bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of Allelic Variants Gly972Arg of IRS-1 and Gly1057Asp of IRS-2 in Moderate-to-Severe Insulin Resistance of Women With Polycystic Ovary Syndrome
Authors: El Mkadem Samira Ait , Lautier Corinne , Macari Françoise , Molinari Nicolas , Lefèbvre Patrick , Renard Eric , Gris Jean Christophe , Cros Gérard , Daurès Jean Pierre , Bringer Jacques , White Morris F. , Grigorescu Florin
Published: March 2007

To assess the role of insulin receptor, insulin receptor substrate (IRS)-1, and IRS-2 genes in insulin resistance, we explored the genomic DNA in women with polycystic ovary syndrome (PCOS) and a variable degree (mean ± SE) of insulin resistance (homeostasis model assessment index for insulin resistance [HOMAIR] 3.2 ± 0.6, n = 53; control subjects 1.56 ± 0.34, n = 102) using direct sequencing. Whereas no novel mutations were found in these genes, gene-dosage effects were found on fasting insulin for the Gly972Arg IRS-1 variant and on 2-h plasma glucose for the Gly1057Asp IRS-2 variant. The Gly972Arg IRS-1 variant was more prevalent in insulin-resistant patients compared with non–insulin-resistant individuals or control subjects (39.3 vs. 4.0 and 16.6%, P < 0.0031, respectively). A multivariate model that included BMI as a variable revealed significant effects of the Gly1057Asp IRS-2 variant on insulin resistance (P < 0.016, odds ratio [OR] 7.2, 95% CI 1.29–43.3). HOMAIR was higher in carriers of both IRS variants than in those with IRS-2 mutations only or those with wild-type variants (6.2 ± 2.3, 2.8 ± 0.5, and 1.8 ± 0.2, respectively; P < 0.01), and it was significantly associated with this genotype (P < 0.0085, OR 1.7, 95% CI 1.09–2.99). We conclude that polymorphic alleles of both IRS-1 and IRS-2, alone or in combination, may have a functional impact on the insulin-resistant component of PCOS.
A P387L Variant in Protein Tyrosine Phosphatase-1B (PTP-1B) Is Associated With Type 2 Diabetes and Impaired Serine Phosphorylation of PTP-1B In Vitro
Authors: Echwald Søren M. , Bach Helle , Vestergaard Henrik , Richelsen Bjørn , Kristensen Kurt , Drivsholm Thomas , Borch-Johnsen Knut , Hansen Torben , Pedersen Oluf
Published: March 2007

In the present study, we tested the hypothesis that variability in the protein tyrosine phosphatase-1B (PTP-1B) gene is associated with type 2 diabetes. Using single-strand conformational polymorphism analysis, we examined cDNA of PTP-1B from 56 insulin-resistant patients with type 2 diabetes as well as cDNA from 56 obese patients. Four silent variants, (NT CGA→CGG) R199R, (NT CCC→CCT) P303P, 3′UTR+104insG, and 3′UTR+86T→G, and one missense variant, P387L, were found. Subsequent analysis on genomic DNA revealed two intron variants, IVS9+57C→T and IVS9+58G→A, and two missense variants, G381S and T420M. The G381S and 3′UTR+104insG insertion variants were not associated with type 2 diabetes. In an association study, the P387L variant was found in 14 of 527 type 2 diabetic subjects (allelic frequency 1.4%, 0.4–2.4 CI) and in 5 of 542 glucose-tolerant control subjects (allelic frequency 0.5%, CI 0.1–1.1), showing a significant association to type 2 diabetes (P = 0.036). In vitro, p34 cell division cycle (p34cdc2) kinase–directed incorporation of [γ-32P]ATP was reduced in a mutant peptide compared with native peptide (387P: 100% vs. 387L: 28.4 ± 5.8%; P = 0.0012). In summary, a rare P387L variant of the PTP-1B gene is associated with a 3.7 (CI 1.26–10.93, P = 0.02) genotype relative risk of type 2 diabetes in the examined population of Danish Caucasian subjects and results in impaired in vitro serine phosphorylation of the PTP-1B peptide.
Intracellular pH Plays a Critical Role in Glucose-Induced Time-Dependent Potentiation of Insulin Release in Rat Islets
Authors: Gunawardana Subhadra C. , Sharp Geoffrey W.G.
Published: March 2007

The underlying mechanisms of glucose-induced time-dependent potentiation in the pancreatic β-cell are unknown. It had been widely accepted that extracellular Ca2+ is essential for this process. However, we consistently observed glucose-induced priming under stringent Ca2+-free conditions, provided that the experiment was conducted in a HEPES-buffered medium as opposed to the bicarbonate (HCO3−)-buffered medium used in previous studies. The critical difference between these two buffering systems is that islets maintain a lower intracellular pH in the presence of HEPES. The addition of HEPES to a HCO3−-buffered medium produced a dramatic decrease in the intracellular pH. If it is the lower intracellular pH in islets in a HEPES-buffered medium that is permissive for glucose-induced time-dependent potentiation (TDP), then experimental lowering of intracellular pH by other means should allow TDP to occur in a Ca2+-free HCO3−-buffered medium, where TDP normally does not occur. As expected, experimental acidification produced by dimethyl amiloride (DMA) allowed glucose to induce TDP in a Ca2+-free HCO3−-buffered medium. DMA also enhanced the priming normally present in HEPES-buffered media. Priming was also enhanced by transient acidification caused by acetate. Experimental alkalinization inhibited the development of priming. In the presence of Ca2+, the magnitude of glucose-induced TDP was higher in a HEPES-buffered medium than in an HCO3−-buffered medium. In summary, glucose-induced priming was consistently observed under conditions of low intracellular pH and was inhibited with increasing intracellular pH, irrespective of the presence of extracellular Ca2+. These data indicate that glucose-induced TDP is critically dependent on intracellular pH.
Basal Insulin Gene Expression Significantly Improves Conventional Insulin Therapy in Type 1 Diabetic Rats
Authors: Dong Hengjiang , Altomonte Jennifer , Morral Nuria , Meseck Marcia , Thung Swan N. , Woo Savio L.C.
Published: March 2007

