Strain-Dependent Prion Infection in Mice Expressing Prion Protein with Deletion of Central Residues 91-106.

Conformational conversion of the cellular prion protein, PrP (c), into the abnormally folded isoform, PrPSc, is a key pathogenic event in prion diseases. However, the exact conversion mechanism remains largely unknown. Transgenic mice expressing PrP with a deletion of the central residues 91-106 were generated in the absence of endogenous PrP (c), designated Tg(PrP increment 91-106)/Prnp(0/0) mice and intracerebrally inoculated with various prions. Tg(PrP increment 91-106)/Prnp(0/0) mice were resistant to RML, 22L and FK-1 prions, neither producing PrPSc increment 91-106 or prions in the brain nor developing disease after inoculation. However, they remained marginally susceptible to bovine spongiform encephalopathy (BSE) prions, developing disease after elongated incubation times and accumulating PrPSc increment 91-106 and prions in the brain after inoculation with BSE prions. Recombinant PrP increment 91-104 converted into PrPSc increment 91-104 after incubation with BSE-PrPSc-prions but not with RML- and 22L-PrPSc-prions, in a protein misfolding cyclic amplification assay. However, digitonin and heparin stimulated the conversion of PrP increment 91-104 into PrPSc increment 91-104 even after incubation with RML- and 22L-PrPSc-prions. These results suggest that residues 91-106 or 91-104 of PrP are crucially involved in prion pathogenesis in a strain-dependent manner and may play a similar role to digitonin and heparin in the conversion of PrP into PrPSc.