Mitochondrial complex subunits, COX activities and mtDNA content in the brain of 12~14 month old mice. (A) Top, Western blot showing the following subunits of the respiratory chain enzyme complexes: Complex I subunit NDUFB8 (I), Complex II subunit 30kDa (II), Complex III subunit Core 2 (III), and Complex IV subunit I (IV) in the cortex of mice at 12~14 months of age. Bottom, quantification of western blot showing protein levels normalized to actin. Data were analyzed using one-way ANOVA followed by Newman-Keuls multiple-comparison test. *p < 0.05. n = 3~4 in each group. (B) Relative complex IV activities in mouse cortex. The bars represent mean ± SEM from two separate experiments with 3~5 animal per group for each experiment. * p < 0.05 by unpaired student’s t-test (n = 6~7). (C) The mtDNA copy number in the striatum, measured as the ratio of mtDNA to nuclear DNA (mtDNA/nDNA) and normalized to WT mice. Mouse rho zero cells lacking mtDNA were used as a negative control (NC). * p < 0.05 by unpaired student’s t-test (n = 3).