Dynamics Of Insulin Secretion Research Articles

Preserving insulin function in diabetes: a case report

BackgroundThis case report explores the long-term dynamics of insulin secretion and glycemic control in two patients with diabetes mellitus type 2 over 20 years. The observations underscore the impact of lifestyle interventions, including weight loss and calorie restriction, on insulin secretion patterns and glucose levels during 75 g oral glucose tolerance tests. Additionally, the role of hemoglobin A1c fluctuations, influenced by various factors such as body weight, exercise, and pharmacological interventions, is investigated.Case presentationCase 1 involves a Japanese woman now in her late 70s who successfully maintained her hemoglobin A1c below 7% for over two decades through sustained weight loss and lifestyle changes. Despite a gradual decline in the homeostasis model assessment of β cell function, the patient exhibited remarkable preservation of insulin secretion patterns over the 20-year follow-up. In case 2, a Japanese woman, now in her early 70s, experienced an improvement in hemoglobin A1c to 6.3% after a period of calorie limitation due to a wrist fracture in 2018. This incident seemed to trigger a temporary rescue of pancreatic β cell function, emphasizing the dynamic nature of insulin secretion. Both cases highlight the potential for pancreatic β cell rescue and underscore the persistence of insulin secretion over the 20-year follow-up. Additionally, we have briefly discussed three additional cases with follow-ups ranging from 10 to 17 years, demonstrating similar trends in glucose and insulin ratios.ConclusionsLong-term lifestyle interventions, such as weight loss and calorie restriction, can preserve pancreatic β cell function and maintain glycemic control in type 2 diabetes patients over 20 years. Two patients showed stable or improved insulin secretion and favorable hemoglobin A1c levels, challenging the traditional view of irreversible β cell decline. The findings highlight the importance of personalized, nonpharmacological approaches, suggesting that sustained lifestyle changes can significantly impact diabetes management and potentially rescue β cell function.

Identifying metabotypes of insulin resistance severity in children with metabolic syndrome

BackgroundInsulin resistance is a frequent precursor of typical obesity and metabolic syndrome complications. However, accurate diagnosis remains elusive because of its pathophysiological complexity and heterogeneity. Herein, we have explored the utility of insulin secretion dynamics in response to an oral glucose tolerance test as a surrogate marker to identify distinct metabotypes of disease severity.MethodsThe study population consisted of children with obesity and insulin resistance, stratified according to the post-challenge insulin peak timing (i.e., early, middle, and late peak), from whom fasting and postprandial plasma and erythrocytes were collected for metabolomics analysis.ResultsChildren with late insulin peak manifested worse cardiometabolic health (i.e., higher blood pressure, glycemia, and HOMA-IR scores) than early responders. These subjects also showed more pronounced changes in metabolites mirroring failures in energy homeostasis, oxidative stress, metabolism of cholesterol and phospholipids, and adherence to unhealthy dietary habits. Furthermore, delayed insulin peak was associated with impaired metabolic flexibility, as reflected in compromised capacity to regulate mitochondrial energy pathways and the antioxidant defense in response to glucose overload.ConclusionsAltogether, these findings suggest that insulin resistance could encompass several phenotypic subtypes characterized by graded disturbances in distinctive metabolic derangements occurring in childhood obesity, which serve as severity predictive markers.

Regulated and adaptive in vivo insulin secretion from islets only containing β-cells

Insulin-producing β-cells in pancreatic islets are regulated by systemic cues and, locally, by adjacent islet hormone-producing ‘non-β-cells’ (namely α-cells, δ-cells and γ-cells). Yet whether the non-β-cells are required for accurate insulin secretion is unclear. Here, we studied mice in which adult islets are exclusively composed of β-cells and human pseudoislets containing only primary β-cells. Mice lacking non-β-cells had optimal blood glucose regulation, enhanced glucose tolerance, insulin sensitivity and restricted body weight gain under a high-fat diet. The insulin secretion dynamics in islets composed of only β-cells was comparable to that in intact islets. Similarly, human β-cell pseudoislets retained the glucose-regulated mitochondrial respiration, insulin secretion and exendin-4 responses of entire islets. The findings indicate that non-β-cells are dispensable for blood glucose homeostasis and β-cell function. These results support efforts aimed at developing diabetes treatments by generating β-like clusters devoid of non-β-cells, such as from pluripotent stem cells differentiated in vitro or by reprograming non-β-cells into insulin producers in situ.

