Washington: Scientists have discovered that the increased release of stress hormones in rats leads to the generation of abnormally phosphorylated tau protein in the brain and ultimately, memory loss.
Protein deposits in nerve cells are a typical feature of Alzheimer`s disease: the excessive alteration of the tau protein through the addition of phosphate groups – a process known as hyperphosphorylation – causes the protein in the cells to aggregate into clumps.
As a result, nerve cells die, particularly 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 higher cognitive functions.
Following up on epidemiological studies, scientists at the Max Planck Institute of Psychiatry hypothesized that adverse life events (stress) may be one trigger of Alzheimer`s disease.
In cooperation with colleagues at the University of Minho in Braga, Portugal, the Munich-based researchers have now shown that stress, and the hormones released during stress, can accelerate the development of Alzheimer disease-like biochemical and behavioural pathology. They found increased hyperphosphorylation of tau protein in the hippocampus and prefrontal cortex of rats that has been subjected to stress (e.g. overcrowding, placement on a vibrating platform) for one hour daily over a period of one month.
Animals showing these changes in tau also showed deficits in memories that depended on an intact hippocampus; also, animals with abnormally hyperphosphorylated tau were impaired in behavioural flexibility, a function that requires proper functioning of the prefrontal cortex.
"Our findings show that stress hormones and stress can cause changes in the tau protein like those that arise in Alzheimer`s disease", said Osborne Almeida from the Max Planck Institute of Psychiatry.