Expansion Of Beta-cell Mass Research Articles

Extra-islet cells expressing insulin or glucagon in the pancreas of young organ donors

AimsThe existence of insulin- or glucagon-expressing extra-islet endocrine cells scattered in the pancreas is well-known, but they have been sparsely characterized. The aim of this study was to examine their density, distribution, transcription-factor expression, and mitotic activity in young non-diabetic subjects.MethodsMultispectral imaging was used to examine PDX1, ARX, Ki67, insulin and glucagon in extra-islet endocrine cells in pancreatic tissue from organ donors aged 1–25 years.ResultsExtra-islet insulin- or glucagon-positive cells were frequent in all donors (median 17.3 and 22.9 cells/mm2 respectively), with an insulin:glucagon cell ratio of 0.9. The density was similar regardless of age. PDX1 localized mainly to insulin-, and ARX mainly to glucagon-positive cells but, interestingly, many of the cells were negative for both transcription factors. Double-hormone-positive cells were rare but found in all age groups, as were insulin-positive cells expressing ARX and glucagon-positive cells expressing PDX1. Extra-islet endocrine cells with Ki67 expression were present but rare (0–2%) in all age groups.ConclusionsExtra-islet endocrine cells are more frequent than islets. The preserved extra-islet cell density during pancreas volume-expansion from childhood- to adulthood indicates that new cells are formed, possibly from replication as cells with mitotic activity were discovered. The lack of transcription-factor expression in many cells indicates that they are immature, newly formed or plastic. This, together with the mitotic activity, suggests that these cells could play an important role in the expansion of beta-cell mass in situations of increasing demand, or in the turnover of the endocrine cell population.

The selective serotonin reuptake inhibitors, sertraline and paroxetine, improve islet beta-cell mass and function in vitro.

To investigate the effects of the selective serotonin reuptake inhibitors (SSRIs) sertraline and paroxetine at therapeutically relevant concentrations on beta-cell mass and function. Viability was quantified in mouse insulinoma (MIN6) beta cells and mouse islets after 48-h exposure to sertraline (1-10 μM) or paroxetine (0.01-1 μM) using the Trypan blue exclusion test. The effects of therapeutic concentrations of these SSRIs on insulin secretion were determined by static incubation and perifusion experiments, while islet apoptosis was investigated by Caspase-Glo 3/7 assay, TUNEL staining and quantitative PCR analysis. Finally, proliferation of MIN6 and mouse islet beta cells was assessed by bromodeoxyuridine (BrdU) enzyme-linked immunosorbent assay and immunofluorescence. Sertraline (0.1-1 μM) and paroxetine (0.01-0.1 μM) were well tolerated by MIN6 beta cells and islets, whereas 10 μM sertraline and 1 μM paroxetine were cytotoxic. Exposure to 1 μM sertraline and 0.1 μM paroxetine significantly potentiated glucose-stimulated insulin secretion from mouse and human islets. Moreover, they showed protective effects against cytokine- and palmitate-induced apoptosis of islets, they downregulated cytokine-induced Stat1 and Traf1 mRNA expression, and they significantly increased proliferation of mouse beta cells. Our data demonstrate that sertraline and paroxetine act directly on beta cells to enhance glucose-stimulated insulin secretion and stimulate beta-cell mass expansion by increasing proliferation and decreasing apoptosis. These drugs are therefore likely to be appropriate for treating depression in people with type 2 diabetes.

The liver-derived exosomes stimulate insulin gene expression in pancreatic beta cells under condition of insulin resistance.

An insufficient functional beta cell mass is a core pathological hallmark of type 2 diabetes (T2D). Despite the availability of several effective pharmaceuticals for diabetes management, there is an urgent need for novel medications to protect pancreatic beta cells under diabetic conditions. Integrative organ cross-communication controls the energy balance and glucose homeostasis. The liver and pancreatic islets have dynamic cross-communications where the liver can trigger a compensatory beta cell mass expansion and enhanced hormonal secretion in insulin-resistant conditions. However, the indispensable element(s) that foster beta cell proliferation and insulin secretion have yet to be completely identified. Exosomes are important extracellular vehicles (EVs) released by most cell types that transfer biological signal(s), including metabolic messengers such as miRNA and peptides, between cells and organs. We investigated whether beta cells can take up liver-derived exosomes and examined their impact on beta cell functional genes and insulin expression. Exosomes isolated from human liver HepG2 cells were characterized using various methods, including Transmission Electron Microscopy (TEM), dynamic light scattering (DLS), and Western blot analysis of exosomal markers. Exosome labeling and cell uptake were assessed using CM-Dil dye. The effect of liver cell-derived exosomes on Min6 beta cells was determined through gene expression analyses of beta cell markers and insulin using qPCR, as well as Akt signaling using Western blotting. Treatment of Min6 beta cells with exosomes isolated from human liver HepG2 cells treated with insulin receptor antagonist S961 significantly increased the expression of beta cell markers Pdx1, NeuroD1, and Ins1 compared to the exosomes isolated from untreated cells. In line with this, the activity of AKT kinase, an integral component of the insulin receptor pathway, is elevated in pancreatic beta cells, as represented by an increase in AKT's downstream substrate, FoxO1 phosphorylation. This study suggests that liver-derived exosomes may carry a specific molecular cargo that can affect insulin expression in pancreatic beta cells, ultimately affecting glucose homeostasis.

