Lee Hsin-Chen, Yin Pen-Hui, Chi Chin-Wen, Wei Yau-Huei
Department of Biochemistry and Center for Cellular and Molecular Biology, National Yang-Ming University, Taipei, Taiwan, ROC.
J Biomed Sci. 2002;9(6 Pt 1):517-26. doi: 10.1007/BF02254978.
Abnormal proliferation of mitochondria generally occurs in muscle of aged individuals and patients with mitochondrial myopathy. An increase in the mitochondrial DNA (mtDNA) copy number has also been observed in aging human tissues. However, the molecular mechanism underlying the increase in mitochondrial mass and mtDNA is still unclear. In a previous study, we demonstrated that sublethal levels of oxidative stress caused an increase in mitochondrial mass in human lung cells. In this communication, we report our recent findings that the mitochondrial mass in human lung fibroblasts (MRC-5) in a later proliferation stage is significantly increased compared to that in the early stages of proliferation. The extent of the increase in mitochondrial mass in the senescent cells was similar to that in cells in the early stages of proliferation that had been treated with low concentrations (< or = 180 microM) of hydrogen peroxide (H(2)O(2)). Moreover, we found that the rate of reactive oxygen species (ROS) production was higher in cells in the later proliferation stage compared to cells in the early proliferation stages. A similar phenomenon was also observed in cells in the early proliferation stages under low levels of oxidative stress. On the other hand, the mRNA levels of many nuclear DNA-encoded proteins involved in mitochondrial biogenesis, particularly nuclear respiratory factor-1, were found to increase in cells in later proliferation stages and in cells in early proliferation stages that had been treated with 180 microM H(2)O(2). Interestingly, the increase in mitochondrial mass in the cells under oxidative stress could be repressed by treatment with cycloheximide or m-chlorocarbonyl cyanide phenylhydrazone but not by chloramphenicol. Furthermore, the mitochondrial mass of mtDNA-less rho(o) cells was also significantly increased by exposure to low concentrations (e.g. 180 microM) of H(2)O(2). These results suggest that the increase in mitochondrial mass in replicative senescent cells may result from an increase in ROS production, and that it is dependent on both de novo synthesis of nuclear DNA-encoded proteins and their import into mitochondria, dictated by the membrane potential of mitochondria.
线粒体的异常增殖通常发生在老年个体的肌肉以及线粒体肌病患者中。在衰老的人体组织中也观察到线粒体DNA（mtDNA）拷贝数增加。然而，线粒体质量和mtDNA增加背后的分子机制仍不清楚。在先前的一项研究中，我们证明亚致死水平的氧化应激会导致人肺细胞中线粒体质量增加。在本通讯中，我们报告了我们最近的发现，即与增殖早期相比，人肺成纤维细胞（MRC-5）在增殖后期的线粒体质量显著增加。衰老细胞中线粒体质量增加的程度与用低浓度（≤180微摩尔）过氧化氢（H₂O₂）处理的增殖早期细胞相似。此外，我们发现与增殖早期的细胞相比，增殖后期的细胞中活性氧（ROS）的产生速率更高。在低水平氧化应激下的增殖早期细胞中也观察到类似现象。另一方面，发现在增殖后期的细胞以及用180微摩尔H₂O₂处理的增殖早期细胞中，许多参与线粒体生物发生的核DNA编码蛋白的mRNA水平会增加。有趣的是，氧化应激下细胞中线粒体质量的增加可以被放线菌酮或间氯羰基亚胺基苯腙处理抑制，但不能被氯霉素抑制。此外，暴露于低浓度（例如180微摩尔）的H₂O₂也会使无mtDNA的ρ⁰细胞的线粒体质量显著增加。这些结果表明，复制性衰老细胞中线粒体质量的增加可能是由于ROS产生增加所致，并且它既依赖于核DNA编码蛋白的从头合成及其向线粒体的导入，这由线粒体的膜电位决定。
