| Summary: | 碩士 === 中山醫學大學 === 生物化學研究所 === 91 === Recent results suggest that both the mitochondrial mass and the mitochondrial DNA (mtDNA) copy number are increased during in vivo aging process and in vitro cellular replicative senescence. During the aging process, oxidative damage and mutation of mtDNA are accumulated and they contribute to the decline in mitochondrial respiratory function. Moreover, the increase in mitochondrial mass and mtDNA copy number in aged tissues was suggested as a result of a feedback mechanism to compensate for the impaired mitochondrial function with age. In a previous study, non-lethal concentration of H2O2 caused an increase in the mitochondrial mass and mtDNA copy number of human lung fibroblast cell MRC-5. However, the molecular mechanism is still unclear. In this thesis, I evaluated the mechanism and the effects of the increase in mitochondria and mtDNA by a previously established experimental model that the MRC-5 cells were treated with 180 μM of H2O2 for 48 hr. The results revealed that non-lethal concentration of H2O2 induced the increase in mitochondrial mass but not elevated the protein expressions of mitochondrial respiratory enzymes, which may thus lead to an increase in the ROS production in the cells harboring increased mitochondrial mass. Morever, the increase in mitochondrial mass induced by H2O2 is not a PPARγ coactivator-1 (PGC-1)-dependent event.
On the other hand, it was shown that H2O2 induced an increase in the intracellular level of acetylated α-tubulin in a dose-dependent manner, and which was not dependent on the de novo protein synthesis. Morever, the level of acetylation in α-tubulin was not induced by CCCP treatment, which caused a loss of mitochondrial membrane potential or by oligomycin treatment, which inhibited mitochondrial ATP synthesis. In addition, an increased level of acetylation in α-tubulin was detected in the cells harboring no mtDNA or higher proportion of mutant mtDNA. The increased acetylated α-tubulin can be detected in the mitochondrial and cytosol fractions. Because the ROS content in these cybrid cells was not significantly changed, the results suggest that the increase in the level of acetylation in α-tubulin may be caused by a ROS-independent pathway.
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