Mechanotransduction through glycoprotein Iba induces a unique series of morphologic changes in translocating platelets

Abstract number: OC406

Maxwell M. J., Dopheide S. M., Turner S., Mistry N., Jackson S. P.

Australian Centre for Blood Diseases, Australia

The platelet glycoprotein (GP) Ib/V/IX complex plays an important role in regulating the morphology of resting platelets and can induce platelet shape change during adhesion to immobilized vWf. In this study we have examined the effects of fluid shear stress on GPIb-dependent changes in platelet morphology during surface translocation on vWf. We demonstrate that translocating platelets undergo a unique series of morphological changes in response to increasing fluid shear stress. Under moderately low shear conditions (600 s^-1), initial platelet shape change involved extension of membrane tethers and/or filopodial from the surface of discoid platelets. With increasing shear, all platelets eventually adopted a spherical morphology with numerous surface projections (1800–5000 s^-1). At high shear wall shear rates (10 000 s^-1), all translocating platelets retracted filopodia leading to the development of a smooth ball-like appearance. This high shear-dependent change in platelet morphology was unique from that induced by all other platelet stimuli in that it was partially inhibited by the Src kinase antagonist, PP2, but occurred independent of cytosolic calcium flux, RhoA kinase activation or increases in the cytosolic levels of cAMP. Analysis of the effects of pharmacological regulators of the actin and microtubular cytoskeleton demonstrated a key role for actin filaments in maintaining the integrity of the platelet surface membrane under high shear whereas microtubules played a potentially important role in regulating filopodial retraction. Functionally, alterations in platelet shape had a major affect on platelet translocation dynamics in that conversion of platelets from disc to spheres resulted in a 3–5-fold increase in platelet rolling velocity. These studies suggest that GP Ib/V/IX acts as a mechanoreceptor to induce shear-specific changes in platelet morphology, and furthermore, establish a potentially important role for cell shape in regulating platelet adhesion dynamics under flow.