Abstract 187: Paraoxonase-2 Regulates Blood Coagulation through Endothelial Redox-Signaling and Inflammation

Background: Enhanced coagulation increases the risk for cardiovascular diseases (CVDs) such as stroke, myocardial infarction or atherosclerosis. Increased oxidative stress and inflammation, predominantly in the vascular wall and platelets, are important underlying mechanisms of a pro-coagulant state. Paraoxonase-2 (PON2), an anti-oxidative protein with anti-inflammatory properties, has an emergent role in CVDs, as it counter-acts atherosclerosis. Previous studies revealed enhanced atherosclerosis in PON2-/- mice and diminished PON2 expression in human atherosclerotic endothelium. We hypothesized that PON2 affects coagulation by controlling redox-mediated inflammatory processes provoking atherosclerosis. Methods and Results: In several coagulation tests, PON2-/- mice showed significantly shortened clotting times (8.58±0.09 sec) compared to WT (9.32±0.16 sec prothrombin time; p<0.001; n=42). Confocal microscopy, flow cytometry and gene expression studies revealed enhanced vascular oxidative stress (p<0.001; n=6) and a pro-inflammatory endothelium in PON2-/- mice. In line with this, the endogenous interleukin-6 plasma level was increased compared to WT (2-fold) as disclosed by cytokine profiling. Additionally, plasmatic coagulation factors VIII, IX and XI displayed significantly elevated activities in PON2-/- mice (p<0.05; n=10). Further, PON2-/- platelets showed a pro-coagulant activity, due to increased endogenous thrombin potentials triggered by an enhanced phosphatidylserine plasma membrane exposure (p<0.01; n=7). To locate PON2’s dominant effect to either endothelial cells, plasma or platelets, we established bone marrow chimeras and transgenic mice with exclusively endothelial and hematopoietic PON2 expression (Tie2cre-PON2-/-). Coagulation time analyses revealed that the pro-coagulant effect was attenuated in WT chimera with PON2-/- bone marrow (9.22±0.15 sec; n=12) and in Tie2cre-PON2-/- (10.02±0.3 sec; n=23), indicating that much of the effects originates from PON2 functions in the endothelium. Conclusion: We found that PON2 regulates specific pathways of blood coagulation based on a redox-mediated endothelial-dependent modulation of important players in inflammation and hemostasis.