Alteration of endogenous coenzyme Q10 and COQ genes in the cybrid with pathogenic mtDNA T8993G mutation and oxidative stress

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Coenzyme Q10 (CoQ10) is not only an electron carrier and an endogenous antioxidant, but also required for the activity of dehydroorotate dehydrogenase (DHODH) in the de novo pyrimidine synthesis. However, the regulation of endogenous CoQ10 and ten genes, PDSS1-2 and COQ2-9, for the terminal biosynthesis of CoQ10 is poorly understood. A cybrid with wild-type mtDNA (wt cybrid) and a cybrid with homoplasmic T8993G mutation on ATP6 gene of mtDNA (T8993G cybrid) from patients with Leigh syndrome were used in this study. We hypothesized that CoQ10 levels and expression of COQ genes in T8993G cybrid would be elevated as a compensatory effect under conditions of increased mitochondrial membrane potential, decreased respiratory rate, and increased production of reactive oxygen species (ROS). The upregulation might be greater without uridine supplementation to compensate for possible decrease of DHODH activity. Our result shows that mRNA levels of several COQ genes and levels of CoQ10 were augmented in T8993G cybrid with a greater extent in the absence of uridine supplementation. Activities of Complex II+III, which is affected by endogenous CoQ10 levels, but that of Complex II were also elevated in T8993G cybird. The levels of ROS were increased in T8993G cybrid with a lesser extent in the absence of uridine supplementation, implicating the antioxidant function of increased levels of CoQ10. Protein levels of mitochondrial superoxide dismutase were increased in T8993G cybrid with uridine supplementation. Protein levels of cytochrome c, another mobile electron carrier in the mitochondria, and mitochondrial transcription factor A were elevated due to the absence of uridine supplementation although not in T8993G cybrid. On the other hand, mitochondrial mass and protein levels of nuclear respiratory factor 1 were decreased in T8993G cybrid. Our results first indicate the upregulation of CoQ10 levels and mRNA levels of COQ genes in response to mtDNA T8993G mutation, and these alterations could be affected by uridine supplementation.