Dataset Information

Normal levels of wild-type mitochondrial DNA maintain cytochrome c oxidase activity for two pathogenic mitochondrial DNA mutations but not for m.3243A-->G.

ABSTRACT: Mitochondrial DNA (mtDNA) mutations are a common cause of human disease and accumulate as part of normal ageing and in common neurodegenerative disorders. Cells express a biochemical defect only when the proportion of mutated mtDNA exceeds a critical threshold, but it is not clear whether the actual cause of this defect is a loss of wild-type mtDNA, an excess of mutated mtDNA, or a combination of the two. Here, we show that segments of human skeletal muscle fibers harboring two pathogenic mtDNA mutations retain normal cytochrome c oxidase (COX) activity by maintaining a minimum amount of wild-type mtDNA. For these mutations, direct measurements of mutated and wild-type mtDNA molecules within the same skeletal muscle fiber are consistent with the "maintenance of wild type" hypothesis, which predicts that there is nonselective proliferation of mutated and wild-type mtDNA in response to the molecular defect. However, for the m.3243A-->G mutation, a superabundance of wild-type mtDNA was found in many muscle-fiber sections with negligible COX activity, indicating that the pathogenic mechanism for this particular mutation involves interference with the function of the wild-type mtDNA or wild-type gene products.

SUBMITTER: Durham SE

PROVIDER: S-EPMC1950909 | biostudies-literature | 2007 Jul

REPOSITORIES: biostudies-literature

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Normal levels of wild-type mitochondrial DNA maintain cytochrome c oxidase activity for two pathogenic mitochondrial DNA mutations but not for m.3243A-->G.

Durham Steve E SE Samuels David C DC Cree Lynsey M LM Chinnery Patrick F PF

American journal of human genetics 20070523 1

Mitochondrial DNA (mtDNA) mutations are a common cause of human disease and accumulate as part of normal ageing and in common neurodegenerative disorders. Cells express a biochemical defect only when the proportion of mutated mtDNA exceeds a critical threshold, but it is not clear whether the actual cause of this defect is a loss of wild-type mtDNA, an excess of mutated mtDNA, or a combination of the two. Here, we show that segments of human skeletal muscle fibers harboring two pathogenic mtDNA ...[more]

PMID: 17564976

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Project description:Mitochondria generate signals of adaptation that regulate nuclear genes expression via retrograde signaling. But this phenomenon is complexified when qualitatively different mitochondria and mitochondrial DNA (mtDNA) coexist within cells. Although this cellular state of heteroplasmy leads to divergent phenotypes clinically, its consequences on cellular function and the cellular transcriptome are unknown. To interrogate this phenomenon, we generated somatic cell cybrids harboring increasing levels of a common mtDNA mutation (tRNALeu(UUR) 3243A>G) and mapped the resulting cellular phenotypes and transcriptional profiles across the complete range of heteroplasmy. Small increases in mutant mtDNAs caused relatively modest defect in mitochondrial oxidative capacity, but resulted in sharp transitions in mitochondrial ultrastructure and in the nuclear and mitochondrial transcriptomes, with the critical functional threshold corresponding to the induction of epigenetic regulatory systems. Principal component analysis underscores how each heteroplasmy level occupies a different "transcriptional space", with low levels heteroplasmy (20-30%) producing a dose-response linear progression in one direction, and mutationload of 50, 60 and 90% producing changes in the opposite direction. Hence, subtle changes in mitochondrial energetics can act through the epigenome to generate the phenotypes of the common “complex” diseases. Cells were generated by transferring the wildtype (3243A) and mutant (3243G) mtDNAs from a heteroplasmic 3243A>G patient’s lymphoblastoid cell line into 143B(TK-) mtDNA-deficient (ρo) cells and selected for transmitochondrial cybrids. Subsequent mtDNA depletion, reamplification, and cloning (Wiseman and Attardi, 1978) resulted in a series of stable cybrids harboring approximately 0, 20, 30, 50, 60, 90, and 100% 3243G mutant mtDNAs. Total RNA extracted from each cell line was then extracted, depleted of rRNA, and measured in sequenced in triplicates.

Dataset Information

Normal levels of wild-type mitochondrial DNA maintain cytochrome c oxidase activity for two pathogenic mitochondrial DNA mutations but not for m.3243A-->G.

Publications

Normal levels of wild-type mitochondrial DNA maintain cytochrome c oxidase activity for two pathogenic mitochondrial DNA mutations but not for m.3243A-->G.

Similar Datasets

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