Β-cell Activity Research Articles

Secretory Functions of Macrophages in the Human Pancreatic Islet Are Regulated by Endogenous Purinergic Signaling.

Endocrine cells of the pancreatic islet interact with their microenvironment to maintain tissue homeostasis. Communication with local macrophages is particularly important in this context, but the homeostatic functions of human islet macrophages are not known. In this study, we show that the human islet contains macrophages in perivascular regions that are the main local source of the anti-inflammatory cytokine interleukin-10 (IL-10) and the metalloproteinase MMP9. Macrophage production and secretion of these homeostatic factors are controlled by endogenous purinergic signals. In obese and diabetic states, macrophage expression of purinergic receptors MMP9 and IL-10 is reduced. We propose that in those states, exacerbated β-cell activity due to increased insulin demand and increased cell death produce high levels of ATP that downregulate purinergic receptor expression. Loss of ATP sensing in macrophages may reduce their secretory capacity.

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

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. 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. 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. 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.

Chronic stimulation induces adaptive potassium channel activity that restores calcium oscillations in pancreatic islets in vitro.

Insulin pulsatility is important to hepatic response in regulating blood glucose. Growing evidence suggests that insulin-secreting pancreatic β-cells can adapt to chronic disruptions of pulsatility to rescue this physiologically important behavior. We determined the time scale for adaptation and examined potential ion channels underlying it. We induced the adaptation both by chronic application of the ATP-sensitive K+ [K(ATP)] channel blocker tolbutamide and by application of the depolarizing agent potassium chloride (KCl). Acute application of tolbutamide without pretreatment results in elevated Ca2+ as measured by fura-2AM and the loss of endogenous pulsatility. We show that after chronic exposure to tolbutamide (12-24 h), Ca2+ oscillations occur with subsequent acute tolbutamide application. The same experiment was conducted with potassium chloride (KCl) to directly depolarize the β-cells. Once again, following chronic exposure to the cell stimulator, the islets produced Ca2+ oscillations when subsequently exposed to tolbutamide. These experiments suggest that it is the chronic stimulation, and not tolbutamide desensitization, that is responsible for the adaptation that rescues oscillatory β-cell activity. This compensatory response also causes islet glucose sensitivity to shift rightward following chronic tolbutamide treatment. Mathematical modeling shows that a small increase in the number of K(ATP) channels in the membrane is one adaptation mechanism that is compatible with the data. To examine other compensatory mechanisms, pharmacological studies provide support that Kir2.1 and TEA-sensitive channels play some role. Overall, this investigation demonstrates β-cell adaptability to overstimulation, which is likely an important mechanism for maintaining glucose homeostasis in the face of chronic stimulation.

The glutamate receptor GluK2 contributes to the regulation of glucose homeostasis and its deterioration during aging

