The Krüppel-like zinc finger protein Glis3 directly and indirectly activates insulin gene transcription

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.

Untangling the genetics of beta cell dysfunction and death in type 1 diabetes

BACKGROUND

Type 1 diabetes (T1D) is a complex multi-system disease which arises from both environmental and genetic factors, resulting in the destruction of insulin-producing pancreatic beta cells. Over the past two decades, human genetic studies have provided new insight into the etiology of T1D, including an appreciation for the role of beta cells in their own demise.

SCOPE OF REVIEW

Here, we outline models supported by human genetic data for the role of beta cell dysfunction and death in T1D. We highlight the importance of strong evidence linking T1D genetic associations to bona fide candidate genes for mechanistic and therapeutic consideration. To guide rigorous interpretation of genetic associations, we describe molecular profiling approaches, genomic resources, and disease models that may be used to construct variant-to-gene links and to investigate candidate genes and their role in T1D.

MAJOR CONCLUSIONS

We profile advances in understanding the genetic causes of beta cell dysfunction and death at individual T1D risk loci. We discuss how genetic risk prediction models can be used to address disease heterogeneity. Further, we present areas where investment will be critical for the future use of genetics to address open questions in the development of new treatment and prevention strategies for T1D.

Variations in the LINGO2 and GLIS3 Genes and Gene-Environment Interactions Increase Gestational Diabetes Mellitus Risk in Chinese Women

Gestational diabetes mellitus (GDM) has been found to be a common complication in pregnant women, known to escalate the risk of negative obstetric outcomes. In our study, we genotyped 1,566 Chinese pregnant women for two single nucleotide polymorphisms (SNPs) in the LINGO2 gene and one SNP in the GLIS3 gene, utilizing targeted next-generation sequencing. The impact of two interacting genes, and the interaction of genes with the environment─including exposure to particulate matter (PM2.5), ozone (O3), and variations in prepregnancy body mass index (BMI)─on the incidence of GDM were analyzed using logistic regression. Our findings identify the variants LINGO2 rs10968576 (P = 0.022, OR = 1.224) and rs1412239 (P = 0.018, OR = 1.231), as well as GLIS3 rs10814916 (P = 0.028, OR = 1.172), as risk mutations significantly linked to increased susceptibility to GDM. Further analysis underscores the crucial role of gene-gene and gene-environment interactions in the development of GDM among Chinese women (P < 0.05). Particularly, the individuals carrying the rs10968576 G-rs1412239 G-rs10814916 C haplotype exhibit increased susceptibility to GDM during the prepregnancy period when interacting with PM2.5, O3, and BMI (P = 8.004 × 10-7, OR = 1.206; P = 6.3264 × 10-11, OR = 1.280; P = 9.928 × 10-7, OR = 1.334, respectively). In conclusion, our research emphasizes the importance of the interaction between specific gene variations─LINGO2 and GLIS3─and environmental factors in influencing GDM risk. Notably, we found significant associations between these gene variations and GDM risk across various environmental exposure periods.

The role of noncoding RNAs in beta cell biology and tissue engineering

The loss or dysfunction of pancreatic β-cells, which are responsible for insulin secretion, constitutes the foundation of all forms of diabetes, a widely prevalent disease worldwide. The replacement of damaged β-cells with regenerated or transplanted cells derived from stem cells is a promising therapeutic strategy. However, inducing the differentiation of stem cells into fully functional glucose-responsive β-cells in vitro has proven to be challenging. Noncoding RNAs (ncRNAs) have emerged as critical regulatory factors governing the differentiation, identity, and function of β-cells. Furthermore, engineered hydrogel systems, biomaterials, and organ-like structures possess engineering characteristics that can provide a three-dimensional (3D) microenvironment that supports stem cell differentiation. This review summarizes the roles and contributions of ncRNAs in maintaining the differentiation, identity, and function of β-cells. And it focuses on regulating the levels of ncRNAs in stem cells to activate β-cell genetic programs for generating alternative β-cells and discusses how to manipulate ncRNA expression by combining hydrogel systems and other tissue engineering materials. Elucidating the patterns of ncRNA-mediated regulation in β-cell biology and utilizing this knowledge to control stem cell differentiation may offer promising therapeutic strategies for generating functional insulin-producing cells in diabetes cell replacement therapy and tissue engineering.

