N-arachidonoyl glycine induces macrophage apoptosis via GPR18.

N-arachidonoyl glycine (NAGly), a member of lipoamino acids, was reported to exhibit anti-inflammatory effects in experimental ear edema or peritonitis. However the underlying mechanisms have not been clarified so far. In this study, we attempt to investigate the effects of NAGly on macrophages, including the relevant signaling pathways. NAGly potently induced apoptosis in mouse macrophage-derived cell line, RAW264.7. Pretreatment with inhibitors for MEK and p38 MAPK prevented the apoptosis induced by NAGly, although NAGly activated ERK1/2, p38 MAPK and JNK. Further, we focused on implication of GPR18, one of the orphan G protein-coupled receptors, because NAGly has been reported as a candidate ligand for GPR18. Pretreatment with pertussis toxin or siRNA to knock down the expression of GPR18 significantly attenuated the apoptosis induced by NAGly. In mouse peritoneal macrophages, the expression of GPR18 mRNA was elevated in proinflammatory stimulated macrophages but not in anti-inflammatory stimulated macrophages; consistently, NAGly remarkably reduced cell viability of the former, as compared to the latter. These results suggest that NAGly might be involved in function of macrophages through GPR18.