New Clue to Who Gets Alzheimer's ; Study Suggests a Protein May Be Key to Protecting Brain from Degeneration

Article excerpt

Harvard scientists may have found an answer to why some people whose brains collect proteins strongly associated with Alzheimer's don't get the disease.

It is one of the big scientific mysteries of Alzheimer's disease: Why do some people whose brains accumulate the plaques and tangles so strongly associated with Alzheimer's not develop the disease?

Now, a series of studies by Harvard scientists suggests a possible answer, one that could lead to new treatments if confirmed by other research.

The memory and thinking problems of Alzheimer's disease and other dementias, which affect an estimated seven million Americans, may be related to a failure in the brain's stress response system, the new research suggests. If this system is working well, it can protect the brain from abnormal Alzheimer's proteins; if it gets derailed, critical areas of the brain start degenerating.

"This is an extremely important study," said Li-Huei Tsai, director of the Picower Institute for Learning and Memory at the Massachusetts Institute of Technology, who was not involved in the research but wrote a commentary accompanying the study. "This is the first study that is really starting to provide a plausible pathway to explain why some people are more vulnerable to Alzheimer's than other people."

The research, published on Wednesday in the journal Nature, focuses on a protein previously thought to act mostly in the brains of developing fetuses. The scientists found that the protein also appears to protect neurons in healthy older people from aging- related stresses. But in people with Alzheimer's and other dementias, the protein is sharply depleted in key brain regions.

Experts said if other scientists could replicate and expand upon the findings, the role of the protein, called REST, could spur development of new drugs for dementia, which has so far been virtually impossible to treat. But they cautioned that much more needed to be determined, including whether the decline of REST was a cause, or an effect, of brain deterioration, and whether it was specific enough to neurological diseases that it could lead to effective therapies.

"You're going to see a lot of papers now following up on it," said Dr. Eric M. Reiman, executive director of the Banner Alzheimer's Institute in Phoenix, who was not involved in the study. "While it's a preliminary finding, it raises an avenue that hasn't been considered before. And if this provides a handle on which to understand normal brain aging, that will be great, too."

REST, a regulator that switches off certain genes, is primarily known to keep fetal neurons in an immature state until they develop to perform brain functions, said Dr. Bruce A. Yankner, a professor of genetics at Harvard Medical School and the lead author of the new study. By the time babies are born, REST becomes inactive, he said, except in some areas outside the brain like the colon, where it seems to suppress cancer.

While investigating how different genes in the brain change as people age, Dr. Yankner's team was startled to find that REST was the most active gene regulator in older brains.

"Why should a fetal gene be coming on in an aging brain?" he wondered.

He hypothesized that it was because in aging, as in birth, brains encounter great stress, threatening neurons that cannot regenerate if harmed. His team discovered that REST appears to switch off genes that promote cell death, protecting neurons from normal aging processes like energy decrease, inflammation and oxidative stress.

Analyzing brains from brain banks and dementia studies, the researchers found that brains of adults ages 20 to 35 contained little REST, while healthy adults between the ages of 73 and 106 had plenty. REST levels grew the older people got, so long as they did not develop dementia, suggesting that REST is related to longevity. …