bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhanced Sarcolemmal FAT/CD36 Content and Triacylglycerol Storage in Cardiac Myocytes From Obese Zucker Rats
Authors: Coort Susan L.M. , Hasselbaink Danny M. , Koonen Debby P.Y. , Willems Jodil , Coumans Will A. , Chabowski Adrian , van der Vusse Ger J. , Bonen Arend , Glatz Jan F.C. , Luiken Joost J.F.P.
Published: March 2007

In obesity, the development of cardiomyopathy is associated with the accumulation of myocardial triacylglycerols (TAGs), possibly stemming from elevation of myocardial long-chain fatty acid (LCFA) uptake. Because LCFA uptake is regulated by insulin and contractions, we examined in cardiac myocytes from lean and obese Zucker rats the effects of insulin and the contraction-mimetic agent oligomycin on the initial rate of LCFA uptake, subcellular distribution of FAT/CD36, and LCFA metabolism. In cardiac myocytes from obese Zucker rats, under basal conditions, FAT/CD36 was relocated to the sarcolemma at the expense of intracellular stores. In addition, the LCFA uptake rate, LCFA esterification rate into TAGs, and the intracellular unesterified LCFA concentration each were significantly increased. All these metabolic processes were normalized by the FAT/CD36 inhibitor sulfo-N-succinimidyloleate, indicating its antidiabetic potential. In cardiac myocytes isolated from lean rats, in vitro administration of insulin induced the translocation of FAT/CD36 to the sarcolemma and stimulated initial rates of LCFA uptake and TAG esterification. In contrast, in myocytes from obese rats, insulin failed to alter the subcellular localization of FAT/CD36 and the rates of LCFA uptake and TAG esterification. In cardiac myocytes from lean and obese animals, oligomycin stimulated the initial rates of LCFA uptake and oxidation, although oligomycin only induced the translocation of FAT/CD36 to the sarcolemma in lean rats. The present results indicate that in cardiac myocytes from obese Zucker rats, a permanent relocation of FAT/CD36 to the sarcolemma is responsible for myocardial TAG accumulation. Furthermore, in vitro these cardiac myocytes, although sensitive to contraction-like stimulation, were completely insensitive to insulin, as the basal conditions in hyperinsulinemic, obese animals resemble the insulin-stimulated condition in lean littermates.
Regulation of Resistin Expression and Circulating Levels in Obesity, Diabetes, and Fasting
Authors: Rajala Michael W. , Qi Yong , Patel Hiral R. , Takahashi Nobuhiko , Banerjee Ronadip , Pajvani Utpal B. , Sinha Madhur K. , Gingerich Ronald L. , Scherer Philipp E. , Ahima Rexford S.
Published: March 2007

Resistin was originally reported as an adipose tissue–specific hormone that provided a link between obesity and diabetes. Resistin protein level was elevated in obese mice and decreased by insulin-sensitizing thiazolidinediones. Immunoneutralization of resistin improved insulin sensitivity in diet-induced obese mice, while the administration of exogenous resistin induced insulin resistance. More recently, we have shown that ablation of the resistin gene in mice decreased fasting glucose through impairment of gluconeogenesis, while resistin treatment in these knockout mice increased hepatic glucose production. However, the link between resistin and glucose homeostasis has been questioned by studies demonstrating reduced, rather than increased, resistin mRNA expression in obese and diabetic mice. To better understand the regulation of resistin, we developed a sensitive and specific RIA resistin that could accurately measure serum resistin levels in several mouse models. We show that while resistin mRNA is indeed suppressed in obese mice, the circulating resistin level is significantly elevated and positively correlated with insulin, glucose, and lipids. Both resistin mRNA expression and protein levels in Lepob/ob mice are suppressed by leptin treatment in parallel with reductions in glucose and insulin. In wild-type mice, serum resistin increases after nocturnal feeding, concordant with rising levels of insulin. Resistin mRNA and protein levels decline in parallel with glucose and insulin during fasting and are restored after refeeding. We performed clamp studies to determine whether resistin is causally related to insulin and glucose. Adipose resistin expression and serum resistin increased in response to hyperinsulinemia and further in response to hyperglycemia. Taken together, these findings suggest that the nutritional regulation of resistin and changes in resistin gene expression and circulating levels in obesity are mediated, at least in part, through insulin and glucose.
Hormone-Sensitive Lipase Has a Role in Lipid Signaling for Insulin Secretion but Is Nonessential for the Incretin Action of Glucagon-Like Peptide 1
Authors: Peyot Marie-Line , Nolan Christopher J. , Soni Krishnakant , Joly Erik , Lussier Roxane , Corkey Barbara E. , Wang Shu Pei , Mitchell Grant A. , Prentki Marc
Published: March 2007

We previously reported decreased glucose-stimulated insulin secretion (GSIS) in hormone-sensitive lipase-null mice (HSL−/−), both in vivo and in vitro. The focus of the current study was to gain further insight into the signaling role and regulation of lipolysis in islet tissue. The effect of glucagon-like peptide 1 (GLP-1) on GSIS was also studied, as GLP-1 could augment GSIS via protein kinase A activation of HSL and lipolysis. Freshly isolated islets from fasted and fed male HSL−/− and wild-type (HSL+/+) mice were studied at ages 4 and 7 months. Neutral cholesteryl ester hydrolase activity was markedly reduced in islets from both 4- and 7-month-old male HSL−/− mice, whereas a marked deficiency in triglyceride lipase activity became evident only in the older mice. The deficiencies in lipase activities were associated with higher islet triglyceride content and reduced lipolysis at basal glucose levels. Lipolysis was stimulated by high glucose in islets of both wild-type and HSL-null mice. Severe deficiencies in GSIS were found, but only in islets from 7-month-old, fasted, male HSL−/− mice. GSIS was less affected in 4-month-old fasted male HSL−/− mice and not reduced in female mice. Exogenous delivery of free fatty acids (FFAs) rescued GSIS, supporting the view that the lack of endogenous FFA supply for lipid-signaling processes in HSL−/− mice was responsible for the loss of GSIS. GLP-1 also rescued GSIS in HSL−/− mice, indicating that signaling via HSL is not a major pathway for its incretin effect. Thus, the secretory phenotype of HSL-null mice is gender dependent, increases with age, and is influenced by the nutritional state. Under most circumstances, the major determinant of lipolytic flux in the β-cell involves an enzyme(s) other than HSL that is acutely activated by glucose. Our results support the view that the availability of endogenous FFA through HSL and an additional enzyme(s) is involved in providing lipid moieties for β-cell signaling for secretion in response to glucose.
The Proximal Islet-Specific Glucose-6-Phosphatase Catalytic Subunit–Related Protein Autoantigen Promoter Is Sufficient to Initiate but not Maintain Transgene Expression in Mouse Islets in Vivo
Authors: Frigeri Claudia , Martin Cyrus C. , Svitek Christina A. , Oeser James K. , Hutton John C. , Gannon Maureen , O’Brien Richard M.
Published: March 2007

