Laboratory mice infected with the agent of scrapie--a brain-wasting disease of sheep--show high levels of the scrapie agent in their heart several hundred days after being infected in the brain, indicating that heart infection might be a new aspect of this disease, according to a research paper released online today by the journal Science.
Collaborators in the work include scientists at the Rocky Mountain Laboratories (RML), part of the National Institute of Allergy and Infectious Diseases (NIAID) of the National Institutes of Health.
"Undoubtedly, this work will enable scientists to pursue new theories about the effects of these deadly brain wasting diseases," says NIH Director Elias A. Zerhouni, M.D. "The implications of this research could be vital to our efforts to slow or stop these diseases."
"Although much work remains to be done, the diseased hearts seen in this mouse study have similarities to human amyloid heart disease, which is potentially significant," says NIAID Director Anthony S. Fauci, M.D.
Scrapie belongs to a group of diseases called prion diseases, also known as transmissible spongiform encephalopathies, or TSEs, because of the sponge-like holes created in the brain. In addition to scrapie in sheep, prion diseases include Creutzfeldt-Jacob disease in humans, mad cow disease in cattle and chronic wasting disease in deer and elk. The cause of prion diseases, still under debate, may be abnormal aggregated forms of prion protein.
The new research has provided cardiologists an animal model in which to study heart amyloidosis, a family of heart diseases that affect humans, says Bruce Chesebro, M.D., an RML virologist and a senior author of the new paper. Amyloidoses involve waxy protein deposits that stiffen the heart, limit its pumping ability and typically lead to fatal heart stoppage.
"Although several types of protein are known to form heart amyloid, this is the first time prion protein amyloid has been found in heart muscle and also found to cause heart malfunction," says Dr. Chesebro. "That's exciting for cardiologists, because this study connects the two fields of research."
Last year, Dr. Chesebro's research group from Hamilton, MT, collaborated with Michael Oldstone, M.D., and other researchers at The Scripps Research Institute in La Jolla, CA, and learned that scrapie-infected mice engineered without an "anchor" between the membrane of cells and the prion protein regularly lived for more than 600 days, ultimately dying of old age, according to Dr. Chesebro. Wild mice infected with scrapie typically die after about 150 days.
In this earlier research, signs of prion protein amyloid were most prominent near blood vessels in the mouse brain. In the newly reported study, researchers at Scripps found similar amyloid in heart muscle. They then 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.
Unusually high levels of scrapie infectivity were also found in the blood of the same mice used in the heart study. In the future, this finding could help scientists develop a blood-based diagnostic test to identify brain-wasting diseases and possibly lead to a way to filter or chemically treat blood to remove any infectious prion disease agents, says Dr. Chesebro.
NIAID is a component of the National Institutes of Health. NIAID supports basic and applied research to prevent, diagnose and treat infectious diseases such as HIV/AIDS and other sexually transmitted infections, influenza, tuberculosis, malaria and illness from potential agents of bioterrorism. NIAID also supports research on basic immunology, transplantation and immune-related disorders, including autoimmune diseases, asthma and allergies.
The National Institutes of Health (NIH)--The Nation's Medical Research Agency--includes 27 Institutes and Centers and is a component of the U. S. Department of Health and Human Services. It is the primary federal agency for conducting and supporting basic, clinical and translational medical research, and it investigates the causes, treatments and cures for both common and rare diseases. For more information about NIH and its programs, visit http://www.nih.gov.
References: MJ Trifilo et al. Prion-induced amyloid heart disease with high blood infectivity in transgenic mice. Science 313:94-97 (2006). DOI: 10.1126/science.1128635.
B Chesebro et al. Anchorless prion protein results in infectious amyloid disease without clinical scrapie. Science 308 (5727):1435-39 (2005). DOI: 10.1126/science.1110837.
News releases, fact sheets and other NIAID-related materials are available on the NIAID Web site at http://www.niaid.nih.gov.
Journal
Science