Ablation of Angiotensin IV Receptor Attenuates Hypofibrinolysis via PAI-1 Downregulation and Reduces Occlusive Arterial Thrombosis

Objectives-Reduced fibrinolytic activity is associated with adverse cardiovascular events. Although insulin-regulated aminopeptidase ( IRAP) was recently identified as the angiotensin (Ang) IV receptor (AT4R), the impact of AngIV-AT4R signaling distal to AngII on the activation of type-1 plasminogen activator inhibitor (PAI-1) in the fibrinolytic process and subsequent formation of thrombosis remains unclarified. Methods and Results-To determine whether AngIV would inhibit fibrinolysis via PAI-1 activation and promote thrombosis, we evaluated the degree of fibrinolysis in thrombosis models and investigated the roles of AT4R after vascular injury using IRAP knockout mice (IRAP(-/-)). In endothelial cells from control mice (WT; C57Bl6/J), both AngII and AngIV treatments increased PAI-1 mRNA expression in a dose-dependent manner, whereas the response was blunted in endothelial cells from IRAP(-/-) mice. FeCl3-induced thrombosis was suppressed in the carotid arteries of IRAP(-/-) mice when compared with WT mice. Similarly, in a model of carotid artery ligation and cuff placement, IRAP(-/-) mice demonstrated accelerated fibrinolysis 7 days after surgery and reduced occlusive thrombosis with negative remodeling at 28 days. Conclusions-AngIV-AT4R signaling has a key role in fibrinolysis and the subsequent formation of arterial thrombosis after vascular injury. AT4R may be a novel therapeutic target against cardiovascular disease. (Arterioscler Thromb Vasc Biol. 2009;29:2102-2108.)