bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of the Liver-Specific Expression of SHIP2 (SH2-Containing Inositol 5′-Phosphatase 2) on Insulin Signaling and Glucose Metabolism in Mice
Authors: Fukui Kazuhito , Wada Tsutomu , Kagawa Syota , Nagira Kiyofumi , Ikubo Mariko , Ishihara Hajime , Kobayashi Masashi , Sasaoka Toshiyasu
Published: March 2007

We investigated the role of hepatic SH2-containing inositol 5′-phosphatase 2 (SHIP2) in glucose metabolism in mice. Adenoviral vectors encoding wild-type SHIP2 (WT-SHIP2) and a dominant-negative SHIP2 (ΔIP-SHIP2) were injected via the tail vein into db/+m and db/db mice, respectively. Four days later, amounts of hepatic SHIP2 protein were increased by fivefold. Insulin-induced phosphorylation of Akt in liver was impaired in WT-SHIP2–expressing db/+m mice, whereas the reduced phosphorylation was restored in ΔIP-SHIP2–expressing db/db mice. The abundance of mRNA for glucose-6-phosphatase (G6Pase) and PEPCK was increased, that for glucokinase (GK) was unchanged, and that for sterol regulatory element–binding protein 1 (SREBP)-1 was decreased in hepatic WT-SHIP2–overexpressing db/+m mice. The increased expression of mRNA for G6Pase and PEPCK was partly suppressed, that for GK was further enhanced, and that for SREBP1 was unaltered by the expression of ΔIP-SHIP2 in db/db mice. The hepatic expression did not affect insulin signaling in skeletal muscle and fat tissue in both mice. After oral glucose intake, blood glucose levels and plasma insulin concentrations were elevated in WT-SHIP2–expressing db/+m mice, while elevated values were decreased by the expression of ΔIP-SHIP2 in db/db mice. These results indicate that hepatic SHIP2 has an impact in vivo on the glucose metabolism in both physiological and diabetic states possibly by regulating hepatic gene expression.
The Regulation of Fatty Acid Synthase by STAT5A
Authors: Hogan Jessica C. , Stephens Jacqueline M.
Published: March 2007

Growth hormone (GH) diminishes adipose tissue mass in vivo and decreases expression and activity of fatty acid synthase (FAS) in adipocytes. GH and prolactin (PRL) are potent activators of STAT5 and exert adipogenic and antiadipogenic effects in adipocytes. In this study, we demonstrate that GH and PRL decrease the mRNA and protein levels of FAS in 3T3-L1 adipocytes. We present evidence that indicates that FAS is repressed at the level of transcription. In addition, PRL responsiveness was shown to exist between −1,594 and −700 of the rat FAS promoter. Moreover, responsiveness to PRL was abolished with mutation of a site at position −908 to −893, which we have shown to bind STAT5A in a PRL-dependent manner. Taken together, these data strongly suggest that PRL directly represses expression of FAS in adipocytes through STAT5A binding to the −908 to −893 site. Furthermore, our results indicate that STAT5A has an antilipogenic function in adipocytes and may contribute to the regulation of energy balance.
Role of Selective Leptin Resistance in Diet-Induced Obesity Hypertension
Authors: Rahmouni Kamal , Morgan Donald A. , Morgan Gina M. , Mark Allyn L. , Haynes William G.
Published: March 2007

Leptin is an adipocyte-derived hormone that plays a key role in the regulation of body weight through its actions on appetite and metabolism. Leptin also increases sympathetic nerve activity (SNA) and blood pressure. We tested the hypothesis that diet-induced obesity is associated with resistance to the metabolic actions of leptin but preservation of its renal SNA and arterial pressure effects, leading to hypertension. Mice were fed a high-fat diet for 10 weeks to induce moderate obesity. The decrease in food intake and body weight induced by intraperitoneal or intracerebroventricular leptin was significantly attenuated in the obese mice. Regional SNA responses to leptin were differentially altered in diet-induced obese mice. Renal SNA response to leptin was preserved, whereas lumbar and brown adipose tissue SNA responses were attenuated in obese mice. Radiotelemetric arterial pressure was ∼10 mmHg higher in obese mice. Furthermore, the increase in arterial pressure in response to long-term (12 days) leptin treatment was preserved in obese mice. Thus, mice with diet-induced obesity exhibit circulating hyperleptinemia and resistance to the metabolic actions of leptin. However, there is preservation of the renal sympathetic and arterial pressure responses to leptin, which represent a potential mechanism for the adverse cardiovascular consequences of obesity.
Targeted Inactivation of Hepatocyte Growth Factor Receptor c-met in β-Cells Leads to Defective Insulin Secretion and GLUT-2 Downregulation Without Alteration of β-Cell Mass
Authors: Roccisana Jennifer , Reddy Vasumathi , Vasavada Rupangi C. , Gonzalez-Pertusa Jose A. , Magnuson Mark A. , Garcia-Ocaña Adolfo
Published: March 2007

Overexpression of hepatocyte growth factor (HGF) in the β-cell of transgenic mice enhances β-cell proliferation, survival, and function. In the current studies, we have used conditional ablation of the c-met gene to uncover the physiological role of HGF in β-cell growth and function. Mice in which c-met is inactivated in the β-cell (MetCKO mice) display normal body weight, blood glucose, and plasma insulin compared with control littermates. In contrast, MetCKO mice displayed significantly diminished glucose tolerance and reduced plasma insulin after a glucose challenge in vivo. This impaired glucose tolerance in MetCKO mice was not caused by insulin resistance because sensitivity to exogenous insulin was similar in both groups. Importantly, in vitro glucose-stimulated insulin secretion in MetCKO islets was decreased by ∼50% at high glucose concentrations compared with control islets. Furthermore, whereas insulin and glucokinase expression in MetCKO islets were normal, GLUT-2 expression was decreased by ∼50%. These changes in β-cell function in MetCKO mice were not accompanied by changes in total β-cell mass, islet morphology, islet cell composition, and β-cell proliferation. Interestingly, however, MetCKO mice display an increased number of small islets, mainly single and doublet β-cells. We conclude that HGF/c-met signaling in the β-cell is not essential for β-cell growth, but it is essential for normal glucose-dependent insulin secretion.
Tissue Factor as a Link Between Wounding and Tissue Repair
Authors: Chen Jiang , Kasper Michael , Heck Tobias , Nakagawa Katsumi , Humpert Per M. , Bai Ling , Wu Gang , Zhang Youming , Luther Thomas , Andrassy Martin , Schiekofer Stephan , Hamann Andreas , Morcos Michael , Chen Baoshen , Stern David M. , Nawroth Peter P. , Bierhaus Angelika
Published: March 2007