Disentangling fetal insulin hypersecretion and insulin resistance

Disentangling which of insulin hypersecretion and insulin resistance is upstream in obesity-related type 2 diabetes (T2D) is challenging. Here, we consider the dynamics of insulin secretion and action in the fetuses of mothers with diabetes. We argue that fetal insulin hypersecretion occurs first, with insulin resistance being an adaptive protective response.

Altered insulin secretion dynamics relate to oxidative stress and inflammasome activation in children with obesity and insulin resistance

BackgroundInsulin resistance (IR) is considered the main driver of obesity related metabolic complications, and is related to oxidative stress and inflammation, which in turn promote each other. There is currently no specific definition of IR in children, rather, that for adult population is used by pediatric endocrinologists instead. Altered insulin secretion dynamics are associated with worse metabolic profiles and type 2 diabetes mellitus development, thus we aimed to test whether insulin response relates to oxidative stress and inflammation in children.MethodsWe conducted a case–control study, including 132 children classified as follows: 33 children without obesity (Lean); 42 with obesity but no IR according to the American Diabetes Association criteria for adults (OBIR-); 25 with obesity and IR and an early insulin response to an oral glucose tolerance test (OGTT) (EP-OBIR +); 32 with obesity, IR, and a late insulin peak (LP-OBIR +); and studied variables associated with lipid and carbohydrate metabolism, oxidative stress, inflammation and inflammasome activation.ResultsThe measured parameters of children with obesity, IR, and an early insulin response were similar to those of children with obesity but without IR. It was late responders who presented an impaired antioxidant system and elevated oxidative damage in erythrocytes and plasma, and inflammasome activation at their white blood cells, despite lower classical inflammation markers. Increased uric acid levels seems to be one of the underlying mechanisms for inflammasome activation.ConclusionsIt is insulin response to an OGTT that identifies children with obesity suffering oxidative stress and inflammasome activation more specifically. Uric acid could be mediating this pathological inflammatory response by activating NLRP3 in peripheral blood mononuclear cells.Graphical

1746-P: The Role of Cell–Cell Junction Associated Mediator in Glucose-Stimulated Insulin Secretion of Pancreatic Islets

Glucose-stimulated insulin secretion from β cells is essential in maintaining glucose homeostasis. Cell-cell communication within the pancreatic islets, mediated by cell-cell junctions and their mediators, regulates insulin secretion dynamics and glucose homeostasis. It has been reported that Nephrin-mediated intercellular junction between β cells is implicated in the regulation of insulin secretion, however, the underlying mechanisms are not fully understood. Here, we investigated the effects of Girdin, a cell-cell junction associated mediator, on insulin release. We found that Girdin was expressed in mouse pancreatic β cells and mediated glucose-stimulated insulin secretion, especially for the second phase. Next, we demonstrated that glucose-stimulated tyrosine phosphorylation of Girdin mediated Nephrin phosphorylation by recruiting Src kinase, which leads to the endocytosis of Nephrin. Furthermore, we observed the glucose-induced Girdin/Nephrin/Src signaling induced downstream Akt phosphorylation and activated Rac1-mediated cytoskeleton reorganization, allowing insulin secretory granules to access the plasma membrane for the second-phase secretion. Finally, we found that Girdin is downregulated in the diabetic islets, and rescue of Girdin restored impaired glucose-stimulated insulin secretion. Taken together, these data provide evidence that the cell-cell junction associated mediator play important roles in fusion of insulin secretory vesicles within the cell and establish a role for Girdin in regulating this process. Disclosure H.Wang: None. Funding National Natural Science Foundation of China

Rapid Quantification of First and Second Phase Insulin Secretion Dynamics using an In vitro Platform for Improving Insulin Therapy

