Abstract 3390: Impairment of Post-ischemic Neovascularization in Mice Lacking IQGAP1, an Actin-binding Scaffold Protein: Role in Macrophage Infiltration and ROS production
Neovascularization is important repair mechanism in response to ischemic injury and its process is in part dependent on reactive oxygen species (ROS). IQGAP1, an actin-binding scaffold protein, is key regulator for actin cytoskeleton and motility. We demonstrated that IQGAP1 is expressed in endothelial cells (ECs) and mediates VEGF-induced ROS production and migration of cultured ECs. However, its role in postnatal neovascularization is unknown. Here we show that neovascularization induced by hindlimb ischemia is significantly inhibited in IQGAP1-deficient mice as evaluated by laser Doppler blood flow (38%), capillary density (48%) and alpha-actin positive arterioles (68%). In wild-type (WT) mice, western and immunofluorescence analysis reveal that IQGAP1 protein expression in ischemic tissues is significantly increased at Mac3+ macrophages and lectin+ capillary-like ECs at 3 days and 7 days after ischemia, respectively, which is associated with increased superoxide production. Of note, macrophage infiltration is important for post-ischemic revascularization. Mice lacking IQGAP1 show significant decrease in the number of infiltrated Mac3-positive macrophage and superoxide production in ischemic muscles (30% and 52%, respectively) as compared to WT mice. Numbers of inflammatory cells and cKit+/Flk1+ endothelial progenitor cells in peripheral blood are not affected in these knockout mice. Moreover, thioglycollate-induced peritoneal leukocyte recruitment and accumulation are significantly inhibited in IQGAP1-deficient mice (53%), whereas white blood cell number is not changed. In vitro, peritonitis-elicited (activated) macrophages obtained from IQGAP1-deficient mice show impaired polarization of actin, as visualized by phalloidin staining as well as complete inhibition of migration towards stromal derived factor-1 and VEGF, as measured by modified Boyden-chambered method. In summary, IQGAP1 plays a key role in reparative neovascularization in response to tissue ischemia by regulating not only ECs but also macrophage migration/infiltration as well as ROS production in the vessel growth area. Thus, IQGAP1 is a potential therapeutic target to promote neovascularization in ischemic cardiovascular diseases.
This research has received full or partial funding support from the American Heart Association, AHA National Center.