The role of HNF4A variants in the risk of type 2 diabetes

Pharmacologic inhibition of HNF4α prevents parenteral nutrition associated cholestasis in mice

Prolonged parenteral nutrition (PN) can lead to PN associated cholestasis (PNAC). Intestinally derived lipopolysaccharides and infused PN phytosterols lead to activation of NFκB, a key factor in PNAC. Our objective was to determine if inhibition of HNF4α could interfere with NFκB to alleviate murine PNAC. We showed that HNF4α antagonist BI6015 (20 mg/kg/day) in DSS-PN (oral DSS x4d followed by Total PN x14d) mice prevented the increased AST, ALT, bilirubin and bile acids and reversed mRNA suppression of hepatocyte Abcg5/8, Abcb11, FXR, SHP and MRP2 that were present during PNAC. Further, NFκB phosphorylation in hepatocytes and its binding to LRH-1 and BSEP promoters in liver, which are upregulated in DSS-PN mice, were inhibited by BI6015 treatment. BI6015 also prevented the upregulation in liver macrophages of Adgre1 (F4/80) and Itgam (CD11B) that occurs in DSS-PN mice, with concomitant induction of anti-inflammatory genes (Klf2, Klf4, Clec7a1, Retnla). In conclusion, HNF4α antagonism attenuates PNAC by suppressing NFκB activation and signaling while inducing hepatocyte FXR and LRH-1 and their downstream bile and sterol transporters. These data identify HNF4α antagonism as a potential therapeutic target for prevention and treatment of PNAC.

Genetic Variants of HNF4A, WFS1, DUSP9, FTO, and ZFAND6 Genes Are Associated with Prediabetes Susceptibility and Inflammatory Markers in the Saudi Arabian Population

Prediabetes is a reversible, intermediate stage of type 2 diabetes mellitus (T2DM). Lifestyle changes that include healthy diet and exercise can substantially reduce progression to T2DM. The present study explored the association of 37 T2DM- and obesity-linked single nucleotide polymorphisms (SNPs) with prediabetes risk in a homogenous Saudi Arabian population. A total of 1129 Saudi adults [332 with prediabetes (29%) and 797 normoglycemic controls] were randomly selected and genotyped using the KASPar SNP genotyping method. Anthropometric and various serological parameters were measured following standard procedures. Heterozygous GA of HNF4A-rs4812829 (0.64; 95% CI 0.47–0.86; p < 0.01), heterozygous TC of WFS1-rs1801214 (0.60; 95% confidence interval (CI) 0.44–0.80; p < 0.01), heterozygous GA of DUSP9-rs5945326 (0.60; 95% CI 0.39–0.92; p = 0.01), heterozygous GA of ZFAND6-rs11634397 (0.75; 95% CI 0.56–1.01; p = 0.05), and homozygous AA of FTO-rs11642841 (1.50; 95% CI 0.8–1.45; p = 0.03) were significantly associated with prediabetes, independent of age and body mass index (BMI). Additionally, C-reactive protein (CRP) levels in rs11634397 (AA) with a median of 5389.0 (2767.4–7412.8) were significantly higher than in the heterozygous GA genotype with a median of 1736.3 (1024.4–4452.0) (p < 0.01). In conclusion, only five of the 37 genetic variants previously linked to T2DM and obesity in the Saudi Arabian population [HNF4A-rs4812829, WFS1-rs1801214, DUSP9-rs5945326, ZFAND6-rs11634397, FTO-rs11642841] were associated with prediabetes susceptibility. Prospective studies are needed to confirm the potential clinical value of the studied genetic variants of interest.