High-throughput quantification of the first- and second-phase insulin secretion dynamics is intractable with current methods. The fact that independent secretion phases play distinct roles in metabolism necessitates partitioning them separately and performing high-throughput compound screening to target them individually. We developed an insulin-nanoluc luciferase reporter system to dissect the molecular and cellular pathways involved in the separate phases of insulin secretion. We validated this method through genetic studies, including knockdown and overexpression, as well as small-molecule screening and their effects on insulin secretion. Furthermore, we demonstrated that the results of this method are well correlated with those of single-vesicle exocytosis experiments conducted on live cells, providing a quantitative reference for the approach. Thus, we have developed a robust methodology for screening small molecules and cellular pathways that target specific phases of insulin secretion, resulting in a better understanding of insulin secretion, which in turn will result in a more effective insulin therapy through the stimulation of endogenous glucose-stimulated insulin secretion.

Fibrocalculous pancreatic diabetes

Chronic Pancreatitis and the type of diabetes associated with it have been named as “Fibrocalcific Pancreatic Diabetes” (FCPD). Initially categorized by WHO in 1985 as a subtype of Malnutrition Related Diabetes Mellitus (MRDM), FCPD has subsequently been included as a disease of the exocrine pancreas under other specific forms of diabetes. Despite many years since its first description, the etiopathogenesis of FCPD remains obscure. While insulin secretion defects are definitely the crux of the problem, there is growing body of evidence to suggest that insulin resistance may play a key role in glucose metabolism in these individuals. Moreover, the role of free fatty acids, counter-regulatory hormones like glucagon and impact of hepatic and peripheral lipid distribution on the dynamics of insulin secretion remains to be explored. Other factors related to alterations in energy expenditure may compound the pathogenetic picture. In fact, not all people with Fibro calculous Pancreatitis will develop diabetes and a search for the exact triggers for hyperglycemia might provide the clue to this enigmatic disease pathophysiology.

Insulin Secretion and β-Cell Function Are Preserved in Patients with Treated Hematological Malignancies

INTRODUCTION Cancer survivors are at elevated risk for developing type 2 diabetes mellitus, which decreases quality of life and increases mortality during cancer survivorship. Type 2 diabetes results from a combination of insulin resistance and decreased insulin secretion. Assessing pancreatic β-cell function by measuring insulin secretion dynamics in response to hyperglycemia can provide insight into the pathogenesis of type 2 diabetes. We investigated insulin secretion in patients with treated hematological malignancies and compared them to non-diabetic controls without cancer. We hypothesized that patients with hematological malignancies will have decreased insulin secretion compared to controls without cancer due to β-cell toxicity from previous treatment and chemotherapy. METHODS We evaluated insulin secretion in 16 non-diabetic adult patients with treated hematological malignancies using a hyperglycemic clamp, which assesses pancreatic β-cell function by measuring insulin secretion in response to hyperglycemia (200 mg/dL) maintained by a dextrose infusion. Clamp outcomes included first phase (T0-10 minutes), second phase (T90-120 minutes), and maximal (L-arginine stimulated) insulin response. The insulin sensitivity index (ISI) and disposition index (DI, a measure of the β-cell function to compensate for insulin resistance) were calculated. Controls (n=32) matched for age, sex, race, and body mass index (BMI) were selected 2:1 from a database of 154 hyperglycemic clamps in participants without diabetes or cancer. Demographic characteristics and clamp outcomes were compared using χ2, Wilcoxon rank-sum test, or linear regression. RESULTS Hyperglycemic clamps were performed in 48 individuals without diabetes (16 patients with treated hematological malignancies and 32 matched controls without cancer). Cancer survivors and controls without malignancy were well-matched for age, sex, race (Table 1). Myeloid malignancies were the most common diagnosis (n=11; 69%) with a median time from diagnosis to metabolic testing of 6 months. Treatment included cytotoxic chemotherapy (n=15; 94%), glucocorticoids (n=7; 44%), and radiation (n=1; 6%) with 7 (44%) patients achieving a remission prior to testing. Compared to controls, patients with malignancy had lower fasting glucose levels (93.0 mg/dL [IQR 86.3-96.6] vs 101.5 [IQR 94.9-107.6], p<0.001) and lower fasting insulin levels (11.5 uU/mL [IQR 9.3-15.0] vs 16.3 [IQR 12.3-21.5], p=0.023), suggesting greater insulin sensitivity within the cancer cohort. In univariable analysis, there were no significant differences between first and second phase insulin response between patients with or without treated hematological malignancies (Table 1). Cancer survivors had a higher maximal (L-arginine stimulated) insulin secretion (3606 uU/mL [IQR 3255-4594] vs 2278 [IQR 1900-3555], p=0.026) and a higher disposition index (2521 mg/kg/min [IQR 1986-3360] vs 1300 [IQR 939-1923], p=0.01) than in controls. Cancer survivors demonstrated a trend toward greater insulin sensitivity compared to controls (6.82 mg/kg/min per uU/mL [IQR 5.53-10.83] vs 4.98 [IQR 3.65-7.28], p=0.092). After adjustment for BMI and fasting glucose in linear regression models, both second phase (β=242.5, p=0.005) and maximal insulin secretion (β=1225.6, p=0.019) were greater in cancer survivors then in controls without cancer (Table 2). CONCLUSION Cancer survivors had higher maximal phase insulin secretion and disposition index (a measure of β-cell function adjusted for insulin resistance) compared to non-diabetic controls without cancer. Our data suggests that cancer survivors have preserved β-cell function following treatment of their hematological malignancies, contrary to our hypothesis. Longitudinal follow-up is needed to determine factors that promote diabetes susceptibility in cancer survivors. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Alpha-cell paracrine signaling in the regulation of beta-cell insulin secretion.

