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Issues and Events

Mon, 05/21/2018 - 13:05
Categories: Diabetes

Issues and Events

Fri, 04/20/2018 - 13:00
Categories: Diabetes

In This Issue of Diabetes

Fri, 04/20/2018 - 13:00
Categories: Diabetes

Metabolic Karma--The Atherogenic Legacy of Diabetes: The 2017 Edwin Bierman Award Lecture

Fri, 04/20/2018 - 13:00

Cardiovascular disease, despite all the recent advances in treatment of the various risk factors, remains the major cause of mortality in both type 1 and type 2 diabetes. Experimental models of diabetes-associated atherosclerosis, despite their limitations in recapitulating the human context, have assisted in the elucidation of molecular and cellular pathways implicated in the development and progression of macrovascular injury in diabetes. Our own studies have emphasized the role of oxidative stress and advanced glycation and identified potential targets for vasoprotective therapies in the setting of diabetes. Furthermore, it has been clearly shown that previous episodes of hyperglycemia play a key role in promoting end-organ injury in diabetes, as shown in clinical trials such as the UK Prospective Diabetes Study (UKPDS), Action in Diabetes and Vascular Disease: Preterax and Diamicron MR Controlled Evaluation Observational Study (ADVANCE-ON), and the Diabetes Control and Complications Trial/ Epidemiology of Diabetes Interventions and Complications (DCCT/EDIC). The cause of this phenomenon, known as metabolic memory, remains to be elucidated, but it appears that epigenetic pathways, including glucose-induced histone methylation, play a central role. Further delineation of these pathways and their link to not only glucose but also other factors implicated in vascular injury should lead to more rational, potentially more effective therapies to retard diabetes-associated cardiovascular disease.

Categories: Diabetes

Perilipin 3 Deficiency Stimulates Thermogenic Beige Adipocytes Through PPAR{alpha} Activation

Fri, 04/20/2018 - 13:00

Beige adipocytes can dissipate energy as heat. Elaborate communication between metabolism and gene expression is important in the regulation of beige adipocytes. Although lipid droplet (LD) binding proteins play important roles in adipose tissue biology, it remains unknown whether perilipin 3 (Plin3) is involved in the regulation of beige adipocyte formation and thermogenic activities. In this study, we demonstrate that Plin3 ablation stimulates beige adipocytes and thermogenic gene expression in inguinal white adipose tissue (iWAT). Compared with wild-type mice, Plin3 knockout mice were cold tolerant and displayed enhanced basal and stimulated lipolysis in iWAT, inducing peroxisome proliferator–activated receptor α (PPARα) activation. In adipocytes, Plin3 deficiency promoted PPARα target gene and uncoupling protein 1 expression and multilocular LD formation upon cold stimulus. Moreover, fibroblast growth factor 21 expression and secretion were upregulated, which was attributable to activated PPARα in Plin3-deficient adipocytes. These data suggest that Plin3 acts as an intrinsic protective factor preventing futile beige adipocyte formation by limiting lipid metabolism and thermogenic gene expression.

Categories: Diabetes

Amylin Selectively Signals Onto POMC Neurons in the Arcuate Nucleus of the Hypothalamus

Fri, 04/20/2018 - 13:00

Amylin phosphorylates ERK (p-ERK) in the area postrema to reduce eating and synergizes with leptin to phosphorylate STAT3 in the arcuate (ARC) and ventromedial (VMN) hypothalamic nuclei to reduce food intake and body weight. The current studies assessed potential amylin and amylin-leptin ARC/VMN interactions on ERK signaling and their roles in postnatal hypothalamic pathway development. In amylin knockout mice, the density of agouti-related protein (AgRP)-immunoreactive (IR) fibers in the hypothalamic paraventricular nucleus (PVN) was increased, while the density of α-melanocyte–stimulating hormone (αMSH) fibers was decreased. In mice deficient of the amylin receptor components RAMP1/3, both AgRP and αMSH-IR fiber densities were decreased, while only αMSH-IR fiber density was decreased in rats injected neonatally in the ARC/VMN with an adeno-associated virus short hairpin RNA against the amylin core receptor. Amylin induced p-ERK in ARC neurons, 60% of which was present in POMC-expressing neurons, with none in NPY neurons. An amylin-leptin interaction was shown by an additive effect on ARC ERK signaling in neonatal rats and a 44% decrease in amylin-induced p-ERK in the ARC of leptin receptor–deficient and of ob/ob mice. Together, these results suggest that amylin directly acts, through a p-ERK–mediated process, on POMC neurons to enhance ARC-PVN αMSH pathway development.

