Caspase-dependent and -independent pathways for cadmium-induced apoptosis in cultured kidney proximal tubule cells

• Published in: American journal of physiology. Renal physiology Vol. 291; no. 4; pp. F823 - F832
• Main Authors: Lee, Wing-Kee, Abouhamed, Marouan, Thévenod, Frank
• Format: Journal Article
• Language: English
• Published: United States 01.10.2006
• Subjects: Acrylates - pharmacology; Animals; Apoptosis - drug effects; Cadmium - toxicity; Caspases - metabolism; Cell Line; Cells, Cultured; Cytochromes c - metabolism; Kidney Tubules, Proximal - cytology; Kidney Tubules, Proximal - drug effects; Kidney Tubules, Proximal - physiology; Rats
• ISSN: 1931-857X; 1522-1466
• DOI: 10.1152/ajprenal.00276.2005

The nephrotoxic metal cadmium at micromolar concentrations induces apoptosis of rat kidney proximal tubule (PT) cells within 3-6 h of exposure. The underlying cell death pathways remain poorly defined. Using Hoechst 33342/ethidium bromide nuclear staining and 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) cell death assays, 10-50 microM cadmium induced apoptosis of immortalized rat kidney cells derived from the S1-segment of PT at 6 and 24 h, but necrosis at 24 h only. Cadmium (10-50 microM) also caused mitochondrial cytochrome c (cyt. c)- and apoptosis-inducing factor release at 24 h, but not at 6 h, as measured by immunofluorescence imaging and immunoblotting. Caspases-9 and -3 were activated only by 10 microM cadmium for 24 h, and accordingly apoptosis was significantly reduced by the respective inhibitors (z-LEHD-fmk, z-DEVD-fmk; 10 microg/ml) at 24 h, but not at 6 h, without affecting necrosis. At 6 h, 10 microM cadmium increased the activity of the calcium-activated protease calpain, but not at 24 h, and calpain inhibitors (ALLN, PD 150606; 10-30 microM) blocked apoptosis by 10 microM cadmium at 3-6 h. However, PD-150606 also attenuated caspase-3 activity and apoptosis at 24 h, suggesting calpain-dependent caspase activation. Thus cadmium-induced apoptosis of PT cells involves a complex and sensitive interplay of signaling cascades involving mitochondrial proapoptotic factors, calpains and caspases, whose activation is also determined by cadmium concentration and the duration of cadmium exposure.