Diabetes News

Objective:

Two type 1 diabetes (T1D) susceptibility genes have been identified in the spontaneously diabetic BBDP rat, the MHC (RT1) Class II u haplotype (Iddm1), and Gimap5 (Iddm2). The strong effects of these have impeded previous efforts to map additional loci. We tested the hypothesis that T1D is a polygenic disease in the BBDP rat.

Research Design and Methods:

We performed the most comprehensive genome-wide linkage analysis for T1D, age of disease onset (AOO), and insulitis sub-phenotypes in 574 F2 animals from a cross-intercross between BBDP and T1D-resistant, double congenic ACI.BBDP-RT1u,GIMAP5 (ACI.BB^1u.lyp) rats, where both Iddm1 and Iddm2 were fixed as BBDP.

Results:

Nineteen percent of these F2 animals developed T1D, and eight T1D susceptibility loci were mapped, six showing significant linkage (chromosomes 1, 3, 6(two loci), 12, and 14) and two (chromosomes 2 and 17), suggestive linkage. The chromosomes 6, 12, and 14 intervals were also linked to the severity of islet infiltration by immunocytes, while those on chromosomes 1, 6(two loci), 14, 17, and a T1D-unlinked chromosome 8 interval showed significant linkage to the degree of islet atrophy. Four loci exhibited suggestive linkage to AOO on chromosomes 2(two loci), 7 and 18 but were unlinked to T1D. INS, PTPN22, IL2/IL21, C1QTNF6 and C12orf30 associated with human T1D, are contained within the chromosomes 1, 2, 7 and 12 loci.

Conclusions:

This study demonstrates that the BBDP diabetic syndrome is a complex, polygenic disease that may share additional susceptibility genes beside MHC Class II, with human T1D.

Objective.

The amount of visceral adipose tissue is a risk factor for the metabolic syndrome. It is unclear how body mass index (BMI) changes during childhood and adolescence predict adult fat distribution. We hypothesized that there are critical periods during development for the prediction of adult subcutaneous and visceral fat mass by BMI changes during childhood and adolescence.

Research Design and Methods.

Detailed growth charts were retrieved for the men participating in the population-based Gothenburg Osteoporosis and Obesity Determinants (GOOD) study (n=612). Body composition was analysed using Dual X-Ray Absorptiometry and adipose tissue areas using abdominal computed tomography at 18-20 years of age.

Results.

The main finding in the present study was that subjects with increases in BMI Z-score of >1 SD during adolescence had, independent of prepubertal BMI, both larger subcutaneous (+138%; p<0.001) and visceral adipose tissue areas (+91%; p< 0.001) than subjects with unchanged BMI Z-score. In contrast, subjects with increases in BMI Z-score of >1 SD during late childhood had larger amount adult subcutaneous adipose tissue (+83%; p< 0.001) than subjects with unchanged BMI Z-score, but unaffected amount of visceral adipose tissue. BMI changes during adolescence predict both visceral and subcutaneous adipose tissue of the abdomen while BMI changes during late childhood predict only the subcutaneous adipose tissue.

Conclusions.

The amount of visceral adipose tissue in young adult men was associated with BMI changes specifically during adolescence, while the amount of subcutaneous adipose tissue was associated with BMI changes during both late childhood and adolescence.

Objective:

Hepatocyte nuclear factor 1β (HNF1B) is a transcription factor that is critical for pancreatic cell formation and glucose homeostasis. Previous studies have reported that common variants of HNF1B were associated with type 2 diabetes in Caucasians and West Africans. However analysis in the subjects from the Botnia study and Malmö Preventive Project produced a conflicting result and the role for HNF1B in type 2 diabetes susceptibility has remained unclear. We therefore investigated common variants across the HNF1B gene in a Chinese population.

Research Design and Methods:

Fifteen tagging SNPs were analyzed for association with type 2 diabetes in subjects with type 2 diabetes (n = 1,859) and normal glucose regulation (n = 1,785).

Results:

Consistent with the initial study, we observed evidence that the risk G allele of rs4430796 in intron 2 was significantly associated with type 2 diabetes (odds ratio [OR] 1.16 [95 CI% 1.05 – 1.29], P = 0.0035, empirical P = 0.0475). Furthermore, the at-risk G allele was associated with earlier age at diagnosis in the type 2 diabetic subjects (P = 0.0228).

Conclusions:

The result of this study provides evidence that variants in the HNF1B region contribute to susceptibility to type 2 diabetes in the Chinese population.

Objective:

Polymorphisms in the human TCF7L2 gene are associated with reduced insulin secretion and an increased risk of type 2 diabetes. However, the mechanisms by which TCF7L2 affects insulin secretion are still unclear. Here we define the effects of TCF7L2 expression level on mature β-cell function and suggest a potential mechanism for its actions.

Research Design and Methods:

TCF7L2 expression in rodent islets and β-cell lines was altered using RNAi or adenoviral transduction. β-cell gene profiles were measured by quantitative real-time PCR and the effects on intracellular signalling and exocytosis by live cell imaging, electron microscopy and patch clamp electrophysiology.

