bluuebunny/crossref_metadata_2025 huggingface dataset:
The Biology of Peroxisome Proliferator-Activated Receptors
Authors: Ferré Pascal
Published: March 2007

Peroxisome proliferator-activated receptors (PPARs) are transcription factors belonging to the superfamily of nuclear receptors. Three isoforms (α, δ, and γ) have been described. They act on DNA response elements as heterodimers with the nuclear retinoic acid receptor. Their natural activating ligands are fatty acids and lipid-derived substrates. PPAR-α is present in liver, heart, and, to a lesser extent, skeletal muscle. When activated, it promotes fatty acid oxidation, ketone body synthesis, and glucose sparing. Fibrates, which are used as hypolipidemic drugs, are ligands of PPAR-α. PPAR-δ is ubiquitous and could also favor fatty acid oxidation in tissues in which PPAR-α is absent or less expressed. PPAR-γ is expressed in adipose tissue, lower intestine, and cells involved in immunity. Activation of PPAR-γ induces the differentiation of preadipocytes into adipocytes and stimulates triglyceride storage. Thiazolidinediones are compounds used as hypoglycemic, muscle insulin-sensitizing agents in type 2 diabetes. Unexpectedly, they are activators of PPAR-γ. Their action on muscle insulin sensitivity may be secondary to the lowering of circulating lipids on PPAR-γ activation and to the secretion by adipocytes of insulin-sensitizing hormones such as adiponectin, all promoting glucose utilization. The PPARs are thus major regulators of lipid and glucose metabolism, allowing adaptation to the prevailing nutritional environment.
Role of Peroxisome Proliferator-Activated Receptor-γ in the Glucose-Sensing Apparatus of Liver and β-Cells
Authors: Kim Ha-il , Ahn Yong-ho
Published: March 2007

Type 2 diabetes develops in the context of both insulin resistance and β-cell failure. Thiazolidinediones are a class of antidiabetic agents that are known to improve insulin sensitivity in various animal models of diabetes. The improved insulin sensitivity may be achieved either by systemic insulin sensitization or by direct action of peroxisome proliferator-activated receptor (PPAR)-γ on the transcription of genes involved in glucose disposal. Evidence supporting the direct action of PPAR-γ on glucose metabolism is observed in the genes involved in insulin-stimulated glucose disposal. We already showed that GLUT2 and β-glucokinase were directly activated by PPAR-γ. Recently, we have identified and characterized the functional PPAR response element in the GLUT2 and liver type glucokinase (LGK) promoter of the liver. It is well known that adipose tissue plays a crucial role in antidiabetic action of PPAR-γ. In addition, PPAR-γ can directly affect liver and pancreatic β-cells to improve glucose homeostasis.
Novel Players in Pancreatic Islet Signaling
Authors: Soria Bernat , Quesada Ivan , Ropero Ana B. , Pertusa José A. , Martín Franz , Nadal Angel
Published: March 2007

Glucose and other nutrients regulate many aspects of pancreatic islet physiology. This includes not only insulin release, but also insulin synthesis and storage and other aspects of β-cell biology, including cell proliferation, apoptosis, differentiation, and gene expression. This implies that in addition to the well-described signals for insulin release, other intracellular signaling mechanisms are needed. Here we describe the role of global and local Ca2+ signals in insulin release, the regulation of these signals by new membrane receptors, and the generation of nuclear Ca2+ signals involved in gene expression. An integrated view of these pathways should improve the present description of the β-cell biology and provide new targets for novel drugs.
Activin A and Betacellulin
Authors: Li Lei , Yi Zhaohong , Seno Masaharu , Kojima Itaru
Published: March 2007

Activin A and betacellulin (BTC) are thought to regulate differentiation of pancreatic β-cells during development and regeneration of β-cells in adults. In the present study, we used neonatal rats treated with streptozotocin (STZ) to investigate the effects of activin A and BTC on regeneration of pancreatic β-cells. One-day-old Sprague-Dawley rats were injected with STZ (85 μg/g) and then administered for 7 days with activin A and/or BTC. Treatment with activin A and BTC significantly reduced the plasma glucose concentration and the plasma glucose response to intraperitoneal glucose loading. The pancreatic insulin content and β-cell mass in rats treated with activin A and BTC were significantly increased compared with the control group on day 8 and at 2 months. Treatment with activin A and BTC significantly increased the DNA synthesis in preexisting β-cells, ductal cells, and δ-cells. The number of islet cell-like clusters (ICCs) and islets was significantly increased by treatment with activin A and BTC. In addition, the number of insulin/somatostatin-positive cells and pancreatic duodenal homeobox-1/somatostatin-positive cells was significantly increased. These results indicate that, in neonatal STZ-treated rats, a combination of activin A and BTC promoted regeneration of pancreatic β-cells and improved glucose metabolism in adults.
Structural and Functional Abnormalities in the Islets Isolated From Type 2 Diabetic Subjects
Authors: Deng Shaoping , Vatamaniuk Marko , Huang Xiaolun , Doliba Nicolai , Lian Moh-Moh , Frank Adam , Velidedeoglu Ergun , Desai Niraj M. , Koeberlein Brigitte , Wolf Bryan , Barker Clyde F. , Naji Ali , Matschinsky Franz M. , Markmann James F.
Published: March 2007

