Prion diseases in humans and animals comprise a group of invariably fatal neurodegenerative diseases characterized by the formation of a pathogenic protein conformer designated PrPSc and infectious particles denoted prions. The cellular prion protein (PrPC) has a central role in the pathogenesis of prion disease. First, it is the precursor of PrPSc and infectious prions and second, its expression on neuronal cells is required to mediate toxic effects of prions. To specifically study the role of PrPC as a mediator of toxic signaling, we have developed novel cell culture models, including primary neurons prepared from PrP-deficient mice. Using these approaches we have been able to show that PrPC can interact with and mediate toxic signaling of various beta-sheet-rich conformers of different origins, including amyloid beta, suggesting a pathophysiological role of the prion protein beyond prion diseases. Copyright (C) 2011 S. Karger AG, Basel