Sustained expression of the transcription factor GLIS3 is required for normal beta cell function in adults

Downregulation of Glis3 in INS1 cells exposed to chronically elevated glucose contributes to glucotoxicity-associated β cell dysfunction

Chronically elevated levels of glucose are deleterious to pancreatic β cells and contribute to β cell dysfunction, which is characterized by decreased insulin production and a loss of β cell identity. The Krüppel-like transcription factor, Glis3 has previously been shown to positively regulate insulin transcription and mutations within the Glis3 locus have been associated with the development of several pathologies including type 2 diabetes mellitus. In this report, we show that Glis3 is significantly downregulated at the transcriptional level in INS1 832/13 cells within hours of being subjected to high glucose concentrations and that diminished expression of Glis3 is at least partly attributable to increased oxidative stress. CRISPR/Cas9-mediated knockdown of Glis3 indicated that the transcription factor was required to maintain normal levels of both insulin and MafA expression and reduced Glis3 expression was concomitant with an upregulation of β cell disallowed genes. We provide evidence that Glis3 acts similarly to a pioneer factor at the insulin promoter where it permissively remodels the chromatin to allow access to a transcriptional regulatory complex including Pdx1 and MafA. Finally, evidence is presented that Glis3 can positively regulate MafA transcription through its pancreas-specific promoter and that MafA reciprocally regulates Glis3 expression. Collectively, these results suggest that decreased Glis3 expression in β cells exposed to chronic hyperglycemia may contribute significantly to reduced insulin transcription and a loss of β cell identity.

eQTL mapping in fetal-like pancreatic progenitor cells reveals early developmental insights into diabetes risk

The impact of genetic regulatory variation active in early pancreatic development on adult pancreatic disease and traits is not well understood. Here, we generate a panel of 107 fetal-like iPSC-derived pancreatic progenitor cells (iPSC-PPCs) from whole genome-sequenced individuals and identify 4065 genes and 4016 isoforms whose expression and/or alternative splicing are affected by regulatory variation. We integrate eQTLs identified in adult islets and whole pancreas samples, which reveal 1805 eQTL associations that are unique to the fetal-like iPSC-PPCs and 1043 eQTLs that exhibit regulatory plasticity across the fetal-like and adult pancreas tissues. Colocalization with GWAS risk loci for pancreatic diseases and traits show that some putative causal regulatory variants are active only in the fetal-like iPSC-PPCs and likely influence disease by modulating expression of disease-associated genes in early development, while others with regulatory plasticity likely exert their effects in both the fetal and adult pancreas by modulating expression of different disease genes in the two developmental stages.

Study of the association between GLIS3 rs10758593 and type 2 diabetes mellitus in Egyptian population

Background

GLIS3 (Gli-similar 3), a transcription factor, is involved in the maturation of pancreatic beta cells in fetal life, maintenance of cell mass as well as the control of insulin gene expression in adults. As a result, GLIS3 was reported as a susceptibility gene for type 1 diabetes, type 2 diabetes, and neonatal diabetes. Therefore, the goal of this study was to look into the association between the rs10758593 single nucleotide polymorphism (SNP) in the GLIS3 gene and T2DM in the Egyptian population.

Methods

Frequencies of the rs10758593 (A/G) SNPs were determined in 100 T2DM patients (cases) and in 100 non-diabetic healthy subjects (controls) using real-time PCR.

Results

The prevalence of the mutant genotypes, AA and AG, differed significantly between patients and controls. The AA genotype was more prevalent in the patients' group. The (AA) was found in 39% of the patients and 18% of the controls. While AG (heterozygous) genotype was found in 61% of the patients and 81% of the controls (p = 0.003). The AA genotype was significantly associated with T2DM. Moreover, The GLIS3 rs 10758593 mutation was found to be associated with the presence of diabetic retinopathy and nephropathy. In diabetic patients, a significant correlation between HbA1c with fasting glucose, fasting insulin, and HOMA-IR was found.

Conclusion

The rs10758593 polymorphism of the GLIS3 gene was found to be significantly associated with T2DM in an Egyptian population sample. Additionally, significant association between GLIS3 rs 10758593 mutation and the glycemic control was found.

Transcriptomic analysis of patients with clinical suspicion of maturity-onset diabetes of the young (MODY) with a negative genetic diagnosis

Background

Diagnosis of mature-onset diabetes of the young (MODY), a non-autoimmune monogenic form of diabetes mellitus, is confirmed by genetic testing. However, a positive genetic diagnosis is achieved in only around 50% of patients with clinical characteristics of this disease.

Results

We evaluated the diagnostic utility of transcriptomic analysis in patients with clinical suspicion of MODY but a negative genetic diagnosis. Using Nanostring nCounter technology, we conducted transcriptomic analysis of 19 MODY-associated genes in peripheral blood samples from 19 patients and 8 healthy controls. Normalized gene expression was compared between patients and controls and correlated with each patient’s biochemical and clinical variables. Z-scores were calculated to identify significant changes in gene expression in patients versus controls. Only 7 of the genes analyzed were detected in peripheral blood. HADH expression was significantly lower in patients versus controls. Among patients with suspected MODY, GLIS3 expression was higher in obese versus normal-weight patients, and in patients aged < 25 versus > 25 years at diabetes onset. Significant alteration with respect to controls of any gene was observed in 57.9% of patients.

Conclusions

Although blood does not seem to be a suitable sample for transcriptomic analysis of patients with suspected MODY, in our study, we detected expression alterations in some of the genes studied in almost 58% of patients. That opens the door for future studies that can clarify the molecular cause of the clinic of these patients and thus be able to maintain a more specific follow-up and treatment in each case.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02263-3.

Decreased GLUT2 and glucose uptake contribute to insulin secretion defects in MODY3/HNF1A hiPSC-derived mutant β cells

Heterozygous HNF1A gene mutations can cause maturity onset diabetes of the young 3 (MODY3), characterized by insulin secretion defects. However, specific mechanisms of MODY3 in humans remain unclear due to lack of access to diseased human pancreatic cells. Here, we utilize MODY3 patient-derived human induced pluripotent stem cells (hiPSCs) to study the effect(s) of a causal HNF1A^+/H126D mutation on pancreatic function. Molecular dynamics simulations predict that the H126D mutation could compromise DNA binding and gene target transcription. Genome-wide RNA-Seq and ChIP-Seq analyses on MODY3 hiPSC-derived endocrine progenitors reveal numerous HNF1A gene targets affected by the mutation. We find decreased glucose transporter GLUT2 expression, which is associated with reduced glucose uptake and ATP production in the MODY3 hiPSC-derived β-like cells. Overall, our findings reveal the importance of HNF1A in regulating GLUT2 and several genes involved in insulin secretion that can account for the insulin secretory defect clinically observed in MODY3 patients.

Heterozygous HNF1A mutations can give rise to maturity onset diabetes of the young 3 (MODY3), characterized by insulin secretion defects. Here the authors show that MODY3-related HNF1A mutation in patient hiPSCderived pancreatic cells decreases glucose transporter GLUT2 expression due to compromised DNA binding.

Neonatal diabetes mutations disrupt a chromatin pioneering function that activates the human insulin gene

Despite the central role of chromosomal context in gene transcription, human noncoding DNA variants are generally studied outside of their genomic location. This limits our understanding of disease-causing regulatory variants. INS promoter mutations cause recessive neonatal diabetes. We show that all INS promoter point mutations in 60 patients disrupt a CC dinucleotide, whereas none affect other elements important for episomal promoter function. To model CC mutations, we humanized an ∼3.1-kb region of the mouse Ins2 gene. This recapitulated developmental chromatin states and cell-specific transcription. A CC mutant allele, however, abrogated active chromatin formation during pancreas development. A search for transcription factors acting through this element revealed that another neonatal diabetes gene product, GLIS3, has a pioneer-like ability to derepress INS chromatin, which is hampered by the CC mutation. Our in vivo analysis, therefore, connects two human genetic defects in an essential mechanism for developmental activation of the INS gene.

