Mitochondrial DNA mutations are an important cause of human disease for which there is no effective treatment.
Myoclonic epilepsy with ragged-red fibers (
MERRF) is a
mitochondrial disease usually caused by point mutations in
transfer RNA genes encoded by
mitochondrial DNA. The most common mutation associated with
MERRF syndrome, m.8344A > G in the gene MT-TK, which encodes
transfer RNA(
Lysine), affects the translation of all
mitochondrial DNA encoded
proteins. This impairs the assembly of the electron transport chain complexes leading to decreased mitochondrial respiratory function. Here we report on how this mutation affects mitochondrial function in primary fibroblast cultures established from patients harboring the A8344G mutation.
Coenzyme Q10 levels, as well as mitochondrial respiratory chain activity, and
mitochondrial protein expression levels were significantly decreased in
MERRF fibroblasts. Mitotracker staining and imaging analysis of individual mitochondria indicated the presence of small, rounded, depolarized mitochondria in
MERRF fibroblasts.
Mitochondrial dysfunction was associated with increased oxidative stress and increased degradation of impaired mitochondria by mitophagy. Transmitochondrial cybrids harboring the A8344G mutation also showed
CoQ10 deficiency,
mitochondrial dysfunction, and increased mitophagy activity. All these abnormalities in patient-derived fibroblasts and cybrids were partially restored by
CoQ10 supplementation, indicating that these cell culture models may be suitable for screening and validation of novel
drug candidates for
MERRF disease.