ObjectiveIslets secrete neurotransmitters including glutamate which participate in fine regulation of islet function. The excitatory ionotropic glutamate receptor GluK2 of the kainate receptor family is widely expressed in brain and also found in islets, mainly in α and γ cells. α cells co-release glucagon and glutamate and the latter increases glucagon release via ionotropic glutamate receptors. However, neither the precise nature of the ionotropic glutamate receptor involved nor its role in glucose homeostasis is known. As isoform specific pharmacology is not available, we investigated this question in constitutive GluK2 knock-out mice (GluK2−/−) using adult and middle-aged animals to also gain insight in a potential role during aging. MethodsWe compared wild-type GluK2+/+ and knock-out GluK2−/− mice using adult (14–20 weeks) and middle-aged animals (40–52 weeks). Glucose (oral OGTT and intraperitoneal IPGTT) and insulin tolerance as well as pyruvate challenge tests were performed according to standard procedures. Parasympathetic activity, which stimulates hormones secretion, was measured by electrophysiology in vivo. Isolated islets were used in vitro to determine islet β-cell electrical activity on multi-electrode arrays and dynamic secretion of insulin as well as glucagon was determined by ELISA. ResultsAdult GluK2−/− mice exhibit an improved glucose tolerance (OGTT and IPGTT), and this was also apparent in middle-aged mice, whereas the outcome of pyruvate challenge was slightly improved only in middle-aged GluK2−/− mice. Similarly, insulin sensitivity was markedly enhanced in middle-aged GluK2−/− animals. Basal and glucose-induced insulin secretion in vivo was slightly lower in GluK2−/− mice, whereas fasting glucagonemia was strongly reduced. In vivo recordings of parasympathetic activity showed an increase in basal activity in GluK2−/− mice which represents most likely an adaptive mechanism to counteract hypoglucagonemia rather than altered neuronal mechanism. In vitro recording demonstrated an improvement of glucose-induced electrical activity of β-cells in islets obtained from GluK2−/− mice at both ages. Finally, glucose-induced insulin secretion in vitro was increased in GluK2−/− islets, whereas glucagon secretion at 2 mmol/l of glucose was considerably reduced. ConclusionsThese observations indicate a general role for kainate receptors in glucose homeostasis and specifically suggest a negative effect of GluK2 on glucose homeostasis and preservation of islet function during aging. Our observations raise the possibility that blockade of GluK2 may provide benefits in glucose homeostasis especially during aging.

Presenilin-1 Established ER-Ca2+ Leak: a Follow Up on Its Importance for the Initial Insulin Secretion in Pancreatic Islets and β-Cells upon Elevated Glucose.

In our recent work, the importance of GSK3β-mediated phosphorylation of presenilin-1 as crucial process to establish a Ca2+ leak in the endoplasmic reticulum and, subsequently, the pre-activation of resting mitochondrial activity in β-cells was demonstrated. The present work is a follow-up and reveals the importance of GSK3β-phosphorylated presenilin-1 for responsiveness of pancreatic islets and β-cells to elevated glucose in terms of cytosolic Ca2+ spiking and insulin secretion. Freshly isolated pancreatic islets and the two pancreatic β-cell lines INS-1 and MIN-6 were used. Cytosolic Ca2+ was fluorometrically monitored using Fura-2/AM and cellular insulin content and secretion were measured by ELISA. Our data strengthened our previous findings of the existence of a presenilin-1-mediated ER-Ca2+ leak in β-cells, since a reduction of presenilin-1 expression strongly counteracted the ER Ca2+ leak. Furthermore, our data revealed that cytosolic Ca2+ spiking upon administration of high D-glucose was delayed in onset time and strongly reduced in amplitude and frequency upon siRNA-mediated knock-down of presenilin-1 or the inhibition of GSK3β in the pancreatic β-cells. Moreover, glucose-triggered initial insulin secretion disappeared by depletion from presenilin-1 and inhibition of GSK3β in the pancreatic β-cells and isolated pancreatic islets, respectively. These data complement our previous work and demonstrate that the sensitivity of pancreatic islets and β-cells to glucose illustrated as glucose-triggered cytosolic Ca2+ spiking and initial but not long-lasting insulin secretion crucially depends on a strong ER Ca2+ leak that is due to the phosphorylation of presenilin-1 by GSK3β, a phenomenon that might be involved in the development of type 2 diabetes.

Glucagon lowers glycemia when β-cells are active.

Glucagon and insulin are commonly believed to have counteracting effects on blood glucose levels. However, recent studies have demonstrated that glucagon has a physiologic role to activate β-cells and enhance insulin secretion. To date, the actions of glucagon have been studied mostly in fasting or hypoglycemic states, yet it is clear that mixed-nutrient meals elicit secretion of both glucagon and insulin, suggesting that glucagon also contributes to glucose regulation in the postprandial state. We hypothesized that the elevated glycemia seen in the fed state would allow glucagon to stimulate insulin secretion and reduce blood glucose. In fact, exogenous glucagon given under fed conditions did robustly stimulate insulin secretion and lower glycemia. Exogenous glucagon given to fed Gcgr:Glp1rβcell-/- mice failed to stimulate insulin secretion or reduce glycemia, demonstrating the importance of an insulinotropic glucagon effect. The action of endogenous glucagon to reduce glycemia in the fed state was tested with administration of alanine, a potent glucagon secretagogue. Alanine raised blood glucose in fasted WT mice or fed Gcgr:Glp1rβcell-/- mice, conditions where glucagon is unable to stimulate β-cell activity. However, alanine given to fed WT mice produced a decrease in glycemia, along with elevated insulin and glucagon levels. Overall, our data support a model in which glucagon serves as an insulinotropic hormone in the fed state and complements rather than opposes insulin action to maintain euglycemia.