OR12-02 NRF2 Is Essential For Expanding Pancreatic Beta-Cell Mass During Pregnancy

Abstract Disclosure: S. Baumel-Alterzon: None. A. Garcia-Ocana: None. D.K. Scott: None. 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, in order to maintain the maternal normal blood glucose levels, maternal beta-cell mass expands leading to increased insulin release. Beta-cell proliferation, beta-cell neogenesis, and decreased beta-cell apoptosis, are major contributors for the beta-cell adaptive response during pregnancy. Defects in these cellular processes can lead to gestational diabetes mellitus (GDM). GDM, which occurs in ∼7-8% of the total pregnancy cases within the U.S, results in adverse outcomes for both the mother and newborn. This highlights the urgent need for exploring the yet undefined intracellular mechanisms that regulate functional beta-cell mass expansion during pregnancy. GWAS analysis revealed several mutations in the Nrf2 antioxidant pathway that are associated with diabetes. Additionally, we previously found that Nrf2 is required for adaptive beta-cell expansion after high fat feeding via stimulation of beta-cell proliferation, increased beta-cell survival, and maintenance of beta-cell identity. Interestingly, Nrf2 expression levels are increased by 4.3-fold (+/- 6.60, p<0.05, n=3-4) in maternal beta-cells during pregnancy, peaking at gestational day (GD)19, while returning to normal levels postpartum. Based on these observations, we hypothesize that Nrf2 might play an important role in expanding beta-cell mass during pregnancy and that disruption of Nrf2 expression or function might lead to GDM. In order to test our hypothesis, we generated tamoxifen (Tam)-induced beta cell-specific deletion of Nrf2 in female mice by crossing MIP-CreERTTAM with Nrf2lox/lox mice (βNrf2KO). In order to exclude any effect of Tam on pregnancy outcomes, females mice were injected with Tam (or vehicle control) a month before gestation. Pancreata were harvested at GD15 or GD19 and immunolabeled with Ki67 and insulin (proliferation assay), TUNEL and insulin (apoptotic assay) or insulin alone (beta-cell mass analysis). Our results show that βNrf2KO mice exhibit 70% reduction (+/- 0.25, p<0.01, n=4-6) in beta-cell proliferation and a 0.13% increase in beta-cell death (+/- 0.03, p<0.05, n=4-6) at GD15 compared to littermate controls. Importantly, βNrf2KO pregnant mice display a remarkable decrease in beta-cell mass at GD19 (50%) (+/- 0.68, p<0.05, n=4) compared with control mice, accompanied by a trending decrease in plasma insulin and increase in blood glucose. No changes were observed in the average number of embryos between βNrf2KO and control pregnant mice. We conclude that Nrf2 is required for beta-cell mass expansion during pregnancy by controlling beta-cell proliferation and survival and alterations in Nrf2 action could potentially lead to development of GDM. Presentation: Friday, June 16, 2023

The Proliferative and Functional Roles of CEBP/A in Ins-1 832/13 Cells and Primary Rat Islets

The beta cell transcription factor Nkx6.1, when overexpressed in primary rodent and human islets, is sufficient to enhance beta cell proliferation, increase insulin secretion and enhance cell survival. We have sought to define the transcriptional targets of Nkx6.1 that allow for its ability to increase functional beta cell mass. We have shown that Nkx6.1 induces expression of the transcription factor CEBP/A. CEBP/A overexpression is sufficient to induce proliferation of Ins-1 832/13 cells and primary rat islets. CEBP/A overexpression enhances glucose stimulated insulin secretion from primary rat islets, while decreasing total insulin content. Finally, CEBPa overexpression protects Ins-1 832/13 cells from thapsigargin and glucolipotoxicity induced cell death but fails to protect against etoposide and camptothecin induced cell death. These data suggest that CEBP/A may play a critical role in Nkx6.1 mediated expansion of functional beta cell mass through a endoplasmic reticulum stress-mediated pathway. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Fetal Programming of the Endocrine Pancreas: Impact of a Maternal Low-Protein Diet on Gene Expression in the Perinatal Rat Pancreas.

