Suppression of Mitochondrial DNA Instability of Autosomal Dominant Forms of Progressive External Ophthalmoplegia-AssociatedANT1Mutations inPodospora anserina

Abstract

Maintenance and expression of mitochondrial DNA (mtDNA) are essential for the cell and the organism. In humans, several mutations in the adenine nucleotide translocase gene ANT1 are associated with multiple mtDNA deletions and autosomal dominant forms of progressive external ophthalmoplegia (adPEO). The mechanisms underlying the mtDNA instability are still obscure. A current hypothesis proposes that these pathogenic mutations primarily uncouple the mitochondrial inner membrane, which secondarily causes mtDNA instability. Here we show that the three adPEO-associated mutations equivalent to A114P, L98P, and V289M introduced into the Podospora anserina ANT1 ortholog dominantly cause severe growth defects, decreased reactive oxygen species production (ROS), decreased mitochondrial inner membrane potential (Dc), and accumulation of large-scale mtDNA deletions leading to premature death. Interestingly, we show that, at least for the adPEO-type M106P and A121P mutant alleles, the associated mtDNA instability cannot be attributed only to a reduced membrane potential or to an increased ROS level since it can be suppressed without restoration of the Dc or modification of the ROS production. Suppression of mtDNA instability due to the M106P and A121P mutations was obtained by an allele of the rmp1 gene involved in nucleo-mitochondrial cross-talk and also by an allele of the AS1 gene encoding a cytosolic ribosomal protein.In contrast, the mtDNA instability caused by the S296M mutation was not suppressed by these alleles.

Adenine Nucleotide Translocase, Mitochondrial Stress, and Degenerative Cell Death

“…DCD is also suppressed by cycloheximide, an inhibitor of cytosolic protein synthesis, which further supports the model that reduced cytosolic protein synthesis suppresses mitochondrial degeneration and DCD [89]. In P. anserina , premature cell death and mtDNA instability induced by ANT1 mutations are suppressed by a mutation in the AS1 gene encoding a ribosomal protein [90]. …”

“…The global mitochondrial damage model is supported by another study from El-Khoury and Sainsard-Chanet using the filamentous fungi Podospora anserina as a model system [90]. The A114P, L98P, and V289M alleles were introduced into the P. anserina ANT1 ortholog, PaANT .…”

Physiological and pathological roles of mitochondrial SLC25 carriers

“…Expression of mutant forms of ANT associated with adPEO reduces ATP/ADP transport [96], and leads to large-scale mtDNA deletions which are characteristic of the disease [97]. ANT deficiency also leads to dilated cardiomyopathy.…”

Misfolding of mutant adenine nucleotide translocase in yeast supports a novel mechanism of Ant1-induced muscle diseases

“…We proposed that the mutant proteins may interfere with general mitochondrial biogenesis in addition to their effect on oxidative phosphorylation and mtDNA stability and that mtDNA instability likely arises as a secondary effect of mitochondrial damage. By using the filamentous fungus Podospora anserine as a model system, El-Khoury and Sainsard-Chanet (2009) also showed that expression of the adPEO-type Ant variants leads to severe mitochondrial damage, as manifested by low mitochondrial membrane potential. The mechanism by which the mutant Ant causes mitochondrial damage is unknown.…”