No significant association of type 2 diabetes‐related genetic risk scores with glycated haemoglobin levels after initiating metformin or sulphonylurea derivatives

AimTo explore the added value of diabetes‐related genetic risk scores (GRSs) to readily available clinical variables in the prediction of glycated haemoglobin (HbA1c) levels after initiation of glucose‐regulating drugs.Materials and methodsWe conducted a cohort study in people with type 2 diabetes (T2DM) from the Groningen Initiative to Analyse Type 2 Diabetes Treatment (GIANTT) database who initiated metformin (MET) or sulphonylurea derivatives (SUs) and for whom blood samples were genotyped. The primary outcome was HbA1c level at 6 months, adjusted for baseline HbA1c. GRSs were based on single nucleotide polymorphisms linked to insulin sensitivity, β‐cell activity, and T2DM risk in general. Associations were analysed using multiple linear regression to assess whether adding the GRSs increased the explained variance in a prediction model that included age, gender, diabetes duration and cardio‐metabolic biomarkers.ResultsWe included 282 patients initiating MET and 89 patients initiating SUs. In the MET prediction model, diabetes duration of >3 months when starting MET was associated with 2.7‐mmol/mol higher HbA1c level. For SUs, no significant clinical predictors were identified. Addition of the GRS linked to insulin sensitivity (for MET), β‐cell activity (for SUs) and T2DM risk (for both) to the models did not improve the explained variance significantly (22% without vs. 22% with GRS) for the MET and (14% without vs. 14% with GRS) for the SUs model, respectively.ConclusionThis study did not indicate a significant effect of GRS related to T2DM in general or to the drugs' mechanism of action for prediction of inter‐individual HbA1c variability in the short term after initiation of MET or SU therapy.

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

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

226-LB: HOMA-ß and ß-Cell Activity in Early and Late Phase during an OGTT Are Independent Risk Factors of Type 2 Diabetes in Japanese Americans

The β-cell plays a major role in type 2 diabetes (T2DM). HOMA-β reflects fasting β-cell activity. Insulin responses during an OGTT reflect β-cell activity during glucose loading, which has two phases, early and late. HOMA-β, early, and late β-cell activity have different pathophysiologies. However, no research has examined whether HOMA-β and early and late phase β-cell activity during an OGTT are independently associated with the risk of T2DM. In a prospective cohort study, 415 nondiabetic Japanese-American men and women were followed for 10-11 years. β-cell activity was assessed by HOMA-β [fasting insulin × 360/(fasting glucose − 63)] as fasting activity, the insulinogenic index (IGI) [?insulin (30-0 min)/?glucose (30-0 min)] during an OGTT as early phase activity, and (area under the curve (AUC) of insulin 60-120 min)/(AUC glucose 60-120 min) as late phase activity. Insulin sensitivity was estimated by Matsuda index [10000/square root of ((fasting glucose) × (fasting insulin) × (AUC glucose 0-120 min/120) × (AUC insulin 0-120 min/120))]. T2DM was diagnosed as fasting plasma glucose level ≥126 mg/dL, 2-hour glucose level ≥200 mg/dL, or taking glucose-lowering medications. During the 10-11 year follow-up, 95 cases of T2DM occurred. HOMA-β, IGI, and late phase β-cell activity were all independently associated with the risk of T2DM. Multiple-adjusted odds ratios of T2DM for tertile 1, 2, and 3 of HOMA-β were 1.00 (reference), 0.25 (95% CI, 0.11-0.57), and 0.14 (0.05-0.37), respectively; those of IGI were 1.00, 0.35 (0.17-0.75), and 0.19 (0.07-0.47), respectively; and those of late phase β-cell activity were 1.00, 0.34 (0.14-0.82), and 0.16 (0.05-0.53), respectively, in the model that included HOMA-β, IGI, late phase β-cell activity, Matsuda index, age, BMI, sex, and family history of T2DM. In conclusion, higher β-cell activity while fasting and in both the early and late phase during an OGTT were all independently associated with a lower risk of T2DM. Disclosure T. Shimojo: None. C. Izumi: None. K.K. Sato: None. D.L. Leonetti: None. S.E. Kahn: Advisory Panel; Self; Boehringer Ingelheim Pharmaceuticals, Inc., Eli Lilly and Company, Intarcia Therapeutics, Inc., Janssen Pharmaceuticals, Inc., Merck & Co., Inc., Novo Nordisk A/S. Consultant; Self; Neurimmune. Other Relationship; Self; Boehringer Ingelheim Pharmaceuticals, Inc., Merck & Co., Inc., Novo Nordisk A/S. W.Y. Fujimoto: None. E.J. Boyko: None. T. Hayashi: None.

