Packaging of prions into exosomes is associated with a novel pathway of PrP processing

Abstract

Prion diseases are fatal, transmissible neurodegenerative disorders associated with conversion of the host-encoded prion protein (PrP(C)) into an abnormal pathogenic isoform (PrP(Sc)). Following exposure to the infectious agent (PrP(Sc)) in acquired disease, infection is propagated in lymphoid tissues prior to neuroinvasion and spread within the central nervous system. The mechanism of prion dissemination is perplexing due to the lack of plausible PrP(Sc)-containing mobile cells that could account for prion spread between infected and uninfected tissues. Evidence exists to demonstrate that the culture media of prion-infected neuronal cells contain PrP(Sc) and infectivity but the nature of the infectivity remains unknown. In this study we have identified PrP(C) and PrP(Sc) in association with endogenously expressing PrP neuronal cell-derived exosomes. The exosomes from our prion-infected neuronal cell line were efficient initiators of prion propagation in uninfected recipient cells and to non-neuronal cells. Moreover, our neuronal cell line was susceptible to infection by non-neuronal cell-derived exosome PrP(Sc). Importantly, these exosomes produced prion disease when inoculated into mice. Exosome-associated PrP is packaged via a novel processing pathway that involves the N-terminal modification of PrP and selection of distinct PrP glycoforms for incorporation into these vesicles. These data extend our understanding of the relationship between PrP and exosomes by showing that exosomes can establish infection in both neighbouring and distant cell types and highlight the potential contribution of differentially processed forms of PrP in disease distribution. These data suggest that exosomes represent a potent pool of prion infectivity and provide a mechanism for studying prion spread and PrP processing in cells endogenously expressing PrP.

A deadly spread: cellular mechanisms of α-synuclein transfer

“…50 Exosomes are small vesicles that can break off from the endocytic machinery of one cell, transverse the extracellular space, and then fuse with the outer membrane of another cell, thus transferring their contents to the new cell. 51 Of relevance to other neurodegenerative disorders, they have been shown to transmit pathogenic prion proteins [52][53][54] and b-amyloid (Ab) aggregates. 55 Recently, a-syn-containing exosomes secreted from neuroblastoma cells overexpressing a-syn were found to transfer a-syn to other cultured neuroblastoma cells.…”

First Demonstration of Transmissible Spongiform Encephalopathy-associated Prion Protein (PrPTSE) in Extracellular Vesicles from Plasma of Mice Infected with Mouse-adapted Variant Creutzfeldt-Jakob Disease by in Vitro Amplification

“…This "Trojan exosome" hypothesis, posited by Gould et al (39), is currently being evaluated in protein-misfolding neurodegenerative diseases as a possible mechanism for the spread of misfolded proteins (40 -45). Cellular prion protein (PrP C ) and misfolded PrP TSE have been identified in exosomes from various TSE models (46 -55) and intracerebral inoculation of exosomes obtained from TSE-infected cell cultures has caused clinical disease in mice (47,49). Little is known about the distribution of PrP TSE in blood.…”

Cell models of prion infection

“…Février et al first reported that abnormal PrP and infectivity actively released from sheep scrapie-infected MovS and Rov cells was associated with small vesicles (50-100 nm) called exosomes [46], raising the possibility that infected exosomes could serve as a vehicle for prion dissemination [108]. Similar findings were later obtained for GT1 cells infected with a mouse-adapted prion strain, indicating that potential spread of infection through cell-free mechanisms is probably not restricted to a particular type of cell or strain [143]. A further support for cell-free transmission of prions was gained by Leblanc et al who showed that retrovirus infection enhances prion infectivity release [76].…”

“…It was recently demonstrated that exosomes released by MovS and Rov cells do contain abnormal PrP and prion infectivity when the cells were infected with a sheep scrapie agent [46]. A similar observation was subsequently reported for GT1 cells infected with a mouse-adapted prion strain [143]. Exosomes are formed in multivesicular bodies (MVB), which could therefore represent an intracellular site for PrP Sc accumulation.…”