CCL21 Enhances Platelet Activation and Atherothrombosis via CCR7 Activation

The homeostatic chemokine CCL21 (C-C motif chemokine ligand 21) is abnormally elevated in coronary artery disease. Plasma CCL21 levels have been found to be independently associated with adverse outcomes after acute coronary syndrome. However, the specific effects of CCL21 on coronary artery disease-associated platelet activation and thrombosis remain poorly understood.

We examined the effects of CCL21 on platelet activation, spreading, clot retraction, in vitro shear stress-induced thrombus formation, in vivo arterial thrombus formation, middle cerebral artery occlusion-induced brain injury, and myocardial ischemia-reperfusion injury. We also investigated the underlying mechanisms and the therapeutic impacts of a CCL21 antibody on platelet activation and in vivo thrombosis in atherosclerosis.

CCL21 potentiated agonist-induced platelet activation, including aggregation, dense granule release, P-selectin exposure, integrin αIIbβ3 activation, spreading, and clot retraction. Furthermore, CCL21 enhanced in vivo thrombosis, whole blood thrombus formation, and middle cerebral artery occlusion-induced brain injury. Mechanistically, CCL21 binds to platelet CCR7 (C-C motif chemokine receptor 7), a G-protein-coupled receptor previously unreported in platelets, activating Gi (inhibitory G protein) and G13 signaling pathways to enhance platelet activation. A CCL21 antibody attenuated platelet activation and inhibited in vivo thrombosis in patients with coronary artery disease and atherosclerotic ApoE^-/- mice. In addition, this antibody mitigated microvascular thrombosis, safeguarding the hearts of atherosclerotic ApoE^-/- mice from severe ischemia-reperfusion injury.

CCL21 enhances platelet activation and atherothrombosis by binding to platelet CCR7 and thus activating downstream Gi and G13 signaling pathways. A CCL21 antibody can counteract these effects in the context of coronary artery disease, supporting its potential as a preventive therapy for thrombotic complications.