Mutations in NEUROD1 are associated with the development of type 2 diabetes mellitus

Identification of HNF4A Mutation p.T130I and HNF1A Mutations p.I27L and p.S487N in a Han Chinese Family with Early-Onset Maternally Inherited Type 2 Diabetes

Maturity-onset diabetes of the young (MODY) is characterized by the onset of diabetes before the age of 25 years, positive family history, high genetic predisposition, monogenic mutations, and an autosomal dominant mode of inheritance. Here, we aimed to investigate the mutations and to characterize the phenotypes of a Han Chinese family with early-onset maternally inherited type 2 diabetes. Detailed clinical assessments and genetic screening for mutations in the HNF4α, GCK, HNF-1α, IPF-1, HNF1β, and NEUROD1 genes were carried out in this family. One HNF4A mutation (p.T130I) and two HNF1A polymorphisms (p.I27L and p.S487N) were identified. Mutation p.T130I was associated with both early-onset and late-onset diabetes and caused downregulated HNF4A expression, whereas HNF1A polymorphisms p.I27L and p.S487N were associated with the age of diagnosis of diabetes. We demonstrated that mutation p.T130I in HNF4A was pathogenic as were the predicted polymorphisms p.I27L and p.S487N in HNF1A by genetic and functional analysis. Our results show that mutations in HNF4A and HNF1A genes might account for this early-onset inherited type 2 diabetes.

Undiagnosed MODY: Time for Action

Maturity-onset diabetes of the young (MODY) is a monogenic form of diabetes that accounts for at least 1 % of all cases of diabetes mellitus. MODY classically presents as non-insulin-requiring diabetes in lean individuals typically younger than 25 with evidence of autosomal dominant inheritance, but these criteria do not capture all cases and can also overlap with other diabetes types. Genetic diagnosis of MODY is important for selecting the right treatment, yet ~95 % of MODY cases in the USA are misdiagnosed. MODY prevalence and characteristics have been well-studied in some populations, such as the UK and Norway, while other ethnicities, like African and Latino, need much more study. Emerging next-generation sequencing methods are making more widespread study and clinical diagnosis increasingly feasible; at the same time, they are detecting other mutations in the same genes of unknown clinical significance. This review will cover the current epidemiological studies of MODY and barriers and opportunities for moving toward a goal of access to an appropriate diagnosis for all affected individuals.

Maturity-Onset Diabetes of the Young: What Do Clinicians Need to Know?

Maturity-onset diabetes of the young (MODY) is a monogenic form of diabetes that is characterized by an early onset, autosomal dominant mode of inheritance and a primary defect in pancreatic β-cell function. MODY represents less than 2% of all diabetes cases and is commonly misdiagnosed as type 1 or type 2 diabetes mellitus. At least 13 MODY subtypes with distinct genetic etiologies have been identified to date. A correct genetic diagnosis is important as it often leads to personalized treatment for those with diabetes and enables predictive genetic testing for their asymptomatic relatives. Next-generation sequencing may provide an efficient method for screening mutations in this form of diabetes as well as identifying new MODY genes. In this review, I discuss a current update on MODY in the literatures and cover the studies that have been performed in Korea.

Gene and protein expression in pituitary corticotroph adenomas: a systematic review of the literature

OBJECT Functional corticotroph pituitary adenomas (PAs) secrete adrenocorticotropic hormone (ACTH) and are the cause of Cushing's disease, which accounts for 70% of all cases of Cushing's syndrome. Current classification systems for PAs rely primarily on laboratory hormone findings, tumor size and morphology, invasiveness, and immunohistochemical findings. Likewise, drug development for functional ACTH-secreting PAs (ACTH-PAs) is limited and has focused largely on blocking the production or downstream effects of excess cortisol. The authors aimed to summarize the findings from previous studies that explored gene and protein expression of ACTH-PAs to prioritize potential genetic and protein targets for improved molecular diagnosis and treatment of Cushing's disease. METHODS A systematic literature review was performed using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A PubMed search of select medical subject heading (MeSH) terms was performed to identify all studies that reported gene- and protein-expression findings in ACTH-PAs from January 1, 1990, to August 24, 2014, the day the search was performed. The inclusion criteria were studies on functional ACTH-PAs compared with normal pituitary glands, on human PA tissue only, with any method of analysis, and published in the English language. Studies using anything other than resected PA tissue, those that compared other adenoma types, those without baseline expression data, or those in which any pretreatment was delivered before analysis were excluded. RESULTS The primary search returned 1371 abstracts, of which 307 were found to be relevant. Of those, 178 were selected for secondary full-text analysis. Of these, 64 articles met the inclusion criteria and an additional 4 studies were identified from outside the search for a total of 68 included studies. Compared with the normal pituitary gland, significant gene overexpression in 43 genes and 22 proteins was reported, and gene underexpression in 58 genes and 15 proteins was reported. Immunohistochemistry was used in 39 of the studies, and reverse transcriptase polymerase chain reaction was used in 26 of the studies, primarily, and as validation for 4 others. Thirteen studies used both immunohistochemistry and reverse transcriptase polymerase chain reaction. Other methods used included microarray, in situ hybridization, Northern blot analysis, and Western blot analysis. Expression of prioritized genes emphasized in multiple studies were often validated on both the gene and protein levels. Genes/proteins found to be overexpressed in ACTH-PAs relative to the normal pituitary gland included hPTTG1/securin, NEUROD1/NeuroD1 (Beta2), HSD11B2/11β-hydroxysteroid dehydrogenase 2, AKT/Akt, protein kinase B, and CCND1/cyclin D1. Candidate genes/proteins found to be underexpressed in ACTH-PAs relative to the normal pituitary gland included CDKN1B/p27(Kip1), CDKN2A/p16, KISS1/kisspeptin, ACTHR/ACTH-R, and miR-493. CONCLUSIONS On the basis of the authors' systematic review, many significant gene and protein targets that may contribute to tumorigenesis, invasion, and hormone production/secretion of ACTH have been identified and validated in ACTH-PAs. Many of these potential targets have not been fully analyzed for their therapeutic and diagnostic potential but may represent candidate molecular targets for biomarker development and drug targeting. This review may help catalyze additional research efforts using modern profiling and sequencing techniques and alteration of gene expression.

Pancreatic islet cell development and regeneration

PURPOSE OF REVIEW

This review will discuss recent advances in understanding mouse and human pancreatic islet cell development, novel concepts related to β cell dysfunction and improved approaches for replenishing β cells to treat diabetes.

RECENT FINDINGS

Considerable knowledge about pancreatic islet development and function has been gained using model systems with subsequent validation in human tissues. Recently, several rodent studies have revealed that differentiated adult islet cells retain remarkable plasticity and can be converted to other islet cell types by perturbing their transcription factor profiles. Furthermore, significant advances have been made in the generation of β-like cells from stem cell populations. Therefore, the generation of functionally mature β cells by the in-situ conversion of non-β cell populations or by the directed differentiation of human pluripotent stem cells could represent novel mechanisms for replenishing β cells in diabetic patients.

SUMMARY

The overall conservation between mouse and human pancreatic development, islet physiology and etiology of diabetes encourages the translation of novel β cell replacement therapies to humans. Further deciphering the molecular mechanisms that direct islet cell regeneration, plasticity and function could improve and expand the β cell replacement strategies for treating diabetes.

