Stress response caused by chronic alcohol intake in aged rat brain

Background: Chronic alcohol consumption may act as a cellular stressor for brain cells, as has been found for aging. In this study we examined one component of the cellular stress response (heat shock proteins) as a function of age and alcohol exposure. We have found that the level of constitutively expressed heat shock protein 70 (heat shock cognate 70, or Hsc70) increases in the aged rat brain. Among many heat shock proteins and molecular chaperones, Hsc70 might be important not only for the normal protein folding pathway but also for refolding of denatured proteins produced by mild and chronic stress. Methods: Male Wistar rats that were 5.5 to 28.5 months old were fed a liquid diet that contained 5% (w/v) alcohol or a control diet for 6 weeks. The effects of alcohol consumption and aging on the expression of Hsc70 in the brain were investigated. The cytosol proteins in the 12,000 X g supernatant fraction were heat-treated at 42degreesC for 1 hr. After the heat treatment, proteins that transferred from the soluble to insoluble aggregated fraction were estimated as heat-unstable proteins. Results: In the 24- and 30-month-old rat brain, chronic consumption of alcohol increased levels of Hsc70 and heat-unstable proteins. On the other hand, those changes were not detected in the younger rat brain. Conclusion: Chronic alcohol intake causes a stress response in the aged rat brain. It is thought that the increased level of Hsc70 is brought about by an increase of denatured proteins.