Research Resource: A Dual Proteomic Approach Identifies Regulated Islet Proteins During β-Cell Mass Expansion In Vivo

Human vascularized macrophage-islet organoids to model immune-mediated pancreatic β cell pyroptosis upon viral infection

There is a paucity of human models to study immune-mediated host damage. Here, we utilized the GeoMx spatial multi-omics platform to analyze immune cell changes in COVID-19 pancreatic autopsy samples, revealing an accumulation of proinflammatory macrophages. Single-cell RNA sequencing (scRNA-seq) analysis of human islets exposed to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) or coxsackievirus B4 (CVB4) viruses identified activation of proinflammatory macrophages and β cell pyroptosis. To distinguish viral versus proinflammatory-macrophage-mediated β cell pyroptosis, we developed human pluripotent stem cell (hPSC)-derived vascularized macrophage-islet (VMI) organoids. VMI organoids exhibited enhanced marker expression and function in both β cells and endothelial cells compared with separately cultured cells. Notably, proinflammatory macrophages within VMI organoids induced β cell pyroptosis. Mechanistic investigations highlighted TNFSF12-TNFRSF12A involvement in proinflammatory-macrophage-mediated β cell pyroptosis. This study established hPSC-derived VMI organoids as a valuable tool for studying immune-cell-mediated host damage and uncovered the mechanism of β cell damage during viral exposure.

Identifying patterns differing between high-dimensional datasets with generalized contrastive PCA

High-dimensional data have become ubiquitous in the biological sciences, and it is often desirable to compare two datasets collected under different experimental conditions to extract low-dimensional patterns enriched in one condition. However, traditional dimensionality reduction techniques cannot accomplish this because they operate on only one dataset. Contrastive principal component analysis (cPCA) has been proposed to address this problem, but it has seen little adoption because it requires tuning a hyperparameter resulting in multiple solutions, with no way of knowing which is correct. Moreover, cPCA uses foreground and background conditions that are treated differently, making it ill-suited to compare two experimental conditions symmetrically. Here we describe the development of generalized contrastive PCA (gcPCA), a flexible hyperparameter-free approach that solves these problems. We first provide analyses explaining why cPCA requires a hyperparameter and how gcPCA avoids this requirement. We then describe an open-source gcPCA toolbox containing Python and MATLAB implementations of several variants of gcPCA tailored for different scenarios. Finally, we demonstrate the utility of gcPCA in analyzing diverse high-dimensional biological data, revealing unsupervised detection of hippocampal replay in neurophysiological recordings and heterogeneity of type II diabetes in single-cell RNA sequencing data. As a fast, robust, and easy-to-use comparison method, gcPCA provides a valuable resource facilitating the analysis of diverse high-dimensional datasets to gain new insights into complex biological phenomena.

Human Vascularized Macrophage-Islet Organoids to Model Immune-Mediated Pancreatic β cell Pyroptosis upon Viral Infection

There is a paucity of human models to study immune-mediated host damage. Here, we utilized the GeoMx spatial multi-omics platform to analyze immune cell changes in COVID-19 pancreatic autopsy samples, revealing an accumulation of proinflammatory macrophages. Single cell RNA-seq analysis of human islets exposed to SARS-CoV-2 or Coxsackievirus B4 (CVB4) viruses identified activation of proinflammatory macrophages and β cell pyroptosis. To distinguish viral versus proinflammatory macrophage-mediated β cell pyroptosis, we developed human pluripotent stem cell (hPSC)-derived vascularized macrophage-islet (VMI) organoids. VMI organoids exhibited enhanced marker expression and function in both β cells and endothelial cells compared to separately cultured cells. Notably, proinflammatory macrophages within VMI organoids induced β cell pyroptosis. Mechanistic investigations highlighted TNFSF12-TNFRSF12A involvement in proinflammatory macrophage-mediated β cell pyroptosis. This study established hPSC-derived VMI organoids as a valuable tool for studying immune cell-mediated host damage and uncovered mechanism of β cell damage during viral exposure.

Sulforaphane induced NRF2 activation in obese pregnancy attenuates developmental redox imbalance and improves early-life cardiovascular function in offspring

In adverse pregnancy a perturbed redox environment is associated with abnormal early-life cardiovascular development and function. Previous studies have noted alterations in the expression and/or activity of Nuclear Factor E2 Related Factor 2 (NRF2) and its antioxidant targets during human gestational diabetic (GDM) pregnancy, however to our knowledge the functional role of NRF2 in fetal 'priming' of cardiovascular dysfunction in obese and GDM pregnancy has not been investigated. Using a murine model of obesity-induced glucose dysregulated pregnancy, we demonstrate that NRF2 activation by maternal sulforaphane (SFN) supplementation normalizes NRF2-linked NQO1, GCL and CuZnSOD expression in maternal and fetal liver placental and fetal heart tissue by gestational day 17.5. Activation of NRF2 in utero in wild type but not NRF2 deficient mice improved markers of placental efficiency and partially restored fetal growth. SFN supplementation was associated with reduced markers of fetal cardiac oxidative stress, including Nox2 and 3-nitrotyrosine, as well as attenuation of cardiac mass and cardiomyocyte area in male offspring by postnatal day 52 and improved vascular function in male and female offspring by postnatal day 98. Our findings are the first to highlight the functional consequences of NRF2 modulation in utero on early-life cardiovascular function in offspring, demonstrating that activation of NRF2 affords cardiovascular protection in offspring of pregnancies affected by redox dysregulation.

