Author(s): Lakics V, Vogel SN
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Abstract Ceramide is a well-known apoptotic agent that has been implicated in LPS signaling. Therefore, we examined whether LPS-induced macrophage cytotoxicity is mediated by mimicking ceramide. Both LPS and the cell-permeable ceramide analogue, C2 ceramide, induced significant cell death in IFN-gamma-activated, thioglycollate-elicited peritoneal macrophages after 48 and 24 h, respectively. Ceramide-induced cell death was neither accompanied by DNA fragmentation nor phosphatidyl serine externalization, characteristics of apoptosis. In contrast, LPS induced a significant fraction of cells to undergo apoptosis, as demonstrated by DNA fragmentation and quantified by DNA analysis on FACS, yet the majority of the cells died in a necrotic fashion. C3H/HeJ Lps(d) macrophages were resistant to LPS-induced cell death and less sensitive to C2 ceramide-evoked cytotoxicity, when compared with Lps(n) macrophages. C2 ceramide plus IFN-gamma failed to activate release of nitric oxide (NO.), whereas LPS-induced cell death, but not C2-induced cytotoxicity, was blocked by an inhibitor of inducible NO. synthase (iNOS), NG-monomethyl-L-arginine. Macrophages from IFN regulatory factor-1 (-/-) mice shown previously to respond marginally to LPS plus IFN-gamma to express iNOS mRNA and NO., were refractory to LPS plus IFN-gamma-induced cytotoxicity and apoptosis. These data suggest that although LPS may mimic certain ceramide effects, signal transduction events that lead to cytotoxicity, as well as the downstream mediators, diverge.
This article was published in J Immunol
and referenced in Journal of Molecular Biomarkers & Diagnosis