Dynamic recruitment of functionally distinct Swi/Snf chromatin remodeling complexes modulates Pdx1 activity in islet β cells

Hyperglycemia influences the cell proliferation and death of the rat endocrine pancreas in the neonatal period

AIMS

To evaluate the cell proliferation and death, and structural morphology of the pancreatic islet cells of the rats with hyperglycemia in the first month of life and compare to those of the control rats.

MAIN METHODS

Female Sprague-Dawley newborn rats received Streptozotocin (a beta-cytotoxic drug) at birth for diabetes induction. Control and hyperglycemic animals were euthanized on different days of life: 5, 10, 15, and 30. The pancreas was collected and processed for immunohistochemical analysis of cleaved Caspase-3 (cell death), Ki-67 (cell proliferation), PDX-1 (transcription factor responsible for insulin synthesis), and endocrine hormones (insulin, glucagon, and somatostatin).

KEY FINDINGS

Control females showed a higher percentage (%) of Ki-67-positive(+) cells on D10 and D15, a higher % of insulin+ and somatostatin+ cells on D15 and D30, a lower % of PDX-1+ cells on D10, and a higher % of glucagon+ cells on D10 and D30. Hyperglycemic females showed a lower % of Ki-67+ cells on D15, a higher % of cleaved Caspase-3+ cells on D15, and insulin+ cells on D15 and D30. In the comparison among the experimental groups, the hyperglycemic females showed an increased % of cleaved Caspase-3+ and Ki-67+ cells and a lower % of PDX-1+ cells.

SIGNIFICANCE

This study enabled a better understanding of the abnormal pancreas development regarding cellular proliferation, apoptosis, and hormonal synthesis in the neonatal period. Thus, the pancreatic islets of hyperglycemic rats do not reestablish the normal endocrine cell population, and cellular apoptosis overcame the proliferative activity of these cells.

Chromatin sensing: integration of environmental signals to reprogram plant development through chromatin regulators

Chromatin regulation in eukaryotes plays pivotal roles in controlling the developmental regulatory gene network. This review explores the intricate interplay between chromatin regulators and environmental signals, elucidating their roles in shaping plant development. As sessile organisms, plants have evolved sophisticated mechanisms to perceive and respond to environmental cues, orchestrating developmental programs that ensure adaptability and survival. A central aspect of this dynamic response lies in the modulation of versatile gene regulatory networks, mediated in part by various chromatin regulators. Here, we summarized current understanding of the molecular mechanisms through which chromatin regulators integrate environmental signals, influencing key aspects of plant development.

The SWI/SNF chromatin remodelling complex regulates pancreatic endocrine cell expansion and differentiation in mice in vivo

AIMS/HYPOTHESIS

Strategies to augment functional beta cell mass include directed differentiation of stem cells towards a beta cell fate, which requires extensive knowledge of transcriptional programs governing endocrine progenitor cell differentiation in vivo. We aimed to study the contributions of the Brahma-related gene-1 (BRG1) and Brahma (BRM) ATPase subunits of the SWI/SNF chromatin remodelling complex to endocrine cell development.

METHODS

We generated mice with endocrine progenitor-specific Neurog3-Cre BRG1 removal in the presence of heterozygous (Brg1Δendo;Brm+/-) or homozygous (double knockout: DKOΔendo) BRM deficiency. Whole-body metabolic phenotyping, islet function characterisation, islet quantitative PCR and histological characterisation were performed on animals and tissues postnatally. To test the mechanistic actions of SWI/SNF in controlling gene expression during endocrine cell development, single-cell RNA-seq was performed on flow-sorted endocrine-committed cells from embryonic day 15.5 control and mutant embryos.

RESULTS

Brg1Δendo;Brm+/- mice exhibit severe glucose intolerance, hyperglycaemia and hypoinsulinaemia, resulting, in part, from reduced islet number; diminished alpha, beta and delta cell mass; compromised islet insulin secretion; and altered islet gene expression programs, including reductions in MAFA and urocortin 3 (UCN3). DKOΔendo mice were not recovered at weaning; however, postnatal day 6 DKOΔendo mice were severely hyperglycaemic with reduced serum insulin levels and beta cell area. Single-cell RNA-seq of embryonic day 15.5 lineage-labelled cells revealed endocrine progenitor, alpha and beta cell populations from SWI/SNF mutants have reduced expression of Mafa, Gcg, Ins1 and Ins2, suggesting limited differentiation capacity. Reduced Neurog3 transcripts were discovered in DKOΔendo endocrine progenitor clusters, and the proliferative capacity of neurogenin 3 (NEUROG3)+ cells was reduced in Brg1Δendo;Brm+/- and DKOΔendo mutants.

CONCLUSIONS/INTERPRETATION

Loss of BRG1 from developing endocrine progenitor cells has a severe postnatal impact on glucose homeostasis, and loss of both subunits impedes animal survival, with both groups exhibiting alterations in hormone transcripts embryonically. Taken together, these data highlight the critical role SWI/SNF plays in governing gene expression programs essential for endocrine cell development and expansion.

DATA AVAILABILITY

Raw and processed data for scRNA-seq have been deposited into the NCBI Gene Expression Omnibus (GEO) database under the accession number GSE248369.

Ablation of Brg1 in fibroblast/myofibroblast lineages attenuates renal fibrosis in mice with diabetic nephropathy

AIMS

Diabetic nephropathy (DN) is one of the most common complications of diabetes and represents a prototypical form of chronic kidney disease (CKD). Interstitial fibrosis is a key pathological feature of DN. During DN-associated renal fibrosis, resident fibroblasts trans-differentiate into myofibroblasts to remodel the extracellular matrix, the underlying epigenetic mechanism of which is not entirely clear.

METHODS

Diabetic nephropathy was induced in C57B6/j mice by a single injection with streptozotocin (STZ). Gene expression was examined by quantitative PCR and Western blotting. Renal fibrosis was evaluated by PicroSirius Red staining.

RESULTS

We report that expression of Brg1, a chromatin remodeling protein, in renal fibroblasts was up-regulated during DN pathogenesis as assessed by single-cell RNA-seq. Treatment with high glucose similarly augmented Brg1 expression in primary renal fibroblasts in vitro. Importantly, Brg1 ablation in quiescent renal fibroblasts or in mature myofibroblasts equivalently attenuated renal fibrosis in the context of diabetic nephropathy in mice. Additionally, administration with a small-molecule Brg1 inhibitor PFI-3 ameliorated renal fibrosis and improved renal function in mice induced to develop DN.

SIGNIFICANCE

In conclusion, our data provide novel genetic evidence that links Brg1 to fibroblast-myofibroblast transition and renewed rationale for targeting Brg1 in the intervention of DN-associated renal fibrosis.