We have previously reported the discovery of an islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) that is predominantly expressed in islet β-cells. IGRP has recently been identified as a major autoantigen in a mouse model of type 1 diabetes. The analysis of IGRP-chloramphenicol acetyltransferase (CAT) fusion gene expression in transiently transfected islet-derived hamster insulinoma tumor and βTC-3 cells revealed that the promoter region located between −306 and +3 confers high-level reporter gene expression. To determine whether this same promoter region is sufficient to confer islet β-cell-specific gene expression in vivo, it was ligated to a β-galactosidase reporter gene, and transgenic mice expressing the resulting fusion gene were generated. In two independent founder lines, this −306 to +3 promoter region was sufficient to drive β-galactosidase expression in newborn mouse islets, predominantly in β-cells, which was initiated during the expected time in development, around embryonic day 12.5. However, unlike the endogenous IGRP gene, β-galactosidase expression was also detected in the cerebellum. Moreover, β-galactosidase expression was almost completely absent in adult mouse islets, suggesting that cis-acting elements elsewhere in the IGRP gene are required for determining appropriate IGRP tissue-specific expression and for the maintenance of IGRP gene expression in adult mice.
Population-Based Incidence Rates and Risk Factors for Type 2 Diabetes in White Individuals
Authors: Bonora Enzo , Kiechl Stefan , Willeit Johann , Oberhollenzer Friedrich , Egger Georg , Meigs James B. , Bonadonna Riccardo C. , Muggeo Michele
Published: March 2007

Incidence rates and risk factors for type 2 diabetes in low-risk populations are not well documented. We investigated these in white individuals who were aged 40–79 years and from the population of Bruneck, Italy. Of an age- and sex-stratified random sample of 1,000 individuals who were identified in 1990, 919 underwent an oral glucose tolerance test (OGTT) and an assessment of physiological risk factors for diabetes, including insulin resistance (homeostasis model assessment, HOMA-IR), and postchallenge insulin response (Sluiter’s Index). Diabetes at baseline by fasting or 2-h OGTT plasma glucose (World Health Organization criteria, n = 82) was excluded, leaving 837 individuals who were followed for 10 years. Incident cases of diabetes were ascertained by confirmed diabetes treatment or a fasting glucose ≥7.0 mmol/l. At follow-up, 64 individuals had developed diabetes, corresponding to a population-standardized incidence rate of 7.6 per 1,000 person-years. Sex- and age-adjusted incidence rates were elevated 11-fold in individuals with impaired fasting glucose at baseline, 4-fold in those with impaired glucose tolerance, 3-fold in overweight individuals, 10-fold in obese individuals, and ∼2-fold in individuals with dyslipidemia or hypertension. Incidence rates increased with increasing HOMA-IR and decreasing Sluiter’s Index. As compared with normal insulin sensitivity and normal insulin response, individuals with low insulin sensitivity and low insulin response had a sevenfold higher risk of diabetes. Baseline impaired fasting glucose, BMI, HOMA-IR, and Sluiter’s Index were the only independent predictors of incident diabetes in multivariate analyses. We conclude that ∼1% of European white individuals aged 40–79 years develop type 2 diabetes annually and that “subdiabetic” hyperglycemia, obesity, insulin resistance, and impaired insulin response to glucose are independent predictors of diabetes.
Advanced Glycation End Product Interventions Reduce Diabetes-Accelerated Atherosclerosis
Authors: Forbes Josephine M. , Yee Louis Teo Loon , Thallas Vicki , Lassila Markus , Candido Riccardo , Jandeleit-Dahm Karin A. , Thomas Merlin C. , Burns Wendy C. , Deemer Elizabeth K. , Thorpe Susan R. , Cooper Mark E. , Allen Terri J.
Published: March 2007

Advanced glycation end product (AGE) formation may contribute to the progression of atherosclerosis, particularly in diabetes. The present study explored atherosclerosis in streptozotocin-induced diabetic apolipoprotein E–deficient (apoE−/−) mice that were randomized (n = 20) to receive for 20 weeks no treatment, the AGE cross-link breaker ALT-711, or the inhibitor of AGE formation aminoguanidine (AG). A sixfold increase in plaque area with diabetes was attenuated by 30% with ALT-711 and by 40% in AG-treated mice. Regional distribution of plaque demonstrated no reduction in plaque area or complexity within the aortic arch with treatment, in contrast to the thoracic and abdominal aortas, where significant attenuation was seen. Diabetes-associated accumulation of AGEs in aortas and plasma and decreases in skin collagen solubility were ameliorated by both treatments, in addition to reductions in the vascular receptor for AGE. Collagen-associated reductions in the AGEs carboxymethyllysine and carboxyethyllysine were identified with both treatments. Diabetes was also accompanied by aortic accumulation of total collagen, specifically collagens I, III, and IV, as well as increases in the profibrotic cytokines transforming growth factor-β and connective tissue growth factor and in cellular α-smooth muscle actin. Attenuation of these changes was seen in both treated diabetic groups. ALT-711 and AG demonstrated the ability to reduce vascular AGE accumulation in addition to attenuating atherosclerosis in these diabetic mice.
Cosegregation of MIDD and MODY in a Pedigree
Authors: Cervin Camilla , Liljeström Brita , Tuomi Tiinamaija , Heikkinen Seija , Tapanainen Juha S. , Groop Leif , Cilio Corrado M.
Published: March 2007