Liver fat storage is controlled by HNF4α through induction of lipophagy and is reversed by a potent HNF4α agonist

We report the discovery of strong HNF4α agonists and their use to uncover a previously unknown pathway by which HNF4α controls the level of fat storage in the liver. This involves the induction of lipophagy by dihydroceramides, the synthesis and secretion of which is controlled by genes induced by HNF4α. The HNF4α activators are N-trans caffeoyltyramine (NCT) and N-trans feruloyltyramine (NFT), which are structurally related to the known drugs alverine and benfluorex, which we previously showed to be weak HNF4α activators. In vitro, NCT and NFT induced fat clearance from palmitate-loaded cells. In DIO mice, NCT led to recovery of hepatic HNF4α expression and reduction of steatosis. Mechanistically, increased dihydroceramide production and action downstream of HNF4α occurred through increased expression of HNF4α downstream genes, including SPNS2 and CYP26A1. NCT was completely nontoxic at the highest dose administered and so is a strong candidate for an NAFLD therapeutic.

Metabolism and Toxicity of Emodin: Genome-Wide Association Studies Reveal Hepatocyte Nuclear Factor 4α Regulates UGT2B7 and Emodin Glucuronidation

Emodin is the main toxic component in Chinese medicinal herbs such as rhubarb. Our previous studies demonstrated that genetic polymorphisms of UDP-glucuronosyltransferase 2B7 (UGT2B7) had an effect on the glucuronidation and detoxification of emodin. This study aimed to reveal the transcriptional regulation mechanism of UGT2B7 on emodin glucuronidation and its effect on toxicity. Emodin glucuronic activity and genome and transcriptome data were obtained from 36 clinical human kidney tissues. The genome-wide association studies (GWAS) identified that four single nucleotide polymorphisms (SNPs) (rs6093966, rs2868094, rs2071197, and rs6073433), which were located on the hepatocyte nuclear factor 4α (HNF4A) gene, were significantly associated with the emodin glucuronidation (p < 0.05). Notably, rs2071197 was significantly associated with the gene expression of HNF4A and UGT2B7 and the glucuronidation of emodin. The gene expression of HNF4A showed a high correlation with UGT2B7 (R² = 0.721, p = 5.83 × 10^-11). The luciferase activity was increased 7.68-fold in 293T cells and 2.03-fold in HepG2 cells, confirming a significant transcriptional activation of UGT2B7 promoter by HNF4A. The knockdown of HNF4A in HepG2 cells (36.6%) led to a significant decrease of UGT2B7 (19.8%) and higher cytotoxicity (p < 0.05). The overexpression of HNF4A in HepG2 cells (31.2%) led to a significant increase of UGT2B7 (24.4%) and improved cell viability (p < 0.05). Besides, HNF4A and UGT2B7 were both decreased in HepG2 cells and rats after treatment with emodin. In conclusion, emodin used long term or in high doses could inhibit the expression of HNF4A, thereby reducing the expression of UGT2B7 and causing hepatotoxicity.

Hepatic TET3 contributes to type-2 diabetes by inducing the HNF4α fetal isoform

Precise control of hepatic glucose production (HGP) is pivotal to maintain systemic glucose homeostasis. HNF4α functions to stimulate transcription of key gluconeogenic genes. HNF4α harbors two promoters (P2 and P1) thought to be primarily active in fetal and adult livers, respectively. Here we report that the fetal version of HNF4α is required for HGP in the adult liver. This isoform is acutely induced upon fasting and chronically increased in type-2 diabetes (T2D). P2 isoform induction occurs in response to glucagon-stimulated upregulation of TET3, not previously shown to be involved in HGP. TET3 is recruited to the P2 promoter by FOXA2, leading to promoter demethylation and increased transcription. While TET3 overexpression augments HGP, knockdown of either TET3 or the P2 isoform alone in the liver improves glucose homeostasis in dietary and genetic mouse models of T2D. These studies unmask an unanticipated, conserved regulatory mechanism in HGP and offer potential therapeutic targets for T2D.

The HNF4α gene contains two promoters, which are thought to be active in the fetal and adult liver, the latter contributing to hepatic glucose production. Here the authors show that the fetal isoform of HNF4a is induced in mouse livers upon fasting and in type-2 diabetes in a manner regulated by TET3.

