Abstract 54: Peptidylarginine Deiminase 4-dependent Generation of Neutrophil Extracellular Traps is Crucial for Deep Vein Thrombosis in Mice

Introduction Histone hypercitrullination by the enzyme peptidylarginine deiminase 4 (PAD4) leads to nuclear chromatin decondensation that is needed for neutrophil extracellular trap (NET) formation. NETs consist of chromatin and granule proteins that are released into the extracellular environment. NETs were shown to be involved in thrombosis by promoting coagulation and platelet adhesion and were identified in the thrombus scaffold in animal models of deep vein thrombosis (DVT). Objective Whether NETs are involved in the pathogenesis of DVT or whether they are merely a consequence of neutrophil recruitment to the thrombus is unknown. We hypothesized that NET formation would be impaired in PAD4-deficient mice during deep vein thrombosis and that this may affect thrombus formation and/or stability. Methods PAD4-deficient mice are incapable of citrullinating histones and therefore fail to decondense chromatin during NETosis. We performed the inferior vena cava stenosis model of DVT in wild-type or PAD4-/- mice. Intravital microscopy was done to assess leukocyte vessel wall interaction in PAD4 deficiency. Results We induced NET formation in isolated peripheral blood mouse neutrophils with ionomycin and found that PAD4-/- neutrophils had a complete inability to produce NETs (WT, 20.65±2.61% NETs; PAD4-/-, not detected. n=4). Leukocyte-endothelial interactions in PAD4-/- mice were not impaired upon induction of systemic Weibel-Palade body release (WT, 55.2±11.8; PAD4-/-, 62.0±17.5 cells/min, n=5-6). In the DVT model, while a majority (9/10) of wild-type mice formed a thrombus 48 hours after stenosis, only 1 of 11 PAD4-/- mice formed a thrombus. Thrombus formation could be rescued by infusions of isolated WT bone marrow neutrophils into PAD4-/- mice, and extracellular H3Cit+ areas were seen within these thrombi. This data suggests that neutrophil PAD4 was essential for thrombus formation in deep veins. Conclusion NETs comprise a crucial part of the pathologic thrombus scaffold, and here we report that the lack of NETs inhibits pathological thrombosis. Chromatin decondensation initiated by PAD4 in neutrophils is a key player in the formation of deep vein thrombi and targeting neutrophil histone modification could be a new way to prevent DVT.

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