Degradation meets development: Implications in β-cell development and diabetes

Pancreatic development is orchestrated by timely synthesis and degradation of stage-specific transcription factors (TFs). The transition from one stage to another stage is dependent on the precise expression of the developmentally relevant TFs. Persistent expression of particular TF would impede the exit from the progenitor stage to the matured cell type. Intracellular protein degradation-mediated protein turnover contributes to a major extent to the turnover of these TFs and thereby dictates the development of different tissues. Since even subtle changes in the crucial cellular pathways would dramatically impact pancreatic β-cell performance, it is generally acknowledged that the biological activity of these pathways is tightly regulated by protein synthesis and degradation process. Intracellular protein degradation is executed majorly by the ubiquitin proteasome system (UPS) and Lysosomal degradation pathway. As more than 90% of the TFs are targeted to proteasomal degradation, this review aims to examine the crucial role of UPS in normal pancreatic β-cell development and how dysfunction of these pathways manifests in metabolic syndromes such as diabetes. Such understanding would facilitate designing a faithful approach to obtain a therapeutic quality of β-cells from stem cells.

Genome-wide analysis study of gestational diabetes mellitus and related pathogenic factors in a Chinese Han population

BACKGROUND

Gestational diabetes mellitus (GDM) affects the metabolism of both the mother and fetus during and after pregnancy. Genetic factors are important in the pathogenesis of GDM, and associations vary by ethnicity. However, related studies about the relationship between the susceptibility genes and glucose traits remain limited in China. This study aimed to identify genes associated with GDM susceptibility in Chinese Han women and validate those findings using clinical data during pregnancy and postpartum period.

METHODS

A genome-wide association study (GWAS) of 398 Chinese Han women (199 each with and without GDM) was conducted and associations between single nucleotide polymorphisms (SNPs) and glucose metabolism were identified by searching public databases. Relationships between filtered differential SNPs and glucose metabolism were verified using clinical data during pregnancy. The GDM group were followed up postpartum to evaluate the progression of glucose metabolism.

RESULTS

We identified five novel SNPs with genome-wide significant associations with GDM: rs62069863 in TRPV3 gene and rs2232016 in PRMT6 gene were positive correlated with 1 h plasma glucose (1hPG) and 2 h plasma glucose (2hPG), rs1112718 in HHEX/EXOC6 gene and rs10460009 in LPIN2 gene were positive associated with fasting plasma glucose, 1hPG and 2hPG, rs927316 in GLIS3 gene was negative correlated with 2hPG. Of the 166 GDM women followed up postpartum, rs62069863 in TRPV3 gene was positively associated with fasting insulin, homoeostasis model assessment of insulin resistance.

CONCLUSIONS

The variants of rs62069863 in TRPV3 gene, rs2232016 in PRMT6 gene, rs1112718 in HHEX/EXOC6 gene, rs927316 in GLIS3 gene, and rs10460009 in LPIN2 gene were newly-identified susceptibility loci for GDM in the Chinese Han population. TRPV3 was associated with worse insulin resistance postpartum.

TRIAL REGISTRATION

This study was registered in the Chinese Clinical Trial Registry.

TRIAL REGISTRATION NUMBER

ChiCTR2100043762. Date of first registration: 28/02/2021.