Computational analyses of type 2 diabetes-associated loci identified by genome-wide association studies

BACKGROUND

Genome-wide association studies (GWAS) of type 2 diabetes (T2D) have discovered a number of loci that contribute to susceptibility to the disease. Future challenges include elucidation of functional mechanisms through which these GWAS-identified loci modulate T2D disease risk. The aim of the present study was to comprehensively characterize T2D associated single nucleotide polymorphisms (SNPs) and genes through computational approaches.

METHODS

Computational biology approaches used in the present study included comparative genomic analyses and functional annotation using GWAS3D and RegulomeDB, investigation of the effects of T2D-associated SNPs on miRNA binding and protein phosphorylation, and gene ontology, pathway enrichment, protein-protein interaction (PPI) networks and functional module analysis of T2D-associated genes from previously published GWAS.

RESULTS

Computational analysis identified a number of T2D GWAS-associated SNPs that were located at protein binding sites, including CCCTC-binding factor (CTCF), E1A binding protein p300 (EP300), hepatocyte nuclear factor 4alpha (HNF4A), transcription factor 7 like 2 (TCF7L2), forkhead box A1 (FOXA1) and A2 (FOXA2), and potentially affected the binding of miRNAs and protein phosphorylation. Pathway enrichment analysis confirmed two well-known maturity onset diabetes of the young and T2D pathways, whereas PPI network analysis identified highly interconnected "hub" genes, such as TCF7L2, melatonin receptor 1B (MTNR1B), and solute carrier family 30 (zinc transporter), member 8 (SLC30A8), that created two tight subnetworks.

CONCLUSIONS

The results provide objectives and clues for future experimental studies and further insights into the molecular pathogenesis of T2D.

ISN Forefronts Symposium 2015: Nuclear Receptors and Diabetic Nephropathy

Diabetic nephropathy (DN) is the major reason for end stage renal disease in the western world. Patients with DN developed more severe cardiovascular complications with worse prognosis. In spite of tight blood pressure and glucose control through applying angiotensin II receptor antagonism, angiotensin receptor inhibitors and even direct renin inhibitors, the progression and development of DN has continued to accelerate. Nuclear receptors are, with few exceptions, ligand-depended transcription factors some of which modulate genes involved in the transportation and metabolism of carbohydrate or lipid, and inflammation. Considering the diverse biological functions of nuclear receptors, efforts have been made to explore their contributions to the pathogenesis of DN and potential therapeutic strategies. This review is mainly focused on the association between various nuclear receptors and the pathogenesis of DN, the potential beneficial effects of targeting these receptors for preventing the progress of DN, and the important role that nuclear receptors may play in future therapeutic strategies for DN.

Analysis of single nucleotide polymorphisms implicate mTOR signalling in the development of new-onset diabetes after transplantation

Introduction

Despite excellent first year outcomes in kidney transplantation, there remain significant long-term complications related to new-onset diabetes after transplantation (NODAT). The purpose of this study was to validate the findings of previous investigations of candidate gene variants in patients undergoing a protocolised, contemporary immunosuppression regimen, using detailed serial biochemical testing to identify NODAT development.

Methods

One hundred twelve live and deceased donor renal transplant recipients were prospectively followed-up for NODAT onset, biochemical testing at days 7, 90, and 365 after transplantation. Sixty-eight patients were included after exclusion for non-white ethnicity and pre-transplant diabetes. Literature review to identify candidate gene variants was undertaken as described previously.

Results

Over 25% of patients developed NODAT. In an adjusted model for age, sex, BMI, and BMI change over 12 months, five out of the studied 37 single nucleotide polymorphisms (SNPs) were significantly associated with NODAT: rs16936667:PRDM14 OR 10.57;95% CI 1.8–63.0;p = 0.01, rs1801282:PPARG OR 8.5; 95% CI 1.4–52.7; p = 0.02, rs8192678:PPARGC1A OR 0.26; 95% CI 0.08–0.91; p = 0.03, rs2144908:HNF4A OR 7.0; 95% CI 1.1–45.0;p = 0.04 and rs2340721:ATF6 OR 0.21; 95%CI 0.04–1.0; p = 0.05.

