Β-cell Dysfunction Research Articles

Overview on Thioredoxin-Interacting Protein (TXNIP): A Potential Target for Diabetes Intervention.

Diabetes mellitus (DM) is a common metabolic disorder characterized by a persistent increment of blood glucose. Type 2 DM is characterized by insulin resistance and β-cell dysfunction. Thioredoxin-interacting protein (TXNIP) is among the factors that control the production and loss of pancreatic β-cells. Recent studies have shown that high glucose can significantly up-regulate the expression of the TXNIP. Overexpression of TXNIP in β-cells not only induced apoptosis but also decreased the production of insulin. At the same time, TXNIP deficiency protected the apoptosis of β-cells, leading to increased insulin production. Therefore, finding small molecules that can modulate TXNIP expression and downstream signalling pathways is essential. Thus, the inhibition of TXNIP has beneficial effects on the cardiovascular system and other tissues such as the heart and the kidney in DM. Therefore, DM treatment must target small TXNIP activity, inhibit expression, and promote endogenous cell mass and insulin production. This review briefly describes the effect mechanism, regulatory mechanism, and crystal structure of TXNIP. In addition, we highlight how TXNIP signalling networks contribute to diabetes and interact with drugs that inhibit the development often and its complexes. Finally, the current status and prospects of TXNIP targeted therapy are also discussed.

Heterogeneous Development of β-Cell Populations in Diabetes-Resistant and -Susceptible Mice.

Progressive dysfunction and failure of insulin-releasing β-cells are a hallmark of type 2 diabetes (T2D). To study mechanisms of β-cell loss in T2D, we performed islet single-cell RNA sequencing of two obese mouse strains differing in their diabetes susceptibility. With mice on a control diet, we identified six β-cell clusters with similar abundance in both strains. However, after feeding of a diabetogenic diet for 2 days, β-cell cluster composition markedly differed between strains. Islets of diabetes-resistant mice developed into a protective β-cell cluster (Beta4), whereas those of diabetes-prone mice progressed toward stress-related clusters with a strikingly different expression pattern. Interestingly, the protective cluster showed indications of reduced β-cell identity, such as downregulation of GLUT2, GLP1R, and MafA, and in vitro knockdown of GLUT2 in β-cells-mimicking its phenotype-decreased stress response and apoptosis. This might explain enhanced β-cell survival of diabetes-resistant islets. In contrast, β-cells of diabetes-prone mice responded with expression changes indicating metabolic pressure and endoplasmic reticulum stress, presumably leading to later β-cell loss. In conclusion, failure of diabetes-prone mice to adapt gene expression toward a more dedifferentiated state in response to rising blood glucose levels leads to β-cell failure and diabetes development.

Rosiglitazone protects INS-1E cells from human islet amyloid polypeptide toxicity

Human islet amyloid polypeptide (hIAPP or amylin) is a hormone co-secreted with insulin by pancreatic β-cells, and is the main component of islet amyloid. Islet amyloid is found in the pancreas of patients with type 2 diabetes and may be involved in β-cell dysfunction and death, observed in this disease. Thus, counteracting islet amyloid toxicity represents a therapeutic approach to preserve β-cell mass and function. In this sense, thiazolidinediones (TZDs), as rosiglitazone, have shown protective effects against other harmful insults to β-cells. For this reason, we investigated whether rosiglitazone could protect β-cells from hIAPP-induced cell death and the underlying mechanisms mediating such effect. Here, we show that rosiglitazone improved the viability of hIAPP-exposed INS-1E cells. This benefit is not dependent on the insulin-degrading enzyme (IDE) since rosiglitazone did not modulate IDE protein content and activity. However, rosiglitazone inhibited hIAPP fibrillation and decreased hIAPP-induced expression of C/EBP homologous protein (CHOP) (CTL 100.0 ± 8.4; hIAPP 182.7 ± 19.1; hIAPP + RGZ 102.8 ± 9.5), activating transcription factor-4 (ATF4) (CTL 100.0 ± 3.1; hIAPP 234.9 ± 19.3; hIAPP + RGZ 129.6 ± 3.0) and phospho-eukaryotic initiation factor 2-alpha (p-eIF2α) (CTL 100.0 ± 31.1; hIAPP 234.1 ± 36.2; hIAPP + RGZ 150.4 ± 18.0). These findings suggest that TZDs treatment may be a promising approach to preserve β-cell mass and function by inhibiting islet amyloid formation and decreasing endoplasmic reticulum stress hIAPP-induced.