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.

Diabetes and Genetics: A Relationship Between Genetic Risk Alleles, Clinical Phenotypes and Therapeutic Approaches

Unveiling human genome through successful completion of Human Genome Project and International HapMap Projects with the advent of state of art technologies has shed light on diseases associated genetic determinants. Identification of mutational landscapes such as copy number variation, single nucleotide polymorphisms or variants in different genes and loci have revealed not only genetic risk factors responsible for diseases but also region(s) playing protective roles. Diabetes is a global health concern with two major types - type 1 diabetes (T1D) and type 2 diabetes (T2D). Great progress in understanding the underlying genetic predisposition to T1D and T2D have been made by candidate gene studies, genetic linkage studies, genome wide association studies with substantial number of samples. Genetic information has importance in predicting clinical outcomes. In this review, we focus on recent advancement regarding candidate gene(s) associated with these two traits along with their clinical parameters as well as therapeutic approaches perceived. Understanding genetic architecture of these disease traits relating clinical phenotypes would certainly facilitate population stratification in diagnosing and treating T1D/T2D considering the doses and toxicity of specific drugs.

Transcription factor GLIS3: Critical roles in thyroid hormone biosynthesis, hypothyroidism, pancreatic beta cells and diabetes

GLI-Similar 3 (GLIS3) is a member of the GLIS subfamily of Krüppel-like zinc finger transcription factors that functions as an activator or repressor of gene expression. Study of GLIS3-deficiency in mice and humans revealed that GLIS3 plays a critical role in the regulation of several biological processes and is implicated in the development of various diseases, including hypothyroidism and diabetes. This was supported by genome-wide association studies that identified significant associations of common variants in GLIS3 with increased risk of these pathologies. To obtain insights into the causal mechanisms underlying these diseases, it is imperative to understand the mechanisms by which this protein regulates the development of these pathologies. Recent studies of genes regulated by GLIS3 led to the identification of a number of target genes and have provided important molecular insights by which GLIS3 controls cellular processes. These studies revealed that GLIS3 is essential for thyroid hormone biosynthesis and identified a critical function for GLIS3 in the generation of pancreatic β cells and insulin gene transcription. These observations raised the possibility that the GLIS3 signaling pathway might provide a potential therapeutic target in the management of diabetes, hypothyroidism, and other diseases. To develop such strategies, it will be critical to understand the upstream signaling pathways that regulate the activity, expression and function of GLIS3. Here, we review the recent progress on the molecular mechanisms by which GLIS3 controls key functions in thyroid follicular and pancreatic β cells and how this causally relates to the development of hypothyroidism and diabetes.

Glis3 as a Critical Regulator of Thyroid Primordium Specification

Background: GLIS3 (GLI-Similar protein 3) is a transcription factor involved in several cellular processes. Homozygous mutations in the GLIS3 gene have been typically associated with neonatal diabetes and congenital hypothyroidism (CH) in a syndrome called NDH. NDH patients present developmental abnormalities including endocrine pancreas defects and a spectrum of thyroid abnormalities, mainly including thyroid dysgenesis (TD). The mouse models revealed a key role of Glis3 in pancreatic islets but not in early thyroid development, as Glis3 was described to retain a role in regulating thyroid hormone synthesis downstream the thyrotropin (TSH)/TSHR signaling pathway and in postnatal follicle proliferation. Hence, in this study, we have been taking advantage of the zebrafish model to gain insights on the Glis3 activity during thyroid organogenesis. Methods: Transient glis3-knockdown zebrafish embryos (called glis3 morphants) were generated by the microinjection of specific glis3 morpholinos at one- to two-cell stage to analyze the thyroid phenotype in vivo. Several additional analyses (in situ hybridization, immunohistochemistry, and pharmacological treatments) were performed for further molecular characterization. Results: The analysis of thyroid embryonic development revealed that Glis3 is involved in early steps of thyroid specification. glis3 morphants exhibited a reduced expression of the early transcription factors nkx2.4 and pax2a at the thyroid primordium level, which is not caused by changes in proliferation or apoptosis of the pharyngeal endoderm. As a result, the differentiated thyroid tissue in morphants appeared reduced in size with decreased expression of tg and slc5a5, a low number of thyroxine (T4)-producing follicles, associated with an elevation of tshba (homologous of the human TSHβ), thus resembling the clinical and biochemical manifestations of patients with TD. Interestingly, glis3 morphants have pancreatic β-cell defects, but not liver defects. In vitro and in vivo data also demonstrated that Glis3 is an effector of the Sonic Hedgehog (SHH) pathway. Molecular and pharmacological inhibition of SHH reproduced the thyroid defects observed in glis3 morphant. Conclusions: Our results demonstrate that glis3, within the SHH pathway, appears to determine the number of endodermal cells committed to a thyroid fate. This is the first evidence of the involvement of Glis3 in TD, thereby expanding the understanding of the genetic basis of thyroid development and CH.

Advances in Knowledge of Candidate Genes Acting at the Beta-Cell Level in the Pathogenesis of T1DM

T1DM (type 1 diabetes mellitus), which results from the irreversible elimination of beta-cells mediated by autoreactive T cells, is defined as an autoimmune disease. It is widely accepted that T1DM is caused by a combination of genetic and environmental factors, but the precise underlying molecular mechanisms are still unknown. To date, more than 50 genetic risk regions contributing to the pathogenesis of T1DM have been identified by GWAS (genome-wide association studies). Notably, more than 60% of the identified candidate genes are expressed in islets and beta-cells, which makes it plausible that these genes act at the beta-cell level and play a key role in the pathogenesis of T1DM. In this review, we focus on the current status of candidate genes that act at the beta-cell level by regulating the innate immune response and antiviral activity, affecting susceptibility to proapoptotic stimuli and influencing the pancreatic beta-cell phenotype.

A GLIS3-CD133-WNT-signaling axis regulates the self-renewal of adult murine pancreatic progenitor-like cells in colonies and organoids

The existence and regenerative potential of resident stem and progenitor cells in the adult pancreas are controversial topics. A question that has been only minimally addressed is the capacity of a progenitor cell to self-renew, a key attribute that defines stem cells. Previously, our laboratory has identified putative stem and progenitor cells from the adult murine pancreas. Using an ex vivo colony/organoid culture system, we demonstrated that these stem/progenitor-like cells have self-renewal and multilineage differentiation potential. We have named these cells pancreatic colony-forming units (PCFUs) because they can give rise to three-dimensional colonies. However, the molecular mechanisms by which PCFUs self-renew have remained largely unknown. Here, we tested the hypothesis that PCFU self-renewal requires GLIS family zinc finger 3 (GLIS3), a zinc-finger transcription factor important in pancreas development. Pancreata from 2- to 4-month-old mice were dissociated, sorted for CD133highCD71low ductal cells, known to be enriched for PCFUs, and virally transduced with shRNAs to knock down GLIS3 and other proteins. We then plated these cells into our colony assays and analyzed the resulting colonies for protein and gene expression. Our results revealed a previously unknown GLIS3-to-CD133-to-WNT signaling axis in which GLIS3 and CD133 act as factors necessary for maintaining WNT receptors and signaling molecules in colonies, allowing responses to WNT ligands. Additionally, we found that CD133, but not GLIS3 or WNT, is required for phosphoinositide 3-kinase (PI3K)/AKT Ser/Thr kinase (AKT)-mediated PCFU survival. Collectively, our results uncover a molecular pathway that maintains self-renewal of adult murine PCFUs.