GLIS3, a novel prognostic indicator of gastric adenocarcinoma, contributes to the malignant biological behaviors of tumor cells via modulating TGF-β1/TGFβR1/Smad1/5 signaling pathway

GLIS3 is highly expressed in multiple cancers, but it has not been studied in gastric adenocarcinoma (GAC). Based on bioinformatics analysis, the prognostic significance of GLIS3 in GAC was analyzed. GAC cells were transfected with small interfering (si)-GLIS3 and GLIS3 overexpression plasmid as well as treated with SB505124 [an inhibitor for transforming growth factor beta receptor 1 (TGFβR1)] and dorsomorphin [an inhibitor for bone morphogenetic protein receptor 1 (BMPR1)]. The GLIS3 expression was detected using qRT-PCR. The impacts of GLIS3 on the proliferation, invasion and migration of GAC cells were measured using cell function assays. The activation of phosphor (p)-Smad1/5 was tested by immunofluorescence. Western blot was utilized to measure the level of transforming growth factor (TGF)-β1/Smad1/5 signaling pathway-related proteins (TGF-β1, p-Smad1, Smad1, p-Smad5, Smad5). GLIS3 was expressed at high levels in GAC tissues and cell lines and its high expression could indicate the poor prognosis of GAC patients. GLIS3 inhibition declined the proliferative, invasive and migratory capabilities as well as TGF-β1 expression and phosphorylation of Smad1/5 in GAC cells. Overexpressed GLIS3 promoted proliferation, migration, invasion, TGF-β1 expression and Smad1/5 phosphorylation in GAC cells, with SB505124 reversing the effects of overexpressed GLIS3 on proliferation, migration, invasion and Smad1/5 phosphorylation whereas dorsomorphin exhibiting no influence on GLIS3-induced effects. GLIS3 facilitated the malignant phenotype of GAC cells via regulating TGF-β1/TGFβR1/Smad1/5 pathway, which may be a novel prognostic indicator of GAC and provided a target for GAC treatment.

GLIS1-3: Links to Primary Cilium, Reprogramming, Stem Cell Renewal, and Disease

The GLI-Similar 1-3 (GLIS1-3) genes, in addition to encoding GLIS1-3 Krüppel-like zinc finger transcription factors, also generate circular GLIS (circGLIS) RNAs. GLIS1-3 regulate gene transcription by binding to GLIS binding sites in target genes, whereas circGLIS RNAs largely act as miRNA sponges. GLIS1-3 play a critical role in the regulation of many biological processes and have been implicated in various pathologies. GLIS protein activities appear to be regulated by primary cilium-dependent and -independent signaling pathways that via post-translational modifications may cause changes in the subcellular localization, proteolytic processing, and protein interactions. These modifications can affect the transcriptional activity of GLIS proteins and, consequently, the biological functions they regulate as well as their roles in disease. Recent studies have implicated GLIS1-3 proteins and circGLIS RNAs in the regulation of stemness, self-renewal, epithelial-mesenchymal transition (EMT), cell reprogramming, lineage determination, and differentiation. These biological processes are interconnected and play a critical role in embryonic development, tissue homeostasis, and cell plasticity. Dysregulation of these processes are part of many pathologies. This review provides an update on our current knowledge of the roles GLIS proteins and circGLIS RNAs in the control of these biological processes in relation to their regulation of normal physiological functions and disease.

The role of long non-coding RNAs in the regulation of pancreatic beta cell identity

Type 2 diabetes (T2D) is a widespread disease affecting millions in every continental population. Pancreatic β-cells are central to the regulation of circulating glucose, but failure in the maintenance of their mass and/or functional identity leads to T2D. Long non-coding RNAs (lncRNAs) represent a relatively understudied class of transcripts which growing evidence implicates in diabetes pathogenesis. T2D-associated single nucleotide polymorphisms (SNPs) have been identified in lncRNA loci, although these appear to function primarily through regulating β-cell proliferation. In the last decade, over 1100 lncRNAs have been catalogued in islets and the roles of a few have been further investigated, definitively linking them to β-cell function. These studies show that lncRNAs can be developmentally regulated and show highly tissue-specific expression. lncRNAs regulate neighbouring β-cell-specific transcription factor expression, with knockdown or overexpression of lncRNAs impacting a network of other key genes and pathways. Finally, gene expression analysis in studies of diabetic models have uncovered a number of lncRNAs with roles in β-cell function. A deeper understanding of these lncRNA roles in maintaining β-cell identity, and its deterioration, is required to fully appreciate the β-cell molecular network and to advance novel diabetes treatments.

