Mixtures of prion substrains in natural scrapie cases revealed by ovinised murine models

Tomás Barrio,Belén Marín,Alicia Otero,Hicham Filali,Vincent Béringue,Juan María Torres,Olivier Andréoletti,Rosa Bolea,Martin Groschup,Enric Vidal,Jessica Sheleby-Elías,Juan José Badiola

doi:10.1038/s41598-020-61977-1

Abstract

Phenotypic variability in prion diseases, such as scrapie, is associated to the existence of prion strains, which are different pathogenic prion protein (PrPSc) conformations with distinct pathobiological properties. To faithfully study scrapie strain variability in natural sheep isolates, transgenic mice expressing sheep cellular prion protein (PrPC) are used. In this study, we used two of such models to bioassay 20 scrapie isolates from the Spain-France-Andorra transboundary territory. Animals were intracerebrally inoculated and survival periods, proteinase K-resistant PrP (PrPres) banding patterns, lesion profiles and PrPSc distribution were studied. Inocula showed a remarkable homogeneity on banding patterns, all of them but one showing 19-kDa PrPres. However, a number of isolates caused accumulation of 21-kDa PrPres in TgShp XI. A different subgroup of isolates caused long survival periods and presence of 21-kDa PrPres in Tg338 mice. It seemed that one major 19-kDa prion isoform and two distinct 21-kDa variants coexisted in source inocula, and that they could be separated by bioassay in each transgenic model. The reason why each model favours a specific component of the mixture is unknown, although PrPC expression level may play a role. Our results indicate that coinfection with more than one substrain is more frequent than infection with a single component.

Highlights

Phenotypic variability in prion diseases, such as scrapie, is associated to the existence of prion strains, which are different pathogenic prion protein (PrPSc) conformations with distinct pathobiological properties
Further demonstration of the existence of scrapie strains was addressed by studies in wild type mice[13,14], which established a methodology to discriminate them according to survival periods and lesion profiles[15,16,17]
With the aim of including as many different scrapie strains as possible, the selection was done according to two criteria: (a) animals coming from geographically distant scrapie outbreaks (Supplementary Fig. S1), and (b) animals presenting distinct clinical signs

Summary

Introduction

Phenotypic variability in prion diseases, such as scrapie, is associated to the existence of prion strains, which are different pathogenic prion protein (PrPSc) conformations with distinct pathobiological properties. A different subgroup of isolates caused long survival periods and presence of 21-kDa PrPres in Tg338 mice It seemed that one major 19-kDa prion isoform and two distinct 21-kDa variants coexisted in source inocula, and that they could be separated by bioassay in each transgenic model. The existence of prion strains can be accommodated within the protein-only hypothesis through the notion that the abnormal conformation of PrPSc is not unique In this model, prion strains are encoded in the conformation of PrPSc molecules, which can adopt several folding states that are associated to different pathological features[22,23,24]. When transmission to wild-type mice is achieved, survival periods tend to be very prolonged and highly variable[26] This phenomenon is known as transmission barrier[31,32] and was observed in experimental transmissions of other TSEs to rodent models[33]. Studying scrapie strain variability by means of bioassay in a model expressing a non-ovine PrPC may alter the original portfolio of prion variants to the point that it keeps little if any resemblance with the original sheep scrapie strain range

Methods

Results

Conclusion