Type 2 diabetic subjects manifest both disordered insulin action and abnormalities in their pancreatic islet cells. Whether the latter represents a primary defect or is a consequence of the former is unknown. To examine the β-cell mass and function of islets from type 2 diabetic patients directly, we isolated islets from pancreata of type 2 diabetic cadaveric donors (n = 14) and compared them with islets from normal donors (n = 14) matched for age, BMI, and cold ischemia time. The total recovered islet mass from type 2 diabetic pancreata was significantly less than that from nondiabetic control subjects (256,260 islet equivalents [2,588 IEq/g pancreas] versus 597,569 islet equivalents [6,037 IEq/g pancreas]). Type 2 diabetic islets were also noted to be smaller on average, and histologically, islets from diabetic patients contained a higher proportion of glucagon-producing α-cells. In vitro study of islet function from diabetic patients revealed an abnormal glucose-stimulated insulin release response in perifusion assays. In addition, in comparison with normal islets, an equivalent number of type 2 diabetic islets failed to reverse hyperglycemia when transplanted to immunodeficient diabetic mice. These results provide direct evidence for abnormalities in the islets of type 2 diabetic patients that may contribute to the pathogenesis of the disease.
The Effects of Dehydroepiandrosterone Sulfate on Counterregulatory Responses During Repeated Hypoglycemia in Conscious Normal Rats
Authors: Sandoval Darleen A. , Ping Ling , Neill Ray Anthony , Morrey Sachiko , Davis Stephen N.
Published: March 2007

We previously determined that both antecedent hypoglycemia and elevated cortisol levels blunt neuroendocrine and metabolic responses to subsequent hypoglycemia in conscious, unrestrained rats. The adrenal steroid dehydroepiandrosterone sulfate (DHEA-S) has been shown in several studies to oppose corticosteroid action. The purpose of this study was to determine if DHEA-S could preserve counterregulatory responses during repeated hypoglycemia. We studied 40 male Sprague-Dawley rats during a series of 2-day protocols. Day 1 consisted of two 2-h episodes of 1) hyperinsulinemic (30 pmol · kg−1 · min−1) euglycemia (6.2 ± 0.2 mmol/l; n = 12; ANTE EUG), 2) hyperinsulinemic euglycemia (6.0 ± 0.1 mmol/l; n = 8) plus simultaneous intravenous infusion of DHEA-S (30 mg/kg; ANTE EUG + DHEA-S), 3) hyperinsulinemic hypoglycemia (2.8 ± 0.1 mmol/l; n = 12; ANTE HYPO), or 4) hyperinsulinemic hypoglycemia (2.8 ± 0.1 mmol/l; n = 8) with simultaneous intravenous infusion of DHEA-S (30 mg/kg; ANTE HYPO + DHEA-S). Day 2 consisted of a single 2-h hyperinsulinemic hypoglycemic (2.8 ± 0.1 mmol/l) clamp. During the final 30 min of day 2, hypoglycemia norepinephrine levels were significantly lower in the ANTE HYPO group versus the ANTE HYPO + DHEA-S group (2.0 ± 0.2 vs. 3.3 ± 0.6 nmol/l; P < 0.05). In addition, epinephrine (8 ± 1 vs. 17 ± 2, 14 ± 3, and 15 ± 3 nmol/l), glucagon (91 ± 8 vs. 273 ± 36, 231 ± 42, and 297 ± 48 ng/l), and corticosterone (1,255 ± 193 vs. 1,915 ± 212, 1,557 ± 112, and 1,668 ± 119 pmol/l) were significantly lower in the ANTE HYPO group versus the ANTE EUG, ANTE EUG + DHEA-S, and ANTE HYPO + DHEA-S groups (P < 0.05). Endogenous glucose production was also significantly less in the ANTE HYPO group versus the ANTE EUG, ANTE EUG + DHEA-S, and ANTE HYPO + DHEA-S groups (13 ± 5 vs. 32 ± 3, 38 ± 7, and 29 ± 8 μmol/l · kg−1 · min−1; P < 0.05). Consequently, the amount of exogenous glucose needed to maintain the glycemic level during the clamp studies was significantly higher in the ANTE HYPO versus the ANTE EUG, ANTE EUG + DHEA-S, and ANTE HYPO + DHEA-S groups (57 ± 8 vs. 22 ± 5, 18 ± 6, and 18 ± 3 μmol/l · kg−1 · min−1; P < 0.05). In summary, day-1 antecedent hypoglycemia blunted neuroendocrine and metabolic responses to next-day hypoglycemia. However, simultaneous DHEA-S infusion during antecedent hypoglycemia preserved neuroendocrine and metabolic counterregulatory responses during subsequent hypoglycemia in conscious rats.
Impaired Pressure-Induced Vasodilation at the Foot in Young Adults With Type 1 Diabetes
Authors: Koı̈tka Audrey , Abraham Pierre , Bouhanick Beatrice , Sigaudo-Roussel Dominique , Demiot Claire , Saumet Jean Louis
Published: March 2007

Vascular and neurological mechanisms are both likely to be involved in foot ulcer. We recently reported a pressure-induced vasodilation (PIV), relying on unmyelinated afferent excitation. We previously found that cutaneous blood flow in response to locally applied pressure might be impaired in diabetic patients because of the combined effects of low cutaneous temperature and alterations in microcirculatory function. Therefore, we aimed to analyze whether, at a relatively high cutaneous temperature, PIV is present in type 1 diabetes and to assess endothelial-dependent vasodilation and endothelium-independent vasodilation. We measured cutaneous blood flow using laser Doppler flowmetry on the head of the first metatarsus in response to applied pressure at 5.0 mmHg/min in warm conditions (29.5 ± 0.2°C). Responses to iontophoresis of acetylcholine (endothelium dependent) and sodium nitroprusside (endothelium independent) were measured using laser Doppler flowmetry in the forearm. The data indicate that PIV exists at the foot level in normal subjects, whereas it was not found in diabetic patients. In diabetic patients, the nonendothelial-mediated response to sodium nitroprusside was preserved, whereas the endothelial-mediated response to acetylcholine was impaired. These findings might be relevant to the high prevalence of foot ulcer that occurs in diabetic patients.
Initial Characterization of a Rat Model of Diabetic Nephropathy
Authors: Nobrega Marcelo A. , Fleming Stewart , Roman Richard J. , Shiozawa Masahide , Schlick Nancy , Lazar Jozef , Jacob Howard J.
Published: March 2007

