bluuebunny/crossref_metadata_2025 huggingface dataset:
Insulin Deficiency Downregulated Heat Shock Protein 60 and IGF-1 Receptor Signaling in Diabetic Myocardium
Authors: Chen Harn-Shen , Shan Yue-Xin , Yang Tung-Lin , Lin Hong-Da , Chen Jaw-Wen , Lin Shing-Jong , Wang Ping H.
Published: March 2007

Heat shock protein (Hsp)60 and IGF-1 receptor signaling protect cardiac muscle against injury. The abundance of cardiac IGF-1 receptor can be upregulated by Hsp60, but how diabetes modulates cardiac muscle Hsp60 has not yet been defined. We investigated the changes of Hsp60 and IGF-1 receptor signaling in the diabetic myocardium and studied how diabetes modulates Hsp60 and IGF-1 receptor in diabetic myocardium. In the streptozotocin (STZ)-induced diabetic rat, downregulation of Hsp60 and IGF-1 receptor occurred 4 days after induction of diabetes. IGF-1 activation of IGF-1 receptor, Mek, and Akt were reduced accordingly in the diabetic myocardium. The independent effect of insulin and hyperglycemia on Hsp60 was investigated in primary cardiomyocytes. Incubating cardiomyocytes with insulin was associated with dose-dependent increase of Hsp60 protein. In contrast, the abundance of Hsp60 was not affected by high concentration of glucose in these cells. To further determine the independent effects of hyperglycemia and insulin deficiency on the changes of myocardial Hsp60 and IGF-1 receptor, we used phlorizin to normalize blood glucose in diabetic rats. In the phlorizin-treated diabetic rats, myocardial Hsp60 was lower than that of the normal controls. In contrast, insulin treatment normalized myocardial Hsp60 in the diabetic rats. Because phlorizin does not alter insulin secretion, Hsp60 expression was modulated by insulin and not by hyperglycemia. Similar changes of Hsp60 and IGF-1 receptor were observed in the skeletal muscle of STZ-induced diabetic rats. These findings suggest that insulin deficiency is a novel mechanism that leads to downregulation of Hsp60 in diabetic muscle tissues. The development of diabetic cardiomyopathy might have involved downregulation of Hsp60 and subsequent reduction of IGF-1 receptor signaling.
A Genome Scan for Fasting Insulin and Fasting Glucose Identifies a Quantitative Trait Locus on Chromosome 17p
Authors: Rich Stephen S. , Bowden Donald W. , Haffner Steven M. , Norris Jill M. , Saad Mohammed F. , Mitchell Braxton D. , Rotter Jerome I. , Langefeld Carl D. , Hedrick Catherine C. , Wagenknecht Lynne E. , Bergman Richard N.
Published: March 2007

Plasma insulin and glucose concentrations are important quantitative phenotypes related to diabetes and the metabolic syndrome. Reports purporting to identify quantitative trait loci (QTLs) that contribute to the variation in fasting insulin and glucose concentrations are discrepant. As part of the Insulin Resistance Atherosclerosis Study (IRAS) Family Study, a genome scan was performed in African-American (n = 42) and Hispanic (n = 90) extended families to identify regions that may contain positional candidate genes for fasting insulin and fasting glucose (n = 1,604 subjects). There was significant evidence for linkage of fasting insulin to the short arm of chromosome 17 (logarithm of odds [LOD] = 3.30; 54 cM between D17S1294 and D17S1299, P = 1.0 × 10−4). The strongest evidence for linkage over all pedigrees for fasting glucose was also observed in this region (LOD = 1.44; 58 cM, P = 9.9 × 10−3). The results of this study provide impetus for future positional cloning of QTLs regulating insulin and glucose levels. Identifying genes in these regions should provide insight into the nature of genetic factors regulating plasma glucose and insulin concentrations.
Increased Phosphorylation of Akt Substrate of 160 kDa (AS160) in Rat Skeletal Muscle in Response to Insulin or Contractile Activity
Authors: Bruss Matthew D. , Arias Edward B. , Lienhard Gustav E. , Cartee Gregory D.
Published: March 2007

In 3T3-L1 adipocytes, insulin-stimulated GLUT4 translocation requires phosphorylation of the protein designated Akt substrate of 160 kDa (AS160). Both insulin and contractions activate Akt in skeletal muscle. Therefore, we assessed the effects in skeletal muscle of each stimulus on phosphorylation of proteins, including AS160, on the Akt phosphomotif. Isolated rat epitrochlearis muscles were incubated with insulin (for time course and dose response), stimulated to contract, or incubated with 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) and used to assess the following: serine-phosphorylation of Akt (P-Akt), immunoreactivity with an antibody recognizing the Akt phosphomotif (α-phospho-[Ser/Thr] Akt substrate [PAS]), and PAS immunoreactivity of samples immunoprecipitated with anti-AS160. P-Akt peaked at 5 min of insulin, and PAS immunoreactivity subsequently peaked for proteins of 250 kDa (10 min) and 160 kDa (15 min). P-Akt, PAS-160, and PAS-250 increased significantly with 0.6 nmol/l insulin. Contractile activity led to increased P-Akt and PAS immunoreactivity of proteins of 160 and 250 kDa. The 160-kDa protein was confirmed to be AS160 based on elevated PAS immunoreactivity in AS160 immunoprecipitates. Wortmannin inhibited insulin (120 nmol/l) and contraction effects on AS160 phosphorylation. Incubation with AICAR caused increased phosphorylation of AMP-activated protein kinase and AS160 but not Akt. Our working hypothesis is that phosphorylation of these putative Akt substrates is important for some of the insulin and contraction bioeffects.
Deficiency of Subsarcolemmal Mitochondria in Obesity and Type 2 Diabetes
Authors: Ritov Vladimir B. , Menshikova Elizabeth V. , He Jing , Ferrell Robert E. , Goodpaster Bret H. , Kelley David E.
Published: March 2007

