Activation of factor VII-activating protease in human inflammation: a sensor for cell death

Factor VII Activating Protease (FSAP) and Its Importance in Hemostasis—Part I: FSAP Structure, Synthesis and Activity Regulation: A Narrative Review

Factor VII activating protease (FSAP) was first isolated from human plasma less than 30 years ago. Since then, many research groups have described the biological properties of this protease and its role in hemostasis and other processes in humans and other animals. With the progress of knowledge about the structure of FSAP, several of its relationships with other proteins or chemical compounds that may modulate its activity have been explained. These mutual axes are described in the present narrative review. The first part of our series of manuscripts on FSAP describes the structure of this protein and the processes leading to the enhancement and inhibition of its activities. The following parts, II and III, concern the role of FSAP in hemostasis and in the pathophysiology of human diseases, with particular emphasis on cardiovascular diseases.

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

The outcome of ischemic stroke can be improved by further refinements of thrombolysis and reperfusion strategies. Factor VII activating protease (FSAP) is a circulating serine protease that could be important in this context. Its levels are raised in patients as well as mice after stroke and a single nucleotide polymorphism (SNP) in the coding sequence, which results in an inactive enzyme, is linked to an increased risk of stroke. In vitro, FSAP cleaves fibrinogen to promote fibrinolysis, activates protease-activated receptors, and decreases the cellular cytotoxicity of histones. Based on these facts, we hypothesized that FSAP can be used as a treatment for ischemic stroke. A combination of tissue plasminogen activator (tPA), a thrombolytic drug, and recombinant serine protease domain of FSAP (FSAP-SPD) improved regional cerebral perfusion and neurological outcome and reduced infarct size in a mouse model of thromboembolic stroke. FSAP-SPD also improved stroke outcomes and diminished the negative consequences of co-treatment with tPA in the transient middle cerebral artery occlusion model of stroke without altering cerebral perfusion. The inactive MI-isoform of FSAP had no impact in either model. FSAP enhanced the lysis of blood clots in vitro, but in the tail transection model of hemostasis, FSAP-SPD treatment provoked a faster clotting time indicating that it also has pro-coagulant actions. Thus, apart from enhancing thrombolysis, FSAP has multiple effects on stroke progression and represents a promising novel therapeutic strategy in the treatment of ischemic stroke.

Identification of a Phage Display-Derived Peptide Interacting with the N-Terminal Region of Factor VII Activating Protease (FSAP) Enables Characterization of Zymogen Activation

Factor VII Activating protease (FSAP) has a protective effect in diverse disease conditions as inferred from studies in FSAP^-/- mice and humans deficient in FSAP activity due to single-nucleotide polymorphism. The zymogen form of FSAP in plasma is activated by extracellular histones that are released during tissue injury or inflammation or by positively charged surfaces. However, it is not clear whether this activation mechanism is specific and amenable to manipulation. Using a phage display approach, we have identified a Cys-constrained 11 amino acid peptide, NNKC9/41, that activates pro-FSAP in plasma. The synthetic linear peptide has a propensity to cyclize through the terminal Cys groups, of which the antiparallel cyclic dimer, but not the monocyclic peptide, is the active component. Other commonly found zymogens in the plasma, related to the hemostasis system, were not activated. Binding studies with FSAP domain deletion mutants indicate that the N-terminus of FSAP is the key interaction site of this peptide. In a monoclonal antibody screen, we identified MA-FSAP-38C7 that prevented the activation of pro-FSAP by the peptide. This antibody bound to the LESLDP sequence (amino acids 30-35) in an intrinsically disordered stretch in the N-terminus of FSAP. The plasma clotting time was shortened by NNKC9/41, and this was reversed by MA-FSAP-38C7, demonstrating the utility of this peptide. Peptide NNKC9/41 will be useful as a tool to delineate the molecular mechanism of activation of pro-FSAP, elucidate its biological role, and provide a starting point for the pharmacological manipulation of FSAP activity.

Factor VII activating protease (FSAP) is not essential in the pathophysiology of angioedema in patients with C1 inhibitor deficiency

BACKGROUND

Excessive bradykinin (BK) generation from high molecular weight kininogen (HK) by plasma kallikrein (PK) due to lack of protease inhibition is central to the pathophysiology of hereditary angioedema (HAE). Inadequate protease inhibition may contribute to HAE through a number of plasma proteases including factor VII activating protease (FSAP) that can also cleave HK.

OBJECTIVE

To investigate the interaction between FSAP and C1 inhibitor (C1Inh) and evaluate the potential role of FSAP in HAE with C1Inh deficiency.

MATERIALS AND METHODS

Plasma samples from 20 persons with HAE types 1 or 2 in remission were studied and compared to healthy controls. We measured and compared antigenic FSAP levels, spontaneous FSAP activity, FSAP generation potential, activation of plasma pre-kallikrein (PPK) by FSAP, and the formation of FSAP-C1Inh and FSAP-alpha2-antiplasmin (FSAP-α2AP) complexes. Furthermore, we measured HK cleavage and PK activation after activation of endogenous pro-FSAP and after addition of exogenous FSAP.

RESULTS

In plasma from HAE patients, there is increased basal FSAP activity compared to healthy volunteers. HAE plasma exhibits decreased formation of FSAP-C1Inh complexes and increased formation of FSAP-α2AP complexes in histone-activated plasma. Although exogenous FSAP can cleave HK in plasma, this was not seen when endogenous plasma pro-FSAP was activated with histones in either group. PK was also not activated by FSAP in plasma.

CONCLUSION

In this study, we established that FSAP activity is increased and the pattern of FSAP-inhibitor complexes is altered in HAE patients. However, we did not find evidence suggesting that FSAP contributes directly to HAE attacks.

The role of extracellular DNA (exDNA) in cellular processes

Nowadays, extracellular DNA or circulating cell-free DNA is considered to be a molecule with clinical applications (diagnosis, prognosis, monitoring of treatment responses, or patient follow-up) in diverse pathologies, especially in cancer. Nevertheless, because of its molecular characteristics, it can have many other functions. This review focuses on the participation of extracellular DNA (exDNA) in fundamental processes such as cell signaling, coagulation, immunity, evolution through horizontal transfer of genetic information, and adaptive response to inflammatory processes. A deeper understanding of its role in each of these processes will allow development of better tools to monitor and control pathologies, as well as helping to generate new therapeutic options, beyond the applicability of DNA in liquid biopsy.

