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This Article Full Text Full Text (PDF) All Versions of this Article: 293/3/C839    most recent 00197.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via ISI Web of Science (2) Citing Articles via Google Scholar Google Scholar Articles by Lee, W.-K. Articles by Thévenod, F. Search for Related Content PubMed PubMed Citation Articles by Lee, W.-K. Articles by Thévenod, F.

GROWTH, DIFFERENTIATION, AND APOPTOSIS

Cadmium-induced ceramide formation triggers calpain-dependent apoptosis in cultured kidney proximal tubule cells

Department of Physiology and Pathophysiology, University of Witten/Herdecke, Witten, Germany

Submitted 16 May 2007 ; accepted in final form 26 June 2007

A major target of cadmium (Cd²⁺) toxicity is the kidney proximal tubule (PT) cell. Cd²⁺-induced apoptosis of PT cells is mediated by sequential activation of calpains at 3–6 h and caspases-9 and -3 after 24-h exposure. Calpains also partly contribute to caspase activation, which emphasizes the importance of calpains for PT apoptosis by Cd²⁺. Upstream processes underlying Cd²⁺-induced calpain activation remain unclear. We describe for the first time that 10–50 µM Cd²⁺ causes a significant increase in ceramide formation by 22% (3 h) and 72% (24 h), as measured by diacylglycerol kinase assay. Inhibition of ceramide synthase with fumonisin B₁ (3 µM) prevents ceramide formation at 3 h and abolishes calpain activation at 6 h, which is associated with significant attenuation of apoptosis at 3–6 h with Hoechst 33342 nuclear staining and/or 3(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) death assays. This indicates that Cd²⁺ enhances de novo ceramide synthesis and that calpains are a downstream target of ceramides in apoptosis execution. Moreover, addition of C₆-ceramide to PT cells increases cytosolic Ca²⁺ and activates calpains. Apoptosis mediated by C₆-ceramide at 24 h is significantly reduced by caspase-3 inhibition, which supports cross talk between calpain- and caspase-dependent apoptotic pathways. We conclude that Cd²⁺-induced apoptosis of PT cells entails endogenous ceramide elevation and subsequent Ca²⁺-dependent calpain activation, which propagates kidney damage by Cd²⁺.

nephrotoxicity; cell signaling; cell biology and structure