Impact of the Mitochondrial Genetic Background in Complex III Deficiency

Abstract

BackgroundIn recent years clinical evidence has emphasized the importance of the mtDNA genetic background that hosts a primary pathogenic mutation in the clinical expression of mitochondrial disorders, but little experimental confirmation has been provided. We have analyzed the pathogenic role of a novel homoplasmic mutation (m.15533 A>G) in the cytochrome b (MT-CYB) gene in a patient presenting with lactic acidosis, seizures, mild mental delay, and behaviour abnormalities.MethodologySpectrophotometric analyses of the respiratory chain enzyme activities were performed in different tissues, the whole muscle mitochondrial DNA of the patient was sequenced, and the novel mutation was confirmed by PCR-RFLP. Transmitochondrial cybrids were constructed to confirm the pathogenicity of the mutation, and assembly/stability studies were carried out in fibroblasts and cybrids by means of mitochondrial translation inhibition in combination with blue native gel electrophoresis.Principal FindingsBiochemical analyses revealed a decrease in respiratory chain complex III activity in patient's skeletal muscle, and a combined enzyme defect of complexes III and IV in fibroblasts. Mutant transmitochondrial cybrids restored normal enzyme activities and steady-state protein levels, the mutation was mildly conserved along evolution, and the proband's mother and maternal aunt, both clinically unaffected, also harboured the homoplasmic mutation. These data suggested a nuclear genetic origin of the disease. However, by forcing the de novo functioning of the OXPHOS system, a severe delay in the biogenesis of the respiratory chain complexes was observed in the mutants, which demonstrated a direct functional effect of the mitochondrial genetic background.ConclusionsOur results point to possible pitfalls in the detection of pathogenic mitochondrial mutations, and highlight the role of the genetic mtDNA background in the development of mitochondrial disorders.

Type II diabetes increases mitochondrial DNA mutations in the left ventricle of the Goto-Kakizaki diabetic rat

“…They observed decreases in the presence of fully assembled Complex I and IV but not Complex II and our results concur. Separate from those studies, two papers examined the impact of mtDNA mutations on OXPHOS assembly (35,91). A mutation in cytochrome b (A15533G) was observed in a patient presenting with lactic acidosis and mild mental decay.…”

“…A mutation in cytochrome b (A15533G) was observed in a patient presenting with lactic acidosis and mild mental decay. Mimicking the mutation in transmutational cybrids resulted in significant alterations in the rate of Complex assembly (35). Using a similar approach and examining mutations common to LHON (Leber's hereditary optic neuropathy), Pello et.…”

The champions' mitochondria: is it genetically determined? A review on mitochondrial DNA and elite athletic performance

“…The mtDNA mutations could also have an effect on the risk of neurodegenerative diseases (77,78) or modulate the biochemical defects and clinical outcome of these disorders (17a). They can influence spermatozoa motility (52,65) or the development of mitochondrial disorders (29). Mitochondrial haplogroups could also have an effect on human longevity, at least in some ethnic/geographical cohorts (18,38,56,63,64,66,75,83).…”

High-resolution melting analysis of 15 genes in 60 patients with cytochrome-c oxidase deficiency

“…However, subtle modification in the rate of complex III biogenesis might occur, as documented by others. 32,33 With the exception of the new homoplasmic m.15866G variant, the patient P25 carried only common SNPs in her mtDNA.…”