The initial phase of wound repair involves inflammation, induction of tissue factor (TF), formation of a fibrin matrix, and growth of new smooth muscle actin (α-SMA)-positive vessels. In diabetes, TF induction in response to cutaneous wounding, which ordinarily precedes increased expression of vascular endothelial growth factor (VEGF) and α-SMA transcription, is diminished, though not to a degree causing excessive local bleeding. Enhanced TF expression in wounds of diabetic mice caused by somatic TF gene transfer increased VEGF transcription and translation and, subsequently, enhanced formation of new blood vessels and elevated blood flow. Furthermore, increased levels of TF in wounds of diabetic mice enhanced wound healing; the time to achieve 50% wound closure was reduced from 5.5 days in untreated diabetic mice to 4.1 days in animals undergoing TF gene transfer (this was not statistically different from wound closure in nondiabetic mice). Thus, cutaneous wounds in diabetic mice display a relative deficiency of TF compared with nondiabetic controls, and this contributes to delayed wound repair. These data establish TF expression as an important link between the early inflammatory response to cutaneous wounding and reparative processes.
The Early Natural History of Nephropathy in Type 1 Diabetes
Authors: Steinke Julia M. , Sinaiko Alan R. , Kramer Michael S. , Suissa Samy , Chavers Blanche M. , Mauer Michael ,   for the International Diabetic Nephropathy Study Group
Published: March 2007

Predictors of albumin excretion rate (AER) abnormalities could provide earlier indicators of diabetic nephropathy risk. Data from the Natural History Study, a prospective 5-year observation of renal structure and function in young type 1 diabetic patients, were examined for predictors of AER patterns in normoalbuminuric type 1 diabetic patients. Included were 170 patients (96 females) (aged 16.7 ± 5.9 years, duration of diabetes 8.0 ± 4.3 years) with normal blood pressure, normoalbuminuria (AER <20 μg/min), and eight or more follow-up visits over 5 years. AER, blood pressure, and HbA1c (A1C) were determined quarterly and glomerular filtration rate (GFR) annually. Persistent microalbuminuria (PMA) was defined as 20–200 μg/min in two of three consecutive values within 6–12 months. Four different AER patterns were identified. Group 1 (n = 99): all values <20 μg/min. Group 2 (n = 49): intermittent levels >20 μg/min but not meeting microalbuminuria criteria. Group 3 (n = 14): PMA during follow-up but normoalbuminuria at study exit. Group 4 (n = 8): microalbuminuria at study exit. Group 4 (497 ± 95 nm, P < 0.01) and group 3 (464 ± 113 nm, P = 0.03) patients had greater baseline glomerular basement membrane (GBM) width versus group 1 (418 ± 67 nm). Baseline GFR in group 4 (163 ± 37 ml · min−1 · 1.73 m−2) was higher than group 1 (143 ± 28 ml · min−1 · 1.73 m−2, P = 0.04). A1C was higher in group 2 (9.0 ± 1.2%) than group 1 (8.4 ± 1.1%, P = 0.008). Thus, greater increases in GBM width and GFR were predictors of PMA. Since 64% of the patients that developed microalbuminuria reverted to normoalbuminuria, the risk of diabetic nephropathy as defined by current microalbuminuria criteria is unclear.
Heparanase-1 Gene Expression and Regulation by High Glucose in Renal Epithelial Cells
Authors: Maxhimer Justin B. , Somenek Michael , Rao Geetha , Pesce Catherine E. , Baldwin David , Gattuso Paolo , Schwartz Melvin M. , Lewis Edmund J. , Prinz Richard A. , Xu Xiulong
Published: March 2007

The molecular mechanisms of heparan sulfate proteoglycan downregulation in the glomerular basement membrane (GBM) of the kidneys with diabetic nephropathy remain controversial. In the present study, we showed that the expression of heparanase-1 (HPR1), a heparan sulfate–degrading endoglycosidase, was upregulated in the renal epithelial cells in the kidney with diabetic nephropathy. Urinary HPR1 levels were elevated in patients with diabetic nephropathy. In vitro cell culture studies revealed that HPR1 promoter–driven luciferase reporter gene expression, HPR1 mRNA, and protein were upregulated in renal epithelial cells under high glucose conditions. Induction of HPR1 expression by high glucose led to decreased cell surface heparan sulfate expression. HPR1 inhibitors were able to restore cell surface heparan sulfate expression. Functional analysis revealed that renal epithelial cells grown under high glucose conditions resulted in an increase of basement membrane permeability to albumin. Our studies suggest that loss of heparan sulfate in the GBM with diabetic nephropathy is attributable to accelerated heparan sulfate degradation by increased HPR1 expression.
Metformin Prevents High-Glucose–Induced Endothelial Cell Death Through a Mitochondrial Permeability Transition-Dependent Process
Authors: Detaille Dominique , Guigas Bruno , Chauvin Christiane , Batandier Cécile , Fontaine Eric , Wiernsperger Nicolas , Leverve Xavier
Published: March 2007

