal mucosae against inflammation. However, the exact molecular links behind HNF4-α and inflammatory bowel diseases remains elusive. In this review, we will summarize the current knowledge about the role of HNF4-α and its isoforms in inflammation. Specific nature of HNF4-α P1 and P2 classes of isoforms will be summarized. HNF4-α role as a hepatocyte mediator for cytokines relays during liver inflammation will be integrated based on documented examples of the literature. Conclusions that can be made from these earlier liver studies will serve as a basis to extrapolate correlations and divergences applicable to intestinal inflammation. Finally, potential functional roles for HNF4-α isoforms in protecting the intestinal mucosae from chronic and pathological inflammation will be presented.

Detection and characterization of two novel mutations in the HNF4A gene in maturity-onset diabetes of the young type 1 in two Japanese families

BACKGROUND

Maturity-onset diabetes of the young (MODY) is a subgroup of monogenic diabetes mellitus, of which MODY1, caused by HNF4A mutations, accounts for only 5% or less and has been rarely reported in East Asian countries. Here we report two novel HNF4A mutations in two Japanese families with MODY1.

METHODS

Proband 1 is an 8-year-old girl and proband 2 is a 14-year-old girl. Both were nonobese, demonstrated elevated HbA1c and negative serum anti-glutamic acid decarboxylase antibodies, and had a family history of diabetes. We directly sequenced HNF4A and performed functional analysis of the detected missense mutation.

RESULTS

Proband 1 had a heterozygous missense mutation, c.824A>G (p.Asn275Ser). Luciferase assay demonstrated a significant reduction in transcriptional activity. A heterozygous frame shift mutation, c.692-695delAGGA (p.Lys231ThrfsX5), was detected in proband 2. Affected family members shared the same mutations, showing high penetrance. Both mutations reside in the HNF4α dimerization domain and the corresponding amino acids are well conserved between species.

CONCLUSIONS

These two mutations are most likely the cause of MODY1 in these families. Considering the effectiveness of sulfonylureas, it is important to correctly diagnose MODY1.

Effects of hepatocyte nuclear factor-1A and -4A on pancreatic stone protein/regenerating protein and C-reactive protein gene expression: implications for maturity-onset diabetes of the young

Background

There is a significant clinical overlap between patients with hepatocyte nuclear factor (HNF)-1A and HNF4A maturity-onset diabetes of the young (MODY), two forms of monogenic diabetes. HNF1A and HNF4A are transcription factors that control common and partly overlapping sets of target genes. We have previously shown that elevated serum pancreatic stone protein / regenerating protein A (PSP/reg1A) levels can be detected in subjects with HNF1A-MODY. In this study, we investigated whether PSP/reg is differentially regulated by HNF1A and HNF4A.

Methods

Quantitative real-time PCR (qPCR) and Western blotting were used to validate gene and protein expression in cellular models of HNF1A- and HNF4A-MODY. Serum PSP/reg1A levels and high-sensitivity C-reactive protein (hsCRP) were measured by ELISA in 31 HNF1A- and 9 HNF4A-MODY subjects. The two groups were matched for age, body mass index, diabetes duration, blood pressure, lipid profile and aspirin and statin use.

Results

Inducible repression of HNF1A and HNF4A function in INS-1 cells suggested that PSP/reg induction required HNF4A, but not HNF1A. In contrast, crp gene expression was significantly reduced by repression of HNF1A, but not HNF4A function. PSP/reg levels were significantly lower in HNF4A subjects when compared to HNF1A subjects [9.25 (7.85-12.85) ng/ml vs. 12.5 (10.61-17.87) ng/ml, U-test P = 0.025]. hsCRP levels were significantly lower in HNF1A-MODY [0.22 (0.17-0.35) mg/L] compared to HNF4A-MODY group [0.81 (0.38-1.41) mg/L, U-test P = 0.002], Parallel measurements of serum PSP/reg1A and hsCRP levels were able to discriminate HNF1A- and HNF4A-MODY subjects.

Conclusion

Our study demonstrates that two distinct target genes, PSP/reg and crp, are differentially regulated by HNF1A and HNF4A, and provides clinical proof-of-concept that serum PSP/reg1A and hsCRP levels may distinguish HNF1A-MODY from HNF4A-MODY subjects.

