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

Monogenic Diabetes: A Comprehensive Overview and Therapeutic Management of Subtypes of Mody

BACKGROUND

Monogenic diabetes often occurs as a result of single-gene mutations. The illness is minimally affected by environmental and behavioral factors, and it constitutes around one to five percent of all cases of diabetes.

METHODS

Newborn diabetes mellitus (NDM) and maturity-onset diabetes of the young (MODY) are the predominant causes of monogenic diabetes, accounting for a larger proportion of cases, while syndromic diabetes represents a smaller percentage. MODY, a group of inherited non-autoimmune diabetes mellitus disorders, is quite common. However, it remains frequently misdiagnosed despite increasing public awareness. The condition is characterized by insulin resistance, the development of diabetes at a young age (before 25 years), mild high blood sugar levels, inheritance in an autosomal dominant pattern, and the preservation of natural insulin production.

RESULTS

Currently, there are 14 distinct subtypes of MODY that have been identified. Each subtype possesses distinct characteristics in terms of their frequency, clinical symptoms, severity of diabetes, related complications, and response to medicinal interventions. Due to the clinical similarities, lack of awareness, and high expense of genetic testing, distinguishing between type I (T1D) and type II diabetes mellitus (T2D) can be challenging, resulting in misdiagnosis of this type of diabetes. As a consequence, a significant number of individuals are being deprived of adequate medical attention. Accurate diagnosis enables the utilization of novel therapeutic strategies and enhances the management of therapy in comparison to type II and type I diabetes.

CONCLUSION

This article offers a concise overview of the clinical subtypes and characteristics of monogenic diabetes. Furthermore, this article discusses the various subtypes of MODY, as well as the process of diagnosing, managing, and treating the condition. It also addresses the difficulties encountered in detecting and treating MODY.

Single-housing-induced islet epigenomic changes are related to polymorphisms in diabetic KK mice

A lack of social relationships is increasingly recognized as a type 2 diabetes (T2D) risk. To investigate the underlying mechanism, we used male KK mice, an inbred strain with spontaneous diabetes. Given the association between living alone and T2D risk in humans, we divided the non-diabetic mice into singly housed (KK-SH) and group-housed control mice. Around the onset of diabetes in KK-SH mice, we compared H3K27ac ChIP-Seq with RNA-Seq using pancreatic islets derived from each experimental group, revealing a positive correlation between single-housing-induced changes in H3K27ac and gene expression levels. In particular, single-housing-induced H3K27ac decreases revealed a significant association with islet cell functions and GWAS loci for T2D and related diseases, with significant enrichment of binding motifs for transcription factors representative of human diabetes. Although these H3K27ac regions were preferentially localized to a polymorphic genomic background, SNVs and indels did not cause sequence disruption of enriched transcription factor motifs in most of these elements. These results suggest alternative roles of genetic variants in environment-dependent epigenomic changes and provide insights into the complex mode of disease inheritance.

NEUROD1: transcriptional and epigenetic regulator of human and mouse neuronal and endocrine cell lineage programs

Transcription factors belonging to the basic helix-loop-helix (bHLH) family are key regulators of cell fate specification and differentiation during development. Their dysregulation is implicated not only in developmental abnormalities but also in various adult diseases and cancers. Recently, the abilities of bHLH factors have been exploited in reprogramming strategies for cell replacement therapy. One such factor is NEUROD1, which has been associated with the reprogramming of the epigenetic landscape and potentially possessing pioneer factor abilities, initiating neuronal developmental programs, and enforcing pancreatic endocrine differentiation. The review aims to consolidate current knowledge on NEUROD1's multifaceted roles and mechanistic pathways in human and mouse cell differentiation and reprogramming, exploring NEUROD1 roles in guiding the development and reprogramming of neuroendocrine cell lineages. The review focuses on NEUROD1's molecular mechanisms, its interactions with other transcription factors, its role as a pioneer factor in chromatin remodeling, and its potential in cell reprogramming. We also show a differential potential of NEUROD1 in differentiation of neurons and pancreatic endocrine cells, highlighting its therapeutic potential and the necessity for further research to fully understand and utilize its capabilities.

Molecular mechanisms linking type 2 diabetes mellitus and late-onset Alzheimer's disease: A systematic review and qualitative meta-analysis

Research evidence indicating common metabolic mechanisms through which type 2 diabetes mellitus (T2DM) increases risk of late-onset Alzheimer's dementia (LOAD) has accumulated over recent decades. The aim of this systematic review is to provide a comprehensive review of common mechanisms, which have hitherto been discussed in separate perspectives, and to assemble and evaluate candidate loci and epigenetic modifications contributing to polygenic risk linkages between T2DM and LOAD. For the systematic review on pathophysiological mechanisms, both human and animal studies up to December 2023 are included. For the qualitative meta-analysis of genomic bases, human association studies were examined; for epigenetic mechanisms, data from human studies and animal models were accepted. Papers describing pathophysiological studies were identified in databases, and further literature gathered from cited work. For genomic and epigenomic studies, literature mining was conducted by formalised search codes using Boolean operators in search engines, and augmented by GeneRif citations in Entrez Gene, and other sources (WikiGenes, etc.). For the systematic review of pathophysiological mechanisms, 923 publications were evaluated, and 138 gene loci extracted for testing candidate risk linkages. 3 57 publications were evaluated for genomic association and descriptions of epigenomic modifications. Overall accumulated results highlight insulin signalling, inflammation and inflammasome pathways, proteolysis, gluconeogenesis and glycolysis, glycosylation, lipoprotein metabolism and oxidation, cell cycle regulation or survival, autophagic-lysosomal pathways, and energy. Documented findings suggest interplay between brain insulin resistance, neuroinflammation, insult compensatory mechanisms, and peripheral metabolic dysregulation in T2DM and LOAD linkage. The results allow for more streamlined longitudinal studies of T2DM-LOAD risk linkages.

Induction of diabetes by Tacrolimus in a phenotypic model of obesity and metabolic syndrome

Introduction

The pathogenesis of Post-Transplant Diabetes Mellitus (PTDM) is complex and multifactorial and it resembles that of Type-2 Diabetes Mellitus (T2DM). One risk factor specific to PTDM differentiates both entities: the use of immunosuppressive therapy. Specifically, Tacrolimus interacts with obesity and insulin resistance (IR) in accelerating the onset of PTDM. In a genotypic model of IR, the obese Zucker rats, Tacrolimus is highly diabetogenic by promoting the same changes in beta-cell already modified by IR. Nevertheless, genotypic animal models have their limitations and may not resemble the real pathophysiology of diabetes. In this study, we have evaluated the interaction between beta-cell damage and Tacrolimus in a non-genotypic animal model of obesity and metabolic syndrome.

Methods

Sprague Dawley rats were fed a high-fat enriched diet during 45 days to induce obesity and metabolic dysregulation. On top of this established obesity, the administration of Tacrolimus (1mg/kg/day) during 15 days induced severe hyperglycaemia and changes in morphological and structural characteristics of the pancreas.

Results

Obese animals administered with Tacrolimus showed increased size of islets of Langerhans and reduced beta-cell proliferation without changes in apoptosis. There were also changes in beta-cell nuclear factors such as a decrease in nuclear expression of MafA and a nuclear overexpression of FoxO1A, PDX-1 and NeuroD1. These animals also showed increased levels of pancreatic insulin and glucagon.

Discussion

This model could be evidence of the relationship between the T2DM and PTDM physiopathology and, eventually, the model may be instrumental to study the pathogenesis of T2DM.

