updated 6/2/2005 7:16:50 AM ET 2005-06-02T11:16:50

Rogue proteins that cause mad cow and other brain-destroying diseases become toxic by latching on to the outside of cell membranes, say government scientists studying how the mysterious substances work.

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If scientists could break the fatty Velcro-like bond that anchors these prion proteins, they might devise a treatment for the deadly illnesses, suggests the research published in Friday’s edition of the journal Science.

“We need to focus on that as a target for drug therapy,” said the lead researcher, Dr. Bruce Chesebro, a virologist at the National Institutes of Health’s Rocky Mountain Laboratories. “Clues are really hard to come by” in prion diseases.

Related diseases — including mad cow, scrapie in sheep and the human Creutzfeldt-Jakob disease — are believed to arise when a protein the body normally harbors folds into an abnormal shape, called a prion, and sets off a chain reaction of misfolds.

When enough abnormal prions accumulate, they deposit plaque on the brain and eventually leave clumps of dead brain cells. Those are the diseases’ hallmark spongy holes.

Scientists are trying to determine what makes these rogue prions poisonous to brain cells.

'A tantalizing inroad'
Chesebro and colleagues genetically engineered mice that lacked the fatty anchor that usually binds prions to the surface of cells. Then the scientists injected the transgenic mice and regular mice with scrapie-causing prions.

All 70 of the regular mice promptly got sick.

But the 128 specially bred mice showed no symptoms of scrapie even though Chesebro watched for up to 600 days. That is far longer than it should take illness to appear.

Under a microscope, their brains show lots of the telltale plaques. But their brain cells had not died.

“We were really surprised,” Chesebro said.

He is continuing to track some of the mice for signs of more subtle damage than scrapie usually causes, such as memory loss.

If the abnormal prions are not bound to cells’ surfaces, they may be unable to disrupt signaling between cells, a leading theory behind their toxicity, said neuropathologist Adriano Aguzzi of the University Hospital of Zurich, Switzerland, in an accompanying editorial.

The work provides “a tantalizing inroad,” he said.

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