The lack of an appropriate animal model that spontaneously develops diabetic nephropathy has been a significant limitation in the search for genetic factors underlying this disease and the development of new therapeutic strategies to prevent progressive renal disease in diabetes. We introgressed the mitochondria and some passenger loci from the FHH/EurMcwi rat into the genetic background of diabetic GK rats, creating a new rat strain, T2DN (T2DN/Mcwi). Despite the high degree of genetic similarity between T2DN and GK rats (97% at 681 loci), diabetes ensues earlier and progresses more severely in T2DN rats. T2DN rats exhibit proteinuria by 6 months of age, accompanied by renal histologic abnormalities such as focal glomerulosclerosis, mesangial matrix expansion, and thickening of basement membranes. These characteristics progress over time, and nearly all T2DN rats exhibit diffuse global glomerulosclerosis with nodule formation and arteriolar hyalinosis by 18 months of age. The histologic changes in the kidney of T2DN rats closely mimic the changes seen in the kidney of patients with diabetes. These results indicate that the T2DN rat is a suitable model for investigating diabetic nephropathy. Here we report the initial genetic and physiological characterization of this new rat model of diabetic nephropathy.
Molecular Profiling of Diabetic Mouse Kidney Reveals Novel Genes Linked to Glomerular Disease
Authors: Susztak Katalin , Böttinger Erwin , Novetsky Akiva , Liang Dan , Zhu Yanqing , Ciccone Emilio , Wu Dona , Dunn Stephen , McCue Peter , Sharma Kumar
Published: March 2007

To describe gene expression changes that characterize the development of diabetic nephropathy, we performed microarray and phenotype analysis on kidneys from db/db mice (a model of type 2 diabetes), streptozotocin-induced diabetic C57BL/6J mice (a model of type 1 diabetes), and nondiabetic controls. Statistical comparisons were implemented based on phenotypic outcome characteristics of the animals. We used weighted vote-based supervised analytical methods to find genes whose expression can classify samples based on the presence or absence of mesangial matrix expansion, the best indicator for the development of end-stage renal disease in humans. We identified hydroxysteroid dehydrogenase-3β isotype 4 and osteopontin as lead classifier genes in relation to the mesangial matrix expansion phenotype. We used the expression levels of these genes in the kidney to classify a separate group of animals for the absence or presence of diabetic glomerulopathy with a high degree of precision. Immunohistochemical analysis of murine and human diabetic kidney samples showed that both markers were expressed in podocytes in the glomeruli and followed regulation similar to that observed in the microarray. The application of phenotype-based statistical modeling approaches has led to the identification of new markers for the development of diabetic kidney disease.
A Genome-Wide Scan for Childhood Obesity–Associated Traits in French Families Shows Significant Linkage on Chromosome 6q22.31-q23.2
Authors: Meyre David , Lecoeur Cécile , Delplanque Jérôme , Francke Stephan , Vatin Vincent , Durand Emmanuelle , Weill Jacques , Dina Christian , Froguel Philippe
Published: March 2007

We conducted a genome-wide search for childhood obesity–associated traits, including BMI ≥95th percentile (PCT95), 97th percentile (PCT97), and 99th percentile (PCT99) as well as age of adiposity rebound (AAR), which corresponds to the beginning of the second rise in childhood adiposity. A set of 431 microsatellite markers was genotyped in 506 subjects from 115 multiplex French Caucasian families, with at least one child with a BMI ≥95th percentile. Among these 115 pedigrees, 97 had at least two sibs with a BMI ≥95th percentile. Fine-mapping was performed in the seven most positive loci. Nonparametric multipoint analyses revealed six regions of significant or suggestive linkage on chromosomes 2q33.2-q36.3, 6q22.31-q23.2, and 17p13 for PCT95, PCT97, or PCT99 and 15q12-q15.1, 16q22.1-q24.1, and 19p13.3-p13.11 for AAR. The strongest evidence of linkage was detected on chromosome 6q22.31 for PCT97 (maximum likelihood score: 4.06) at the marker D6S287. This logarithm of odds score meets genome-wide significance tested through simulation (empirical genome-wide P = 0.01 [0.0027–0.0254]). Six independent ge-nome scans in adults have reported quantitative trait loci on 6q linked to energy or glucose homeostasis-associated phenotypes. Possible candidate genes in this region include SIM1, MCHR2, and PC-1.
Genetic Polymorphisms in Peroxisome Proliferator-Activated Receptor δ Associated With Obesity
Authors: Shin Hyoung Doo , Park Byung Lae , Kim Lyoung Hyo , Jung Hye Seung , Cho Young Min , Moon Min Kyong , Park Young Joo , Lee Hong Kyu , Park Kyong Soo
Published: March 2007

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors regulating the expression of genes involved in lipid and glucose metabolism. Three different PPARs, PPAR-α, -γ, and -δ, have been characterized, and they are distinguished from each other by tissue distribution and cell activation. All PPARs are, to different extents, activated by fatty acids and derivatives. Recently, it has been shown that PPAR-δ serves as a widespread regulator of fat burning, suggesting that it might be a potential target in the treatment of obesity and type 2 diabetes. In an effort to identify polymorphic markers in potential candidate genes for type 2 diabetes, we have sequenced PPAR-δ, including −1,500 bp of the 5′ flanking region. Nine polymorphisms were identified in PPAR-δ: four in the intron, one in the 5′ untranslated region (UTR), and four in the 3′ UTR. Among identified polymorphisms, five common sites, including c.−13454G>T, c.−87T>C, c.2022+12G>A, c.2629T>C, and c.2806C>G, were genotyped in subjects with type 2 diabetes and normal control subjects (n = 702). The genetic associations with the risk of type 2 diabetes and metabolic phenotype were analyzed. No significant associations with the risk of type 2 diabetes were detected. However, several positive associations of PPAR-δ polymorphisms with fasting plasma glucose and BMI were detected in nondiabetic control subjects. The genetic information about PPAR-δ from this study would be useful for further genetic study of obesity, diabetes, and other metabolic diseases.
Angiopoietin-2 Causes Pericyte Dropout in the Normal Retina
Authors: Hammes Hans-Peter , Lin Jihong , Wagner Patrick , Feng Yuxi , vom Hagen Franziska , Krzizok Thomas , Renner Oliver , Breier Georg , Brownlee Michael , Deutsch Urban
Published: March 2007