Association of β-cell function and cognitive impairment in patients with abnormal glucose metabolism

BackgroundInsulin has been demonstrated to play an important role in the occurrence and development of Alzheimer’s disease, especially in those with diabetes. β cells are important insulin-producing cells in human pancreas. This study aimed to investigate the association between β-cell dysfunction and cognitive impairment among patients over 40-year-old with abnormal glucose metabolism in Chinese rural communities.MethodsA sample of 592 participants aged 40 years or older from the China National Stroke Prevention Project (CSPP) between 2015 and 2017 were enrolled in this study. Abnormal glucose metabolism was defined when hemoglobin Alc ≥ 5.7%. Cognitive function was assessed by the Beijing edition of the Montreal Cognitive Assessment scale. Homeostasis assessment of β-cell function was performed and classified into 4 groups according to the quartiles. A lower value of HOMA-β indicated a worse condition of β-cell function. Multivariate logistic regression was used to analyze the association between β-cell function and cognitive impairment.ResultsIn a total of 592 patients with abnormal glucose metabolism, the average age was 60.20 ± 7.63 years and 60.1% patients had cognitive impairment. After adjusting for all potential risk factors, we found the first quartile of β-cell function was significantly associated with cognitive impairment (OR: 2.27, 95%CI: 1.32–3.92), especially at the domains of language (OR: 1.64, 95%CI: 1.01–2.65) and abstraction (OR: 2.29, 95%CI: 1.46–3.58).ConclusionsOur study showed that worse β-cell function is associated with cognitive impairment of people over 40-year-old with abnormal glucose metabolism in Chinese rural communities, especially in the cognitive domains of abstraction and language.

Gestational Diabetes Mellitus and Energy-Dense Diet: What Is the Role of the Insulin/IGF Axis?

Gestational diabetes mellitus (GDM), is one of the most important pregnancy complications affecting approximately 15% of pregnant women. It is related to several gestational adverse outcomes in the fetus, e.g., macrosomia, shoulder dystocia, stillbirth, neonatal hypoglycemia, and respiratory distress. Women with GDM have a high risk of developing type 2 diabetes in the future. The pathogenesis of GDM is not completely understood; nevertheless, two factors could contribute to its development: β-cell dysfunction and failure in insulin secretion in response to insulin resistance induced by gestation. Both processes, together with the physiological activities of the insulin-like growth factors (IGFs), play a crucial role in glucose transport to the fetus and hence, fetal growth and development. IGFs (both IGF-1 and IGF-2) and their binding proteins (IGFBPs) regulate glucose metabolism and insulin sensitivity. Maternal nutritional status determines the health of the newborn, as it has substantial effects on fetal growth and development. Maternal obesity and an energy-dense diet can cause an increase in insulin and IGF-1 serum levels, producing metabolic disorders, such as insulin resistance, GDM, and high birth weight (> 4,000 g) due to a higher level of body fat. In this way, in GDM pregnancies there is an increase in IGF-1 and IGF-2 serum levels, and a decrease in IGFBP-1 and 4 serum levels, suggesting the crucial role of the insulin/IGF system in this gestational outcome. Here, the present review tries to elucidate the role that energy-dense diets and the insulin/IGF-1 signaling pathway perform in GDM pregnancies.

Prospective Risk of Type 2 Diabetes in Normal Weight Women with Polycystic Ovary Syndrome.

Background: Polycystic ovary syndrome (PCOS) is associated with obesity and increased risk for type 2 diabetes (T2D). However, the prospective risk of T2D in normal weight women with PCOS is debated, together with the relevant prospective screening programs for T2D in normal weight women with PCOS. Aim: To review and discuss prospective risk of T2D in normal weight women with PCOS, and to give recommendations regarding prospective screening for T2D in normal weight women with PCOS. Methods: Systematic review. Results: A systematic literature search resulted in 15 published prospective studies (10 controlled studies and 5 uncontrolled studies) regarding risk of T2D in study cohorts of PCOS, where data from normal weight women with PCOS were presented separately. In controlled studies, higher risk of T2D in normal weight women with PCOS compared to controls was reported in 4/10 studies, which included one study where T2D diagnosis was based on glucose measurement, two register-based studies, and one study where diagnosis of T2D was self-reported. Six of the 10 controlled studies reported no increased risk of T2D in normal weight women with PCOS. Four of these studies based the diagnosis of T2D on biochemical measurements, which supported the risk of surveillance bias in PCOS. In uncontrolled studies, 2/5 reported a higher risk of T2D in lean women with PCOS compared to the general population. We discuss the evidence for insulin resistance and β-cell dysfunction in normal weight women with PCOS, and aggravation in the hyperandrogenic phenotype, ageing women, and women with Asian ethnicity. Impaired glucose tolerance could be an important metabolic and vascular risk marker in PCOS. Conclusions: The risk of T2D may be increased in some normal weight women with PCOS. Individual risk markers such as hyperandrogenism, age >40 years, Asian ethnicity, and weight gain should determine prospective screening programs in normal weight women with PCOS.