As an incretin hormone, glucagon-like peptide 1 (GLP-1) lowers blood glucose levels by enhancing glucose-stimulated insulin secretion from pancreatic beta-cells. Therapies targeting the GLP-1 receptor (GLP-1R) use the classical incretin model as a physiological framework in which GLP-1 secreted from enteroendocrine L-cells acts on the beta-cell GLP-1R. However, this model has come into question, as evidence demonstrating local, intra-islet GLP-1 production has advanced the competing hypothesis that the incretin activity of GLP-1 may reflect paracrine signaling of GLP-1 from alpha-cells on GLP-1Rs on beta-cells. Additionally, recent studies suggest that alpha-cell-derived glucagon can serve as an additional, albeit less potent, ligand for the beta-cell GLP-1R, thereby expanding the role of alpha-cells beyond that of a counterregulatory cell type. Efforts to understand the role of the alpha-cell in the regulation of islet function have revealed both transcriptional and functional heterogeneity within the alpha-cell population. Further analysis of this heterogeneity suggests that functionally distinct alpha-cell subpopulations display alterations in islet hormone profile. Thus, the role of the alpha-cell in glucose homeostasis has evolved in recent years, such that alpha-cell to beta-cell communication now presents a critical axis regulating the functional capacity of beta-cells. Herein, we describe and integrate recent advances in our understanding of the impact of alpha-cell paracrine signaling on insulin secretory dynamics and how this intra-islet crosstalk more broadly contributes to whole-body glucose regulation in health and under metabolic stress. Moreover, we explore how these conceptual changes in our understanding of intra-islet GLP-1 biology may impact our understanding of the mechanisms of incretin-based therapeutics.

359-OR: Imaging Pancreatic Blood Flow during Stimulation of Insulin Secretion in Humans