Maturity onset diabetes of the young in India - a distinctive mutation pattern identified through targeted next-generation sequencing

OBJECTIVE

To establish and utilize a Next-Generation Sequencing (NGS)-based strategy to screen for maturity onset diabetes of the young (MODY) gene mutations in subjects with early-onset diabetes.

PATIENTS AND METHODS

Maturity onset diabetes of the young (MODY) genetic testing was carried out in 80 subjects of Asian Indian origin with young onset diabetes to identify mutations in a comprehensive panel of ten MODY genes. A novel multiplex polymerase chain reaction (PCR)-based target enrichment was established, followed by NGS on the Ion Torrent Personal Genome Machine (PGM). All the mutations and rare variants were confirmed by Sanger sequencing.

RESULTS

We identified mutations in 11 (19%) of the 56 clinically diagnosed MODY subjects and seven of these mutations were novel. The identified mutations include p.H241Q, p.E59Q, c.-162G>A 5' UTR in NEUROD1, p.V169I cosegregating with c.493-4G>A and c.493-20C>T, p.E271K in HNF4A, p.A501S in HNF1A, p.E440X in GCK, p.V177M in PDX1, p.L92F in HNF1B and p.R31L in PAX4 genes. Interestingly, two patients with NEUROD1 mutation were also positive for the p.E224K mutation in PDX1 gene. These patients with coexisting NEUROD1-PDX1 mutations showed a marked reduction in glucose-induced insulin secretion. All 24 subjects who had not met the clinical criteria of MODY were negative for the mutations. To the best of our knowledge, this is the first report of PDX1, HNF1B, NEUROD1 and PAX4 mutations from India.

CONCLUSIONS

Multiplex PCR coupled with NGS provides a rapid, cost-effective and accurate method for comprehensive parallelized genetic testing of MODY. When compared to earlier reports, we have identified a higher frequency and a novel digenic mutation pattern involving NEUROD1 and PDX1 genes.

Regenerative medicine in diabetes

Diabetes is a common multisystem disease that results in hyperglycemia due to a relative or absolute insulin deficiency. Improved glycemic control decreases the risk of development and progression of microvascular and, to a lesser extent, macrovascular complications and prevents symptomatic hyperglycemia. However, complex treatment regimens aimed at improving glycemic control are associated with an increased incidence of hypoglycemia. On paper at least, cellular therapies arising from reprogramed stem cells or other somatic cell types would provide ideal therapy for diabetes and the prevention of its complications. This hypothesis has led to intensive efforts to grow β cells from various sources. In this review, we provide an overview of β-cell development as well as the efforts reported to date in terms of cellular therapy for diabetes. Engineering β-cell replacement therapy requires an understanding of how β cells respond to other metabolites such as amino acids, free fatty acids, and ketones. Indeed, efforts thus far have been characterized by an inability of cellular replacement products to adequately respond to metabolites that normally couple the metabolic state to β-cell function and insulin secretion. Efforts to date intended to capitalize on current knowledge of islet cell development and stimulus-secretion coupling of the β cell are encouraging but as yet of little clinical relevance.

Recent advances in histogenesis research of lung neuroendocrine cancers: Evidence obtained from functional analyses of primitive neural/neuroendocrine cell-specific transcription factors

Small cell carcinoma (SmCC) and large cell neuroendocrine carcinoma (LENEC) are categorized as neuroendocrine cancers (NECs) of the lung and have extremely poor prognoses. The lack of an effective therapeutic strategy against SmCC and LCNEC is a serious issue. Because the regulation of the cellular phenotype is complicated by the actions of various transcription factors, investigations into the function of neural/neuroendocrine cell-specific transcription factors are important for elucidating the cellular characteristics and histogenesis of SmCC and LCNEC and for establishing innovative therapeutic strategies against them. In this review, the functions of ASCL1, NeuroD1, REST, TTF1, and class III/IV POU, that are specifically and highly expressed in lung NECs, are introduced. These transcription factors transactivate and/or transrepress various genes and are involved in neural progenitor phenotyping, neuroendocrine and stem cell marker expression, and epithelial-to-mesenchymal transition. Based on the evidence that certain carcinoids express ASCL1, NeuroD1, TTF1, and class III/IV POU and that lung NECs can develop from non-NE cells/non-NEC cells, the relationships among lung NECs, carcinoid tumors, and non-NECs are discussed. Finally, a model of the histogenesis of lung NECs in view of similarities in the expression of primitive neural/neuroendocrine cell-specific transcription factors is proposed.

Roles of HNF1α and HNF4α in pancreatic β-cells: lessons from a monogenic form of diabetes (MODY)

Mutations in the genes encoding hepatocyte nuclear factor (HNF)1α and HNF4α cause a monogenic form of diabetes mellitus known as maturity-onset diabetes of the young (MODY). The primary cause of MODY is an impairment of glucose-stimulated insulin secretion by pancreatic β-cells, indicating the important roles of HNF1α and HNF4α in β-cells. Large-scale genetic studies have clarified that the common variants of HNF1α and HNF4α genes are also associated with type 2 diabetes, suggesting that they are involved in the pathogenesis of both diseases. Recent experimental studies revealed that HNF1α controls both β-cell function and growth by regulating target genes such as glucose transporter 2, pyruvate kinase, collectrin, hepatocyte growth factor activator, and HNF4α. In contrast, HNF4α mainly regulates the function of β-cells. Although direct target genes of HNF4α in β-cells are largely unknown, we recently identified Anks4b as a novel target of HNF4α that regulates β-cell susceptibility to endoplasmic reticulum stress. Studies of MODY have led to a better understanding of the molecular mechanism of glucose-stimulated insulin secretion by pancreatic β-cells.

Pharmacogenomics of glinides

Glinides, including repaglinide, nateglinide and mitiglinide, are a type of fasting insulin secretagogue that could help to mimic early-phase insulin release, thus providing improved control of the postprandial glucose levels. Glinides stimulate insulin secretion by inhibiting ATP-sensitive potassium channels in the pancreatic β-cell membrane. Although glinides have been widely used clinically and display excellent safety and efficacy, the response to glinides varies among individuals, which is partially due to genetic factors involved in drug absorption, distribution, metabolism and targeting. Several pharmacogenomic studies have demonstrated that variants of genes involved in the pharmacokinetics or pharmacodynamics of glinides are associated with the drug response. Polymorphisms of genes involved in drug metabolism, such as CYP2C9, CYP2C8 and SLCO1B1, may influence the efficacy of glinides and the incidence of adverse effects. In addition, Type 2 diabetes mellitus susceptibility genes, such as KCNQ1, PAX4 and BETA2, also influence the efficacy of glinides. In this article, we review and discuss current pharmacogenomics researches on glinides, and hopefully provide useful data and proof for clinical application.

Transcriptomic analysis of the lesser spotted catshark (Scyliorhinus canicula) pancreas, liver and brain reveals molecular level conservation of vertebrate pancreas function

Background

Understanding the evolution of the vertebrate pancreas is key to understanding its functions. The chondrichthyes (cartilaginous fish such as sharks and rays) have often been suggested to possess the most ancient example of a distinct pancreas with both hormonal (endocrine) and digestive (exocrine) roles. The lack of genetic, genomic and transcriptomic data for cartilaginous fish has hindered a more thorough understanding of the molecular-level functions of the chondrichthyan pancreas, particularly with respect to their “unusual” energy metabolism (where ketone bodies and amino acids are the main oxidative fuel source) and their paradoxical ability to both maintain stable blood glucose levels and tolerate extensive periods of hypoglycemia. In order to shed light on some of these processes, we carried out the first large-scale comparative transcriptomic survey of multiple cartilaginous fish tissues: the pancreas, brain and liver of the lesser spotted catshark, Scyliorhinus canicula.

