bluuebunny/crossref_metadata_2025 huggingface dataset:
A Gene Conferring Susceptibility to Type 2 Diabetes in Conjunction With Obesity Is Located on Chromosome 18p11
Authors: Parker Alex , Meyer Joanne , Lewitzky Steve , Rennich Jean S. , Chan Gayun , Thomas Jeffrey D. , Orho-Melander Marju , Lehtovirta Mikko , Forsblom Carol , Hyrkkö Auli , Carlsson Martin , Lindgren Cecilia , Groop Leif C.
Published: March 2007

Genome-wide nonparametric linkage analysis of 480 sib-pairs affected with type 2 diabetes revealed linkage to a previously unreported susceptibility locus on chromosome 18p11. This result improved with stringent subphenotyping using age- and sex-adjusted BMI, ultimately reaching a logarithm of odds of 3.82 (allele sharing 0.6654) at a point between markers D18S976 and D18S391 when the most obese 20% of the sample was analyzed. Several genes on chromosome 18 have been suggested as metabolic disease candidates, but none of these colocalize with our linkage result. We conclude that our results provide support for the presence of a currently uncharacterized gene on chromosome 18p, certain alleles of which confer increased susceptibility to type 2 diabetes in conjunction with obesity. We additionally observed moderate evidence for linkage to chromosome 1, near marker D1S3462; chromosome 4, near marker D4S2361; chromosome 5, near marker D5S1505; and chromosome 17, near marker D17S1301.
Evidence for Gene-Nutrient Interaction at the PPARγ Locus
Authors: Luan Jian’an , Browne Paul O. , Harding Anne-Helen , Halsall David J. , O’Rahilly Stephen , Chatterjee V.K. Krishna , Wareham Nicholas J.
Published: March 2007

The importance of the nuclear receptor peroxisome proliferator–activated receptor-γ (PPARγ) in regulating insulin resistance and blood pressure has been demonstrated in families with loss of function mutations. Gain of function mutations has been associated with severe obesity. However, previous population studies of the common variant Pro12Ala have produced conflicting results. As it is likely that the natural ligands for this receptor may include fatty acids, we hypothesized that the effect of this common variant may be altered by the character of the diet, particularly the ratio of dietary polyunsaturated fat to saturated fat (P:S ratio). We studied 592 nondiabetic participants in an ongoing population-based cohort study who were genotyped for the Pro12Ala polymorphism in the PPAR γ2 isoform. As the Ala homozygotes were uncommon (2.0%), all analyses were conducted comparing Pro homozygotes (79.1%) to Ala allele carriers. There was no difference in fasting insulin concentration or BMI between Ala allele carriers and Pro homozygotes. The fasting insulin concentration was negatively associated with the P:S ratio (P = 0.0119) after adjustment for age and sex, and a strong interaction was evident between the P:S ratio and the Pro12Ala polymorphism for both BMI (P = 0.0038) and fasting insulin (P = 0.0097). The data suggest that when the dietary P:S ratio is low, the BMI in Ala carriers is greater than that in Pro homozygotes, but when the dietary ratio is high, the opposite is seen. This gene-nutrient interaction emphasizes the difficulty of examining the effect of common polymorphisms in the absence of data on nongenetic exposures, and may explain the heterogeneity of findings in previous studies.
In Vitro and In Vivo Studies of a Naturally Occurring Variant of the Human p85α Regulatory Subunit of the Phosphoinositide 3-Kinase
Authors: Hansen Lars , Zethelius Björn , Berglund Lars , Reneland Richard , Hansen Torben , Berne Christian , Lithell Hans , Hemmings Brian A. , Pedersen Oluf
Published: March 2007

In humans, the Met326Ile missense variant of the p85α regulatory subunit of the phosphoinositide 3-kinase (PI3K) has been associated with either significant reductions in glucose effectiveness and intravenous glucose tolerance in Caucasians or a significantly higher insulin secretory response in Pima Indians. In the present study, we genotyped 1,190 Caucasian males to evaluate the impact in vivo of the Met326Ile variant of the p85α subunit of PI3K on the acute insulin response, intravenous glucose tolerance, insulin-mediated glucose uptake, and the prevalence of type 2 diabetes after 20 years of follow-up. We also expressed the variant in vitro to evaluate the impact on insulin-stimulated activation of protein kinase B (PKB). The Met326Ile variant of p85α was not associated with type 2 diabetes or with alterations in insulin secretion, insulin sensitivity, or intravenous glucose tolerance in vivo. Expressed in vitro, the Ile326 and the Met326 variant acted equally as a dominant-negative and prevented (60–70% inhibition) insulin-mediated activation of PKB by inhibiting the phosphorylation of PKB at Thr308. We conclude that the Met326Ile variant of the p85α regulatory subunit of PI3K is likely to be as functionally normal in vivo as in vitro.
Mutations in the Coding Region of the Neurogenin 3 Gene (NEUROG3) Are Not a Common Cause of Maturity-Onset Diabetes of the Young in Japanese Subjects
Authors: del Bosque-Plata Laura , Lin Joseph , Horikawa Yukio , Schwarz Peter E.H. , Cox Nancy J. , Iwasaki Naoko , Ogata Makiko , Iwamoto Yasuhiko , German Michael S. , Bell Graeme I.
Published: March 2007

