Insulin Secretion In Islets Research Articles

The Effects of Bariatric Surgery on Islet Function, Insulin Secretion, and Glucose Control.

Although bariatric surgery was developed primarily to treat morbid obesity, evidence from the earliest clinical observations to the most recent clinical trials consistently demonstrates that these procedures have substantial effects on glucose metabolism. A large base of research indicates that bariatric surgeries such as Roux-en-Y gastric bypass (RYGB), vertical sleeve gastrectomy (VSG), and biliopancreatic diversion (BPD) improve diabetes in most patients, with effects frequently evident prior to substantial weight reduction. There is now unequivocal evidence from randomized controlled trials that the efficacy of surgery is superior to intensive life-style/medical management. Despite advances in the clinical understanding and application of bariatric surgery, there remains only limited knowledge of the mechanisms by which these procedures confer such large changes to metabolic physiology. The improvement of insulin sensitivity that occurs with weight loss (e.g., the result of diet, illness, physical training) also accompanies bariatric surgery. However, there is evidence to support specific effects of surgery on insulin clearance, hepatic glucose production, and islet function. Understanding the mechanisms by which surgery affects these parameters of glucose regulation has the potential to identify new targets for therapeutic discovery. Studies to distinguish among bariatric surgeries on key parameters of glucose metabolism are limited but would be of considerable value to assist clinicians in selecting specific procedures and investigators in delineating the resulting physiology. This review is based on literature related to factors governing glucose metabolism and insulin secretion after the commonly used RYGB and VSG, and the less frequently used BPD and adjustable gastric banding.

Gestational Diabetes Adversely Affects Pancreatic Islet Architecture and Function in the Male Rat Offspring.

Fetal exposure to gestational diabetes mellitus (GDM) and poor postnatal diet are strong risk factors for type 2 diabetes development later in life, but the mechanisms connecting GDM exposure to offspring metabolic health remains unclear. In this study, we aimed to determine how GDM interacts with the postnatal diet to affect islet function in the offspring as well as characterize the gene expression changes in the islets. GDM was induced in female rats using a high-fat, high-sucrose (HFS) diet, and litters from lean or GDM dams were weaned onto a low-fat (LF) or HFS diet. Compared with the lean control offspring, GDM exposure reduced glucose-stimulated insulin secretion in islets isolated from 15-week-old offspring, which was additively worsened when GDM exposure was combined with postnatal HFS diet consumption. In the HFS diet-fed offspring of lean dams, islet size and number increased, an adaptation that was not observed in the HFS diet-fed offspring of GDM dams. Islet gene expression in the offspring of GDM dams was altered in such categories as inflammation (e.g., Il1b, Ccl2), mitochondrial function/oxidative stress resistance (e.g., Atp5f1, Sod2), and ribosomal proteins (e.g., Rps6, Rps14). These results demonstrate that GDM exposure induced marked changes in gene expression in the male young adult rat offspring that cumulatively interact to worsen islet function, whole-body glucose homeostasis, and adaptations to HFS diets.

NeuropeptideB stimulates insulin secretion and expression but not proliferation in rat insulin‑producing INS‑1E cells.

NeuropeptideB (NPB) regulates food intake, body weight and energy homeostasis by interacting with NPBW1/NPBW2 in humans and NPBW1 in rodents. NPB and NPBW1 are widely expressed in the central nervous system and peripheral tissues including pancreatic islets. Although previous studies have demonstrated a prominent role for NPB and NPBW1 in controlling glucose and energy homeostasis, it remains unknown as to whether NPB modulates pancreatic β‑cell functions. Therefore, the aim of the present study was to investigate the effects of NPB on insulin expression and secretion invitro. Furthermore, the role of NPB in the modulation of INS‑1E cell growth, viability and death was examined. Gene expression was assessed by reverse transcription‑quantitative PCR. Cell proliferation and viability were determined by BrdU or MTT tests, respectively. Apoptotic cell death was evaluated by relative quantification histone‑complexed DNA fragments (mono‑and oligonucleosomes). Insulin secretion was studied using an ELISA test. Protein phosphorylation was assessed by western blot analysis. NPB and NPBW1 mRNA was expressed in INS‑1E cells and rat pancreatic islets. In INS‑1E cells, NPB enhanced insulin 1 mRNA expression via an ERK1/2‑dependent mechanism. Furthermore, NPB stimulated insulin secretion from INS‑1E cells and rat pancreatic islets. By contrast, NPB failed to affect INS‑1E cell growth or death. We conclude that NPB may regulate insulin secretion and expression in INS‑1E cells and insulin secretion in rat pancreatic islets.

