Defective PAX4 R192H transcriptional repressor activities associated with maturity onset diabetes of the young and early onset-age of type 2 diabetes

Investigation of Monogenic Diabetes Genes in Thai Children with Autoantibody Negative Diabetes Requiring Insulin

Purpose

The objective of this study was to clarify the phenotypic characteristics of monogenic diabetes abnormalities in Thai children with autoantibody-negative insulin.

Patients and Methods

Two hundred and thirty-one Thai type 1 diabetes (T1D) patients out of 300 participants with recent-onset diabetes were analyzed for GAD65 and IA2 pancreatic autoantibodies. A total of 30 individuals with T1D patients with negative autoantibody were screened for 32 monogenic diabetes genes by whole-exome sequencing (WES).

Results

All participants were ten men and twenty women. The median age to onset of diabetes was 8 years and 3 months. A total of 20 people with monogenic diabetes carried genes related to monogenic diabetes. The PAX4 (rs2233580) in ten patients with monogenic diabetes was found. Seven variants of WFS1 (Val412Ala, Glu737Lys, Gly576Ser, Cys673Tyr, Arg456His, Lys424Glu, and Gly736fs) were investigated in patients in this study. Furthermore, the pathogenic variant, rs115099192 (Pro407Gln) in the GATA4 gene was found. Most patients who carried PAX4 (c.575G>A, rs2233580) did not have a history of DKA. The pathogenic variant GATA4 variant (c.1220C>A, rs115099192) was found in a patient with a history of DKA.

Conclusion

This study demonstrated significant genetic overlap between autoantibody-negative diabetes and monogenic diabetes using WES. All candidate variants were considered disease risk with clinically significant variants. WES screening was the first implemented to diagnose monogenic diabetes in Thai children, and fourteen novel variants were identified in this study and need to be investigated in the future.

Molecular diagnosis in patients with monogenic diabetes mellitus, and detection of a novel candidate gene

AIM

We aimed to investigate molecular genetic basis of monogenic diabetes (DM) and novel responsible candidate genes with targeted Next Generation Sequencing (NGS) and Whole Exome Sequencing (WES).

METHODS

A hundred cases presenting with clinical findings and a family history of monogenic DM were included in the study. Molecular analysis was performed using an NGS panel including 14 genes. Following targeted NGS, WES was planned in cases in whom no variant was detected.

RESULTS

Thirty different disease-causing variants in seven different genes were detected in thirty-five (35 %) cases with targeted NGS approach. Most common pathogenic variant was found in GCK gene in 25 (25 %) cases. Four different variants were detected in 4 (4 %) patients in ABCC8 gene. In 45 of 65 cases; WES analyses were done. A heterozygous c.2635C > T(p.Gln879Ter) variant was detected in IFIH1 gene in a patient with incidental hyperglycemia. In the segregation analysis affected mother was shown to be heterozygous for the same variant.

CONCLUSION

Molecular etiology was determined in 35 % cases with the NGS targeted panel. Seventeen novel variants in monogenic DM genes have been identified. A candidate gene determined by WES analysis in a case that could not be diagnosed with NGS panel in this study.

PAX4 loss of function increases diabetes risk by altering human pancreatic endocrine cell development

The coding variant (p.Arg192His) in the transcription factor PAX4 is associated with an altered risk for type 2 diabetes (T2D) in East Asian populations. In mice, Pax4 is essential for beta cell formation but its role on human beta cell development and/or function is unknown. Participants carrying the PAX4 p.His192 allele exhibited decreased pancreatic beta cell function compared to homozygotes for the p.192Arg allele in a cross-sectional study in which we carried out an intravenous glucose tolerance test and an oral glucose tolerance test. In a pedigree of a patient with young onset diabetes, several members carry a newly identified p.Tyr186X allele. In the human beta cell model, EndoC-βH1, PAX4 knockdown led to impaired insulin secretion, reduced total insulin content, and altered hormone gene expression. Deletion of PAX4 in human induced pluripotent stem cell (hiPSC)-derived islet-like cells resulted in derepression of alpha cell gene expression. In vitro differentiation of hiPSCs carrying PAX4 p.His192 and p.X186 risk alleles exhibited increased polyhormonal endocrine cell formation and reduced insulin content that can be reversed with gene correction. Together, we demonstrate the role of PAX4 in human endocrine cell development, beta cell function, and its contribution to T2D-risk.