The current study addresses a novel hypothesis of subcellular distribution of mitochondrial dysfunction in skeletal muscle in type 2 diabetes. Vastus lateralis muscle was obtained by percutaneous biopsy from 11 volunteers with type 2 diabetes; 12 age-, sex-, and weight-matched obese sedentary nondiabetic volunteers; and 8 lean volunteers. Subsarcolemmal and intermyofibrillar mitochondrial fractions were isolated by differential centrifugation and digestion techniques. Overall electron transport chain activity was similar in type 2 diabetic and obese subjects, but subsarcolemmal mitochondria electron transport chain activity was reduced in type 2 diabetic subjects (0.017 ± 0.003 vs. 0.034 ± 0.007 units/mU creatine kinase [CK], P = 0.01) and sevenfold reduced compared with lean subjects (P < 0.01). Electron transport chain activity in intermyofibrillar mitochondria was similar in type 2 diabetic and obese subjects, though reduced compared with lean subjects. A reduction in subsarcolemmal mitochondria was confirmed by transmission electron microscopy. Although mtDNA was lower in type 2 diabetic and obese subjects, the decrement in electron transport chain activity was proportionately greater, indicating functional impairment. Because of the potential importance of subsarcolemmal mitochondria for signal transduction and substrate transport, this deficit may contribute to the pathogenesis of muscle insulin resistance in type 2 diabetes.
Activation of the Peripheral Endocannabinoid System in Human Obesity
Authors: Engeli Stefan , Böhnke Jana , Feldpausch Mareike , Gorzelniak Kerstin , Janke Jürgen , Bátkai Sándor , Pacher Pál , Harvey-White Judy , Luft Friedrich C. , Sharma Arya M. , Jordan Jens
Published: March 2007

Obesity is the main risk factor for the development of type 2 diabetes. Activation of the central endocannabinoid system increases food intake and promotes weight gain. Blockade of the cannabinoid type 1 (CB-1) receptor reduces body weight in animals by central and peripheral actions; the role of the peripheral endocannabinoid system in human obesity is now being extensively investigated. We measured circulating endocannabinoid concentrations and studied the expression of CB-1 and the main degrading enzyme, fatty acid amide hydrolase (FAAH), in adipose tissue of lean (n = 20) and obese (n = 20) women and after a 5% weight loss in a second group of women (n = 17). Circulating levels of anandamide and 1/2-arachidonoylglycerol were increased by 35 and 52% in obese compared with lean women (P < 0.05). Adipose tissue mRNA levels were reduced by −34% for CB-1 and −59% for FAAH in obese subjects (P < 0.05). A strong negative correlation was found between FAAH expression in adipose tissue and circulating endocannabinoids. Circulating endocannabinoids and CB-1 or FAAH expression were not affected by 5% weight loss. The expression of CB-1 and FAAH was increased in mature human adipocytes compared with in preadipocytes and was found in several human tissues. Our findings support the presence of a peripheral endocannabinoid system that is upregulated in human obesity.
Attenuated Wnt Signaling Perturbs Pancreatic Growth but Not Pancreatic Function
Authors: Papadopoulou Stella , Edlund Helena
Published: March 2007

Mesenchymal-epithelial interactions are pivotal for proper pancreatic growth and development. We have earlier shown that the fibroblast growth factor (FGF) receptor 2 is expressed in pancreatic progenitor cells and that FGF10, the high-affinity ligand of the FGF receptor 2 isoform FGF receptor 2b, promotes expansion of pancreatic progenitors. The Wnt family of ligands, which signal to the Frizzled (Frz) type receptors, have also been shown to mediate mesenchymal-epithelial interactions and cell proliferation in a variety of different systems. Here, we show that Frz3, like FGF receptor 2, is expressed in the pancreatic epithelium during the proliferative phase of the embryonic pancreas in mice and that overexpression of a dominant-negative form of mouse Frz8 in pancreatic progenitors severely perturbs pancreatic growth. Nevertheless, the transgenic mice remain normoglycemic and display normal glucose tolerance and glucose-stimulated insulin secretion when challenged with exogenous glucose. The maintenance of normoglycemia in these mice appears to be the consequence of a relative increase in endocrine cell number per pancreatic area combined with enhanced insulin biosynthesis and insulin secretion. Collectively, our data provide evidence that Wnt signaling is required for pancreatic growth but not adult β-cell function.
Membrane Phosphoinositides Control Insulin Secretion Through Their Effects on ATP-Sensitive K+ Channel Activity
Authors: Lin Chia-Wei , Yan Feifei , Shimamura Satoko , Barg Sebastian , Shyng Show-Ling
Published: March 2007

ATP-sensitive K+ channels (KATP channels) of pancreatic β-cells play key roles in glucose-stimulated insulin secretion by linking metabolic signals to cell excitability. Membrane phosphoinositides, in particular phosphatidylinositol 4,5-bisphosphates (PIP2), stimulate KATP channels and decrease channel sensitivity to ATP inhibition; as such, they have been postulated as critical regulators of KATP channels and hence of insulin secretion in β-cells. Here, we tested this hypothesis by manipulating the interactions between KATP channels and membrane phospholipids in a β-cell line, INS-1, and assessing how the manipulations affect membrane excitability and insulin secretion. We demonstrate that disruption of channel interactions with PIP2 by overexpressing PIP2-insensitive channel subunits leads to membrane depolarization and elevated basal level insulin secretion at low glucose concentrations. By contrast, facilitation of channel interactions with PIP2 by upregulating PIP2 levels via overexpression of a lipid kinase, phosphatidylinositol 4-phosphate 5 kinase, decreases the ATP sensitivity of endogenous KATP channels by ∼26-fold and renders INS-1 cells hyperpolarized, unable to secrete insulin properly in the face of high glucose. Our results establish an important role of the interaction between membrane phosphoinositides and KATP channels in regulating insulin secretion.
ATP-Sensitive K+ Channel Signaling in Glucokinase-Deficient Diabetes
Authors: Remedi Maria S. , Koster Joseph C. , Patton Brian L. , Nichols Colin G.
Published: March 2007

