Experiments on mice, conducted at the University of California, San Diego, have shown that chronic stress triggers the production and accumulation of insoluble tau proteins in brain cells.
Tau proteins are present in the healthy human brain, they are necessary for normal functioning of neurons. In the brain of the patients, suffering from Alzheimer’s disease, tau proteins form aggregates called neurofibrillary tangles, which change their structure, and it is one of the physiological symptoms of Alzheimer’s disease.
The author of the study Robert A. Rissman, Ph.D., assistant professor of neurology, says that the data obtained from this experiment on mice may at least partly explain why clinical trials used to show a close relationship between stress and the development of sporadic diseases such as Alzheimer’s disease.
Through experiments with mice, U.S. researchers have found that repetitive episodes of emotional stress in rodents, which can be compared with what an average person experiences in everyday life, caused a process of phosphorylation, i.e. adherence of the remains of phosphoric acid to a substrate and change in solubility of tau proteins in neurons.
Rissman noted that this effect was mostly observed in the hippocampus, a brain area that is associated with the formation, organization and storage of memories. As a rule, the patients with Alzheimer’s disease suffer from pathology (cell death) in the hippocampus. He also explained that not all forms of stress are equally threatening to health. In an earlier study, Rissman and his colleagues found that acute stress did not cause fatal changes in tau proteins. On the contrary, it could even be useful for the “plasticity” of the brain, helping to improve skills and learning processes. Chronic stress can also lead to pathological changes in the brain, especially in the elderly people.