Characterization of the prion protein in relation to normal cellular function and in disease

Transmissible spongiform encephalopathies (TSEs), also known as prion diseases, are a group of rare and fatal neurodegenerative disorders that can affect both human and animals. Evidence indicates that the key event in prion disease pathogenesis is the conformational conversion of the normal cellular prion protein (PrPC) into an aggregated isoform called the scrapie prion protein (PrPSc). The normal function of PrPC is still not known but the protein is essential for transmission of prion diseases. Defining the physiological activities of PrPC is crucial for understanding the normal function and pathogenesis of prion diseases. In this thesis, the proteolytic cleavages and shedding of PrPC were studied. PrPC was shown to be released from the cell by three different mechanisms. The first mechanism released a N-terminal fragment of PrPC by α-cleavage, the second released the full length PrPC and a C-terminal fragment without GPI-anchor via an extreme C-terminal cleavage and a third mechanism released PrPC in association with exosomes. It was also shown that a deletion in the α-cleavage site inhibited the α-cleavage of PrPC and that the α-cleavage likely took place at the cell surface. Metalloproteases have been suggested to be involved in the different cleavages. Here, it was shown that metalloproteases were involved in the cleavage of the extreme C-terminal end, but not in the α-cleavage of PrPC. Nor98/atypical scrapie was identified in Norway for the first time in 1998. Characterization of the molecular and genetic properties in two Swedish cases of Nor98 showed that unique proteinase K (PK)-resistant fragments are present in Nor98-affected sheep. The existence of two PK-resistant fragments that share overlapping regions suggests that at least two distinct PrP conformations are present in brain extracts from affected sheep. Chronic wasting disease (CWD) affects cervids in North America. Here, it was shown that the PrP sequence of cervids in Scandinavia is similar to genotypes connected with CWD susceptibility in North American cervid species. Also, the European moose was shown to have a unique variation in codon 109 with 109K/Q and 109Q/Q