Hypoxia and low-glucose environments co-induced HGDILnc1 promote glycolysis and angiogenesis

Small bowel vascular malformation disease (SBVM) commonly causes obscure gastrointestinal bleeding (OGIB). However, the pathogenetic mechanism and the role of lncRNAs in SBVM remain largely unknown. Here, we found that hypoxia and low-glucose environments co-augment angiogenesis and existed in SBVM. Mechanistically, hypoxia and low-glucose environments supported angiogenesis via activation of hypoxia and glucose deprivation-induced lncRNA (HGDILnc1) transcription by increasing binding of the NeuroD1 transcription factor to the HGDILnc1 promoter. Raised HGDILnc1 acted as a suppressor of α-Enolase 1 (ENO1) small ubiquitin-like modifier modification (SUMOylation)-triggered ubiquitination, and an activator of transcription of Aldolase C (ALDOC) via upregulation of Histone H2B lysine 16 acetylation (H2BK16ac) level in the promoter of ALDOC, and consequently promoting glycolysis and angiogenesis. Moreover, HGDILnc1 was clinically positively correlated with Neurogenic differentiation 1 (NeuroD1), ENO1, and ALDOC in SBVM tissues, and could function as a biomarker for SBVM diagnosis and therapy. These findings suggest that hypoxia and low-glucose environments were present in SBVM tissues, and co-augmented angiogenesis. Hypoxia and low-glucose environments co-induced HGDILnc1, which is higher expressed in SBVM tissue compared with normal tissue, could promoted glycolysis and angiogenesis.

The first compound heterozygous mutations in SLC12A3 and PDX1 genes: a unique presentation of Gitelman syndrome with distinct insulin resistance and familial diabetes insights

Background

Gitelman Syndrome (GS) patients frequently exhibit disrupted glucose metabolism, attributed to hypokalemia, hypomagnesemia and heightened aldosterone. This study delved into the genetic underpinnings linked to insulin resistance and diabetes in a GS patient, contextualized within his family history.

Methods

The hydrochlorothiazide and furosemide loading test were performed to ascertain the presence of GS. Oral glucose tolerance test (OGTT) evaluated glucose metabolism and insulin sensitivity. Whole-exome sequencing, validated by Sanger sequencing, was employed to confirm gene mutations, which were then tracked among the patient's relatives.

Results

Symptoms and laboratory examination confirmed the clinical diagnosis of GS. Comprehensive whole-exome sequencing, augmented by Sanger sequencing validation, revealed a compound heterozygous mutation within the SLC12A3 gene (c.1108G>C in exon 9, c.676G>A in exon 5 and c.2398G>A in exon 20) in the patient. The OGTT affirmed diabetes and heightened insulin resistance, distinct from previous patients with GS we evaluated. Further genetic analysis identified a missense heterozygous mutation (c.97C>G in exon 1) within the PDX1 gene, inherited from the patient's diabetic mother without GS. Furthermore, the patient's brother, with impaired glucose tolerance but regular potassium levels, also bore this mutation, hinting at additional impacts of the PDX1 gene mutation on glucose metabolism regulation beyond the known impacts of GS.

Conclusion

This study unveils unprecedented compound heterozygous mutations in the SLC12A3 and PDX1 genes in a GS patient. These findings illuminate the potential complex genetic factors influencing glucose metabolism disruptions in GS.

Take-home message

This research uncovers a novel combination of SLC12A3 and PDX1 gene mutations in a Gitelman Syndrome patient, revealing intricate genetic factors that potentially disrupt glucose metabolism and shedding light on familial diabetes links.

Identification of gene mutations associated with type 1 diabetes by next-generation sequencing in affected Palestinian families

Introduction: Diabetes Mellitus is a group of metabolic disorders characterized by hyperglycemia secondary to insulin resistance or deficiency. It is considered a major health problem worldwide. T1DM is a result of a combination of genetics, epigenetics, and environmental factors. Several genes have been associated with T1DM, including HLA, INS, CTLA4, and PTPN22. However, none of these findings have been based on linkage analysis because it is rare to find families with several diabetic individuals. Two Palestinian families with several afflicted members with variations in the mode of inheritance were identified and selected for this study. This study aimed to identify the putative causative gene(s) responsible for T1DM development in these families to improve our understanding of the molecular genetics of the disease. Methods: One afflicted member from each family was selected for Whole-Exome Sequencing. Data were mapped to the reference of the human genome, and the resulting VCF file data were filtered. The variants with the highest phenotype correlation score were checked by Sanger sequencing for all family members. The confirmed variants were analyzed in silico by bioinformatics tools. Results: In one family, the IGF1R p.V579F variant, which follows autosomal dominant inheritance, was confirmed and segregated in the family. In another family, the NEUROD1 p.P197H variant, which follows autosomal recessive inheritance, was positively confirmed and segregated. Conclusion: IGF1R p.V579F and NEUROD1 p.P197H variants were associated with T1DM development in the two inflicted families. Further analysis and functional assays will be performed, including the generation of mutant model cell systems, to unravel their specific molecular mechanism in the disease development.

Warming during embryogenesis induces a lasting transcriptomic signature in fishes

Exposure to elevated temperatures during embryogenesis can influence the plasticity of tissues in later life. Despite these long-term changes in plasticity, few differentially expressed genes are ever identified, suggesting that the developmental programming of later life plasticity may occur through the modulation of other aspects of transcriptomic architecture, such as gene network organisation. Here, we use network modelling approaches to demonstrate that warm temperatures during embryonic development (developmental warming) have consistent effects in later life on the organisation of transcriptomic networks across four diverse species of fishes: Scyliorhinus canicula, Danio rerio, Dicentrarchus labrax, and Gasterosteus aculeatus. The transcriptomes of developmentally warmed fishes are characterised by an increased entropy of their pairwise gene interaction networks, implying a less structured, more 'random' set of gene interactions. We also show that, in zebrafish subject to developmental warming, the entropy of an individual gene within a network is associated with that gene's probability of expression change during temperature acclimation in later life. However, this association is absent in animals reared under 'control' conditions. Thus, the thermal environment experienced during embryogenesis can alter transcriptomic organisation in later life, and these changes may influence an individual's responsiveness to future temperature challenges.

Enteroendocrine cell regulation of the gut-brain axis

Enteroendocrine cells (EECs) are an essential interface between the gut and brain that communicate signals about nutrients, pain, and even information from our microbiome. EECs are hormone-producing cells expressed throughout the gastrointestinal epithelium and have been leveraged by pharmaceuticals like semaglutide (Ozempic, Wegovy), terzepatide (Mounjaro), and retatrutide (Phase 2) for diabetes and weight control, and linaclotide (Linzess) to treat irritable bowel syndrome (IBS) and visceral pain. This review focuses on role of intestinal EECs to communicate signals from the gut lumen to the brain. Canonically, EECs communicate information about the intestinal environment through a variety of hormones, dividing EECs into separate classes based on the hormone each cell type secretes. Recent studies have revealed more diverse hormone profiles and communication modalities for EECs including direct synaptic communication with peripheral neurons. EECs known as neuropod cells rapidly relay signals from gut to brain via a direct communication with vagal and primary sensory neurons. Further, this review discusses the complex information processing machinery within EECs, including receptors that transduce intraluminal signals and the ion channel complement that govern initiation and propagation of these signals. Deeper understanding of EEC physiology is necessary to safely treat devastating and pervasive conditions like irritable bowel syndrome and obesity.

NEUROD1 reinforces endocrine cell fate acquisition in pancreatic development

NEUROD1 is a transcription factor that helps maintain a mature phenotype of pancreatic β cells. Disruption of Neurod1 during pancreatic development causes severe neonatal diabetes; however, the exact role of NEUROD1 in the differentiation programs of endocrine cells is unknown. Here, we report a crucial role of the NEUROD1 regulatory network in endocrine lineage commitment and differentiation. Mechanistically, transcriptome and chromatin landscape analyses demonstrate that Neurod1 inactivation triggers a downregulation of endocrine differentiation transcription factors and upregulation of non-endocrine genes within the Neurod1-deficient endocrine cell population, disturbing endocrine identity acquisition. Neurod1 deficiency altered the H3K27me3 histone modification pattern in promoter regions of differentially expressed genes, which resulted in gene regulatory network changes in the differentiation pathway of endocrine cells, compromising endocrine cell potential, differentiation, and functional properties.

