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

In Vitro Functional Analysis Can Aid Precision Diagnostics of HNF1B-MODY

Precision medicine relies on accurate and consistent classification of sequence variants. A correct diagnosis of hepatocyte nuclear factor (HNF) 1B maturity-onset diabetes of the young, caused by pathogenic variants in the HNF1B gene, is important for optimal disease management and prognosis, and it has implications for genetic counseling and follow-up of at-risk family members. We hypothesized that the functional characterization could provide valuable information to assist the interpretation of pathogenicity of HNF1B variants. Using different in vitro functional assays, variants identified among 313 individuals, suspected to have monogenic diabetes with or without kidney disease, were characterized. The data from the functional assays were subsequently conjugated with obtained clinical, biochemical, and in silico data. Two variants (p.A167P, p.H336Pfs∗22) showed severe loss of function due to impaired transactivation, reduced DNA binding (p.A167P), and mRNA instability (p.A167P). Although both these variant carriers were diagnosed with diabetes, the p.H336Pfs∗22 carrier also had congenital absence of a kidney, which is a characteristic trait for HNF1B maturity-onset diabetes of the young. Functional analysis of the p.A167P variant revealed damaging effects on HNF-1B protein function, which may warrant imaging of the kidneys and/or pancreas. In addition, the current study has generated important data, including evidence supporting the benign functional impact of five variants (p.D82N, p.T88A, p.N394D, p.V458G, and p.T544A), and piloting new approaches that will prove critical for the growth of HNF1B-diabetes diagnosis.

Lysine 117 Residue Is Essential for the Function of the Hepatocyte Nuclear Factor 1α

Hepatocyte nuclear factor 1α (HNF1α) plays essential roles in controlling development and metabolism; its mutations are clearly linked to the occurrence of maturity-onset diabetes of the young (MODY3) in humans. Lysine 117 (K117) to glutamic acid (E117) mutation in the HNF1α gene has been clinically associated with MODY3, but no functional data on this variant are available. Here, we addressed the role of lysine 117 in HNF1α function using a knock-in animal model and site-directed mutagenesis. HNF1α K117E homozygous mice exhibited dwarfism, hepatic dysfunction, renal Fanconi syndrome, and progressive wasting syndrome. These phenotypes were very similar to those of mice with complete HNF1α deficiency, suggesting that K117 is critical to HNF1α functions. K117E homozygotes developed diabetes in the early postnatal period. The relative deficiency of serum insulin levels and the normal response to insulin treatment in homozygous mice were markedly similar to those in the MODY3 disorder in humans. Moreover, K117E heterozygous mutant causes age-dependent glucose intolerance, which is similar to the pathogenesis of MODY3 as well. K117 mutants significantly reduced the overall transactivation and DNA binding capacity of HNF1α by disrupting dimerization. Collectively, our findings reveal a previously unappreciated role of POU domain of HNF1α in homodimerization and provide important clues for identifying the molecular basis of HNF1α-related diseases such as MODY3.

ARTICLE HIGHLIGHTS

HNF1α K117E homozygous mice exhibited dwarfism, hepatic dysfunction, renal Fanconi syndrome, and progressive wasting syndrome. K117E homozygotes developed diabetes in the early postnatal period. K117E heterozygous mutant causes age-dependent glucose intolerance, which is similar to the pathogenesis of maturity-onset diabetes of the young. K117 mutants significantly reduced the overall transactivation and DNA binding capacity of HNF1α by disrupting dimerization.

Human gain-of-function variants in HNF1A confer protection from diabetes but independently increase hepatic secretion of atherogenic lipoproteins

Loss-of-function mutations in hepatocyte nuclear factor 1A (HNF1A) are known to cause rare forms of diabetes and alter hepatic physiology through unclear mechanisms. In the general population, 1:100 individuals carry a rare, protein-coding HNF1A variant, most of unknown functional consequence. To characterize the full allelic series, we performed deep mutational scanning of 11,970 protein-coding HNF1A variants in human hepatocytes and clinical correlation with 553,246 exome-sequenced individuals. Surprisingly, we found that ∼1:5 rare protein-coding HNF1A variants in the general population cause molecular gain of function (GOF), increasing the transcriptional activity of HNF1A by up to 50% and conferring protection from type 2 diabetes (odds ratio [OR] = 0.77, p = 0.007). Increased hepatic expression of HNF1A promoted a pro-atherogenic serum profile mediated in part by enhanced transcription of risk genes including ANGPTL3 and PCSK9. In summary, ∼1:300 individuals carry a GOF variant in HNF1A that protects carriers from diabetes but enhances hepatic secretion of atherogenic lipoproteins.

Molecular characterization and re-interpretation of HNF1A variants identified in Indian MODY subjects towards precision medicine

Background

HNF1A is an essential component of the transcription factor network that controls pancreatic β-cell differentiation, maintenance, and glucose stimulated insulin secretion (GSIS). A continuum of protein malfunction is caused by variations in the HNF1A gene, from severe loss-of-function (LOF) variants that cause the highly penetrant Maturity Onset Diabetes of the Young (MODY) to milder LOF variants that are far less penetrant but impart a population-wide risk of type 2 diabetes that is up to five times higher. Before classifying and reporting the discovered variations as relevant in clinical diagnosis, a critical review is required. Functional investigations offer substantial support for classifying a variant as pathogenic, or otherwise as advised by the American College of Medical Genetics and Genomics (ACMG) and the Association for Molecular Pathology (AMP) ACMG/AMP criteria for variant interpretation.

Objective

To determine the molecular basis for the variations in the HNF1A gene found in patients with monogenic diabetes in India.

