Glycerophosphodiesterase GDE4 as a novel lysophospholipase D: a possible involvement in bioactive N-acylethanolamine biosynthesis.

Bioactive N-acylethanolamines include anti-inflammatory palmitoylethanolamide, anorexic oleoylethanolamide, and an endocannabinoid arachidonoylethanolamide (anandamide). In animal tissues, these molecules are biosynthesized from N-acylethanolamine phospholipids directly by phospholipase D-type enzyme or through multi-step routes via N-acylethanolamine lysophospholipids. We previously found that mouse brain has a lysophospholipase D (lysoPLD) activity hydrolyzing N-acylethanolamine lysophospholipids to N-acylethanolamines and that this activity could be partially attributed to glycerophosphodiesterase (GDE) 1. In the present study, we examined catalytic properties of GDE4, another member of the GDE family. When overexpressed in HEK293 cells, murine GDE4 mostly resided in the membrane fraction. Purified GDE4 showed lysoPLD activity toward various lysophospholipids, including N-acylethanolamine lysophospholipids as well as lysophosphatidylethanolamine and lysophosphatidylcholine. When HEK293 cells were metabolically labeled with N-[(14)C]palmitoylethanolamine lysophospholipid, the transient expression of GDE4 increased the [(14)C]palmitoylethanolamide level, while the knockdown of endogenous GDE4 decreased this level. These results suggested that GDE4 functions as an N-acylethanolamine-generating lysoPLD in living cells. Moreover, the expression of GDE4 increased most species of lysophosphatidic acid (LPA), which can be produced from various lysophospholipids by the lysoPLD activity of GDE4. GDE4 mRNA was widely distributed among mouse tissues including brain, stomach, ileum, colon, and testis. In conclusion, GDE4 may act as a lysoPLD, which is involved in the generation of N-acylethanolamines and LPA.