Biosynthesis of an Endogenous Cannabinoid Precursor in Neurons and its Control by Calcium and cAMP

Abstract

Understanding the mechanisms involved in the biogenesis ofN-arachidonoylethanolamine (anandamide) andNpalmitoylethanolamine is important in view of the possible role of these lipids as endogenous cannabinoid substances. Anandamide (which activates cannabinoid CB1 receptors) andN-palmitoylethanolamine (which activates a CB2-like receptor subtype in mast cells) may both derive from cleavage of precursor phospholipid,N-acylphosphatidylethanolamine (NAPE), catalyzed by Ca²⁺-activated D-type phosphodiesterase activity. We report here that thede novobiosynthesis of NAPE is enhanced in a Ca²⁺-dependent manner when rat cortical neurons are stimulated with the Ca²⁺-ionophore ionomycin or with membrane-depolarizing agents such as veratridine and kainate. This reaction is likely to be mediated by a neuronalN-acyltransferase activity, which catalyzes the transfer of an acyl group from phosphatidylcholine to the ethanolamine moiety of phosphatidylethanolamine. In addition, we show that Ca²⁺-dependent NAPE biosynthesis is potentiated by agents that increase cAMP levels, including forskolin and vasoactive intestinal peptide. Our results thus indicate that NAPE levels in cortical neurons are controlled by Ca²⁺ions and cAMP. Such regulatory effect may participate in maintaining a supply of cannabimimeticN-acylethanolamines during synaptic activity, and prime target neurons for release of these bioactive lipids.