Biology of Prion Protein and the TSE Diseases

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Prion diseases or transmissible spongiform encephalopathies are infectious neurodegenerative diseases of humans and animals. A major feature of prion diseases is the refolding and aggregation of a normal host protein, prion protein (PrP), into a disease-associated form which may contribute to brain damage. In uninfected individuals normal PrP is anchored to the outer cell membrane by a sugar-phosphate-lipid linker molecule, known as GPI. In FY11 we investigated the role of anchoring of PrP to the cell membrane in the process of transport of infection to the brain from sites of inoculation outside the brain. We found that cell membrane anchored PrP was very important for the transport of infection to brain via nerves such as the sciatic nerve or nerves from the tongue or eye. Furthermore, transport to brain by blood after direct intravenous inoculation was also rare and very slow, requiring 400 to 600 days. Together these data indicate that spread of prion infectivity to brain from peripheral sites requires nerves which express membrane anchored PrP. The mechanism of the role of membrane anchored PrP in nerval transport of prion infectivity remains unknown. In other experiments in FY11, we found that expression of normal cellular prion protein was able to influence glutamate uptake by mouse astrocytes in vitro. PrP knockout (KO) astrocytes transported glutamate almost twice as fast as normal astrocytes. Furthermore, mixed cultures of astrocytes plus neurons from PrPKO mice were more sensitive to glutamate-induced excitotoxicity than similar cultures from normal mice. The molecular mechanism of this effect is currently under investigation. In FY11 experiments using chronic wasting disease (CWD) infectivity in transgenic (tg) mice expressing deer PrP showed that tg mice with the 96SS deer PrP allele were resistant to CWD from 96SS deer or from deer with other PrP alleles. Thus these tg mice appeared to have a very strong resistance to infection by all forms of CWD tested to date.