Abstract

The large chronic wasting disease (CWD)-affected cervid population in the USA and Canada, and the risk of the disease being transmitted to humans through intermediate species, is a highly worrying issue that is still poorly understood. In this case, recombinant protein misfolding cyclic amplification was used to determine, in vitro, the relevance of each individual amino acid on cross-species prion transmission. Others and we have found that the β2–α2 loop is a key modulator of transmission barriers between species and markedly influences infection by sheep scrapie, bovine spongiform encephalopathy (BSE), or elk CWD. Amino acids that differentiate ovine and deer normal host prion protein (PrPC) and associated with structural rigidity of the loop β2–α2 (S173N, N177T) appear to confer resistance to some prion diseases. However, addition of methionine at codon 208 together with the previously described rigid loop substitutions seems to hide a key in this species barrier, as it makes sheep recombinant prion protein highly susceptible to CWD-induced misfolding. These studies indicate that interspecies prion transmission is not only governed just by the β2–α2 loop amino acid sequence but also by its interactions with the α3-helix as shown by substitution I208M. Transmissible spongiform encephalopathies, characterized by long incubation periods and spongiform changes associated with neuronal loss in the brain, have been described in several mammalian species appearing either naturally (scrapie in sheep and goats, bovine spongiform encephalopathy in cattle, chronic wasting disease in cervids, Creutzfeldt–Jakob disease in humans) or by experimental transmission studies (scrapie in mice and hamsters). Much of the pathogenesis of the prion diseases has been determined in the last 40 years, such as the etiological agent or the fact that prions occur as different strains that show distinct biological and physicochemical properties. However, there are many unanswered questions regarding the strain phenomenon and interspecies transmissibility. To assess the risk of interspecies transmission between scrapie and chronic wasting disease, an in vitro prion propagation method has been used. This technique allows to predict the amino acids preventing the transmission between sheep and deer prion diseases.

Highlights

  • Transmissible spongiform encephalopathies (TSEs) or prionopathies are fatal neurodegenerative disorders affectingChafik Harrathi, Natalia Fernández-Borges and Hasier Eraña contributed to this work.Mol Neurobiol (2019) 56:5287–5303 its spread [2]

  • Using a variant of this technique, in which recombinant PrP is used as source of PrP instead of brain homogenates [37–39], we aim to decipher the determinants of the sheep–deer transmission barrier as proof of concept for the rec-protein misfolding cyclic amplification (PMCA) as a tool by which we can determine the relevance of each amino acid residue in prion proteins that could be involved in a particular species barrier

  • Minute amounts of classical scrapie (Dawson, Langlade, UKA2 and SC21), bovine spongiform encephalopathy (BSE), atypical BSE (BSE-H and BSE-L), and chronic wasting disease (CWD) were subjected to serial rounds of rec-PMCA using ovine and cervine Recombinant ovine or cervine PrPs (rec-PrP) substrates complemented with PRNP−/− brain homogenate

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Summary

Introduction

Transmissible spongiform encephalopathies (TSEs) or prionopathies are fatal neurodegenerative disorders affectingChafik Harrathi, Natalia Fernández-Borges and Hasier Eraña contributed to this work.Mol Neurobiol (2019) 56:5287–5303 its spread [2]. Substitutions into the Ovine Rec-PrP That Has Cervine Substitutions at the β2–α2 Loop Strongly Influences Interspecies Transmissibility In Vitro Previous studies in both transgenic mouse and cell-culture models of prion conversion led to the identification of two residues within the loop between β-sheet 2 and α-helix 2 of the PrP which, when mutated, resulted in loop rigidity. This occurs in species such as the wallaby, horse, and rabbit and increases the propensity of the PrP to misfold in both in vitro and in vivo systems [28, 43–46]. In the absence of one of the substitutions (S173N) that defines the β-sheet 2–α-helix 2 loop rigidity, S98T substitution together with the N177T showed a significant recovery of cervine seed propagation ability that was able to replicate until 10−7 dilution

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