Zn(2+) Induces Permeability Transition Pore Opening and Release of Pro-apoptotic Peptides from Neuronal Mitochondria

Rapid entry of Ca(2+) or Zn(2+) kills neurons. Mitochondria are major sites of Ca(2+)-dependent toxicity. This study examines Zn(2+)-initiated mitochondrial cell death signaling. 10 nm Zn(2+) induced acute swelling of isolated mitochondria, which was much greater than that induced by higher Ca(2+) levels. Zn(2+) entry into mitochondria was dependent upon the Ca(2+) uniporter, and the consequent swelling resulted from opening of the mitochondrial permeability transition pore. Confocal imaging of intact neurons revealed entry of Zn(2+) (with Ca(2+)) to cause pronounced mitochondrial swelling, which was far greater than that induced by Ca(2+) entry alone. Further experiments compared the abilities of Zn(2+) and Ca(2+) to induce mitochondrial release of cytochrome c (Cyt-c) or apoptosis-inducing factor. In isolated mitochondria, 10 nm Zn(2+) exposures induced Cyt-c release. Induction of Zn(2+) 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 [Ca(2+)](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 Zn(2+)-dependent release of the factors and attenuated neuronal cell death as assessed by trypan blue staining 5-6 h after the exposures.