Multiparity increases the risk of diabetes by impairing the proliferative capacity of pancreatic β cells

Pregnancy imposes a substantial metabolic burden on women, but little is known about whether or how multiple pregnancies increase the risk of maternal postpartum diabetes. In this study, we assessed the metabolic impact of multiple pregnancies in humans and in a rodent model. Mice that underwent multiple pregnancies had increased adiposity, but their glucose tolerance was initially improved compared to those of age-matched virgin mice. Later, however, insulin resistance developed over time, but insulin secretory function and compensatory pancreatic β cell proliferation were impaired in multiparous mice. The β cells of multiparous mice exhibited aging features, including telomere shortening and increased expression of Cdkn2a. Single-cell RNA-seq analysis revealed that the β cells of multiparous mice exhibited upregulation of stress-related pathways and downregulation of cellular respiration- and oxidative phosphorylation-related pathways. In humans, women who delivered more than three times were more obese, and their plasma glucose concentrations were elevated compared to women who had delivered three or fewer times, as assessed at 2 months postpartum. The disposition index, which is a measure of the insulin secretory function of β cells, decreased when women with higher parity gained body weight after delivery. Taken together, our findings indicate that multiple pregnancies induce cellular stress and aging features in β cells, which impair their proliferative capacity to compensate for insulin resistance.

NRF2 Dysregulation in Mice Leads to Inadequate Beta-Cell Mass Expansion during Pregnancy and Gestational Diabetes

The late stages of the mammalian pregnancy are accompanied with increased insulin resistance due to the increased glucose demand of the growing fetus. Therefore, as a compensatory response to maintain the maternal normal blood glucose levels, maternal beta-cell mass expands leading to increased insulin release. Defects in beta-cell adaptive expansion during pregnancy can lead to gestational diabetes mellitus (GDM). Although the exact mechanisms that promote GDM are poorly understood, GDM strongly associates with impaired beta-cell proliferation and with increased levels of reactive oxygen species (ROS). Here, we show that NRF2 levels are upregulated in mouse beta-cells at gestation day 15 (GD15) concomitant with increased beta-cell proliferation. Importantly, mice with tamoxifen-induced beta-cell-specific NRF2 deletion display inhibition of beta-cell proliferation, increased beta-cell oxidative stress and elevated levels of beta-cell death at GD15. This results in attenuated beta-cell mass expansion and disturbed glucose homeostasis towards the end of pregnancy. Collectively, these results highlight the importance of NRF2-oxidative stress regulation in beta-cell mass adaptation to pregnancy and suggest NRF2 as a potential therapeutic target for treating GDM.

Helicase-like transcription factor (Hltf)-deletion activates Hmgb1-Rage axis and granzyme A-mediated killing of pancreatic β cells resulting in neonatal lethality

Epigenetic mechanisms are integral to pancreatic β cell function. Promoter hypermethylation of the helicase like-transcription factor (HLTF) gene-a component of the cellular DNA damage response that contributes to genome stability-has been implicated in age-associated changes in β cells. To study HLTF, we generated global and β cell-specific (β) Hltf knockout (KO) immune competent (IC) and immune deficient (ID) Rag2-/IL2- mice. IC global and β Hltf KO mice were neonatal lethal whereas ID global and β Hltf KO newborn mice had normal survival. This focused our investigation on the effects of Rag2 interruption with common gamma chain interruption on β cell function/survival. Three-way transcriptomic (RNAseq) analyses of whole pancreata from IC and ID newborn β Hltf KO and wild type (Hltf +/+) controls combined with spatially resolved transcriptomic analysis of formalin fixed paraffin embedded tissue, immunohistochemistry and laser scanning confocal microscopy showed DNA damage caused by β Hltf KO in IC mice upregulated the Hmgb1-Rage axis and a gene signature for innate immune cells. Perforin-delivered granzyme A (GzmA) activation of DNase, Nme1, showed damaged nuclear single-stranded DNA (γH2AX immunostaining). This caspase-independent method of cell death was supported by transcriptional downregulation of Serpinc1 gene that encodes a serine protease inhibitor of GzmA. Increased transcriptional availability of complement receptors C3ar1 and C5ar1 likely invited crosstalk with Hmgb1 to amplify inflammation. This study explores the complex dialog between β cells and immune cells during development. It has implications for the initiation of type I diabetes in utero when altered gene expression that compromises genome stability invokes a localized inflammatory response.