Mutations in transcription factors that play a role in the development of the endocrine pancreas, such as insulin promoter factor-1 and NeuroD1/BETA2, have been associated with diabetes. Cell type–specific members of the basic helix-loop-helix (bHLH) family of transcription factors play essential roles in the development and maintenance of many differentiated cell types, including pancreatic β-cells. Neurogenin 3 is a bHLH transcription factor that is expressed in the developing central nervous system and the embryonic pancreas. Mice lacking this transcription factor fail to develop any islet endocrine cells and die postnatally from diabetes. Because neurogenin 3 is required for the development of β-cells and other pancreatic islet cell types, we considered it a candidate diabetes gene. We screened the coding region of the human neurogenin 3 gene (NEUROG3) for mutations in a group of unrelated Japanese subjects with maturity-onset diabetes of the young (MODY). We found three sequence variants: a deletion of 2-bp in the 5′-untranslated region (NEUROG3-g.-44–45delCA), a G-to-A substitution in codon 167 (g.499G/A), resulting in a Gly-to-Arg replacement (G/R167), and a T-to-C substitution in codon 199 (g.596T/C), resulting in a Phe/Ser polymorphism F/S199. These polymorphisms were not associated with MODY, thereby suggesting that mutations in NEUROG3 are not a common cause of MODY in Japanese patients.
Control of Glycogen Synthesis by Glucose, Glycogen, and Insulin in Cultured Human Muscle Cells
Authors: Halse Reza , Bonavaud Sylvie M. , Armstrong Jane L. , McCormack James G. , Yeaman Stephen J.
Published: March 2007

A key feature of type 2 diabetes is impairment in the stimulation of glycogen synthesis in skeletal muscle by insulin. Glycogen synthesis and the activity of the enzyme glycogen synthase (GS) have been studied in human myoblasts in culture under a variety of experimental conditions. Incubation in the absence of glucose for up to 6 h caused an ∼50% decrease in glycogen content, which was associated with a small decrease in the fractional activity of GS. Subsequent reincubation with physiological concentrations of glucose led to a dramatic increase in the rate of glycogen synthesis and in the fractional activity of GS, an effect which was both time- and glucose concentration–dependent and essentially additive with the effects of insulin. This effect was seen only after glycogen depletion. Inhibitors of signaling pathways involved in the stimulation of glycogen synthesis by insulin were without significant effect on the stimulatory action of glucose. These results indicate that at least two distinct mechanisms exist to stimulate glycogen synthesis in human muscle: one acting in response to insulin and the other acting in response to glucose after glycogen depletion, such as that which results from exercise or starvation.
In Normal Men, Free Fatty Acids Reduce Peripheral but Not Splanchnic Glucose Uptake
Authors: Rigalleau Vincent , Binnert Christophe , Minehira Kaori , Stefanoni Nathalie , Schneiter Phillippe , Henchoz Emmanuel , Matzinger Oscar , Cayeux Christine , Jéquier Eric , Tappy Luc
Published: March 2007

Raising plasma free fatty acid (FFA) levels reduces muscle glucose uptake, but the effect of FFAs on splanchnic glucose uptake, total glucose output, and glucose cycling may also be critical to producing lipid-induced glucose intolerance. In eight normal volunteers, we measured glucose turnover and cycling rates ([2H7]glucose infusion) during a moderately hyperglycemic (7.7 mmol/l) hyperinsulinemic clamp, before and after ingestion of a labeled (dideuterated) oral glucose load (700 mg/kg). Each test was performed twice, with either a lipid or a saline infusion; four subjects also had a third test with a glycerol infusion. As shown by similar rates of exogenous glucose appearance, the lipid infusion did not reduce first-pass splanchnic glucose uptake (saline 1.48 ± 0.18, lipid 1.69 ± 0.17, and glycerol 1.88 ± 0.17 mmol/kg per 180 min; NS), but it reduced peripheral glucose uptake by 40% (P < 0.01 vs. both saline and glycerol infusions). Before oral ingestion of glucose, total glucose output was similarly increased by the lipid and glycerol infusions. Total glucose output was significantly increased by FFAs after oral ingestion of glucose (saline 3.68 ± 1.15, glycerol 3.68 ± 1.70, and lipid 7.92 ± 0.88 μmol · kg–1 · min–1; P < 0.01 vs. saline and P < 0.05 vs. glycerol). The glucose cycling rate was ∼2.7 μmol · kg–1 · min–1 with the three infusions and tended to decrease all along the lipid infusion, which argues against a stimulation of glucose-6-phosphatase by FFAs. It is concluded that in situations of moderate hyperinsulinemia-hyperglycemia, FFAs reduce peripheral but not splanchnic glucose uptake. Total glucose output is increased by FFAs, by a mechanism that does not seem to involve stimulation of glucose-6-phosphatase.
Cerulenin Mimics Effects of Leptin on Metabolic Rate, Food Intake, and Body Weight Independent of the Melanocortin System, but Unlike Leptin, Cerulenin Fails to Block Neuroendocrine Effects of Fasting
Authors: Makimura Hideo , Mizuno Tooru M. , Yang Xue-Jun , Silverstein Jeff , Beasley Joe , Mobbs Charles V.
Published: March 2007

Cerulenin and a related compound, C75, have recently been reported to reduce food intake and body weight independent of leptin through a mechanism hypothesized, like leptin, to involve hypothalamic nutrition-sensitive neurons. To assess whether these inhibitors act through mechanisms similar to mechanisms engaged by leptin, ob/ob and Ay (agouti) mice, as well as fed and fasted wild-type mice, were treated with cerulenin. Like leptin, cerulenin reduced body weight and food intake and increased metabolic rate in ob/ob mice, and cerulenin produced the same effects in wild-type mice, whereas lithium chloride, at doses that produce conditioned taste aversion, reduced metabolic rate. However, in contrast to leptin, cerulenin did not prevent effects of fasting on plasma corticosterone or hypothalamic levels of neuropeptide Y, agouti-related peptide, pro-opiomelanocortin, or cocaine- and amphetamine-related peptide mRNA. Also, in contrast to leptin, cerulenin was highly effective to reduce body weight in Ay mice, in which obesity is caused by blockade of the melanocortin receptor. These data demonstrate that cerulenin produces metabolic effects similar to effects of leptin, but through mechanisms that are independent of, or down-stream from, both leptin and melanocortin receptors.
Development and Function of Diabetogenic T-cells in B-cell–Deficient Nonobese Diabetic Mice
Authors: Chiu Priscilla P.L. , Serreze David V. , Danska Jayne S.
Published: March 2007