Protective Effect of Peroxiredoxin 6 Against Toxic Effects of Glucose and Cytokines in Pancreatic RIN-m5F β-Cells.

Taking into account a special role of pancreatic β-cells in the development of diabetes mellitus, the effects of peroxiredoxin 6 (Prx6) on the viability and functional activity of rat insulinoma RIN-m5F β-cells were studied under diabetes-simulating conditions. For this purpose, the cells were cultured at elevated glucose concentrations or in the presence of pro-inflammatory cytokines (TNF-α and IL-1) known for their special role in the cytotoxic autoimmune response in diabetes. It was found that the increased glucose concentration of 23-43 mM caused death of 20-60% β-cells. Prx6 added to cells significantly reduced the level of reactive oxygen species and protected the RIN-m5F β-cells from hyperglycemia, reducing the death of these cells by several fold. A measurement of insulin secretion by the RIN-m5F β-cells showed a significant stimulatory effect of Prx6 on the insulin-producing activity of pancreatic β-cells. It should be noted that the stimulatory activity of Prx6 was detected during culturing the cells under both normal and unfavorable conditions. The regulation of the NF-κB signaling cascade could be one of the mechanisms of Prx6 action on β-cells, in particular, through activation of RelA/p65 phosphorylation at Ser536.

1612-P: Insulinogenic Index and HOMA-ß Are Independent Risk Factors for Future Type 2 Diabetes

