We live in increasingly stressful times and stress, as we know, is not good for our health. It has been implicated in the development of heart disease and cancer and now it would seem stress may play a role in the development of Alzheimer’s disease.
This week in the Journal of Neuroscience researchers from the Max Planck Institute of Psychiatry in Munich reported that increased levels of stress and stress hormones in rats leads to the production of abnormal tau protein in the brain and memory loss.
Deposits of abnormal protein in the brain are a feature of Alzheimer’s and other dementias and are also found in conditions such as Progressive supranuclear palsy, Cortico basal degeneration, Pick’s disease and Parkinson’s disease with dementia. Tau protein, a naturally occurring material in the brain, becomes hyperphosphorylated (has extra phosphorus molecules added to it) and clumps together to form aggregates inside the brain cells. The appearance of hyperphosphorylated tau aggregates (e.g., neurofibrillary tangles) is linked with the death of nerve cells in those regions of the brain associated with the different neurological diseases. In Alzheimer’s disease, nerve cells die in the hippocampus, a part of the brain that plays an important role in learning and memory, as well as in the prefrontal cortex which regulates the higher cognitive functions (e.g., our ability to plan and organise).
It is thought that less than ten percent of Alzheimer’s cases have a genetic basis; however, the factors that contribute to the majority of cases are unknown. The Munich research team hypothesized that adverse life events (stress) might be a trigger for Alzheimer’s disease.
To test their hypothesis they subjected laboratory rats to stress (overcrowding and placement on a vibrating platform) for one hour a day for a month. Stress (and the hormones released during stress) was found to accelerate the development of Alzheimer’s-like biochemical and behavioural features. Increased levels of hyperphosphorylated tau protein were reported in the hippocampus and prefrontal cortex of the stressed rats which also showed memory deficits and impaired behavioural flexibility, indicating impaired functioning of the hippocampus and prefrontal cortex respectively.
The findings from this study indicate that in rats stress can cause changes in tau protein like those found in Alzheimer’s disease. What now needs to be established is whether stress in humans can cause changes in tau protein.
In contrast to the Alzheimer’s findings, work published this week in the journal ‘Neurology’ reports that severe stress does not appear to increase a person’s risk of developing Multiple sclerosis. Previous work has shown that stressful life events increase the risk of MS episodes but it wasn’t known if stress could lead to development of the disease.
Researchers at the University of Bergen in Norway studied two groups of female nurses from the Nurses’ Health Study. The first group of 121,700 nurses between the ages of 30 and 55 were followed starting in 1976. The second group of 116,671 nurses aged between 25 and 42 were followed from 1989. Participants were asked to report general stress at home and at work, including physical and sexual abuse in childhood and as teenagers. In the first group, 77 people developed MS by 2005. In the second group, 292 people developed the disease by 2004. After considering factors such as age, ethnicity, latitude of birth and smoking, the study found that severe stress at home did not increase the risk of developing MS. There was also no significant increased risk of developing MS in those who reported severe physical or sexual abuse during childhood or adolescence. The researchers concluded that this rules out stress as a major risk factor for MS.
MS is an inflammatory disease in which the body’s own immune system attacks and damages the fatty myelin sheaths around the axons of nerve cells in the brain and spinal cord leading to demyelination and the formation of scleroses (plaques or lesions) particularly in the white matter of the brain and spinal cord. Unlike Alzheimer’s disease and the other tauopathies, MS is not associated with the accumulation of abnormal tau protein in the brain.