Factor VII Activating Protease Expression in Human Platelets and Accumulation in Symptomatic Carotid Plaque

Background

Factor VII activating protease (FSAP) is of interest as a marker for vascular inflammation and plaque destabilization. The aim of this study was to analyze the expression profile of FSAP in endarterectomy specimens that were taken from patients with asymptomatic and symptomatic carotid atherosclerotic plaques and to compare them with circulating FSAP levels.

Methods and Results

Plasma FSAP concentration, activity, and mRNA expression were measured in endarterectomy specimens and in monocytes and platelets. Plaque and plasma FSAP levels were higher in symptomatic patients (n=10) than in asymptomatic patients (n=14). Stronger FSAP immunostaining was observed in advanced symptomatic lesions, in intraplaque hemorrhage‐related structures, and in lipid‐rich areas within the necrotic core. FSAP was also colocalized with monocytes and macrophages (CD11b/CD68‐positive cells) and platelets (CD41‐positive cells) of the plaques. Moreover, human platelets expressed FSAP in vitro, at both the mRNA and protein levels. Expression is stimulated by thrombin receptor‐activating peptide and ADP and reduced by acetylsalicylic acid.

Conclusions

Plasma FSAP levels were significantly increased in patients with symptomatic carotid stenosis and thus may be involved in plaque development This plaque‐associated FSAP may be produced by platelets or macrophages or may be taken up from the circulation. To establish FSAP’s utility as a circulating or plaque biomarker in patients with symptomatic carotid atherosclerotic plaques, further studies are needed.

Cellular effects of factor VII activating protease (FSAP)

Factor VII activating protease (FSAP) is a circulating serine protease of broad specificity that is likely to be involved in many pathophysiological processes. The activation of the circulating zymogen form of FSAP by histones, released from damaged cells, underlines its roles in regulating host responses to tissue damage and inflammation. Some of the direct cellular effects of FSAP are mediated through protease-activated receptors (PARs). Knock-down of each one of the four PARs in endothelial cells indicated that PAR-1 and -3 are involved in regulating endothelial permeability in response to FSAP. Overexpression of PARs in cell lines led to the conclusion that PAR-2 and -1 were the main receptors for FSAP. Studies with synthetic peptides and receptor mutants demonstrate that FSAP cleaves PAR-1 and -2 at their canonical cleavage site. However, PAR-1 is not activated by FSAP in all cells, which may be related to other, as yet, undefined factors. Inhibition of apoptosis by FSAP is mediated through PAR-1 and was observed in neurons, astrocytes and A549 cells. FSAP also mediates cellular effects by modulating the activity of growth factors, generation of bradykinin, C5a and C3a generation or histone inactivation. These cellular effects need to be further investigated at the in vivo level.

Fluorescent activity-based probe for the selective detection of Factor VII activating protease (FSAP) in human plasma

The zymogen form of circulating Factor VII activating protease (FSAP) is activated by histones that are released as a consequence of tissue damage or excessive inflammation. This is likely to have consequences in a number of disease conditions such as stroke, atherosclerosis, liver fibrosis, thrombosis and cancer. To investigate the existence, as well as the concentration of active FSAP (FSAPa) in complex biological systems an active site probe is needed. We used Hybrid Combinatorial Substrate Library (HyCoSuL) to screen for natural and unnatural amino acids that specifically bind to P4-P2 pockets of FSAPa. This information was used to designing a fluorogenic substrate (Ac-Pro-DTyr-Lys-Arg-ACC) as well as an irreversible, fluorogenic activity-based probe Cy5-6-Ahx-Pro-DTyr-Lys-Arg^P(OPh)₂. In normal human plasma the probe showed very low non-specific reactivity with some plasma proteins but upon activation of pro-FSAP with histones, strong labelling of FSAPa was observed. This labelling could be inhibited by aprotinin and was not found in the plasma of a subject that was homozygous for a polymorphism, which leads to loss of activity, or in plasma that was depleted of FSAP by antibodies. This 2nd generation substrate exhibited 6-fold higher catalytic efficiency than the 1st generation substrate and a much higher selectivity for FSAPa over other plasma proteases. This substrate and probe can be useful to detect and localize FSAPa in normal and pathological tissue and plasma to gain more insight into its functions.

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

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.

Expression of the Marburg I Single Nucleotide Polymorphism (MI-SNP) and the Marburg II Single Nucleotide Polymorphism (MII-SNP) of the Factor VII-Activating Protease (FSAP) Gene and Risk of Coronary Artery Disease (CAD): A Pilot Study in a Single Population

Background

Factor VII-activating protease (FSAP) has a role in vascular inflammation and may have a role coronary artery disease (CAD). The aim of this study was to investigate the association between two naturally occurring single nucleotide polymorphisms (SNPs) in the FSAP gene and the risk of coronary artery disease (CAD).

Material/Methods

Of 733 patients, 173 patients had symptoms of angina, and 560 patients had CAD confirmed by coronary angiography. All patients were genotyped for SNPs of the FSAP gene, Marburg I (MI-SNP) and Marburg II (MII-SNP), using 5′ exonuclease TaqMan assays. Logistic regression analysis was used to evaluate the association between two gene polymorphisms, metabolic and other cardiovascular risk factors in patients with CAD.

Results

The presence of MI-SNP and MII-SNP FSAP gene polymorphisms were not associated with the presence of CAD. However, the MII-SNP polymorphism was significantly associated with a reduced risk of developing CAD (OR=0.422; 95% CI, 0.194–0.920; P=0.035); the MI-SNP polymorphism was associated with absence of hyperlipoproteinemia (OR=0.601; 95% CI, 0.344–1.051; P=0.074). There was no significant association between expression of the MI-SNP and MII-SNP FSAP gene polymorphisms and the incidence of myocardial infarction, or of a history of diabetes mellitus, arterial hypertension, obesity, or smoking.

Conclusions

The MI-SNP and MII-SNP FSAP gene polymorphisms were not predictive or prognostic biomarkers for CAD or its main risk factors. However, the presence of the MII-SNP polymorphism was associated with a reduced risk of developing CAD.

Factor VII activating protease

Factor VII activating protease (FSAP) is a circulating serine protease with high homology to fibrinolytic enzymes. A role in the regulation of coagulation and fibrinolysis is suspected based on in vitro studies demonstrating activation of FVII or pro-urokinase plasminogen activator (uPA). However, considering the paucity of any studies in animal models or any correlative studies in humans the role of FSAP in haemostasis remains unclear. In relation to vascular remodeling processes or inflammation it has been convincingly shown that FSAP interacts with growth factors as well as protease activated receptors (PAR). Against this sparse background there are a plethora of studies which have investigated the linkage of single nucleotide polymorphisms (SNP) in the FSAP gene (HABP2) to various diseases. The G534E SNP of FSAP is associated with a low proteolytic activity due to an amino acid exchange in the protease domain. This and other SNPs have been linked to carotid stenosis, stroke as well as thrombosis in the elderly and plaque calcification. These SNP analyses indicate an important role for FSAP in the regulation of the haemostasis system as well as fibroproliferative inflammatory processes.