Non-invasive imaging of endocrine pancreatic function could provide valuable insights into the magnitude and temporal pattern of β-cell dysfunction in diabetes. Islets comprise 1-2% of pancreatic mass, but receive about 10-20% of pancreatic blood flow, which increases further during stimulation of insulin secretion. We examined the relationship between pancreatic blood flow (PBF) and insulin secretory dynamics in 12 healthy volunteers (6M / 6F, age = 29 ± 5 yrs, BMI = 24.0 ± 2.7 kg/m², HbA1c = 5.1 ± 0.3 %, FPG = 88 ± mg/dl, fasting insulin = 3.7 ± 2.3 μU/ml) . PBF was measured by pseudo-continuous arterial spin labeling (ASL) MRI, with the labeling plane positioned 5-6 cm superior to the imaging slice to label blood in the descending aorta. Fasting subjects were placed in a 3T scanner, and PBF was measured during 1) a 15 min basal period, 2) a +100 mg/dl hyperglycemic clamp for 40 min, followed by 3) a 5 gm bolus of arginine to assess maximal acute insulin response (AIRmax) . First phase (0-min) insulin response to hyperglycemia was 181 ± 96 μU/ml · min, and AIRmax after arginine + hyperglycemia (40-50 min) was 1097 ± 629 μU/ml · min. Basal PBF (188 ± 53 ml/100 gm/min) increased during first phase insulin release, peaking at 212 ± 66 at 12 min, subsequently returned to basal levels (176 ± 59) from 10-40 min during sustained hyperglycemia,and peaked again at 2± 62 at 2 min after arginine. Although there were no significant correlations between glucose, insulin or c-peptide levels and PBF, time-series Granger causality analysis demonstrated that the time-derivative of c-peptide and insulin concentrations, reflectingacute changes in insulin secretion, preceded the increase in PBF (p=0.03 for d[c-peptide]/dt, and p = 0.for d[insulin]/dt) . Conclusions: 1) Changes in PBF during stimulation of insulin secretion in humans can be imaged non-invasively by ASL, 2) Insulin secretion precedes changes in PBF, and 3) The rate of change in insulin and c-peptide release predicts subsequent modulation of PBF. Disclosure D.C.Simonson: Stock/Shareholder; GI Windows, Phase V Technologies, Inc. M.Taso: Research Support; GE Healthcare Systems. C.Mcgrath: None. S.A.Waldman: None. F.Papadopoulou: None. D.C.Alsop: Other Relationship; GE Healthcare Systems, Hitachi, Ltd., Philips Healthcare, Siemens, UIH America, Research Support; GE Healthcare Systems.

Understanding the Mechanism of Diabetes Mellitus in a LRBA-Deficient Patient.

Simple SummaryDeficiency of lipopolysaccharide responsive beige like anchoring protein (LRBA) has been reported to cause immunological complications that can be fatal in children. Diabetes mellitus (DM) has been reported in some patients with LRBA deficiency. However, the underlying mechanism of the DM is not known. The current study provides potential novel insights into the underlying mechanism of DM in a LRBA-deficient patient. Additionally, in mouse pancreatic β-cells, we show that LRBA plays a role in the dynamics of insulin secretion and biosynthesis.The scope of this study is to show that DM in a LRBA-deficient patient with a stop codon mutation (c.3999 G > A) was not mediated through autoimmunity. We have evaluated the ability of the proband’s T cells to be activated by assessing their CTLA-4 expression. A nonsignificant difference was seen in the CTLA-4 expression on CD3+ T cells compared to the healthy control at basal level and after stimulation with PMA/ionomycin. Blood transcriptomic analysis have shown a remarkable increase in abundance of transcripts related to CD71+ erythroid cells. There were no differences in the expression of modules related to autoimmunity diseases between the proband and pooled healthy controls. In addition, our novel findings show that siRNA knockdown of LRBA in mouse pancreatic β-cells leads reduced cellular proinsulin, insulin and consequently insulin secretion, without change in cell viability in cultured MIN6 cells.

The effects of beta-cell mass and function, intercellular coupling, and islet synchrony on {text {Ca}}^{2+} dynamics

Type 2 diabetes (T2D) is a challenging metabolic disorder characterized by a substantial loss of beta -cell mass and alteration of beta -cell function in the islets of Langerhans, disrupting insulin secretion and glucose homeostasis. The mechanisms for deficiency in beta -cell mass and function during the hyperglycemia development and T2D pathogenesis are complex. To study the relative contribution of beta -cell mass to beta -cell function in T2D, we make use of a comprehensive electrophysiological model of human beta -cell clusters. We find that defect in beta -cell mass causes a functional decline in single beta -cell, impairment in intra-islet synchrony, and changes in the form of oscillatory patterns of membrane potential and intracellular {text {Ca}}^{2+} concentration, which can lead to changes in insulin secretion dynamics and in insulin levels. The model demonstrates a good correspondence between suppression of synchronizing electrical activity and published experimental measurements. We then compare the role of gap junction-mediated electrical coupling with both beta -cell synchronization and metabolic coupling in the behavior of {text {Ca}}^{2+} concentration dynamics within human islets. Our results indicate that inter-beta -cellular electrical coupling depicts a more important factor in shaping the physiological regulation of islet function and in human T2D. We further predict that varying the whole-cell conductance of delayed rectifier text {K}^{+} channels modifies oscillatory activity patterns of beta -cell population lacking intercellular coupling, which significantly affect {text {Ca}}^{2+} concentration and insulin secretion.