GLIS3 binds pancreatic beta cell regulatory regions alongside other islet transcription factors

The Krüppel-like zinc finger transcription factor Gli-similar 3 (GLIS3) plays a critical role in the regulation of pancreatic beta cells, with global Glis3 knockout mice suffering from severe hyperglycemia and dying by post-natal day 11. In addition, GLIS3 has been shown to directly regulate the early endocrine marker Ngn3, as well as Ins2 gene expression in mature beta cells. We hypothesize that GLIS3 regulates several other genes critical to beta cell function, in addition to Ins2, by directly binding to regulatory regions. We therefore generated a pancreas-specific Glis3 deletion mouse model (Glis3Δpanc) using a Pdx1-driven Cre mouse line. Roughly 20% of these mice develop hyperglycemia by 8-weeks and lose most of their insulin expression. However, this did not appear to be due to loss of the beta cells themselves, as no change in cell death was observed. Indeed, presumptive beta cells appeared to persist as PDX1+/INS-/MAFA-/GLUT2- cells. Islet RNA-seq analysis combined with GLIS3 ChIP-seq analysis revealed apparent direct regulation of a variety of diabetes related genes, including Slc2a2 and Mafa. GLIS3 binding near these genes coincided with binding for other islet-enriched transcription factors, indicating these are distinct regulatory hubs. Our data indicates that GLIS3 not only regulates insulin expression, but several additional genes critical for beta cell function.

ATAC-seq reveals alterations in open chromatin in pancreatic islets from subjects with type 2 diabetes

Impaired insulin secretion from pancreatic islets is a hallmark of type 2 diabetes (T2D). Altered chromatin structure may contribute to the disease. We therefore studied the impact of T2D on open chromatin in human pancreatic islets. We used assay for transposase-accessible chromatin using sequencing (ATAC-seq) to profile open chromatin in islets from T2D and non-diabetic donors. We identified 57,105 and 53,284 ATAC-seq peaks representing open chromatin regions in islets of non-diabetic and diabetic donors, respectively. The majority of ATAC-seq peaks mapped near transcription start sites. Additionally, peaks were enriched in enhancer regions and in regions where islet-specific transcription factors (TFs), e.g. FOXA2, MAFB, NKX2.2, NKX6.1 and PDX1, bind. Islet ATAC-seq peaks overlap with 13 SNPs associated with T2D (e.g. rs7903146, rs2237897, rs757209, rs11708067 and rs878521 near TCF7L2, KCNQ1, HNF1B, ADCY5 and GCK, respectively) and with additional 67 SNPs in LD with known T2D SNPs (e.g. SNPs annotated to GIPR, KCNJ11, GLIS3, IGF2BP2, FTO and PPARG). There was enrichment of open chromatin regions near highly expressed genes in human islets. Moreover, 1,078 open chromatin peaks, annotated to 898 genes, differed in prevalence between diabetic and non-diabetic islet donors. Some of these peaks are annotated to candidate genes for T2D and islet dysfunction (e.g. HHEX, HMGA2, GLIS3, MTNR1B and PARK2) and some overlap with SNPs associated with T2D (e.g. rs3821943 near WFS1 and rs508419 near ANK1). Enhancer regions and motifs specific to key TFs including BACH2, FOXO1, FOXA2, NEUROD1, MAFA and PDX1 were enriched in differential islet ATAC-seq peaks of T2D versus non-diabetic donors. Our study provides new understanding into how T2D alters the chromatin landscape, and thereby accessibility for TFs and gene expression, in human pancreatic islets.

Identification of placental genes linked to selective intrauterine growth restriction (IUGR) in dichorionic twin pregnancies: gene expression profiling study

A linkage of dichorionic (DC) twin pregnancies with selective intrauterine growth restriction (IUGR) to alterations in placental gene expression is unclear. The aim of the study was to identify placental genes related to hypoxia, adipogenesis and human growth which may contribute to IUGR development. The study group (IUGR/AGA) comprised dichorionic (DC) twin pregnancies, where the weight of the twins differed by > 15%; in addition, one twin was small for gestational age (< 10th percentile-SGA) (IUGR) while the other was appropriate for gestational age (> 10th percentile-AGA). In the control group (AGA/AGA), both fetuses were AGA and their weights differed by < 15%. In the first step (selection), placental expression of 260 genes was analysed by commercial PCR profiler array or qPCR primer assay between six pairs of IUGR/AGA twins. In the second stage (verification), the expression of 20 genes with fold change (FC) > 1.5 selected from the first stage was investigated for 75 DC pregnancies: 23 IUGR/AGA vs. 52 AGA/AGA. The expression of Angiopoetin 2, Leptin and Kruppel-like factor 4 was significantly higher, and Glis Family Zinc Finger 3 was lower, in placentas of SGA fetuses (FC = 3.3; 4.4; 1.6; and - 1.8, respectively; p < 0.05). The dysregulation of gene expression related to angiogenesis and growth factors in placentas of twins born from IUGR/AGA pregnancies suggest that these alternations might represent biological fetal adaptation to the uteral condition. Moreover, DC twin pregnancies may be a good model to identify the differences in placental gene expression between SGA and AGA fetuses.

GLIS1-3 transcription factors: critical roles in the regulation of multiple physiological processes and diseases

Krüppel-like zinc finger proteins form one of the largest families of transcription factors. They function as key regulators of embryonic development and a wide range of other physiological processes, and are implicated in a variety of pathologies. GLI-similar 1-3 (GLIS1-3) constitute a subfamily of Krüppel-like zinc finger proteins that act either as activators or repressors of gene transcription. GLIS3 plays a critical role in the regulation of multiple biological processes and is a key regulator of pancreatic β cell generation and maturation, insulin gene expression, thyroid hormone biosynthesis, spermatogenesis, and the maintenance of normal kidney functions. Loss of GLIS3 function in humans and mice leads to the development of several pathologies, including neonatal diabetes and congenital hypothyroidism, polycystic kidney disease, and infertility. Single nucleotide polymorphisms in GLIS3 genes have been associated with increased risk of several diseases, including type 1 and type 2 diabetes, glaucoma, and neurological disorders. GLIS2 plays a critical role in the kidney and GLIS2 dysfunction leads to nephronophthisis, an end-stage, cystic renal disease. In addition, GLIS1-3 have regulatory functions in several stem/progenitor cell populations. GLIS1 and GLIS3 greatly enhance reprogramming efficiency of somatic cells into induced embryonic stem cells, while GLIS2 inhibits reprogramming. Recent studies have obtained substantial mechanistic insights into several physiological processes regulated by GLIS2 and GLIS3, while a little is still known about the physiological functions of GLIS1. The localization of some GLIS proteins to the primary cilium suggests that their activity may be regulated by a downstream primary cilium-associated signaling pathway. Insights into the upstream GLIS signaling pathway may provide opportunities for the development of new therapeutic strategies for diabetes, hypothyroidism, and other diseases.

Discovering human diabetes-risk gene function with genetics and physiological assays

Developing systems to identify the cell type-specific functions regulated by genes linked to type 2 diabetes (T2D) risk could transform our understanding of the genetic basis of this disease. However, in vivo systems for efficiently discovering T2D risk gene functions relevant to human cells are currently lacking. Here we describe powerful interdisciplinary approaches combining Drosophila genetics and physiology with human islet biology to address this fundamental gap in diabetes research. We identify Drosophila orthologs of T2D-risk genes that regulate insulin output. With human islets, we perform genetic studies and identify cognate human T2D-risk genes that regulate human beta cell function. Loss of BCL11A, a transcriptional regulator, in primary human islet cells leads to enhanced insulin secretion. Gene expression profiling reveals BCL11A-dependent regulation of multiple genes involved in insulin exocytosis. Thus, genetic and physiological systems described here advance the capacity to identify cell-specific T2D risk gene functions.

