Maintenance of β-cell maturity and plasticity in the adult pancreas: developmental biology concepts in adult physiology

Molecular Mechanisms Linking Diabetes with Increased Risk of Thrombosis

This review will provide an overview of what is currently known about mechanisms linking poor glycaemic control with increased thrombotic risk. The leading causes of death in people with diabetes are strokes and cardiovascular disease. Significant morbidity is associated with an increased risk of thrombosis, resulting in myocardial infarction, ischaemic stroke, and peripheral vascular disease, along with the sequelae of these events, including loss of functional ability, heart failure, and amputations. While the increased platelet activity, pro-coagulability, and endothelial dysfunction directly impact this risk, the molecular mechanisms linking poor glycaemic control with increased thrombotic risk remain unclear. This review highlights the complex mechanisms underlying thrombosis prevalence in individuals with diabetes and hyperglycaemia. Post-translational modifications, such as O-GlcNAcylation, play a crucial role in controlling protein function in diabetes. However, the role of O-GlcNAcylation remains poorly understood due to its intricate regulation and the potential involvement of multiple variables. Further research is needed to determine the precise impact of O-GlcNAcylation on specific disease processes.

Presence of immunogenic alternatively spliced insulin gene product in human pancreatic delta cells

AIMS/HYPOTHESIS

Transcriptome analyses revealed insulin-gene-derived transcripts in non-beta endocrine islet cells. We studied alternative splicing of human INS mRNA in pancreatic islets.

METHODS

Alternative splicing of insulin pre-mRNA was determined by PCR analysis performed on human islet RNA and single-cell RNA-seq analysis. Antisera were generated to detect insulin variants in human pancreatic tissue using immunohistochemistry, electron microscopy and single-cell western blot to confirm the expression of insulin variants. Cytotoxic T lymphocyte (CTL) activation was determined by MIP-1β release.

RESULTS

We identified an alternatively spliced INS product. This variant encodes the complete insulin signal peptide and B chain and an alternative C-terminus that largely overlaps with a previously identified defective ribosomal product of INS. Immunohistochemical analysis revealed that the translation product of this INS-derived splice transcript was detectable in somatostatin-producing delta cells but not in beta cells; this was confirmed by light and electron microscopy. Expression of this alternatively spliced INS product activated preproinsulin-specific CTLs in vitro. The exclusive presence of this alternatively spliced INS product in delta cells may be explained by its clearance from beta cells by insulin-degrading enzyme capturing its insulin B chain fragment and a lack of insulin-degrading enzyme expression in delta cells.

CONCLUSIONS/INTERPRETATION

Our data demonstrate that delta cells can express an INS product derived from alternative splicing, containing both the diabetogenic insulin signal peptide and B chain, in their secretory granules. We propose that this alternative INS product may play a role in islet autoimmunity and pathology, as well as endocrine or paracrine function or islet development and endocrine destiny, and transdifferentiation between endocrine cells. INS promoter activity is not confined to beta cells and should be used with care when assigning beta cell identity and selectivity.

DATA AVAILABILITY

The full EM dataset is available via www.nanotomy.org (for review: http://www.nanotomy.org/OA/Tienhoven2021SUB/6126-368/ ). Single-cell RNA-seq data was made available by Segerstolpe et al [13] and can be found at https://sandberglab.se/pancreas . The RNA and protein sequence of INS-splice was uploaded to GenBank (BankIt2546444 INS-splice OM489474).

The pathological characters of islets aging in old rhesus monkeys

The loss of β cell mass and function in aged population plays a critical role in the prevalence of Type 2 diabetes. However, the causal relations between aging and age-related pancreatic islets degeneration still have not been fully elucidated. Rhesus monkey is one of the most ideal nonhuman primate animal models of a wide range of human diseases, including diabetes and aging-related diseases. In the present study, we observed the overall physiological function, glycolipid metabolism and islet function of middle-age and elderly rhesus monkeys, and compared their gene expression profiles by transcriptome sequencing of isolated islets. Through these analyses, we are aimed to evaluate the pathological characters of islets of old rhesus monkeys in the process of aging, and to provide some tips for the prevention and treatment of diabetes in the elderly population. The results suggested that there was no significant physiological disorder in monkeys of approximately 20 years old, except the glucose metabolism was mildly disturbed. In pancreas tissues and isolated islets of elderly monkeys, we found that the islets sizes were distinctly decreased, and the insulin secretion was compromised. Notably, the islets fibrosis and proportion of insulin/glucagon co-expressing cells increased significantly. Moreover, the β cell identity markers, transcription factors PDX1 and Nkx6.1 were losing with advancing age. Analysis of the RNA sequencing of isolated islets showed the genes related to type 1 diabetes and β cell function changed markedly. In conclusion, we found that in the elderly monkeys around 20 years old, the decreased islets size and compromised insulin secretion may contribute to the disturbed glucose metabolism, and the loss of β cell identity markers is a typical molecular change of islet senescence.

Dynamic Ins2 Gene Activity Defines β-Cell Maturity States

Transcriptional and functional cellular specialization has been described for insulin-secreting β-cells of the endocrine pancreas. However, it is not clear whether β-cell heterogeneity is stable or reflects dynamic cellular states. We investigated the temporal kinetics of endogenous insulin gene activity using live cell imaging, with complementary experiments using FACS and single-cell RNA sequencing, in β-cells from Ins2GFP knockin mice. In vivo staining and FACS analysis of islets from Ins2GFP mice confirmed that at a given moment, ∼25% of β-cells exhibited significantly higher activity at the evolutionarily conserved insulin gene, Ins2. Live cell imaging over days captured Ins2 gene activity dynamics in single β-cells. Autocorrelation analysis revealed a subset of oscillating cells, with mean oscillation periods of 17 h. Increased glucose concentrations stimulated more cells to oscillate and resulted in higher average Ins2 gene activity per cell. Single-cell RNA sequencing showed that Ins2(GFP)HIGH β-cells were enriched for markers of β-cell maturity. Ins2(GFP)HIGH β-cells were also significantly less viable at all glucose concentrations and in the context of endoplasmic reticulum stress. Collectively, our results demonstrate that the heterogeneity of insulin production, observed in mouse and human β-cells, can be accounted for by dynamic states of insulin gene activity.

Cell Networks in Endocrine/Neuroendocrine Gland Function

Reproduction, growth, stress, and metabolism are determined by endocrine/neuroendocrine systems that regulate circulating hormone concentrations. All these systems generate rhythms and changes in hormone pulsatility observed in a variety of pathophysiological states. Thus, the output of endocrine/neuroendocrine systems must be regulated within a narrow window of effective hormone concentrations but must also maintain a capacity for plasticity to respond to changing physiological demands. Remarkably most endocrinologists still have a "textbook" view of endocrine gland organization which has emanated from 20^th century histological studies on thin 2D tissue sections. However, 21^st -century technological advances, including in-depth 3D imaging of specific cell types have vastly changed our knowledge. We now know that various levels of multicellular organization can be found across different glands, that organizational motifs can vary between species and can be modified to enhance or decrease hormonal release. This article focuses on how the organization of cells regulates hormone output using three endocrine/neuroendocrine glands that present different levels of organization and complexity: the adrenal medulla, with a single neuroendocrine cell type; the anterior pituitary, with multiple intermingled cell types; and the pancreas with multiple intermingled cell types organized into distinct functional units. We give an overview of recent methodologies that allow the study of the different components within endocrine systems, particularly their temporal and spatial relationships. We believe the emerging findings about network organization, and its impact on hormone secretion, are crucial to understanding how homeostatic regulation of endocrine axes is carried out within endocrine organs themselves. © 2022 American Physiological Society. Compr Physiol 12:3371-3415, 2022.