Partners in Crime: Beta-Cells and Autoimmune Responses Complicit in Type 1 Diabetes Pathogenesis

Type 1 diabetes (T1D) is an autoimmune disease characterized by autoreactive T cell-mediated destruction of insulin-producing pancreatic beta-cells. Loss of beta-cells leads to insulin insufficiency and hyperglycemia, with patients eventually requiring lifelong insulin therapy to maintain normal glycemic control. Since T1D has been historically defined as a disease of immune system dysregulation, there has been little focus on the state and response of beta-cells and how they may also contribute to their own demise. Major hurdles to identifying a cure for T1D include a limited understanding of disease etiology and how functional and transcriptional beta-cell heterogeneity may be involved in disease progression. Recent studies indicate that the beta-cell response is not simply a passive aspect of T1D pathogenesis, but rather an interplay between the beta-cell and the immune system actively contributing to disease. Here, we comprehensively review the current literature describing beta-cell vulnerability, heterogeneity, and contributions to pathophysiology of T1D, how these responses are influenced by autoimmunity, and describe pathways that can potentially be exploited to delay T1D.

100 YEARS OF INSULIN: A brief history of diabetes genetics: insights for pancreatic beta-cell development and function

Since the discovery of insulin 100 years ago, our knowledge and understanding of diabetes have grown exponentially. Specifically, with regards to the genetics underlying diabetes risk, our discoveries have paralleled developments in our understanding of the human genome and our ability to study genomics at scale; these advancements in genetics have both accompanied and led to those in diabetes treatment. This review will explore the timeline and history of gene discovery and how this has coincided with progress in the fields of genomics. Examples of genetic causes of monogenic diabetes are presented and the continuing expansion of allelic series in these genes and the challenges these now cause for diagnostic interpretation along with opportunities for patient stratification are discussed.

Case Report: Neonatal Diabetes Mellitus Caused by a Novel GLIS3 Mutation in Twins

Background

Mutations in GLIS3 cause a rare syndrome characterized by neonatal diabetes mellitus (NDM), congenital hypothyroidism, congenital glaucoma and cystic kidneys. To date, 14 mutations in GLIS3 have been reported, inherited in an autosomal recessive manner. GLIS3 is a key transcription factor involved in β-cell development, insulin expression, and development of the thyroid, eyes, liver and kidneys.

Cases

We describe non-identical twins born to consanguineous parents presenting with NDM, congenital hypothyroidism, congenital glaucoma, hepatic cholestasis, cystic kidney and delayed psychomotor development. Sequence analysis of GLIS3 identified a novel homozygous nonsense mutation, c.2392C>T, p.Gln798Ter (p.Q798*), which results in an early stop codon. The diabetes was treated with a continuous subcutaneous insulin infusion pump and continuous glucose monitoring. Fluctuating blood glucose and intermittent hypoglycemia were observed on follow-up.

Conclusions

This report highlights the importance of early molecular diagnosis for appropriate management of NDM. We describe a novel nonsense mutation of GLIS3 causing NDM, extend the phenotype, and discuss the challenges in clinical management. Our findings provide new areas for further investigation into the roles of GLIS3 in the pathophysiology of diabetes mellitus.

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.

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.

The Role of Grass MUTE Orthologues During Stomatal Development

Gas exchange between the plant and the atmosphere takes place through stomatal pores formed by paired guard cells. Grasses develop a unique stomatal structure that consists of two dumbbell-shaped guard cells flanked by lateral subsidiary cells. These structures confer a very efficient gas exchange capacity, which may have contributed to the evolutionary success of grasses. Recent works have identified orthologues of Arabidopsis MUTE in three grass species: BdMUTE in Brachypodium distachyon, BZU2/ZmMUTE in maize, and OsMUTE in rice. These genes induce the recruitment of subsidiary cells, and it appears to rely upon the ability of intercellular movement, from the guard mother cell to subsidiary mother cells, of the proteins encoded by them. Unexpectedly, this function of these grass MUTE genes contrasts with that of Arabidopsis MUTE, which promotes guard mother cell identity. These MUTE orthologues also appear to control guard mother cell fate progression, with the action of BdMUTE being less severe than those of BZU2/ZmMUTE and OsMUTE. The emerging picture unravels that grass MUTE genes have not only diverged, due to neo-functionalization, from Arabidopsis MUTE, but also among them.

