bluuebunny/crossref_metadata_2025 huggingface dataset:
Kir6.2 Mutations Are a Common Cause of Permanent Neonatal Diabetes in a Large Cohort of French Patients
Authors: Vaxillaire Martine , Populaire Céline , Busiah Kanetee , Cavé Hélène , Gloyn Anna L. , Hattersley Andrew T. , Czernichow Paul , Froguel Philippe , Polak Michel
Published: March 2007

Permanent neonatal diabetes (PND), requiring insulin within the first months of life, is unexplained at the molecular level in most cases. It has very recently been shown that heterozygous activating mutations in the KCNJ11 gene, encoding the Kir6.2 subunit of the pancreatic ATP-sensitive K+ channel involved in the regulation of insulin secretion, cause PND. In the present study, we screened the KCNJ11 gene for mutations in French patients with PND. Patients were recruited through the French network for the study of neonatal diabetes. Seventeen at-term babies with a median age at diagnosis of diabetes of 64 days (range 1–260) were included. We identified in nine patients seven heterozygous nonsynonymous mutations: three of them (V59M, R201C, and R201H) were already described, and the four novel mutations resulted in an amino acid change of Kir6.2 at positions F35L, G53N, E322K, and Y330C. More patients with a Kir6.2 mutation (six of nine) were reported to have a smaller birth weight than those without mutation (two of eight). Although Kir6.2 mutation carriers do not represent a phenotypically specific form of PND, an impaired function of Kir6.2 is associated with in utero insulin secretory insufficiency and growth retardation. In conclusion, we confirmed that Kir6.2 mutations are a common cause (53%) of PND in Caucasians.
A New ATP-Sensitive K+ Channel–Independent Mechanism Is Involved in Glucose-Excited Neurons of Mouse Arcuate Nucleus
Authors: Fioramonti Xavier , Lorsignol Anne , Taupignon Anne , Pénicaud Luc
Published: March 2007

Glucose is known to modify electrical activity of neurons in different hypothalamic areas such as the arcuate nucleus (ARC) or the ventromedian nucleus. In these structures, it has been demonstrated that glucose-induced excitation of neurons involves ATP-sensitive K+ (KATP) channel closure. The aim of the present study was to determine whether ARC neurons were able to detect high extracellular glucose concentrations and which mechanisms were involved in this detection by using whole-cell and cell-attached patch-clamp techniques in acute mouse brain slices. An increase from 5 to 20 mmol/l glucose stimulated 19% and inhibited 9% of ARC neurons. Because of the high-glucose concentrations used, we called these neurons high-glucose–excited (HGE) and high-glucose–inhibited (HGI) neurons, respectively. Glucose-induced depolarization of HGE neurons was not abolished by tetrodotoxin treatment and was correlated with an increase of membrane conductance that reversed at ∼20 mV. Experiments with diazoxide, pinacidil, or tolbutamide showed that KATP channels were present and functional in most of the ARC neurons but were mostly closed at 5 mmol/l glucose. Moreover, HGE neurons were also present in ARC of Kir6.2 null mice. These results suggested that ARC neurons have the ability to sense higher glucose concentrations than 5 mmol/l through a new KATP channel–independent mechanism.
Fas Deficiency Prevents Type 1 Diabetes by Inducing Hyporesponsiveness in Islet β-Cell−Reactive T-Cells
Authors: Vence Luis , Benoist Christophe , Mathis Diane
Published: March 2007

Type 1 diabetes is an autoimmune disease wherein autoreactive T-cells promote the specific destruction of pancreatic islet β-cells. Evidence for a crucial role for Fas/FasL interactions in this destruction has been highly controversial because of the pleiotropic effects of Fas deficiency on the lymphoid and other systems. Fas-deficient mice are protected from spontaneous development of diabetes not because Fas has a role in the destruction of β-cells, but rather because insulitis is abrogated. Fas may somehow be involved in the series of events provoking insulitis; for example, it may play a role in the physiological wave of β-cell death believed to result in the export of pancreatic antigens to the pancreatic lymph nodes and, thereby, to circulating, naive, diabetogenic T-cells for the first time. To explore the implication of Fas in these events, we crossed the lpr mutation into the BDC2.5 model of type 1 diabetes to make it easier to monitor direct effects on the pathogenic specificity. We demonstrated that BDC2.5/NODlpr/lpr mice have qualitatively and quantitatively less aggressive insulitis than do BDC2.5/NOD mice. In vitro proliferation assays showed that BDC2.5/NODlpr/lpr splenocytes proliferated less vigorously than those from control mice in the presence of islet extracts, which reflects their inability to produce interleukin-2, resulting in weaker pathogenicity.
Intracellular Stress Signaling Pathways Activated During Human Islet Preparation and Following Acute Cytokine Exposure
Authors: Abdelli Saida , Ansite Jeff , Roduit Raphael , Borsello Tiziana , Matsumoto Ippei , Sawada Toshiya , Allaman-Pillet Nathalie , Henry Hugues , Beckmann Jacques S. , Hering Bernhard J. , Bonny Christophe
Published: March 2007

Pancreatic islet transplantation may successfully restore normoglycemia in type 1 diabetic patients. However, successful grafting requires transplantation of a sufficient number of islets, usually requiring two or more donors. During the isolation process and following clinical transplantation, islets are subjected to severe adverse conditions that impair survival and ultimately contribute to graft failure. Here, we have mapped the major intracellular stress-signaling pathways that may mediate human islet loss during isolation and following cytokine attack. We found that the isolation procedure potently recruits two pathways consisting of |mitogen-activated protein kinase kinase (MKK)7 → Jun NH2-terminal kinase (JNK)/p38 → c-fos| and the |nuclear factor-κB (NF-κB) → iNOS| module. Cytokines activate the |NF-κB → iNOS| and |MKK4/MKK3/6 → JNK/p38| pathways without recruitment of c-fos. Culturing the islets for 48 h after isolation allows for the activated pathways to return to background levels, with expression of MKK7 becoming undetectable. These data indicate that isolation and cytokines recruit different death pathways. Therefore, strategies might be rationally developed to avoid possible synergistic activation of these pathways in mediating islet loss during isolation and following grafting.
A Prospective Study of Serum Lipids and Risk of Diabetic Macular Edema in Type 1 Diabetes
Authors: Miljanovic Biljana , Glynn Robert J. , Nathan David M. , Manson JoAnn E. , Schaumberg Debra A.
Published: March 2007