Methods

We performed functional protein analyses such as transactivation, protein expression, DNA binding, nuclear localization, and glucose stimulated insulin secretion (GSIS) assay, along with structural prediction analysis for 14 HNF1A variants found in 20 patients with monogenic diabetes.

Results

Of the 14 variants, 4 (28.6%) were interpreted as pathogenic, 6 (42.8%) as likely pathogenic, 3 (21.4%) as variants of uncertain significance, and 1 (7.14%) as benign. Patients harboring the pathogenic/likely pathogenic variants were able to successfully switch from insulin to sulfonylureas (SU) making these variants clinically actionable.

Conclusion

Our findings are the first to show the need of using additive scores during molecular characterization for accurate pathogenicity evaluations of HNF1A variants in precision medicine.

HNF1α upregulation and promoter hypermethylation as a cause of glucose dysregulation: a case-control study of Kashmiri MODY population

AIM

HNF1α transcription factor regulates a network of genes involved in the development of β-cells and also serves as a model for transcription defects in pancreatic β-cells; mutations in this gene cause MODY. The goal of this study was to assess the promoter methylation and expression profile of the most common MODY causing gene, HNF1α, in Kashmiri MODY patients, as factors responsible for glucose dysregulation, as no such study had been performed on MODY patients in Kashmir previously.

METHODS

The study included 85 Kashmiri subjects. Samples were extracted for DNA and RNA using standard protocols. The HNF1α promoter methylation profile was assessed by bisulfite conversion of the DNA followed by MSP, whereas qPCR was used for expression analysis.

RESULTS

The expression of HNF1α was found to be upregulated (p value 0.0349*) in majority of MODY (60%) and T1D (72%) cases (p value 0.0349*). HNF1α expression was 1.33-fold higher in MODY cases with hypermethylated HNF1α promoters (p value 0.0360*). HNF1α expression was upregulated by 2.3-fold in MODY patients with HbA1c levels > 7% (p value 0.0025**). MODY cases with FBS levels > 7.7 mmol/l were upregulated by 0.646-fold than those with FBS levels ≤ 7.7 mmol/l (p value 0.0161*).

CONCLUSION

In this study, we found that as glucose dysregulation progresses, blood FBS, RBS, and HbA1c levels rise, and that at higher levels, HNF1α expression rises as well. From the results obtained, we may conclude that HNF1α is strongly upregulated in MODY, thus indicating the deleterious effect of over expression of HNF1α gene on glucose regulation.

HNF1A POU Domain Mutations Found in Japanese Liver Cancer Patients Cause Downregulation of HNF4A Promoter Activity with Possible Disruption in Transcription Networks

Hepatocyte nuclear factor 1A (HNF1A) is the master regulator of liver homeostasis and organogenesis and regulates many aspects of hepatocyte functions. It acts as a tumor suppressor in the liver, evidenced by the increased proliferation in HNF1A knockout (KO) hepatocytes. Hence, we postulated that any loss-of-function variation in the gene structure or composition (mutation) could trigger dysfunction, including disrupted transcriptional networks in liver cells. From the International Cancer Genome Consortium (ICGC) database of cancer genomes, we identified several HNF1A mutations located in the functional Pit-Oct-Unc (POU) domain. In our biochemical analysis, we found that the HNF1A POU-domain mutations Y122C, R229Q and V259F suppressed HNF4A promoter activity and disrupted the binding of HNF1A to its target HNF4A promoter without any effect on the nuclear localization. Our results suggest that the decreased transcriptional activity of HNF1A mutants is due to impaired DNA binding. Through structural simulation analysis, we found that a V259F mutation was likely to affect DNA interaction by inducing large conformational changes in the N-terminal region of HNF1A. The results suggest that POU-domain mutations of HNF1A downregulate HNF4A gene expression. Therefore, to mimic the HNF1A mutation phenotype in transcription networks, we performed siRNA-mediated knockdown (KD) of HNF4A. Through RNA-Seq data analysis for the HNF4A KD, we found 748 differentially expressed genes (DEGs), of which 311 genes were downregulated (e.g., HNF1A, ApoB and SOAT2) and 437 genes were upregulated. Kyoto Encyclopedia of Genes and Genomes (KEGG) mapping revealed that the DEGs were involved in several signaling pathways (e.g., lipid and cholesterol metabolic pathways). Protein–protein network analysis suggested that the downregulated genes were related to lipid and cholesterol metabolism pathways, which are implicated in hepatocellular carcinoma (HCC) development. Our study demonstrates that mutations of HNF1A in the POU domain result in the downregulation of HNF1A target genes, including HNF4A, and this may trigger HCC development through the disruption of HNF4A–HNF1A transcriptional networks.

Stem Cell-Derived β Cells: A Versatile Research Platform to Interrogate the Genetic Basis of β Cell Dysfunction

Pancreatic β cell dysfunction is a central component of diabetes progression. During the last decades, the genetic basis of several monogenic forms of diabetes has been recognized. Genome-wide association studies (GWAS) have also facilitated the identification of common genetic variants associated with an increased risk of diabetes. These studies highlight the importance of impaired β cell function in all forms of diabetes. However, how most of these risk variants confer disease risk, remains unanswered. Understanding the specific contribution of genetic variants and the precise role of their molecular effectors is the next step toward developing treatments that target β cell dysfunction in the era of personalized medicine. Protocols that allow derivation of β cells from pluripotent stem cells, represent a powerful research tool that allows modeling of human development and versatile experimental designs that can be used to shed some light on diabetes pathophysiology. This article reviews different models to study the genetic basis of β cell dysfunction, focusing on the recent advances made possible by stem cell applications in the field of diabetes research.