Overexpression of hepatocyte nuclear factor-4α initiates cell cycle entry, but is not sufficient to promote β-cell expansion in human islets

The transcription factor HNF4α (hepatocyte nuclear factor-4α) is required for increased β-cell proliferation during metabolic stress in vivo. We hypothesized that HNF4α could induce proliferation of human β-cells. We employed adenoviral-mediated overexpression of an isoform of HNF4α (HNF4α8) alone, or in combination with cyclin-dependent kinase (Cdk)6 and Cyclin D3, in human islets. Heightened HNF4α8 expression led to a 300-fold increase in the number of β-cells in early S-phase. When we overexpressed HNF4α8 together with Cdk6 and Cyclin D3, β-cell cycle entry was increased even further. However, the punctate manner of bromodeoxyuridine incorporation into HNF4α(High) β-cells indicated an uncoupling of the mechanisms that control the concise timing and execution of each cell cycle phase. Indeed, in HNF4α8-induced bromodeoxyuridine(+,punctate) β-cells we observed signs of dysregulated DNA synthesis, cell cycle arrest, and activation of a double stranded DNA damage-associated cell cycle checkpoint mechanism, leading to the initiation of loss of β-cell lineage fidelity. However, a substantial proportion of β-cells stimulated to enter the cell cycle by Cdk6 and Cyclin D3 alone also exhibited a DNA damage response. HNF4α8 is a mitogenic signal in the human β-cell but is not sufficient for completion of the cell cycle. The DNA damage response is a barrier to efficient β-cell proliferation in vitro, and we suggest its evaluation in all attempts to stimulate β-cell replication as an approach to diabetes treatment.

Differential effects of HNF-1α mutations associated with familial young-onset diabetes on target gene regulation

Hepatocyte nuclear factor 1-α (HNF-1α) is a homeodomain transcription factor expressed in a variety of tissues (including liver and pancreas) that regulates a wide range of genes. Heterozygous mutations in the gene encoding HNF-1α (HNF1A) cause familial young-onset diabetes, also known as maturity-onset diabetes of the young, type 3 (MODY3). The variability of the MODY3 clinical phenotype can be due to environmental and genetic factors as well as to the type and position of mutations. Thus, functional characterization of HNF1A mutations might provide insight into the molecular defects explaining the variability of the MODY3 phenotype. We have functionally characterized six HNF1A mutations identified in diabetic patients: two novel ones, p.Glu235Gly and c-57-64delCACGCGGT;c-55G>C; and four previously described, p.Val133Met, p.Thr196Ala, p.Arg271Trp and p.Pro379Arg. The effects of mutations on transcriptional activity have been measured by reporter assays on a subset of HNF-1α target promoters in Cos7 and Min6 cells. Target DNA binding affinities have been quantified by electrophoretic mobility shift assay using bacterially expressed glutathione-S-transferase (GST)-HNF-1α fusion proteins and nuclear extracts of transfected Cos7 cells. Our functional studies revealed that mutation c-57-64delCACGCGGT;c-55G>C reduces HNF1A promoter activity in Min6 cells and that missense mutations have variable effects. Mutation p.Arg271Trp impairs HNF-1α activity in all conditions tested, whereas mutations p.Val133Met, p.Glu235Gly and p.Pro379Arg exert differential effects depending on the target promoter. In contrast, substitution p.Thr196Ala does not appear to alter HNF-1α function. Our results suggest that HNF1A mutations may have differential effects on the regulation of specific target genes, which could contribute to the variability of the MODY3 clinical phenotype.

Distinct regulation of hepatic nuclear factor 1alpha by NKX6.1 in pancreatic beta cells

Hepatic nuclear factor 1alpha (HNF1alpha) is a key regulator of development and function in pancreatic beta cells and is specifically involved in regulation of glycolysis and glucose-stimulated insulin secretion. Abnormal expression of HNF1alpha leads to development of MODY3 (maturity-onset diabetes of the young 3). We report that NK6 homeodomain 1 (NKX6.1) binds to a cis-regulatory element in the HNF1alpha promoter and is a major regulator of this gene in beta cells. We identified an NKX6.1 recognition sequence in the distal region of the HNF1alpha promoter and demonstrated specific binding of NKX6.1 in beta cells by electrophoretic mobility shift and chromatin immunoprecipitation assays. Site-directed mutagenesis of the NKX6.1 core-binding sequence eliminated NKX6.1-mediated activation and substantially decreased activity of the HNF1alpha promoter in beta cells. Overexpression or small interfering RNA-mediated knockdown of the Nkx6.1 gene resulted in increased or diminished HNF1alpha gene expression, respectively, in beta cells. We conclude that NKX6.1 is a novel regulator of HNF1alpha in pancreatic beta cells. This novel regulatory mechanism for HNF1alpha in beta cells may provide new molecular targets for the diagnosis of MODY3.