Polarized macrophages promote gestational beta cell growth through extracellular signal-regulated kinase 5 signalling

AIM

To show that depletion of pancreatic macrophages impairs gestational beta cell proliferation and leads to glucose intolerance.

MATERIALS AND METHODS

Genetic animal models were applied to study the effects of depletion of pancreatic macrophges on gestational beta-cell proliferaiton and glucose response. The crosstalk between macrophages and beta-cells was studied in vivo using beta-cell-specific extracellular-signal-regulated kinase 5 (ERK5) knockout and epidermal growth receptor (EGFR) knockout mice, and in vitro using a co-culture system.

RESULTS

Beta cell-derived placental growth factor (PlGF) recruited naïve macrophages and polarized them towards an M2-like phenotype. These macrophages then secreted epidermal growth factor (EGF), which activated extracellular signal-regulated kinase 5 (ERK5) signalling in beta cells to promote gestational beta cell proliferation. On the other hand, activation of ERK5 signalling in beta cells likely, in turn, enhanced the production and secretion of PlGF by beta cells.

CONCLUSIONS

Our study shows a regulatory loop between macrophages and beta cells through PlGF/EGF/ERK5 signalling cascades to regulate gestational beta cell growth.

Potential role of oxidative stress in the pathogenesis of diabetic bladder dysfunction

Diabetes mellitus is a chronic metabolic disease, posing a considerable threat to global public health. Treating systemic comorbidities has been one of the greatest clinical challenges in the management of diabetes. Diabetic bladder dysfunction, characterized by detrusor overactivity during the early stage of the disease and detrusor underactivity during the late stage, is a common urological complication of diabetes. Oxidative stress is thought to trigger hyperglycaemia-dependent tissue damage in multiple organs; thus, a growing body of literature has suggested a possible link between functional changes in urothelium, muscle and the corresponding innervations. Improved understanding of the mechanisms of oxidative stress could lead to the development of novel therapeutics to restore the redox equilibrium and scavenge excessive free radicals to normalize bladder function in patients with diabetes.

Adaptive Changes in Glucose Homeostasis and Islet Function During Pregnancy: A Targeted Metabolomics Study in Mice

OBJECTIVE

Pregnancy is a dynamic state involving multiple metabolic adaptions in various tissues including the endocrine pancreas. However, a detailed characterization of the maternal islet metabolome in relation to islet function and the ambient circulating metabolome during pregnancy has not been established.

METHODS

A timed-pregnancy mouse model was studied, and age-matched non-pregnant mice were used as controls. Targeted metabolomics was applied to fasting plasma and purified islets during each trimester of pregnancy. Glucose homeostasis and islet function was assessed. Bioinformatic analyses were performed to reveal the metabolic adaptive changes in plasma and islets, and to identify key metabolic pathways associated with pregnancy.

RESULTS

Fasting glucose and insulin were found to be significantly lower in pregnant mice compared to non-pregnant controls, throughout the gestational period. Additionally, pregnant mice had superior glucose excursions and greater insulin response to an oral glucose tolerance test. Interestingly, both alpha and beta cell proliferation were significantly enhanced in early to mid-pregnancy, leading to significantly increased islet size seen in mid to late gestation. When comparing the plasma metabolome of pregnant and non-pregnant mice, phospholipid and fatty acid metabolism pathways were found to be upregulated throughout pregnancy, whereas amino acid metabolism initially decreased in early through mid pregnancy, but then increased in late pregnancy. Conversely, in islets, amino acid metabolism was consistently enriched throughout pregnancy, with glycerophospholid and fatty acid metabolism was only upregulated in late pregnancy. Specific amino acids (glutamate, valine) and lipids (acyl-alkyl-PC, diacyl-PC, and sphingomyelin) were found to be significantly differentially expressed in islets of the pregnant mice compared to controls, which was possibly linked to enhanced insulin secretion and islet proliferation.

CONCLUSION

Beta cell proliferation and function are elevated during pregnancy, and this is coupled to the enrichment of islet metabolites and metabolic pathways primarily associated with amino acid and glycerophospholipid metabolism. This study provides insight into metabolic adaptive changes in glucose homeostasis and islet function seen during pregnancy, which will provide a molecular rationale to further explore the regulation of maternal metabolism to avoid the onset of pregnancy disorders, including gestational diabetes.