Pericyte loss is an early pathologic feature of diabetic retinopathy, consistently present in retinae of diabetic humans and animals. Because pericyte recruitment and endothelial cell survival are controlled, in part, by the angiopoietin/Tie2 ligand/receptor system, we studied the expression of angiopoietin-2 and -1 in relation to the evolution of pericyte loss in diabetic rat retinae, using quantitative retinal morphometry, and in retinae from mice with heterozygous angiopoietin deficiency (Ang-2 LacZ knock-in mice). Finally, recombinant angiopoietin-2 was injected into eyes of nondiabetic rats, and pericyte numbers were quantitated in retinal capillaries. Angiopoietin-1 protein was present in the normal maturing retina and was upregulated 2.5-fold in diabetic retinae over 3 months of diabetes. In contrast, angiopoietin-2 protein was consistently upregulated more than 30-fold in the retinae of diabetic rats, preceding the onset of pericyte loss. Heterozygous angiopoietin-2 deficiency completely prevented diabetes-induced pericyte loss and reduced the number of acellular capillary segments. Injection of angiopoietin-2 into the eyes of normal rats induced a dose-dependent pericyte loss. These data show that upregulation of angiopoietin-2 plays a critical role in the loss of pericytes in the diabetic retina.
Adiponectin Gene Polymorphisms and Adiponectin Levels Are Independently Associated With the Development of Hyperglycemia During a 3-Year Period
Authors: Fumeron Frédéric , Aubert Roberte , Siddiq Afshan , Betoulle Dina , Péan Frank , Hadjadj Samy , Tichet Jean , Wilpart Elsie , Chesnier Marie-Claude , Balkau Beverley , Froguel Philippe , Marre Michel ,   for the Epidemiologic Data on the Insulin Resistance Syndrome (DESIR) Study Group
Published: March 2007

The plasma concentration of the adipocyte-derived peptide adiponectin is decreased in patients with obesity and type 2 diabetes. The adiponectin gene is located on chromosome 3q27, where a diabetes susceptibility locus has been mapped. Adiponectin gene polymorphisms (single nucleotide polymorphisms [SNPs]) have been associated with BMI, insulin sensitivity, and type 2 diabetes in some cross-sectional studies. Our aim was to assess the contribution of these SNPs in the development of features of the insulin resistance syndrome in a 3-year prospective study in ∼4,500 French Caucasian subjects from the Epidemiologic Data on the Insulin Resistance Syndrome (DESIR) cohort. For subjects who were normoglycemic at baseline, the 3-year risk of becoming hyperglycemic (diabetes or impaired fasting glucose) was affected by two SNPs: G-11391A and T45G. For G-11391A, the risk was increased in GA carriers (odds ratio [OR] adjusted for sex [versus GG] = 1.60 [95% CI 1.16–2.20]; P = 0.004). For T45G, it was increased in GG carriers (OR [versus TT] = 2.71 [1.31–5.60]; P = 0.007). After 3 years, GG subjects had a greater increase in BMI (P = 0.009) and waist-to-hip ratio (P = 0.007). Adiponectin levels at baseline were associated with the development of hyperglycemia (P = 0.005), but the predictive effects on the risk for hyperglycemia were independent of adiponectin genotypes. In conclusion, in the DESIR study, variations at the adiponectin locus affect body weight gain, body fat distribution, and onset of hyperglycemia, as well as adiponectin levels. Adiponectin gene SNPs may have several phenotypic effects that co-occur with the development of the metabolic syndrome.
Lack of Association of the Ala45Thr Polymorphism and Other Common Variants of the NeuroD Gene With Type 1 Diabetes
Authors: Vella Adrian , Howson Joanna M.M. , Barratt Bryan J. , Twells Rebecca C.J. , Rance Helen E. , Nutland Sarah , Tuomilehto-Wolf Eva , Tuomilehto Jaakko , Undlien Dag E. , Rønningen Kjersti S. , Guja Cristian , Ionescu-Tîrgovişte Constantin , Savage David A. , Todd John A.
Published: March 2007

Variation in genes necessary for normal functioning and development of β-cells, e.g., NEUROD1, which encodes a transcription factor for the insulin gene and is important in β-cell development, causes maturity-onset diabetes of the young. Some studies have reported an association between a nonsynonymous Ala45Thr (+182G→A) single nucleotide polymorphism (SNP) in NEUROD1 and type 1 diabetes, but this result has not been consistently found. To clarify this, we genotyped Ala45Thr in 2,434 type 1 diabetic families of European descent and Caucasian ethnicity from five different countries. Taking the allele frequency of 36% for Thr45 and an odds ratio (OR) of 1.2, this sample provided >99% power to detect an association (P < 0.05). We could not confirm the association (P = 0.77). No evidence of population heterogeneity in the lack of association of Thr45 with type 1 diabetes was observed. To evaluate the possibility that another NEUROD1 variant was associated with type 1 diabetes, we resequenced the gene in 32 U.K. affected individuals and identified and genotyped all common SNPs (minor allele frequency >10%; n = 5) in 786 families. We report no evidence of association of these common variants in NEUROD1 and type 1 diabetes in these samples.
Linkage of the Metabolic Syndrome to 1q23-q31 in Hispanic Families
Authors: Langefeld Carl D. , Wagenknecht Lynne E. , Rotter Jerome I. , Williams Adrienne H. , Hokanson John E. , Saad Mohammad F. , Bowden Donald W. , Haffner Stephen , Norris Jill M. , Rich Stephen S. , Mitchell Braxton D.
Published: March 2007

