Abstract

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.

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