Protein Misfolding Cyclic Amplification Cross-Species Products of Mouse-Adapted Scrapie Strain 139A and Hamster-Adapted Scrapie Strain 263K with Brain and Muscle Tissues of Opposite Animals Generate Infectious Prions

Transmission of prions between mammalian species is limited by a "species barrier," a biological effect involving an increase in incubation period to decrease the percentage of animals succumbing to disease. In this study, we used protein misfolding cyclic amplification (PMCA) technique, which accelerates the conversion of prion proteins in vitro. Direct interspecies PMCA involving 144 cycles confirmed that both mouse-adapted scrapie strain 139A and hamster-adapted 263K could use brain homogenates of opposite species to form proteinase K (PK)-resistant PrP proteins (PrPres). Newly formed interspecies prions could stably propagate themselves in subsequent serial PMCA passages. The two types of PMCA-generated cross-species PrPres changed their glycosylation profiles, which was similar to that observed during interspecies infection by the mouse agent 139A in vivo. These profiles were distinct from individual seeded PrPSc and possessed properties of new hosts. Comparative analysis with respect to PK resistance showed no significant diversity between PMCA-PrPres and native PrPSc or between brain and muscle PrPres. However, PrPres from the relatively early cycles of serial PMCA showed lower PK resistance than those from later cycles. Inoculation of these PMCA products amplified with homogeneous or heterogeneous brain tissues (cross-species products) induced experimental transmissible spongiform encephalopathies. These results suggested that PMCA can help prion strains to overcome species barrier and to propagate efficiently both in vitro and in vivo.