We evaluated the relationships between serum lipid levels and clinically significant macular edema (CSME), hard exudates, and other diabetic retinopathy (DR) end points in a population with type 1 diabetes. We studied data from serum lipids that were measured annually among the 1,441 Diabetes Control and Complications Trial (DCCT) participants. We used proportional hazards regression models to examine the relationship of the cumulative average of lipid levels (total, LDL, and HDL cholesterol, total–to–HDL cholesterol ratio, and triglycerides) with development of CSME, hard exudate, DR progression, and development of proliferative DR (PDR). In models controlling for primary prevention versus secondary intervention subgroup, randomized treatment assignment, HbA1c, and other risk factors, both total–to–HDL cholesterol ratio and LDL predicted development of CSME (rate ratio [RR] for extreme quintiles 3.84, P for trend = 0.03 for total–to–HDL cholesterol ratio, and RR 1.95, P for trend = 0.03 for LDL) and hard exudate (RR 2.44, P for trend = 0.0004 for total–to–HDL cholesterol ratio, and RR 2.77, P for trend = 0.002 for LDL). Relationships of lipids with progression of DR and development of PDR were weaker and not significant after adjustment for HbA1c. Higher serum lipids are associated with increased risk of CSME and retinal hard exudate. Lipid-lowering treatment among type 1 diabetic subjects, recommended to prevent cardiovascular disease, may also decrease risk of CSME, an important cause of vision loss.
Tumor Necrosis Factor-α in Diabetic Plasma Increases the Activity of Core 2 GlcNAc-T and Adherence of Human Leukocytes to Retinal Endothelial Cells
Authors: Ben-Mahmud Bahaedin M. , Mann Giovanni E. , Datti Alessandro , Orlacchio Aldo , Kohner Eva M. , Chibber Rakesh
Published: March 2007

A large body of evidence now implicates increased leukocyte-endothelial cell adhesion as a key early event in the development of diabetic retinopathy. We recently reported that raised activity of the glycosylating enzyme core 2 β 1,6-N-acetylglucosaminyltransferase (GlcNAc-T) through protein kinase C (PKC)β2-dependent phosphorylation plays a fundamental role in increased leukocyte-endothelial cell adhesion and capillary occlusion in retinopathy. In the present study, we demonstrate that following exposure to plasma from diabetic patients, the human promonocytic cell line U937 exhibits a significant elevation in core 2 GlcNAc-T activity and increased adherence to cultured retinal capillary endothelial cells. These effects of diabetic plasma on enzyme activity and cell adhesion, mediated by PKCβ2-dependent phosphorylation of the core 2 GlcNAc-T protein, were found to be triggered by increased plasma levels of tumor necrosis factor (TNF)-α. Levels of enzyme activity in plasma-treated U937 cells were closely dependent on the severity of diabetic retinopathy, with the highest values observed upon treatment with plasma of patients affected by proliferative retinopathy. Furthermore, we noted much higher correlation, as compared with control subjects, between increased values of core 2 GlcNAc-T activity and cell adhesion properties. Based on the prominent role of TNF-α in the development of diabetic retinopathy, these observations further validate the significance of core 2 GlcNAc-T in the pathogenesis of capillary occlusion, thereby enhancing the therapeutic potential of specific enzyme inhibitors.
Variation in NCB5OR
Authors: Andersen Gitte , Wegner Lise , Rose Christian Schack , Xie Jianxin , Zhu Hao , Larade Kevin , Johansen Anders , Ek Jakob , Lauenborg Jeannet , Drivsholm Thomas , Borch-Johnsen Knut , Damm Peter , Hansen Torben , Bunn H. Franklin , Pedersen Oluf
Published: March 2007

Recent data show that homozygous Ncb5or−/− knock-out mice present with an early-onset nonautoimmune diabetes phenotype. Furthermore, genome-wide scans have reported linkage to the chromosome 6q14.2 region close to the human NCB5OR. We therefore considered NCB5OR to be a biological and positional candidate gene and examined the coding region of NCB5OR in 120 type 2 diabetic patients and 63 patients with maturity-onset diabetes of the young using denaturing high-performance liquid chromatography. We identified a total of 22 novel nucleotide variants. Three variants [IVS5+7del(CT), Gln187Arg, and His223Arg] were genotyped in a case-control design comprising 1,246 subjects (717 type 2 diabetic patients and 529 subjects with normal glucose tolerance). In addition, four rare variants were investigated for cosegregation with diabetes in multiplex type 2 diabetic families. The IVS5+7del(CT) variant was associated with common late-onset type 2 diabetes; however, we failed to relate this variant to any diabetes-related quantitative traits among the 529 control subjects. Thus, variation in the coding region of NCB5OR is not a major contributor in the pathogenesis of nonautoimmune diabetes.
Common Variants of the Hepatocyte Nuclear Factor-4α P2 Promoter Are Associated With Type 2 Diabetes in the U.K. Population
Authors: Weedon Michael N. , Owen Katharine R. , Shields Beverley , Hitman Graham , Walker Mark , McCarthy Mark I. , Love-Gregory Latisha D. , Permutt M. Alan , Hattersley Andrew T. , Frayling Timothy M.
Published: March 2007