Spatiotemporal role of SETD2-H3K36me3 in murine pancreatic organogenesis

Pancreas development is tightly controlled by multilayer mechanisms. Despite years of effort, large gaps remain in understanding how histone modifications coordinate pancreas development. SETD2, a predominant histone methyltransferase of H3K36me3, plays a key role in embryonic stem cell differentiation, whose role in organogenesis remains elusive. Here, by combination of cleavage under targets and tagmentation (CUT&Tag), assay for transposase-accessible chromatin using sequencing (ATAC-seq), and bulk RNA sequencing, we show a dramatic increase in the H3K36me3 level from the secondary transition phase and decipher the related transcriptional alteration. Using single-cell RNA sequencing, we define that pancreatic deletion of Setd2 results in abnormalities in both exocrine and endocrine lineages: hyperproliferative tip progenitor cells lead to abnormal differentiation; Ngn3+ endocrine progenitors decline due to the downregulation of Nkx2.2, leading to insufficient endocrine development. Thus, these data identify SETD2 as a crucial player in embryonic pancreas development, providing a clue to understanding the dysregulation of histone modifications in pancreatic disorders.

Dynamic regulation of pancreatic β cell function and gene expression by the SND1 coregulator in vitro

The pancreatic β cell synthesizes, packages, and secretes insulin in response to glucose-stimulation to maintain blood glucose homeostasis. Under diabetic conditions, a subset of β cells fail and lose expression of key transcription factors (TFs) required for insulin secretion. Among these TFs is Pancreatic and duodenal homeobox 1 (PDX1), which recruits a unique subset of transcriptional coregulators to modulate its activity. Here we describe a novel interacting partner of PDX1, the Staphylococcal Nuclease and Tudor domain-containing protein (SND1), which has been shown to facilitate protein-protein interactions and transcriptional control through diverse mechanisms in a variety of tissues. PDX1:SND1 interactions were confirmed in rodent β cell lines, mouse islets, and human islets. Utilizing CRISPR-Cas9 gene editing technology, we deleted Snd1 from the mouse β cell lines, which revealed numerous differentially expressed genes linked to insulin secretion and cell proliferation, including limited expression of Glp1r. We observed Snd1 deficient β cell lines had reduced cell expansion rates, GLP1R protein levels, and limited cAMP accumulation under stimulatory conditions, and further show that acute ablation of Snd1 impaired insulin secretion in rodent and human β cell lines. Lastly, we discovered that PDX1:SND1 interactions were profoundly reduced in human β cells from donors with type 2 diabetes (T2D). These observations suggest the PDX1:SND1 complex formation is critical for controlling a subset of genes important for β cell function and is targeted in diabetes pathogenesis.

The Chd4 Helicase Regulates Chromatin Accessibility and Gene Expression Critical for β-Cell Function In Vivo

The transcriptional activity of Pdx1 is modulated by a diverse array of coregulatory factors that govern chromatin accessibility, histone modifications, and nucleosome distribution. We previously identified the Chd4 subunit of the nucleosome remodeling and deacetylase complex as a Pdx1-interacting factor. To identify how loss of Chd4 impacts glucose homeostasis and gene expression programs in β-cells in vivo, we generated an inducible β-cell-specific Chd4 knockout mouse model. Removal of Chd4 from mature islet β-cells rendered mutant animals glucose intolerant, in part due to defects in insulin secretion. We observed an increased ratio of immature-to-mature insulin granules in Chd4-deficient β-cells that correlated with elevated levels of proinsulin both within isolated islets and from plasma following glucose stimulation in vivo. RNA sequencing and assay for transposase-accessible chromatin with sequencing showed that lineage-labeled Chd4-deficient β-cells have alterations in chromatin accessibility and altered expression of genes critical for β-cell function, including MafA, Slc2a2, Chga, and Chgb. Knockdown of CHD4 from a human β-cell line revealed similar defects in insulin secretion and alterations in several β-cell-enriched gene targets. These results illustrate how critical Chd4 activities are in controlling genes essential for maintaining β-cell function.

ARTICLE HIGHLIGHTS

Pdx1-Chd4 interactions were previously shown to be compromised in β-cells from human donors with type 2 diabetes. β-Cell-specific removal of Chd4 impairs insulin secretion and leads to glucose intolerance in mice. Expression of key β-cell functional genes and chromatin accessibility are compromised in Chd4-deficient β-cells. Chromatin remodeling activities enacted by Chd4 are essential for β-cell function under normal physiological conditions.

Hunter C. LDB1-mediated transcriptional complexes are sensitive to islet stress

Excess nutrients and proinflammatory cytokines impart stresses on pancreatic islet β-cells that, if unchecked, can lead to cellular dysfunction and/or death. Among these stress-induced effects is loss of key β-cell transcriptional regulator mRNA and protein levels required for β-cell function. Previously, our lab and others reported that LIM-domain complexes comprised the LDB1 transcriptional co-regulator and Islet-1 (ISL1) transcription factor are required for islet β-cell development, maturation, and function. The LDB1:ISL1 complex directly occupies and regulates key β-cell genes, including MafA, Pdx1, and Slc2a2, to maintain β-cell identity and function. Given the importance of LDB1:ISL1 complexes, we hypothesized that LDB1 and/or ISL1 levels, like other transcriptional regulators, are sensitive to β-cell nutrient and cytokine stresses, likely contributing to β-cell (dys)function under various stimuli. We tested this by treating β-cell lines or primary mouse islets with elevating glucose concentrations, palmitate, or a cytokine cocktail of IL-1β, TNFα, and IFNγ. We indeed observed that LDB1 mRNA and/or protein levels were reduced upon palmitate and cytokine (cocktail or singly) incubation. Conversely, acute high glucose treatment of β-cells did not impair LDB1 or ISL1 levels, but increased LDB1:ISL1 interactions. These observations suggest that LDB1:ISL1 complex formation is sensitive to β-cell stresses and that targeting and/or stabilizing this complex may rescue lost β-cell gene expression to preserve cellular function.

PDX1 is the cornerstone of pancreatic β-cell functions and identity

Diabetes has been a worldwide healthcare problem for many years. Current methods of treating diabetes are still largely directed at symptoms, aiming to control the manifestations of the pathology. This creates an overall need to find alternative measures that can impact on the causes of the disease, reverse diabetes, or make it more manageable. Understanding the role of key players in the pathogenesis of diabetes and the related β-cell functions is of great importance in combating diabetes. PDX1 is a master regulator in pancreas organogenesis, the maturation and identity preservation of β-cells, and of their role in normal insulin function. Mutations in the PDX1 gene are correlated with many pancreatic dysfunctions, including pancreatic agenesis (homozygous mutation) and MODY4 (heterozygous mutation), while in other types of diabetes, PDX1 expression is reduced. Therefore, alternative approaches to treat diabetes largely depend on knowledge of PDX1 regulation, its interaction with other transcription factors, and its role in obtaining β-cells through differentiation and transdifferentiation protocols. In this article, we review the basic functions of PDX1 and its regulation by genetic and epigenetic factors. Lastly, we summarize different variations of the differentiation protocols used to obtain β-cells from alternative cell sources, using PDX1 alone or in combination with various transcription factors and modified culture conditions. This review shows the unique position of PDX1 as a potential target in the genetic and cellular treatment of diabetes.

