Early translational changes in neurons in prion disease

Neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease, are a growing problem in an ageing population, but are currently untreatable from the point when neurons are lost, as these cannot be replaced. However, changes prior to this point common to various neurodegenerative diseases, including synapse loss and inhibition of translation, can be reversed, and in the case of translational changes this reversal can completely stop further disease progression in some models. With this in mind, this project uses prion disease in mice as a predictable, well defined model of neurodegenerative diseases to investigate what changes, particularly in protein synthesis, take place at the synapse early in the disease, and how this may contribute to ongoing pathology. In order to do this more effectively, a protocol was developed to efficiently isolate intact synapses from whole hippocampal tissue in sufficient volume for further experimentation, consistently and with minimal contamination from cell body or glial proteins. At the same time, microarray analysis of polysomal and subpolysomal RNA from hippocampi of wild-type and prion inoculated mice was carried out, in order to examine global changes in polysome association of different RNAs, a correlate of rate of translation. Changes in polysome association were seen in RNAs previously associated with neurodegenerative diseases and synaptic function, with a particularly significant change seen in the translation of ribosomal sub-units. This included a large number of mRNAs which are specifically regulated by the mTOR pathway, TOP (terminal oligopyrimidine) mRNAs. In neurons, the mTOR pathway is associated with regulation of cellular growth, apoptosis, synaptic plasticity and translation. Changes were seen in the phosphorylation of proteins in this pathway, suggesting altered activation in early prion disease which could be associated with synaptic and translational deficits. This suggests a possible new target for manipulation in order to better understand and treat later neurodegeneration.