Although a conventional insulin regimen for type 1 diabetes with twice-daily insulin injections is effective in preventing postprandial blood glucose excursions, this treatment is limited by its inadequate control of fasting hyperglycemia. Alternatively, sustained basal hepatic insulin gene expression has been shown to result in fasting normoglycemia in type 1 diabetic rats, although the treated animals still exhibited moderate postprandial hyperglycemia. To test the hypothesis that basal hepatic insulin production can be used as an auxiliary treatment to conventional insulin therapy for achieving better glycemic control, streptozotocin-induced diabetic rats were treated with twice-daily insulin injections, basal hepatic insulin production, or both in combination. Diabetic rats treated by conventional insulin therapy still suffered from fasting hyperglycemia, but when complemented with basal hepatic insulin production, near-normoglycemia under both fed and fasting conditions was achieved without fasting hypoglycemia. In addition, the combination-treated animals showed significantly enhanced glucose tolerance and markedly improved profiles in lipid metabolism. Furthermore, the combination treatment reduced the elevated fructosamine, glycated hemoglobin, and advanced glycation end products concentrations to normal. These results provide a proof of concept for basal hepatic insulin production as an adjuvant treatment to conventional insulin therapy in type 1 diabetes.
Hyperglycemia-Induced Apoptosis in Human Umbilical Vein Endothelial Cells
Authors: Ido Yasuo , Carling David , Ruderman Neil
Published: March 2007

Apoptosis has been observed in vascular cells, nerve, and myocardium of diabetic humans and experimental animals, although whether it contributes to or is a marker of complications in these tissues is unclear. Previous studies have shown that incubation of human umbilical vein endothelial cells (HUVECs) with 30 vs. 5 mmol/l glucose for 72 h causes a significant increase in apoptosis, possibly related to an increase in oxidative stress. We report here that this increase in apoptosis (assessed morphologically by TdT-mediated dUTP nick- end labeling staining) is preceded (24 h of incubation) by inhibition of fatty acid oxidation, by increases in diacylglycerol synthesis, the concentration of malonyl CoA, and caspase-3 activity, and by decreases in mitochondrial membrane potential and cellular ATP content. In addition, the phosphorylation of Akt in the presence of 150 μU/ml insulin was impaired. No increases in ceramide content or its de novo synthesis were observed. AMP-activated protein kinase (AMPK) activity was not diminished; however, incubation with the AMPK activator 5-aminoimidazole-4-carboxamide-riboside increased AMPK activity twofold and completely prevented all of these changes. Likewise, expression of a constitutively active AMPK in HUVEC prevented the increase in caspase-3 activity. The results indicate that alterations in fatty-acid metabolism, impaired Akt activation by insulin, and increased caspase-3 activity precede visible evidence of apoptosis in HUVEC incubated in a hyperglycemic medium. They also suggest that AMPK could play an important role in protecting the endothelial cell against the adverse effects of sustained hyperglycemia.
Phosphatidylinositol 3-Kinase Redistribution Is Associated With Skeletal Muscle Insulin Resistance in Gestational Diabetes Mellitus
Authors: Shao Jianhua , Yamashita Hiroshi , Qiao Liping , Draznin Boris , Friedman Jacob E.
Published: March 2007

Insulin resistance during pregnancy provokes gestational diabetes mellitus (GDM); however, the cellular mechanisms for this type of insulin resistance are not well understood. We evaluated the mechanisms(s) for insulin resistance in skeletal muscle from an animal model of spontaneous GDM, the heterozygous C57BL/KsJ-db/+ mouse. Pregnancy triggered a novel functional redistribution of the insulin-signaling environment in skeletal muscle in vivo. This environment preferentially increases a pool of phosphatidylinositol (PI) 3-kinase activity associated with the insulin receptor, away from insulin receptor substrate (IRS)-1. In conjunction with the redistribution of PI 3-kinase to the insulin receptor, there is a selective increase in activation of downstream serine kinases Akt and p70S6. Furthermore, we show that redistribution of PI 3-kinase to the insulin receptor increases insulin-stimulated IRS-1 serine phosphorylation, impairs IRS-1 expression and its tyrosine phosphorylation, and decreases the ability of IRS-1 to bind and activate PI 3-kinase in response to insulin. Thus, the pool of IRS-1–associated PI 3-kinase activity is reduced, resulting in the inability of insulin to stimulate GLUT4 translocation to the plasma membrane. These defects are unique to pregnancy and suggest that redistribution of PI 3-kinase to the insulin receptor may be a primary defect underlying insulin resistance in skeletal muscle during gestational diabetes.
Predictability of Childhood Adiposity and Insulin for Developing Insulin Resistance Syndrome (Syndrome X) in Young Adulthood
Authors: Srinivasan Sathanur R. , Myers Leann , Berenson Gerald S.
Published: March 2007