Biophysical insights into glucose-dependent transcriptional regulation by PDX1

The pancreatic and duodenal homeobox 1 (PDX1) is a central regulator of glucose-dependent transcription of insulin in pancreatic β cells. PDX1 transcription factor activity is integral to the development and sustained health of the pancreas; accordingly, deciphering the complex network of cellular cues that lead to PDX1 activation or inactivation is an important step toward understanding the etiopathologies of pancreatic diseases and the development of novel therapeutics. Despite nearly 3 decades of research into PDX1 control of Insulin expression, the molecular mechanisms that dictate the function of PDX1 in response to glucose are still elusive. The transcriptional activation functions of PDX1 are regulated, in part, by its two intrinsically disordered regions, which pose a barrier to its structural and biophysical characterization. Indeed, many studies of PDX1 interactions, clinical mutations, and posttranslational modifications lack molecular level detail. Emerging methods for the quantitative study of intrinsically disordered regions and refined models for transactivation now enable us to validate and interrogate the biochemical and biophysical features of PDX1 that dictate its function. The goal of this review is to summarize existing PDX1 studies and, further, to generate a comprehensive resource for future studies of transcriptional control via PDX1.

SMNDC1 links chromatin remodeling and splicing to regulate pancreatic hormone expression

Insulin expression is primarily restricted to the pancreatic β cells, which are physically or functionally depleted in diabetes. Identifying targetable pathways repressing insulin in non-β cells, particularly in the developmentally related glucagon-secreting α cells, is an important aim of regenerative medicine. Here, we perform an RNA interference screen in a murine α cell line to identify silencers of insulin expression. We discover that knockdown of the splicing factor Smndc1 triggers a global repression of α cell gene-expression programs in favor of increased β cell markers. Mechanistically, Smndc1 knockdown upregulates the β cell transcription factor Pdx1 by modulating the activities of the BAF and Atrx chromatin remodeling complexes. SMNDC1's repressive role is conserved in human pancreatic islets, its loss triggering enhanced insulin secretion and PDX1 expression. Our study identifies Smndc1 as a key factor connecting splicing and chromatin remodeling to the control of insulin expression in human and mouse islet cells.

The Ldb1 transcriptional co-regulator is required for establishment and maintenance of the pancreatic endocrine lineage

Pancreatic islet cell development is regulated by transcription factors (TFs) that mediate embryonic progenitor differentiation toward mature endocrine cells. Prior studies from our lab and others showed that the islet-enriched TF, Islet-1 (Isl1), interacts with the broadly-expressed transcriptional co-regulator, Ldb1, to regulate islet cell maturation and postnhyperatal function (by embryonic day (E)18.5). However, Ldb1 is expressed in the developing pancreas prior to Isl1 expression, notably in multipotent progenitor cells (MPCs) marked by Pdx1 and endocrine progenitors (EPs) expressing Neurogenin-3 (Ngn3). MPCs give rise to the endocrine and exocrine pancreas, while Ngn3⁺ EPs specify pancreatic islet endocrine cells. We hypothesized that Ldb1 is required for progenitor identity in MPC and EP populations during development to impact islet appearance and function. To test this, we generated a whole-pancreas Ldb1 knockout, termed Ldb1^ΔPanc , and observed severe developmental and postnatal pancreas defects including disorganized progenitor pools, a significant reduction of Ngn3-expressing EPs, Pdx1^HI β-cells, and early hormone⁺ cells. Ldb1^ΔPanc neonates presented with severe hyperglycemia, hypoinsulinemia, and drastically reduced hormone expression in islets, yet no change in total pancreas mass. This supports the endocrine-specific actions of Ldb1. Considering this, we also developed an endocrine-enriched model of Ldb1 loss, termed Ldb1^ΔEndo . We observed similar dysglycemia in this model, as well as a loss of islet identity markers. Through in vitro and in vivo chromatin immunoprecipitation experiments, we found that Ldb1 occupies key Pdx1 and Ngn3 promoter domains. Our findings provide insight into novel regulation of endocrine cell differentiation that may be vital toward improving cell-based diabetes therapies.

The Chd4 subunit of the NuRD complex regulates Pdx1-controlled genes involved in β-cell function

Type 2 diabetes (T2D) is associated with loss of transcription factors (TFs) from a subset of failing β-cells. Among these TFs is Pdx1, which controls the expression of numerous genes involved in maintaining β-cell function and identity. Pdx1 activity is modulated by transcriptional coregulators and has recently been shown, through an unbiased screen, to interact with the Chd4 ATPase subunit of the nucleosome remodeling and deacetylase complex. Chd4 contributes to the maintenance of cellular identity and functional status of numerous different cell types. Here, we demonstrated that Pdx1 dynamically interacts with Chd4 under physiological and stimulatory conditions within islet β-cells and established a fundamental role for Chd4 in regulating insulin secretion and modulating numerous Pdx1-bound genes in vitro, including the MafA TF, where we discovered Chd4 is bound to the MafA region 3 enhancer. Furthermore, we found that Pdx1:Chd4 interactions are significantly compromised in islet β-cells under metabolically induced stress in vivo and in human donor tissues with T2D. Our findings establish a fundamental role for Chd4 in regulating insulin secretion and modulating Pdx1-bound genes in vitro, and disruption of Pdx1:Chd4 interactions coincides with β-cell dysfunction associated with T2D.

Secretome effect of adipose tissue-derived stem cells cultured two-dimensionally and three-dimensionally in mice with streptozocin induced type 1 diabetes

Aims

To analyze therapeutic potential of the conditioned medium from adipose tissue-derived stem cells (ASC) cultivated in 2D (CM-2D) and 3D (CM-3D) models, in mice with Type 1 diabetes (T1D) induced by streptozotocin.

Main methods

Viability andCD105 expression of 2D and 3D ASC were analyzed by flow cytometry. T1D was induced in mice by multiple injections of streptozocin. On the 28th and 29th days after the first injection of streptozocin, diabetic animals received CM-2D or CM-3D. Pancreatic, CM-2D, and CM-3D cytokines were analyzed by cytometric bead array (CBA) and insulin and PDX-1 were observed and quantified by immunohistochemistry. Apoptosis-related proteins were quantified by Western Blotting.

Key findings

ASC in three-dimensional culture released increased levels of IL-6 and IL-2, while IL-4 was decreased. CM-2D induced pancreatic PDX-1 expression and was able to reduce glycemia in diabetic mice one week after injections but not CM-3D. On the other hand, CM-2D and CM-3D were not able to reverse apoptosis of pancreatic cells in diabetic mice nor to increase insulin expression.

Significance

Together, these results demonstrate that the 3D cell culture secretome was not able to improve diabetes type 1 symptoms at the times observed, while 2D cell secretome improved glycemic levels in T1D mice.

Regulation of Pdx1 by oxidative stress and Nrf2 in pancreatic beta-cells

The beta-cell identity gene, pancreatic duodenal homeobox 1 (Pdx1), plays critical roles in many aspects of the life of beta-cells including differentiation, maturation, function, survival and proliferation. High levels of reactive oxygen species (ROS) are extremely toxic to cells and especially to beta-cells due to their relatively low expression of antioxidant enzymes. One of the major mechanisms for beta-cell dysfunction in type-2 diabetes results from oxidative stress-dependent inhibition of PDX1 levels and function. ROS inhibits Pdx1 by reducing Pdx1 mRNA and protein levels, inhibiting PDX1 nuclear localization, and suppressing PDX1 coactivator complexes. The nuclear factor erythroid 2-related factor (Nrf2) antioxidant pathway controls the redox balance and allows the maintenance of high Pdx1 levels. Therefore, pharmacological activation of the Nrf2 pathway may alleviate diabetes by preserving Pdx1 levels.

