Age-dependent changes in the protein expression levels of Redd1 and mTOR in the gerbil hippocampus during normal aging

Redd1, also known as RTP801/Dig2/DDIT4, is a stress-induced protein and a negative regulator of mammalian target of rapamycin (mTOR). Redd1 is also closely associated with oxidative stress and DNA damage. In the present study, age-related changes in the protein expression levels of mTOR and Redd1 were investigated using immunohistochemistry and western blot in the gerbil hippocampus at postnatal month (PM) 3, 6, 12 and 24. No significant differences were identified in the levels of mTOR among the experimental groups, whereas, the levels of phosphorylated mTOR decreased with age. The protein expression levels of Redd1 were observed to gradually increase with age; in the PM 24 group, the level was significantly increased (~189.2%), compared with the PM 3 group. In addition, Redd1 immunoreactivity was significantly increased in the hippocampal principal neurons of the PM 24 group, including the pyramidal cells in the hippocampus proper and granule cells in the dentate gyrus, compared with the other experimental groups. These results demonstrated that the protein expression of Redd1 in the hippocampus was markedly increased during normal aging, indicating that the age-related increase in the expression of Redd1 may be closely associated with age-related hippocampal change.