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pubmed:abstractText |
To investigate whether protein import is defective in mitochondrial disease, we compared the rate of import and the expression of protein import machinery components in skin fibroblasts from control subjects and a patient with multiple mitochondrial disease (MMD). The patient exhibited a 35% decrease in cytochrome c oxidase activity and a 59% decrease in cellular oxygen consumption compared to control. Western blot analyses revealed that patient levels of MDH, mtHSP70, HSP60, and Tom20 protein were 57%, 20%, 75% and 100% of control cells, respectively. MDH and Tom20 mRNA levels were not different from control levels, whereas mtHSP70 mRNA were 50% greater than control. Radiolabeled MDH was imported into mitochondria with equal efficiency between patient (44% of total synthesized) and control (43%) cells, although the total MDH synthesized in patient cells was reduced by about 40%. The unaffected levels of mRNA and post-translational import into mitochondria, combined with reduced protein levels of MDH, mtHSP70, and HSP60 suggest a translational defect in this patient with MMD. This was verified by the 50% reduction in overall cellular protein synthesis in the patient compared to control. Further, the similar import rates between patient and control cells suggest an important role for Tom20, but a lesser role for mtHSP70 in regulating protein import into mitochondria.
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