Cellular prion protein is expressed on endothelial cells and is released during apoptosis on membrane microparticles found in human plasma.
BACKGROUND
Blood and plasma of animals experimentally infected with transmissible spongiform encephalopathies (TSEs) can transmit TSE infection by transfusion. A conformational isoform of prion protein (PrPsc) is believed to be the TSE-infectious agent that propagates by converting the cellular prion protein (PrPc) to additional molecules of PrPsc. In orally infected animals, PrPsc accumulates in intestinal endothelial cells. In blood, two thirds of PrPc resides in plasma, but its source is not known.


METHODS
The expression of PrPc in cultured human umbilical vein endothelial cells (HUVECs) was studied using flow cytometry, immunoblotting, and RT-PCR. Flow cytometry was used to characterize endothelial membrane microparticles (MPs) in cell culture supernatants and in normal human plasma.


RESULTS
HUVECs and bovine aorta endothelial cells express PrPc. The number of surface PrPc molecules per cell in HUVECs was 58,000 +/- 2,800. The induction of apoptosis in HUVECs led to a marked release of membrane MPs (60,000-80,000 MPs/10(3) cells) that expressed PrPc and other endothelial antigens. The presence of endothelial cell-derived MPs expressing PrPc was demonstrated in platelet-free human plasma.


CONCLUSIONS
Endothelial cell apoptosis is associated with the release of PrPc-positive MPs. These MPs contribute to the PrPc pool in plasma and may have a role in disseminating TSE infectivity in blood.
Simák
Jan
J
Laboratory of Cellular Hematology, Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, Maryland 28092, USA.
Holada
Karel
K
D'Agnillo
Felice
F
Janota
Jan
J
Vostal
Jaroslav G
JG
D000818:Animals; D017304:Annexin A5 / Q000378:metabolism; D000911:Antibodies, Monoclonal; D001011:Aorta; D017209:Apoptosis / Q000187:drug effects; D001792:Blood Platelets / Q000648:ultrastructure; D002166:Camptothecin / Q000494:pharmacology; D002417:Cattle; D018929:Cell Culture Techniques; D002462:Cell Membrane / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D004730:Endothelium, Vascular / Q000378:metabolism* / Q000648:ultrastructure; D005434:Flow Cytometry; D006801:Humans; D015151:Immunoblotting; D007962:Leukocytes / Q000648:ultrastructure; D018621:PrPC Proteins / Q000097:blood / Q000235:genetics / Q000378:metabolism*; D017096:Prion Diseases / Q000097:blood; D012333:RNA, Messenger / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012756:Sheep; D014471:Umbilical Veins
D017304:Annexin A5; D000911:Antibodies, Monoclonal; D018621:PrPC Proteins; D012333:RNA, Messenger; D002166:Camptothecin