The aim of this study was characterization of a family carrying two mutations known to cause monogenic forms of diabetes, the M626K mutation in the HNF1α gene (MODY3) and the A3243G in mtDNA. β-Cell function and insulin sensitivity were assessed with the Botnia clamp. Heteroplasmy of the A3243G mutation and variants in type 2 diabetes susceptibility genes were determined, and transcriptional activity, DNA binding, and subcellular localization of mutated HNF1α were studied. Thirteen family members carried the mutation in mtDNA; 6 of them also had the M626K mutation, whereas none had only the M626K mutation. The protective Ala12 allele in peroxisome proliferator–activated receptor (PPAR)γ was present in two nondiabetic individuals. Carriers of both mtDNA and HNF1α mutations showed an earlier age at onset of diabetes than carriers of only the mtDNA mutation (median 22 vs. 45 years) but no clear difference in β-cell function or insulin sensitivity. In vitro, the M626K mutation caused a 53% decrease in transcriptional activity in HeLa cells. The mutated protein showed normal nuclear targeting but increased DNA binding. These data demonstrate that several genetic factors might contribute to diabetes risk, even in families with mtDNA and HNF1α mutations.
Polymorphisms in Type II SH2 Domain–Containing Inositol 5-Phosphatase (INPPL1, SHIP2) Are Associated With Physiological Abnormalities of the Metabolic Syndrome
Authors: Kaisaki Pamela J. , Delépine Marc , Woon Peng Y. , Sebag-Montefiore Liam , Wilder Steven P. , Menzel Stephan , Vionnet Nathalie , Marion Evelyne , Riveline Jean-Pierre , Charpentier Guillaume , Schurmans Stéphane , Levy Jonathan C. , Lathrop Mark , Farrall Martin , Gauguier Dominique
Published: March 2007

Type II SH2 domain–containing inositol 5-phosphatase (INPPL1, or SHIP2) plays an important role in the control of insulin sensitivity. INPPL1 mutations affecting gene function have been found in rat models of type 2 diabetes and hypertension and in type 2 diabetic patients. We investigated the influence of nucleotide variation in INPPL1 on components of the metabolic syndrome. Following comprehensive resequencing of the gene, we genotyped 12 informative polymorphisms in 1,304 individuals from 424 British type 2 diabetes families that were characterized for several metabolic phenotypes. We have found highly significant associations of single nucleotide polymorphisms (SNPs) and haplotypes of INPPL1 with hypertension as well as with other components of the metabolic syndrome. In a cohort of 905 French type 2 diabetic patients, we found evidence of association of INPPL1 SNPs with the presence of hypertension. We conclude that INPPL1 variants may impact susceptibility to disease and/or to subphenotypes involved in the metabolic syndrome in some diabetic patients.
A Novel Missense Substitution (Val1483Ile) in the Fatty Acid Synthase Gene (FAS) Is Associated With Percentage of Body Fat and Substrate Oxidation Rates in Nondiabetic Pima Indians
Authors: Kovacs Peter , Harper Inge , Hanson Robert L. , Infante Aniello M. , Bogardus Clifton , Tataranni P. Antonio , Baier Leslie J.
Published: March 2007

Inhibition of fatty acid synthase (FAS) induces a rapid decline in fat stores in mice, suggesting a role for this enzyme in energy homeostasis. The human FAS gene (FAS) maps to chromosome 17q25, a region previously shown to have suggestive linkage to adiposity in a genome-wide linkage scan for genetic determinants of obesity in Pima Indians. To investigate the potential role of FAS in the pathophysiology of human obesity, the FAS gene was sequenced and 13 single nucleotide polymorphisms (SNPs) were identified. Five representative SNPs were genotyped in 216 full-blooded, nondiabetic Pima Indians for association analyses. A Val1483Ile polymorphism (GTC to ATC; allele frequency of A = 0.10) was associated with percentage of body fat and 24-h substrate oxidation rates measured in a respiratory chamber. Compared with homozygotes for the Val variant, subjects with Ile/x had a lower mean percentage of body fat (30 ± 1 vs. 33 ± 1%, P = 0.002; adjusted for age, sex, and family membership) and a lower mean carbohydrate oxidation rate (983 ± 41 vs. 1,094 ± 19 kcal/day, P = 0.03), which resulted in a lower mean 24-h respiratory quotient (0.845 ± 0.01 vs. 0.850 ± 0.01 kcal/day, P = 0.04; both adjusted for age, sex, family membership, percentage of body fat, and energy balance). Our findings indicate that the Val1483Ile substitution in FAS is protective against obesity in Pima Indians, an effect possibly explained by the role of this gene in the regulation of substrate oxidation.
Characterization of Adenosine-A1 Receptor–Mediated Antilipolysis in Rats by Tissue Microdialysis, 1H-Spectroscopy, and Glucose Clamp Studies
Authors: Schoelch Corinna , Kuhlmann Johanna , Gossel Matthias , Mueller Guenter , Neumann-Haefelin Claudia , Belz Ulrich , Kalisch Juergen , Biemer-Daub Gabriele , Kramer Werner , Juretschke Hans-Paul , Herling Andreas W.
Published: March 2007

