Calcium signalling-dependent mitochondrial dysfunction and bioenergetics regulation in respiratory chain Complex II deficiency

Despite advanced knowledge on the genetic basis of oxidative phosphorylation-related diseases, the molecular and/or cellular determinants for tissue-specific dysfunction are not completely understood. Here, we report the cellular events associated with mitochondrial respiratory Complex II deficiency occurring before cell death. Mutation or chronic inhibition of Complex II determined a large increase of basal and agonist-evoked Ca 2+ signals in the cytosol and the mitochondria, in parallel with mitochondrial dysfunction characterized by membrane potential (Δ ψ mit ) loss, [ATP] reduction and increased reactive oxygen species production. Cytosolic and mitochondrial Ca 2+ overload are linked to increased endoplasmic reticulum (ER) Ca 2+ leakage, and to SERCA2b and PMCA proteasome-dependent degradation. Increased [Ca 2+ ] mit is also contributed by decreased mitochondrial motility and increased ER-mitochondria contact sites. Interestingly, increased intracellular [Ca 2+ ] activated on the one hand a compensatory Ca 2+ -dependent glycolytic ATP production and determined on the second hand mitochondrial pathology. These results revealed the primary function for Ca 2+ signalling in the control of mitochondrial dysfunction and cellular bioenergetics outcomes linked to respiratory chain Complex II deficiency.