β-cell dysfunction is major risk factor for type 2 diabetes. As HOMA-β reflects fasting β-cell function and insulinogenic index reflects early phase insulin response during an oral glucose tolerance test (OGTT), these two indices represent different aspects of insulin and glucose metabolism. It is not known whether HOMA-β and insulinogenic index are independently associated with type 2 diabetes risk. In a prospective cohort study, 415 nondiabetic Japanese-American men and women were followed for 10-11 years. Insulin sensitivity was assessed by HOMA-IR. β-cell activity was assessed by HOMA-β [fasting plasma insulin (μU/mL) × 360/(fasting plasma glucose (mg/dL) - 63)] and the insulinogenic index [Δinsulin (30-0 min) (μU/mL)/Δglucose (30-0 min) (mg/dL)] obtained during a 75-g OGTT. Type 2 diabetes was diagnosed as fasting plasma glucose level ≥126 mg/dL, 2-hour glucose level ≥200 mg/dL, or taking glucose-lowering medications. Logistic regression analysis was used to estimate odds ratios (OR) of incident diabetes. A total of 95 participants developed type 2 diabetes over 10-11 years. Insulinogenic index and HOMA-β were independently associated with the risk of type 2 diabetes. In multiple-adjusted models that included insulinogenic index, HOMA-β, HOMA-IR, age, BMI, gender, and family history of diabetes, OR of future type 2 diabetes for tertile 2 and 3 of insulinogenic index were 0.43 (95% CI, 0.22-0.85) and 0.31 (0.14-0.67), respectively, compared to tertile 1, and those for tertile 2 and 3 of HOMA-β were 0.31 (0.14-0.69) and 0.25 (0.10-0.63), respectively, compared to tertile 1. HOMA-IR was also associated with the risk of type 2 diabetes independent of these two indices. OR of tertile 2 and 3 of HOMA-IR were 1.75 (0.82-3.74) and 9.17 (3.78-22.28), respectively, compared to tertile 1. In conclusion, both higher insulinogenic index and HOMA-β were independently associated with a lower risk of type 2 diabetes independent of insulin sensitivity. Disclosure K.K. Sato: None. T. Hayashi: None. S. Uehara: None. Y. Onishi: None. D.L. Leonetti: None. S.E. Kahn: Advisory Panel; Self; Boehringer Ingelheim Pharmaceuticals, Inc., Eli Lilly and Company, Intarcia Therapeutics, Inc., Janssen Pharmaceuticals, Inc., Merck & Co., Inc., Novo Nordisk A/S. Consultant; Self; Neurimmune. Other Relationship; Self; Boehringer Ingelheim Pharmaceuticals, Inc., Merck & Co., Inc., Novo Nordisk A/S. W.Y. Fujimoto: None. E.J. Boyko: None.

2195-P: Identification of the Regulatory Mechanism of mTORC1 Signaling Activity in Pancreatic Beta Cells in GCN2 Knockout Mice

Background and Objective: A single-nucleotide polymorphism (SNP) analysis of Japanese type 2 diabetes (T2DM) patients has revealed a significant correlation between a SNP of GCN2 and T2DM. We have demonstrated that islets isolated from GCN2 knockout (GCN2-/-) mice fed a high-fat diet (HFD) exhibited decreased expression of ATF4, a downstream molecule of GCN2, and pancreatic β-cell failure via hyperactivation of mTORC1 signaling. However, the mechanism of activated mTORC1 signaling has remained unclear. Therefore, our objective is to identify the regulatory mechanism of mTORC1 signaling activity in pancreatic β-cells of GCN2-/- mice fed an HFD. Methods: We analyzed using islets isolated from GCN2-/- mice and wild type mice fed an HFD, and pancreatic β-cell lines. Results: In pancreatic islets isolated from GCN2-/- mice fed an HFD, the phosphorylation of TSC2 was enhanced. Therefore, we speculated that there would be a pathway which regulated mTORC1 signaling via TSC2. It has been reported that TSC2 phosphorylation is regulated by its association with 14-3-3. We started to identify the molecule X downstream of GCN2, which involved in the regulation of mTORC1 signaling activity by competitively inhibiting the binding of TSC2 and 14-3-3. We carried out a proteome analysis to explore the molecules whose binding with 14-3-3 varied depending on the presence or the absence of GCN2. As a result, five molecules were listed, and Asparaginase was identified as the candidate of the molecule X. We revealed that Asparaginase was abundantly expressed in pancreatic islets following heart in mice tissues. In glucose loaded MIN6 cells and amino acid deficient MIN6 cells, the expression of Asparaginase was increased. Furthermore, the increased expression of Asparaginase by amino acid deficiency was decreased by ATF4 knocking down. Conclusion: It was suggested that Asparaginase was involved in the regulation of mTORC1 signaling activity downstream of GCN2-ATF4 pathway. Disclosure M. Kudo: None. S. Asahara: Research Support; Spouse/Partner; AstraZeneca. A. Kanno: None. Y. Kido: Research Support; Self; AstraZeneca.