A Microfluidic Hanging-Drop-Based Islet Perifusion System for Studying Glucose-Stimulated Insulin Secretion From Multiple Individual Pancreatic Islets.

Islet perifusion systems can be used to monitor the highly dynamic insulin release of pancreatic islets in glucose-stimulated insulin secretion (GSIS) assays. Here, we present a new generation of the microfluidic hanging-drop-based islet perifusion platform that was developed to study the alterations in insulin secretion dynamics from single pancreatic islet microtissues at high temporal resolution. The platform was completely redesigned to increase experimental throughput and to reduce operational complexity. The experimental throughput was increased fourfold by implementing a network of interconnected hanging drops, which allows for performing GSIS assays with four individual islet microtissues in parallel with a sampling interval of 30 s. We introduced a self-regulating drop-height mechanism that enables continuous flow and maintains a constant liquid volume in the chip, which enables simple and robust operation. Upon glucose stimulation, reproducible biphasic insulin release was simultaneously observed from all islets in the system. The measured insulin concentrations showed low sample-to-sample variation as a consequence of precise liquid handling with stable drop volumes, equal flow rates in the channels, and accurately controlled sampling volumes in all four drops. The presented device will be a valuable tool in islet and diabetes research for studying dynamic insulin secretion from individual pancreatic islets.

In Vivo ZIMIR Imaging of Mouse Pancreatic Islet Cells Shows Oscillatory Insulin Secretion.

Appropriate insulin secretion is essential for maintaining euglycemia, and impairment or loss of insulin release represents a causal event leading to diabetes. There have been extensive efforts of studying insulin secretion and its regulation using a variety of biological preparations, yet it remains challenging to monitor the dynamics of insulin secretion at the cellular level in the intact pancreas of living animals, where islet cells are supplied with physiological blood circulation and oxygenation, nerve innervation, and tissue support of surrounding exocrine cells. Herein we presented our pilot efforts of ZIMIR imaging in pancreatic islet cells in a living mouse. The imaging tracked insulin/Zn2+ release of individual islet β-cells in the intact pancreas with high spatiotemporal resolution, revealing a rhythmic secretion activity that appeared to be synchronized among islet β-cells. To facilitate probe delivery to islet cells, we also developed a chemogenetic approach by expressing the HaloTag protein on the cell surface. Finally, we demonstrated the application of a fluorescent granule zinc indicator, ZIGIR, as a selective and efficient islet cell marker in living animals through systemic delivery. We expect future optimization and integration of these approaches would enable longitudinal tracking of beta cell mass and function in vivo by optical imaging.

Caloric restriction recovers impaired β-cell-β-cell gap junction coupling, calcium oscillation coordination, and insulin secretion in prediabetic mice.