Categories: Diabetes

Hepatic F-Box Protein FBXW7 Maintains Glucose Homeostasis Through Degradation of Fetuin-A

Fri, 04/20/2018 - 13:00

Type 2 diabetes mellitus (T2DM) has become one of the most serious and long-term threats to human health. However, the molecular mechanism that links obesity to insulin resistance remains largely unknown. Here, we show that F-box and WD repeat domain-containing 7 (FBXW7), an E3 ubiquitin protein ligase, is markedly downregulated in the liver of two obese mouse models and obese human subjects. We further identify a functional low-frequency human FBXW7 coding variant (p.Ala204Thr) in the Chinese population, which is associated with elevated blood glucose and T2DM risk. Notably, mice with liver-specific knockout of FBXW7 develop hyperglycemia, glucose intolerance, and insulin resistance even on a normal chow diet. Conversely, overexpression of FBXW7 in the liver not only prevents the development of high-fat diet–induced insulin resistance but also attenuates the disease signature of obese mice. Mechanistically, FBXW7 directly binds to hepatokine fetuin-A to induce its ubiquitination and subsequent proteasomal degradation, comprising an important mechanism maintaining glucose homeostasis. Thus, we provide evidence showing a beneficial role of FBXW7 in glucose homeostasis.

Categories: Diabetes

Reduced Nonexercise Activity Attenuates Negative Energy Balance in Mice Engaged in Voluntary Exercise

Fri, 04/20/2018 - 13:00

Exercise alone is often ineffective for treating obesity despite the associated increase in metabolic requirements. Decreased nonexercise physical activity has been implicated in this resistance to weight loss, but the mechanisms responsible are unclear. We quantified the metabolic cost of nonexercise activity, or "off-wheel" activity (OWA), and voluntary wheel running (VWR) and examined whether changes in OWA during VWR altered energy balance in chow-fed C57BL/6J mice (n = 12). Energy expenditure (EE), energy intake, and behavior (VWR and OWA) were continuously monitored for 4 days with locked running wheels followed by 9 days with unlocked running wheels. Unlocking the running wheels increased EE as a function of VWR distance. The metabolic cost of exercise (kcal/m traveled) decreased with increasing VWR speed. Unlocking the wheel led to a negative energy balance but also decreased OWA, which was predicted to mitigate the expected change in energy balance by ~45%. A novel behavioral circuit involved repeated bouts of VWR, and roaming was discovered and represented novel predictors of VWR behavior. The integrated analysis described here reveals that the weight loss effects of voluntary exercise can be countered by a reduction in nonexercise activity.

Categories: Diabetes

Catestatin Inhibits Obesity-Induced Macrophage Infiltration and Inflammation in the Liver and Suppresses Hepatic Glucose Production, Leading to Improved Insulin Sensitivity

