Chronic Stress, Aging and the Risk of Alzheimer's Disease
Researchers from the University of California, San Diego School of Medicine have found that exposing mice to repeated triggers of stress resulted in the production and accumulation of insoluble tau protein inside the brain cells of mice. Scientists believe that during Alzheimer's amyloid protein is produced first, and triggers the accumulation of tau, which is toxic to nerve cells.
Published in the March 26 Online Early Edition of the Proceedings of the National Academy of Sciences, the study's main author, Robert A. Rissman, believes their findings may help explain the link of people prone to stress and the development of sporadic Alzheimer's disease. Sporadic cases of Alzheimer's disease are said to account for about 95% of all cases of Alzheimer's disease.
Mice models are used in this and many other types of Alzheimer's research. Doctor Rissman says, "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 altered tau.
The researchers have shown that not all types of stress result in the same changes in the brains of the mice. A previous study found that acute single and passing episodes of stress did not result in any permanent changes in tau.
Aging and Stress
This leads to another possible explanation of the link between stress and Alzheimer's disease that many of us can relate to. That is, the effect aging has on the way we cope with stress. We can see it clearly in our elderly relatives and friends. Changes in routines, activities, household management and even simple demands by outside agencies become difficult to cope with and cause anxiety.
Dr. Rissman talks of brain plasticity, that is, the ability of the brain to reorganize neural pathways based on new experiences, and he offers a theory about why older brains may become affected by Alzheimer's. He says that chronic stress and continuous activation of the stress pathways may lead to physical changes in stress circuits in the central nervous system. So as we age these neuronal circuits perhaps become less ‘plastic' and as they continue to be activated physically deteriorate and some ‘succumb'.
Their research may contribute to growing body of evidence as to how chronic stress affects the immune system and contributes to increased vulnerability of infection and inflammation - other areas thought to have a bearing on Alzheimer's vulnerability.
Primary Source: (2012). Corticotropin-releasing factor receptor-dependent effects of repeated stress on tau phosphorylation, solubility, and aggregation. Proceeding of the National Academy of Science, Retrieved from http://www.pnas.org/content/early/2012/03/22/1203140109.abstract
University of California, San Diego News Center Deahttp://ucsdnews.ucsd.edu/pressreleases/chronic_stress_spawns_protein_aggregates_linked_to_alzheimers/