Insulin-dependent diabetes (type 1 diabetes) in the NOD mouse is a T-cell–mediated autoimmune disease. However, B-cells may also play a critical role in disease pathogenesis, as genetically B-cell–deficient NOD mice (NOD.μMT) have been shown to be protected from type 1 diabetes and to display reduced responses to certain islet autoantigens. To examine the requirements for B-cells in the development of type 1 diabetes, we generated a B-cell–naive T-cell repertoire by transplantation of NOD fetal thymuses (FTs) into NOD.scid recipients. Surprisingly, these FT-derived NOD T-cells were diabetogenic in 36% of NOD.scid recipients, despite the absence of B-cells. In addition, T-cells isolated from NOD.μMT mice were diabetogenic in 22% of NOD.scid recipients. Together, these results indicate that B-cells are not an absolute requirement for the generation or effector function of an islet-reactive T-cell repertoire in NOD mice. We suggest that conditions favoring rapid lymphocyte expansion can reveal autoreactive T-cell activity and precipitate disease in genetically susceptible individuals.
Mucosal Antigen Primes Diabetogenic Cytotoxic T-Lymphocytes Regardless of Dose or Delivery Route
Authors: Hänninen Arno , Braakhuis Andrea , Heath William R. , Harrison Leonard C.
Published: March 2007

Administration of antigens via mucosal routes, such as orally or intranasally, can induce specific immunological tolerance and has been used as a rational basis for the treatment of autoimmune diseases, including type 1 diabetes. Recently, however, orally delivered antigens were shown to induce CD8 cytotoxic T-lymphocytes (CTLs) capable of causing autoimmune diabetes. In this report, we have examined several mucosal routes for their ability to induce CTLs and autoimmune diabetes, with the aim of identifying approaches that would maximize tolerance and minimize CTL generation. In normal C57BL/6 mice, ovalbumin (OVA) delivered by either the oral or nasal routes or by aerosol inhalation was able to prime CTL immunity in both high- and low-dose regimens. To address the relevance of these CTLs to autoimmune disease, OVA was given to mice that transgenically expressed this antigen in their pancreatic β-cells. Irrespective of antigen dose or the route of delivery, mucosal OVA triggered diabetes, particularly after intranasal administration. These findings suggest that CTL immunity is likely to be a consequence of mucosal antigen delivery, regardless of the regimen, and should be considered in the clinical application of mucosal tolerance to autoimmune disease prevention.
Glucagon-Like Peptide 1 Increases Secretory Burst Mass of Pulsatile Insulin Secretion in Patients With Type 2 Diabetes and Impaired Glucose Tolerance
Authors: Ritzel Robert , Schulte Miriam , Pørksen Niels , Nauck Markus S. , Holst Jens J. , Juhl Claus , März Winfried , Schmitz Ole , Schmiegel Wolff H. , Nauck Michael A.
Published: March 2007

The insulinotropic gut hormone glucagon-like peptide (GLP)-1 increases secretory burst mass and the amplitude of pulsatile insulin secretion in healthy volunteers without affecting burst frequency. Effects of GLP-1 on secretory mechanisms in type 2 diabetic patients and subjects with impaired glucose tolerance (IGT) known to have impaired pulsatile release of insulin have not yet been studied. Eight type 2 diabetic patients (64 ± 9 years, BMI 28.9 ± 7.2 kg/m2, HbA1c 7.7 ± 1.3%) and eight subjects with IGT (63 ± 10 years, BMI 31.7 ± 6.4 kg/m2, HbA1c 5.7 ± 0.4) were studied on separate occasions in the fasting state during the continued administration of exogenous GLP-1 (1.2 pmol · kg−1 · min−1, started at 10:00 p.m. the evening before) or placebo. For comparison, eight healthy volunteers (62 ± 7 years, BMI 27.7 ± 4.8 kg/m2, HbA1c 5.4 ± 0.5) were studied only with placebo. Blood was sampled continuously over 60 min (roller-pump) in 1-min fractions for the measurement of plasma glucose and insulin. Pulsatile insulin secretion was characterized by deconvolution, autocorrelation, and spectral analysis and by estimating the degree of randomness (approximate entropy). In type 2 diabetic patients, exogenous GLP-1 at ∼90 pmol/l improved plasma glucose concentrations (6.4 ± 2.1 mmol/l vs. placebo 9.8 ± 4.1 mmol/l, P = 0.0005) and significantly increased mean insulin burst mass (by 68%, P = 0.007) and amplitude (by 59%, P = 0.006; deconvolution analysis). In IGT subjects, burst mass was increased by 45% (P = 0.019) and amplitude by 38% (P = 0.02). By deconvolution analysis, insulin secretory burst frequency was not affected by GLP-1 in either type 2 diabetic patients (P = 0.15) or IGT subjects (P = 0.76). However, by both autocorrelation and spectral analysis, GLP-1 prolonged the period (lag time) between subsequent maxima of insulin concentrations significantly from ∼9 to ∼13 min in both type 2 diabetic patients and IGT subjects. Under placebo conditions, parameters of pulsatile insulin secretion were similar in normal subjects, type 2 diabetic patients, and IGT subjects based on all methodological approaches (P > 0.05). In conclusion, intravenous GLP-1 reduces plasma glucose in type 2 diabetic patients and improves the oscillatory secretion pattern by amplifying insulin secretory burst mass, whereas the oscillatory period determined by autocorrelation and spectral analysis is significantly prolonged. This was not the case for the interpulse interval determined by deconvolution. Together, these results suggest a normalization of the pulsatile pattern of insulin secretion by GLP-1, which supports the future therapeutic use of GLP-1–derived agents.
Glucagon-Like Peptide 1 Induces Differentiation of Islet Duodenal Homeobox-1–Positive Pancreatic Ductal Cells Into Insulin-Secreting Cells
Authors: Hui Hongxiang , Wright Chris , Perfetti Riccardo
Published: March 2007

