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 β and γ interferon (IFN), respectively, which act directly upon erythroid colony forming units (CFU-E). The in vitro inhibitory effect of γIFN but not βIFN 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 γIFN. 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 (C2-ceramide; 5 and 10 mM) significantly inhibited bone marrow CFU-E colony formation. This effect was reversed by the ceramide antagonist sphingosine-1-phosphate (S-1-P). Inhibition of CFU-E by rhγIFN, but not rhβIFN, was significantly reversed by S-1-P. rhEPO 10 U/mL reversed CFU-E inhibition by C2-ceramide 10 mM. Exposure of marrow cells to rhγIFN 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 rhγIFN can be reversed by the ceramide antagonist S-1-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 by γIFN.