Mitochondrial respiration maintains autophagy to support stress resistance in quiescent cells

Mitochondrial oxidative phosphorylation (OXPHOS) generates ATP and is required for pyrimidine nucleotide synthesis during proliferation. In contrast, the role of OXPHOS in post-mitotic cells, beyond its contribution to ATP production, is less understood. Here, we show that in non-proliferating cells, OXPHOS ensures protection against oxidative stress by sustaining autophagy. Autophagy is suppressed and oxidative stress resistance is compromised in OXPHOS-deficient non-proliferating cells in vitro and in TFAM knockout mice in vivo, while attenuation of autophagy in OXPHOS-functional cells phenocopies the effects of OXPHOS deficiency. Mechanistically, the regulation of the autophagy / stress response by OXPHOS does not require changes in gene expression, AMPK/mTOR1/ULK1 signaling or NADH levels. Instead, OXPHOS maintains ROS levels to prevent activation of ATG4, a ROS-activated inhibitor of autophagy. We propose that protection against oxidative stress via the ROS-ATG4 axis is a novel function of mitochondrial respiration in non-proliferating cells that may have consequences for cancer therapy and beyond. Overall design: Cultured Ea.hy926 cells, parental (Eahy) and OXPHOS-deficient (Rho0), were grown to confluence and 4 biological replicates were collected for bulk RNA-seq analysis.