Increased supply of fatty acids to muscle and liver is causally involved in the insulin resistance syndrome. Using a tissue microdialysis technique in Wistar and Zucker fatty (ZF) rats, we determined tissue glycerol levels as a marker of lipolysis in gastrocnemius muscle (gMT), subcutaneous adipose (SAT), and visceral adipose tissue (VAT) as well as the reduction of plasma free fatty acids, glycerol, and triglycerides caused by the antilipolysis-specific adenosine-A1 receptor agonist (ARA). In Wistar and ZF rats, ARA significantly lowered dialysate glycerol levels in SAT, VAT, and gMT. Whereas in SAT and VAT the decrease in dialysate glycerol indicated adipocytic antilipolysis, this decrease in gMT was not caused by a direct effect of ARA on intramyocellular lipolysis, as demonstrated by the lack of inhibition of the protein kinase A activity ratio in gMT. In addition, no differences of the fed-starved-refed dynamics of intramyocellular triglyceride levels compared with untreated controls were measured by in vivo 1H-spectroscopy, excluding any adenylate cyclase–independent antilipolysis in muscle. Treatment with ARA resulted in pronounced reductions of plasma free fatty acids, glycerol, and triglycerides. Furthermore, in ZF rats, ARA treatment caused an immediate improvement of peripheral insulin sensitivity measured by the euglycemic-hyperinsulinemic glucose clamp technique.
Islet Allograft Survival Induced by Costimulation Blockade in NOD Mice Is Controlled by Allelic Variants of Idd3
Authors: Pearson Todd , Weiser Peter , Markees Thomas G. , Serreze David V. , Wicker Linda S. , Peterson Laurence B. , Cumisky Anne-Marie , Shultz Leonard D. , Mordes John P. , Rossini Aldo A. , Greiner Dale L.
Published: March 2007

NOD mice develop type 1 autoimmune diabetes and exhibit genetically dominant resistance to transplantation tolerance induction. These two phenotypes are genetically separable. Costimulation blockade fails to prolong skin allograft survival in (NOD × C57BL/6)F1 mice and in NOD-related strains made diabetes-resistant by congenic introduction of protective major histocompatibility complex (MHC) or non-MHC Idd region genes. Here, we tested the hypothesis that the genetic basis for the resistance of NOD mice to skin allograft tolerance also applies to islet allografts. Surprisingly, costimulation blockade induced permanent islet allograft survival in (NOD × C57BL/6)F1 mice but not in NOD mice. After costimulation blockade, islet allograft survival was prolonged in diabetes-resistant NOD.B6 Idd3 mice and shortened in diabetes-free C57BL/6 mice congenic for the NOD Idd3 variant. Islet allograft tolerance could not be induced in diabetes-resistant NOD.B10 Idd5 and NOD.B10 Idd9 mice. The data demonstrate that 1) NOD mice resist islet allograft tolerance induction; 2) unlike skin allografts, resistance to islet allograft tolerance is a genetically recessive trait; 3) an Idd3 region gene(s) is an important determinant of islet allograft tolerance induction; and 4) there may be overlap in the mechanism by which the Idd3 resistance locus improves self-tolerance and the induction of allotolerance.
Major Histocompatibility Complex Class I Shedding and Programmed Cell Death Stimulated Through the Proinflammatory P2X7 Receptor
Authors: Elliott James I. , Higgins Christopher F.
Published: March 2007

It has been hypothesized that type 1 diabetes is initiated by neonatal physiological pancreatic β-cell death, indicating that the early stages of this autoimmune response may reflect a dysregulated response to immune “danger” signals. One potential danger signal is ATP, high concentrations of which stimulate the purinergic receptor P2X7 on hematopoietic cells. We compared the sensitivity of lymphocytes from model type 1 diabetic (NOD) and control (C57BL/10) mice to activation of this pathway. Stimulation of the P2X7 receptor of NOD mice resulted in more pronounced shedding of the lymphocyte homing receptor CD62L and in increased programmed cell death. Levels of major histocompatibility complex class I molecules, which have previously been reported to be poorly expressed on NOD lymphocytes, were initially normal, but the molecules were shed preferentially from NOD cells after P2X7 receptor stimulation. Thus, although NOD lymphocytes have been considered resistant to programmed cell death, they are highly sensitive to that stimulated through the P2X7 receptor. Because NOD mice express a low activation threshold allele of the P2X7 receptor and the P2X7 gene maps to a locus associated with disease, P2X7 is a good candidate susceptibility gene for NOD diabetes.
Insulin Dose-Response Curves for Stimulation of Splanchnic Glucose Uptake and Suppression of Endogenous Glucose Production Differ in Nondiabetic Humans and Are Abnormal in People With Type 2 Diabetes
Authors: Basu Rita , Basu Ananda , Johnson C. Michael , Schwenk W. Frederick , Rizza Robert A.
Published: March 2007

To determine whether the insulin dose-response curves for suppression of endogenous glucose production (EGP) and stimulation of splanchnic glucose uptake (SGU) differ in nondiabetic humans and are abnormal in type 2 diabetes, 14 nondiabetic and 12 diabetic subjects were studied. Glucose was clamped at ∼9.5 mmol/l and endogenous hormone secretion inhibited by somatostatin, while glucagon and growth hormone were replaced by an exogenous infusion. Insulin was progressively increased from ∼150 to ∼350 and ∼700 pmol/l by means of an exogenous insulin infusion, while EGP, SGU, and leg glucose uptake (LGU) were measured using the splanchnic and leg catheterization methods, combined with a [3-3H]glucose infusion. In nondiabetic subjects, an increase in insulin from ∼150 to ∼350 pmol/l resulted in maximal suppression of EGP, whereas SGU continued to increase (P < 0.001) when insulin was increased to ∼700 pmol/l. In contrast, EGP progressively decreased (P < 0.001) and SGU progressively increased (P < 0.001) in the diabetic subjects as insulin increased from ∼150 to ∼700 pmol/l. Although EGP was higher (P < 0.01) in the diabetic than nondiabetic subjects only at the lowest insulin concentration, SGU was lower (P < 0.01) in the diabetic subjects at all insulin concentrations tested. On the other hand, in contrast to LGU and overall glucose disposal, the increment in SGU in response to both increments in insulin did not differ in the diabetic and nondiabetic subjects, implying a right shifted but parallel dose-response curve. These data indicate that the dose-response curves for suppression of glucose production and stimulation of glucose uptake differ in nondiabetic subjects and are abnormal in people with type 2 diabetes. Taken together, these data also suggest that agents that enhance SGU in diabetic patients (e.g. glucokinase activators) are likely to improve glucose tolerance.
Adiponectin Receptor 1 Gene (ADIPOR1) as a Candidate for Type 2 Diabetes and Insulin Resistance
Authors: Wang Hua , Zhang Hailing , Jia Yiwen , Zhang Zhengxian , Craig Rebekah , Wang Xiaoqin , Elbein Steven C.
Published: March 2007