FSAP, a new player in inflammation?

Factor VII-activating protease (FSAP) is a serine protease in plasma that has a role in coagulation and fibrinolysis. FVII could be activated by purified FSAP in a tissue factor independent manner and pro-urokinase has been demonstrated to be a substrate for purified FSAP in-vitro. However, the physiological role of FSAP in haemostasis remains unclear. More recently FSAP is suggested to be involved in inflammation. It modulates vascular permeability directly and indirectly by the generation of bradykinin. Furthermore, FSAP is activated by dead cells induced by the inflammatory response and subsequently removes nucleosomes from apoptotic cells. FSAP activation can be detected in sepsis patients as well. However, whether FSAP activation upon inflammation is beneficial or detrimental remains an open question.

In this review the structure, activation mechanisms and the possible role of FSAP in inflammation are discussed.

DNA and factor VII-activating protease protect against the cytotoxicity of histones

Circulating histones have been implicated as major mediators of inflammatory disease because of their strong cytotoxic effects. Histones form the protein core of nucleosomes; however, it is unclear whether histones and nucleosomes are equally cytotoxic. Several plasma proteins that neutralize histones are present in plasma. Importantly, factor VII-activating protease (FSAP) is activated upon contact with histones and subsequently proteolyzes histones. We aimed to determine the effect of FSAP on the cytotoxicity of both histones and nucleosomes. Indeed, FSAP protected against histone-induced cytotoxicity of cultured cells in vitro. Upon incubation of serum with histones, endogenous FSAP was activated and degraded histones, which also prevented cytotoxicity. Notably, histones as part of nucleosome complexes were not cytotoxic, whereas DNA digestion restored cytotoxicity. Histones in nucleosomes were inefficiently cleaved by FSAP, which resulted in limited cleavage of histone H3 and removal of the N-terminal tail. The specific isolation of either circulating nucleosomes or free histones from sera of Escherichia coli challenged baboons or patients with meningococcal sepsis revealed that histone H3 was present in the form of nucleosomes, whereas free histone H3 was not detected. All samples showed signs of FSAP activation. Markedly, we observed that all histone H3 in nucleosomes from the patients with sepsis, and most histone H3 from the baboons, was N-terminally truncated, giving rise to a similarly sized protein fragment as through cleavage by FSAP. Taken together, our results suggest that DNA and FSAP jointly limit histone cytotoxicity and that free histone H3 does not circulate in appreciable concentrations in sepsis.

A Positively Charged Surface Triggers Coagulation Activation Through Factor VII Activating Protease (FSAP)

Contact between biomedical materials and blood often initiates undesirable pro-coagulant and pro-inflammatory processes. On negatively charged materials, blood coagulation is known to be triggered through autoactivation of Factor XII, while activation on cationic surfaces follows a distinct and so far enigmatic mechanism. Because Factor VII activating protease (FSAP) is known to be activated on positively and on negatively charged macromolecules in plasma, we have investigated its interaction with charged biomaterials and its consequences for coagulation. Several activation processes in blood and plasma were characterized after contact with material surfaces with varied charge. FSAP was found to be exclusively activated by the positively charged surfaces polyethylenimine (PEI) and poly-l-lysine (PLL), not by the negatively charged glass or self-assembled monolayer with carboxyl group termination (SAM-COOH), as well as uncharged (Teflon AF) surfaces. Whole blood incubation on PEI showed that this activation was concomitant with coagulation as determined by thrombin and fibrin formation, which was high for glass (F1+2, 138 nM) and PEI (F1+2, 44 nM) but low for Teflon AF (F1+2, 3.3 nM) and SAM COOH (F1+2, 5.8 nM). Contact phase inhibitor diminished coagulation to background levels for all surfaces except PEI (F1+2: ^PEI 43 to 25 nM; glass, 58 to 1.5 nM) indicating that coagulation activation is not dependent on FXII activation on the PEI surface. A decisive role of endogenous FSAP for coagulation however was confirmed with the use of FSAP inhibitory antibodies which showed no influence on Teflon AF, glass and SAM COOH but diminished F1+2 on PEI to less than 50%. We propose that FSAP activation could be a novel mechanism of surface-driven coagulation. An inhibition of this protease might improve hemocompatibility of cationic surfaces and therefore facilitate the application of polycationic surfaces in blood.

Interaction of factor VII activating protease (FSAP) with neutrophil extracellular traps (NETs)

The circulating zymogen form of Factor VII activating protease (FSAP) can be activated by histones and nucleosomes in vivo. These cell-death-associated nuclear factors are also actively extruded into the extracellular space by neutrophils through a process called neutrophil extracellular trap (NET) formation (NETosis). NETs are thought to be involved in host defense, inflammation as well as thrombosis. We have investigated the bidirectional interactions of FSAP and NETs. Phorbol ester-mediated NET formation was marginally stimulated by FSAP. Plasma-derived FSAP as well as exogenous FSAP bound to NETs. There was co-localization of FSAP and NETs in coronary thrombi from patients with acute myocardial infarction. Contrary to our expectations no activation of pro-FSAP by NETs was evident. However, after disintegration of NETs with DNase, a robust activation of pro-FSAP, due to release of histones from nucleosomes, was detected. The released histones were in turn degraded by FSAP. Histone cytotoxicity towards endothelial cells was neutralized by FSAP more potently than by activated protein C (APC). One more consequence of histone degradation was a decrease in nucleosome release from apoptotic neutrophils. Taken together, NETs bind to FSAP, but do not activate pro-FSAP unless histones are released from NETs by DNAse. This activation of FSAP is likely to be important in diminishing the cytotoxic effect of histones, thus limiting the damaging effect of NETosis.

Neutrophil extracellular traps in patients with pulmonary tuberculosis

Tuberculosis is a devastating infectious disease causing many deaths worldwide. Recent investigations have implicated neutrophil extracellular traps (NETs) in the host response to tuberculosis. The aim of the current study was to obtain evidence for NETs release in the circulation during human tuberculosis. For this we measured the plasma concentrations of nucleosomes in conjunction with neutrophil elastase, in 64 patients with active pulmonary tuberculosis and 32 healthy controls. Patients with active tuberculosis had elevated plasma levels of nucleosomes and elastase when compared with local healthy blood donors. Furthermore nucleosome and elastase levels showed a positive correlation. These findings provide the first evidence for the release of NETs in the circulation of patients with active pulmonary tuberculosis.