Hepatocyte nuclear factor (HNF)-4α is part of a transcription factor network that is key for the development and function of the β-cell. Rare mutations in the HNF4α gene cause maturity-onset diabetes of the young. A number of type 2 diabetes linkage studies have found evidence of linkage to 20q12–13.1 where the HNF4α gene is located. Two recent studies have found an association between four common variants of the alternative P2 promoter region and type 2 diabetes. These variants are in strong linkage disequilibrium, and the minor alleles define one common risk haplotype. In both studies, the risk haplotype explained a large proportion of the evidence of linkage to 20q12–13.1. We aimed to assess this haplotype in a U.K. Caucasian study of 5,256 subjects. We typed two single nucleotide polymorphisms tagging the risk haplotype (rs4810424 and rs2144908) and found evidence of association in both case-control and family-based studies; rs4810424 marginally demonstrated the stronger association with an overall estimated odds ratio of 1.15 (95% CI 1.02–1.33) (P = 0.02). The effect of the P2 haplotype on type 2 diabetes risk is less than in the initial studies, probably reflecting that these studies used 20q12–13.1–linked cases. In conclusion, we have replicated the association of the HNF4α P2 promoter haplotype with type 2 diabetes in a U.K. Caucasian population where there is no evidence of linkage to 20q.
Exercise-Induced Changes in Insulin and Glucagon Are Not Required for Enhanced Hepatic Glucose Uptake After Exercise but Influence the Fate of Glucose Within the Liver
Authors: Pencek R. Richard , James Freyja D. , Lacy D. Brooks , Jabbour Kareem , Williams Phillip E. , Fueger Patrick T. , Wasserman David H.
Published: March 2007

To test whether pancreatic hormonal changes that occur during exercise are necessary for the postexercise enhancement of insulin-stimulated net hepatic glucose uptake, chronically catheterized dogs were exercised on a treadmill or rested for 150 min. At the onset of exercise, somatostatin was infused into a peripheral vein, and insulin and glucagon were infused in the portal vein to maintain basal levels (EX-Basal) or simulate the response to exercise (EX-Sim). Glucose was infused as needed to maintain euglycemia during exercise. After exercise or rest, somatostatin infusion was continued in exercised dogs and initiated in dogs that had remained sedentary. In addition, basal glucagon, glucose, and insulin were infused in the portal vein for 150 min to create a hyperinsulinemic-hyperglycemic clamp in EX-Basal, EX-Sim, and sedentary dogs. Steady-state measurements were made during the final 50 min of the clamp. During exercise, net hepatic glucose output (mg · kg−1 · min−1) rose in EX-Sim (7.6 ± 2.8) but not EX-Basal (1.9 ± 0.3) dogs. During the hyperinsulinemic-hyperglycemic clamp that followed either exercise or rest, net hepatic glucose uptake (mg · kg−1 · min−1) was elevated in both EX-Basal (4.0 ± 0.7) and EX-Sim (4.6 ± 0.5) dogs compared with sedentary dogs (2.0 ± 0.3). Despite this elevation in net hepatic glucose uptake after exercise, glucose incorporation into hepatic glycogen, determined using [3-3H]glucose, was not different in EX-Basal and sedentary dogs, but was 50 ± 30% greater in EX-Sim dogs. Exercise-induced changes in insulin and glucagon, and consequent glycogen depletion, are not required for the increase in net hepatic glucose uptake after exercise but result in a greater fraction of the glucose consumed by the liver being directed to glycogen.
The α2–5′AMP-Activated Protein Kinase Is a Site 2 Glycogen Synthase Kinase in Skeletal Muscle and Is Responsive to Glucose Loading
Authors: Jørgensen Sebastian B. , Nielsen Jakob N. , Birk Jesper B. , Olsen Grith Skytte , Viollet Benoit , Andreelli Fabrizio , Schjerling Peter , Vaulont Sophie , Hardie D. Grahame , Hansen Bo F. , Richter Erik A. , Wojtaszewski Jørgen F.P.
Published: March 2007

The 5′AMP-activated protein kinase (AMPK) is a potential antidiabetic drug target. Here we show that the pharmacological activation of AMPK by 5-aminoimidazole-1-β-4-carboxamide ribofuranoside (AICAR) leads to inactivation of glycogen synthase (GS) and phosphorylation of GS at Ser 7 (site 2). In muscle of mice with targeted deletion of the α2-AMPK gene, phosphorylation of GS site 2 was decreased under basal conditions and unchanged by AICAR treatment. In contrast, in α1-AMPK knockout mice, the response to AICAR was normal. Fuel surplus (glucose loading) decreased AMPK activation by AICAR, but the phosphorylation of the downstream targets acetyl-CoA carboxylase-β and GS was normal. Fractionation studies suggest that this suppression of AMPK activation was not a direct consequence of AMPK association with membranes or glycogen, because AMPK was phosphorylated to a greater extent in response to AICAR in the membrane/glycogen fraction than in the cytosolic fraction. Thus, the downstream action of AMPK in response to AICAR was unaffected by glucose loading, whereas the action of the kinase upstream of AMPK, as judged by AMPK phosphorylation, was decreased. The fact that α2-AMPK is a GS kinase that inactivates GS while simultaneously activating glucose transport suggests that a balanced view on the suitability for AMPK as an antidiabetic drug target should be taken.
Massive Augmentation of Stimulated Insulin Secretion Induced by Fatty Acid–Free BSA in Rat Pancreatic Islets
Authors: Straub Susanne G. , Sharp Geoffrey W. G.
Published: March 2007