Results

We generated a mutli-tissue assembly comprising 86,006 contigs, of which 44,794 were assigned to a particular tissue or combination of tissues based on mapping of sequencing reads. We have characterised transcripts encoding genes involved in insulin regulation, glucose sensing, transcriptional regulation, signaling and digestion, as well as many peptide hormone precursors and their receptors for the first time. Comparisons to mammalian pancreas transcriptomes reveals that mechanisms of glucose sensing and insulin regulation used to establish and maintain a stable internal environment are conserved across jawed vertebrates and likely pre-date the vertebrate radiation. Conservation of pancreatic hormones and genes encoding digestive proteins support the single, early evolution of a distinct pancreatic gland with endocrine and exocrine functions in jawed vertebrates. In addition, we demonstrate that chondrichthyes lack pancreatic polypeptide (PP) and that reports of PP in the literature are likely due cross-reaction with PYY and/or NPY in the pancreas. A three hormone islet organ is therefore the ancestral jawed vertebrate condition, later elaborated upon only in the tetrapod lineage.

Conclusions

The cartilaginous fish are a great untapped resource for the reconstruction of patterns and processes of vertebrate evolution and new approaches such as those described in this paper will greatly facilitate their incorporation into the rank of “model organism”.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-1074) contains supplementary material, which is available to authorized users.

A homozygous missense mutation in NEUROD1 is associated with nonsyndromic autosomal recessive retinitis pigmentosa

PURPOSE

Mutations in the same gene can lead to different clinical phenotypes. In this study, we aim to identify novel genotype-phenotype correlations and novel disease genes by analyzing an unsolved autosomal recessive retinitis pigmentosa (ARRP) Han Chinese family.

METHODS

Whole exome sequencing was performed for one proband from the consanguineous ARRP family. Stringent variants filtering and prioritizations were applied to identify the causative mutation.

RESULTS

A homozygous missense variant, c.724G>A; p.V242I, in NEUROD1 was identified as the most likely cause of disease. This allele perfectly segregates in the family and affects an amino acid, which is highly conserved among mammals. A previous study showed that a homozygous null allele in NEUROD1 causes severe syndromic disease with neonatal diabetes, systematic neurological abnormalities, and early-onset retinal dystrophy. Consistent with these results, our patients who are homozygous for a less severe missense allele presented only late-onset retinal degeneration without any syndromic symptoms.

CONCLUSIONS

We identified a potential novel genotype-phenotype correlation between NEUROD1 and nonsyndromic ARRP. Our study supports the idea that NEUROD1 is important for maintenance of the retina function and partial loss-of-function mutation in NEUROD1 is likely a rare cause of nonsyndromic ARRP.

Maturity onset diabetes of the young (MODY)--history, first case reports and recent advances

The world is seemingly facing a global increase in people suffering from diabetes especially in developing countries. The worldwide occurrence of diabetes for all age groups in year 2000 was estimated to be 2.8% and this number is most certainly expected to rise to 4.4% by 2030. Maturity-onset of diabetes of the young, or MODY, is a form of monogenic diabetes that is caused by mutations occurring in a number of different genes. Mutations in different genes tend to cause a slightly different variant of diabetes. MODY is typically diagnosed during late childhood, adolescence, or early adulthood and is usually observed to develop in adults during their late 50's. One of the main drawbacks in its diagnosis is that many people with MODY are misdiagnosed as having type 1 or type 2 diabetes. However, a molecular and genetic diagnosis can result in a better treatment and could also help in identifying other family members with MODY. This article explores the historical prospect and the genetic background of MODY, a brief summary of the first case reported and the significant factors that differentiate it from type 1 and type 2 diabetes.

Pdx1 and USF transcription factors co-ordinately regulate Alx3 gene expression in pancreatic β-cells

We investigated the transcriptional mechanisms regulating the expression of Alx3 in pancreatic islets. We found that the transcriptional transactivation of Alx3 in β-cells requires the co-operation of the islet-specific homeoprotein Pdx1 with the transcription factors USF1 and USF2.

Gene-specific function prediction for non-synonymous mutations in monogenic diabetes genes

The rapid progress of genomic technologies has been providing new opportunities to address the need of maturity-onset diabetes of the young (MODY) molecular diagnosis. However, whether a new mutation causes MODY can be questionable. A number of in silico methods have been developed to predict functional effects of rare human mutations. The purpose of this study is to compare the performance of different bioinformatics methods in the functional prediction of nonsynonymous mutations in each MODY gene, and provides reference matrices to assist the molecular diagnosis of MODY. Our study showed that the prediction scores by different methods of the diabetes mutations were highly correlated, but were more complimentary than replacement to each other. The available in silico methods for the prediction of diabetes mutations had varied performances across different genes. Applying gene-specific thresholds defined by this study may be able to increase the performance of in silico prediction of disease-causing mutations.

Revealing transcription factors during human pancreatic β cell development

Developing cell-based diabetes therapies requires examining transcriptional mechanisms underlying human β cell development. However, increased knowledge is hampered by low availability of fetal pancreatic tissue and gene targeting strategies. Rodent models have elucidated transcription factor roles during islet organogenesis and maturation, but differences between mouse and human islets have been identified. The past 5 years have seen strides toward generating human β cell lines, the examination of human transcription factor expression, and studies utilizing induced pluripotent stem cells (iPS cells) and human embryonic stem (hES) cells to generate β-like cells. Nevertheless, much remains to be resolved. We present current knowledge of developing human β cell transcription factor expression, as compared to rodents. We also discuss recent studies employing transcription factor or epigenetic modulation to generate β cells.

Transcriptional control of mammalian pancreas organogenesis

The field of pancreas development has markedly expanded over the last decade, significantly advancing our understanding of the molecular mechanisms that control pancreas organogenesis. This growth has been fueled, in part, by the need to generate new therapeutic approaches for the treatment of diabetes. The creation of sophisticated genetic tools in mice has been instrumental in this progress. Genetic manipulation involving activation or inactivation of genes within specific cell types has allowed the identification of many transcription factors (TFs) that play critical roles in the organogenesis of the pancreas. Interestingly, many of these TFs act at multiple stages of pancreatic development, and adult organ function or repair. Interaction with other TFs, extrinsic signals, and epigenetic regulation are among the mechanisms by which TFs may play context-dependent roles during pancreas organogenesis. Many of the pancreatic TFs directly regulate each other and their own expression. These combinatorial interactions generate very specific gene regulatory networks that can define the different cell lineages and types in the developing pancreas. Here, we review recent progress made in understanding the role of pancreatic TFs in mouse pancreas formation. We also summarize our current knowledge of human pancreas development and discuss developmental pancreatic TFs that have been associated with human pancreatic diseases.

