Mechanisms of Prion Protein Toxicity

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The overall goal of this application is to understand the mechanisms by which prions cause damage to synapses, and establish and maintain a self-propagating infection in the CNS. We also wish to develop pharmacologic therapies for these disorders based on our knowledge of the molecular and cellular mechanisms underlying the disease process. Although the molecular templating model for prion propagation, in which PrPC is converted into infectious PrPSc, is now widely accepted, the mechanisms by which prions actually cause neurodegeneration have remained mysterious. There is now considerable evidence that cell- surface PrPC mediates many of the neurotoxic effects of PrPSc, likely by serving as a receptor that binds PrPSc during the first step of the prion conversion process. However, how this initiates downstream toxic signals in the cytoplasm, and how these signals alter synaptic structure or function were largely unknown. The work we have accomplished during the previous grant cycle has provided key insights into this issue by defining a PrPC/NMDAR/p38 MAPK signaling pathway that mediates the earliest effects of PrPSc synaptotoxicity. Based on a combination of structural analysis and functional assays, we have proposed a model in which the N-terminal domain of PrPC serves as a toxic effector that is regulated by specific docking interactions with the C-terminal domain. Artificial disruption of this intramolecular interaction results in a variety of toxic activities in cellular and transgenic models. In this renewal application, we propose, first, to elucidate how prion synaptotoxic signaling is initiated at the cell surface. Second, we plan to dissect the intracellular signaling cascades that are activated by prions, and how they result in synaptic dysfunction. Third, we will investigate the mechanisms by which cells establish and maintain prion infection. We anticipate that the studies proposed here will provide powerful insights into biological mechanisms that are common to multiple neurodegenerative disorders caused by toxic protein aggregates in the brain, and will lead to the discovery of shared therapeutic approaches that can be used to treat them.