Stress contributes to the development of central insulin resistance during aging: Implications for Alzheimer's disease

It is becoming evident that chronic exposure to stress not only might result in insulin resistance or cognitive deficits, but may also be considered a risk factor for pathologies such as depression or Alzheimer's disease (AD). There is great interest in determining the molecular mechanisms underlying interactions between stress, aging, memory and Alzheimer's disease (AD). We have used the chronic mild stress (CMS) model to study the effects of chronic stress on the aging process and the development of central insulin resistance and AD pathology. CMS aged mice showed cognitive impairments in the novel object recognition test. In addition, CMS aged mice displayed both peripheral insulin resistance, as shown by HOMA index, and decreased hippocampal levels of pIRS and downstream intracellular signaling (pAKT, pGSK and pERK1/2). Interestingly, there was a significant increase in both C99:C83 ratio and BACE1 levels in the hippocampus of CMS aged mice. Increased expression of the AD marker pTau was also found in stressed aged mice. Increased expression of the stress-activated protein kinase JNK was found in CMS aged mice, accompanied by significant decreases in glucocorticoid receptor (GR) expression and increases in mineralocorticoid receptor (MR) expression. It is suggested that the interaction of stress with aging should be considered when studying determinants of the onset and progression of AD.