A New Mechanism for Transmissible Prion Diseases

Abstract

The transmissible agent of prion disease consists of prion protein in β-sheet rich state (PrPSc), which can replicate its conformation according to a template-assisted mechanism. This mechanism postulates that the folding pattern of a newly recruited polypeptide accurately reproduces that of the PrPSc template. Here three conformationally distinct amyloid states were prepared in vitro using Syrian hamster recombinant PrP (rPrP) in the absence of cellular cofactors. Surprisingly, no signs of prion infection were found in Syrian hamsters inoculated with rPrP fibrils that resembled PrPSc, whereas an alternative amyloid state, with a folding pattern different from that of PrPSc induced a pathogenic process that led to transmissible prion disease. An atypical proteinase K-resistant, transmissible PrP form that resembled the structure of the amyloid seeds was observed during a clinically silent stage before authentic PrPSc emerged. The dynamics between the two forms suggest that atypical PrPres gave rise to PrPSc. While no PrPSc was found in preparations of fibrils using Protein Misfolding Cyclic Amplification with beads (PMCAb), rPrP fibrils gave rise to atypical PrPres in modified PMCAb suggesting that atypical PrPres was the first product of PrPC misfolding triggered by fibrils. The current work demonstrates that a new mechanism responsible for prion diseases different from the PrPSc-templated or spontaneous conversion of PrPC into PrPSc exists. This study provides compelling evidence that non-infectious amyloids with a structure different from that of PrPSc could lead to transmissible prion disease. This work has numerous implications for understanding the etiology of prion and other neurodegenerative diseases.

Synthesis of High Titer Infectious Prions with Cofactor Molecules

“…7 -fold lower than brain-derived prions or PE-PrP Sc molecules), it is unclear whether these minimal amounts of infectivity observed are due to either the presence of a small amount of bacterially derived cofactor(s) in the purified recPrP preparation or the creation of a minimally infectious conformation that can gradually adapt after inoculation into animals, possibly by interacting with endogenous cofactor molecules (23)(24)(25). In the case of "protein-only" samples produced by PMCA (as opposed to amyloid fibrils produced by chemical denaturation), it is also possible that either a correspondingly small fraction of PrP Sc molecules truly formed without cofactors or an accidental contamination of the sample with very small quantities of infectious prions occurred.…”

Isolation of Novel Synthetic Prion Strains by Amplification in Transgenic Mice Coexpressing Wild-Type and Anchorless Prion Proteins

“…It is unclear how this high-temperature "annealing" would be reproduced by physiological processes in cells. In a very recent paper, TSE disease also arose after serial passage of one of three fibril preparations generated without annealing (37).…”

Truncated forms of the prion protein PrP demonstrate the need for complexity in prion structure

“…This route of infection represents a pathway parallel to the natural etiology and would most likely be caused by a process of deformed templating (heterogeneous seeding). 17,18,19 Regardless of the mechanism of infectivity, it is clear that the generic stacked-sheet structure has very little infectivity if any, and is very different, both structurally and functionally, from the b-solenoidal structure. HET-s exhibits a similar polymorphism: 20 the wild-type protein at neutral pH and many mutants form b-solenoids, but other mutants and the wildtype protein at acidic pH form non-infectious 21 stacked sheets.…”

“…27 Perhaps the greatest value for prion studies of at least the larger fragments of PrP lies in their use not as structural models for the active prion itself, but as templates that illustrate the phenomenon of heterogeneous seeding or deformed templating. 17,18,19,28 The infectivity of PrP55, for example, may well come from heterogeneous seeding, that is, seeding between distinct amyloid architectures. With two rungs of a b-solenoid, PrP55 could easily contain a structured segment that can act as a seed, in distinct contrast to PrP21 and other short, noninfectious fragments.…”