Increased expression of adenylyl cyclase 3 in pancreatic islets and central nervous system of diabetic Goto-Kakizaki rats: a possible regulatory role in glucose homeostasis.

Adenylyl cyclase 3 (AC3) is expressed in pancreatic islets of the Goto-Kakizaki (GK) rat, a spontaneous animal model of type 2 diabetes (T2D), and also exerts genetic effects on the regulation of body weight in man. In addition to pancreatic islets, the central nervous system (CNS) plays an important role in the pathogenesis of T2D and obesity by regulating feeding behavior, body weight and glucose metabolism. In the present study, we have investigated AC3 expression in pancreatic islets, striatum and hypothalamus of GK rats to evaluate its role in the regulation of glucose homeostasis. GK and Wistar rats at the age of 2.5 mo were used. A group of GK rats were implanted with sustained insulin release chips for 15 d. Plasma glucose and serum insulin levels were measured. AC3 gene expression levels in pancreatic islets, striatum and hypothalamus were determined by using real-time RT-PCR. Results indicated that plasma glucose levels in Wistar rats were found to be similar to insulin-treated GK rats, and significantly lower compared with non-treated GK rats. AC3 expression levels in pancreatic islets, striatum and hypothalamus of GK rats were higher compared with Wistar rats, while the levels were intermediate in insulin-treated GK rats. The AC3 expression display patterns between pancreatic islets and striatum-hypothalamus were similar. The present study thus provides the first evidence that AC3 is overexpressed in the regions of striatum and hypothalamus of brain, and similarly in pancreatic islets of GK rats suggesting that AC3 plays a role in regulation of glucose homeostasis via CNS and insulin secretion.

Distribution of neuropeptide Y Leu7Pro polymorphism in patients with type 1 diabetes and diabetic nephropathy among Swedish and American populations.

OBJECTIVE: The distribution of Leu7Pro polymorphism in the neuropeptide Y gene shows a geographical north to south gradient of decreasing frequency, suggesting that it may be a population-specific causal variant. This polymorphism is found to be associated with diabetic nephropathy (DN) and coronary heart disease in Finnish women with type 1 diabetes (T1D). The present study aims to evaluate the susceptibility of this polymorphism to the development of DN in two different populations. DESIGN: One sample set consists of 174 (females 98 and males 76) Swedish T1D patients with DN and 249 (females 132 and males 117) patients without DN. Another sample set includes 597 (females 356 and males 241) American T1D patients without DN and 577 (females 264 and males 313) patients with DN, who were descents of European Caucasians and were from the Genetics of Kidneys in Diabetes (GoKinD) Study. METHODS: Genotyping of Leu7Pro polymorphism was performed by dynamic allele-specific hybridization. RESULTS: The C allele frequencies of Leu7Pro polymorphism in T1D patients between Swedish and American GoKinD populations were significantly different (6.3 vs 4.0%; P=0.006). Particularly, the C allele frequency in Swedish female T1D patients with DN was significantly higher in comparison with T1D patients without DN (10.2 vs 4.2%; P=0.011, OR=2.614, 95% confidence intervals: 1.249-5.467). No significant association of this polymorphism with DN was observed in Swedish male T1D patients and the patients from GoKinD. CONCLUSIONS: The present study provides further evidence that Leu7Pro polymorphism confers the susceptibility to the development of DN in Swedish female T1D patients.

Genetic variation in receptor protein tyrosine phosphatase sigma is associated with type 2 diabetes in Swedish Caucasians.

OBJECTIVE: Previously, it has been demonstrated that receptor protein tyrosine phosphatase sigma (RPTPsigma) is involved in glucose homeostasis and insulin signaling in several animal models. The aim of this study was to evaluate whether polymorphisms in this gene influence the development of type 2 diabetes (T2D) in humans. DESIGN: We investigated how genetic variations in the RPTPsigma gene influence susceptibility to impaired glucose tolerance (IGT) and T2D, in Swedish men and women. METHODS: Genotyping of single nucleotide polymorphisms (SNPs) was performed by dynamic allele-specific hybridization in a total of 1057 Swedish Caucasians including 497 subjects with normal glucose tolerance (NGT), 262 subjects with IGT, and 298 patients with T2D. RESULTS: SNPs rs1143699, rs4807015, and rs1978237 were found to be associated with T2D. SNP rs1143699 was associated with male T2D patients when compared with NGT controls (odds ratio; OR = 1.57; P = 0.029). SNP rs4807015 showed association with T2D patients when compared with NGT controls (OR = 1.32; P = 0.025). Finally, SNP rs1978237 was associated with T2D patients when compared with NGT controls (OR = 1.59; P = 0.002). Logistic regression analysis demonstrated that for SNP rs1143699 in men, C/C homozygosity conveys an increased risk of T2D (OR = 2.19; P = 0.035), while SNP rs4807015 was associated with an increased risk of T2D in both men and women (OR = 1.74; P = 0.029). SNP rs1978237 also demonstrated a risk of T2D in men and women (OR = 1.59; P = 0.026). CONCLUSIONS: This study provides evidence for association of SNPs in the RPTPsigma gene with T2D in Swedish Caucasians. SNPs rs1143699, rs4807015, and rs1978237 confer an increased risk of developing T2D.

Quantitative trait loci near the insulin-degrading enzyme (IDE) gene contribute to variation in plasma insulin levels.

Insulin-degrading enzyme (IDE) plays a principal role in the proteolysis of several peptides in addition to insulin and is encoded by IDE, which resides in a region of chromosome 10q that is linked to type 2 diabetes. Two recent studies presented genetic association data on IDE and type 2 diabetes (one positive and the other negative), but neither explored the fundamental question of whether polymorphism in IDE has a measurable influence on insulin levels in human populations. To address this possibility, 14 single nucleotide polymorphisms (SNPs) from a linkage disequilibrium block encompassing IDE have been genotyped in a sample of 321 impaired glucose tolerant and 403 nondiabetic control subjects. Analyses based on haplotypic genotypes (diplotypes), constructed with SNPs that differentiate common extant haplotypes extending across IDE, provided compelling evidence of association with fasting insulin levels (P = 0.0009), 2-h insulin levels (P = 0.0027), homeostasis model assessment of insulin resistance (P = 0.0001), and BMI (P = 0.0067), with effects exclusively evident in men. The strongest evidence for an effect of a single marker was obtained for rs2251101 (located near the 3' untranslated region of IDE) on 2-h insulin levels (P = 0.000023). Diplotype analyses, however, suggest the presence of multiple interacting trait-modifying sequences in the region. Results indicate that polymorphism in/near IDE contributes to a large proportion of variance in plasma insulin levels and correlated traits, but questions of sex specificity and allelic heterogeneity will need to be taken into consideration as the molecular basis of the observed phenotypic effects unfolds.