As the rate-limiting controller of glucose metabolism, glucokinase represents the primary β-cell “glucose sensor.” Inactivation of both glucokinase (GK) alleles results in permanent neonatal diabetes; inactivation of a single allele causes maturity-onset diabetes of the young type 2 (MODY-2). Similarly, mice lacking both alleles (GK−/−) exhibit severe neonatal diabetes and die within a week, whereas heterozygous GK+/− mice exhibit markedly impaired glucose tolerance and diabetes, resembling MODY-2. Glucose metabolism increases the cytosolic [ATP]-to-[ADP] ratio, which closes ATP-sensitive K+ channels (KATP channels), leading to membrane depolarization, Ca2+ entry, and insulin exocytosis. Glucokinase insufficiency causes defective KATP channel regulation, which may underlie the impaired secretion. To test this prediction, we crossed mice lacking neuroendocrine glucokinase (nGK+/−) with mice lacking KATP channels (Kir6.2−/−). Kir6.2 knockout rescues perinatal lethality of nGK−/−, although nGK−/−Kir6.2−/− animals are postnatally diabetic and still die prematurely. nGK+/− animals are diabetic on the Kir6.2+/+ background but only mildly glucose intolerant on the Kir6.2−/− background. In the presence of glutamine, isolated nGK+/−Kir6.2−/− islets show improved insulin secretion compared with nGK+/−Kir6.2+/+. The significant abrogation of nGK−/− and nGK+/− phenotypes in the absence of KATP demonstrate that a major factor in glucokinase deficiency is indeed altered KATP signaling. The results have implications for understanding and therapy of glucokinase-related diabetes.
Serum Glucagon Counterregulatory Hormonal Response to Hypoglycemia Is Blunted in Congenital Hyperinsulinism
Authors: Hussain Khalid , Bryan Joseph , Christesen Henrick T. , Brusgaard Klaus , Aguilar-Bryan Lydia
Published: March 2007

The mechanisms involved in the release of glucagon in response to hypoglycemia are unclear. Proposed mechanisms include the activation of the autonomic nervous system via glucose-sensing neurons in the central nervous system, via the regulation of glucagon secretion by intra-islet insulin and zinc concentrations, or via direct ionic control, all mechanisms that involve high-affinity sulfonylurea receptor/inwardly rectifying potassium channel-type ATP-sensitive K+ channels. Patients with congenital hyperinsulinism provide a unique physiological model to understand glucagon regulation. In this study, we compare serum glucagon responses to hyperinsulinemic hypoglycemia versus nonhyperinsulinemic hypoglycemia. In the patient group (n = 20), the mean serum glucagon value during hyperinsulinemic hypoglycemia was 17.6 ± 5.7 ng/l compared with 59.4 ± 7.8 ng/l in the control group (n = 15) with nonhyperinsulinemic hypoglycemia (P < 0.01). There was no difference between the serum glucagon responses in children with diffuse, focal, and diazoxide-responsive forms of hyperinsulinism. The mean serum epinephrine and norepinephrine concentrations in the hyperinsulinemic group were 2,779 ± 431 pmol/l and 2.9 ± 0.7 nmol/l and appropriately rose despite the blunted glucagon response. In conclusion, the loss of ATP-sensitive K+ channels and or elevated intraislet insulin cannot explain the blunted glucagon release in all patients with congenital hyperinsulinism. Other possible mechanisms such as the suppressive effect of prolonged hyperinsulinemia on α-cell secretion should be considered.
Genetic and Nongenetic Regulation of CAPN10 mRNA Expression in Skeletal Muscle
Authors: Carlsson Emma , Poulsen Pernille , Storgaard Heidi , Almgren Peter , Ling Charlotte , Jensen Christine Bjørn , Madsbad Sten , Groop Leif , Vaag Allan , Ridderstråle Martin
Published: March 2007

The gene encoding calpain-10 (CAPN10) has been identified as a candidate gene for type 2 diabetes. Our aim was to study the impact of genetic (heritability and polymorphisms) and nongenetic (insulin, free fatty acids, and age) factors on CAPN10 mRNA expression in skeletal muscle using two different study designs. Muscle biopsies were obtained before and after hyperinsulinemic-euglycemic clamps from 166 young and elderly monozygotic and dizygotic twins as well as from 15 subjects with normal (NGT) or impaired glucose tolerance (IGT) exposed to an Intralipid infusion. We found hereditary effects on both basal and insulin-exposed CAPN10 mRNA expression. Carriers of the type 2 diabetes–associated single nucleotide polymorphism (SNP)-43 G/G genotype had reduced CAPN10 mRNA levels compared with subjects carrying the SNP-43 A-allele. Age had no significant influence on CAPN10 mRNA levels. Insulin had no significant effect on CAPN10 mRNA levels, neither in the twins nor in the basal state of the Intralipid study. However, after a 24-h infusion of Intralipid, we noted a significant increase in CAPN10 mRNA in response to insulin in subjects with NGT but not in subjects with IGT. In conclusion, we provide evidence that mRNA expression of CAPN10 in skeletal muscle is under genetic control. Glucose-tolerant but not glucose-intolerant individuals upregulate their CAPN10 mRNA levels in response to prolonged exposure to fat.
The CIDEA Gene V115F Polymorphism Is Associated With Obesity in Swedish Subjects
Authors: Dahlman Ingrid , Kaaman Maria , Jiao Hong , Kere Juha , Laakso Markku , Arner Peter
Published: March 2007

The cell death–inducing DFFA (DNA fragmentation factor-α)-like effector A (CIDEA) gene is implicated as an important regulator of body weight in mice and humans and is therefore a candidate gene for human obesity. Here, we characterize common CIDEA gene polymorphisms and investigate them for association with obesity in two independent Swedish samples; the first comprised 981 women and the second 582 men. Both samples display a large variation in BMI. The only detected coding polymorphism encodes an exon 4 V115F amino acid substitution, which is associated with BMI in both sexes (P = 0.021 for women, P = 0.023 for men, and P = 0.0015 for joint analysis). These results support a role for CIDEA alleles in human obesity. CIDEA-deficient mice display higher metabolic rate, and the gene cross-talks with tumor necrosis factor-α (TNF-α) in fat cells. We hypothesize that CIDEA alleles regulate human obesity through impact on basal metabolic rate and adipocyte TNF-α signaling.
The Human Glomerular Podocyte Is a Novel Target for Insulin Action
Authors: Coward Richard J.M. , Welsh Gavin I. , Yang Jing , Tasman Candida , Lennon Rachel , Koziell Ania , Satchell Simon , Holman Geoffrey D. , Kerjaschki Dontscho , Tavaré Jeremy M. , Mathieson Peter W. , Saleem Moin A.
Published: March 2007