Possible clinical applications of knowledge about the genetics of type 2 diabetes

Type 2 diabetes mellitus (T2DM) is a polygenic disease that develops as a result of the interaction of hereditary predisposition and environmental factors. The predisposition to develop T2DM is associated with the inheritance of certain alleles of “healthy” genes. More than 100 polymorphic variants of genes that increase the risk of developing T2DM have already been described. Today, genes predisposing to the development of β-cell dysfunction and insulin resistance (IR) are the most well studied. In addition, genes that affect lipid metabolism and eating behavior and genes of some cytokines can participate in the formation of a genetic predisposition to the development of T2DM. Our article reviews the most promising potential areas of application of knowledge about the genetics of T2DM in clinical practice. The first direction is to specify the classification and stratification of T2DM into subclasses/clasters. The second one is an individual assessment of the risk of developing T2DM and its complications. Today, predictive models of the risk of developing type 2 diabetes are not accurate enough for widespread use in clinical practice, but now researchers are actively working to improve their accuracy and effectiveness. And finally, knowledge about the genetics of T2DM can help predict the effectiveness of glucose-lowering therapy. In this review, we also discuss the topic of metabolic disease endophenotypes. The concept of endophenotypes suggests the presence of certain pathogenic common links in the pathogenesis of IR, obesity, T2DM, cardiovascular diseases, non-alcoholic fatty liver disease and chronic kidney disease, which are based on certain polymorphic gene variants. The results of research in the field of genetics of T2DM give us new possibilities for a personalized approach to the management of this complex disease.

Comparison of adiposity indices and their association with insulin resistance and β-cell dysfunction in primary prevention for diabetes in Mexican population

IntroductionImpaired adiposity function, Insulin resistance (IR), and β-cell dysfunction predispose to type 2 diabetes (T2D). Some indices, such as the Visceral Adiposity Index (VAI), Dysfunctional Adiposity Index (DAI), and Atherogenic Index of Plasma (AIP), have been developed as surrogates of dysfunctional adiposity. However, the association of these indices with IR and β-cell dysfunction in primary prevention for T2D has not been fully studied. Materials and MethodsThis was a cross-sectional study that included 401 asymptomatic subjects with at least two risk factors for T2D that underwent an oral glucose tolerance test. A HOMA-IR ≥2.5 and a Disposition Index ≤1.24 were used to define IR and β-cell dysfunction, respectively. ResultsMean age of the subjects was 50.4 ± 9.6 years, 71.6% were women, had a mean BMI of 30.3 ± 6.4 kg/m2 27.6% and 11.6% had newly diagnosed T2D. After multiple regression analysis the VAI, DAI, and AIP were associated with IR (1.218 [1.103–1.345], 1.355 [1.150–1.597], and 2.533 [1.733–3.703], respectively), and β-cell dysfunction (1.119 [1.029–1.217], 1.193 [1.034–1.376], and 1.960 [1.357–2.830], respectively). Likewise, the AIP was the only index associated for newly T2D diagnosis (1.974 [1.224–3.184]). ConclusionsThe VAI, DAI and AIP were independently associated with IR and β-cell dysfunction in patients at high risk for T2D.

Uncoupling protein 2 and aldolase B impact insulin release by modulating mitochondrial function and Ca2+ release from the ER

SummaryUncoupling 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 this increase in UCP2 expression is unclear. In this study, we highlight the molecular link between the increase in UCP2 expression in β-cells and β-cell failure by using genetically engineered mice and human islets. β-cell-specific UCP2-overexpressing transgenic mice (βUCP2Tg) exhibited glucose intolerance and a reduction in insulin secretion. Decreased mitochondrial function and increased aldolase B (AldB) expression through oxidative-stress-mediated pathway were observed in βUCP2Tg islets. AldB, a glycolytic enzyme, was associated with reduced insulin secretion via mitochondrial dysfunction and impaired calcium release from the endoplasmic reticulum (ER). Taken together, our findings provide a new mechanism of β-cell dysfunction by UCP2 and AldB. Targeting the UCP2/AldB axis is a promising approach for the recovery of β-cell function.