Hyperglycemia-induced oxidative stress is detrimental for endothelial cells, contributing to the vascular complications of diabetes. The mitochondrial permeability transition pore (PTP) is an oxidative stress–sensitive channel involved in cell death; therefore, we have examined its potential role in endothelial cells exposed to oxidative stress or high glucose level. Metformin, an antihyperglycemic agent used in type 2 diabetes, was also investigated because it inhibits PTP opening in transformed cell lines. Cyclosporin A (CsA), the reference PTP inhibitor, and a therapeutic dose of metformin (100 μmol/l) led to PTP inhibition in permeabilized human microvascular endothelial cells (HMEC-1). Furthermore, exposure of intact HMEC-1 or primary endothelial cells from either human umbilical vein or bovine aorta to the oxidizing agent tert-butylhydroperoxide or to 30 mmol/l glucose triggered PTP opening, cytochrome c decompartmentalization, and cell death. CsA or metformin prevented all of these effects. The antioxidant N-acetyl-l-cysteine also prevented hyperglycemia-induced apoptosis. We conclude that 1) elevated glucose concentration leads to an oxidative stress that favors PTP opening and subsequent cell death in several endothelial cell types and 2) metformin prevents this PTP opening–related cell death. We propose that metformin improves diabetes-associated vascular disease both by lowering blood glucose and by its effect on PTP regulation.
The Effect of Ruboxistaurin on Visual Loss in Patients With Moderately Severe to Very Severe Nonproliferative Diabetic Retinopathy
Authors:   The PKC-DRS Study Group
Published: March 2007

The purpose of this study was to evaluate the Safety and efficacy of the orally administered protein kinase C (PKC) β isoform-selective inhibitor ruboxistaurin (RBX) in subjects with moderately severe to very severe nonproliferative diabetic retinopathy (NPDR). In this multicenter, double-masked, randomized, placebo-controlled study, 252 subjects received placebo or RBX (8, 16, or 32 mg/day) for 36–46 months. Patients had an Early Treatment Diabetic Retinopathy Study (ETDRS) retinopathy severity level between 47B and 53E inclusive, an ETDRS visual acuity of 20/125 or better, and no history of scatter (panretinal) photocoagulation. Efficacy measures included progression of DR, moderate visual loss (MVL) (doubling of the visual angle), and sustained MVL (SMVL). RBX was well tolerated without significant adverse effects but had no significant effect on the progression of DR. Compared with placebo, 32 mg/day RBX was associated with a delayed occurrence of MVL (log rank, P = 0.038) and of SMVL (P = 0.226). RBX reduction of SMVL was evident only in eyes with definite diabetic macular edema at baseline (10% 32 mg/day RBX vs. 25% placebo, P = 0.017). In multivariable Cox proportional hazard analysis, 32 mg/day RBX significantly reduced the risk of MVL compared with placebo (hazard ratio 0.37 [95% CI 0.17–0.80], P = 0.012). In this clinical trial, RBX was well tolerated and reduced the risk of visual loss but did not prevent DR progression.
Genetic Variation in Adiponectin Receptor 1 and Adiponectin Receptor 2 Is Associated With Type 2 Diabetes in the Old Order Amish
Authors: Damcott Coleen M. , Ott Sandra H. , Pollin Toni I. , Reinhart Laurie J. , Wang Jian , O’Connell Jeffrey R. , Mitchell Braxton D. , Shuldiner Alan R.
Published: March 2007

Adiponectin receptor 1 (ADIPOR1) and adiponectin receptor 2 (ADIPOR2) are newly identified receptors for adiponectin, an adipocytokine with anti-inflammatory and insulin-sensitizing properties. We screened for polymorphisms by performing sequence analysis on all eight exons, splice junctions, and ∼2 kb of the 5′ flanking regions of each receptor. We detected 5 single nucleotide polymorphisms (SNPs) in ADIPOR1 and 16 SNPs in ADIPOR2. We genotyped these SNPs in Amish subjects with type 2 diabetes (n = 137), impaired glucose tolerance (IGT) (n = 139), and normal glucose tolerance (n = 342) to test for association with type 2 diabetes. Three intronic SNPs in ADIPOR1 were significantly associated with type 2 diabetes (P = 0.014–0.007; odds ratio [OR] 1.61–1.65) and in high linkage disequilibrium (r2 = 0.97–1.0). In ADIPOR2, we found that five SNPs delineated one large haplotype block (r2 = 0.9–1.0) spanning >98 kb of the gene and promoter region, which was strongly associated with the combined type 2 diabetes/IGT trait (P ≤ 0.001; OR 1.64–1.71). To our knowledge, these data provide the first evidence for association between variation in the adiponectin receptors and type 2 diabetes.
Donor Islet Endothelial Cells Participate in Formation of Functional Vessels Within Pancreatic Islet Grafts
Authors: Nyqvist Daniel , Köhler Martin , Wahlstedt Helene , Berggren Per-Olof
Published: March 2007

Pancreatic islet transplantation has emerged as a therapy for type 1 diabetes and is today performed using both freshly isolated and cultured islets. Islet blood vessels are disrupted during islet isolation; therefore, proper revascularization of the transplanted islets is of great importance for islet graft function and survival. We have studied intraislet endothelial cells after islet isolation, during islet culture, and following islet transplantation. By isolating islets from the transgenic Tie2-GFP (green fluorescent protein) mouse, characterized by an endothelial cell–specific expression of GFP, living endothelial cells could be studied in intact islets utilizing two-photon laser-scanning microscopy (TPLSM). Intraislet endothelial cells were found to survive islet transplantation but to rapidly disappear during islet culture. By transplanting freshly isolated Tie2-GFP islets and applying a novel ex vivo model for simultaneous perfusion and TPLSM imaging of the graft-bearing kidneys, GFP fluorescent endothelial cells were found to extensively contribute to vessels within the islet graft vasculature. Real-time imaging of the flow through the islet graft vasculature confirmed that the donor-derived vessels were functionally integrated. Hence, intraislet endothelial cells have the capability of participating in revascularization of pancreatic islets subsequent to transplantation. Therefore, preservation of intraislet endothelial cell mass may improve long-term graft function.
Expression of CD68 and Macrophage Chemoattractant Protein-1 Genes in Human Adipose and Muscle Tissues
Authors: Di Gregorio Gina B. , Yao-Borengasser Aiwei , Rasouli Neda , Varma Vijayalakshmi , Lu Tong , Miles Leslie M. , Ranganathan Gouri , Peterson Charlotte A. , McGehee Robert E. , Kern Philip A.
Published: March 2007