Microalbuminuria is significant both as the earliest stage of diabetic nephropathy and as an independent cardiovascular risk factor in nondiabetic subjects, in whom it is associated with insulin resistance. The link between disorders of cellular insulin metabolism and albuminuria has been elusive. Here, we report using novel conditionally immortalized human podocytes in vitro and human glomeruli ex vivo that the podocyte, the principal cell responsible for prevention of urinary protein loss, is insulin responsive and able to approximately double its glucose uptake within 15 min of insulin stimulation. Conditionally immortalized human glomerular endothelial cells do not respond to insulin, suggesting that insulin has a specific effect on the podocyte in the glomerular filtration barrier. The insulin response of the podocyte occurs via the facilitative glucose transporters GLUT1 and GLUT4, and this process is dependent on the filamentous actin cytoskeleton. Insulin responsiveness in this key structural component of the glomerular filtration barrier may have central relevance for understanding of diabetic nephropathy and for the association of albuminuria with states of insulin resistance.
Large Genomic Rearrangements in the Hepatocyte Nuclear Factor-1β (TCF2) Gene Are the Most Frequent Cause of Maturity-Onset Diabetes of the Young Type 5
Authors: Bellanné-Chantelot Christine , Clauin Séverine , Chauveau Dominique , Collin Philippe , Daumont Michèle , Douillard Claire , Dubois-Laforgue Danièle , Dusselier Laurent , Gautier Jean-François , Jadoul Michel , Laloi-Michelin Marie , Jacquesson Laetitia , Larger Etienne , Louis Jacques , Nicolino Marc , Subra Jean-François , Wilhem Jean-Marie , Young Jacques , Velho Gilberto , Timsit José
Published: March 2007

Maturity-onset diabetes of the young (MODY) 5 is caused by mutations in the TCF2 gene encoding the transcription factor hepatocyte nuclear factor-1β. However, in 60% of the patients with a phenotype suggesting MODY5, no point mutation is detected in TCF2. We have hypothesized that large genomic rearrangements of TCF2 that are missed by conventional screening methods may account for this observation. In 40 unrelated patients presenting with MODY5 phenotype, TCF2 was screened for mutations by sequencing. Patients without mutations were then screened for TCF2 rearrangements by the quantitative multiplex PCR of short fluorescent fragments (QMPSF). Among the 40 patients, the overall detection rate was 70%: 18 had point mutations, 9 had whole-gene deletions, and 1 had a deletion of a single exon. Similar phenotypes were observed in patients with mutations and in subjects with large deletions. These results suggest that MODY5 is more prevalent than previously reported, with one-third of the cases resulting from large deletions of TCF2. Because QMPSF is more rapid and cost effective than sequencing, we propose that patients whose phenotype is consistent with MODY5 should be screened first with the QMPSF assay. In addition, other MODY genes should be screened for large genomic rearrangements.
Effect of a Sustained Reduction in Plasma Free Fatty Acid Concentration on Intramuscular Long-Chain Fatty Acyl-CoAs and Insulin Action in Type 2 Diabetic Patients
Authors: Bajaj Mandeep , Suraamornkul Swangjit , Romanelli Anthony , Cline Gary W. , Mandarino Lawrence J. , Shulman Gerald I. , DeFronzo Ralph A.
Published: March 2007

To investigate the effect of a sustained (7-day) decrease in plasma free fatty acid (FFA) concentrations on insulin action and intramyocellular long-chain fatty acyl-CoAs (LCFA-CoAs), we studied the effect of acipimox, a potent inhibitor of lipolysis, in seven type 2 diabetic patients (age 53 ± 3 years, BMI 30.2 ± 2.0 kg/m2, fasting plasma glucose 8.5 ± 0.8 mmol/l, HbA1c 7.5 ± 0.4%). Subjects received an oral glucose tolerance test (OGTT) and 120-min euglycemic insulin (80 mU/m2 per min) clamp with 3-[3H]glucose/vastus lateralis muscle biopsies to quantitate rates of insulin-mediated whole-body glucose disposal (Rd) and intramyocellular LCFA-CoAs before and after acipimox (250 mg every 6 h for 7 days). Acipimox significantly reduced fasting plasma FFAs (from 563 ± 74 to 230 ± 33 μmol/l; P < 0.01) and mean plasma FFAs during the OGTT (from 409 ± 44 to 184 ± 22 μmol/l; P < 0.01). After acipimox, decreases were seen in fasting plasma insulin (from 78 ± 18 to 42 ± 6 pmol/l; P < 0.05), fasting plasma glucose (from 8.5 ± 0.8 to 7.0 ± 0.5 mmol/l; P < 0.02), and mean plasma glucose during the OGTT (from 14.5 ± 0.8 to 13.0 ± 0.8 mmol/l; P < 0.05). After acipimox, insulin-stimulated Rd increased from 3.3 ± 0.4 to 4.4 ± 0.4 mg · kg−1 · min−1 (P < 0.03), whereas suppression of endogenous glucose production (EGP) was similar and virtually complete during both insulin clamp studies (0.16 ± 0.10 vs. 0.14 ± 0.10 mg · kg−1 · min−1; P > 0.05). Basal EGP did not change after acipimox (1.9 ± 0.2 vs. 1.9 ± 0.2 mg · kg−1 · min−1). Total muscle LCFA-CoA content decreased after acipimox treatment (from 7.26 ± 0.58 to 5.64 ± 0.79 nmol/g; P < 0.05). Decreases were also seen in muscle palmityl CoA (16:0; from 1.06 ± 0.10 to 0.75 ± 0.11 nmol/g; P < 0.05), palmitoleate CoA (16:1; from 0.48 ± 0.05 to 0.33 ± 0.05 nmol/g; P = 0.07), oleate CoA (18:1; from 2.60 ± 0.11 to 1.95 ± 0.31 nmol/g; P < 0.05), linoleate CoA (18:2; from 1.81 ± 0.26 to 1.38 ± 0.18 nmol/g; P = 0.13), and linolenate CoA (18:3; from 0.27 ± 0.03 to 0.19 ± 0.02 nmol/g; P < 0.03) levels after acipimox treatment. Muscle stearate CoA (18:0) did not decrease after acipimox treatment. The increase in Rd correlated strongly with the decrease in muscle palmityl CoA (r = 0.75, P < 0.05), oleate CoA (r = 0.76, P < 0.05), and total muscle LCFA-CoA (r = 0.74, P < 0.05) levels. Plasma adiponectin did not change significantly after acipimox treatment (7.9 ± 1.8 vs. 7.5 ± 1.5 μg/ml). These data demonstrate that the reduction in intramuscular LCFA-CoA content is closely associated with enhanced insulin sensitivity in muscle after a chronic reduction in plasma FFA concentrations in type 2 diabetic patients despite the lack of an effect on plasma adiponectin concentration.
Adipocyte Lipases and Defect of Lipolysis in Human Obesity
Authors: Langin Dominique , Dicker Andrea , Tavernier Geneviève , Hoffstedt Johan , Mairal Aline , Rydén Mikael , Arner Erik , Sicard Audrey , Jenkins Christopher M. , Viguerie Nathalie , van Harmelen Vanessa , Gross Richard W. , Holm Cecilia , Arner Peter
Published: March 2007