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.

Emerging Roles of GLI-Similar Krüppel-like Zinc Finger Transcription Factors in Leukemia and Other Cancers

GLI-similar 1-3 (GLIS1-3), a subfamily of Krüppel-like zinc finger transcription factors, function as key regulators of several biological processes important to oncogenesis, including control of cell proliferation, differentiation, self-renewal, and epithelial-mesenchymal transition. This review provides a short overview of the critical roles genetic changes in GLIS1-3 play in the development of several malignancies. This includes intrachromosomal translocations involving GLIS2 and ETO2/CBFA2T3 in the development of pediatric non-Down's syndrome (DS), acute megakaryoblastic leukemia (AMKL), a malignancy with poor prognosis, and an association of interchromosomal translocations between GLIS3, GLIS1, and PAX8, and between GLIS3 and CLPTM1L with hyalinizing trabecular tumors (HTTs) and fibrolamellar hepatocellular carcinoma (FHCC), respectively. Targeting upstream signaling pathways that regulate GLIS signaling may offer new therapeutic strategies in the management of cancer.

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.

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.

Genetic variants of gestational diabetes mellitus: a study of 112 SNPs among 8722 women in two independent populations

AIMS/HYPOTHESIS

Gestational diabetes mellitus (GDM) is a common complication of pregnancy that has substantial short- and long-term adverse health implications for women and their children. However, large-scale studies on genetic risk loci for GDM remain sparse.

METHODS

We conducted a case-control study among 2636 women with GDM and 6086 non-GDM control women from the Nurses' Health Study II and the Danish National Birth Cohort. A total of 112 susceptibility genetic variants confirmed by genome-wide association studies for type 2 diabetes were selected and measured. A weighted genetic risk score (GRS) was created based on variants that were significantly associated with risk of GDM after correcting for the false discovery rate.

RESULTS

For the first time, we identified eight variants associated with GDM, namely rs7957197 (HNF1A), rs10814916 (GLIS3), rs3802177 (SLC30A8), rs9379084 (RREB1), rs34872471 (TCF7L2), rs7903146 (TCF7L2), rs11787792 (GPSM1) and rs7041847 (GLIS3). In addition, we confirmed three variants, rs10830963 (MTNR1B), rs1387153 (MTNR1B) and rs4506565 (TCF7L2), that had previously been significantly associated with GDM risk. Furthermore, compared with participants in the first (lowest) quartile of weighted GRS based on these 11 SNPs, the ORs for GDM were 1.07 (95% CI 0.93, 1.22), 1.23 (95% CI 1.07, 1.41) and 1.53 (95% CI 1.34, 1.74) for participants in the second, third and fourth (highest) quartiles, respectively. The significant positive associations between the weighted GRS and risk of GDM persisted across most of the strata of major risk factors for GDM, including family history of type 2 diabetes, smoking status, BMI and age.

CONCLUSIONS/INTERPRETATION

In this large-scale case-control study with women from two independent populations, eight novel GDM SNPs were identified. These findings offer the potential to improve our understanding of the aetiology of GDM, and particularly of biological mechanisms related to beta cell function.

PIAS-family proteins negatively regulate Glis3 transactivation function through SUMO modification in pancreatic β cells

Gli-similar 3 (Glis3) is Krüppel-like transcription factor associated with the transcriptional regulation of insulin. Mutations within the Glis3 locus have been implicated in a number of pathologies including diabetes mellitus and hypothyroidism. Despite its clinical significance, little is known about the proteins and posttranslational modifications that regulate Glis3 transcriptional activity. In this report, we demonstrate that the SUMO-pathway associated proteins, PIASy and Ubc9 are capable of regulating Glis3 transactivation function through a SUMO-dependent mechanism. We present evidence that SUMOylation of Glis3 by PIAS-family proteins occurs at two conserved lysine residues within the Glis3 N-terminus and modification of Glis3 by SUMO dramatically inhibited insulin transcription. Finally, we provide evidence that Glis3 SUMOylation increases under conditions of chronically elevated glucose and correlates with decreased insulin transcription. Collectively, these results indicate that SUMOylation may serve as a mechanism to regulate Glis3 activity in β cells.