Fri, 04/20/2018 - 13:00

The activation of Kupffer cells (KCs) and monocyte-derived recruited macrophages (McMs) in the liver contributes to obesity-induced insulin resistance and type 2 diabetes. Mice with diet-induced obesity (DIO mice) treated with chromogranin A peptide catestatin (CST) showed several positive results. These included decreased hepatic/plasma lipids and plasma insulin, diminished expression of gluconeogenic genes, attenuated expression of proinflammatory genes, increased expression of anti-inflammatory genes in McMs, and inhibition of the infiltration of McMs resulting in improvement of insulin sensitivity. Systemic CST knockout (CST-KO) mice on normal chow diet (NCD) ate more food, gained weight, and displayed elevated blood glucose and insulin levels. Supplementation of CST normalized glucose and insulin levels. To verify that the CST deficiency caused macrophages to be very proinflammatory in CST-KO NCD mice and produced glucose intolerance, we tested the effects of (sorted with FACS) F4/80+Ly6C– cells (representing KCs) and F4/80–Ly6C+ cells (representing McMs) on hepatic glucose production (HGP). Both basal HGP and glucagon-induced HGP were markedly increased in hepatocytes cocultured with KCs and McMs from NCD-fed CST-KO mice, and the effect was abrogated upon pretreatment of CST-KO macrophages with CST. Thus, we provide a novel mechanism of HGP suppression through CST-mediated inhibition of macrophage infiltration and function.

Categories: Diabetes

Regulation of KATP Channel Trafficking in Pancreatic {beta}-Cells by Protein Histidine Phosphorylation

Fri, 04/20/2018 - 13:00

Protein histidine phosphatase 1 (PHPT-1) is an evolutionarily conserved 14-kDa protein that dephosphorylates phosphohistidine. PHPT-1–/– mice were generated to gain insight into the role of PHPT-1 and histidine phosphorylation/dephosphorylation in mammalian biology. PHPT-1–/– mice exhibited neonatal hyperinsulinemic hypoglycemia due to impaired trafficking of KATP channels to the plasma membrane in pancreatic β-cells in response to low glucose and leptin and resembled patients with congenital hyperinsulinism (CHI). The defect in KATP channel trafficking in PHPT-1–/– β-cells was due to the failure of PHPT-1 to directly activate transient receptor potential channel 4 (TRPC4), resulting in decreased Ca2+ influx and impaired downstream activation of AMPK. Thus, these studies demonstrate a critical role for PHPT-1 in normal pancreatic β-cell function and raise the possibility that mutations in PHPT-1 and/or TRPC4 may account for yet to be defined cases of CHI.

Categories: Diabetes

HLA-B*07, HLA-DRB1*07, HLA-DRB1*12, and HLA-C*03:02 Strongly Associate With BMI: Data From 1.3 Million Healthy Chinese Adults

Fri, 04/20/2018 - 13:00

Strong associations between HLA alleles and infectious and autoimmune diseases are well established. Although obesity is also associated with these diseases, the relationship between HLA and obesity has not been systematically investigated in a large cohort. In the current study, we analyzed the association of HLA alleles with BMI using data from 1.3 million healthy adult donors from the Chinese Marrow Donor Program (CMDP). We found 23 HLA alleles, including 12 low-resolution and 11 high-resolution alleles, were significantly associated with BMI after correction for multiple testing. Alleles associated with high BMI were enriched in haplotypes that were common in both Chinese and European populations, whereas the alleles associated with low BMI were enriched in haplotypes common only in Asians. Alleles B*07, DRB1*07, DRB1*12, and C*03:02 provided the strongest associations with BMI (P = 6.89 x 10–10, 1.32 x 10–9, 1.52 x 10–9, and 4.45 x 10–8, respectively), where B*07 and DRB1*07 also had evidence for sex-specific effects (Pheterogeneity = 0.0067 and 0.00058, respectively). These results, which identify associations between alleles of HLA-B, DRB1, and C with BMI in Chinese young adults, implicate a novel biological connection between HLA alleles and obesity.