Glucagon-like peptide-1 (GLP-1) is an incretin hormone capable of restoring normal glucose tolerance in aging glucose-intolerant Wistar rats. Whether the antidiabetic properties of GLP-1 are exclusively due to its insulin secretory activity remains to be determined. A GLP-1–dependent differentiation of pancreatic precursor cells into mature β-cells has recently been proposed. The aim of this study was to investigate whether pancreatic ductal epithelial cells could be differentiated into insulin-secreting cells by exposing them to GLP-1. Rat (ARIP) and human (PANC-1) cell lines, both derived from the pancreatic ductal epithelium, were used to test this hypothesis. A major difference distinguishes these two cell lines: whereas ARIP cells spontaneously express the β-cell differentiation factor islet duodenal homeobox-1 (IDX-1), PANC-1 cells are characteristically IDX-1 negative. GLP-1 induced the differentiation of ARIP cells into insulin-synthesizing cells, although it did not affect the phenotype of PANC-1 cells, as determined by fluorescence-activated cell sorting (FACS) analysis. Differentiation of ARIP cells by exposure to human GLP-1 occurs in a time- and dose-dependent manner, and this is associated with an increase in IDX-1 and insulin mRNA levels. Secretion of insulin was also induced in a parallel manner, and it was regulated by the concentration of glucose in the culture medium. Interestingly, PANC-1 cells, when stably transfected with human IDX-1, gained responsiveness to GLP-1 and were able to differentiate into β-cells, as determined by FACS analysis, insulin gene expression, intracellular insulin content, and insulin accumulation in the culture medium. Finally, we demonstrated that the receptor for GLP-1 is constitutively expressed by ARIP and PANC-1 cells and that the mRNA level for this transcript was increased by cellular transfection with human IDX-1. In summary, our study provides evidence that GLP-1 is a differentiation factor for pancreatic ductal cells and that its effect requires the expression of IDX-1.
The Novel Imidazoline Compound BL11282 Potentiates Glucose-Induced Insulin Secretion in Pancreatic β-Cells in the Absence of Modulation of KATP Channel Activity
Authors: Efanov Alexander M. , Zaitsev Sergei V. , Mest Hans-Juergen , Raap Achim , Appelskog Ioulia B. , Larsson Olof , Berggren Per-Olof , Efendic Suad
Published: March 2007

The insulinotropic activity of the novel imidazoline compound BL11282 was investigated. Intravenous administration of BL11282 (0.3 mg · kg–1 · min–1) to anesthetized rats did not change blood glucose and insulin levels under basal conditions, but produced a higher increase in blood insulin levels and a faster glucose removal from the blood after glucose infusion. Similarly, in isolated Wistar rat pancreatic islets, 0.1–100 μmol/l BL11282 potently stimulated glucose-induced insulin secretion but did not modulate basal insulin secretion. Unlike previously described imidazolines, BL11282 did not block ATP-dependent K+ channels. Furthermore, the compound stimulated insulin secretion in islets depolarized with high concentrations of KCl or permeabilized with electric shock. Insulinotropic activity of BL11282 was dependent on activity of protein kinases A and C. In pancreatic islets from spontaneously diabetic GK rats, the imidazoline compound restored the impaired insulin response to glucose. In conclusion, the imidazoline BL11282 constitutes a new class of insulinotropic compounds that exerts an exclusive glucose-dependent insulinotropic activity in pancreatic islets by stimulating insulin exocytosis.
Skeletal Muscle Lipid Content and Oxidative Enzyme Activity in Relation to Muscle Fiber Type in Type 2 Diabetes and Obesity
Authors: He Jing , Watkins Simon , Kelley David E.
Published: March 2007

In obesity and type 2 diabetes, skeletal muscle has been observed to have a reduced oxidative enzyme activity, increased glycolytic activity, and increased lipid content. These metabolic characteristics are related to insulin resistance of skeletal muscle and are factors potentially related to muscle fiber type. The current study was undertaken to examine the interactions of muscle fiber type in relation to oxidative enzyme activity, glycolytic enzyme activity, and muscle lipid content in obese and type 2 diabetic subjects compared with lean healthy volunteers. The method of single-fiber analysis was used on vastus lateralis muscle obtained by percutaneous biopsy from 22 lean, 20 obese, and 20 type 2 diabetic subjects (ages 35 ± 1, 42 ± 2, and 52 ± 2 years, respectively), with values for BMI that were similar in obese and diabetic subjects (23.7 ± 0.7, 33.2 ± 0.8, and 31.8 ± 0.8 kg/m2, respectively). Oxidative enzyme activity followed the order of type I > type IIa > type IIb, but within each fiber type, skeletal muscle from obese and type 2 diabetic subjects had lower oxidative enzyme activity than muscle from lean subjects (P < 0.01). Muscle lipid content followed a similar pattern in relation to fiber type, and within each fiber type, muscle from obese and type 2 diabetic subjects had greater lipid content (P < 0.01). In summary, based on single-fiber analysis, skeletal muscle in obese and type 2 diabetic subjects mani-fests disturbances of oxidative enzyme activity and increased lipid content that are independent of the effect of fiber type.
The Q Allele Variant (GLN121) of Membrane Glycoprotein PC-1 Interacts With the Insulin Receptor and Inhibits Insulin Signaling More Effectively Than the Common K Allele Variant (LYS121)
Authors: Costanzo Benedetta V. , Trischitta Vincenzo , Di Paola Rosa , Spampinato Daniela , Pizzuti Antonio , Vigneri Riccardo , Frittitta Lucia
Published: March 2007