β-Cell pre-mir-21 induces dysfunction and loss of cellular identity by targeting transforming growth factor beta 2 (Tgfb2) and Smad family member 2 (Smad2) mRNAs

OBJECTIVE

β-cell microRNA-21 (miR-21) is increased by islet inflammatory stress but it decreases glucose-stimulated insulin secretion (GSIS). Thus, we sought to define the effects of miR-21 on β-cell function using in vitro and in vivo systems.

METHODS

We developed a tetracycline-on system of pre-miR-21 induction in clonal β-cells and human islets, along with transgenic zebrafish and mouse models of β-cell-specific pre-miR-21 overexpression.

RESULTS

β-cell miR-21 induction markedly reduced GSIS and led to reductions in transcription factors associated with β-cell identity and increased markers of dedifferentiation, which led us to hypothesize that miR-21 induces β-cell dysfunction by loss of cell identity. In silico analysis identified transforming growth factor-beta 2 (Tgfb2) and Smad family member 2 (Smad2) mRNAs as predicted miR-21 targets associated with the maintenance of β-cell identity. Tgfb2 and Smad2 were confirmed as direct miR-21 targets through RT-PCR, immunoblot, pulldown, and luciferase assays. In vivo zebrafish and mouse models exhibited glucose intolerance, decreased peak GSIS, decreased expression of β-cell identity markers, increased insulin and glucagon co-staining cells, and reduced Tgfb2 and Smad2 expression.

CONCLUSIONS

These findings implicate miR-21-mediated reduction of mRNAs specifying β-cell identity as a contributor to β-cell dysfunction by the loss of cellular differentiation.

Harnessing the Endogenous Plasticity of Pancreatic Islets: A Feasible Regenerative Medicine Therapy for Diabetes?

Diabetes is a chronic metabolic disease caused by an absolute or relative deficiency in functional pancreatic β-cells that leads to defective control of blood glucose. Current treatments for diabetes, despite their great beneficial effects on clinical symptoms, are not curative treatments, leading to a chronic dependence on insulin throughout life that does not prevent the secondary complications associated with diabetes. The overwhelming increase in DM incidence has led to a search for novel antidiabetic therapies aiming at the regeneration of the lost functional β-cells to allow the re-establishment of the endogenous glucose homeostasis. Here we review several aspects that must be considered for the development of novel and successful regenerative therapies for diabetes: first, the need to maintain the heterogeneity of islet β-cells with several subpopulations of β-cells characterized by different transcriptomic profiles correlating with differences in functionality and in resistance/behavior under stress conditions; second, the existence of an intrinsic islet plasticity that allows stimulus-mediated transcriptome alterations that trigger the transdifferentiation of islet non-β-cells into β-cells; and finally, the possibility of using agents that promote a fully functional/mature β-cell phenotype to reduce and reverse the process of dedifferentiation of β-cells during diabetes.

Cellular stressors may alter islet hormone cell proportions by moderation of alternative splicing patterns

Changes to islet cell identity in response to type 2 diabetes (T2D) have been reported in rodent models, but are less well characterized in humans. We assessed the effects of aspects of the diabetic microenvironment on hormone staining, total gene expression, splicing regulation and the alternative splicing patterns of key genes in EndoC-βH1 human beta cells. Genes encoding islet hormones [somatostatin (SST), insulin (INS), Glucagon (GCG)], differentiation markers [Forkhead box O1 (FOXO1), Paired box 6, SRY box 9, NK6 Homeobox 1, NK6 Homeobox 2] and cell stress markers (DNA damage inducible transcript 3, FOXO1) were dysregulated in stressed EndoC-βH1 cells, as were some serine arginine rich splicing factor splicing activator and heterogeneous ribonucleoprotein particle inhibitor genes. Whole transcriptome analysis of primary T2D islets and matched controls demonstrated dysregulated splicing for ~25% of splicing events, of which genes themselves involved in messenger ribonucleic acid processing and regulation of gene expression comprised the largest group. Approximately 5% of EndoC-βH1 cells exposed to these factors gained SST positivity in vitro. An increased area of SST staining was also observed ex vivo in pancreas sections recovered at autopsy from donors with type 1 diabetes (T1D) or T2D (9.3% for T1D and 3% for T2D, respectively compared with 1% in controls). Removal of the stressful stimulus or treatment with the AKT Serine/Threonine kinase inhibitor SH-6 restored splicing factor expression and reversed both hormone staining effects and patterns of gene expression. This suggests that reversible changes in hormone expression may occur during exposure to diabetomimetic cellular stressors, which may be mediated by changes in splicing regulation.

Mesenchymal stem cells ameliorate β cell dysfunction of human type 2 diabetic islets by reversing β cell dedifferentiation

Background

A physiological hallmark of patients with type 2 diabetes mellitus (T2DM) is β cell dysfunction. Despite adequate treatment, it is an irreversible process that follows disease progression. Therefore, the development of novel therapies that restore β cell function is of utmost importance.

Methods

This study aims to unveil the mechanistic action of mesenchymal stem cells (MSCs) by investigating its impact on isolated human T2DM islets ex vivo and in vivo.

Findings

We propose that MSCs can attenuate β cell dysfunction by reversing β cell dedifferentiation in an IL-1Ra-mediated manner. In response to the elevated expression of proinflammatory cytokines in human T2DM islet cells, we observed that MSCs was activated to secret IL-1R antagonist (IL-1Ra) which acted on the inflammed islets and reversed β cell dedifferentiation, suggesting a crosstalk between MSCs and human T2DM islets. The co-transplantation of MSCs with human T2DM islets in diabetic SCID mice and intravenous infusion of MSCs in db/db mice revealed the reversal of β cell dedifferentiation and improved glycaemic control in the latter.

Interpretation

This evidence highlights the potential of MSCs in future cell-based therapies regarding the amelioration of β cell dysfunction.

Enhanced expression of β cell CaV3.1 channels impairs insulin release and glucose homeostasis

We reveal that increased expression of Ca_V3.1 channels in rat islets selectively impairs first-phase glucose-stimulated insulin secretion. This deterioration is recapitulated in human islets. Its causal role in diabetes development is clearly manifested in an in vivo diabetic model. Mechanistically, this is due to reduction of phosphorylated FoxO1 in the cytoplasm, elevated FoxO1 nuclear retention, and decreased syntaxin 1A, SNAP-25, and synaptotagmin III in a Ca_V3.1 channel- and calcineurin-dependent manner. Our findings suggest that elevated expression of Ca_V3.1 channels in pancreatic islets drives FoxO1-mediated down-regulation of exocytotic proteins resulting in the diabetic phenotypes of impaired insulin secretion and aberrant glucose homeostasis. This causal connection pinpoints β cell Ca_V3.1 channels as a potential druggable target for antidiabetes therapy.

Voltage-gated calcium 3.1 (Ca_V3.1) channels are absent in healthy mouse β cells and mediate minor T-type Ca²⁺ currents in healthy rat and human β cells but become evident under diabetic conditions. Whether more active Ca_V3.1 channels affect insulin secretion and glucose homeostasis remains enigmatic. We addressed this question by enhancing de novo expression of β cell Ca_V3.1 channels and exploring the consequent impacts on dynamic insulin secretion and glucose homeostasis as well as underlying molecular mechanisms with a series of in vitro and in vivo approaches. We now demonstrate that a recombinant adenovirus encoding enhanced green fluorescent protein–Ca_V3.1 subunit (Ad-EGFP-Ca_V3.1) efficiently transduced rat and human islets as well as dispersed islet cells. The resulting Ca_V3.1 channels conducted typical T-type Ca²⁺ currents, leading to an enhanced basal cytosolic-free Ca²⁺ concentration ([Ca²⁺]_i). Ad-EGFP-Ca_V3.1-transduced islets released significantly less insulin under both the basal and first phases following glucose stimulation and could no longer normalize hyperglycemia in recipient rats rendered diabetic by streptozotocin treatment. Furthermore, Ad-EGFP-Ca_V3.1 transduction reduced phosphorylated FoxO1 in the cytoplasm of INS-1E cells, elevated FoxO1 nuclear retention, and decreased syntaxin 1A, SNAP-25, and synaptotagmin III. These effects were prevented by inhibiting Ca_V3.1 channels or the Ca²⁺-dependent phosphatase calcineurin. Enhanced expression of β cell Ca_V3.1 channels therefore impairs insulin release and glucose homeostasis by means of initial excessive Ca²⁺ influx, subsequent activation of calcineurin, consequent dephosphorylation and nuclear retention of FoxO1, and eventual FoxO1-mediated down-regulation of β cell exocytotic proteins. The present work thus suggests an elevated expression of Ca_V3.1 channels plays a significant role in diabetes pathogenesis.

