The research team demonstrated that this complex protective mechanism involves the activity of an enzyme, matrix metalloprotease 2/9, which breaks down large proteins and is known to play a role in blood vessel development and in stroke.

The researchers also found that the ability to move the blockage out of the blood vessel diminished with age. Young mice (age 4 months) were able to clear blockages more quickly and thoroughly than older mice (age 22 months). The incomplete removal of blockages in the brains of older mice led to a prolonged shortage of oxygen to the surrounding nerve cells and damaged the connections between nerve cells in the vicinity of the obstructed blood vessels.

"The reduced efficiency of this protective mechanism in the older brain and its effect on the function of nerve cells in the brain may significantly contribute to age-related cognitive decline," said Suzana Petanceska, Ph.D., of the Neurobiology of Aging Branch in NIA's Division of Neuroscience, which funded the research. "This may also be part of the mechanism by which vascular risk factors such as high blood pressure and diabetes increase the risk of Alzheimer's disease with age."

Source: NIH/National Institute on Aging