Discovery of a drug candidate for GLIS3-associated diabetes

GLIS3 mutations are associated with type 1, type 2, and neonatal diabetes, reflecting a key function for this gene in pancreatic β-cell biology. Previous attempts to recapitulate disease-relevant phenotypes in GLIS3^−/− β-like cells have been unsuccessful. Here, we develop a “minimal component” protocol to generate late-stage pancreatic progenitors (PP2) that differentiate to mono-hormonal glucose-responding β-like (PP2-β) cells. Using this differentiation platform, we discover that GLIS3^−/− hESCs show impaired differentiation, with significant death of PP2 and PP2-β cells, without impacting the total endocrine pool. Furthermore, we perform a high-content chemical screen and identify a drug candidate that rescues mutant GLIS3-associated β-cell death both in vitro and in vivo. Finally, we discovered that loss of GLIS3 causes β-cell death, by activating the TGFβ pathway. This study establishes an optimized directed differentiation protocol for modeling human β-cell disease and identifies a drug candidate for treating a broad range of GLIS3-associated diabetic patients.

GLIS3 mutations are associated with type 1, type 2, and neonatal diabetes. Here, the authors generate mono-hormonal glucose-responding pancreatic β-like cells in vitro and through a screen identify a drug that rescues pancreatic β-like cell death in GLIS3 mutants by inhibiting the abnormally activated TGFβ pathway.

Loss of Glis3 causes dysregulation of retrotransposon silencing and germ cell demise in fetal mouse testis

Fetal germ cell development is regulated by an elaborate combination of cell-extrinsic and cell-intrinsic signals. Here we identify a novel role for the Krüppel-like transcription factor Gli-Similar 3 (Glis3) in male germ cell development in the mouse embryos. Glis3 is expressed in male germ cells during the brief window of time prior to initiation of piRNA-dependent retrotransposon surveillance. Disruption of Glis3 function led to a widespread reduction in retrotransposon silencing factors, aberrant retrotransposon expression and pronounced germ cell loss. Experimental induction of precocious Glis3 expression in vivo before its normal expression resulted in premature expression of several piRNA pathway members, suggesting that GLIS3 is necessary for the activation of the retrotransposon silencing programs. Our findings reveal an unexpected role for GLIS3 in the development of male germ cells and point to a central role for GLIS3 in the control of retrotransposon silencing in the fetal germline.

Interactions among the variants of insulin-related genes and nutrients increase the risk of type 2 diabetes

Asians easily develops type 2 diabetes (T2DM) since they have insufficient glucose-stimulated insulin secretion (GSIS) in insulin resistant states. Since this may be associated with genetic background, the hypothesis of this study was that inter-genetic and gene-nutrient interactions may explain the low insulin secretory capacity of Asians. Accordingly, we identified the best gene-gene and gene-nutrient interactions using generalized multifactor dimensionality reduction (GMDR) in a large Korean cohort (n=8,842). Initially, we used 105 genetic variants associated with GSIS to identify the best gene-gene interaction model using the GMDR method. The best model included six SNPs, FNBP1L-rs4847428, FNBP1L-rs23766, GLIS3-rs2027393, GLIS3-rs3892354, GLIS3-rs486163 and DLC1-rs17093957. For each individual, we obtained the genetic risk scores based on the best model (GRSBM) to predict the GSIS levels. The GRSBM were divided into low, medium and high groups, and the association between T2DM and the GRSBM was measured using logistic regression. We analyzed the interaction between the GRSBM and the nutrition intakes. The adjusted odds ratios for T2DM risk increased by 1.701 fold in the high-score group compared to the low-score group. HOMA-B, an index of insulin secretion capacity, but not insulin resistance index was much lower in the high-score group than the low-score group. The association between the GRSBM and T2DM risk was greater in subjects with high energy intakes and low Ca intake, than those with low energy intake and high Ca intake. The high-score group was susceptible to T2DM incidence due to lower GSIS than the low-score group especially in subjects with high energy intake. In conclusion, the hypothesis of the study was accepted. These findings suggested that individuals with high GRSBM of the 6 genes in the model should avoid diets in high energy and low in calcium (<500 mg/day) to protect against T2DM.

Type 1 diabetes genome-wide association studies: not to be lost in translation

Genetic studies have identified >60 loci associated with the risk of developing type 1 diabetes (T1D). The vast majority of these are identified by genome-wide association studies (GWAS) using large case-control cohorts of European ancestry. More than 80% of the heritability of T1D can be explained by GWAS data in this population group. However, with few exceptions, their individual contribution to T1D risk is low and understanding their function in disease biology remains a huge challenge. GWAS on its own does not inform us in detail on disease mechanisms, but the combination of GWAS data with other omics-data is beginning to advance our understanding of T1D etiology and pathogenesis. Current knowledge supports the notion that genetic variation in both pancreatic β cells and in immune cells is central in mediating T1D risk. Advances, perspectives and limitations of GWAS are discussed in this review.

GLIS3 is indispensable for TSH/TSHR-dependent thyroid hormone biosynthesis and follicular cell proliferation

Deficiency in Krüppel-like zinc finger transcription factor GLI-similar 3 (GLIS3) in humans is associated with the development of congenital hypothyroidism. However, the functions of GLIS3 in the thyroid gland and the mechanism by which GLIS3 dysfunction causes hypothyroidism are unknown. In the current study, we demonstrate that GLIS3 acts downstream of thyroid-stimulating hormone (TSH) and TSH receptor (TSHR) and is indispensable for TSH/TSHR-mediated proliferation of thyroid follicular cells and biosynthesis of thyroid hormone. Using ChIP-Seq and promoter analysis, we demonstrate that GLIS3 is critical for the transcriptional activation of several genes required for thyroid hormone biosynthesis, including the iodide transporters Nis and Pds, both of which showed enhanced GLIS3 binding at their promoters. The repression of cell proliferation of GLIS3-deficient thyroid follicular cells was due to the inhibition of TSH-mediated activation of the mTOR complex 1/ribosomal protein S6 (mTORC1/RPS6) pathway as well as the reduced expression of several cell division-related genes regulated directly by GLIS3. Consequently, GLIS3 deficiency in a murine model prevented the development of goiter as well as the induction of inflammatory and fibrotic genes during chronic elevation of circulating TSH. Our study identifies GLIS3 as a key regulator of TSH/TSHR-mediated thyroid hormone biosynthesis and proliferation of thyroid follicular cells and uncovers a mechanism by which GLIS3 deficiency causes neonatal hypothyroidism and prevents goiter development.

GLIS1-3: emerging roles in reprogramming, stem and progenitor cell differentiation and maintenance

Recent studies have provided evidence for a regulatory role of GLI-similar (GLIS) transcription factors in reprogramming, maintenance and differentiation of several stem and progenitor cell populations. GLIS1, in conjunction with several other reprogramming factors, was shown to markedly increase the efficiency of generating induced pluripotent stem cells (iPSC) from somatic cells. GLIS2 has been reported to contribute to the maintenance of the pluripotent state in hPSCs. In addition, GLIS2 has a function in regulating self-renewal of hematopoietic progenitors and megakaryocytic differentiation. GLIS3 plays a critical role during the development of several tissues. GLIS3 is able to promote reprogramming of human fibroblasts into retinal pigmented epithelial (RPE) cells. Moreover, GLIS3 is essential for spermatogonial stem cell renewal and spermatogonial progenitor cell differentiation. During pancreas development, GLIS3 protein is first detectable in bipotent pancreatic progenitors and pro-endocrine progenitors and plays a critical role in the generation of pancreatic beta cells. Here, we review the current status of the roles of GLIS proteins in the maintenance and differentiation of these different stem and progenitor cells.