β-cell mass in people with type 2 diabetes

The early occurrence of β‐cell dysfunction has been broadly recognized as a critical determinant of the development and progression of type 2 diabetes. β‐cell dysfunction might be induced by insufficient β‐cell mass, by a dysfunction of the β‐cells, or both. Whether or not β‐cell dysfunction constitutes a cause of reduced β‐cells or vice‐versa currently remains unclear. The results of some studies have measured the loss of β‐cells in type 2 diabetic patients at between 22 and 63% by planimetric measurements. Because β‐cell hypertrophy has been noted in type 2 diabetic patients, the loss of β‐cell number should prove more profound than what has thus far been reported. Furthermore, β‐cell volumes are reduced even in patients with impaired fasting glucose. Such defects in β‐cell mass are associated with increased apoptosis rather than insufficient replication or neogenesis of β‐cells. With these results, although they still require clarification, the peak β‐cell mass might be determined at quite an early stage of life, and then might decline progressively over time as the result of exposure to harmful environmental influences over one’s lifetime. In this review, we have summarized the relevant studies regarding β‐cell mass in patients with type 2 diabetes, and then presented a review of the various causes of β‐cell loss in adults. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00072.x, 2010)

Many faces of monogenic diabetes

Monogenic diabetes represents a heterogeneous group of disorders resulting from defects in single genes. Defects are categorized primarily into two groups: disruption of β-cell function or a reduction in the number of β-cells. A complex network of transcription factors control pancreas formation, and a dysfunction of regulators high in the hierarchy leads to pancreatic agenesis. Dysfunction among factors further downstream might cause organ hypoplasia, absence of islets of Langerhans or a reduction in the number of β-cells. Many transcription factors have pleiotropic effects, explaining the association of diabetes with other congenital malformations, including cerebellar agenesis and pituitary agenesis. Monogenic diabetes variants are classified conventionally according to age of onset, with neonatal diabetes occurring before the age of 6 months and maturity onset diabetes of the young (MODY) manifesting before the age of 25 years. Recently, certain familial genetic defects were shown to manifest as neonatal diabetes, MODY or even adult onset diabetes. Patients with neonatal diabetes require a thorough genetic work-up in any case, and because extensive phenotypic overlap exists between monogenic, type 2, and type 1 diabetes, genetic analysis will also help improve diagnosis in these cases. Next generation sequencing will facilitate rapid screening, leading to the discovery of digenic and oligogenic diabetes variants, and helping to improve our understanding of the genetics underlying other types of diabetes. An accurate diagnosis remains important, because it might lead to a change in the treatment of affected subjects and influence long-term complications.

Clinical utility of next-generation sequencing for the molecular diagnosis of monogenic diabetes

Monogenic diabetes resulting from mutations that primarily reduce insulin-secreting pancreatic β-cell function accounts for 1-2% of all cases of diabetes, and is genetically and clinically heterogeneous. Currently, genetic testing for monogenic diabetes relies on selection of the appropriate gene for analysis based on the availability of comprehensive phenotypic information, which can be time consuming, costly and can limit the differential diagnosis to a few selected genes. In recent years, the exponential growth in the field of high-throughput capture and sequencing technology has made it possible and cost effective to sequence many genes simultaneously, making it an efficient diagnostic tool for clinically and genetically heterogeneous disorders such as monogenic diabetes. Making a diagnosis of monogenic diabetes is important as it enables more appropriate treatment, better prediction of disease prognosis and progression, and counseling and screening of family members. We provide a concise overview of the genetic etiology of some forms of monogenic diabetes, as well as a discussion of the clinical utility of genetic testing by comprehensive multigene panel using next-generation sequencing methodologies.

Effect of NeuroD gene silencing on the migration and invasion of human pancreatic cancer cells PANC-1

The aim of this study is to investigate the influence of Lenti-EGFP-NeuroD-miR, RNAi lentiviral expression vector, on the expression level of NeuroD and migration, and invasion of PANC-1 cell line. PANC-1 cells were cultured and cotransfected with Lenti-EGFP-NeuroD-miR and Lenti-GFP. The infection rate of lentivirus was determined by fluorescence. The interfering effection by the expression of NeuroD mRNA in PANC-1 cells was analyzed by real-time PCR after transfected. Biological behavior of PANC-1 cells transinfected was observed, and the migration and invasion were studied by transwell assay. Intrapancreatic allografts model in nude mice was established to observe the effects of NeuroD on tumorigenesis, tumor growth, and invasion in vivo. The expression of NeuroD mRNA decreased significantly after RNAi lentivirus transinfecting PANC-1 cell. The cell's migration and invasion ability decreased obviously as soon as down regulate of NeuroD in PANC-1 cells. Comparing with control group, the tumors were smaller in size and the invasiveness was inhibited after 8 weeks intrapancreatic allografts in nude mice. Lenti-EGFP-NeuroD-miR transfected into PANC-1 cells shows a stable, effective, and especial blocking expression of NeuroD in mRNA level. The RNAi of lentiviral vector target NeuroD can reduce the migration and invasion abilities of PANC-1 cells.

Proneural bHLH genes in development and disease

Proneural genes encode evolutionarily conserved basic-helix-loop-helix transcription factors. In Drosophila, proneural genes are required and sufficient to confer a neural identity onto naïve ectodermal cells, inducing delamination and subsequent neuronal differentiation. In vertebrates, proneural genes are expressed in cells that already have a neural identity, but they are still required and sufficient to initiate neurogenesis. In all organisms, proneural genes control neurogenesis by regulating Notch-mediated lateral inhibition and initiating the expression of downstream differentiation genes. The general mode of proneural gene function has thus been elucidated. However, the regulatory mechanisms that spatially and temporally control proneural gene function are only beginning to be deciphered. Understanding how proneural gene function is regulated is essential, as aberrant proneural gene expression has recently been linked to a variety of human diseases-ranging from cancer to neuropsychiatric illnesses and diabetes. Recent insights into proneural gene function in development and disease are highlighted herein.

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.

New opportunities: harnessing induced pluripotency for discovery in diabetes and metabolism

The landmark discovery of induced pluripotent stem cells (iPSCs) by Shinya Yamanaka has transformed regenerative biology. Previously, insights into the pathogenesis of chronic human diseases have been hindered by the inaccessibility of patient samples. However, scientists are now able to convert patient fibroblasts into iPSCs and differentiate them into disease-relevant cell types. This ability opens new avenues for investigating disease pathogenesis and designing novel treatments. In this review, we highlight the uses of human iPSCs to uncover the underlying causes and pathological consequences of diabetes and metabolic syndromes, multifactorial diseases whose etiologies have been difficult to unravel using traditional methodologies.

Mutations in KCNJ11 are associated with the development of autosomal dominant, early-onset type 2 diabetes

AIMS/HYPOTHESIS

More than 90% of Chinese familial early-onset type 2 diabetes mellitus is genetically unexplained. To investigate the molecular aetiology, we identified and characterised whether mutations in the KCNJ11 gene are responsible for these families.

METHODS

KCNJ11 mutations were screened for 96 familial early-onset type 2 diabetic probands and their families. Functional significance of the identified mutations was confirmed by physiological analysis, molecular modelling and population survey.

