Annexin A5 controls VDAC1-dependent mitochondrial Ca(2+) homeostasis and determines cellular susceptibility to apoptosis.

Annexin A5 (AnxA5) is a Ca(2+)-dependent phospholipid-binding protein associated with the regulation of intracellular Ca(2+) homeostasis. However, the precise role of AnxA5 in controlling mitochondrial Ca(2+) signaling remains elusive. Here, we introduce a novel function of AnxA5 in regulating mitochondrial Ca(2+) signaling. Our investigation revealed that AnxA5 localizes at and in the mitochondria and orchestrates intermembrane space Ca(2+) signaling upon high Ca(2+) elevations induced by ER Ca(2+) release. Proximity ligation assays and co-immunoprecipitation revealed a close association but no direct contact of AnxA5 with the voltage-dependent anion channel (VDAC1) in the outer mitochondrial membrane (OMM). In single-cell mitochondrial Ca(2+) measurements and electrophysiological recordings, AnxA5 was found to enhance Ca(2+) flux through the OMM by promoting the Ca(2+)-permeable state of VDAC1. By modulating intermembrane space Ca(2+) signaling, AnxA5 shapes mitochondrial ultrastructure and influences the dynamicity of the mitochondrial Ca(2+) uniporter. Furthermore, by controlling VDAC1's oligomeric state, AnxA5 is protective against cisplatin and selenite-induced apoptotic cell death. Our study uncovers AnxA5 as an integral regulator of VDAC1 in physiological and pathological conditions.