Trans-11 vaccenic acid improves glucose homeostasis in a model of type 2 diabetes by promoting insulin secretion via GPR40

Abstract It is largely unknown whether and how trans-11 vaccenic acid (VA), a ruminant trans-fatty acid with health benefits, influences glucose homeostasis in type 2 diabetes (T2D). VA was provided in diet to rats and in vitro to human/rat islets with diabetogenic challenges. Compared to rats with T2D induced by high-fat diet/streptozotocin, T2D + VA animals had improved ambient and fasting blood glucose, β-cell area, in vivo insulin secretion, and ex vivo glucose-stimulated insulin secretion (GSIS) in islets from T2D + VA rats, which were accompanied with higher islet mRNA and protein expression of G-protein coupled receptor 40 (GPR40). In vitro, VA enhanced GPR40 protein expression and protein kinase D1 phosphorylation, and promoted GSIS in rat and human islets, an effect blocked by the inhibition of GPR40 and protein kinase D. These results indicate that VA may improve glycemic control by promoting insulin secretion in T2D, at least partly through stimulating GPR40 expression and signaling.

RGD-containing elastin-like polypeptide improves islet transplantation outcomes in diabetic mice

Successful islet transplantation critically depends on the isolation of healthy islets. However, the islet isolation procedure itself contributes to islet death due to the destruction of intra- and peri-islet extracellular matrices (ECMs) during digestion. We investigated whether an RGD-containing elastin-like polypeptide (REP) could function as a self-assembling matrix to replenish ECMs and protects islets from cell death. Immediately following isolation, islets were coated with REP coacervate particles via isothermal adsorption of an REP solution followed by thermal gelation. REP-coated islets displayed increased viability and insulin secretory capacity in pretransplant culture compared to untreated islets. Co-transplantation of REP-treated islets and REP beneath the renal sub-capsule in streptozotocin-induced diabetic mice restored normoglycemia and serum insulin levels. Mice that received co-transplants maintained normoglycemia for a longer period of time than those receiving untreated islets without REP. Moreover, co-transplantation sites exhibited enhanced β-cell proliferation and vascularization. Thus, the REP-based coacervation strategy improve the survival, function and therapeutic potential of transplanted islets. Statement of Significance1). An artificial matrix polypeptide comprised of thermoresponsive elastin-like peptides and integrin-stimulatory RGD ligands (REP) to reconstitute damaged or lost matrices.2). Through body temperature-induced coacervation, REP reconstitutes intra-islet environment and enhances islet viability and insulin secretion by activating the pro-survival and insulin signaling pathways.3). REP-coated islets were transplanted together with the matrix polypeptide under the kidney sub-capsule of mice, it develops a new peri-insular environment, which protects the islet grafts from immune rejection thus extending islet longevity.4). Our data suggest that in situ self-assembly of biomimetic islet environments become a new platform allowing for improved islet transplantation at extrahepatic sites.

Low extracellular magnesium does not impair glucose-stimulated insulin secretion.

There is an increasing amount of clinical evidence that hypomagnesemia (serum Mg2+ levels < 0.7 mmol/l) contributes to type 2 diabetes mellitus pathogenesis. Amongst other hypotheses, it has been suggested that Mg2+ deficiency affects insulin secretion. The aim of this study was, therefore, to investigate the acute effects of extracellular Mg2+ on glucose-stimulated insulin secretion in primary mouse islets of Langerhans and the rat insulinoma INS-1 cell line. Here we show that acute lowering of extracellular Mg2+ concentrations from 1.0 mM to 0.5 mM did not affect glucose-stimulated insulin secretion in islets or in insulin-secreting INS-1 cells. The expression of key genes in the insulin secretory pathway (e.g. Gck, Abcc8) was also unchanged in both experimental models. Knockdown of the most abundant Mg2+ channel Trpm7 by siRNAs in INS-1 cells resulted in a 3-fold increase in insulin secretion at stimulatory glucose conditions compared to mock-transfected cells. Our data suggest that insulin secretion is not affected by acute lowering of extracellular Mg2+ concentrations.

