Platelets: Small in Size But Essential in the Regulation of Vascular Homeostasis - Translation From Basic Science to Clinical Medicine.

Platelets are small blood cells that adhere to the site of vessel injury where von Willebrand factor (VWF) is expressed. Platelets bind to VWF through interaction with a membrane protein, glycoprotein (GP) Ibα. Next, the accumulated platelets are activated to change their morphological and biochemical characteristics. Various vasoactive substances, such as immune-regulatory CD40 ligand, are released locally from activated platelet cells to maintain homeostasis of the vascular system. Major roles played by platelets in the regulation of hemostasis and thrombus formation include local activation of the coagulation cascade. Translocation of negatively charged phospholipids to the surface of activated platelets helps in the formation of prothrombinase complex, which efficiently produces thrombin. Thrombin produces fibrin around the activated platelets and further activates the platelets through thrombin receptor stimulation. Of the various platelet-stimulating receptors and activation signals, cyclo-oxygenase-1, P2Y12 adenosine 5'-diphosphate receptor, and thrombin receptor (protease activated receptor)-1 blockers are used clinically as antiplatelet agents. In the future, precise understanding of the quantitative contribution of platelet function in hemostasis and pathological thrombus formation should lead to the development of effective antithrombotic agents without increasing the risk of serious bleeding complications.