In rats, the time of birth is characterized by a transient rise in beta cell replication, as well as beta cell neogenesis and the functional maturation of the endocrine pancreas. However, the knowledge of the gene expression during this period of beta cell expansion is incomplete. The aim was to characterize the perinatal rat pancreas transcriptome and to identify regulatory pathways differentially regulated at the whole organ level in the offspring of mothers fed a regular control diet (CO) and of mothers fed a low-protein diet (LP). We performed mRNA expression profiling via the microarray analysis of total rat pancreas samples at embryonic day (E) 20 and postnatal days (P) 0 and 2. In the CO group, pancreas metabolic pathways related to sterol and lipid metabolism were highly enriched, whereas the LP diet induced changes in transcripts involved in RNA transcription and gene regulation, as well as cell migration and apoptosis. Moreover, a number of individual transcripts were markedly upregulated at P0 in the CO pancreas: growth arrest specific 6 (Gas6), legumain (Lgmn), Ets variant gene 5 (Etv5), alpha-fetoprotein (Afp), dual-specificity phosphatase 6 (Dusp6), and angiopoietin-like 4 (Angptl4). The LP diet induced the downregulation of a large number of transcripts, including neurogenin 3 (Neurog3), Etv5, Gas6, Dusp6, signaling transducer and activator of transcription 3 (Stat3), growth hormone receptor (Ghr), prolactin receptor (Prlr), and Gas6 receptor (AXL receptor tyrosine kinase; Axl), whereas upregulated transcripts were related to inflammatory responses and cell motility. We identified differentially regulated genes and transcriptional networks in the perinatal pancreas. These data revealed marked adaptations of exocrine and endocrine in the pancreas to the low-protein diet, and the data can contribute to identifying novel regulators of beta cell mass expansion and functional maturation and may provide a valuable tool in the generation of fully functional beta cells from stem cells to be used in replacement therapy.

Exogenous Lactogenic Signaling Stimulates Beta Cell Replication In Vivo and In Vitro.

As patients recently diagnosed with T1D and patients with T2D have residual beta cell mass, there is considerable effort in beta cell biology to understand the mechanisms that drive beta cell regeneration as a potential cellular therapy for expanding patients’ residual beta cell population. Both mouse and human studies have established that beta cell mass expansion occurs rapidly during pregnancy. To investigate the mechanisms of beta cell mass expansion during pregnancy, we developed a novel in vivo and in vitro models of pseudopregnancy. Our models demonstrate that pseudopregnancy promotes beta cell mass expansion in parous mice, and this expansion is driven by beta cell proliferation rather than hypertrophy. Importantly, estrogen, progesterone, and placental lactogen induce STAT5A signaling in the pseudopregnancy model, demonstrating that this model successfully recapitulates pregnancy-induced beta cell replication. We then created an in vitro model of pseudopregnancy and found that the combination of estrogen and placental lactogen induced beta cell replication in human islets and rat insulinoma cells. Therefore, beta cells both in vitro and in vivo increase proliferation when subjected to the pseudopregnancy cocktail compared to groups treated with estradiol or placental lactogen alone. The pseudopregnancy models described here may help inform novel methods of inducing beta cell replication in patients with diabetes.

Deletion of ABCB10 in beta-cells protects from high-fat diet induced insulin resistance

