Location: Virus and Prion ResearchTitle: Stability properties of PrPSc from cattle with experimental transmissible spongiform encephalopathies) Author
Submitted to: BioMed Central (BMC) Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/2013
Publication Date: 8/15/2013
Citation: Vrentas, C.E., Greenlee, J.J., Baron, T., Caramelli, M., Czub, S., Nicholson, E.M. 2013. Stability properties of PrPSc from cattle with experimental transmissible spongiform encephalopathies: use of a rapid whole homogenate, protease-free assay. BMC Veterinary Research. 9:167. Interpretive Summary: Transmissible spongiform encephalopathies (TSEs), including scrapie in sheep, chronic wasting disease in cervids, and bovine spongiform encephalopathy (BSE) in cattle, are fatal diseases of the nervous system associated with the accumulation of a misfolded form of the prion protein (PrP**Sc). Different strains of BSE exist, including classical (infectious) BSE and atypical BSE (the H-type and L-type strains, proposed to arise spontaneously; and E211K BSE, an inherited form). TSE strains can be differentiated by a combination of features including a stability assay that measures the unfolding of PrP**Sc. In this work, we provide the first direct application of the stability assay to strains of BSE (as well as other cattle-passaged TSEs) in order to assess potential uses of this assay in strain discrimination as well as to improve our understanding of the properties and relationships of these disease strains. Overall, we demonstrate that the stability of cattle PrP**Sc is largely invariant with the exception of H-type BSE, which exhibits a higher stability. The stability of E211K BSE is consistent with its previous assignment as an H-type strain. While the difference in stability under these experimental conditions is not large enough for rapid use in the diagnostic laboratory, future research on the role of sample conditions in this assay may be able to utilize these differences for assay development. In addition, our results highlight the need for continuing research on the biochemical nature of BSE strains, in order to the understand the relationships between stability properties and other assays used to discriminate between strains, as well as to understand the origin of tissue-specific differences in PrP**Sc.
Technical Abstract: Transmissible Spongiform Encephalopathies (TSEs), including scrapie in sheep, chronic wasting disease (CWD) in cervids, and bovine spongiform encephalopathy (BSE), are fatal diseases of the nervous system associated with accumulation of misfolded prion protein (PrPSc). Different strains of BSE exist, including classical BSE, H- and L-type atypical BSE, and H-type BSE associated with the inherited E211K prion protein polymorphism. Strains are associated with different PrPSc conformations that can be probed by the stability assay, in which PrPSc is treated with increasing concentrations of the denaturant guanidine hydrochloride (GdnHCl). Here, we provide the first comprehensive application of the stability assay to brain tissue from cattle experimentally infected with various TSE isolates. Consistent with previous findings from a single Japanese isolate, the L-type form of BSE is not distinguishable from classical BSE in this assay. In contrast, H-type BSE, as well as E211K BSE, exhibits higher stability than classical BSE, suggesting that increased protection against protease digestion at the BSE N-terminus is associated with a higher stability in GdnHCl. While the difference in stability is not large enough in our version of the assay for effective use in a diagnostic laboratory setting, the use of alternative experimental conditions may enhance this effect. TSEs from other natural host species that have been passaged in cattle, including CWD and transmissible mink encephalopathy, were not distinguishable from cattle classical BSE. These results suggest that the core of PrPSc, as probed in this assay, has similar stability properties among cattle-passaged TSE strains and that the conformational differences that lead to changes in the proteinase K cleavage site do not cause large changes in the stability of PrPSc from BSE-affected cattle.