The occurrence of insulin resistance syndrome (syndrome X) is common in the general population. However, information is scant on the childhood predictors of syndrome X. This study examined the relative contribution of childhood adiposity and insulin to the adulthood risk of developing syndrome X in a biracial (black-white) community-based longitudinal cohort (n = 745; baseline age, 8–17 years; mean ± SD follow-up period, 11.6 ± 3.4 years). The four criterion risk variables considered were the highest quartile (specific for age, race, sex, and study year) of 1) BMI, 2) fasting insulin, 3) systolic or mean arterial blood pressure, and 4) total cholesterol to HDL cholesterol ratio or triglycerides to HDL cholesterol ratio. Clustering was defined as the combination of all four risk variables. In addition to the criterion risk variables, clustered adults had adverse levels of total cholesterol, triglycerides, LDL cholesterol, HDL cholesterol, diastolic blood pressure, and glucose compared with those who did not cluster (P < 0.001). Childhood variables, except glucose, showed adverse trends with increasing number of criterion risk variables present in adulthood (P for trend, 0.01–0.0001). The proportion of individuals who developed clustering as adults increased across childhood BMI (P for trend <0.0001) and insulin (P for trend <0.01) quartiles. The relationship to childhood BMI remained significant even after adjusting for childhood insulin. In contrast, corresponding association with childhood insulin disappeared after adjusting for childhood BMI. In a logistic regression model, childhood BMI and insulin were significant predictors of adulthood clustering, with BMI being the strongest and showing a curvilinear relationship. Using an insulin resistance index instead of insulin did not change the above findings. These results indicate that childhood obesity is a powerful predictor of development of syndrome X and underscore the importance of weight control early in life.
Congenic Mapping of the Diabetogenic LocusIdd4to a 5.2-cM Region of Chromosome 11 in NOD Mice
Authors: Grattan Marsha , Mi Qing-Sheng , Meagher Craig , Delovitch Terry L.
Published: March 2007

Twenty diabetes susceptibility loci on 12 mouse chromosomes have been identified to control the development of type 1 diabetes at the level of either initiation of insulitis or progression from insulitis to overt diabetes or both. Previously, we demonstrated that the genetic control of T-cell proliferative unresponsiveness in nonobese diabetic (NOD) mice is linked to Idd4 on mouse chromosome 11. Here, we show by congenic mapping of three newly generated NOD.B6Idd4 diabetes-resistant mouse strains that Idd4 is limited to a 5.2-cM interval of chromosome 11. This B6-derived region expressed in NOD.B6Idd4A mice maps between the D11Nds1 (43.8 cM) and D11Mit38/D11Mit325 (49.0 cM) markers and dramatically reduces the development of both insulitis and type 1 diabetes. NOD.B6Idd4B and NOD.B6Idd4C mice, which carry a smaller B6-derived segment of chromosome 11 that spans <5.2 cM distal to D11Nds1, exhibit protection against type 1 diabetes with the restoration of T-cell proliferation. Our findings suggest that diabetes resistance conferred by Idd4 may be mediated by the Idd4.1 and Idd4.2 subloci. Idd4.1 is localized in the D11Nds1 interval that influences both diabetes and insulitis. Idd4.2 is localized within the D11Mit38/325 interval that mainly influences diabetes incidence and restores T-cell proliferative responsiveness. Three potential candidate genes, platelet activating factor acetylhydrolase Ib1, nitric oxide synthase-2, and CC chemokine genes, are localized in the 5.2-cM interval.
PAX6 Mutation as a Genetic Factor Common to Aniridia and Glucose Intolerance
Authors: Yasuda Tetsuyuki , Kajimoto Yoshitaka , Fujitani Yoshio , Watada Hirotaka , Yamamoto Shuji , Watarai Takao , Umayahara Yutaka , Matsuhisa Munehide , Gorogawa Shin-ichi , Kuwayama Yasuaki , Tano Yasuo , Yamasaki Yoshimitsu , Hori Masatsugu
Published: March 2007

A paired homeodomain transcription factor, PAX6, is a well-known regulator of eye development, and its heterozygous mutations in humans cause congenital eye anomalies such as aniridia. Because it was recently shown that PAX6 also plays an indispensable role in islet cell development, a PAX6 gene mutation in humans may lead to a defect of the endocrine pancreas. Whereas heterozygous mutations in islet-cell transcription factors such as IPF1/IDX-1/STF-1/PDX-1 and NEUROD1/BETA2 serve as a genetic cause of diabetes or glucose intolerance, we investigated the possibility of PAX6 gene mutations being a genetic factor common to aniridia and diabetes. In five aniridia and one Peters’ anomaly patients, all of the coding exons and their flanking exon-intron junctions of the PAX6 gene were surveyed for mutations. The results of direct DNA sequencing revealed three different mutations in four aniridia patients: one previously reported type of mutation and two unreported types. In agreement with polypeptide truncation and a lack of the carboxyl-terminal transactivation domain in all of the mutated PAX6 proteins, no transcriptional activity was found in the reporter gene analyses. Oral glucose tolerance tests revealed that all of the patients with a PAX6 gene mutation had glucose intolerance characterized by impaired insulin secretion. Although we did not detect a mutation within the characterized portion of the PAX6 gene in one of the five aniridia patients, diabetes was cosegregated with aniridia in her family, and a single nucleotide polymorphism in intron 9 of the PAX6 gene was correlated with the disorders, suggesting that a mutation, possibly located in an uncharacterized portion of the PAX6 gene, can explain both diabetes and aniridia in this family. In contrast, the patient with Peters’ anomaly, for which a PAX6 gene mutation is a relatively rare cause, showed normal glucose tolerance (NGT) and did not show a Pax6 gene mutation. Taken together, our present observations suggest that heterozygous mutations in the PAX6 gene can induce eye anomaly and glucose intolerance in individuals harboring these mutations.
A Novel Homozygous Missense Mutation of Melanocortin-4 Receptor (MC4R) in a Japanese Woman With Severe Obesity
Authors: Kobayashi Hiromasa , Ogawa Yoshihiro , Shintani Mitsuyo , Ebihara Ken , Shimodahira Makiko , Iwakura Toshio , Hino Megumu , Ishihara Takashi , Ikekubo Katsuji , Kurahachi Hiroyuki , Nakao Kazuwa
Published: March 2007