The metabolic syndrome is characterized by central obesity, dyslipidemia, elevated blood pressure, and hyperglycemia. The Insulin Resistance Atherosclerosis Study (IRAS) Family Study recruited extended pedigrees of Hispanic descent from San Antonio, TX (SA) and San Luis Valley, CO (SLV). Thirty-five of these pedigrees (27 SA and 8 SLV) had at least 2 individuals with metabolic syndrome (216 affected individuals and 563 affected relative pairs). The prevalence of metabolic syndrome and component criteria in subjects from these pedigrees were 35% metabolic syndrome, 43% increased waist circumference, 31% hypertriglyceridemia, 69% low HDL cholesterol, 31% increased blood pressure, and 25% either increased fasting glucose or presence of diabetes. Nonparametric linkage analysis provided evidence for linkage of metabolic syndrome to 1q23-q31 (D1S518; logarithm of odds [LOD] 1.6) with significant site heterogeneity (SA LOD 2.6 and SLV LOD 0.0), and removing all individuals with diabetes reduced, but did not eliminate, the evidence for linkage to this region (LOD 1.2). This heterogeneity may partially be explained by phenotypic differences. Members in the SA pedigrees were older, had greater central obesity, had higher prevalence of the metabolic syndrome, and were from a more urban environment than members of the SLV pedigrees. These results contribute to the growing evidence that chromosome 1q harbors at least one locus related to the metabolic precursors of diabetes.
Glucose Regulates the Expression of the Farnesoid X Receptor in Liver
Authors: Duran-Sandoval Daniel , Mautino Gisèle , Martin Geneviève , Percevault Fréderic , Barbier Olivier , Fruchart Jean-Charles , Kuipers Folkert , Staels Bart
Published: March 2007

An increased prevalence of hypertriglyceridemia and gallbladder disease occurs in patients with diabetes or insulin resistance. Hypertriglyceridemia is positively associated to gall bladder disease risk. The farnesoid X receptor (FXR) is a bile acid-activated nuclear receptor that plays a key role in bile acid and triglyceride homeostasis. The mechanisms controlling FXR gene expression are poorly understood. This study evaluated whether FXR gene expression is regulated by alterations in glucose homeostasis. FXR expression was decreased in livers of streptozotocin-induced diabetic rats and normalized upon insulin supplementation. Concomitantly with diabetes progression, FXR expression also decreased in aging diabetic Zucker rats. In primary rat hepatocytes, d-glucose increased FXR mRNA in a dose- and time-dependent manner, whereas insulin counteracted this effect. Addition of xylitol, a precursor of xylulose-5-phosphate, to primary rat hepatocytes increased FXR expression to a comparable level as d-glucose. Finally, expression of the FXR target genes, SHP and apolipoprotein C-III, were additively regulated by d-glucose and FXR ligands. This study demonstrates that FXR is decreased in animal models of diabetes. In addition, FXR is regulated by glucose likely via the pentose phosphate pathway. Dysregulation of FXR expression may contribute to alterations in lipid and bile acid metabolism in patients with diabetes or insulin resistance.
Protein Kinase B-α Inhibits Human Pyruvate Dehydrogenase Kinase-4 Gene Induction by Dexamethasone Through Inactivation of FOXO Transcription Factors
Authors: Kwon Hye-Sook , Huang Boli , Unterman Terry G. , Harris Robert A.
Published: March 2007

Starvation and diabetes increase pyruvate dehydrogenase kinase-4 (PDK4) expression, which conserves gluconeogenic substrates by inactivating the pyruvate dehydrogenase complex. Mechanisms that regulate PDK4 gene expression, previously established to be increased by glucocorticoids and decreased by insulin, were studied. Treatment of HepG2 cells with dexamethasone increases the relative abundance of PDK4 mRNA, and insulin blocks this effect. Dexamethasone also increases human PDK4 (hPDK4) promoter activity in HepG2 cells, and insulin partially inhibits this effect. Expression of constitutively active PKBα abrogates dexamethasone stimulation of hPDK4 promoter activity, while coexpression of constitutively active FOXO1a or FOXO3a, which are mutated to alanine at the three phosphorylation sites for protein kinase B (PKB), disrupts the ability of PKBα to inhibit promoter activity. A glucocorticoid response element for glucocorticoid receptor (GR) binding and three insulin response sequences (IRSs) that bind FOXO1a and FOXO3a are identified in the hPDK4 promoter. Mutation of the IRSs reduces the ability of glucocorticoids to stimulate PDK4 transcription. Transfection studies with E1A, which binds to and inactivates p300/CBP, suggest that interactions between p300/CBP and GR as well as FOXO factors are important for glucocorticoid-stimulated hPDK4 expression. Insulin suppresses the hPDK4 induction by glucocorticoids through inactivation of the FOXO factors.
Prolonged Incubation in PUGNAc Results in Increased Protein O-Linked Glycosylation and Insulin Resistance in Rat Skeletal Muscle
Authors: Arias Edward B. , Kim Junghoon , Cartee Gregory D.
Published: March 2007

Increased flux through the hexosamine biosynthetic pathway and increased O-linked glycosylation (N-acetylglucosamine [O-GlcNAc]) of proteins have been implicated in insulin resistance. Previous research in 3T3-L1 adipocytes indicated that insulin-stimulated glucose uptake and phosphorylation of Akt were reduced after incubation with O-(2-acetamido-2-deoxy-d-glucopyranosylidene)amino-N-phenylcarbamate (PUGNAc; 100 μmol/l), an inhibitor of the O-GlcNAcase that catalyzes removal of O-GlcNAc from proteins. Therefore, in this study, we tested the effects of PUGNAc on skeletal muscle. Incubation of rat epitrochlearis muscles for 19 h with 100 μmol/l PUGNAc resulted in a marked increase in O-GlcNAcylation of multiple proteins. Incubation with PUGNAc reduced glucose transport with a physiologic insulin concentration without affecting glucose transport without insulin or with supraphysiologic insulin. PUGNAc did not significantly alter insulin-stimulated phosphorylation of Akt (serine and threonine) or its substrates glycogen synthase kinase (GSK)3α and GSK3β. Insulin stimulated a dose-dependent (12.0 > 0.6 > 0 nmol/l) increase in the phosphorylation of a 160-kDa protein detected using an antibody against an Akt substrate phosphomotif. PUGNAc treatment did not alter phosphorylation of this protein. These results indicate that PUGNAc is an effective inhibitor of O-GlcNAcase in skeletal muscle and suggest that O-GlcNAc modification of proteins can induce insulin resistance in skeletal muscle independent of attenuated phosphorylation of Akt, GSK3α, GSK3β, and a 160-kDa protein with an Akt phosphomotif.
Evidence of Functional Impairment of Syngeneically Transplanted Mouse Pancreatic Islets Retrieved from the Liver
Authors: Mattsson Göran , Jansson Leif , Nordin Astrid , Andersson Arne , Carlsson Per-Ola
Published: March 2007