Conclusion

This study represents a replication study of candidate SNPs associated with developing NODAT and implicates mTOR as the central regulator via altered insulin sensitivity, pancreatic β cell, and mitochondrial survival and dysfunction as evidenced by the five SNPs.

General significance

1)

Highlights the importance of careful biochemical phenotyping with oral glucose tolerance tests to diagnose NODAT in reducing time to diagnosis and missed cases.

2)

This alters potential genotype:phenotype association.

3)

The replication study generates the hypothesis that mTOR signalling pathway may be involved in NODAT development.

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Oral glucose tolerance tests reduce time to NODAT diagnosis and missed cases

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Biochemical testing changes genotype:phenotype association

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mTOR signalling pathway may be involved in NODAT development

Differential transcriptomic and metabolic profiles of M. africanum- and M. tuberculosis-infected patients after, but not before, drug treatment

The epidemiology of Mycobacterium tuberculosis (Mtb) and M. africanum (Maf) suggest differences in their virulence, but the host immune profile to better understand the pathogenesis of tuberculosis (TB) have not been studied. We compared the transcriptomic and metabolic profiles between Mtb and Maf-infected TB cases to identify host biomarkers associated with lineages-specific pathogenesis and response to anti-TB chemotherapy. Venous blood samples from Mtb- and Maf-infected patients obtained before and after anti-TB treatment were analysed for cell composition, gene expression and metabolic profiles. Prior to treatment, similar transcriptomic profiles were seen in Maf- and Mtb-infected patients. In contrast, post-treatment, over 1600 genes related to immune responses and metabolic diseases were differentially expressed between the groups. Notably, the upstream regulator hepatocyte nuclear factor 4-alpha (HNF4α), which regulated 15% of these genes, was markedly enriched. Serum metabolic profiles were similar in both group pre-treatment, but the decline in pro-inflammatory metabolites post-treatment were most pronounced in Mtb-infected patients. Together, the differences in both peripheral blood transcriptomic and serum metabolic profiles between Maf- and Mtb-infected patients observed over the treatment period, might be indicative of intrinsic host factors related to susceptibility to TB and/or differential efficacy of the standard anti-TB treatment on the two lineages.

Genetic variants in transcription factors are associated with the pharmacokinetics and pharmacodynamics of metformin

One-third of type 2 diabetes patients do not respond to metformin. Genetic variants in metformin transporters have been extensively studied as a likely contributor to this high failure rate. Here, we investigate, for the first time, the effect of genetic variants in transcription factors on metformin pharmacokinetics (PK) and response. Overall, 546 patients and healthy volunteers contributed their genome-wide, pharmacokinetic (235 subjects), and HbA1c data (440 patients) for this analysis. Five variants in specificity protein 1 (SP1), a transcription factor that modulates the expression of metformin transporters, were associated with changes in treatment HbA1c (P < 0.01) and metformin secretory clearance (P < 0.05). Population pharmacokinetic modeling further confirmed a 24% reduction in apparent clearance in homozygous carriers of one such variant, rs784888. Genetic variants in other transcription factors, peroxisome proliferator-activated receptor-α and hepatocyte nuclear factor 4-α, were significantly associated with HbA1c change only. Overall, our study highlights the importance of genetic variants in transcription factors as modulators of metformin PK and response.

Hepatocyte nuclear factor 4α transactivates the mitochondrial alanine aminotransferase gene in the kidney of Sparus aurata

