Molecular basis of prion protein-induced neurodegeneration - Prion diseases are rare, invariably fatal neurodegenerative disorders with pathologic features in common with Alzheimer’s disease, including extracellular protein aggregates, synaptic loss, and neuritic dystrophy. In prion and Alzheimer’s disease models, depletion of neuronal cellular prion protein (PrPC) ameliorates synaptic impairment and clinical disease, strongly implicating neuronal PrPC expression in the altered signal transduction cascades that may underlie synaptotoxicity and endolysosomal dysfunction. We have engineered the first knock-in mouse model with a point mutation in Prnp that develops a striking and severe spongiform encephalopathy, neuritic dystrophy, and altered post-synaptic receptor phosphorylation, in the absence of prion aggregates. Cultured cortical neurons from these knock-in mice show an increased sensitivity to glutamate and dendritic varicosities, suggestive of excitotoxicity. Thus, this PrP knock-in model provides a unique opportunity to elucidate key PrPC interactions and altered signal transduction pathways at the synapse and to determine the molecular mechanisms that link PrPC to synaptic loss and endolysosomal dysregulation. Our long-term goal is to understand how PrPC triggers aberrant neuronal signaling that may drive impaired proteostasis and synaptotoxicity in prion disease. Using cultured primary neurons and mice, we will first determine how the mutant PrPC interactions impact pre- and post-synaptic neuronal protein levels and glutamate receptor function. We will then identify how mutant PrPC dysregulates endolysosomal and proteostatic activity. Finally, we use highly sensitive and quantitative proteomics to define the PrP interactome and phosphoproteome network alterations in the brain by tandem mass tag mass spectrometry analysis. For all aims, we will directly test how the findings from the mutant PrPC-expressing brain compare to prion-infected mouse and human brain. These studies are the first to target the neuronal endolysosomal and synaptic pathways in a knock-in mouse model expressing mutant PrPC, and outcomes are expected to provide key insights into the role of PrPC in synapse maintenance and the signaling pathways inciting synaptic loss, thus revealing new therapeutic targets for prion disease.