RESULTS

Three novel KCNJ11 mutations, R27H, R192H and S116F117del, were identified in three families with early-onset type 2 diabetes mellitus. Mutated KCNJ11 with R27H or R192H markedly reduced ATP sensitivity (E23K>R27H>C42R>R192H>R201H), but no ATP-sensitive potassium channel currents were detected in the loss-of-function S116F117del channel in vitro. Molecular modelling indicated that R192H had a larger effect on the channel ATP-binding pocket than R27H, which may qualitatively explain why the ATP sensitivity of the R192H mutation is seven times less than R27H. The shape of the S116F117del channel may be compressed, which may explain why the mutated channel had no currents. Discontinuation of insulin and implementation of sulfonylureas for R27H or R192H carriers and continuation/switch to insulin therapy for S116F117del carriers resulted in good glycaemic control.

CONCLUSIONS/INTERPRETATION

Our results suggest that genetic diagnosis for the KCNJ11 mutations in familial early-onset type 2 diabetes mellitus may help in understanding the molecular aetiology and in providing more personalised treatment for these specific forms of diabetes in Chinese and other Asian patients.

SEL1L regulates adhesion, proliferation and secretion of insulin by affecting integrin signaling

SEL1L, a component of the endoplasmic reticulum associated degradation (ERAD) pathway, has been reported to regulate the (i) differentiation of the pancreatic endocrine and exocrine tissue during the second transition of mouse embryonic development, (ii) neural stem cell self-renewal and lineage commitment and (iii) cell cycle progression through regulation of genes related to cell-matrix interaction. Here we show that in the pancreas the expression of SEL1L is developmentally regulated, such that it is readily detected in developing islet cells and in nascent acinar clusters adjacent to basement membranes, and becomes progressively restricted to the islets of Langherans in post-natal life. This peculiar expression pattern and the presence of two inverse RGD motifs in the fibronectin type II domain of SEL1L protein indicate a possible interaction with cell adhesion molecules to regulate islets architecture. Co-immunoprecipitation studies revealed SEL1L and ß1-integrin interaction and, down-modulation of SEL1L in pancreatic ß-cells, negatively influences both cell adhesion on selected matrix components and cell proliferation likely due to altered ERK signaling. Furthermore, the absence of SEL1L protein strongly inhibits glucose-stimulated insulin secretion in isolated mouse pancreatic islets unveiling an important role of SEL1L in insulin trafficking. This phenotype can be rescued by the ectopic expression of the ß1-integrin subunit confirming the close interaction of these two proteins in regulating the cross-talk between extracellular matrix and insulin signalling to create a favourable micro-environment for ß-cell development and function.

Assessing the phenotypic effects in the general population of rare variants in genes for a dominant Mendelian form of diabetes

Genome sequencing can identify individuals in the general population who harbor rare coding variants in genes for Mendelian disorders and who may consequently have increased disease risk. Previous studies of rare variants in phenotypically extreme individuals display ascertainment bias and may demonstrate inflated effect-size estimates. We sequenced seven genes for maturity-onset diabetes of the young (MODY) in well-phenotyped population samples (n = 4,003). We filtered rare variants according to two prediction criteria for disease-causing mutations: reported previously in MODY or satisfying stringent de novo thresholds (rare, conserved and protein damaging). Approximately 1.5% and 0.5% of randomly selected individuals from the Framingham and Jackson Heart Studies, respectively, carry variants from these two classes. However, the vast majority of carriers remain euglycemic through middle age. Accurate estimates of variant effect sizes from population-based sequencing are needed to avoid falsely predicting a substantial fraction of individuals as being at risk for MODY or other Mendelian diseases.

Microphthalmia transcription factor regulates pancreatic β-cell function

Precise regulation of β-cell function is crucial for maintaining blood glucose homeostasis. Pax6 is an essential regulator of β-cell-specific factors like insulin and Glut2. Studies in the developing eye suggest that Pax6 interacts with Mitf to regulate pigment cell differentiation. Here, we show that Mitf, like Pax6, is expressed in all pancreatic endocrine cells during mouse postnatal development and in the adult islet. A Mitf loss-of-function mutation results in improved glucose tolerance and enhanced insulin secretion but no increase in β-cell mass in adult mice. Mutant β-cells secrete more insulin in response to glucose than wild-type cells, suggesting that Mitf is involved in regulating β-cell function. In fact, the transcription of genes critical for maintaining glucose homeostasis (insulin and Glut2) and β-cell formation and function (Pax4 and Pax6) is significantly upregulated in Mitf mutant islets. The increased Pax6 expression may cause the improved β-cell function observed in Mitf mutant animals, as it activates insulin and Glut2 transcription. Chromatin immunoprecipitation analysis shows that Mitf binds to Pax4 and Pax6 regulatory regions, suggesting that Mitf represses their transcription in wild-type β-cells. We demonstrate that Mitf directly regulates Pax6 transcription and controls β-cell function.

Evaluation of variant A45T in NEUROD1/BETA2 for its association with type 2 diabetes mellitus

Heterozygous loss-of-function mutations in NEUROD1 have been identified as a very rare cause of maturity-onset diabetes of the young and neonatal diabetes. Previous studies showed that a common A45T variant located in NEUROD1 was inconsistently associated with type 2 diabetes mellitus (T2DM) in different ethnic populations. This study aimed to evaluate the contribution of variant A45T in the genetic pathogenesis of T2DM. A case-control study in a Chinese Han population was conducted, which included 3,554 (1,155 males/2,399 females) patients with T2DM and 4,181 (1,798 males/2,383 females) control subjects from 13 different regions of China. The A45T variant was genotyped by the Illumina GoldenGate platform. A meta-analysis was used to estimate the effects of variant A45T in populations from different ethnic backgrounds. No association in Chinese Han subjects was confirmed in our case control study. A relationship between variant A45T and postprandial glucose was observed in the control group (β = 0.05, p = 0.002). Meta-analyses did not find an association of this polymorphism with T2DM in Chinese, Japanese, and East Asian descent, but did for European descent Caucasians (odds ratio = 1.15, 95 %CI 1.03-1.28, p = 0.01). Our study suggests the variant A45T does not play a major role in the development of T2DM in East Asian descent, and the role in European descent Caucasian needs to be confirmed.

Maturity onset diabetes of the young: identification and diagnosis

Maturity-onset diabetes of the young (MODY) is a monogenic disorder that results in a familial, young-onset non-insulin dependent form of diabetes, typically presenting in lean young adults before 25 years. Approximately 1% of diabetes has a monogenic cause but this is frequently misdiagnosed as Type 1 or Type 2 diabetes. A correct genetic diagnosis is important as it often leads to improved treatment for those affected with diabetes and enables predictive genetic testing for their asymptomatic relatives. An early diagnosis together with appropriate treatment is essential for reducing the risk of diabetic complications in later life. Mutations in the GCK and HNF1A/4 A genes account for up to 80% of all MODY cases. Mutations in the GCK gene cause a mild, asymptomatic and non-progressive fasting hyperglycaemia from birth usually requiring no treatment. In contrast, mutations in the genes encoding the transcription factors HNF1A and HNF4A cause a progressive insulin secretory defect and hyperglycaemia that can lead to vascular complications. The diabetes in these patients is usually well controlled with sulphonylurea tablets although insulin treatment may be required in later life. In this review, we outline the key clinical and laboratory characteristics of the common and rarer causes of MODY with the aim of raising awareness of this condition amongst health-care scientists.

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.