When overexpressed, the membrane glycoprotein PC-1 may play a role in human insulin resistance through the inhibition of insulin receptor (IR) autophosphorylation. A PC-1 variant (K121Q, with lysine 121 replaced by glutamine) is also associated with whole-body insulin resistance when not overexpressed. To better understand the effects of the Q allele on IR function and downstream signaling, we transfected cultured cells with cDNAs for either the Q or the K alleles. In human MCF-7 cells, the Q allele was severalfold more effective (P < 0.05–0.01) than the K allele in reducing insulin stimulation of IR autophosphorylation, insulin receptor substrate-1 phosphorylation, phosphatidylinositol 3-kinase activity, glycogen synthesis, and cell proliferation. Similar data on IR autophosphorylation inhibition were also obtained in mouse R−/hIR and human HEK 293 cell lines. In transfected MCF-7 cells, 125I-labeled insulin binding and IR content were unchanged, and PC-1 overexpression did not influence IGF-1 stimulation of IGF-1 receptor autophosphorylation. Both the Q and K alleles directly interacted with the IR, as documented by coimmunoprecipitation assays. This interaction was greater for the Q allele than for the K allele (P < 0.01), suggesting that direct PC-1–IR interactions are important for the PC-1 inhibitory effect on insulin signaling. In conclusion, the Q allele has stronger inhibitory activity on IR function and insulin action than the more common K allele, and this is likely a consequence of the intrinsic characteristics of the molecule, which more strongly interacts with the IR.
Diabetes Accelerates Smooth Muscle Accumulation in Lesions of Atherosclerosis
Authors: Suzuki Lucy A. , Poot Martin , Gerrity Ross G. , Bornfeldt Karin E.
Published: March 2007

In combination with other factors, hyperglycemia may cause the accelerated progression of atherosclerosis in people with diabetes. Arterial smooth muscle cell (SMC) proliferation and accumulation contribute to formation of advanced atherosclerotic lesions. Therefore, we investigated the effects of hyperglycemia on SMC proliferation and accumulation in vivo and in isolated arteries and SMCs by taking advantage of a new porcine model of diabetes-accelerated atherosclerosis, in which diabetic animals are hyperglycemic without receiving exogenous insulin. We show that diabetic animals fed a cholesterol-rich diet, like humans, develop severe lesions of atherosclerosis characterized by SMC accumulation and proliferation, whereas lesions in nondiabetic animals contain fewer SMCs after 20 weeks. However, high glucose (25 mmol/l) does not directly stimulate the proliferation of SMCs in isolated arterial tissue from diabetic or nondiabetic animals, or of cultured SMCs from these animals or from humans. Furthermore, the mitogenic actions of platelet-derived growth factor, IGF-I, or serum are not enhanced by high glucose. High glucose increases SMC glucose metabolism through the citric acid cycle and the pentose phosphate pathway by 240 and 90%, respectively, but <10% of consumed glucose is metabolized through these pathways. Instead, most of the consumed glucose is converted into lactate and secreted by the SMCs. Thus, diabetes markedly accelerates SMC proliferation and accumulation in atherosclerotic lesions. The stimulatory effect of diabetes on SMCs is likely to be mediated by effects secondary to the hyperglycemic state.
Angiotensin II Induces Expression of the Tie2 Receptor Ligand, Angiopoietin-2, in Bovine Retinal Endothelial Cells
Authors: Otani Atsushi , Takagi Hitoshi , Oh Hideyasu , Koyama Shinji , Honda Yoshihito
Published: March 2007

Recent studies have shown that angiopoietins (Angs) and their receptor, Tie2, play a role in vascular integrity and neovascularization. The renin-angiotensin system has been hypothesized to contribute to the development of diabetic retinopathy. In this study, we investigated the effect of angiotensin II (AII) on Ang1 and Ang2 expression in cultured bovine retinal endothelial cells (BRECs). AII stimulated Ang2 but not Ang1 mRNA expression in a dose- and time-dependent manner. This response was inhibited completely by angiotensin type 1 receptor (AT1) antagonist. AII increased the transcription of Ang2 mRNA, but did not change the half-life. Protein kinase C (PKC) inhibitor completely inhibited AII-induced Ang2 expression, and the mitogen-activated protein kinase (MAPK) inhibitor also inhibited it by 69.4 ± 15.6%. In addition, we confirmed the upregulation of Ang2 in an AII-induced in vivo rat corneal neovascularization model. These data suggest that AII stimulates Ang2 expression through AT1 receptor-mediated PKC and MAPK pathways in BREC, and AII may play a novel role in retinal neovascularization.
The Pro12→Ala Substitution in PPAR-γ Is Associated With Resistance to Development of Diabetes in the General Population
Authors: Mori Hiroyuki , Ikegami Hiroshi , Kawaguchi Yoshihiko , Seino Susumu , Yokoi Norihide , Takeda Jun , Inoue Ituro , Seino Yutaka , Yasuda Koichiro , Hanafusa Toshiaki , Yamagata Kazuya , Awata Takuya , Kadowaki Takashi , Hara Kazuo , Yamada Nobuhiro , Gotoda Takanari , Iwasaki Naoko , Iwamoto Yasuhiko , Sanke Tokio , Nanjo Kishio , Oka Yoshitomo , Matsutani Akira , Maeda Eiichi , Kasuga Masato
Published: March 2007

The allele frequencies for a Pro12→Ala substitution in peroxisome proliferator–activated receptor-γ differ among ethnic groups, and its relationship with diabetes and associated diseases is controversial. The prevalence of this polymorphism and its effects on clinical characteristics have now been evaluated with a large number of Japanese individuals with type 2 diabetes (n = 2,201) and normal control subjects (n = 1,212) recruited by 10 institutions located in seven different cities in Japan. The allele frequency for the Ala12 variant was significantly lower in the type 2 diabetic group than in the control group (2.39 vs. 4.13%, P = 0.000054). However, compared with subjects without the Ala12 variant, the diabetic subjects with this variant exhibited a significantly higher serum concentration of total cholesterol (P = 0.001), manifested a reduced capacity for insulin secretion as evaluated by homeostasis model assessment (P = 0.007), and tended to possess a higher level of HbA1c. These data suggest that the Ala12 variant is associated with a reduced risk for the development of diabetes in the general population, but that it may be also a risk factor for insulin deficiency and disease severity in individuals with type 2 diabetes.
β-Cell Mass Dynamics in Zucker Diabetic Fatty Rats
Authors: Finegood Diane T. , McArthur M. Dawn , Kojwang David , Thomas Marion J. , Topp Brian G. , Leonard Thomas , Buckingham Robin E.
Published: March 2007

