Studies of the variable expressivity of the factor V Leiden mutation: Disease-modulating role of the endothelium in factor V Leiden thrombophilia

• Applicants: Professor Dr. Bernd Pötzsch; Professor Dr. Heiko Rühl
• Subject Area: Hematology, Oncology ; Public Health, Healthcare Research, Social and Occupational Medicine
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 419450023

Why some carriers of the thrombophilic factor V Leiden mutation (FVL) develop thrombosis while others remain asymptomatic throughout life remains largely unknown. One possible explanation emerged from an in vivo model established by our group, in which thrombin and activated protein C (APC) formation is stimulated using recombinant activated factor VII. In this model, asymptomatic FVL carriers showed higher plasma levels of APC than those with a history of thrombosis. In the first funding phase, these subgroups were systematically examined for differences in the pathways of thrombin and APC generation as well as the fibrinolytic system. An ex vivo model of the protein C system, consisting of cultured patient-derived endothelial cells and autologous plasma, enabled personalized analysis of endothelial APC formation. The APC response, i.e., APC generation induced by thrombin stimulation, was significantly more pronounced in asymptomatic FVL carriers. No differences were observed in the expression of thrombomodulin (TM) and endothelial protein C receptor (EPCR), the inactivation kinetics of APC, or the influence of angiopoietin. Crossover experiments identified endothelial cells as the causal factor for the differences in APC response. These findings demonstrate that endothelial factors contribute to the variable clinical expressivity of the FVL mutation. Since 2025, the project has been continued in a second funding phase approved on the basis of a continuation proposal. The aim is to characterize the molecular mechanisms underlying the endothelial modulation of the APC response. Central to this are detailed investigations of key proteins of the protein C system, including TM, EPCR, and tissue factor pathway inhibitor (TFPI). These studies are combined with transcriptomic and proteomic analyses to identify regulatory differences between asymptomatic and symptomatic FVL carriers. Another target is endothelial factor V. The project examines how the FVL mutation affects its synthesis rate, cellular processing, and procoagulant activity. In addition, potential protective effects of elevated APC levels are investigated. In addition to its anticoagulant function, APC exerts anti-inflammatory and cytoprotective effects via protease-activated receptors (PAR), which are also a focus of the study. Furthermore, the role of APC in regulating the balance between coagulation and fibrinolysis is analyzed, with particular emphasis on thrombin-activatable fibrinolysis inhibitor (TAFI) and plasminogen activator inhibitor 1 (PAI-1). In the long term, the results are expected to contribute to personalized strategies for prevention, diagnosis, and therapy in hereditary thrombophilia due to the FVL mutation.

• DFG Programme: Research Grants
• Co-Investigators: Professor Dr. Jens Müller; Privatdozentin Dr. Sara Reda