Researchers from Harvard Medical School have made what they believe to be a key discovery in the cause of Alzheimer’s disease. Their research found that people who suffer from a form of dementia that affects memory have a certain type of plaque in their brains. The plaque is made up of a sticky protein known as beta-amyloid.
Scientists have long questioned whether the presence of this plaque is an underlying cause, or merely a side effect, of the disease. Another protein, known as tau, is also involved, and some experts suspect it may be the underlying cause.
The Harvard researchers, led by Dr. Ganesh M. Shankar and Dr. Dennis J. Selkoe, were able to induce Alzheimer’s symptoms in rats by injecting them with one particular form of beta-amyloid. Injections with other forms of beta-amyloid did not produce symptoms, a finding that may explain why some people with beta-amyloid plaque in their brains do not show disease symptoms.
Using extracts from the brains of people who had donated their bodies to medicine, the researchers developed forms of soluble beta-amyloid containing different numbers of molecules, as well as insoluble cores of the brain plaque. Both forms were injected into the brains of the rats, but the researchers detected no effect from the insoluble plaque or the soluble one-molecule or three-molecule forms.
However, the two-molecule form of soluble beta-amyloid produced symptoms characteristic of Alzheimer’s in the rats, the researchers wrote in a report about their study. Specifically, the rats demonstrated impaired memory function, particularly with newly learned behaviors. Additional studies were also conducted on mice, which found a 47 percent reduction in brain cell density. The researchers concluded that the beta-amyloid seemed to affect the brain’s synapses, inter-cellular connections critical for cell-to-cell communications.
Dr. Marcelle Morrison-Bogorad, director of the division of neuroscience at the National Institute on Aging, told the Associated Press that the research was a first in demonstrating the effect of a particular type of beta-amyloid in the brain. The National Institute on Aging helped fund the Harvard research.
“It was surprising that only one of the three types had an effect,” she said, adding that the findings may help explain why some people with plaque in their brains do not develop dementia.
Doctors have long wondered why, during autopsies, they find some brains in that are heavily coated with beta-amyloid even though the person did not have Alzheimer’s. The answer may involve the two types of beta-amyloid that did not produce symptoms.
The reason why one form has a detrimental effect, while others do not, is still not clear.
“A lot of work needs to be done,” Morrison-Bogorad told the AP.
“Nature keeps sending us down paths that look straight at the beginning, but there are a lot of curves before we get to the end.”
“While more research is needed to replicate and extend these findings, this study has put yet one more piece into place in the puzzle that is Alzheimer’s,” Dr. Richard J. Hodes, director of the National Institute on Aging, told the Associated Press.
The research was funded by The National Institute on Aging, Science Foundation Ireland, the McKnight and Ellison foundations, Wellcome Trust and the Lefler Small Grant Fund.
The research was published Sunday in the online edition of the journal Nature Medicine.
—
On the Net:
Comments