Molecular genetics of the transcription factor GLIS3 identifies its dual function in beta cells and neurons

The GLIS family zinc finger 3 isoform (GLIS3) is a risk gene for Type 1 and Type 2 diabetes, glaucoma and Alzheimer's disease endophenotype. We identified GLIS3 binding sites in insulin secreting cells (INS1) (FDR q<0.05; enrichment range 1.40-9.11 fold) sharing the motif wrGTTCCCArTAGs, which were enriched in genes involved in neuronal function and autophagy and in risk genes for metabolic and neuro-behavioural diseases. We confirmed experimentally Glis3-mediated regulation of the expression of genes involved in autophagy and neuron function in INS1 and neuronal PC12 cells. Naturally-occurring coding polymorphisms in Glis3 in the Goto-Kakizaki rat model of type 2 diabetes were associated with increased insulin production in vitro and in vivo, suggestive alteration of autophagy in PC12 and INS1 and abnormal neurogenesis in hippocampus neurons. Our results support biological pleiotropy of GLIS3 in pathologies affecting β-cells and neurons and underline the existence of trans‑nosology pathways in diabetes and its co-morbidities.

GLIS3 rs7020673 and rs10758593 polymorphisms interact in the susceptibility for type 1 diabetes mellitus

AIMS

The transcription factor Gli-similar 3 (GLIS3) plays a key role in the development and maintenance of pancreatic beta cells as well as in the regulation of Insulin gene expression in adults. Accordingly, genome-wide association studies identified GLIS3 as a susceptibility locus for type 1 diabetes mellitus (T1DM) and glucose metabolism traits. Therefore, the aim of this study was to replicate the association of the rs10758593 and rs7020673 single nucleotide polymorphisms (SNPs) in the GLIS3 gene with T1DM in a Brazilian population.

METHODS

Frequencies of the rs7020673 (G/C) and rs10758593 (A/G) SNPs were analyzed in 503 T1DM patients (cases) and in 442 non-diabetic subjects (controls). Haplotypes constructed from the combination of these SNPs were inferred using a Bayesian statistical method.

RESULTS

Genotype and allele frequencies of rs7020673 and rs10758593 SNPs did not differ significantly between case and control groups. However, the frequency of ≥3 minor alleles of the analyzed SNPs in haplotypes was higher in T1DM patients compared to non-diabetic subjects (6.2 vs. 1.6%; P = 0.001). The presence of ≥3 minor alleles remained independently associated with risk of T1DM after adjustment for T1DM high-risk HLA DR/DQ haplotypes, age and ethnicity (OR = 3.684 95% CI 1.220-11.124). Moreover, levels of glycated hemoglobin seem to be higher in T1DM patients with rs10758593 A/A genotype than patients carrying the G allele of this SNP (P = 0.038), although this association was not kept after Bonferroni correction.

CONCLUSIONS

Our results indicate that individually the rs7020673 and rs10758593 SNPs are not significantly associated with T1DM but seem to interact in the predisposition for this disease.

Extended clinical features associated with novel Glis3 mutation: a case report

BACKGROUND

Mutations in the GLI-similar 3 (GLIS3) gene encoding the transcription factor GLIS3 are a rare cause of neonatal diabetes and congenital hypothyroidism with 12 reported patients to date. Additional features, previously described, include congenital glaucoma, hepatic fibrosis, polycystic kidneys, developmental delay, facial dysmorphism, osteopenia, sensorineural deafness, choanal atresia, craniosynostosis and pancreatic exocrine insufficiency.

CASE PRESENTATION

We report a new case for consanguineous parents with homozygous novel mutation in GLIS3 gene who presented with neonatal diabetes mellitus, severe resistant congenital hypothyroidism, cholestatic liver disease, bilateral congenital glaucoma and facial dysmorphism. There were associated abnormalities in the external genitalia in form of bifid scrotum, bilateral undescended testicles, microphallus and scrotal hypospadias which might be a coincidental finding.

CONCLUSIONS

We suggest that infants with neonatal diabetes associated with dysmorphism should be screened for GLIS3 gene mutations.

The role of GLIS3 in thyroid disease as part of a multisystem disorder

Congenital hypothyroidism is the most common hereditary endocrine disorder. In a small number of cases, mutations have been identified that are associated with maldevelopment and maldescent of the thyroid. Some of these mutations present as syndromes with a multisystem phenotype such as NKX2-1, PAX8, and FOXE. The association of permanent neonatal diabetes and congenital hypothyroidism was first reported in 2003 and subsequently led to the identification GLIS3 as the mutation responsible for this presentation. GLIS3 is a member of the GLI-similar zinc finger protein family encoding for a nuclear protein with five zinc finger domains and maps to chromosome 9p24. Given the role of GLIS3 in transcriptional activation and repression during embryogenesis, in humans, GLIS3 mutations present with multisystem involvement that also includes renal cystic dysplasia, progressive liver fibrosis and osteopenia. Thyroid findings in GLIS3 patients include thyroid aplasia, diminished colloid with interstitial fibrosis at post-mortem, and apparently normal gross thyroid anatomy on ultrasonography but with temporary TSH resistance on treatment. To date no biological mechanism has explained this variable presentation.

Type 1 Diabetes Candidate Genes Linked to Pancreatic Islet Cell Inflammation and Beta-Cell Apoptosis

Type 1 diabetes (T1D) is a chronic immune-mediated disease resulting from the selective destruction of the insulin-producing pancreatic islet β-cells. Susceptibility to the disease is the result of complex interactions between environmental and genetic risk factors. Genome-wide association studies (GWAS) have identified more than 50 genetic regions that affect the risk of developing T1D. Most of these susceptibility loci, however, harbor several genes, and the causal variant(s) and gene(s) for most of the loci remain to be established. A significant part of the genes located in the T1D susceptibility loci are expressed in human islets and β cells and mounting evidence suggests that some of these genes modulate the β-cell response to the immune system and viral infection and regulate apoptotic β-cell death. Here, we discuss the current status of T1D susceptibility loci and candidate genes with focus on pancreatic islet cell inflammation and β-cell apoptosis.

Emerging roles of GLIS3 in neonatal diabetes, type 1 and type 2 diabetes

GLI-similar 3 (GLIS3), a member of the Krüppel-like zinc finger protein subfamily, is predominantly expressed in the pancreas, thyroid and kidney. Glis3 mRNA can be initially detected in mouse pancreas at embryonic day 11.5 and is largely restricted to β cells, pancreatic polypeptide-expressing cells, as well as ductal cells at later stage of pancreas development. Mutations in GLIS3 cause a neonatal diabetes syndrome, characterized by neonatal diabetes, congenital hypothyroidism and polycystic kidney. Importantly, genome-wide association studies showed that variations of GLIS3 are strongly associated with both type 1 diabetes (T1D) and type 2 diabetes (T2D) in multiple populations. GLIS3 cooperates with pancreatic and duodenal homeobox 1 (PDX1), v-maf musculoaponeurotic fibrosarcoma oncogene family, protein A (MAFA), as well as neurogenic differentiation 1 (NEUROD1) and potently controls insulin gene transcription. GLIS3 also plays a role in β cell survival and likely in insulin secretion. Any perturbation of these functions may underlie all three forms of diabetes. GLIS3, synergistically with hepatocyte nuclear factor 6 (HNF6) and forkhead box A2 (FOXA2), controls fetal islet differentiation via transactivating neurogenin 3 (NGN3) and impairment of this function leads to neonatal diabetes. In addition, GLIS3 is also required for the compensatory β cell proliferation and mass expansion in response to insulin resistance, which if disrupted may predispose to T2D. The increasing understanding of the mechanisms of GLIS3 in β cell development, survival and function maintenance will provide new insights into disease pathogenesis and potential therapeutic target identification to combat diabetes.

