RNA Interference Suggests a Primary Role for Monoacylglycerol Lipase in the Degradation of the Endocannabinoid 2-Arachidonoylglycerol

• Published in: Molecular pharmacology 2004-11, Vol.66 (5), p.1260-1264
• Main Authors: Dinh, Thien P, Kathuria, Satish, Piomelli, Daniele
• Format: Article
• Language: English
• Subjects: Animals; Arachidonic Acids - metabolism; Brain - enzymology; Cannabinoid Receptor Modulators - metabolism; Cells, Cultured; Endocannabinoids; Gene Silencing - drug effects; Glycerides - metabolism; HeLa Cells; Humans; Hydrolysis; Monoacylglycerol Lipases - antagonists & inhibitors; Monoacylglycerol Lipases - genetics; Monoacylglycerol Lipases - metabolism; Oligonucleotides - pharmacology; Rats; RNA Interference - physiology
• ISSN: 0026-895X; 1521-0111
• DOI: 10.1124/mol.104.002071

The endogenous cannabinoid 2-arachidonoylglycerol (2-AG) is produced by neurons and other cells in a stimulus-dependent manner and undergoes rapid biological inactivation through transport into cells and catalytic hydrolysis. The enzymatic pathways responsible for 2-AG degradation are only partially understood. We have shown previously that overexpression of monoacylglycerol lipase (MGL), a cytosolic serine hydrolase that cleaves 1- and 2-monoacylglycerols to fatty acid and glycerol, reduces stimulus-dependent 2-AG accumulation in primary cultures of rat brain neurons. We report here that RNA interference-mediated silencing of MGL expression greatly enhances 2-AG accumulation in HeLa cells. After stimulation with the calcium ionophore ionomycin, 2-AG levels in MGL-silenced cells were comparable with those found in cells in which 2-AG degradation had been blocked using methyl arachidonyl fluorophosphonate, a nonselective inhibitor of 2-AG hydrolysis. The results indicate that MGL plays an important role in the degradation of endogenous 2-AG in intact HeLa cells. Furthermore, immunodepletion experiments show that MGL accounts for at least 50% of the total 2-AG–hydrolyzing activity in soluble fractions of rat brain, suggesting that this enzyme also contributes to 2-AG deactivation in the central nervous system.