A drawback in pancreatic islet transplantation is the large number of islets needed to obtain insulin independence in patients with diabetes. This most likely reflects extensive posttransplantation islet cell death and functional impairment of the remaining endocrine cells. We aimed to develop an experimental method to retrieve transplanted islets from the mouse liver, which would enable comparisons of transplanted and endogenous islets and provide valuable information on functional changes induced by intraportal transplantation. Transplanted islets were obtained by retrograde perfusion of the liver with collagenase. The identity of retrieved tissue as transplanted islets was confirmed by intravital staining, immunohistochemistry, and electron microscopy. The retrieved islets, irrespective of whether they had resided in diabetic or nondiabetic recipients, had a markedly lower insulin content and glucose-stimulated insulin release when compared with isolated endogenous islets. The glucose oxidation rate was also markedly lower in the retrieved islets, suggesting mitochondrial dysfunction. These disturbances in insulin content, insulin release, and glucose oxidation rate were not reversed by a few days of culture after retrieval. The results implicate changes in islet function after intraportal transplantation. Such dysfunction may contribute to the high number of islets needed for successful transplantation in diabetic individuals.
Elevated Vascular Endothelial Growth Factor Production in Islets Improves Islet Graft Vascularization
Authors: Zhang Nan , Richter Anja , Suriawinata Jenny , Harbaran Sonal , Altomonte Jennifer , Cong Lin , Zhang Haojiang , Song Keying , Meseck Marcia , Bromberg Jonathan , Dong Hengjiang
Published: March 2007

Successful islet transplantation depends on the infusion of sufficiently large quantities of islets, of which only ∼30% become stably engrafted. Rapid and adequate revascularization of transplanted islets is important for islet survival and function. Delayed and insufficient revascularization can deprive islets of oxygen and nutrients, resulting in islet cell death and early graft failure. To improve islet revascularization, we delivered human vascular endothelial growth factor (VEGF) cDNA to murine islets, followed by transplantation under the renal capsule in diabetic mice. Diabetic animals receiving a marginal mass of 300 islets that were pretransduced with a VEGF vector exhibited near normoglycemia. In contrast, diabetic mice receiving an equivalent number of islets that were transduced with a control vector remained hyperglycemic. Immunohistochemistry with anti-insulin and anti-CD31 antibodies revealed a relatively higher insulin content and greater degree of microvasculature in the VEGF vector–transduced islet grafts, which correlated with significantly improved blood glucose profiles and enhanced insulin secretion in response to glucose challenge in this group of diabetic recipient mice. These results demonstrate that VEGF production in islets stimulates graft angiogenesis and enhances islet revascularization. This mechanism might be explored as a novel strategy to accelerate islet revascularization and improve long-term survival of functional islet mass posttransplantation.
Differential Recognition and Activation Thresholds in Human Autoreactive GAD-Specific T-Cells
Authors: Mallone Roberto , Kochik Sharon A. , Laughlin Elsa M. , Gersuk Vivian H. , Reijonen Helena , Kwok William W. , Nepom Gerald T.
Published: March 2007

The activation requirements of autoreactive CD4+ T-cells were investigated in GAD65-specific HLA-DR0401–restricted clones derived from a diabetic patient using major histocompatibility complex (MHC) class II tetramers (TMrs) as stimulating agents. Despite the fact that TMrs loaded with an immunodominant-altered GAD peptide (TMr-GAD) bound a limited number of T-cell receptors, they were capable of efficiently delivering activation signals. These signals ranged from the early steps of phospholipase C (PLC)-γ1 phosphorylation and Ca2+ mobilization to more complex events, such as CD69 upregulation, cytokine mRNA transcription and secretion, and proliferation. All the effects triggered by TMr-GAD were dose dependent. On the contrary, [3H]-thymidine incorporation decreased at high TMr-GAD concentrations because of activation-induced cell death (AICD) after initial proliferation. Lower-avidity clones (as defined by TMr-GAD binding) were less sensitive to activation as well as less susceptible to AICD compared with higher-avidity clones. Induction of apoptosis is a potential immunomodulatory target for therapeutic applications of MHC class II multimers, but the relative resistance of low-avidity T-cells may limit its benefits.
Improved Islet Morphology after Blockade of the Renin- Angiotensin System in the ZDF Rat
Authors: Tikellis Christos , Wookey Peter J. , Candido Riccardo , Andrikopoulos Sof , Thomas Merlin C. , Cooper Mark E.
Published: March 2007

