Cardiovascular disease accounts for an overwhelming proportion of the morbidity and mortality suffered by patients with diabetes mellitus. Insulin resistance in obesity and type 2 diabetes, characterized by excess circulating non-esterified fatty acids (NEFA) and cytokines such as TNFalpha, and the hyperglycemia of overt diabetes are associated with endothelial dysfunction that contributes to the atherosclerotic process. Adiponectin is an abundant plasma protein secreted from adipose tissue that exhibits potent anti-inflammatory effects in the vasculature as well as insulin-sensitizing properties in metabolically-active tissues. In extensive preliminary studies, we have made the novel observations that the recombinant globular domain of adiponectin (gAd) exhibits a number of salutary effects in cultured endothelial cells, including enhanced nitric oxide (NO) production associated with activation of AMP kinase, and reduced superoxide generation induced by oxidized LDL (oxLDL) which is associated with cellular NAD(P)H oxidase activity. In addition, gAd inhibits superoxide production in endothelial cells exposed to high glucose, blocks the oxidation of native LDL by endothelial cells, and suppresses cell proliferation and MAP kinase activation stimulated by oxLDL. By quantitative intravital microscopy in the db/db mouse, we have also found in our initial studies that overexpression of gAd by adenoviral gene delivery in vivo ameliorates the increased leukocyte/endothelial interactions characteristic of the endothelial dysfunction in this model of insulin resistant type 2 diabetes. We propose here to combine studies of endothelial cells in vitro with intravital microscopy in situ to examine the cellular responses and signaling mechanisms of the two major forms of adiponectin (full-length and gAd) and test the hypotheses that adiponectin: (1) enhances NO production in states of endothelial dysfunction via an AMP kinase-linked pathway; (2) suppresses superoxide production by endothelial cells treated with oxLDL or high glucose, possibly via an NAD(P)H oxidase-linked pathway; and (3) ameliorates endothelial dysfunction in vivo in rodent models of obesity with insulin resistance and/or diabetes as evidenced by salutary effects on leukocyte/endothelial interactions, expression of cell adhesion molecules and NO production. These studies will provide insight into the cellular mechanisms employed by adiponectin to ameliorate endothelial dysfunction in states of insulin resistance and type 2 diabetes, and may lead to improved strategies to reduce the excessive cardiovascular risk associated with these disorders.