Improved conditional expression systems resulting in physiological level of HNF4alpha expression confirm HNF4alpha induced apoptosis in the pancreatic beta-cell line INS-1

Background

To analyze gene function in mammalian cells tetracycline inducible expression of a gene-of-interest at a specific genomic location (Flp-In T-REx™) is most attractive. However, leakiness of basal transgene expression and artificially high expression level upon tetracycline addition may be disadvantageous.

Findings

To solve these problems, we developed two different approaches to improve our pancreatic β-cell line INS-1 Flp-In T-REx™ expressing the tissue restricted transcription factor HNF4α under control of tetracycline. On the one hand we replaced the strong full length CMV promoter (CMV-Wt) with a weaker 5'-deleted CMV promoter fragment of 138 nucleotides in length (CMV-138). On the other hand we extended our INS-1 Flp-In T-REx™ cell lines with a Shield-1 dependent conditional control system of protein stability. Therefore, we fused HNF4α to the destabilization domain (DD) deduced from human FKBP12 protein. As a result in both approaches basal transgene expression level was markedly reduced, but HNF4α induction could still be maintained. Additionally, we could show that a low increase in HNF4α induces caspase activity indicating an apoptotic effect of HNF4α in these cells.

Conclusion

In the present study we considerably improved our INS-1 Flp-In T-REx™ cell lines conditionally expressing HNF4α to reduce leakiness and to optimize exogenous HNF4α protein expression to a physiological level. As an important result we could extend our previous results that HNF4α induces apoptosis in the pancreatic β-cell line INS-1 with the new aspect that an expression level of the HNF4α transgene marginally exceeding the endogenous level is sufficient to trigger apoptosis.

Expression of HNF4alpha in the human and rat choroid plexus: implications for drug transport across the blood-cerebrospinal-fluid (CSF) barrier

Background

The choroid plexus consists of highly differentiated epithelium and functions as a barrier at the interface of the blood-cerebrospinal-fluid (CSF). This tissue may therefore determine the bioavailability and transport of drugs to the brain. Little is known about the expression of drug and xenobiotic metabolizing enzymes (DME) and of drug transporters in the human choroid plexus. Notably, the transcription factor and zinc finger protein HNF4alpha is a master regulator of DMEs and of drug transporters. As of today its activity in the blood-CSF barrier is unknown. Here we report our efforts in determining HNF4alpha activity in the regulation of ABC transporters in the human and rat choroid plexus.

Results

We report expression of HNF4alpha by qRT-PCR and by immunohistochemistry and evidence transcript expression of the ATP-binding cassette transporters ABCB1, ABCB4, ABCC1-6 in choroid plexus. Additionally, HNF4alpha DNA binding activity at regulatory sequences of ABCB4 and ABCC1 was determined by EMSA bandshift assays with a specific antibody. We then performed siRNA mediated functional knock down of HNF4alpha in Caco-2 cells and found ABCC1 gene expression to be repressed in cell culture experiments.

Conclusion

Our study evidences activity of HNF4alpha in human and rat choroid plexus. This transcription factor targets DMEs and drug transporters and may well determine availability of drugs at the blood-CSF barrier.

HNF4alpha and HNF1alpha dysfunction as a molecular rational for cyclosporine induced posttransplantation diabetes mellitus

