Strategies for eliminating PrPc as substrate for prion conversion and for enhancing PrPSc degradation

Prion diseases are fatal neurodegenerative infectious disorders for which no therapeutic or prophylactic regimens exist. Our work aims to eliminate PrPc as substrate for the conversion into PrPSc and to increase the cellular clearance capacity of PrPSc. In order to achieve the first objective, we used chemical compounds which interfere with the subcellular trafficking of PrPc, e.g. by intracellular re-routing. Recently, we found that PrPc requires cholesterol for cell surface localisation. Treatment with mevinolin significantly reduced the amount of cell surface PrPc and led to its accumulation in the Golgi compartment. These data show that cholesterol is essential for the cell surface localisation of PrPc, which is in turn known to be necessary for the formation of PrPSc. Another anti-prion strategy uses RNA and peptide aptamers directed against PrPc. We have selected peptide aptamers using a constrained peptide library presented on the active site loop of the Escherichia coli protein TrxA in a Y2H screen. Several peptides reproducibly binding to PrPc in several assays were identified. Preliminary data indicate that selected peptide aptamers are able to interfere with prion propagation in prion-infected cells. To obtain additive effects we have tried to clarify cellular mechanisms that enable cells to clear prion infectivity. This goal was achieved by selective interference in intracellular signalling pathways which apparently also increase the cellular autophagy machinery. Finally, we have tried to establish an active auto-vaccination approach directed against PrP, which gave some positive preliminary results in the mouse system. This might open the door to classical immunological interference techniques.