Early ethanolamine phospholipid translocation marks stress-induced apoptotic cell death in oligodendroglial cells

The consequences of H2O2/Fe2+-induced oxidative stress on translocation of ethanolamine phosphoglyceride (EPG) and serine phosphoglyceride (SPG) were studied in an oligodendroglia-like cell line (OLN 93) following 3 days of s upplementation with 0.1 mm docosahexaenoic acid (DHA) and a series of polar head group precursors, including N-monomethyl- and N,N-dimethylethanolamin e at millimolar concentrations. Added DHA was predominantly esterified in E PG species and those cells enriched in DHA showed enhanced sensitivity to o xidative stress and eventually died by apoptosis. Co-supplements with ethan olamine and DHA resulted in a rapid, but transient, EPG translocation with a maximum at 30 min following stress, as characterized by a trinitrobenzene sulfonic acid reagent. There was no significant translocation of SPG as evi denced by annexin V binding. Unlike SPG, which is usually irreversibly tran slocated to subserve as a tag for phagocytosis, EPG acted as a signaling mo lecule with biphasic kinetic characteristics. N-Monomethyl- and N,N-dimethy lethanolamine supplements reduced EPG synthesis, prevented its externalizat ion and rescued cells from apoptotic death. Following stress, the fatty aci d profile of the externalized EPG showed marked losses in polyunsaturated f atty acids and aldehydes compared with the remaining intracellular EPG. Pre vention of EPG species selective translocation to the outer membrane leafle t by altering phospholipid asymmetry may be important in the mechanism of r escue from cell death.