Analysis of the substrate specificity of Factor VII activating protease (FSAP) and design of specific and sensitive peptide substrates

Factor VII (FVII) activating protease (FSAP) is a circulating serine protease that is likely to be involved in a number of disease conditions such as stroke, atherosclerosis, liver fibrosis, thrombosis and cancer. To date, no systematic information is available about the substrate specificity of FSAP. Applying phage display and positional scanning substrate combinatorial library (PS-SCL) approaches we have characterised the specificity of FSAP towards small peptides. Results were evaluated in the context of known protein substrates as well as molecular modelling of the peptides in the active site of FSAP. The representative FSAP-cleaved sequence obtained from the phage display method was Val-Leu-Lys-Arg-Ser (P4-P1'). The sequence X-Lys/Arg-Nle-Lys/Arg (P4-P1) was derived from the PS-SCL method. These results show a predilection for cleavage at a cluster of basic amino acids on the nonprime side. Quenched fluorescent substrate (Ala-Lys-Nle-Arg-AMC) (amino methyl coumarin) and (Ala-Leu-Lys-Arg-AMC) had a higher selectivity for FSAP compared to other proteases from the hemostasis system. These substrates could be used to measure FSAP activity in a complex biological system such as plasma. In histone-treated plasma there was a specific activation of pro-FSAP as validated by the use of an FSAP inhibitory antibody, corn trypsin inhibitor to inhibit Factor XIIa and hirudin to inhibit thrombin, which may account for some of the haemostasis-related effects of histones. These results will aid the development of further selective FSAP activity probes as well as specific inhibitors that will help to increase the understanding of the functions of FSAP in vivo.

Extracellular nucleic acids in immunity and cardiovascular responses: between alert and disease

Severe inflammatory complications are a potential consequence in patients with predetermined conditions of infections, pulmonary diseases, or cardiovascular disorders. Notably, the amplitude of the inflammatory response towards these complications can dictate the disease progression and outcome. During the recent years, evidence from basic research as well as from clinical studies has identified self-extracellular nucleic acids as important players in the crosstalk between immunity and cardiovascular diseases. These stress- or injury-induced endogenous polymeric macromolecules not only serve as "alarmins" or "Danger-associated molecular patterns" (DAMPs), but their functional repertoire goes far beyond such activities in innate immunity. In fact, (patho-) physiological functions of self-extracellular DNA and RNA are associated and in many cases causally related to arterial and venous thrombosis, atherosclerosis, ischemia-reperfusion injury or tumour progression. Yet, the underlying molecular mechanisms are far from being completely understood. Interestingly enough, however, novel antagonistic approaches in vitro and in vivo, particularly using natural endonucleases or synthetic nucleic acid binding polymers, appear to be promising and safe therapeutic options for future studies. The aim of this review article is to provide an overview of the current state of (patho-) physiological functions of self-extracellular nucleic acids with special emphasis on their role as beneficial / alerting or adverse / damaging factors in connection with immune responses, inflammation, thrombosis, and cardiovascular diseases.

The various assays for measuring activity states of factor VIIa in plasma and therapeutic products: Diagnostic value and analytical usefulness in various pathophysiological states

The key coagulation factor FVII, and its activated form FVIIa, present a major interest for their role at the initiation phase of blood coagulation, and because they can activate all blood coagulation cascade, through the extrinsic, but also the intrinsic pathway. Blood activation initiated through FVII is first presented, as it is understood nowadays. Measurement of FVII and FVIIa were of main interest for epidemiological studies, but FVIIa contribution to assay results was only deduced. The introduction of specific FVIIa assays, functional or immunoassays, allowed measuring directly FVIIa without any interference of non-activated FVII, or other coagulation factors or their activated forms. The various methods available, and their characteristics are presented, with a special focus on two assays developed by our group for FVIIa (a clotting one and a chromogenic one). The FVIIa clotting assay shows evident superiority for measuring its activity in plasma, in pathophysiological conditions. The normal range is <2.5ng/ml, which represents less than 0.5% of the FVII protein. FVIIa is elevated in some pathological states. The chromogenic assay is of interest for assigning the potency of FVIIa concentrates, as it has a higher dynamic range. Both assays are fully automatable on laboratory instruments, and standardized in a satisfactory manner thanks to the use of the FVIIa concentrate WHO International Standard (NIBSC). The various applications and usefulness of FVIIa laboratory assays are discussed, for the measurement of therapeutic products, or for following recoveries in treated patients, including hemophiliacs with inhibitors, patients with severe bleeding risk (liver diseases, surgery, trauma, …), and lastly for measurement of its activity in therapeutic products.

Transforming Growth Factor-β (TGF-β) Inhibits the Expression of Factor VII-activating Protease (FSAP) in Hepatocytes

Deletion of the Habp2 gene encoding Factor VII-activating protease (FSAP) increases liver fibrosis in mice. A single nucleotide polymorphism (G534E) in HABP2 leads to lower enzymatic activity and is associated with enhanced liver fibrosis in humans. Liver fibrosis is associated with a decrease in FSAP expression but, to date, nothing is known about how this might be regulated. Primary mouse hepatocytes or the hepatocyte cell line, AML12, were treated with different factors, and expression of FSAP was determined. Of the various regulatory factors tested, only transforming growth factor-β (TGF-β) demonstrated a concentration- and time-dependent inhibition of FSAP expression at the mRNA and protein level. The TGF-β-Type I receptor (ALK-5) antagonist SB431542 and Smad2 siRNA, but neither SIS3, which inhibits SMAD3, nor siRNA against Smad3 could block this effect. Various regions of the HABP2 promoter region were cloned into reporter constructs, and the promoter activity was determined. Accordingly, the promoter activity, which could phenocopy changes in Habp2 mRNA in response to TGF-β, was found to be located in the 177-bp region upstream of the transcription start site, and this region did not contain any SMAD binding sites. Mutation analysis of the promoter and chromatin immunoprecipitation assays were performed to identify an important role for the ATF3 binding element. Thus, TGF-β is the most likely mediator responsible for the decrease in FSAP expression in liver fibrosis.

