Effect of Exogenous Coenzyme Q9 or Coenzyme Q10 on Coenzyme Q10 Levels, Expression of Coq Proteins and Genes, and the Stability of the Coq Protein Complex in Human Cybrids with A8344g Mutation of Mtdna

Coenzyme Q (CoQ) is essential for the electron transport chain in oxidative phosphorylation (OXPHOS). CoQ is primarily present in the form of CoQ10, CoQ9, and CoQ6 in humans, rodents, and yeast, respectively. Nine Coq proteins (Coq1-Coq9) are required for the CoQ6 biosynthesis in yeast and are mitochondrial proteins. Coq1 in yeast corresponds to PDSS1 and PDSS2 subunits in humans. Several of the Coq polypeptides form a Coq protein complex for CoQ6 biosynthesis in yeast, and CoQ6 interacts with the protein complex for its stabilization. Human mitochondrial DNA (mtDNA) encodes 13 subunits of complexes I, III, IV, and V of OXPHOS. Mitochondrial matrix proteins encoded by nuclear DNA (nDNA) need to be imported from cytosol into mitochondria using membrane potential and mitochondrial ATP as an energy sources to form mature proteins. Myoclonic epilepsy with ragged-red fibers (MERRF) is an inherited disease caused by A8344G mutation in a tRNA gene of mtDNA that decreases translation of mtDNA-encoded proteins. Patients with pathogenic mtDNA mutations often had secondary CoQ10 deficiency disease and are treated with CoQ10. Our research demonstrated that disruption of mitochondrial membrane potential by FCCP decreased CoQ10 levels, suppressed COQ5 protein maturation, and hindered the formation of the COQ5-containing protein complex in the mitochondria of human 143B cells. Moreover, we have obtained a cybrid with A8344G mutation (B2 cybrid) and its wild-type control cybrid (D5 cybrid). CoQ10 levels and mitochondrial membrane potential were decreased in B2 cybrids. Although there was a moderate suppression in COQ5 maturation, there was increased expression of COQ5 and near disappearance of the COQ5-containing protein complex in B2 cybrids. The hypothesis of this study is that supplementation of exogenous CoQ9 or CoQ10 may stabilize certain COQ proteins or the COQ protein complex, which in turn may partially restore endogenous CoQ10 biosynthesis and improve mitochondrial status in B2 cybrids. There are two specific aims for each year of the project. In the first year, we will investigate whether exogenous CoQ10 can restore the COQ5 maturation and stabilize the COQ5-containing protein complex in B2 cybrids, and examine whether that is due to the enhancement of endogenous CoQ10 levels by adding exogenous CoQ9 to cybrids. In the second year, we will investigate whether exogenous CoQ9 or CoQ10 can improve cell viability, mitochondrial energy production, and status of nDNA-encoded subunits of OXPHOS in B2 cybris. Possible changes in mRNA levels of various PDSS and COQ genes in B2 versus D5 cybrids will also be compared. In the third year, we will investigate whether levels of various PDSS and COQ proteins other than COQ5 are decreased in B2 cybrids and whether they could be stabilized by exogenous CoQ10. Moreover, the possible role of COQ5 in promoting the beneficial effect of exogenous CoQ will be explored by overexpression of COQ5 in B2 cybrids during CoQ supplementation. Results from this study will be helpful for the understanding on the molecular mechanisms toward the potential benefit of CoQ10 supplementation for the treatment of secondary CoQ10 deficiency caused by mtDNA mutations.

Project ID:PC10508-0615
External Project ID:MOST105-2320-B182-026