Ontology of the apelinergic system in mouse pancreas during pregnancy and relationship with β-cell mass

The apelin receptor (Aplnr) and its ligands, Apelin and Apela, contribute to metabolic control. The insulin resistance associated with pregnancy is accommodated by an expansion of pancreatic β-cell mass (BCM) and increased insulin secretion, involving the proliferation of insulin-expressing, glucose transporter 2-low (Ins+Glut2LO) progenitor cells. We examined changes in the apelinergic system during normal mouse pregnancy and in pregnancies complicated by glucose intolerance with reduced BCM. Expression of Aplnr, Apelin and Apela was quantified in Ins+Glut2LO cells isolated from mouse pancreata and found to be significantly higher than in mature β-cells by DNA microarray and qPCR. Apelin was localized to most β-cells by immunohistochemistry although Aplnr was predominantly associated with Ins+Glut2LO cells. Aplnr-staining cells increased three- to four-fold during pregnancy being maximal at gestational days (GD) 9-12 but were significantly reduced in glucose intolerant mice. Apelin-13 increased β-cell proliferation in isolated mouse islets and INS1E cells, but not glucose-stimulated insulin secretion. Glucose intolerant pregnant mice had significantly elevated serum Apelin levels at GD 9 associated with an increased presence of placental IL-6. Placental expression of the apelinergic axis remained unaltered, however. Results show that the apelinergic system is highly expressed in pancreatic β-cell progenitors and may contribute to β-cell proliferation in pregnancy.

Type 1 Diabetes and the HLA Region: Genetic Association Besides Classical HLA Class II Genes

Type 1 diabetes is an autoimmune disease with rising incidence in high-income countries. Genetic and environmental predisposing factors contribute to the etiology of the disease, although their interaction is not sufficiently understood to allow for preventive action. Strongest known associations with genetic variation map to classical HLA class II genes. Because of its genetic complexity, the HLA region has been under-represented in genome-wide association studies, having potentially hindered the identification of relevant associations underlying the etiology of the disease. Here, we performed a comprehensive HLA-wide genetic association analysis of type 1 diabetes including multi-allelic and rare variants. We used high-density whole-exome sequencing data of the HLA region in the large UK Biobank dataset to apply gene-based association tests with a carefully defined type 1 diabetes phenotype (97 cases and 48,700 controls). Exon-based and single-variant association tests were used to complement the analysis. We replicated the known association of type 1 diabetes with the classical HLA-DQ gene. Tailoring the analysis toward rare variants, we additionally identified the lysine methyl transferase EHMT2 as associated. Deeper insight into genetic variation associated with disease as presented and discussed in detail here can help unraveling mechanistic details of the etiology of type 1 diabetes. More specifically, we hypothesize that genetic variation in EHMT2 could impact autoimmunity in type 1 diabetes development.

Diabetes during Pregnancy: A Maternal Disease Complicating the Course of Pregnancy with Long-Term Deleterious Effects on the Offspring. A Clinical Review

In spite of the huge progress in the treatment of diabetes mellitus, we are still in the situation that both pregestational (PGDM) and gestational diabetes (GDM) impose an additional risk to the embryo, fetus, and course of pregnancy. PGDM may increase the rate of congenital malformations, especially cardiac, nervous system, musculoskeletal system, and limbs. PGDM may interfere with fetal growth, often causing macrosomia, but in the presence of severe maternal complications, especially nephropathy, it may inhibit fetal growth. PGDM may also induce a variety of perinatal complications such as stillbirth and perinatal death, cardiomyopathy, respiratory morbidity, and perinatal asphyxia. GDM that generally develops in the second half of pregnancy induces similar but generally less severe complications. Their severity is higher with earlier onset of GDM and inversely correlated with the degree of glycemic control. Early initiation of GDM might even cause some increase in the rate of congenital malformations. Both PGDM and GDM may cause various motor and behavioral neurodevelopmental problems, including an increased incidence of attention deficit hyperactivity disorder (ADHD) and autism spectrum disorder (ASD). Most complications are reduced in incidence and severity with the improvement in diabetic control. Mechanisms of diabetic-induced damage in pregnancy are related to maternal and fetal hyperglycemia, enhanced oxidative stress, epigenetic changes, and other, less defined, pathogenic mechanisms.

Chromogranin A-positive hormone-negative endocrine cells in pancreas in human pregnancy

Introduction

We sought to determine whether chromogranin A‐positive hormone‐negative (CPHN) endocrine cells are increased in the pancreas of pregnant women, offering potential evidence in support of neogenesis.

Methods

Autopsy pancreata from pregnant women (n = 14) and age‐matched non‐pregnant control women (n = 9) were obtained. Staining of pancreatic sections for chromogranin A, insulin and a cocktail of glucagon, somatostatin, pancreatic polypeptide and ghrelin was undertaken, with subsequent evaluation for CPHN cell frequency.

Results

The frequency of clustered β‐cells was increased in pregnant compared to non‐pregnant subjects (46.6 ± 5.0 vs. 31.8 ± 5.0% clustered β‐cells of total clustered endocrine cells, pregnant vs. non‐pregnant, p < .05). Frequency of endocrine cocktail cells was lower in pregnant women than non‐pregnant women (36.2 ± 4.0 vs. 57.0 ± 6.8% clustered endocrine cocktail cells of total clustered endocrine cells, pregnant vs. non‐pregnant, p < .01). No difference in frequency of CPHN cells was found in islets, nor in clustered or single cells scattered throughout the exocrine pancreas, between pregnant and non‐pregnant women. The frequency of CPHN cells in pregnancy was independent of the number of pregnancies (gravidity).

