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Updated: May 19, 2026
Measurement of Factor V Activity in Human Plasma Using a Microplate Coagulation Assay
Published on: September 9, 2012
The Marburg I polymorphism of factor VII activating protease is associated with low proteolytic and low pro-coagulant
1Department of Hematology/Transfusion Medicine, Paul Ehrlich Institute, Langen, Germany. michael.etscheid@pei.de
Introduction:
Factor VII activating protease (FSAP) is a plasma protease with FVII and pro-urokinase (pro-uPA) activating properties. A single nucleotide polymorphism (SNP) (Marburg I, MI) in the FSAP gene (HABP-2) leads to a low activity of the MI-FSAP towards pro-uPA, but supposedly not towards FVII and is described as a risk factor for athero-thrombosis and liver fibrosis. Recently we found, however, that FVII is an extremely poor substrate of FSAP and identified tissue factor pathway inhibitor (TFPI) as a novel substrate for FSAP. This prompted us to re-investigate the proteolytic activity profile of FSAP and to re-define its role in haemostasis.
Material And Methods:
Using purified protein and genotyped plasma samples, we systematically compared the activities of wild type (WT) and MI-FSAP towards natural plasma substrates. The influence of FSAP on coagulation was studied in prothrombin time assays.
Results:
FSAP from homozygous MI-carriers has a general low proteolytic activity making this variant a natural "knock-down". In human plasma WT-FSAP, but not MI-FSAP, accelerated the extrinsic coagulation by inactivation of TFPI. The diminished ability of MI-FSAP to cleave TFPI is reflected by a positive correlation between the FSAP enzymatic activity and cleaved TFPI in the circulation.
Conclusion:
Most likely TFPI cleavage by WT-FSAP occurs in vivo and contributes to an elevated level of endogenous FVIIa. This may explain why MI-FSAP is not a clear indicator for deep vein thrombosis in population studies. The loss of the pro-fibrinolytic protective function of FSAP in carriers of the MI-SNP may account for the association of the MI-SNP with atherosclerosis and thromboembolic complications.
Insights
The Marburg I (MI) variant of Factor VII activating protease (FSAP) exhibits reduced activity, particularly against tissue factor pathway inhibitor (TFPI). This deficiency in MI-FSAP impacts coagulation and may explain its association with thromboembolic complications.
Area of Science:
- Biochemistry and Molecular Biology
- Hematology and Thrombosis Research
- Genetics and Cardiovascular Disease
Background:
- Factor VII activating protease (FSAP) is a plasma protease involved in coagulation and fibrinolysis.
- A specific SNP, Marburg I (MI), in the FSAP gene (HABP-2) results in reduced FSAP activity.
- Previous findings suggested MI-FSAP has low activity towards pro-urokinase (pro-uPA) but not FVII, linking it to athero-thrombosis and liver fibrosis.
Purpose of the Study:
- To re-evaluate the proteolytic activity profile of FSAP, specifically comparing wild type (WT) and MI variants.
- To investigate the role of FSAP and its MI variant in hemostasis, focusing on novel substrates.
- To clarify the mechanism behind the association of the MI-SNP with athero-thrombotic and thromboembolic diseases.
Main Methods:
- Systematic comparison of WT-FSAP and MI-FSAP activities using purified proteins and genotyped plasma samples.
- Assessment of FSAP's influence on coagulation through prothrombin time assays.
- Investigation of FSAP's interaction with natural plasma substrates, including tissue factor pathway inhibitor (TFPI).
Main Results:
- Homozygous MI-FSAP exhibits generally low proteolytic activity, acting as a natural 'knock-down' variant.
- WT-FSAP, but not MI-FSAP, accelerated extrinsic coagulation by inactivating TFPI in human plasma.
- A positive correlation was observed between FSAP enzymatic activity and cleaved TFPI levels in circulation, reflecting MI-FSAP's diminished TFPI cleavage.
Conclusions:
- WT-FSAP-mediated TFPI cleavage likely occurs in vivo, contributing to elevated endogenous FVIIa levels.
- The reduced TFPI inactivation by MI-FSAP may explain why MI-FSAP is not a definitive marker for deep vein thrombosis.
- The loss of FSAP's pro-fibrinolytic function in MI-SNP carriers could underlie its association with atherosclerosis and thromboembolic complications.
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