NeuroD1 regulates survival and migration of neuroendocrine lung carcinomas via signaling molecules TrkB and NCAM

Small-cell lung cancer and other aggressive neuroendocrine cancers are often associated with early dissemination and frequent metastases. We demonstrate that neurogenic differentiation 1 (NeuroD1) is a regulatory hub securing cross talk among survival and migratory-inducing signaling pathways in neuroendocrine lung carcinomas. We find that NeuroD1 promotes tumor cell survival and metastasis in aggressive neuroendocrine lung tumors through regulation of the receptor tyrosine kinase tropomyosin-related kinase B (TrkB). Like TrkB, the prometastatic signaling molecule neural cell adhesion molecule (NCAM) is a downstream target of NeuroD1, whose impaired expression mirrors loss of NeuroD1. TrkB and NCAM may be therapeutic targets for aggressive neuroendocrine cancers that express NeuroD1.

Mutations in the genes encoding the transcription factors hepatocyte nuclear factor 1 alpha and 4 alpha in maturity-onset diabetes of the young and hyperinsulinemic hypoglycemia

Maturity-onset diabetes of the young (MODY) is a monogenic disorder characterized by autosomal dominant inheritance of young-onset (typically <25 years), noninsulin-dependent diabetes due to defective insulin secretion. MODY is both clinically and genetically heterogeneous with mutations in at least 10 genes. Mutations in the HNF1A gene encoding hepatocyte nuclear factor-1 alpha are the most common cause of MODY in most adult populations studied. The number of different pathogenic HNF1A mutations totals 414 in 1,247 families. Mutations in the HNF4A gene encoding hepatocyte nuclear factor-4 alpha are a rarer cause of MODY with 103 different mutations reported in 173 families to date. Sensitivity to treatment with sulfonylurea tablets is a feature of both HNF1A and HNF4A mutations. The HNF4A MODY phenotype has been expanded by the reports of macrosomia in ∼50% of babies, and more rarely, neonatal hyperinsulinemic hypoglycemia. The identification of an HNF1A or HNF4A gene mutation has important implications for clinical management in diabetes and pregnancy, but MODY is significantly underdiagnosed. Current research is focused on identifying biomarkers and developing probability models to identify those patients most likely to have MODY, until next generation sequencing technology enables cost-effective gene analysis for all patients with young onset diabetes.

Individualized therapy for type 2 diabetes: clinical implications of pharmacogenetic data

Type 2 diabetes mellitus (T2DM) is characterized by insulin resistance, abnormally elevated hepatic glucose production, and reduced glucose-stimulated insulin secretion. Treatment with antihyperglycemic agents is initially successful in type 2 diabetes, but it is often associated with a high secondary failure rate, and the addition of insulin is eventually necessary for many patients, in order to restore acceptable glycemic control and to reduce the risk of development and progression of disease complications. Notably, even patients who appear to have similar requirements of antidiabetic regimens show great variability in drug disposition, glycemic response, tolerability, and incidence of adverse effects during treatment. Pharmacogenomics is a promising area of investigation and involves the search for genetic polymorphisms that may explain the interindividual variability in antidiabetic therapy response. The initial positive results portend that genomic efforts will be able to shed important light on variability in pharmacologic traits. In this review, we summarize the current understanding of genetic polymorphisms that may affect the responses of subjects with T2DM to antidiabetic treatment. These genes belong to three major classes: genes involved in drug metabolism and transporters that influence pharmacokinetics (including the cytochrome P450 [CYP] superfamily, the organic anion transporting polypeptide [OATP] family, and the polyspecific organic cation transporter [OCT] family); genes encoding drug targets and receptors (including peroxisome proliferator-activated receptor gamma [PPARG], the adenosine triphosphate [ATP]-sensitive potassium channel [K(ATP)], and incretin receptors); and genes involved in the causal pathway of T2DM that are able to modify the effects of drugs (including adipokines, transcription factor 7-like 2 (T cell specific, HMG-box) [TCF7L2], insulin receptor substrate 1 [IRS1], nitric oxide synthase 1 (neuronal) adaptor protein [NOS1AP], and solute carrier family 30 (zinc transporter), member 8 [SLC30A8]). In addition to these three major classes, we also review the available evidence on novel genes (CDK5 regulatory subunit associated protein 1-like 1 [CDKAL1], insulin-like growth factor 2 mRNA binding protein 2 [IGF2BP2], potassium voltage-gated channel, KQT-like subfamily, member 1 [KCNQ1], paired box 4 [PAX4] and neuronal differentiation 1 [NEUROD1] transcription factors, ataxia telangiectasia mutated [ATM], and serine racemase [SRR]) that have recently been proposed as possible modulators of therapeutic response in subjects with T2DM.

NeuroD1 A45T and PAX4 R121W polymorphisms are associated with plasma glucose level of repaglinide monotherapy in Chinese patients with type 2 diabetes

AIMS

We aimed to determine whether NeuroD1/BETA2 and PAX4 polymorphisms were associated with the therapeutic efficacy of repaglinide in Chinese type 2 diabetes mellitus (T2DM) patients.

METHODS

Three hundred and sixty-eight T2DM patients and 132 healthy control subjects were genotyped by restriction fragment length polymorphism. Forty-three patients with various genotypes were randomly selected to undergo 8 weeks of repaglinide treatment (3 mg day(-1)). Fasting plasma glucose, postprandial plasma glucose, glycated haemoglobin, fasting and postprandial serum insulin (FINS, PINS), homeostasis model assessment for insulin resistance, serum triglyceride, total cholesterol, low-density lipoprotein-cholesterol and high-density lipoprotein-cholesterol were determined before and after repaglinide treatment.

RESULTS

The allelic frequency of NeuroD1/BETA2 T45 was higher in T2DM patients than in the control subjects [13.45 vs. 6.82%, P < 0.01, odds ratios = 2.342 (1.365, 4.019), P= 0.002]. Type 2 diabetes mellitus patients with the mutated allele of NeuroD1/BETA2 A45T polymorphism showed higher FINS (13.46 ± 12.57 vs. 10.04 ± 7.09 mU l(-1) , P < 0.05) (11.67, 14.83 vs. 8.38, 11.37) and PINS (52.11 ± 40.93 vs. 68.66 ± 43.87 mU l(-1), P < 0.05) (44.89, 58.35 vs. 55.35, 88.87) than individuals with the T allele. The PAX4 R121W R allele carriers had higher PINS (52.11 ± 40.93 vs. 68.66 ± 43.87 mU l(-1), P < 0.05) (44.89, 58.35 vs. 55.35, 88.87) than subjects with the W allele. After repaglinide treatment, patients with the T allele of NeuroD1/BETA2 A45T polymorphisms had attenuated efficacy on fasting plasma glucose (-2.79 ± 2.14 vs.-0.99 ± 1.80 mmol l(-1), P < 0.01) (-3.53, -1.84 vs.-1.99, -0.13) and postprandial plasma glucose (-6.71 ± 5.90 vs.-2.54 ± 3.39 mmol l(-1), P < 0.01) (-9.28, -4.62 vs.-4.34, -0.84). Patients with the RR genotype of PAX4 R121W showed better efficacy with respect to the level of postprandial plasma glucose than R/W genotypes (-6.53 ± 6.52 vs.-2.95 ± 1.17 mmol l(-1), P < 0.05) (-8.20, -4.89 vs.-3.92, -1.20).

CONCLUSIONS

The NeuroD1/BETA2 and PAX4 polymorphisms were substantially associated with plasma glucose level after repaglinide monotherapy.