The renin-angiotensin system (RAS) has an important role in the endocrine pancreas. Although angiotensin II has significant effects on cell proliferation and apoptosis, the contribution of the RAS to changes in islet structure and function associated with type 2 diabetes is yet to be defined. This study examined the specific effects of RAS blockade on islet structure and function in diabetes. Thirty-six male Zucker diabetic fatty (ZDF) rats, 10 weeks of age, were randomized to receive the angiotensin-converting enzyme inhibitor perindopril (8 mg/l in drinking water; n = 12), irbesartan (15 mg/kg via gavage; n = 12), or no treatment (n = 12) for 10 weeks. Results were compared with lean littermates (ZL) (n = 12) studied concurrently. ZDF rats had increased intra-islet expression of components of the RAS correlating with increased intraislet fibrosis, apoptosis, and oxidative stress. Disordered islet architecture, seen in ZDF rats, was attenuated after treatment with perindopril or irbesartan. Islet fibrogenesis was also diminished, as measured by picrosirius staining and expression of collagens I and IV. Gene expression of transforming growth factor-β1 was increased in the ZDF pancreas (ZL, 1.0 ± 0.1; ZDF, 2.0 ± 0.3; P < 0.05) and reduced after blockade of the RAS (ZDF + P, 1.3 ± 0.2; ZDF + I, 1.5 ± 0.1; vs. ZDF, both P < 0.05). Improvements in structural parameters were also associated with functional improvements in first-phase insulin secretion. These findings provide a possible mechanism for the reduced incidence of new-onset diabetes that has been observed in clinical trials of RAS blockade.
Effects of Dietary Monosaccharides on Sympathetic Nervous System Activity in Adipose Tissues of Male Rats
Authors: Young James B. , Weiss Jeffrey , Boufath Nadine
Published: March 2007

Dietary carbohydrate activates the sympathetic nervous system (SNS). As the mechanisms underlying this response are not fully characterized, studies were undertaken to compare SNS responses to ingestion of glucose, fructose, and galactose. SNS activity was examined using techniques of [3H]norepinephrine ([3H]NE) turnover in brown and white fat. In addition, gene expression for several sympathetically related proteins was also analyzed in these tissues. [3H]NE turnover in interscapular brown adipose tissue (IBAT) and retroperitoneal fat increased in response to glucose and fructose in the diet, whereas [3H]NE turnover in epididymal fat did not respond to either monosaccharide. Galactose feeding, by contrast, decreased [3H]NE turnover in IBAT, but increased it in epididymal, though not retroperitoneal, fat. Expression of GLUT4 was more abundant in IBAT and retroperitoneal fat from glucose- and fructose-fed animals than from diet- or galactose-fed rats. Chemical sympathectomy abolished the GLUT4 response in retroperitoneal fat, but was without effect on GLUT4 in epididymal fat. These studies are consistent with activation of a neural pathway by oral glucose or fructose, leading to SNS activation in IBAT and retroperitoneal fat and enhanced GLUT4 expression.
Islet Cell Autoimmunity in a Triethnic Adult Population of the Third National Health and Nutrition Examination Survey
Authors: Barinas-Mitchell Emma , Pietropaolo Susan , Zhang Ying-Jian , Henderson Tyona , Trucco Massimo , Kuller Lewis H. , Pietropaolo Massimo
Published: March 2007

Markers of humoral islet cell autoimmunity, such as autoantibodies (AAs) against the 65-kDa isoform of GAD (GAD65), serve as determinants of risk for autoimmune diabetes. Despite the high prevalence of diabetes in U.S. racial and ethnic minority adult populations, little is known concerning the prevalence of GAD65 AA in these groups. We estimated the prevalence of GAD65 AA in 1,064 diabetic and 1,036 nondiabetic participants who were 40–90 years of age from the Third National Health and Nutrition Examination Survey (NHANES III), which provides a representative ethnic sample of the U.S. diabetic population. The prevalence of GAD65 AA was higher in diabetic participants compared with nondiabetic participants in non-Hispanic whites (n = 920; 6.3% vs. 2.0%; P = 0.001) and non-Hispanic blacks (n = 534; 3.7% vs. 1.3%; P = 0.08) but not in Mexican Americans (n = 646; 1.2% vs. 2.6%; P = 0.18). Among diabetic non-Hispanic whites and non-Hispanic blacks, being GAD65 AA positive was associated with lower BMI and C-peptide (P < 0.05). These results may reflect the outcome of an autoimmune process leading to β-cell destruction/dysfunction in non-Hispanic white and non-Hispanic black adult diabetic patients as it occurs in a similar manner in type 1 diabetes. Among diabetic Mexican Americans, the lower prevalence of GAD65 AA suggests a lower frequency of autoimmune-related diabetes.
Prevalence of Hepatic Steatosis After Islet Transplantation and Its Relation to Graft Function
Authors: Bhargava Ravi , Senior Peter A. , Ackerman Thomas E. , Ryan Edmond A. , Paty Breay W. , Lakey Jonathan R.T. , Shapiro A.M. James
Published: March 2007

Islet allotransplantation can provide insulin independence in selected individuals with type 1 diabetes. The long-term effects of these transplants on the liver are unknown. Recently, two cases of periportal steatosis after islet transplantation have been described. In this study, we performed ultrasound and magnetic resonance imaging (MRI) in 30 C-peptide−positive islet transplant recipients to detect steatosis and to explore the association of the radiological findings with clinical and metabolic factors. Steatosis was observed on MRI in six (20%) subjects. Histological findings of hepatic steatosis concurred with the imaging findings. Steatosis completely resolved in one subject whose graft failed. More subjects with steatosis required supplementary exogenous insulin than not (67 vs. 21%; P < 0.05). The clinical features of subjects with and without steatosis were otherwise similar, although C-peptide levels were higher in insulin-independent subjects with steatosis (0.98 ± 0.12 vs. 0.70 ± 0.18 nmol/l; P = 0.05), despite similar blood glucose levels. Serum triglycerides and the use of exogenous insulin were associated with increased odds of steatosis in a logistic regression model (χ2 [degrees freedom] = 13.6 [2]); P = 0.001). MRI-detected steatosis is a common finding; the steatosis appears to be due to a paracrine action of insulin secreted from intrahepatic islets. Hepatic steatosis may be associated with insulin resistance or graft dysfunction.
Insulin Generates Free Radicals by an NAD(P)H, Phosphatidylinositol 3′-Kinase-Dependent Mechanism in Human Skin Fibroblasts Ex Vivo
Authors: Ceolotto Giulio , Bevilacqua Michela , Papparella Italia , Baritono Elisabetta , Franco Lorenzo , Corvaja Carlo , Mazzoni Martina , Semplicini Andrea , Avogaro Angelo
Published: March 2007

