Double-edged sword: flavivirus NS1 enhances human plasmin-mediated fibrinolysis while being targeted for cleavage and...

Dengue virus (DENV) is the most prevalent arbovirus in the world, being transmitted to humans through the bite of infected Aedes mosquitoes. Symptomatic individuals may develop a haemorrhagic fever leading to plasma leakage, hypovolaemic shock and death. A key player in viral pathogenesis is the non-structural protein 1 (NS1), which is secreted by infected cells and disrupts platelet and endothelial barrier function, contributing to plasma extravasation. Importantly, dengue patients present abnormal haemostasis, with concomitant activation of both coagulation and fibrinolytic systems correlating with disease severity. However, a direct role played by NS1 in fibrinolysis has never been shown. Here, we investigated the interaction between NS1 and plasminogen, the precursor of the fibrinolytic enzyme plasmin, aiming to characterize its implications in clot turnover during infection. We showed that binding of plasminogen to NS1 is dependent on lysine-binding sites in plasminogen, implicating NS1 as a plasmin substrate. We also demonstrated that NS1 is cleaved by plasmin, which, in turn, blocks its effect on endothelial glycocalyx layer disruption and endothelial hyperpermeability. Using euglobulin clot lysis assays, we showed that DENV NS1 enhances fibrin clot lysis and that this effect is conserved for other flaviviruses, including Zika and West Nile viruses. Altogether, we identified a novel mechanism by which NS1 might contribute to bleeding disorders, highlighting the relevance of the plasminogen/plasmin system for DENV pathogenesis in humans.