ObjectiveThe contribution of beta-cell dysfunction to type 2 diabetes (T2D) is not restricted to insulinopenia in the late stages of the disease. Elevated fasting insulinemia in normoglycemic humans is a major factor predicting the onset of insulin resistance and T2D, demonstrating an early alteration of beta-cell function in T2D. Moreover, an early and chronic increase in fasting insulinemia contributes to insulin resistance in high-fat diet (HFD)-fed mice. However, whether there are genetic factors that promote beta-cell-initiated insulin resistance remains undefined. Human variants of the mitochondrial transporter ABCB10, which regulates redox by increasing bilirubin synthesis, have been associated with an elevated risk of T2D. The effects of T2D ABCB10 variants on ABCB10 expression and the actions of ABCB10 in beta-cells are unknown. MethodsThe expression of beta-cell ABCB10 was analyzed in published transcriptome datasets from human beta-cells carrying the T2D-risk ABCB10 variant. Insulin sensitivity, beta-cell proliferation, and secretory function were measured in beta-cell-specific ABCB10 KO mice (Ins1Cre-Abcb10flox/flox). The short-term role of beta-cell ABCB10 activity on glucose-stimulated insulin secretion (GSIS) was determined in isolated islets. ResultsCarrying the T2Drisk allele G of ABCB10 rs348330 variant was associated with increased ABCB10 expression in human beta-cells. Constitutive deletion of Abcb10 in beta-cells protected mice from hyperinsulinemia and insulin resistance by limiting HFD-induced beta-cell expansion. An early limitation in GSIS and H2O2-mediated signaling caused by elevated ABCB10 activity can initiate an over-compensatory expansion of beta-cell mass in response to HFD. Accordingly, increasing ABCB10 expression was sufficient to limit GSIS capacity. In health, ABCB10 protein was decreased during islet maturation, with maturation restricting beta-cell proliferation and elevating GSIS. Finally, ex-vivo and short-term deletion of ABCB10 in islets isolated from HFD-fed mice increased H2O2 and GSIS, which was reversed by bilirubin treatments. ConclusionsBeta-cell ABCB10 is required for HFD to induce insulin resistance in mice by amplifying beta-cell mass expansion to maladaptive levels that cause fasting hyperinsulinemia.

Maternal vitamin D administration attenuates metabolic disturbances induced by prenatal exposure to dexamethasone in a sex-dependent manner

PurposeThe overexposure to synthetic glucocorticoids (GC) during pregnancy can predispose to metabolic diseases during adulthood. Vitamin D is not only crucial for fetal development, but also exerts direct effects on the GC sensitivity and down-regulates GC receptors. Given the vitamin D effects on glucocorticoid-related parameters, we aimed to investigate a possible protective role of maternal vitamin D administration on the glucose homeostasis of rats exposed to dexamethasone in utero. MethodsPregnant rats received dexamethasone (0.1 mg/kg, Dex) daily between the 14th and 19th days of pregnancy. A subgroup of dexamethasone-treated dams received oral administration of vitamin D (500UI, DexVD) during the whole gestation. The corresponding control groups of dams were included (CTL and VD groups, respectively). Male and female offspring were evaluated at 3, 6 and 12 months of age. ResultsPrenatal exposure to dexamethasone caused metabolic disruption in an age and sex-dependent manner being the older male offspring more susceptible to insulin resistance, fatty liver and beta-cell mass expansion than females. Furthermore, we demonstrated that prenatal GC led to glucose intolerance in male and female offspring in an age-dependent manner. Maternal vitamin D administration did not influence glucose intolerance but attenuated the insulin resistance, liver lipid accumulation and prevented the beta-cell mass expansion caused by prenatal dexamethasone in the male offspring. ConclusionMaternal vitamin D administration mitigates metabolic disturbances that occur later in life in male rats exposed to GC in utero. Moreover, our data suggest vitamin D as an important nutritional supplement for pregnant overexposed to GC during gestation.

\u03b2-Arrestin-1 is required for adaptive \u03b2-cell mass expansion during obesity

Obesity is the key driver of peripheral insulin resistance, one of the key features of type 2 diabetes (T2D). In insulin-resistant individuals, the expansion of beta-cell mass is able to delay or even prevent the onset of overt T2D. Here, we report that beta-arrestin-1 (barr1), an intracellular protein known to regulate signaling through G protein-coupled receptors, is essential for beta-cell replication and function in insulin-resistant mice maintained on an obesogenic diet. Specifically, insulin-resistant beta-cell-specific barr1 knockout mice display marked reductions in beta-cell mass and the rate of beta-cell proliferation, associated with pronounced impairments in glucose homeostasis. Mechanistic studies suggest that the observed metabolic deficits are due to reduced Pdx1 expression levels caused by beta-cell barr1 deficiency. These findings indicate that strategies aimed at enhancing barr1 activity and/or expression in beta-cells may prove useful to restore proper glucose homeostasis in T2D.

Increased alpha and beta cell mass during mouse pregnancy is not dependent on transdifferentiation.