Pax4 in Health and Diabetes

Paired box 4 (Pax4) is a key transcription factor involved in the embryonic development of the pancreatic islets of Langerhans. Consisting of a conserved paired box domain and a homeodomain, this transcription factor plays an essential role in early endocrine progenitor cells, where it is necessary for cell-fate commitment towards the insulin-secreting β cell lineage. Knockout of Pax4 in animal models leads to the absence of β cells, which is accompanied by a significant increase in glucagon-producing α cells, and typically results in lethality within days after birth. Mutations in Pax4 that cause an impaired Pax4 function are associated with diabetes pathogenesis in humans. In adulthood, Pax4 expression is limited to a distinct subset of β cells that possess the ability to proliferate in response to heightened metabolic needs. Upregulation of Pax4 expression is known to promote β cell survival and proliferation. Additionally, ectopic expression of Pax4 in pancreatic islet α cells or δ cells has been found to generate functional β-like cells that can improve blood glucose regulation in experimental diabetes models. Therefore, Pax4 represents a promising therapeutic target for the protection and regeneration of β cells in the treatment of diabetes. The purpose of this review is to provide a thorough and up-to-date overview of the role of Pax4 in pancreatic β cells and its potential as a therapeutic target for diabetes.

Ethnic-Specific Type 2 Diabetes Risk Factor PAX4 R192H Is Associated with Attention-Specific Cognitive Impairment in Chinese with Type 2 Diabetes

Background: Type 2 diabetes mellitus (T2DM) has been shown to increase the risks of cognitive decline and dementia. Paired box gene 4 (PAX4), a transcription factor for beta cell development and function, has recently been implicated in pathways intersecting Alzheimer’s disease and T2DM. Objective: In this report, we evaluated the association of the ethnic-specific PAX4 R192H variant, a T2DM risk factor for East Asians which contributes to earlier diabetes onset, and cognitive function of Chinese T2DM patients. Methods: 590 Chinese patients aged 45–86 from the SMART2D study were genotyped for PAX4 R192H variation using Illumina OmniExpress-24 Array. The Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) which had been validated in the Singapore population was administered to assess five cognitive domains: immediate memory, visuospatial/constructional, language, attention, and delayed memory. Multiple linear regression was used to assess the association of the R192H risk allele and cognitive domains. Results: Patients with two PAX4 R192H risk alleles showed significantly lower attention index score (β= –8.46, 95% CI [–13.71, –3.21], p = 0.002) than patients with wild-type alleles after adjusting for age, gender, diabetes onset age, HbA1c, body-mass index, renal function, lipid profiles, systolic blood pressure, metformin usage, smoking history, education level, Geriatric Depression Scale score, and presence of APOE ɛ4 allele. Conclusion: Ethnic-specific R192H variation in PAX4 is associated with attention-specific cognitive impairment in Chinese with T2DM. Pending further validation studies, determining PAX4 R192H genotype may be helpful for early risk assessment of early-onset T2DM and cognitive impairment to improve diabetes care.

Pax4 Gene Delivery Improves Islet Transplantation Efficacy by Promoting β Cell Survival and α-to-β Cell Transdifferentiation

The transcription factor Pax4 plays an essential role in the development of insulin-producing β cells in pancreatic islets. Ectopic Pax4 expression not only promotes β cell survival but also induces α-to-β cell transdifferentiation. This dual functionality of Pax4 makes it an appealing therapeutic target for the treatment of insulin-deficient type 1 diabetes (T1D). In this study, we demonstrated that Pax4 gene delivery by an adenoviral vector, Ad5.Pax4, improved β cell function of mouse and human islets by promoting islet cell survival and α-to-β cell transdifferentiation, as assessed by multiple viability assays and lineage-tracing analysis. We then explored the therapeutic benefits of Pax4 gene delivery in the context of islet transplantation using T1D mouse models. Both mouse-to-mouse and human-to-mouse islet transplantation, via either kidney capsule or portal vein, were examined. In all settings, Ad5.Pax4-treated donor islets (mouse or human) showed substantially better therapeutic outcomes. These results suggest that Pax4 gene delivery into donor islets may be considered as an adjunct therapy for islet transplantation, which can either improve the therapeutic outcome of islet transplantation using the same amount of donor islets or allow the use of fewer donor islets to achieve normoglycemia.

