Abstract 346: Essential Role of Extracellular SOD in Reparative Neovascularization Induced by Hindlimb Ischemia
Neovascularization is important physiological repair mechanism in response to ischemic injury and its process is dependent on reactive oxygen species (ROS). Overproduction of superoxide anion (O2· −) rather contributes to various cardiovascular diseases. The extracellular superoxide dismutase (ecSOD) is the major antioxidant enzymes against O2· − in vascular extracellular space; however, its role in neovascularization induced by tissue ischemia is unknown. Here we show that hindlimb ischemia of mice stimulates a significant increase in ecSOD activity in ischemic tissues where ecSOD protein is highly expressed at arterioles. In mice lacking ecSOD, ischemia-induced increase in blood flow recovery, collateral vessel formation and capillary density are significantly inhibited as compared to wild-type (WT) mice (37.6 %, 36.5%, and 26.4% decrease, respectively). Impaired neovascularization in ecSOD knockout (KO) mice is associated with enhanced ischemia induced O2· − production by 1.5 fold, TUNEL-positive apoptotic cells by 2.8 fold, and decreased levels of NO2−/NO3− and cGMP (48.2 and 85.3 % decrease, respectively) in ischemic tissues as compared to WT mice, and they are rescued by infusion of the SOD mimetic tempol. Recruitment of inflammatory cells into ischemic tissues as well as numbers of inflammatory cells and endothelial progenitor cells (EPCs)(c-kit+/CD31+cells) in both PB and BM are significantly reduced in these knockout mice. Of note, ecSOD protein expression is markedly increased in BM after ischemia by 7.5 fold, and NO2−/NO3− and cGMP levels are decreased in ecSOD-KO BM. Moreover, differentiation of BM mononuclear cells into EPCs, as detected by Dil-acLDL and BS lectin double positive cells, was markedly decreased in ecSOD KO mice (21.5% decrease). Transplantation of wild-type BM into ecSOD-KO mice rescued the defective neovascularization, while WT mice transplanted with ecSOD-KO BM showed significant decrease of flow recovery. Thus, ecSOD in BM and ischemic tissues induced by hindlimb ischemia may represent an important compensatory mechanism that blunts the overproduction of O2· −, which may contribute to reparative neovascularization in response to ischemic injury.