Abstract 4915: IQGAP1 Expressed in Macrophage and Endothelial Cells Plays an Important Role in ROS-dependent Ischemia-induced Neovascularization

Abstract

Not only endothelial cells (ECs) but also macrophage play a key role in ischemia-induced angiogenesis which is dependent on inflammation and reactive oxygen species (ROS). IQGAP1, an actin- and Rac1-binding scaffold protein, is a key regulator for actin cytoskeleton and motility. We demonstrated that IQGAP1 is involved in VEGF-induced ROS production and migration in cultured ECs; however, its role in post-ischemic neovascularization remains unknown. Using hindlimb ischemia model of mice, here we show that IQGAP1-expressing Mac3-positive macrophage and lectin-positive ECs (5.5 and 10.2-fold) are increased in ischemic limb tissues at 3 days and 7 days after ischemia, respectively. Ischemia-induced neovascularization is significantly impaired in IQGAP1 knockout (KO) mice as compared to wild-type (WT) mice as evaluated by laser Doppler blood flow (38% decrease), capillary density (48% decrease), and alpha-actin+ arterioles (68% decrease). In IQGAP1 KO mice, the number of infiltrated Mac3-positive macrophage and ROS production in ischemic muscles are significantly decreased (30% and 52%, respectively). In contrast, numbers of inflammatory cells and cKit+/Flk1+ endothelial progenitor cells (EPCs) in peripheral blood are not affected in these knockout mice. As compared to WT-BM transplantation to irradiated WT mice, WT-BM to irradiated KO mice inhibits ischemia-induced in blood flow recovery (22%) and CD31+ capillary density (5%), while KO-BM to irradiated WT mice shows decreases in flow recovery (48%) and capillary density (23%). These findings indicate that IQGAP1 KO mice impair function of BM derived cells without affecting their mobilization from BM. Furthermore, in vitro, BM-derived macrophages obtained from KO mice show defective polarization of actin (88% decrease), as visualized by phalloidin staining as well as inhibition of migration induced by SDF-1 (92%) or wound scratch (38%). VEGF- or wound scratch-induced EC migration is inhibited in IQGAP1-depleted ECs. In summary, IQGAP1 upregulated in macrophage and ECs after hindlimb ischemia plays an important role in ROS-dependent postnatal neovascularization. Thus, IQGAP1 is a potential therapeutic target for inflammation- and angiogenesis-dependent cardiovascular diseases. This research has received full or partial funding support from the American Heart Association, Midwest Affiliate (Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, South Dakota & Wisconsin).