The mobilization of fat stored in adipose tissue is mediated by hormone-sensitive lipase (HSL) and the recently characterized adipose triglyceride lipase (ATGL), yet their relative importance in lipolysis is unknown. We show that a novel potent inhibitor of HSL does not inhibit other lipases. The compound counteracted catecholamine-stimulated lipolysis in mouse adipocytes and had no effect on residual triglyceride hydrolysis and lipolysis in HSL-null mice. In human adipocytes, catecholamine- and natriuretic peptide–induced lipolysis were completely blunted by the HSL inhibitor. When fat cells were not stimulated, glycerol but not fatty acid release was inhibited. HSL and ATGL mRNA levels increased concomitantly during adipocyte differentiation. Abundance of the two transcripts in human adipose tissue was highly correlated in habitual dietary conditions and during a hypocaloric diet, suggesting common regulatory mechanisms for the two genes. Comparison of obese and nonobese subjects showed that obesity was associated with a decrease in catecholamine-induced lipolysis and HSL expression in mature fat cells and in differentiated preadipocytes. In conclusion, HSL is the major lipase for catecholamine- and natriuretic peptide–stimulated lipolysis, whereas ATGL mediates the hydrolysis of triglycerides during basal lipolysis. Decreased catecholamine-induced lipolysis and low HSL expression constitute a possibly primary defect in obesity.
Mechanisms of Glucose-Induced Secretion of Pancreatic-Derived Factor (PANDER or FAM3B) in Pancreatic β-Cells
Authors: Yang Jichun , Robert Claudia E. , Burkhardt Brant R. , Young Robert A. , Wu Jianmei , Gao Zhiyong , Wolf Bryan A.
Published: March 2007

Pancreatic-derived factor (PANDER) is an islet-specific cytokine present in both pancreatic α- and β-cells, which, in vitro, induces β-cell apoptosis of primary islet and cell lines. In this study, we investigated whether PANDER is secreted by pancreatic α- and β-cells and whether PANDER secretion is regulated by glucose and other insulin secretagogues. In mouse-derived insulin-secreting β-TC3 cells, PANDER secretion in the presence of stimulatory concentrations of glucose was 2.8 ± 0.4-fold higher (P < 0.05) than without glucose. Insulin secretion was similarly increased by glucose in the same cells. The total concentration of secreted PANDER in the medium was ∼6–10 ng/ml (0.3–0.5 nmol/l) after a 24-h culture with glucose. l-Glucose failed to stimulate PANDER secretion in β-TC3 cells. KCl stimulated PANDER secretion 2.1 ± 0.1-fold compared with control without glucose. An l-type Ca2+ channel inhibitor, nifedipine, completely blocked both glucose- or KCl-induced insulin and PANDER secretion. In rat-derived INS-1 cells, glucose (20 mmol/l) stimulated PANDER secretion 4.4 ± 0.9-fold, while leucine plus glutamine stimulated 4.4 ± 0.7-fold compared with control without glucose. In mouse islets overexpressing PANDER, glucose (20 mmol/l) stimulated PANDER secretion 3.2 ± 0.5-fold (P < 0.05) compared with basal (3 mmol/l glucose). PANDER was also secreted by α-TC3 cells but was not stimulated by glucose. Mutations of cysteine 229 or of cysteines 91 and 229 to serine, which may form one disulfide bond, and truncation of the COOH-terminus or NH2-terminus of PANDER all resulted in failure of PANDER secretion, even though these mutant or truncated PANDERs were highly expressed within the cells. In conclusion, we found that 1) PANDER is secreted from both pancreatic α- and β-cells, 2) glucose stimulates PANDER secretion dose dependently in β-cell lines and primary islets but not in α-cells, 3) PANDER is likely cosecreted with insulin via the same regulatory mechanisms, and 4) structure and conformation is vital for PANDER secretion.
Protein Tyrosine Phosphatase-1B Gene PTPN1
Authors: Spencer-Jones Nicola J. , Wang Xiaoling , Snieder Harold , Spector Tim D. , Carter Nicholas D. , O’Dell Sandra D.
Published: March 2007

