Abstract
Prion diseases, also known as transmissible spongiform encephalopathies (TSEs), are a group of neurodegenerative disorders that affect humans and other mammals. Prions are comprised of PrPSc, the self-templating disease specific conformation of the cellular prion protein, PrPC. Synthetic prions are generated in vitro from minimal components and cause bona fide prion disease in animals. It is unknown, however, if synthetic prions can cross the species barrier following interspecies transmission or if synthetic strains recapitulate brain-derived strains.
To investigate this, either murine or hamster synthetic prions, including wild-type and three mutants, were inoculated into male Syrian hamsters. All animals inoculated with murine synthetic prions developed prion disease characterized by a striking uniformity of clinical onset and signs of disease. Serial intraspecies transmission resulted in a rapid adaptation to hamsters. During the adaptation process, PrPSc electrophoretic migration, glycoform ratios, conformational stability and biological activity as measured by protein misfolding cyclic amplification remained constant. Interestingly, the strain that emerged shares a strikingly similar transmission history, incubation period, clinical course of disease, pathology and biochemical and biological features of PrPSc with 139H, a hamster adapted form of the murine strain 139A. Combined, these data suggest that murine synthetic prions are comprised of bona fide PrPSc with 139A-like strain properties that efficiently crosses the species barrier and rapidly adapts to hamsters resulting in the emergence of a single strain.
In contrast, all animals inoculated with hamster synthetic prions (HSP) did not develop clinical signs of prion disease. Western blot analysis of brain homogenate from HSP-infected (wildtype and the D54 mutant) identified protease-resistant PrPSc, suggesting subclinical infection. Serial intraspecies transmission resulted in clinical disease and a divergence of disease phenotype between the wildtype and the D54 mutant. These results suggest the HSP are not authentic PrPSc and instead replicate through conversion model termed deformed templating.
The efficiency and specificity of interspecies transmission of murine synthetic prions to hamsters, with relevance to brain derived prions, could be a useful model for identification of structure function relationships between PrPSc and PrPC from different species. The inefficiency of the intraspecies transmission of hamster synthetic prions to hamsters emphasize the important role of cofactors in generation of bona fide PrPSc.
The objectives for this dissertation were to further our understanding of synthetic prions and their relationship to brain-derived prions. This was accomplished by studying transmission and adaptation of synthetic prions in hamsters.