InsP3R signaling mediates mitochondrial stress-induced longevity through actomyosin-dependent mitochondrial dynamics.

Certain forms of mitochondrial impairment confer longevity, while mitochondrial dysfunction arising from aging and disease-associated mutations triggers severe pathogenesis. The adaptive pathways that distinguish benefit from pathology remain unclear. Here we reveal that longevity induced by mitochondrial Complex I/ mutation in is dependent on the endoplasmic reticulum (ER) Ca channel, InsP3R. We find that the InsP3R promotes mitochondrial respiration, but the mitochondrial calcium uniporter is dispensable for both respiration and lifespan extension in Complex I mutants, suggesting InsP3R action is independent of matrix Ca flux. Transcriptomic profiling and imaging reveal a previously unrecognized role for the InsP3R in regulating mitochondrial scaling, where InsP3R impairment results in maladaptive hyper-expansion of dysfunctional mitochondrial networks. We reveal a conserved InsP3R signaling axis through which calmodulin and actomyosin remodeling machineries, including Arp2/3, formin FHOD-1, and MLCK, constrain mitochondrial expansion and promote longevity. Disruption of actin remodeling or autophagy mimics InsP3R loss. Conversely, driving fragmentation ameliorates mitochondrial expansion and rescues longevity, supporting a model in which InsP3R-dependent actin remodeling sustains mitochondrial turnover. These findings establish an inter-organelle signaling axis by which ER calcium release orchestrates mitochondrial-based longevity through cytoskeletal effectors.