Homophilic Interactions of Platelet F11R/JAM-A with Its Surface-Bound Counterpart Facilitate Thrombus Formation

F11Receptor/junctional adhesion molecule-A (F11R/JAM-A) is a transmembrane protein expressed in endothelial cells, epithelial cells, and in blood platelets. In blood platelets, F11R/JAM-A participates in adhesion under static conditions, suppresses the activation of the platelet α_IIbβ₃ integrin and was shown to activate blood platelets as soluble form via homophilic interactions.The purpose of presented study was to evaluate whether F11R/JAM-A is involved in platelet adhesion under flow conditions and in thrombus formation.F11R/JAM-A contribution to platelet adhesion under flow conditions was assessed using flow chamber assay. Monoclonal antibodies and recombinant F11R/ JAM-A were used to assess the effects of F11R/JAM-A blockade on platelet aggregation and thrombus formation using total thrombus formation analysis system. Effects of F11R/JAM-A blockade on thrombus formation in vivo were evaluated in murine models of carotid artery injury.F11R/JAM-A was not capable of capturing flowing blood platelets alone but enhanced platelet adhesion to fibrinogen under flow conditions. Blocking of F11R/JAM-A homophilic interactions with specific monoclonal antibodies or with recombinant F11R/JAM-A impaired thrombus formation in vitro in human blood and in vivo in the models of thrombosis in mice.Interactions of F11R/JAM-A located on flowing platelets with its surface-bound counterpart enhance platelet binding to fibrinogen under high shear stress conditions. Blocking of these homophilic interactions compromises thrombus formation. While previously published studies pointed at a significant role of soluble F11R/JAM-A in priming platelets during thrombus formation, our results highlight the role of surface-bound F11R/JAM-A in this process.