Molecular Profiling of Ovine Prion Diseases by Using Thermolysin-Resistant PrP Sc and Endogenous C2 PrP Fragments

Abstract

ABSTRACT Disease-associated PrP fragments produced upon in vitro or in vivo proteolysis can provide significant insight into the causal strain of prion disease. Here we describe a novel molecular strain typing assay that used thermolysin digestion of caudal medulla samples to produce PrP res signatures on Western blots that readily distinguished experimental sheep bovine spongiform encephalopathy (BSE) from classical scrapie. Furthermore, the accumulation of such PrP res species within the cerebellum also appeared to be dependent upon the transmissible spongiform encephalopathy (TSE) strain, allowing discrimination between two experimental strains of scrapie and grouping of natural scrapie isolates into two profiles. The occurrence of endogenously produced PrP fragments, namely, glycosylated and unglycosylated C2, within different central nervous system (CNS) regions is also described; this is the first detailed description of such scrapie-associated fragments within a natural host. The advent of C2 fragments within defined CNS regions, compared between BSE and scrapie cases and also between two experimental scrapie strains, appeared to be largely dependent upon the TSE strain. The combined analyses of C2 fragments and thermolysin-resistant PrP species within caudal medulla, cerebellum, and spinal cord samples allowed natural scrapie isolates to be separated into four distinct molecular profiles: most isolates produced C2 and PrP res in all CNS regions, a second group lacked detectable cerebellar C2 fragments, one isolate lacked both cerebellar PrP res and C2, and a further isolate lacked detectable C2 within all three CNS regions and also lacked cerebellar PrP res . This CNS region-specific deposition of disease-associated PrP species may reflect the natural heterogeneity of scrapie strains in the sheep population in the United Kingdom.