Effects of chronic variable stress on cognition and Bace1 expression among wild-type mice

Stressful life events, activation of the hypothalamic-pituitary-adrenal (HPA) axis and glucocorticoids are now thought to have a role in the development of several neurodegenerative and psychiatric disorders including Alzheimer's disease (AD) through mechanisms that may include exacerbation of cognitive impairment, neuronal loss, and beta-amyloid (Aβ) and tau neuropathology. In the current study, we use a wild-type mouse model to demonstrate that chronic variable stress impairs cognitive function and that aged mice are particularly susceptible. We also find that stress exposure is associated with a 1.5- to 2-fold increase in the expression of Bace1 in the hippocampus of young adult mice and the hippocampus, prefrontal cortex and amygdala of aged mice. Further, the increased expression of Bace1 was associated with decreased methylation of several CpGs in the Bace1 promoter region. In a second series of experiments, exposure to environmental enrichment (EE) prevented the stress-related changes in cognition, gene expression and DNA methylation. Together, these findings re-affirm the adverse effects of stress on cognition and further suggest that aged individuals are especially susceptible. In addition, demonstrating that chronic stress results in decreased DNA methylation and increased expression of Bace1 in the brain may provide a novel link between stress, Aβ pathology and AD. Finally, understanding the mechanisms by which EE prevented the effects of stress on cognition and Bace1 expression will be an important area of future study that may provide insights into novel approaches to the treatment of AD.