Abstract
IntroductionPrevious studies established that prion disease with unique strain-specific phenotypes could be induced by in vitro-formed recombinant PrP (rPrP) fibrils with structures different from that of authentic prions, or PrPSc. To explain the etiology of prion diseases, new mechanism proposed that in animals the transition from rPrP fibrils to PrPSc consists of two main steps: the first involves fibril-induced formation of atypical PrPres, a self-replicating but clinically silent state, and the second consists of atypical PrPres-dependent formation of PrPSc via rare deformed templating events.ResultsIn the current study, atypical PrPres with characteristics similar to those of brain-derived atypical PrPres was generated in vitro. Upon inoculation into animals, in vitro-generated atypical PrPres gave rise to PrPSc and prion disease with a phenotype similar to those induced by rPrP fibrils. Significant differences in the sialylation pattern between atypical PrPres and PrPSc suggested that only a small sub-fraction of the PrPC that is acceptable as a substrate for PrPSc could be also recruited by atypical PrPres. This can explain why atypical PrPres replicates slower than PrPSc and why PrPSc outcompetes atypical PrPres.ConclusionsThis study illustrates that transmissible prion diseases with very similar disease phenotypes could be produced via two alternative procedures: direct inoculation of recombinant PrP amyloid fibrils or in vitro-produced atypical PrPres. Moreover, this work showed that preparations of atypical PrPres free of PrPSc can give rise to transmissible diseases in wild type animals and that atypical PrPres generated in vitro is an adequate model for brain-derived atypical PrPres.Electronic supplementary materialThe online version of this article (doi:10.1186/s40478-015-0248-5) contains supplementary material, which is available to authorized users.
Highlights
Previous studies established that prion disease with unique strain-specific phenotypes could be induced by in vitro-formed recombinant PrP fibrils with structures different from that of authentic prions, or PrPSc
Triggering atypical PrPres in vitro is a generic property of recombinant PrP (rPrP) fibrils In previous studies, upon inoculations into animals, rPrP fibrils were shown to induce misfolding of PrPC into atypical PrPres [11, 12]. To test whether this process could be recapitulated in vitro, rPrP fibrils were prepared according to the protocols used in previous studies for making fibrils that induced transmissible prion diseases [10,11,12, 29]
When serial Protein Misfolding Cyclic Amplification reactions with beads (PMCAb) reactions, instead of dgPMCAb, were seeded with the same fibril preparations, no Proteinase K (PK)-resistant products were found (Fig. 2a). This result is in agreement with the previous studies that rPrP fibrils do not seed PrPSc nor contain small amounts of PrPSc amplifiable by PMCAb [11, 12, 33]. rPrP fibril-induced formation of atypical PrPres in dgPMCAb was robust and highly reproducible (Fig. 1b)
Summary
Previous studies established that prion disease with unique strain-specific phenotypes could be induced by in vitro-formed recombinant PrP (rPrP) fibrils with structures different from that of authentic prions, or PrPSc. Prions spread between organisms or from cell to cell by replicating their disease-specific misfolded structures via a template-assisted mechanism [2]. This mechanism postulates that PrPSc template recruits and converts PrPC expressed by a host into PrPSc. This mechanism postulates that PrPSc template recruits and converts PrPC expressed by a host into PrPSc According to this mechanism, the folding pattern of a newly formed PrPSc accurately replicates that of the PrPSc template, and prion replication exhibits high fidelity [2]
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