C-Abl tyrosine kinase inhibition attenuate oxidative stress-induced pancreatic β-Cell dysfunction via glutathione antioxidant system

Chronic oxidative stress, which is caused by aberrant non-receptor tyrosine kinase (c-Abl) signaling, plays a key role in the progression of β-cell loss in diabetes mellitus. Recent studies, however, have linked ferroptotic-like death to the β-cell loss in diabetes mellitus. Here, we report that oxidative stress-driven reduced/oxidized glutathione (GSH/GSSG) loss and proteasomal degradation of glutathione peroxidase 4 (GPX4) promote ferroptotic-like cell damage through increased lipid peroxidation. Mechanistically, treatment with GNF2, a non-ATP competitive c-Abl kinase inhibitor, selectively preserves β-cell function by inducing the orphan nuclear receptor estrogen-related receptor gamma (ERRγ). ERRγ-driven glutaminase 1 (GLS1) expression promotes the elevation of the GSH/GSSG ratio, and this increase leads to the inhibition of lipid peroxidation by GPX4. Strikingly, pharmacological inhibition of ERRγ represses the expression of GLS1 and reverses the GSH/GSSG ratio linked to mitochondrial dysfunction and increased lipid peroxidation mediated by GPX4 degradation. Inhibition of GLS1 suppresses the ERRγ agonist DY131-induced GSH/GSSG ratio linked to ferroptotic-like death owing to the loss of GPX4. Furthermore, immunohistochemical analysis showed enhanced ERRγ and GPX4 expression in the pancreatic islets of GNF2-treated mice compared to that in streptozotocin-treated mice. Altogether, our results provide the first evidence that the orphan nuclear receptor ERRγ-induced GLS1 expression augments the glutathione antioxidant system, and its downstream signaling leads to improved β-cell function and survival under oxidative stress conditions.

Hydroxybenzamide derivatives protect pancreatic β cell by suppressing unfolded protein response activation.

Endoplasmic reticulum (ER) stress-induced Pancreatic β-cell dysfunction and death plays important roles in the development of diabetes. The 1,2,3-triazole derivative 1 is one of only a few structures that have thus far been identified that protect β cells against ER stress, but it is limited for its narrow activity range. In this study, we designed and synthesized a series of hydroxybenzamide (HBA) derivatives in which the triazole pharmacophore was substituted with an amide linker. Structure-activity relationship studies identified WO3i (3-hydroxy-N-(4-[trifluoromethyl]benzyl)benzamide) that possesses β-cell protective activity against ER stress at a 100% maximal activity with EC50 at 0.19 μM). We showed that WO3i suppresses the expression of CHOP, a key mediator of ER stress-induced apoptosis, and the activation of apoptotic genes. Mechanistically, we further showed that WO3i suppresses the ER stress-induced activation of all three pathways of unfolded protein response-ATF6, IRE1α, and PERK. Identification of this novel β-cell-protective scaffold thus provides a new promising modality for the potential for drug development for the treatment of diabetes.

Activation of inflammatory pathways in PBMCs linking type 2 diabetes in older adults without obesity.

The mechanism that underlies the dysregulation of glucose metabolism in older adults without obesity has yet to be thoroughly understood. This study investigated the risk of developing Type 2 diabetes (T2D) in older adults without obesity (BMI: 18.5 to <25kg/m2). Data on glucose levels (measured by an oral glucose tolerance test), body composition, physical activity level, lipid profile, inflammatory cytokines, and nuclear factor kappa B (NF-κB) and Sirtuin 1 (SIRT1) signaling pathways in peripheral blood mononuclear cells (PBMCs) in older adults with normal glucose tolerance (NGT, n=17) and those with prediabetes (n=20) or T2D (n=8) were gathered. As expected, participants with T2D exhibited higher insulin resistance; β-cell dysfunction; and higher levels of triglycerides and tumor necrosis factor-α (TNF-α) than those with NGT. No differences in physical activity, lean mass, body fat, or cholesterol were observed between the NGT, prediabetes, and T2D groups. Downregulation of SIRT1 and activation of NF-κB signaling in PBMCs were observed in the T2D group. Increased phosphorylation of NF-κB and low SIRT1 protein expression in PBMCs were associated with insulin resistance and β-cell dysfunction. NF-κB and its upstream inhibitor IκBα were positively and inversely correlated with TNF-α, respectively. SIRT1 expression was positively correlated with IL-10. Activation of NF-κB signaling pathways and downregulation of SIRT1 in PBMCs were associated with the inflammatory milieu in older adults without obesity.

