A key role for diacylglycerol lipase-α in metabotropic glutamate receptor-dependent endocannabinoid mobilization

Activation of group I metabotropic glutamate ( mGlu) receptors recruits the endocannabinoid system to produce both shortand long- term changes in synaptic strength in many regions of the brain. Although there is evidence that the endocannabinoid 2- arachidonoylglycerol ( 2- AG) mediates this process, the molecular mechanism underlying 2- AG mobilization remains unclear. In the present study, we used a combination of genetic and targeted lipidomic approaches to investigate the role of the postsynaptic membrane- associated lipase, diacylglycerol lipase type- alpha ( DGL- alpha), in mGlu receptor- dependent 2- AG mobilization. DGL- alpha overexpression in mouse neuroblastoma Neuro- 2a cells increased baseline 2- AG levels. This effect was accompanied by enhanced utilization of the 2- AG precursor 1- stearoyl, 2- arachidonoyl- sn- glycerol and increased accumulation of the 2- AG breakdown product arachidonic acid. A similar, albeit less marked response was observed with other unsaturated and polyunsaturated monoacylglycerols, 1,2- diacylglycerols, and fatty acids. Silencing of DGL- alpha by RNA interference elicited lipidomic changes opposite those of DGL- alpha overexpression and abolished group I mGlu receptor- dependent 2- AG mobilization. Coimmunoprecipitation and site- directed mutagenesis experiments revealed that DGL- alpha interacts, via a PPxxF domain, with the coiled- coil ( CC)- Homer proteins Homer- 1b and Homer- 2, two components of the molecular scaffold that enables group I mGlu signaling. DGL- alpha mutants that do not bind Homer maintained their ability to generate 2- AG in intact cells but failed to associate with the plasma membrane. The findings indicate that DGL- alpha mediates group I mGlu receptor- induced 2- AG mobilization. They further suggest that the interaction of CC- Homer with DGL- alpha is necessary for appropriate function of this lipase.