Formation of N-acyl-phosphatidylethanolamines by cytosolic phospholipase Aε in an ex vivo murine model of brain ischemia.

N-Acyl-phosphatidylethanolamines (NAPEs), a minor class of membrane glycerophospholipids, accumulate along with their bioactive metabolites, N-acylethanolamines (NAEs) during ischemia. NAPEs can be formed through N-acylation of phosphatidylethanolamine by cytosolic phospholipase Aε (cPLAε, also known as PLA2G4E) or members of the phospholipase A and acyltransferase (PLAAT) family. However, the enzyme responsible for the NAPE production in brain ischemia has not yet been clarified. Here, we investigated a possible role of cPLAε using cPLAε-deficient (Pla2g4e) mice. As analyzed with brain homogenates of wild-type mice, the age dependency of Ca-dependent NAPE-forming activity showed a bell-shape pattern being the highest at the first week of postnatal life, and the activity was completely abolished in Pla2g4e mice. However, liquid chromatography-tandem mass spectrometry revealed that the NAPE levels of normal brain were similar between wild-type and Pla2g4e mice. In contrast, post-mortal accumulations of NAPEs and most species of NAEs were only observed in decapitated brains of wild-type mice. These results suggested that cPLAε is responsible for Ca-dependent formation of NAPEs in the brain as well as the accumulation of NAPEs and NAEs during ischemia, while other enzyme(s) appeared to be involved in the maintenance of basal NAPE levels.