Defective TNF-α–mediated hepatocellular apoptosis and liver damage in acidic sphingomyelinase knockout mice
Carmen García-Ruiz, … , Carlos Enrich, José C. Fernández-Checa
Carmen García-Ruiz, … , Carlos Enrich, José C. Fernández-Checa
Published January 15, 2003
Citation Information: J Clin Invest. 2003;111(2):197-208. https://doi.org/10.1172/JCI16010.
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Article

Defective TNF-α–mediated hepatocellular apoptosis and liver damage in acidic sphingomyelinase knockout mice

Abstract

This study addressed the contribution of acidic sphingomyelinase (ASMase) in TNF-α–mediated hepatocellular apoptosis. Cultured hepatocytes depleted of mitochondrial glutathione (mGSH) became sensitive to TNF-α, undergoing a time-dependent apoptotic cell death preceded by mitochondrial membrane depolarization, cytochrome c release, and caspase activation. Cyclosporin A treatment rescued mGSH-depleted hepatocytes from TNF-α–induced cell death. In contrast, mGSH-depleted hepatocytes deficient in ASMase were resistant to TNF-α–mediated cell death but sensitive to exogenous ASMase. Furthermore, although in vivo administration of TNF-α or LPS to galactosamine-pretreated ASMase+/+ mice caused liver damage, ASMase–/– mice exhibited minimal hepatocellular injury. To analyze the requirement of ASMase, we assessed the effect of glucosylceramide synthetase inhibition on TNF-α–mediated apoptosis. This approach, which blunted glycosphingolipid generation by TNF-α, protected mGSH-depleted ASMase+/+ hepatocytes from TNF-α despite enhancement of TNF-α–stimulated ceramide formation. To further test the involvement of glycosphingolipids, we focused on ganglioside GD3 (GD3) because of its emerging role in apoptosis through interaction with mitochondria. Analysis of the cellular redistribution of GD3 by laser scanning confocal microscopy revealed the targeting of GD3 to mitochondria in ASMase+/+ but not in ASMase–/– hepatocytes. However, treatment of ASMase–/– hepatocytes with exogenous ASMase induced the colocalization of GD3 and mitochondria. Thus, ASMase contributes to TNF-α–induced hepatocellular apoptosis by promoting the mitochondrial targeting of glycosphingolipids.

Authors

Carmen García-Ruiz, Anna Colell, Montserrat Marí, Albert Morales, María Calvo, Carlos Enrich, José C. Fernández-Checa

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Mitochondrial GSH depletion facilitates TNF-α–mediated mitochondrial dep...
Mitochondrial GSH depletion facilitates TNF-α–mediated mitochondrial depolarization. (a) Cultured rat hepatocytes were pretreated with HP (1 mM) for 5 minutes and then fractionated to obtain cytosol and mitochondria for GSH determination by high-performance liquid chromatography. Results are expressed as means ± SD (n = 4 or 5). *P < 0.05 versus control. (b) After HP treatment, hepatocytes were then exposed to TNF-α (280 ng/ml) for 15–60 minutes. Peroxide formation and mitochondrial membrane potential were determined upon staining of cells with DFCDA and TMRM, respectively, and fluorescence of both fluorochromes was determined by flow cytometry. A representative profile of four independent experiments is shown. (c) Hepatocytes treated with TNF-α (280 ng/ml) over time with or without HP pretreatment were permeabilized with digitonin, and cell extracts were analyzed for cytochrome c or cytochrome c oxidase as indicated in the Methods. (d and e) Aliquots of cell extracts were used for the detection of active caspase 3 fragments by immunoblotting (d) or activity determination using a fluorescent peptide (e). Results are expressed as means ± SD (n = 3 or 4 independent experiments).