From glucose sensing to exocytosis: takes from maturity onset diabetes of the young

Monogenic diabetes gave us simplified models of complex molecular processes occurring within β-cells, which allowed to explore the roles of numerous proteins from single protein perspective. Constellation of characteristic phenotypic features and wide application of genetic sequencing techniques to clinical practice, made the major form of monogenic diabetes - the Maturity Onset Diabetes of the Young to be distinguishable from type 1, type 2 as well as neonatal diabetes mellitus and understanding underlying molecular events for each type of MODY contributed to the advancements of antidiabetic therapy and stem cell research tremendously. The functional analysis of MODY-causing proteins in diabetes development, not only provided better care for patients suffering from diabetes, but also enriched our comprehension regarding the universal cellular processes including transcriptional and translational regulation, behavior of ion channels and transporters, cargo trafficking, exocytosis. In this review, we will overview structure and function of MODY-causing proteins, alterations in a particular protein arising from the deleterious mutations to the corresponding gene and their consequences, and translation of this knowledge into new treatment strategies.

PIMT Controls Insulin Synthesis and Secretion through PDX1

Pancreatic beta cell function is an important component of glucose homeostasis. Here, we investigated the function of PIMT (PRIP-interacting protein with methyl transferase domain), a transcriptional co-activator binding protein, in the pancreatic beta cells. We observed that the protein levels of PIMT, along with key beta cell markers such as PDX1 (pancreatic and duodenal homeobox 1) and MafA (MAF bZIP transcription factor A), were reduced in the beta cells exposed to hyperglycemic and hyperlipidemic conditions. Consistently, PIMT levels were reduced in the pancreatic islets isolated from high fat diet (HFD)-fed mice. The RNA sequencing analysis of PIMT knockdown beta cells identified that the expression of key genes involved in insulin secretory pathway, Ins1 (insulin 1), Ins2 (insulin 2), Kcnj11 (potassium inwardly-rectifying channel, subfamily J, member 11), Kcnn1 (potassium calcium-activated channel subfamily N member 1), Rab3a (member RAS oncogene family), Gnas (GNAS complex locus), Syt13 (synaptotagmin 13), Pax6 (paired box 6), Klf11 (Kruppel-Like Factor 11), and Nr4a1 (nuclear receptor subfamily 4, group A, member 1) was attenuated due to PIMT depletion. PIMT ablation in the pancreatic beta cells and in the rat pancreatic islets led to decreased protein levels of PDX1 and MafA, resulting in the reduction in glucose-stimulated insulin secretion (GSIS). The results from the immunoprecipitation and ChIP experiments revealed the interaction of PIMT with PDX1 and MafA, and its recruitment to the insulin promoter, respectively. Importantly, PIMT ablation in beta cells resulted in the nuclear translocation of insulin. Surprisingly, forced expression of PIMT in beta cells abrogated GSIS, while Ins1 and Ins2 transcript levels were subtly enhanced. On the other hand, the expression of genes, PRIP/Asc2/Ncoa6 (nuclear receptor coactivator 6), Pax6, Kcnj11, Syt13, Stxbp1 (syntaxin binding protein 1), and Snap25 (synaptosome associated protein 25) associated with insulin secretion, was significantly reduced, providing an explanation for the decreased GSIS upon PIMT overexpression. Our findings highlight the importance of PIMT in the regulation of insulin synthesis and secretion in beta cells.

Monogenic diabetes

Monogenic diabetes includes several clinical conditions generally characterized by early-onset diabetes, such as neonatal diabetes, maturity-onset diabetes of the young (MODY) and various diabetes-associated syndromes. However, patients with apparent type 2 diabetes mellitus may actually have monogenic diabetes. Indeed, the same monogenic diabetes gene can contribute to different forms of diabetes with early or late onset, depending on the functional impact of the variant, and the same pathogenic variant can produce variable diabetes phenotypes, even in the same family. Monogenic diabetes is mostly caused by impaired function or development of pancreatic islets, with defective insulin secretion in the absence of obesity. The most prevalent form of monogenic diabetes is MODY, which may account for 0.5-5% of patients diagnosed with non-autoimmune diabetes but is probably underdiagnosed owing to insufficient genetic testing. Most patients with neonatal diabetes or MODY have autosomal dominant diabetes. More than 40 subtypes of monogenic diabetes have been identified to date, the most prevalent being deficiencies of GCK and HNF1A. Precision medicine approaches (including specific treatments for hyperglycaemia, monitoring associated extra-pancreatic phenotypes and/or following up clinical trajectories, especially during pregnancy) are available for some forms of monogenic diabetes (including GCK- and HNF1A-diabetes) and increase patients' quality of life. Next-generation sequencing has made genetic diagnosis affordable, enabling effective genomic medicine in monogenic diabetes.

Atypical familial diabetes associated with a novel NEUROD1 nonsense variant

OBJECTIVES

We aimed to identify the origin of atypical diabetes in a family with four generations of diabetes from South Asia. The family members showed different clinical phenotypes. Members of generation one to three were presumed to have type 2 diabetes and generation four to have type 1 diabetes.

CASE PRESENTATION

We performed a genetic analysis of the family using targeted high throughput sequencing.

CONCLUSIONS

We identified a novel nonsense variant in the neurogenic differentiation 1 (NEUROD1) gene, co-segregating with diabetes. The variant was located in the DNA-binding domain, altering a protein residue that was very well conserved among different species.

Bulk and single-cell transcriptome analyses of islet tissue unravel gene signatures associated with pyroptosis and immune infiltration in type 2 diabetes

INTRODUCTION

Type 2 diabetes (T2D) is a common chronic heterogeneous metabolic disorder. However, the roles of pyroptosis and infiltrating immune cells in islet dysfunction of patients with T2D have yet to be explored. In this study, we aimed to explore potential crucial genes and pathways associated with pyroptosis and immune infiltration in T2D.

METHODS

To achieve this, we performed a conjoint analysis of three bulk RNA-seq datasets of islets to identify T2D-related differentially expressed genes (DEGs). After grouping the islet samples according to their ESTIMATE immune scores, we identified immune- and T2D-related DEGs. A clinical prediction model based on pyroptosis-related genes for T2D was constructed. Weighted gene co-expression network analysis was performed to identify genes positively correlated with pyroptosis-related pathways. A protein-protein interaction network was established to identify pyroptosis-related hub genes. We constructed miRNA and transcriptional networks based on the pyroptosis-related hub genes and performed functional analyses. Single-cell RNA-seq (scRNA-seq) was conducted using the GSE153885 dataset. Dimensionality was reduced using principal component analysis and t-distributed statistical neighbor embedding, and cells were clustered using Seurat. Different cell types were subjected to differential gene expression analysis and gene set enrichment analysis (GSEA). Cell-cell communication and pseudotime trajectory analyses were conducted using the samples from patients with T2D.

RESULTS

We identified 17 pyroptosis-related hub genes. We determined the abundance of 13 immune cell types in the merged matrix and found that these cell types were correlated with the 17 pyroptosis-related hub genes. Analysis of the scRNA-seq dataset of 1892 islet samples from patients with T2D and controls revealed 11 clusters. INS and IAPP were determined to be pyroptosis-related and candidate hub genes among the 11 clusters. GSEA of the 11 clusters demonstrated that the myc, G2M checkpoint, and E2F pathways were significantly upregulated in clusters with several differentially enriched pathways.

DISCUSSION

This study elucidates the gene signatures associated with pyroptosis and immune infiltration in T2D and provides a critical resource for understanding of islet dysfunction and T2D pathogenesis.

Disease-causing mutations in genes encoding transcription factors critical for photoreceptor development

Photoreceptor development of the vertebrate visual system is controlled by a complex transcription regulatory network. OTX2 is expressed in the mitotic retinal progenitor cells (RPCs) and controls photoreceptor genesis. CRX that is activated by OTX2 is expressed in photoreceptor precursors after cell cycle exit. NEUROD1 is also present in photoreceptor precursors that are ready to specify into rod and cone photoreceptor subtypes. NRL is required for the rod fate and regulates downstream rod-specific genes including the orphan nuclear receptor NR2E3 which further activates rod-specific genes and simultaneously represses cone-specific genes. Cone subtype specification is also regulated by the interplay of several transcription factors such as THRB and RXRG. Mutations in these key transcription factors are responsible for ocular defects at birth such as microphthalmia and inherited photoreceptor diseases such as Leber congenital amaurosis (LCA), retinitis pigmentosa (RP) and allied dystrophies. In particular, many mutations are inherited in an autosomal dominant fashion, including the majority of missense mutations in CRX and NRL. In this review, we describe the spectrum of photoreceptor defects that are associated with mutations in the above-mentioned transcription factors, and summarize the current knowledge of molecular mechanisms underlying the pathogenic mutations. At last, we deliberate the outstanding gaps in our understanding of the genotype-phenotype correlations and outline avenues for future research of the treatment strategies.