Protein tyrosine phosphatase-1B negatively regulates leptin and insulin signaling, potentially contributing to hormonal resistance. We selected six tagging single nucleotide polymorphisms (SNPs) representing 18 common variants in the protein tyrosine phosphatase-1B gene (PTPN1) and tested their effect on serum leptin, body fat, and measures of insulin sensitivity and the metabolic syndrome in a large sample of normal female Caucasian twins (n = 2,777; mean age, 47.4 ± 12.5 years) from the St. Thomas’ U.K. Adult Twin Registry. SNP rs718049 was significantly associated with waist circumference (P = 0.008) and central fat (P = 0.035) and also with Avignon’s insulin sensitivity index (SiM) (P = 0.007), fasting insulin (P = 0.004), fasting glucose (P = 0.022), triglyceride (P = 0.023), and systolic blood pressure (P = 0.046). SNPs rs2282146 and rs1885177 were associated with SiM (P = 0.049 and P = 0.013, respectively), and 1484insG was associated with triglyceride (P = 0.029). A risk haplotype (7.3%) was associated with lower SiM (P = 0.036) and a protective haplotype (5.2%) with higher SiM (P = 0.057), with mean values in homozygotes differing by >1 SD (P = 0.003). The protective haplotype also showed lower triglyceride (P = 0.045) and lower systolic blood pressure (P = 0.006). Fine mapping analyses predicted significant associations with SiM and fasting insulin for several ungenotyped SNPs. PTPN1 variants appear to contribute to central fat and metabolic syndrome traits, secondary to their effect on insulin sensitivity.
A Polygenic Model of the Metabolic Syndrome With Reduced Circulating and Intra-Adipose Glucocorticoid Action
Authors: Morton Nicholas M. , Densmore Valerie , Wamil Malgorzata , Ramage Lynne , Nichol Katherine , Bünger Lutz , Seckl Jonathan R. , Kenyon Christopher J.
Published: March 2007

Despite major advances in understanding monogenic causes of morbid obesity, the complex genetic and environmental etiology of idiopathic metabolic syndrome remains poorly understood. One hypothesis suggests that similarities between the metabolic disease of plasma glucocorticoid excess (Cushing’s syndrome) and idiopathic metabolic syndrome results from increased glucocorticoid reamplification within adipose tissue by 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD-1). Indeed, 11β-HSD-1 is now a major therapeutic target. Because much supporting evidence for a role of adipose 11β-HSD-1 comes from transgenic or obese rodents with single-gene mutations, we investigated whether the predicted traits of metabolic syndrome and glucocorticoid metabolism were coassociated in a unique polygenic model of obesity developed by long-term selection for divergent fat mass (Fat and Lean mice with 23 vs. 4% fat as body weight, respectively). Fat mice exhibited an insulin-resistant metabolic syndrome including fatty liver and hypertension. Unexpectedly, Fat mice had a marked intra-adipose (11β-HSD-1) and plasma glucocorticoid deficiency but higher liver glucocorticoid action. Furthermore, metabolic disease was exacerbated only in Fat mice when challenged with exogenous glucocorticoids or a high-fat diet. Our data suggest that idiopathic metabolic syndrome might associate with such a novel pattern of glucocorticoid action and sensitivity in humans, with implications for tissue-specific therapeutic targeting of 11β-HSD-1.
On the Edge of Autoimmunity
Authors: Bruder Dunja , Westendorf Astrid M. , Hansen Wiebke , Prettin Silvia , Gruber Achim D. , Qian Yingjie , von Boehmer Harald , Mahnke Karsten , Buer Jan
Published: March 2007

Targeting of antigens to immature dendritic cells has been shown to result in antigen-specific T-cell tolerance in vivo. In the INS-HA/TCR-HA transgenic mouse model for type 1 diabetes, we tested the potential of the dendritic cell–specific monoclonal antibody DEC-205 conjugated to the hemagglutinin (HA) antigen (DEC-HA) to prevent disease onset. Whereas untreated INS-HA/TCR-HA mice all develop insulitis, and ∼40% of these mice become diabetic, repeated injection of newborn mice with DEC-HA protected almost all mice from disease development. Histological examination of the pancreata revealed significant reduction of peri-islet infiltrations in DEC-HA–treated mice, and the islet structure remained intact. Moreover, HA-specific CD4+ T-cells from anti–DEC-HA–treated INS-HA/TCR-HA mice exhibited increased expression of Foxp3, cytotoxic T-lymphocyte–associated antigen-4, and the immunosuppressive cytokines interleukin-10 and transforming growth factor-β. The findings indicate that targeting of the HA antigen to immature dendritic cells in vivo leads to a relative increase of antigen-specific Foxp3+ regulatory T-cells that suppress the development of type 1 diabetes. Our results provide a basis for the development of novel strategies focusing on prevention rather than treatment of autoimmune diseases.
Inhibition of Preproinsulin Gene Expression by Leptin Induction of Suppressor of Cytokine Signaling 3 in Pancreatic β-Cells
Authors: Laubner Katharina , Kieffer Timothy J. , Lam Ni T. , Niu Xinjie , Jakob Franz , Seufert Jochen
Published: March 2007

Leptin inhibits insulin secretion and preproinsulin gene expression in pancreatic β-cells, but signal transduction pathways and molecular mechanisms underlying this effect are poorly characterized. In this study, we analyzed leptin-mediated signal transduction and preproinsulin gene regulation at the molecular level in pancreatic β-cells. Leptin stimulation led to janus kinase (JAK)2-dependent phosphorylation and nuclear translocation of the transcription factors signal transducer and activator of transcription (STAT)3 and STAT5b in INS-1 β-cells. Leptin also induced mRNA expression of the JAK-STAT inhibitor suppressor of cytokine signaling (SOCS)3 in INS-1 β-cells and human pancreatic islets in vitro and in pancreatic islets of ob/ob mice in vivo. Transcriptional activation of the rat SOCS3 promoter by leptin was observed with concomitant leptin-induced STAT3 and STAT5b DNA binding to specific promoter regions. Unexpectedly, SOCS3 inhibited both basal and STAT3/5b-dependent rat preproinsulin 1 gene promoter activity in INS-1 cells. These results suggest that SOCS3 represents a transcriptional inhibitor of preproinsulin gene expression, which is induced by leptin through JAK-STAT3/5b signaling in pancreatic β-cells. In conclusion, although SOCS3 is believed to be a negative feedback regulator of JAK-STAT signaling, our findings suggest involvement of SOCS3 in a direct gene regulatory pathway downstream of leptin-activated JAK-STAT signaling in pancreatic β-cells.
Skeletal Muscle Insulin Signaling Defects Downstream of Phosphatidylinositol 3-Kinase at the Level of Akt Are Associated With Impaired Nonoxidative Glucose Disposal in HIV Lipodystrophy
Authors: Haugaard Steen B. , Andersen Ove , Madsbad Sten , Frøsig Christian , Iversen Johan , Nielsen Jens Ole , Wojtaszewski Jørgen F.P.
Published: March 2007