To examine the role of adipose-resident macrophages in insulin resistance, we examined the gene expression of CD68, a macrophage marker, along with macrophage chemoattractant protein-1 (MCP-1) in human subcutaneous adipose tissue using real-time RT-PCR. Both CD68 and MCP-1 mRNAs were expressed in human adipose tissue, primarily in the stromal vascular fraction. When measured in the adipose tissue from subjects with normal glucose tolerance, covering a wide range of BMI (21–51 kg/m2) and insulin sensitivity (SI) (0.6–8.0 × 10−4min−1 · μU–1 · ml–1), CD68 mRNA abundance, which correlated with the number of CD68-positive cells by immunohistochemistry, tended to increase with BMI but was not statistically significant. However, there was a significant inverse relation between CD68 mRNA and SI (r = −0.55, P = 0.02). In addition, there was a strong positive relationship among adipose tissue CD68 mRNA, tumor necrosis factor-α (TNF-α) secretion in vitro (r = 0.79, P < 0.005), and plasma interleukin-6 (r = 0.67, P < 0.005). To determine whether improving SI in subjects with impaired glucose tolerance (IGT) was associated with decreased CD68 expression, IGT subjects were treated for 10 weeks with pioglitazone or metformin. Pioglitazone increased SI by 60% and in the same subjects reduced both CD68 and MCP-1 mRNAs by >50%. Furthermore, pioglitazone resulted in a reduction in the number of CD68-positive cells in adipose tissue and reduced plasma TNF-α. Metformin had no effect on any of these measures. Thus, treatment with pioglitazone reduces expression of CD68 and MCP-1 in adipose tissue, apparently by reducing macrophage numbers, resulting in reduced inflammatory cytokine production and improvement in SI.
Carnosine as a Protective Factor in Diabetic Nephropathy
Authors: Janssen Bart , Hohenadel Daniela , Brinkkoetter Paul , Peters Verena , Rind Nina , Fischer Christine , Rychlik Ivan , Cerna Marie , Romzova Marianna , de Heer Emile , Baelde Hans , Bakker Stephan J.L. , Zirie Mahmoud , Rondeau Eric , Mathieson Peter , Saleem Moin A. , Meyer Jochen , Köppel Hannes , Sauerhoefer Sibylle , Bartram Claus R. , Nawroth Peter , Hammes Hans-Peter , Yard Benito A. , Zschocke Johannes , van der Woude Fokko J.
Published: March 2007

The risk of diabetic nephropathy is partially genetically determined. Diabetic nephropathy is linked to a gene locus on chromosome 18q22.3-q23. We aimed to identify the causative gene on chromosome 18 and to study the mechanism by which the product of this gene could be involved in the development of diabetic nephropathy. DNA polymorphisms were determined in 135 case (diabetic nephropathy) and 107 control (diabetes without nephropathy) subjects. The effect of carnosine on the production of extracellular matrix components and transforming growth factor-β (TGF-β) after exposure to 5 and 25 mmol/l d-glucose was studied in cultured human podocytes and mesangial cells, respectively. A trinucleotide repeat in exon 2 of the CNDP1 gene, coding for a leucine repeat in the leader peptide of the carnosinase-1 precursor, was associated with nephropathy. The shortest allelic form (CNDP1 Mannheim) was more common in the absence of nephropathy (P = 0.0028, odds ratio 2.56 [95% CI 1.36–4.84]) and was associated with lower serum carnosinase levels. Carnosine inhibited the increased production of fibronectin and collagen type VI in podocytes and the increased production of TGF-β in mesangial cells induced by 25 mmol/l glucose. Diabetic patients with the CNDP1 Mannheim variant are less susceptible for nephropathy. Carnosine protects against the adverse effects of high glucose levels on renal cells.
Regulation of Renal Lipid Metabolism, Lipid Accumulation, and Glomerulosclerosis in FVBdb/db Mice With Type 2 Diabetes
Authors: Wang Zhuowei , Jiang Tao , Li Jinping , Proctor Gregory , McManaman James L. , Lucia Scott , Chua Streamson , Levi Moshe
Published: March 2007

Diabetic kidney disease has been associated with the presence of lipid deposits, but the mechanisms for the lipid accumulation have not been fully determined. In the present study, we found that db/db mice on the FVB genetic background with loss-of-function mutation of the leptin receptor (FVB-Leprdb mice or FVBdb/db) develop severe diabetic nephropathy, including glomerulosclerosis, tubulointerstitial fibrosis, increased expression of type IV collagen and fibronectin, and proteinuria, which is associated with increased renal mRNA abundance of transforming growth factor-β, plasminogen activator inhibitor-1, and vascular endothelial growth factor. Electron microscopy demonstrates increases in glomerular basement membrane thickness and foot process (podocyte) length. We found that there is a marked increase in neutral lipid deposits in glomeruli and tubules by oil red O staining and biochemical analysis for cholesterol and triglycerides. We also detected a significant increase in the renal expression of adipocyte differentiation-related protein (adipophilin), a marker of cytoplasmic lipid droplets. We examined the expression of sterol regulatory element–binding protein (SREBP)-1 and -2, transcriptional factors that play an important role in the regulation of fatty acid, triglyceride, and cholesterol synthesis. We found significant increases in SREBP-1 and -2 protein levels in nuclear extracts from the kidneys of FVBdb/db mice, with increases in the mRNA abundance of acetyl-CoA carboxylase, fatty acid synthase, and 3-hydroxy-3-methylglutaryl-CoA reductase, which mediates the increase in renal triglyceride and cholesterol content. Our results indicate that in FVBdb/db mice, renal triglyceride and cholesterol accumulation is mediated by increased activity of SREBP-1 and -2. Based on our previous results with transgenic mice overexpressing SREBP-1 in the kidney, we propose that increased expression of SREBPs plays an important role in causing renal lipid accumulation, glomerulosclerosis, tubulointerstitial fibrosis, and proteinuria in mice with type 2 diabetes.
Disruption of the γ-Interferon Signaling Pathway at the Level of Signal Transducer and Activator of Transcription-1 Prevents Immune Destruction of β-cells
Authors: Gysemans Conny A. , Ladrière Laurence , Callewaert Hanne , Rasschaert Joanne , Flamez Daisy , Levy David E. , Matthys Patrick , Eizirik Décio L. , Mathieu Chantal
Published: March 2007