The melanocortin-4 receptor (MC4R) is a member of the seven membrane–spanning G protein–coupled receptor superfamily and signals through the activation of adenylyl cyclase. The MC4R mutations are the most common known monogenic cause of human obesity. However, no such mutations have been found in Japanese obese subjects. Here we report a novel homozygous missense mutation of MC4R (G98R) in a nondiabetic Japanese woman with severe early-onset obesity, which is located in its second transmembrane domain. Her birth weight was 3,360 g, and she gained weight progressively from 10 months of age. At 40 years of age, her weight reached 160 kg and a BMI of 62 kg/m2. Her parents, who are heterozygous for the mutation, have BMIs of 26 and 27 kg/m2. In vitro transient transfection assays revealed no discernable agonist ligand binding and cAMP production in HEK293 cells expressing the mutant receptor, indicating a severe loss-of-function mutation. This study represents the first demonstration of a pathogenic mutation of MC4R in Japan and will provide further insight into the pathophysiologic role of the hypothalamic melanocortin system in human obesity.
Association of the T-G Polymorphism in Adiponectin (Exon 2) With Obesity and Insulin Sensitivity
Authors: Stumvoll Michael , Tschritter Otto , Fritsche Andreas , Staiger Harald , Renn Walter , Weisser Melanie , Machicao Fausto , Häring Hans
Published: March 2007

The adipocyte-derived hormone adiponectin seems to protect from insulin resistance, a key factor in the pathogenesis of type 2 diabetes. Genome-wide scans have mapped a susceptibility locus for type 2 diabetes and the metabolic syndrome to chromosome 3q27, where the adiponectin gene is located. A common silent T-G exchange in nucleotide 94 (exon 2) of the adiponectin gene has been associated with increased circulating adiponectin levels. Metabolic abnormalities associated with the G allele have not been reported. We therefore assessed whether this polymorphism alters insulin sensitivity and/or measures of obesity using the Tübingen Family Study database (prevalence of the G allele, 28%). In 371 nondiabetic individuals, we found a significantly greater BMI in GG + GT (25.5 ± 0.7 kg/m2) compared with TT (24.1 ± 0.3 kg/m2; P = 0.02). Insulin sensitivity (determined by euglycemic clamp, n = 209) was significantly lower in GG + GT (0.089 ± 0.007 units) compared with TT (0.112 ± 0.005 units; P = 0.02). This difference disappeared completely on adjustment for BMI. Because our population contains a relatively high proportion of first-degree relatives of patients with type 2 diabetes, we stratified by family history (FHD). Much to our surprise, the genotype differences in BMI and insulin sensitivity in the whole population were attributable entirely to differences in the subgroup without FHD, whereas in the subgroup with FHD, the G allele had absolutely no effect. Moreover, individuals without FHD had a significantly lower BMI than individuals with FHD (25.2 ± 0.4 vs. 26.2 ± 0.5 kg/m2; P = 0.01), which was not the case for the GG + GT subgroup without FHD (27.0 ± 0.9 kg/m2; NS). This suggests that in individuals without familial predisposition for type 2 diabetes, the adiponectin polymorphism may mildly increase the obesity risk (and secondarily insulin resistance). In contrast, in individuals who are already burdened by other genetic factors, this small effect may be very hard to detect.
Human Pancreatic Islets Produce and Secrete MCP-1/CCL2: Relevance in Human Islet Transplantation
Authors: Piemonti Lorenzo , Leone Biagio Eugenio , Nano Rita , Saccani Alessandra , Monti Paolo , Maffi Paola , Bianchi Giancarlo , Sica Antonio , Peri Giuseppe , Melzi Raffaella , Aldrighetti Luca , Secchi Antonio , Di Carlo Valerio , Allavena Paola , Bertuzzi Federico
Published: March 2007

We investigated the capacity of human islets to produce monocyte chemoattractant protein-1 (MCP-1). Primary cultures of pancreatic islets expressed and secreted MCP-1, as determined by Northern blot, immunohistochemistry, in situ hybridization, and enzyme-linked immunosorbent assay. The produced MCP-1 was biologically active as it attracted monocytes in chemotaxis assay, and chemotactic activity was almost abrogated by a neutralizing anti–MCP-1 monoclonal antibody. Expression of MCP-1 was increased by primary inflammatory cytokines (interleukin-1β, tumor necrosis factor-α) and lipopolysaccharide at both the mRNA and protein levels but not by glucose. However, MCP-1 did not modulate insulin secretion. MCP-1 secreted by pancreatic islets plays a relevant role in the clinical outcome of islet transplant in patients with type 1 diabetes. In fact, low MCP-1 secretion resulted as the most relevant factor for long-lasting insulin independence. This finding opens new approaches in the management of human islet transplantation. Finally, the finding that MCP-1 appears constitutively present in normal human islet β-cells (immunohistochemistry and in situ hybridization), in the absence of an inflammatory infiltrate, suggests that this chemokine could have functions other than monocyte recruitment and opens a new link between the endocrine and immune systems.
Polyunsaturated Fatty Acids and Acetoacetate Downregulate the Expression of the ATP-Binding Cassette Transporter A1
Authors: Uehara Yoshinari , Engel Thomas , Li Zhengchen , Goepfert Christian , Rust Stephan , Zhou Xiaoqin , Langer Claus , Schachtrup Christian , Wiekowski Johannes , Lorkowski Stefan , Assmann Gerd , von Eckardstein Arnold
Published: March 2007

Low HDL cholesterol is a frequent cardiovascular risk factor in diabetes. Because of its pivotal role for the regulation of HDL plasma levels, we investigated in vivo and in vitro regulation of the ATP-binding cassette transporter A1 (ABCA1) by insulin and metabolites accumulating in diabetes. Compared with euglycemic control mice, ABCA1 gene expression was severely decreased in the liver and peritoneal macrophages of diabetic mice. Treatment with insulin restored this deficit. Incubation of cultivated HepG2 hepatocytes and RAW264.7 macrophages with unsaturated fatty acids or acetoacetate, but not with insulin, glucose, saturated fatty acids, or hydroxybutyrate, downregulated ABCA1 mRNA and protein. The suppressive effect of unsaturated fatty acids and acetoacetate became most obvious in cells stimulated with oxysterols or retinoic acid but was independent of the expression of the thereby regulated transcription factors liver-X-receptor α (LXRα) and retinoid-X-receptor α (RXRα), respectively. Unsaturated fatty acids and acetoacetate also reduced ABCA1 promotor activity in RAW264.7 macrophages that were transfected with a 968-bp ABCA1 promotor/luciferase gene construct. As the functional consequence, unsaturated fatty acids and acetoacetate inhibited cholesterol efflux from macrophages. Downregulation of ABCA1 by unsaturated fatty acids and acetoacetate may contribute to low HDL cholesterol and increased cardiovascular risk of diabetic patients.
Tumor Necrosis Factor-α Stimulates Lipolysis in Differentiated Human Adipocytes Through Activation of Extracellular Signal-Related Kinase and Elevation of Intracellular cAMP
Authors: Zhang Hui H. , Halbleib Melanie , Ahmad Faiyaz , Manganiello Vincent C. , Greenberg Andrew S.
Published: March 2007

