Von Willebrand factor self-association on platelet GpIbalpha under hydrodynamic shear: effect on shear-induced platelet activation.

ABSTRACT: The function of the mechanosensitive, multimeric blood protein von Willebrand factor (VWF) is dependent on its size. We tested the hypothesis that VWF may self-associate on the platelet glycoprotein Ib? (GpIb?) receptor under hydrodynamic shear. Consistent with this proposition, whereas Alexa-488-conjugated VWF (VWF-488) bound platelets at modest levels, addition of unlabeled VWF enhanced the extent of VWF-488 binding. Recombinant VWF lacking the A1-domain was conjugated with Alexa-488 to produce ?A1-488. Although ?A1-488 alone did not bind platelets under shear, this protein bound GpIb? on addition of either purified plasma VWF or recombinant full-length VWF. The extent of self-association increased with applied shear stress more than ? 60 to 70 dyne/cm(2). ?A1-488 bound platelets in the milieu of plasma. On application of fluid shear to whole blood, half of the activated platelets had ?A1-488 bound, suggesting that VWF self-association may be necessary for cell activation. Shearing platelets with 6-?m beads bearing either immobilized VWF or anti-GpIb? mAb resulted in cell activation at shear stress down to 2 to 5 dyne/cm(2). Taken together, the data suggest that fluid shear in circulation can increase the effective size of VWF bound to platelet GpIb? via protein self-association. This can trigger mechanotransduction and cell activation by enhancing the drag force applied on the cell-surface receptor.

SUBMITTER: Dayananda KM 

PROVIDER: S-EPMC2981547 | biostudies-other | 2010 Nov

REPOSITORIES: biostudies-other