Conclusions

Our findings of no increase in CPHN cell frequency in pancreas of pregnant women suggest that this potential β‐cell regenerative mechanism is not that by which the increased β‐cell mass of pregnancy is achieved. However, an increase in the percentage of clustered β‐cells was found in pregnancy, with decreased frequency of other endocrine cells in clusters, suggesting a compensatory shift from other pancreatic endocrine cell types to β‐cells as a mechanism to meet the increased insulin demands of pregnancy.

Nrf2: The Master and Captain of Beta Cell Fate

Prolonged hyperglycemia is toxic to pancreatic β cells, generating excessive reactive oxygen species, defective glucose-stimulated insulin secretion, decreased insulin production, and eventually β cell death and diabetes. Nrf2 is a master regulator of cellular responses to counteract dangerous levels of oxidative stress. Maintenance of β cell mass depends on Nrf2 to promote the survival, function, and proliferation of β cells. Indeed, Nrf2 activation decreases inflammation, increases insulin sensitivity, reduces body weight, and preserves β cell mass. Therefore, numerous pharmacological activators of Nrf2 are being tested in clinical trials for the treatment of diabetes and diabetic complications. Modulating Nrf2 activity in β cells is a promising therapeutic approach for the treatment of diabetes.

The many lives of Myc in the pancreatic β-cell

Diabetes results from insufficient numbers of functional pancreatic β-cells. Thus, increasing the number of available functional β-cells ex vivo for transplantation, or regenerating them in situ in diabetic patients, is a major focus of diabetes research. The transcription factor, Myc, discovered decades ago lies at the nexus of most, if not all, known proliferative pathways. Based on this, many studies in the 1990s and early 2000s explored the potential of harnessing Myc expression to expand β-cells for diabetes treatment. Nearly all these studies in β-cells used pathophysiological or supraphysiological levels of Myc and reported enhanced β-cell death, dedifferentiation, or the formation of insulinomas if cooverexpressed with Bcl-xL, an inhibitor of apoptosis. This obviously reduced the enthusiasm for Myc as a therapeutic target for β-cell regeneration. However, recent studies indicate that "gentle" induction of Myc expression enhances β-cell replication without induction of cell death or loss of insulin secretion, suggesting that appropriate levels of Myc could have therapeutic potential for β-cell regeneration. Furthermore, although it has been known for decades that Myc is induced by glucose in β-cells, very little is known about how this essential anabolic transcription factor perceives and responds to nutrients and increased insulin demand in vivo. Here we summarize the previous and recent knowledge of Myc in the β-cell, its potential for β-cell regeneration, and its physiological importance for neonatal and adaptive β-cell expansion.

Integrative transcriptomic analysis of pancreatic islets from patients with prediabetes/type 2 diabetes

AIM

To identify new transcriptomic alterations in pancreatic islets associated with metabolic dysfunctions in people with prediabetes (PD)/type 2 diabetes (T2D).

MATERIALS AND METHODS

We collected information from public data repositories T2D related microarray datasets from pancreatic islets. We identified Differential Expressed Genes (DEGs) in non-diabetic (ND) vs people with T2D in each study. To identify relevant DEGs in T2D, we selected those that varied consistently in the different studies for further meta-analysis and functional enrichment analysis. DEGs were also evaluated at the PD stage.

RESULTS

A total of seven microarray datasets were collected and analysed to find the DEGs in each study and meta-analysis was performed with 245 ND and 96 T2D cases. We identified 55 transcriptional alterations potentially associated with specific metabolic dysfunctions in T2D. Meta-analysis showed that 87% of transcripts identified as DEGs (48 out of 55) were confirmed as having statistically significant up- or down-modulation in T2D compared to ND. Notably, nine of these DEGs have not been previously reported as dysregulated in pancreatic islets from people with T2D. Consistently, the most significantly enriched pathways were related to the metabolism and/or development/maintenance of β-cells. Eighteen of the 48 selected DEGs (38%) showed an altered expression in islets from people with PD.

CONCLUSIONS

These results provide new evidence to interpret the pathogenesis of T2D and the transition from PD to T2D. Further studies are necessary to validate its potential use for the development/implementation of efficient new strategies for the prevention, diagnosis/prognosis and treatment of T2D.

Regulation of integrin α6A by lactogenic hormones in rat pancreatic β-cells: Implications for the physiological adaptation to pregnancy

AIM

During pregnancy, the maternal β-cell mass is increased in order to adapt to the physiological changes in insulin demand. Lactogenic hormones stimulate rodent β-cell attachment and proliferation in vitro. The aim of this study was to identify adhesion molecules involved in expansion of the β-cell mass during pregnancy in the rat.

