Vascular endothelial growth factor (VEGF), a major mediator of vascular permeability and angiogenesis, may play a pivotal role in mediating the development and progression of diabetic retinopathy. In the present study, we examined the genetic variations of the VEGF gene to assess its possible relation to diabetic retinopathy in type 2 diabetic patients. Among seven common polymorphisms in the promoter region, 5-untranslated region (UTR) and 3UTR of the VEGF gene, genotype distribution of the C(؊634)G polymorphism differed significantly (P ‫؍‬ 0.011) between patients with (n ‫؍‬ 150) and without (n ‫؍‬ 118) retinopathy, and the C allele was significantly increased in patients with retinopathy compared with those without retinopathy (P ‫؍‬ 0.0037). The odds ratio (OR) for the CC genotype of C(؊634)G to the GG genotype was 3.20 (95% CI 1.45-7.05, P ‫؍‬ 0.0046). The ؊634C allele was significantly increased in patients with nonproliferative diabetic retinopathy (non-PDR) (P ‫؍‬ 0.0026) and was insignificantly increased in patients with proliferative diabetic retinopathy (PDR) (P ‫؍‬ 0.081) compared with patients without retinopathy, although frequencies of the allele did not differ significantly between the non-PDR and PDR groups. Logistic regression analysis revealed that the C(؊634)G polymorphism was strongly associated with an increased risk of retinopathy (P ‫؍‬ 0.0018). Furthermore, VEGF serum levels were significantly higher in healthy subjects with the CC genotype of the C(؊634)G polymorphism than in those with the other genotypes. These data suggest that the C(؊634)G polymorphism in the 5UTR of the VEGF gene is a novel genetic risk factor for diabetic retinopathy.

Glucose-stimulated insulin secretion, glucose transport, glucose phosphorylation and glucose utilization have been characterized in the insulinoma cell line MIN6, which is derived from a transgenic mouse expressing the large T-antigen of SV40 in pancreatic beta cells. Glucose-stimulated insulin secretion occurred progressively from 5 mmol/l glucose, reached the maximal level approximately seven-fold above the basal level at 25 mmol/l, and remained at this level up to 50 mmol/l. Glucose transport was very rapid with the half-maximal uptake of 3-O-methyl-D-glucose being reached within 15 s at 22 degrees C. Glucose phosphorylating activity in the cell homogenate was due mainly to glucokinase; the Vmax value of glucokinase activity was estimated to be 255 +/- 37 nmol.h-1.mg protein-1, constituting approximately 80% of total phosphorylating activity, whereas hexokinase activity constituted less than 20%. MIN6 cells exhibited mainly the high Km component of glucose utilization with a Vmax of 289 +/- 18 nmol.h-1.mg protein-1. Thus, glucose utilization quantitatively and qualitatively reflected glucose phosphorylation in MIN6 cells. In contrast, MIN7 cells, which exhibited only a small increase in insulin secretion in response to glucose, had 4.7-fold greater hexokinase activity than MIN6 cells with a comparable activity of glucokinase. These characteristics of MIN6 cells are very similar to those of isolated islets, indicating that this cell line is an appropriate model for studying the mechanism of glucose-stimulated insulin secretion in pancreatic beta cells.

The hallmark of type 2 diabetes, the most common metabolic disorder, is a defect in insulin-stimulated glucose transport in peripheral tissues. Although a role for phosphoinositide-3-kinase (PI3K) activity in insulin-stimulated glucose transport and glucose transporter isoform 4 (Glut4) translocation has been suggested in vitro, its role in vivo and the molecular link between activation of PI3K and translocation has not yet been elucidated. To determine the role of PI3K in glucose homeostasis, we generated mice with a targeted disruption of the gene encoding the p85alpha regulatory subunit of PI3K (Pik3r1; refs 3-5). Pik3r1-/- mice showed increased insulin sensitivity and hypoglycaemia due to increased glucose transport in skeletal muscle and adipocytes. Insulin-stimulated PI3K activity associated with insulin receptor substrates (IRSs) was mediated via full-length p85 alpha in wild-type mice, but via the p50 alpha alternative splicing isoform of the same gene in Pik3r1-/- mice. This isoform switch was associated with an increase in insulin-induced generation of phosphatidylinositol(3,4,5)triphosphate (PtdIns(3,4,5)P3) in Pik3r1-/- adipocytes and facilitation of Glut4 translocation from the low-density microsome (LDM) fraction to the plasma membrane (PM). This mechanism seems to be responsible for the phenotype of Pik3r1-/- mice, namely increased glucose transport and hypoglycaemia. Our work provides the first direct evidence that PI3K and its regulatory subunit have a role in glucose homeostasis in vivo.

No abstract

Compared with pioglitazone, ipragliflozin exerts equally beneficial effects on NAFLD and glycemic control during the treatment of patients with type 2 diabetes complicated by NAFLD. Furthermore, ipragliflozin significantly reduced body weight and abdominal fat area.