Differential Gene Dosage Effects of Diabetes-Associated Gene GLIS3 in Pancreatic β Cell Differentiation and Function

Mutations of GLI-similar 3 (GLIS3) underlie a neonatal diabetes syndrome. Genome-wide association studies revealed that GLIS3 variants are associated with both common type 1 and type 2 diabetes. Global Glis3-deficient (Glis3-/-) mice die of severe diabetes shortly after birth. GLIS3 controls islet differentiation by transactivating neurogenin 3 (Ngn3). To unravel the function of Glis3 in adults, we generated inducible global Glis3-deficient mice (Glis3fl/fl/RosaCreERT2). Tamoxifen (TAM)-treated Glis3fl/fl/RosaCreERT2 mice developed severe diabetes, which was reproduced in TAM-treated β cell-specific Glis3fl/fl/Pdx1CreERT mice, but not in TAM-treated Glis3fl/fl/MipCreERT mice. Furthermore, we generated constitutive β cell- or pancreas-specific Glis3-deficient mice using either RipCre (Glis3fl/fl/RipCre) or Pdx1Cre (Glis3fl/fl/Pdx1Cre) coexpressing mice. We observed that, remarkably, neither type of β cell- or pancreas-specific Glis3-deficient mice phenocopied the lethal neonatal diabetes observed in Glis3-/- mice. All Glis3fl/fl/RipCre mice survived to adulthood with normal glucose tolerance. Thirty percent of Glis3fl/fl/Pdx1Cre mice developed severe diabetes at 3 to 4 weeks of age, whereas 55% of them developed mild diabetes with age. In contrast to the >90% reduction of Ngn3 and near-total absence of insulin (Ins) in the embryonic pancreas of Glis3-/- mice, we found only 75%-80% reduction of Ngn3 and Ins messenger RNA or protein expression in the fetal pancreas of Glis3fl/fl/Pdx1Cre mice. The expression levels of Ngn3 and Ins correlated negatively with the extent of Cre-mediated Glis3 deletion. These mouse models are powerful tools to decipher Glis3 gene dosage effects and the role of GLIS3 mutations/variants in a spectrum of β cell dysfunction in people.

Drosophila as a Model for Diabetes and Diseases of Insulin Resistance

Despite the importance of insulin signaling pathways in human disease, initial concerns that insect physiology and sugar metabolism differ enough from humans that flies would not model human disease hampered research in this area. However, during the past 10-15 years, evidence has accumulated that flies can indeed model various aspects of diabetes and related human disorders. This cluster of diseases impact insulin and insulin signaling pathways, fields which have been discussed in many excellent review articles in recent years. In this chapter, we restrict our focus to specific examples of diabetes-related disease models in Drosophila, discussing the advantages and limitations of these models in light of physiological similarities and differences between insects and mammals. We discuss features of metabolism and sugar regulation that are shared between flies and mammals, and specific Drosophila models for Type 1 and Type 2 diabetes, Metabolic syndrome, and related abnormalities including insulin resistance and heart disease. We conclude that fly models for diabetes and related disorders enhance our ability to identify genes and discern functional interactions that can be exploited for disease intervention.

Transcription Factor GLIS3: A New and Critical Regulator of Postnatal Stages of Mouse Spermatogenesis

In this study, we identify a novel and essential role for the Krüppel-like zinc finger transcription factor GLI-similar 3 (GLIS3) in the regulation of postnatal spermatogenesis. We show that GLIS3 is expressed in gonocytes, spermatogonial stem cells (SSCs) and spermatogonial progenitors (SPCs), but not in differentiated spermatogonia and later stages of spermatogenesis or in somatic cells. Spermatogenesis is greatly impaired in GLIS3 knockout mice. Loss of GLIS3 function causes a moderate reduction in the number of gonocytes, but greatly affects the generation of SSCs/SPCs, and as a consequence the development of spermatocytes. Gene expression profiling demonstrated that the expression of genes associated with undifferentiated spermatogonia was dramatically decreased in GLIS3-deficient mice and that the cytoplasmic-to-nuclear translocation of FOXO1, which marks the gonocyte-to-SSC transition and is necessary for SSC self-renewal, is inhibited. These observations suggest that GLIS3 promotes the gonocyte-to-SSC transition and is a critical regulator of the dynamics of early postnatal spermatogenesis. Stem Cells 2016;34:2772-2783.

The Spatiotemporal Pattern of Glis3 Expression Indicates a Regulatory Function in Bipotent and Endocrine Progenitors during Early Pancreatic Development and in Beta, PP and Ductal Cells

The transcription factor Glis-similar 3 (Glis3) has been implicated in the development of neonatal, type 1 and type 2 diabetes. In this study, we examined the spatiotemporal expression of Glis3 protein during embryonic and neonatal pancreas development as well as its function in PP cells. To obtain greater insights into the functions of Glis3 in pancreas development, we examined the spatiotemporal expression of Glis3 protein in a knockin mouse strain expressing a Glis3-EGFP fusion protein. Immunohistochemistry showed that Glis3-EGFP was not detectable during early pancreatic development (E11.5 and E12.5) and at E13.5 and 15.5 was not expressed in Ptf1a⁺ cells in the tip domains indicating that Glis3 is not expressed in multipotent pancreatic progenitors. Glis3 was first detectable at E13.5 in the nucleus of bipotent progenitors in the trunk domains, where it co-localized with Sox9, Hnf6, and Pdx1. It remained expressed in preductal and Ngn3⁺ endocrine progenitors and at later stages becomes restricted to the nucleus of pancreatic beta and PP cells as well as ductal cells. Glis3-deficiency greatly reduced, whereas exogenous Glis3, induced Ppy expression, as reported for insulin. Collectively, our study demonstrates that Glis3 protein exhibits a temporal and cell type-specific pattern of expression during embryonic and neonatal pancreas development that is consistent with a regulatory role for Glis3 in promoting endocrine progenitor generation, regulating insulin and Ppy expression in beta and PP cells, respectively, and duct morphogenesis.

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.

Transcription factor regulation of pancreatic organogenesis, differentiation and maturation

Lineage tracing studies have revealed that transcription factors play a cardinal role in pancreatic development, differentiation and function. Three transitions define pancreatic organogenesis, differentiation and maturation. In the primary transition, when pancreatic organogenesis is initiated, there is active proliferation of pancreatic progenitor cells. During the secondary transition, defined by differentiation, there is growth, branching, differentiation and pancreatic cell lineage allocation. The tertiary transition is characterized by differentiated pancreatic cells that undergo further remodeling, including apoptosis, replication and neogenesis thereby establishing a mature organ. Transcription factors function at multiple levels and may regulate one another and auto-regulate. The interaction between extrinsic signals from non-pancreatic tissues and intrinsic transcription factors form a complex gene regulatory network ultimately culminating in the different cell lineages and tissue types in the developing pancreas. Mutations in these transcription factors clinically manifest as subtypes of diabetes mellitus. Current treatment for diabetes is not curative and thus, developmental biologists and stem cell researchers are utilizing knowledge of normal pancreatic development to explore novel therapeutic alternatives. This review summarizes current knowledge of transcription factors involved in pancreatic development and β-cell differentiation in rodents.