Posttransplantation diabetes mellitus (PTDM) is a frequent complication in immunosuppressive therapy. To better understand the molecular events associated with PTDM we investigated the effect of cyclosporine on expression and activity of hepatic nuclear factor (HNF)1alpha and 4alpha and on genes coding for glucose metabolism in cultures of the rat insulinoma cell line INS-1E, the human epithelial cell line Caco-2 and with Zucker diabetic fatty (ZDF) rats. In the pancreas of untreated but diabetic animals expression of HNF4alpha, insulin1, insulin2 and of phosphoenolpyruvate carboxykinase was significantly repressed. Furthermore, cyclosporine treatment of the insulinoma-1E cell line resulted in remarkable reduction in HNF4alpha protein and INS1 as well as INS2 gene expression, while transcript expression of HNF4alpha, apolipoprotein C2, glycerolkinase, pyruvatekinase and aldolase B was repressed in treated Caco-2 cells. Furthermore, with nuclear extracts of cyclosporine treated cell lines protein expression and DNA binding activity of hepatic nuclear factors was significantly repressed. As cyclosporine inhibits the calcineurin dependent dephosphorylation of nuclear factor of activated T-cells (NFAT) we also searched for binding sites for NFAT in the pancreas specific P2 promoter of HNF4alpha. Notably, we observed repressed NFAT binding to a novel DNA binding site in the P2 promoter of HNF4alpha. Thus, cyclosporine caused inhibition of DNA binding of two important regulators for insulin signaling, i.e. NFAT and HNF4alpha. We further investigated HNF4alpha transcript expression and observed >200-fold differences in abundance in n = 14 patients. Such variability in expression might help to identify individuals at risk for developing PTDM. We propose cyclosporine to repress HNF4alpha gene and protein expression, DNA-binding to targeted promoters and subsequent regulation of genes coding for glucose metabolism and of pancreatic beta-cell function.

Morphogenetic competence of HNF4 alpha-deficient mouse hepatic cells

BACKGROUND/AIMS

To specify roles of HNF 4 alpha in mouse liver development, we have analyzed the ex vivo morphogenetic potential of HNF4 alpha-null embryonic hepatic cells.

METHODS

Using mice with floxed or deficiency alleles of HNF4 alpha, hepatic cells lacking this transcription factor were explanted into primary culture and derived into cell lines.

RESULTS

Contrary to behavior in vivo where HNF4 alpha-null liver cells fail to show normal polarity and epithelialization, e18.5 hepatic cells in primary culture from mutant embryos show restoration of apical expression of tight junction protein-1 and of transcripts for E-cadherin. Clones of control and HNF4 alpha-null cell lines were indistinguishable, even when differentiation of bile canalicular formation was induced. HNF4 alpha-null and control cell lines showed similar potential to colonize livers of the murine ALB-uPA/SCID model of liver regeneration, but null cells formed only bile ducts and not clusters of hepatocytes. Finally, analysis of mutant embryonic livers revealed a transcriptional signature consistent with a stress response, which could underlie the morphogenetic defects observed in vivo.

CONCLUSIONS

We conclude that the lack of epithelialization characteristic of the HNF4 alpha-null embryonic liver is due, at least in part, to non-cell autonomous defects, and that null cells do not suffer intrinsic defects in polarization.

Hepatocyte nuclear factor-4alpha is a central transactivator of the mouse Ntcp gene

Sodium taurocholate cotransporting polypeptide (Ntcp) is the major uptake system for conjugated bile acids. Deletions of hepatocyte nuclear factor (HNF)-1alpha and retinoid X receptor-alpha:retinoic acid receptor-alpha binding sites in the mouse 5'-flanking region corresponding to putatively central regulatory elements of rat Ntcp do not significantly reduce promoter activity. We hypothesized that HNF-4alpha, which is increasingly recognized as a central regulator of hepatocyte function, may directly transactivate mouse (mNtcp). A 1.1-kb 5'-upstream region including the mouse Ntcp promoter was cloned and compared with the rat promoter. In contrast to a moderate 3.5-fold activation of mNtcp by HNF-1alpha, HNF-4alpha cotransfection led to a robust 20-fold activation. Deletion analysis of mouse and rat Ntcp promoters mapped a conserved HNF-4alpha consensus site at -345/-326 and -335/-316 bp, respectively. p-475bpmNtcpLUC is not transactivated by HNF-1alpha but shows a 50-fold enhanced activity upon cotransfection with HNF-4alpha. Gel mobility shift assays demonstrated a complex of the HNF-4alpha-element formed with liver nuclear extracts that was blocked by an HNF-4alpha specific antibody. HNF-4alpha binding was confirmed by chromatin immunoprecipitation. Using Hepa 1-6 cells, HNF-4alpha-knockdown resulted in a significant 95% reduction in NTCP mRNA. In conclusion, mouse Ntcp is regulated by HNF-4alpha via a conserved distal cis-element independently of HNF-1alpha.