Alanine aminotransferase (ALT) plays an important role in amino acid metabolism and gluconeogenesis. The preference of carnivorous fish for protein amino acids instead of carbohydrates as a source of energy lead us to study the transcriptional regulation of the mitochondrial ALT (mALT) gene and to characterize the enzyme kinetics and modulation of mALT expression in the kidney of gilthead sea bream (Sparus aurata) under different nutritional and hormonal conditions. 5'-Deletion analysis of mALT promoter in transiently transfected HEK293 cells, site-directed mutagenesis and electrophoretic mobility shift assays allowed us to identify HNF4α as a new factor involved in the transcriptional regulation of mALT expression. Quantitative RT-PCR assays showed that starvation and the administration of streptozotocin (STZ) decreased HNF4α levels in the kidney of S. aurata, leading to the downregulation of mALT transcription. Analysis of the tissue distribution showed that kidney, liver, and intestine were the tissues with higher mALT and HNF4α expression. Kinetic analysis indicates that mALT enzyme is more efficient in catalyzing the conversion of L: -alanine to pyruvate than the reverse reaction. From these results, we conclude that HNF4α transactivates the mALT promoter and that the low levels of mALT expression found in the kidney of starved and STZ-treated fish result from a decreased expression of HNF4α. Our findings suggest that the mALT isoenzyme plays a major role in oxidazing dietary amino acids, and points to ALT as a target for a biotechnological action to spare protein and optimize the use of dietary nutrients for fish culture.

Upregulation of Scavenger Receptor BI by Hepatic Nuclear Factor 4α through a Peroxisome Proliferator-Activated Receptor γ-Dependent Mechanism in Liver

Hepatic nuclear factor 4α (HNF4α) modulates the transcriptional activation of numerous metabolic genes in liver. In this study, gene-array analysis revealed that HNF4α overexpression increased peroxisome proliferator-activated receptorγ (PPARγ) greatly in cultured rat primary hepatocytes. PPAR-response-element-driven reporter gene expression could be elevated by HNF4α. Bioinformatics analysis revealed a high-affinity HNF4α binding site in the human PPARγ2 promoter and in vitro experiments showed that this promoter could be transactivated by HNF4α. The presence of HNF4α on the promoter was then confirmed by ChIP assay. In vivo, hepatic overexpression of HNF4α decreased cholesterol levels both in plasma and liver and several hepatic genes related to cholesterol metabolism, including scavenger receptor BI (SR-BI), were upregulated. The upregulation of SR-BI by HNF4α could be inhibited by a PPARγ antagonist in vitro. In conclusion, HNF4α regulates cholesterol metabolism in rat by modulating the expression of SR-BI in the liver, in which the upregulation of PPARγ was involved.

Nuclear hormone receptors in diabetic nephropathy

Diabetes is the leading cause of end-stage renal disease in developed countries. In spite of glucose and blood pressure control, for example by use of angiotensin II receptor blockers, diabetic nephropathy still develops and progresses in affected patients and the development of additional protective therapeutic interventions is, therefore, required. Nuclear hormone receptors are transcription factors that regulate carbohydrate metabolism, lipid metabolism, the immune response, and inflammation. These receptors also modulate the development of fibrosis. As a result of their diverse biological effects, nuclear hormone receptors have become major pharmaceutical targets for the treatment of a host of diseases. The increasing prevalence of diabetic nephropathy has led intense investigation into the role that nuclear hormone receptors may have in slowing or preventing the progression of renal disease. This role of nuclear hormone receptors would be associated with improvements in metabolism, the immune response, and inflammation. Eight nuclear receptors have shown a renoprotective effect in the context of diabetic nephropathy. This Review discusses the evidence regarding the beneficial effects of the activation of these receptors in preventing the progression of diabetic nephropathy and describes how the discovery and development of compounds that modulate the activity of nuclear hormone receptors may provide potential additional therapeutic approaches in the management of diabetic nephropathy.

Complete complement deficiency in a large cohort of familial systemic lupus erythematosus

Genetic complete deficiency of the early complement components such as C1, C2 and C4 commonly results in a monogenetic form of systemic lupus erythematosus (SLE). However, previous studies have examined groups of complete complement deficient subjects for SLE, while a familial SLE cohort has not been studied for deficiencies of complement. Thus, we undertook the present study to determine the frequency of hereditary complete complement deficiencies among families with two or more SLE patients. All SLE patients from 544 such families had CH50 determined. Medical records were examined for past CH50 values. There were 66 individuals in whom all available CH50 values were zero. All but four of these had a SLE-affected relative with a non-zero CH50; thus, these families did not have monogenetic complement deficient related SLE. The four remaining SLE-affected subjects were in fact two sets of siblings in which three of the four SLE patients had onset of disease at <18 years of age. Both patients in one of these families had been determined to have C4 deficiency, while the other family had no clinical diagnosis of complement deficiency. In this second family, one of the SLE patients had had normal C4 and C3 values, indicating that either C1q or C2 deficiency was possible. Thus, only 2 of 544 SLE families had definite or possible complement deficiency; however, 1 of 7 families in which all SLE patients had pediatric onset and 2 of 85 families with at least 1 pediatric-onset SLE patent had complete complement deficiency. SLE is found commonly among families with hereditary complement deficiency but the reverse is not true. Complete complement deficiency is rare among families with two or more SLE patients, but is concentrated among families with onset of SLE prior to age 18.