1455-P: The Loss of Pancreatic ß-Cell Complement 1q-Like-3 Secreted Protein Increases Insulin Secretion in Lean and Obese Mice

Previously, we identified complement-1q like-3 (C1ql3) secreted protein as a hub gene affecting pancreatic islet function in obese mice using network biology. We demonstrated that the recombinant C1ql3 protein inhibits insulin secretion stimulated by exendin-4 (an agonist for GLP-1 receptor) from human and mouse islets. Our goal is to investigate the role of β-cell C1ql3 in pancreatic β-cell function in physiological and pathophysiological states. We generated mice with β-cell-specific deletion of C1ql3 (βKO) by crossing C1ql3fl/fl and RIP-Cre+ mice. C1ql3 βKO mice showed significantly improved glucose clearance after oral glucose challenge than control mice, whereas no difference in insulin action was observed. Moreover, the plasma insulin levels were significantly increased at 15 min after the glucose challenge in the C1ql3 βKO vs. control mice. C1ql3 βKO islets significantly increased insulin secretion stimulated by cAMP and Exendin-4 than control islets. These results suggest that the loss of C1ql3 in β-cells increases insulin secretion to improve glucose tolerance. Obesity increases the expression-coupled secretion of C1ql3 from mouse islets. Adenovirus mediated overexpression of C1ql3 in islets showed increased ER stress - a key trigger for β-cell dysfunction in obesity- as well as decreased expression of genes involving β-cell function and maintenance. Interestingly, reduction in C1ql3 secretion is inversely correlated with increased glucose stimulated insulin secretion from islets of C1ql3 βKO Leptinob/ob compared to Leptinob/ob control mice. These findings identify that the loss of β-cell C1ql3 maintains ER stress to compensate β-cell workload during obesity and increases insulin secretion to maintain glucose homeostasis. Our work shows that an autocrine regulation of the C1ql3-signaling pathway contributes to β-cell dysfunction in obesity and type 2 diabetes. Disclosure M.Rahman: None. H.Alsharif: n/a. S.Bhatnagar: None. Funding American Diabetes Association (1-18-PDF-103) ; 1R01DK120684-01

Interplay of retinol binding protein 4 with obesity and associated chronic alterations (Review).

Obesity is a multifactorial disease, defined as excessive fat deposition in adipose tissue. Adipose tissue is responsible for the production and secretion of numerous adipokines that induce metabolic disorders. Retinol-binding protein 4 (RBP4) is an adipokine that transports vitamin A or retinol in the blood. High levels of RBP4 are associated with development of metabolic disease, including obesity, insulin resistance (IR), metabolic syndrome, and type 2 diabetes (T2D). The present review summarizes the role of RBP4 in obesity and associated chronic alterations. Excessive synthesis of RBP4 contributes to inflammatory characteristic of obesity by activation of immune cells and release of proinflammatory cytokines, such as TNFα and ILs, via the Toll-like receptor/JNK pathway. The retinol-RBP4 complex inhibits insulin signaling directly in adipocytes by activating Janus kinase 2 (JAK2)/STAT5/suppressor of cytokine signaling 3 signaling. This mechanism is retinol-dependent and requires vitamin A receptor stimulation by retinoic acid 6 (STRA6). In muscle, RBP4 is associated with increased serine 307 phosphorylation of insulin receptor substrate-1, which decreases its affinity to PI3K and promotes IR. In the liver, RBP4 increases hepatic expression of phosphoenolpyruvate carboxykinase, which increases production of glucose. Elevated serum RBP4 levels are associated with β-cell dysfunction in T2D via the STRA6/JAK2/STAT1/insulin gene enhancer protein 1 pathway. By contrast, RBP4 induces endothelial inflammation via the NF-κB/nicotinamide adenine dinucleotide phosphate oxidase pathway independently of retinol and STRA6, which stimulates expression of proinflammatory molecules, such as vascular cell adhesion molecule 1, E-selectin, intercellular adhesion molecule 1, monocyte chemoattractant protein 1 and TNFα. RBP4 promotes oxidative stress by decreasing endothelial mitochondrial function; overall, it may serve as a useful biomarker in the diagnosis of obesity and prognosis of associated disease, as well as a potential therapeutic target for treatment of these diseases.