More than 40% of HIV-infected patients on highly active antiretroviral therapy (HAART) experience fat redistribution (lipodystrophy), a syndrome associated with insulin resistance primarily affecting insulin-stimulated nonoxidative glucose metabolism (NOGMins). Skeletal muscle biopsies, obtained from 18 lipodystrophic nondiabetic patients (LIPO) and 18 nondiabetic patients without lipodystrophy (NONLIPO) before and during hyperinsulinemic (40 mU · m−2 · min−1)-euglycemic clamps, were analyzed for insulin signaling effectors. All patients were on HAART. Both LIPO and NONLIPO patients were normoglycemic (4.9 ± 0.1 and 4.8 ± 0.1 mmol/l, respectively); however, NOGMins was reduced by 49% in LIPO patients (P < 0.001). NOGMins correlated positively with insulin-stimulated glycogen synthase activity (I-form, P < 0.001, n = 36). Glycogen synthase activity (I-form) correlated inversely with phosphorylation of glycogen synthase sites 2+2a (P < 0.001, n = 36) and sites 3a+b (P < 0.001, n = 36) during clamp. Incremental glycogen synthase-kinase–3α and –3β phosphorylation was attenuated in LIPO patients (Ps < 0.05). Insulin-stimulated Akt Ser473 and Akt Thr308 phosphorylation was decreased in LIPO patients (P < 0.05), whereas insulin receptor substrate-1–associated phosphatidylinositol (PI) 3-kinase activity increased significantly (P < 0.001) and similarly (NS) in both groups during clamp. Thus, low glycogen synthase activity explained impaired NOGMins in HIV lipodystrophy, and insulin signaling defects were downstream of PI 3-kinase at the level of Akt. These results suggest mechanisms for the insulin resistance greatly enhancing the risk of type 2 diabetes in HIV lipodystrophy.
Unraveling the Temporal Pattern of Diet-Induced Insulin Resistance in Individual Organs and Cardiac Dysfunction in c57bl/6 Mice
Authors: Park So-Young , Cho You-Ree , Kim Hyo-Jeong , Higashimori Takamasa , Danton Cheryl , Lee Mi-Kyung , Dey Asim , Rothermel Beverly , Kim Young-Bum , Kalinowski April , Russell Kerry S. , Kim Jason K.
Published: March 2007

Type 2 diabetes is a heterogeneous disease characterized by insulin resistance and altered glucose and lipid metabolism in multiple organs. To understand the complex series of events that occur during the development of obesity-associated diabetes, we examined the temporal pattern of changes in insulin action and glucose metabolism in individual organs during chronic high-fat feeding in C57BL/6 mice. Insulin-stimulated cardiac glucose metabolism was significantly reduced after 1.5 weeks of high-fat feeding, and cardiac insulin resistance was associated with blunted Akt-mediated insulin signaling and GLUT4 levels. Insulin resistance in skeletal muscle, adipose tissue, and liver developed in parallel after 3 weeks of high-fat feeding. Diet-induced whole-body insulin resistance was associated with increased circulating levels of resistin and leptin but unaltered adiponectin levels. High-fat feeding caused insulin resistance in skeletal muscle that was associated with significantly elevated intramuscular fat content. In contrast, diet-induced hepatic insulin resistance developed before a marked increase in intrahepatic triglyceride levels. Cardiac function gradually declined over the course of high-fat feeding, and after 20 weeks of high-fat diet, cardiac dysfunction was associated with mild hyperglycemia, hyperleptinemia, and reduced circulating adiponectin levels. Our findings demonstrate that cardiac insulin resistance is an early adaptive event in response to obesity and develops before changes in whole-body glucose homeostasis. This suggests that obesity-associated defects in cardiac function may not be due to insulin resistance per se but may be attributable to chronic alteration in cardiac glucose and lipid metabolism and circulating adipokines.
Plasma Cholesteryl Ester Transfer Is a Determinant of Intima-Media Thickness in Type 2 Diabetic and Nondiabetic Subjects
Authors: de Vries Rindert , Perton Frank G. , Dallinga-Thie Geesje M. , van Roon Arie M. , Wolffenbuttel Bruce H.R. , van Tol Arie , Dullaart Robin P.F.
Published: March 2007

We tested whether carotid artery intima-media thickness (IMT) is associated with plasma cholesteryl ester transfer (CET) and/or the plasma cholesteryl ester transfer protein (CETP) concentration in type 2 diabetic and control subjects. In 87 male and female subjects with type 2 diabetes (nonsmokers, no insulin or lipid-lowering drug treatment) and 82 control subjects, IMT, plasma CET, CETP mass, and lipids were determined. HDL cholesterol was lower, whereas IMT, pulse pressure, plasma triglycerides, and plasma CET and CETP concentration were higher in diabetic patients versus control subjects. In diabetic patients, plasma CET was positively determined by triglycerides (P < 0.001), non-HDL cholesterol (P < 0.001), CETP (P = 0.002), and the interaction between CETP and triglycerides (P = 0.004). In control subjects, plasma CET was positively related to triglycerides (P < 0.001) and non-HDL cholesterol (P < 0.001). HDL cholesterol was inversely related to plasma CET in each group (P < 0.01 for both). IMT was positively associated with plasma CET in diabetic (P = 0.05) and control (P < 0.05) subjects after adjustment for age, sex, and pulse pressure. No independent relationship with plasma CETP mass was found. Plasma CET is a positive determinant of IMT. Plasma CETP mass, in turn, is a determinant of CET with an increasing effect at higher triglycerides. These data, therefore, provide a rationale to evaluate the effects of CETP inhibitor treatment on plasma CET and on cardiovascular risk in diabetes-associated hypertriglyceridemia.
HFE Genetic Variability, Body Iron Stores, and the Risk of Type 2 Diabetes in U.S. Women
Authors: Qi Lu , Meigs James , Manson JoAnn E. , Ma Jing , Hunter David , Rifai Nader , Hu Frank B.
Published: March 2007

