Adhesion Mechanisms in Platelet Function

Abstract

Abstract-Platelet adhesion is an essential function in response to vascular injury and is generally viewed as the first step during which single platelets bind through specific membrane receptors to cellular and extracellular matrix constituents of the vessel wall and tissues. This response initiates thrombus formation that arrests hemorrhage and permits wound healing. Pathological conditions that cause vascular alterations and blood flow disturbances may turn this beneficial process into a disease mechanism that results in arterial occlusion, most frequently in atherosclerotic vessels of the heart and brain. Besides their relevant role in hemostasis and thrombosis, platelet adhesive properties are central to a variety of pathophysiological processes that extend from inflammation to immune-mediated host defense and pathogenic mechanisms as well as cancer metastasis. All of these activities depend on the ability of platelets to circulate in blood as sentinels of vascular integrity, adhere where alterations are detected, and signal the abnormality to other platelets and blood cells. In this respect, therefore, platelet adhesion to vascular wall structures, to one another (aggregation), or to other blood cells, represent different aspects of the same fundamental biological process. Detailed studies by many investigators over the past several years have been aimed to dissect the complexity of these functions, and the results obtained now permit an attempt to integrate all the available information into a picture that highlights the balanced diversity and synergy of distinct platelet adhesive interactions. (Circ Res. 2007;100:1673-1685.)Key Words: adhesion molecules Ⅲ platelets Ⅲ vascular biology Ⅲ extracellular matrix Ⅲ collagen P latelets in mammals are anucleated cells that originate from the cytoplasm of bone marrow megakaryocytes 1 and circulate in blood as sentinels of vascular integrity. They show no interaction with the inner surface of normal vessels but adhere promptly where endothelial cells are altered or extracellular matrix substrates are exposed. 2 This is a critical initial step in hemostasis and thrombosis, as well as in inflammatory 3,4 and immunopathogenic responses. 5 The functions of mammalian platelets are conserved throughout evolution and closely reflect those of nucleated thrombocytes in all other vertebrates. 6 -9 After adhering to vascular lesions, platelets can rapidly recruit to the site of injury additional platelets, which are necessary to achieve hemostasis, or different types of leukocytes, which set off host defense responses. Such selective recruitment is orchestrated by activation pathways stimulated by the initial adhesive interactions and by soluble agonists released or generated locally, which lead to the appearance on the platelet membrane of different adhesive molecules capable of attracting distinct circulating cells. Platelet adhesion in a broad sense is the Original received January 2, 2007; revision received March 13, 2007; accepted April 11, 2007 study of the adhesive p...

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