244-OR: Moderate Intensity Endurance Exercise Training Improves Late-Phase ß-Cell Function in Humans with Type 2 Diabetes

Type 2 diabetes (T2D) is associated with β-cell dysfunction. Although exercise is considered beneficial in T2D, the effects of moderate intensity endurance exercise training on β-cell function in humans with T2D are not known. GWAS uncovered Ras-Responsive Element Binding Protein 1 (RREB1) as a risk factor for T2D and in vitro studies suggest RREB1 impairs β-cell function; no studies have investigated exercise effects on RREB1. Here, we determined the effects of moderate intensity exercise training on β-cell function, RREB1, insulin, glucagon, and amylin in humans with T2D (7F/3M, 49±5y, BMI 30±3kg/m2) . Subjects completed 10-weeks of supervised exercise (Wks 1-3: 20-30min/day; 3X/wk; ∼50% VO2peak and Wks 4-10: 45-60min/day; 4X/wk; ∼70% VO2peak) . Fasting blood samples for OGTT, HbA1c, and hormones were obtained pre- and post-training (48hr) . Serum RREB1 was measured pre- and post-training and also in response to a single bout of maximal exercise. Training decreased HbA1c (7.7% to 7.2%, P=0.01) , pro-insulin (-18%, P=0.03) , pro-insulin/c-peptide ratio (-8%, P=0.03) , and glucose (OGTT: 90min, -18%, P=0.01; 120min, -15%, P&amp;lt;0.001) . Both β-cell function (late-phase disposition index, +38%, P=0.01) and insulin sensitivity (Stumvoll Index, +25%, P=0.01) improved. Body weight and composition, VO2peak, glucagon, amylin, c-peptide, and insulin were unchanged. Baseline RREB1 negatively correlated with the exercise-induced increase in late-phase disposition index (R= -0.71, P=0.03) , consistent with an inhibitory role of RREB1. Training did not alter serum RREB1, but interestingly, acute exercise decreased RREB1 both before (-51%, P&amp;lt;0.01) and after training (-11%, P=0.04) . Thus, RREB1 is an exercise-regulated serum factor whose decrease may function to improve β-cell function with exercise. In conclusion, moderate intensity exercise training, in the absence of increased VO2peak, improves late phase β-cell function and glucose control in humans with T2D. Disclosure H.Zhang: None. R.Middelbeek: Research Support; Novo Nordisk. L.Simpson: None. N.P.Carbone: None. L.J.Goodyear: None. Funding National Institutes of Health (K23-DK114550, R01-DK112283, 5P30DK36836, 5P30DK057521-20)

1457-P: Cholesterol Accumulation in Islets Increases Steroidogenic Acute Regulatory (StAR) Protein Expression and Decreases Islet Cell Viability and ß-Cell Function