1772-P: Insulin Granule Biogenesis at the Golgi Requires a Metabolically-Regulated, Non-centrosomal Subpopulation of Microtubules

Insulin undergoes biogenesis through the ER and Golgi, ultimately leading to packaging into vesicles that are secreted in response to glucose. The movement between these membranes and the process of budding from the Golgi are vital steps. Previous work has found a role for microtubules (MTs) in these processes in both pancreatic β-cells and other cell types. Here, we show that the last stages of this process are regulated by a specific subpopulation of MTs that are non-centrosomal. Their formation, or nucleation, at the Golgi membrane is regulated by a glucose signal-transduction pathway through cAMP and its effector EPAC2. This effect is especially pronounced during the first, rapid phase of insulin secretion, during which EPAC2 levels increase at the sites of their nucleation. Preventing new nucleation of this specific population dramatically affects the pipeline of insulin production, storage and release. There is an overall reduction of β-cell insulin content, and the remaining insulin becomes retained within the Golgi, likely because of stalling of insulin-granule budding. This diminished granule availability substantially effects the level of both basal and stimulated insulin secretion, though not the ratio between these levels during the first wave. Constant dynamic maintenance of this network is therefore critical for normal β-cell physiology. This is the first demonstration that the biogenesis of post-Golgi carriers, particularly large secretory granules, requires ongoing nucleation/replenishment of this network. We are further looking at the role of MTs in β-cell secretory activity in intact islets. We have observed that MTs promote β-cell heterogeneity by restricting secretion from a specific β-cell sub-population, where insulin release can be activated upon disruption of the entire MT network by the drug nocodazole. Disclosure K. Trogden: None. C.V. Wright: None. G. Gu: None. I. Kaverina: None. Funding National Institutes of Health (1F32DK117529-01A1)

194-OR: A Versatile Platform for Intravital Imaging of Biosensor-Labelled Beta Cells In Situ

The pancreatic islet is a complex system containing numerous cell types, including endocrine, immune, and endothelial. The pathologies of T1D and T2D originate in this organized, multicellular environment in vivo, and thus can only be fully understood in this context. We have developed several adaptable tools to generate a versatile platform combining intravital microscopy (IVM), virally-packaged biosensors, and abdominal imaging windows (AIW) allowing us to gather β cell specific measurements in vivo longitudinally. Here, we present characterization of in vivo physiology of mouse β-cells using two virally-packaged biosensors roGFP2 and GcAMP6s. To achieve in vivo expression of the biosensors, we used IP injected AAV8 to transduce in situ β cells. Using redox-sensitive roGPF2, we measured the response in biosensor signal after IV administration of the cytotoxic glucose analog alloxan from islets in situ (∼5-fold change vs. saline). To test the portability of the platform, we utilized Alox15 knockout mice (Alox15-/-), which show protection against oxidative stress. We observed a rapid 4.6-fold increase in biosensor signal ratio in WT mice, compared to a 3.3-fold increase in Alox15-/- mice after IV alloxan treatment. Using AAV8-GcAMP6s, we measured calcium activity of β-cells in situ after a glucose bolus and detected a small sub-population of β cells that oscillate at a 2x frequency compared to the entire islet. To overcome the endpoint nature of standard IVM, we next implanted AIWs over the pancreas of biosensor-labeled mice, which allows for stable, longitudinal imaging of islets in situ over for several weeks. Using IVM through AIW’s in AAV8-roGFP2 transduced mice, we monitored individual islets, before, during, and after streptozotocin-induced β cell ablation. We measured a ∼75% reduction in islet area by 10 days post ablation. Altogether, this versatile platform can lead to novel experiments examining β-cell physiology and signaling in vivo longitudinally in a variety of unique scenarios. Disclosure C.A. Reissaus: None. S.A. Tersey: None. K.W. Dunn: None. A.K. Linnemann: None. R. Mirmira: None.

