Abstract 230: Disturbed Blood Flow-induced Platelet Transmigration Via C-type Lectin-like Receptor-2 Modulating Vascular Inflammation

Abstract

Atherosclerosis preferentially develops at sites under disturbed blood flow (d-flow) that leads to steep multidirectional gradients of wall shear stress at vascular predilection sites, promoting an oxidative, proapoptotic, and proinflammatory gene expression profile in endothelial cells. Sustained d-flow causes endothelial injury characterized by leukocyte infiltration, endothelial barrier dysfunction, and eventually the formation of atherosclerotic plaques. While previous studies suggest a proinflammatory role of platelets via promoting leukocyte activation in atherogenesis, whether and how platelets are regulated by d-flow remains largely unclear. In this study, we showed that d-flow induced by partial carotid ligation (PCL) causes platelet adhesion, endothelial damage and leukocyte recruitment in mice. Unexpectedly, PCL induces platelet transmigration into the subendothelial space. Transmigrated platelets at 2 days of PCL appeared inside the intercellular crevices beneath the damaged endothelium. After sustained d-flow (5-7 days after PCL), more adherent leukocytes and platelets with pseudopodia were observed in the seriously damaged endothelium. In investigating the mechanism of this unexpected observation, we found that mice with platelet-specific deficiency of C-type lectin-like receptor-2 (CLEC-2) showed ~80% reduction in platelet endothelial accumulation and no subendothelial localization of platelets under d-flow, indicating an essential role of CLEC-2 in mediating platelet transmigration. Enhanced platelet transmigration exacerbated monocyte accumulation, while leukocyte depletion or PSGL-1 deletion did not affect platelet transmigration under d-flow. Our results revealed unprecedented platelet transmigration mediated by CLEC-2 in the rheological regulation of vascular homeostasis, controlling vascular inflammation.