Best practice guidelines for the molecular genetic diagnosis of maturity-onset diabetes of the young

AIMS/HYPOTHESIS

Mutations in the GCK and HNF1A genes are the most common cause of the monogenic forms of diabetes known as 'maturity-onset diabetes of the young'. GCK encodes the glucokinase enzyme, which acts as the pancreatic glucose sensor, and mutations result in stable, mild fasting hyperglycaemia. A progressive insulin secretory defect is seen in patients with mutations in the HNF1A and HNF4A genes encoding the transcription factors hepatocyte nuclear factor-1 alpha and -4 alpha. A molecular genetic diagnosis often changes management, since patients with GCK mutations rarely require pharmacological treatment and HNF1A/4A mutation carriers are sensitive to sulfonylureas. These monogenic forms of diabetes are often misdiagnosed as type 1 or 2 diabetes. Best practice guidelines for genetic testing were developed to guide testing and reporting of results.

METHODS

A workshop was held to discuss clinical criteria for testing and the interpretation of molecular genetic test results. The participants included 22 clinicians and scientists from 13 countries. Draft best practice guidelines were formulated and edited using an online tool (http://www.coventi.com).

RESULTS

An agreed set of clinical criteria were defined for the testing of babies, children and adults for GCK, HNF1A and HNF4A mutations. Reporting scenarios were discussed and consensus statements produced.

CONCLUSIONS/INTERPRETATION

Best practice guidelines have been established for monogenic forms of diabetes caused by mutations in the GCK, HNF1A and HNF4A genes. The guidelines include both diagnostic and predictive genetic tests and interpretation of the results.

Ptf1a binds to and activates area III, a highly conserved region of the Pdx1 promoter that mediates early pancreas-wide Pdx1 expression

The critical pancreatic transcription factor Pdx1 is expressed throughout the pancreas early but enriched in insulin-producing beta cells postnatally. Previous studies showed that the 5' conserved promoter regions areas I and II (Pdx1(PB)) direct endocrine cell expression, while an adjacent region (Pdx1(XB)) containing conserved area III directs transient beta-cell expression. In this study, we used Cre-mediated lineage tracing to track cells that activated these regions. Pdx1(PB)Cre mediated only endocrine cell recombination, while Pdx1(XB)Cre directed broad and early recombination in the developing pancreas. Also, a reporter transgene containing areas I, II, and III was expressed throughout the embryonic day 10.5 (E10.5) pancreas and gradually became beta cell enriched, similar to endogenous Pdx1. These data suggested that sequences within area III mediate early pancreas-wide Pdx1 expression. Area III contains a binding site for PTF1, a transcription factor complex essential for pancreas development. This site contributed to area III-dependent reporter gene expression in the acinar AR42J cell line, while PTF1 specifically trans-activated area III-containing reporter expression in a nonpancreatic cell line. Importantly, Ptf1a occupied sequences spanning the endogenous PTF1 site in area III of E11.5 pancreatic buds. These data strongly suggest that PTF1 is an important early activator of Pdx1 in acinar and endocrine progenitor cells during pancreas development.

Insights on pathogenesis of type 2 diabetes from MODY genetics

Maturity-onset diabetes of the young (MODY) is a type of non-insulin-dependent diabetes mellitus caused by rare autosomal-dominant mutations. MODY genes play key biochemical roles in the pancreatic beta cell; therefore, common variants of MODY genes are excellent candidate genes for type 2 diabetes. We review recent studies that suggest that common MODY gene variation contributes modestly to the heritability of type 2 diabetes.

Common variants in MODY genes increase the risk of gestational diabetes mellitus

AIMS/HYPOTHESIS

Impaired beta cell function is the hallmark of gestational diabetes mellitus (GDM) and MODY. In addition, women with MODY gene mutations often present with GDM, but it is not known whether common variants in MODY genes contribute to GDM.

SUBJECTS AND METHODS

We genotyped five common variants in the glucokinase (GCK, commonly known as MODY2), hepatocyte nuclear factor 1-alpha (HNF1A, commonly known as MODY3) and 4-alpha (HNF4A commonly known as MODY1) genes in 1,880 Scandinavian women (648 women with GDM and 1,232 pregnant non-diabetic control women).

RESULTS

The A allele of the GCK -30G-->A polymorphism was more common in GDM women than in control subjects (odds ratio [OR] 1.28 [95% CI 1.06-1.53], p=0.008, corrected p value, p=0.035). Under a recessive model [AA vs GA+GG], the OR increased further to 2.12 (95% CI 1.21-3.72, p=0.009). The frequency of the L allele of the HNF1A I27L polymorphism was slightly higher in GDM than in controls (1.16 [95% CI 1.001-1.34], p=0.048, corrected p value, p=0.17). However, the OR increased under a dominant model (LL+IL vs II; 1.31 [95% CI 1.08-1.60], p=0.007). The rs2144908, rs2425637 and rs1885088 variants, which are located downstream of the primary beta cell promoter (P2) of HNF4A, were not associated with GDM.

