Epidermal growth factor inhibits ceramide-induced apoptosis and lowers ceramide levels in primary placental trophoblasts

The activation of sphingomyelinase and the subsequent generation of ceramid e are emerging as important components of signaling pathways leading to apo ptosis. The combination of tumor necrosis factor-alpha (TNF-alpha) and inte rferon-gamma (IFN-gamma) induces apoptosis of primary placental trophoblast s in vitro. This apoptosis is inhibited completely by cotreatment with epid ermal growth factor (EGF). We therefore examined the role of sphingomyelina se and ceramide in trophoblast apoptosis and how this may be influenced by EGF. Exogenous C-16-ceramide (20 mu M) and acid sphingomyelinase induced tr ophoblast apoptosis, an effect abrogated completely by cotreatment with 10 ng/ml EGF. Neutral sphingomyelinase also increased ceramide levels but did not induce apoptosis. Treatment with EGF alone decreased cellular ceramide levels. This decrease could be blocked by cotreatment with the acid ceramid ase inhibitor N-oleoylethanolamine (OE). OE alone increased ceramide levels and induced apoptosis that could not be blocked by cotreatment with EGF. I n contrast, the alkaline ceramidase inhibitor D-MAPP, although it also incr eased ceramide levels, did not induce apoptosis nor did it affect TNF-alpha /IFN-alpha-induced cell death. These results implicate sphingolipids as imp ortant mediators in trophoblast apoptosis and suggest that the antiapoptoti c properties of EGF can in part be explained by its control of ceramide con centrations in trophoblasts. (C) 1999 Wiley-Liss, Inc.