Oxidative stress may be involved in the development of vascular complications associated with diabetes; however, the molecular mechanism responsible for increased production of free radicals in diabetes remains uncertain. Therefore, we examined whether acute hyperinsulinemia increases the production of free radicals and whether this condition affects proliferative extracellular signal-regulated kinase (ERK-1 and -2) signaling in human fibroblasts in vitro. Insulin treatment significantly increased intracellular superoxide anion (O2−) production, an effect completely abolished by Tiron, a cell-permeable superoxide dismutase (SOD) mimetic and by polyethylene glycol (PEG)-SOD, but not by PEG catalase. Furthermore, insulin-induced O2− production was attenuated by the NAD(P)H inhibitor apocynin, but not by rotenone or oxypurinol. Inhibition of the phosphatidylinositol 3′-kinase (PI 3′-kinase) pathway with LY294002 blocked insulin-stimulated O2− production, suggesting a direct involvement of PI 3′-kinase in the activation of NAD(P)H oxidase. The insulin-induced free radical production led to membranous translocation of p47phox and markedly enhanced ERK-1 and -2 activation in human fibroblasts. In conclusion, these findings provided direct evidence that elevated insulin levels generate O2− by an NAD(P)H-dependent mechanism that involves the activation of PI 3′-kinase and stimulates ERK-1- and ERK-2-dependent pathways. This effect of insulin may contribute to the pathogenesis and progression of cardiovascular disease in the insulin resistance syndrome.
Human Pancreatic Duct Cells Exert Tissue Factor-Dependent Procoagulant Activity
Authors: Beuneu Claire , Vosters Olivier , Movahedi Babak , Remmelink Myriam , Salmon Isabelle , Pipeleers Daniel , Pradier Olivier , Goldman Michel , Verhasselt Valérie
Published: March 2007

Activation of the coagulation cascade contributes to early graft loss and intraportal thrombotic events in clinical islet transplantation. Although these complications were shown to be related to the presence of tissue factor in human islet preparations, the contribution of duct cells, which represent a major contaminant of clinical islet isolates, has not been specified so far. Herein, we used flow cytometry, immunohistochemistry, RT-PCR, and functional coagulation assays to demonstrate that duct cells exert a potent factor VII-dependent procoagulant activity related to their expression of tissue factor. Both the classical membrane-bound and the recently described soluble form of tissue factor were shown to be synthesized by duct cells. We conclude that contaminating duct cells contribute to early β-cell damage after islet transplantation through their involvement in tissue factor-mediated thrombotic and inflammatory events.
Oxidative Capacity, Lipotoxicity, and Mitochondrial Damage in Type 2 Diabetes
Authors: Schrauwen Patrick , Hesselink Matthijs K.C.
Published: March 2007

Recent evidence points toward decreased oxidative capacity and mitochondrial aberrations as a major contributor to the development of insulin resistance and type 2 diabetes. In this article we will provide an integrative view on the interrelation between decreased oxidative capacity, lipotoxicity, and mitochondrial aberrations in type 2 diabetes. Type 2 diabetes is characterized by disturbances in fatty acid metabolism and is accompanied by accumulation of fatty acids in nonadipose tissues. In metabolically active tissues, such as skeletal muscle, fatty acids are prone to so-called oxidative damage. In addition to producing energy, mitochondria are also a major source of reactive oxygen species, which can lead to lipid peroxidation. In particular, the mitochondrial matrix, which contains DNA, RNA, and numerous enzymes necessary for substrate oxidation, is sensitive to peroxide-induced oxidative damage and needs to be protected against the formation and accumulation of lipids and lipid peroxides. Recent evidence reports that mitochondrial uncoupling is involved in the protection of the mitochondrial matrix against lipid-induced mitochondrial damage. Disturbances in this protection mechanism can contribute to the development of type 2 diabetes.
Glucose and Insulin Treatment of Insulinoma Cells Results in Transcriptional Regulation of a Common Set of Genes
Authors: Ohsugi Mitsuru , Cras-Méneur Corentin , Zhou Yiyong , Warren Wesley , Bernal-Mizrachi Ernesto , Permutt M. Alan
Published: March 2007

Glucose and insulin are important regulators of islet β-cell growth and function by activating signaling pathways resulting in transcriptional changes that lead to adaptive responses. Several immediate early genes have been shown to be rapidly induced by glucose-activated depolarization in islet β-cells. The current studies address aspects of glucose-regulated transcription: 1) the number and characteristics of these genes, 2) if depolarization is the major mechanism, and 3) if glucose-stimulated insulin secretion is responsible, because insulin per se can activate transcription. Here, the expression profiles of glucose-responsive insulinoma cells 45 min after the addition of glucose, KCl to induce depolarization, or insulin were assessed by endocrine pancreas cDNA microarrays. Glucose activated more than 90 genes, representing diverse gene ontology functions, and most were not previously known to be glucose responsive. KCl activated 80% of these same glucose-regulated genes and, along with the effects of pretreatment with diazoxide, suggested that glucose signaling is mediated primarily via depolarization. There were >150 genes activated by insulin, and remarkably 71% were also regulated by glucose. Preincubation with a phosphatidylinositol (PI) 3-kinase inhibitor resulted in almost total inhibition of depolarization and insulin-activated transcriptional responses. Thus, through gene expression profiling, these data demonstrate that glucose and insulin rapidly activate a PI 3-kinase pathway, resulting in transcription of a common set of genes. This is consistent with glucose activation of gene transcription either directly or indirectly through a paracrine/autocrine effect via insulin release. These results illustrate that expression gene profiling can contribute to the elucidation of important β-cell biological functions.