Platelet Protein Disulfide Isomerase Promotes Glycoprotein Ib-Mediated Platelet-Neutrophil Interactions Under Thromboinflammatory Conditions (vol 139, pg 1300, 2018)

Background: Platelet-neutrophil interactions contribute to vascular occlusion and tissue damage in thromboinflammatory disease. Platelet glycoprotein Ib (GPIb), a key receptor for the cell-cell interaction, is believed to be constitutively active for ligand binding. Here, we established the role of platelet-derived protein disulfide isomerase (PDI) in reducing the allosteric disulfide bonds in GPIb and enhancing the ligand-binding activity under thromboinflammatory conditions. Methods: Bioinformatic analysis identified 2 potential allosteric disulfide bonds in GPIb. Agglutination assays, flow cytometry, surface plasmon resonance analysis, a protein-protein docking model, proximity ligation assays, and mass spectrometry were used to demonstrate a direct interaction between PDI and GPIb and to determine a role for PDI in regulating GPIb function and platelet-neutrophil interactions. Also, real-time microscopy and animal disease models were used to study the pathophysiological role of PDI-GPIb signaling under thromboinflammatory conditions. Results: Deletion or inhibition of platelet PDI significantly reduced GPIb-mediated platelet agglutination. Studies using PDI-null platelets and recombinant PDI or Anfibatide, a clinical-stage GPIb inhibitor, revealed that the oxidoreductase activity of platelet surface-bound PDI was required for the ligand-binding function of GPIb. PDI directly bound to the extracellular domain of GPIb on the platelet surface and reduced the Cys4-Cys17 and Cys209-Cys248 disulfide bonds. Real-time microscopy with platelet-specific PDI conditional knockout and sickle cell disease mice demonstrated that PDI-regulated GPIb function was essential for platelet-neutrophil interactions and vascular occlusion under thromboinflammatory conditions. Studies using a mouse model of ischemia/reperfusion-induced stroke indicated that PDI-GPIb signaling played a crucial role in tissue damage. Conclusions: Our results demonstrate that PDI-facilitated cleavage of the allosteric disulfide bonds tightly regulates GPIb function, promoting platelet-neutrophil interactions, vascular occlusion, and tissue damage under thromboinflammatory conditions.