Results:

Reducing TCF7L2 expression levels by RNAi decreased glucose-, but not KCl-induced, insulin secretion. The glucose-induced increments in both ATP/ADP ratio and cytosolic free Ca²⁺ concentration ([Ca²⁺]_i) were increased compared to controls. Over-expression of TCF7L2 exerted minor inhibitory effects on glucose-regulated changes in [Ca²⁺]_i and insulin release. Gene expression profiling in TCF7L2-silenced cells revealed increased levels of mRNA encoding syntaxin 1A, but decreased Munc18-1 and ZnT8 mRNA. Whereas the number of morphologically-docked vesicles was unchanged by TCF7L2 suppression, secretory granule movement increased and capacitance changes decreased, indicative of defective vesicle fusion.

Conclusion:

TCF7L2 is involved in maintaining expression of β-cell genes regulating secretory granule fusion. Defective insulin exocytosis may thus underlie increased diabetes incidence in carriers of the at risk TCF7L2 allelles.

Objective.

Obesity is associated with insulin resistance and type 2 diabetes, although the mechanisms linking these pathologies remain undetermined. Recent studies in rodent models revealed endoplasmic reticulum (ER) stress in adipose and liver tissues and demonstrated that ER stress could cause insulin resistance. Therefore, we tested whether these stress pathways were also present in obese human subjects and/or regulated by weight loss.

Research Design and Methods.

Eleven obese men and women (BMI: 51.3 ± 3.0 kg/m²) were studied before and 1 year after gastric bypass (GBP) surgery. We examined systemic insulin sensitivity using hyperinsulinemic-euglycemic clamp studies before and after surgery and collected subcutaneous adipose and liver tissues to examine ER stress markers.

Results.

Subjects lost 39±9% body weight at 1 year after GBP surgery (p<0.001), which was associated with a marked improvement in hepatic, skeletal muscle and adipose tissue insulin sensitivity. Markers of ER stress in adipose tissue significantly decreased with weight loss. Specifically, Grp78 and spliced XBP-1 mRNA levels were reduced, as were phosphorylated eIF2 and stress kinase JNK1 (all p values <0.05). Liver sections from a subset of subjects showed intense staining for Grp78 and phosphorylated eIF2 before surgery, which was reduced in post-GBP sections.

Conclusions.

This study presents important evidence that ER stress pathways are present in selected tissues of obese humans, and that these signals are regulated by marked weight loss and metabolic improvement. Hence, this suggests the possibility of a relationship between obesity-related ER stress and metabolic dysfunction in obese humans.

Objective.

This study is aimed to verify whether the decreased VEGF/PEDF ratio can serve as an indicator for the protective effect of angiotensin-converting enzyme inhibitors (ACEI) on diabetic retinopathy (DR), and to investigate the role of mitochondrial reactive oxygen species (ROS) in the down-regulated VEGF/PEDF ratio.

Research Design and Methods.

Diabetic rats and control animals were randomly assigned to receive perindopril or vehicle for 24 weeks, and bovine retinal capillary endothelial cells (BRECs) were incubated with normal or high glucose with or without perindopril. VEGF, PEDF, PPAR, and UCP-2 in the rat retinas or BRECs extracts were examined by Western blotting and real-time RT-PCR. The levels of VEGF and PEDF in cell culture media were examined by ELISA. Mitochondrial membrane potential (m) and ROS production were assayed using JC-1 or CM-H2DCFDA.

Results.

The VEGF/PEDF ratio was increased in the retina of diabetic rats; perindopril lowered the increased VEGF/PEDF ratio in diabetic rats and ameliorated the retinal damages. In BRECs, perindopril lowered the hyperglycemia-induced elevation of VEGF/PEDF ratio by reducing mitochondrial ROS. Besides, we found the decreased ROS production was a result of perindopril-induced up-regulation of PPAR and UCP-2 expression and the subsequent decrease of m.

Conclusions.

It is concluded that the protective effect of ACEI on DR is associated with a decreased VEGF/PEDF ratio, which involves the mitochondria-ROS pathway through PPAR-mediated changes of UCP-2. This study paves a way for future application of ACEI in treatment of DR.

Objective.

Embryos exposed to a diabetic environment in utero have an increased risk to develop congenital heart malformations. The mechanism behind the teratogenicity of diabetes still remains enigmatic. Detrimental effects of glycation products in diabetic patients have been well documented. We therefore studied a possible link between glycation products and the development of congenital cardiovascular malformations. Furthermore we investigated other possible mechanisms involved in this pathogenesis: alterations in the levels of vascular endothelial growth factor (VEGF) or phosphorylated Smad2, the latter can be induced by both glycation products and VEGF.

Research Design and Methods.

We examined the temporal spatial patterning of the glycation products N(carboxymethyl)lysine (CML) and Methylglyoxal (MG)-adducts, VEGF-expression, and phosphorylated Smad2 during cardiovascular development in embryos from normal and diabetic rats.

Results.