Considerable data support adiponectin as an important adipose-derived insulin sensitizer that enhances fatty acid oxidation and alters hepatic gluconeogenesis. Adiponectin acts by way of two receptors, ADIPOR1 and ADIPOR2. ADIPOR1 is widely expressed in tissues, including muscle, liver, and pancreas, and binds the globular form of adiponectin with high affinity. To test the hypothesis that sequence variations in or near the ADIPOR1 gene contribute to the risk of developing type 2 diabetes and the metabolic syndrome, we screened the eight exons (including the untranslated exon 1) of the ADIPOR1 gene with flanking intronic sequences and the 5′ and 3′ flanking sequences. We identified 22 single nucleotide polymorphisms (SNPs) in Caucasian and African-American subjects, of which a single nonsynonymous SNP (N44K) in exon 2 was present only in African-American subjects. We typed 14 sequence variants that had minor allele frequencies >5%. No SNP was associated with type 2 diabetes in Caucasians or African Americans, and no SNP was a determinant of insulin sensitivity or insulin secretion among nondiabetic members of high-risk Caucasian families. However, the two alleles of a SNP in the 3′ untranslated region were expressed unequally, and ADIPOR1 mRNA levels were significantly lower among transformed lymphocytes from diabetic African-American individuals than among control cell lines. This altered gene expression might suggest a role for ADIPOR1 in the metabolic syndrome.
SREBF-1 Gene Polymorphisms Are Associated With Obesity and Type 2 Diabetes in French Obese and Diabetic Cohorts
Authors: Eberlé Delphine , Clément Karine , Meyre David , Sahbatou Mourad , Vaxillaire Martine , Le Gall Annie , Ferré Pascal , Basdevant Arnaud , Froguel Philippe , Foufelle Fabienne
Published: March 2007

Sterol regulatory element–binding protein (SREBP)-1 transcription factors play a central role in energy homeostasis by promoting glycolysis, lipogenesis, and adipogenesis. The sterol regulatory element–binding protein gene (SREBF)-1 is a good candidate gene for obesity and obesity-related metabolic traits such as type 2 diabetes and dyslipidemia. The SREBF-1 molecular screening of 40 unrelated obese patients by PCR/single-strand conformation polymorphism revealed 19 single nucleotide polymorphisms (SNPs). Six SNPs were genotyped for an association study in large French obese and nonobese cohorts. Case-control studies using two independent nonobese cohorts indicated that SNP17 (54G/C, exon 18c) is associated with morbid obesity (odds ratio 1.5, P = 0.006 and P = 0.02, respectively). SNP3 (−150G/A, exon 1a), SNP5 (−36delG, exon 1a), and SNP17 are found in high linkage disequilibrium (D′ > 0.8). The haplotype including wild-type alleles of these SNPs (C/G/G/T/C/G, HAP2) is identified as a risk factor for morbid obesity (P = 0.003). In the obese group, SNP3, SNP5, and SNP17 are associated with male-specific hypertriglyceridemia (P = 0.07, P = 0.01, and P = 0.05, respectively). SNP17 is also associated with type 2 diabetes (P = 0.03) and increased prevalence of nephropathy (P = 0.028) in a diabetic cohort. Our results indicate a role of the SREBF-1 gene in genetic predisposition of metabolic diseases such as obesity, type 2 diabetes, and dyslipidemia.
DPB1 Alleles Are Associated With Type 1 Diabetes Susceptibility in Multiple Ethnic Groups
Authors: Cruz Thomas D. , Valdes Ana M. , Santiago Alma , Frazer de Llado Teresa , Raffel Leslie J. , Zeidler Adina , Rotter Jerome I. , Erlich Henry A. , Rewers Marian , Bugawan Teodorica , Noble Janelle A.
Published: March 2007

Genetic associations between type 1 diabetes and alleles at the HLA class II locus DPB1 have been previously reported. Observed associations could be due to variation in the DPB1 locus itself or to linkage disequilibrium (LD) between DPB1 alleles and other susceptibility loci. One measure of whether the association of an allele with a disease reflects a true effect of the locus or is simply due to LD is the observation of that association in multiple ethnic groups. Previous type 1 diabetes associations have been reported for DPB1*0301 and DPB1*0202 (predisposing) and for DPB1*0402 (protective). In this study, results are reported from testing these associations in three different sample sets: 1) Puerto Rican case and control subjects, 2) Mexican-American simplex families, and 3) high-risk (DR3/DR4) individuals with and without an affected relative. DPB1*0301 was associated in all three groups, even after accounting for LD with DRB1-DQB1. DPB1*0202 and DPB1*0402 were positively and negatively associated, respectively, in two of the three populations. These results suggest that the observed DPB1 associations, especially that of the DPB1*0301 allele, with type 1 diabetes are likely to be true associations. This supports the concept that multiple genes in the HLA region can affect type 1 diabetes susceptibility.
Therapeutic Strategies Based on Glucagon-Like Peptide 1
Authors: Deacon Carolyn F.
Published: March 2007

