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Tuesday, January 25, 2011

Generation of a new form of human PrPSc in vitro by inter-species transmission from cervids prions

Marcelo A. Barria1, Glenn C. Telling2, Pierluigi Gambetti3, James A. Mastrianni4 and Claudio Soto1,*

1Mitchell Center for Alzheimer’s disease and related Brain disorders, Dept of Neurology, University of Texas Houston Medical School, Houston, TX 77030, USA

2Dept of Microbiology, Immunology & Molecular Genetics, and Neurology, Sanders Brown Center on Aging, University of Kentucky Medical Center, Lexington, KY, USA

3Institute of Pathology, Case Western Reserve University, Cleveland, OH, USA

4Dept of Neurology, University of Chicago, Chicago, IL, USA.

Running Title: Conversion of human PrPC by cervid PrPSc

Keywords: Prion / transmissible spongiform encephalopathy / infectivity / misfolded prion protein / prion strains

* To whom correspondence should be addressed. University of Texas Houston Medical School, 6431 Fannin St, Houston, TX 77030. Tel 713-5007086; Fax 713-5000667; E-mail [email protected]

Prion diseases are infectious neurodegenerative disorders affecting humans and animals that result from the conversion of normal prion protein (PrPC) into the misfolded prion protein (PrPSc). Chronic wasting disease (CWD) is a prion disorder of increasing prevalence within the United States that affects a large population of wild and captive deer and elk. Determining the risk of transmission of CWD to humans is of utmost importance, considering that people can be infected by animal prions, resulting in new fatal diseases. To study the possibility that human PrPC can be converted into the misfolded form by CWD PrPSc we performed experiments using the Protein Misfolding Cyclic Amplification (PMCA) technique, which mimic in vitro the process of prion replication. Our results show that cervid PrPSc can induce the conversion of human PrPC, but only after the CWD prion strain has been stabilized by successive passages in vitro or in vivo. Interestingly, the newly generated human PrPSc exhibits a distinct biochemical pattern that differs from any of the currently known forms of human PrPSc. Our results also have profound implications for understanding the mechanisms of prion species barrier and indicate that the transmission barrier is a dynamic process that depend on the strain and moreover the degree of adaptation of the strain. If our findings are corroborated by infectivity assays, they will imply that CWD prions have the potential to infect humans, and that this ability depends on CWD strain adaptation.


Besides the importance of our results for public health in relation to the putative transmissibility of CWD to humans, our data also illustrate a very important and novel scientific concept related to the mechanism of prion transmission across species barriers. Today the view is that species barrier is mostly controlled by the degree of similarity on the sequence of the prion protein between the host and the infectious material (4). In our study we show that the strain and moreover the stabilization of the strain plays a major role in the inter-species transmission. In our system there is no change on the protein sequence, but yet strain adaptation results in a complete change on prion transmissibility with potentially dramatic consequences. Therefore, our findings lead to a new view of the species barrier that should not be seen as a static process, but rather a dynamic biological phenomenon that can change over time when prion strains mature and evolve. It remains to be investigated if other species barriers also change upon progressive strain adaptation of other prion forms (e.g. the sheep/human barrier).

Our results have far-reaching implications for human health, since they indicate that cervid PrPSc can trigger the conversion of human PrPC into PrPSc, suggesting that CWD might be infectious to humans. Interestingly our findings suggest that unstable strains from CWD affected animals might not be a problem for humans, but upon strain stabilization by successive passages in the wild, this disease might become progressively more transmissible to man.

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Tuesday, January 25, 2011

Generation of a new form of human PrPSc in vitro by inter-species transmission from cervids prions

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