Mitochondrial DNA mutations provoke dominant inhibition of mitochondrial inner membrane fusion

PLoS One. 2012;7(11):e49639. doi: 10.1371/journal.pone.0049639. Epub 2012 Nov 16.

Abstract

Mitochondria are highly dynamic organelles that continuously move, fuse and divide. Mitochondrial dynamics modulate overall mitochondrial morphology and are essential for the proper function, maintenance and transmission of mitochondria and mitochondrial DNA (mtDNA). We have investigated mitochondrial fusion in yeast cells with severe defects in oxidative phosphorylation (OXPHOS) due to removal or various specific mutations of mtDNA. We find that, under fermentative conditions, OXPHOS deficient cells maintain normal levels of cellular ATP and ADP but display a reduced mitochondrial inner membrane potential. We demonstrate that, despite metabolic compensation by glycolysis, OXPHOS defects are associated to a selective inhibition of inner but not outer membrane fusion. Fusion inhibition was dominant and hampered the fusion of mutant mitochondria with wild-type mitochondria. Inhibition of inner membrane fusion was not systematically associated to changes of mitochondrial distribution and morphology, nor to changes in the isoform pattern of Mgm1, the major fusion factor of the inner membrane. However, inhibition of inner membrane fusion correlated with specific alterations of mitochondrial ultrastructure, notably with the presence of aligned and unfused inner membranes that are connected to two mitochondrial boundaries. The fusion inhibition observed upon deletion of OXPHOS related genes or upon removal of the entire mtDNA was similar to that observed upon introduction of point mutations in the mitochondrial ATP6 gene that are associated to neurogenic ataxia and retinitis pigmentosa (NARP) or to maternally inherited Leigh Syndrome (MILS) in humans. Our findings indicate that the consequences of mtDNA mutations may not be limited to OXPHOS defects but may also include alterations in mitochondrial fusion. Our results further imply that, in healthy cells, the dominant inhibition of fusion could mediate the exclusion of OXPHOS-deficient mitochondria from the network of functional, fusogenic mitochondria.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • DNA, Mitochondrial*
  • GTP-Binding Proteins / metabolism
  • Membrane Fusion*
  • Membrane Potential, Mitochondrial
  • Mitochondria / genetics
  • Mitochondria / metabolism
  • Mitochondria / ultrastructure
  • Mitochondrial Membranes / metabolism*
  • Mitochondrial Proteins / metabolism
  • Mitochondrial Proton-Translocating ATPases / genetics
  • Mitochondrial Proton-Translocating ATPases / metabolism
  • Mutation*
  • Oxidative Phosphorylation
  • Saccharomyces cerevisiae / genetics
  • Saccharomyces cerevisiae / metabolism
  • Saccharomyces cerevisiae Proteins / genetics
  • Saccharomyces cerevisiae Proteins / metabolism

Substances

  • ATP6 protein, S cerevisiae
  • DNA, Mitochondrial
  • MGM1 protein, S cerevisiae
  • Mitochondrial Proteins
  • Saccharomyces cerevisiae Proteins
  • GTP-Binding Proteins
  • Mitochondrial Proton-Translocating ATPases

Grant support

This work was supported by Centre National de la Recherche Scientifique (CNRS), Université Bordeaux Segalen, Conseil Régional d’Aquitaine (CRA), Association Française contre les Myopathies (AFM) and Fondation pour la Recherche Médicale (FRM). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.