Research on abnormal mitochondria and its change in gene expression in cellular senescence.

体外培养的皮肤成纤维细胞具有有限的复制潜能，并随着连续培养而降低。这种潜能被称为细胞寿命，其过程被称为细胞（复制）衰老。线粒体负责细胞的呼吸功能，在细胞的维持中起着不可缺少的作用。线粒体一直处于功能性氧暴露状态，是过氧化物损伤细胞的主要目标。线粒体有自己的环状DNA，并进行自己的复制和转录。这些基因不受组蛋白的保护，也没有自己的DNA修复系统。因此，DNA损伤在线粒体基因组中比在细胞基因组中更容易积累。在本研究中，我们使用人类线粒体DNA M1片段作为探针，通过Northern分析观察了线粒体基因组在年轻和衰老培养的皮肤成纤维细胞和来自Werner综合征患者的成纤维细胞中的表达。结果，衰老细胞和Werner细胞的线粒体基因组表达低于年轻成纤维细胞。此外，电镜观察发现，衰老细胞中异常线粒体的比例增加，其特征是细长结构、低通透性和嵴丢失。但在Werner的细胞中没有观察到形态学的变化，由于一种特殊的基因缺陷而失去了复制潜力。最后，推测这些形态变化是由累积复制引起的，而不是由复制终止引起的。

Cultured skin fibroblasts have a limited replicative potential and it decreased by serial cultivations. This potential is called as cellular life span and its process is termed as cellular(replicative) senescence. By the way, mitochondria have charge of cellular respiratory function and indispensable in cellular maintenance. Mitochondria are always functionally exposed to oxygen and are main target of cellular damages by peroxides. Mitochondria have their own circular DNA and perform their own replication and transcription. The genes are not protected by histone proteins and do not have their own DNA repair systems. So, DNA damages are easily accumulate in mitochondrial genomes than in cellular genomes, In this research, we observed expression of mitochondrial genome by Northern analysis using a fragment of human mitochondrial DNA M1 as a probe in young and senescent cultured skin fibroblasts and fibroblasts from a patient with Werner syndrome. As a result, expressions of mitochondrial genome were decreased in senescent cells and Werner's cells than in young fibroblasts. Furthermore, we found that ratio of abnormal mitochondria being characterized by thin and long configurations, lower permiability and loss of cristae is increased in senescent cells with electron microscopy. But the morphological changes were not observed in Werner's cells which lost replicative potential by a special gene defect. Finally, these morphological changes were speculated to be induced by cumulative replications but not by replicative termination.