A revised model of platelet aggregation
Suhasini Kulkarni, … , Francois Lanza, Shaun P. Jackson
Suhasini Kulkarni, … , Francois Lanza, Shaun P. Jackson
Published March 15, 2000
Citation Information: J Clin Invest. 2000;105(6):783-791. https://doi.org/10.1172/JCI7569.
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Article

A revised model of platelet aggregation

Abstract

In this study we have examined the mechanism of platelet aggregation under physiological flow conditions using an in vitro flow-based platelet aggregation assay and an in vivo rat thrombosis model. Our studies demonstrate an unexpected complexity to the platelet aggregation process in which platelets in flowing blood continuously tether, translocate, and/or detach from the luminal surface of a growing platelet thrombus at both arterial and venous shear rates. Studies of platelets congenitally deficient in von Willebrand factor (vWf) or integrin αIIbβ3 demonstrated a key role for platelet vWf in mediating platelet tethering and translocation, whereas integrin αIIbβ3 mediated cell arrest. Platelet aggregation under flow appears to be a multistep process involving: (a) exposure of vWf on the surface of immobilized platelets; (b) a reversible phase of platelet aggregation mediated by the binding of GPIbα on the surface of free-flowing platelets to vWf on the surface of immobilized platelets; and (c) an irreversible phase of aggregation dependent on integrin αIIbβ3. Studies of platelet thrombus formation in vivo demonstrate that this multistep adhesion mechanism is indispensable for platelet aggregation in arterioles and also appears to promote platelet aggregate formation in venules. Together, our studies demonstrate an important role for platelet vWf in initiating the platelet aggregation process under flow and challenge the currently accepted view that the vWf-GPIbα interaction is exclusively involved in initiating platelet aggregation at elevated shear rates.

Authors

Suhasini Kulkarni, Sacha M. Dopheide, Cindy L. Yap, Catherine Ravanat, Monique Freund, Pierre Mangin, Kathryn A. Heel, Alison Street, Ian S. Harper, Francois Lanza, Shaun P. Jackson

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Figure 4

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Dynamics of rat platelet aggregation in vitro and in vivo. Fluorescently...
Dynamics of rat platelet aggregation in vitro and in vivo. Fluorescently labeled rat platelets in whole blood were perfused over spread rat platelet monolayers at 150, 600, and 1800 s–1 for 1 minute. (a) The percentage of tethered platelets translocating and/or detaching over a 10-second period is demonstrated. (b) Before perfusion, blood was incubated for 10 minutes with buffer (control), anti-αIIbβ3 (α-αIIbβ3), anti-GPV (α-GPV), or anti-GPIbα (α-Ibα) antibody fragments. In these studies the number of platelets tethering over a 5-second time period is demonstrated. Results represent mean ± SEM (n = 4). (c) Dynamics of platelet aggregation in vivo. Vascular injury and thrombus formation in rat mesenteric vessels was induced by photoactivation of Rose Bengal. The percentage of platelets translocating and/or detaching from the surface of arterial and venous thrombi was examined over a 10-second time period using DIC microscopy. (d) Following thrombus formation, fluorescently labeled, washed rat platelets, preincubated with buffer (control), anti-GPIbα (α-GPIbα), anti-αIIbβ3 (α-αIIbβ3), or anti-GPV (α-GPV) antibody fragments were injected intravenously. Pre-formed platelet thrombi (white arrowheads) were viewed by differential interference contrast (upper panels; DIC) whereas tethering of injected platelets to the surface of pre-formed thrombi was observed by fluorescence microscopy (lower panels; ×63). For clarity, the mesenteric arteriole walls have been demarcated using continuous lines, whereas the surface of thrombi have been outlined using discontinuous lines. Uninjured refers to a mesenteric vessel that has not been subjected to photo-induced injury. These images are from 5 experiments and are representative of more than 50 independent experiments. Note the α-αIIbβ3–treated platelets that adhered to the surface of arterial thrombi formed transient tethers. All these cells subsequently translocated and/or detached from the thrombus.