Genes affecting β-cell function in type 1 diabetes

Type 1 diabetes (T1D) is a multifactorial disease resulting from an immune-mediated destruction of the insulin-producing pancreatic β cells. Several environmental and genetic risk factors predispose to the disease. Genome-wide association studies (GWAS) have identified around 50 genetic regions that affect the risk of developing T1D, but the disease-causing variants and genes are still largely unknown. In this review, we discuss the current status of T1D susceptibility loci and candidate genes with focus on the β cell. At least 40 % of the genes in the T1D susceptibility loci are expressed in human islets and β cells, where they according to recent studies modulate the β-cell response to the immune system. As most of the risk variants map to noncoding regions of the genome, i.e., promoters, enhancers, intergenic regions, and noncoding genes, their possible involvement in T1D pathogenesis as gene regulators will also be addressed.

Expanding the Clinical Spectrum Associated With GLIS3 Mutations

CONTEXT

GLIS3 (GLI-similar 3) is a member of the GLI-similar zinc finger protein family encoding for a nuclear protein with 5 C2H2-type zinc finger domains. The protein is expressed early in embryogenesis and plays a critical role as both a repressor and activator of transcription. Human GLIS3 mutations are extremely rare.

OBJECTIVE

The purpose of this article was determine the phenotypic presentation of 12 patients with a variety of GLIS3 mutations.

METHODS

GLIS3 gene mutations were sought by PCR amplification and sequence analysis of exons 1 to 11. Clinical information was provided by the referring clinicians and subsequently using a questionnaire circulated to gain further information.

RESULTS

We report the first case of a patient with a compound heterozygous mutation in GLIS3 who did not present with congenital hypothyroidism. All patients presented with neonatal diabetes with a range of insulin sensitivities. Thyroid disease varied among patients. Hepatic and renal disease was common with liver dysfunction ranging from hepatitis to cirrhosis; cystic dysplasia was the most common renal manifestation. We describe new presenting features in patients with GLIS3 mutations, including craniosynostosis, hiatus hernia, atrial septal defect, splenic cyst, and choanal atresia and confirm further cases with sensorineural deafness and exocrine pancreatic insufficiency.

CONCLUSION

We report new findings within the GLIS3 phenotype, further extending the spectrum of abnormalities associated with GLIS3 mutations and providing novel insights into the role of GLIS3 in human physiological development. All but 2 of the patients within our cohort are still alive, and we describe the first patient to live to adulthood with a GLIS3 mutation, suggesting that even patients with a severe GLIS3 phenotype may have a longer life expectancy than originally described.

Pancreatic islet cell development and regeneration

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

HECT E3 Ubiquitin Ligase Itch Functions as a Novel Negative Regulator of Gli-Similar 3 (Glis3) Transcriptional Activity

The transcription factor Gli-similar 3 (Glis3) plays a critical role in the generation of pancreatic ß cells and the regulation insulin gene transcription and has been implicated in the development of several pathologies, including type 1 and 2 diabetes and polycystic kidney disease. However, little is known about the proteins and posttranslational modifications that regulate or mediate Glis3 transcriptional activity. In this study, we identify by mass-spectrometry and yeast 2-hybrid analyses several proteins that interact with the N-terminal region of Glis3. These include the WW-domain-containing HECT E3 ubiquitin ligases, Itch, Smurf2, and Nedd4. The interaction between Glis3 and the HECT E3 ubiquitin ligases was verified by co-immunoprecipitation assays and mutation analysis. All three proteins interact through their WW-domains with a PPxY motif located in the Glis3 N-terminus. However, only Itch significantly contributed to Glis3 polyubiquitination and reduced Glis3 stability by enhancing its proteasomal degradation. Itch-mediated degradation of Glis3 required the PPxY motif-dependent interaction between Glis3 and the WW-domains of Itch as well as the presence of the Glis3 zinc finger domains. Transcription analyses demonstrated that Itch dramatically inhibited Glis3-mediated transactivation and endogenous Ins2 expression by increasing Glis3 protein turnover. Taken together, our study identifies Itch as a critical negative regulator of Glis3-mediated transcriptional activity. This regulation provides a novel mechanism to modulate Glis3-driven gene expression and suggests that it may play a role in a number of physiological processes controlled by Glis3, such as insulin transcription, as well as in Glis3-associated diseases.

Long noncoding RNAs in diseases of aging

Aging is a process during which progressive deteriorating of cells, tissues, and organs over time lead to loss of function, disease, and death. Towards the goal of extending human health span, there is escalating interest in understanding the mechanisms that govern aging-associated pathologies. Adequate regulation of expression of coding and noncoding genes is critical for maintaining organism homeostasis and preventing disease processes. Long noncoding RNAs (lncRNAs) are increasingly recognized as key regulators of gene expression at all levels--transcriptional, post-transcriptional and post-translational. In this review, we discuss our emerging understanding of lncRNAs implicated in aging illnesses. We focus on diseases arising from age-driven impairment in energy metabolism (obesity, diabetes), the declining capacity to respond homeostatically to proliferative and damaging stimuli (cancer, immune dysfunction), and neurodegeneration. We identify the lncRNAs involved in these ailments and discuss the rising interest in lncRNAs as diagnostic and therapeutic targets to ameliorate age-associated pathologies and prolong health. This article is part of a Special Issue entitled: Clues to long noncoding RNA taxonomy1, edited by Dr. Tetsuro Hirose and Dr. Shinichi Nakagawa.

A genetic strategy to measure circulating Drosophila insulin reveals genes regulating insulin production and secretion

Insulin is a major regulator of metabolism in metazoans, including the fruit fly Drosophila melanogaster. Genome-wide association studies (GWAS) suggest a genetic basis for reductions of both insulin sensitivity and insulin secretion, phenotypes commonly observed in humans with type 2 diabetes mellitus (T2DM). To identify molecular functions of genes linked to T2DM risk, we developed a genetic tool to measure insulin-like peptide 2 (Ilp2) levels in Drosophila, a model organism with superb experimental genetics. Our system permitted sensitive quantification of circulating Ilp2, including measures of Ilp2 dynamics during fasting and re-feeding, and demonstration of adaptive Ilp2 secretion in response to insulin receptor haploinsufficiency. Tissue specific dissection of this reduced insulin signaling phenotype revealed a critical role for insulin signaling in specific peripheral tissues. Knockdown of the Drosophila orthologues of human T2DM risk genes, including GLIS3 and BCL11A, revealed roles of these Drosophila genes in Ilp2 production or secretion. Discovery of Drosophila mechanisms and regulators controlling in vivo insulin dynamics should accelerate functional dissection of diabetes genetics.

TRANSCRIPTION FACTOR GLI-SIMILAR 3 (GLIS3): IMPLICATIONS FOR THE DEVELOPMENT OF CONGENITAL HYPOTHYROIDISM

Congenital hypothyroidism (CH) is the most frequent endocrine disorder in neonates. While several genetic mutations have been identified that result in developmental defects of the thyroid gland or thyroid hormone synthesis, genetic factors have yet to be identified in many CH patients along with the mechanisms underlying their pathophysiology. Mutations in the gene encoding the Krüppel-like transcription factor, GLI-similar 3 (GLIS3) have been associated with the development of a syndrome characterized by congenital hypothyroidism and neonatal diabetes and similar phenotypes were observed in mouse knockout models of Glis3. Patients with GLIS3-mediated CH exhibit diminished serum levels of thyroxine (T4) and triiodothyronine (T3) and elevated thyroid stimulating hormone (TSH) and thyroglobulin (TG). However, the inconsistent presentation of clinical features associated with this CH has made it difficult to ascertain a causative mechanism. Future elucidation of the biological functions of GLIS3 in the thyroid will be crucial to the discovery of new therapeutic opportunities for the treatment of CH.