Tumor necrosis factor-α (TNF-α) stimulates lipolysis in human adipocytes. However, the mechanisms regulating this process are largely unknown. We demonstrate that TNF-α increases lipolysis in differentiated human adipocytes by activation of mitogen-activated protein kinase kinase (MEK), extracellular signal-related kinase (ERK), and elevation of intracellular cAMP. TNF-α activated ERK and increased lipolysis; these effects were inhibited by two specific MEK inhibitors, PD98059 and U0126. TNF-α treatment caused an electrophoretic shift of perilipin from 65 to 67 kDa, consistent with perilipin hyperphosphorylation by activated cAMP-dependent protein kinase A (PKA). Coincubation with TNF-α and MEK inhibitors caused perilipin to migrate as a single 65-kDa band. Consistent with the hypothesis that TNF-α induces perilipin hyperphosphorylation by activating PKA, TNF-α increased intracellular cAMP ∼1.7-fold, and the increase was abrogated by PD98059. Furthermore, H89, a specific PKA inhibitor, blocked TNF-α-induced lipolysis and the electrophoretic shift of perilipin, suggesting a role for PKA in TNF-α-induced lipolysis. Finally, TNF-α decreased the expression of cyclic-nucleotide phosphodiesterase 3B (PDE3B) by ∼50%, delineating a mechanism by which TNF-α could increase intracellular cAMP. Cotreatment with PD98059 restored PDE3B expression. These studies suggest that in human adipocytes, TNF-α stimulates lipolysis through activation of MEK-ERK and subsequent increase in intracellular cAMP.
Skeletal Muscle Insulin Resistance in Obesity-Associated Type 2 Diabetes in Monkeys Is Linked to a Defect in Insulin Activation of Protein Kinase C-ζ/λ/ι
Authors: Standaert Mary L. , Ortmeyer Heidi K. , Sajan Mini P. , Kanoh Yoshinori , Bandyopadhyay Gautam , Hansen Barbara C. , Farese Robert V.
Published: March 2007

Rhesus monkeys frequently develop obesity and insulin resistance followed by type 2 diabetes when allowed free access to chow. This insulin resistance is partly due to defective glucose transport into skeletal muscle. In this study, we examined signaling factors required for insulin-stimulated glucose transport in muscle biopsies taken during euglycemic-hyperinsulinemic clamps in nondiabetic, obese prediabetic, and diabetic monkeys. Insulin increased activities of insulin receptor substrate (IRS)-1-dependent phosphatidylinositol (PI) 3-kinase and its downstream effectors, atypical protein kinase Cs (aPKCs) (ζ/λ/ι) and protein kinase B (PKB) in muscles of nondiabetic monkeys. Insulin-induced increases in glucose disposal and aPKC activity diminished progressively in prediabetic and diabetic monkeys. Decreases in aPKC activation appeared to be at least partly due to diminished activation of IRS-1-dependent PI 3-kinase, but direct activation of aPKCs by the PI 3-kinase lipid product PI-3,4,5-(PO4)3 was also diminished. In conjunction with aPKCs, PKB activation was diminished in prediabetic muscle but, differently from aPKCs, seemed to partially improve in diabetic muscle. Interestingly, calorie restriction and avoidance of obesity largely prevented development of defects in glucose disposal and aPKC activation. Our findings suggest that defective activation of aPKCs contributes importantly to obesity-dependent development of skeletal muscle insulin resistance in prediabetic and type 2 diabetic monkeys.
Thymectomy and Radiation-Induced Type 1 Diabetes in Nonlymphopenic BB Rats
Authors: Ramanathan Sheela , Bihoreau Marie-Therese , Paterson Andrew D. , Marandi Leili , Gauguier Dominique , Poussier Philippe
Published: March 2007

Spontaneous type 1 diabetes in BB rats is dependent on the RT1u MHC haplotype and homozygosity for an allele at the Lyp locus, which is responsible for a peripheral T-lymphopenia. Genetic studies have shown that there are other, as yet unidentified, genetic loci contributing to diabetes susceptibility in this strain. BB rats carrying wild-type Lyp alleles are not lymphopenic and are resistant to spontaneous diabetes (DR). Here we show that thymectomy and exposure to one sublethal dose of γ-irradiation (TX-R) at 4 weeks of age result in the rapid development of insulitis followed by diabetes in 100% of DR rats. Administration of CD4+45RC− T-cells from unmanipulated, syngeneic donors immediately after irradiation prevents the disease. Splenic T-cells from TX-R-induced diabetic animals adoptively transfer type 1 diabetes to T-deficient recipients. ACI, WF, WAG, BN, LEW, PVG, and PVG.RT1u strains are resistant to TX-R-induced insulitis/diabetes. Genetic analyses revealed linkage between regions on chromosomes 1, 3, 4, 6, 9, and 16, and TX-R-induced type 1 diabetes in a cohort of nonlymphopenic F2 (Wistar Furth × BBDP) animals. This novel model of TX-R-induced diabetes in nonlymphopenic BB rats can be used to identify environmental and cellular factors that are responsible for the initiation of antipancreatic autoimmunity.
Early, Selective, and Marked Loss of Sympathetic Nerves From the Islets of BioBreeder Diabetic Rats
Authors: Mei Qi , Mundinger Thomas O. , Lernmark Ake , Taborsky Gerald J.
Published: March 2007