A general integrative genomic feature transcription factor binding site prediction method applied to analysis of USF1 binding in cardiovascular disease

Transcription factors are key mediators of human complex disease processes. Identifying the target genes of transcription factors will increase our understanding of the biological network leading to disease risk. The prediction of transcription factor binding sites (TFBSs) is one method to identify these target genes; however, current prediction methods need improvement. We chose the transcription factor upstream stimulatory factor l (USF1) to evaluate the performance of our novel TFBS prediction method because of its known genetic association with coronary artery disease (CAD) and the recent availability of USF1 chromatin immunoprecipitation microarray (ChIP-chip) results. The specific goals of our study were to develop a novel and accurate genome-scale method for predicting USF1 binding sites and associated target genes to aid in the study of CAD. Previously published USF1 ChIP-chip data for 1 per cent of the genome were used to develop and evaluate several kernel logistic regression prediction models. A combination of genomic features (phylogenetic conservation, regulatory potential, presence of a CpG island and DNaseI hypersensitivity), as well as position weight matrix (PWM) scores, were used as variables for these models. Our most accurate predictor achieved an area under the receiver operator characteristic curve of 0.827 during cross-validation experiments, significantly outperforming standard PWM-based prediction methods. When applied to the whole human genome, we predicted 24,010 USF1 binding sites within 5 kilobases upstream of the transcription start site of 9,721 genes. These predictions included 16 of 20 genes with strong evidence of USF1 regulation. Finally, in the spirit of genomic convergence, we integrated independent experimental CAD data with these USF1 binding site prediction results to develop a prioritised set of candidate genes for future CAD studies. We have shown that our novel prediction method, which employs genomic features related to the presence of regulatory elements, enables more accurate and efficient prediction of USF1 binding sites. This method can be extended to other transcription factors identified in human disease studies to help further our understanding of the biology of complex disease.

Novel P2 promoter-derived HNF4alpha isoforms with different N-terminus generated by alternate exon insertion

Hepatocyte nuclear factor 4alpha (HNF4alpha) is a critical transcription factor for pancreas and liver development and functions in islet beta cells to maintain glucose homeostasis. Mutations in the human HNF4A gene lead to maturity onset diabetes of the young (MODY1) and polymorphisms are associated with increased risk for type 2 diabetes mellitus (T2DM). Expression of six HNF4alpha variants, three each from two developmentally regulated promoters, has been firmly established. We have now detected a new set of HNF4alpha variants designated HNF4alpha10-12 expressed from distal promoter P2. These variants, generated by inclusion of previously undetected exon 1E (human=222 nt, rodent=136 nt) following exon 1D have an altered N-terminus but identical remaining reading frame. HNF4alpha10-alpha12 are expressed in pancreatic islets (and liver) and exhibit transactivation potentials similar to the corresponding alpha7-alpha9 isoforms. DNA-binding analyses implied much higher protein levels of HNF4alpha10-alpha12 in liver than expected from the RT-PCR data. Our results provide evidence for a more complex expression pattern of HNF4alpha than previously appreciated. We recommend inclusion of exon 1E and nearby DNA sequences in screening for HNF4alpha mutations and polymorphisms in genetic analyses of MODY1 and T2DM.