Identification of Variants Responsible for Monogenic Forms of Diabetes in Brazil

Monogenic forms of diabetes mellitus may affect a significant number of patients of this disease, and it is an important molecular cause to be investigated. However, studies of the genetic causes of monogenic diabetes, especially in populations with mixed ethnic backgrounds, such as the one in Brazil, are scarce. The aim of this study was to screen several genes associated with monogenic diabetes in fifty-seven Brazilian patients with recurrence of the disease in their families and thirty-four relatives. Inclusion criteria were: Age of onset ≤ 40 years old, BMI < 30 kg/m², at least two affected generations and negative anti-GAD and anti-IA2 antibodies. MODY genes HNF4A, GCK, HNF1A, HNF1B, NEUROD1, KLF11, PAX4, INS, KCNJ11, and MT-TL1 were sequenced by Sanger sequencing. We identified a total of 20 patients with variants, 13 GCK-MODY, four HNF1A-MODY, and one variant in each of the following genes, HNF4A, HNF1B and MT-TL1. Segregation analysis was performed in 13 families. Four variants were novel, two in GCK (p.(Met115Val) [c.343A>G] and p.(Asp365GlufsTer95) [c.1094_1095insGCGA]) and two in HNF1A (p.(Tyr163Ter) [c.489C>G] and p.(Val380CysfsTer39) [c.1136_1137insC]). Here we highlight the importance of screening for monogenic diabetes in admixed populations.

HNF1A：From Monogenic Diabetes to Type 2 Diabetes and Gestational Diabetes Mellitus

Diabetes, a disease characterized by hyperglycemia, has a serious impact on the lives and families of patients as well as on society. Diabetes is a group of highly heterogeneous metabolic diseases that can be classified as type 1 diabetes (T1D), type 2 diabetes (T2D), gestational diabetes mellitus (GDM), or other according to the etiology. The clinical manifestations are more or less similar among the different types of diabetes, and each type is highly heterogeneous due to different pathogenic factors. Therefore, distinguishing between various types of diabetes and defining their subtypes are major challenges hindering the precise treatment of the disease. T2D is the main type of diabetes in humans as well as the most heterogeneous. Fortunately, some studies have shown that variants of certain genes involved in monogenic diabetes also increase the risk of T2D. We hope this finding will enable breakthroughs regarding the pathogenesis of T2D and facilitate personalized treatment of the disease by exploring the function of the signal genes involved. Hepatocyte nuclear factor 1 homeobox A (HNF1α) is widely expressed in pancreatic β cells, the liver, the intestines, and other organs. HNF1α is highly polymorphic, but lacks a mutation hot spot. Mutations can be found at any site of the gene. Some single nucleotide polymorphisms (SNPs) cause maturity-onset diabetes of the young type 3 (MODY3) while some others do not cause MODY3 but increase the susceptibility to T2D or GDM. The phenotypes of MODY3 caused by different SNPs also differ. MODY3 is among the most common types of MODY, which is a form of monogenic diabetes mellitus caused by a single gene mutation. Both T2D and GDM are multifactorial diseases caused by both genetic and environmental factors. Different types of diabetes mellitus have different clinical phenotypes and treatments. This review focuses on HNF1α gene polymorphisms, HNF1A-MODY3, HNF1A-associated T2D and GDM, and the related pathogenesis and treatment methods. We hope this review will provide a valuable reference for the precise and individualized treatment of diabetes caused by abnormal HNF1α by summarizing the clinical heterogeneity of blood glucose abnormalities caused by HNF1α mutation.

A Comprehensive Analysis of Hungarian MODY Patients-Part I: Gene Panel Sequencing Reveals Pathogenic Mutations in HNF1A, HNF1B, HNF4A, ABCC8 and INS Genes

Maturity-onset diabetes of the young (MODY) has about a dozen known causal genes to date, the most common ones being HNF1A, HNF4A, HNF1B and GCK. The phenotype of this clinically and genetically heterogeneous form of diabetes depends on the gene in which the patient has the mutation. We have tested 450 Hungarian index patients with suspected MODY diagnosis with Sanger sequencing and next-generation sequencing and found a roughly 30% positivity rate. More than 70% of disease-causing mutations were found in the GCK gene, about 20% in the HNF1A gene and less than 10% in other MODY-causing genes. We found 8 pathogenic and 9 likely pathogenic mutations in the HNF1A gene in a total of 48 patients and family members. In the case of HNF1A-MODY, the recommended first-line treatment is low dose sulfonylurea but according to our data, the majority of our patients had been on unnecessary insulin therapy at the time of requesting their genetic testing. Our data highlights the importance of genetic testing in the diagnosis of MODY and the establishment of the MODY subtype in order to choose the most appropriate treatment.

A Review of Functional Characterization of Single Amino Acid Change Mutations in HNF Transcription Factors in MODY Pathogenesis

Mutations in HNF transcription factor genes cause the most common subtypes of maturity-onset of diabetes of youth (MODY), a monogenic form of diabetes mellitus. Mutations in the HNF1-α, HNF4-α, and HNF1-β genes are primarily considered as the cause of MODY3, MODY1, and MODY5 subtypes, respectively. Although patients with different subtypes display similar symptoms, they may develop distinct diabetes-related complications and require different treatments depending on the type of the mutation. Genetic analysis of MODY patients revealed more than 400 missense/nonsense mutations in HNF1-α, HNF4-α, and HNF1-β genes, however only a small portion of them are functionally characterized. Evaluation of nonsense mutations are more direct as they lead to premature stop codons and mostly in mRNA decay or nonfunctional truncated proteins. However, interpretation of the single amino acid change (missense) mutation is not such definite, as effect of the variant may vary depending on the location and also the substituted amino acid. Mutations with benign effect on the protein function may not be the pathologic variant and further genetic testing may be required. Here, we discuss the functional characterization analysis of single amino acid change mutations identified in HNF1-α, HNF4-α, and HNF1-β genes and evaluate their roles in MODY pathogenesis. This review will contribute to comprehend HNF nuclear family-related molecular mechanisms and to develop more accurate diagnosis and treatment based on correct evaluation of pathologic effects of the variants.