The evolution of diabetes in the male leptin receptor−deficient (fa/fa) Zucker diabetic fatty (ZDF) rat is associated with disruption of normal islet architecture, β-cell degranulation, and increased β-cell death. It is unknown whether these changes precede or develop as a result of the increasing plasma glucose, or whether the increased β-cell death can be prevented. Early intervention with thiazolidinediones prevents disruption of the islet architecture. To determine the specific effects of rosiglitazone (RSG) on β-cell mass dynamics, male fa/fa (obese) and +/fa or +/+ (lean) rats age 6 weeks were fed either chow (control group [CN]) or chow mixed with rosiglitazone (RSG group) at a dosage of 10 μmol · kg−1 body wt · day−1. Rats were killed after 0, 2, 4, 6, or 10 weeks of treatment (at age 6, 8, 10, 12, or 16 weeks). Plasma glucose increased from 8.9 ± 0.4 mmol/l at 0 weeks to 34.2 ± 1.8 mmol/l (P = 0.0001) at 6 weeks of treatment in obese CN rats and fell from 8.0 ± 0.3 to 6.3 ± 0.4 mmol/l in obese RSG rats (P = 0.02). β-cell mass fell by 51% from 2 to 6 weeks of treatment (ages 8–12 weeks) in obese CN rats (6.9 ± 0.9 to 3.4 ± 0.5 mg; P < 0.05), whereas β-cell mass was unchanged in obese RSG rats. At 10 weeks of treatment (age 16 weeks), β-cell mass in obese CN rats was only 56% of that of obese RSG rats (4.4 ± 0.4 vs. 7.8 ± 0.3 mg, respectively; P = 0.0001). The β-cell replication rate fell from a baseline value of 0.95 ± 0.12% in lean rats and 0.94 ± 0.07% in obese rats (at 0 weeks) to ∼0.3–0.5% in all groups by 6 weeks of treatment (age 12 weeks). After 10 weeks of treatment, β-cell replication was higher in obese RSG rats than in CN rats (0.59 ± 0.14 vs. 0.28 ± 0.05%, respectively; P < 0.02). Application of our mass balance model of β-cell turnover indicated that net β-cell death was fivefold higher in obese CN rats as compared with RSG rats after 6 weeks of treatment (age 12 weeks). The increase in β-cell death in obese CN rats during the 6-week observation period was well correlated with the increase in plasma glucose (r2 = 0.90, P < 0.0001). These results suggest that the development of hyperglycemia in ZDF rats is concomitant with increasing net β-cell death. β-cell proliferation compensates for the increased β-cell loss at a time when plasma glucose is moderately elevated, but compensation ultimately fails and the plasma glucose levels increase beyond ∼20 mmol/l. Treatment with rosiglitazone, previously shown to reduce insulin resistance, prevents the loss of β-cell mass in obese ZDF rats by maintaining β-cell proliferation and preventing increased net β-cell death.
Overexpressing Human Lipoprotein Lipase in Mouse Skeletal Muscle Is Associated With Insulin Resistance
Authors: Ferreira Luis D.M.C.-B. , Pulawa Leslie K. , Jensen Dalan R. , Eckel Robert H.
Published: March 2007

Lipoprotein lipase (LPL) plays a rate-limiting role in triglyceride-rich lipoprotein metabolism and is expressed in most tissues. Overexpression of LPL in skeletal muscle has been linked with higher plasma glucose levels suggesting insulin resistance (Jensen et al., Am J Physiol 273:R683–R689, 1997). The aim of our study was to ascertain whether the overexpression of human LPL in skeletal muscle leads to insulin resistance and to investigate the mechanism. Respiratory quotient measurements in both transgenic (MCKhLPL) and nontransgenic mice on a high-carbohydrate diet were conducted and showed a shift in fuel usage in transgenic mice when fasting but not when actively feeding. An increase in citrate and glucose 6-phosphate levels in fasted MCKhLPL mice further supports this preferential use of lipids. When challenged with an intraperitoneal injection of glucose (1 g/kg), MCKhLPL mice had a higher plasma glycemic excursion than nontransgenic mice. No differences in insulin response were observed between the two groups. Further investigation using hyperinsulinemic-euglycemic clamps revealed insulin resistance in MCKhLPL mice. Despite signs of insulin resistance, there was no associated increase in free fatty acids, hypertriglyceridemia, or hyperinsulinemia in MCKhLPL mice. In conclusion, MCKhLPL mice are insulin resistant, presumably due to increased delivery of lipoprotein-derived fatty acids to muscle.
Effects of Tumor Necrosis Factor-α on Insulin Action in Cultured Human Muscle Cells
Authors: Halse Reza , Pearson Samantha L. , McCormack James G. , Yeaman Stephen J. , Taylor Roy
Published: March 2007

Reported discrepancies in the effects of tumor necrosis factor (TNF)-α in modulating insulin sensitivity of cultured cells may relate both to cell types studied and to the time course of exposure to the cytokine. Additionally, the relationship of effects on glucose metabolism to changes in the insulin signaling pathway cannot be assumed. For in vitro study, the cell type most relevant to insulin resistance in humans is the cultured human muscle cell. In the present study, TNF brought about no change in the rate of glycogen synthesis in cultured human muscle cells unless present during differentiation. The presence of TNF (5 ng/ml) during the process of differentiation of myoblasts into mature myotubes diminished the response of glycogen synthesis to acute insulin stimulation. This finding was associated with an impairment of differentiation-dependent increases in total cellular glycogen synthase (GS) activity. Under the same conditions of TNF exposure, there was no effect on the response to acute insulin stimulation of the fractional activity of GS. Similarly, there was no effect on the insulin stimulation of protein kinase B (PKB) and inhibition of glycogen synthase kinase 3 (GSK-3). Acute insulin stimulation brought about a 4.08 ± 0.44–fold stimulation of activity of PKB in the absence of TNF, with 4.81 ± 0.70–fold stimulation in cells exposed to TNF. GSK-3 activity decreased to 74.0 ± 5.8% of basal after insulin stimulation without TNF and 78.3 ± 5.0% after TNF exposure. However, differentiation of myocytes, as defined by an increase in the acetylcholine receptor, myogenin, and mature creatine kinase isoform expression, was impaired in TNF-treated cells. These studies demonstrate that TNF, if present during differentiation, decreases insulin-stimulated rates of storage of glucose as glycogen and total GS activity but does not downregulate the insulin-signaling system to GS. More generally, TNF also inhibits differentiation of human muscle cells in culture.
Effect of Experimental Elevation of Free Fatty Acids on Insulin Secretion and Insulin Sensitivity in Healthy Carriers of the Pro12Ala Polymorphism of the Peroxisome Proliferator–Activated Receptor-γ2 Gene
Authors: Stefan Norbert , Fritsche Andreas , Häring Hans , Stumvoll Michael
Published: March 2007

