Summary
The recently shown transmissibility of variant Creutzfeldt-Jakob disease (vCJD) by
blood transfusion emphasises the need for better understanding of the cellular prion
protein (PrPc) in blood. A substantial amount of cell-associated PrPc in blood resides
in platelets. Platelet activation leads to up-regulation of PrPc on the platelet surface
and its release on exosomes and microparticles. The sub-cellular localisation and
function of platelet PrPc, however, is poorly understood. In the present study, we
investigated the association of PrPc with platelet lipid rafts and the platelet cytoskeleton.
Immuno-fluorescence microscopy showed that the signals of PrPc and P-selectin, both
of which occupy intracellular alpha granules, were separated on the membrane, suggesting
organisation in different membrane domains. A flotation assay of platelet lysates
demonstrated that a relatively small portion of platelet PrPc floats with lipid rafts,
regardless of platelet activation status. This was reversed by depolymerisation of
the platelet cytoskeleton, which led to flotation of most platelet PrPc, suggesting
that interactions with the cytoskeleton prevent flotation of PrPc rafts. This association
of PrPc with the platelet cytoskeleton was confirmed by its presence in both the isolated
membrane skeleton and actin cytoskeleton. Platelet activation significantly increased
the amount of PrPc associated with the cytoskeleton. Our results indicate that the
localisation of PrPc in platelets is complex, with the majority of PrPc present within
platelet lipid rafts linked to the platelet cytoskeleton. This localisation places
PrPc in a position where it can interact with proteins involved in platelet signalling
and eventually with vCJD prions.
Keywords
Blood platelets - cytoskeleton - lipid rafts - prion protein - PrPc