The Transcriptome and Epigenome Reveal Novel Changes in Transcription Regulation During Pancreatic Rat Islet Maturation

Islet function is critical for normal glucose homeostasis. Unlike adult β cells, fetal and neonatal islets are more proliferative and have decreased insulin secretion in response to stimuli. However, the underlying mechanisms governing functional maturity of islets have not been completely elucidated. Pancreatic islets comprise different cell types. The microenvironment of islets and interactions between these cell types are critical for β-cell development and maturation. Thus, the study of intact islets is optimal to identify novel molecular mechanisms controlling islet functional development. Transcriptomes and genome-wide histone landscapes of H3K4me3, H3K27me3, and H3K27Ac from intact islets isolated from 2- and 10-week-old Sprague-Dawley rats were integrated to elucidate genes and pathways modulating islet development, as well as the contribution of epigenetic regulation. A total of 4489 differentially expressed genes were identified; 2289 and 2200 of them were up- and down-regulated in 10-week islets, respectively. Ingenuity Pathway Analysis revealed critical pathways regulating functional maturation of islets, including nutrient sensing, neuronal function, immune function, cell replication, and extracellular matrix. Furthermore, we identified significant changes in enrichment of H3K4me3, H3K27me3, and H3K27Ac marks, which correlated with expression changes of genes critical for islet function. These histone marks were enriched at critical transcription factor-binding motifs, such as Hoxa9, C/EBP-β, Gata1, Foxo1, E2f1, E2f3, and Mafb. In addition, our chromatin immunoprecipitation sequencing data revealed multiple potential bivalent genes whose poised states changed with maturation. Collectively, our current study identified critical novel pathways for mature islet function and suggested a role for histone modifications in regulating islet development and maturation.

Epigenetic Regulation of β Cell Identity and Dysfunction

β cell dysfunction and failure are driving forces of type 2 diabetes mellitus (T2DM) pathogenesis. Investigating the underlying mechanisms of β cell dysfunction may provide novel targets for the development of next generation therapy for T2DM. Epigenetics is the study of gene expression changes that do not involve DNA sequence changes, including DNA methylation, histone modification, and non-coding RNAs. Specific epigenetic signatures at all levels, including DNA methylation, chromatin accessibility, histone modification, and non-coding RNA, define β cell identity during embryonic development, postnatal maturation, and maintain β cell function at homeostatic states. During progression of T2DM, overnutrition, inflammation, and other types of stress collaboratively disrupt the homeostatic epigenetic signatures in β cells. Dysregulated epigenetic signatures, and the associating transcriptional outputs, lead to the dysfunction and eventual loss of β cells. In this review, we will summarize recent discoveries of the establishment and disruption of β cell-specific epigenetic signatures, and discuss the potential implication in therapeutic development.

Epigenetics, microRNA and Metabolic Syndrome: A Comprehensive Review

Epigenetics refers to the DNA chemistry changes that result in the modification of gene transcription and translation independently of the underlying DNA coding sequence. Epigenetic modifications are reported to involve various molecular mechanisms, including classical epigenetic changes affecting DNA methylation and histone modifications and small RNA-mediated processes, particularly that of microRNAs. Epigenetic changes are reversible and are closely interconnected. They are recognised to play a critical role as mediators of gene regulation, and any alteration in these mechanisms has been identified to mediate various pathophysiological conditions. Moreover, genetic predisposition and environmental factors, including dietary alterations, lifestyle or metabolic status, are identified to interact with the human epigenome, highlighting the importance of epigenetic factors as underlying processes in the aetiology of various diseases such as MetS. This review will reflect on how both the classical and microRNA-regulated epigenetic changes are associated with the pathophysiology of metabolic syndrome. We will then focus on the various aspects of epigenetic-based strategies used to modify MetS outcomes, including epigenetic diet, epigenetic drugs, epigenome editing tools and miRNA-based therapies.

Groucho co-repressor proteins regulate β cell development and proliferation by repressing Foxa1 in the developing mouse pancreas

Groucho-related genes (GRGs) are transcriptional co-repressors that are crucial for many developmental processes. Several essential pancreatic transcription factors are capable of interacting with GRGs; however, the in vivo role of GRG-mediated transcriptional repression in pancreas development is still not well understood. In this study, we used complex mouse genetics and transcriptomic analyses to determine that GRG3 is essential for β cell development, and in the absence of Grg3 there is compensatory upregulation of Grg4 Grg3/4 double mutant mice have severe dysregulation of the pancreas gene program with ectopic expression of canonical liver genes and Foxa1, a master regulator of the liver program. Neurod1, an essential β cell transcription factor and predicted target of Foxa1, becomes downregulated in Grg3/4 mutants, resulting in reduced β cell proliferation, hyperglycemia, and early lethality. These findings uncover novel functions of GRG-mediated repression during pancreas development.

The Contribution of Transcriptional Coregulators in the Maintenance of β-cell Function and Identity

Islet β-cell dysfunction that leads to impaired insulin secretion is a principal source of pathology of diabetes. In type 2 diabetes, this breakdown in β-cell health is associated with compromised islet-enriched transcription factor (TF) activity that disrupts gene expression programs essential for cell function and identity. TF activity is modulated by recruited coregulators that govern activation and/or repression of target gene expression, thereby providing a supporting layer of control. To date, more than 350 coregulators have been discovered that coordinate nucleosome rearrangements, modify histones, and physically bridge general transcriptional machinery to recruited TFs; however, relatively few have been attributed to β-cell function. Here, we will describe recent findings on those coregulators with direct roles in maintaining islet β-cell health and identity and discuss how disruption of coregulator activity is associated with diabetes pathogenesis.

Pancreas development and the Polycomb group protein complexes

The dual nature of pancreatic tissue permits both endocrine and exocrine functions. Enzymatic secretions by the exocrine pancreas help digestive processes while the pancreatic hormones regulate glucose homeostasis and energy metabolism. Pancreas organogenesis is defined by a conserved array of signaling pathways that act on common gut progenitors to bring about the generation of diverse cell types. Multiple cellular processes characterize development of the mature organ. These processes are mediated by signaling pathways that regulate lineage-specific transcription factors and chromatin modifications guiding long-term gene expression programs. The chromatin landscape is altered chiefly by DNA or histone modifications, chromatin remodelers, and non-coding RNAs. Amongst histone modifiers, several studies have identified Polycomb group (PcG) proteins as crucial determinants mediating transcriptional repression of genes involved in developmental processes. Although PcG-mediated chromatin modifications define cellular transitions and influence cell identity of multipotent progenitors, much remains to be understood regarding coordination between extracellular signals and their impact on Polycomb functions during the pancreas lineage progression. In this review, we discuss interactions between sequence-specific DNA binding proteins and chromatin regulators underlying pancreas development and insulin producing β-cells, with particular focus on Polycomb group proteins. Understanding such basic molecular mechanisms would improve current strategies for stem cell-based differentiation while also help elucidate the pathogenesis of several pancreas-related maladies, including diabetes and pancreatic cancer.