Many faces of monogenic diabetes

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

Elevation of NR4A3 expression and its possible role in modulating insulin expression in the pancreatic beta cell

Background

NR4A3/NOR-1 is a member of the NR4A orphan nuclear receptor subfamily, which contains early response genes that sense and respond to a variety of stimuli in the cellular environment. The role of NR4A3 in insulin expression in pancreatic beta cells remains unknown.

Methods

Dynamic changes in NR4A3 were examined in a pancreatic beta-cell line, MIN6, treated with thapsigargin (TG), palmitate (PA), tunicamycin (TM), and dithiothreitol (DTT), chemicals that produce cell stress and even apoptosis. We exploited virus infection techniques to induce expression of NR4A3 or three deletion mutants, and determined expression of insulin and insulin regulatory genes in MIN6 cells.

Results

TG and PA, two endoplasmic reticulum (ER) stress inducers, were able to induce unfolded protein response (UPR) activation and elevation of NR4A3 expression in MIN6 cells, whereas TM and DTT, two other ER stress inducers, were able to induce UPR activation but not NR4A3 elevation. MIN6 cells over-expressing NR4A3 protein after adenoviral infection exhibited reduced transcription of the insulin genes Ins1 and Ins2, and reduced insulin protein secretion, which were negatively correlated with NR4A3 expression levels. Functional analysis of different deletion mutants of NR4A3 showed that deleting the activation domain AF1 or the DNA-binding domain abolished the down-regulation of insulin transcription by NR4A3 in MIN6 cells, indicating that this down-regulative role was closely related to the NR4A3 trans-activation activity. Over-expression of NR4A3 in MIN6 cells resulted in reduced mRNA transcription of the insulin positive-regulation genes, Pdx1 and NeuroD1.

Conclusion

Some ER stress inducers, such as TG or PA, are able to elevate NR4A3 expression in MIN6 cells, while others, such as TM or DTT, are not. Over-expression of NR4A3 in MIN6 cells results in down-regulation of insulin gene transcription and insulin secretion. NR4A3 reduces insulin gene expression by modulating the expression of Pdx1 and NeuroD1.

Candidate genes for type 1 diabetes modulate pancreatic islet inflammation and β-cell apoptosis

Genome-wide association studies (GWAS) have identified more than 50 loci associated with genetic risk of type 1 diabetes (T1D). Several T1D candidate genes have been suggested or identified within these regions, but the molecular mechanisms by which they contribute to insulitis and β-cell destruction remain to be clarified. More than 60% of the T1D candidate genes are expressed in human pancreatic islets, suggesting that they contribute to T1D by regulating at least in part pathogenic mechanisms at the β-cell level. Recent studies by our group indicate that important genetically regulated pathways in β-cells include innate immunity and antiviral activity, involving RIG-like receptors (particularly MDA5) and regulators of type I IFNs (i.e. PTPN2 and USP18), and genes related to β-cell phenotype and susceptibility to pro-apoptotic stimuli (i.e. GLIS3). These observations reinforce the concept that the early pathogenesis of T1D is characterized by a dialogue between the immune system and pancreatic β-cells. This dialogue is probably influenced by polymorphisms in genes expressed at the β-cell and/or immune system level, leading to inadequate responses to environmental cues such as viral infections. Further studies are needed to clarify how these disease-associated variants affect pancreatic β-cell responses to inflammation and the subsequent triggering of autoimmune responses and progressive β-cell loss.

The Krüppel-like protein Gli-similar 3 (Glis3) functions as a key regulator of insulin transcription

Transcriptional regulation of insulin in pancreatic β-cells is mediated primarily through enhancer elements located within the 5' upstream regulatory region of the preproinsulin gene. Recently, the Krüppel-like transcription factor, Gli-similar 3 (Glis3), was shown to bind the insulin (INS) promoter and positively influence insulin transcription. In this report, we examined in detail the synergistic activation of insulin transcription by Glis3 with coregulators, CREB-binding protein (CBP)/p300, pancreatic and duodenal homeobox 1 (Pdx1), neuronal differentiation 1 (NeuroD1), and v-maf musculoaponeurotic fibrosarcoma oncogene homolog A (MafA). Our data show that Glis3 expression, the binding of Glis3 to GlisBS, and its recruitment of CBP are required for optimal activation of the insulin promoter in pancreatic β-cells not only by Glis3, but also by Pdx1, MafA, and NeuroD1. Mutations in the GlisBS or small interfering RNA-directed knockdown of GLIS3 diminished insulin promoter activation by Pdx1, NeuroD1, and MafA, and neither Pdx1 nor MafA was able to stably associate with the insulin promoter when the GlisBS were mutated. In addition, a GlisBS mutation in the INS promoter implicated in the development of neonatal diabetes similarly abated activation by Pdx1, NeuroD1, and MafA that could be reversed by increased expression of exogenous Glis3. We therefore propose that recruitment of CBP/p300 by Glis3 provides a scaffold for the formation of a larger transcriptional regulatory complex that stabilizes the binding of Pdx1, NeuroD1, and MafA complexes to their respective binding sites within the insulin promoter. Taken together, these results indicate that Glis3 plays a pivotal role in the transcriptional regulation of insulin and may serve as an important therapeutic target for the treatment of diabetes.

A low-frequency GLIS3 variant associated with resistance to Japanese type 1 diabetes

The role of low-frequency variants in type 1 diabetes (T1D) susceptibility still remains to be clarified. In the present study, we analyzed low-frequency variants of the T1D candidate genes in Japanese. We first screened for protein-changing variants of 24 T1D candidate genes in 96 T1D patients and 96 control subjects, and then the association with T1D was tested in 706 T1D patients and 863 control subjects recruited from the collaborating institutions in Japan. In total, 56 protein-changing variants were discovered; among them, 34 were low-frequency variants (allele frequency < 5%). The association analysis of the low-frequency variants revealed that only the A908V variant of GLIS3 was strongly associated with resistance to T1D (Haldane's odds ratio = 0.046, p = 8.21 × 10(-4), and pc=2.22 × 10(-2)). GLIS3 is a zinc finger transcription factor that is highly expressed in pancreatic beta cells, and regulates beta cell development and insulin gene expression. GLIS3 mRNA is also moderately expressed in the human thymus. The precise mechanism responsible for the association is unclear at present, but the A908V variant may affect autoimmunity to the GLIS3 protein itself; the 908V containing epitope may induce central or peripheral tolerance more efficiently than that of 908A.

The pancreatic β cell and type 1 diabetes: innocent bystander or active participant?

Type 1 diabetes mellitus (T1DM) is a chronic disease resulting from destruction of insulin-producing pancreatic β cells. Genetic and environmental factors contribute to T1DM onset. Use of high-throughput DNA sequencing has allowed geneticists to perform genome-wide association studies (GWAS) to identify novel gene loci associated with T1DM. Interestingly, >50% of these genes encode products that are expressed in β cells. These studies, coupled with emerging molecular evidence that β cells are impaired by gain-of-function or loss-of-function of these loci, suggest an active role for the β cell in eliciting its own demise. Although immune dysregulation plays a vital role in T1DM pathogenesis, understanding the mechanisms contributing to β cell failure may lead to new strategies to preserve or improve β cell function in patients with T1DM.