Zn2+ induces permeability transition pore opening and release of pro-apoptotic peptides from neuronal mitochondria

Rapid entry of Ca2+ or Zn2+ kills neurons. Mitochondria are major sites of Ca2+-dependent toxicity. This study examines Zn2+-initiated mitochondrial cell death signaling. 10 nm Zn2+ induced acute swelling of isolated mitochondria, which was much greater than that induced by higher Ca2+ levels. Zn2+ entry into mitochondria was dependent upon the Ca2+ uniporter, and the consequent swelling resulted from opening of the mitochondrial permeability transition pore. Confocal imaging of intact neurons revealed entry of Zn2+ (with Ca2+) to cause pronounced mitochondrial swelling, which was far greater than that induced by Ca2+ entry alone. Further experiments compared the abilities of Zn2+ and Ca2+ to induce mitochondrial release of cytochrome c (Cyt-c) or apoptosis-inducing factor. In isolated mitochondria, 10 nm Zn2+ exposures induced Cyt-c release. Induction of Zn2+ entry into cortical neurons resulted in distinct increases in cytosolic Cyt-c immunolabeling and in cytosolic and nuclear apoptosis-inducing factor labeling within 60 min. In comparison, higher absolute [Ca2+](i) rises were less effective in inducing release of these factors. Addition of the mitochondrial permeability transition pore inhibitors cyclosporin A and bongkrekic acid decreased Zn2+-dependent release of the factors and attenuated neuronal cell death as assessed by trypan blue staining 5-6 h after the exposures.