Purpose of this project is to advance understanding of coagulation mechanisms that promote hemostasis in response to vascular injury but also cause diseases involving vascular thrombosis.
In Aim 1, we will delineate a previously unrecognized convergence of extrinsic and intrinsic coagulation pathways differentially regulated by physiological and pharmacologic inhibitors and relevant to thrombin generation.
This aim i s predicated on the novel observation that, without thrombin feedback contribution, nascent FXa generated by TF-FVIIa can provide the activated cofactors, FVIIIa and FVa, required for assembly of functional intrinsic tenase (FIXa- FVIIIa) and prothrombinase (FXa-FVa) complexes, respectively. We will define the mechanisms underlying this newly recognized synergistic coagulation pathway studying reactions with purified components or in plasma; and we will establish how these mechanisms contribute to thrombus formation in blood flowing over TF and collagen as model thrombogenic surfaces, thus evaluating individual variability in response.
In Aim 2, we will dissect the distinct contributions of different coagulation pathways to pro-hemostatic or thrombogenic processes. These studies stem from the observation that physiological coagulation inhibitors and FXa-directed anticoagulants differentially regulate the TF-dependent FXa activity generating FVIIIa and FVa as opposed to FXa required for prothrombinase function. Consequently, thrombin generation directly linked to TF pathway activation may be markedly inhibited while preserving TF-dependent FVIIIa and FVa cofactor production required for intrinsic tenase-driven prothrombinase activity. We hypothesize, therefore, that thrombin generation during hemostasis or thrombosis may involve a different balance of procoagulant and anticoagulant pathways in response to distinct vascular lesions and/or blood conditions that variably activate extrinsic and intrinsic coagulation pathways. Thus, we will evaluate the variability in the response of individual plasma samples to the anticoagulant effect of direct FXa inhibitors in clinical use - such as rivaroxaban and apixaban - and study mechanisms of thrombus formation elicited by cellular and matrix components of the vessel wall to define their relative contribution to coagulation initiation. Moreover, we will establish how different coagulation pathways, including the newly identified synergistic link between extrinsic and intrinsic coagulation, contribute to platelet thrombus formation and fibrin deposition induced by components of the atherosclerotic plaque. Recognizing the distinct coagulation pathways contributing to thrombus formation that may differentiate normal hemostasis from thrombosis will advance our understanding of serious pathological conditions resulting from vascular occlusion as well as excessive bleeding. Ultimately, our studies will have a positive impact on basic and translational research relevant to the prevention and treatment of socially relevant diseases associated with arterial and venous thrombosis or hemorrhage.

Public Health Relevance

Hemostasis is an essential defense mechanism to arrest bleeding from wounds, but the same processes can cause clots that occlude veins and arteries (thrombosis). The purpose of our work is to understand how beneficial hemostasis and dangerous thrombosis differ, focusing of variations of mechanisms in different individuals. The final goal is to delineate new strategies for defining personal thrombotic risk and, when needed, the risk of bleeding when given drugs for treating or preventing vascular clots. Our studies may also lead to improved antithrombotic therapy.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL117722-03
Application #
9198882
Study Section
Special Emphasis Panel (ZRG1)
Program Officer
Kindzelski, Andrei L
Project Start
2014-12-01
Project End
2018-11-30
Budget Start
2016-12-01
Budget End
2017-11-30
Support Year
3
Fiscal Year
2017
Total Cost
Indirect Cost
Name
Scripps Research Institute
Department
Type
DUNS #
781613492
City
La Jolla
State
CA
Country
United States
Zip Code
92037
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