Categories: Diabetes

CDKN2A/B T2D Genome-Wide Association Study Risk SNPs Impact Locus Gene Expression and Proliferation in Human Islets

Fri, 04/20/2018 - 13:00

Genome-wide association studies link the CDKN2A/B locus with type 2 diabetes (T2D) risk, but mechanisms increasing risk remain unknown. The CDKN2A/B locus encodes cell cycle inhibitors p14, p15, and p16; MTAP; and ANRIL, a long noncoding RNA. The goal of this study was to determine whether CDKN2A/B T2D risk SNPs impact locus gene expression, insulin secretion, or β-cell proliferation in human islets. Islets from donors without diabetes (n = 95) were tested for SNP genotype (rs10811661, rs2383208, rs564398, and rs10757283), gene expression (p14, p15, p16, MTAP, ANRIL, PCNA, KI67, and CCND2), insulin secretion (n = 61), and β-cell proliferation (n = 47). Intriguingly, locus genes were coregulated in islets in two physically overlapping cassettes: p14-p16-ANRIL, which increased with age, and MTAP-p15, which did not. Risk alleles at rs10811661 and rs2383208 were differentially associated with expression of ANRIL, but not p14, p15, p16, or MTAP, in age-dependent fashion, such that younger homozygous risk donors had higher ANRIL expression, equivalent to older donor levels. We identified several risk SNP combinations that may impact locus gene expression, suggesting possible mechanisms by which SNPs impact locus biology. Risk allele carriers at ANRIL coding SNP rs564398 had reduced β-cell proliferation index. In conclusion, CDKN2A/B locus SNPs may impact T2D risk by modulating islet gene expression and β-cell proliferation.

Categories: Diabetes

Elevated Medium-Chain Acylcarnitines Are Associated With Gestational Diabetes Mellitus and Early Progression to Type 2 Diabetes and Induce Pancreatic {beta}-Cell Dysfunction

Fri, 04/20/2018 - 13:00

Specific circulating metabolites have emerged as important risk factors for the development of diabetes. The acylcarnitines (acylCs) are a family of metabolites known to be elevated in type 2 diabetes (T2D) and linked to peripheral insulin resistance. However, the effect of acylCs on pancreatic β-cell function is not well understood. Here, we profiled circulating acylCs in two diabetes cohorts: 1) women with gestational diabetes mellitus (GDM) and 2) women with recent GDM who later developed impaired glucose tolerance (IGT), new-onset T2D, or returned to normoglycemia within a 2-year follow-up period. We observed a specific elevation in serum medium-chain (M)-acylCs, particularly hexanoyl- and octanoylcarnitine, among women with GDM and individuals with T2D without alteration in long-chain acylCs. Mice treated with M-acylCs exhibited glucose intolerance, attributed to impaired insulin secretion. Murine and human islets exposed to elevated levels of M-acylCs developed defects in glucose-stimulated insulin secretion and this was directly linked to reduced mitochondrial respiratory capacity and subsequent ability to couple glucose metabolism to insulin secretion. In conclusion, our study reveals that an elevation in circulating M-acylCs is associated with GDM and early stages of T2D onset and that this elevation directly impairs β-cell function.

Categories: Diabetes

Role of Protein Phosphatase 1 and Inhibitor of Protein Phosphatase 1 in Nitric Oxide-Dependent Inhibition of the DNA Damage Response in Pancreatic {beta}-Cells

Fri, 04/20/2018 - 13:00

Nitric oxide is produced at micromolar levels by pancreatic β-cells during exposure to proinflammatory cytokines. While classically viewed as damaging, nitric oxide also activates pathways that promote β-cell survival. We have shown that nitric oxide, in a cell type–selective manner, inhibits the DNA damage response (DDR) and, in doing so, protects β-cells from DNA damage–induced apoptosis. This study explores potential mechanisms by which nitric oxide inhibits DDR signaling. We show that inhibition of DDR signaling (measured by H2AX formation and the phosphorylation of KAP1) is selective for nitric oxide, as other forms of reactive oxygen/nitrogen species do not impair DDR signaling. The kinetics and broad range of DDR substrates that are inhibited suggest that protein phosphatase activation may be one mechanism by which nitric oxide attenuates DDR signaling in β-cells. While protein phosphatase 1 (PP1) is a primary regulator of DDR signaling and an inhibitor of PP1 (IPP1) is selectively expressed only in β-cells, disruption of either IPP1 or PP1 does not modify the inhibitory actions of nitric oxide on DDR signaling in β-cells. These findings support a PP1-independent mechanism by which nitric oxide selectively impairs DDR signaling and protects β-cells from DNA damage–induced apoptosis.