The transcription of many genes involved in lipid metabolism is regulated by the peroxisome proliferator–activated receptor-γ (PPAR-γ). The Pro12Ala polymorphism in the PPAR-γ2 gene has been associated with reduced transcriptional activity in vitro and increased insulin sensitivity in vivo. Although PPAR-γ has been demonstrated in human β-cells, it is unknown whether the Pro12Ala polymorphism plays a role in insulin secretion. Moreover, it is also unknown if and how the effect of free fatty acids (FFAs) on insulin secretion and insulin sensitivity is modulated by the presence of this polymorphism. We therefore performed hyperglycemic clamps (8 mmol/l, 140 min, 5 g arginine bolus at min 120) in 10 healthy subjects with the (X/Ala) polymorphism and in 10 subjects without the polymorphism (Pro/Pro) basally and after 5 h infusion of Intralipid plus heparin. FFA concentrations increased from 473 ± 61 μmol/l to 1,732 ± 163 μmol/l in the Pro/Pro and from 372 ± 46 μmol/l to 1,630 ± 96 μmol/l in the X/Ala group (P = 0.68). Basally, neither insulin sensitivity nor insulin secretion were significantly different between the two groups. During infusion of Intralipid, first-phase insulin secretion remained unchanged in both groups (P = 0.21). In the Pro/Pro group, second-phase insulin secretion remained unchanged (444 ± 67 vs. 471 ± 93 pmol/min) and the response to arginine increased from 5,007 ± 41 to 6,072 ± 732 pmol/min. In contrast, in the X/Ala group, there was a decrease of both second-phase insulin secretion (533 ± 58 to 427 ± 48 pmol/min, P = 0.02 vs. Pro/Pro) and in the response to arginine (from 7,518 ± 1,306 to 6,458 ± 1,040 pmol/min, P = 0.014 vs. Pro/Pro). The insulin sensitivity index decreased comparably in Pro/Pro and X/Ala (to 71 ± 8 vs. 74 ± 9% of basal, P = 0.8). In conclusion, these results provide evidence that the Pro12Ala polymorphism in the PPAR-γ2 gene might be involved in a differential regulation of insulin secretion in response to increased FFAs in humans.
Isomer-Specific Antidiabetic Properties of Conjugated Linoleic Acid
Authors: Ryder J.W. , Portocarrero C.P. , Song X.M. , Cui L. , Yu M. , Combatsiaris T. , Galuska D. , Bauman D.E. , Barbano D.M. , Charron M.J. , Zierath J.R. , Houseknecht K.L.
Published: March 2007

Conjugated linoleic acid (CLA) isomers have a number of beneficial health effects, as shown in biomedical studies with animal models. Previously, we reported that a mixture of CLA isomers improved glucose tolerance in ZDF rats and activated peroxisome proliferator–activated receptor (PPAR)-γ response elements in vitro. Here, our aim was to elucidate the effect(s) of specific CLA isomers on whole-body glucose tolerance, insulin action in skeletal muscle, and expression of genes important in glucose and lipid metabolism. ZDF rats were fed either a control diet (CON), one of two CLA supplemented diets (1.5% CLA) containing differing isoforms of CLA (47% c9,t11; 47.9% c10,t12, 50:50; or 91% c9,t11, c9,t11 isomers), or were pair-fed CON diet to match the intake of 50:50. The 50:50 diet reduced adiposity and improved glucose tolerance compared with all other ZDF treatments. Insulin-stimulated glucose transport and glycogen synthase activity in skeletal muscle were improved with 50:50 compared with all other treatments. Neither phosphatidlyinositol 3-kinase activity nor Akt activity in muscle was affected by treatment. Uncoupling protein 2 in muscle and adipose tissue was upregulated by c9,t11 and 50:50 compared with ZDF controls. PPAR-γ mRNA was downregulated in liver of c9,t11 and pair-fed ZDF rats. Thus, the improved glucose tolerance in 50:50 rats is attributable to, at least in part, improved insulin action in muscle, and CLA effects cannot be explained simply by reduced food intake.
No Evidence for Linkage or for Diabetes-Associated Mutations in the Activin Type 2B Receptor Gene (ACVR2B) in French Patients With Mature-Onset Diabetes of the Young or Type 2 Diabetes
Authors: Dupont Sophie , Hani El Habib , Cras-Méneur Corentin , De Matos Frédérique , Lobbens Stéphane , Lecoeur Cécile , Vaxillaire Martine , Scharfmann Raphaël , Froguel Philippe
Published: March 2007

Activins are members of the transforming growth factor-β superfamily. They have a wide range of biological effects on cell growth and differentiation. For transmembrane signaling, activins bind directly to activin receptor type 2A (ACVR2A) or 2B (ACVR2B). Transgenic and knock-out mice for the ACVR2B gene display various endocrine pancreas-related abnormalities, including islet hypoplasia and glucose intolerance, demonstrating the crucial role of ACVR2B in the regulation of pancreas development. We have thus examined the contribution of this factor to the development of mature-onset diabetes of the young (MODY) and type 2 diabetes. No evidence of linkage at the ACVR2B locus has been detected in MODY families with unknown etiology for diabetes or found in affected sib pairs from families with type 2 diabetes. Mutation screening of the coding sequence in MODY probands and in a family with severe type 2 diabetes, including a case of pancreatic agenesis, showed single nucleotide polymorphisms that did not cosegregate with MODY and were not associated with type 2 diabetes. Our results indicate that ACVR2B does not represent a common cause of either MODY or type 2 diabetes in the French Caucasian population.
AMP-Activated Protein Kinase (AMPK) Is Activated in Muscle of Subjects With Type 2 Diabetes During Exercise
Authors: Musi Nicolas , Fujii Nobuharu , Hirshman Michael F. , Ekberg Ingvar , Fröberg Sven , Ljungqvist Olle , Thorell Anders , Goodyear Laurie J.
Published: March 2007

