The Size And Stability Of Infectious Prion Aggregates Fluctuate Dynamically During Cellular Uptake And Disaggregation

Prion diseases arise when PrPSc, an aggregated, infectious, and insoluble conformer of the normally soluble mammalian prion protein, PrPC, catalyzes the conversion of PrPC into more PrPSc, which then accumulates in the brain leading to disease. PrPSc is the primary, if not sole, component of the infectious prion. Despite the stability and protease insensitivity of PrPSc aggregates, they can be degraded after cellular uptake. However, how cells disassemble and degrade PrPSc is poorly understood. In this work, we analyzed how the protease sensitivity and size distribution of PrPSc aggregates from two different mouse-adapted prion strains, 22L, that can persistently infect cells and 87V, that cannot, changed during cellular uptake. We show that within the first 4 h following uptake large PrPSc aggregates from both prion strains become less resistant to digestion by proteinase K (PK) through a mechanism that is dependent upon the acidic environment of endocytic vesicles. We further show that during disassembly, PrPSc aggregates from both strains become more resistant to PK digestion through the apparent removal of protease-sensitive PrPSc, with PrPSc from the 87V strain, disassembled more readily than PrPSc from the 22L strain. Taken together, our data demonstrate that the sizes and stabilities of PrPSc from different prion strains change during cellular uptake and degradation, thereby potentially impacting the ability of prions to infect cells.