Hyperreactivity of Junctional Adhesion Molecule A-Deficient Platelets Accelerates Atherosclerosis in Hyperlipidemic Mice

Rationale: Besides their essential role in hemostasis, platelets also have functions in inflammation. In platelets, junctional adhesion molecule (JAM)-A was previously identified as an inhibitor of integrin alpha(IIb)beta(3)-mediated outside-in signaling and its genetic knockdown resulted in hyperreactivity. Objective: This gain-of-function was specifically exploited to investigate the role of platelet hyperreactivity in plaque development. Methods and Results: JAM-A-deficient platelets showed increased aggregation and cellular and sarcoma tyrosine-protein kinase activation. On alpha(IIb)beta(3) ligation, JAM-A was shown to be dephosphorylated, which could be prevented by protein tyrosine phosphatase nonreceptor type 1 inhibition. Mice with or without platelet-specific (tr) JAM-A-deficiency in an apolipoprotein e (apoe(-/-)) background were fed a high-fat diet. After <= 12 weeks of diet, trJAM-A(-/-) apoe(-/-) mice showed increased aortic plaque formation when compared with trJAM-A(+/+) apoe(-/-) controls, and these differences were most evident at early time points. At 2 weeks, the plaques of the trJAM-A(-/-) apoe(-/-) animals revealed increased macrophage, T cell, and smooth muscle cell content. Interestingly, plasma levels of chemokines CC chemokine ligand 5 and CXC-chemokine ligand 4 were increased in the trJAM-A(-/-) apoe(-/-) mice, and JAMA-deficient platelets showed increased binding to monocytes and neutrophils. Whole-blood perfusion experiments and intravital microscopy revealed increased recruitment of platelets and monocytes to the inflamed endothelium in blood of trJAM-A(-/-) apoe(-/-) mice. Notably, these proinflammatory effects of JAM-A-deficient platelets could be abolished by the inhibition of a alpha(IIb)beta(3) signaling in vitro. Conclusions: Deletion of JAM-A causes a gain-of-function in platelets, with lower activation thresholds and increased inflammatory activities. This leads to an increase of plaque formation, particularly in early stages of the disease.