METHODS

Quantitative RT-PCR was used to evaluate the expression of several integrins and laminins in isolated neonatal rat islets in response to growth hormone (GH) and prolactin (PRL) treatment. Double-immunofluorescence staining of rat pancreas was used to localize the expression of integrin α6β1. β-cell proliferation was evaluated by incorporation of bromodeoxyuridine (BrdU). The role of STAT5 phosphorylation was tested by addition of STAT5 mutants.

RESULTS

We found that the mRNA level of integrin-α6A, was upregulated 2.5-fold by PRL or GH. During pregnancy, a biphasic 3.4-4.5-fold increase of integrin-α6A and B mRNA levels was detected. A disintegrin peptide (DP) reduced the hormone-stimulated mitotic activity in neonatal rat β-cells from 2.9 ± 0.4-fold to 1.3 ± 0.3-fold. The hormone-induced expression of α6β1 integrin was shown to be mediated via STAT5 as a dominant negative (DN) mutant prevented and a constitutive active (CA) mutant augmented the hGH-stimulated expression. The DP was found to inhibit hGH-induced transactivation of the PRL receptor promoter 1A and reduce the hGH-induced phosphorylation of STAT5.

CONCLUSION

These results show that integrin-α6 in β-cells is upregulated by lactogenic hormones and is required but not sufficient for the expansion of the β-cell mass in pregnancy in the rat, which may have implications for the understanding and treatment of gestational diabetes mellitus.

Myc Is Required for Adaptive β-Cell Replication in Young Mice but Is Not Sufficient in One-Year-Old Mice Fed With a High-Fat Diet

Failure to expand pancreatic β-cells in response to metabolic stress leads to excessive workload resulting in β-cell dysfunction, dedifferentiation, death, and development of type 2 diabetes. In this study, we demonstrate that induction of Myc is required for increased pancreatic β-cell replication and expansion during metabolic stress-induced insulin resistance with short-term high-fat diet (HFD) in young mice. β-Cell-specific Myc knockout mice fail to expand adaptively and show impaired glucose tolerance and β-cell dysfunction. Mechanistically, PKCζ, ERK1/2, mTOR, and PP2A are key regulators of the Myc response in this setting. DNA methylation analysis shows hypomethylation of cell cycle genes that are Myc targets in islets from young mice fed with a short-term HFD. Importantly, DNA hypomethylation of Myc response elements does not occur in islets from 1-year-old mice fed with a short-term HFD, impairing both Myc recruitment to cell cycle regulatory genes and β-cell replication. We conclude that Myc is required for metabolic stress-mediated β-cell expansion in young mice, but with aging, Myc upregulation is not sufficient to induce β-cell replication by, at least partially, an epigenetically mediated resistance to Myc action.

miRDRN-miRNA disease regulatory network: a tool for exploring disease and tissue-specific microRNA regulatory networks

BACKGROUND

MicroRNA (miRNA) regulates cellular processes by acting on specific target genes, and cellular processes proceed through multiple interactions often organized into pathways among genes and gene products. Hundreds of miRNAs and their target genes have been identified, as are many miRNA-disease associations. These, together with huge amounts of data on gene annotation, biological pathways, and protein-protein interactions are available in public databases. Here, using such data we built a database and web service platform, miRNA disease regulatory network (miRDRN), for users to construct disease and tissue-specific miRNA-protein regulatory networks, with which they may explore disease related molecular and pathway associations, or find new ones, and possibly discover new modes of drug action.

METHODS

Data on disease-miRNA association, miRNA-target association and validation, gene-tissue association, gene-tumor association, biological pathways, human protein interaction, gene ID, gene ontology, gene annotation, and product were collected from publicly available databases and integrated. A large set of miRNA target-specific regulatory sub-pathways (RSPs) having the form (T, G 1, G 2) was built from the integrated data and stored, where T is a miRNA-associated target gene, G 1 (G 2) is a gene/protein interacting with T (G 1). Each sequence (T, G 1, G 2) was assigned a p-value weighted by the participation of the three genes in molecular interactions and reaction pathways.

RESULTS

A web service platform, miRDRN (http://mirdrn.ncu.edu.tw/mirdrn/), was built. The database part of miRDRN currently stores 6,973,875 p-valued RSPs associated with 116 diseases in 78 tissue types built from 207 diseases-associated miRNA regulating 389 genes. miRDRN also provides facilities for the user to construct disease and tissue-specific miRNA regulatory networks from RSPs it stores, and to download and/or visualize parts or all of the product. User may use miRDRN to explore a single disease, or a disease-pair to gain insights on comorbidity. As demonstrations, miRDRN was applied: to explore the single disease colorectal cancer (CRC), in which 26 novel potential CRC target genes were identified; to study the comorbidity of the disease-pair Alzheimer's disease-Type 2 diabetes, in which 18 novel potential comorbid genes were identified; and, to explore possible causes that may shed light on recent failures of late-phase trials of anti-AD, BACE1 inhibitor drugs, in which genes downstream to BACE1 whose suppression may affect signal transduction were identified.

