Assessment of the Zoonotic Potential of Atypical Scrapie Prions in Humanized Mice Reveals Rare Phenotypic Convergence but Not Identity With Sporadic Creutzfeldt-Jakob Disease Prions

Abstract

Background Atypical/Nor98 scrapie (AS) is an idiopathic infectious prion disease affecting sheep and goats. Recent findings suggest that zoonotic prions from bovine spongiform encephalopathy (C-BSE) may co-propagate with atypical/Nor98 prions in AS sheep brains. Investigating the risk AS poses to humans is crucial. Methods To assess the risk of sheep/goat-to-human transmission of AS, we serially inoculated brain tissue from field and laboratory isolates into transgenic mice overexpressing human prion protein (Met129 allele). We studied clinical outcomes as well as presence of prions in brains and spleens. Results No transmission occurred on the primary passage, with no clinical disease or pathological prion protein in brains and spleens. On subsequent passages, one isolate gradually adapted, manifesting as prions with a phenotype resembling those causing MM1-type sporadic Creutzfeldt-Jakob disease in humans. However, further characterization using in vivo and in vitro techniques confirmed both prion agents as different strains, revealing a case of phenotypic convergence. Importantly, no C-BSE prions emerged in these mice, especially in the spleen, which is more permissive than the brain for C-BSE cross-species transmission. Conclusions The results obtained suggest a low the zoonotic for AS. Rare adaptation may allow the emergence of prions phenotypically resembling those spontaneously forming in humans.

Human PrP E219K as a new and promising substrate for RT-QuIC amplification of human prion strains: a first step towards strain discrimination

“…Of note, we also were able to discriminate tg650-MM2-c from the other tg650-sCJD strains, and we show that tg650-MM1 and tg650-MV1 which give similar phenotypes in tg650 mice have different seeding activities and are thus likely to be associated with different prion strains. RT-QuIC kinetic parameters and conditions appear as tools to discriminate between prion strains, as shown here or as shown to discriminated between tg650-adaptated MM1 and atypical scrapie [37]. Testing a lager cohort of samples and RT-QuIC conditions would be of interest to better achieve prion strain discrimination.…”

“…Two uL of these dilutions were then used to initiate RT-QuIC reactions. As previously reported in [37,39], the fitted fluorescence intensity mean of the positive reaction at each dilution for each strain as a function of time is presented in supplementary Figure 1. From these curves, the lag time was calculated for each positive reaction.…”

“…Real Time-Quaking Induced Conversion (RT-QuIC) RT-QuIC amplifications were performed as previously described [37,39]. In brief, 1 µL of 10% human BHs or 20% mouse BHs underwent serial 10-fold dilution in 20 mM sodium phosphate buffer pH 7.4, 130 mM NaCl, 0.1% SDS and 1X N2 supplement (Thermo Fisher, France).…”

“…The parameters calculated from the fit included the increase in fluorescence intensity, the slope at the inflection point and the lag time (estimated by extending the tangent at the inflection point to the initial baseline Ymin) [37,39]. The seeding activity titer (SD50; seeding dose giving thioflavin-T positivity in 50% of the replicates) was estimated using the Spearman-Kärber method [38].…”