β-Cells under immune attack are destroyed by the aberrant activation of key intracellular signaling cascades. The aim of the present study was to evaluate the contribution of the signal transducer and activator of transcription (STAT)-1 pathway for β-cell apoptosis by studying the sensitivity of β-cells from STAT-1 knockout (−/−) mice to immune-mediated cell death in vitro and in vivo. Whole islets from STAT-1−/− mice were completely resistant to interferon (IFN)-γ (studied in combination with interleukin [IL]-1β)-mediated cell death (92 ± 4% viable cells in STAT-1−/− mice vs. 56 ± 3% viable cells in wild-type controls, P ≤ 0.001) and had preserved insulin release after exposure to IL-1β and IFN-γ. Moreover, analysis of cell death in cytokine-exposed purified β-cells confirmed that protection was due to absence of STAT-1 in the β-cells themselves. Deficiency of STAT-1 in islets completely prevented cytokine-induced upregulation of IL-15, interferon inducible protein 10, and inducible nitric oxide synthase transcription but did not interfere with monocyte chemoattractant protein 1 and macrophage inflammatory protein 3α expression. In vivo, STAT-1−/− mice were partially resistant to development of diabetes after multiple low-dose streptozotocin injections as reflected by mean blood glucose at 12 days after first injection (159 ± 28 vs. 283 ± 81 mg/dl in wild-type controls, P ≤ 0.05) and diabetes incidence at the end of the follow-up period (39 vs. 73% in wild-type controls, P ≤ 0.05). In conclusion, the present results indicate that STAT-1 is a crucial transcription factor in the process of IFN-γ–mediated β-cell death and the subsequent development of immune-mediated diabetes.
Role of Insulin Secretion and Sensitivity in the Evolution of Type 2 Diabetes in the Diabetes Prevention Program
Authors:   The Diabetes Prevention Program Research Group
Published: March 2007

Insulin resistance and β-cell dysfunction, two factors central to the pathogenesis of type 2 diabetes, were studied in relation to the development of diabetes in a group of participants with impaired glucose tolerance in the Diabetes Prevention Program (DPP) at baseline and after specific interventions designed to prevent diabetes. Participants were randomly assigned to placebo (n = 1,082), metformin (850 mg twice a day) (n = 1,073), or intensive lifestyle intervention (n = 1,079). The diabetes hazard rate was negatively associated with baseline insulin sensitivity (hazard rate ratio = 0.62–0.94 per SD difference, depending on treatment group and measure of sensitivity) and with baseline insulin secretion (hazard rate ratio = 0.57–0.76 per SD). Improvements in insulin secretion and insulin sensitivity were associated with lower hazard rates in all treatment arms (hazard rate ratio = 0.46–0.95 per SD increase and 0.29–0.79 per SD increase, respectively). In multivariate models that included the three metabolic variables (changes in body weight, insulin sensitivity, and insulin secretion) each significantly and independently predicted progression to diabetes when adjusted for the other two variables. The intensive lifestyle intervention, which elicited the greatest reduction in diabetes incidence, produced the greatest improvement in insulin sensitivity and the best preservation of β-cell function after 1 year, whereas the placebo group, which had the highest diabetes incidence, had no significant change in insulin sensitivity and β-cell function after 1 year. In the metformin group, diabetes risk, insulin sensitivity, and β-cell function at 1 year were intermediate between those in the intensive lifestyle and placebo groups. In conclusion, higher insulin secretion and sensitivity at baseline and improvements in response to treatment were associated with lower diabetes risk in the DPP. The better preventive effectiveness of intensive lifestyle may be due to improved insulin sensitivity concomitant with preservation of β-cell function.
3,4-Dideoxyglucosone-3-ene Induces Apoptosis in Renal Tubular Epithelial Cells
Authors: Justo Pilar , Sanz Ana Belén , Egido Jesús , Ortiz Alberto
Published: March 2007

Diabetes complications are caused by hyperglycemia. Hyperglycemia results in increased concentrations of glucose degradation products. The study of peritoneal dialysis solution biocompatibility has highlighted the adverse effects of glucose degradation products. Recently, 3,4-dideoxyglucosone-3-ene (3,4-DGE) has been identified as the most toxic glucose degradation product in peritoneal dialysis fluids. Its role in renal pathophysiology has not been addressed. 3,4-DGE induces apoptosis in murine renal tubular epithelial cells in a dose- and time-dependent manner. Peak apoptosis is observed after 72 h of culture. The lethal concentration range is 25–50 μmol/l. 3,4-DGE results in Bax oligomerization, release of cytochrome c from mitochondria, activation of caspases-9 and -3, and Bid proteolysis. Apoptosis induced by 3,4-DGE is caspase dependent and could be prevented by the broad-spectrum caspase inhibitor zVAD-fmk (Z-Val-Ala-dl-Asp-fluoromethylketone) and by specific inhibitors of caspases-2, -8, and -9. However, caspase inhibition did not prevent eventual cell death. In contrast, antagonism of Bax by a Ku-70–derived peptide or antisense oligonucleotides prevented both apoptosis and cell death. In conclusion, 3,4-DGE promotes apoptosis of cultured renal parenchymal cells by a Bax- and caspase-dependent mechanism. A role for 3,4-DGE in diabetes complications in the kidney and in the modulation of residual renal function in peritoneal dialysis should be further explored.
Chemical Ablation of Gastric Inhibitory Polypeptide Receptor Action by Daily (Pro3)GIP Administration Improves Glucose Tolerance and Ameliorates Insulin Resistance and Abnormalities of Islet Structure in Obesity-Related Diabetes
Authors: Gault Victor A. , Irwin Nigel , Green Brian D. , McCluskey Jane T. , Greer Brett , Bailey Clifford J. , Harriott Patrick , O’Harte Finbarr P.M. , Flatt Peter R.
Published: March 2007

