Abstract 607: Kininogen Regulates Thrombin Generation in a Mouse Model of Sickle Cell Disease

Abstract

Sickle cell disease (SCD) is associated with activation of coagulation and vascular inflammation. We previously demonstrated that, in mouse models of SCD, tissue factor (TF) expressed on leukocytes activates coagulation and contributes to inflammation via microvascular thrombosis, whereas non-coagulant form of TF expressed by endothelial cells mediates factor Xa (FXa)-PAR2 signalling and contributes to inflammation via IL-6 expression. We also showed that both rivaroxaban and dabigatran, oral inhibitors of FXa and thrombin, attenuated the hypercoagulable state in sickle mice. It has been proposed that anticoagulants that target the intrinsic coagulation pathway may be associated with a lower risk of bleeding compared to targeting the extrinsic or common coagulation pathways. Therefore, we tested if the intrinsic pathway contributes to the activation of coagulation in sickle cell mice. Bone marrow from sickle (SS) and non-sickle (AA) Townes mice was transplanted into wild-type (WT) (n=18 AA, 15 SS), FXII-/- (n=14 AA, 22 SS), or FXI-/- (n=21 AA, 23 SS) recipients (all on C57Bl/6 genetic background). In addition, bone marrow from AA or SS mice was transplanted into high molecular weight kininogen (HK)+/+ (n=17 AA, 16 SS) or HK-/- (n=10 AA, 19 SS) mice. All mice were used for experiments 5 months after BMT. Thrombin generation, measured by plasma thrombin anti-thrombin (TAT) levels, was increased in WT mice injected with SS bone marrow (WT/BMSS) compared to WT/BMAA mice (4.4±0.7 vs 2.6±0.3 ng/mL, p<0.05, mean ± S.E.M), however neither FXII nor FXI deficiency affected this parameter. Consistent with these data, inhibition of FXIIa-dependent activation of FXI with 14E11 antibody also did not reduce plasma TAT levels in SS Townes mice. Interestingly, elevated plasma TAT levels observed in HK+/+/BMSS mice was significantly reduced in HK-/-/BMSS mice (4.8±0.5 versus 3.48±0.2 ng/mL, p<0.05). These data indicate that HK, but not FXII and FXI, contributes to thrombin generation in SCD at steady state of disease. In vitro, HK fragments induce TF expression on monocytes via activation of CD11b/18. We are now investigating if inhibition of HK fragments-induced TF expression on monocytes may attenuate the hypercoagulabIe state in SCD mice without impacting hemostasis.