Mitochondria-associated condensates maintain mitochondrial homeostasis and promote lifespan

Abstract

Membraneless organelles assembled by liquid-liquid phase separation interact with diverse membranous organelles to regulate distinct cellular processes. It remains unknown how membraneless organelles are engaged in mitochondrial homeostasis. Here we demonstrate that mitochondria-associated translation organelles (MATOs) mediate local synthesis of proteins required for structural and functional maintenance of mitochondria. In Caenorhabditis elegans, the RNA-binding protein LARP-1 (La-related protein 1) orchestrates coalescence of translation machinery and multiple RNA-binding proteins via liquid-liquid phase separation into MATOs that associate with mitochondria in a translocase of the outer membrane complex-dependent manner. LARP-1 deficiency markedly reduces mitochondrial protein levels, impairing cristae organization and ATP production. Specifically, we show that the membrane-shaping MICOS subunit IMMT-1(MIC60) and the ATP synthase β subunit ATP-2, both being important for cristae organization, are synthesized in LARP-1 MATOs. During aging and starvation, LARP-1 MATOs dissociate from mitochondria; however, mitochondrion-persistent LARP-1 MATOs protect mitochondrial health and greatly extend lifespan. These findings suggest an important mitochondrion-regulating mechanism in aging and stress.