Abstract
Abstract: :
Purpose: The mammalian respiratory NADH–ubiquinone oxidoreductase (complex I) is the largest and least understood component of the mitochondrial oxidative phosphorylation system. It is consisted of at least 46 subunits, and seven of them are encoded by mitochondrial DNA (mtDNA). Mutations in genes encoding subunits of complex I are associated with diseases, in particular the various forms of Leber’s hereditary optic neuropathy (LHON). Impaired complex I activity has also been reported to be related to neurodegenerative diseases like Parkinson’s disease and aging. The ability to repair mutations in mitochondrial complex I via gene therapy holds the promise of treatment of mitochondrial diseases such as LHON. In this study, we isolated and analyzed a revertant which compensated mitochondrial deficiency caused by a mtDNA mutation. Methods:A revertant for a cell line carrying a mtDNA mutation was isolated. MtDNA sequencing, mitochondrial protein synthesis, respiration activity and growth capacity in galactose–containing medium analysis were performed. Mitochondrial–mediated transformation was also carried out to determine the contribution from either nuclear or mitochondrial genomes. Results: Several mutations in mtDNA–encoded complex I subunit ND6 gene have been reported to associate with LHON. To establish a cell model to study the pathogenesis and therapy of LHON, we isolated a mouse cell line containing a frameshift mutation in ND6 gene. This mutation abolished the complex I assembly, and disrupted the respiratory function of complex I. We then further isolated a spontaneous derivative that retains mutant mitochondrial DNA but has nevertheless reverted complex I assembly, respiratory activity and oxidative phosphorylation capability. Conclusions: Compensatory change in nuclear genome can restore the mitochondrial function in cells carrying pathogenic mtDNA mutation. We hope further study will help us to understand the regulation mechanism of complex I activity, and pave a way to develop new therapeutic approaches for mitochondrial diseases associated complex I deficiencies including LHON.
Keywords: gene/expression • protein structure/function • proteins encoded by disease genes