Plg-RKT facilitates plasminogen incorporation and restrains thrombus growth under arterial shear in mice.

Platelets bind plasminogen facilitating surface-bound plasmin generation. We previously reported that the plasminogen receptor, Plg-RKT, retains plasminogen on activated platelets. Here, we investigate the significance of the interaction of Plg-RKT on thrombus formation, growth and stability. Whole blood from Plg-RKT-/- or littermate Plg-RKT+/+ mice was flowed over collagen/tissue factor-coated microfluidic biochips at 250 or 1000 s-1 to reflect venous and arterial shear rates. AlexaFluor488-fibrinogen and Dylight633-labelled-plasminogen accumulation was monitored in real-time by fluorescence microscopy in the presence or absence of tissue plasminogen activator (tPA). At 1000 s-1, plasminogen accumulation was reduced in thrombi formed from Plg-RKT-/- mice compared to Plg-RKT+/+ mice. Fibrin(ogen) accumulation in Plg-RKT-/- mice persisted for the duration of the experiment, indicating impaired fibrinolysis compared to Plg-RKT+/+ mice. Mice were subjected to FeCl3 carotid artery model of thrombosis followed by tPA infusion. Initial platelet deposition was faster in Plg-RKT-/- mice compared to Plg-RKT+/+ mice. Fibrin(ogen) accumulation and persistence was enhanced in Plg-RKT-/- mice indicating impaired fibrinolysis. We demonstrate for the first time that under arterial shear, Plg-RKT facilitates plasminogen incorporation and limits both platelet recruitment to the forming thrombus and fibrin accumulation. These data highlight that Plg-RKT and potentially plasmin on the platelet surface regulate arterial thrombus growth.