HNF1A-MODY Mutations in Nuclear Localization Signal Impair HNF1A-Import Receptor KPNA6 Interactions

Mutations in hepatocyte nuclear factor (HNF)1A gene cause the most common form of Maturity-onset diabetes of the young (MODY), a monogenic subtype of diabetes mellitus. Functional characterization of mutant proteins reveals that mutations may disrupt DNA binding capacity, transactivation ability and nuclear localization of HNF1A depending on the position of the mutation. Previously identified Arg271Trp and Ser345Tyr mutations in HNF1A were found to be defective in nuclear localization. Arg271 residue resides in a region similar to classical nuclear localization signal (NLS) motif, while Ser345 does not. Importin α family members recognize NLS motifs on cargo proteins and subsequently translocate them into nucleus. Here, we first investigated the nuclear localization mechanism of wild type HNF1A protein. For this purpose, we analyzed the interaction of HNF1A with three mouse homolog importin α proteins (KPNA2, KPNA4 and KPNA6) by co-immunoprecipitation assay and molecular docking simulation. Hereby, KPNA6 was identified as the main import receptor, which is responsible for the transport of HNF1A into the nucleus. Immunolocalization studies in mouse pancreatic cells (Min6) also confirmed the co-localization of HNF1A and KPNA6 in the cytoplasm. Secondly, the interaction between KPNA6 and mutant HNF1A proteins (Arg271Trp and Ser345Tyr) was assessed. Co-immunoprecipitation studies revealed a reduced interaction compared to wild type HNF1A. Our study demonstrated for the first time that HNF1A transcription factor is recognized and transported by importin/karyopherin import family, and mutations in NLS motifs may disrupt the interaction leading to nuclear localization abnormalities and MODY phenotype.

Analysis of the promoter regions of disease-causing genes in maturity-onset diabetes of the young patients

Maturity-onset diabetes of the young (MODY) is a form of monogenic diabetes caused by the variants in MODY-related genes. In addition to coding variants, variants in the promoter region of MODY-related genes can cause the disease as well. In this study, we screened the promoter regions of the most common MODY-related genes GCK, HNF1A, HNF4A and HNF1B in our cohort of 29 MODY patients. We identified one genetic variant in the HNF1A gene, a 7 bp insertion c.-154-160insTGGGGGT, and three variants in the GCK gene, -282C>T; -194A>G; 402C>G appearing as set. Chloramphenicol acetyltransferase (CAT) assay was performed to test the effect of the 7 bp insertion and the variant set on the activity of the reporter gene in HepG2 and RIN-5F cell, respectively, where a decreasing trend was observed for both variants. In silico analysis and electrophoretic mobility shift assay showed that the 7 bp insertion did not create the binding site for new transcriptional factors, but gave rise to additional binding sites for the existing ones. Results from our study indicated that the 7 bp insertion in the HNF1A gene could be associated with the patient's diabetes. As for the GCK variant set, it is probably not associated with diabetes in patients, but it may modify the fasting glucose level by causing small elevation in variant set carriers. We have presented two promoter variants in MODY-related genes. Variant in the HNF1A gene is presumed to be disease-causing and the GCK promoter variant set could be a phenotype modifier.

Homozygous Hypomorphic HNF1A Alleles Are a Novel Cause of Young-Onset Diabetes and Result in Sulfonylurea-Sensitive Diabetes

OBJECTIVE

Heterozygous loss-of-function mutations in HNF1A cause maturity-onset diabetes of the young (MODY). Affected individuals can be treated with low-dose sulfonylureas. Individuals with homozygous HNF1A mutations causing MODY have not been reported.

RESEARCH DESIGN AND METHODS

We phenotyped a kindred with young-onset diabetes and performed molecular genetic testing, a mixed meal tolerance test, a sulfonylurea challenge, and in vitro assays to assess variant protein function.

RESULTS

A homozygous HNF1A variant (p.A251T) was identified in three insulin-treated family members diagnosed with diabetes before 20 years of age. Those with the homozygous variant had low hs-CRP levels (0.2-0.8 mg/L), and those tested demonstrated sensitivity to sulfonylurea given at a low dose, completely transitioning off insulin. In silico modeling predicted a variant of unknown significance; however, in vitro studies supported a modest reduction in transactivation potential (79% of that for the wild type; P < 0.05) in the absence of endogenous HNF1A.

CONCLUSIONS

Homozygous hypomorphic HNF1A variants are a cause of HNF1A-MODY. We thus expand the allelic spectrum of variants in dominant genes causing diabetes.

Novel insights into genetics and clinics of the HNF1A-MODY

MODY (Maturity Onset Diabetes of the Young) is a type of diabetes resulting from a pathogenic effect of gene mutations. Up to date, 13 MODY genes are known. Gene HNF1A is one of the most common causes of MODY diabetes (HNF1A-MODY; MODY3). This gene is polymorphic and more than 1200 pathogenic and non-pathogenic HNF1A variants were described in its UTRs, exons and introns. For HNF1A-MODY, not just gene but also phenotype heterogeneity is typical. Although there are some clinical instructions, HNF1A-MODY patients often do not meet every diagnostic criteria or they are still misdiagnosed as type 1 and type 2 diabetics. There is a constant effort to find suitable biomarkers to help with in distinguishing of MODY3 from Type 1 Diabetes (T1D) and Type 2 Diabetes (T2D). DNA sequencing is still necessary for unambiguous confirmation of clinical suspicion of MODY. NGS (Next Generation Sequencing) methods brought discoveries of multiple new gene variants and new instructions for their pathogenicity classification were required. The most actual problem is classification of variants with uncertain significance (VUS) which is a stumbling-block for clinical interpretation. Since MODY is a hereditary disease, DNA analysis of family members is helpful or even crucial. This review is updated summary about HNF1A-MODY genetics, pathophysiology, clinics functional studies and variant classification.

