Increase in Trx2/Prx3 redox system immunoreactivity in the spinal cord and hippocampus of aged dogs.

We previously reported that no distinct neuronal loss occurred in the aged dog spinal cord, although oxidative stress was increased in the aged dog spinal cord. Thioredoxin 2 (Trx2)/peroxiredoxin 3 (Prx3) redox system is a major route for removing H(2)O(2) in the central nervous system. In the present study, we compared the distribution and immunoreactivity of thioredoxin reductase 2 (TrxR2), Trx2 and Prx3 and their protein levels in the spinal cord and hippocampus between the adult (2-3 years) and aged (10-12 years) dogs. The number of TrxR2-immunoreactive neurons was slightly increased; however, its immunoreactivity was significantly increased in the aged spinal cord compared to that in the adult spinal cord. On the other hand, the number and immunoreactivity of both Trx2- and Prx3-immunoreactive neurons were significantly increased in the spinal cord of the aged dog. Similarly, in the hippocampus of the aged dog, TrxR2, Trx2 and Prx3 immunoreactivity and protein levels were markedly increased compared to those in the adult dog. These results indicate that the increases of TrxR2, Trx2 and Prx3 immunoreactivity and their protein levels in the aged spinal cord and hippocampus may contribute to reducing neuronal damage against oxidative stresses during normal aging.