Hereditary and acquired C1-inhibitor-dependent angioedema: from pathophysiology to treatment

Uncontrolled generation of bradykinin (BK) due to insufficient levels of protease inhibitors controlling contact phase (CP) activation, increased activity of CP proteins, and/or inadequate degradation of BK into inactive peptides increases vascular permeability via BK-receptor 2 (BKR2) and results in subcutaneous and submucosal edema formation. Hereditary and acquired angioedema due to C1-inhibitor deficiency (C1-INH-HAE and -AAE) are diseases characterized by serious and potentially fatal attacks of subcutaneous and submucosal edemas of upper airways, facial structures, abdomen, and extremities, due to inadequate control of BK generation. A decreased activity of C1-inhibitor is the hallmark of C1-INH-HAE (types 1 and 2) due to a mutation in the C1-inhibitor gene, whereas the deficiency in C1-inhibitor in C1-INH-AAE is the result of autoimmune phenomena. In HAE with normal C1-inhibitor, a significant percentage of patients have an increased activity of factor XIIa due to a FXII mutation (FXII-HAE). Treatment of C1-inhibitor-dependent angioedema focuses on restoring control of BK generation by inhibition of CP proteases by correcting the balance between CP inhibitors and BK breakdown or by inhibition of BK-mediated effects at the BKR2 on endothelial cells. This review will address the pathophysiology, clinical picture, diagnosis and available treatment in C1-inhibitor-dependent angioedema focusing on BK-release and its regulation. Key Messages Inadequate control of bradykinin formation results in the formation of characteristic subcutaneous and submucosal edemas of the skin, upper airways, facial structures, abdomen and extremities as seen in hereditary and acquired C1-inhibitor-dependent angioedema. Diagnosis of hereditary and acquired C1-inhibitor-dependent angioedema may be troublesome as illustrated by the fact that there is a significant delay in diagnosis; a certain grade of suspicion is therefore crucial for quick diagnosis. Submucosal edema formation in hereditary and acquired C1-inhibitor-dependent angioedema is potentially life threatening and can occur at any age. To date effective therapies for acute and prophylactic treatment are available.

Increased Nucleosomes and Neutrophil Activation Link to Disease Progression in Patients with Scrub Typhus but Not Murine Typhus in Laos

Cell-mediated immunity is essential in protection against rickettsial illnesses, but the role of neutrophils in these intracellular vasculotropic infections remains unclear. This study analyzed the plasma levels of nucleosomes, FSAP-activation (nucleosome-releasing factor), and neutrophil activation, as evidenced by neutrophil-elastase (ELA) complexes, in sympatric Lao patients with scrub typhus and murine typhus. In acute scrub typhus elevated nucleosome levels correlated with lower GCS scores, raised respiratory rate, jaundice and impaired liver function, whereas neutrophil activation correlated with fibrinolysis and high IL-8 plasma levels, a recently identified predictor of severe disease and mortality. Nucleosome and ELA complex levels were associated with a 4.8-fold and 4-fold increased risk of developing severe scrub typhus, beyond cut off values of 1,040 U/ml for nucleosomes and 275 U/ml for ELA complexes respectively. In murine typhus, nucleosome levels associated with pro-inflammatory cytokines and the duration of illness, while ELA complexes correlated strongly with inflammation markers, jaundice and increased respiratory rates. This study found strong correlations between circulating nucleosomes and neutrophil activation in patients with scrub typhus, but not murine typhus, providing indirect evidence that nucleosomes could originate from neutrophil extracellular trap (NET) degradation. High circulating plasma nucleosomes and ELA complexes represent independent risk factors for developing severe complications in scrub typhus. As nucleosomes and histones exposed on NETs are highly cytotoxic to endothelial cells and are strongly pro-coagulant, neutrophil-derived nucleosomes could contribute to vascular damage, the pro-coagulant state and exacerbation of disease in scrub typhus, thus indicating a detrimental role of neutrophil activation. The data suggest that increased neutrophil activation relates to disease progression and severe complications, and increased plasma levels of nucleosomes and ELA complexes represent independent risk factors for developing severe scrub typhus.

Tropical rickettsial illnesses, especially scrub typhus and murine typhus, are increasingly recognized as a leading cause of treatable undifferentiated febrile illness in Asia, but remain severely neglected and under appreciated diseases in many areas. In this study we investigated the relationship of markers of neutrophil activation and cell death with disease severity in patients with acute scrub typhus and murine typhus in Laos. These easily measurable circulating markers were associated with a 4 to 5-fold increased risk of developing severe clinical disease manifestations in scrub typhus and represent independent predictors of severe disease, and possibly death. We also found strong correlations between circulating markers of cell death and neutrophil activation in patients with scrub typhus, but not murine typhus, providing indirect evidence that neutrophil extracellular traps could contribute to the vascular damage and pro-coagulant state leading to exacerbation of disease in scrub typhus, thus indicating a detrimental role of neutrophil activation. The data suggest that increased neutrophil activation relates to disease progression and severe complications, and increased plasma levels of nucleosomes and ELA complexes represent independent risk factors for developing severe scrub typhus.

Association of circulating factor seven activating protease (FSAP) and of oral Omega-3 fatty acids supplements with clinical outcome in patients with atrial fibrillation: the OMEGA-AF study

Factor VII Activating Protease (FSAP) activates factor VII (FVII) as well as pro-urokinase (uPA). Our goal was to evaluate the relation between plasma levels of FSAP and clinical instability in atrial fibrillation (AF) and possible effects of oral omega-3 fatty acids (FA) supplements. 101 patients with persistent AF were analyzed in the OMEGA-AF Study. Plasma FSAP levels were measured at baseline and after 12 weeks of treatment with omega-3 FA. The median FSAP antigen concentration, in contrast to FSAP activity, was higher in patients with persistent AF. The maintenance of SR after successful cardioversion (CV) did not lead to a normalization of FSAP concentration. Supplementation with omega-3 FA but not placebo significantly reduced elevated FSAP concentration. Furthermore, elevated FSAP levels did not indicate a significantly increased risk of recurrence of AF after electrical CV or cardiovascular clinical events during 1 year of follow-up. Plasma FSAP concentration was increased in patients with AF and may be involved in the pathogenesis of this condition. The possible effects of omega-3 FA on clinical AF potential could be linked with modulation of circulating FSAP levels.

Diabetes-independent increase of factor VII-activating protease activation in patients with Gram-negative sepsis (melioidosis)

BACKGROUND

The plasma protease factor VII-activating protease (FSAP) can release nucleosomes from late apoptotic cells. Nucleosomes are markers of cell death, and extracellular cell-free DNA has been suggested to play an important role in inflammation and has been demonstrated to correlate with severity and outcome in sepsis patients.

OBJECTIVE

To investigate FSAP activation in patients suffering from Burkholderia pseudomallei infection (melioidosis), an important cause of Gram-negative sepsis in Southeast Asia. As diabetes mellitus (DM) is the most important risk factor for both melioidosis and sepsis, we were also able to examine the role of DM in FSAP activation in this cohort of patients.