Epigenetics in β-cell adaptation and type 2 diabetes

Healthy pancreatic β-cells adapt to systemic insulin resistance to maintain normal blood glucose levels, and a failure of this adaptation leads to type 2 diabetes in humans. While genome-wide association studies have uncovered genetic variants that are associated with type 2 diabetes, it is still insufficient to explain the high prevalence of this disease. Epigenetics is the study of gene expression changes that do not involve DNA sequence alterations such as DNA methylation, histone modification, and non-coding RNAs. Over the last decade, a large number of studies have reported on the role of epigenetics in β-cell biology. In this review, we summarize the epigenetic mechanisms in β-cell adaptation and type 2 diabetes, including alterations in three-dimensional chromatin structure and RNA modifications.

Epigenetic Modifications Associated with the Pathogenesis of Type 2 Diabetes Mellitus

BACKGROUND AND OBJECTIVE

Type 2 diabetes mellitus (T2DM) is a multifactorial metabolic disorder. Pancreatic β-cell dysfunction and insulin resistance are the most common and crucial events of T2DM. Increasing evidence suggests the association of epigenetic modifications with the pathogenesis of T2DM through the changes in important biological processes including pancreatic β- cell differentiation, development and maintenance of normal β-cell function. Insulin sensitivity by the peripheral glucose uptake tissues is also changed by the altered epigenetic mechanisms. In this review, we discussed the major epigenetic alterations and their effects on β-cell function, insulin secretion and insulin resistance in context of T2DM.

METHODS

We investigated the presently available epigenetic modifications including DNA methylation, posttranslational histone modifications, ATP-dependent chromatin remodeling and non-coding RNAs related to the pathogenesis of T2DM. Published literatures on this topic were searched both on Google Scholar and Pubmed with related keywords and investigated for relevant information.

RESULTS

The epigenetic modifications introduce changes in gene expression which are essential for appropriate β-cell development and functions, insulin secretion and sensitivity resulting in the pathogenesis of T2DM. Interestingly, T2DM could also be a prominent reason for the mentioned epigenetic alterations.

CONCLUSION

This review article emphasized on the epigenetic modifications associated with T2DM and discussed the consequences in deterioration of the disease condition.

Effects and mechanism of stem cells from human exfoliated deciduous teeth combined with hyperbaric oxygen therapy in type 2 diabetic rats

OBJECTIVES

Mesenchymal stem cells (MSCs) are potentially ideal for type 2 diabetes treatment, owing to their multidirectional differentiation ability and immunomodulatory properties. Here we investigated whether the stem cells from human exfoliated deciduous teeth (SHED) in combination with hyperbaric oxygen (HBO) could treat type 2 diabetic rats, and explored the underlying mechanism.

METHODS

SD rats were used to generate a type 2 diabetes model, which received stem cell therapy, HBO therapy, or both together. Before and after treatment, body weight, blood glucose, and serum insulin, blood lipid, pro-inflammatory cytokines (tumor necrosis factor-alpha and interleukin-6), and urinary proteins were measured and compared. After 6 weeks, rats were sacrificed and their organs were subjected to hematoxylin and eosin staining and immunofluorescence staining for insulin and glucagon; apoptosis and proliferation were analyzed in islet cells. Structural changes in islets were observed under an electron microscope. Expression levels of Pdx1, Ngn3, and Pax4 mRNAs in the pancreas were assessed by real-time quantitative polymerase chain reaction (RT-qPCR).

RESULTS

In comparison with diabetic mice, those treated with the combination or SHE therapy showed decreased blood glucose, insulin resistance, serum lipids, and pro-inflammatory cytokines and increased body weight and serum insulin. The morphology and structure of pancreatic islets improved, as evident from an increase in insulin-positive cells and a decrease in glucagon-positive cells. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining of islet cells revealed the decreased apoptosis index, while Ki67 and proliferating cell nuclear antigen staining showed increased proliferation index. Pancreatic expression of Pdx1, Ngn3, and Pax4 was upregulated.

CONCLUSION

SHED combined with HBO therapy was effective for treating type 2 diabetic rats. The underlying mechanism may involve SHED-mediated increase in the proliferation and trans-differentiation of islet β-cells and decrease in pro-inflammatory cytokines and apoptosis of islets.

The Emerging Roles of ATP-Dependent Chromatin Remodeling Complexes in Pancreatic Cancer

Pancreatic cancer is an aggressive cancer with low survival rates. Genetic and epigenetic dysregulation has been associated with the initiation and progression of pancreatic tumors. Multiple studies have pointed to the involvement of aberrant chromatin modifications in driving tumor behavior. ATP-dependent chromatin remodeling complexes regulate chromatin structure and have critical roles in stem cell maintenance, development, and cancer. Frequent mutations and chromosomal aberrations in the genes associated with subunits of the ATP-dependent chromatin remodeling complexes have been detected in different cancer types. In this review, we summarize the current literature on the genomic alterations and mechanistic studies of the ATP-dependent chromatin remodeling complexes in pancreatic cancer. Our review is focused on the four main subfamilies: SWItch/sucrose non-fermentable (SWI/SNF), imitation SWI (ISWI), chromodomain-helicase DNA-binding protein (CHD), and INOsitol-requiring mutant 80 (INO80). Finally, we discuss potential novel treatment options that use small molecules to target these complexes.

Unwinding chromatin at the right places: how BAF is targeted to specific genomic locations during development

The BAF (SWI/SNF) chromatin remodeling complex plays a crucial role in modulating spatiotemporal gene expression during mammalian development. Although its remodeling activity was characterized in vitro decades ago, the complex actions of BAF in vivo have only recently begun to be unraveled. In living cells, BAF only binds to and remodels a subset of genomic locations. This selectivity of BAF genomic targeting is crucial for cell-type specification and for mediating precise responses to environmental signals. Here, we provide an overview of the distinct molecular mechanisms modulating BAF chromatin binding, including its combinatory assemblies, DNA/histone modification-binding modules and post-translational modifications, as well as its interactions with proteins, RNA and lipids. This Review aims to serve as a primer for future studies to decode the actions of BAF in developmental processes.

The Pdx1-Bound Swi/Snf Chromatin Remodeling Complex Regulates Pancreatic Progenitor Cell Proliferation and Mature Islet β-Cell Function

Transcription factors positively and/or negatively impact gene expression by recruiting coregulatory factors, which interact through protein-protein binding. Here we demonstrate that mouse pancreas size and islet β-cell function are controlled by the ATP-dependent Swi/Snf chromatin remodeling coregulatory complex that physically associates with Pdx1, a diabetes-linked transcription factor essential to pancreatic morphogenesis and adult islet cell function and maintenance. Early embryonic deletion of just the Swi/Snf Brg1 ATPase subunit reduced multipotent pancreatic progenitor cell proliferation and resulted in pancreas hypoplasia. In contrast, removal of both Swi/Snf ATPase subunits, Brg1 and Brm, was necessary to compromise adult islet β-cell activity, which included whole-animal glucose intolerance, hyperglycemia, and impaired insulin secretion. Notably, lineage-tracing analysis revealed Swi/Snf-deficient β-cells lost the ability to produce the mRNAs for Ins and other key metabolic genes without effecting the expression of many essential islet-enriched transcription factors. Swi/Snf was necessary for Pdx1 to bind to the Ins gene enhancer, demonstrating the importance of this association in mediating chromatin accessibility. These results illustrate how fundamental the Pdx1:Swi/Snf coregulator complex is in the pancreas, and we discuss how disrupting their association could influence type 1 and type 2 diabetes susceptibility.