339-LB: Modulation of Insulin and Glucagon Secretion by Optogenetic Control of Delta-Cell Electrical Activity in Pancreatic Islets

Somatostatin secreted from pancreatic delta-cells is a strong paracrine inhibitor of both insulin and glucagon secretion in islets. However, little is known about the regulatory mechanisms of delta cells. This is mainly due to the scarcity of these cells (∼5-10% of islet cell population) and difficulties in maintaining their morphology and function after cell dispersion. Here, we developed an optogenetic approach, through tissue-specific expression of light-sensitive channels in delta cells, to investigate the paracrine modulation of alpha/beta cells by delta cells within intact islets. We generated a mouse model using Cre-loxp recombination to enable the specific expression of a light-sensitive cation channel Channelrhodopsin-2 (ChR2) in the pancreatic delta cells (SST-ChR2 mouse). In the presence of 1 mM glucose (when ?-cells are not electrically active), light activation of ChR2 (with 470 nm LED light) rapidly depolarised delta- cells (from -66±4 mV to -19±2 mV, n=4). Similar depolarising effect was observed in delta-cells exposed to 10 mM glucose (from -59±5 mV to -19±4 mV, n=4). Delta-cells activation with light transiently repolarised alpha cells by 5 mV (n=2) at 1 mM glucose and beta cells by 4 mV (n=3) at 10 mM glucose, which correlated with a mild decrease in intracellular Ca2+ concentration. Optoactivation of delta-cells inhibited glucagon secretion in islets exposed to 1 mM glucose by 48%. Whilst not affecting that at 20 mM glucose. Interestingly, despite the effects on beta-cell membrane potential, light exposure to SST-ChR2 islets did not affect insulin secretion stimulated by 20 mM glucose, possibly suggesting that insulin secretion is already maximally inhibited by glucose-induced somatostatin secretion. We propose that the SST-ChR2 mouse model represents a powerful tool for studying spatial and temporal paracrine crosstalk between different islet cells and the role of somatostatin in islet hormone secretion. Disclosure H. Dou: None. C.A. Miranda: None. Q. Zhang: None. P. Rorsman: None. J. Tolö: None. Funding Swedish Research Council

2161-P: Overexpression of UCP2 in Pancreatic Beta Cells Caused Impaired Insulin Secretion through Mitochondrial Dysfunction and Aldolase B Expression

Uncoupling protein 2 (UCP2), a mitochondrial protein, is known to be upregulated in pancreatic islets of patients with type 2 diabetes (T2DM); however, the pathological significance of the increase in UCP2 expression remained unclear. In this study, we investigated the regulatory mechanisms of UCP2 expression and its effects on β-cell functions. The mRNA expression of UCP2 in mouse islets was upregulated by the treatment with glucose, glucokinase activator, or insulin (p&amp;lt;0.05), while metformin downregulated it (p&amp;lt;0.01). Islets from db/db mice and insulin receptor substrate-2 knockout (IRS-2KO) mice showed the increment in the UCP2 expression. Transgenic mouse with specific UCP2 overexpression in β-cells (βUCP2Tg) demonstrated impaired glucose tolerance due to reduced insulin secretion. Adenoviral expression of UCP2 in MIN6-M9 β-cell line also attenuated glucose-induced insulin secretion. The ATP production in response to glucose and mitochondrial Complex I protein level were reduced (p&amp;lt;0.01) in βUCP2Tg islets. Dilatation (1.8-fold, p&amp;lt;0.05) and morphological alteration of mitochondria were observed in βUCP2Tg β-cells. Gene expression microarray analysis revealed 18 upregulated genes (1.5-fold, p&amp;lt;0.05) and 2 downregulated genes (&amp;lt;67%, p&amp;lt;0.05) in βUCP2Tg islets. The most upregulated mRNA by UCP2 expression encoded the aldolase B (Aldob) (77-fold), whose expression was reported to be negatively associated with insulin secretion in human islets (J Clin Endocrinol Metab. 103(12):4373-4383, 2018). We validated increased Aldob expression in islets from βUCP2Tg mice, db/db mice, and IRS-2KO mice. Taken together, UCP2 expression seemed to be increased under T2DM conditions including hyperglycemia or hyperinsulinemia. Our data also suggested that the increase in UCP2 expression in T2DM β-cells cell-autonomously attenuated glucose-induced insulin secretion, possibly via mitochondrial abnormality and Aldob expression. Disclosure R. Inoue: None. J. Shirakawa: None. Y. Togashi: None. Y. Terauchi: Advisory Panel; Self; AstraZeneca, Daiichi Sankyo Company, Limited, Eli Lilly and Company, Merck Sharp &amp; Dohme Corp., Mitsubishi Tanabe Pharma Corporation, Novo Nordisk A/S, Sanofi. Research Support; Self; Daiichi Sankyo Company, Limited, Eli Lilly and Company, Merck Sharp &amp; Dohme Corp., Novartis Pharmaceuticals Corporation, Novo Nordisk A/S, Ono Pharmaceutical Co., Ltd., Sanofi, Shionogi &amp; Co., Ltd., Sumitomo Dainippon Pharma Co., Ltd. Speaker's Bureau; Self; Astellas Pharma Inc., AstraZeneca, Bayer Yakuhin, Ltd., Daiichi Sankyo Company, Limited, Eli Lilly and Company, Merck Sharp &amp; Dohme Corp., Mitsubishi Tanabe Pharma Corporation, Novartis Pharmaceuticals Corporation, Novo Nordisk A/S, Ono Pharmaceutical Co., Ltd., Sanofi, Sanwa Kagaku Kenkyusho, Shionogi &amp; Co., Ltd., Sumitomo Dainippon Pharma Co., Ltd.