Incubation of rat pancreatic islets for 4–6 h with 100 μmol/l fatty acid-free BSA induced a 3- to 10-fold enhancement of insulin release to a subsequent challenge with 16.7 mmol/l glucose, without changing the typical biphasic pattern of the response. A similar enhancement was observed with other stimuli, such as leucine, depolarizing concentrations of KCl and tolbutamide, pointing to a general phenomenon and common mechanism for the augmentation. Norepinephrine completely blocked the stimulated response. The protein kinase C (PKC) inhibitor Ro 31-8220, which acts at the ATP-binding site and inhibits all PKC isoforms, strongly inhibited the enhancement of a subsequent glucose challenge when present during the BSA pretreatment period. In contrast, Go 6976, an inhibitor of conventional PKC isoforms, was without effect, even at the high concentration of 1 μmol/l. Preincubation with calphostin C, which competes for the diacylglycerol (DAG)-binding site, therefore inhibiting conventional, novel, and PKC isoforms of the PKD type, completely abolished the enhancing effect of the BSA but did not affect secretion in islets treated with 10 μmol/l fatty acid-free BSA. We conclude that the remarkable enhancement of insulin release is due to a change in glucose signaling and activation of a novel PKC isoform or a DAG-binding protein.
Effects of Polyol Pathway Hyperactivity on Protein Kinase C Activity, Nociceptive Peptide Expression, and Neuronal Structure in Dorsal Root Ganglia in Diabetic Mice
Authors: Uehara Kenji , Yamagishi Shin-Ichiro , Otsuki Saori , Chin Shyunsuke , Yagihashi Soroku
Published: March 2007

We explored the specific impact of polyol pathway hyperactivity on dorsal root ganglia (DRG) using transgenic mice that overexpress human aldose reductase because DRG changes are crucial for the development of diabetic sensory neuropathy. Littermate mice served as controls. Half of the animals were made diabetic by streptozotocin injection and followed for 12 weeks. After diabetes onset, diabetic transgenic mice showed a significant elevation of pain sensation threshold after transient decrease and marked slowing of motor and sensory nerve conduction at the end of the study, while these changes were modest in diabetic littermate mice. Protein kinase C (PKC) activities were markedly reduced in diabetic transgenic mice, and the changes were associated with reduced expression of membrane PKC-α isoform that was translocated to cytosol. Membrane PKC-βII isoform expression was contrariwise increased. Calcitonin gene-related peptide–and substance P–positive neurons were reduced in diabetic transgenic mice and less severely so in diabetic littermate mice. Morphometric analysis disclosed neuronal atrophy only in diabetic transgenic mice. Treatment with an aldose reductase inhibitor (fidarestat 4 mg · kg−1 · day−1, orally) corrected all of the changes detected in diabetic transgenic mice. These findings underscore the pathogenic role of aldose reductase in diabetic sensory neuropathy through the altered cellular signaling and peptide expressions in DRG neurons.
Genetic Determinants of Energy Expenditure and Insulin Resistance in Diet-Induced Obesity in Mice
Authors: Almind Katrine , Kahn C. Ronald
Published: March 2007

Diet-induced obesity is the primary determinant of the current epidemic of diabetes. We have explored the role of genetics in this phenomenon, using C57Bl/6 (B6), 129S6/SvEvTac (129), and intercross (B6 × 129)F2 mice on a low- or high-fat diet. Over an 18-week period, B6 and F2 mice gained more weight, had higher levels of insulin and leptin, and showed greater glucose intolerance than 129 mice, despite lower food intake. By contrast, metabolic rate and diet-induced thermogenesis were significantly higher in the 129 mice. Genome-wide scans identified several quantitative trait loci, including a quantitative trait locus that was linked with hyperinsulinemia/insulin resistance on chromosome 14 in a region similar to that seen in mice with genetically induced insulin resistance. Microarray analysis indicated significant changes in expression levels between B6 and 129 mice in the identified chromosomal area of Wnt5a and protein kinase Cδ (PKCδ). Thus, caloric efficiency, i.e., the “thrifty gene,” is a dominant-acting genetic determinant of diet-induced obesity in mice and can be linked to a locus on chromosome 14, including genes linked to adipose development and insulin sensitivity.
Calsquestrin 1 (CASQ1) Gene Polymorphisms Under Chromosome 1q21 Linkage Peak Are Associated With Type 2 Diabetes in Northern European Caucasians
Authors: Das Swapan Kumar , Chu Winston , Zhang Zhengxian , Hasstedt Sandra J. , Elbein Steven C.
Published: March 2007

Genome-wide scans in multiple populations have identified chromosome 1q21-q24 as one susceptibility region for type 2 diabetes. To map the susceptibility genes, we first placed a dense single nucleotide polymorphism (SNP) map across the linked region. We identified two SNPs that showed strong associations, and both mapped to within intron 2 of the calsequestrin 1 (CASQ1) gene. We tested the hypothesis that sequence variation in or near CASQ1 contributed to type 2 diabetes susceptibility in Northern European Caucasians by identifying additional SNPs from the public database and by screening the CASQ1 gene for additional variation. In addition to 15 known SNPs in this region, we found 8 new SNPs, 3 of which were in exons. A single rare nonsynonymous SNP in exon 11 (A348V) was not associated with type 2 diabetes. The associated SNPs were localized to the region between −1,404 in the 5′ flanking region and 2,949 in intron 2 (P = 0.002 to P = 0.034). No SNP 3′ to intron 2, including the adjacent gene PEA15, showed an association. The strongest associations were restricted to individuals of Northern European ancestry ascertained in Utah. A six-marker haplotype was also associated with type 2 diabetes (P = 0.008), but neither transmission disequilibrium test nor family-based association studies were significant for the most strongly associated SNP in intron 2 (SNP CASQ2312). An independent association of SNPs in introns 2 and 4 with type 2 diabetes is reported in Amish families with linkage to chromosome 1q21-q24. Our findings suggest that noncoding SNPs in CASQ1 alter diabetes susceptibility, either by a direct effect on CASQ1 gene expression or perhaps by regulating a nearby gene such as PEA15.
Strength Training Increases Insulin-Mediated Glucose Uptake, GLUT4 Content, and Insulin Signaling in Skeletal Muscle in Patients With Type 2 Diabetes
Authors: Holten Mads K. , Zacho Morten , Gaster Michael , Juel Carsten , Wojtaszewski Jørgen F.P. , Dela Flemming
Published: March 2007