The missing link between genetic association and regulatory function

The genetic basis of most traits is highly polygenic and dominated by non-coding alleles. It is widely assumed that such alleles exert small regulatory effects on the expression of cis-linked genes. However, despite the availability of gene expression and epigenomic datasets, few variant-to-gene links have emerged. It is unclear whether these sparse results are due to limitations in available data and methods, or to deficiencies in the underlying assumed model. To better distinguish between these possibilities, we identified 220 gene-trait pairs in which protein-coding variants influence a complex trait or its Mendelian cognate. Despite the presence of expression quantitative trait loci near most GWAS associations, by applying a gene-based approach we found limited evidence that the baseline expression of trait-related genes explains GWAS associations, whether using colocalization methods (8% of genes implicated), transcription-wide association (2% of genes implicated), or a combination of regulatory annotations and distance (4% of genes implicated). These results contradict the hypothesis that most complex trait-associated variants coincide with homeostatic expression QTLs, suggesting that better models are needed. The field must confront this deficit and pursue this 'missing regulation.'

Statistical evidence for high-penetrance MODY-causing genes in a large population-based cohort

AIMS

Numerous genes have been proposed as causal for maturity-onset diabetes of the young (MODY). Scoring systems to annotate mutation pathogenicity have been widely used; however, statistical evidence for being a highly penetrant MODY gene has not been well-established.

METHODS

Participants were from the UK Biobank with whole-exome sequencing data, including 14,622 with and 185,509 without diagnosis of diabetes. Pathogenic/likely pathogenic (P/LP) mutations in 14 reported and 3 possible MODY genes were annotated using American College of Medical Genetics criteria. Evidence for being a high-penetrant MODY gene used two statistical criteria: frequency of aggregate P/LP mutations in each gene are (1) significantly more common in participants with a diagnosis of diabetes than without using the SKAT-O (p < .05) and (2) lower than the maximum credible frequency in the general population.

RESULTS

Among the 17 genes, 6 (GCK, HNF1A, HNF4A, NEUROD1, KCNJ11 and HNF1B) met both criteria, 7 (ABCC8, KLF11, RFX6, PCBD1, WFS1, INS and PDX1) met only one criterion, and the remaining 4 (CEL, BLK, APPL1 and PAX4) failed both criteria, and were classified as 'consistent', 'inconclusive' and 'inconsistent' for being highly penetrant diabetes genes, respectively. Diabetes participants with mutations in the 'consistent' genes had clinical presentations that were most consistent with MODY. In contrast, the 'inconclusive' and 'inconsistent' genes did not differ clinically from non-carriers in diabetes-related characteristics.

CONCLUSIONS

Data from a large population-based study provided novel statistical evidence to identify 6 MODY genes as consistent with being highly penetrant. These results have potential implications for interpreting genetic testing results and clinical diagnosis of MODY.

How do I diagnose Maturity Onset Diabetes of the Young in my patients?

Maturity Onset Diabetes of the Young (MODY) is a monogenic form of diabetes diagnosed in young individuals that lack the typical features of type 1 and type 2 diabetes. The genetic subtype of MODY determines the most effective treatment and this is the driver for MODY genetic testing in diabetes populations. Despite the obvious clinical and health economic benefits, MODY is significantly underdiagnosed with the majority of patients being inappropriately managed as having type 1 or type 2 diabetes. Low detection rates result from the difficulty in identifying patients with a likely diagnosis of MODY from the high background population of young onset type 1 and type 2 diabetes, compounded by the lack of MODY awareness and education in diabetes care physicians. MODY diagnosis can be improved through (1) access to education and training, (2) the use of sensitive and specific selection criteria based on accurate prediction models and biomarkers to identify patients for testing, (3) the development and mainstream implementation of simple criteria-based selection pathways applicable across a range of healthcare settings and ethnicities to select the most appropriate patients for genetic testing and (4) the correct use of next generation sequencing technology to provide accurate and comprehensive testing of all known MODY and monogenic diabetes genes. The creation and public sharing of educational materials, clinical and scientific best practice guidelines and genetic variants will help identify the missing patients so they can benefit from the more effective clinical care that a genetic diagnosis brings.

ABCC8-related maturity-onset diabetes of the young: Clinical features and genetic analysis of one case

OBJECTIVE

To confirm the diagnosis of a 13-year-old adolescent with familial diabetes and further examine his genetic pathogeny.

RESEARCH DESIGN AND METHODS

Clinical data were collected, and genetic examination was performed. PolyPhen-2 and Mutation Taster were used to predict the deleterious effects of the variant. Clustal Omega software was used to confirm the conservation of amino acid substitutions. To examine changes in the expression of proteins, recombinant vectors were constructed, and the expression of wild-type and variant target genes was detected through quantitative polymerase chain reaction. Furthermore, the wild-type and variant eukaryotic recombinant vectors were treated with a ubiquitin degradation inhibitor (MG132) and a lysosomal degradation pathway inhibitor (CQ, 3-mA). The expression of target proteins was detected through Western blot analysis.

RESULTS

The patient had hyperglycaemia (27 mmol/L), a high HbA1c level (13.1%), a decreased C-peptide level (0.63 ng/ml) and no diabetes antibodies. The patient had a family history of diabetes. The novel variation of ABCC8 c.2477G>A was detected in the proband and his relatives. The mutation was predicted to be harmful. Changes in the protein structure were observed. The ABCC8 c.2477G >A variant resulted in an increase in ABCC8 expression. Furthermore, changes in the expression of the ABCC8 variant was observed after 3-MA treatment, especially after treatment with MG132. At the follow-up, the patient's glucose level was normal without drug therapy for more than 2 years until until he started taking Trelagliptin Succinate to control hyperglycemia within the recent 6 months.

CONCLUSIONS

The diagnosis of maturity-onset diabetes of the young (MODY)12 was confirmed in our patient. The ABCC8 variant inhibited both ubiquitination and autophagy lysosome degradation pathways, especially the ubiquitination degradation pathway.

YY1 Regulates Glucose Homeostasis Through Controlling Insulin Transcription in Pancreatic β-Cells

To date, identification of nonislet-specific transcriptional factors in the regulation of insulin gene expression has been little studied. Here, we report that the expression level of the transcription factor YY1 is increased dramatically in both human and mouse pancreatic β-cells after birth. Nevertheless, the physiological role of YY1 during β-cell development and its regulatory mechanism in β-cell function remain largely unknown. After β-cell ablation of Yy1, we observed rapid onset of hyperglycemia, impaired glucose tolerance, and reduced β-cell mass in neonatal and adult mice. These mice also had hypoinsulinemia with normal insulin sensitivity compared with their wild-type littermates, manifesting as a type 1 diabetic phenotype. Mechanistically, genome-wide RNA sequencing has defined dysregulated insulin signaling and defective glucose responsiveness in β-cells devoid of YY1. Integrative analyses coupled with chromatin immunoprecipitation assays targeting YY1, and histone modifications, including H3K4me1, H3K27ac, and H3K27me3, have further identified Ins1 and Ins2 as direct gene targets of YY1. Luciferase reporter assays and loss- and gain-of-function experiments also demonstrated that YY1 binds to the enhancer regions in exon 2 of Ins1 and Ins2, activating insulin transcription and, therefore, proinsulin and insulin production in pancreatic β-cells. YY1 also directly interacts with RNA polymerase II, potentially stabilizing the enhancer-promoter interaction in the multiprotein-DNA complex during transcription initiation. Taken together, our findings suggest a role for YY1 as a transcriptional activator of insulin gene expression, assisting β-cell maturation and function after birth. These analyses may advance our understanding of β-cell biology and provide clinically relevant insights targeting the pathophysiological origins of diabetes.