CONCLUSIONS/INTERPRETATION

The -30G-->A polymorphism of the beta-cell-specific promoter of GCK and the I27L polymorphism of HNF1A seem to increase the risk of GDM in Scandinavian women.

The position of premature termination codons in the hepatocyte nuclear factor -1 beta gene determines susceptibility to nonsense-mediated decay

The nonsense-mediated decay (NMD) pathway is an mRNA surveillance mechanism that detects and degrades transcripts containing premature termination codons. The position of a truncating mutation can govern the resulting phenotype as mutations in the last exon evade NMD. In this study we investigated the susceptibility to NMD of six truncating HNF-1beta mutations by allele-specific quantitative real-time PCR using transformed lymphoblastoid cell lines. Four of six mutations (R181X, Q243fsdelC, P328L329fsdelCCTCT and A373fsdel29) showed evidence of NMD with levels of mutant transcript at 71% (p=0.009), 24% (p=0.008), 22% (p=0.008) and 3% (p=0.016) of the wild-type allele respectively. Comparable results were derived from lymphoblastoid cells and renal tubule cells isolated from a patient's overnight urine confirming that cell lines provide a good model for mRNA analysis. Two mutations (H69fsdelAC and P159fsdelT) produced transcripts unexpectedly immune to NMD. We conclude that truncating mutant transcripts of the HNF-1beta gene do not conform to the known rules governing NMD susceptibility, but instead demonstrate a previously unreported 5' to 3' polarity. We hypothesise that this may be due to reinitiation of translation downstream of the premature termination codon. Our study suggests that reinitiation of translation may be an important mechanism in the evasion of NMD, but that other factors such as the distance from the native initiation codon may also play a part.

Genetic epidemiology of diabetes

Conventional genetic analysis focuses on the genes that account for specific phenotypes, while traditional epidemiology is more concerned with the environmental causes and risk factors related to traits. Genetic epidemiology is an alliance of the 2 fields that focuses on both genetics, including allelic variants in different populations, and environment, in order to explain exactly how genes convey effects in different environmental contexts and to arrive at a more complete comprehension of the etiology of complex traits. In this review, we discuss the epidemiology of diabetes and the current understanding of the genetic bases of obesity and diabetes and provide suggestions for accelerated accumulation of clinically useful genetic information.

Molecular genetics and phenotypic characteristics of MODY caused by hepatocyte nuclear factor 4alpha mutations in a large European collection

AIMS/HYPOTHESIS

Heterozygous mutations in the gene of the transcription factor hepatocyte nuclear factor 4alpha (HNF-4alpha) are considered a rare cause of MODY with only 14 mutations reported to date. The description of the phenotype is limited to single families. We investigated the genetics and phenotype of HNF-4alpha mutations in a large European Caucasian collection.

METHODS

HNF-4alpha was sequenced in 48 MODY probands, selected for a phenotype of HNF-1alpha MODY but negative for HNF-1alpha mutations. Clinical characteristics and biochemistry were compared between 54 HNF-4alpha mutation carriers and 32 familial controls from ten newly detected or previously described families.

RESULTS

Mutations in HNF-4alpha were found in 14/48 (29%) probands negative for HNF-1alpha mutations. The mutations found included seven novel mutations: S34X, D206Y, E276D, L332P, I314F, L332insCTG and IVS5nt+1G>A. I314F is the first reported de novo HNF-4alpha mutation. The average age of diagnosis was 22.9 years with frequent clinical evidence of sensitivity to sulphonylureas. Beta cell function, but not insulin sensitivity, was reduced in diabetic mutation carriers compared to control subjects (homeostasis model assessment of beta cell function 29% p<0.001 vs controls). HNF-4alpha mutations were associated with lower apolipoprotein A2 (p=0.001), A1 (p=0.04) and total HDL-cholesterol (p=0.02) than in control subjects. However, in contrast to some previous reports, levels of triglycerides and apolipoprotein C3 were normal.