Coordinated control of energy metabolism and glucose homeostasis requires communication between organs and tissues. We identified a neuronal pathway that participates in the cross talk between the liver and adipose tissue. By studying a mouse model, we showed that adenovirus-mediated expression of peroxisome proliferator-activated receptor (PPAR)-g2 in the liver induces acute hepatic steatosis while markedly decreasing peripheral adiposity. These changes were accompanied by increased energy expenditure and improved systemic insulin sensitivity. Hepatic vagotomy and selective afferent blockage of the hepatic vagus revealed that the effects on peripheral tissues involve the afferent vagal nerve. Furthermore, an antidiabetic thiazolidinedione, a PPARg agonist, enhanced this pathway. This neuronal pathway from the liver may function to protect against metabolic perturbation induced by excessive energy storage.

Resistin is a hormone secreted by adipocytes that acts on skeletal muscle myocytes, hepatocytes, and adipocytes themselves, reducing their sensitivity to insulin. In the present study, we investigated how the expression of resistin is affected by glucose and by mediators known to affect insulin sensitivity, including insulin, dexamethasone, tumor necrosis factor-␣ (TNF-␣), epinephrine, and somatropin. We found that resistin expression in 3T3-L1 adipocytes was significantly upregulated by high glucose concentrations and was suppressed by insulin. Dexamethasone increased expression of both resistin mRNA and protein 2.5-to 3.5-fold in 3T3-L1 adipocytes and by ϳ70% in white adipose tissue from mice. In contrast, treatment with troglitazone, a thiazolidinedione antihyperglycemic agent, or TNF-␣ suppressed resistin expression by ϳ80%. Epinephrine and somatropin were both moderately inhibitory, reducing expression of both the transcript and the protein by 30 -50% in 3T3-L1 adipocytes. Taken together, these data make it clear that resistin expression is regulated by a variety of hormones and that cytokines are related to glucose metabolism. Furthermore, they suggest that these factors affect insulin sensitivity and fat tissue mass in part by altering the expression and eventual secretion of resistin from adipose cells.

Phosphatidylinositol 3-kinase (PI 3-kinase) is stimulated by association with a variety of tyrosine kinase receptors and intracellular tyrosine-phosphorylated substrates. We isolated a cDNA that encodes a 50-kDa regulatory subunit of PI 3-kinase with an expression cloning method using 32 P-labeled insulin receptor substrate-1 (IRS-1). This 50-kDa protein contains two SH2 domains and an inter-SH2 domain of p85␣, but the SH3 and bcr homology domains of p85␣ were replaced by a unique 6-amino acid sequence. Thus, this protein appears to be generated by alternative splicing of the p85␣ gene product. We suggest that this protein be called p50␣. Northern blotting using a specific DNA probe corresponding to p50␣ revealed 6.0-and 2.8-kb bands in hepatic, brain, and renal tissues. The expression of p50␣ protein and its associated PI 3-kinase were detected in lysates prepared from the liver, brain, and muscle using a specific antibody against p50␣. Taken together, these observations indicate that the p85␣ gene actually generates three protein products of 85, 55, and 50 kDa. The distributions of the three proteins (p85␣, p55␣, and p50␣), in various rat tissues and also in various brain compartments, were found to be different. Interestingly, p50␣ forms a heterodimer with p110 that can as well as cannot be labeled with wortmannin, whereas p85␣ and p55␣ associate only with p110 that can be wortmanninlabeled. Furthermore, p50␣ exhibits a markedly higher capacity for activation of associated PI 3-kinase via insulin stimulation and has a higher affinity for tyrosinephosphorylated IRS-1 than the other isoforms. Considering the high level of p50␣ expression in the liver and its marked responsiveness to insulin, p50␣ appears to play an important role in the activation of hepatic PI 3-kinase. Each of the three ␣ isoforms has a different function and may have specific roles in various tissues.A variety of growth factors and hormones mediate their cellular effects via interactions with cell surface receptors that possess protein kinase activity (1, 2). The interaction of most of these ligands with their receptors induces tyrosine kinase activation and autophosphorylation of the receptor, resulting in physical association of these receptors with several cytoplasmic substrates having SH2 domains. Phosphatidylinositol 3-kinase (PI 3-kinase) 1 has been identified through its ability to associate with cellular protein kinases, including numerous growth factor receptors and oncogene products (3, 4). This lipid kinase phosphorylates phosphatidylinositol at the D-3 position of the inositol ring in response to stimulation with a variety of growth factors and hormones (5). Although the role of this lipid product in cellular regulation remains unclear, recent reports suggest that the activation of PI 3-kinase leads to the activation of c-Akt, Rac, PKC-␥ isoform, and p70 S6 kinase (6 -9). As a result, PI 3-kinase has been suggested to play essential roles in the regulation of various cellular activities, including proliferation (10, 11), differen...