title: Roles for C16-ceramide and sphingosine 1-phosphate in regulating hepatocyte apoptosis in response to tumor necrosis factor-alpha.
abstract: Tumor necrosis factor (TNF)-alpha signals cell death and simultaneously induces the generation of ceramide, which is metabolized to sphingosine and sphingosine 1-phosphate (S1P) by ceramidase (CDase) and sphingosine kinase. Because the dynamic balance between the intracellular levels of ceramide and S1P (the "ceramide/S1P rheostat") may determine cell survival, we investigated these sphingolipid signaling pathways in TNF-alpha-induced apoptosis of primary hepatocytes. Endogenous C16-ceramide was elevated during TNF-alpha-induced apoptosis in both rat and mouse primary hepatocytes. The putative acid sphingomyelinase (ASMase) inhibitor imipramine inhibited TNF-alpha-induced apoptosis and C16-ceramide increase as did the knock out of ASMase. Overexpression of neutral CDase (NCDase) inhibited the TNF-alpha-induced increase of C16-ceramide and apoptosis in rat primary hepatocytes. Moreover, NCDase inhibited liver injury and hepatocyte apoptosis in mice treated with D-galactosamine plus TNF-alpha. This protective effect was abrogated by the sphingosine kinase inhibitor N,N-demethylsphingosine, suggesting that the survival effect of NCDase is due to not only C16-ceramide reduction but also S1P formation. Administration of S1P or overexpression of NCDase activated the pro-survival kinase AKT, and overexpression of dominant negative AKT blocked the survival effect of NCDase. In conclusion, activation of ASMase and generation of C16-ceramide contributed to TNF-alpha-induced hepatocyte apoptosis. NCDase prevented apoptosis both by reducing C16-ceramide and by activation of AKT through S1P formation. Therefore, the cross-talk between sphingolipids and AKT pathway may determine hepatocyte apoptosis by TNF-alpha.
authors.affiliation: Department of Medicine, Columbia University, College of Physicians and Surgeons, New York, New York 10032, USA.
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Osawa
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Uchinami
authors.forename: Jacek
authors.initials: J
authors.lastname: Bielawski
authors.forename: Robert F
authors.initials: RF
authors.lastname: Schwabe
authors.forename: Yusuf A
authors.initials: YA
authors.lastname: Hannun
authors.forename: David A
authors.initials: DA
authors.lastname: Brenner
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D016923:Cell Death; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D002518:Ceramides / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005799:Genes, Dominant; D017930:Genes, Reporter; D049452:Green Fluorescent Proteins / Q000378:metabolism; D022781:Hepatocytes / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D007099:Imipramine / Q000494:pharmacology; D050356:Lipid Metabolism; D008246:Lysophospholipids / Q000378:metabolism / Q000502:physiology*; D008297:Male; D013058:Mass Spectrometry; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D008954:Models, Biological; D016328:NF-kappa B / Q000378:metabolism; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013107:Sphingolipids / Q000378:metabolism; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000502:physiology; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
chemical_list: D002518:Ceramides; D018076:DNA, Complementary; D008246:Lysophospholipids; D016328:NF-kappa B; D013107:Sphingolipids; D014409:Tumor Necrosis Factor-alpha; D049452:Green Fluorescent Proteins; C060506:sphingosine 1-phosphate; C097760:N-palmitoylsphingosine; D013110:Sphingosine; D007099:Imipramine