Missense Variants in PAX4 Are Associated with Early-Onset Diabetes in Chinese

INTRODUCTION

East Asians are more susceptible to early-onset diabetes than Europeans and exhibit reduced insulin secretion at earlier stages. PAX4 plays a critical role in the development of β-cells. The dysfunction-missense variants PAX4 R192H and PAX4 R192S are common in East Asians but rare in Europeans. Therefore, we aim to investigate the diabetes-associated genes, including PAX4 R192H/S, in East Asians with early-onset diabetes.

METHODS

Exome variants of 80 Chinese early-onset diabetes patients (onset age < 35 years) after the exclusion of type 1 diabetes (T1D) were detected by a customized gene panel covering 32 known diabetes-associated genes. Then, 229 subjects with early-onset diabetes (T1D excluded) and 1679 controls from the Chinese population were genotyped to validate the association of PAX4 R192H/S with early-onset diabetes and related phenotypes.

RESULTS

The gene panel detected 11 monogenic diabetes patients with five novel mutations among the 80 early-onset diabetes patients. Asian-specifically enriched PAX4 R192H and R192S were associated with early-onset diabetes (R192H: OR 1.88, 95% CI 1.37-2.60, P = 8.41 × 10^-5; R192S: OR 1.71, 95% CI 1.17-2.51, P = 0.005). In early-onset diabetes patients, PAX4 R192H carriers had higher haemoglobin A1c (HbA1c) levels (P = 0.030) and lower 2 h C-peptide levels in the oral glucose tolerance test (OGTT) (P = 0.040); R192S carriers had lower fasting C-peptide (FCP) (P = 0.011) and 2 h C-peptide levels (P = 0.033) in OGTT than non-variant carriers.

CONCLUSIONS

The ethnic-specific enrichment of PAX4 R192H/S predisposing East Asians to early-onset diabetes with decreased C-peptide levels may be one explanation of the discrepancy of diabetes between East Asians and Europeans.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov (NCT01938365).

Precision Therapy for a Chinese Family With Maturity-Onset Diabetes of the Young

OBJECTIVE

To determine the pathogenic gene and explore the clinical characteristics of maturity-onset diabetes of the young type 2 (MODY2) pedigree caused by a mutation in the glucokinase (GCK) gene.

METHODS

Using whole-exome sequencing (WES), the pathogenic gene was detected in the proband-a 20-year-old young man who was accidentally found with hyperglycemia, no ketosis tendency, and a family history of diabetes. The family members of the proband were examined. In addition, relevant clinical data were obtained and genomic DNA from peripheral blood was obtained. Pathologic variants of the candidate were verified by Sanger sequencing technology, and cosegregation tests were conducted among other family members and non-related healthy controls. After adjusting the treatment plan based on the results of genetic testing, changes in biochemical parameters, such as blood glucose levels and HAblc levels were determined.

RESULTS

In the GCK gene (NM_000162) in exon 9, a heterozygous missense mutation c.1160C > T (p.Ala387Val) was found in the proband, his father, uncle, and grandmother. Thus mutation, which was found to co-segregate with diabetes, was the first discovery of such a mutation in the Asian population. After stopping hypoglycemic drug treatment, good glycemic control was achieved with diet and exercise therapy.

CONCLUSION

GCK gene mutation c.1160C > T (p.Ala387Val) is the pathogenic gene in the GCK-MODY pedigree. Formulating an optimized and personalized treatment strategy can reduce unnecessary excessive medical treatment and adverse drug reactions, and maintain a good HbA1c compliance rate.

From Genetic Association to Molecular Mechanisms for Islet-cell Dysfunction in Type 2 Diabetes

Genome-wide association studies (GWAS) have identified over 400 signals robustly associated with risk for type 2 diabetes (T2D). At the vast majority of these loci, the lead single nucleotide polymorphisms (SNPs) reside in noncoding regions of the genome, which hampers biological inference and translation of genetic discoveries into disease mechanisms. The study of these T2D risk variants in normoglycemic individuals has revealed that a significant proportion are exerting their disease risk through islet-cell dysfunction. The central role of the islet is also demonstrated by numerous studies, which have shown an enrichment of these signals in islet-specific epigenomic annotations. In recent years the emergence of authentic human beta-cell lines, and advances in genome-editing technologies coupled with improved protocols differentiating human pluripotent stem cells into beta-like cells has opened up new opportunities for T2D disease modeling. Here we review the current understanding on the genetic basis of T2D focusing on approaches, which have facilitated the identification of causal variants and their effector transcripts in human islets. We will present examples of functional studies based on animal and conventional cellular systems and highlight the potential of novel stem cell-based T2D disease models.

