InsP3R signaling and actomyosin-dependent mitochondrial dynamics play essential roles in mitochondrial stress-induced longevity.

Certain forms of mitochondrial impairment confer longevity, while disease-associated mitochondrial dysfunction triggers pathogenesis. The adaptive pathways that distinguish benefit from pathology remain unclear. Here we reveal that longevity induced by mitochondrial Complex I/nuo-6 mutation in C. elegans is dependent on the endoplasmic reticulum (ER) Ca2+ channel, InsP3R. To explain this connection, we test multiple candidate links between Ca2+ and mitochondrial homeostasis previously established in vitro, including mitochondrial calcium uniporter (MCU)-dependent stimulation of respiration and cytosolic pathways regulating mitochondrial dynamics. We find that MCU is dispensable for both respiration and longevity in Complex I mutants. Conversely, transcriptomic profiling and imaging reveal InsP3R impairment results in maladaptive expansion of compromised mitochondrial networks. We provide evidence that this aberrant mitochondrial expansion results from disruption of a conserved, InsP3R-dependent actin remodeling network centered on Arp2/3. Disruption of actin remodeling or autophagy mimics the mitochondrial expansion and longevity suppression of InsP3R mutants. Conversely, driving mitochondrial fragmentation ameliorates mitochondrial expansion and rescues longevity in InsP3R mutants, supporting a model in which InsP3R-dependent actin remodeling is required for segregation and clearance of mitochondria. These findings identify an inter-organelle signaling axis linking ER calcium release and cytoskeletal remodeling to adaptive mitochondrial responses associated with longevity.