Maternal pancreatic beta-cell mass (BCM) increases during pregnancy to compensate for relative insulin resistance. If BCM expansion is suboptimal, gestational diabetes mellitus can develop. Alpha-cell mass (ACM) also changes during pregnancy, but there is a lack of information about α-cell plasticity in pregnancy and whether α- to β-cell transdifferentiation can occur. To investigate this, we used a mouse model of gestational glucose intolerance induced by feeding low-protein (LP) diet from conception until weaning and compared pregnant female offspring to control diet-fed animals. Control and LP pancreata were collected for immunohistochemical analysis and serum glucagon levels were measured. In order to lineage trace α- to β-cell conversion, we utilized transgenic mice expressing yellow fluorescent protein behind the proglucagon gene promoter (Gcg-Cre/YFP) and collected pancreata for histology at various gestational timepoints. Alpha-cell proliferation increased significantly at gestational day (GD) 9.5 in control pregnancies resulting in an increased ACM at GD18.5, and this was significantly reduced in LP animals. Despite these changes, serum glucagon was higher in LP mice at GD18.5. Pregnant Gcg-Cre/YFP mice showed no increase in the abundance of insulin+YFP+glucagon- cells (phenotypic β-cells). A second population of insulin+YFP+glucagon+ cells was identified which also did not alter during pregnancy. However, there was an altered anatomical distribution within islets with fewer insulin+YFP+glucagon- cells but more insulin+YFP+glucagon+ cells being present in the islet mantle at GD18.5. These findings demonstrate that dynamic changes in ACM occur during normal pregnancy and were altered in glucose-intolerant pregnancies.

Aberrant methylation underlies insulin gene expression in human insulinoma

Human insulinomas are rare, benign, slowly proliferating, insulin-producing beta cell tumors that provide a molecular “recipe” or “roadmap” for pathways that control human beta cell regeneration. An earlier study revealed abnormal methylation in the imprinted p15.5-p15.4 region of chromosome 11, known to be abnormally methylated in another disorder of expanded beta cell mass and function: the focal variant of congenital hyperinsulinism. Here, we compare deep DNA methylome sequencing on 19 human insulinomas, and five sets of normal beta cells. We find a remarkably consistent, abnormal methylation pattern in insulinomas. The findings suggest that abnormal insulin (INS) promoter methylation and altered transcription factor expression create alternative drivers of INS expression, replacing canonical PDX1-driven beta cell specification with a pathological, looping, distal enhancer-based form of transcriptional regulation. Finally, NFaT transcription factors, rather than the canonical PDX1 enhancer complex, are predicted to drive INS transactivation.

Redox homeostasis and cell cycle activation mediate beta-cell mass expansion in aged, diabetes-prone mice under metabolic stress conditions: Role of thioredoxin-interacting protein (TXNIP)

Overnutrition contributes to insulin resistance, obesity and metabolic stress, initiating a loss of functional beta-cells and diabetes development. Whether these damaging effects are amplified in advanced age is barely investigated. Therefore, New Zealand Obese (NZO) mice, a well-established model for the investigation of human obesity-associated type 2 diabetes, were fed a metabolically challenging diet with a high-fat, carbohydrate restricted period followed by a carbohydrate intervention in young as well as advanced age. Interestingly, while young NZO mice developed massive hyperglycemia in response to carbohydrate feeding, leading to beta-cell dysfunction and cell death, aged counterparts compensated the increased insulin demand by persistent beta-cell function and beta-cell mass expansion. Beta-cell loss in young NZO islets was linked to increased expression of thioredoxin-interacting protein (TXNIP), presumably initiating an apoptosis-signaling cascade via caspase-3 activation. In contrast, islets of aged NZOs exhibited a sustained redox balance without changes in TXNIP expression, associated with higher proliferative potential by cell cycle activation. These findings support the relevance of a maintained proliferative potential and redox homeostasis for preserving islet functionality under metabolic stress, with the peculiarity that this adaptive response emerged with advanced age in diabetes-prone NZO mice.

Dynamic Regulation of JAK-STAT Signaling Through the Prolactin Receptor Predicted by Computational Modeling