To discover whether islet sympathetic nerves are damaged during the autoimmune destruction of islet B-cells, we immunostained sections of pancreas from BioBreeder (BB) diabetic rats, using antibodies against vesicular monoamine transporter 2 (VMAT2), a marker of sympathetic nerve terminals. We found a marked decrease in the VMAT2-positive fiber area in the islets of BB rats that had been diabetic for only 1–2 weeks compared with their nondiabetic controls. In contrast, there was no significant decrease in the VMAT2-positive fiber area in the exocrine pancreas in these early diabetic BB rats. Furthermore, streptozotocin-diabetic rats showed no decrease in VMAT2-positive fiber area in their islets compared with controls. The classical diabetic autonomic neuropathy (DAN) that eventually occurs in the heart was not present in BB diabetic rats at this early stage as evidenced by normal cardiac VMAT2 immunostaining and normal cardiac norepinephrine content. Also, in contrast to DAN, this islet neuropathy did not worsen with duration of diabetes. These data provide evidence of a heretofore unrecognized early sympathetic islet neuropathy (eSIN). Because eSIN occurs selectively in the islet, is rapid in onset, and is associated with autoimmune but not chemically induced diabetes, it is distinct from DAN in location, time course, and mechanism.
Evidence for a Matrix Metalloproteinase Induction/Activation System in Arterial Vasculature and Decreased Synthesis and Activity in Diabetes
Authors: Portik-Dobos Vera , Anstadt Mark P. , Hutchinson Jimmie , Bannan Mary , Ergul Adviye
Published: March 2007

Pathological remodeling characterized by extracellular matrix (ECM) deposition contributes to the diabetic vascular complications. Matrix metalloproteinases (MMPs) regulate ECM turnover. However, the expression profile of the MMP system in diabetic human tissue remains unknown. The objectives of this study were 1) to identify a local MMP induction/activation system that exists in arterial vasculature and 2) to determine how the MMP system may be altered in diabetes. Internal mammary artery specimens were obtained from patients who did (n = 14) and did not (n = 14) have diabetes and were undergoing coronary artery bypass grafting surgery. ECM inducer protein (EMMPRIN); membrane-type MMP (MT-MMP); and MMP-1, -2, and -9 were quantified by immunoblotting and densitometric scanning (pixels). Pro-MMP-1 and MMP-2 levels were decreased from 952 ± 120 and 1,081 ± 508 pixels, respectively, in nondiabetic tissue to 398 ± 62 and 249 ± 42 pixels in the diabetic tissue (P < 0.05). Both EMMPRIN and MT-MMP expression and total MMP activity were decreased by twofold in diabetic patients (P < 0.05). These results demonstrated for the first time that an MMP induction and activation system exists in human arterial vasculature and that it is downregulated in diabetes. Decreased MMP activity may contribute to increased collagen deposition and pathological remodeling in diabetes.
Variations in Insulin Secretion in Carriers of the E23K Variant in the KIR6.2 Subunit of the ATP-Sensitive K+ Channel in the β-Cell
Authors: ‘t Hart Leen M. , van Haeften Timon W. , Dekker Jacqueline M. , Bot Martine , Heine Robert J. , Maassen J. Antonie
Published: March 2007

An association between type 2 diabetes and genetic variation in the KIR6.2 gene has been reported in several populations. Based on in vitro studies with cell lines expressing the Glu23Lys (E23K) mutation, it was recently suggested that this mutation might result in altered insulin secretion. We have examined glucose-stimulated insulin secretion in relation to this KIR6.2 gene variant in two independent Dutch cohorts. Subjects with normal (n = 65) or impaired (n = 94) glucose tolerance underwent 3-h hyperglycemic clamps at 10 mmol/l glucose. We did not observe significant differences in first- or second-phase insulin secretion between carriers and noncarriers of the gene variant in either of the study populations (all P > 0.45). Furthermore, we found no evidence for a significant interaction with disease-associated gene variants in the sulfonylurea receptor (SUR1) gene. We conclude that the E23K mutation in the KIR6.2 gene is not associated with detectable alterations in glucose-stimulated insulin secretion in two independent populations from the Netherlands.
While Tinkering With the β-Cell… Metabolic Regulatory Mechanisms and New Therapeutic Strategies
Authors: Newgard Christopher B.
Published: March 2007

A common feature of the two major forms of human diabetes is the partial or complete loss of insulin secretion from β-cells in the pancreatic islets of Langerhans. In this article, we review the development of a set of tools for studying β-cell biology and their application to understanding of fuel-mediated insulin secretion and enhancement of β-cell survival. Insights into these basic issues are likely to be useful for the design of new drug and cell-based diabetes therapies.
Effects of Insulin Deficiency or Excess on Hepatic Gluconeogenic Flux During Glycogenolytic Inhibition in the Conscious Dog
Authors: Edgerton Dale S. , Cardin Sylvain , Pan Catherine , Neal Doss , Farmer Ben , Converse Margaret , Cherrington. Alan D.
Published: March 2007

The direct acute effects of insulin on the regulation of hepatic gluconeogenic flux to glucose-6-phosphate (G6P) in vivo may be masked by the hormone’s effects on net hepatic glycogenolytic flux and the resulting changes in glycolysis. To investigate this possibility, we used a glycogen phosphorylase inhibitor (BAY R3401) to inhibit glycogen breakdown in the overnight-fasted dog, and the effects of complete insulin deficiency or a fourfold rise in the plasma insulin level were assessed during a 5-h experimental period. Hormone levels were controlled using somatostatin with portal insulin and glucagon infusion. After the control period, plasma insulin infusion 1) was discontinued, creating insulin deficiency; 2) increased fourfold; or 3) was continued at the basal rate. During insulin deficiency, glucose production and the plasma level and net hepatic uptake of nonesterified free fatty acids increased, whereas during hyperinsulinemia they decreased. Net hepatic lactate uptake increased sixfold during insulin deficiency and 2.5-fold during hyperinsulinemia. Net hepatic gluconeogenic flux increased more than fourfold during insulin deficiency but was not reduced by hyperinsulinemia. We conclude that in the absence of appreciable glycogen breakdown, an acute gluconeogenic effect of hypoinsulinemia becomes manifest, whereas inhibition of the process by a physiologic rise in insulin was not evident.
Altered Myocellular and Abdominal Fat Partitioning Predict Disturbance in Insulin Action in HIV Protease Inhibitor-Related Lipodystrophy
Authors: Gan Seng Khee , Samaras Katherine , Thompson Campbell H. , Kraegen Edward W. , Carr Andrew , Cooper David A. , Chisholm Donald J.
Published: March 2007