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.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

HNF4 alpha and the Ca-channel TRPC1 are novel disease candidate genes in diabetic nephropathy

OBJECTIVE

The nuclear receptor hepatic nuclear factor 4 alpha (HNF 4 alpha) is a master regulatory protein and an essential player in the control of a wide range of metabolic processes. Dysfunction of HNF 4 alpha is associated with metabolic disorders including diabetes. We were particularly interested in investigating molecular causes associated with diabetic nephropathy.

RESEARCH DESIGN AND METHODS

Novel disease candidate genes were identified by the chromatin immunoprecipitation-cloning assay and by sequencing of immunoprecipitated DNA. Expression of candidate genes was analyzed in kidney and liver of Zucker diabetic fatty (ZDF) and of streptozotocin (STZ)-administered rats and after siRNA-mediated silencing of HNF 4 alpha.

RESULTS

We identified the calcium-permeable nonselective transient receptor potential cation channel, subfamily C, member 1 (TRPC1) as a novel HNF 4 alpha gene target. Strikingly, TRPC1 is localized on human chromosome 3q22-24, i.e., a region considered to be a hotspot for diabetic nephropathy. We observed a significant reduction of TRPC1 gene expression in kidney and liver of diabetic ZDF and of STZ-administered rats as a result of HNF 4 alpha dysfunction. We found HNF 4 alpha and TRPC1 protein expression to be repressed in kidneys of diabetic patients diagnosed with nodular glomerulosceloris as evidenced by immunohistochemistry. Finally, siRNA-mediated functional knock down of HNF 4 alpha repressed TRPC1 gene expression in cell culture experiments.

CONCLUSIONS

Taken collectively, results obtained from animal studies could be translated to human diabetic nephropathy; there is evidence for a common regulation of HNF 4 alpha and TRPC1 in human and rat kidney pathologies. We propose dysregulation of HNF 4 alpha and TRPC1 as a possible molecular rationale in diabetic nephropathy.

HNF4A genetic variants: role in diabetes

PURPOSE OF REVIEW

Variants in the hepatocyte nuclear factor 4alpha (HNF4A) gene play a role in the development of diabetes mellitus. Although genetic variation in and around HNF4A regulatory regions has received considerable attention, the significance of these variants in the common type 2 diabetes varies in the literature. This review will provide a general overview of recent genetic studies involving the evaluation of HNF4A as a contributor to the risk and pathophysiology of diabetes mellitus and related risk factors.

RECENT FINDINGS

These studies report newly identified variants, evaluate previously reported polymorphisms that were associated with type 2 diabetes in several distinct populations with maturity-onset diabetes of the young, type 2 diabetes, gestational diabetes, and diabetes related risk factors, and propose a role for HNF4A in insulin secretion via the potassium ATP channel.

SUMMARY

HNF4A variants identified so far appear to modestly contribute to predisposition for type 2 diabetes. Continued identification and especially functional characterization of variants, however, will be critical in future studies to enhance our understanding of the metabolic impact of this gene.

Evaluation of polymorphisms known to contribute to risk for diabetes in African and African-American populations

PURPOSE OF REVIEW

Populations of direct African ancestry have much greater genetic diversity than do other populations. African-American populations exhibit twice the prevalence of type 2 diabetes as compared with their Caucasian counterparts. African-American populations are likely to have unique genetic susceptibility to type 2 diabetes. This review addresses current knowledge of susceptibility genes that are shared with other groups and those that are unique to populations of African descent.

RECENT FINDINGS

When compared with the plethora of Caucasian studies, relatively few studies have been conducted in African or African-American populations. The most exciting findings have been family-based linkage studies, which point to multiple regions that may harbor susceptibility genes. Recent work suggests that the major Caucasian locus, TCF7L2, plays a role in some African-based populations, whereas unique factors remain to be confirmed.

SUMMARY

Although progress has been made in finding the genetic cause of type 2 diabetes in African and African-American populations, at this time no variant can be considered unequivocally confirmed as a diabetes susceptibility locus.

