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 (V-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 (ETC) 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 (CCCP). By co-treatment with AA, mitochondrial and intracellular reactive oxygen species (ROS) 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.