Platelet Control of Fibrin Distribution and Microelasticity in Thrombus Formation Under Flow

Abstract

Objective-Platelet-and fibrin-dependent thrombus formation is regulated by blood flow and exposure of collagen and tissue factor. However, interactions between these blood-borne and vascular components are not well understood. Approach and Results-Here, we developed a method to assess whole-blood thrombus formation on microspots with defined amounts of collagen and tissue factor, allowing determination of the mechanical properties and intrathrombus composition. Confining the collagen content resulted in diminished platelet deposition and fibrin formation at high shear flow conditions, but this effect was compensated by a larger thrombus size and increased accumulation of fibrin in the luminal regions of the thrombi at the expense of the base regions. These thrombi were more dependent on tissue factortriggered thrombin generation. Microforce nanoindentation analysis revealed a significantly increased microelasticity of thrombi with luminal-oriented fibrin. At a low shear rate, fibrin fibers tended to luminally cover the thrombi, again resulting in a higher microelasticity. Studies with blood from patients with distinct hemostatic insufficiencies indicated an impairment in the formation of a platelet-fibrin thrombus in the cases of dilutional coagulopathy, thrombocytopenia, Scott syndrome, and hemophilia B. Conclusions-Taken together, our data indicate that (1) thrombin increases the platelet thrombus volume; (2) tissue factor drives the formation of fibrin outside of the platelet thrombus; (3) limitation of platelet adhesion redirects fibrin from bottom to top of the thrombus; (4) a lower shear rate promotes thrombus coverage with fibrin; (5) the fibrin distribution pattern determines thrombus microelasticity; and (6) the thrombus-forming process is reduced in patients with diverse hemostatic defects. Swieringa et al Platelet Control of Fibrin Distribution in Thrombus Formation 693Together, these in vivo findings indicate that the relative availability of platelet-adhesive (like collagen) and coagulation-triggering (like TF) substances determines the buildup of a thrombus and, by implication, the roles of thrombin and fibrin herein. In support of this idea, different patterns of fibrin deposition have been detected in injury models, such as fibrin structures around a thrombus, 16 and thrombin/fibrin-rich areas in the thrombus core region. 17,18 How the platelet and coagulant activities of the thrombogenic surface, for example, the relative abundance of collagen and TF, influence the buildup and composition of a platelet-fibrin thrombus has not been examined so far.Viscoelasticity is considered to be an important hemostatic property of a fibrin-containing thrombus. For instance, in patients with severe factor XI deficiency, a low-density fibrin network is associated with impaired hemostasis. 19,20 However, the conditions that favor high elasticity of a platelet-fibrin thrombus or clot are largely unknown. The limited evidence available suggests that a local, high concentration of thrombin enforces the fibrin net...

Fibrin Formation, Structure and Properties

“…Blood flow is one of the most important physical factors that affects profoundly formation of the fibrin network, its structure and properties in vivo (Swieringa et al 2016). Clot formation in static conditions stops when all soluble fibrinogen is converted to insoluble fibrin.…”

Fibrinogen and Fibrin in Hemostasis and Thrombosis

“…Furthermore, the shear rate affects clot formation triggered on tissue factor- plus collagen-coated plates, resulting in different fibrin deposition in different regions of a thrombus. 48 Nanoindentation analysis to evaluate clot biophysical properties shows this fibrin distribution pattern determines clot microelasticity, which may impact thrombus stability and risk of embolization. 48 Fourth, thrombin movement through the thrombus is substantially influenced by solute transport mechanisms mediated by cell packing density; this may also influence the amount of fibrin deposition in different regions of the clot.…”

Thrombotic Regulation From the Endothelial Cell Perspectives

“…5 Despite these differences, platelet adhesion/activation, and fibrin deposition as the result of coagulation constitute the fundamental processes of thrombus formation. 6,7 Platelet activation occurs when they interact with activated ECs (with increased VWF release and selectin expression) via glycoprotein Ib-V-IX complex binding to VWF, or when they expose to subendothelial extracellular matrix components, such as collagen (via glycoprotein VI receptor), in the cases of endothelial injury or plaques rupture. 1,8 Coagulation cascade is triggered by coagulation factor VII binding to tissue factor (TF; extrinsic pathway) or by contact system activation via factor XII (FXII; intrinsic pathway), followed by a common pathway that leads to fibrin formation through intricate enzymatic actions of different coagulation factors (Figure).…”