IntroductionThe expansion of insulin-producing beta cells during pregnancy is critical to maintain glucose homeostasis in the face of increasing insulin resistance. Prolactin receptor (PRLR) signaling is one of the primary mediators of beta cell expansion during pregnancy, and loss of PRLR signaling results in reduced beta cell mass and gestational diabetes. Harnessing the proliferative potential of prolactin signaling to expand beta cell mass outside of the context of pregnancy requires quantitative understanding of the signaling at the molecular level.MethodsA mechanistic computational model was constructed to describe prolactin-mediated JAK-STAT signaling in pancreatic beta cells. The effect of different regulatory modules was explored through ensemble modeling. A Bayesian approach for likelihood estimation was used to fit the model to experimental data from the literature.ResultsIncluding receptor upregulation, with either inhibition by SOCS proteins, receptor internalization, or both, allowed the model to match experimental results for INS-1 cells treated with prolactin. The model predicts that faster dimerization and nuclear import rates of STAT5B compared to STAT5A can explain the higher STAT5B nuclear translocation. The model was used to predict the dose response of STAT5B translocation in rat primary beta cells treated with prolactin and reveal possible strategies to modulate STAT5 signaling.ConclusionsJAK-STAT signaling must be tightly controlled to obtain the biphasic response in STAT5 activation seen experimentally. Receptor up-regulation, combined with SOCS inhibition, receptor internalization, or both is required to match experimental data. Modulating reactions upstream in the signaling can enhance STAT5 activation to increase beta cell survival.

86-OR: High-Fat Diet Prevents Autoimmune Diabetes in NOD Mice

Type 1 diabetes (T1D) has a strong genetic predisposition and requires an environmental trigger to initiate autoimmune destruction of beta cells. The rate of childhood obesity has risen in parallel to the rate of T1D, suggesting high fat diet (HFD) may be an environmental trigger in the development of autoimmune diabetes. Supporting this hypothesis, HFD can induce insulin resistance, beta cell stress, dysfunctional insulin production, and beta cell death. To explore the role of HFD in the development of T1D, 4 week-old non-obese diabetic (NOD) female mice were placed on HFD or chow diet (CD). At 10 weeks of age NOD mice fed with HFD demonstrated a significant increase in body weight and non-fasting blood glucose along with mild glucose intolerance compared with NOD CD fed mice. Histological analysis at 10 weeks of age revealed significantly less pancreatic immune cell infiltration and increased beta cell mass in HFD fed mice compared to CD fed mice. By 15 weeks of age, HFD fed NOD animals demonstrated impaired glucose tolerance similar to CD fed mice, increased glucose-stimulated insulin secretion and total insulin content, and insulin resistance. Surprisingly, at 25 weeks of age the HFD fed NOD mice were completely protected from the development of diabetes, while as expected 70% of NOD CD fed mice had developed diabetes. In summary, this study demonstrates that in the NOD model of T1D HFD reduced islet immune cell infiltration, increased beta cell mass, insulin content and insulin secretion protecting the mice from development of diabetes. The mechanism underlying this protection seems to be two-fold: expansion of beta cell mass and prevention of autoimmune-mediated beta cell death. Our data correlate with other recent studies indicating that early stimulation of beta cell replication can induce immune tolerance in NOD animals preventing T1D. Identification of the mechanisms by which HFD leads to prevention of diabetes in NOD animals may lead to the development of novel therapeutic interventions to prevent T1D in humans. Disclosure A.L. Clark: None. Z. Yan: None. S.X. Chen: None. M. Fuess: None. G. McGinn: None. M.S. Remedi: None. Funding National Institutes of Health (P30DK020579, K12HD076224-04)

Exposure of Pancreatic β-Cells to Excess Glucose Results in Bimodal Activation of mTORC1 and mTOR-Dependent Metabolic Acceleration.

SummaryChronic exposure of pancreatic β-cells to excess glucose can lead to metabolic acceleration and loss of stimulus-secretion coupling. Here, we examined how exposure to excess glucose (defined here as concentrations above 5 mM) affects mTORC1 signaling and the metabolism of β-cells. Acute exposure to excess glucose stimulated glycolysis-dependent mTORC1 signaling, without changes in the PI3K or AMPK pathways. Prolonged exposure to excess glucose led to hyperactivation of mTORC1 and metabolic acceleration, characterized by higher basal respiration and maximal respiratory capacity, increased energy demand, and enhanced flux through mitochondrial pyruvate metabolism. Inhibition of pyruvate transport to the mitochondria decelerated the metabolism of β-cells chronically exposed to excess glucose and re-established glucose-dependent mTORC1 signaling, disrupting a positive feedback loop for mTORC1 hyperactivation. mTOR inhibition had positive and negative impacts on various metabolic pathways and insulin secretion, demonstrating a role for mTOR signaling in the long-term metabolic adaptation of β-cells to excess glucose.