Pancreatic-Like Cells Derived From Mouse Embryonic Stem Cells Are Regulated by Pdx1 Involving the Notch Pathway

OBJECTIVES

Embryonic stem cells (ESCs)-derived pancreatic precursor cells have great potential for pancreas repair. Expression of pancreatic duodenal homeobox 1 (Pdx1) in definitive endoderm (DE) cells is the premise that DE cells differentiate into pancreatic cells. To achieve the required number of Pdx1-expressing DE cells for cell transplantation therapy, a valid model must be established. Using this model, researchers investigated how Pdx1 regulates ESC differentiation into pancreatic cells.

METHODS

Tet-On inducible lentiviral vector encoding Pdx1 or mock vector was transduced into mouse ESC (ES-E14TG2a). The mouse ESCs were divided into 3 groups: control (ESC), mock vector (Pdx1 - -ESC), and vector encoding Pdx1 (Pdx1 + -ESC). All groups were separately cocultured with the DE cells sorted by immune beads containing CXCR-4 + (C-X-C chemokine receptor type-4) antibody. Doxycycline induced the expression of Pdx1 on the Pdx1 + -ESC cells. The markers of cell differentiation and Notch pathway were examined.

RESULTS

Significantly increased expression levels of Ptf1a, CK19, and amylase on day (d) 3 and d7, Neuro-D1 on d10 and d14, Pax6 and insulin on d14, as well as Notch1, Notch2, Hes1, and Hes5 on d3 and thereafter declined on d14 were observed in Pdx1 + -ESC group.

CONCLUSIONS

Pdx1 + -ESC could differentiate into pancreatic-like cells with involvement of the Notch pathway.

The application of precision medicine in monogenic diabetes

INTRODUCTION

Monogenic diabetes, a form of diabetes mellitus, is caused by a mutation in a single gene and may account for 1-2% of all clinical forms of diabetes. To date, more than 40 loci have been associated with either isolated or syndromic monogenic diabetes.

AREAS COVERED

While the request of a genetic test is mandatory for cases with diabetes onset in the first 6 months of life, a decision may be difficult for childhood or adolescent diabetes. In an effort to assist the clinician in this task, we have grouped monogenic diabetes genes according to the age of onset (or incidental discovery) of hyperglycemia and described the additional clinical features found in syndromic diabetes. The therapeutic options available are reviewed.

EXPERT OPINION

Technical improvements in DNA sequencing allow for rapid, simultaneous analysis of all genes involved in monogenic diabetes, progressively shrinking the area of unsolved cases. However, the complexity of the analysis of genetic data requires close cooperation between the geneticist and the diabetologist, who should play a proactive role by providing a detailed clinical phenotype that might match a specific disease gene.

Diabetes Mellitus Diagnosed in Childhood and Adolescence With Negative Autoimmunity: Results of Genetic Investigation

Monogenic diabetes is a rare form of diabetes, accounting for approximately 1% to 6% of pediatric diabetes patients. Some types of monogenic diabetes can be misdiagnosed as type 1 diabetes in children or adolescents because of similar clinical features. Identification of the correct etiology of diabetes is crucial for clinical, therapeutic, and prognostic issues. Our main objective was to determine the prevalence of monogenic diabetes in patients with diabetes mellitus, diagnosed in childhood or in adolescence, and negative autoimmunity. We retrospectively analyzed clinical data of 275 patients diagnosed with insulin-dependent diabetes at age <18yr in the last 10 years. 8.4% of subjects has negative autoimmunity. Their DNA was sequenced by NGS custom panel composed by 45 candidate genes involved in glucose metabolism disorder. Two novel heterozygous pathogenic or likely pathogenic variants (10,5% of autoantibody negative subjects) were detected: the frameshift variant c.617_618insA in NEUROD1 exon 2 and the missense change c.116T>C in INS exon 2. Our study corroborates previous results of other reports in literature. NGS assays are useful methods for a correct diagnosis of monogenic diabetes, even of rarest forms, highlighting mechanisms of pediatric diabetes pathogenesis.

Epigenetic models developed for plains zebras predict age in domestic horses and endangered equids

Effective conservation and management of threatened wildlife populations require an accurate assessment of age structure to estimate demographic trends and population viability. Epigenetic aging models are promising developments because they estimate individual age with high accuracy, accurately predict age in related species, and do not require invasive sampling or intensive long-term studies. Using blood and biopsy samples from known age plains zebras (Equus quagga), we model epigenetic aging using two approaches: the epigenetic clock (EC) and the epigenetic pacemaker (EPM). The plains zebra EC has the potential for broad application within the genus Equus given that five of the seven extant wild species of the genus are threatened. We test the EC's ability to predict age in sister taxa, including two endangered species and the more distantly related domestic horse, demonstrating high accuracy in all cases. By comparing chronological and estimated age in plains zebras, we investigate age acceleration as a proxy of health status. An interaction between chronological age and inbreeding is associated with age acceleration estimated by the EPM, suggesting a cumulative effect of inbreeding on biological aging throughout life.

Maturity-Onset Diabetes of the Young (MODY): Genetic Causes, Clinical Characteristics, Considerations for Testing, and Treatment Options

Maturity Onset Diabetes of the Young (MODY) encompasses a group of rare monogenic forms of diabetes distinct in etiology and clinical presentation from the more common forms of Type 1 (autoimmune) and Type 2 diabetes. Since its initial description as a clinical entity nearly 50 years ago, the underlying genetic basis for the various forms of MODY has been increasingly better elucidated. Clinically, the diagnosis may be made in childhood or young adulthood and can present as overt hyperglycemia requiring insulin therapy or as a subtle form of slowly progressive glucose impairment. Due to the heterogeneity of clinical symptoms, patients with MODY may be misdiagnosed as possessing another form of diabetes, resulting in potentially inappropriate treatment and delays in screening of affected family members and associated comorbidities. In this review, we highlight the various known genetic mutations associated with MODY, clinical presentation, indications for testing, and the treatment options available.

Revisiting astrocyte to neuron conversion with lineage tracing in vivo

In vivo cell fate conversions have emerged as potential regeneration-based therapeutics for injury and disease. Recent studies reported that ectopic expression or knockdown of certain factors can convert resident astrocytes into functional neurons with high efficiency, region specificity, and precise connectivity. However, using stringent lineage tracing in the mouse brain, we show that the presumed astrocyte-converted neurons are actually endogenous neurons. AAV-mediated co-expression of NEUROD1 and a reporter specifically and efficiently induces reporter-labeled neurons. However, these neurons cannot be traced retrospectively to quiescent or reactive astrocytes using lineage-mapping strategies. Instead, through a retrograde labeling approach, our results reveal that endogenous neurons are the source for these viral-reporter-labeled neurons. Similarly, despite efficient knockdown of PTBP1 in vivo, genetically traced resident astrocytes were not converted into neurons. Together, our results highlight the requirement of lineage-tracing strategies, which should be broadly applied to studies of cell fate conversions in vivo.

Mass spectrometry-based direct detection of multiple types of protein thiol modifications in pancreatic beta cells under endoplasmic reticulum stress

Thiol-based post-translational modifications (PTMs) play a key role in redox-dependent regulation and signaling. Functional cysteine (Cys) sites serve as redox switches, regulated through multiple types of PTMs. Herein, we aim to characterize the complexity of thiol PTMs at the proteome level through the establishment of a direct detection workflow. The LC-MS/MS based workflow allows for simultaneous quantification of protein abundances and multiple types of thiol PTMs. To demonstrate its utility, the workflow was applied to mouse pancreatic β-cells (β-TC-6) treated with thapsigargin to induce endoplasmic reticulum (ER) stress. This resulted in the quantification of >9000 proteins and multiple types of thiol PTMs, including intra-peptide disulfide (S–S), S-glutathionylation (SSG), S-sulfinylation (SO₂H), S-sulfonylation (SO₃H), S-persulfidation (SSH), and S-trisulfidation (SSSH). Proteins with significant changes in abundance were observed to be involved in canonical pathways such as autophagy, unfolded protein response, protein ubiquitination pathway, and EIF2 signaling. Moreover, ~500 Cys sites were observed with one or multiple types of PTMs with SSH and S–S as the predominant types of modifications. In many cases, significant changes in the levels of different PTMs were observed on various enzymes and their active sites, while their protein abundance exhibited little change. These results provide evidence of independent translational and post-translational regulation of enzyme activity. The observed complexity of thiol modifications on the same Cys residues illustrates the challenge in the characterization and interpretation of protein thiol modifications and their functional regulation.

