Studies on Pathogenesis of Mitochondrial Diseases

我们研究了最常见的遗传缺陷3243突变在18例MELAS患者骨骼肌中的分布和表达。这种mtDNA突变存在于18例患者中的12例(67%)。该突变在肌肉中的比例从50%到80%不等，在家族性研究中，MELAS患者的这种突变比例明显高于他们的少症状或无症状亲属。此外，骨骼肌中3243突变的比例与首次卒中样发作的年龄有很好的关系。在酶学研究中，所有患者骨骼肌线粒体中复合体I-III活性明显降低。复合体I的减少也与该mtDNA突变的群体有明显关系。这是因为复合体I比复合体IV(COX)编码更多的mtDNA多肽，mtDNA突变对其组装的危害更大。这一事实可能导致MELAS患者肌肉线粒体中复合体I活性的普遍下降。我们通过融合P0-HeLa细胞和具有3243突变的核DNA无DNA成纤维细胞来研究胞质冒号，发现COX AT活性迅速下降，占突变总数的95%以上。然而，在该突变的较低群体中，复合体I的活性已经下降，而不是COX的正常活性。我们的数据似乎表明，3243突变直接影响氧化磷酸化的抑制，其数量是该突变导致MELAS的主要因素。

We investigated the distribution and expression of 3243 mutation,the most common genetic defect, in the skeletal muscle of 18 patients with MELAS. This mtDNA mutation was present in 12 of 18 patients(67%). The proportion of this mutation in muscle ranged from 50 to 80% and was significantly higher in the patients with MELAS than in their oligosymptomatic or asymptomatic relatives on family study. Furthermore the proportion of 3243 mutation in skeletal muscle had good relation to an age of suffering first stroke like attack.In the enzymatic study,complex I-III activity was markedly decreased in the skeletal muscle mitochondria of all the patients with this mutation. The decrease of complex I had also clear relation to the population of this mtDNA mutation. It is reason that complex I is more components of peptides encoding from mtDNA than complex IV(COX), and mtDNA mutation is more harmful to its assembly.This fact is likely to accord a common decrease of complex I activity in muscle mitochondria from MELAS patients.We investigated the cybrid colons by fusing p0-HeLa cell and nuclear DNA- less fibroblasts with 3243 mutation showed quickly declined activity of COX at consisting more than 95% of this mutation. However the activity of complex I already decreased at lower population of this mutation instead of the normal activity of COX.Our data seems to indicate that 3243 mutation directly affects the inhibit of oxidative phospholyration and its quantity is a main factor to onset of MELAS with this mutation.