METHODS

In a prospective observational study, complexes of FSAP with α2 -antiplasmin (AP) were assayed in 44 patients with melioidosis, 34 of whom were classified as diabetic. Eighty-two healthy subjects served as controls (52 with DM and 30 without).

RESULTS

FSAP-AP complex levels were markedly elevated in patients as compared with controls. The FSAP level increased by 16.82 AU mL(-1) in patients with melioidosis after adjustment for the effect of DM in the regression model. As expected, FSAP activation was correlated with nucleosome release (slope = 0.74). No difference in FSAP activation on admission was seen between survivors and non-survivors, but the extent of FSAP activation correlated with stage of the disease; repeated testing during convalescence showed a return towards normal values (day 0 vs. day 28, 4.16 AU mL(-1) , 95% confidence interval [CI] 1.42-12.22).

CONCLUSION

Patients with Gram-negative sepsis caused by B. pseudomallei have abundant FSAP activation, which significantly correlates with stage of disease. The presence of DM, however, does not influence the extent of FSAP activation.

Complement, thrombotic microangiopathy and disseminated intravascular coagulation

In the blurring boundaries between clinical practice and scientific observations, it is increasingly attractive to propose shared disease mechanisms that could explain clinical experience. With the advent of available therapeutic options for complement inhibition, there is a push for more widespread application in patients, despite a lack of clinically relevant research. Patients with disseminated intravascular coagulation (DIC) and thrombotic microangiopathies (TMA) frequently exhibit complement activation and share the clinical consequences of thrombocytopenia, microangiopathic hemolytic anemia, and microvascular thrombosis. However, they arise from very different molecular etiologies giving rise to cautious questions about inclusive treatment approaches because most clinical observations are associative and not cause-and-effect. Complement inhibition is successful in many cases of atypical hemolytic uremic syndrome, greatly reducing morbidity and mortality of patients by minimizing thrombocytopenia, microangiopathic hemolytic anemia, and microvascular thrombosis. But is this success due to targeting disease etiology or because complement is a sufficiently systemic target or both? These questions are important because complement activation and similar clinical features also are observed in many DIC patients, and there are mounting calls for systemic inhibition of complement mediators despite the enormous differences in the primary diseases complicated by DIC. We are in great need of thoughtful and standardized assessment with respect to both beneficial and potentially harmful consequences of complement activation in these patient populations. In this review, we discuss about what needs to be done in terms of establishing the strategy for complement inhibition in TMA and DIC, based on the current knowledge.

Defective thrombus formation in mice lacking endogenous factor VII activating protease (FSAP)

Factor VII (FVII) activating protease (FSAP) is a circulating protease with a putative function in blood coagulation and fibrinolysis. Genetic epidemiological studies have implied a role for FSAP in carotid stenosis, stroke and thrombosis. To date, no in vivo evidence is available to support these claims. We have, for the first time, used FSAP-/- mice to define its role in thrombosis and haemostasis in vivo and to characterise the molecular mechanisms involved. FeCl3-induced arterial thrombosis in carotid and mesenteric artery revealed that the occlusion time was significantly increased in FSAP-/- mice (p< 0.01) and that some FSAP-/- mice did not occlude at all. FSAP-/- mice were protected from lethal pulmonary thromboembolism induced by collagen/ epinephrine infusion (p< 0.01). Although no spontaneous bleeding was evident, in the tail bleeding assay a re-bleeding pattern was observed in FSAP-/- mice. To explain these observations at a mechanistic level we then determined how haemostasis factors and putative FSAP substrates were altered in FSAP-/- mice. Tissue factor pathway inhibitor (TFPI) levels were higher in FSAP-/- mice compared to WT mice whereas FVIIa levels were unchanged. Other coagulation factors as well as markers of platelet activation and function revealed no significant differences between WT and FSAP-/- mice. This phenotype of FSAP-/- mice could be reversed by application of exogenous FSAP. In conclusion, a lack of endogenous FSAP impaired the formation of stable, occlusive thrombi in mice. The underlying in vivo effect of FSAP is more likely to be related to the modulation of TFPI rather than FVIIa.

Influence of resuscitation fluids, fresh frozen plasma and antifibrinolytics on fibrinolysis in a thrombelastography-based, in-vitro, whole-blood model

Hyperfibrinolysis has been identified as a mechanism of trauma coagulopathy associated with poor outcome. The aim of the study was to create a trauma coagulopathy model (TCM) with a hyperfibrinolysis thrombelastography (TEG) pattern similar to injured patients and test the effects of different resuscitation fluids and antifibrinolytics on fibrinolysis. TCM was established from whole blood by either 15% dilution with isotonic saline, lactated Ringer's, Plasma-Lyte, 5% albumin, Voluven, Hextend, 6% dextran in isotonic saline or 30% dilution with lactated Ringer's plus Voluven and supplementation with tissue factor and tissue plasminogen activator (tPA). These combinations resulted in a TCM that could then be 'treated' with tranexamic acid (TXA) or 6-aminocaproic acid (ACA). Clot formation was evaluated by TEG. Whole-blood dilution by 15% with crystalloids and albumin in the presence of tissue factor plus tPA resulted in an abnormal TEG pattern and increased fibrinolysis, as did dilution with synthetic colloids. TXA 1 μg/ml or ACA 10 μg/ml were sufficient to suppress fibrinolysis when TCM was diluted 15% with lactated Ringer's, but 3 μg/ml of TXA or 30 μg/ml of ACA were needed for fibrinolysis inhibition induced by simultaneous euvolemic dilution with lactated Ringer's plus Voluven by 30%. A total of 15% dilution of whole blood in the presence of tissue factor plus tPA results in a hyperfibrinolysis TEG pattern similar to that observed in severely injured patients. Synthetic colloids worsen TEG variables with a further increase of fibrinolysis. Low concentrations of TXA or ACA reversed hyperfibrinolysis, but the efficient concentrations were dependent on the degree of fibrinolysis and whole-blood dilution.