Caloric restriction can decrease the incidence of metabolic diseases, such as obesity and Type 2 diabetes mellitus. The mechanisms underlying the benefits of caloric restriction involved in insulin secretion and glucose homeostasis are not fully understood. Intercellular communication within the islets of Langerhans, mediated by Connexin36 (Cx36) gap junctions, regulates insulin secretion dynamics and glucose homeostasis. The goal of this study was to determine whether caloric restriction can protect against decreases in Cx36 gap junction coupling and altered islet function induced in models of obesity and prediabetes. C57BL6 mice were fed with a high-fat diet (HFD), showing indications of prediabetes after 2 mo, including weight gain, insulin resistance, and elevated fasting glucose and insulin levels. Subsequently, mice were submitted to 1 mo of 40% caloric restriction (2 g/day of HFD). Mice under 40% caloric restriction showed reversal in weight gain and recovered insulin sensitivity, fasting glucose, and insulin levels. In islets of mice fed the HFD, caloric restriction protected against obesity-induced decreases in gap junction coupling and preserved glucose-stimulated calcium signaling, including Ca2+ oscillation coordination and oscillation amplitude. Caloric restriction also promoted a slight increase in glucose metabolism, as measured by increased NAD(P)H autofluorescence, as well as recovering glucose-stimulated insulin secretion. We conclude that declines in Cx36 gap junction coupling that occur in obesity can be completely recovered by caloric restriction and obesity reversal, improving Ca2+ dynamics and insulin secretion regulation. This suggests a critical role for caloric restriction in the context of obesity to prevent islet dysfunction.

2076-P: Increased Gap Junction Coupling in the Islet of Langerhans following Caloric Restriction

Intercellular communication mediated by connexin 36 gap junction channels coordinate and regulate the dynamics of islet calcium oscillations and insulin secretion. Impaired gap junction coupling occurs in prediabetic mice under a high fat diet. Dietary interventions, such as calorie restriction, can regain weight and modulate insulin secretion. However, it is unknown whether caloric restriction can recover impaired gap junctions coupling and calcium regulation in islets of mice fed a high fat diet. Here, we tested if caloric restriction can protect against obesity-induced decreases in connexin36 coupling and altered islet function. We used C57BL6 mice under a normal diet (Envigo 2020X), or a high fat diet (HFD) (Envigo TD.03584) which causes prediabetes after three months. HFD mice were also submitted to 40% caloric restriction (2g/day) for one month. We performed intraperitoneal glucose tolerance tests, insulin tolerance tests, in vivo insulin level measurements. In isolated islets we measured glucose-stimulated insulin secretion, islet Ca2+ dynamics, metabolic activity, along with gap junction permeability. We observed that caloric restriction improved glucose tolerance (p=0.002), insulin sensitivity (p=0.001), and islet function. This included normalization glucose-induced insulin secretion (p=0.01), enhanced Ca2+ oscillation amplitude (p=0.002) and greater coordination (p=0.04). These improvements correlated with restoration in gap junction permeability (p=0.02). Caloric restriction also promoted a slight increase in NAD(P)H increase by elevated glucose (p=0.04) indicating improved metabolic activity and viability of these cells. We conclude that the decline in gap junction coupling. mediated by connexin 36 in islets that occurs in diet-induced obesity, is improved by short term caloric restriction. This improvement contributes to improved islet function. Disclosure M.C. Amaral: None. V. Kravets: None. J.M. Dwulet: None. N.L. Farnsworth: None. R.A. Piscopio: None. W. Schleicher: None. J. Miranda: None. R.K. Benninger: None. Funding JDRF (5-CDA-2014-198-A-N); National Institutes of Health (R01DK102950, R01DK106412 to R.K.B.); Fundação de Amparo à Pesquisa do Estado de São Paulo (2018/04536-6)

The inducible β5i proteasome subunit contributes to proinsulin degradation in GRP94-deficient β-cells and is overexpressed in type 2 diabetes pancreatic islets

Proinsulin is a misfolding-prone protein, and its efficient breakdown is critical when β-cells are confronted with high-insulin biosynthetic demands, to prevent endoplasmic reticulum stress, a key trigger of secretory dysfunction and, if uncompensated, apoptosis. Proinsulin degradation is thought to be performed by the constitutively expressed standard proteasome, while the roles of other proteasomes are unknown. We recently demonstrated that deficiency of the proinsulin chaperone glucose-regulated protein 94 (GRP94) causes impaired proinsulin handling and defective insulin secretion associated with a compensated endoplasmic reticulum stress response. Taking advantage of this model of restricted folding capacity, we investigated the role of different proteasomes in proinsulin degradation, reasoning that insulin secretory dynamics require an inducible protein degradation system. We show that the expression of only one enzymatically active proteasome subunit, namely, the inducible β5i-subunit, was increased in GRP94 CRISPR/Cas9 knockout (KO) cells. Additionally, the level of β5i-containing intermediate proteasomes was significantly increased in these cells, as was β5i-related chymotrypsin-like activity. Moreover, proinsulin levels were restored in GRP94 KO upon β5i small interfering RNA-mediated knockdown. Finally, the fraction of β-cells expressing the β5i-subunit is increased in human islets from type 2 diabetes patients. We conclude that β5i is an inducible proteasome subunit dedicated to the degradation of mishandled proinsulin.