Glucose-dependent insulinotropic polypeptide (gastric inhibitory polypeptide [GIP]) is an important incretin hormone secreted by endocrine K-cells in response to nutrient ingestion. In this study, we investigated the effects of chemical ablation of GIP receptor (GIP-R) action on aspects of obesity-related diabetes using a stable and specific GIP-R antagonist, (Pro3)GIP. Young adult ob/ob mice received once-daily intraperitoneal injections of saline vehicle or (Pro3)GIP over an 11-day period. Nonfasting plasma glucose levels and the overall glycemic excursion (area under the curve) to a glucose load were significantly reduced (1.6-fold; P < 0.05) in (Pro3)GIP-treated mice compared with controls. GIP-R ablation also significantly lowered overall plasma glucose (1.4-fold; P < 0.05) and insulin (1.5-fold; P < 0.05) responses to feeding. These changes were associated with significantly enhanced (1.6-fold; P < 0.05) insulin sensitivity in the (Pro3)GIP-treated group. Daily injection of (Pro3)GIP reduced pancreatic insulin content (1.3-fold; P < 0.05) and partially corrected the obesity-related islet hypertrophy and β-cell hyperplasia of ob/ob mice. These comprehensive beneficial effects of (Pro3)GIP were reversed 9 days after cessation of treatment and were independent of food intake and body weight, which were unchanged. These studies highlight a role for GIP in obesity-related glucose intolerance and emphasize the potential of specific GIP-R antagonists as a new class of drugs for the alleviation of insulin resistance and treatment of type 2 diabetes.
Association of Non-HLA Genes With Type 1 Diabetes Autoimmunity
Authors: Steck Andrea K. , Bugawan Teodorica L. , Valdes Ana Maria , Emery Lisa M. , Blair Alan , Norris Jill M. , Redondo Maria J. , Babu Sunanda R. , Erlich Henry A. , Eisenbarth George S. , Rewers Marian J.
Published: March 2007

Approximately 50% of the genetic risk for type 1 diabetes is attributable to the HLA region. We evaluated associations between candidate genes outside the HLA region–INS, cytotoxic T-lymphocyte–associated antigen (CTLA)-4, interleukin (IL)-4, IL-4R, and IL-13 and islet autoimmunity among children participating in the Diabetes Autoimmunity Study in the Young (DAISY). Children with persistent islet autoantibody positivity (n = 102, 38 of whom have already developed diabetes) and control subjects (n = 198) were genotyped for single nucleotide polymorphisms (SNPs) in the candidate genes. The INS-23Hph1 polymorphism was significantly associated with both type 1 diabetes (OR = 0.30; 95% CI 0.13–0.69) and persistent islet autoimmunity but in the latter, only in children with the HLA-DR3/4 genotype (0.40; 0.18–0.89). CTLA-4 promoter SNP was significantly associated with type 1 diabetes (3.52; 1.22–10.17) but not with persistent islet autoimmunity. Several SNPs in the IL-4 regulatory pathway appeared to have a predisposing effect for type 1 diabetes. Associations were found between both IL-4R haplotypes and IL-4–IL-13 haplotypes and persistent islet autoimmunity and type 1 diabetes. This study confirms the association between the INS and CTLA-4 loci and type 1 diabetes. Genes involved in the IL-4 regulatory pathway (IL-4, IL-4R, IL-13) may confer susceptibility or protection to type 1 diabetes depending on individual SNPs or specific haplotypes.
Activating Mutations in Kir6.2 and Neonatal Diabetes
Authors: Hattersley Andrew T. , Ashcroft Frances M.
Published: March 2007

Closure of ATP-sensitive K+ channels (KATP channels) in response to metabolically generated ATP or binding of sulfonylurea drugs stimulates insulin release from pancreatic β-cells. Heterozygous gain-of-function mutations in the KCJN11 gene encoding the Kir6.2 subunit of this channel are found in ∼47% of patients diagnosed with permanent diabetes at <6 months of age. There is a striking genotype-phenotype relationship with specific Kir6.2 mutations being associated with transient neonatal diabetes, permanent neonatal diabetes alone, and a novel syndrome characterized by developmental delay, epilepsy, and neonatal diabetes (DEND) syndrome. All mutations appear to cause neonatal diabetes by reducing KATP channel ATP sensitivity and increasing the KATP current, which inhibits β-cell electrical activity and insulin secretion. The severity of the clinical symptoms is reflected in the ATP sensitivity of heterozygous channels in vitro with wild type > transient neonatal diabetes > permanent neonatal diabetes > DEND syndrome channels. Sulfonylureas still close mutated KATP channels, and many patients can discontinue insulin injections and show improved glycemic control when treated with high-dose sulfonylurea tablets. In conclusion, the finding that Kir6.2 mutations can cause neonatal diabetes has enabled a new therapeutic approach and shed new light on the structure and function of the Kir6.2 subunit of the KATP channel.
Cardiac-Specific Overexpression of Peroxisome Proliferator–Activated Receptor-α Causes Insulin Resistance in Heart and Liver
Authors: Park So-Young , Cho You-Ree , Finck Brian N. , Kim Hyo-Jeong , Higashimori Takamasa , Hong Eun-Gyoung , Lee Mi-Kyung , Danton Cheryl , Deshmukh Swati , Cline Gary W. , Wu Julie J. , Bennett Anton M. , Rothermel Beverly , Kalinowski April , Russell Kerry S. , Kim Young-Bum , Kelly Daniel P. , Kim Jason K.
Published: March 2007

