Nanopost Arrays Indicate that GPIb-VWf Interactions Play a Role in Platelet Contractility Independent of Integrin αIIbβ3

The first step of hemostasis involves recognition of von Willebrand factor (VWF) by platelets. These cells bind to domains of VWF using GPIb-IV-X and αIIbβ3 receptors. Because platelets must contract to shrink and stabilize the hemostatic clot, we investigated the contribution of each of these receptors in supporting platelet forces. For this, we developed a new tool using E-beam lithography to fabricate nanoposts for force measurements (Fig A). VWF was adsorbed to the tips of these posts to allow for platelet adhesion (Fig B). Nanoposts were fluorescently labeled to track deflections created by individual platelets (Fig C). Our results show that platelets treated with antibodies 7E3 and AK2, which inhibit αIIbβ3 and GPIb respectively, exerted significantly lower forces. To confirm that GPIb-VWF interaction can support platelet contraction, we used the recombinant GPIb-IX-V binding region of VWF (A1 domain) (Fig D). Platelets were unable to generate force on A1 domain in the presence of soluble GPIb, or using bovine serum albumin and Pluronic F-127 as a substrate. Together, these results indicate that platelets are able to transmit cytoskeletal contractile forces in an integrin-independent manner.View Large Image | View Hi-Res Image | Download PowerPoint Slide