Categories: Diabetes

Postnatal Ontogenesis of the Islet Circadian Clock Plays a Contributory Role in {beta}-Cell Maturation Process

Fri, 04/20/2018 - 13:00

Development of cell replacement therapies in diabetes requires understanding of the molecular underpinnings of β-cell maturation. The circadian clock regulates diverse cellular functions important for regulation of β-cell function and turnover. However, postnatal ontogenesis of the islet circadian clock and its potential role in β-cell maturation remain unknown. To address this, we studied wild-type Sprague-Dawley as well as Period1 luciferase transgenic (Per1:LUC) rats to determine circadian clock function, clock protein expression, and diurnal insulin secretion during islet development and maturation process. We additionally studied β-cell–specific Bmal1-deficient mice to elucidate a potential role of this key circadian transcription factor in β-cell functional and transcriptional maturation. We report that emergence of the islet circadian clock 1) occurs during the early postnatal period, 2) depends on the establishment of global behavioral circadian rhythms, and 3) leads to the induction of diurnal insulin secretion and gene expression. Islet cell maturation was also characterized by induction in the expression of circadian transcription factor BMAL1, deletion of which altered postnatal development of glucose-stimulated insulin secretion and the associated transcriptional network. Postnatal development of the islet circadian clock contributes to early-life β-cell maturation and should be considered for optimal design of future β-cell replacement strategies in diabetes.

Categories: Diabetes

Improved Murine MHC-Deficient HLA Transgenic NOD Mouse Models for Type 1 Diabetes Therapy Development

Fri, 04/20/2018 - 13:00

Improved mouse models for type 1 diabetes (T1D) therapy development are needed. T1D susceptibility is restored to normally resistant NOD.β2m–/– mice transgenically expressing human disease–associated HLA-A*02:01 or HLA-B*39:06 class I molecules in place of their murine counterparts. T1D is dependent on pathogenic CD8+ T-cell responses mediated by these human class I variants. NOD.β2m–/–-A2.1 mice were previously used to identify β-cell autoantigens presented by this human class I variant to pathogenic CD8+ T cells and for testing therapies to attenuate such effectors. However, NOD.β2m–/– mice also lack nonclassical MHC I family members, including FcRn, required for antigen presentation, and maintenance of serum IgG and albumin, precluding therapies dependent on these molecules. Hence, we used CRISPR/Cas9 to directly ablate the NOD H2-Kd and H2-Db classical class I variants either individually or in tandem (cMHCI–/–). Ablation of the H2-Ag7 class II variant in the latter stock created NOD mice totally lacking in classical murine MHC expression (cMHCI/II–/–). NOD-cMHCI–/– mice retained nonclassical MHC I molecule expression and FcRn activity. Transgenic expression of HLA-A2 or -B39 restored pathogenic CD8+ T-cell development and T1D susceptibility to NOD-cMHCI–/– mice. These next-generation HLA-humanized NOD models may provide improved platforms for T1D therapy development.