Strength training represents an alternative to endurance training for patients with type 2 diabetes. Little is known about the effect on insulin action and key proteins in skeletal muscle, and the necessary volume of strength training is unknown. A total of 10 type 2 diabetic subjects and 7 healthy men (control subjects) strength-trained one leg three times per week for 6 weeks while the other leg remained untrained. Each session lasted no more than 30 min. After strength training, muscle biopsies were obtained, and an isoglycemic-hyperinsulinemic clamp combined with arterio-femoral venous catheterization of both legs was carried out. In general, qualitatively similar responses were obtained in both groups. During the clamp, leg blood flow was higher (P < 0.05) in trained versus untrained legs, but despite this, arterio-venous extraction glucose did not decrease in trained legs. Thus, leg glucose clearance was increased in trained legs (P < 0.05) and more than explained by increases in muscle mass. Strength training increased protein content of GLUT4, insulin receptor, protein kinase B-α/β, glycogen synthase (GS), and GS total activity. In conclusion, we found that strength training for 30 min three times per week increases insulin action in skeletal muscle in both groups. The adaptation is attributable to local contraction-mediated mechanisms involving key proteins in the insulin signaling cascade.
Hexokinase II Overexpression Improves Exercise-Stimulated But Not Insulin-Stimulated Muscle Glucose Uptake in High-Fat-Fed C57BL/6J Mice
Authors: Fueger Patrick T. , Bracy Deanna P. , Malabanan Carlo M. , Pencek R. Richard , Granner Daryl K. , Wasserman David H.
Published: March 2007

The aim of the present study was to determine the specific sites of impairment to muscle glucose uptake (MGU) in the insulin-resistant high-fat-fed, conscious C57BL/6J mouse. Wild type (WT) and hexokinase II overexpressing (HKTg) mice were fed either a standard diet or high-fat diet and studied at 4 months of age. A carotid artery and jugular veins had catheters chronically implanted for sampling and infusions, respectively, and mice were allowed to recovery for at least 5 days. Mice were fasted for 5 h and underwent a hyperinsulinemic-euglycemic clamp or saline infusion for 120 min. Separate groups of mice were studied during 30-min sedentary or treadmill exercise periods. A bolus of 2-deoxy[3H]glucose was administered 25 min before the end of each study for determination of Rg, an index of tissue-specific glucose uptake. Fasting blood glucose was increased in high-fat compared with standard diet-fed WT (194 ± 4 vs. 171 ± 4 mg/dl) but not HKTg (179 ± 5 vs. 171 ± 3 mg/dl) mice. High-fat feeding created hyperinsulinemia in both WT and HKTg mice (58 ± 8 and 77 ± 15 μU/ml) compared with standard diet-fed mice (21 ± 2 and 20 ± 1 μU/ml). Rg was not affected by genotype or diet during either saline infusion or sedentary conditions. HK II overexpression augmented insulin-stimulated Rg in standard diet-fed but not high-fat-fed mice. Exercise-stimulated Rg was impaired by high-fat feeding in WT mice, but this impairment was largely rectified in HKTg mice. In conclusion, high-fat feeding impairs both insulin- and exercise-stimulated MGU, but only exercise-stimulated MGU was corrected by HK II overexpression.
Prevention of Obesity and Insulin Resistance in Mice Lacking Plasminogen Activator Inhibitor 1
Authors: Ma Li-Jun , Mao Su-Li , Taylor Kevin L. , Kanjanabuch Talerngsak , Guan YouFei , Zhang YaHua , Brown Nancy J. , Swift Larry L. , McGuinness Owen P. , Wasserman David H. , Vaughan Douglas E. , Fogo Agnes B.
Published: March 2007

Increased plasminogen activator inhibitor 1 (PAI-1) has been linked to not only thrombosis and fibrosis but also to obesity and insulin resistance. Increased PAI-1 levels have been presumed to be consequent to obesity. We investigated the interrelationships of PAI-1, obesity, and insulin resistance in a high-fat/high-carbohydrate (HF) diet–induced obesity model in wild-type (WT) and PAI-1–deficient mice (PAI-1−/−). Obesity and insulin resistance developing in WT mice on an HF diet were completely prevented in mice lacking PAI-1. PAI-1−/− mice on an HF diet had increased resting metabolic rates and total energy expenditure compared with WT mice, along with a marked increase in uncoupling protein 3 mRNA expression in skeletal muscle, likely mechanisms contributing to the prevention of obesity. In addition, insulin sensitivity was enhanced significantly in PAI-1−/− mice on an HF diet, as shown by euglycemic-hyperinsulinemic clamp studies. Peroxisome proliferator–activated receptor (PPAR)-γ and adiponectin mRNA, key control molecules in lipid metabolism and insulin sensitivity, were maintained in response to an HF diet in white adipose tissue in PAI-1−/− mice, contrasting with downregulation in WT mice. This maintenance of PPAR-γ and adiponectin may also contribute to the observed maintenance of body weight and insulin sensitivity in PAI-1−/− mice. Treatment in WT mice on an HF diet with the angiotensin type 1 receptor antagonist to downregulate PAI-1 indeed inhibited PAI-1 increases and ameliorated diet-induced obesity, hyperglycemia, and hyperinsulinemia. PAI-1 deficiency also enhanced basal and insulin-stimulated glucose uptake in adipose cells in vitro. Our data suggest that PAI-1 may not merely increase in response to obesity and insulin resistance, but may have a direct causal role in obesity and insulin resistance. Inhibition of PAI-1 might provide a novel anti-obesity and anti–insulin resistance treatment.
Regulation of ATP/ADP in Pancreatic Islets
Authors: Sweet Ian R. , Cook Daniel L. , DeJulio Eric , Wallen Angela R. , Khalil Gamal , Callis James , Reems JoAnna
Published: March 2007

