Abstract 14079: Outside-in Signaling of Integrin αIIbβ3 Mediates Shear-dependent Platelet Microvesicle Formation and Phosphatidylserine Exposure
Introduction and Hypothesis: Platelets promote coagulation mainly by exposing membrane phosphatidylserine (PS) and releasing PS-expressing microvesicles (MV). We have recently shown that PS exposure and MV release induced by platelet agonists requires shear stress. To identify the receptor responsible for the shear-dependent signaling leading to PS exposure and MV release, we investigated the hypothesis that Integrin αIIbβ3 may play a role in shear-dependent platelet MV release and PS exposure.
Methods and Results: To determine the role of integrin αIIbβ3 in shear-dependent PS exposure and MV release, we compared platelets from β3-/- mice and wild-type mice in MV release and PS exposure under shear introduced using a cone-plate rheometer. MV release and PS exposure were determined by flow cytometry. Shear-dependent PS exposure and MV release were significantly suppressed in β3-/- platelets. Similarly, Wild type platelets treated with integrin antagonists also showed defective PS exposure and MV release. These data indicate an important role for the ligand binding function of integrin αIIbβ3 in shear-dependent MV release and PS exposure. To determine whether the role of integrin αIIbβ3 is due to its outside-in signaling, β3-/- platelets were transplanted with wild type β3 or a mutant β3 with the critical Gα13 binding site of the β3 cytoplasmic domain (EEE) changed to alanines (AAA), which selectively abolish outside-in signaling of αIIbβ3. Transplantation of wild type β3 rescued the defective MVs release and PS exposure of β3-/- platelets. In contrast, AAA mutant failed to rescue these defects. Consistently, wild type platelets treated with the selective inhibitor of Gα13-integrin interaction, inhibited integrin outside-in signaling and also PS exposure and MV release under shear stress. Furthermore, inhibition of Src, which is important in outside-in signaling downtream of Gα13, also abolished shear-dependent MV release and PS exposure.
Conclusions: These data suggest that integrin outside-in signaling mediated by the Gα13-β3 interaction and Src-dependent signaling pathway plays an important role in transmitting shear-induced mechanical signals leading to MV release and PS exposure in activated platelets.
Author Disclosures: A. Pang: None. Y. Cui: None. M.K. Delaney: None. A. Stojanovic: None. X. Du: None.
- © 2016 by American Heart Association, Inc.