Platelet Function in Thrombosis and Hemostasis.

Abstract

Platelets represent the main effectors in the formation of the initial hemostatic plug through an elaborate response to vascular injury, and furthermore, platelets play an essential role in secondary hemostasis.1 However, platelets are also important contributors to pathological thrombus formation and vessel occlusion when activated inappropriately. Moreover, platelets contribute to processes beyond hemostasis and thrombosis such as inflammation, wound healing, and maintenance of vascular integrity.2 In the present issue of Seminars inThrombosis &Hemostasis, the focus is on the physiology of platelets as well as diagnostic issues, both as regard to bleeding disorders and thromboembolic risk. In a series of articles, the issue provides an overviewof some of themain conditions influencing platelet function and of different diagnostic approaches to investigating platelet function. The role of platelets in cardiovascular disease and venous thromboembolism and the effect of antiplatelet drugs are reviewed and discussed in another series of articles. First, Lassila introduces the reader to the overall role of platelets as well as issues to consider when testing platelet function in bleeding disorders.3 Following this introduction, Gremmel et al provide a comprehensive review on platelet physiology, with particular focus on structure, granules, surface glycoproteins, and activation pathways.4 The authors illustrate how new imaging techniques have improved the knowledge on platelet structure, secretion, adhesion, and activation, and how these techniques have expanded our understanding of the role of platelets in health and disease. Recent research has revealed platelets as more active components of the immune system besides the previously considered passive immune-modulatory role. Through a cross-talk with the immune system, platelets have emerged as both critical modulators of atherothrombosis and vascular inflammation and as effector cells in the combat of microbial infection. Chatterjee and Geisler provide an overview of the complex area of platelet-derived targets involved in inflammatory pathways and platelets as regulator of the immune system.5 Although platelets are anucleate cells, they retain many of the RNA metabolic processes of nucleated cells. Lindsay and Edelstein outline the current knowledge as regard to platelets and microRNA, and the possible role for platelet function in disease and in the regulation of platelet physiology.6 The subsequent section contains reviews on the role of platelets in several disease entities. First, Pasalic et al discuss biomarkers of cardiovascular disease with focus on the role of platelets.7 They also provide a comprehensive review presenting the significance of measures of platelet activity and platelet aggregation as risk markers of cardiovascular disease. Several methods of platelet function testing have been evaluated for these conditions, but these data remain conflicting, and platelet biomarkers have not beenwidely incorporated in cardiovascular risk scores so far. The risk of cardiovascular disease among patients with type 2 diabetes mellitus has attracted increased attention during the recent decades. The significance is underlined by the fact that patients with prediabetes also have an increased risk of cardiovascular events.8 Therefore, Neergaard-Petersen et al summarize current knowledge on the potential cardiovascular role of platelets in patients with diabetes.9 This review also provides an updated status on the benefits and limitations of antiplatelet therapy in diabetic patients with cardiovascular disease. As regard to thromboembolic disease, platelets have been ascribed far more significance in arterial cardiovascular disease than in venous thromboembolic disease. MontoroGarcia et al present recent evidence suggesting that platelets may play a more important role in venous thromboembolism than previously anticipated.10 This review also discusses the potential applications of platelets as novel risk factors for venous thromboembolic disease. The authors additionally point to future important issues, such as whether the contribution of platelet-associated risk factors is dependent on