On circulating platelets amyloid β is bound to the O-glycoproteins of adhering triplets rather than to GPIIb/IIIa
We showed recently that AOP1 and AOP2, in free form, in complexes with albumin or in anti-Gal/ABG-AOP1/AOP2-albumin triplet, captures amyloid β(Aβ-42) by offering the STPS on the O-glycoproteins as ligands for the peptide while albumin, electrophoretically separated from these O-glycoproteins, was inert towards the peptide and that albumin sample used in reports [25] that claimed amyloid β binding to this protein, contained AOP1 and AOP2 [3]. This agreed with the reported binding of amyloid β to the STPS-rich GPIIb/IIIa [26]. Results in Fig.7 showed that native and denuded platelets captured nearly the same amount of a limited amount of amyloid β presented to them, confirming that newly exposed O-glycoproteins in denuded platelets are capable of capturing amyloid β. However upon treatment of the resulting amyloid β-bearing platelets with sugars that can release the triplets, the amount of amyloid β released to the supernatant by denuded platelets was far less than by the same number of native platelets, suggesting that on native platelets amyloid β bound to the triplets using the STPS on their AOP1 and AOP2, so that they could be liberated along with the triplets by antibody-specific sugars. In contrast amyloid β bound to denuded platelets could have utilized the STPS on membrane O-glycoproteins that are newly exposed following release of triplets, so that antibody-specific sugar could not elute the peptide. Since GPIIb/IIIa is the most abundant O-glycoprotein on platelet surface and is reported to be an amyloid β receptor [26], this result also suggested a likely role for GPIIb/IIIa in triplet adhesion to platelets.