Abstract 8689: Platelet CD40 Receptor Expression Accelerates Platelet Induced Atherogenesis

Abstract

Beyond an eminent role in hemostasis and thrombosis, platelets are important mediators of inflammation and protagonists of atherogenesis. Here we investigated the inflammatory propensity of platelet-specific expression of the CD40 receptor, an integral membrane protein of the tumor necrosis factor receptor (TNF-R) family. Besides its presence on immune and other cell types the CD40 receptor is constitutively expressed on platelets where its function remains unknown. Platelets were isolated from Apoe−/− or Cd40−/−Apoe−/− mice, activated with thrombin, and injected (3x107 platelets, i.v.), into 17-week-old Apoe−/− mice every 5 days for 12 weeks. Compared to infusion of activated Apoe−/− (wild type) platelets, injection of activated Cd40−/−Apoe−/− platelets caused a 73% decrease in plaque size (Apoe−/− platelets 18.3x104 + 2.7x104 μm2 vs Cd40−/−Apoe−/− platelets 6.7 x104 + 2.1 x104 μm2, Vehicle 9.8 x104 + 2.8 x104 μm2, p<0.05) in the aortic arch. Absence of CD40 on platelets reduced the absolute number of plaque macrophages (Mac-3) by 39% but did not affect the content of CD45+ cells and CD3+ T lymphocytes. Flow cytometric analysis revealed an elevated number of circulating Ly6G+ neutrophils (+32%) upon injection of activated platelets. However, this increase was absent when CD40-deficient platelets, were injected highlighting the inflammatory potential of platelets and a central role for CD40 in this process. In addition, we detected a 20% decrease in the formation of platelet-leukocyte aggregates in vitro while intravital microscopy in carotid arteries showed a 2-fold decrease of platelet adhesion to the vessel wall of mice, injected with activated Cd40-/- platelets, In sum, this study reveals that platelet CD40 promotes atherosclerosis by interaction with both neutrophils and endothelial cells, thereby amplifying leukocyte recruitment to sites of vascular injury.