Platelets have more than one binding site for von Willebrand factor.

Abstract

A B ST R A CT The binding of '251-von Willebrand factor to platelets stimulated by thrombin, ADP, and a combination of ADP + epinephrine (EPI) is specific, saturable, and reversible. Active platelet metabolism and divalent cations are required for binding induced by these stimuli, but not by ristocetin, suggesting the existence of different mechanisms involved in the vWF-platelet interaction. A monoclonal antibody directed against an epitope of membrane glycoprotein (GP) lb had no effect on the binding of '251-vWF to normal platelets stimulated by thrombin or a combination of ADP + EPI, but completely blocked ristocetin-induced binding. Binding induced by thrombin to GPIb-blocked platelets was specific. Moreover, thrombin-induced binding of 1251-vWF was increased, rather than decreased, in two patients with the Bernard-Soulier syndrome whose platelets lacked GPIb. Conversely, monoclonal antibodies directed against the GPIIb/IIIa complex had no effect on ristocetininduced binding of (vWF)' is a large multimeric glycoprotein that circulates in blood complexed with the Factor VIII procoagulant activity protein (1). It plays an essential role in platelet function as shown by the prolonged bleeding time in von Willebrand disease (1). Specific binding sites for vWF are induced on the platelet membrane by the antibiotic ristocetin (2), a nonphysiologic agent, as well as by thrombin (3, 4) and ADP (5). Platelet membrane glycoprotein (GP) lb is considered to function as the surface receptor for vWF (6). In the Bernard-Soulier syndrome, a congenital bleeding disorder, platelets lack GPIb (7) and the ristocetin-induced binding of vWF is decreased (8). On the other hand, in Glanzmann thrombasthenia, another congenital platelet abnormality, there is a marked decrease of the membrane GP complex Ilb/Illa but normal content of GPIb (9). The ristocetin-induced binding of vWF to thrombasthenic platelets has been reported to be normal (8). In contrast, we have recently shown that binding of vWF to thrombasthenic platelets stimulated by thrombin is severely deficient (4). Therefore, we postulated that different sites are involved in ' Abbreviations used Marguerie et al. (12). The final platelet suspensions were all in modified calcium-free Tyrode buffer, containing 137 mM NaCI, 2 mM MgCI2, 0.42 mM NaH2PO4, 11.9 mM NaHCO3, 2.9 mM KCI, 5.5 mM glucose, 10 mM Hepes, pH 7.35, and 20 mg/ml bovine serum albumin (Fraction V, CalbiochemBehring Corp., American Hoechst Corp., San Diego, CA). When experiments of serotonin release were performed, PRP was labeled before washing by incubating 20 ml with 0. (3.3,M). However, ADG-washed platelets usually gave reversible aggregation to ADP and were unresponsive to epinephrine (EPI). On the contrary, gel-filtered platelets always gave irreversible aggregation to ADP, and responded to 20 MM EPI in the presence of fibrinogen (3.3 ,M) with a typical two-wave aggregation. Contamination of plasma vWF in all washed platelet preparations was below 5 X 10' U/dl (1 dl of a normal plasma pool contains ...

Von Willebrand factor-binding protein is a hysteretic conformational activator of prothrombin

“…In the context of endocarditis, the initial vascular injury of the endothelium on heart valves at high shear rates activates coagulation, with VWF mediating the early stages of platelet accumulation by tethering through exposed subendothelial collagen and the platelet GPIb␣ receptor, followed by conversion of Fbg to Fbn within the thrombus (29). Additional binding of platelets by VWF occurs after platelet activation by thrombin and depends on the platelet integrin ␣ IIb ␤ 3 (30). S. aureus concurrently adheres to multiple extracellular matrix proteins, including fibronectin, collagen, and Fbn, through microbial surface components recognizing adhesive matrix molecules (MSCRAMMs) (31).…”

Cochlin in the eye: Functional implications

“…The von Willebrand A (vWFA) is a well studied domain participating in shear-induced self-aggregation and in cell adhesion (Ruggeri et al, 1983;Tuckwell, 1999). A number of human diseases are associated with mutations in vWFA domains (Whittaker and Hynes, 2002).…”

“…The vWFA domains have also been implicated in host defense mechanisms and in hemostasis as complement factor C, factor B, integrins LFA-1, Mac-1, VLA-1 and 2, p150 and p95 are part of the immune system that harbor vWF domains (Colombatti and Bonaldo, 1991;Colombatti et al, 1993). A number of proteins such as collagen, GpIbα, and integrin αIibβ3 are known to interact with vWF domains (Ruggeri et al, 1983;Eble and Tuckwell, 2003;Vanhoorelbeke et al, 2003). Many of these interactions play a role in different regimes of fluid dynamics (Shankaran et al, 2003) and have been implicated in adherence to platelets and possibly also to macrophages.…”

A mechanobiological investigation of platelets

“…Thrombospondin platelet aggregation (20) cofactor in coagulation (22), not enzymatically active encourages angiogenesis (14) heparin antagonist (16), angiogenesis inhibitor (23) clotting factor, stimulates neutrophils (chemotaxis, degranulation, adhesion) (24) maintains blood volume (25); impairs platelet aggregation (26) platelet adhesion (16) angiogenesis inhibitor (14); platelet adhesion (16) von Willebrand factor (vWF) (platelets, endothelial platelet-platelet adhesion (16) binds to thrombin cells) and ADP (27) Evidently, the platelet is one essential blood component regulating the haemostatic process because of its adhesive, aggregative and clotting abilities that govern the coagulation cascade. For the same reasons, the platelet is also significant in pathological thrombosis.…”