Glucagon-like peptide (GLP)-1 is an incretin hormone with potent glucose-dependent insulinotropic and glucagonostatic actions, trophic effects on the pancreatic β-cells, and inhibitory effects on gastrointestinal secretion and motility, which combine to lower plasma glucose and reduce glycemic excursions. Furthermore, via its ability to enhance satiety, GLP-1 reduces food intake, thereby limiting weight gain, and may even cause weight loss. Taken together, these actions give GLP-1 a unique profile, considered highly desirable for an antidiabetic agent, particularly since the glucose dependency of its antihyperglycemic effects should minimize any risk of severe hypoglycemia. However, its pharmacokinetic/pharmacodynamic profile is such that native GLP-1 is not therapeutically useful. Thus, while GLP-1 is most effective when administered continuously, single subcutaneous injections have short-lasting effects. GLP-1 is highly susceptible to enzymatic degradation in vivo, and cleavage by dipeptidyl peptidase IV (DPP-IV) is probably the most relevant, since this occurs rapidly and generates a noninsulinotropic metabolite. Strategies for harnessing GLP-1’s therapeutic potential, based on an understanding of factors influencing its metabolic stability and pharmacokinetic/pharmacodynamic profile, have therefore been the focus of intense research in both academia and the pharmaceutical industry. Such strategies include DPP-IV–resistant GLP-1 analogs and selective enzyme inhibitors to prevent in vivo degradation of the peptide.
An Adenovirus Vector for Efficient RNA Interference–Mediated Suppression of Target Genes in Insulinoma Cells and Pancreatic Islets of Langerhans
Authors: Bain James R. , Schisler Jonathan C. , Takeuchi Koji , Newgard Christopher B. , Becker Thomas C.
Published: March 2007

Silencing gene expression by RNA interference (RNAi) can provide insight into gene function but requires efficient delivery of small interfering RNAs (siRNAs) into cells. Introduction of exogenous nucleic acids can be especially difficult in cultured pancreatic islets. This article describes a method for making recombinant adenoviruses that efficiently drive expression of siRNAs in islet β-cells and a β-cell–derived cell line. Transduction with a virus expressing an siRNA specific for GLUT2 reduced GLUT2 mRNA and protein levels by 80% in the INS-1–derived β-cell line, 832/13, and GLUT2 protein levels by >90% in primary rat islets. Another virus expressing an siRNA specific for glucokinase (GK) caused 80% suppression of GK mRNA and 50% suppression of GK protein levels in 832/13 cells. These experiments validate recombinant adenoviral RNAi vectors as a useful tool for suppression of the expression of specific genes in pancreatic islets and β-cell lines. Advantages of this approach include 1) the high efficiency of adenovirus-mediated gene transfer in insulinoma cell lines and rat islets and 2) the rapidity with which RNAi constructs can be prepared and tested relative to stable-transfection strategies.
Suppressor of Cytokine Signaling 3 Expression and Insulin Resistance in Skeletal Muscle of Obese and Type 2 Diabetic Patients
Authors: Rieusset Jennifer , Bouzakri Karim , Chevillotte Emmanuel , Ricard Nadège , Jacquet Delphine , Bastard Jean-Philippe , Laville Martine , Vidal Hubert
Published: March 2007

Interleukin-6 (IL-6) could be a possible mediator of insulin resistance. We investigated whether IL-6 could inhibit insulin signaling in human skeletal myotubes and whether suppressor of cytokine signaling 3 (SOCS-3) could be related to insulin resistance in vivo in humans. IL-6 inhibited insulin signaling and induced SOCS-3 expression in differentiated myotubes. SOCS-3 mRNA levels were significantly increased in the skeletal muscle of type 2 diabetic patients compared with control subjects and correlated with reduced insulin-stimulated glucose uptake. In contrast, SOCS-3 mRNA levels were reduced in muscle of obese nondiabetic subjects compared with type 2 diabetic patients, despite similar circulating concentrations of IL-6. Increased SOCS-3 mRNA levels in diabetes were not attributable to hyperglycemia, as type 1 diabetic patients had normal SOCS-3 mRNA expression in muscle. However, the combination of high glucose and IL-6 levels in type 2 diabetic patients may induce SOCS-3 expression, as has been seen in human muscle cells. In subcutaneous adipose tissue, SOCS-3 mRNA levels were increased in obese individuals and strongly correlated with IL-6 expression, supporting a paracrine effect of IL-6 on SOCS-3 expression in fat. Taken together, our results showed that SOCS-3 expression in human skeletal muscle in vivo is not related to insulin resistance in the presence of elevated IL-6 concentrations and suggest that cytokine action could differ in type 2 diabetic patients and nondiabetic obese subjects.
Dissecting the Role of Glucocorticoids on Pancreas Development
Authors: Gesina Emilie , Tronche François , Herrera Pedro , Duchene Belinda , Tales Willemène , Czernichow Paul , Breant Bernadette
Published: March 2007

To determine whether glucocorticoids are involved in pancreas development, glucocorticoid treatment of rat pancreatic buds in vitro was combined with the analysis of transgenic mice lacking the glucocorticoid receptor (GR) in specific pancreatic cells. In vitro treatment of embryonic pancreata with dexamethasone, a glucocorticoid agonist, induced a decrease of insulin-expressing cell numbers and a doubling of acinar cell area, indicating that glucocorticoids favored acinar differentiation; in line with this, expression of Pdx-1, Pax-6, and Nkx6.1 was downregulated, whereas the mRNA levels of Ptf1-p48 and Hes-1 were increased. The selective inactivation of the GR gene in insulin-expressing β-cells in mice (using a RIP-Cre transgene) had no measurable consequences on β- or α-cell mass, whereas the absence of GR in the expression domain of Pdx-1 (Pdx-Cre transgene) led to a twofold increased β-cell mass, with increased islet numbers and size but normal α-cell mass in adults. These results demonstrate that glucocorticoids play an important role in pancreatic β-cell lineage, acting before hormone gene expression onset and possibly also modulating the balance between endocrine and exocrine cell differentiation.
Studies of the Peptide YY and Neuropeptide Y2 Receptor Genes in Relation to Human Obesity and Obesity-Related Traits
Authors: Connie Hung Chiao-Chien , Pirie Fraser , Luan Jian’an , Lank Emma , Motala Ayesha , Yeo Giles S.H. , Keogh Julia M. , Wareham Nicholas J. , O’Rahilly Stephen , Farooqi I. Sadaf
Published: March 2007