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.

Pancreatic Histopathology of Human Monogenic Diabetes Due to Causal Variants in KCNJ11, HNF1A, GATA6, and LMNA

CONTEXT

Monogenic diabetes is thought to account for 2% of all diabetes cases, but most patients receive misdiagnoses of type 1 or type 2 diabetes. To date, little is known about the histopathological features of pancreata from patients with monogenic diabetes.

OBJECTIVE

Retrospective study of the JDRF Network for Pancreatic Organ Donors with Diabetes biorepository to identify possible cases of monogenic diabetes and to compare effects of genetic variants on pancreas histology.

METHODS

We selected cases of diabetes for genetic testing on the basis of criteria that included young age at diagnosis, low body mass index, negative autoantibody status, and/or detectable C-peptide level. Samples underwent next-generation-targeted sequencing of 140 diabetes/diabetes-related genes. Pancreas weight and histopathology were reviewed.

RESULTS

Forty-one of 140 cases of diabetes met the clinical inclusion criteria, with 38 DNA samples available. Genetic variants of probable clinical significance were found in four cases: one each in KCNJ11, HNF1A, GATA6, and LMNA. The KCNJ11 and HNF1A samples had significantly decreased pancreas weight and insulin mass similar to that of type 1 diabetes but had no insulitis. The GATA6 sample had severe pancreatic atrophy but with abundant β cells and severe amyloidosis similar to type 2 diabetes. The LMNA sample had preserved pancreas weight and insulin mass but abnormal islet architecture and exocrine fatty infiltrates.

CONCLUSIONS

Four cases of diabetes had putative causal variants in monogenic diabetes genes. This study provides further insight into the heterogeneous nature of monogenic diabetes cases that exhibited clinical and pathophysiological features that overlap with type 1/type 2 diabetes.

GLIS3 and Thyroid: A Pleiotropic Candidate Gene for Congenital Hypothyroidism

Variations in the transcription factor Gli-similar 3 (GLIS3) gene have been associated to variable congenital endocrine defects, including both morphogenetic and functional thyroid alterations. Evidence from Glis3 knockout mice indicates a relevant role for GLIS3 in thyroid hormone biosynthesis and postnatal thyroid gland growth, with a mechanism of action downstream of the TSH/TSHR interaction. However, the pathophysiological role of this transcription factor during the embryonic thyroid development remains unexplored. In this manuscript, we will provide an overview of the current knowledge on GLIS3 function during development. As a perspective, we will present preliminary evidence in the zebrafish model in support of a potential role for this pleiotropic transcription factor in the early stages of thyroid gland development.

Zinc Supplementation Improves Glucose Homeostasis in High Fat-Fed Mice by Enhancing Pancreatic β-Cell Function

Zinc is an essential component of the insulin granule and it possibly modulates insulin secretion and signaling. Since insulin resistance is a hallmark in the development of type 2 diabetes mellitus, this study aimed at investigating if zinc supplementation is able to improve glucose tolerance and β-cell function in a model of insulin resistance. Male C57BL/6 mice were distributed in four groups according to the diet: normal fat (NF); normal fat supplemented with ZnCl₂ (NFZ); high-fat (HF); and, high-fat chow supplemented with ZnCl₂ (HFZ). Intraperitoneal glucose (ipGTT) and insulin (ipITT) tolerance, glycemia, insulinemia, HOMA-IR, and HOMA-β were determined after 15 weeks in each diet. Glucose-stimulated insulin secretion (GSIS) was investigated in isolated islets. The insulin effect on glucose uptake, metabolism, and signaling was investigated in soleus muscle. ZnCl₂ did not affect body mass or insulin sensitivity as assessed by ipITT, HOMA-IR, muscle glucose metabolism, and Akt and GSK3-β phosphorylation. However, glucose tolerance, HOMA-β, and GSIS were significantly improved by ZnCl₂ supplementation. Therefore, ZnCl₂ supplementation improves glucose homeostasis in high fat-fed mice by a mechanism that enhances β-cell function, rather than whole-body or muscle insulin sensitivity.