PAX proteins and their role in pancreas

Gene regulatory factors that govern the expression of heritable information come in an array of flavors, chiefly with transcription factors, the proteins which bind to regions of specific genes and modulate gene transcription, subsequently altering cellular function. PAX transcription factors are sequence-specific DNA-binding proteins exerting its regulatory activity in many tissues. Notably, three members of the PAX family namely PAX2, PAX4 and PAX6 have emerged as crucial players at multiple steps of pancreatic development and differentiation and also play a pivotal role in the regulation of pancreatic islet hormones synthesis and secretion. Providing a comprehensive outline of these transcription factors and their primordial and divergent roles in the pancreas is far-reaching in contemporary diabetes research. Accordingly, this review furnishes an outline of the role of pancreatic specific PAX regulators in the development of the pancreas and its associated disorders.

Recent advances and perspectives in next generation sequencing application to the genetic research of type 2 diabetes

Type 2 diabetes (T2D) mellitus is a common complex disease that currently affects more than 400 million people worldwide and has become a global health problem. High-throughput sequencing technologies such as whole-genome and whole-exome sequencing approaches have provided numerous new insights into the molecular bases of T2D. Recent advances in the application of sequencing technologies to T2D research include, but are not limited to: (1) Fine mapping of causal rare and common genetic variants; (2) Identification of confident gene-level associations; (3) Identification of novel candidate genes by specific scoring approaches; (4) Interrogation of disease-relevant genes and pathways by transcriptional profiling and epigenome mapping techniques; and (5) Investigation of microbial community alterations in patients with T2D. In this work we review these advances in application of next-generation sequencing methods for elucidation of T2D pathogenesis, as well as progress and challenges in implementation of this new knowledge about T2D genetics in diagnosis, prevention, and treatment of the disease.

PAX4 R192H is associated with younger onset of Type 2 diabetes in East Asians in Singapore

AIMS

Young-onset T2D (YT2D) is associated with a more fulminant course and greater propensity for diabetic complications. The association of PAX4 R192H (rs2233580) variation with YT2D was inconsistent partly because of its Asian-specificity and under-representation of Asians in international consortiums. Interestingly, in our preliminary YT2D (mean = 25 years old) cohort, the prevalence of PAX4 R192H variant was remarkably higher (21.4%) than the general population. Therefore, we sought to determine whether PAX4 R192H is associated with younger onset of T2D in our East Asian (Chinese) population.

METHODS

Genotyping of PAX4 R192H was carried out using Illumina OmniExpress BeadChips as part of a genome-wide association study. Data analysis was performed using SPSS Ver. 22.

RESULTS

PAX4 R192H genotype was associated with younger onset age (CC: 47.1, CT: 46.0, TT: 42.6) after adjusting for gender, F = 5.402, p = 0.005. Independently, onset of diabetes was younger among males by 2.52 years, 95% CI [-3.45, -1.59], p < 0.0001. HOMA-IR and HOMA-%B were not significantly different across genotypes for a subset (n = 1045) of the cohort.

CONCLUSIONS

Minor allele (T) of PAX4 R192H is associated with younger onset diabetes among Chinese in Singapore. Determining this genotype is important for identifying at-risk individuals for earlier onset diabetes and diabetic complications.

Regenerating β cells of the pancreas - potential developments in diabetes treatment

INTRODUCTION

The etiology of diabetes is mainly attributed to insulin deficiency due to the lack of β cells (type 1), or to insulin resistance that eventually results in β cell dysfunction (type 2). Therefore, an ultimate cure for diabetes requires the ability to replace the lost insulin-secreting β cells. Strategies for regenerating β cells are under extensive investigation.

AREAS COVERED

Herein, the authors first summarize the mechanisms underlying embryonic β cell development and spontaneous adult β cell regeneration, which forms the basis for developing β cell regeneration strategies. Then the rationale and progress of each β cell regeneration strategy is reviewed. Current β cell regeneration strategies can be classified into two main categories: in vitro β cell regeneration using pluripotent stem cells and in vivo reprogramming of non-β cells into β cells. Each has its own advantages and disadvantages.

