Proteomic identification of specific oxidized proteins in ApoE-knockout mice: relevance to Alzheimer's disease.

We have examined oxidized proteins in the brain regions of wild-type (WT) and ApoE-knockout (KO) animals. Total protein oxidation in the hippocampus of young-KO (6 month) animals was approximately 2-fold greater than that of young-WT (6 month) animals and was similar to that of old-WT (18 month) and old-KO (18 month) animals. In the cortex of the same animals, the levels of total protein oxidation in all four groups were not significantly different. Two-dimensional electrophoresis (2-DE) coupled with immunostaining for protein carbonylation revealed six specific oxidation-sensitive proteins, the oxidation levels of which were increased in young-KO, old-WT, and old-KO mice compared with young-WT mice. These six oxidation-sensitive proteins were identified by mass spectrometry as glial fibrillary acidic protein, creatine kinase BB, disulfide isomerase, chaperonin subunit 5, dihydropyrimidase-related protein 2, and mortalin. These results indicate that the ApoE gene product offers protection against age-associated oxidative damage in the brain. Moreover, two of these proteins, creatine kinase and dihydropyrimidase-related protein 2, have recently been found to be oxidized in the brains of human subjects with Alzheimer's disease [Aksenov et al. J. Neurochem. 74: 2520-2527; 2000; Castegna et al. J. Neurochem. 82: 1524-1532; 2002]. These data suggest that the ApoE-knockout mouse serves as an appropriate model for studying pathogenic oxidative mechanisms influencing risk and progression of Alzheimer's disease.