These findings raise the possibility that heart infection could be a new aspect of prion diseases, including those that affect humans and livestock, and that these diseases could travel through the blood.
The paper is being published on Friday, July 7 in an advanced, online edition of the journal Science.
Prion diseases-also known as transmissible spongiform encephalopathies because of the sponge-like holes created in the brain-include scrapie in sheep, mad cow disease in cattle, chronic wasting disease in deer and elk, and new variant Creutzfeldt-Jacob disease in humans. These diseases are unusual because unlike other infectious diseases, prion diseases appear to be transmitted by a protein, specifically a misfolded form of a normal cellular protein, the prion.
"Until now, prion disease has been thought of as a chronic neurological condition," says Scripps Research Professor Michael B. Oldstone, M.D., who led the research. "Our study has shown, however, that it can have other manifestations, therefore expanding the types of conditions it could cause."
In the newly reported study, investigators at Scripps Research found infectious misfolded prion protein in heart muscle. Although several types of protein are known to form heart amyloid, this is the first time prion protein amyloid in heart tissue has been identified. Only misfolded prion proteins are infectious.
After making this surprising finding, Scripps Research investigators secured the help of Kirk Knowlton, M.D., chief of the division of cardiology at the University of California, San Diego, who investigated the effect of prion protein amyloid on mouse heart function, discovering that it decreased the heart's ability to pump blood.
Significantly, unusually high levels of scrapie infectivity were also identified in the blood of the same mice used in the heart study. "This is the first system in which prion disease agents were found reproducibly an
Contact: Keith McKeown
Scripps Research Institute