POTENTIAL HOLISTIC PREVENTIVE AND THERAPEUTIC EFFECTS OF GARCINIA MANGOSTANA EXTRACT OR ISOLATES IN TYPE 2 DIABETES MELLITUS: A REVIEW

Objective: The need for long-term medication in diabetes mellitus has led to a search for herbal medicines as alternative treatments. Several studies have shown that extract or isolates of Garcinia mangostana can help prevent and treat type 2 diabetes mellitus (T2DM).
 Methods: This review was conducted by searching various databases, including PubMed, ClinicalKey, ScienceDirect, and EBSCOhost. We analyzed papers published within the previous 10 y.
 Results: All in vitro, in vivo, and clinical studies that evaluated the pharmacological effects of extract or isolates of G. mangostana in T2DM were reviewed. G. mangostana was found to suppress adipogenesis and regulate lipid homeostasis, thus improving lipid profiles and preventing T2DM. G. mangostana also demonstrated hypoglycemic properties, including the ability to decrease fasting blood glucose and mildly increase pancreatic β-cell numbers and activity. The mangosteen-treated group in one study showed a decrease in Homeostatic Model Assesment for Insulin Resistance (HOMA-IR), indicating improved insulin sensitivity, along with a significant decrease in the high-sensitivity CRP (hs-CRP) levels. Histopathology showed that the α-mangostin-treated group had less damage to pancreatic β cells, healthier hepatocytes and central veins, and less glomerular and tubular epithelial necrosis than the diabetic control group. Moreover, the antioxidant effect of G. mangostana was shown to protect against the micro-and macrovascular damage caused by T2DM.
 Conclusion: Extract or isolates of G. mangostana possess strong potential to prevent and treat T2DM. Further research evaluating long-term outcome biomarkers in humans is needed to confirm the drug’s glycemic control capacity.

Students of color show health advantages when they attend schools that emphasize the value of diversity

As the United States becomes more diverse, the ways in which mainstream institutions recognize and address race and ethnicity will be increasingly important. Here, we show that one novel and salient characteristic of an institutional environment, that is, whether a school emphasizes the value of racial and ethnic diversity, predicts better cardiometabolic health among adolescents of color. Using a diverse sample of adolescents who attend more than 100 different schools in predominantly urban locations, we find that when schools emphasize the value of diversity (operationalized as mentioning diversity in their mission statements), students of color, but not white students, have lower values on a composite of five biomarkers of inflammation, have less insulin resistance and compensatory β-cell activity, and have fewer metabolic syndrome signs and score lower on a continuous metabolic syndrome composite. These results suggest that institutions that emphasize diversity may play an unacknowledged role in protecting the health of people of color and, thus, may be a site for future interventions to reduce health disparities.

Association of EGF A61G polymorphism and EGF expression with type 2 diabetes mellitus in Indian population

BackgroundEpidermal Growth Factor (EGF) plays critical role in regeneration of pancreatic β-cells and insulin secretion. The deficiency in EGF expression affects pancreatic β-cell's proliferation, maintenance and its function like insulin secretion which may result in individual susceptibility to Type 2 Diabetes Mellitus (T2DM). EGF A61G is a functional SNP that modulate EGF levels and eventually affects activity of β-cells. ObjectiveThe present study explores EGF A61G polymorphism (rs4444903) and correlates it with the risk of developing T2DM and mRNA expression. MethodsThe study included 90 subjects, T2DM patients (n = 30) and healthy controls (n = 60). Blood sample was collected from subjects to study EGF A61G polymorphism by PCR-RFLP and EGF mRNA expression level by Real-time PCR. ResultsThe EGF gene A61G polymorphism was found to be in significant association with T2DM. A/G genotype (OR = 4.07, 95%CI = 1.303 to 12.71, p = 0.0206) and ‘A’ allele (OR = 1.91, 95%CI = 1.017 to 3.568, p = 0.043) were significantly associated with risk of T2DM. The prevalence of allele ‘A’ was found to be higher in diabetic males and females (52.5% and 55% respectively). As compared to healthy subjects EGF mRNA expression levels showed significant down-regulation in T2DM patients (p = 0.005). The relative EGF mRNA expression in A/A and A/G genotype was significantly lower than G/G genotype. ConclusionThe present study suggests that EGF gene A61G polymorphism may be a genetic risk factor for susceptibility of T2DM in Indian population. However, this marker deserves further investigation using more sample size.

