Temporal inhibition of the electron transport chain attenuates stress‐induced cellular senescence by prolonged disturbance of proteostasis in human fibroblasts

We previously developed a stress‐induced premature senescence (SIPS) model in which normal human fibroblast MRC‐5 cells were treated with either the proteasome inhibitor MG132 or the vacuolar‐type ATPase inhibitor bafilomycin A1 (BAFA1). To clarify the involvement of mitochondrial function in our SIPS model, MRC‐5 cells were treated with MG132 or BAFA1 along with an inhibitor targeting either the electron transport chain complex I or complex III, or with a mitochondrial uncoupler. SIPS induced by MG132 or BAFA1 was significantly attenuated by short‐term co‐treatment with the complex III inhibitor, antimycin A (AA), but not the complex I inhibitor, rotenone or the mitochondrial uncoupler, carbonyl cyanide 3‐chlorophenylhydrazone. By co‐treatment with AA, mitochondrial and intracellular reactive oxygen species levels, accumulation of protein aggregates and mitochondrial unfolded protein responses (UPR mt ) were remarkably suppressed. Furthermore, AA co‐treatment suppressed the hyperpolarization of the mitochondrial membrane and the induction of mitophagy observed in MG132‐treated cells and enhanced mitochondrial biogenesis. These findings provide evidence that the temporal inhibition of mitochondrial respiration exerts protective effects against the progression of premature senescence caused by impaired proteostasis.