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Simultaneous quantification of protein abundances and multiple types of thiol PTMs.

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Multiple types PTMs observed on the same Cys sites for redox-regulated proteins.

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Data revealed complexity of thiol PTMs and their regulation.

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Distinctive translational and post-translational regulation under ER stress in β-cells.

Monogenic Childhood Diabetes: Dissecting Clinical Heterogeneity by Next-Generation Sequencing in Maturity-Onset Diabetes of the Young

Diabetes is a common disorder with a heterogeneous clinical presentation and an enormous burden on health care worldwide. About 1-6% of patients with diabetes suffer from maturity-onset diabetes of the young (MODY), the most common form of monogenic diabetes with autosomal dominant inheritance. MODY is genetically and clinically heterogeneous and caused by genetic variations in pancreatic β-cell development and insulin secretion. We report here new findings from targeted next-generation sequencing (NGS) of 13 MODY-related genes. A sample of 22 unrelated pediatric patients with MODY and 13 unrelated healthy controls were recruited from a Turkish population. Targeted NGS was performed with Miseq 4000 (Illumina) to identify genetic variations in 13 MODY-related genes: HNF4A, GCK, HNF1A, PDX1, HNF1B, NEUROD1, KLF11, CEL, PAX4, INS, BLK, ABCC8, and KCNJ11. The NGS data were analyzed adhering to the Genome Analysis ToolKit (GATK) best practices pipeline, and variant filtering and annotation were performed. In the patient sample, we identified 43 MODY-specific genetic variations that were not present in the control group, including 11 missense mutations and 4 synonymous mutations. Importantly, and to the best of our knowledge, the missense mutations NEUROD1 p.D202E, KFL11 p.R461Q, BLK p.G248R, and KCNJ11 p.S385F were first associated with MODY in the present study. These findings contribute to the worldwide knowledge base on MODY and molecular correlates of clinical heterogeneity in monogenic childhood diabetes. Further comparative population genetics and functional genomics studies are called for, with an eye to discovery of novel diagnostics and personalized medicine in MODY. Because MODY is often misdiagnosed as type 1 or type 2 diabetes mellitus, advances in MODY diagnostics with NGS stand to benefit diabetes overall clinical care as well.

NEUROD1 Is Required for the Early α and β Endocrine Differentiation in the Pancreas

Diabetes is a metabolic disease that involves the death or dysfunction of the insulin-secreting β cells in the pancreas. Consequently, most diabetes research is aimed at understanding the molecular and cellular bases of pancreatic development, islet formation, β-cell survival, and insulin secretion. Complex interactions of signaling pathways and transcription factor networks regulate the specification, growth, and differentiation of cell types in the developing pancreas. Many of the same regulators continue to modulate gene expression and cell fate of the adult pancreas. The transcription factor NEUROD1 is essential for the maturation of β cells and the expansion of the pancreatic islet cell mass. Mutations of the Neurod1 gene cause diabetes in humans and mice. However, the different aspects of the requirement of NEUROD1 for pancreas development are not fully understood. In this study, we investigated the role of NEUROD1 during the primary and secondary transitions of mouse pancreas development. We determined that the elimination of Neurod1 impairs the expression of key transcription factors for α- and β-cell differentiation, β-cell proliferation, insulin production, and islets of Langerhans formation. These findings demonstrate that the Neurod1 deletion altered the properties of α and β endocrine cells, resulting in severe neonatal diabetes, and thus, NEUROD1 is required for proper activation of the transcriptional network and differentiation of functional α and β cells.

Neuronal Differentiation 1 gene Ala45Thr polymorphism and type 2 diabetes mellitus: A meta-analysis of 7,940 subjects

BACKGROUND AND AIMS

Previous studies have shown that there was a possible relationship between human Neuronal Differentiation 1 (NEUROD1) gene Ala45Thr polymorphism and type 2 diabetes mellitus (T2DM) susceptibility. Nevertheless, no public opinion has been formed because of the conflicting results in the past studies. In order to illuminate the potential association of human NEUROD1 gene Ala45Thr polymorphism and T2DM, the present meta-analysis was conducted.

METHODS AND RESULTS

In the current meta-analysis, 7940 subjects from 14 individual studies were included. The fixed or random effects models were used to evaluate the pooled odds ratios (ORs) and their corresponding 95% confidence intervals (CIs). The current meta-analysis found a significant association between NEUROD1 gene Ala45Thr polymorphism and T2DM under allelic (OR: 1.21, 95% CI: 1.04-1.41, P = 0.01), dominant (OR: 0.819, 95% CI: 0.734-0.913, P = 3.31 × 10^-4), heterozygous (OR:1.199, 95% CI: 1.068-1.346, P = 0.002), and additive (OR: 1.33, 95% CI: 1.09-1.62, P = 0.004) genetic models.

CONCLUSIONS

NEUROD1 gene Ala45Thr polymorphism was significantly related to T2DM, especially in the Asian population. More particularly, the Thr45 allele carriers of the NEUROD1 gene may be more susceptible to T2DM.

Identification of candidate gene variants of monogenic diabetes using targeted panel sequencing in early onset diabetes patients

INTRODUCTION

Monogenic diabetes is attributed to genetic variations in a single gene. Maturity-onset diabetes of the young (MODY) is the most common phenotype associated with monogenic diabetes, but is frequently misdiagnosed as either type 1 or type 2 diabetes. Increasing our basic understanding of genetic variations in MODY may help to improve the accuracy of providing the correct diagnosis and personalize subsequent treatment regimens in different racial populations. For this reason, this study was designed to identify nucleotide variants in early onset diabetes patients with clinically suspected MODY in a Korean population.

RESEARCH DESIGN AND METHODS

Among 2908 Korean patients diagnosed with diabetes, we selected 40 patients who were diagnosed before 30 years old and were clinically suspected of MODY. Genetic testing was performed using a targeted gene sequencing panel that included 30 known monogenic diabetes genes. The pathogenicity of the identified variants was assessed according to the American College of Medical Genetics and Genomics and Association for Molecular Pathology (ACMG-AMP) guidelines.

RESULTS

A total of six rare missense variants (p.Ala544Thr in HNF1A, p.Val601Ile and p.His103Tyr in ABCC8, p.Pro33Ala in PDX1, p.Gly18Glu in INS, and p.Arg164Gln in PAX4) in five distinct MODY genes were identified in five patients. In addition, a variant was identified in mitochondrial DNA at 3243A>G in one patient. The identified variants were either absent or detected at a rare frequency in the 1000 Genomes Project. These variants were classified as uncertain significance using the ACMG-AMP guidelines.

CONCLUSION

Using a targeted gene sequencing panel, we identified seven variants in either MODY genes or mitochondrial DNA using a Korean patient population with early onset diabetes who were clinically suspected of MODY. This genetic approach provides the ability to compare distinct populations of racial and ethnic groups to determine whether specific gene is involved in their diagnosis of MODY.

Human Pluripotent Stem Cells Go Diabetic: A Glimpse on Monogenic Variants

Diabetes, as one of the major diseases in industrial countries, affects over 350 million people worldwide. Type 1 (T1D) and type 2 diabetes (T2D) are the most common forms with both types having invariable genetic influence. It is accepted that a subset of all diabetes patients, generally estimated to account for 1-2% of all diabetic cases, is attributed to mutations in single genes. As only a subset of these genes has been identified and fully characterized, there is a dramatic need to understand the pathophysiological impact of genetic determinants on β-cell function and pancreatic development but also on cell replacement therapies. Pluripotent stem cells differentiated along the pancreatic lineage provide a valuable research platform to study such genes. This review summarizes current perspectives in applying this platform to study monogenic diabetes variants.

