Inhibition of human erythroid colony formation by ceramide

In previous studies, we have demonstrated that the inhibitory effects of tumor necrosis factor (TNF) and interleukin (IL)-1 on human erythroid colony formation are indirect and mediated by beta and gamma interferon (IFN), respectively, which act directly upon erythroid colony forming units (CFU-E). The in vitro inhibitory effect of gamma IFN but not beta IFN is reversed by exposure to high concentrations of recombinant human (rh) erythropoietin (EPO), Ceramide, a product of sphingomyelin hydrolysis, is a known mediator of apoptotic effects of TNF, IL-1, and gamma IFN, In this report, the effects of ceramide on CFU-E colony formation and its implication in the model described above are evaluated. Endogenous ceramide produced by exposure to bacterial sphingomyelinase (0.2-2.0 U/mL) and exogenous cell-permeable ceramide (C-2-ceramide; 5 and 10 mM) significantly inhibited bone marrow CFU-E colony formation, This effect was reversed by the ceramide antagonist sphingosine-1l-phosphate (S-1-P), Inhibition of CFU-E by rh gamma IFN, but not rh beta IFN, was significantly reversed by S-1-P, rhEPO 10 U/mL reversed CFU-E inhibition by Cz-ceramide 10 mM, Exposure of marrow cells to rh gamma IFN led to a 57% increase in ceramide content, The present study demonstrates that colony formation by human CFU-E is inhibited by endogenous and exogenous ceramide, and that inhibition by rh gamma IFN can be reversed by the ceramide antagonist S-I-P, Inhibition of CFU-E colony formation by ceramide and by are both reversed by high concentrations of rhEPO, These findings strongly suggest that ceramide mediates inhibition of human CFU-E colony formation hv gamma IFN. (C) 1999 International Society for Experimental Hematology. Published by Elsevier Science Inc.