338-LB: ACh Esterase Is a Novel Regulator of Insulin Secretion in Human Islets

The neurotransmitter acetylcholine (ACh) plays a major role in regulating insulin secretion. While in several species parasympathetic innervation provides cholinergic input to beta cells, it is the glucagon secreting alpha cell the major source of ACh in human islets. It is still unclear, however, what is the contribution of cholinergic signaling to beta cell function in humans. Here we analyzed how ACh impacts human beta cell function and insulin secretion, using a combination of in vitro and in vivo approaches. To determine the effect of endogenous ACh in insulin secretion, we manipulated ACh esterase activity using different inhibitors such as pyridostigmine and galantamine. Inhibition of ACh esterase led to a significant increase in insulin secretion in isolated human islets in perifusion experiments. To assess the effect of endogenous ACh on human beta cell function in vivo, we transplanted human islets into the anterior chamber of immunocompromised Nude mice. ACh esterase activity was inhibited by local administration of the ACh esterase inhibitor pyridostigmine as eye drops. To control that the inhibitor was entering the anterior chamber of the eye and reaching the islets, we measured the effect it had on pupil size. 30 microM pyridostigmine induced approximately a 20-30% reduction in pupil size. Importantly, mice treated with 30 microM pyridostigmine showed decreased glucose excursion curves and slightly increased insulin levels 15 min after glucose injection. These results indicate that endogenously released ACh from human alpha cells increases insulin secretion from beta cells in vitro and in vivo. ACh esterase is potential novel target for the treatment of diabetes in humans. Disclosure A.M. Tamayo: None. A. Caicedo: None. Funding American Diabetes Association (1-17-ICTS-052 to A.C.)

310-OR: Integrating Islet and Skeletal Muscle Enhancer RNA Signatures with Diverse Omics Data Enables Fine-Mapping of Diabetes and Related Trait GWAS Loci

Type 2 diabetes (T2D) results from interaction between genetic variation and environmental exposures that influence insulin secretion in pancreatic islets and insulin resistance in skeletal muscle and other peripheral tissues. Genome-wide association studies (GWAS) have identified hundreds of loci that modulate risk for T2D and related insulin traits. These loci mostly occur in non protein-coding regions which makes identification of causal regulatory single nucleotide polymorphisms (SNPs) and their associated mechanisms difficult. Previous studies show that many active enhancers are transcribed into enhancer RNA (eRNA). To identify actively transcribed regulatory elements with high genomic resolution and prioritize SNPs, we generated eRNA profiles using cap analysis of gene expression (CAGE) across 57 islet and 146 skeletal muscle samples and 15 replicates of the human beta cell line EndoC-BH1. We computationally integrated these CAGE profiles with ChIP-seq profiles for five histone marks along with open chromatin ATAC-seq profiles to generate high-resolution cross-tissue chromatin states. We identify multiple CAGE-enriched chromatin states that correspond to actively transcribed promoter or enhancer regions, which are supported by diverse patterns of chromatin activity across an orthogonal set of 127 human epigenome maps. We find 11,856 CAGE+ promoter regions across islets and muscle and 54% are shared across the two tissues, whereas we observe 1,712 CAGE+ eRNA regions and only 7% are shared, indicating the cell-identity nature of these eRNA states. We find significant enrichment for GWAS and eQTL SNPs to overlap these CAGE+ chromatin states. Finally, at a subset of loci, we validate these findings using a modified high-throughput STARR-seq assay where we observe allelic activity. These results provide the highest-resolution epigenome maps for islets and muscle to date, and we are using them to fine-map GWAS SNPs. Disclosure S. Parker: None. A. Varshney: None. Funding American Diabetes Association/Pathway to Stop Diabetes (1-14-INI-07 to S.P.); National Institutes of Health (1R01DK117960)

Characterization of the Effects of Mesenchymal Stromal Cells on Mouse and Human Islet Function.

