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

Annexin A5 (AnxA5) is a Ca-dependent phospholipid-binding protein associated with the regulation of intracellular Ca homeostasis. However, the precise role of AnxA5 in controlling mitochondrial Ca signaling remains elusive. Here, we introduce a novel function of AnxA5 in regulating mitochondrial Ca signaling. Our investigation revealed that AnxA5 localizes at and in the mitochondria and orchestrates intermembrane space Ca signaling upon high Ca elevations induced by ER Ca 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 measurements and electrophysiological recordings, AnxA5 was found to enhance Ca flux through the OMM by promoting the Ca-permeable state of VDAC1. By modulating intermembrane space Ca signaling, AnxA5 shapes mitochondrial ultrastructure and influences the dynamicity of the mitochondrial Ca 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.