Altered structure and function of fibrinogen after cleavage by Factor VII Activating Protease (FSAP)

Abstract

Factor VII Activating Protease (FSAP) is a plasma protease affecting both coagulation and fibrinolysis. Although a role in hemostasis is still unclear, the identification of additional physiologic substrates will help to elucidate its role in this context. FSAP has been reported to cleave fibrinogen, but the functional consequences of this are not known. We have therefore undertaken this study to determine the implications of this cleavage for fibrin-clot formation and its lysis. Treatment of human fibrinogen with FSAP released an N-terminal peptide from the Bβ chain (Bβ1-53) and subsequently the fibrinopeptide B; within the Aα chain a partial truncation of the αC-region by multiple cleavages was seen. The truncated fibrinogen showed a delayed thrombin-catalyzed polymerization and formed fibrin clots of reduced turbidity, indicative of thinner fibrin fibers. Confocal laser scanning and scanning electron microscopy of these clots revealed a less coarse fibrin network with thinner fibers and a smaller pore size. A lower pore size was also seen in permeability studies. Unexpectedly, FSAP-treated fibrinogen or plasma exhibited a significantly faster tPA-driven lysis, which correlated exclusively with cleavage of fibrinogen and not with activation of plasminogen activators. Similar observations were also made in plasma after activation of endogenous zymogen FSAP, but not in plasma of carrier of the rare Marburg I single nucleotide polymorphism. In conclusion, altering fibrin clot properties by fibrinogenolysis is a novel function of FSAP in the vasculature, which facilitates clot lysis and may in vivo contribute to reduced fibrin deposition during thrombosis.

Factor VII activating protease (FSAP) inhibits the outcome of ischemic stroke in mouse models

“…3). WT- or MI-SPD alone, had no direct effect on clot lysis as reported earlier with human plasma-FSAP in human plasma clots 13 . Application of FSAP-SPD in mice lead to the formation of FSAP inhibitor complexes which were not investigated further (Suppl.…”

“…1a). Since FSAP alone did not to exhibit any fibrinolytic activity 13 , WT-SPD was not tested on its own. Treatment infusions were started 60 min after the onset of thrombosis in the carotid artery.…”

“…Although the activation of FVII has been the name-giving property of this protein 8 , a number of other activities have been ascribed to it in relation to thrombosis and hemostasis. It can activate pro-urokinase (uPA) 8 , cleave TFPI and decrease its activity 12 , and cleave fibrinogen and speed up lysis of clots 13 . In light of these antagonistic effects on coagulation it is difficult to ascertain its net effect in vivo .…”

“…Thus, converging lines of evidence from human genetic investigations, mouse models and in vitro studies 6,11,13,18,23 indicate that FSAP may be a candidate for the therapy of ischemic stroke. A recent study shows that high molecular weight-hyaluronic acid, which is a pleiotropic factor with multiple functions 24 , downregulates endogenous FSAP expression and improves the outcome of ischemic stroke in mice 9 .…”

Fibrin Polymer on the Surface of Biomaterial Implants Drives the Foreign Body Reaction

“…Curiously, fibrin deposited on the surface did not interact with mAb 59D8 which recognizes the N-terminal portion of the β-chain of fibrinogen after cleavage of FpB. This finding can be explained by the propensity of the β-chain to undergo rapid degradation by various proteases releasing the β15-41 and β42-53 fragments (40, 41) or by the fact that the epitope is not exposed in the surface-deposited fibrin.…”