Project 1: Modeling the Mechanisms of Prion Transmission, Strain Selection, Mutation and Species Barrier in Transgenic Mice

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Our broad, long-term objectives are to are to decipher the mechanisms by which infectious prions replicate, encode strain information, and evolve to acquire new properties. We propose four Specific Aims to address our central hypothesis that incompletely adapted prion strains are comprised of poorly optimized ensembles of PrPSc quasi species conformers that evolve under selective pressure towards states of enhanced stability and pathogenicity. Our particular focus is chronic wasting disease (CWD), an uncontrollable contagious epidemic of cervids of uncertain zoonotic potential. Using genetically engineered CWD-susceptible mice, cultured cells, cell free amplification, and antibodies recognizing defined conformation-dependent PrP epitopes, Aim I will address the mechanism of adaptation of unstable emergent CWD prions in response to physical and chemical constraints. In Aim II we will address the hypothesis that that residue 226 and other cervid PrP polymorphisms influence selection of distinct portfolios of CWD strain conformers with different adaptive potentials. Using gene targeted mice expressing physiologically controlled levels of PrP variants and in vitro systems for prion replication, we will characterize the properties of strains propagated in these backgrounds and explore whether interference between them affects selection and adaptation of CWD. In Aim III, we will assess the properties of emergent Norwegian moose and reindeer CWD strains experimentally propagated in deer and compare with established North American CWD. Aim IV will address an unmet need in the field of significant importance, namely the paucity of model systems and tools for studying human prions. Using newly generated gene targeted mice expressing physiological levels of human PrP and novel approaches to derive susceptible human neuroblastoma cells, we will assess the zoonotic potential of emergent CWD strains and their adapted derivatives propagated in different cervid PrP backgrounds. Our ultimate goal is to assess and manage the risk posed to humans from continually evolving prions, specifically those causing CWD, by understanding the means by which they propagate and exist as heritable strains with protean host range properties that adapt and evolve under selective pressure.