C1-inhibitor efficiently inhibits Escherichia coli-induced tissue factor mRNA up-regulation, monocyte tissue factor expression and coagulation activation in human whole blood

Both the complement system and tissue factor (TF), a key initiating component of coagulation, are activated in sepsis, and cross-talk occurs between the complement and coagulation systems. C1-inhibitor (C1-INH) can act as a regulator in both systems. Our aim in this study was to examine this cross-talk by investigating the effects of C1-INH on Escherichia coli-induced haemostasis and inflammation. Fresh human whole blood collected in lepirudin was incubated with E. coli or ultrapurified E. coli lipopolysaccharide (LPS) in the absence or presence of C1-INH or protease-inactivated C1-INH. C3 activation was blocked by compstatin, a specific C3 convertase inhibitor. TF mRNA was measured using reverse transcription-quantitative polymerase chain reaction (RT-qPCR), and TF surface expression was measured by flow cytometry. In plasma, the terminal complement complex, prothrombin F1·2 (PTF1·2) and long pentraxin 3 (PTX3) were measured by enzyme-linked immunosorbent assay (ELISA). Cytokines were analysed using a multiplex kit. C1-INH (1·25-5 mg/ml) reduced both LPS- and E. coli-induced coagulation, measured as a reduction of PTF1·2 in plasma, efficiently and dose-dependently (P < 0·05). Both LPS and E. coli induced marked up-regulation of TF mRNA levels and surface expression on whole blood monocytes. This up-regulation was reduced efficiently by treatment with C1-INH (P < 0·05). C1-INH reduced the release of PTX3 (P < 0·05) and virtually all cytokines measured (P < 0·05). Complement activation was inhibited more efficiently with compstatin than with C1-INH. C1-INH inhibited most of the other readouts more efficiently, consistent with additional non-complement-dependent effects. These results indicate that complement plays a role in activating coagulation during sepsis and that C1-INH is a broad-spectrum attenuator of the inflammatory and haemostatic responses.

Regulation of monocyte/macrophage function by factor VII activating protease (FSAP)

OBJECTIVE

Factor VII activating protease (FSAP) is a novel regulator of vascular inflammation and hemostasis. However, the molecular mechanism by which circulating FSAP influences inflammatory events and progression of atherosclerosis is not yet entirely understood. Here we have investigated the influence of FSAP on monocyte/macrophage functions.

METHODS

We stimulated human monocyte-derived macrophages with FSAP and analyzed their cellular responses.

RESULTS

FSAP induced IκB-dependent NF-κB activation in a time- and concentration-dependent fashion. FSAP also activated the phosphorylation and proteolytic degradation of the inhibitor protein IκBα. The phosphorylation of the p65 subunit of NF-κB was induced by FSAP, which is known to contribute to the enhancement of DNA-binding activity of NF-κB. Concomitantly, FSAP up-regulated the expression of pro-inflammatory cytokines, matrix metalloproteinases, cell adhesion molecules and tissue factor. In the presence of FSAP there was increased monocytes adhesion and transendothelial migration in a beta2 integrin dependent manner.

CONCLUSIONS

Our findings suggest that FSAP activates the NF-κB pathway and the associated downstream pro-inflammatory factors in monocytic cells. This adds to a spectrum of FSAP effects on the vascular system that may explain its association with cardiovascular diseases.

The factor VII-activating protease (FSAP) enhances the activity of bone morphogenetic protein-2 (BMP-2)

Factor VII-activating protease (FSAP) is a circulating protease involved in the pathogenesis of atherosclerosis, calcification, and fibrotic processes. To understand how FSAP controls the balance of local growth factors, we have investigated its effect on the regulation of bone morphogenetic proteins (BMPs). BMP-2 is produced as a large pro-form and secreted as a mature heparin-binding growth factor after intracellular processing by pro-protein convertases (PCs). In this study, we discovered that FSAP enhances the biological activity of mature BMP-2 as well as its pro-form, as shown by osteogenic differentiation of C2C12 myoblasts. These findings were complemented by knockdown of FSAP in hepatocytes, which revealed BMP-2 processing by endogenous FSAP. N-terminal sequencing indicated that pro-BMP-2 was cleaved by FSAP at the canonical PC cleavage site, giving rise to mature BMP-2 (Arg(282)↓Gln(283)), as well as in the N-terminal heparin binding region of mature BMP-2, generating a truncated mature BMP-2 peptide (Arg(289)↓Lys(290)). Similarly, mature BMP-2 was also cleaved to a truncated peptide within its N-terminal region (Arg(289)↓Lys(290)). Plasmin exhibited a similar activity, but it was weaker compared with FSAP. Thrombin, Factor VIIa, Factor Xa, and activated protein C were not effective. These results were further supported by the observation that the mutation of the heparin binding region of BMP-2 inhibited the processing by FSAP but not by PC. Thus, the proteolysis and activation of pro-BMP-2 and mature BMP-2 by FSAP can regulate cell differentiation and calcification in vasculature and may explain why polymorphisms in the gene encoding for FSAP are related to vascular diseases.

Factor VII activating protease (FSAP) exerts anti-inflammatory and anti-fibrotic effects in liver fibrosis in mice and men

BACKGROUND & AIMS

Factor VII activating protease (FSAP) is a circulating serine protease produced in the liver. A single nucleotide polymorphism (G534E, Marburg I, MI-SNP) in the gene encoding FSAP (HABP2) leads to lower enzymatic activity and is associated with enhanced liver fibrosis in humans. FSAP is activated by damaged cells and its substrates include growth factors and hemostasis proteins.

METHODS

We have investigated the progression of liver fibrosis in FSAP deficient mice and FSAP expression in human liver fibrosis.

RESULTS

Serum FSAP concentrations declined in patients with end-stage liver disease, and hepatic FSAP expression was decreased in patients with advanced liver fibrosis and liver inflammation. Moreover, there was an inverse correlation between hepatic FSAP expression and inflammatory chemokines, chemokine receptors as well as pro-fibrotic mediators. Upon experimental bile duct ligation, FSAP(-/-) mice showed enhanced liver fibrosis in comparison to wild type mice, alongside increased expression of α-smooth muscle actin, collagen type I and fibronectin that are markers of stellate cell activation. Microarray analyses indicated that FSAP modulates inflammatory pathways.

CONCLUSIONS

Lower FSAP expression is associated with enhanced liver fibrosis and inflammation in patients with chronic hepatic disorders and murine experimental liver injury. This strengthens the concept that FSAP is a "protective factor" in liver fibrosis and explains why carriers of the Marburg I SNP have more pronounced liver fibrosis.

Circulating Nucleosomes and Neutrophil Activation as Risk Factors for Deep Vein Thrombosis

Objective—

The formation of neutrophil extracellular traps and the exposure of nucleosomes on these neutrophil extracellular traps contribute to coagulation activation and the propagation of deep vein thrombosis (DVT) in animal models. However, no data are available on the role of neutrophil extracellular traps or nucleosomes in patients with thrombosis.