Epigenetics and Type 2 Diabetes Risk

PURPOSE OF REVIEW

The influence of environmental factors on type 2 diabetes (T2D) risk is now well recognized and highlights the contribution of epigenetic mechanisms. This review will focus on the role of epigenetic factors in the risk and pathogenesis of T2D.

RECENT FINDINGS

Epigenetic dysregulation has emerged as a key mechanism underpinning the pathogenesis of T2D and its complications. Environmental variations, including alterations in lifestyle, nutrition, and metabolic demands during prenatal and postnatal life can induce epigenetic changes that may impact glucose homeostasis and the function of different metabolic organs. Accumulating data continues to uncover the specific pathways that are epigenetically dysregulated in T2D, providing an opportunity for therapeutic targeting. Environmental changes can disrupt specific epigenetic mechanisms underlying metabolic homeostasis, thus contributing to T2D pathogenesis. Such epigenetic changes can be transmitted to the next generation, contributing to the inheritance of T2D risk. Recent advances in epigenome-wide association studies and epigenetic editing tools present the attractive possibility of identifying epimutations associated with T2D, correcting specific epigenetic alterations, and designing novel epigenetic biomarkers and interventions for T2D.

LIM-domain transcription complexes interact with ring-finger ubiquitin ligases and thereby impact islet β-cell function

Diabetes is characterized by a loss of β-cell mass, and a greater understanding of the transcriptional mechanisms governing β-cell function is required for future therapies. Previously, we reported that a complex of the Islet-1 (Isl1) transcription factor and the co-regulator single-stranded DNA-binding protein 3 (SSBP3) regulates the genes necessary for β-cell function, but few proteins are known to interact with this complex in β-cells. To identify additional components, here we performed SSBP3 reverse-cross-linked immunoprecipitation (ReCLIP)- and MS-based experiments with mouse β-cell extracts and compared the results with those from our previous Isl1 ReCLIP study. Our analysis identified the E3 ubiquitin ligases ring finger protein 20 (RNF20) and RNF40, factors that in nonpancreatic cells regulate transcription through imparting monoubiquitin marks on histone H2B (H2Bub1), a precursor to histone H3 lysine 4 trimethylation (H3K4me3). We hypothesized that RNF20 and RNF40 regulate similar genes as those regulated by Isl1 and SSBP3 and are important for β-cell function. We observed that Rnf20 and Rnf40 depletion reduces β-cell H2Bub1 marks and uncovered several target genes, including glucose transporter 2 (Glut2), MAF BZIP transcription factor A (MafA), and uncoupling protein 2 (Ucp2). Strikingly, we also observed that Isl1 and SSBP3 depletion reduces H2Bub1 and H3K4me3 marks, suggesting that they have epigenetic roles. We noted that the RNF complex is required for glucose-stimulated insulin secretion and normal mitochondrial reactive oxygen species levels. These findings indicate that RNF20 and RNF40 regulate β-cell gene expression and insulin secretion and establish a link between Isl1 complexes and global cellular epigenetics.

Epigenetics of metabolic syndrome

The dramatic increase in global prevalence of metabolic disease is inexplicable when considering only environmental or only genetic factors, leading to the need to explore the possible roles of epigenetic factors. A great deal of progress has been made in this interdisciplinary field in recent years, with many studies investigating various aspects of the metabolic syndrome and its associated epigenetic changes. Rodent models of metabolic diseases have been particularly illuminating because of the ability to leverage tools such as genetic and environmental modifications. The current review summarizes recent breakthroughs regarding epigenetic markers in studies of obesity, Type II diabetes, and cardiovascular disease, the three major disorders associated with metabolic syndrome. We also discuss open questions and future directions for integrating genomic, epigenomic, and phenotypic big biodata toward understanding metabolic syndrome etiology.

The BRG1/SOX9 axis is critical for acinar cell-derived pancreatic tumorigenesis

Chromatin remodeler Brahma related gene 1 (BRG1) is silenced in approximately 10% of human pancreatic ductal adenocarcinomas (PDAs). We previously showed that BRG1 inhibits the formation of intraductal pancreatic mucinous neoplasm (IPMN) and that IPMN-derived PDA originated from ductal cells. However, the role of BRG1 in pancreatic intraepithelial neoplasia-derived (PanIN-derived) PDA that originated from acinar cells remains elusive. Here, we found that exclusive elimination of Brg1 in acinar cells of Ptf1a-CreER; KrasG12D; Brg1fl/fl mice impaired the formation of acinar-to-ductal metaplasia (ADM) and PanIN independently of p53 mutation, while PDA formation was inhibited in the presence of p53 mutation. BRG1 bound to regions of the Sox9 promoter to regulate its expression and was critical for recruitment of upstream regulators, including PDX1, to the Sox9 promoter and enhancer in acinar cells. SOX9 expression was downregulated in BRG1-depleted ADMs/PanINs. Notably, Sox9 overexpression canceled this PanIN-attenuated phenotype in KBC mice. Furthermore, Brg1 deletion in established PanIN by using a dual recombinase system resulted in regression of the lesions in mice. Finally, BRG1 expression correlated with SOX9 expression in human PDAs. In summary, BRG1 is critical for PanIN initiation and progression through positive regulation of SOX9. Thus, the BRG1/SOX9 axis is a potential target for PanIN-derived PDA.

Clec16a, Nrdp1, and USP8 Form a Ubiquitin-Dependent Tripartite Complex That Regulates β-Cell Mitophagy

Mitophagy is a cellular quality-control pathway, which is essential for elimination of unhealthy mitochondria. While mitophagy is critical to pancreatic β-cell function, the posttranslational signals governing β-cell mitochondrial turnover are unknown. Here, we report that ubiquitination is essential for the assembly of a mitophagy regulatory complex, comprised of the E3 ligase Nrdp1, the deubiquitinase enzyme USP8, and Clec16a, a mediator of β-cell mitophagy with unclear function. We discover that the diabetes gene Clec16a encodes an E3 ligase, which promotes nondegradative ubiquitin conjugates to direct its mitophagy effectors and stabilize the Clec16a-Nrdp1-USP8 complex. Inhibition of the Clec16a pathway by the chemotherapeutic lenalidomide, a selective ubiquitin ligase inhibitor associated with new-onset diabetes, impairs β-cell mitophagy, oxygen consumption, and insulin secretion. Indeed, patients treated with lenalidomide develop compromised β-cell function. Moreover, the β-cell Clec16a-Nrdp1-USP8 mitophagy complex is destabilized and dysfunctional after lenalidomide treatment as well as after glucolipotoxic stress. Thus, the Clec16a-Nrdp1-USP8 complex relies on ubiquitin signals to promote mitophagy and maintain mitochondrial quality control necessary for optimal β-cell function.

Epigenetics in formation, function, and failure of the endocrine pancreas

Background

Epigenetics, in the broadest sense, governs all aspects of the life of any multicellular organism, as it controls how differentiated cells arrive at their unique phenotype during development and differentiation, despite having a uniform (with some exceptions such as T-cells and germ cells) genetic make-up. The endocrine pancreas is no exception. Transcriptional regulators and epigenetic modifiers shape the differentiation of the five major endocrine cell types from their common precursor in the fetal pancreatic bud. Beyond their role in cell differentiation, interactions of the organism with the environment are also often encoded into permanent or semi-permanent epigenetic marks and affect cellular behavior and organismal health. Epigenetics is defined as any heritable – at least through one mitotic cell division – change in phenotype or trait that is not the result of a change in genomic DNA sequence, and it forms the basis that mediates the environmental impact on diabetes susceptibility and islet function.

