Altered proteins accumulate in various tissues with age. Both constitutive and inducible heat shock proteins (HSPs) play an important role in the renaturation of conformationally altered proteins. Decrease in the expression of HSPs might contribute to an increase in the amount of altered proteins in cells. In this study, we investigated the effect of aging on the expression of hsp25 and hsp70 genes in the brain, liver and heart of unstressed rats (F344/DuCrj).
No detectable levels of protein and mRNA for hsp70 were observed in the liver and kidney of unstressed young and old rats. Although hsp70 mRNA was not detected in the heart, the protein level of HSP70 in old rats was about 30% higher than that in young ones. Higher levels of the mRNA and protein of hsp25 were observed in the heart of both young and old rats. The mRNA and protein levels of hsp25 in the heart tended to increase with age but no statistically significant difference was observed between young and old animals. Hsp25 mRNA was not detectable in the liver and brain by Northern blot but the protein level in both tissues increased by about two fold with age. RT-PCR analysis showed no significant difference in the level of hsp25 mRNA in the liver and brain between young and old. These results suggest that the increase in the protein level of HSP25 in these tissues with age is due to change(s) in translational or post-translational rather than transcriptional regulations.