HIV protease inhibitor-related lipodystrophy is characterized by peripheral fat loss, hyperlipidemia, and insulin resistance. Increased availability of lipid to muscle may be one of the mechanisms that induce insulin resistance. Regional fat, intramyocellular lipid (by 1H-magnetic resonance spectroscopy), serum lipids, and insulin-stimulated glucose disposal (by hyperinsulinemic-euglycemic clamp) were quantified in 10 men who had HIV-1 infection with moderate to severe lipodystrophy and a control group of 10 nonlipodystrophic men who had HIV-1 infection and were naïve to protease inhibitors to examine the effects of lipodystrophy on glucose and lipid metabolism. Lipodystrophic subjects showed lower insulin-stimulated glucose disposal than control subjects (P = 0.001) and had increased serum triglycerides (P = 0.03), less limb fat (P = 0.02), increased visceral fat as a proportion of total abdominal fat (P = 0.003), and increased intramyocellular lipid (1.90 ± 0.15 vs. 1.23 ± 0.16% of water resonance peak area; P = 0.007). In both groups combined, visceral fat related strongly to intramyocellular lipid (r = 0.83, P < 0.0001) and intramyocellular lipid related negatively to insulin-stimulated glucose disposal (r = −0.71, P = 0.0005). Fasting serum cholesterol and triglycerides related positively to intramyocellular lipid and visceral fat in lipodystrophic subjects only. The data indicate that lipodystrophy is associated with increased lipid content in muscle accompanying impaired insulin action. The results do not establish causation but emphasize the interrelationships among visceral fat, myocyte lipid, and insulin action.
Vascularized Islet Cell Transplantation in Miniature Swine
Authors: Kumagai Naoki , LaMattina John C. , Kamano Chisako , Vagefi Parsia A. , Barth Rolf N. , O’Neil John J. , Yamamoto Shin , Moran Shannon G. , Utsugi Ryu , Sachs David H. , Yamada Kazuhiko
Published: March 2007

We have previously reported the preparation of vascularized islet-kidneys (IKs) by transplantation of islets under the autologous kidney capsule. Here, we compare the efficacy of transplanting vascularized versus nonvascularized islets into diabetic allogeneic swine recipients. In the vascularized islet transplantation (5,000 islet equivalents [IE]/kg), recipients received minor-mismatched (n = 4) or fully-mismatched (n = 2) IKs after pancreatectomy, with a 12-day course of cyclosporine A (CyA) or FK506, respectively. For the nonvascularized islet transplantation (7,000 IE/kg), three recipients received minor-mismatched islets alone and two recipients received minor-mismatched donor islets placed in a donor kidney on the day of transplantation. All recipients of nonvascularized islets were treated with a 12-day course of CyA. With vascularized islet transplantation, pancreatectomized recipients were markedly hyperglycemic pretransplant (fasting blood glucose >300 mg/dl). After composite IK transplantation, all recipients developed and maintained normoglycemia (<120 mg/dl) and stable renal function indefinitely (>3 months), and insulin therapy was not required. Major histocompatibility complex-mismatched recipients demonstrated in vitro donor-specific unresponsiveness. In contrast, recipients of nonvascularized islets remained hyperglycemic. In conclusion, IK allografts cured surgically induced diabetes across allogeneic barriers, whereas nonvascularized islet transplants did not. These data indicate that prevascularization of islet allografts is crucial for their subsequent engraftment and that composite IKs may provide a strategy for successful islet transplantation.
Theiddm4Locus Segregates With Diabetes Susceptibility in Congenic WF.iddm4Rats
Authors: Mordes John P. , Leif Jean , Novak Stephen , DeScipio Cheryl , Greiner Dale L. , Blankenhorn Elizabeth P.
Published: March 2007

Viral antibody–free BBDR and WF rats never develop spontaneous diabetes. BBDR rats, however, develop autoimmune diabetes after perturbation of the immune system, e.g., by viral infection. We previously identified a disease-susceptibility locus in the BBDR rat, iddm4, which is associated with the development of autoimmune diabetes after treatment with polyinosinic:polycytidylic acid and an antibody that depletes ART2+ regulatory cells. We have now developed lines of congenic WF.iddm4 rats and report that in an intercross of N5 generation WF.iddm4 rats, ∼70% of animals either homozygous or heterozygous for the BBDR origin allele of iddm4 became hyperglycemic after treatment to induce diabetes. Fewer than 20% of rats expressing the WF origin allele of iddm4 became diabetic. Testing the progeny of various recombinant N5 WF.iddm4 congenic rats for susceptibility to diabetes suggests that iddm4 is centered on a small segment of chromosome 4 bounded by the proximal marker D4Rat135 and the distal marker D4Got51, an interval of <2.8 cM. The allele at iddm4 has 79% sensitivity and 80% specificity in prediction of diabetes in rats that are segregating for this locus. These characteristics suggest that iddm4 is one of the most powerful non–major histocompatibility complex determinants of susceptibility to autoimmune diabetes described to date.
Activation of Cyclin D1-Cdk4 and Cdk4-Directed Phosphorylation of RB Protein in Diabetic Mesangial Hypertrophy
Authors: Féliers Denis , Frank Meredith A. , Riley Daniel J.
Published: March 2007