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.

The Potential Role of Krüppel-Like Zinc-Finger Protein Glis3 in Genetic Diseases and Cancers

Gli-similar 3 (Glis3) belongs to a Glis subfamily of Krüppel-like zinc-finger transcription factors characterized to regulate a set of downstream targets essential for cellular functions, including pancreatic development, β-cell maturation and maintenance, and insulin production. Examination of the DNA-binding domain of Glis3 reveals that this domain contains a repeated cysteine 2/histidine 2 (Cys2/His2) zinc-finger motif in the central region where the recognized DNA sequence binds. The loss of the production of pancreatic hormones, such as insulin 1 and 2, is linked to the down-regulation of β cells-related genes and promotes the apoptotic death of β cells found in mutant Glis3. Although accumulating studies converge on the Glis3 functioning in β cells, recently, there have been developments in the field of Glis3 using knockdown/mutant mice to better understand the role of Glis3 in diseases. The Glis3 mutant mice have been characterized for their propensity to develop congenital hypothyroidism, polycystic kidney disease, and some types of cancer. In this review, we attempt to comprehensively summarize the knowledge of Glis3, including its structure and general function in cells. We also collected and organized the academic achievements related to the possible mechanisms of Glis3-related diseases.

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.

Using Drosophila to discover mechanisms underlying type 2 diabetes

Mechanisms of glucose homeostasis are remarkably well conserved between the fruit flyDrosophila melanogasterand mammals. From the initial characterization of insulin signaling in the fly came the identification of downstream metabolic pathways for nutrient storage and utilization. Defects in these pathways lead to phenotypes that are analogous to diabetic states in mammals. These discoveries have stimulated interest in leveraging the fly to better understand the genetics of type 2 diabetes mellitus in humans. Type 2 diabetes results from insulin insufficiency in the context of ongoing insulin resistance. Although genetic susceptibility is thought to govern the propensity of individuals to develop type 2 diabetes mellitus under appropriate environmental conditions, many of the human genes associated with the disease in genome-wide association studies have not been functionally studied. Recent advances in the phenotyping of metabolic defects have positionedDrosophilaas an excellent model for the functional characterization of large numbers of genes associated with type 2 diabetes mellitus. Here, we examine results from studies modeling metabolic disease in the fruit fly and compare findings to proposed mechanisms for diabetic phenotypes in mammals. We provide a systematic framework for assessing the contribution of gene candidates to insulin-secretion or insulin-resistance pathways relevant to diabetes pathogenesis.

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.

Alteration of GLIS3 gene expression pattern in patients with breast cancer

BACKGROUND

The GLIS family members are zinc fingers with transcriptional repression and activation function. GLIS3 is one of these family members, which aberrant expression of it revealed to be related to several different cancer types. Regarding to the role of GLIS3 in tumor genesis and its probable connection with β-catenin signaling pathway, one of the pathways that involves in both normal development and tumor genesis of breast tissue, the aim of this study is investigating the alteration of GLIS3 mRNA expression level in breast cancer.

MATERIALS AND METHODS

Real-time polymerase chain reaction performed with GLIS3 and GAPDH genes primer on the RNA which extracted from 15 fresh frozen breast tumor tissue samples and also 15 normal samples with slight distance from site of tumor.

RESULTS

The relative expression of GLIS3 in breast cancer tissues revealed a 4 times increase comparing normal breast tissues; with a significant difference between cancer and normal samples (P = 0.027) and in patients without lymph node involvement and tissues that had estrogen receptor (ER(-)) and progesterone receptor (PR(-)) statuses. We see no significant difference between cancer and normal tissues based on lobular or ductal origin of the tumor as well as the tumor grade.