Pituitary gland development and disease: from stem cell to hormone production

Many aspects of pituitary development have become better understood in the past two decades. The signaling pathways regulating pituitary growth and shape have emerged, and the balancing interactions between the pathways are now appreciated. Markers for multipotent progenitor cells are being identified, and signature transcription factors have been discovered for most hormone-producing cell types. We now realize that pulsatile hormone secretion involves a 3D integration of cellular networks. About a dozen genes are known to cause pituitary hypoplasia when mutated due to their essential roles in pituitary development. Similarly, a few genes are known that predispose to familial endocrine neoplasia, and several genes mutated in sporadic pituitary adenomas are documented. In the next decade, we anticipate gleaning a deeper appreciation of these processes at the molecular level, insight into the development of the hypophyseal portal blood system, and evolution of better therapeutics for congenital and acquired hormone deficiencies and for common craniopharyngiomas and pituitary adenomas.

Variants of the HNF1α gene: A molecular approach concerning diabetic patients from southern Brazil

Maturity Onset Diabetes of the Young (MODY) presents monogenic inheritance and mutation factors which have already been identified in six different genes. Given the wide molecular variation present in the hepatocyte nuclear factor-1α gene (HNF1α) MODY3, the aim of this study was to amplify and sequence the coding regions of this gene in seven patients from the Campos Gerais region, Paraná State, Brazil, presenting clinical MODY3 features. Besides the synonymous variations, A15A, L17L, Q141Q, G288G and T515T, two missense mutations, I27L and A98V, were also detected. Clinical and laboratory data obtained from patients were compared with the molecular findings, including the I27L polymorphism that was revealed in some overweight/obese diabetic patients of this study, this corroborating with the literature. We found certain DNA variations that could explain the hyperglycemic phenotype of the patients.

Monogenic models: what have the single gene disorders taught us?

Monogenic diabetes constitutes a heterogeneous group of single gene disorders. The molecular background and clinical picture of many of these diseases have been described. While each of these forms is much less prevalent than multifactorial type 1 and type 2 diabetes mellitus (T2DM), together they affect millions of patients worldwide. Genetic diagnosis, which has become widely available, is of great clinical importance for patients with single gene diabetes. It helps to fully understand the pathophysiology of the disease, tailor the optimal hypoglycemic treatment, and define the prognosis for the entire family. Monogenic diabetes forms can be divided into 2 large groups, resulting from impaired insulin secretion or from an abnormal response to insulin. There are several lessons we have been taught by single-gene diabetes. We learned that the gene responsible for the occurrence of diabetes can be identified if an appropriate search strategy is used. In addition, discoveries of genes responsible for monogenic disorders pointed to them as susceptibility candidates for T2DM. Moreover, establishing that some families of proteins or biological pathways, such as transcription factors or potassium channel subunits, are involved in monogenic diabetes sparked research on their involvement in multifactorial diabetes. Finally, the example of single gene diabetes, particularly HNF1A MODY and permanent neonatal diabetes associated with the KCNJ11 and ABCC8 genes, all efficiently controlled on sulfonylurea, inspires us to continue the efforts to tailor individual treatment for T2DM patients. In this review paper, we summarize the impact of single gene disease discoveries on diabetes research and clinical practice.

Functional analyses of the mutation nt-128 T→G in the hepatocyte nuclear factor-1α promoter region in Chinese diabetes pedigrees

AIMS

Hepatocyte nuclear factor-1α (HNF-1α) regulates the expression of genes encoding proteins involved in glucose metabolism and insulin secretion. Mutations in the HNF-1α gene cause maturity-onset diabetes of the young Type 3. However, the mechanism leading to this disease has not been completely ascertained. Previously, we found a novel mutation in the regulatory element of the human HNF-1α gene in two Chinese diabetes pedigrees. The nucleotide at position -128 T was substituted by G (nt-128 T→G). In this study, we analysed the functional defect of nt-128 T→G in HNF-1α transcription activity.

METHODS

Luciferase reporter gene assays were carried out to examine the functional characteristics of this mutant. Electrophoretic mobility shift assays and chromatin immunoprecipitation were performed to confirm the binding of nuclear proteins to oligonucleotides.

RESULTS

The variant construct (nt-128 T→G) had a 1.65-fold increase in promoter activity compared with that of the wild-type construct in HepG2 cells and a 1.33-fold increase in MIN6 cells, respectively. The variant resided at a FOXA/HNF-3 binding site identified by a series of competitive electrophoretic mobility shift assays and antibody supershift analyses. The assays showed a differential binding affinity in the wild-type and the nt-128 T→G mutant fragments by FOXA/HNF-3. Chromatin immunoprecipitation indicated that FOXA/HNF-3 bound to this region in vivo. One nucleotide substitution in the FOXA/HNF-3 site in the human HNF-1α regulatory element caused an increase of HNF-1α transcriptional activity.

CONCLUSIONS

Our data suggested that this substitution in the promoter region affects DNA-protein interaction and HNF-1α gene transcription. The mutant may contribute to the development of diabetes in these two nt-128 T→G pedigrees of Chinese.

Dietary selenium deficiency partially rescues type 2 diabetes-like phenotypes of glutathione peroxidase-1-overexpressing male mice

This study was conducted to determine whether dietary Se deficiency precluded overproduction of glutathione peroxidase-1 (GPX1) activity in mice overexpressing (OE) this gene and thus rescued their type 2 diabetes-like phenotypes. A total of 20 male OE and wild-type (WT) mice were fed an Se-deficient (<0.02 mg/kg) diet or an Se-supplemented (0.3 mg/kg as sodium selenite) diet from 1 to 5 mo of age. Dietary Se deficiency eliminated or attenuated (P < 0.05) genotype differences in concentrations of blood glucose, plasma insulin, and/or hepatic lipids, insulin sensitivity, and glucose-stimulated insulin secretion at the end of the study. Dietary Se deficiency decreased (P < 0.05) OE islet mRNA levels of 2 key transcriptional activators (Beta2 and Foxa2) and removed genotype differences in islet mRNA levels of 7 genes (Beta2, Cfos, Foxa2, Pregluc, Ins1, p53, and Sur1) related to insulin synthesis and secretion. Compared with those of the Se-adequate OE mice, the Se-deficient OE mice had lower (P < 0.05) hepatic mRNA levels of 2 key rate-limiting enzymes for lipogenesis (Acc1) and glycolysis (Gk1), along with lower (P < 0.05) activities of hepatic glucokinase and muscle phosphoenolpyruvate carboxykinase. Dietary Se deficiency also decreased (P < 0.05) blood glucose and hepatic lipid concentrations in the WT mice. In conclusion, dietary Se deficiency precluded the overproduction of GPX1 in full-fed OE mice and partially rescued their metabolic syndromes. This alleviation resulted from modulating the expression and/or function of proinsulin genes, lipogenesis rate-limiting enzyme genes, and key glycolysis and gluconeogenesis enzymes in islets, liver, and muscle.

A systems genetics approach identifies genes and pathways for type 2 diabetes in human islets

Close to 50 genetic loci have been associated with type 2 diabetes (T2D), but they explain only 15% of the heritability. In an attempt to identify additional T2D genes, we analyzed global gene expression in human islets from 63 donors. Using 48 genes located near T2D risk variants, we identified gene coexpression and protein-protein interaction networks that were strongly associated with islet insulin secretion and HbA(1c). We integrated our data to form a rank list of putative T2D genes, of which CHL1, LRFN2, RASGRP1, and PPM1K were validated in INS-1 cells to influence insulin secretion, whereas GPR120 affected apoptosis in islets. Expression variation of the top 20 genes explained 24% of the variance in HbA(1c) with no claim of the direction. The data present a global map of genes associated with islet dysfunction and demonstrate the value of systems genetics for the identification of genes potentially involved in T2D.