To determine the role of cell-cycle proteins in regulating pathological renal hypertrophy, diabetes was induced in mice expressing a human retinoblastoma (RB) transgene and in wild-type littermates. Whole-kidney and glomerular hypertrophy caused by hyperglycemia was associated with specific G1 phase cell-cycle events: early and sustained increase in expression of cyclin D1 and activation of cyclin D1-cdk4 complexes, but no change in expression of cyclin E or cdk2 activity. Overexpression of RB alone likewise caused hypertrophy and increased only cyclin D1-cdk4 activity; these effects were not further augmented by high glucose. Identical observations were made when isolated mesangial cells conditionally overexpressing RB from a tetracycline-repressible system hypertrophied in response to high glucose. A mitogenic signal in the same cell-culture system, in contrast, transiently and sequentially activated both cyclin D1-cdk4 and cyclin E-cdk2. In vivo and in cultured mesangial cells, high glucose resulted in persistent partial phosphorylation of RB, an event catalyzed specifically by cyclin D1-cdk4. These data indicate that mesangial hypertrophy caused by hyperglycemia in diabetes results in sustained cyclin D1-cdk4-dependent phosphorylation of RB and maintenance of mesangial cells in the early-to-middle G1 phase of the cell cycle.
Linkage and Association With Type 1 Diabetes on Chromosome 1q42
Authors: Ewens Kathryn G. , Johnson Lindsey N. , Wapelhorst Beth , O’Brien Kristin , Gutin Sarah , Morrison V. Anne , Street Craig , Gregory Simon G. , Spielman Richard S. , Concannon Patrick
Published: March 2007

Type 1 diabetes is a complex disorder with multiple genetic loci and environmental factors contributing to disease etiology. In the current study, a human type 1 diabetes candidate region on chromosome 1q42 was mapped at high marker density in a panel of 616 multiplex type 1 diabetic families. To facilitate the identification and evaluation of candidate genes, a physical map of the 7-cM region surrounding the maximum logarithm of odds (LOD) score (2.46, P = 0.0004) was constructed. Genes were identified in the 500-kb region surrounding the marker yielding the peak LOD score and evaluated for polymorphism by resequencing. Single-nucleotide polymorphisms (SNPs) identified in these genes as well as other anonymous markers were tested for allelic association with type 1 diabetes by both family-based and case-control methods. A haplotype formed by common alleles at three adjacent markers (D1S225, D1S2383, and D1S251) was preferentially transmitted to affected offspring in type 1 diabetic families (nominal P = 0.006). These findings extend the evidence supporting the existence of a type 1 diabetes susceptibility locus on chromosome 1q42 and identify a candidate region amenable to positional cloning efforts.
Molecular Analysis of KCNJ10 on 1q as a Candidate Gene for Type 2 Diabetes in Pima Indians
Authors: Farook Vidya S. , Hanson Robert L. , Wolford Johanna K. , Bogardus Clifton , Prochazka Michal
Published: March 2007

The KCNJ10 gene is located within a region on chromosome 1q linked to type 2 diabetes in the Pima Indians and six other populations. We therefore investigated this gene as a potential type 2 diabetes candidate gene in Pima Indians. KCNJ10 consists of two exons, spans ∼33 kb, and we identified eight single-nucleotide polymorphisms (SNPs), including one (SNP2) in the coding region leading to a Glu359Lys substitution. Association studies were carried out in a case-control group composed of 149 affected and 150 unaffected Pimas, and the linkage analysis was performed in a linkage set of 1,338 Pimas. SNP1 in the promoter and SNP2 in the intron, which were in a complete linkage disequilibrium, and SNP5 in the 3′ untranslated region showed association with diabetes in the case-control group (P = 0.02 and P = 0.01, respectively). When genotyped in the linkage set, only the KCNJ10-SNP1 variant showed a modest association with type 2 diabetes (P = 0.01). KCNJ10-SNP1 is in a strong linkage disquilibrium with SNP14 of the adjacent KCNJ9 locus, which we previously found to be associated with type 2 diabetes. After adjustment for KCNJ10-SNP1, the original linkage score at this locus was marginally reduced from 3.1 to 2.9. We conclude that these variants in KCNJ10 are unlikely to be the cause of linkage of type 2 diabetes with 1q in Pima Indians.
Identification of the Insulin-Regulated Interaction of Phosphodiesterase 3B With 14-3-3 β Protein
Authors: Onuma Hiroshi , Osawa Haruhiko , Yamada Kazuya , Ogura Takahiro , Tanabe Fumiko , Granner Daryl K. , Makino Hideichi
Published: March 2007

Phosphodiesterase (PDE)-3B, a major PDE isoform in adipocytes, plays a pivotal role in the antilipolytic action of insulin. Insulin-induced phosphorylation and activation of PDE3B is phosphatidylinositol 3-kinase (PI3-K) and Akt dependent, but the precise mechanism of PDE3B activation is not fully understood. We have identified 14-3-3 β, a critical scaffolding molecule in signal transduction, as a protein that interacts with PDE3B using the yeast two-hybrid system. The interaction between PDE3B and 14-3-3 β was then confirmed in vitro. The glutathione S-transferase (GST)-tagged 14-3-3 β interacts with endogenous PDE3B of rat adipocytes, and this interaction is enhanced when adipocytes are treated with insulin. Coimmunoprecipitation experiments reveal that endogenous PDE3B also associates with endogenous 14-3-3 β in rat adipocytes, and this interaction is enhanced by insulin. Two different PI3-K inhibitors, wortmannin and Ly294002, block this induction, suggesting that PI3-K is required. Synthetic 15 amino acid peptides of rat PDE3B containing phosphorylated Ser-279 or -302 inhibit this interaction, indicating that the insulin-regulated phosphorylation of these serine residues is involved. Because insulin receptor substrate-1 also associates with 14-3-3, the dimeric 14-3-3 β could function as a scaffolding protein in the activation of PDE3B by insulin.