CONCLUSIONS

Our study suggested a probable relationship between GLIS3 overexpression and breast cancer. Furthermore, detection of a probable association between GLIS3 overexpression and triple-negative breast cancer (ER(-)/PR(-)/human epidermal growth factor receptor 2(-)) might be useful for prognostic and diagnostic uses or as a probable target for treatment of these patients.

Pancreatic Beta Cell Survival and Signaling Pathways: Effects of Type 1 Diabetes-Associated Genetic Variants

Type 1 diabetes (T1D) is a complex autoimmune disease in which pancreatic beta cells are specifically destroyed by the immune system. The disease has an important genetic component and more than 50 loci across the genome have been associated with risk of developing T1D. The molecular mechanisms by which these putative T1D candidate genes modulate disease risk, however, remain poorly characterized and little is known about their effects in pancreatic beta cells. Functional studies in in vitro models of pancreatic beta cells, based on techniques to inhibit or overexpress T1D candidate genes, allow the functional characterization of several T1D candidate genes. This requires a multistage procedure comprising two major steps, namely accurate selection of genes of potential interest and then in vitro and/or in vivo mechanistic approaches to characterize their role in pancreatic beta cell dysfunction and death in T1D. This chapter details the methods and settings used by our groups to characterize the role of T1D candidate genes on pancreatic beta cell survival and signaling pathways, with particular focus on potentially relevant pathways in the pathogenesis of T1D, i.e., inflammation and innate immune responses, apoptosis, beta cell metabolism and function.

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.

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.

Insulin-like genes in ascidians: findings in Ciona and hypotheses on the evolutionary origins of the pancreas

Insulin plays an extensively characterized role in the control of sugar metabolism, growth and homeostasis in a wide range of organisms. In vertebrate chordates, insulin is mainly produced by the beta cells of the endocrine pancreas, while in non-chordate animals insulin-producing cells are mainly found in the nervous system and/or scattered along the digestive tract. However, recent studies have indicated the notochord, the defining feature of the chordate phylum, as an additional site of expression of insulin-like peptides. Here we show that two of the three insulin-like genes identified in Ciona intestinalis, an invertebrate chordate with a dual life cycle, are first expressed in the developing notochord during embryogenesis and transition to distinct areas of the adult digestive tract after metamorphosis. In addition, we present data suggesting that the transcription factor Ciona Brachyury is involved in the control of notochord expression of at least one of these genes, Ciona insulin-like 2. Finally, we review the information currently available on insulin-producing cells in ascidians and on pancreas-related transcription factors that might control their expression.

Apoptosis of beta cells in diabetes mellitus

Diabetes mellitus is a multifactorial metabolic disorder characterized by hyperglycemia. Apoptosis in beta cells has been observed in response to diverse stimuli, such as glucose, cytokines, free fatty acids, leptin, and sulfonylureas, leading to the activation of polyol, hexosamine, and diacylglycerol/protein kinase-C (DAG/PKC) pathways that mediate oxidative and nitrosative stress causing the release of different cytokines. Cytokines induce the expression of Fas and tumor necrosis factor-alpha (TNF-α) by activating the transcription factor, nuclear factor-κb, and signal transducer and activator of transcription 1 (STAT-1) in the β cells in the extrinsic pathway of apoptosis. Cytokines produced in beta cells also induce proapoptotic members of the intrinsic pathway of apoptosis. The genetic alterations in apoptosis signaling machinery and the pathogenesis of diabetes include Fas, FasL, Akt, caspases, calpain-10, and phosphatase and tensin homolog (Pten). The other gene products that are involved in diabetes are nitric oxide synthase-2 (NOS2), small ubiquitin-like modifier (SUMO), apolipoprotein CIII (ApoCIII), forkhead box protein O1 (FOXO1), and Kruppel-like zinc finger protein Gli-similar 3 (GLIS3). The gene products having antiapoptotic nature are Bcl-2 and Bcl-XL. Epigenetic mechanisms play an important role in type I and type II diabetes. Further studies on the apoptotic genes and gene products in diabetics may be helpful in pharmacogenomics and individualized treatment along with antioxidants targeting apoptosis in diabetes.