Islet transplantation has the potential to cure type 1 diabetes, but current transplantation protocols are not optimal and there is extensive loss of islet β‐cell insulin secretory function during the immediate post‐transplantation period. Studies using experimental models of diabetes have shown that the coculture of islets with mesenchymal stromal cells (MSCs) prior to transplantation improves graft function, but several variables differed among research groups (e.g., type of MSCs used and the treatment conditions). We have therefore assessed the effects of MSCs on mouse and human islets by investigating the importance of tissue source for MSCs, the coculture protocol configuration and length, the effect of activated MSCs, and different β‐cell secretory stimuli. MSCs derived from adipose tissue (aMSCs) were the most effective at supporting β‐cell insulin secretion in both mouse and human islets, in a direct contact coculture configuration. Preculture with aMSCs enhanced both phases of glucose‐induced insulin secretion and further enhanced secretory responses to the non‐nutrients carbachol and arginine. These effects required a coculture period of 48–72 hours and were not dependent on activation of the MSCs. Thus, direct contact coculture with autologous, adipose‐derived MSCs for a minimum of 48 hours before implantation is likely to be an effective addition to human islet transplantation protocols. stem cells translational medicine 2019;8:935&944

Central and Peripheral Administration of Fibroblast Growth Factor 1 Improves Pancreatic Islet Insulin Secretion in Diabetic Mouse Models.

Fibroblast growth factor 1 (FGF1) has been shown to reverse hyperglycemia in diabetic rodent models through peripheral and central administration routes. Previous studies demonstrated that insulin is required for central and peripheral FGF1 metabolic improvements; however, it is unknown if FGF1 targets insulin secretion at the islet level. Here we show for the first time that FGF1 increases islet insulin secretion in diabetic mouse models. FGF1 was administered via a single intracerebroventricular or multiple subcutaneous injections to leptin receptor-deficient (db/db), diet-induced obese, and control mice; pancreatic islets were isolated 7 days later for analysis of insulin secretion. Central and peripheral FGF1 significantly lowered blood glucose in vivo and increased ex vivo islet insulin secretion from diabetic, but not control, mice. FGF1 injections to the cisterna magna mimicked intracerebroventricular outcomes, pointing to a novel therapeutic potential. Central effects of FGF1 appeared dependent on reductions in food intake, whereas peripheral FGF1 had acute actions on islet function prior to significant changes in food intake or blood glucose. Additionally, peripheral, but not central, FGF1 increased islet β-cell density, suggesting that peripheral FGF1 may induce long-term changes in islet structure and function that are not present with central treatment.

Transplantation of MHC-mismatched Mouse Embryonic Stem Cell-Derived Thymic Epithelial Progenitors Prevents Autoimmune Diabetes

Abstract Type 1 diabetes (T1D) is an autoimmune disease results from the destruction of insulin-secreting islet β-cells by autoreactive T cells. NOD mice are the widely used animal model for human T1D. Autoimmunity in NOD mice is associated with particular MHC loci and impaired islet autoantigen expression and/or presentation in the thymus, which results in defects in both central and peripheral tolerance. It has been reported that induction of mixed chimerism with MHC-mismatched, but not MHC-matched donor bone marrow (BM) transplants prevents the development T1D in NOD mice. We have reported that mouse embryonic stem cells (mESCs) can be selectively induced in vitro to generate thymic epithelial progenitors (TEPs) that further develop into thymic epithelial cells (TECs) in vivo to support T cell development. We show here that transplantation of MHC-mismatched mESC-TEPs and MHC-matched donor BM prevents insulitis and T1D development in NOD mice. This is associated with higher expression of proinsulin 2, a key islet autoantigen, in the mESC-TECs, and an increased number of regulatory T cells. Our results suggest that embryonic stem cell-derived TEPs may offer a new approach to control T1D.

