Characterization of de novo generation of infectious prions

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DESCRIPTION (provided by applicant): Transmissible spongiform encephalopathies (TSEs) are a group of neurodegenerative disorders affecting both humans and animals. There is no available treatment or therapy for these fatal diseases. TSEs can have diverse origins, including hereditary, sporadic (putatively spontaneous), and infectious. The occurrence of spontaneous cases of prion diseases in humans (sporadic CJD) and in other species, i.e. Bovine spongiform encephalopathy (BSE) in US cattle and Nor98 (atypical scrapie) in New Zealand sheep, provide evidence that this infrequent spontaneous phenomenon may occur naturally. There are no reported cases of spontaneously- occurring (de novo) prion disease in experimental wild-type rodent models. The infectious agent associated with TSEs, the prion, appears to be composed uniquely of a protein which is a conformationally-modified version (PrPSc) of a natural prion protein (PrPC). The disease is transmitted by the conversion of host PrPC into PrPSc induced by small quantities of PrPSc contained in the infectious agent. We have recently described a novel technique, Protein Misfolding Cyclic Amplification (PMCA), which mimics this process in vitro, but with greatly accelerated kinetics, enabling PrPSc amplification in the test tube. This technique has been used to efficiently amplify a variety of prion strains from mice, hamsters, bank voles, deer, cattle, sheep, and humans. In addition, the in vitro generated prions possess key prion features, i.e., they are infectious in vivo and maintain their prion strain specificity. However, it has not been previously possible to generate infectivity de novo, starting with healthy material. In other words, the spontaneous generation of prions has been hypothesized to be restricted to an infrequent in vivo phenomenon in only a few species. To mimic spontaneous generation of infectivity in vitro is one of the most important challenges that the prion field currently faces. In preliminary studies, we have generated infectious prions from ten different rodent species (including wild animals) starting with non-infectious brains. The major goal of this project is the de novo generation and characterization of a diversity of infectious prion strains using several in vitro and in vivo approaches as well as revealing the intrinsic mechanisms involved by distinguishing amplification of minimal preexisting seed PrPSc from "in vitro spontaneous" generation. Finally, we will extend this study to other species to mimic what may already be happening in nature. PUBLIC HEALTH RELEVANCE: Prion diseases are a group of fatal and infectious neurodegenerative disorders affecting humans and animals for which no therapy is available. The nature of the infectious agent is at the center of passionate controversy. The mechanism by prion agent propagates the disease in vivo is being subject to intense investigation. The most common origin of the disease is an unfamiliar spontaneous phenomenon. Unfortunately, there are no reported cases of spontaneously-occurring (de novo) prion diseases in experimental models making the study of this intriguing occurrence more difficult. In this proposal, we show strong evidence using rodent models where this phenomenon can be mimicked in vitro. This find opens enormous possibilities for understanding the prion diseases and for designing new therapies inconceivable until now.