Vascular disease is a major cause of morbidity and mortality in patients with Type 1 diabetes. Hyperglycemia causes endothelial dysfunction, a pathological state consisting of reduced nitric oxide (NO) bioavailability, increased cellular superoxide production and activation of an inflammatory cascade with increased expression of adhesion molecules at the endothelial cell surface, that leads to the initiation and progression of vascular disease in diabetes. In preliminary studies, we have found that adiponectin, an abundant circulating plasma protein, suppresses high glucose-induced endothelial superoxide generation and enhances NO production in vascular endothelial cells. We and others have also found that adiponectin activates AMP kinase in various cell types including endothelial cells. In this project, we will characterize the signaling mechanism(s) used by adiponectin to improve endothelial function under high glucose conditions. By studying endothelial cells in culture in vitro and mesenteric microvascular endothelial cells in situ by intravital microscopy, we will test the hypotheses that the globular domain of adiponectin (gAd) expressed in a bacterial system and the full-length adiponectin protein (fAd) expressed in a recombinant eukaryotic system: (1) suppress superoxide production by endothelial cells treated with high glucose, possibly via an NAD(P)H oxidase-linked pathway regulated by protein kinase C; (2) enhance NO production by endothelial cells treated with high glucose, possibly via an AMP kinase-linked pathway; and (3) ameliorate endothelial dysfunction in vivo in rodent models of hyperglycemia as evidenced by salutary effects on leukocyte-endothelial interactions, expression of cell adhesion molecules and NO production. The in vivo studies will also be facilitated by using adiponectin knock-out mice, available to us by a research collaboration, which should demonstrate augmented vascular effects of adiponectin when the various forms are administered on a background of no endogenous circulating adiponectin. This powerful combination of in vitro and in vivo techniques will provide insight into adiponectin signal transduction in endothelial cells and may lead to new targets to reduce the heightened vascular risk associated with type 1 diabetes.
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