Key Points

  • Impaired cell surface tissue plasminogen activator-dependent plasmin generation is associated with venous thromboembolism.

  • Reduced expression of the cell surface fibrinolytic co-receptor, annexin A2, may constitute a risk factor for venous thromboembolism.

Reduced plasma fibrinolysis has been identified as a potential risk factor for venous thromboembolism (VTE), but the role of cell surface fibrinolysis in VTE is unknown. The annexin A2/S100A10 complex serves as a co-receptor for plasminogen and tissue plasminogen activator (tPA), augmenting plasmin generation by 60-fold on the endothelial cell surface. Several studies in both mice and humans support the concept that A2 regulates fibrin homeostasis and intravascular thrombosis in vivo. Here, we examined A2 protein expression and function in 115 adult subjects with venous thromboembolism (VTE) and 87 healthy controls. Using peripheral blood mononuclear cells (PBMCs) as a surrogate for endothelial cells, we found a 41% mean decrease in cell surface tPA-dependent fibrinolytic activity in subjects who had a positive personal and family history of VTE, but tested negative for known inherited thrombophilias. A2 protein was reduced on average by 70%, and mRNA levels by 30%, but neither decrease correlated with anticoagulant therapy. [Sentence omitted] Neither cell A2 protein nor cell surface plasmin generation correlated with plasma-based clot lysis times, suggesting that the plasma and cell surface fibrinolytic systems operate independently of one another. These data suggest that reduced expression of annexin A2 protein is associated with cell surface hypofibrinolysis and may represent a novel risk factor for inherited thrombophilia.

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