323-LB: Activation of the GLP-1 Receptor Signaling Prevents Beta-Cell Dedifferentiation in a Mouse Model of Wolfram Syndrome through Modulating TXNIP Expression

Loss of functional β cells results in a gradual progression of insulin insufficiency in Wolfram syndrome caused by recessive WFS1 mutations. Currently, there are no specific treatment recommendations for the disease. We have so far evidenced that, in the Wfs1-/- mice, β cells become dedifferentiated and revert to endocrine progenitor-like cells expressing Ngn3, and a subset of β cells takes α cell fate. Such β cell plasticity appears after nursing, independently of hyperglycaemia, and becomes more apparent along with diabetes progression accompanied with no significant increase in apoptosis. In this study, we examined the potential effects of a GLP-1 receptor agonist on β cell plasticity and glucose homeostasis in young Wfs1−/− mice without noticeable hyperglycaemia. Results: Four weeks administration of Ex-4 resulted in an off-drug amelioration of glucose excursions after glucose loading in Wfs1−/− mice, with insulin secretory dynamics that were indistinguishable from those in WT mice, despite no alteration in beta cell mass. In association with the functional improvements, Ex-4 alleviated β cell dedifferentiation evidenced by a decrease of MafA and a Ngn3 emergence. At the same time, Ex-4 reversed a robust increase in thioredoxin interacting protein (TXNIP) in Wfs1-/- β cells. Mechanistically, Ex-4 suppressed it at both transcriptional and post-translational levels. Furthermore, we have found that genetic ablation of Txnip in Wfs1-/- mice inhibited β cell dedifferentiation, resulting in prevention of diabetes progression with preservation of β cell mass. Our finding implies that activation of the GLP-1 receptor signaling may prevent β cells from becoming dedifferentiated by modulating Txnip and may slow diabetes progression in Wolfram syndrome. Disclosure K. Tanabe: None. K. Amo-Shiinoki: None. M. Hatanaka: None. Y. Tanizawa: None. Funding Japan Society for the Promotion of Science (16K09752, 15K21198, 15K09390); Japan Diabetes Society; Japan Association for Diabetes Education and Care

Layer-by-Layer Cerium Oxide Nanoparticle Coating for Antioxidant Protection of Encapsulated Beta Cells.

In type 1 diabetes, the replacement of the destroyed beta cells could restore physiological glucose regulation and eliminate the need for exogenous insulin. Immunoisolation of these foreign cellular transplants via biomaterial encapsulation is widely used to prevent graft rejection. While highly effective in blocking direct cell-to-cell contact, nonspecific inflammatory reactions to the implant lead to the overproduction of reactive oxygen species, which contribute to foreign body reaction and encapsulated cell loss. For antioxidant protection, cerium oxide nanoparticles (CONPs) are a self-renewable, ubiquitous, free radical scavenger currently explored in several biomedical applications. Herein, 2-12 alternating layers of CONP/alginate are assembled onto alginate microbeads containing beta cells using a layer-by-layer (LbL) technique. The resulting nanocomposite coatings demonstrate robust antioxidant activity. The degree of cytoprotection correlates with layer number, indicating tunable antioxidant protection. Coating of alginate beads with 12 layers of CONP/alginate provides complete protection to the entrapped beta cells from exposure to 100 × 10-6 m H2 O2 , with no significant changes in cellular metabolic activity, oxidant capacity, or insulin secretion dynamics, when compared to untreated controls. The flexibility of this LbL method, as well as its nanoscale profile, provides a versatile approach for imparting antioxidant protection to numerous biomedical implants, including beta cell transplantation.