Determining the relative susceptibility of four prion protein genotypes to atypical scrapie

Authors: Silva, Christopher - Chris; Erickson-Beltran, Melissa; MARTÍN-BURRIEL, INMACULADA - University Of Zaragoza; BADIOLA, JUAN JOSE' - University Of Zaragoza; REQUENA, JESUS - University Of Santiago De Compostela; BOLEA, ROSA - University Of Zaragoza

Submitted to: Analytical Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/14/2017
Publication Date: 12/14/2017
Citation: Silva, C.J., Erickson-Beltran, M.L., Martín-Burriel, I., Badiola, J., Requena, J.R., Bolea, R. 2017. Determining the relative susceptibility of four prion protein genotypes to atypical scrapie. Analytical Chemistry. 90(2):1255-1262. https://doi.org/10.1021/acs.analchem.7b03985.
DOI: https://doi.org/10.1021/acs.analchem.7b03985

Interpretive Summary: Atypical scrapie is a fatal prion disease of sheep that is thought to arise spontaneously. Prions are infectious proteins that are able to convert a normal cellular prion protein into a prion to propagate an infection in the brain. Each sheep receives a copy of the gene producing the normal cellular prion protein from its parents. Animals with two different genes produce two differently substituted forms of the normal cellular prion protein and are referred to as heterozygotes. Since atypical scrapie is a spontaneous disease, heterozygotes allow a direct comparison of prion propagation rates in the same animal producing two different normal cellular prion proteins. The amount of normal cellular prion protein that an animal produces influences the course of prion disease. The more normal cellular prion protein an animal produces, the faster the prion disease progresses. Four heterozygous sheep naturally (not experimentally) infected with atypical scrapie and two uninfected sheep were analyzed. The amount of normal cellular prion protein present in their brains was determined. In addition, the relative amounts of each normal cellular prion protein polymorphism found in the prions were also determined. The amount of normal cellular prion protein in both the infected and uninfected sheep was similar, which indicates that atypical scrapie is not caused by sheep producing more of the normal cellular prion protein. In these experimental animals, both forms of the normal cellular prion protein propagated prions at a similar rate. This indicates that there are likely to be no prion polymorphisms that will protect sheep from atypical scrapie.

Technical Abstract: Atypical scrapie is a sheep prion (PrPSc) disease whose epidemiology is consistent with a sporadic origin and is associated with specific polymorphisms of the normal cellular prion protein (PrPC). We describe a mass spectrometry-based method of detecting and quantifying the polymorphisms of sheep PrPC associated with atypical scrapie. Chymotrypsin was used digest the PrP protein to generate characteristic peptides spanning polymorphisms at positions 136, 141, 154, 171 and 172 of sheep PrPC. A multiple reaction monitoring method (MRM) employing 15N-labeled internal standards was used to detect and quantify the amounts of these polymorphisms present in both the PrPSc and PrPC from heterozygous (ALRRY and ALHQY or ALRQY or ALRQD or AFRQY) sheep infected with atypical scrapie, or uninfected controls. Heterozygous animals express their PrPC polymorphisms in equal amounts and the overall amount of PrPC present in the infected or uninfected animals was similar. PrPSc isolated from those heterozygotes was composed of significant amounts of both PrP polymorphisms. Thus, an atypical scrapie infection does not result from an overexpression of sheep PrPC and the replication of all atypical scrapie prions (A136/A136 homozygotes) occur at comparable rates, despite polymorphisms at positions 141, 154, 171, or 172.