Methods and Results—

We conducted a case–control study, in which levels of circulating nucleosomes and neutrophil elastase–α1-antitrypsin complexes were assessed in plasma from 150 patients with objectified symptomatic DVT (cases) and compared with 195 patients with a clinical suspicion of DVT but in whom DVT was excluded (controls). We explored the association between both nucleosomes and elastase–α1-antitrypsin complexes, and the presence of DVT by calculating the odds ratio with corresponding 95% CIs. Elevated levels of both circulating nucleosomes and elastase–α1-antitrypsin complexes were associated with a 3-fold risk of DVT, and the associations remained similar after adjustment for potential confounders (malignancy, smoking, recent immobilization, recent hospitalization). The risk increased with higher nucleosome and elastase–α1-antitrypsin complex levels, suggesting a dose-dependent relationship among circulating nucleosomes, activated neutrophils, and DVT.

Conclusion—

Our study suggests an association among circulating nucleosomes, activated neutrophils, and presence of DVT in humans, which might have implications for treatment and prevention.

Tissue factor pathway inhibitor is an inhibitor of factor VII-activating protease

BACKGROUND

Factor VII-activating protease (FSAP) is a serine protease that circulates in plasma in its inactive single-chain form and can be activated upon contact with dead cells. When activated by apoptotic cells, FSAP leads to the release of nucleosomes. The serpins C1-inhibitor and α(2) -antiplasmin are reported to be the major inhibitors of FSAP. However, regulation of FSAP activity by Kunitz-type inhibitors is not well studied.

OBJECTIVES

To compare the inhibition of FSAP activity and FSAP-induced nucleosome release from apoptotic cells by tissue factor pathway inhibitor (TFPI) with that of C1-inhibitor and α(2) -antiplasmin.

METHODS

Apoptotic cells were incubated with plasma or FSAP in presence of the inhibitor, and nucleosome release was analyzed with flow cytometry. Monoclonal antibodies against TFPI and altered forms of TFPI were used to investigate which domains of TFPI contribute to FSAP inhibition.

RESULTS AND CONCLUSIONS

We show that TFPI abrogates FSAP activity and nucleosome release from apoptotic cells. TFPI is a much more efficient inhibitor than C1-inhibitor or α(2) -antiplasmin. The active site of K2 is required for inhibition of FSAP. A direct binding interaction between FSAP and the C-terminal domain of TFPI is also required for efficient inhibition. Inhibition of FSAP-induced nucleosome release by recombinant TFPI might, in part, explain the anti-inflammatory effects of recombinant TFPI infusion observed in animal and human sepsis.

Plasma factor VII-activating protease antigen levels and activity are increased in ischemic stroke

BACKGROUND

Factor VII-activating protease (FSAP) is a recently discovered plasma protease with a role in the regulation of hemostasis and vascular remodeling processes. Higher levels and activity of FSAP have been reported in patients with deep vein thrombosis, but there are no data on plasma FSAP in ischemic stroke (IS).

OBJECTIVE

To investigate whether FSAP antigen levels and activity are associated with IS and/or etiologic subtypes of IS.

PATIENTS AND METHODS

To assess the potential association between FSAP and IS, plasma FSAP antigen levels and activity were measured in 600 consecutive IS patients and 600 population-based controls from the case-control study the Sahlgrenska Academy Study on Ischemic Stroke (SAHLSIS). Blood sampling was performed in the acute phase and 3 months after the index stroke. FSAP was also investigated at the genetic level by genotyping of 33 single-nucleotide polymorphisms.

RESULTS

Increased FSAP antigen level and activity, at both time-points, were independently associated with IS. Subtype analysis revealed similar associations for both FSAP measures, at both time-points, in all main IS subtypes. FSAP genotypes showed association with both FSAP plasma measurements, but not with IS.

CONCLUSIONS

Increased plasma FSAP antigen levels and activity were associated with IS and all main etiologic subtypes, suggesting a possible role for FSAP in the pathophysiology of IS, irrespective of the underlying etiology.

Factor VII-activating protease is activated in multiple trauma patients and generates anaphylatoxin C5a

Severe tissue injury results in early activation of serine protease systems including the coagulation and complement cascade. In this context, little is known about factor VII-activating protease (FSAP), which is activated by substances released from damaged cells such as histones and nucleosomes. Therefore, we have measured FSAP activation in trauma patients and have identified novel FSAP substrates in human plasma. Mass spectrometry-based methods were used to identify FSAP binding proteins in plasma. Anaphylatoxin generation was measured by ELISA, Western blotting, protein sequencing, and chemotaxis assays. Plasma samples from trauma patients were analyzed for FSAP Ag and activity, nucleosomes, C5a, and C3a. Among others, we found complement components C3 and C5 in FSAP coimmunoprecipitates. C3 and C5 were cleaved by FSAP in a dose- and time-dependent manner generating functional C3a and C5a anaphylatoxins. Activation of endogenous FSAP in plasma led to increased C5a generation, but this was not the case in plasma of a homozygous carrier of Marburg I single nucleotide polymorphism with lower FSAP activity. In multiple trauma patients there was a large increase in circulating FSAP activity and nucleosomes immediately after the injury. A high correlation between FSAP activity and C5a was found. These data suggest that activation of FSAP by tissue injury triggers anaphylatoxin generation and thereby modulates the posttraumatic inflammatory response in vivo. A strong link between C5a, nucleosomes, and FSAP activity indicates that this new principle might be important in the regulation of inflammation.

Factor VII-activating protease promotes the proteolysis and inhibition of tissue factor pathway inhibitor

OBJECTIVE

Factor VII-activating protease (FSAP) activates both factor VII and pro-urokinase and inhibits platelet-derived growth factor-BB, thus regulating hemostasis- and remodeling-associated processes in the vasculature. A genetic variant of FSAP (Marburg I polymorphism) results in low enzymatic activity and is associated with an enhanced risk of carotid stenosis and stroke. We postulate that there are additional substrates for FSAP that will help to explain its role in vascular biology and have searched for such a substrate.

METHODS AND RESULTS

Using screening procedures to determine the influence of FSAP on various hemostasis-related processes on endothelial cells, we discovered that FSAP inhibited tissue factor pathway inhibitor (TFPI), a major anticoagulant secreted by these cells. Proteolytic degradation of TFPI by FSAP could also be demonstrated by Western blotting, and the exact cleavage sites were determined by N-terminal sequencing. The Marburg I variant of FSAP had a diminished ability to inhibit TFPI. A monoclonal antibody to FSAP that specifically inhibited FSAP binding to TFPI reversed the inhibitory effect of FSAP on TFPI.

CONCLUSIONS

The identification of TFPI as a sensitive substrate for FSAP increases our understanding of its role in regulating hemostasis and proliferative remodeling events in the vasculature.