Abstract 18175: Interaction of Platelets, Leukocytes and Released Neutrophil Extracellular Traps (NETs) Promote Deep Vein Thrombosis in vivo

Abstract

Objective: Venous thromboembolism has a major medical impact and is the third leading cause of cardiovascular associated death. While the critical contribution of platelets to arterial thrombosis has been recognized, the mechanisms that trigger the development of deep vein thrombosis (DVT) are not yet fully understood and are believed to be mainly dependent on coagulation. Current in vivo models associated with endothelial disruption or complete stasis only incompletely reflect the pathophysiology of DVT in humans and hinder further understanding of this process. Here, we established a novel mouse model of DVT formation and assessed the dynamics of leukocyte (lc) and platelet (pt) recruitment in vivo. Methods: In our new model DVT was induced by reduction of blood flow in the inferior vena cava (IVC) (to 23.8% of baseline) in the absence of endothelial injury. Layered thrombi develop slowly over a prolonged period of time (>6-12hrs) and occlude the entire IVC 24-48hrs later mimicking human venous thrombi. We observed the dynamics of pt (GPIb-/-, GPIIb-/-), lc (CX3CR1-EGFP, LysM-EGFP), and microparticle recruitment in the IVC in vivo by intravital microscopy. Results: Using corresponding transgenic mice we show here that lc accumulation required endothelial P-selectin, and, besides monocytes, consisted mainly of neutrophils which contribute to DVT development by NET release. In addition to innate immune cells, pts are indispensable for the initiation of venous thrombosis. Further, using low-TF and hTF mice we demonstrate that blood derived tissue factor (TF), exposed on NETs and microparticles, creates a procoagulatory environment that is supported by pt adhesion and activation. The intrinsic pathway of coagulation is also involved in DVT formation, since a factor XIIa inhibitor markedly impaired DVT development. Conclusion: Together, venous thrombosis in our model is driven by a concerted interaction of pts, lcs, and the coagulation cascade. Pts bind to endothelial cells mediated by GPIbα and GPIIb-IIIa, recruited lcs, and triggered NET release thereby initiating DVT. A modulation can be attained in three different ways: by aiming on the coagulation cascade (heparins, factor inhibitors), by impairing pt function and/or by inhibiting lc activation.