title: 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 Ibα (GpIbα) 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 ΔA1-488. Although ΔA1-488 alone did not bind platelets under shear, this protein bound GpIbα 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). ΔA1-488 bound platelets in the milieu of plasma. On application of fluid shear to whole blood, half of the activated platelets had ΔA1-488 bound, suggesting that VWF self-association may be necessary for cell activation. Shearing platelets with 6-μm beads bearing either immobilized VWF or anti-GpIbα 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 GpIbα via protein self-association. This can trigger mechanotransduction and cell activation by enhancing the drag force applied on the cell-surface receptor.
authors.affiliation: Chemical and Biological Engineering, State University of New York, Buffalo, NY 14260, USA.
authors.forename: Kannayakanahalli M
authors.initials: KM
authors.lastname: Dayananda
authors.forename: Indrajeet
authors.initials: I
authors.lastname: Singh
authors.forename: Nandini
authors.initials: N
authors.lastname: Mondal
authors.forename: Sriram
authors.initials: S
authors.lastname: Neelamegham
mesh_terms: D000911:Antibodies, Monoclonal; D001792:Blood Platelets / Q000378:metabolism; D018056:Hemorheology; D006801:Humans; D057446:Hydrodynamics; D066298:In Vitro Techniques; D040542:Mechanotransduction, Cellular; D015539:Platelet Activation / Q000502:physiology*; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D055503:Protein Multimerization; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013314:Stress, Mechanical; D014841:von Willebrand Factor / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; D019038:Platelet Glycoprotein GPIb-IX Complex; D011994:Recombinant Proteins; D014841:von Willebrand Factor