To determine whether the HFE gene variants H63D and C282Y are associated with body iron stores and the risk of type 2 diabetes, we conducted a nested case-control study of 714 incident cases of type 2 diabetes and 1,120 matching control subjects in a prospective cohort, the Nurses’ Health Study. In both healthy control and diabetic case subjects, H63D homozygosity, C282Y, and the compound heterozygotes were associated with significantly higher levels of plasma ferritin and significantly lower ratios of transferrin receptors to ferritin. Such effects were independent of age, BMI, and lifestyle factors. Overall, there were no significant differences in genotypes of H63D and C282Y between the case and control subjects. A meta-analysis of 4,245 case and 5,982 control subjects indicated a null association of C282Y with diabetes risk, whereas carriers of H63D or the compound heterozygotes had marginally increased risk (odds ratio [OR] 1.11 [95% CI 1.00–1.25] and 1.60 [0.99–2.60], respectively). In addition, we found a significant interaction between HFE variants and heme iron intake (P for interaction = 0.029). The ORs of type 2 diabetes across increasing quartiles of heme iron were 1.00, 1.21 (0.72–2.01), 1.72 (1.03–2.88), and 1.49 (0.91–2.46) among the participants with either the H63D or C282Y variant, whereas the ORs were 1.00, 0.71 (0.49–1.05), 1.12 (0.76–1.66), and 0.96 (0.65–1.42) among those with wild-type genotypes. Our data indicate significant effects of H63D and C282Y on body iron stores and suggest a potential interaction between HFE genotypes and heme iron intake in relation to the risk of type 2 diabetes.
Increased Hepatic Levels of the Insulin Receptor Inhibitor, PC-1/NPP1, Induce Insulin Resistance and Glucose Intolerance
Authors: Dong Hengjiang , Maddux Betty A. , Altomonte Jennifer , Meseck Marcia , Accili Domenico , Terkeltaub Robert , Johnson Kristen , Youngren Jack F. , Goldfine Ira D.
Published: March 2007

The ectoenzyme, plasma cell membrane glycoprotein-1 (PC-1), is an insulin receptor (IR) inhibitor that is elevated in cells and tissues of insulin-resistant humans. However, the effects of PC-1 overexpression on insulin action have not been studied in animal models. To produce mice with overexpression of PC-1 in liver, a key glucose regulatory organ in this species, we injected them with a PC-1 adenovirus vector that expresses human PC-1. Compared with controls, these mice had two- to threefold elevations of PC-1 content in liver but no changes in other tissues such as skeletal muscle. In liver of PC-1 animals, insulin-stimulated IR tyrosine kinase and Akt/protein kinase B activation were both decreased. In this tissue, the IR-dependent nuclear factor Foxo1 was increased along with two key gluconeogenic enzymes, glucose-6-phosphatase and phosphenolpyruvate carboxykinase. The PC-1 animals had 30–40 mg/dl higher glucose levels and twofold higher insulin levels. During glucose tolerance tests, these animals had peak glucose levels that were >100 mg/dl higher than those of controls. These in vivo data support the concept, therefore, that PC-1 plays a role in insulin resistance and suggest that animals with overexpression of human PC-1 in liver may be interesting models to investigate this pathological process.
Interaction of Fish Oil and Conjugated Linoleic Acid in Affecting Hepatic Activity of Lipogenic Enzymes and Gene Expression in Liver and Adipose Tissue
Authors: Ide Takashi
Published: March 2007

The interaction of dietary fish oil and conjugated linoleic acid (CLA) in affecting the activity of hepatic lipogenic enzymes and gene expression in liver and adipose tissue was examined in mice. A diet containing 1.0% CLA, mainly composed of 9cis,11trans- and 10trans,12cis-octadecadienoic acids at equivalent amounts, greatly decreased adipose tissue weight and serum concentrations of leptin and adiponectin and was accompanied by a downregulation of the expression of various adipocyte-abundant genes in epididymal adipose tissue. However, CLA increased the serum insulin concentration fourfold, and it caused hepatomegaly, with huge increases in the triacylglycerol level and the activity and mRNA levels of hepatic lipogenic enzymes. Different amounts (1.5, 3, and 6%) of fish oil added to CLA-containing diets dose-dependently downregulated parameters of lipogenesis and were accompanied by a parallel decrease in the triacylglycerol level in the liver. The supplementation of CLA-containing diets with fish oil was also associated with an increase in fat pad mass and mRNA levels of many adipocyte-abundant genes in epididymal adipose tissue along with a normalization of serum concentrations of leptin and adiponectin in a dose-dependent manner. However, in mice fed a diet containing 1.5% fish oil and CLA in whom fat pad mass was still low and comparable to that in the animals fed CLA alone, the serum insulin concentration greatly exceeded (twofold) the value observed in mice fed CLA alone, indicating an aggravation of insulin resistance. This hyperinsulinemia was ameliorated with increasing amounts of fish oil in the diets. Apparently, many of the physiological effects of CLA can be reversed by fish oil.
High Glucose Inhibits Apoptosis Induced by Serum Deprivation in Vascular Smooth Muscle Cells via Upregulation of Bcl-2 and Bcl-xl
Authors: Li Haikun , Télémaque Sabine , Miller Richard E. , Marsh James D.
Published: March 2007

Apoptosis plays a critical role in normal vascular development and atherosclerosis. To test the hypothesis that diabetic vasculopathy may be due in part to altered apoptosis pathways, we investigated the effects of high glucose treatment on serum withdrawal–induced apoptosis, expression of Bcl-2 family members, and inhibitor of apoptosis protein (IAP)-1 in vascular smooth muscle cells (VSMCs). Treatment with a high concentration of glucose (22 mmol/l) significantly attenuated apoptosis in response to serum withdrawal in cultured rat VSMCs compared with cells treated with a normal glucose concentration (5.5 mmol/l). This attenuation was accompanied by a significant decrease in the caspase-3 activity in comparison with the normal glucose group. Furthermore, exposure of VSMCs to high glucose markedly increased the abundance of Bcl-2 and Bcl-xl mRNAs compared with treatment with normal glucose, while expression of bax and IAP-1 mRNA remained unchanged. Our results suggest that high glucose suppresses serum withdrawal–induced apoptosis in VSMCs by upregulating expression of Bcl-2 and Bcl-xl, suggesting that enhanced expression of antiapoptotic proteins may play an important role in the development of macrovascular complications in diabetes.