Categories: Diabetes

Detection and Characterization of CD8+ Autoreactive Memory Stem T Cells in Patients With Type 1 Diabetes

Fri, 04/20/2018 - 13:00

Stem memory T cells (Tscm) constitute the earliest developmental stage of memory T cells, displaying stem cell–like properties, such as self-renewal capacity. Their superior immune reconstitution potential has sparked interest in cancer immune therapy, vaccine development, and immune reconstitution, whereas their role in autoimmunity is largely unexplored. Here we show that autoreactive CD8+ Tscm specific for β-cell antigens GAD65, insulin, and IGRP are present in patients with type 1 diabetes (T1D). In vitro, the generation of autoreactive Tscm from naive precursors required the presence of the homeostatic cytokine interleukin-7 (IL-7). IL-7 promotes glucose uptake via overexpression of GLUT1 and upregulation of the glycolytic enzyme hexokinase 2. Even though metabolism depends on glucose uptake, the subsequent oxidation of pyruvate in the mitochondria was necessary for Tscm generation from naive precursors. In patients with T1D, high expression of GLUT1 was a hallmark of circulating Tscm, and targeting glucose uptake via GLUT1 using the selective inhibitor WZB117 resulted in inhibition of Tscm generation and expansion. Our results suggest that autoreactive Tscm are present in patients with T1D and can be selectively targeted by inhibition of glucose metabolism.

Categories: Diabetes

A Novel Strategy to Prevent Advanced Atherosclerosis and Lower Blood Glucose in a Mouse Model of Metabolic Syndrome

Fri, 04/20/2018 - 13:00

Cardiovascular disease caused by atherosclerosis is the leading cause of mortality associated with type 2 diabetes and metabolic syndrome. Insulin therapy is often needed to improve glycemic control, but it does not clearly prevent atherosclerosis. Upon binding to the insulin receptor (IR), insulin activates distinct arms of downstream signaling. The IR-Akt arm is associated with blood glucose lowering and beneficial effects, whereas the IR-Erk arm might exert less desirable effects. We investigated whether selective activation of the IR-Akt arm, leaving the IR-Erk arm largely inactive, would result in protection from atherosclerosis in a mouse model of metabolic syndrome. The insulin mimetic peptide S597 lowered blood glucose and activated Akt in insulin target tissues, mimicking insulin’s effects, but only weakly activated Erk and even prevented insulin-induced Erk activation. Strikingly, S597 retarded atherosclerotic lesion progression through a process associated with protection from leukocytosis, thereby reducing lesional accumulation of inflammatory Ly6Chi monocytes. S597-mediated protection from leukocytosis was accompanied by reduced numbers of the earliest bone marrow hematopoietic stem cells and reduced IR-Erk activity in hematopoietic stem cells. This study provides a conceptually novel treatment strategy for advanced atherosclerosis associated with metabolic syndrome and type 2 diabetes.

Categories: Diabetes

RAGE Deletion Confers Renoprotection by Reducing Responsiveness to Transforming Growth Factor-{beta} and Increasing Resistance to Apoptosis

Fri, 04/20/2018 - 13:00

Signaling via the receptor of advanced glycation end products (RAGE)—though complex and not fully elucidated in the setting of diabetes—is considered a key injurious pathway in the development of diabetic nephropathy (DN). We report here that RAGE deletion resulted in increased expression of fibrotic markers (collagen I and IV, fibronectin) and the inflammatory marker MCP-1 in primary mouse mesangial cells (MCs) and in kidney cortex. RNA sequencing analysis in MCs from RAGE–/– and wild-type mice confirmed these observations. Nevertheless, despite these gene expression changes, decreased responsiveness to transforming growth factor-β was identified in RAGE–/– mice. Furthermore, RAGE deletion conferred a more proliferative phenotype in MCs and reduced susceptibility to staurosporine-induced apoptosis. RAGE restoration experiments in RAGE–/– MCs largely reversed these gene expression changes, resulting in reduced expression of fibrotic and inflammatory markers. This study highlights that protection against DN in RAGE knockout mice is likely to be due in part to the decreased responsiveness to growth factor stimulation and an antiapoptotic phenotype in MCs. Furthermore, it extends our understanding of the role of RAGE in the progression of DN, as RAGE seems to play a key role in modulating the sensitivity of the kidney to injurious stimuli such as prosclerotic cytokines.

Categories: Diabetes

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