Analysis of the mitochondrial proteome of cybrid cells harbouring a truncative mitochondrial DNA mutation in respiratory complex I.

Transmitochondrial cytoplasmic hybrids (cybrids) are well established model systems to reveal the effects of mitochondrial DNA (mtDNA) mutations on cell metabolism excluding the interferences of a different nuclear background. The m.3571insC mutation in the MTND1 gene of respiratory complex I (CI) is commonly detected in oncocytic tumors, in which it causes a severe CI dysfunction leading to an energetic impairment when present above 83% mutant load. To assess whether the energetic deficit may alter the mitochondrial proteome, OS-78 and OS-93 cybrid cell lines bearing two different degrees of the m.3571insC mutation (78% and 92.8%, respectively) and control cybrids bearing wild-type mtDNA (CC) were analyzed. Two-dimensional electrophoresis and mass spectrometry revealed significant alterations only in cybrids above the threshold (OS-93). All differentially expressed proteins are decreased. In particular, the levels of the pyruvate dehydrogenase E1 chain B subunit (E1β), of lipoamide dehydrogenase (E3), the enzyme component of pyruvate and 2-oxoglutarate dehydrogenase complexes, and of lactate dehydrogenase B (LDHB) were reduced. Moreover, a significant decrease of the pyruvate dehydrogenase complex activity was found when OS-93 cybrid cells were grown in galactose medium, a metabolic condition that forces cells to use respiration. These results demonstrate that the energetic impairment caused by the almost homoplasmic m.3571insC mutation perturbs cellular metabolism leading to a decreased steady state level of components of very important mitochondrial NAD-dependent dehydrogenases.