Death versus dedifferentiation: The molecular bases of beta cell mass reduction in type 2 diabetes

Diabetes Mellitus is currently affecting more than 425 million people worldwide, among which over 90 % of the cases belong to type 2 diabetes. The number is growing quickly every year. Together with its many complications, the disease is causing tremendous social and economic burden and is classified as one of the leading causes of high morbidity and mortality rate. Residing in the islets of Langerhans, pancreatic beta cell serves as a central mediator in glucose homeostasis through secreting insulin, the only hormone that could reduce glucose level in the body, into the blood. Abnormality in pancreatic beta cell is generally considered as the fundamental reason which is responsible for the development of diabetes. Evidence shows that beta cell mass is greatly reduced in the biopsy of type 2 diabetic patients. Since then, large amount of research was conducted in order to decipher the molecular mechanisms behind the phenotype above and enormous progression has been made. The aim of this review is to summarize and provide a rudimentary molecular road map for beta cell mass reduction from the aspects of apoptosis and dedifferentiation based on recent research advances. Hopefully, this review could give the community some enlightenment for the next-step research and, more importantly, could provide avenues for developing novel and effective therapies to restrain or reverse beta cell loss in type 2 diabetes in the clinic.

Navigating Two Roads to Glucose Normalization in Diabetes: Automated Insulin Delivery Devices and Cell Therapy

Incredible strides have been made since the discovery of insulin almost 100 years ago. Insulin formulations have improved dramatically, glucose levels can be measured continuously, and recently first-generation biomechanical "artificial pancreas" systems have been approved by regulators around the globe. However, still only a small fraction of patients with diabetes achieve glycemic goals. Replacement of insulin-producing cells via transplantation shows significant promise, but is limited in application due to supply constraints (cadaver-based) and the need for chronic immunosuppression. Over the past decade, significant progress has been made to address these barriers to widespread implementation of a cell therapy. Can glucose levels in people with diabetes be normalized with artificial pancreas systems or via cell replacement approaches? Here we review the road ahead, including the challenges and opportunities of both approaches.

Negative Effects of Cyclic Palmitate Treatment on Glucose Responsiveness and Insulin Production in Mouse Insulinoma Min6 Cells Are Reversible

Pancreatic β-cell failure is characterized by compromised insulin secretion in response to glucose, which ultimately results in hyperglycemia, the clinical hallmark of type 2 diabetes mellitus (T2DM). Acute exposure to plasma free fatty acids (FFAs) potentiates glucose stimulated insulin secretion (GSIS), while chronic exposure impairs GSIS, and the latter has been associated with the mechanism of β cell failure in obesity linked T2DM. By contrast, growth hormone (GH) signaling has been linked positively to GSIS in β cells. Numerous studies have examined chronic exposure of β cells to elevated FFAs both with in vivo cohorts and in vitro models. Little attention, however, has been given to the fluctuation of plasma FFA levels due to rhythmic effects that are affected by daily diet and fat intake. Mouse insulinoma Min6 cells were exposed to cyclic/daily palmitate treatment over 2 and 3 days to assess effects on GSIS. Cyclic/daily palmitate treatment with a period of recovery negatively affected GSIS in a dose-dependent manner. Removal of palmitate after two cycles/day resulted in reversal of the effect on GSIS, which was also reflected by relative gene expression involved in insulin biosynthesis (Ins1, Ins2, Pdx1, and MafA) and GSIS (glucose 2 transporter and glucokinase). Modest positive effects on GSIS and glucokinase transcript levels were also observed when Min6 cells were cotreated with human GH and palmitate. These observations indicate that like continuous palmitate treatment, cyclic exposure to palmitate can acutely impair GSIS over 48 and 72 h. However, they also suggest that the negative effects of short periods of exposure to FFAs on β cell function remain reversible.

Pancreatic islet-autonomous insulin and smoothened-mediated signalling modulate identity changes of glucagon+ α-cells

The mechanisms that restrict regeneration and maintain cell identity following injury are poorly characterized in higher vertebrates. Following β-cell loss, 1-2% of the glucagon-producing α-cells spontaneously engage in insulin production in mice. Here we explore the mechanisms inhibiting α-cell plasticity. We show that adaptive α-cell identity changes are constrained by intra-islet insulin- and Smoothened-mediated signalling, among others. The combination of β-cell loss or insulin-signalling inhibition, with Smoothened inactivation in α- or δ-cells, stimulates insulin production in more α-cells. These findings suggest that the removal of constitutive 'brake signals' is crucial to neutralize the refractoriness to adaptive cell-fate changes. It appears that the maintenance of cell identity is an active process mediated by repressive signals, which are released by neighbouring cells and curb an intrinsic trend of differentiated cells to change.

Apolipoprotein E is a pancreatic extracellular factor that maintains mature β-cell gene expression

The in vivo microenvironment of tissues provides myriad unique signals to cells. Thus, following isolation, many cell types change in culture, often preserving some but not all of their in vivo characteristics in culture. At least some of the in vivo microenvironment may be mimicked by providing specific cues to cultured cells. Here, we show that after isolation and during maintenance in culture, adherent rat islets reduce expression of key β-cell transcription factors necessary for β-cell function and that soluble pancreatic decellularized matrix (DCM) can enhance β-cell gene expression. Following chromatographic fractionation of pancreatic DCM, we performed proteomics to identify soluble factors that can maintain β-cell stability and function. We identified Apolipoprotein E (ApoE) as an extracellular protein that significantly increased the expression of key β-cell genes. The ApoE effect on beta cells was mediated at least in part through the JAK/STAT signaling pathway. Together, these results reveal a role for ApoE as an extracellular factor that can maintain the mature β-cell gene expression profile.

Investigation of post-translational modifications in type 2 diabetes

The investigation of post-translational modifications (PTMs) plays an important role for the study of type 2 diabetes. The importance of PTMs has been realized with the advancement of analytical techniques. The challenging detection and analysis of post-translational modifications is eased by different enrichment methods and by high throughput mass spectrometry based proteomics studies. This technology along with different quantitation methods provide accurate knowledge about the changes happening in disease conditions as well as in normal conditions. In this review, we have discussed PTMs such as phosphorylation, N-glycosylation, O-GlcNAcylation, acetylation and advanced glycation end products in type 2 diabetes which have been characterized by high throughput mass spectrometry based proteomics analysis.

Regeneration of insulin-producing islets from dental pulp stem cells using a 3D culture system

AIM

In this study, we aimed to establish the differentiation protocol of dental pulp stem cells (DPSCs) into pancreatic islets using a 3D structure.

MATERIALS & METHODS

DPSCs were differentiated in a 3D culture system using a stepwise protocol. Expression of β-cell markers, glucose-stimulated insulin secretion, and PI3K/AKT and WNT pathways were compared between monolayer-cultured pancreatic cells and islets.

RESULTS

Islet formation increased insulin and C-peptide production, and enhanced the expression of pancreatic markers. Glucose-dependent secretion of insulin was increased by islets. Pancreatic endocrine markers, transcriptional factors, and the PI3K/AKT and WNT pathways were also upregulated.

