Abstract 587: Ablation of AngiotensinIV Receptor Attenuates Hypofibrinolysis and Inhibits Neointimal Formation in Murine Vascular Injury Model
Reduced fibrinolytic activity is associated with adverse cardiovascular events. Recently, it has been shown that angiotensin (Ang) IV receptor (AT4R) regulated fibrinolyasis via plasminogen activator inhibitor-1 (PAI-1) activation. However, it remains unknown how much this Ang IV-AT4R signaling affects the neointimal formation in the reparative process after vascular injury. To investigate if AngIV would inhibit fibrinolysis and promote neointimal formation, we evaluated the degree of proliferation of vascular smooth muscle cells and compared with the role of AT1R using AT1R and AT4R knockout mice (AT1R −/−and AT4R −/−, respectively).
[Methods and Results] AT1R −/−and AT4R −/− showed normal hemostasis patterns including bleeding time if compared with wild type mice (C57BL6/J; WT). To assess fibrinolysis in an acute thrombosis model, renal glomerular fibrin deposition was counted after lipopolysaccharide injection (0.2mg/kg, i.v., n=5). Fibrin deposition was reduced in AT4R −/−as compared to WT and AT1R −/−at 4 hrs (12±3% of total glomeruli, 27±4% and 25±4%, p=0.012 vs. WT). The levels of plasma active PAI-1 antigen measured by ELISA were also reduced in the order of AT4R −/−, AT1R −/− and WT (4.2±0.8*, 8.0±1 and 14±3 ng/mL, *p<0.001vs. WT). For a vascular injury model, neointimal formation was observed over 7 days after carotid artery ligation and cuff placement. In the carotid arteries of WT and AT1R −/−, significant hyperplasia of adventitial tissues and neointimal formation were observed after vascular injury, while those of AT4R −/− were minimally affected (n=6 each) in accordance with greater lumen diameters. In this model, genetic ablation of AT4R, but not AT1R, showed beneficial effects in vascular remodeling.
[Conclusions] In murine vascular injury model, disruption of AngIV-AT4R signaling leads to accelerated fibrinolysis and decreased neointimal formation, suggesting that AT4R is a novel therapeutic target against cardiovascular disease.