Molecular Behaviors of “CH1641-Like” Sheep Scrapie Isolates in Ovine Transgenic Mice (TgOvPrP4)

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Abstract
Molecular analyses of the protease-resistant prion protein (PrP res ) from a few natural scrapie isolates showed by Western blotting some partial similarities with those observed in experimental ovine bovine spongiform encephalopathy (BSE). They showed a low apparent molecular mass of unglycosylated PrP res , although diglycosylated PrP res was less abundant than in ovine BSE. The prototype of such cases is the CH1641 experimental scrapie isolate. We analyzed PrP res molecular features from three French natural “CH1641-like” isolates, in comparison with CH1641 and BSE, after transmission of the disease in ovine transgenic mice (TgOvPrP4). One of these isolates (TR316211) behaved like the CH1641 isolate, with PrP res features in mice similar to those in the sheep brain. From two other isolates (O100 and O104), two distinct PrP res phenotypes were identified in mouse brains, with either high (h-type) or low (l-type) apparent molecular masses of unglycosylated PrP res , the latter being similar to that observed with CH1641, TR316211, or BSE. Both phenotypes could be found in variable proportions in the brains of the individual mice. In contrast with BSE, l-type PrP res from “CH1641-like” isolates showed lower levels of diglycosylated PrP res . From one of these cases (O104), a second passage in mice was performed for two mice with distinct PrP res profiles. This showed a partial selection of the l-type phenotype in mice infected with a mouse brain with predominant l-type PrP res , and it was accompanied by a significant increase in the proportions of the diglycosylated band. These results are discussed in relation to the diversity of scrapie and BSE strains.