Cd -induced cytochrome c release in apoptotic proximal tubule cells: role of mitochondrial permeability transition pore and Ca uniporter

Lee, Wing-Kee, Ulrich Bork, Fatemeh Gholamrezaei, and Frank Thévenod. Cd -induced cytochrome c release in apoptotic proximal tubule cells: role of mitochondrial permeability transition pore and Ca uniporter. Am J Physiol Renal Physiol 288: F27–F39, 2005. First published August 31, 2004; doi:10.1152/ajprenal. 00224.2004.—Cd induces apoptosis of kidney proximal tubule (PT) cells. Mitochondria play a pivotal role in toxic compoundinduced apoptosis by releasing cytochrome c. Our objective was to investigate the mechanisms underlying Cd -induced cytochrome c release from mitochondria in rat PT cells. Using Hoechst 33342 or MTT assay, 10 M Cd induced 5–10% apoptosis in PT cells at 6 and 24 h, which was associated with cytochrome c and apoptosisinducing factor release at 24 h only. This correlated with previously described maximal intracellular Cd concentrations at 24 h, suggesting that elevated Cd may directly induce mitochondrial liberation of proapoptotic factors. Indeed, Cd caused swelling of energized isolated kidney cortex mitochondria (EC50 9 M) and cytochrome c release, which were independent of permeability transition pore (PTP) opening since PTP inhibitors cyclosporin A or bongkrekic acid had no effect. On the contrary, Cd inhibited swelling and cytochrome c release induced by PTP openers (PO4 3 or H2O2 Ca ). The mitochondrial Ca uniporter (MCU) played a key role in mitochondrial damage: 1) MCU inhibitors (La , ruthenium red, Ru360) prevented swelling and cytochrome c release; and 2) ruthenium red attenuated Cd inhibition of PO4 3 -induced swelling. Using the Cd -sensitive fluorescent indicator FluoZin-1, Cd was also taken up by mitoplasts. The aquaporin inhibitor AgNO3 abolished Cd -induced swelling of mitoplasts. This could be partially mediated by activation of the mitoplast-enriched water channel aquaporin-8. Thus cytosolic Cd concentrations exceeding a certain threshold may directly cause mitochondrial damage and apoptotic development by interacting with MCU and water channels in the inner mitochondrial membrane.