Human iPSCs-Derived Endothelial Cells with Mutation in HNF1A as a Model of Maturity-Onset Diabetes of the Young

Patients with HNF1A-maturity-onset diabetes of the young (MODY) often develop endothelial dysfunction and related microvascular complications, like retinopathy. As the clinical phenotype of HNF1A-MODY diabetes varies considerably, we used human induced pluripotent stem cells (hiPSCs) from two healthy individuals (control) to generate isogenic lines with mutation in HNF1A gene. Subsequently, control hiPSCs and their respective HNF1A clones were differentiated toward endothelial cells (hiPSC-ECs) and different markers/functions were compared. Human iPSC-ECs from all cell lines showed similar expression of CD31 and Tie-2. VE-cadherin expression was lower in HNF1A-mutated isogenic lines, but only in clones derived from one control hiPSCs. In the other isogenic set and cells derived from HNF1A-MODY patients, no difference in VE-cadherin expression was observed, suggesting the impact of the genetic background on this endothelial marker. All tested hiPSC-ECs showed an expected angiogenic response regardless of the mutation introduced. Isogenic hiPSC-ECs responded similarly to stimulation with pro-inflammatory cytokine TNF-α with the increase in ICAM-1 and permeability, however, HNF1A mutated hiPSC-ECs showed higher permeability in comparison to the control cells. Summarizing, both mono- and biallelic mutations of HNF1A in hiPSC-ECs lead to increased permeability in response to TNF-α in normal glycemic conditions, which may have relevance to HNF1A-MODY microvascular complications.

Functional characterization of p.Pro409His variant in HNF1A, a hypomorphic mutation involved in pancreatic β-cell dysfunction

AIMS

HNF1A is a gene coding for the transcription factor HNF1-α, mutated in some forms of MODY and type 2 diabetes mellitus characterized by a strong genetic component. The penetrance of HNF1A variants differs considerably; thus, to assess the genetic risk of diabetes in carrier subjects of a HNF1A mutant allele, a functional characterization of mutant forms is of paramount importance.

METHODS

The HNF1A gene was sequenced in two patients with partly discordant diabetic phenotype, carrying the p.Pro409His variant. To evaluate the pathogenicity of the variant, we measured the transactivation power of the corresponding P408H HNF1-α mutant mouse form on HNF1-α target promoters.

RESULTS

We found a lower but detectable activity of transactivation of the mutant form compared with the wild-type form and we excluded mechanisms of protein degradation or nuclear mislocalization.

CONCLUSIONS

The HNF1A mutation p.Pro409His can be considered a mild variant that confers a moderate risk of type 2 diabetes mellitus in heterozygous carriers.

Maturity Onset Diabetes of the Young is Not Necessarily Associated with Autosomal Inheritance: Case Description of a De Novo HFN1A Mutation

Maturity onset diabetes of the young (MODY) accounts for up to 4% of all cases of diabetes in pediatric patients. MODY is usually characterized by autosomal dominant inheritance, impaired insulin secretion, and an average age at diagnosis of 18-26 years. Mutations in the hepatocyte nuclear factor 1-alpha (HNF1A), glucokinase, hepatocyte nuclear factor 4-alpha, and hepatocyte nuclear factor 1-beta genes are the mutations most frequently observed in cases of MODY. We herein report a case of HNF1A-MODY characterized by an early onset of diabetes. Genetic investigations revealed a de novo heterozygous substitution, N237D (HNF1A c.709A>G), in exon 3 of the HNF1A gene. Our case supports the hypothesis that de novo mutations are more frequent than expected. This recent evidence may suggest that conventional clinical diagnostic criteria for MODY should be revised and personalized according to the individual patient.

Novel mechanisms of regulation of the expression and transcriptional activity of hepatocyte nuclear factor 4α

Hepatocyte nuclear factor 4α (HNF4α) is a master regulator of development and function of digestive tissues. The HNF4A gene uses two separate promoters P1 and P2, with P1 products predominant in adult liver, whereas P2 products prevalent in fetal liver, pancreas, and liver/colon cancer. To date, the mechanisms for the regulation of HNF4A and the dynamic switch of P1-HNF4α and P2-HNF4α during ontogenesis and carcinogenesis are still obscure. Our study validated the previously reported self-stimulation of P1-HNF4α but invalidated the reported synergism between HNF4α and HNF1α. HNF4A-AS1, a long noncoding RNA, is localized between the P2 and P1 promoters of HNF4A. We identified critical roles of P1-HNF4α in regulating the expression of HNF4A-AS1 and its mouse ortholog Hnf4a-os. Paired box 6 (PAX6), a master regulator of pancreas development overexpressed in colon cancer, cooperated with HNF1α to induce P2-HNF4α but antagonized HNF4α in HNF4A-AS1 expression. Thus, PAX6 may be important in determining ontogenic and carcinogenic changes of P2-HNF4α and HNF4A-AS1 in the pancreas and intestine. We also interrogated transactivation activities on multiple gene targets by multiple known and novel HNF4α mutants identified in patients with maturity onset diabetes of the young 1 (MODY1) and liver cancer. Particularly, HNF4α-D78A and HNF4α-G79S, two mutants found in liver cancer with mutations in DNA-binding domain, displayed highly gene-specific transactivation activities. Interestingly, HNF4α-Q277X, a MODY1 truncation mutant, antagonized the transactivation activities of HNF1α and farnesoid X receptor, key regulators of insulin secretion. Taken together, our study provides novel mechanistic insights regarding the transcriptional regulation and transactivation activity of HNF4α in digestive tissues.

