Prohibitin depletion extends lifespan of a TORC2/SGK‐1 mutant through autophagy and the mitochondrial UPR

Abstract Mitochondrial prohibitins (PHB) are highly conserved proteins with a peculiar effect on lifespan. While PHB depletion shortens lifespan of wild‐type animals, it enhances longevity of a plethora of metabolically compromised mutants, including target of mTOR(definition)-inhibiting drug studied for extending healthspan and lifespan." style="text-decoration:underline dotted; text-underline-offset:2px; cursor:help;">rapamycin(definition) complex 2 (TORC2) mutants sgk ‐ 1 and rict ‐ 1 . Here, we show that sgk ‐ 1 mutants have impaired mitochondrial homeostasis, lipogenesis and yolk formation, plausibly due to alterations in membrane lipid and sterol homeostasis. Remarkably, all these features are suppressed by PHB depletion. Our analysis shows the requirement of SRBP1/SBP‐1 for the lifespan extension of sgk ‐ 1 mutants and the further extension conferred by PHB depletion. Moreover, although the mitochondrial unfolded protein response (UPR mt ) and autophagy(definition) are induced in sgk ‐ 1 mutants and upon PHB depletion, they are dispensable for lifespan. However, the enhanced longevity caused by PHB depletion in sgk ‐ 1 mutants requires both, the UPR mt and autophagy, but not mitophagy. We hypothesize that UPR mt induction upon PHB depletion extends lifespan of sgk ‐ 1 mutants through autophagy and probably modulation of lipid metabolism.