CONCLUSION

Pancreatic islets were generated from DPSCs in a 3D culture system. This system could provide novel strategies for controlling diabetes through regenerative medicine.

ZBED6 negatively regulates insulin production, neuronal differentiation, and cell aggregation in MIN6 cells

Zinc finger BED domain containing protein 6 ( Zbed6) has evolved from a domesticated DNA transposon and encodes a transcription factor unique to placental mammals. The aim of the present study was to investigate further the role of ZBED6 in insulin-producing cells, using mouse MIN6 cells, and to evaluate the effects of Zbed6 knockdown on basal β-cell functions, such as morphology, transcriptional regulation, insulin content, and release. Zbed6-silenced cells and controls were characterized with a range of methods, including RNA sequencing, chromatin immunoprecipitation sequencing, insulin content and release, subplasma membrane Ca²⁺ measurements, cAMP determination, and morphologic studies. More than 700 genes showed differential expression in response to Zbed6 knockdown, which was paralleled by increased capacity to generate cAMP, as well as by augmented subplasmalemmal calcium concentration and insulin secretion in response to glucose stimulation. We identified >4000 putative ZBED6-binding sites in the MIN6 genome, with an enrichment of ZBED6 sites at upregulated genes, such as the β-cell transcription factors v-maf musculoaponeurotic fibrosarcoma oncogene homolog A and Nk6 homeobox 1. We also observed altered morphology/growth patterns, as indicated by increased cell clustering, and in the appearance of axon-like Neurofilament, medium polypeptide and tubulin β 3, class III-positive protrusions. We conclude that ZBED6 acts as a transcriptional regulator in MIN6 cells and that its activity suppresses insulin production, cell aggregation, and neuronal-like differentiation.-Wang, X., Jiang, L., Wallerman, O., Younis, S., Yu, Q., Klaesson, A., Tengholm, A., Welsh, N., Andersson, L. ZBED6 negatively regulates insulin production, neuronal differentiation, and cell aggregation in MIN6 cells.

The Polycomb-Dependent Epigenome Controls β Cell Dysfunction, Dedifferentiation, and Diabetes

To date, it remains largely unclear to what extent chromatin machinery contributes to the susceptibility and progression of complex diseases. Here, we combine deep epigenome mapping with single-cell transcriptomics to mine for evidence of chromatin dysregulation in type 2 diabetes. We find two chromatin-state signatures that track β cell dysfunction in mice and humans: ectopic activation of bivalent Polycomb-silenced domains and loss of expression at an epigenomically unique class of lineage-defining genes. β cell-specific Polycomb (Eed/PRC2) loss of function in mice triggers diabetes-mimicking transcriptional signatures and highly penetrant, hyperglycemia-independent dedifferentiation, indicating that PRC2 dysregulation contributes to disease. The work provides novel resources for exploring β cell transcriptional regulation and identifies PRC2 as necessary for long-term maintenance of β cell identity. Importantly, the data suggest a two-hit (chromatin and hyperglycemia) model for loss of β cell identity in diabetes.

Cyclin D2 is sufficient to drive β cell self-renewal and regeneration

Diabetes results from an inadequate mass of functional β cells, due to either β cell loss caused by autoimmune destruction (type I diabetes) or β cell failure in response to insulin resistance (type II diabetes). Elucidating the mechanisms that regulate β cell mass may be key to developing new techniques that foster β cell regeneration as a cellular therapy to treat diabetes. While previous studies concluded that cyclin D2 is required for postnatal β cell self-renewal in mice, it is not clear if cyclin D2 is sufficient to drive β cell self-renewal. Using transgenic mice that overexpress cyclin D2 specifically in β cells, we show that cyclin D2 overexpression increases β cell self-renewal post-weaning and results in increased β cell mass. β cells that overexpress cyclin D2 are responsive to glucose stimulation, suggesting they are functionally mature. β cells that overexpress cyclin D2 demonstrate an enhanced regenerative capacity after injury induced by streptozotocin toxicity. To understand if cyclin D2 overexpression is sufficient to drive β cell self-renewal, we generated a novel mouse model where cyclin D2 is only expressed in β cells of cyclin D2^−/− mice. Transgenic overexpression of cyclin D2 in cyclin D2^−/− β cells was sufficient to restore β cell mass, maintain normoglycaemia, and improve regenerative capacity when compared with cyclin D2^−/− littermates. Taken together, our results indicate that cyclin D2 is sufficient to regulate β cell self-renewal and that manipulation of its expression could be used to enhance β cell regeneration.

The triggering pathway to insulin secretion: Functional similarities and differences between the human and the mouse β cells and their translational relevance

In β cells, stimulation by metabolic, hormonal, neuronal, and pharmacological factors is coupled to secretion of insulin through different intracellular signaling pathways. Our knowledge about the molecular machinery supporting these pathways and the patterns of signals it generates comes mostly from rodent models, especially the laboratory mouse. The increased availability of human islets for research during the last few decades has yielded new insights into the specifics in signaling pathways leading to insulin secretion in humans. In this review, we follow the most central triggering pathway to insulin secretion from its very beginning when glucose enters the β cell to the calcium oscillations it produces to trigger fusion of insulin containing granules with the plasma membrane. Along the way, we describe the crucial building blocks that contribute to the flow of information and focus on their functional role in mice and humans and on their translational implications.

Increased vimentin in human α- and β-cells in type 2 diabetes

Type 2 diabetes (T2DM) is associated with pancreatic islet dysfunction. Loss of β-cell identity has been implicated via dedifferentiation or conversion to other pancreatic endocrine cell types. How these transitions contribute to the onset and progression of T2DM in vivo is unknown. The aims of this study were to determine the degree of epithelial-to-mesenchymal transition occurring in α and β cells in vivo and to relate this to diabetes-associated (patho)physiological conditions. The proportion of islet cells expressing the mesenchymal marker vimentin was determined by immunohistochemistry and quantitative morphometry in specimens of pancreas from human donors with T2DM (n = 28) and without diabetes (ND, n = 38) and in non-human primates at different stages of the diabetic syndrome: normoglycaemic (ND, n = 4), obese, hyperinsulinaemic (HI, n = 4) and hyperglycaemic (DM, n = 8). Vimentin co-localised more frequently with glucagon (α-cells) than with insulin (β-cells) in the human ND group (1.43% total α-cells, 0.98% total β-cells, median; P < 0.05); these proportions were higher in T2DM than ND (median 4.53% α-, 2.53% β-cells; P < 0.05). Vimentin-positive β-cells were not apoptotic, had reduced expression of Nkx6.1 and Pdx1, and were not associated with islet amyloidosis or with bihormonal expression (insulin + glucagon). In non-human primates, vimentin-positive β-cell proportion was larger in the diabetic than the ND group (6.85 vs 0.50%, medians respectively, P < 0.05), but was similar in ND and HI groups. In conclusion, islet cell expression of vimentin indicates a degree of plasticity and dedifferentiation with potential loss of cellular identity in diabetes. This could contribute to α- and β-cell dysfunction in T2DM.

Adult muscle-derived stem cells engraft and differentiate into insulin-expressing cells in pancreatic islets of diabetic mice

Background

Pancreatic beta cells are unique effectors in the control of glucose homeostasis and their deficiency results in impaired insulin production leading to severe diabetic diseases. Here, we investigated the potential of a population of nonadherent muscle-derived stem cells (MDSC) from adult mouse muscle to differentiate in vitro into beta cells when transplanted as undifferentiated stem cells in vivo to compensate for beta-cell deficiency.