363-OR: ChREBP-Beta Controls Both Proliferation and Cell Death of Pancreatic Beta Cells

Glucose is a key physiological driver of adaptive beta cell mass expansion, promoting beta cell proliferation both in vitro and in vivo. Carbohydrate response element binding protein β (ChREBPβ) is upregulated in response to glucose and is required for glucose-stimulated beta cell proliferation. To study the role of ChREBPβ in beta cells, we knocked out (KO) or overexpressed (OE) ChREBPβ in mouse pancreatic beta cells using Cre LoxP approaches with either MIP-CreERT (induced by tamoxifen at 3 months of age), or the RIP-Cre model which leads to recombination specifically in β cells, early during embryogenesis (E9). We performed intraperitoneal glucose tolerance tests (IPGTTs) and assessed pancreata for proliferation (Ki67), cell death (TUNEL) and beta cell mass in the 4 mouse models. ChREBPβ MIP-CreERT KO mice displayed impaired glucose tolerance, with an increase of 25.3 ± 7.9% (N=3-4, P<0.05) in the area under the curve (AUC) of IPGTT. Heterozygous or complete Chrebpβ KOs in the RIP-Cre model resulted in an increase in the AUC of IPGTT compared with control littermates (20.1 ± 13.7% and 56 ± 7.1%, respectively; n=2-4). Beta cells from isolated ChREBPβ KO islets had 60.4 ± 17.4% less proliferation compared to control islets in 6 mM glucose, and 22.9 ± 2.4% (P<0.05, N=5) less in 20 mM glucose. Inducible OE of ChREBPβ resulted in 97.7 ± 6% increase in AUC of IPGTT (N=3, p<0.01) and fasting blood glucose levels were increased by 89 ± 13.2% (P<0.01). Similarly, when ChREBPβ was OE early in the embryogenesis of β cells, we observed AUC for GTT was increased by 2.4 ± 0.5 fold compared to non-Cre expressing litter mates (N=5, p<0.05). In both mouse models, the OE of ChREBPβ resulted in β cell death as assessed by TUNEL along with increased in Ki67 staining. Remarkably, the RIP-Cre mice had almost no remaining β cells at 4 months of age and were overtly diabetic. Taken these data together, we propose a molecular regulatory mechanism where ChREBPβ controls both beta cell proliferation and cell death depending on its abundance. Disclosure L.S. Katz: None. G. Brill: None. M.A. Herman: None. D. Scott: None. Funding National Institutes of Health

2141-P: Nrf2 Mediates Glucose-Stimulated Beta-Cell Proliferation

Glucose catabolism drives adaptive beta cell mass expansion by promoting proliferation under conditions of increased insulin demand. Previously, we showed that induction of the antioxidant regulator, Nrf2, is required for glucose-stimulated β-cell proliferation, and that overexpression of Nrf2 stimulates human beta cell proliferation. Here we manipulate the Nrf2 pathway using pharmacological and genetic approaches to explore the link between glucose metabolism, Nrf2 activation and beta cell proliferation. Treatment of isolated mouse islets with either a Nrf2 inhibitor (brusatol) or Cre-recombinase deleted Nrf2, resulted in complete inhibition of glucose-stimulated proliferation (both n=3, p < 0.01). Conversely, stimulation of Nrf2 by CDDO-me or genetic gain of function (Cre-mediated depletion of Nrf2 inhibitor, Keap1) increased beta cell proliferation of beta cells from isolated mouse islets cultured in 5 mM glucose (4.9 ± 0.2 fold and 6.9 ± 1.4 fold, respectively; n=3, p < 0.05). Inhibition or depletion of Nrf2 was associated with a remarkable decrease in insulin content, suggesting that beta cell identity requires basal levels of Nrf2 expression. Importantly, isolated human beta cells displayed similar responses to Nrf2 loss and gain of function. Activation and nuclear translocation of Nrf2 requires dissociation from its inhibitor, Keap1, and phosphorylation of Ser-40 on Nrf2. Five minutes of 20 mM glucose treatment profoundly increased Ser-40 phosphorylation and translocation of Nrf2, while the same effect by CDDO-Me treatment took 50 minutes in INS1 cells. The glucose-mediated activation and translocation of Nrf2 was blocked by the antioxidant N-acetylcysteine (NAC), which also attenuated glucose-stimulated proliferation of isolated mouse beta cells. In addition, the activation and phosphorylation of Nrf2 was prevented by the pan-PKC inhibitor, calphostin C. We conclude that manipulation of the Nrf2 pathway is an exciting novel target for regulation of beta cell proliferation. Disclosure S. Baumel-Alterzon: None. L.S. Katz: None. G. Brill: None. A. Garcia-Ocaña: None. D. Scott: None. Funding American Diabetes Association (1-17-IBS-116 to D.S.); National Institutes of Health