Cx36 is a target of Beta2/NeuroD1, which associates with prenatal differentiation of insulin-producing β cells

The insulin-producing β cells of pancreatic islets are coupled by connexin36 (Cx36) channels. To investigate what controls the expression of this connexin, we have investigated its pattern during mouse pancreas development, and the influence of three transcription factors that are critical for β-cell development and differentiation. We show that (1) the Cx36 gene (Gjd2) is activated early in pancreas development and is markedly induced at the time of the surge of the transcription factors that determine β-cell differentiation; (2) the cognate protein is detected about a week later and is selectively expressed by β cells throughout the prenatal development of mouse pancreas; (3) a 2-kbp fragment of the Gjd2 promoter, which contains three E boxes for the binding of the bHLH factor Beta2/NeuroD1, ensures the expression of Cx36 by β cells; and (4) Beta2/NeuroD1 binds to these E boxes and, in the presence of the E47 ubiquitous cofactor, transactivates the Gjd2 promoter. The data identify Cx36 as a novel early marker of β cells and as a target of Beta2/NeuroD1, which is essential for β-cell development and differentiation.

ATOH7 mutations cause autosomal recessive persistent hyperplasia of the primary vitreous

The vertebrate basic helix-loop-helix (bHLH) transcription factor ATOH7 (Math5) is specifically expressed in the embryonic neural retina and is required for the genesis of retinal ganglion cells (RGCs) and optic nerves. In Atoh7 mutant mice, the absence of trophic factors secreted by RGCs prevents the development of the intrinsic retinal vasculature and the regression of fetal blood vessels, causing persistent hyperplasia of the primary vitreous (PHPV). We therefore screened patients with hereditary PHPV, as well as bilateral optic nerve aplasia (ONA) or hypoplasia (ONH), for mutations in ATOH7. We identified a homozygous ATOH7 mutation (N46H) in a large family with an autosomal recessive PHPV disease trait linked to 10q21, and a heterozygous variant (R65G, p.Arg65Gly) in one of five sporadic ONA patients. High-density single-nucleotide polymorphism analysis also revealed a CNTN4 duplication and an OTX2 deletion in the ONA cohort. Functional analysis of ATOH7 bHLH domain substitutions, by electrophoretic mobility shift and luciferase cotransfection assays, revealed that the N46H variant cannot bind DNA or activate transcription, consistent with structural modeling. The N46H variant also failed to rescue RGC development in mouse Atoh7-/- retinal explants. The R65G variant retains all of these activities, similar to wild-type human ATOH7. Our results strongly suggest that autosomal recessive persistent hyperplastic primary vitreous is caused by N46H and is etiologically related to nonsyndromic congenital retinal nonattachment. The R65G allele, however, cannot explain the ONA phenotype. Our study firmly establishes ATOH7 as a retinal disease gene and provides a functional basis to analyze new coding variants.

Deregulation of CREB signaling pathway induced by chronic hyperglycemia downregulates NeuroD transcription

CREB mediates the transcriptional effects of glucose and incretin hormones in insulin-target cells and insulin-producing β-cells. Although the inhibition of CREB activity is known to decrease the β-cell mass, it is still unknown what factors inversely alter the CREB signaling pathway in β-cells. Here, we show that β-cell dysfunctions occurring in chronic hyperglycemia are not caused by simple inhibition of CREB activity but rather by the persistent activation of CREB due to decreases in protein phophatase PP2A. When freshly isolated rat pancreatic islets were chronically exposed to 25 mM (high) glucose, the PP2A activity was reduced with a concomitant increase in active pCREB. Brief challenges with 15 mM glucose or 30 µM forskolin after 2 hour fasting further increased the level of pCREB and consequently induced the persistent expression of ICER. The excessively produced ICER was sufficient to repress the transcription of NeuroD, insulin, and SUR1 genes. In contrast, when islets were grown in 5 mM (low) glucose, CREB was transiently activated in response to glucose or forskolin stimuli. Thus, ICER expression was transient and insufficient to repress those target genes. Importantly, overexpression of PP2A reversed the adverse effects of chronic hyperglycemia and successfully restored the transient activation of CREB and ICER. Conversely, depletion of PP2A with siRNA was sufficient to disrupt the negative feedback regulation of CREB and induce hyperglycemic phenotypes even under low glucose conditions. Our findings suggest that the failure of the negative feedback regulation of CREB is the primary cause for β-cell dysfunctions under conditions of pathogenic hyperglycemia, and PP2A can be a novel target for future therapies aiming to protect β-cells mass in the late transitional phase of non-insulin dependent type 2 diabetes (NIDDM).

Developmental transcriptional networks are required to maintain neuronal subtype identity in the mature nervous system

During neurogenesis, transcription factors combinatorially specify neuronal fates and then differentiate subtype identities by inducing subtype-specific gene expression profiles. But how is neuronal subtype identity maintained in mature neurons? Modeling this question in two Drosophila neuronal subtypes (Tv1 and Tv4), we test whether the subtype transcription factor networks that direct differentiation during development are required persistently for long-term maintenance of subtype identity. By conditional transcription factor knockdown in adult Tv neurons after normal development, we find that most transcription factors within the Tv1/Tv4 subtype transcription networks are indeed required to maintain Tv1/Tv4 subtype-specific gene expression in adults. Thus, gene expression profiles are not simply “locked-in,” but must be actively maintained by persistent developmental transcription factor networks. We also examined the cross-regulatory relationships between all transcription factors that persisted in adult Tv1/Tv4 neurons. We show that certain critical cross-regulatory relationships that had existed between these transcription factors during development were no longer present in the mature adult neuron. This points to key differences between developmental and maintenance transcriptional regulatory networks in individual neurons. Together, our results provide novel insight showing that the maintenance of subtype identity is an active process underpinned by persistently active, combinatorially-acting, developmental transcription factors. These findings have implications for understanding the maintenance of all long-lived cell types and the functional degeneration of neurons in the aging brain.

For neurons to function properly, they must establish and then maintain their unique, subtype-specific gene expression profiles. These unique gene expression profiles are established during development by networks of DNA–binding proteins, termed transcription factors (TFs). However, how neurons maintain their unique gene expression profiles in the mature and aging brain is largely unknown. Recent advances in inducible genetic technologies now allow us to manipulate gene expression in adult neurons, after normal development. Applying such techniques, we examined the effect of knocking down TF expression in two adult neuronal subtypes. We show that the TF networks that establish unique gene expression profiles during development are then required to maintain them thereafter. Thus, gene expression profiles are not simply “locked-in,” but must be actively maintained by persistent developmental TF networks. However, we found that critical cross-regulatory relationships that had existed between TFs during development were not present in the adult, even between persisting TFs. This highlights important differences between developmental and maintenance transcriptional networks in individual neurons. The dependence of subtype gene expression on active mechanisms represents a potential Achilles heel for long-lived cells, as deterioration of those active mechanisms could lead to functional degeneration of neurons with advancing age.