The amino acid residue in position 163 of canine PrPC is critical to the exceptional resistance of dogs to prion infections: evidence from transgenic mouse models

Abstract

Unlike other species, such as cattle, cats or humans, prion disease has never been described in dogs, even though they were similarly exposed to the bovine spongiform encephalopathy (BSE) agent. This resistance prompted a thorough analysis of the canine PRNP gene and the presence of a negatively charged amino acid residue in position 163 was readily identified as potentially fundamental as it differed from all known susceptible species. Furthermore, recent results from our group demonstrated that mouse PRNP with the dog substitution N158D (mouse equivalent to position 163) rendered mice resistant to prion infection. In the present study, a transgenic mouse model was generated expressing dog prion protein (with glutamic acid at position 163) and challenged intracerebrally with a panel of prion isolates (including cattle BSE, sheep scrapie, atypical sheep scrapie, atypical BSE-L, sheep-BSE and chronic wasting disease, among others) none of which could infect them. The brains of these mice were subjected to in vitro prion amplification and failed to find even minimal amounts of misfolded prions providing definitive experimental evidence that dogs are resistant to prion disease. Subsequently, a second transgenic model was generated in which aspartic acid in position 163 was substituted for asparagine (the most common amino acid in this position in prion susceptible species) and this mutation resulted in susceptibility to BSE-derived isolates.\n\nThese findings strongly support the hypothesis that the amino acid residue at position 163 of canine PrPC is a major determinant of the exceptional resistance of the canidae family to prion infection and establish this as a promising therapeutic target for prion diseases.\n\nAUTHOR SUMMARYCats, cattle, people and dogs were all exposed to mad cow disease but, unlike the other three, dogs never succumbed to the disease. We generated a mouse model expressing canine prion protein (instead of mouse prion protein) to provide experimental evidence that dogs are resistant to prion infection by challenging the mice with a panel of prion isolates. None of the prions could infect our transgenic mice that expressed dog prion protein. When the prion protein amino acid sequence of dogs was compared to that of other susceptible species, one amino acid in a specific position was found to be different to all the prion-susceptible animals. To determine if this amino acid was the one responsible for dogs resistance to prions, a second mouse model was generated with the canine prion protein but the critical amino acid was substituted for the one susceptible species have. When this model was challenged with the same panel of prions it could be infected with at least one of them. These results demonstrate the relevance of this amino acid position in determining susceptibility or resistance to prions, and this information can be used to design preventative treatments for prion diseases.