Abstract 39: Myeloid Klf2 Regulates Arterial and Venous Thrombosis

Abstract

Experimental, clinical and pathological studies have indicated an important link between inflammation and thrombosis. However, the precise mechanisms regulating myeloid cell function and the importance of various myeloid lineages involved in thrombosis remain incompletely defined. Published work from our group shows that a systemic deficiency of KLF2 renders animals susceptible to thrombosis. Using conditional knockouts, we examined the role of myeloid KLF2 in thrombosis. Carotid thrombosis assay (Rose Bengal model) show a robust reduction in time to occlusion in MY-K2-KO mice. No difference was noted in complete blood counts and coagulation assays between MY-K2-KO and control mice. Adoptive transfer of KLF2-KO neutrophils significantly shortened the time to occlusive thrombosis in control mice compared with the occlusion time in control mice given control neutrophils. No change in thrombosis time was noted in MY-K2-KO mice transfused with either control or KLF2-KO neutrophils. Neutrophil depletion with Ly6G antibody reversed the prothrombotic phenotype in MY-K2-KO mice and prolonged thrombosis time while no change was noted in thrombosis time in control mice following neutropenia. MY-K2-KO mice also developed significantly larger venous clot burden as compared to controls (complete ligation of inferior vena cava model). KLF2 deleted neutrophils demonstrated significantly increased tissue factor (TF) expression and activity. KLF2 deleted monocytes did not reveal change in TF expression as compared to controls. MY-K2-KO neutrophils also demonstrated increased generation of neutrophil extracellular traps and increased expression of neutrophil elastase (NE) and myeloperoxidase (MPO) as compared to controls. Other enzymes reported as important to the generation of NETs were not altered. TF, NE and MPO promoter-luciferase reporter assays demonstrated that KLF2 overexpression significantly abrogates p65-induced promoter activity. Collectively these studies identify neutrophil KLF2 as an important regulator of both arterial and venous thrombosis and illuminate the molecular mechanisms involved suggesting that modulation of neutrophil KLF2 may alter thrombosis.