Results

In vitro, cultured MDSC spontaneously differentiated into insulin-expressing islet-like cell clusters as revealed using MDSC from transgenic mice expressing GFP or mCherry under the control of an insulin promoter. Differentiated clusters of beta-like cells co-expressed insulin with the transcription factors Pdx1, Nkx2.2, Nkx6.1, and MafA, and secreted significant levels of insulin in response to glucose challenges. In vivo, undifferentiated MDSC injected into streptozotocin (STZ)-treated mice engrafted within 48 h specifically to damaged pancreatic islets and were shown to differentiate and express insulin 10–12 days after injection. In addition, injection of MDSC into hyperglycemic diabetic mice reduced their blood glucose levels for 2–4 weeks.

Conclusion

These data show that MDSC are capable of differentiating into mature pancreatic beta islet-like cells, not only upon culture in vitro, but also in vivo after systemic injection in STZ-induced diabetic mouse models. Being nonteratogenic, MDSC can be used directly by systemic injection, and this potential reveals a promising alternative avenue in stem cell-based treatment of beta-cell deficiencies.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0539-9) contains supplementary material, which is available to authorized users.

Hydrogen sulfide enhances pancreatic β-cell differentiation from human tooth under normal and glucotoxic conditions

Aim: Glucotoxicity obstructs pancreatic differentiation from adult stem cells. The aim was to develop a novel protocol for differentiation of dental pulp stem cells (DPSCs) into pancreatic β cells and determine the effect of H2S on glucotoxicity. Materials & methods: DPSCs were differentiated with media containing 5.5 or 25.0 mM glucose, exposed to 1 ng/ml H2S. Glucotoxicity, expression of β-cell markers, INS, PDX1 and GLUT2, and PI3K/AKT pathway were assessed. Results: H2S exposure increased insulin and C-peptide, and protected DPSC-derived pancreatic β-like cells from glucotoxicity and upregulated INS, PDX1 and GLUT2, and genes of PI3K/AKT pathway. Conclusion: H2S improved effects of glucotoxicity on β-like cells via PI3K/AKT pathway. The protocol for pancreatic β-cell differentiation might have applications in regenerative medicine rather than swine pancreas transplantation.

A causal role for hyperinsulinemia in obesity

Insulin modulates the biochemical pathways controlling lipid uptake, lipolysis and lipogenesis at multiple levels. Elevated insulin levels are associated with obesity, and conversely, dietary and pharmacological manipulations that reduce insulin have occasionally been reported to cause weight loss. However, the causal role of insulin hypersecretion in the development of mammalian obesity remained controversial in the absence of direct loss-of-function experiments. Here, we discuss theoretical considerations around the causal role of excess insulin for obesity, as well as recent studies employing mice that are genetically incapable of the rapid and sustained hyperinsulinemia that normally accompanies a high-fat diet. We also discuss new evidence demonstrating that modest reductions in circulating insulin prevent weight gain, with sustained effects that can persist after insulin levels normalize. Importantly, evidence from long-term studies reveals that a modest reduction in circulating insulin is not associated with impaired glucose homeostasis, meaning that body weight and lipid homeostasis are actually more sensitive to small changes in circulating insulin than glucose homeostasis in these models. Collectively, the evidence from new studies on genetic loss-of-function models forces a re-evaluation of current paradigms related to obesity, insulin resistance and diabetes. The potential for translation of these findings to humans is briefly discussed.

Specialized Hub Beta Cells Trade Maximal Insulin Production for Perfect Timing

The pulsatility of insulin release is disturbed early in type 2 diabetes, but it is not clear whether specialized pacemaker cells drive islet oscillations. In this issue of Cell Metabolism, Johnston et al. (2016) show that specialized hubs, identified as 1%-10% of beta cells with more active mitochondria and less insulin, synchronize beta cell oscillations.

Pancreatic β-cell identity in diabetes

Recovery of functional β-cell mass continues to be an ongoing challenge in treating diabetes. Initial work studying β-cells suggested apoptotic β-cell death as a main contributor for the loss of β-cell mass in diabetes. Restoration of β-cells either by transplant or stimulating proliferation of remaining β-cells or precursors would then logically be a viable therapeutic option for diabetes. However, recent work has highlighted the inherent β-cell plasticity and the critical role of loss of β-cell identity in diabetes, and has suggested that β-cells fail to maintain a fully differentiated glucose-responsive and drug-responsive state, particularly in diabetic individuals with poorly controlled, long-lasting periods of hyperglycaemia. Understanding the underlying mechanisms of loss of β-cell identity and conversion in other cell types, as well as how to regain their mature differentiated functional state, is critical to develop novel therapeutic strategies to prevent or reverse these processes. In this review, we discuss the role of plasticity and loss of β-cell identity in diabetes, the current understanding of mechanisms involved in altering this mature functional β-cell state and potential progresses to identify novel therapeutic targets providing better opportunities for slowing or preventing diabetes progression.

Statistical approaches and software for clustering islet cell functional heterogeneity

Worldwide efforts are underway to replace or repair lost or dysfunctional pancreatic β-cells to cure diabetes. However, it is unclear what the final product of these efforts should be, as β-cells are thought to be heterogeneous. To enable the analysis of β-cell heterogeneity in an unbiased and quantitative way, we developed model-free and model-based statistical clustering approaches, and created new software called TraceCluster. Using an example data set, we illustrate the utility of these approaches by clustering dynamic intracellular Ca(2+) responses to high glucose in ∼300 simultaneously imaged single islet cells. Using feature extraction from the Ca(2+) traces on this reference data set, we identified 2 distinct populations of cells with β-like responses to glucose. To the best of our knowledge, this report represents the first unbiased cluster-based analysis of human β-cell functional heterogeneity of simultaneous recordings. We hope that the approaches and tools described here will be helpful for those studying heterogeneity in primary islet cells, as well as excitable cells derived from embryonic stem cells or induced pluripotent cells.

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.

Xenopus as a model system for studying pancreatic development and diabetes

Diabetes is a chronic disease caused by the loss or dysfunction of the insulin-producing β-cells in the pancreas. To date, much of our knowledge about β-cells in humans comes from studying rare monogenic forms of diabetes. Importantly, the majority of mutations so far associated to monogenic diabetes are in genes that exert a regulatory role in pancreatic development and/or β-cell function. Thus, the identification and study of novel mutations open an unprecedented window into human pancreatic development. In this review, we summarize major advances in the genetic dissection of different types of monogenic diabetes and the insights gained from a developmental perspective. We highlight future challenges to bridge the gap between the fast accumulation of genetic data through next-generation sequencing and the need of functional insights into disease mechanisms. Lastly, we discuss the relevance and advantages of studying candidate gene variants in vivo using the Xenopus as model system.

Reduced Insulin Production Relieves Endoplasmic Reticulum Stress and Induces β Cell Proliferation

Pancreatic β cells are mostly post-mitotic, but it is unclear what locks them in this state. Perturbations including uncontrolled hyperglycemia can drive β cells into more pliable states with reduced cellular insulin levels, increased β cell proliferation, and hormone mis-expression, but it is unknown whether reduced insulin production itself plays a role. Here, we define the effects of ∼50% reduced insulin production in Ins1(-/-):Ins2(f/f):Pdx1Cre(ERT):mTmG mice prior to robust hyperglycemia. Transcriptome, proteome, and network analysis revealed alleviation of chronic endoplasmic reticulum (ER) stress, indicated by reduced Ddit3, Trib3, and Atf4 expression; reduced Xbp1 splicing; and reduced phospho-eIF2α. This state was associated with hyper-phosphorylation of Akt, which is negatively regulated by Trib3, and with cyclinD1 upregulation. Remarkably, β cell proliferation was increased 2-fold after reduced insulin production independently of hyperglycemia. Eventually, recombined cells mis-expressed glucagon in the hyperglycemic state. We conclude that the normally high rate of insulin production suppresses β cell proliferation in a cell-autonomous manner.

