Role of the goat K222-PrP(C) polymorphic variant in prion infection resistance

Abstract

The prion protein-encoding gene (prnp) strongly influences the susceptibility of small ruminants to transmissible spongiform encephalopathies (TSEs). Hence, selective breeding programs have been implemented to increase sheep resistance to scrapie. For goats, epidemiological and experimental studies have provided some association between certain polymorphisms of the cellular prion protein (PrP(C)) and resistance to TSEs. Among them, the Q/K polymorphism at PrP(C) codon 222 (Q/K222) yielded the most promising results. In this work, we investigated the individual effects of the K222-PrP(C) variant on the resistance/susceptibility of goats to TSEs. For that purpose, we generated two transgenic mouse lines, expressing either the Q222 (wild type) or K222 variant of goat PrP(C). Both mouse lines were challenged intracerebrally with a panel of TSE isolates. Transgenic mice expressing the wild-type (Q222) allele were fully susceptible to infection with all tested isolates, whereas transgenic mice expressing similar levels of the K222 allele were resistant to all goat scrapie and cattle BSE isolates but not to goat BSE isolates. Finally, heterozygous K/Q222 mice displayed a reduced susceptibility to the tested panel of scrapie isolates. These results demonstrate a highly protective effect of the K222 variant against a broad panel of different prion isolates and further reinforce the argument supporting the use of this variant in breeding programs to control TSEs in goat herds.

Importance: The objective of this study was to determine the role of the K222 variant of the prion protein (PrP) in the susceptibility/resistance of goats to transmissible spongiform encephalopathies (TSEs). Results showed that transgenic mice expressing the goat K222-PrP polymorphic variant are resistant to scrapie and bovine spongiform encephalopathy (BSE) agents. This protective effect was also observed in heterozygous Q/K222 animals. Therefore, the single amino acid exchange from Q to K at codon 222 of the cellular prion protein provides resistance against TSEs. All the results presented here support the view that the K222 polymorphic variant is a good candidate for selective breeding programs to control and eradicate scrapie in goat herds.

FIG 1

Brain PrP^C expression in hemizygous Q₂₂₂-Tg501 (A) and K₂₂₂-Tg516 (B) mouse lines in comparison with that in goat brain. Immunoblotting of PrP^C was performed with the 12B2 MAb. Direct samples (10% brain homogenates) and 1/2 serial dilutions were loaded onto 12% Bis-Tris gels. The figure illustrates a representative set of data for three independent experiments. Relative molecular masses (kDa) are indicated on the left.

FIG 2

PrP^res of goat scrapie isolates both before and after transmission in Q₂₂₂-Tg501 mice. Immunoblots show brain PrP^res detected with the Sha31 MAb. Similar quantities of PrP^res were loaded for adequate comparison. Molecular masses (kDa) are shown on the right.

FIG 3

PrP^res of BSE isolates before and after transmission in either Q₂₂₂-Tg501 or K₂₂₂-Tg516 mice. Immunoblots show brain PrP^res detected with the Sha31 MAb. Similar quantities of PrP^res were loaded for adequate comparison. Molecular masses (kDa) are shown on the right.