38-OR: Beta-Arrestin-1 Regulates Pancreatic Beta-Cell Function and Plays a Key Role in Maintaining Whole Body Glucose Homeostasis

Beta-arrestin-1 and -2 (barr1 and barr2, respectively) are major GPCR-associated signaling molecules that are widely expressed throughout the body. Studies with whole body barr1 and barr2 KO mice have shown that beta-arrestins play important roles in key metabolic functions. In this study, we inactivated the barr1 gene in a conditional fashion specifically in beta-cells of adult mice (beta-barr1-KO mice). In vivo studies showed that beta-barr1-KO mice exhibited a pronounced impairment in glucose tolerance and glucose-stimulated insulin secretion (GSIS), when mice were maintained on high-fat diet (HFD). Studies with isolated perifused pancreatic islets prepared from HFD beta-barr1-KO mice confirmed that barr1 deletion in beta-cells led to a significant decrease in GSIS. Interestingly, HFD beta-barr1-KO mice displayed pronounced reductions in beta-cell mass and the rate of beta-cell proliferation, suggesting that barr1 is required for the expansion of beta-cell mass that occurs during HFD feeding. To test whether enhanced barr1 signaling in beta-cells might ameliorate the metabolic deficits associated with the consumption of a HFD, we also generated transgenic mice over-expressing barr1 in beta-cells (RIPII-barr1 mice). These transgenic mice displayed metabolic phenotypes that were opposite to those observed with the beta-barr1-KO mice, including improved glucose tolerance and GSIS in vivo as well as increased beta-cell mass. This is the first study demonstrating that barr1 is critical for the proper function of pancreatic beta-cells and for maintaining whole body glucose homeostasis. Identification of the cellular mechanisms through which barr1 signaling promotes beta-cell function and proliferation may lead to the development of novel drugs useful for the treatment of type 2 diabetes. Disclosure L.F. Barella: None. M. Rossi: None. S. Pydi: None. S. Jain: None. L. Zhu: None. W. Chen: None. J. Wess: None. Funding National Institute of Diabetes and Digestive and Kidney Diseases

SAT-LB035 The G Protein-Coupled Estrogen Receptor GPER Plays a Dominant Role in Human Islet Cell Proliferation upon High Glucose

Estrogen exerts its effects through genomic and rapid extra-nuclear signaling pathways. The classic estrogen receptors, ERα and ERβ have demonstrated favorable effects on beta-cell function and survival but their clinical utility has been questioned owing to oncogenic potential and concerns regarding feminizing effects in men. Recent work indicates, however, that the G-protein coupled estrogen receptor (GPER), expressed in pancreatic islet cells retains the estrogenic beta-cell protective effects, without the shortcomings of the classic ERs. GPER activation enhances glucose stimulated insulin secretion, reduces islet apoptosis upon insult and has been implicated in beta-cell mass expansion during pregnancy in rodent islets. Since GPER can thus comprise an attractive treatment target in hyperglycemic states we examined the effects of the three ERs on proliferation of human pancreatic islets in the presence of hyperglycemia. Islets from eight non diabetic human donors (6 males and 2 females) were grown at glucose concentrations of either 11mM or 25mM for 24 hours and examined for DNA synthesis after treatment with E2 (at increasing concentrations) and with specific agonists for ERα, ERβ and GPER (PPT 10nM, DPN 10nM and G1 100nM, respectively). At a glucose concentration of 11mM, E2 and all three ER agonists induced a significant ~2 folds increase in 3[H]-thymidine incorporation. However, under still higher glucose conditions (HG; 25mM) only the GPER agonist G1 increased proliferation equipotently (~2.5 folds; p<0.001), while stimulation of ERα and ERβ enhanced proliferation by ~1.4 folds only (p<0.05 for ERα). In search for an explanation for the differential effects, we examined expression of the three ERs at glucose concentrations of 11mM and 25mM, by qRT-PCR. High glucose reduced expression of ERα and ERβ (by 15%; p<0.05) but not the expression of GPER. Although beta-cells comprise the majority (~70%) of cells in human islets, expression of GPER has also been demonstrated in alpha and delta cells and thus the full effect of hyperglycemia on GPER expression in beta-cells may be masked. Hence, extending previous reports, our results suggest that GPER may comprise an attractive target in the therapy of human diabetes and point to the phenomenon of species specificity regarding effects of glucose on estrogen receptor subtype expression and activity. Unless otherwise noted, all abstracts presented at ENDO are embargoed until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. s presented at a news conference are embargoed until the date and time of the news conference. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.