Phospholipid-bound tissue factor modulates both thrombin generation and APC-mediated factor Va inactivation

Area of Science:

• Biochemistry
• Hematology
• Molecular Biology

Background:

• Hemostasis is initiated by tissue factor (TF) on phospholipid (PL) membranes, driving thrombin generation.
• Thrombin binding to thrombomodulin (TM) activates the protein C pathway, generating activated protein C (APC) for feedback inhibition.

Purpose of the Study:

• To develop a novel assay for simultaneous thrombin and APC generation measurement.
• To investigate the effect of TF concentration and surface density on hemostasis and the protein C pathway.

Main Methods:

• Developed a new assay system for simultaneous thrombin and APC generation in defibrinated plasma.
• Utilized large unilamellar PL vesicles complexed with recombinant TF (TF:PL) to induce hemostasis.
• Studied factor Va inactivation by APC on TF:PL surfaces in a non-plasma system.

Main Results:

• Low TF concentrations resulted in lower thrombin generation and reduced TM-mediated inhibition.
• High TF concentrations led to increased thrombin generation, with maximal APC generation but no feedback inhibition.
• TF surface density showed an inverse correlation with APC-mediated factor Va inactivation, suggesting a novel inhibitory role.

Conclusions:

• TF exhibits a previously unrecognized surface density-dependent inhibition of APC's anticoagulant effect.
• High TF concentrations and surface density synergistically promote coagulation and inhibit anticoagulation, maximizing hemostasis post-injury.