CONCLUSIONS/INTERPRETATION

HNF-4alpha mutations are common when no HNF-1alpha mutation is found in strictly defined MODY families. The HNF-4alpha clinical phenotype and beta cell dysfunction are similar to HNF-1alpha MODY and are associated with reduced apolipoprotein A2 levels. We suggest that sequencing of HNF-4alpha should be performed in patients with clinical characteristics of HNF-1alpha MODY in whom mutations in HNF-1alpha are not found.

The MODY1 gene HNF-4alpha regulates selected genes involved in insulin secretion

Mutations in the gene encoding hepatocyte nuclear factor-4alpha (HNF-4alpha) result in maturity-onset diabetes of the young (MODY). To determine the contribution of HNF-4alpha to the maintenance of glucose homeostasis by the beta cell in vivo, we derived a conditional knockout of HNF-4alpha using the Cre-loxP system. Surprisingly, deletion of HNF-4alpha in beta cells resulted in hyperinsulinemia in fasted and fed mice but paradoxically also in impaired glucose tolerance. Islet perifusion and calcium-imaging studies showed abnormal responses of the mutant beta cells to stimulation by glucose and sulfonylureas. These phenotypes can be explained in part by a 60% reduction in expression of the potassium channel subunit Kir6.2. We demonstrate using cotransfection assays that the Kir6.2 gene is a transcriptional target of HNF-4alpha. Our data provide genetic evidence that HNF-4alpha is required in the pancreatic beta cell for regulation of the pathway of insulin secretion dependent on the ATP-dependent potassium channel.

The MODY1 gene HNF-4alpha regulates selected genes involved in insulin secretion

Mutations in the gene encoding hepatocyte nuclear factor-4alpha (HNF-4alpha) result in maturity-onset diabetes of the young (MODY). To determine the contribution of HNF-4alpha to the maintenance of glucose homeostasis by the beta cell in vivo, we derived a conditional knockout of HNF-4alpha using the Cre-loxP system. Surprisingly, deletion of HNF-4alpha in beta cells resulted in hyperinsulinemia in fasted and fed mice but paradoxically also in impaired glucose tolerance. Islet perifusion and calcium-imaging studies showed abnormal responses of the mutant beta cells to stimulation by glucose and sulfonylureas. These phenotypes can be explained in part by a 60% reduction in expression of the potassium channel subunit Kir6.2. We demonstrate using cotransfection assays that the Kir6.2 gene is a transcriptional target of HNF-4alpha. Our data provide genetic evidence that HNF-4alpha is required in the pancreatic beta cell for regulation of the pathway of insulin secretion dependent on the ATP-dependent potassium channel.

Variation near the hepatocyte nuclear factor (HNF)-4alpha gene associates with type 2 diabetes in the Danish population

AIMS/HYPOTHESIS

The hepatocyte nuclear factor (HNF)-4alpha is an orphan nuclear receptor, which plays crucial roles in regulating hepatic gluconeogenesis and insulin secretion. The gene encoding HNF-4alpha (HNF4A) is located on chromosome 20q12-q13 in a region that in several studies has shown linkage with type 2 diabetes. Recently, two independent studies identified single nucleotide polymorphisms (SNPs) in a 90-kb region spanning HNF4A, which showed strong association with type 2 diabetes in the Finnish and Ashkenazi Jewish populations. In an attempt to replicate and extend these findings, we selected four SNPs in the same HNF4A region, which in the Finnish and Ashkenazi Jewish populations were associated with type 2 diabetes, and examined their relationships with type 2 diabetes and prediabetic phenotypes in the Danish Caucasian population.

METHODS

The rs1884614, rs2425637, rs1885088 and rs3818247 were analysed in case-control studies of 1387, 1429, 1417 and 1371 type 2 diabetic patients and 4766, 4727, 4665 and 4748 glucose-tolerant subjects respectively. Genotype-quantitative trait analyses comprised 4430, 4394, 4336 and 4413 middle-aged glucose-tolerant subjects from the population-based Inter99 cohort for the rs1884614, rs2425637, rs1885088 and rs3818247 respectively.

RESULTS

The risk allele of the rs1884614, which is located 4 kb upstream of the HNF4A P2 promoter, was associated with type 2 diabetes (odds ratio [OR]=1.14, p=0.02) and with a subtle increase in post-OGTT plasma glucose levels in glucose-tolerant subjects (additive model, p=0.05).