Progress and challenges in macroencapsulation approaches for type 1 diabetes (T1D) treatment: Cells, biomaterials, and devices

Macroencapsulation technology has been an attractive topic in the field of treatment for Type 1 diabetes due to mechanical stability, versatility, and retrievability of the macro-capsule design. Macro-capsules can be categorized into extravascular and intravascular devices, in which solute transport relies either on diffusion or convection, respectively. Failure of macroencapsulation strategies can be due to limited regenerative capacity of the encased insulin-producing cells, sub-optimal performance of encapsulation biomaterials, insufficient immunoisolation, excessive blood thrombosis for vascular perfusion devices, and inadequate modes of mass transfer to support cell viability and function. However, significant technical advancements have been achieved in macroencapsulation technology, namely reducing diffusion distance for oxygen and nutrients, using pro-angiogenic factors to increase vascularization for islet engraftment, and optimizing membrane permeability and selectivity to prevent immune attacks from host's body. This review presents an overview of existing macroencapsulation devices and discusses the advances based on tissue-engineering approaches that will stimulate future research and development of macroencapsulation technology. Biotechnol. Bioeng. 2016;113: 1381-1402. © 2015 Wiley Periodicals, Inc.

High-content screening identifies a role for Na(+) channels in insulin production

Insulin production is the central feature of functionally mature and differentiated pancreatic β-cells. Reduced insulin transcription and dedifferentiation have been implicated in type 2 diabetes, making drugs that could reverse these processes potentially useful. We have previously established ratiometric live-cell imaging tools to identify factors that increase insulin promoter activity and promote β-cell differentiation. Here, we present a single vector imaging tool with eGFP and mRFP, driven by the Pdx1 and Ins1 promoters, respectively, targeted to the nucleus to enhance identification of individual cells in a high-throughput manner. Using this new approach, we screened 1120 off-patent drugs for factors that regulate Ins1 and Pdx1 promoter activity in MIN6 β-cells. We identified a number of compounds that positively modulate Ins1 promoter activity, including several drugs known to modulate ion channels. Carbamazepine was selected for extended follow-up, as our previous screen also identified this use-dependent sodium channel inhibitor as a positive modulator of β-cell survival. Indeed, carbamazepine increased Ins1 and Ins2 mRNA in primary mouse islets at lower doses than were required to protect β-cells. We validated the role of sodium channels in insulin production by examining Nav1.7 (Scn9a) knockout mice and remarkably islets from these animals had dramatically elevated insulin content relative to wild-type controls. Collectively, our experiments provide a starting point for additional studies aimed to identify drugs and molecular pathways that control insulin production and β-cell differentiation status. In particular, our unbiased screen identified a novel role for a β-cell sodium channel gene in insulin production.

Early and Late G1/S Cyclins and Cdks Act Complementarily to Enhance Authentic Human β-Cell Proliferation and Expansion

β-Cell regeneration is a key goal of diabetes research. Progression through the cell cycle is associated with retinoblastoma protein (pRb) inactivation via sequential phosphorylation by the "early" cyclins and cyclin-dependent kinases (cdks) (d-cyclins cdk4/6) and the "late" cyclins and cdks (cyclin A/E and cdk1/2). In β-cells, activation of either early or late G1/S cyclins and/or cdks is an efficient approach to induce cycle entry, but it is unknown whether the combined expression of early and late cyclins and cdks might have synergistic or additive effects. Thus, we explored whether a combination of both early and late cyclins and cdks might more effectively drive human β-cell cell cycle entry than either group alone. We also sought to determine whether authentic replication with the expansion of adult human β-cells could be demonstrated. Late cyclins and cdks do not traffic in response to the induction of replication by early cyclins and cdks in human β-cells but are capable of nuclear translocation when overexpressed. Early plus late cyclins and cdks, acting via pRb phosphorylation on distinct residues, complementarily induce greater proliferation in human β-cells than either group alone. Importantly, the combination of early and late cyclins and cdks clearly increased human β-cell numbers in vitro. These findings provide additional insight into human β-cell expansion. They also provide a novel tool for assessing β-cell expansion in vitro.

Loss of β-Cell Identity Occurs in Type 2 Diabetes and Is Associated With Islet Amyloid Deposits

Loss of pancreatic islet β-cell mass and β-cell dysfunction are central in the development of type 2 diabetes (T2DM). We recently showed that mature human insulin-containing β-cells can convert into glucagon-containing α-cells ex vivo. This loss of β-cell identity was characterized by the presence of β-cell transcription factors (Nkx6.1, Pdx1) in glucagon(+) cells. Here, we investigated whether the loss of β-cell identity also occurs in vivo, and whether it is related to the presence of (pre)diabetes in humans and nonhuman primates. We observed an eight times increased frequency of insulin(+) cells coexpressing glucagon in donors with diabetes. Up to 5% of the cells that were Nkx6.1(+) but insulin(-) coexpressed glucagon, which represents a five times increased frequency compared with the control group. This increase in bihormonal and Nkx6.1(+)glucagon(+)insulin(-) cells was also found in islets of diabetic macaques. The higher proportion of bihormonal cells and Nkx6.1(+)glucagon(+)insulin(-) cells in macaques and humans with diabetes was correlated with the presence and extent of islet amyloidosis. These data indicate that the loss of β-cell identity occurs in T2DM and could contribute to the decrease of functional β-cell mass. Maintenance of β-cell identity is a potential novel strategy to preserve β-cell function in diabetes.

A live-cell, high-content imaging survey of 206 endogenous factors across five stress conditions reveals context-dependent survival effects in mouse primary beta cells

AIMS/HYPOTHESIS

Beta cell death is a hallmark of diabetes. It is not known whether specific cellular stresses associated with type 1 or type 2 diabetes require specific factors to protect pancreatic beta cells. No systematic comparison of endogenous soluble factors in the context of multiple pro-apoptotic conditions has been published.

METHODS

Primary mouse islet cells were cultured in conditions mimicking five type 1 or type 2 diabetes-related stresses: basal 5 mmol/l glucose, cytokine cocktail (25 ng/ml TNF-α, 10 ng/ml IL-1β, 10 ng/ml IFN-γ), 1 μmol/l thapsigargin, 1.5 mmol/l palmitate and 20 mmol/l glucose (all in the absence of serum). We surveyed the effects of a library of 206 endogenous factors (selected based on islet expression of their receptors) on islet cell survival through multi-parameter, live-cell imaging.

RESULTS

Our survey pointed to survival factors exhibiting generalised protective effects across conditions meant to model different types of diabetes and stages of the diseases. For example, our survey and follow-up experiments suggested that OLFM1 is a novel protective factor for mouse and human beta cells across multiple conditions. Most strikingly, we also found specific protective survival factors for each model stress condition. For example, semaphorin4A (SEMA4A) was toxic to islet cells in the serum-free baseline and serum-free 20 mmol/l glucose conditions, but protective in the context of lipotoxicity. Rank product testing supported the consistency of our observations.

CONCLUSIONS/INTERPRETATION

Collectively, our survey reveals previously unidentified islet cell survival factors and suggest their potential utility in individualised medicine.

Insm1 cooperates with Neurod1 and Foxa2 to maintain mature pancreatic β-cell function

Key transcription factors control the gene expression program in mature pancreatic β-cells, but their integration into regulatory networks is little understood. Here, we show that Insm1, Neurod1 and Foxa2 directly interact and together bind regulatory sequences in the genome of mature pancreatic β-cells. We used Insm1 ablation in mature β-cells in mice and found pronounced deficits in insulin secretion and gene expression. Insm1-dependent genes identified previously in developing β-cells markedly differ from the ones identified in the adult. In particular, adult mutant β-cells resemble immature β-cells of newborn mice in gene expression and functional properties. We defined Insm1, Neurod1 and Foxa2 binding sites associated with genes deregulated in Insm1 mutant β-cells. Remarkably, combinatorial binding of Insm1, Neurod1 and Foxa2 but not binding of Insm1 alone explained a significant fraction of gene expression changes. Human genomic sequences corresponding to the murine sites occupied by Insm1/Neurod1/Foxa2 were enriched in single nucleotide polymorphisms associated with glycolytic traits. Thus, our data explain part of the mechanisms by which β-cells maintain maturity: Combinatorial Insm1/Neurod1/Foxa2 binding identifies regulatory sequences that maintain the mature gene expression program in β-cells, and disruption of this network results in functional failure.