SAT-260 Selective Nonpeptide Somatostatin Subtype 5 (sst5) Agonists Suppress Induced Insulin Secretion in Pancreatic Islets from both Rats and Healthy Human Donors

Hyperinsulinemia is a heterogeneous condition in which dangerously low blood sugar levels are caused by improperly regulated insulin secretion from pancreatic ß-cells. The most severe form of hyperinsulinemia arises from congenital hyperinsulinism (CHI), a set of genetic disorders in which the underlying pathology is driven by mutations in key genes that regulate insulin secretion. CHI is the most common cause of persistent hypoglycemia in newborns and infants, and prompt recognition and treatment are vital to prevent coma, long-term neurological complications, and even death. The neuropeptide somatostatin is an important modulator of hormonal signaling from the pancreas mediated by different somatostatin receptor (sst) subtypes. Glucagon secretion from α-cells is inhibited through sst2 receptor activation and insulin secretion from β-cells is inhibited through sst2, sst3, and sst5. The injectable peptide drugs octreotide and lanreotide are primarily agonists at sst2 and are often prescribed for these patients in an attempt to reduce insulin secretion, but their efficacy is limited, and they carry the risk of impairing glucagon secretion, an important defense mechanism against hypoglycemia. We hypothesize that an orally available selective sst5 agonist may be a useful new approach to managing hyperinsulinemia. We launched an iterative medicinal chemistry program that led to the discovery of selective sst5 agonists, with multiple nonpeptide series possessing EC50s < 1 nM in cell-based assays of receptor activation (these compounds also routinely possess similar potencies for the rat sst5 receptor). We have shown that these sst5 agonists potently suppress insulin and raise plasma glucose in multiple glycemic studies in rats. To explore the mechanism of selective sst agonism and its translation from rat studies to humans, we undertook a series of studies using pancreatic islets isolated from human donors and from naïve Sprague Dawley rats. Selective sst5 agonists were compared to selective sst2 and selective sst3 agonists as well as somatostatin peptides for their capacity to suppress insulin and/or glucagon from islets under various conditions including increasing glucose concentrations and the presence of a sulfonylurea (the increased insulin secretion mimics many CHI patients). In both human and rat islets, we found that selective sst5 agonists potently suppressed insulin secretion more effectively than selective sst2 or sst3 agonists, while having little effect on glucagon secretion, demonstrating their potential efficacy in the human condition. These studies support our program to identify and develop potent nonpeptide selective sst5 agonists with pharmaceutical and safety characteristics suitable for evaluation in human clinical trials.

Lipotoxicity reduces β cell survival through islet stellate cell activation regulated by lipid metabolism-related molecules

BackgroundIslet stellate cells (ISCs) activation is mainly associated with islet fibrosis, which contributes to the progression of type 2 diabetes. However, the molecular mechanism underlying this process is not fully understood. MethodsIn order to investigate this process the current study examined ectopic fat accumulation in rats with high-fat diet (HFD) induced obesity. Levels of lipotoxicity-induced ISC activation and islet function were assessed via intraperitoneal glucose and insulin tolerance tests, and immunohistochemistry. The expression of lipid metabolism- and ISC activation-related markers was evaluated in cultured ISCs treated with palmitic acid (PA) using quantitative PCR and western blotting. We also overexpressed sterol regulatory element-binding protein (SREBP)-1c in ISCs by lentiviral transduction, and assessed the effects on insulin release in co-cultures with isolated rat islets. ResultsHFD increased body weight and ectopic fat accumulation in pancreatic islets. Lipotoxicity caused progressive glucose intolerance and insulin resistance, upregulated α-smooth muscle actin, and stimulated the secretion of extracellular matrix. Lipotoxicity reduced the expression of lipid metabolism-related molecules in ISCs treated with PA, especially SREBP-1c. Overexpression of SREBP-1c in ISCs improved islet viability and insulin secretion in co-cultures. ConclucionsThese results indicate that lipotoxicity-induced ISC activation alters islet function via regulation of lipid metabolism, suggesting that therapeutic strategies targeting activated ISC may be an effective treatment for prevention of ISC activation-associated islet dysfunction.

Role of the heterotrimeric inhibitory G‐protein, Gαz, and its unique G‐protein coupled receptor, EP3, in the progression and pathophysiology of Type 2 Diabetes