Diabetes is associated with elevated plasma cholesterol (Chol) , with its intracellular accumulation resulting in β-cell dysfunction. In steroidogenic tissues, StAR facilitates Chol transport from the outer to inner mitochondrial membrane for subsequent metabolism. We have shown that StAR is expressed in β cells and its upregulation increases mitochondrial Chol content and decreases mitochondrial function. To determine whether excess Chol per se increases StAR expression and reduces islet viability, we cultured mouse islets for 24 hours in Chol and quantified mRNA levels of Star and genes involved in Chol synthesis (Hmgcr) , uptake (Ldlr) and efflux (Abca1) , cell viability and glucose stimulated insulin secretion (GSIS) . Islet Chol content increased with increasing Chol concentrations (27.1±1.7, 55.3±0.5 and 72.7±5.2 µg/mg protein for 0, 0.25 and 0.5 mM respectively; n=3, p&amp;lt;0.0by ANOVA) , with mitochondrial Chol increasing 2.4-fold in 0.5 mM (9.1±0.2 to 22.4±1.9 µg/mg protein; n=3, p&amp;lt;0.005) . This was associated with increased Star mRNA expression (1.0±0.1, 3.0±0.9 and 7.0±1.5; n=3, p=0.014) . Further, mRNA expression of Hmgcr tended to decrease (1.0±0.2, 0.8±0.3 and 0.3±0.0; n=3, p=0.088) , whereas expression of Ldlr and Abca1 did not change (Ldlr: 1.7±0.8, 1.1±0.7 and 0.5±0.3; n=3, p=0.508; Abca1: 1.1±0.3, 1.9±0.7 and 1.1±0.1; n=3, p=0.413) . These changes were associated with reductions in cell viability (100±15.7%, 68.0±12.6% and 57.3±9.6%; n=2, p=0.025) and GSIS in response to 20 mM glucose (fold increase over 2.8 mM: 0 mM Chol 28.5±0.6, 0.25 mM Chol 8.9±0.5, 0.5 mM Chol 10.8±0.9; n=2, p&amp;lt;0.0001) . In summary, islet cholesterol accumulation is associated with increased StAR expression, decreased cell viability and reduced β-cell function. These data suggest that elevated cholesterol in diabetes may contribute to β-cell dysfunction by increasing StAR expression and mitochondrial cholesterol accumulation. Disclosure R.Akter: None. M.F.Hogan: Employee; NanoString. N.Esser: None. J.J.Castillo: None. R.L.Hull-meichle: Research Support; Casma Therapeutics. S.Zraika: None. S.E.Kahn: Advisory Panel; Bayer AG, Boehringer Ingelheim International GmbH, Eli Lilly and Company, Intarcia Therapeutics, Inc., Merck &amp; Co., Inc., Novo Nordisk, Pfizer Inc. Funding VA (I01BX001060) ,VA (IBX004063) ,NIDDK (P30 DK017047) ,NIDDK (T32 DK007247)

The Genetics of Type 2 Diabetes in Youth: Where We Are and the Road Ahead

The Genetics of Type 2 Diabetes in Youth: Where We Are and the Road Ahead

1354-P: Alternate-Day Intermittent Fasting Improves Diabetes and Protects Beta-Cell Function in Polygenic Mouse Models of T2DM

Type 2 diabetes (T2DM) , caused by the interaction of multiple genes and environmental factors, is characterized by hyperglycemia, insulin secretion deficiency and insulin resistance. Chronic hyperglycemia induces β-cell dysfunction and loss of β-cell mass/identity, increased apoptosis and β-cell dedifferentiation. Intermittent fasting (IF) , either alternate-day fasting (ADF) or time-restricted feeding, commonly used regimens for weight-loss, also induces metabolic benefits including reduced blood glucose, improved insulin sensitivity, reduced adiposity, inflammation and oxidative-stress, and increased fatty-acid oxidation; however, the mechanisms underlying these effects remain elusive. KK and KKAy, mouse models of polygenic T2DM spontaneously develop hyperglycemia, glucose intolerance, glucosuria, impaired insulin secretion and insulin resistance. To determine the long-term effects of IF on T2DM, 6-weeks old KK and KKAy mice were subjected to ADF for 16-weeks. While KKAy mice fed ad-libitum demonstrated severe hyperglycemia (˜500mg/dL) , increased plasma insulin, impaired glucose tolerance and insulin resistance at 8 weeks of age, KK mice showed blood glucose levels of ˜200mg/dL, but progressively became as severely diabetic as KKAy mice by 22-weeks. Strikingly, both KK and KKAy mice subjected to ADF showed reduced blood glucose and plasma insulin levels, decreased body weight gain despite increased food intake, reduced plasma triglycerides and cholesterol, and improved insulin sensitivity. They also demonstrated enhanced expression of the β-cell transcription factors PDX1 and NKX6.1, suggesting protection from loss of β-cell identity/dedifferentiation by IF. In addition, respiratory exchange ratio (RER) and movement were significantly enhanced in the ADF group, indicating peripheral benefits of IF. These results have important implications as an optional intervention for preservation of β-cell mass and function in T2DM. Disclosure S.Patel: None. Z.Yan: None. M.S.Remedi: None. Funding National Institutes of Health (R01DK123163)

1376-P: Comparison of a-Cell Response to Intravenous or Oral Glucose in Nondiabetic Humans

