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.