The hyperglycemia of Type 2 Diabetes (T2D) results from a combination of factors, including insulin resistance, impaired and inefficient insulin secretion, and destruction of pancreatic beta‐cells. Pathways that inhibit beta‐cell cyclic AMP (cAMP) production are pathologically upregulated in T2D. Prostaglandin E2 (PGE2) receptor 3 (EP3), a G protein‐coupled receptor whose expression is up‐regulated in islets of T2D mice and humans, acts through a unique inhibitory G protein, Gz to reduce islet cAMP production. In contrast to expectations, genetic deletion of EP3 greatly accelerates hyperglycemia in the BTBRLeptinOb/Ob(BTBR‐Ob) model of T2D, likely through unregulated adipose tissue lipolysis and severe glucolipotoxicity. In contrast to the ubiquitously‐expressed EP3, the catalytic α‐subunit of Gz (Gαz) is quite tissue‐limited. We back‐crossed the Gαz‐null mutation into the BTBR‐Ob strain for more than 10 generations. Gαz‐null BTBR‐Ob mice maintained normal fasting blood glucose levels, even though they were as obese and insulin resistant as T2D wild‐type controls. Euglycemia correlated directly with elevated plasma insulin levels, islet insulin content and insulin secretion, the latter stimulated by glucose or the glucagon‐like peptide 1 (GLP‐1) agonist, exendin‐4. With the known paracrine effect(s) of GLP‐1 and other islet hormones on beta‐cell function and mass, we quantified the percentage of GLP‐1‐postive alpha‐cells by immunofluorescence of pancreas sections, revealing a strong effect of the Gαz‐null mutation independent of the Ob mutation. To confirm effects on GLP‐1 secretion, isolated islets were cultured overnight and the medium assayed for active GLP‐1. Somatostatin, expressed in delta‐cells and a negative regulator of beta‐cell cAMP production, was also analyzed. Islets from Ob mice secreted significantly more active GLP‐1 into culture medium than lean controls, with no further impact of the Gαz‐null mutation: a result at odds with active GLP‐1 immunofluorescence data. Islets from lean Gαz‐null mice and wild‐type BTBR‐Ob mice secreted significantly more somatostatin into culture medium than wild‐type lean controls, with the Gαz‐null mutation reversing this effect in the BTBR‐Ob background. These somewhat paradoxical results may be due to multiple factors, including islet isolation selecting for healthier, intact islets and/or maintenance of glucolipotoxic conditions being necessary in culturing islets isolated from BTBR‐Ob mice. We are currently exploring the effects of glucolipotoxicity on our hormone secretion assays. To summarize, we have identified a central role for Gαz in the islet pathophysiology of T2D, potentially through both beta‐cell autonomous and intra‐islet cell‐cell communication mechanisms, confirming loss of Gαz permits a more efficient beta‐cell response to glucose and GLP‐1, a physiologic regulator of beta‐cell function and mass.Support or Funding InformationVA Merit Review Award: I01 BX003700‐01A1, VA BLR&amp;DR01 DK102598, NIH/NIDDKAmerican Diabetes Association Innovative Basic Science Award: 1‐14‐BS‐115This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The polymorphic region an interleukin B1 is highly associated with type 1 diabetes in Saudis

Type 1 diabetes (T1D) is an auto‐immune disease mediated by T lymphocytes that lead to insulin secreting islet B cell destruction. T1D is a multifactorial disease with strong genetic component. Pancreatic sample from patients with T1D showed mononuclear cell infiltration in islets, include mainly B cells and T cells that required for disease development.In this study, we genotyped a group of Single Nucleotide Polymorphisms (SNPs) that located at IL1B1 (rs16944), IL1A (rs1800587), IL1B (rs1143634), IL1R (rs2234650) and IL1RN (rs315952) cytokines and cytokine receptors to investigate a possible association between these genetic markers and T1D.Sequence‐specific forward and reverse primers and two TaqMan® MGB probes with dyes (VIC/FAM) were used to detect allele 1 and allele 2 of each SNP. 150 patients with T1D and 150 normal healthy individuals with no history of auto‐immune disease were recruited. The genotype models for each SNP (codominant, dominant and recessive traits) were derived using the SNPStat software, Fisher exact test and logistic regression methods were used to compare patient and control results. The dominant model of rs16944 (G/G vs G/A‐A/A)) was found highly significant in patient than in control (41.3% vs 14.6%, p value &lt;0.0001) and considered as a risk factor for T1D development and individuals having this genotype are 4 fold susceptible to develop the disease. No other significant association was detected.In conclusion, rs16944G/G model is considered positively associated with T1D.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Human mesenchymal stem cells improve rat islet functionality under cytokine stress with combined upregulation of heme oxygenase-1 and ferritin

