Transgenic Mouse Bioassay: Evidence That Rabbits Are Susceptible to a Variety of Prion Isolates

Abstract

Interspecies transmission of prions is a well-established phenomenon, both experimentally and under field conditions. Upon passage through new hosts, prion strains have proven their capacity to change their properties and this is a source of strain diversity which needs to be considered when assessing the potential risks associated with consumption of prion contaminated protein sources. Rabbits were considered for decades to be a prion resistant species until proven otherwise recently. To determine the extent of rabbit susceptibility to prions and to assess the effects of passage of different prion strains through this species a transgenic mouse model overexpressing rabbit PrPC was developed (TgRab). Intracerebral challenges with prion strains originating from a variety of species including field isolates (ovine SSBP/1 scrapie, Nor98- scrapie; cattle BSE, BSE-L and cervid CWD), experimental murine strains (ME7 and RML) and experimentally obtained ruminant (sheepBSE) and rabbit (de novo NZW) strains were performed. On first passage TgRab were susceptible to the majority of prions (Cattle BSE, SheepBSE, BSE-L, de novo NZW, ME7 and RML) tested with the exception of SSBP/1 scrapie, CWD and Nor98 scrapie. Furthermore, TgRab were capable of propagating strain-specific features such as differences in incubation periods, histological brain lesions, abnormal prion (PrPd) deposition profiles and proteinase-K (PK) resistant western blotting band patterns. Our results confirm previous studies proving that rabbits are not resistant to prion infection and show for the first time that rabbits are susceptible to PrPd originating in a number of other species. This should be taken into account when choosing protein sources to feed rabbits.

Prion replication without host adaptation during interspecies transmissions

“…Even in the rare event that pathogenic horse prions are produced during infection, replication by NAPA ensures that they are paradoxically not optimized for further conversion of EqPrP C upon passage. The properties of horse PrP C therefore differ significantly from rabbit PrP C , a species incorrectly thought to be resistant to prion infection (15,36). Nonetheless, several lines of evidence confirm that our description of NAPA in TgEq is not the result of an idiosyncratic resistance of EqPrP C to support prion replication.…”

“…The importance of primary structural incompatibilities between PrP Sc constituting the prion and PrP C expressed in the new host paved the way for transgenic (Tg) models that abrogate transmission barriers to prions from various species in mice (14) or that model susceptibility of at-risk or seemingly resistant species (15,16). Prion strain properties also influence interspecies prion transmissions.…”

Dogs are resistant to prion infection, due to the presence of aspartic or glutamic acid at position 163 of their prion protein

“…The theoretical susceptibility can be predicted by examining the misfolding capability of the chosen species’ PrP C in vitro by protein misfolding cyclic amplification (PMCA) . Rabbits, a species with no reported field cases of transmissible spongiform encephalopathy (TSE) despite being sympatric with several prion susceptible ruminant species, were shown to have PrP C that was readily misfolded by BSE in vitro, and susceptibility to this prion strain was further corroborated by bioassay in transgenic mice with rabbit PRNP and experimentally in vivo . However, the scenario in horses, another putatively prion‐resistant species, is somewhat different as horse PrP C can be misfolded, either in vitro by PMCA or by means of bioassay in mice expressing equine PrP C (TgEq) (albeit with low efficiency), but the resultant horse‐adapted prions are unable to propagate disease in TgEq mice, even though their ability to infect the original species remains unaltered.…”

In Vitro Approach To Identify Key Amino Acids in Low Susceptibility of Rabbit Prion Protein to Misfolding

“…However, different in vitro experimental approaches developed to study interspecies transmission barriers proved that the existence of mammalian species resistant to prion infection may have been an incorrect assumption (6). This was shown recently by use of protein misfolding cyclic amplification (PMCA) (7) to generate rabbit prions in vitro and resulted in the first TSE reported for leporids (8) and also for transgenic mice expressing rabbit PrP (9). Although the putative resistance to prion diseases of rabbits was disproven, the apparently low attack rate, long incubation period, and requirement for adaptation through PMCA (10,11) to achieve infection demonstrated their low susceptibility to TSE infection (9).…”