Neutrophil α-defensins promote thrombosis in vivo by altering fibrin formation, structure, and stability

Abstract

Inflammation and thrombosis are integrated, mutually reinforcing processes, but the interregulatory mechanisms are incompletely defined. Here, we examined the contribution of α-defensins (α-defs), antimicrobial proteins released from activated human neutrophils, on clot formation in vitro and in vivo. Activation of the intrinsic pathway of coagulation stimulates release of α-defs from neutrophils. α-Defs accelerate fibrin polymerization, increase fiber density and branching, incorporate into nascent fibrin clots, and impede fibrinolysis in vitro. Transgenic mice (Def++) expressing human α-Def-1 developed larger, occlusive, neutrophil-rich clots after partial inferior vena cava (IVC) ligation than those that formed in wild-type (WT) mice. IVC thrombi extracted from Def++ mice were composed of a fibrin meshwork that was denser and contained a higher proportion of tightly packed compressed polyhedral erythrocytes than those that developed in WT mice. Def++ mice were resistant to thromboprophylaxis with heparin. Inhibiting activation of the intrinsic pathway of coagulation, bone marrow transplantation from WT mice or provision of colchicine to Def++ mice to inhibit neutrophil degranulation decreased plasma levels of α-defs, caused a phenotypic reversion characterized by smaller thrombi comparable to those formed in WT mice, and restored responsiveness to heparin. These data identify α-defs as a potentially important and tractable link between innate immunity and thrombosis.

The distinctive structure and composition of arterial and venous thrombi and pulmonary emboli

“…Platelet-driven clot contraction results in compression of RBCs into a tightly packed interior core with an accompanying shape change to polyhedral cells, named polyhedrocytes, whereas fibrin and platelets are mostly on the surface 17 . Polyhedrocytes have also been observed in intracoronary thrombi taken from patients post ST-elevation myocardial infarction 8,17,18 as well as in ex vivo thrombi, venous clots and postmortem pulmonary emboli 12,19,20 . In vitro studies of clot contraction have demonstrated that the kinetics of clot contraction are accelerated and extent of contraction is enhanced by higher platelet levels and inhibited by RBCs and higher fibrinogen concentrations 21 .…”

“…It is generally thought that RBCs are trapped in venous clots and might thereby increase vascular occlusion, but that they otherwise contribute little to arterial occlusion. There is now increasing evidence that RBCs play a substantial role in clotting 12 . Sub-fractions of RBCs express phosphatidylserine on their surface and thus support thrombin generation 13,14 .…”

Contact system sends defensins to the rescue

“…In this issue of Blood, Langerak et al report on the prognostic value of minimal residual disease (MRD) status in elderly patients with comorbid chronic lymphocytic leukemia (CLL) who were treated on the phase 3 CLL11 trial with chlorambucil plus rituximab (R-Chl) or chorambucil plus obinutuzumab (G-Chl). 1 The authors found that high levels of MRD were independently associated with shorter progression-free survival (PFS) and overall survival (OS) and reported that the G-Chl regimen was superior to R-Chl in terms of inducing MRD-negative remissions. 2 On the basis of these findings and the growing pool of data about posttherapy MRD status in CLL patients, the authors suggest that MRD has the potential to become a surrogate marker for survival in clinical trials.…”

Modulating the rate of fibrin formation and clot structure attenuates microvascular thrombosis in systemic inflammation

“…It is well appreciated that alterations in the fibrin clot profile are directly associated with different clinical pathologies, including conditions associated with bleeding and thrombosis. [7][8][9][10][11][12] Therefore, the development of interventions to modify fibrin clot structure and stability to prevent pathologic hemorrhage and thrombosis in systemic inflammation is an unmet medical need.…”