Scope of review

We will summarize the impact of epigenetic regulation on islet cell development, maturation, function, and pathophysiology. We will briefly recapitulate the major epigenetic marks and their relationship to gene activity, and outline novel strategies to employ targeted epigenetic modifications as a tool to improve islet cell function.

Major conclusions

The improved understanding of the epigenetic underpinnings of islet cell differentiation, function and breakdown, as well as the development of innovative tools for their manipulation, is key to islet cell biology and the discovery of novel approaches to therapies for islet cell failure.

LDB1 Regulates Energy Homeostasis During Diet-Induced Obesity

The broadly expressed transcriptional coregulator LDB1 is essential for β-cell development and glucose homeostasis. However, it is unclear whether LDB1 has metabolic roles beyond the β-cell, especially under metabolic stress. Global Ldb1 deletion results in early embryonic lethality; thus, we used global heterozygous Ldb1+/- and inducible β-cell-specific Ldb1-deficient (Ldb1Δβ-cell) mice. We assessed glucose and insulin tolerance, body composition, feeding, and energy expenditure during high-fat diet exposure. Brown adipose tissue (BAT) biology was evaluated by thermogenic gene expression and LDB1 chromatin immunoprecipitation analysis. We found that partial loss of Ldb1 does not impair the maintenance of glucose homeostasis; rather, we observed improved insulin sensitivity in these mice. Partial loss of Ldb1 also uncovered defects in energy expenditure in lean and diet-induced obese (DIO) mice. This decreased energy expenditure during DIO was associated with significantly altered BAT gene expression, specifically Cidea, Elovl3, Cox7a1, and Dio2. Remarkably, the observed changes in energy balance during DIO were absent in Ldb1Δβ-cell mice, despite a similar reduction in plasma insulin, suggesting a role for LDB1 in BAT. Indeed, LDB1 is expressed in brown adipocytes and occupies a regulatory domain of Elovl3, a gene crucial to normal BAT function. We conclude that LDB1 regulates energy homeostasis, in part through transcriptional modulation of critical regulators in BAT function.

Mafa Enables Pdx1 to Effectively Convert Pancreatic Islet Progenitors and Committed Islet α-Cells Into β-Cells In Vivo

Among the therapeutic avenues being explored for replacement of the functional islet β-cell mass lost in type 1 diabetes (T1D), reprogramming of adult cell types into new β-cells has been actively pursued. Notably, mouse islet α-cells will transdifferentiate into β-cells under conditions of near β-cell loss, a condition similar to T1D. Moreover, human islet α-cells also appear to poised for reprogramming into insulin-positive cells. Here we have generated transgenic mice conditionally expressing the islet β-cell-enriched Mafa and/or Pdx1 transcription factors to examine their potential to transdifferentiate embryonic pan-islet cell Ngn3-positive progenitors and the later glucagon-positive α-cell population into β-cells. Mafa was found to both potentiate the ability of Pdx1 to induce β-cell formation from Ngn3-positive endocrine precursors and enable Pdx1 to produce β-cells from α-cells. These results provide valuable insight into the fundamental mechanisms influencing islet cell plasticity in vivo.

PAX4 promotes PDX1-induced differentiation of mesenchymal stem cells into insulin-secreting cells

A shortage of postmortem pancreatic tissue for islet isolation impedes the application of cell replacement therapy in patients with diabetes. As an alternative for islet cell transplantation, transcription factors, including PDX1, PAX4, and neurogenin-3, that aid in the formation of insulin-producing β cells during development have been investigated. The present study evaluated the effects of PAX4 and PDX1 on the differentiation of mesenchymal stem cells (MSCs) into insulin-producing β-like cells in vitro using recombinant adenoviruses carrying PDX1 or PDX1 plus PAX4. RT-PCR, Western blot, and immunofluorescence assays were used to detect the expression levels of relevant genes and proteins, and enzyme-linked immunosorbent assays were used to determine the amount of insulin and C-peptide secreted by the virus-infected cells following stimulation with high glucose. The results showed that PAX4 markedly enhanced the propensity of PDX1-positive MSCs to form mature islet-like clusters and functional insulin-producing β-like cells. Our findings provide a novel foundation for generating β-like cells from MSCs with PAX4 and PDX1 for future clinical application.

Epigenetic control of β-cell function and failure

Type 2 diabetes is a highly heritable disease, but only ∼15% of this heritability can be explained by known genetic variant loci. In fact, body mass index is more predictive of diabetes than any of the common risk alleles identified by genome-wide association studies. This discrepancy may be explained by epigenetic inheritance, whereby changes in gene regulation can be passed along to offspring. Epigenetic changes throughout an organism's lifetime, based on environmental factors such as chemical exposures, diet, physical activity, and age, can also affect gene expression and susceptibility to diabetes. Recently, novel genome-wide assays of epigenetic marks have resulted in a greater understanding of how genetics, epigenetics, and the environment interact in the development and inheritance of diabetes.

The mammal-specific Pdx1 Area II enhancer has multiple essential functions in early endocrine cell specification and postnatal β-cell maturation

The transcription factor Pdx1 is required for multiple aspects of pancreatic organogenesis. It remains unclear to what extent Pdx1 expression and function depend upon trans-activation through 5' conserved cis-regulatory regions and, in particular, whether the mammal-specific Area II (-2139 to -1958 bp) affects minor or major aspects of organogenesis. We show that Area II is a primary effector of endocrine-selective transcription in epithelial multipotent cells, nascent endocrine progenitors, and differentiating and mature β cells in vivo Pdx1^ΔAREAII/- mice exhibit a massive reduction in endocrine progenitor cells and progeny hormone-producing cells, indicating that Area II activity is fundamental to mounting an effective endocrine lineage-specification program within the multipotent cell population. Creating an Area II-deleted state within already specified Neurog3-expressing endocrine progenitor cells increased the proportion of glucagon⁺ α relative to insulin⁺ β cells, associated with the transcriptional and epigenetic derepression of the α-cell-determining Arx gene in endocrine progenitors. There were also glucagon and insulin co-expressing cells, and β cells that were incapable of maturation. Creating the Pdx1^ΔAREAII state after cells entered an insulin-expressing stage led to immature and dysfunctional islet β cells carrying abnormal chromatin marking in vital β-cell-associated genes. Therefore, trans-regulatory integration through Area II mediates a surprisingly extensive range of progenitor and β-cell-specific Pdx1 functions.

