title: Defective TNF-alpha-mediated hepatocellular apoptosis and liver damage in acidic sphingomyelinase knockout mice.
abstract: This study addressed the contribution of acidic sphingomyelinase (ASMase) in TNF-alpha-mediated hepatocellular apoptosis. Cultured hepatocytes depleted of mitochondrial glutathione (mGSH) became sensitive to TNF-alpha, 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-alpha-induced cell death. In contrast, mGSH-depleted hepatocytes deficient in ASMase were resistant to TNF-alpha-mediated cell death but sensitive to exogenous ASMase. Furthermore, although in vivo administration of TNF-alpha 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-alpha-mediated apoptosis. This approach, which blunted glycosphingolipid generation by TNF-alpha, protected mGSH-depleted ASMase(+/+) hepatocytes from TNF-alpha despite enhancement of TNF-alpha-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-alpha-induced hepatocellular apoptosis by promoting the mitochondrial targeting of glycosphingolipids.
authors.affiliation: Liver Unit, Instituto de Malalties Digestives, Hospital Clinic i Provincial, Instituto de Investigaciones Biomédicas August Pi Suñer, Barcelona, Spain.
authors.forename: Carmen
authors.initials: C
authors.lastname: García-Ruiz
authors.forename: Anna
authors.initials: A
authors.lastname: Colell
authors.forename: Montserrat
authors.initials: M
authors.lastname: Marí
authors.forename: Albert
authors.initials: A
authors.lastname: Morales
authors.forename: María
authors.initials: M
authors.lastname: Calvo
authors.forename: Carlos
authors.initials: C
authors.lastname: Enrich
authors.forename: José C
authors.initials: JC
authors.lastname: Fernández-Checa
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D002478:Cells, Cultured; D002518:Ceramides / Q000502:physiology; D005732:Gangliosides / Q000502:physiology; D005978:Glutathione / Q000378:metabolism; D006028:Glycosphingolipids / Q000502:physiology; D022781:Hepatocytes / Q000187:drug effects* / Q000473:pathology; D008099:Liver / Q000187:drug effects* / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008930:Mitochondria, Liver / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2; D013108:Sphingomyelin Phosphodiesterase / Q000502:physiology*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D051028:bcl-2-Associated X Protein
chemical_list: D002518:Ceramides; D005732:Gangliosides; D006028:Glycosphingolipids; D016328:NF-kappa B; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D014409:Tumor Necrosis Factor-alpha; D051028:bcl-2-Associated X Protein; C026226:ganglioside, GD3; D013108:Sphingomyelin Phosphodiesterase; D005978:Glutathione