Protein l-isoaspartyl methyltransferase: developmentally redulated gene expression and protein localization in the central nervous system of aged rat

We have cloned a cDNA encoding protein L-isoaspartyl methyltransferase (PIMT) and characterized gene expression in the development, maturation, and the aging process of the central nervous system by RNA blot analysis, western blot analysis, and immunohistochemistry. PIMT transcript was detected in rat embryonic brain and showed a linear up-regulation during the maturation of the brain and maintained its level in aged rat brain. Immunoblot analysis also supported a linear increase in the amount of PIMT in the maturation process of rat brains. An immunohistochemical study showed that PIMT is strongly expressed in neurons and weakly but definitively in glial cells and oligodendrocytes. These immunoreactivities significantly increased in some neurons of the hippocampus, cerebral cortex, and the brain stem of aged rat brain. The present results suggest that the expression of PIMT is associated with the amount of racemized/isomerized proteins accumulated during the developmental and aging process of the central nervous system.