EXPERT OPINION

Regenerating β cells has shown its potential as a cure for the treatment of insulin-deficient diabetes. Much progress has been made, and β cell regeneration therapy is getting closer to a clinical reality. Nevertheless, more hurdles need to be overcome before any of the strategies suggested can be fully translated from bench to bedside.

Exome-chip association analysis reveals an Asian-specific missense variant in PAX4 associated with type 2 diabetes in Chinese individuals

AIMS/HYPOTHESIS

Genome-wide association studies (GWASs) have identified many common type 2 diabetes-associated variants, mostly at the intronic or intergenic regions. Recent advancements of exome-array genotyping platforms have opened up a novel means for detecting the associations of low-frequency or rare coding variants with type 2 diabetes. We conducted an exomechip association analysis to identify additional type 2 diabetes susceptibility variants in the Chinese population.

METHODS

An exome-chip association study was conducted by genotyping 5640 Chinese individuals from Hong Kong, using a custom designed exome array, the Asian Exomechip. Single variant association analysis was conducted on 77,468 single nucleotide polymorphisms (SNPs). Fifteen SNPs were subsequently genotyped for replication analysis in an independent Chinese cohort comprising 12,362 individuals from Guangzhou. A combined analysis involving 7189 cases and 10,813 controls was performed.

RESULTS

In the discovery stage, an Asian-specific coding variant rs2233580 (p.Arg192His) in PAX4, and two variants at the known loci, CDKN2B-AS1 and KCNQ1, were significantly associated with type 2 diabetes with exome-wide significance (p _discovery < 6.45 × 10^-7). The risk allele (T) of PAX4 rs2233580 was associated with a younger age at diabetes diagnosis. This variant was replicated in an independent cohort and demonstrated a stronger association that reached genome-wide significance (p _{meta-analysis} [p _meta] = 3.74 × 10^-15) in the combined analysis.

CONCLUSIONS/INTERPRETATION

We identified the association of a PAX4 Asian-specific missense variant rs2233580 with type 2 diabetes in an exome-chip association analysis, supporting the involvement of PAX4 in the pathogenesis of type 2 diabetes. Our findings suggest PAX4 is a possible effector gene of the 7q32 locus, previously identified from GWAS in Asians.

Targeting pancreatic expressed PAX genes for the treatment of diabetes mellitus and pancreatic neuroendocrine tumors

INTRODUCTION

Four members of the PAX family, PAX2, PAX4, PAX6 and PAX8 are known to be expressed in the pancreas. Accumulated evidences indicate that several pancreatic expressed PAX genes play a significant role in pancreatic development/functionality and alterations in these genes are involved in the pathogenesis of pancreatic diseases. Areas covered: In this review, we summarize the ongoing research related to pancreatic PAX genes in diabetes mellitus and pancreatic neuroendocrine tumors. We dissect the current knowledge at different levels; from mechanistic studies in cell lines performed to understand the molecular processes controlled by pancreatic PAX genes, to in vivo studies using rodent models that over-express or lack specific PAX genes. Finally, we describe human studies associating variants on pancreatic-expressed PAX genes with pancreatic diseases. Expert opinion: Based on the current literature, we propose that future interventions to treat pancreatic neuroendocrine tumors and diabetes mellitus could be developed via the modulation of PAX4 and/or PAX6 regulated pathways.

The genetic architecture of type 2 diabetes

The genetic architecture of common traits, including the number, frequency, and effect sizes of inherited variants that contribute to individual risk, has been long debated. Genome-wide association studies have identified scores of common variants associated with type 2 diabetes, but in aggregate, these explain only a fraction of the heritability of this disease. Here, to test the hypothesis that lower-frequency variants explain much of the remainder, the GoT2D and T2D-GENES consortia performed whole-genome sequencing in 2,657 European individuals with and without diabetes, and exome sequencing in 12,940 individuals from five ancestry groups. To increase statistical power, we expanded the sample size via genotyping and imputation in a further 111,548 subjects. Variants associated with type 2 diabetes after sequencing were overwhelmingly common and most fell within regions previously identified by genome-wide association studies. Comprehensive enumeration of sequence variation is necessary to identify functional alleles that provide important clues to disease pathophysiology, but large-scale sequencing does not support the idea that lower-frequency variants have a major role in predisposition to type 2 diabetes.