Plasma Fucosylated Glycans and C-Reactive Protein as Biomarkers of HNF1A-MODY in Young Adult-Onset Nonautoimmune Diabetes

OBJECTIVE

Maturity-onset diabetes of the young (MODY) due to variants in HNF1A is the most common type of monogenic diabetes. Frequent misdiagnosis results in missed opportunity to use sulfonylureas as first-line treatment. A nongenetic biomarker could improve selection of subjects for genetic testing and increase diagnosis rates. We previously reported that plasma levels of antennary fucosylated N-glycans and high-sensitivity C-reactive protein (hs-CRP) are reduced in individuals with HNF1A-MODY. In this study, we examined the potential use of N-glycans and hs-CRP in discriminating individuals with damaging HNF1A alleles from those without HNF1A variants in an unselected population of young adults with nonautoimmune diabetes.

RESEARCH DESIGN AND METHODS

We analyzed the plasma N-glycan profile, measured hs-CRP, and sequenced HNF1A in 989 individuals with diabetes diagnosed when younger than age 45, persistent endogenous insulin production, and absence of pancreatic autoimmunity. Systematic assessment of rare HNF1A variants was performed.

RESULTS

We identified 29 individuals harboring 25 rare HNF1A alleles, of which 3 were novel, and 12 (in 16 probands) were considered pathogenic. Antennary fucosylated N-glycans and hs-CRP were able to differentiate subjects with damaging HNF1A alleles from those without rare HNF1A alleles. Glycan GP30 had a receiver operating characteristic curve area under the curve (AUC) of 0.90 (88% sensitivity, 80% specificity, cutoff 0.70%), whereas hs-CRP had an AUC of 0.83 (88% sensitivity, 69% specificity, cutoff 0.81 mg/L).

CONCLUSIONS

Half of rare HNF1A sequence variants do not cause MODY. N-glycan profile and hs-CRP could both be used as tools, alone or as adjuncts to existing pathways, for identifying individuals at high risk of carrying a damaging HNF1A allele.

Genetics of Monogenic Diabetes: Present Clinical Challenges

PURPOSE OF REVIEW

Monogenic forms of diabetes have specific treatments that differ from the standard care provided for type 1 and type 2 diabetes, making the appropriate diagnosis essential. In this review, we discuss current clinical challenges that remain, including improving case-finding strategies, particularly those that have transethnic applicability, and understanding the interpretation of genetic variants as pathogenic, with clinically meaningful impacts.

RECENT FINDINGS

Biomarker approaches to the stratification for genetic testing now appear to be most effective in identifying cases of monogenic diabetes, and use of genetic risk scores may also prove useful. However, applicability in all ethnic groups is lacking. Challenges remain in the classification of genes as diabetes-causing and the interpretation of genetic variants at the clinical interface. Since the discovery that genetic defects can cause neonatal or young-onset diabetes, multiple causal genes have been identified and there have been many advances in strategies to detect genetic forms of diabetes and their treatments. Approaches learnt from monogenic diabetes are now being translated to polygenic diabetes.

Genetic Testing of Maturity-Onset Diabetes of the Young Current Status and Future Perspectives

Diabetes is a global epidemic problem growing exponentially in Asian countries posing a serious threat. Among diabetes, maturity-onset diabetes of the young (MODY) is a heterogeneous group of monogenic disorders that occurs due to β cell dysfunction. Genetic defects in the pancreatic β-cells result in the decrease of insulin production required for glucose utilization thereby lead to early-onset diabetes (often <25 years). It is generally considered as non-insulin dependent form of diabetes and comprises of 1-5% of total diabetes. Till date, 14 genes have been identified and mutation in them may lead to MODY. Different genetic testing methodologies like linkage analysis, restriction fragment length polymorphism, and DNA sequencing are used for the accurate and correct investigation of gene mutations associated with MODY. The next-generation sequencing has emerged as one of the most promising and effective tools to identify novel mutated genes related to MODY. Diagnosis of MODY is mainly relying on the sequential screening of the three marker genes like hepatocyte nuclear factor 1 alpha (HNF1α), hepatocyte nuclear factor 4 alpha (HNF4α), and glucokinase (GCK). Interestingly, MODY patients can be managed by diet alone for many years and may also require minimal doses of sulfonylureas. The primary objective of this article is to provide a review on current status of MODY, its prevalence, genetic testing/diagnosis, possible treatment, and future perspective.

Functional Investigations of HNF1A Identify Rare Variants as Risk Factors for Type 2 Diabetes in the General Population

Variants in HNF1A encoding hepatocyte nuclear factor 1α (HNF-1A) are associated with maturity-onset diabetes of the young form 3 (MODY 3) and type 2 diabetes. We investigated whether functional classification of HNF1A rare coding variants can inform models of diabetes risk prediction in the general population by analyzing the effect of 27 HNF1A variants identified in well-phenotyped populations (n = 4,115). Bioinformatics tools classified 11 variants as likely pathogenic and showed no association with diabetes risk (combined minor allele frequency [MAF] 0.22%; odds ratio [OR] 2.02; 95% CI 0.73-5.60; P = 0.18). However, a different set of 11 variants that reduced HNF-1A transcriptional activity to <60% of normal (wild-type) activity was strongly associated with diabetes in the general population (combined MAF 0.22%; OR 5.04; 95% CI 1.99-12.80; P = 0.0007). Our functional investigations indicate that 0.44% of the population carry HNF1A variants that result in a substantially increased risk for developing diabetes. These results suggest that functional characterization of variants within MODY genes may overcome the limitations of bioinformatics tools for the purposes of presymptomatic diabetes risk prediction in the general population.

