Adaptive selection of a prion strain conformer corresponding to established North American CWD during propagation of novel emergent Norwegian strains in mice expressing elk or deer prion protein

Abstract

Prions are infectious proteins causing fatal, transmissible neurodegenerative diseases of animals and humans. Replication involves template-directed refolding of host encoded prion protein, PrPC, by its infectious conformation, PrPSc. Following its discovery in captive Colorado deer in 1967, uncontrollable contagious transmission of chronic wasting disease (CWD) led to an expanded geographic range in increasing numbers of free-ranging and captive North American (NA) cervids. Some five decades later, detection of PrPSc in free-ranging Norwegian (NO) reindeer and moose marked the first indication of CWD in Europe. To assess the properties of these emergent NO prions and compare them with NA CWD we used transgenic (Tg) and gene targeted (Gt) mice expressing PrP with glutamine (Q) or glutamate (E) at residue 226, a variation in wild type cervid PrP which influences prion strain selection in NA deer and elk. Transmissions of NO moose and reindeer prions to Tg and Gt mice recapitulated the characteristic features of CWD in natural hosts, revealing novel prion strains with disease kinetics, neuropathological profiles, and capacities to infect lymphoid tissues and cultured cells that were distinct from those causing NA CWD. In support of strain variation, PrPSc conformers comprising emergent NO moose and reindeer CWD were subject to selective effects imposed by variation at residue 226 that were different from those controlling established NA CWD. Transmission of particular NO moose CWD prions in mice expressing E at 226 resulted in selection of a kinetically optimized conformer, subsequent transmission of which revealed properties consistent with NA CWD. These findings illustrate the potential for adaptive selection of strain conformers with improved fitness during propagation of unstable NO prions. Their potential for contagious transmission has implications for risk analyses and management of emergent European CWD. Finally, we found that Gt mice expressing physiologically controlled PrP levels recapitulated the lymphotropic properties of naturally occurring CWD strains resulting in improved susceptibilities to emergent NO reindeer prions compared with over-expressing Tg counterparts. These findings underscore the refined advantages of Gt models for exploring the mechanisms and impacts of strain selection in peripheral compartments during natural prion transmission.

A single amino acid residue in bank vole prion protein drives permissiveness to Nor98/atypical scrapie and the emergence of multiple strain variants

“…Data points represent the mean ± SEM of at least five mice per group. Brain-scoring areas: medulla [ 1 ], cerebellum [ 2 ], superior colliculus [ 3 ], hypothalamus [ 4 ], thalamus [ 5 ], hippocampus [ 6 ], septum [ 7 ], retrosplenial and adjacent motor cortex [ 8 ], and cingulate and adjacent motor cortex [ 9 ]. (B) Representative western blot showing PK-treated PrP Sc from brains of tg338 mice inoculated with the AS isolates (indicated on the top of the blot).…”

“…We previously reported the lack of transmission of AS isolates from Norway and UK in bank voles carrying methionine at PrP codon 109 (BvM) [55,72]. In this study, we challenged BvM superior colliculus [3], hypothalamus [4], thalamus [5], hippocampus [6], septum [7], retrosplenial and adjacent motor cortex [8], and cingulate and adjacent motor cortex [9]. Immunohistochemical detection of PrP Sc in the cerebellar cortex was performed with SAF84 mAb.…”

“…Animal TSEs present largely as acquired diseases: classical scrapie (CS) in small ruminants, bovine spongiform encephalopathy (BSE) in cattle, chronic wasting disease (CWD) in cervids, and, likely, the recently discovered prion disease of dromedary camels [2,3]. However, the existence of sporadic or idiopathic forms in animals is increasingly recognized: H-and L-BSE in cattle [4,5], Nor98/atypical scrapie (AS) in small ruminants [6] and, possibly, the newly discovered forms of CWD in some European cervid species [7][8][9][10][11] do not show an obvious infectious origin and are often supposed to be spontaneous.…”

No evidence of uptake or propagation of reindeer CWD prions in environmentally exposed sheep

“…However, it is important to acknowledge that transmission studies using North American CWD isolates must be interpreted with caution. Several recent papers report differences between Norwegian and North American CWD isolates [ 13 , 62 , 63 ]. Norwegian reindeer CWD has a remarkably low attack rate in bank voles [ 12 ] but transmits efficiently into transgenic and gene-targeted cervidized mice, albeit with longer incubation times than North American moose CWD [ 62 ].…”

“…Several recent papers report differences between Norwegian and North American CWD isolates [ 13 , 62 , 63 ]. Norwegian reindeer CWD has a remarkably low attack rate in bank voles [ 12 ] but transmits efficiently into transgenic and gene-targeted cervidized mice, albeit with longer incubation times than North American moose CWD [ 62 ]. An in vitro protein misfolding cyclic amplification (PMCA) study suggests that Norwegian reindeer CWD may be transmitted easier than North American isolates to sheep, cattle, hamsters, and mice (all transgenic mice substrates), but less efficiently to humans (substrate from humanized mice) compared to North American isolates [ 63 ].…”