Von Willebrand factor accelerates platelet adhesion and thrombus formation on a collagen surface in platelet-reduced blood under flow conditions

Abstract

Plasma von Willebrand factor (VWF) has been identified as an indispensable factor for platelet adhesion and thrombus formation on a collagen surface under flow conditions. VWF binds to collagen and then tethers platelets to the collagen surface through interaction with platelet glycoprotein Ib and also contributes to the thrombus formation on the collagen surface. In the present study, we demonstrated that the addition of VWF/factor VIII complex or purified VWF (> 2 ristocetin cofactor activity units/mL) increased platelet adhesion to the collagen surface in platelet-reduced blood (ϳ 5 ؋ 10 4 platelets/L) to the normal level. VWF had no stimulatory effect when it was allowed to bind to the collagen surface before blood flow was initiated. Addition of an excess of FITC (fluorescein-5-isothiocyanate)-labeled VWF to platelet-reduced blood under these flow conditions demonstrated that the VWF was mainly incorporated into the platelet aggregates. These results indicated that the supplemented VWF stimulates the platelet adhesion onto the collagen surface by enhancing platelet aggregation in the platelet-reduced condition. This also suggests a possibility that supplementation of VWF to individuals with thrombocytopenia might be effective for increasing their hemostatic potential. ( IntroductionProper formation of a platelet plug at sites of vascular injury requires a spatially and temporally coordinated series of events that allow circulating platelets to adhere onto exposed collagen, become activated, and recruit additional platelets, and form multicellular aggregates, including platelets that are stabilized by fibrin. Von Willebrand factor (VWF), an adhesive plasma glycoprotein, has been indicated to play fundamental roles in the platelet plug formation under physiologic conditions. 1-4 VWF is composed of identical disulfide-linked subunits, each comprising 2050 amino acid residues and up to 22 carbohydrate chains for a total mass of 250 kDa. 5 VWF subunits are crosslinked at the COOH-terminal ends to form a dimer, and the dimer is further converted to a multimeric form with molecular mass from 5 ϫ 10 2 kDa to 2 ϫ 10 4 kDa by intersubunit disulfide linkages at the NH 2 -terminal ends of the dimers. 6 VWF is present in the circulation at a plasma concentration of 5 to 10 g/mL. It is also released from ␣-granules of megakaryocytes and platelets and Weibel-Palade bodies of endothelial cells. 7,8 VWF was shown to have a critical role in platelet adhesion to a collagen surface under flow conditions, especially under high shear rate. 4,9,10 Although platelets do not bind human VWF in solution under low shear rate, VWF binds reversibly with platelet glycoprotein (GP) Ib under high shear rate, and shear stress induces a permanent interaction between VWF and integrin ␣ ⌱⌱b ␤ 3 (GPIIb/IIIa) after the initial binding of GPIb with VWF. 1,11 Moroi et al 12 found that the reversible binding of platelets to immobilized VWF and the tethering speed of platelets was related to the density of VWF on the surface. These and many other r...

Fibrin Affinity of Erythrocyte-Coupled Tissue-Type Plasminogen Activators Endures Hemodynamic Forces and Enhances Fibrinolysis in Vivo

“…The important role of hemodynamic forces in the RBC/PA behavior is concordant with effects of shear stress on coagulation and clot lysis, adhesion of factor VIII to collagen, platelet activation, and adhesion of blood cells to endothelium (Anand and Diamond, 1996;Fisher and Kohnert, 1997;Falati et al, 2002;Einav and Bluestein, 2004;Frenette, 2004;Leytin et al, 2004;Tomokiyo et al, 2005). Most in vitro studies of antithrombotic drugs have been performed in static models.…”

A mechanism to safeguard platelet adhesion under high shear flow: von Willebrand factor–glycoprotein Ib and integrin α2β1–collagen interactions make complementary, collagen‐type‐specific contributions to adhesion

“…Factor VIII‐free VWF was kindly provided by K. Tomokiyo (The Chemo‐Sero‐Therapeutic Research Institute, Kumamoto, Japan) [6], and the purified VWF was radiolabeled with Na 125 I using IODOBEADS (Pierce Biochemicals, Rockford, IL, USA) according to the manufacturer’s instructions (specific activity: 500–1000 cpm ng −1 of VWF).…”

“…This is the first reaction in platelet interaction with the collagen surface under blood flow, and deficiency in one of these proteins induces severe loss of platelet adhesion. VWF also functions in thrombus formation [4–6]. At this stage, VWF interacts with both gpIb/IX/V and integrin α IIb β 3 , thereby contributing to the formation of large thrombi.…”

Proteins, platelets, and blood coagulation at biomaterial interfaces

“…In considering surface-induced thrombosis, albumin is generally considered to be inert towards platelet adhesion and activation 19 , while fibrinogen is a central protein in the process of biomaterial-induced thrombosis 20–22 . Other plasma proteins such as fibronectin 23,24 , vitronectin 25,26 , and von Willebrand factor (vWF) 27,28 , have been shown to be capable of mediating platelet adhesion to materials when pre-adsorbed to the surface. These adsorbed proteins can bind to platelets via cell membrane receptors such as GPIIb/IIIa (known as integrin α IIb β 3 ), GPIb, and other receptors, and such binding will induce platelet adhesion and aggregation.…”