BackgroundIslets of Langerhans transplantation is a promising therapy for type 1 diabetes mellitus, but this technique is compromised by transplantation stresses including inflammation. In other tissues, co-transplantation with mesenchymal stem cells has been shown to reduce damage by improving anti-inflammatory and anti-oxidant defences. Therefore, we probed the protection afforded by bone marrow mesenchymal stem cells to islets under pro-inflammatory cytokine stress.MethodsIn order to evaluate the cytoprotective potential of mesenchymal stem cells on rat islets, co-cultures were exposed to the interleukin-1, tumour necrosis factor α and interferon γ cocktail for 24 h. Islet viability and functionality tests were performed. Reactive oxygen species and malondialdehyde were measured. Expression of stress-inducible genes acting as anti-oxidants and detoxifiers, such as superoxide dismutases 1 and 2, NAD(P)H quinone oxidoreductase 1, heme oxygenase-1 and ferritin H, was compared to non-stressed cells, and the corresponding proteins were measured. Data were analysed by a two-way ANOVA followed by a Holm-Sidak post hoc analysis.ResultsExposure of rat islets to cytokines induces a reduction in islet viability and functionality concomitant with an oxidative status shift with an increase of cytosolic ROS production. Mesenchymal stem cells did not significantly increase rat islet viability under exposure to cytokines but protected islets from the loss of insulin secretion. A drastic reduction of the antioxidant factors heme oxygenase-1 and ferritin H protein levels was observed in islets exposed to the cytokine cocktail with a prevention of this effect by the presence of mesenchymal stem cells.ConclusionsOur data evidenced that MSCs are able to preserve islet insulin secretion through a modulation of the oxidative imbalance mediated by heme and iron via heme oxygenase-1 and ferritin in a context of cytokine exposure.

Mechanisms of octanoic acid potentiation of insulin secretion in isolated islets

ABSTRACTA potentiating effect of medium-chain triglycerides on glucose-stimulated insulin secretion (GSIS) has been observed since the 1960s. Subsequent observations identified octanoic acid (OA), the main component of medium-chain triglyceride, as the potentiator of GSIS, but the mechanism was unclear. We used wild-type (WT), short-chain 3-hydroxyacyl-CoA dehydrogenase knockout (Hadh-/-), and sulfonylurea receptor 1 knockout (Sur1-/-) mouse islets to define the mechanism of OA potentiation of insulin secretion. Application of OA alone induced a 2- to 3- fold increase of insulin secretion with an apparent threshold of 3 mM in WT mouse islets, suggesting that OA itself is a weak insulin secretagogue. However, OA at 1 mM strongly potentiated fuel-stimulated insulin secretion, especially GSIS. The potentiating effect on fuel-stimulated insulin secretion by OA did not require fatty acid β-oxidation because OA also potentiated amino acid-stimulated insulin secretion in islets isolated from Hadh-/- mice, which cannot fully oxidize OA. Measurements using Sur1-/- islets indicated that the potentiating effect of OA on fuel-stimulated insulin secretion is Ca2+ dependent and is often accompanied by β-cell membrane potential depolarization, and may also involve the Ca2+/calmodulin complex. Experiments using DCPIB, an ethacrynic acid derivative, to inhibit volume-sensitive anion channels (VSACs) in Sur1-/- islets demonstrated that the potentiation effects of OA on insulin secretion are in part medicated by activation of VSAC. In addition, inhibition of IP3 receptor also abolishes the OA-induced intracellular Ca2+ increase in Sur1-/- islets.

Glutamate decarboxylase 67 contributes to compensatory insulin secretion in aged pancreatic islets

ABSTRACTPancreatic islets play an essential role in regulating blood glucose levels. Age-dependent development of glucose intolerance and insulin resistance results in hyperglycemia, which in turn stimulates insulin synthesis and secretion from aged islets, to fulfill the increased demand for insulin. However, the mechanism underlying enhanced insulin secretion remains unknown. Glutamic acid decarboxylase 67 (GAD67) catalyzes the conversion of glutamate into γ-aminobutyric acid (GABA) and CO2. Both glutamate and GABA can affect islet function. Here, we investigated the role of GAD67 in insulin secretion in young (3 month old) and aged (24 month old) C57BL/6J male mice. Unlike young mice, aged mice displayed glucose-intolerance and insulin-resistance. However, aged mice secreted more insulin and showed lower fed blood glucose levels than young mice. GAD67 levels in primary islets increased with aging and in response to high glucose levels. Inhibition of GAD67 activity using a potent inhibitor of GAD, 3-mercaptopropionic acid, abrogated glucose-stimulated insulin secretion from a pancreatic β-cell line and from young and aged islets. Collectively, our results suggest that blood glucose levels regulate GAD67 expression, which contributes to β-cell responses to impaired glucose homeostasis caused by advanced aging.