In this project, mice were inoculated intracerebrally with recombinant PrP that had been refolded into alpha monomeric, oligomeric or amyloid fibril conformations. Mouse lines used expressed either wild type murine PrP, or murine PrP containing a proline to leucine mutation at codon 101 (101LL mice). This mutant line had previously been shown to accumulate PrP amyloid plaques following inoculation of brain material from a case of human prion disease in which the pathology was mainly associated with amyloid plaque deposition.
Wild type mice showed no evidence of PrP accumulation in the brain after receiving any of the refolded recombinant isoforms. 101LL mice also showed no PrP accumulation after receiving alpha monomeric or oligomeric isoforms, but several 101LL mice that received recombinant PrP amyloid fibrils showed the presence of large PrP amyloid plaques in the brain after>300 days post inoculation. Fibrils refolded from both wild type and 101L recombinant PrP induced plaque formation in 101LL mice, indicating that the amino acid sequence of the seed is not critical to initiate seeding, but the amyloid conformation is essential. These experiments therefore show that PrP plaques can be seeded in healthy mice using refolded recombinant PrP amyloid fibrils, and that this seeding activity does not require brain homogenate from a case of Prion disease, but could potenitally be initiated by any fibrilar seed intorduced into the brain.