PAX4 R192H and P321H polymorphisms in type 2 diabetes and their functional defects

We have previously identified PAX4 mutations causing MODY9 and a recent genome-wide association study reported a susceptibility locus of type 2 diabetes (T2D) near PAX4. In this study, we aim to investigate the association between PAX4 polymorphisms and T2D in Thai patients and examine functions of PAX4 variant proteins. PAX4 rs2233580 (R192H) and rs712701 (P321H) were genotyped in 746 patients with T2D and 562 healthy normal control subjects by PCR and restriction-fragment length polymorphism method. PAX4 variant proteins were investigated for repressor function on human insulin and glucagon promoters and for cell viability and apoptosis upon high glucose exposure. Genotype and allele frequencies of PAX4 rs2233580 were more frequent in patients with T2D than in control subjects (P=0.001 and 0.0006, respectively) with odds ratio of 1.66 (P=0.001; 95% confidence interval, 1.22-2.27). PAX4 rs712701 was not associated with T2D but it was in linkage disequilibrium with rs2233580. The 192H/321H (A/A) haplotype was more frequent in T2D patients than in controls (9.5% vs 6.6%; P=0.009). PAX4 R192H, but not PAX4 P321H, impaired repression activities on insulin and glucagon promoters and decreased transcript levels of genes required to maintain β-cell function, proliferation and survival. Viability of β-cell was reduced under glucotoxic stress condition for the cells overexpressing either PAX4 R192H or PAX4 P321H or both. Thus these PAX4 polymorphisms may increase T2D risk by defective transcription regulation of target genes and/or decreased β-cell survival in high glucose condition.

Monogenic Diabetes: What It Teaches Us on the Common Forms of Type 1 and Type 2 Diabetes

To date, more than 30 genes have been linked to monogenic diabetes. Candidate gene and genome-wide association studies have identified > 50 susceptibility loci for common type 1 diabetes (T1D) and approximately 100 susceptibility loci for type 2 diabetes (T2D). About 1-5% of all cases of diabetes result from single-gene mutations and are called monogenic diabetes. Here, we review the pathophysiological basis of the role of monogenic diabetes genes that have also been found to be associated with common T1D and/or T2D. Variants of approximately one-third of monogenic diabetes genes are associated with T2D, but not T1D. Two of the T2D-associated monogenic diabetes genes-potassium inward-rectifying channel, subfamily J, member 11 (KCNJ11), which controls glucose-stimulated insulin secretion in the β-cell; and peroxisome proliferator-activated receptor γ (PPARG), which impacts multiple tissue targets in relation to inflammation and insulin sensitivity-have been developed as major antidiabetic drug targets. Another monogenic diabetes gene, the preproinsulin gene (INS), is unique in that INS mutations can cause hyperinsulinemia, hyperproinsulinemia, neonatal diabetes mellitus, one type of maturity-onset diabetes of the young (MODY10), and autoantibody-negative T1D. Dominant heterozygous INS mutations are the second most common cause of permanent neonatal diabetes. Moreover, INS gene variants are strongly associated with common T1D (type 1a), but inconsistently with T2D. Variants of the monogenic diabetes gene Gli-similar 3 (GLIS3) are associated with both T1D and T2D. GLIS3 is a key transcription factor in insulin production and β-cell differentiation during embryonic development, which perturbation forms the basis of monogenic diabetes as well as its association with T1D. GLIS3 is also required for compensatory β-cell proliferation in adults; impairment of this function predisposes to T2D. Thus, monogenic forms of diabetes are invaluable "human models" that have contributed to our understanding of the pathophysiological basis of common T1D and T2D.

Aberrant mRNA splicing of paired box 4 (PAX4) IVS7-1G>A mutation causing maturity-onset diabetes of the young, type 9

AIMS

Paired box 4 (PAX4) mutations cause maturity-onset diabetes of the young, type 9 (MODY9). The molecular defect and alteration of PAX4 function associated with the mutation PAX4 IVS7-1G>A in a family with MODY9 and severe diabetic complications were studied.

METHODS

We investigated the functional consequences of PAX4 IVS7-1G>A on mRNA splicing using minigene assays. Wild-type and mutant PAX4 were expressed in mouse pancreatic β- and α-cell lines, and protein levels and translocation of PAX4 into the nucleus were determined. We also examined transcriptional repression of PAX4 target-gene promoters and β-cell viability under diabetic-like (high-glucose) conditions.

