UNDERSTANDING THE ROLE OF ADIPONECTIN PROCESSING IN AMELIORATING INSULIN RESISTANCE AND RELATED COMPLICATIONS

Abstract

BACKGROUND: The rising prevalence of obesity is recognized as one of the most important risk factors for the development of diabetes and associated cardiovascular complications. The precise mechanisms that link obesity to diabetes and increased atherosclerotic vascular diseases are not yet fully understood. Insulin resistance, a decreased sensitivity to the actions of insulin, results in impaired glucose metabolism and contributes to the cardiovascular complications associated with diabetes. Secretion of adiponectin, an antiatherogenic and anti-diabetic adipokine is decreased in obesity, as fat accumulates and adipocytes enlarge. Even though a link between adipose dysfunction, insulin resistance and diabetes has been identified, the direct physiological effects of adiponectin processing on obesity induced diabetes have yet to be investigated. Recently, it was hypothesized that full-length adiponectin (fAcrp) is inactive and that globular adiponectin (gAcrp) is the functional adipokine. Our group has identified thrombin and not trypsin or leukocyte elastase as generally believed, as the protease responsible for generating gAcrp. Preliminary studies showed that the gAcrp and not fAcrp inhibited the proliferation of primary smooth muscle cells in vitro in response to PDGF. Hence we hypothesize that the generation of gAcrp from fAcrp is essential for eliciting the beneficial actions of adiponectin in reversing insulin resistance. Our aim is to compare the effects of different forms of adiponectin namely fAcrp, gAcrp and prAcrp (protease resistant mutant of fAcrp that cannot be cleaved into gAcrp) on insulin resistance. METHODS AND RESULTS: In in vivo studies, we will use a dietinduced obese adiponectin knockout mouse model and compare the ability of different adiponectin forms to rescue the metabolic phenotype of these mice. In in vitro studies, human umbilical vein endothelial cells (HUVEC) and hepatoma cells (HepG2) will be serum starved prior to treatment with different forms of adiponectin and activation of downstream molecular signatories such as AMPKa, MAPK p44/42, p38 MAPK, ACC and Akt will be measured by Western blotting. The purified recombinant fAcrp and prAcrp proteins were tested for sensitivity to thrombin in an in vitro cleavage assay. Recombinant fAcrp was digested in a dose dependent manner. CONCLUSION: Treatment of fAcrp but not prAcrp with thrombin resulted in the formation of gAcrp. The expression level of adiponectin receptor1, receptor2 and T-cadherin was similar in different primary human endothelial cells and hepatoma cells. Serum starvation of HUVECs for 6hours in 0% FBS and 16hours in 0.5% FBS was optimum for MAPK p44/42 and AMPK regulation by adiponectin. 428 MAXIMAL CCA IMT AND CARDIOVASCULAR OUTCOMES