Prolactin Receptor Signaling Regulates a Pregnancy-Specific Transcriptional Program in Mouse Islets

Pancreatic β-cells undergo profound hyperplasia during pregnancy to maintain maternal euglycemia. Failure to reprogram β-cells into a more replicative state has been found to underlie susceptibility to gestational diabetes mellitus (GDM). We recently identified a requirement for prolactin receptor (PRLR) signaling in the metabolic adaptations to pregnancy, where β-cell-specific PRLR knockout (βPRLRKO) mice exhibit a metabolic phenotype consistent with GDM. However, the underlying transcriptional program that is responsible for the PRLR-dependent metabolic adaptations during gestation remains incompletely understood. To identify PRLR signaling gene regulatory networks and target genes within β-cells during pregnancy, we performed a transcriptomic analysis of pancreatic islets isolated from either βPRLRKO mice or littermate controls in late gestation. Gene set enrichment analysis identified forkhead box protein M1 and polycomb repressor complex 2 subunits, Suz12 and enhancer of zeste homolog 2 (Ezh2), as novel candidate regulators of PRLR-dependent β-cell adaptation. Gene ontology term pathway enrichment revealed both established and novel PRLR signaling target genes that together promote a state of increased cellular metabolism and/or proliferation. In contrast to the requirement for β-cell PRLR signaling in maintaining euglycemia during pregnancy, PRLR target genes were not induced following high-fat diet feeding. Collectively, the current study expands our understanding of which transcriptional regulators and networks mediate gene expression required for islet adaptation during pregnancy. The current work also supports the presence of pregnancy-specific adaptive mechanisms distinct from those activated by nutritional stress.

Glucose-dependent phosphorylation signaling pathways and crosstalk to mitochondrial respiration in insulin secreting cells

Background

Glucose is the main secretagogue of pancreatic beta-cells. Uptake and metabolism of the nutrient stimulates the beta-cell to release the blood glucose lowering hormone insulin. This metabolic activation is associated with a pronounced increase in mitochondrial respiration. Glucose stimulation also initiates a number of signal transduction pathways for the coordinated regulation of multiple biological processes required for insulin secretion.

Methods

Shotgun proteomics including TiO₂ enrichment of phosphorylated peptides followed by liquid chromatography tandem mass spectrometry on lysates from glucose-stimulated INS-1E cells was used to identify glucose regulated phosphorylated proteins and signal transduction pathways. Kinase substrate enrichment analysis (KSEA) was applied to identify key regulated kinases and phosphatases. Glucose-induced oxygen consumption was measured using a XF96 Seahorse instrument to reveal cross talk between glucose-regulated kinases and mitochondrial activation.

Results

Our kinetic analysis of substrate phosphorylation reveal the molecular mechanism leading to rapid activation of insulin biogenesis, vesicle trafficking, insulin granule exocytosis and cytoskeleton remodeling. Kinase-substrate enrichment identified upstream kinases and phosphatases and time-dependent activity changes during glucose stimulation. Activity trajectories of well-known glucose-regulated kinases and phosphatases are described. In addition, we predict activity changes in a number of kinases including NUAK1, not or only poorly studied in the context of the pancreatic beta-cell. Furthermore, we pharmacologically tested whether signaling pathways predicted by kinase-substrate enrichment analysis affected glucose-dependent acceleration of mitochondrial respiration. We find that phosphoinositide 3-kinase, Ca2+/calmodulin dependent protein kinase and protein kinase C contribute to short-term regulation of energy metabolism.

Conclusions

Our results provide a global view into the regulation of kinases and phosphatases in insulin secreting cells and suggest cross talk between glucose-induced signal transduction and mitochondrial activation.

Electronic supplementary material

The online version of this article (10.1186/s12964-019-0326-6) contains supplementary material, which is available to authorized users.

Maternal β-Cell Adaptations in Pregnancy and Placental Signalling: Implications for Gestational Diabetes

Rates of gestational diabetes mellitus (GDM) are on the rise worldwide, and the number of pregnancies impacted by GDM and resulting complications are also increasing. Pregnancy is a period of unique metabolic plasticity, during which mild insulin resistance is a physiological adaptation to prioritize fetal growth. To compensate for this, the pancreatic β-cell utilizes a variety of adaptive mechanisms, including increasing mass, number and insulin-secretory capacity to maintain glucose homeostasis. When insufficient insulin production does not overcome insulin resistance, hyperglycemia can occur. Changes in the maternal system that occur in GDM such as lipotoxicity, inflammation and oxidative stress, as well as impairments in adipokine and placental signalling, are associated with impaired β-cell adaptation. Understanding these pathways, as well as mechanisms of β-cell dysfunction in pregnancy, can identify novel therapeutic targets beyond diet and lifestyle interventions, insulin and antihyperglycemic agents currently used for treating GDM.