ATP and ADP levels are critical regulators of glucose-stimulated insulin secretion. In many aerobic cell types, the phosphorylation potential (ATP/ADP/Pi) is controlled by sensing mechanisms inherent in mitochondrial metabolism that feed back and induce compensatory changes in electron transport. To determine whether such regulation may contribute to stimulus-secretion coupling in islet cells, we used a recently developed flow culture system to continuously and noninvasively measure cytochrome c redox state and oxygen consumption as indexes of electron transport in perifused isolated rat islets. Increasing substrate availability by increasing glucose increased cytochrome c reduction and oxygen consumption, whereas increasing metabolic demand with glibenclamide increased oxygen consumption but not cytochrome c reduction. The data were analyzed using a kinetic model of the dual control of electron transport and oxygen consumption by substrate availability and energy demand, and ATP/ADP/Pi was estimated as a function of time. ATP/ADP/Pi increased in response to glucose and decreased in response to glibenclamide, consistent with what is known about the effects of these agents on energy state. Therefore, a simple model representing the hypothesized role of mitochondrial coupling in governing phosphorylation potential correctly predicted the directional changes in ATP/ADP/Pi. Thus, the data support the notion that mitochondrial-coupling mechanisms, by virtue of their role in establishing ATP and ADP levels, may play a role in mediating nutrient-stimulated insulin secretion. Our results also offer a new method for continuous noninvasive measures of islet cell phosphorylation potential, a critical metabolic variable that controls insulin secretion by ATP-sensitive K+–dependent and –independent mechanisms.
Diabetes Increases Formation of Advanced Glycation End Products on Sarco(endo)plasmic Reticulum Ca2+-ATPase
Authors: Bidasee Keshore R. , Zhang Yinong , Shao Chun Hong , Wang Mu , Patel Kaushik P. , Dincer Ü. Deniz , Besch Henry R.
Published: March 2007

Prolongation of relaxation is a hallmark of diabetic cardiomyopathy. Most studies attribute this defect to decreases in sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA2a) expression and SERCA2a-to-phospholamban (PLB) ratio. Since its turnover rate is slow, SERCA2a is susceptible to posttranslational modifications during diabetes. These modifications could in turn compromise conformational rearrangements needed to translocate calcium ions, also leading to a decrease in SERCA2a activity. In the present study one such modification was investigated, namely advanced glycation end products (AGEs). Hearts from 8-week streptozotocin-induced diabetic (8D) rats showed typical slowing in relaxation, confirming cardiomyopathy. Hearts from 8D animals also expressed lower levels of SERCA2a protein and higher levels of PLB. Analysis of matrix-assisted laser desorption/ionization time-of-flight mass data files from trypsin-digested SERCA2a revealed several cytosolic SERCA2a peptides from 8D modified by single noncrosslinking AGEs. Crosslinked AGEs were also found. Lysine residues within actuator and phosphorylation domains were cross-linked to arginine residues within the nucleotide binding domain via pentosidine AGEs. Two weeks of insulin-treatment initiated after 6 weeks of diabetes attenuated these changes. These data demonstrate for the first time that AGEs are formed on SERCA2a during diabetes, suggesting a novel mechanism by which cardiac relaxation can be slowed during diabetes.
Linkage and Association Mapping of a Chromosome 1q21-q24 Type 2 Diabetes Susceptibility Locus in Northern European Caucasians
Authors: Das Swapan Kumar , Hasstedt Sandra J. , Zhang Zhengxian , Elbein Steven C.
Published: March 2007

We have identified a region on chromosome 1q21-q24 that was significantly linked to type 2 diabetes in multiplex families of Northern European ancestry and also in Pima Indians, Amish families, and families from France and England. We sought to narrow and map this locus using a combination of linkage and association approaches by typing microsatellite markers at 1.2 and 0.5 cM densities, respectively, over a region of 37 cM (23.5 Mb). We tested linkage by parametric and nonparametric approaches and association using both case-control and family-based methods. In the 40 multiplex families that provided the previous evidence for linkage, the highest parametric, recessive logarithm of odds (LOD) score was 5.29 at marker D1S484 (168.5 cM, 157.5 Mb) without heterogeneity. Nonparametric linkage (NPL) statistics (P = 0.00009), SimWalk2 Statistic A (P = 0.0002), and sib-pair analyses (maximum likelihood score = 6.07) all mapped to the same location. The one LOD CI was narrowed to 156.8–158.9 Mb. Under recessive, two-point linkage analysis, adjacent markers D1S2675 (171.5 cM, 158.9 Mb) and D1S1679 (172 cM, 159.1 Mb) showed LOD scores >3.0. Nonparametric analyses revealed a second linkage peak at 180 cM near marker D1S1158 (163.3 Mb, NPL score 3.88, P = 0.0001), which was also supported by case-control (marker D1S194, 178 cM, 162.1 Mb; P = 0.003) and family-based (marker ATA38A05, 179 cM, 162.5 Mb; P = 0.002) association studies. We propose that the replicated linkage findings actually encompass at least two closely spaced regions, with a second susceptibility region located telomeric at 162.5–164.7 Mb.
Haplotype Tag Single Nucleotide Polymorphism Analysis of the Human Orthologues of the Rat Type 1 Diabetes GenesIan4(Lyp/Iddm1) andCblb
Authors: Payne Felicity , Smyth Deborah J. , Pask Rebecca , Barratt Bryan J. , Cooper Jason D. , Twells Rebecca C.J. , Walker Neil M. , Lam Alex C. , Smink Luc J. , Nutland Sarah , Rance Helen E. , Todd John A.
Published: March 2007

