Abstract 13650: Role of PI3K/Akt in Insulin-Mediated Regulation of Cu Transporter ATP7A Function Required for Full Activation of Extracellular SOD in Vasculature: Novel Protective Mechanism for Endothelial Dysfunction in Type I Diabetes
Altered insulin level associated with diabetes mellitus (DM), which affects PI3K/Akt pathway, contributes to increased oxidative stress, endothelial dysfunction, and cardiovascular diseases with unknown mechanisms. Extracellular SOD (ecSOD), a secretory Cu enzyme, preserves endothelial function by modulating extracellular superoxide (O2•-), and its full activity requires Cu transporter ATP7A. Thus, we hypothesized that endothelial dysfunction in type I DM with hypoinsulinemia is mediated by altering ecSOD and ATP7A function. In cultured VSMC, insulin significantly increases ATP7A protein expression peaked at 12h (1.7-fold) without affecting transcription, which is associated with reduction of ATP7A ubiquitination. These insulin-induced responses are significantly inhibited by PI3K and Akt inhibitors. In organoid culture of mouse aorta, insulin also increases ecSOD specific activity (47%) and ATP7A expression. Of note, ecSOD is found in caveolin (Cav) enriched lipid raft (C/LR) in mouse aorta and specific activity of vascular ecSOD and endothelial function are impaired in Cav-1-/- mice, suggesting the importance of C/LR in activation of ecSOD. Insulin stimulation for 2h with peak promotes ATP7A translocation to the C/LR as well as ATP7A binding to ecSOD via PI3K/Akt, reflecting Cu delivery to ecSOD via ATP7A. Mechanistically, insulin induces ATP7A binding to pAkt and its Ser phosphorylation in a PI3K-dependent manner, thereby inducing N-glycosylation of ATP7A, which promotes translocation to the C/LR. Functional significance in vivo is demonstrated in DM mice with hypoinsulinemia induced by streptozotocin. In diabetic vessels, ATP7A expression and specific activity of ecSOD (35.5%), but not Cu/Zn SOD, are decreased, while O2•- production (2.7-fold) is enhanced. Acetylcholine-induced vasorelaxation is significantly impaired in DM mice (25 %), which is rescued by gene transfer of ecSOD. In summary, insulin activates ecSOD by regulating ATP7A expression and translocation to the C/LR to transfer Cu to ecSOD via PI3K/Akt in VSMC, which in turn reduces O2•- level and preserve endothelial function. Thus, ecSOD and its regulator ATP7A are potential therapeutic targets for treatment of DM with hypoinsulinemia and endothelial dysfunction.
- © 2011 by American Heart Association, Inc.