A systems approach to hemostasis: 3. Thrombus consolidation regulates intrathrombus solute transport and local thrombin activity

Abstract

Hemostatic thrombi formed after a penetrating injury have a distinctive structure in which a core of highly activated, closely packed platelets is covered by a shell of less-activated, loosely packed platelets. We have shown that differences in intrathrombus molecular transport emerge in parallel with regional differences in platelet packing density and predicted that these differences affect thrombus growth and stability. Here we test that prediction in a mouse vascular injury model. The studies use a novel method for measuring thrombus contraction in vivo and a previously characterized mouse line with a defect in integrin αIIbβ3 outside-in signaling that affects clot retraction ex vivo. The results show that the mutant mice have a defect in thrombus consolidation following vascular injury, resulting in an increase in intrathrombus transport rates and, as predicted by computational modeling, a decrease in thrombin activity and platelet activation in the thrombus core. Collectively, these data (1) demonstrate that in addition to the activation state of individual platelets, the physical properties of the accumulated mass of adherent platelets is critical in determining intrathrombus agonist distribution and platelet activation and (2) define a novel role for integrin signaling in the regulation of intrathrombus transport rates and localization of thrombin activity.

Plasminogen associates with phosphatidylserine-exposing platelets and contributes to thrombus lysis under flow

“…Thrombi perfused with whole blood containing heparin lysed significantly faster than whole blood alone, highlighting the importance of on-going fibrin formation in these thrombi as a result of procoagulant activity. Notable work by Stalker et al 66 has recently shown that integrin a IIb b 3 outside-in signaling localizes thrombin activity within the core region of thrombi by minimizing solute transport. Our studies on plasminogen localization and plasmin activity suggest that it may be regulated by similar mechanisms via the interaction of fibrin(ogen) with a IIb b 3 within the microenvironment of the thrombus.…”

Defective release of α granule and lysosome contents from platelets in mouse Hermansky-Pudlak syndrome models

“…Thrombin activity in this model extends as a gradient from the site of vascular injury [73][74][75][76] and is necessary for full platelet activation and a granule secretion. 51,77 Our results indicate that ADP signaling reinforces platelet activation at the edge of this gradient where thrombin activity starts to decline.…”

Interplay of Platelet Contractility and Elasticity of Fibrin/Erythrocytes in Blood Clot Retraction

“…Cross-linking results in the stabilization of the viscoelastic fibrin network, which has many fibers originating from platelet aggregates (6)(7)(8)(9). The activated platelets are able to generate contractile forces that are propagated through the cross-linked fibrin fibers (10,11), effectively resulting in a reduction of the clot volume (12,13). The volume reduction of the clot, or clot contraction, has been suggested to play a critical role in hemostasis (14), wound healing, and the restoration of blood flow past otherwise obstructive blood clots (15).…”