Genomewide association study of C-peptide surfaces key regulatory genes in Indians

Insulin is a commonly used measure of pancreatic β-cell function but exhibits a short half-life in the human body. During biosynthesis, insulin release is accompanied by C-peptide at an equimolar concentration which has a much higher plasma half-life and is therefore projected as a precise measure of β-cell activity than insulin. Despite this, genetic studies of metabolic traits haveneglected the regulatory potential of C-peptide for therapeutic intervention of type-2 diabetes. The present study is aimed to search genomewide variants governing C-peptide levels in genetically diverse and high risk population for metabolic diseases-Indians. We performed whole genome genotyping in 877 healthy Indians of Indo-European origin followed by replication of variants with P ≤ 1 × 10-3 in an independent sample-set of 1829 Indians. Lead-associated signals were also tested in-silico in 773 Hispanics. To secure biological rationale for observed association, we further carried out DNA methylation quantitative trait loci analysis in 233 Indians and publicly available regulatory data was mined. We discovered novel lncRNA gene AC073333.8 with the strongest association with C-peptide levels in Indians that however missed genomewide significance. Also, noncoding genes, RP1-209A6.1 and RPS3AP5; protein gene regulators, ZNF831 and ETS2; and solute carrier protein gene SLC15A5 retained robust association with C-peptide after meta-analysis. Integration of methylation data revealed ETS2 and ZNF831 single-nucleotide polymorphisms as significant meth-QTLs in Indians. All genes showed reasonable expression in the human lung, signifying alternate important organs for C-peptide biology. Our findings mirror polygenic nature of C-peptide where multiple small-effect size variants in the regulatory genome principally govern the trait biology.

Functional peroxisomes are required for β-cell integrity in mice

ObjectivesPeroxisomes play a crucial role in lipid and reactive oxygen species metabolism, but their importance for pancreatic β-cell functioning is presently unknown. To examine the contribution of peroxisomal metabolism to β-cell homeostasis in mice, we inactivated PEX5, the import receptor for peroxisomal matrix proteins, in an inducible and β-cell restricted manner (Rip-Pex5−/− mice). MethodsAfter tamoxifen-induced recombination of the Pex5 gene at the age of 6 weeks, mice were fed either normal chow or a high-fat diet for 12 weeks and were subsequently phenotyped. ResultsIncreased levels of very long chain fatty acids and reduced levels of plasmalogens in islets confirmed impairment of peroxisomal fatty acid oxidation and ether lipid synthesis, respectively. The Rip-Pex5−/− mice fed on either diet exhibited glucose intolerance associated with impaired insulin secretion. Ultrastructural and biochemical analysis revealed a decrease in the density of mature insulin granules and total pancreatic insulin content, which was further accompanied by mitochondrial disruptions, reduced complex I activity and massive vacuole overload in β-cells. RNAseq analysis suggested that cell death pathways were affected in islets from HFD-fed Rip-Pex5−/− mice. Consistent with this change we observed increased β-cell apoptosis in islets and a decrease in β-cell mass. ConclusionsOur data indicate that normal peroxisome metabolism in β-cells is crucial to preserve their structure and function.

Electrophysiology of the pancreatic islet β-cell sweet taste receptor TIR3.

Over recent years, the presence of the sweet taste receptor TIR3 in rodent and human insulin-producing pancreatic islet β-cells was documented. The activation of this receptor by sweet-tasting sucralose mimics several biochemical and functional effects of D-glucose in the β-cells. The present study extends this analogy to the bioelectrical response of β-cells. In this respect, sucralose was inefficient in the absence of D-glucose, but induced on occasion electrical activity in mouse β-cells exposed to low non-stimulatory concentrations of the hexose and potentiated, in a concentration-related manner, the response to stimulatory concentrations of D-glucose. These data indicate that sucralose, acting as an agonist of the TIR3 receptor, exerts an excitatory effect upon pancreatic β-cell bioelectrical activity.