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

Abstract

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.

Presynaptic Monoacylglycerol Lipase Activity Determines Basal Endocannabinoid Tone and Terminates Retrograde Endocannabinoid Signaling in the Hippocampus

“…Alternatively, if URB754 does not inhibit MGL, as demonstrated recently by Saario et al (2006), the results in Figure 1 are inconclusive and a possibility remains that MGL contributes to DSI termination. To test this possibility, we examined effects of the classical MGL inhibitors MAFP (Goparaju et al, 1999;Dinh et al, 2002Dinh et al, , 2004Savinainen et al, 2003;Saario et al, 2004;Walter et al, 2004) and ATFMK (Dinh et al, 2002;Walter et al, 2004) on DSI and 2AG-induced suppression of IPSCs.…”

Implication of the anti-inflammatory bioactive lipid prostaglandin D2-glycerol ester in the control of macrophage activation and inflammation by ABHD6

“…2-AG exerts a plethora of effects in vivo, all of which were studied by increasing its levels through MAGL inhibition (5-9). Indeed, until recently, data pointed to MAGL as the primary enzyme responsible for 2-AG hydrolysis, at least in the brain (13,14). The role of ABHD6 in 2-AG hydrolysis was first put forth in BV2 cells that did not express MAGL (16) and subsequently in neurons (17,18).…”

“…Therefore, this anti-inflammatory effect in the cerebellum might be a consequence of the systemic anti-inflammatory effect of ABHD6 inhibition in the periphery. The lack of effect of ABHD6 inhibition on 2-AG levels in the cerebellum might be explained by the prevalent role exerted by MAGL on brain 2-AG hydrolysis (13,14). Therefore, ABHD6 inhibition might be a way to increase peripheral 2-AG levels and, consequently, to exert an anti-inflammatory effect without the central side effects of MAGL inhibition.…”

“…Monoacylglycerol lipase (MAGL) is thought to be the primary enzyme responsible for 2-AG metabolism. Although this has been proven in the brain, where MAGL controls around 80% of 2-AG hydrolysis, it remains unclear whether this occurs in other tissues (13,14). Because of this control of brain 2-AG levels, inhibition of MAGL leads to increased central levels of 2-AG and therefore to undesirable psychotropic side effects due to activation of the CB 1 cannabinoid receptor (15).…”

Cannabinoid as a neuroprotective strategy in perinatal hypoxic-ischemic injury

“…The serine hydrolase monoacyl glycerol lipase (MAGL) is mainly responsible for its metabolism in vivo, although it can also be metabolized by FAAH as well as by cyclooxygenase-2 and lipoxygenases [83,84,88,89] .…”