CBP/p300 HAT maintains the gene network critical for β cell identity and functional maturity

Loss of β cell identity and functional immaturity are thought to be involved in β cell failure in type 2 diabetes. CREB-binding protein (CBP) and its paralogue p300 act as multifunctional transcriptional co-activators and histone acetyltransferases (HAT) with extensive biological functions. However, whether the regulatory role of CBP/p300 in islet β cell function depends on the HAT activity remains uncertain. In this current study, A-485, a selective inhibitor of CBP/p300 HAT activity, greatly impaired glucose-stimulated insulin secretion from rat islets in vitro and in vivo. RNA-sequencing analysis showed a comprehensive downregulation of β cell and α cell identity genes in A-485-treated islets, without upregulation of dedifferentiation markers and derepression of disallowed genes. A-485 treatment decreased the expressions of genes involved in glucose sensing, not in glycolysis, tricarboxylic acid cycle, and oxidative phosphorylation. In the islets of prediabetic db/db mice, CBP/p300 displayed a significant decrease with key genes for β cell function. The deacetylation of histone H3K27 as well as the transcription factors Hnf1α and Foxo1 was involved in CBP/p300 HAT inactivation-repressed expressions of β cell identity and functional genes. These findings highlight the dominant role of CBP/p300 HAT in the maintenance of β cell identity by governing transcription network.

Constrained chromatin accessibility in PU.1-mutated agammaglobulinemia patients

The pioneer transcription factor (TF) PU.1 controls hematopoietic cell fate by decompacting stem cell heterochromatin and allowing nonpioneer TFs to enter otherwise inaccessible genomic sites. PU.1 deficiency fatally arrests lymphopoiesis and myelopoiesis in mice, but human congenital PU.1 disorders have not previously been described. We studied six unrelated agammaglobulinemic patients, each harboring a heterozygous mutation (four de novo, two unphased) of SPI1, the gene encoding PU.1. Affected patients lacked circulating B cells and possessed few conventional dendritic cells. Introducing disease-similar SPI1 mutations into human hematopoietic stem and progenitor cells impaired early in vitro B cell and myeloid cell differentiation. Patient SPI1 mutations encoded destabilized PU.1 proteins unable to nuclear localize or bind target DNA. In PU.1-haploinsufficient pro–B cell lines, euchromatin was less accessible to nonpioneer TFs critical for B cell development, and gene expression patterns associated with the pro– to pre–B cell transition were undermined. Our findings molecularly describe a novel form of agammaglobulinemia and underscore PU.1’s critical, dose-dependent role as a hematopoietic euchromatin gatekeeper.

Molecular mechanisms of β-cell dysfunction and death in monogenic forms of diabetes

Monogenetic forms of diabetes represent 1%-5% of all diabetes cases and are caused by mutations in a single gene. These mutations, that affect genes involved in pancreatic β-cell development, function and survival, or insulin regulation, may be dominant or recessive, inherited or de novo. Most patients with monogenic diabetes are very commonly misdiagnosed as having type 1 or type 2 diabetes. The severity of their symptoms depends on the nature of the mutation, the function of the affected gene and, in some cases, the influence of additional genetic or environmental factors that modulate severity and penetrance. In some patients, diabetes is accompanied by other syndromic features such as deafness, blindness, microcephaly, liver and intestinal defects, among others. The age of diabetes onset may also vary from neonatal until early adulthood manifestations. Since the different mutations result in diverse clinical presentations, patients usually need different treatments that range from just diet and exercise, to the requirement of exogenous insulin or other hypoglycemic drugs, e.g., sulfonylureas or glucagon-like peptide 1 analogs to control their glycemia. As a consequence, awareness and correct diagnosis are crucial for the proper management and treatment of monogenic diabetes patients. In this chapter, we describe mutations causing different monogenic forms of diabetes associated with inadequate pancreas development or impaired β-cell function and survival, and discuss the molecular mechanisms involved in β-cell demise.

Normal and defective pathways in biogenesis and maintenance of the insulin storage pool

Both basal and glucose-stimulated insulin release occur primarily by insulin secretory granule exocytosis from pancreatic β cells, and both are needed to maintain normoglycemia. Loss of insulin-secreting β cells, accompanied by abnormal glucose tolerance, may involve simple exhaustion of insulin reserves (which, by immunostaining, appears as a loss of β cell identity), or β cell dedifferentiation, or β cell death. While various sensing and signaling defects can result in diminished insulin secretion, somewhat less attention has been paid to diabetes risk caused by insufficiency in the biosynthetic generation and maintenance of the total insulin granule storage pool. This Review offers an overview of insulin biosynthesis, beginning with the preproinsulin mRNA (translation and translocation into the ER), proinsulin folding and export from the ER, and delivery via the Golgi complex to secretory granules for conversion to insulin and ultimate hormone storage. All of these steps are needed for generation and maintenance of the total insulin granule pool, and defects in any of these steps may, weakly or strongly, perturb glycemic control. The foregoing considerations have obvious potential relevance to the pathogenesis of type 2 diabetes and some forms of monogenic diabetes; conceivably, several of these concepts might also have implications for β cell failure in type 1 diabetes.

Approach to the Patient with MODY-Monogenic Diabetes

Maturity-onset diabetes of the young, or MODY-monogenic diabetes, is a not-so-rare collection of inherited disorders of non-autoimmune diabetes mellitus that remains insufficiently diagnosed despite increasing awareness. These cases are important to efficiently and accurately diagnose, given the clinical implications of syndromic features, cost-effective treatment regimen, and the potential impact on multiple family members. Proper recognition of the clinical manifestations, family history, and cost-effective lab and genetic testing provide the diagnosis. All patients must undergo a thorough history, physical examination, multigenerational family history, lab evaluation (glycated hemoglobin A1c [HbA1c], glutamic acid decarboxylase antibodies [GADA], islet antigen 2 antibodies [IA-2A], and zinc transporter 8 [ZnT8] antibodies). The presence of clinical features with 3 (or more) negative antibodies may be indicative of MODY-monogenic diabetes, and is followed by genetic testing. Molecular genetic testing should be performed before attempting specific treatments in most cases. Additional testing that is helpful in determining the risk of MODY-monogenic diabetes is the MODY clinical risk calculator (>25% post-test probability in patients not treated with insulin within 6 months of diagnosis should trigger genetic testing) and 2-hour postprandial (after largest meal of day) urinary C-peptide to creatinine ratio (with a ≥0.2 nmol/mmol to distinguish HNF1A- or 4A-MODY from type 1 diabetes). Treatment, as well as monitoring for microvascular and macrovascular complications, is determined by the specific variant that is identified. In addition to the diagnostic approach, this article will highlight recent therapeutic advancements when patients no longer respond to first-line therapy (historically sulfonylurea treatment in many variants).

LEARNING OBJECTIVES

Upon completion of this educational activity, participants should be able to.

TARGET AUDIENCE

This continuing medical education activity should be of substantial interest to endocrinologists and all health care professionals who care for people with diabetes mellitus.

Human Pluripotent Stem Cells to Model Islet Defects in Diabetes

Diabetes mellitus is characterized by elevated levels of blood glucose and is ultimately caused by insufficient insulin production from pancreatic beta cells. Different research models have been utilized to unravel the molecular mechanisms leading to the onset of diabetes. The generation of pancreatic endocrine cells from human pluripotent stem cells constitutes an approach to study genetic defects leading to impaired beta cell development and function. Here, we review the recent progress in generating and characterizing functional stem cell-derived beta cells. We summarize the diabetes disease modeling possibilities that stem cells offer and the challenges that lie ahead to further improve these models.

The epidemiology, molecular pathogenesis, diagnosis, and treatment of maturity-onset diabetes of the young (MODY)

Background

The most common type of monogenic diabetes is maturity-onset diabetes of the young (MODY), a clinically and genetically heterogeneous group of endocrine disorders that affect 1–5% of all patients with diabetes mellitus. MODY is characterized by autosomal dominant inheritance but de novo mutations have been reported. Clinical features of MODY include young-onset hyperglycemia, evidence of residual pancreatic function, and lack of beta cell autoimmunity or insulin resistance. Glucose-lowering medications are the main treatment options for MODY. The growing recognition of the clinical and public health significance of MODY by clinicians, researchers, and governments may lead to improved screening and diagnostic practices. Consequently, this review article aims to discuss the epidemiology, pathogenesis, diagnosis, and treatment of MODY based on relevant literature published from 1975 to 2020.

