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Protein Branded As Culprit in Mad Cow Disease

THURSDAY June 11, 2009 -- Mad cow disease and similar conditions may start with one protein that somehow goes astray and deprives the healthy brain cells of another essential protein, researchers say.

Mad cow disease is considered a prion disease because it has been found to be tied to the prion protein, or PrP, which normally is found on the surface of many cells -- including those found in the brain. When the amino acids that make up PrP are folded or configured abnormally during their creation, these malfunctioning proteins can end up in other parts of the cell and that is when the trouble begins.

Scientists at the National Institutes of Health (NIH) found that misfolded or mislocated PrP can bind with another protein called Mahogunin, which is thought to be vital to brain cells. The binding appears to reduce the effectiveness of Mahogunin, leading to the death of healthy brain tissue and the onset of neurodegenerative disease. Mad cow disease, formally known as bovine spongiform encephalopathy, occurs when misfolded PrP binds with normal PrP in the body and converts it into more misfolded protein.

"This advance sets the stage for future efforts to develop potential treatments for prion diseases or perhaps to prevent them from occurring," Dr. Duane Alexander, director of the Eunice Kennedy Shriver National Institute of Child Health and Human Development, said in a NIH news release.

The findings, published in the current issue of Cell, were made after NIH scientists noticed similarities to the damage done to brain tissue by prion disease and that occurring in mice deprived of Mahogunin because of a defective gene. Tests done in lab cultures revealed that when misfolded PrP enters cell cytoplasm, it binds to Mahogunin and damages cells in a fashion similar to if the cells have been deprived of Mahogunin.

Previous studies on laboratory mice done by the researchers had found that brain deterioration follows when cytoplasm contains too much PrP.

To further solidify this finding, a subsequent study on mice with Gerstmann-Straussler-Scheinker (GSS) Syndrome -- a rare neurodegenerative disease in which PrP is found in cell cytoplasm -- found that some brain cells lacked Mahogunin in these mice. A similar Mahogunin depletion did not occur if the scientists altered the PrP to avoid contact with the cytoplasm.

"PrP probably interferes with other proteins, too. But our findings strongly suggest that the loss of Mahogunin is an important factor," study co-author Dr. Ramanujan S. Hegde, of the National Institute of Child Health and Human Development's cell biology and metabolism program, said in the news release.

More information

The U.S. Food and Drug Administration has more about mad cow disease.

Posted: June 2009


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