Glycerol kinase deficiency alters expression of genes involved in lipid metabolism, carbohydrate metabolism, and insulin signaling

Glycerol kinase (GK) is at the interface of fat and carbohydrate metabolism and has been implicated in insulin resistance and type 2 diabetes mellitus. To define GK's role in insulin resistance, we examined gene expression in brown adipose tissue in a glycerol kinase knockout (KO) mouse model using microarray analysis. Global gene expression profiles of KO mice were distinct from wild type with 668 differentially expressed genes. These include genes involved in lipid metabolism, carbohydrate metabolism, insulin signaling, and insulin resistance. Real-time polymerase chain reaction analysis confirmed the differential expression of selected genes involved in lipid and carbohydrate metabolism. PathwayAssist analysis confirmed direct and indirect connections between glycerol kinase and genes in lipid metabolism, carbohydrate metabolism, insulin signaling, and insulin resistance. Network component analysis (NCA) showed that the transcription factors (TFs) PPAR-gamma, SREBP-1, SREBP-2, STAT3, STAT5, SP1, CEBPalpha, CREB, GR and PPAR-alpha have altered activity in the KO mice. NCA also revealed the individual contribution of these TFs on the expression of genes altered in the microarray data. This study elucidates the complex network of glycerol kinase and further confirms a possible role for glycerol kinase deficiency, a simple Mendelian disorder, in insulin resistance, and type 2 diabetes mellitus, a common complex genetic disorder.

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.

Mutations in the genes encoding the transcription factors hepatocyte nuclear factor 1 alpha (HNF1A) and 4 alpha (HNF4A) in maturity-onset diabetes of the young

Maturity-onset diabetes of the young (MODY) is a monogenic form of diabetes mellitus characterized by autosomal dominant inheritance, early age of onset (often <25 years of age), and pancreatic beta-cell dysfunction. MODY is both clinically and genetically heterogeneous, with six different genes identified to date; glucokinase (GCK), hepatocyte nuclear factor-1 alpha (HNF1A, or TCF1), hepatocyte nuclear factor-4 alpha (HNF4A), insulin promoter factor-1 (IPF1 or PDX1), hepatocyte nuclear factor-1 beta (HNF1B or TCF2), and neurogenic differentiation 1 (NEUROD1). Mutations in the HNF1A gene are a common cause of MODY in the majority of populations studied. A total of 193 different mutations have been described in 373 families. The most common mutation is Pro291fs (P291fsinsC) in the polycytosine (poly C) tract of exon 4, which has been reported in 65 families. HNF4A mutations are rarer; 31 mutations reported in 40 families. Sensitivity to treatment with sulfonylurea tablets is a feature of both HNF1A and HNF4A mutations. The identification of an HNF1A or 4A gene mutation confirms a diagnosis of MODY and has important implications for clinical management.

Common variants in maturity-onset diabetes of the young genes contribute to risk of type 2 diabetes in Finns

Prior reports have suggested that variants in the genes for maturity-onset diabetes of the young (MODY) may confer susceptibility to type 2 diabetes, but results have been conflicting and coverage of the MODY genes has been incomplete. To complement our previous studies of HNF4A, we examined the other five known MODY genes for association with type 2 diabetes in Finnish individuals. For each of the five genes, we selected 1) nonredundant single nucleotide polymorphisms (SNPs) (r(2)< 0.8 with other SNPs) from the HapMap database or another linkage disequilibrium map, 2) SNPs with previously reported type 2 diabetes association, and 3) nonsynonymous coding SNPs. We tested 128 SNPs for association with type 2 diabetes in 786 index cases from type 2 diabetic families and 619 normal glucose-tolerant control subjects. We followed up 35 of the most significant SNPs by genotyping them on another 384 case subjects and 366 control subjects from Finland. We also supplemented our previous HNF4A results by genotyping 12 SNPs on additional Finnish samples. After correcting for testing multiple correlated SNPs within a gene, we find evidence of type 2 diabetes association with SNPs in five of the six known MODY genes: GCK, HNF1A, HNF1B, NEUROD1, and HNF4A. Our data suggest that common variants in several MODY genes play a modest role in type 2 diabetes susceptibility.