The diabetes-prone BioBreeding (BB) and Komeda diabetes-prone (KDP) rats are both spontaneous animal models of human autoimmune, T-cell-associated type 1 diabetes. Both resemble the human disease, and consequently, susceptibility genes for diabetes found in these two strains can be considered as potential candidate genes in humans. Recently, a frameshift deletion in Ian4, a member of the immune-associated nucleotide (Ian)-related gene family, has been shown to map to BB rat Iddm1. In the KDP rat, a nonsense mutation in the T-cell regulatory gene, Cblb, has been described as a major susceptibility locus. Following a strategy of examining the human orthologues of susceptibility genes identified in animal models for association with type 1 diabetes, we identified single nucleotide polymorphisms (SNPs) from each gene by resequencing PCR product from at least 32 type 1 diabetic patients. Haplotype tag SNPs (htSNPs) were selected and genotyped in 754 affected sib-pair families from the U.K. and U.S. Evaluation of disease association by a multilocus transmission/disequilibrium test (TDT) gave a P value of 0.484 for IAN4L1 and 0.692 for CBLB, suggesting that neither gene influences susceptibility to common alleles of human type 1 diabetes in these populations.
β-Cell Glucose Toxicity, Lipotoxicity, and Chronic Oxidative Stress in Type 2 Diabetes
Authors: Robertson R. Paul , Harmon Jamie , Tran Phuong Oanh T. , Poitout Vincent
Published: March 2007

The relentless decline in β-cell function frequently observed in type 2 diabetic patients, despite optimal drug management, has variously been attributed to glucose toxicity and lipotoxicity. The former theory posits hyperglycemia, an outcome of the disease, as a secondary force that further damages β-cells. The latter theory suggests that the often-associated defect of hyperlipidemia is a primary cause of β-cell dysfunction. We review evidence that patients with type 2 diabetes continually undergo oxidative stress, that elevated glucose concentrations increase levels of reactive oxygen species in β-cells, that islets have intrinsically low antioxidant enzyme defenses, that antioxidant drugs and overexpression of antioxidant enzymes protect β-cells from glucose toxicity, and that lipotoxicity, to the extent it can be attributable to hyperlipidemia, occurs only in the context of preexisting hyperglycemia, whereas glucose toxicity can occur in the absence of hyperlipidemia.
Update on Adipocyte Hormones
Authors: Havel Peter J.
Published: March 2007

Hormones produced by adipose tissue play a critical role in the regulation of energy intake, energy expenditure, and lipid and carbohydrate metabolism. This review will address the biology, actions, and regulation of three adipocyte hormones—leptin, acylation stimulating protein (ASP), and adiponectin—with an emphasis on the most recent literature. The main biological role of leptin appears to be adaptation to reduced energy availability rather than prevention of obesity. In addition to the well-known consequences of absolute leptin deficiency, subjects with heterozygous leptin gene mutations have low circulating leptin levels and increased body adiposity. Leptin treatment dramatically improves metabolic abnormalities (insulin resistance and hyperlipidemia) in patients with relative leptin deficiency due to lipoatrophy. Leptin production is primarily regulated by insulin-induced changes of adipocyte metabolism. Dietary fat and fructose, which do not increase insulin secretion, lead to reduced leptin production, suggesting a mechanism for high-fat/high-sugar diets to increase energy intake and weight gain. ASP increases the efficiency of triacylglycerol synthesis in adipocytes leading to enhanced postprandial lipid clearance. In mice, ASP deficiency results in reduced body fat, obesity resistance, and improved insulin sensitivity. Adiponectin production is stimulated by thiazolidinedione agonists of peroxisome proliferator-activated receptor-γ and may contribute to increased insulin sensitivity. Adiponectin and leptin cotreatment normalizes insulin action in lipoatrophic insulin-resistant animals. These effects may be mediated by AMP kinase-induced fat oxidation, leading to reduced intramyocellular and liver triglyceride content. The production of all three hormones is influenced by nutritional status. These hormones, the pathways controlling their production, and their receptors are promising targets for managing obesity, hyperlipidemia, and insulin resistance.
The Role of Cytosolic Phospholipase A2 in Insulin Secretion
Authors: Jones Peter M. , Burns Christopher J. , Belin Véronique D. , Roderigo-Milne Helen M. , Persaud Shanta J.
Published: March 2007

Cytosolic phospholipase A2 (cPLA2) comprises a widely expressed family of enzymes, some members of which have the properties required of signal transduction elements in electrically excitable cells. Thus, α- and β-isoforms of cPLA2 are activated by the increases in intracellular Ca2+ concentration ([Ca2+]i) achieved in depolarized cells. Activation is associated with a redistribution of the enzyme within the cell; activation of cPLA2 generates arachidonic acid (AA), a biologically active unsaturated fatty acid that can be further metabolized to generate a plethora of biologically active molecules. Studies using relatively nonselective pharmacological inhibitors have implicated cPLA2 in insulin secretory responses to stimuli that elevate β-cell [Ca2+]i; therefore, we have investigated the role of cPLA2 in β-cell function by generating β-cell lines that under- or overexpress the α-isoform of cPLA2. The functional phenotype of the modified cells was assessed by observation of cellular ultrastructure, by measuring insulin gene expression and insulin protein content, and by measuring the effects of insulin secretagogues on cPLA2 distribution, on changes in [Ca2+]i, and on the rate and pattern of insulin secretion. Our results suggest that cPLA2 is not required for the initiation of insulin secretion from β-cells, but that it plays an important role in the maintenance of β-cell insulin stores. Our data also demonstrate that excessive production of, or exposure to, AA is deleterious to normal β-cell secretory function through metabolic dysfunction.
Differential Levels of Diabetogenic Stress in Two New Mouse Models of Obesity and Type 2 Diabetes
Authors: Leiter Edward H. , Reifsnyder Peter C.
Published: March 2007