Diabetic heart failure may be causally associated with alterations in cardiac energy metabolism and insulin resistance. Mice with heart-specific overexpression of peroxisome proliferator–activated receptor (PPAR)α showed a metabolic and cardiomyopathic phenotype similar to the diabetic heart, and we determined tissue-specific glucose metabolism and insulin action in vivo during hyperinsulinemic-euglycemic clamps in awake myosin heavy chain (MHC)-PPARα mice (12–14 weeks of age). Basal and insulin-stimulated glucose uptake in heart was significantly reduced in the MHC-PPARα mice, and cardiac insulin resistance was mostly attributed to defects in insulin-stimulated activities of insulin receptor substrate (IRS)-1–associated phosphatidylinositol (PI) 3-kinase, Akt, and tyrosine phosphorylation of signal transducer and activator of transcription 3 (STAT3). Interestingly, MHC-PPARα mice developed hepatic insulin resistance associated with defects in insulin-mediated IRS-2–associated PI 3-kinase activity, increased hepatic triglyceride, and circulating interleukin-6 levels. To determine the underlying mechanism, insulin clamps were conducted in 8-week-old MHC-PPARα mice. Insulin-stimulated cardiac glucose uptake was similarly reduced in 8-week-old MHC-PPARα mice without changes in cardiac function and hepatic insulin action compared with the age-matched wild-type littermates. Overall, these findings indicate that increased activity of PPARα, as occurs in the diabetic heart, leads to cardiac insulin resistance associated with defects in insulin signaling and STAT3 activity, subsequently leading to reduced cardiac function. Additionally, age-associated hepatic insulin resistance develops in MHC-PPARα mice that may be due to altered cardiac metabolism, functions, and/or inflammatory cytokines.
Very Slow Turnover of β-Cells in Aged Adult Mice
Authors: Teta Monica , Long Simon Y. , Wartschow Lynn M. , Rankin Matthew M. , Kushner Jake A.
Published: March 2007

Although many signaling pathways have been shown to promote β-cell growth, surprisingly little is known about the normal life cycle of preexisting β-cells or the signaling pathways required for β-cell survival. Adult β-cells have been speculated to have a finite life span, with ongoing adult β-cell replication throughout life to replace lost cells. However, little solid evidence supports this idea. To more accurately measure adult β-cell turnover, we performed continuous long-term labeling of proliferating cells with the DNA precursor analog 5-bromo-2-deoxyuridine (BrdU) in 1-year-old mice. We show that β-cells of aged adult mice have extremely low rates of replication, with minimal evidence of turnover. Although some pancreatic components acquired BrdU label in a linear fashion, only 1 in ∼1,400 adult β-cells were found to undergo replication per day. We conclude that adult β-cells are very long lived.
Characterization of Susceptibility of Inbred Mouse Strains to Diabetic Nephropathy
Authors: Qi Zhonghua , Fujita Hiroki , Jin Jianping , Davis Linda S. , Wang Yihan , Fogo Agnes B. , Breyer Matthew D.
Published: March 2007

Differential susceptibility to diabetic nephropathy has been observed in humans, but it has not been well defined in inbred strains of mice. The present studies characterized the severity of diabetic nephropathy in six inbred mouse strains including C57BL/6J, DBA/2J, FVB/NJ, MRL/MpJ, A/J, and KK/HlJ mice. Diabetes mellitus was induced using low-dose streptozotocin injection. Progression of renal injury was evaluated by serial measurements of urinary albumin excretion, glomerular filtration rate (GFR), and terminal assessment of renal morphology over 25 weeks. Despite comparable levels of hyperglycemia, urinary albumin excretion and renal histopathological changes were dramatically different among strains. DBA/2J and KK/HlJ mice developed significantly more albuminuria than C57BL/6J, MRL/MpJ, and A/J mice. Severe glomerular mesangial expansion, nodular glomerulosclerosis, and arteriolar hyalinosis were observed in diabetic DBA/2J and KK/HlJ mice. Glomerular hyperfiltration was observed in all diabetic strains studied except A/J. The significant decline in GFR was not evident over the 25-week period of study, but diabetic DBA/2J mice exhibited a tendency for GFR to decline. Taken together, these results indicate that differential susceptibility to diabetic nephropathy exists in inbred mice. DBA/2J and KK/HlJ mice are more prone to diabetic nephropathy, whereas the most widely used C57BL/6J mice are relatively resistant to development of diabetic nephropathy.
Co-occurrence of Two Partially Inactivating Polymorphisms of MC3R Is Associated With Pediatric-Onset Obesity
Authors: Feng Ningping , Young Sharla F. , Aguilera Greti , Puricelli Elena , Adler-Wailes Diane C. , Sebring Nancy G. , Yanovski Jack A.
Published: March 2007

Both human linkage studies and MC3R knockout mouse models suggest that the MC3R may play an important role in energy homeostasis. Here we show that among 355 overweight and nonoverweight children, 8.2% were double homozygous for a pair of missense MC3R sequence variants (Thr6Lys and Val81Ile). Such children were significantly heavier (BMI and BMI SD score: P < 0.0001), had more body fat (body fat mass and percentage fat mass: P < 0.001), and had greater plasma leptin (P < 0.0001) and insulin concentrations (P < 0.001) and greater insulin resistance (P < 0.008) than wild-type or heterozygous children. Both sequence variants were more common in African-American than Caucasian children. In vitro expression studies found the double mutant MC3R was partially inactive, with significantly fewer receptor binding sites, decreased signal transduction, and less protein expression. We conclude that diminished MC3R expression in this double MC3R variant may be a predisposing factor for excessive body weight gain in children.
Adiponectin Is Lower Among African Americans and Is Independently Related to Insulin Sensitivity in Children and Adolescents
Authors: Bush Nikki C. , Darnell Betty E. , Oster Robert A. , Goran Michael I. , Gower Barbara A.
Published: March 2007