Development, growth and maintenance of β-cell mass: models are also part of the story

Pancreatic β-cells in the islets of Langerhans play a crucial role in regulating glucose homeostasis in the circulation. Loss of β-cell mass or function due to environmental, genetic and immunological factors leads to the manifestation of diabetes mellitus. The mechanisms regulating the dynamics of pancreatic β-cell mass during normal development and diabetes progression are complex. To fully unravel such complexity, experimental and clinical approaches need to be combined with mathematical and computational models. In the natural sciences, mathematical and computational models have aided the identification of key mechanisms underlying the behavior of systems comprising multiple interacting components. A number of mathematical and computational models have been proposed to explain the development, growth and death of pancreatic β-cells. In this review, we discuss some of these models and how their predictions provide novel insight into the mechanisms controlling β-cell mass during normal development and diabetes progression. Lastly, we discuss a handful of the major open questions in the field.

Transcriptional profiling and functional network analyses of islet-like clusters (ILCs) generated from pancreatic stem cells in vitro

We have earlier reported the generation of islet-like clusters (ILCs) from mesenchymal stromal cell (MSC)-like cells present in murine pancreas. Here we compare these ILCs to native primary islets by transcriptome screening. Genes were categorized into functional clusters and network analysis was done by Ingenuity Pathway Analysis (IPA). The fold changes for a selected panel of molecules were validated with quantitative real time PCR. A differential expression of 6516 genes (p-value ≤ 0.05, 1.5 fold change) with upregulated expression of numerous inflammatory and 'Epithelial to Mesenchymal Transition' molecules (EMT) was seen. A significant increase in the early β-cell marker expression in the ILCs indicated their progenitor status. Although not fully mature, ILCs offer certain advantages including the large number of easily inducible initiator MSCs. These 'naïve' cells may aid to devise protocols for generating functional islet equivalents. Moreover their maturation upon transplantation under local microenvironmental niche is highly possible.

Structural similarities and differences between the human and the mouse pancreas

Mice remain the most studied animal model in pancreas research. Since the findings of this research are typically extrapolated to humans, it is important to understand both similarities and differences between the 2 species. Beside the apparent difference in size and macroscopic organization of the organ in the 2 species, there are a number of less evident and only recently described differences in organization of the acinar and ductal exocrine tissue, as well as in the distribution, composition, and architecture of the endocrine islets of Langerhans. Furthermore, the differences in arterial, venous, and lymphatic vessels, as well as innervation are potentially important. In this article, the structure of the human and the mouse pancreas, together with the similarities and differences between them are reviewed in detail in the light of conceivable repercussions for basic research and clinical application.

Intrinsic islet heterogeneity and gap junction coupling determine spatiotemporal Ca²⁺ wave dynamics

Insulin is released from the islets of Langerhans in discrete pulses that are linked to synchronized oscillations of intracellular free calcium ([Ca(2+)]i). Associated with each synchronized oscillation is a propagating calcium wave mediated by Connexin36 (Cx36) gap junctions. A computational islet model predicted that waves emerge due to heterogeneity in β-cell function throughout the islet. To test this, we applied defined patterns of glucose stimulation across the islet using a microfluidic device and measured how these perturbations affect calcium wave propagation. We further investigated how gap junction coupling regulates spatiotemporal [Ca(2+)]i dynamics in the face of heterogeneous glucose stimulation. Calcium waves were found to originate in regions of the islet having elevated excitability, and this heterogeneity is an intrinsic property of islet β-cells. The extent of [Ca(2+)]i elevation across the islet in the presence of heterogeneity is gap-junction dependent, which reveals a glucose dependence of gap junction coupling. To better describe these observations, we had to modify the computational islet model to consider the electrochemical gradient between neighboring β-cells. These results reveal how the spatiotemporal [Ca(2+)]i dynamics of the islet depend on β-cell heterogeneity and cell-cell coupling, and are important for understanding the regulation of coordinated insulin release across the islet.

Generation of insulin-producing cells from the mouse liver using β cell-related gene transfer including Mafa and Mafb

Recent studies on the large Maf transcription factors have shown that Mafb and Mafa have respective and distinctive roles in β-cell development and maturation. However, whether this difference in roles is due to the timing of the gene expression (roughly, expression of Mafb before birth and of Mafa after birth) or to the specific function of each gene is unclear. Our aim was to examine the functional differences between these genes that are closely related to β cells by using an in vivo model of β-like cell generation. We monitored insulin gene transcription by measuring bioluminescence emitted from the liver of insulin promoter-luciferase transgenic (MIP-Luc-VU) mice. Adenoviral gene transfers of Pdx1/Neurod/Mafa (PDA) and Pdx1/Neurod/Mafb (PDB) combinations generated intense luminescence from the liver that lasted for more than 1 week and peaked at 3 days after transduction. The peak signal intensities of PDA and PDB were comparable. However, PDA but not PDB transfer resulted in significant bioluminescence on day 10, suggesting that Mafa has a more sustainable role in insulin gene activation than does Mafb. Both PDA and PDB transfers ameliorated the glucose levels in a streptozotocin (STZ)-induced diabetic model for up to 21 days and 7 days, respectively. Furthermore, PDA transfer induced several gene expressions necessary for glucose sensing and insulin secretion in the liver on day 9. However, a glucose tolerance test and liver perfusion experiment did not show glucose-stimulated insulin secretion from intrahepatic β-like cells. These results demonstrate that bioluminescence imaging in MIP-Luc-VU mice provides a noninvasive means of detecting β-like cells in the liver. They also show that Mafa has a markedly intense and sustained role in β-like cell production in comparison with Mafb.

Could microRNAs contribute to the maintenance of β cell identity?

Normal physiology depends on defined functional output of differentiated cells. However, differentiated cells are often surprisingly fragile. As an example, phenotypic collapse and dedifferentiation of β cells were recently discovered in the pathogenesis of type 2 diabetes (T2D). These discoveries necessitate the investigation of mechanisms that function to maintain robust cell type identity. microRNAs (miRNAs), which are small non-coding RNAs, are known to impart robustness to development. miRNAs are interlaced within networks, that include also transcriptional and epigenetic regulators, for continuous control of lineage-specific gene expression. In this Opinion article, we provide a framework for conceptualizing how miRNAs might participate in adult β cell identity and suggest that miRNAs may function as important genetic components in metabolic disorders, including diabetes.

Development of a conditionally immortalized human pancreatic β cell line

Diabetic patients exhibit a reduction in β cells, which secrete insulin to help regulate glucose homeostasis; however, little is known about the factors that regulate proliferation of these cells in human pancreas. Access to primary human β cells is limited and a challenge for both functional studies and drug discovery progress. We previously reported the generation of a human β cell line (EndoC-βH1) that was generated from human fetal pancreas by targeted oncogenesis followed by in vivo cell differentiation in mice. EndoC-βH1 cells display many functional properties of adult β cells, including expression of β cell markers and insulin secretion following glucose stimulation; however, unlike primary β cells, EndoC-βH1 cells continuously proliferate. Here, we devised a strategy to generate conditionally immortalized human β cell lines based on Cre-mediated excision of the immortalizing transgenes. The resulting cell line (EndoC-βH2) could be massively amplified in vitro. After expansion, transgenes were efficiently excised upon Cre expression, leading to an arrest of cell proliferation and pronounced enhancement of β cell-specific features such as insulin expression, content, and secretion. Our data indicate that excised EndoC-βH2 cells are highly representative of human β cells and should be a valuable tool for further analysis of human β cells.