Identification and functional analysis of c.422_423InsT, a novel mutation of the HNF1A gene in a patient with diabetes

BACKGROUND

HNF1A gene regulates liver-specific genes, and genes that have a role in glucose metabolism, transport, and secretion of insulin. HNF1A gene mutations are frequently associated with type 2 diabetes. HNF1A protein has three domains: the dimerization domain, the DNA-binding domain, and the trans-activation domain. Some mutations in the dimerization or DNA-binding domains have no influence on the normal allele, while others have dominant negative effects. The I27L, A98V, and S487N polymorphisms are common variants of the HNF1A gene; they have been found in T2D and non-diabetic subjects.

METHODS AND RESULTS

We searched for mutations in the first three exons of the HNF1A gen in an Amerindian population of 71 diabetic patients. DNA sequencing revealed the previously reported I27L polymorphism (c.79A>C) in 53% of diabetic patients and in 67% of the control group. Thus, the I27L/L27L polymorphism might be a marker of Amerindians. In addition, we found the c.422_423InsT mutation in the HNF1A gene of one patient, which had not been previously reported. This mutation resulted in a frame shift of the open reading frame and a new translation stop in codon 187, leading to a truncated polypeptide of 186 amino acids (Q141Hfs*47). This novel mutation affects the DNA-binding capacity of the mutant HNF1A protein by EMSA; its intracellular localization by fluorescence and confocal microscopy, and a dominant-negative effect affecting the DNA-binding capacity of the normal HNF1A by EMSA. We also studied the homology modeling structure to understand the effect of this mutation on its DNA-binding capacity and its dominant negative effect.

CONCLUSION

The HNF1A Q141Hfs*47 mutant polypeptide has no DNA-binding capacity and exerts a dominant negative effect on the HNF1A protein. Therefore, it might produce severe phenotypic effects on the expression levels of a set of β-cell genes. Consequently, its screening should be included in the genetic analysis of diabetic patients after more functional studies are performed.

When is it MODY? Challenges in the Interpretation of Sequence Variants in MODY Genes

The genomics revolution has raised more questions than it has provided answers. Big data from large population-scale resequencing studies are increasingly deconstructing classic notions of Mendelian disease genetics, which support a simplistic correlation between mutational severity and phenotypic outcome. The boundaries are being blurred as the body of evidence showing monogenic disease-causing alleles in healthy genomes, and in the genomes of individu-als with increased common complex disease risk, continues to grow. In this review, we focus on the newly emerging challenges which pertain to the interpretation of sequence variants in genes implicated in the pathogenesis of maturity-onset diabetes of the young (MODY), a presumed mono-genic form of diabetes characterized by Mendelian inheritance. These challenges highlight the complexities surrounding the assignments of pathogenicity, in particular to rare protein-alerting variants, and bring to the forefront some profound clinical diagnostic implications. As MODY is both genetically and clinically heterogeneous, an accurate molecular diagnosis and cautious extrapolation of sequence data are critical to effective disease management and treatment. The biological and translational value of sequence information can only be attained by adopting a multitude of confirmatory analyses, which interrogate variant implication in disease from every possible angle. Indeed, studies which have effectively detected rare damaging variants in known MODY genes in normoglycemic individuals question the existence of a sin-gle gene mutation scenario: does monogenic diabetes exist when the genetic culprits of MODY have been systematical-ly identified in individuals without MODY?

Berry Phenolic Compounds Increase Expression of Hepatocyte Nuclear Factor-1α (HNF-1α) in Caco-2 and Normal Colon Cells Due to High Affinities with Transcription and Dimerization Domains of HNF-1α

Hepatocyte nuclear factor-1α (HNF-1α) is found in the kidneys, spleen, thymus, testis, skin, and throughout the digestive organs. It has been found to promote the transcription of various proteins involved in the management of type II diabetes, including dipeptidyl peptidase-IV (DPP-IV). Phenolic compounds from berries and citrus fruits are known to inhibit DPP-IV, but have not been tested for their interactions with wild-type HNF-1α. By studying the interactions of compounds from berries and citrus fruits have with HNF-1α, pre-transcriptional mechanisms that inhibit the expression of proteins such as DPP-IV may be elucidated. In this study, the interactions of berry phenolic compounds and citrus flavonoids with the dimerization and transcriptional domains of HNF-1α were characterized using the molecular docking program AutoDock Vina. The anthocyanin delphinidin-3-O-arabinoside had the highest binding affinity for the dimerization domain as a homodimer (-7.2 kcal/mol) and transcription domain (-8.3 kcal/mol) of HNF-1α. Anthocyanins and anthocyanidins had relatively higher affinities than resveratrol and citrus flavonoids for both, the transcription domain and the dimerization domain as a homodimer. The flavonoid flavone had the highest affinity for a single unit of the dimerization domain (-6.5 kcal/mol). Nuclear expression of HNF-1α was measured in Caco-2 and human normal colon cells treated with blueberry and blackberry anthocyanin extracts. All extracts tested increased significantly (P < 0.05) the nuclear expression of HNF-1α in Caco-2 cells by 85.2 to 260% compared to a control. The extracts tested increased significantly (P < 0.02) the nuclear expression of HNF-1α in normal colon cells by 48.6 to 243%. It was confirmed that delphinidin-3-O-glucoside increased by 3-fold nuclear HNF-1α expression in Caco-2 cells (P < 0.05). Anthocyanins significantly increased nuclear HNF-1α expression, suggesting that these compounds might regulate the genes HNF-1α promotes.

