Selective amplification of classical and atypical prions using modified protein misfolding cyclic amplification

With the development of protein misfolding cyclic amplification (PMCA), the topic of faithful propagation of prion strain-specific structures has been constantly debated. Here we show that by subjecting brain material of a synthetic strain consisting of a mixture of self-replicating states to PMCAb, selective amplification of PrP(Sc) could be achieved, and that PMCAb mimicked the evolutionary trend observed during serial transmission in animals. On the other hand, using modified PMCAb conditions that employ partially deglycosylated PrP(C) (dgPMCAb), an alternative transmissible state referred to as atypical protease-resistant form of the prion protein (atypical PrPres) was selectively amplified from a mixture. Surprisingly, when hamster-adapted strains (263K and Hyper) were subjected to dgPMCAb, their proteinase K digestion profile underwent a dramatic transformation, suggesting that a mixture of atypical PrPres and PrP(Sc) might be present in brain-derived materials. However, detailed analysis revealed that the proteinase K-resistant profile of PrP(Sc) changed in response to dgPMCAb. Despite these changes, the 263K strain-specific disease phenotype was preserved after passage through dgPMCAb. This study revealed that the change in PrP(Sc) biochemical phenotype does not always represent an irreversible transformation of a strain, but rather demonstrated the existence of a wide range of variation for strain-specific physical features in response to a change in prion replication environment. The current work introduced a new PMCA technique for amplification of atypical PrPres and raised a number of questions about the need for a clever distinction between actual strain mutation and variation of strain-specific features in response to a change in the replication environment.