Peptide-YY (PYY) is secreted from endocrine L-cells of the gastrointestinal tract in response to caloric ingestion and may mediate postprandial satiety through the hypothalamic neuropeptide Y2 receptor (Y2R). We examined whether variants in the genes encoding PYY and Y2R might be associated with obesity-related phenotypes in humans. Among 101 subjects with severe early-onset obesity and a history of hyperphagia, we found two rare sequence variants—L73P and IVS2 + 32delG—in PYY and three rare missense mutations—L40F, F87I, and A172T—in Y2R. Although none of these were found in 100 normal-weight white control subjects, L73P in PYY and F87I and A172T in Y2R did not segregate with obesity in family studies, and family data were unavailable for IVS2 + 32delG in PYY and L40F in Y2R. Two common single nucleotide polymorphisms (SNPs), R72T and IVS3 + 68C>T, in PYY were in tight linkage disequilibrium but showed no association with BMI in a large white population. In the Y2R, two SNPs, 585T>C and 936T>C, were found and were in tight linkage disequilibrium. Men, homozygous for the rarer variant, had significantly lower BMI (P = 0.017), waist-to-hip ratio (P = 0.013), and, surprisingly, higher nonesterified fatty acid levels (P = 0.01). In conclusion, mutations in PYY and Y2R are not commonly found in humans with severe early-onset obesity. The relationship between common variants in Y2R and obesity-related traits deserves further exploration in other populations.
Genetic Variation in BEACON Influences Quantitative Variation in Metabolic Syndrome–Related Phenotypes
Authors: Jowett Jeremy B. , Elliott Kate S. , Curran Joanne E. , Hunt Nicola , Walder Ken R. , Collier Greg R. , Zimmet Paul Z. , Blangero John
Published: March 2007

The BEACON gene (also known as UBL5) was identified as differentially expressed between lean and obese Psammomys obesus, a polygenic animal model of obesity, type 2 diabetes, and dyslipidemia. The human homologue of BEACON is located on chromosome 19p, a region likely to contain genes affecting metabolic syndrome–related quantitative traits as established by linkage studies. To assess whether the human BEACON gene may be involved in influencing these traits, we exhaustively analyzed the complete gene for genetic variation in 40 unrelated individuals and identified four variants (three novel). The two more common variants were tested for association with a number of quantitative metabolic syndrome–related traits in two large cohorts of unrelated individuals. Significant associations were found between these variants and fat mass (P = 0.026), percentage of fat (P = 0.001), and waist-to-hip ratio (P = 0.031). The same variants were also associated with total cholesterol (P = 0.024), LDL cholesterol (P = 0.019), triglycerides (P = 0.006), and postglucose load insulin levels (P = 0.018). Multivariate analysis of these correlated phenotypes also yielded a highly significant association (P = 0.0004), suggesting that BEACON may influence phenotypic variation in metabolic syndrome–related traits.
Glucose Dependence of Imidazoline-Induced Insulin Secretion
Authors: Bleck Claudia , Wienbergen Antje , Rustenbeck Ingo
Published: March 2007

The glucose dependence of the insulinotropic action of KATP channel–blocking imidazoline compounds was investigated. Administration of 100 μmol/l phentolamine, but not 100 μmol/l efaroxan, markedly increased insulin secretion of freshly isolated mouse islets when the perifusion medium contained 5 mmol/l glucose. When the glucose concentration was raised to 10 mmol/l in the continued presence of either imidazoline, a clear potentiation of secretion occurred as compared with 10 mmol/l glucose alone. In the presence of efaroxan, a brisk first-phase–like increase was followed by a sustained phase, whereas a more gradual increase resulted in the presence of phentolamine. Administration of 100 μmol/l phentolamine was somewhat more effective than 100 μmol/l efaroxan to inhibit KATP channel activity in intact cultured β-cells (reduction by 96 vs. 83%). Both compounds were similarly effective to depolarize the β-cells. When measured by the perforated patch-technique, the depolarization by efaroxan was often oscillatory, whereas that by phentolamine was sustained. In perifused cultured islets, both compounds increased the cytosolic calcium concentration ([Ca2+]c) in the presence of 5 and 10 mmol/l glucose. Efaroxan induced large amplitude oscillations of [Ca2+]c, whereas phentolamine induced a sustained increase. It appears that a KATP channel block by imidazolines is not incompatible with a glucose-selective enhancement of insulin secretion. The glucose selectivity of efaroxan may involve an inhibitory effect distal to [Ca2+]c increase and/or the generation of [Ca2+]c oscillations.
Roles of ATP-Sensitive K+ Channels as Metabolic Sensors
Authors: Minami Kohtaro , Miki Takashi , Kadowaki Takashi , Seino Susumu
Published: March 2007