Maturity-onset diabetes of the young (MODY): an update

Maturity-onset diabetes of the young (MODY) is a group of monogenic disorders characterized by autosomal dominantly inherited non-insulin dependent form of diabetes classically presenting in adolescence or young adults before the age of 25 years. MODY is a rare cause of diabetes (1% of all cases) and is frequently misdiagnosed as Type 1 diabetes (T1DM) or Type 2 diabetes (T2DM). A precise molecular diagnosis is essential because it leads to optimal treatment of the patients and allows early diagnosis for their asymptomatic family members. Mutations in the glucokinase (GCK) (MODY 2) and hepatocyte nuclear factor (HNF)1A/4A (MODY 3 and MODY 1) genes are the most common causes of MODY. GCK mutations cause a mild, asymptomatic, and stable fasting hyperglycemia usually requiring no specific treatment. However, mutations in the HNF1A and HNF4A cause a progressive pancreatic β-cell dysfunction and hyperglycemia that can result in microvascular complications. Sulfonylureas are effective in these patients by acting on adenosine triphosphate (ATP)-sensitive potassium channels, although insulin therapy may be required later in life. Mutations in the HNF1B (MODY 5) is associated with pancreatic agenesis, renal abnormalities, genital tract malformations, and liver dysfunction. Compared to MODY 1, 2, 3, and 5, the remaining subtypes of MODY have a much lower prevalence. In this review, we summarize the main clinical and laboratory characteristics of the common and rarer causes of MODY.

Serine 249 phosphorylation by ATM protein kinase regulates hepatocyte nuclear factor-1α transactivation

Hepatocyte nuclear factor-1 alpha (HNF1α) exerts important effects on gene expression in multiple tissues. Several studies have directly or indirectly supported the role of phosphorylation processes in the activity of HNF1α. However, the molecular mechanism of this phosphorylation remains largely unknown. Using microcapillary liquid chromatography MS/MS and biochemical assays, we identified a novel phosphorylation site in HNF1α at Ser249. We also found that the ATM protein kinase phosphorylated HNF1α at Ser249 in vitro in an ATM-dependent manner and that ATM inhibitor KU55933 treatment inhibited phosphorylation of HNF1α at Ser249 in vivo. Coimmunoprecipitation assays confirmed the association between HNF1α and ATM. Moreover, ATM enhanced HNF1α transcriptional activity in a dose-dependent manner, whereas the ATM kinase-inactive mutant did not. The use of KU55933 confirmed our observation. Compared with wild-type HNF1α, a mutation in Ser249 resulted in a pronounced decrease in HNF1α transactivation, whereas no dominant-negative effect was observed. The HNF1αSer249 mutant also exhibited normal nuclear localization but decreased DNA-binding activity. Accordingly, the functional studies of HNF1αSer249 mutant revealed a defect in glucose metabolism. Our results suggested that ATM regulates the activity of HNF1α by phosphorylation of serine 249, particularly in glucose metabolism, which provides valuable insights into the undiscovered mechanisms of ATM in the regulation of glucose homeostasis.

Alterations in bile acid synthesis in carriers of hepatocyte nuclear factor 1α mutations

OBJECTIVES

Heterozygous mutations in hepatocyte nuclear factor 1α (HNF1α) cause maturity onset diabetes of the young 3 (MODY3), an autosomal dominant form of diabetes. Deficiency of HNF1α in mice results in diabetes, hypercholesterolaemia and increased bile acid (BA) and cholesterol synthesis. Little is known about alterations in lipid metabolism in patients with MODY3. The aim of this study was to investigate whether patients with MODY3 have altered cholesterol and BA synthesis and intestinal cholesterol absorption. A secondary aim was to investigate the effects of HNF1α mutations on the transcriptional regulation of BA metabolism.

METHODS

Plasma biomarkers of BA and cholesterol synthesis and intestinal cholesterol absorption were measured in patients with MODY3 (n = 19) and in matched healthy control subjects (n = 15). Cotransfection experiments were performed with several promoters involved in BA metabolism along with expression vectors carrying the mutations found in these patients.

RESULTS

Plasma analysis showed higher levels of BA synthesis in patients with MODY3. No differences were observed in cholesterol synthesis or intestinal cholesterol absorption. Cotransfection experiments showed that one of the mutations (P379A) increased the induction of the cholesterol 7α-hydroxylase promoter compared with HNF1α, without further differences in other studied promoters. By contrast, the other four mutations (L107I, T260M, P291fsinsC and R131Q) reduced the induction of the farnesoid X receptor (FXR) promoter, which was followed by reduced repression of the small heterodimer partner promoter. In addition, these mutations also reduced the induction of the apical sodium-dependent bile salt transporter promoter.

CONCLUSIONS

BA synthesis is increased in patients with MODY3 compared with control subjects. Mutations in HNF1α affect promoters involved in BA metabolism.

Molecular diagnosis of maturity onset diabetes of the young in India

Diabetes is highly prevalent in India and the proportion of younger patients developing diabetes is on the increase. Apart from the more universally known type 1 diabetes and obesity related type 2 diabetes, monogenic forms of diabetes are also suspected to be prevalent in many young diabetic patients. The identification of the genetic basis of the disease not only guides in therapeutic decision making, but also aids in genetic counselling and prognostication. Genetic testing may establish the occurrence and frequency of early diabetes in our population. This review attempts to explore the utilities and horizons of molecular genetics in the field of maturity onset diabetes of the young (MODY), which include the commoner forms of monogenic diabetes.