Abstract 18848: Role of Extracellular Superoxide Dismutase, Copper Transporter ATP7A and Caveolae/lipid rafts in Endothelial Dysfunction in Type I Diabetic Mice
Oxidative stress and endothelial dysfunction contributes to diabetes mellitus (DM). Extracellular superoxide dismutase (ecSOD), a secretory copper (Cu) enzyme, regulates endothelial function by modulating levels of extracellular superoxide anion (O2•-). We previously demonstrated that copper transporter ATP7A is required for full activity of ecSOD. However, the role of ecSOD in DM is unclear. Here we show that vascular specific activity of ecSOD, but not Cu/Zn SOD, is decreased (35.5%), which is associated with increased O2•- (2.7-fold) and decrease in ATP7A expression in streptozotocin (STZ)-induced diabetic mice. Exogenous Cu partially rescued ecSOD activity in excised DM aortas. Functionally, acetylcholine induced vasorelaxation is significantly impaired in mesenteric arteries of DM mice vs. control (67±2% vs 92±2%), which is rescued by the SOD mimetic tempol. Since STZ-induced DM has low level of circulating insulin, we next examine if insulin is responsible for regulating ecSOD activity via ATP7A. In cultured vascular smooth muscle cells (VSMCs), insulin (10 nM) promotes ATP7A translocation to the plasma membrane as well as increases its protein expression, as assessed by immunofluorescence, western and biotinylation analysis. These insulin-induced effects are inhibited by PI3K/Akt inhibitors. In organoid culture of mouse aorta, insulin also increases ecSOD specific activity and ATP7A expression. Mechanistically, vascular ecSOD is found in caveolae/lipid raft (C/LR), and insulin promoted ATP7A translocation to the C/LR and concomitant reduction of Cu content (35%) in these microdomains, which may reflect secretion of Cu or Cu-binding proteins. Functional significance of the localization at C/LR is shown by decreased specific activity of vascular ecSOD and endothelial function in caveolin-1−/− mice. In summary, decrease in ecSOD specific activity in DM with hypoinsulinemia promotes overproduction of O2•-, thereby causing endothelial dysfunction. Insulin increases ATP7A expression and translocation to the C/LR where ecSOD obtains Cu to increase its specific activity in VSMCs. Thus, ATP7A is a potential therapeutic target for oxidant stress-dependent cardiovascular and metabolic diseases.
- © 2010 by American Heart Association, Inc.