Procoagulant platelet activation promotes venous thrombosis.

• Procoagulant platelets are found in the circulation and thrombi of mammals with deep vein thrombosis

• Genetic or pharmacological interference with procoagulant platelet activation ameliorates flow reduction-induced DVT formation.

Platelets are key players in cardiovascular disease and platelet aggregation represents a central pharmacological target, particularly in secondary prevention. However, inhibition of adenosine diphosphate and thromboxane signaling has low efficacy in preventing venous thromboembolism, necessitating the inhibition of the plasmatic coagulation cascade in this disease. Anticoagulation carries a significantly higher risk of bleeding complications, highlighting the need of alternative therapeutic approaches. We hypothesized that procoagulant activation (PA) of platelets promotes venous thrombus formation and that targeting PA could alleviate venous thrombosis. Here, we found elevated levels of procoagulant platelets in the circulation of patients with deep vein thrombosis (DVT) and pulmonary embolism, and in mice developing DVT following inferior vena cava stenosis. Further, we detected procoagulant activation of recruited platelets within murine and human venous thrombi. Mice with platelet-specific deficiency in central pathways of procoagulant activation - cyclophilin D and transmembrane protein 16F - were more resistant towards low flow-induced venous thrombosis. Finally, we found that a clinically approved carbonic anhydrase inhibitor, methazolamide, reduced platelet procoagulant activity and alleviated murine thrombus formation without affecting trauma-associated hemostasis. These findings identify an essential role of platelet procoagulant function in venous thrombosis and delineate novel pharmacological strategies targeting platelets in preventing venous thromboembolism.