Anti-prion Protein Antibody 6D11 Restores Cellular Proteostasis of Prion Protein Through Disrupting Recycling Propagation of PrP ^Sc and Targeting PrP ^Sc for Lysosomal Degradation

PrP ^Sc is an infectious and disease-specific conformer of the prion protein, which accumulation in the CNS underlies the pathology of prion diseases. PrP ^Sc replicates by binding to the cellular conformer of the prion protein (PrP ^C ) expressed by host cells and rendering its secondary structure a likeness of itself. PrP ^C is a plasma membrane anchored protein, which constitutively recirculates between the cell surface and the endocytic compartment. Since PrP ^Sc engages PrP ^C along this trafficking pathway, its replication process is often referred to as “recycling propagation.” Certain monoclonal antibodies (mAbs) directed against prion protein can abrogate the presence of PrP ^Sc from prion-infected cells. However, the precise mechanism(s) underlying their therapeutic propensities remains obscure. Using N2A murine neuroblastoma cell line stably infected with 22L mouse-adapted scrapie strain (N2A/22L), we investigated here the modus operandi of the 6D11 clone, which was raised against the PrP ^Sc conformer and has been shown to permanently clear prion-infected cells from PrP ^Sc presence. We determined that 6D11 mAb engages and sequesters PrP ^C and PrP ^Sc at the cell surface. PrP ^C /6D11 and PrP ^Sc /6D11 complexes are then endocytosed from the plasma membrane and are directed to lysosomes, therefore precluding recirculation of nascent PrP ^Sc back to the cell surface. Targeting PrP ^Sc by 6D11 mAb to the lysosomal compartment facilitates its proteolysis and eventually shifts the balance between PrP ^Sc formation and degradation. Ongoing translation of PrP ^C allows maintaining the steady-state level of prion protein within the cells, which was not depleted under 6D11 mAb treatment. Our findings demonstrate that through disrupting recycling propagation of PrP ^Sc and promoting its degradation, 6D11 mAb restores cellular proteostasis of prion protein.