Cd(2+)-induced cytochrome c release in apoptotic proximal tubule cells: role of mitochondrial permeability transition pore and Ca(2+) uniporter.
Cd(2+) induces apoptosis of kidney proximal tubule (PT) cells. Mitochondria play a pivotal role in toxic compound-induced apoptosis by releasing cytochrome c. Our objective was to investigate the mechanisms underlying Cd(2+)-induced cytochrome c release from mitochondria in rat PT cells. Using Hoechst 33342 or MTT assay, 10 muM Cd(2+) induced approximately 5-10% apoptosis in PT cells at 6 and 24 h, which was associated with cytochrome c and apoptosis-inducing factor release at 24 h only. This correlated with previously described maximal intracellular Cd(2+) concentrations at 24 h, suggesting that elevated Cd(2+) may directly induce mitochondrial liberation of proapoptotic factors. Indeed, Cd(2+) caused swelling of energized isolated kidney cortex mitochondria (EC(50) approximately 9 muM) 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(2+) inhibited swelling and cytochrome c release induced by PTP openers (PO(4)(3-) or H(2)O(2)+Ca(2+)). The mitochondrial Ca(2+) uniporter (MCU) played a key role in mitochondrial damage: 1) MCU inhibitors (La(3+), ruthenium red, Ru360) prevented swelling and cytochrome c release; and 2) ruthenium red attenuated Cd(2+) inhibition of PO(4)(3-)-induced swelling. Using the Cd(2+)-sensitive fluorescent indicator FluoZin-1, Cd(2+) was also taken up by mitoplasts. The aquaporin inhibitor AgNO(3) abolished Cd(2+)-induced swelling of mitoplasts. This could be partially mediated by activation of the mitoplast-enriched water channel aquaporin-8. Thus cytosolic Cd(2+) 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.
Lee
Wing-Kee
WK
Department of Physiology and Pathophysiology, Faculty of Medicine, University of Witten/Herdecke, D-58448 Witten, Germany.
Bork
Ulrich
U
Gholamrezaei
Fatemeh
F
Thévenod
Frank
F
D000818:Animals; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D002104:Cadmium / Q000494:pharmacology*; D015220:Calcium Channels; D002135:Calcium-Binding Proteins / Q000502:physiology*; D002460:Cell Line; D045304:Cytochromes c / Q000378:metabolism*; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism; D007473:Ion Channels / Q000187:drug effects* / Q000502:physiology; D007687:Kidney Tubules, Proximal / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D008933:Mitochondrial Swelling / Q000187:drug effects; D010539:Permeability; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
D015220:Calcium Channels; D002135:Calcium-Binding Proteins; D007473:Ion Channels; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; C034703:mitochondrial calcium uniporter; D002104:Cadmium; D045304:Cytochromes c