Multiparameter screening reveals a role for Na+ channels in cytokine-induced β-cell death

Pancreatic β-cell death plays a role in both type 1 and type 2 diabetes, but clinical treatments that specifically target β-cell survival have not yet been developed. We have recently developed live-cell imaging-based, high-throughput screening methods capable of identifying factors that modulate pancreatic β-cell death, with the hope of finding drugs that can intervene in this process. In the present study, we used a high-content screen and the Prestwick Chemical Library of small molecules to identify drugs that block cell death resulting from exposure to a cocktail of cytotoxic cytokines (25 ng/mL TNF-α, 10 ng/mL IL-1β, and 10 ng/mL IFN-γ). Data analysis with self-organizing maps revealed that 19 drugs had profiles similar to that of the no cytokine condition, indicating protection. Carbamazepine, an antiepileptic Na(+) channel inhibitor, was particularly interesting because Na(+) channels are not generally considered targets for antiapoptotic therapy in diabetes and because the function of these channels in β-cells has not been well studied. We analyzed the expression and characteristics of Na(+) currents in mature β-cells from MIP-GFP mice. We confirmed the dose-dependent protective effects of carbamazepine and another use-dependent Na(+) channel blocker in cytokine-treated mouse islet cells. Carbamazepine down-regulated the proapoptotic and endoplasmic reticulum stress signaling induced by cytokines. Together, these studies point to Na(+) channels as a novel therapeutic target in diabetes.

Intraislet SLIT-ROBO signaling is required for beta-cell survival and potentiates insulin secretion

We previously cataloged putative autocrine/paracrine signaling loops in pancreatic islets, including factors best known for their roles in axon guidance. Emerging evidence points to nonneuronal roles for these factors, including the Slit-Roundabout receptor (Robo) family, in cell growth, migration, and survival. We found SLIT1 and SLIT3 in both beta cells and alpha cells, whereas SLIT2 was predominantly expressed in beta cells. ROBO1 and ROBO2 receptors were detected in beta and alpha cells. Remarkably, even modest knockdown of Slit production resulted in significant beta-cell death, demonstrating a critical autocrine/paracrine survival role for this pathway. Indeed, recombinant SLIT1, SLIT2, and SLIT3 decreased serum deprivation, cytokine, and thapsigargin-induced cell death under hyperglycemic conditions. SLIT treatment also induced a gradual release of endoplasmic reticulum luminal Ca(2+), suggesting a unique molecular mechanism capable of protecting beta cells from endoplasmic reticulum stress-induced apoptosis. SLIT treatment was also associated with rapid actin remodeling. SLITs potentiated glucose-stimulated insulin secretion and increased the frequency of glucose-induced Ca(2+) oscillations. These observations point to unexpected roles for local Slit secretion in the survival and function of pancreatic beta cells. Because diabetes results from a deficiency in functional beta-cell mass, these studies may contribute to therapeutic approaches for improving beta-cell survival and function.

Single-cell sequencing-based technologies will revolutionize whole-organism science

The unabated progress in next-generation sequencing technologies is fostering a wave of new genomics, epigenomics, transcriptomics and proteomics technologies. These sequencing-based technologies are increasingly being targeted to individual cells, which will allow many new and longstanding questions to be addressed. For example, single-cell genomics will help to uncover cell lineage relationships; single-cell transcriptomics will supplant the coarse notion of marker-based cell types; and single-cell epigenomics and proteomics will allow the functional states of individual cells to be analysed. These technologies will become integrated within a decade or so, enabling high-throughput, multi-dimensional analyses of individual cells that will produce detailed knowledge of the cell lineage trees of higher organisms, including humans. Such studies will have important implications for both basic biological research and medicine.

Conversion of mature human β-cells into glucagon-producing α-cells

Conversion of one terminally differentiated cell type into another (or transdifferentiation) usually requires the forced expression of key transcription factors. We examined the plasticity of human insulin-producing β-cells in a model of islet cell aggregate formation. Here, we show that primary human β-cells can undergo a conversion into glucagon-producing α-cells without introduction of any genetic modification. The process occurs within days as revealed by lentivirus-mediated β-cell lineage tracing. Converted cells are indistinguishable from native α-cells based on ultrastructural morphology and maintain their α-cell phenotype after transplantation in vivo. Transition of β-cells into α-cells occurs after β-cell degranulation and is characterized by the presence of β-cell-specific transcription factors Pdx1 and Nkx6.1 in glucagon(+) cells. Finally, we show that lentivirus-mediated knockdown of Arx, a determinant of the α-cell lineage, inhibits the conversion. Our findings reveal an unknown plasticity of human adult endocrine cells that can be modulated. This endocrine cell plasticity could have implications for islet development, (patho)physiology, and regeneration.

Herbal therapies for type 2 diabetes mellitus: chemistry, biology, and potential application of selected plants and compounds

Diabetes mellitus has been recognized since antiquity. It currently affects as many as 285 million people worldwide and results in heavy personal and national economic burdens. Considerable progress has been made in orthodox antidiabetic drugs. However, new remedies are still in great demand because of the limited efficacy and undesirable side effects of current orthodox drugs. Nature is an extraordinary source of antidiabetic medicines. To date, more than 1200 flowering plants have been claimed to have antidiabetic properties. Among them, one-third have been scientifically studied and documented in around 460 publications. In this review, we select and discuss blood glucose-lowering medicinal herbs that have the ability to modulate one or more of the pathways that regulate insulin resistance, β-cell function, GLP-1 homeostasis, and glucose (re)absorption. Emphasis is placed on phytochemistry, anti-diabetic bioactivities, and likely mechanism(s). Recent progress in the understanding of the biological actions, mechanisms, and therapeutic potential of compounds and extracts of plant origin in type 2 diabetes is summarized. This review provides a source of up-to-date information for further basic and clinical research into herbal therapy for type 2 diabetes. Emerging views on therapeutic strategies for type 2 diabetes are also discussed.

Herbal therapies for type 2 diabetes mellitus: chemistry, biology, and potential application of selected plants and compounds

Background:

Diabetes mellitus, becoming the third killer of mankind after cancer and cardiovascular diseases, is one of the most challenging diseases facing health care professionals today. That is why; there has been a growing interest in the therapeutic use of natural products for diabetes, especially those derived from plants.

Aim:

To evaluate the anti-diabetic activity together with the accompanying biological effects of the fractions and the new natural compounds of Hyphaene thebaica (HT) epicarp.

Materials and Methods:

500 g of coarsely powdered of (HT) fruits epicarp were extracted by acetone. The acetone crude extract was fractionated with methanol and ethyl acetate leaving a residual water-soluble fraction WF. The anti-diabetic effects of the WF and one of its compounds of the acetone extract of the (HT) epicarp were investigated in this study using 40 adult male rats.

Results:

Phytochemical investigation of active WF revealed the presence of ten different flavonoids, among which two new natural compounds luteolin 7-O-[6”-O-α-Lrhamnopyranosyl]-β-D-galactopyranoside 3 and chrysoeriol 7-O-β-D-galactopyranosyl(1→2)-α-L-arabinofuranoside 5 were isolated. Supplementation of the WF improved glucose and insulin tolerance and significantly lowered blood glycosylated hemoglobin levels. On the other hand, compound 5 significantly reduced AST and ALT levels of liver, respectively. Likewise, the kidney functions were improved for both WF and compound 5, whereby both urea and creatinine levels in serum were highly significant

Conclusion:

The results justify the use of WF and compound 5 of the (HT) epicarp as anti-diabetic agent, taking into consideration that the contents of WF were mainly flavonoids