Activation of Nrf2 Is Required for Normal and ChREBPα-Augmented Glucose-Stimulated β-Cell Proliferation

Patients with both major forms of diabetes would benefit from therapies that increase β-cell mass. Glucose, a natural mitogen, drives adaptive expansion of β-cell mass by promoting β-cell proliferation. We previously demonstrated that a carbohydrate response element-binding protein (ChREBPα) is required for glucose-stimulated β-cell proliferation and that overexpression of ChREBPα amplifies the proliferative effect of glucose. Here we found that ChREBPα reprogrammed anabolic metabolism to promote proliferation. ChREBPα increased mitochondrial biogenesis, oxygen consumption rates, and ATP production. Proliferation augmentation by ChREBPα required the presence of ChREBPβ. ChREBPα increased the expression and activity of Nrf2, initiating antioxidant and mitochondrial biogenic programs. The induction of Nrf2 was required for ChREBPα-mediated mitochondrial biogenesis and for glucose-stimulated and ChREBPα-augmented β-cell proliferation. Overexpression of Nrf2 was sufficient to drive human β-cell proliferation in vitro; this confirms the importance of this pathway. Our results reveal a novel pathway necessary for β-cell proliferation that may be exploited for therapeutic β-cell regeneration.

Diabetes in pregnancy: a new decade of challenges ahead

Every 10 years, the Diabetic Pregnancy Study Group, a study group of the EASD, conducts an audit meeting to review the achievements of the preceding decade and to set the directions for research and clinical practice improvements for the next decade. The most recent meeting focused on the following areas: improving pregnancy outcomes for women with pregestational type 1 diabetes and type 2 diabetes; the influence of obesity and gestational diabetes on pregnancy outcomes; the determinants and assessment of fetal growth and development; and public health issues, including consideration of transgenerational consequences and economic burden. The audit meeting also considered the likely impact of 'omics' on research within the field and the potential of these technologies to enable precision-medicine approaches to management. Through sharing of the findings and ideas of audit meeting participants, the DPSG hopes to promote networking, research and advances in clinical care, to improve outcomes for all women and their offspring affected by diabetes and obesity in pregnancy.

Advances in β cell replacement and regeneration strategies for treating diabetes

In the past decade, new approaches have been explored that are aimed at restoring functional β cell mass as a treatment strategy for diabetes. The two most intensely pursued strategies are β cell replacement through conversion of other cell types and β cell regeneration by enhancement of β cell replication. The approach closest to clinical implementation is the replacement of β cells with human pluripotent stem cell-derived (hPSC-derived) cells, which are currently under investigation in a clinical trial to assess their safety in humans. In addition, there has been success in reprogramming developmentally related cell types into β cells. Reprogramming approaches could find therapeutic applications by inducing β cell conversion in vivo or by reprogramming cells ex vivo followed by implantation. Finally, recent studies have revealed novel pharmacologic targets for stimulating β cell replication. Manipulating these targets or the pathways they regulate could be a strategy for promoting the expansion of residual β cells in diabetic patients. Here, we provide an overview of progress made toward β cell replacement and regeneration and discuss promises and challenges for clinical implementation of these strategies.

Pancreatic Islet Responses to Metabolic Trauma

Carbohydrate, lipid, and protein metabolism are largely controlled by the interplay of various hormones, which includes those secreted by the pancreatic islets of Langerhans. While typically representing only 1% to 2% of the total pancreatic mass, the islets have a remarkable ability to adapt to disparate situations demanding a change in hormone release, such as peripheral insulin resistance. There are many different routes to the onset of insulin resistance, including obesity, lipodystrophy, glucocorticoid excess, and the chronic usage of atypical antipsychotic drugs. All of these situations are coupled to an increase in pancreatic islet size, often with a corresponding increase in insulin production. These adaptive responses within the islets are ultimately intended to maintain glycemic control and to promote macronutrient homeostasis during times of stress. Herein, we review the consequences of specific metabolic trauma that lead to insulin resistance and the corresponding adaptive alterations within the pancreatic islets.

Beta cell adaptation in pregnancy: a tribute to Claes Hellerström

Pregnancy is associated with a compensatory increase in beta cell mass. It is well established that somatolactogenic hormones contribute to the expansion both indirectly by their insulin antagonistic effects and directly by their mitogenic effects on the beta cells via receptors for prolactin and growth hormone expressed in rodent beta cells. However, the beta cell expansion in human pregnancy seems to occur by neogenesis of beta cells from putative progenitor cells rather than by proliferation of existing beta cells. Claes Hellerström has pioneered the research on beta cell growth for decades, but the mechanisms involved are still not clarified. In this review the information obtained in previous studies is recapitulated together with some of the current attempts to resolve the controversy in the field: identification of the putative progenitor cells, identification of the factors involved in the expansion of the beta cell mass in human pregnancy, and the relative roles of endocrine factors and nutrients.