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Cellular prion protein is expressed on endothelial cells and is released during apoptosis on membrane microparticles
Jan Simák1, Karel Holada, Felice D'Agnillo
1Laboratory of Cellular Hematology, Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, Maryland 28092, USA.
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.
Study Design And 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.
Conclusion:
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.
Insights
Cellular prion protein (PrPc) is released from endothelial cells via microparticles during apoptosis. These PrPc-positive microparticles contribute to plasma PrPc levels and may spread transmissible spongiform encephalopathy (TSE) infectivity in blood.
Area of Science:
- Biochemistry
- Cell Biology
- Neuroscience
Background:
- Transmissible spongiform encephalopathies (TSEs) are infectious diseases transmitted via blood transfusion.
- The infectious agent is a misfolded prion protein (PrPsc), which converts normal prion protein (PrPc).
- PrPc is abundant in plasma, but its origin in blood is unknown.
Purpose of the Study:
- To investigate the source of cellular prion protein (PrPc) in human plasma.
- To determine if endothelial cells express and release PrPc.
Main Methods:
- Cultured human umbilical vein endothelial cells (HUVECs) were analyzed for PrPc expression using flow cytometry, immunoblotting, and RT-PCR.
- Endothelial membrane microparticles (MPs) in cell culture and plasma were characterized.
Main Results:
- HUVECs express PrPc on their surface.
- Apoptosis in HUVECs induced significant release of PrPc-expressing MPs.
- Endothelial cell-derived MPs expressing PrPc were detected in human plasma.
Conclusions:
- Endothelial cell apoptosis releases PrPc-positive MPs into circulation.
- These MPs contribute to plasma PrPc and may facilitate TSE dissemination in blood.