Energetic requirements and bioenergetic modulation of mitochondrial morphology and dynamics.

Mitochondria are the site where oxidative phosphorylations (OXPHOSs) take place. Fusion and fission reactions allow them to change their overall morphology, which ranges from networks of elongated and branched filaments to collections of small individual organelles. It is assumed that mitochondrial bioenergetics and dynamics are linked and that mitochondrial morphology reflects their functional status. This review shows that the links between mitochondrial dynamics and bioenergetics are complex and that mitochondrial deficiencies are not systematically associated to fragmentation. In mammals, mitochondrial fragmentation is observed upon inhibition of OXPHOS with drugs, but not in most cellular models with OXPHOS deficits of genetic origin. In yeast, mitochondrial biogenesis and filament interconnectivity augment with increasing respiratory capacity, but mutation or inhibition of the respiratory chain does not provoke major morphological changes. Significant structural and morphological alterations appear restricted to mutation of genes involved in assembly or function of the F(1)F(0)-ATP-synthase. Finally, ex vivo studies (in mammals) and in vitro studies (in yeast) confirm the essential role of the inner membrane potential for mitochondrial fusion.