Main body

The estimated prevalence of MODY from European cohorts is 1 per 10,000 in adults and 1 per 23,000 in children. Since little is known about the prevalence of MODY in African, Asian, South American, and Middle Eastern populations, further research in non-European cohorts is needed to help elucidate MODY’s exact prevalence. Currently, 14 distinct subtypes of MODY can be diagnosed through clinical assessment and genetic analysis. Various genetic mutations and disease mechanisms contribute to the pathogenesis of MODY. Management of MODY is subtype-specific and includes diet, oral antidiabetic drugs, or insulin.

Conclusions

Incidence and prevalence estimates for MODY are derived from epidemiologic studies of young people with diabetes who live in Europe, Australia, and North America. Mechanisms involved in the pathogenesis of MODY include defective transcriptional regulation, abnormal metabolic enzymes, protein misfolding, dysfunctional ion channels, or impaired signal transduction. Clinicians should understand the epidemiology and pathogenesis of MODY because such knowledge is crucial for accurate diagnosis, individualized patient management, and screening of family members.

Involvement of Essential Signaling Cascades and Analysis of Gene Networks in Diabesity

(1) Aims: Diabesity, defined as diabetes occurring in the context of obesity, is a serious health problem that is associated with an increased risk of premature heart attack, stroke, and death. To date, a key challenge has been to understand the molecular pathways that play significant roles in diabesity. In this study, we aimed to investigate the genetic links between diabetes and obesity in diabetic individuals and highlight the role(s) of shared genes in individuals with diabesity. (2) Methods: The interactions between the genes were analyzed using the Search Tool for the Retrieval of Interacting Genes (STRING) tool after the compilation of obesity genes associated with type 1 diabetes (T1D), type 2 diabetes (T2D), and maturity-onset diabetes of the young (MODY). Cytoscape plugins were utilized for enrichment analysis. (3) Results: We identified 546 obesity genes that are associated with T1D, T2D, and MODY. The network backbone of the identified genes comprised 514 nodes and 4126 edges with an estimated clustering coefficient of 0.242. The Molecular Complex Detection (MCODE) generated three clusters with a score of 33.61, 16.788, and 6.783, each. The highest-scoring nodes of the clusters were AGT, FGB, and LDLR genes. The genes from cluster 1 were enriched in FOXO-mediated transcription of oxidative stress, renin secretion, and regulation of lipolysis in adipocytes. The cluster 2 genes enriched in Src homology 2 domain-containing (SHC)-related events triggered by IGF1R, regulation of lipolysis in adipocytes, and GRB2: SOS produce a link to mitogen-activated protein kinase (MAPK) signaling for integrins. The cluster 3 genes ere enriched in IGF1R signaling cascade and insulin signaling pathway. (4) Conclusion: This study presents a platform to discover potential targets for diabesity treatment and helps in understanding the molecular mechanism.

Pathophysiology of diabetes: An overview

Diabetes mellitus is a chronic heterogeneous metabolic disorder with complex pathogenesis. It is characterized by elevated blood glucose levels or hyperglycemia, which results from abnormalities in either insulin secretion or insulin action or both. Hyperglycemia manifests in various forms with a varied presentation and results in carbohydrate, fat, and protein metabolic dysfunctions. Long-term hyperglycemia often leads to various microvascular and macrovascular diabetic complications, which are mainly responsible for diabetes-associated morbidity and mortality. Hyperglycemia serves as the primary biomarker for the diagnosis of diabetes as well. In this review, we would be focusing on the classification of diabetes and its pathophysiology including that of its various types.

Identification of the First PAX4-MODY Family Reported in Brazil

PURPOSE

The aim of this study was to sequence the coding region of the PAX4 gene in a Brazilian cohort with clinical manifestations of monogenic diabetes.

PATIENTS AND METHODS

This study included 31 patients with autosomal dominant history of diabetes, age at diagnosis ≤40 years, BMI <30 kg/m2, and no mutations in GCK or HNF1A, HNF4A, and HNF1B. Screening of the PAX4 coding region was performed by Sanger sequencing. In silico algorithms were used to assess the potential impact of amino acid substitutions on protein structure and function. Additionally, PAX4-MODY family members and 158 control subjects without diabetes were analyzed for the identified mutation.

RESULTS

The molecular analysis of PAX4 has detected one missense mutation, p.Arg164Gln (c.491G>A), segregating with diabetes in a large Brazilian family. The mutation was absent among the control group. The index case is a woman diagnosed at 32 years of age with polyneuropathy and treated with insulin. She did not present diabetic renal disease or retinopathy. Family members with the PAX4 p.Arg164Gln mutation have a heterogeneous clinical manifestation and treatment response, with age at diagnosis ranging from 24 years to 50 years.

CONCLUSION

To the best of our knowledge, this is the first study to report a PAX4-MODY family in Brazil. The age of PAX4-MODY diagnosis in the Brazilian family seems to be higher than the classical criteria for MODY. Our results reinforce the importance of screening large monogenic diabetes families for the understanding of the clinical manifestations of rare forms of diabetes for the specific and personalized treatment.

Genetics and Pathophysiology of Maturity-onset Diabetes of the Young (MODY): A Review of Current Trends

Single gene mutations have been implicated in the pathogenesis of a form of diabetes mellitus (DM) known as the maturity-onset diabetes of the young (MODY). However, there are diverse opinions on the suspect genes and pathophysiology, necessitating the need to review and communicate the genes to raise public awareness. We used the Google search engine to retrieve relevant information from reputable sources such as PubMed and Google Scholar. We identified 14 classified MODY genes as well as three new and unclassified genes linked with MODY. These genes are fundamentally embedded in the beta cells, the most common of which are HNF1A, HNF4A, HNF1B, and GCK genes. Mutations in these genes cause β-cell dysfunction, resulting in decreased insulin production and hyperglycemia. MODY genes have distinct mechanisms of action and phenotypic presentations compared with type 1 and type 2 DM and other forms of DM. Healthcare professionals are therefore advised to formulate drugs and treatment based on the causal genes rather than the current generalized treatment for all types of DM. This will increase the effectiveness of diabetes drugs and treatment and reduce the burden of the disease.

A CRISPR/Cas9 genome editing pipeline in the EndoC-βH1 cell line to study genes implicated in beta cell function

Type 2 diabetes (T2D) is a global pandemic with a strong genetic component, but most causal genes influencing the disease risk remain unknown. It is clear, however, that the pancreatic beta cell is central to T2D pathogenesis. In vitro gene-knockout (KO) models to study T2D risk genes have so far focused on rodent beta cells. However, there are important structural and functional differences between rodent and human beta cell lines. With that in mind, we have developed a robust pipeline to create a stable CRISPR/Cas9 KO in an authentic human beta cell line (EndoC-βH1). The KO pipeline consists of a dual lentiviral sgRNA strategy and we targeted three genes ( INS, IDE, PAM) as a proof of concept. We achieved a significant reduction in mRNA levels and complete protein depletion of all target genes. Using this dual sgRNA strategy, up to 94 kb DNA were cut out of the target genes and the editing efficiency of each sgRNA exceeded >87.5%. Sequencing of off-targets showed no unspecific editing. Most importantly, the pipeline did not affect the glucose-responsive insulin secretion of the cells. Interestingly, comparison of KO cell lines for NEUROD1 and SLC30A8 with siRNA-mediated knockdown (KD) approaches demonstrate phenotypic differences. NEUROD1-KO cells were not viable and displayed elevated markers for ER stress and apoptosis. NEUROD1-KD, however, only had a modest elevation, by 34%, in the pro-apoptotic transcription factor CHOP and a gene expression profile indicative of chronic ER stress without evidence of elevated cell death. On the other hand, SLC30A8-KO cells demonstrated no reduction in K ATP channel gene expression in contrast to siRNA silencing. Overall, this strategy to efficiently create stable KO in the human beta cell line EndoC-βH1 will allow for a better understanding of genes involved in beta cell dysfunction, their underlying functional mechanisms and T2D pathogenesis.