Mammalian Endocannabinoids in Early Land Plants and their Implications

Endocannabinoids are derivatives of arachidonate-based lipids that activate a network of signaling pathways in eukaryotes. Specifically, in mammals, a C20 N-acylethanolamine (NAE) or anandamide is a ligand for cannabinoid receptor (a G protein-coupled receptor) and acts as neuromodulator for a variety of physiological processes, including pain sensation and protection against stroke. Interestingly, while only C12-C18 NAEs occur in seed plants, anandamide and its membrane lipid precursor, N-arachidonylphosphatidylethanolamine were identified in a nonseed early land plant, Physcomitrella patens. Selective lipidomics also revealed other 20C-derived NAEs including eicosapentaenoyl ethanolamide (EPEA or NAE20:5) that were previously unidentified in angiosperms. Furthermore, putative genes that likely encode for enzymes that participate in NAE metabolism were also identified in P. patens and were heterologously expressed. Fatty acid amide hydrolase (FAAH), an enzyme that catabolizes NAEs showed preferential activity towards NAE20:4 at pH 8.0 and 30 C. While biological implications of anandamide and its metabolic pathway in mosses are still under investigation, we show that both AEA and EPEA and their corresponding fatty acids act as potent inhibitors of protonema and gametophore growth in a dose-dependent manner and similar to ABA. Furthermore, short-term exposure to AEA or ABA inhibited tip growth that was associated with depolymerization of F-actin but not microtubule organization, which remained unaffected. While these data indicate that the occurrence of NAEs and their metabolism is evolutionarily conserved and composition in early land plants is unique, if the functions of AEA are mediated by a G-protein coupled receptor, similar to ABA, and endocannabinoid signaling in mammals, remains to be elucidated