Insulin-stimulated GLUT4 translocation is impaired in people with type 2 diabetes. In contrast, exercise results in a normal increase in GLUT4 translocation and glucose uptake in these patients. Several groups have recently hypothesized that exercise increases glucose uptake via an insulin-independent mechanism mediated by the activation of AMP-activated protein kinase (AMPK). If this hypothesis is correct, people with type 2 diabetes should have normal AMPK activation in response to exercise. Seven subjects with type 2 diabetes and eight matched control subjects exercised on a cycle ergometer for 45 min at 70% of maximum workload. Biopsies of vastus lateralis muscle were taken before exercise, after 20 and 45 min of exercise, and at 30 min postexercise. Blood glucose concentrations decreased from 7.6 to 4.77 mmol/l with 45 min of exercise in the diabetic group and did not change in the control group. Exercise significantly increased AMPK α2 activity 2.7-fold over basal at 20 min in both groups and remained elevated throughout the protocol, but there was no effect of exercise on AMPK α1 activity. Subjects with type 2 diabetes had similar protein expression of AMPK α1, α2, and β1 in muscle compared with control subjects. AMPK α2 was shown to represent approximately two-thirds of the total α mRNA in the muscle from both groups. In conclusion, people with type 2 diabetes have normal exercise-induced AMPK α2 activity and normal expression of the α1, α2 and β1 isoforms. Pharmacological activation of AMPK may be an attractive target for the treatment of type 2 diabetes.
Inhibition of GSK-3 Selectively Reduces Glucose-6-Phosphatase and Phosphoenolpyruvate Carboxykinase Gene Expression
Authors: Lochhead Pamela A. , Coghlan Matthew , Rice Simon Q.J. , Sutherland Calum
Published: March 2007

A major action of insulin is to regulate the transcription rate of specific genes. The expression of these genes is dramatically altered in type 2 diabetes. For example, the expression of two hepatic genes, glucose-6-phosphatase and PEPCK, is normally inhibited by insulin, but in type 2 diabetes, their expression is insensitive to insulin. An agent that mimics the effect of insulin on the expression of these genes would reduce gluconeogenesis and hepatic glucose output, even in the presence of insulin resistance. The repressive actions of insulin on these genes are dependent on phosphatidylinositol (PI) 3-kinase. However, the molecules that lie between this lipid kinase and the two gene promoters are unknown. Glycogen synthase kinase-3 (GSK-3) is inhibited following activation of PI 3-kinase and protein kinase B. In hepatoma cells, we find that selectively reducing GSK-3 activity strongly reduces the expression of both gluconeogenic genes. The effect is at the level of transcription and is observed with induced or basal gene expression. In addition, GSK-3 inhibition does not result in the subsequent activation of protein kinase B or inhibition of the transcription factor FKHR, which are candidate regulatory molecules for these promoters. Thus, GSK-3 activity is required for basal activity of each promoter. Inhibitors of GSK-3 should therefore reduce hepatic glucose output, as well as increase the synthesis of glycogen from l-glucose. These findings indicate that GSK-3 inhibitors may have greater therapeutic potential for lowering blood glucose levels and treating type 2 diabetes than previously realized.
Insulin’s Effect on Synthesis Rates of Liver Proteins
Authors: Ahlman Bo , Charlton Michael , Fu Aizhong , Berg Carole , O’Brien Peter , Nair K. Sreekumaran
Published: March 2007

Insulin’s effect on the synthesis of liver proteins remains to be fully defined. Previous studies using various surrogate measures of amino acyl–tRNA have reported variable results of insulin’s effect on liver protein synthesis. We determined the effect of insulin with or without amino acid supplementation on the synthesis rates of liver proteins (tissue, albumin, and fibrinogen) using l-[1-13C]Leu as a tracer in 24 male miniature swine. In addition, we compared the isotopic enrichment of different precursors of liver proteins with that of amino acyl−tRNA using l-[1-13C]Leu and l-[15N]Phe as tracers. Although liver tissue fluid enrichment of [13C]Leu and [15N]Phe and that of plasma [13C]ketoisocaproatic acid (KIC) were very similar to that of tRNA, plasma isotopic enrichment of both Leu and Phe were substantially higher (P < 0.01) and VLDL apolipoprotein-B100 enrichment was lower (P < 0.01) than the respective amino acyl−tRNA enrichment. Plasma KIC enrichment most accurately predicted leucyl-tRNA enrichment, whereas plasma Leu enrichment was best correlated with that of tRNA. Neither insulin alone nor insulin plus amino acid infusion had an effect on liver tissue protein synthesis. In contrast, insulin alone decreased the albumin synthesis rate, and insulin with amino acids maintained the albumin synthesis rate. Insulin with or without amino acids inhibited the fibrinogen synthesis rate. These results, based on synthetic rates using amino acyl–tRNA, were consistent with those obtained using KIC or tissue fluid Leu or Phe as precursor pools. These studies demonstrated that plasma KIC enrichment is a convenient and reliable surrogate measure of leucyl-tRNA in liver. We also concluded that insulin has differential effects on the synthesis rates of liver proteins. Whereas insulin with or without amino acid supplement has no acute effect on the synthesis of liver tissue protein, insulin has a substantial inhibitory effect on fibrinogen synthesis. In contrast, insulin administration along with amino supplement is necessary to maintain albumin synthesis rate.