The genetic basis for the more common forms of human obesity predisposing to insulin resistance and development of type 2 diabetes is multigenic rather than monogenic in origin. New mouse “diabesity” models have been created by combining independent diabetes risk-conferring quantitative trait loci from two unrelated parental strains: New Zealand Obese (NZO/HlLt) and Nonobese Nondiabetic (NON/Lt). F1 hybrid males, heterozygous at all polymorphic autosomal loci distinguishing the two parental strains, are driven to obesity-induced diabetes (diabesity) at high frequencies. This review focuses on two new recombinant congenic strains (RCSs) developed by introgressing multiple NZO/HlLt chromosomal segments into the nominally diabesity-resistant NON/Lt strain background. Both RCSs gain more weight than NON animals. Although exhibiting comparable weight gain and adiposity, only one of the two RCSs develops diabetes. Hence, these two RCSs will be instructive in elucidating genetic and pathophysiological differences underlying uncomplicated obesity syndromes versus diabetogenic obesity (diabesity) syndromes. Unlike mice with null mutations in a single gene producing morbid obesity, the new models develop a more moderate obesity produced by the interaction of numerous genes with relatively small effects. These RCSs are differentially sensitive to adverse side effects of thiazolidinediones and thus should be particularly useful for pharmacogenetic analyses.
Potential Role of Peroxisome Proliferator-Activated Receptor-α in the Modulation of Glucose-Stimulated Insulin Secretion
Authors: Sugden Mary C. , Holness Mark J.
Published: March 2007

In this review, we discuss the influence of peroxisome proliferator-activated receptor (PPAR)-α on islet insulin secretion and develop the hypothesis that modulation of PPAR-α function may be important for the regulation of compensatory insulin secretion. We have attempted to analyze the role of PPAR-α-linked fatty acid metabolism in islet function in health and in insulin-resistant states linked to lifestyle factors, in particular pregnancy and a diet inappropriately high in saturated fat. We have emphasized the potential for both actions of PPAR-α on insulin sensitivity that may be relayed systemically to the islet, leading to modulation of the insulin response in accordance with changes in insulin sensitivity, and direct effects of PPAR-α action on the islet itself. Finally, we have developed the concept that compensatory insulin secretion may have a function not only in glucoregulation but also in liporegulation. Thus, augmented insulin secretion may reflect a requirement for lipid lowering as well as for increased glucose disposal and is perceived to aim to compensate for impaired suppression of islet lipid delivery by insulin. This introduces the possibility of a continuum between liporegulation with islet compensation and lipodysregulation leading to islet decompensation in the development of type 2 diabetes.
Nuclear Protein p8 Is Associated With Glucose-Induced Pancreatic β-Cell Growth
Authors: Päth Günter , Opel Anne , Knoll Anita , Seufert Jochen
Published: March 2007

On its own, glucose is a major factor for proliferation of pancreatic β-cells and is also an essential prerequisite for IGF-I and growth hormone-induced growth of these cells. p8 was originally identified as an emergency gene product upregulated in pancreatic acinar cells in response to acute pancreatitis. p8 was further shown to be involved in a broad range of biological functions, including cell growth, growth arrest, apoptosis, and tumor development. These in part opposite actions may be related to distinct stimuli and pathways in certain conditions and cell types. Here we demonstrate that p8 is widely expressed in human pancreatic islets in vivo and in several β-cell lines in vitro. Based on this observation, we tested the hypothesis that p8 production in pancreatic β-cells is regulated by glucose. Incubation of rat INS-1 β-cells with 25 mmol/l glucose resulted in a continuous increase of proliferating cell numbers. This was accompanied by a strong upregulation of p8 mRNA and protein expression, indicating that p8 is a physiological mediator of glucose-induced pancreatic β-cell growth. Binding of glucose-activated protein kinase C (PKC) to two PKC sites within a highly conserved region of the p8 protein may be a possible mechanism linking glucose and p8 pathways leading to proliferation.
Roles of Mitochondria in Health and Disease
Authors: Duchen Michael R.
Published: March 2007

Mitochondria play a central role in cell life and cell death. An increasing number of studies place mitochondrial dysfunction at the heart of disease, most notably in the heart and the central nervous system. In this article, I review some of the key features of mitochondrial biology and focus on the pathways of mitochondrial calcium accumulation. Substantial evidence now suggests that the accumulation of calcium into mitochondria may play a key role as a trigger to mitochondrial pathology, especially when that calcium uptake is accompanied by another stressor, in particular nitrosative or oxidative stress. The major process involved is the opening of the mitochondrial permeability transition pore, a large conductance pore that causes a collapse of the mitochondrial membrane potential, leading to ATP depletion and necrotic cell death or to cytochrome c release and apoptosis, depending on the rate of ATP consumption. I discuss two models in particular in which these processes have been characterized. The first is a model of oxidative stress in cardiomyocytes, in which reperfusion after ischemia causes mitochondrial calcium overload, and oxidative stress. Recent experiments suggest that cardioprotection by hypoxic preconditioning or exposure to the ATP-dependent K+ channel opener diazoxide increases mitochondrial resistance to oxidative injury. In a second model, of calcium overload in neurons, the neurotoxicity of glutamate depends on mitochondrial calcium uptake, but the toxicity to mitochondria also requires the generation of nitric oxide. Glutamate toxicity after activation of N-methyl-d-aspartate (NMDA) receptors results from the colocalization of NMDA receptors with neuronal nitric oxide synthase (nNOS). The calcium increase mediated by NMDA receptor activation is thus associated with nitric oxide generation, and the combination leads to the collapse of mitochondrial membrane potential followed by cell death.