Factor XI is a key component of the intrinsic pathway of coagulation. The functions of this protein in fibrin formation initiated by contact activation in vitro are well described; however, the mechanisms responsible for factor XI activation in vivo and the role of this protein in normal hemostasis and pathologic coagulation are not clear. In current models of hemostasis, normal coagulation is initiated by the factor VIIa/tissue factor complex, and not through contact activation. Factor XI would function in these schemes to sustain coagulation by activating factor IX, after initial thrombin formation through factor VIIa/tissue factor. The protease that activates factor XI in the absence of contact activation in vivo is not known, but thrombin has been demonstrated to activate factor XI in vitro plasma systems. The goals of this proposal are to evaluate the mechanisms by which zymogen factor XI becomes an active serine protease and to investigate the contributions of factor XI to normal hemostasis. We have expressed and purified chimeric recombinant factor XI molecules in which domains have been replaced with corresponding domains from the related protease prekallikrein. These proteins have been used to identify binding sites for the proteases known to activate factor XI. The mechanism of activation and role of factor XI in a recently developed model of fibrin clot resistance to fibrinolysis will also be studied. Ultimately, to fully understand the contributions of factor XI to coagulation, studies in animals will be required. Using the technique of homologous recombination in murine embryonic stem cells, a murine model of factor XI deficiency has been created in our laboratory. These animals will be used to evaluate the role of factor XI in primary hemostasis and in bleeding in the presence of activators of fibrinolysis, anti-platelet agents, and anticoagulants. The studies will substantially increase our knowledge of factor XI biochemistry and physiology and provide a firmer knowledge base from which to study the contribution of this protein to thromboembolic diseases.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
1R01HL058837-01
Application #
2389101
Study Section
Hematology Subcommittee 2 (HEM)
Project Start
1997-07-01
Project End
2001-06-30
Budget Start
1997-07-01
Budget End
1998-06-30
Support Year
1
Fiscal Year
1997
Total Cost
Indirect Cost
Name
Vanderbilt University Medical Center
Department
Pathology
Type
Schools of Medicine
DUNS #
004413456
City
Nashville
State
TN
Country
United States
Zip Code
37212
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Ivanov, Ivan; Matafonov, Anton; Sun, Mao-Fu et al. (2017) Proteolytic properties of single-chain factor XII: a mechanism for triggering contact activation. Blood 129:1527-1537
Ivanov, Ivan; Shakhawat, Ruhama; Sun, Mao-Fu et al. (2017) Nucleic acids as cofactors for factor XI and prekallikrein activation: Different roles for high-molecular-weight kininogen. Thromb Haemost 117:671-681
Woodruff, R S; Ivanov, I; Verhamme, I M et al. (2017) Generation and characterization of aptamers targeting factor XIa. Thromb Res 156:134-141

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