Evidence for multiple prion conformers in natural scrapie isolates

Prion strains in infected animals may exist as heterogeneous populations composed of a major prion conformer responsible for the dominant disease phenotype and minor conformers that are phenotypically silent or difficult to detect. However, the presence and biological significance of such minor conformers in natural prion isolates remain poorly understood. Identifying and characterizing these hidden substrains is important for understanding prion strain diversity and for assessing potential transmission risks to humans and livestock. In this study, we utilized a modified protein misfolding cyclic amplification (PMCA) method to detect substrains within classical scrapie isolates. Our analysis provided evidence consistent with the coexistence of multiple prion conformers, including previously unrecognized conformers, within single prion isolates. Furthermore, we observed changes in the detectable substrain composition during passages in animal hosts. These findings support the idea that scrapie prion populations can contain diverse conformers and that changes in detectable conformer populations during passage may contribute to the overall diversity of scrapie prions.Author summary: Prions are infectious proteins that can cause fatal neurodegenerative diseases in humans and animals. Different prion strains can produce different disease patterns, even when the host prion protein has the same amino acid sequence. Natural prion infections may contain not only the major strain that determines the apparent disease type, but also minor hidden variants that are difficult to detect. These hidden variants may become important when prions pass into a new host or are transmitted repeatedly. In this study, we used a highly sensitive in vitro amplification method to examine scrapie prions from naturally and experimentally infected animals. This approach allowed us to detect prion variants that were not readily visible by conventional biochemical methods. Our results provide evidence that scrapie isolates can contain multiple prion conformers and that the detectable composition of these conformers can change during passage. These findings suggest that hidden prion diversity may contribute to changes in prion strain properties during transmission, although the results of in vitro amplification should be interpreted together with biological data from animal studies.