ATP-sensitive K+ channels (KATP channels) are present in various tissues, including pancreatic β-cells, heart, skeletal muscles, vascular smooth muscles, and brain. KATP channels are hetero-octameric proteins composed of inwardly rectifying K+ channel (Kir6.x) and sulfonylurea receptor (SUR) subunits. Different combinations of Kir6.x and SUR subunits comprise KATP channels with distinct electrophysiological and pharmacological properties. Recent studies of genetically engineered mice have provided insight into the physiological and pathophysiological roles of Kir6.x-containing KATP channels. Analysis of Kir6.2 null mice has shown that Kir6.2/SUR1 channels in pancreatic β-cells and the hypothalamus are essential in glucose-induced insulin secretion and hypoglycemia-induced glucagon secretion, respectively, and that Kir6.2/SUR2 channels are involved in glucose uptake in skeletal muscles. Kir6.2-containing KATP channels in brain also are involved in protection from hypoxia-induced generalized seizure. In cardiovascular tissues, Kir6.1-containing KATP channels are involved in regulation of vascular tonus. In addition, the Kir6.1 null mouse is a model of Prinzmetal angina in humans. Our studies of Kir6.2 null and Kir6.1 null mice reveal that KATP channels are critical metabolic sensors in acute metabolic changes, including hyperglycemia, hypoglycemia, ischemia, and hypoxia.
Beta-Cell Function in Obesity
Authors: Ferrannini Ele , Camastra Stefania , Gastaldelli Amalia , Sironi Anna Maira , Natali Andrea , Muscelli Elza , Mingrone Geltrude , Mari Andrea
Published: March 2007

In nondiabetic subjects, obesity is associated with a modest expansion of β-cell mass, possibly amounting—according to the best available estimates—to 10–30% for each 10 kg of weight excess. Whether age of onset and duration of obesity, recent changes in body weight, and body fat distribution have any effect on β-cell mass in humans is unknown. Both fasting insulin secretion and the total insulin response to oral glucose have the following characteristics: 1) they increase with BMI in an approximately linear fashion, 2) both fat-free and fat mass are significant positive correlates, and 3) BMI exerts a positive effect separate from that of insulin resistance (i.e., obesity may be a state of primary insulin hypersecretion). The mechanisms are currently unknown, though chronic small increments in plasma glucose may play a role. In contrast, dynamic properties of β-cell function, such as glucose sensitivity (i.e., dose-response function), rate sensitivity, and potentiation, do not appear to be substantially altered by the presence of obesity, body fat distribution, or insulin resistance as long as glucose tolerance is maintained. Weight loss, by diet or restrictive bariatric surgery, is associated with consensual decrements in insulin resistance and insulin hypersecretion. The latter, however, seems to be more persistent, suggesting that the postobese state may reproduce the primary insulin hypersecretion of the obese state. Malabsorptive bariatric surgery, in contrast, normalizes insulin sensitivity and abolishes insulin hypersecretion even before achievement of ideal body weight. Lipid-triggered messages from the gastrointestinal tract to the insulin target tissues and endocrine pancreas are the subject of intense investigation.
β-Cell Function Following Human Islet Transplantation for Type 1 Diabetes
Authors: Rickels Michael R. , Schutta Mark H. , Markmann James F. , Barker Clyde F. , Naji Ali , Teff Karen L.
Published: March 2007

Islet transplantation can provide metabolic stability for patients with type 1 diabetes; however, more than one donor pancreas is usually required to achieve insulin independence. To evaluate possible mechanistic defects underlying impaired graft function, we studied five subjects at 3 months and four subjects at 12 months following intraportal islet transplantation who had received comparable islet equivalents per kilogram (12,601 ± 1,732 vs. 14,384 ± 2,379, respectively). C-peptide responses, as measures of β-cell function, were significantly impaired in both transplant groups when compared with healthy control subjects (P < 0.05) after intravenous glucose (0.3 g/kg), an orally consumed meal (600 kcal), and intravenous arginine (5 g), with the greatest impairment to intravenous glucose and a greater impairment seen in the 12-month compared with the 3-month transplant group. A glucose-potentiated arginine test, performed only in insulin-independent transplant subjects (n = 5), demonstrated significant impairments in the glucose-potentiation slope (P < 0.05) and the maximal response to arginine (ARmax; P < 0.05), a measure of β-cell secretory capacity. Because ARmax provides an estimate of the functional β-cell mass, these results suggest that a low engrafted β-cell mass may account for the functional defects observed after islet transplantation.
Uncoupling of Nutrient Metabolism From Insulin Secretion by Overexpression of Cytosolic Phospholipase A2
Authors: Milne Helen M. , Burns Chris J. , Squires Paul E. , Evans Nicholas D. , Pickup John , Jones Peter M. , Persaud Shanta J.
Published: March 2007

We have generated MIN6 β-cells that stably overexpress cytosolic phospholipase A2 (cPLA2) and show a ninefold increase in cPLA2 activity. Overexpression of cPLA2 did not affect the capacity of MIN6 cells to show elevations in intracellular Ca2+ concentration ([Ca2+]i) in response to tolbutamide and KCl, and these depolarizing stimuli produced insulin secretion profiles in cPLA2-overexpressing cells similar to those they produced in passage-matched nontransfected MIN6 cells. However, cPLA2-overexpressing MIN6 cells did not respond to elevations in extracellular glucose with increases in ATP, [Ca2+]i, or insulin secretion. Nontransfected MIN6 cells showed a rapid and sustained increase in NAD(P)H autofluorescence in response to 25 mmol/l glucose, and this was reduced by ∼95% in MIN6 cells overexpressing cPLA2. This effect was mimicked in nontransfected MIN6 cells by p-(trifluoromethoxy) phenylylhydrazone, a mitochondrial uncoupler. Quantitative RT-PCR indicated that mRNA for uncoupling protein-2 (UCP-2) was increased in the cPLA2-overexpressing MIN6 cells, and this could be prevented by exposure to 100 μmol/l methyl arachidonyl fluorophosphate, a cPLA2 inhibitor. Glucose caused a decrease in rhodamine 123 fluorescence in control cells, but not in those overexpressing cPLA2, consistent with the transfected cells being unable to maintain mitochondrial proton gradients as a consequence of UCP-2 upregulation. Our data indicate that overexpression of cPLA2 results in severe impairment of the calcium and secretory responses of β-cells to glucose through upregulation of UCP-2 and uncoupling of mitochondrial metabolism from ATP generation.