Platelet interaction with von Willebrand factor is enhanced by shear-induced clustering of glycoprotein Ibα

Initial platelet arrest at the exposed arterial vessel wall is mediated through glycoprotein Ib alpha binding to the A1 domain of von Willebrand factor. This interaction occurs at sites of elevated shear force, and strengthens upon increasing hydrodynamic drag. The increased interaction requires shear-dependent exposure of the von Willebrand factor A1 domain, but the contribution of glycoprotein Ib alpha remains ill defined. We have previously found that glycoprotein Ib alpha forms clusters upon platelet cooling and hypothesized that such a property enhances the interaction with von Willebrand factor under physiological conditions. We analyzed the distribution of glycoprotein Iba with Forster resonance energy transfer using time-gated fluorescence lifetime imaging microscopy. Perfusion at a shear rate of 1,600 s(-1) induced glycoprotein Ib alpha clusters on platelets adhered to von Willebrand factor, while clustering did not require von Willebrand factor contact at 10,000 s(-1). Shear-induced clustering was reversible, not accompanied by granule release or alpha IIb beta 3 activation and improved glycoprotein Ib alpha-dependent platelet interaction with von Willebrand factor. Clustering required glycoprotein Ib alpha translocation to lipid rafts and critically depended on arachidonic acid-mediated binding of 14-3-3 zeta to its cytoplasmic tail. This newly identified mechanism emphasizes the ability of platelets to respond to mechanical force and provides new insights into how changes in hemodynamics influence arterial thrombus formation.