Maternal diabetes increased the CML accumulation in the areas susceptible to diabetes induced congenital heart disease (CHD), including the outflow tract of the heart and the aortic arch. No MG-adducts could be detected, suggesting that CML is more likely to be indicative for increased oxidative stress than for glycation. An increase of CML in the outflow tract of the heart was accompanied by an increase in phosphorylated Smad2, unrelated to VEGF. VEGF showed a time specific decrease in the outflow tract of embryos from diabetic dams.

Conclusions.

From our results we can conclude that maternal diabetes results in transient and localized alterations in CML, VEGF expression and Smad2 phosphorylation overlapping with those regions of the developing heart that are most sensitive to diabetes induced CHD.

Objective

The evolutionary conservation of transcriptional mechanisms has been widely exploited to understand human biology and disease. Recent findings, however, unexpectedly showed that the transcriptional regulators HNF1 and HNF4 rarely bind to the same genes in mice and humans, leading to the proposal that tissue-specific transcriptional regulation has undergone extensive divergence in the two species. Such observations have major implications for the use of mouse models to understand HNF1 and HNF4-deficient diabetes. However, the significance of studies that assess binding without considering regulatory function is poorly understood.

Research Design and Methods

We compared previously reported mouse and human HNF1 and HNF4 binding studies with independent binding experiments. We also integrated binding studies with mouse and human loss of function gene expression datasets.

Results

(i) We confirmed the existence of species-specific HNF1 and HNF4 binding, yet observed incomplete detection of binding in the different datasets, causing an underestimation of binding conservation. (ii) Only a minor fraction of HNF1 and HNF4-bound genes were downregulated in the absence of these regulators. This subset of functional targets did not show evidence for evolutionary divergence of binding or binding sequence motifs. (iii) We observed differences between conserved and species-specific binding properties. For example, conserved binding was more frequently located near transcriptional start sites, and was more likely to involve multiple binding events in the same gene.

Conclusions

Despite evolutionary changes in binding, essential direct transcriptional functions of HNF1 and HNF4 are largely conserved between mice and humans.

Objective

Patients with diabetes are at an increased risk for developing corneal complications and delayed wound healing. This study investigated the effects of high glucose (HG) on epidermal growth factor receptor (EGFR) signaling and on epithelial wound healing in the cornea.

Research Design and Methods

Effects of HG on wound healing and on EGFR signaling were investigated in cultured porcine corneas, human corneal epithelial cells (CECs), and human corneas using Western blotting and immunofluorescence. Effects of HG on reactive oxygen species (ROS) and glutathione (GSH) levels and on EGFR pathways were assessed in porcine and primary human CECs, respectively. The effects of EGFR ligands and antioxidants on HG-delayed epithelial wound healing were assessed in cultured porcine corneas.

Results

HG impaired ex vivo epithelial wound healing and disturbed cell responses and EGFR signaling to wounding. HG suppressed AKT phosphorylation in an ROS sensitive manner and decreased intracellular GSH in cultured porcine corneas. Exposure to HG for 24 hrs resulted in an increase in ROS positive cells in primary human CECs. While heparin-binding EGF-like growth factor and antioxidant N-acetylcysteine had beneficial effects on epithelial wound closure, their combination significantly accelerated HG-delayed wound healing to a level similar to that seen in controls. Finally, AKT signaling pathway was perturbed in the epithelia of human diabetic corneas, but not in the corneas of non-diabetic, age-matched donors.

Conclusions

HG, likely through ROS, impairs EGFR-phosphatidylinositol 3-kinase-AKT pathway, resulting in delayed corneal epithelial wound healing. Antioxidants in combination with EGFR ligands may be promising potential therapeutics for diabetic keratopathy.

Objective

Perturbations to the prenatal environment has been associated with the development of adult chronic disease, findings that gave rise to the “Barker Hypothesis” or the “developmental origins of adult disease” concept. In this study we used an animal model to determine the metabolic consequences of maternal prenatal stress and high fat feeding on the developing offspring.

Research Design and Methods

Pregnant female Sprague-Dawley rats were maintained on standard chow (CHOW) or 60% high fat (HF) diet throughout gestation and lactation. Half of each group were exposed to a novel variable stress paradigm (STRESS) during the third week of gestation while control dams were left undisturbed (CON). Body weight, body composition, glucose tolerance and endocrine parameters were measured in offspring through early adulthood.

Results

Male and female pups from dams that experienced prenatal stress and/or were on HF diet weighed more beginning on postnatal day 7 compared to CHOW-CON. Access to HF diet at weaning enhanced increased the body weight effect through early adulthood and was attributable to greater adiposity. Pups weaned onto CHOW diet showed no significant difference in glucose clearance or insulin secretion. However, pups weaned onto HF diet had impaired glucose tolerance if their dams were on HF diet, experienced prenatal stress, or both.

Conclusions

Our data demonstrate that prenatal stress and/or high fat diet during the intrauterine or postnatal environment affects offspring in a manner that increases their susceptibility to diet-induced obesity and leads to secondary adverse metabolic consequences.