Adiponectin is inversely related to adiposity and positively correlated with insulin sensitivity (Si). Sparse data exist on the contributions of ethnicity and body fat distribution to variance in serum adiponectin. Hypotheses tested were that adiponectin would be lower in African Americans compared with Caucasians; that adiponectin would be inversely related to central, not peripheral, fat; that adiponectin would be positively associated with Si; and that baseline adiponectin would predict change in Si over 2 years in 150 African-American and Caucasian youth. Multiple linear regression modeling showed that adiponectin was lower in African-American versus Caucasian children (adjusted means 10.8 ± 0.5 vs. 12.3 ± 0.5 μg/ml, respectively; P < 0.05); inversely related to trunk fat (P < 0.05); and positively related to limb fat (P < 0.01). Addition of the acute insulin response to glucose to the model eliminated the significance of ethnicity. Si, which was positively related to adiponectin (P < 0.05), was lower in African Americans (P < 0.001) and girls (P < 0.05). Baseline adiponectin did not predict change in Si over 2 years. In conclusion, adiponectin was positively correlated with Si, inversely related to central fat, and positively related to peripheral fat. In addition, higher acute insulin response to glucose explained lower adiponectin among African-American children.
Mechanisms of β-Cell Death in Type 2 Diabetes
Authors: Donath Marc Y. , Ehses Jan A. , Maedler Kathrin , Schumann Desiree M. , Ellingsgaard Helga , Eppler Elisabeth , Reinecke Manfred
Published: March 2007

A decrease in the number of functional insulin-producing β-cells contributes to the pathophysiology of type 2 diabetes. Opinions diverge regarding the relative contribution of a decrease in β-cell mass versus an intrinsic defect in the secretory machinery. Here we review the evidence that glucose, dyslipidemia, cytokines, leptin, autoimmunity, and some sulfonylureas may contribute to the maladaptation of β-cells. With respect to these causal factors, we focus on Fas, the ATP-sensitive K+ channel, insulin receptor substrate 2, oxidative stress, nuclear factor-κB, endoplasmic reticulum stress, and mitochondrial dysfunction as their respective mechanisms of action. Interestingly, most of these factors are involved in inflammatory processes in addition to playing a role in both the regulation of β-cell secretory function and cell turnover. Thus, the mechanisms regulating β-cell proliferation, apoptosis, and function are inseparable processes.
Environmental Triggers and Determinants of Type 1 Diabetes
Authors: Knip Mikael , Veijola Riitta , Virtanen Suvi M. , Hyöty Heikki , Vaarala Outi , Åkerblom Hans K.
Published: March 2007

Type 1 diabetes is perceived as a chronic immune-mediated disease with a subclinical prodromal period characterized by selective loss of insulin-producing β-cells in the pancreatic islets in genetically susceptible subjects. A series of evidence supports a critical role of exogenous factors in the development of type 1 diabetes, such as 1) the fact that <10% of individuals with HLA-conferred diabetes susceptibility do progress to clinical disease, 2) a pairwise concordance of type 1 diabetes of <40% among monozygotic twins, 3) a more than 10-fold difference in the disease incidence among Caucasians living in Europe, 4) a several-fold increase in the incidence over the last 50 years, and 5) migration studies indicating that the disease incidence has increased in population groups who have moved from a low-incidence to a high-incidence region. This article discusses the trigger-booster hypothesis claiming that the diabetic disease process is triggered by an exogenous factor with definite seasonal variation and driven by one or several other environmental determinants. In addition, there are a series of modifying factors affecting the fate and pace of the process. Accordingly, progression to clinical type 1 diabetes typically requires the unfortunate combination of genetic disease susceptibility, a diabetogenic trigger, and a high exposure to a driving antigen.
Natural History of Type 1 Diabetes
Authors: Achenbach Peter , Bonifacio Ezio , Koczwara Kerstin , Ziegler Anette-G.
Published: March 2007

The natural history of autoimmune type 1 diabetes in children is associated with the appearance of islet autoantibodies early in life, which is influenced by genetic and environmental factors. Once islet autoantibodies have developed, the progression to diabetes in antibody-positive individuals is determined by the age of antibody appearance and by the magnitude of the autoimmunity, in turn related to the age of the subject. Characteristics that describe the magnitude of the autoimmunity can stage progression to type 1 diabetes in islet autoantibody–positive subjects regardless of genetic background or age.
Natural History of β-Cell Function in Type 1 Diabetes
Authors: Sherry Nicole A. , Tsai Emily B. , Herold Kevan C.
Published: March 2007

Despite extensive and ongoing investigations of the immune mechanisms of autoimmune diabetes in humans and animal models, there is much less information about the natural history of insulin secretion before and after the clinical presentation of type 1 diabetes and the factors that may affect its course. Studies of insulin production previously published and from the Diabetes Prevention Trial (DPT)-1 suggest that there is progressive impairment in insulin secretory responses but the reserve in response to physiological stimuli may be significant at the time of diagnosis, although maximal responses are more significantly impaired. Other factors, including insulin resistance, may play a role in the timing of clinical presentation along this continuum. The factors that predict the occurrence and rapidity of decline in β-cell function are still largely unknown, but most studies have identified islet cell autoantibodies as predictors of future decline and age as a determinant of residual insulin production at diagnosis. Historical as well as recent clinical experience has emphasized the importance of residual insulin production for glycemic control and prevention of end-organ complications. Understanding the modifiers and predictors of β-cell function would allow targeting immunological approaches to those individuals most likely to benefit from therapy.