Factor XI-dependent reciprocal thrombin generation consolidates blood coagulation when tissue factor is not available

Area of Science:

• Hemostasis and Thrombosis Research
• Biochemistry of Coagulation
• Platelet Signaling Pathways

Background:

• Thrombin feedback activation of factor XI is a potential alternative to tissue factor (TF)-dependent thrombus propagation.
• The role of thrombin in initiating and propagating its own formation in a factor XI and platelet-dependent manner in plasma has not been fully elucidated.

Purpose of the Study:

• To investigate the mechanism of thrombin generation initiation and propagation.
• To determine the necessity of platelets and factor XI in thrombin-initiated thrombin generation.
• To assess the contribution of platelet-associated tissue factor and factor VIII in this process.

Main Methods:

• Investigated thrombin generation in recalcified platelet-rich plasma.
• Activated plasma with varying concentrations of thrombin or factor VIIa.
• Utilized a tissue factor-neutralizing antibody and assessed the impact of factor VIII absence.

Main Results:

• Thrombin dose-dependently initiated and propagated thrombin generation exclusively in the presence of platelets and plasma factor XI.
• Platelet-associated tissue factor was not involved in thrombin formation.
• Thrombin could not initiate its own formation without factor VIII, and factor VIIa-induced thrombin generation was reduced.
• Collagen significantly enhanced both thrombin-initiated and factor VIIa-initiated thrombin generation.

Conclusions:

• Platelet-localized feedback activation of factor XI by thrombin is critical for maintaining hemostasis.
• This pathway is essential for sustaining thrombus formation, particularly when the TF pathway is inhibited by TFPI.