Type 2 Diabetes (T2DM) and prediabetes are characterized by β-cell and α-cell dysfunction which can occur independently. Defects in α-cell response to rising glucose can be evaluated with an oral or intravenous challenge: the former reflects normal physiology, the latter is unaffected by incretins or gut motility. We compared Glucagon Secretion Rate (GSR) in response to rising glucose during a Graded Glucose Infusion (GGI) and an Oral Glucose Tolerance Test (OGTT) . We studied 39 non-diabetic, weight-stable subjects (53 ± 2 yrs, 29 ± 1 Kg/M2) , with different fasting and glucose tolerance status. All subjects underwent a 75g OGTT and a GGI, with glucose infusion doubling every hour for 4 hours. GSR was calculated by deconvolution from plasma concentrations of glucagon on both study days (GSRGGI and GSROGTT) . The suppression of GSRGGI could be described with a single-exponential relationship between GSR and glucose concentrations. The slope of the log-transformed secretion line allows estimation of the change in glucose necessary to suppress GSR by 50% (G50) . This index of suppressibility is elevated in people with impaired fasting glucose compared to normal fasting glucose (2.7 ± 0.2 vs. 3.8 ± 0.4 mmol/L, p=0.01) . Intriguingly, GSROGTT, exhibited a delayed response to rising glucose (compared to GSRGGI) , during the early part of the OGTT. However, the relationship of GSROGTT to glucose did not differ from that of GSRGGI during the fasting state and at the time of peak postprandial suppression. This allowed the calculation of G50 during the OGTT, which was similar to that observed during the GGI (R2=0.66) and correlated with weight, age and fasting glucose (R2=0.49) . These data demonstrate the ability of a novel index (G50) , to reproducibly quantify α-cell suppression by oral or intravenous glucose in non-diabetic subjects. Future studies will be necessary to determine if this relationship also applies to T2DM and how gastrointestinal and other factors alter the rate of GSR suppression during an OGTT. Disclosure M.C.Laurenti: None. A.Manduca: None. C.Cobelli: None. C.Dalla man: Research Support; Becton, Dickinson and Company, Sanofi-Aventis Deutschland GmbH. A.Vella: Advisory Panel; Crinetics Pharmaceuticals, Inc., Rezolute, Inc., vTv Therapeutics, Zealand Pharma A/S, Other Relationship; Novo Nordisk. Funding National Institutes of Health (DK078646, DK116231)

12-OR: Preventing ß-Cell Death under Glucotoxic Conditions: The Role of ChREBPb

Glucotoxicity is a major mediator of β-cell dysfunction derived from prolonged hyperglycemia. A better understanding of glucotoxicity and preservation of β-cell mass are urgently needed. Carbohydrate response element binding protein (ChREBP) is a glucose-responsive, lipogenic transcription factor with two splice isoforms, ChREBPα and ChREBPβ. We previously showed ChREBPβ is induced by glucose and is required for glucose-stimulated β-cell proliferation in both rodent and human β-cells. In addition, we identified ChREBPβ as a marker for hyperglycemia in β-cells, with its nuclear expression reflecting the progression and severity of the diabetic state. Here, we demonstrate that β-cell death due to glucolipotoxicity (20 mM glucose + 1 mM palmitate) can be prevented by silencing ChREBPβ (6.5±3.1% TUNEL+/Insulin+ in ChREBPβ knock-out islets compared with 47.2±13.6% in control islets, N=7) , most likely via inhibition of lipogenesis and prevention of ceramide-mediated β-cell death. Furthermore, we generated mice with β-cell specific overexpression of ChREBPβ. These mice exhibited increased non-fasting blood glucose levels, impaired glucose tolerance and a marked decrease in β-cell mass, all in a gene dose-dependent manner (OE of one or two alleles of ChREBPβ, N=5) . ChREBPβ overexpression in human beta cells also mimicked glucotoxicity (93.6±3.1% TUNEL+/Insulin+, N=3) . Importantly, we show that ChREBPβ-mediated rodent and human β-cell death was rescued by co-expression with ChREBPα, or by pharmacological activation of Nrf2, a downstream effector of ChREBPα (6.6±1.9 and 2.8±0.9%, respectively, TUNEL+/Insulin+, N=3) . Altogether, our data demonstrate that ChREBPβ is a marker and a causative effector of glucotoxicity, and that downregulating ChREBPβ levels or upregulating ChREBPα levels or its downstream effector (NRF2) rescues β-cells from glucotoxicity. These results position ChREBPβ as a therapeutic target for the prevention of β-cell loss in T2D, an important unmet need in diabetes research. Disclosure L.S.Katz: None. G.Brill: None. M.A.Herman: Research Support; Eli Lilly and Company. A.Garcia-ocana: Consultant; Sun Pharmaceutical Industries Ltd. D.Scott: None. Funding NIH, R01DK130300NIH, R01DK114338NIH, R01DK108905