Alterations of Epigenetic Regulators in Pancreatic Cancer and Their Clinical Implications

Pancreatic cancer is one of the most aggressive human cancer types with a five-year survival less than 7%. Emerging evidence revealed that many genetic alterations in pancreatic cancer target epigenetic regulators. Some of these mutations are driver mutations in cancer development. Several most important mechanisms of epigenetic regulations include DNA methylation, histone modifications (methylation, acetylation, and ubiquitination), chromatin remodeling, and non-coding ribonucleic acids (RNAs). These modifications can alter chromatin structure and promoter accessibility, and thus lead to aberrant gene expression. However, exactly how these alterations affect epigenetic reprogramming in pancreatic cancer cells and in different stages of tumor development is still not clear. This mini-review summarizes the current knowledge of epigenetic alterations in pancreatic cancer development and progression, and discusses the clinical applications of epigenetic regulators as diagnostic biomarkers and therapeutic targets in pancreatic cancer.

β-cell differentiation status in type 2 diabetes

Type 2 diabetes (T2D) affects 415 million people worldwide and is characterized by chronic hyperglycaemia and insulin resistance, progressing to insufficient insulin production, as a result of β-cell failure. Over time, chronic hyperglycaemia can ultimately lead to loss of β-cell function, leaving patients insulin-dependent. Until recently the loss of β-cell mass seen in T2D was considered to be the result of increased rates of apoptosis; however, it has been proposed that apoptosis alone cannot account for the extent of β-cell mass loss seen in the disease, and that a loss of function may also occur as a result of changes in β-cell differentiation status. In the present review, we consider current knowledge of determinants of β-cell fate in the context of understanding its relevance to disease process in T2D, and also the impact of a diabetogenic environment (hyperglycaemia, hypoxia, inflammation and dyslipidaemia) on the expression of genes involved in maintenance of β-cell identity. We describe current knowledge of the impact of the diabetic microenvironment on gene regulatory processes such alternative splicing, the expression of disallowed genes and epigenetic modifications. Elucidating the molecular mechanisms that underpin changes to β-cell differentiation status and the concomitant β-cell failure offers potential treatment targets for the future management of patients with T2D.

Impact of Pdx1-associated chromatin modifiers on islet β-cells

Diabetes mellitus arises from insufficient insulin secretion from pancreatic islet β-cells. In type 2 diabetes (T2D), β-cell dysfunction is associated with inactivation and/or loss of transcription factor (TF) activity, including Pdx1. Notably, this particular TF is viewed as a master regulator of pancreas development and islet β-cell formation, identity and function. TFs, like Pdx1, recruit coregulators to transduce activating and/or repressing signals to the general transcriptional machinery for controlling gene expression, including modifiers of DNA, histones and nucleosome architecture. These coregulators impart a secondary layer of control that can be exploited to modulate TF activity. In this review, we describe Pdx1-recruited coregulators that impact chromatin structure, consequently influencing normal β-cell function and likely Pdx1 activity in pathophysiological settings.

Mass production of functional human pancreatic β-cells: why and how?

Diabetes (either type 1 or type 2) is due to insufficient functional β-cell mass. Research has, therefore, aimed to discover new ways to maintain or increase either β-cell mass or function. For this purpose, rodents have mainly been used as model systems and a large number of discoveries have been made. Meanwhile, although we have learned that rodent models represent powerful systems to model β-cell development, function and destruction, we realize that there are limitations when attempting to transfer the data to what is occurring in humans. Indeed, while human β-cells share many similarities with rodent β-cells, they also differ on a number of important parameters. In this context, developing ways to study human β-cell development, function and death represents an important challenge. This review will describe recent data on the development and use of convenient sources of human β-cells that should be useful tools to discover new ways to modulate functional β-cell mass in humans.

The Role of SWI/SNF Chromatin Remodeling Complexes in Hormone Crosstalk

SWI/SNF-type ATP-dependent chromatin remodeling complexes (CRCs) are evolutionarily conserved multiprotein machineries controlling DNA accessibility by regulating chromatin structure. We summarize here recent advances highlighting the role of SWI/SNF in the regulation of hormone signaling pathways and their crosstalk in Arabidopsis thaliana. We discuss the functional interdependences of SWI/SNF complexes and key elements regulating developmental and hormone signaling pathways by indicating intriguing similarities and differences in plants and humans, and summarize proposed mechanisms of SWI/SNF action on target loci. We postulate that, given their viability, several plant SWI/SNF mutants may serve as an attractive model for searching for conserved functions of SWI/SNF CRCs in hormone signaling, cell cycle control, and other regulatory pathways.

Chromatin Regulators in Pancreas Development and Diabetes

The chromatin landscape of a cell is dynamic and can be altered by chromatin regulators that control nucleosome placement and DNA or histone modifications. Together with transcription factors, these complexes help dictate the transcriptional output of a cell and, thus, balance cell proliferation and differentiation while restricting tissue-specific gene expression. In this review, we describe current research on chromatin regulators and their roles in pancreas development and the maintenance of mature β cell function, which, once elucidated, will help us better understand how β cell differentiation occurs and is maintained. These studies have so far implicated proteins from several complexes that regulate DNA methylation, nucleosome remodeling, and histone acetylation and methylation that could become promising targets for diabetes therapy and stem cell differentiation.

Implication of epigenetics in pancreas development and disease

Pancreas development is controlled by a complex interaction of signaling pathways and transcription factor networks that determine pancreatic specification and differentiation of exocrine and endocrine cells. Epigenetics adds a new layer of gene regulation. DNA methylation, histone modifications and non-coding RNAs recently appeared as important epigenetic factors regulating pancreas development. In this review, we report recent findings obtained by analyses in model organisms as well as genome-wide approaches that demonstrate the role of these epigenetic regulators in the control of exocrine and endocrine cell differentiation, identity, function, proliferation and regeneration. We also highlight how altered epigenetic processes contribute to pancreatic disorders: diabetes and pancreatic cancer. Uncovering these epigenetic events can help to better understand these diseases, provide novel therapeutical targets for their treatment, and improve cell-based therapies for diabetes.

SSBP3 Interacts With Islet-1 and Ldb1 to Impact Pancreatic β-Cell Target Genes

Islet-1 (Isl1) is a Lin11, Isl1, Mec3 (LIM)-homeodomain transcription factor important for pancreatic islet cell development, maturation, and function, which largely requires interaction with the LIM domain-binding protein 1 (Ldb1) coregulator. In other tissues, Ldb1 and Isl1 interact with additional factors to mediate target gene transcription, yet few protein partners are known in β-cells. Therefore, we hypothesize that Ldb1 and Isl1 participate in larger regulatory complexes to impact β-cell gene expression. To test this, we used cross-linked immunoprecipitation and mass spectrometry to identify interacting proteins from mouse β-cells. Proteomic datasets revealed numerous interacting candidates, including a member of the single-stranded DNA-binding protein (SSBP) coregulator family, SSBP3. SSBPs potentiate LIM transcription factor complex activity and stability in other tissues. However, nothing was known of SSBP3 interaction, expression, or activity in β-cells. Our analyses confirmed that SSBP3 interacts with Ldb1 and Isl1 in β-cell lines and in mouse and human islets and demonstrated SSBP3 coexpression with Ldb1 and Isl1 pancreas tissue. Furthermore, β-cell line SSBP3 knockdown imparted mRNA deficiencies similar to those observed upon Ldb1 reduction in vitro or in vivo. This appears to be (at least) due to SSBP3 occupancy of known Ldb1-Isl1 target promoters, including MafA and Glp1r. This study collectively demonstrates that SSBP3 is a critical component of Ldb1-Isl1 regulatory complexes, required for expression of critical β-cell target genes.