CONCLUSIONS/INTERPRETATION

Consistent with results from studies of Finnish and Ashkenazi Jewish subjects, variation near the P2 region of HNF4A is associated with type 2 diabetes in the Danish population.

Pattern of genes influenced by conditional expression of the transcription factors HNF6, HNF4alpha and HNF1beta in a pancreatic beta-cell line

Using the rat insulinoma cell line INS-1 we generated beta-cell clones that are most efficient for gene transfer, as they contain an FRT site for Flp recombinase-mediated, site-directed integration of a single copy transgene. Therefore, the gene-of-interest can be introduced by DNA transfection without the need to select individual cell clones. Additionally, the clones contain the tetracycline repressor allowing tetracycline induction of the transgene. By oligonucleotide microarray we define the beta-cell specific phenotype of the Flp-In T-REx cell clones. Using a clone expressing the HNF6, HNF4alpha and HNF1beta transcription factors at a limited level, we introduced the expression vectors encoding these factors. We show efficient tetracycline induction of these transcription factors by western blots and immunocytochemistry. Microarrays reveal that these three factors affect a similar number of genes with only few genes regulated in common. Statistical analysis reveals that the three transcription factors affect genes categorized to different biological processes. Furthermore, we document the usefulness of these Flp-In T-REx cells for the functional analysis of mutated HNF1beta transcription factors found in human MODY5 patients. We show that the expression of the mutant P328L329del and A263insGG affects only very few transcripts and these are predominantly distinct from those induced by wild-type HNF1beta.

Transcriptional networks controlling pancreatic development and beta cell function

Transcription factors provide the genetic instructions that drive pancreatic development and enable mature beta cells to function properly. To understand fully how this is accomplished, it is necessary to unravel the regulatory networks formed by transcription factors acting on their genomic targets. This article discusses recent advances in our understanding of how transcriptional networks control early pancreas organogenesis, embryonic endocrine cell formation and the differentiated function of adult beta cells. We discuss how mutations in several transcription factor genes involved in such networks cause Maturity onset diabetes of the young (MODY). Finally, we propose that pancreatic gene programs might be manipulated to generate beta cells or to enhance the function of existing beta cells, thereby providing a possible treatment of different forms of diabetes.

Expression and localization of P1 promoter-driven hepatocyte nuclear factor-4α (HNF4α) isoforms in human and rats

BACKGROUND

Hepatocyte nuclear factor-4α (HNF4α; NR2A1) is an orphan member of the nuclear receptor superfamily involved in various processes that could influence endoderm development, glucose and lipid metabolism. A loss-of-function mutation in human HNF4α causes one form of diabetes mellitus called maturity-onset diabetes of the young type 1 (MODY1) which is characterized in part by a diminished insulin secretory response to glucose. The expression of HNF4α in a variety of tissues has been examined predominantly at the mRNA level, and there is little information regarding the cellular localization of the endogenous HNF4α protein, due, in part, to the limited availability of human HNF4α-specific antibodies.

RESULTS

Monoclonal antibodies have been produced using baculovirus particles displaying gp64-HNF4α fusion proteins as the immunizing agent. The mouse anti-human HNF4α monoclonal antibody (K9218) generated against human HNF4α1/α2/α3 amino acids 3-49 was shown to recognize not only the transfected and expressed P1 promoter-driven HNF4α proteins, but also endogenous proteins. Western blot analysis with whole cell extracts from Hep G2, Huh7 and Caco-2 showed the expression of HNF4α protein, but HEK293 showed no expression of HNF4α protein. Nuclear-specific localization of the HNF4α protein was observed in the hepatocytes of liver cells, proximal tubular epithelial cells of kidney, and mucosal epithelial cells of small intestine and colon, but no HNF4α protein was detected in the stomach, pancreas, glomerulus, and distal and collecting tubular epithelial cells of kidney. The same tissue distribution of HNF4α protein was observed in humans and rats. Electron microscopic immunohistochemistry showed a chromatin-like localization of HNF4α in the liver and kidney. As in the immunohistochemical investigation using K9218, HNF4α mRNA was found to be localized primarily to liver, kidney, small intestine and colon by RT-PCR and GeneChip analysis.

CONCLUSION

These results suggest that this method has the potential to produce valuable antibodies without the need for a protein purification step. Immunohistochemical studies indicate the tissue and subcellular specific localization of HNF4α and demonstrate the utility of K9218 for the detection of P1 promoter-driven HNF4α isoforms in humans and in several other mammalian species.