Long-term Effects of Chronic Stress

Alzheimers disease marker linked to chronic stress in mice

(RxWiki News) Prolonged periods of stress can have negative effects on the human body - but the extent of these effects is still being explored. New data suggests that chronic stress may be linked to Alzheimer’s disease.

Tau, a naturally occurring protein in the human body, becomes misshapen in those with Alzheimer’s disease. The misshapen protein has toxic effects on the brain. A new study found that mice subjected to continuous stress showed an increase in the misshapen tau protein.

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"In the mouse models, we found that repeated episodes of emotional stress, which has been demonstrated to be comparable to what humans might experience in ordinary life, resulted in the phosphorylation and altered solubility of tau proteins in neurons,” says Robert A. Rissman, Ph.D., assistant professor of neurosciences at the University of California - San Diego.

The research team subjected some mice to 14 days of repeated stress. Another group of mice was not subjected to stress. The mice who had undergone repeated stress showed an increase in the toxic tau protein over those mice who did not experience stress.

The hippocampus, a brain region involved with the formation, organization, and storage of memories, showed the highest increase in number of tau proteins in the mice.

In humans, the hippocampus is typically the first brain region to show signs of damage due to Alzheimer’s disease. The hippocampus is also the brain region that suffers the greatest damage in those with Alzheimer’s

The researchers note, however, that not all stress is equal. Acute stress, or a single episode of stress, has not been linked to the accumulation of the toxic tau protein.

Chronic stress, on the other hand, is a period of continuous stress. This condition may lead to pathological changes in the brain that results in the accumulation of tau.

Rissman notes that, "Acute stress may be useful for brain plasticity and helping to facilitate learning. Chronic stress and continuous activation of stress pathways may lead to pathological changes in stress circuitry. It may be too much of a good thing.”

While more research is needed, the researchers believe that it may be more difficult for brain neurons to deal with stress as we age.

 “Age is the primary, known risk factor for Alzheimer's disease. It may be that as we age, our neurons just aren't as plastic as they once were and some succumb," adds Rissman.

The study was published March 26th, 2012, online in Proceedings of the National Academy of Sciences and was funded by the National Institutes of Health, the Alzheimer's Art Quilt Initiative, the Alzheimer's Association, the Foundation for Medical Research, and the Shiley-Marcos Alzheimer's Disease Research Center at the University of California - San Diego.

Review Date: 
March 25, 2012