RESULTS

PAX4 IVS7-1G>A disrupts an acceptor splice site, causing an adjacent cryptic splice site within exon 8 to be used, resulting in a three-nucleotide deletion and glutamine deletion at position 250 (p.Q250del). Wild-type and PAX4 Q250del proteins were expressed at similar levels and could translocate normally into the nucleus in βTC3 and αTC1.9 cells. However, the repressor functions of PAX4 Q250del on human insulin and glucagon promoters in INS-1 832/13 and αTC1.9 cells were significantly decreased, compared with that of wild-type PAX4. Moreover, the rate of apoptosis was increased in INS-1 cells over-expressing PAX4 Q250del when cultured in high-glucose conditions.

CONCLUSIONS

PAX4 IVS7-1G>A caused aberrant mRNA splicing and PAX4 Q250 deletion. The mutation impaired PAX4 repressor functions on target-gene promoters and increased susceptibility to apoptosis upon high glucose exposure. Thus, PAX4 IVS7-1G>A contributes to the pathogenesis of diabetes in this MODY9 family through β-cell dysfunction.

PAX4 Gene Transfer Induces α-to-β Cell Phenotypic Conversion and Confers Therapeutic Benefits for Diabetes Treatment

The transcription factor Pax4 plays a critical role in the determination of α- versus β-cell lineage during endocrine pancreas development. In this study, we explored whether Pax4 gene transfer into α-cells could convert them into functional β-cells and thus provide therapeutic benefits for insulin-deficient diabetes. We found that Pax4 delivered by adenoviral vector, Ad5.Pax4, induced insulin expression and reduced glucagon expression in αTC1.9 cells. More importantly, these cells exhibited glucose-stimulated insulin secretion, a key feature of functional β-cells. When injected into streptozotocin-induced diabetic mice, Pax4-treated αTC1.9 cells significantly reduced blood glucose, and the mice showed better glucose tolerance, supporting that Pax4 gene transfer into αTC1.9 cells resulted in the formation of functional β-cells. Furthermore, treatment of primary human islets with Ad5.Pax4 resulted in significantly improved β-cell function. Detection of glucagon(+)/Pax4(+)/Insulin(+) cells argued for Pax4-induced α-to-β cell transitioning. This was further supported by quantification of glucagon and insulin bi-hormonal cells, which was significantly higher in Pax4-treated islets than in controls. Finally, direct administration of Ad5.Pax4 into the pancreas of insulin-deficient mice ameliorated hyperglycemia. Taken together, our data demonstrate that manipulating Pax4 gene expression represents a viable therapeutic strategy for the treatment of insulin deficient diabetes.

Association of PAX4 genetic variants with oral antidiabetic drugs efficacy in Chinese type 2 diabetes patients

The aim of this study was to investigate the association of PAX4 variants with therapeutic effect of oral antidiabetic drugs in Chinese type 2 diabtes mellitus (T2DM) patients. A total of 209 newly diagnosed T2DM patients were randomly assigned to treatment with repaglinide or rosiglitazone for 48 weeks, and the therapeutic effects were compared. In the rosiglitazone cohort, rs6467136 GA+AA carriers showed greater decrease in 2-h glucose levels (P=0.0063) and higher cumulative attainment rates of target 2-h glucose levels (Plog rank=0.0093) than GG homozygotes. In the subgroup with defective β-cell function, rs6467136 GA+AA carriers exhibited greater decrements of 2-h glucose level and improvement of homeostasis model assessment of insulin resistance (P=0.0143). Moreover, GA+AA carriers were more likely to attain the target fasting and 2-h glucose level (Plog rank=0.0091 and 0.007, respectively). However, these single-nucleotide polymorphisms showed no effect on repaglinide efficacy. In conclusion, PAX4 variant rs6467136 was associated with the therapeutic effect of rosiglitazone in Chinese T2DM patients.

Pax genes: regulators of lineage specification and progenitor cell maintenance

Pax genes encode a family of transcription factors that orchestrate complex processes of lineage determination in the developing embryo. Their key role is to specify and maintain progenitor cells through use of complex molecular mechanisms such as alternate RNA splice forms and gene activation or inhibition in conjunction with protein co-factors. The significance of Pax genes in development is highlighted by abnormalities that arise from the expression of mutant Pax genes. Here, we review the molecular functions of Pax genes during development and detail the regulatory mechanisms by which they specify and maintain progenitor cells across various tissue lineages. We also discuss mechanistic insights into the roles of Pax genes in regeneration and in adult diseases, including cancer.

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.