A Key Role for Diacylglycerol Lipase-α in Metabotropic Glutamate Receptor-Dependent Endocannabinoid Mobilization

Abstract

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-␣ (DGL-␣), in mGlu receptor-dependent 2-AG mobilization. DGL-␣ 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-␣ by RNA interference elicited lipidomic changes opposite those of DGL-␣ overexpression and abolished group I mGlu receptor-dependent 2-AG mobilization. Coimmunoprecipitation and site-directed mutagenesis experiments revealed that DGL-␣ 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-␣ 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-␣ mediates group I mGlu receptor-induced 2-AG mobilization. They further suggest that the interaction of CC-Homer with DGL-␣ is necessary for appropriate function of this lipase.

Rapid and profound rewiring of brain lipid signaling networks by acute diacylglycerol lipase inhibition

“…S3). Finally, DH376 and DO34 showed KT172 (1) DO34 (5) DH376 (4) DO53 (8) minimal and negligible binding, respectively, to cannabinoid CB 1 (CB 1 R) and CB 2 (CB 2 R) receptors as measured with radioligand binding assays (IC 50 values > 1 μM) (SI Appendix, Fig. S4).…”

Glutamate Delta-1 Receptor Regulates Metabotropic Glutamate Receptor 5 Signaling in the Hippocampus

“…Homer proteins are known to link mGluRs to other postsynaptic density proteins (Shiraishi-Yamaguchi and Furuichi, 2007;Niswender and Conn, 2010) and play a vital role in coupling the receptors with downstream effectors (Mao et al, 2005;Jung et al, 2007;Won et al, 2009). Disrupted interaction between mGlu5 and the long isoform of Homer leads to deficits in mTOR signaling, protein translation, as well as synaptic plasticity in the FMR1 knockout mouse model (Ronesi and Huber, 2008;Ronesi et al, 2012).…”

A neuroscientist's guide to lipidomics

“…2c, inset), which is also regulated by physiological stimuli, generates the second messengers inositol polyphosphate 3 (which releases Ca 2+ from the endoplasmic reticulum), and 1,2-DAG, (which activates protein kinase C, protein kinase D and other effector proteins) 27,28 . In addition to acting as a second messenger molecule, 1,2-DAG is also the starting point for two important biochemical transformations: DAG-kinases catalyse the phosphorylation of 1,2-DAG to phosphatidic acid (an intracellular messenger and phospholipid precursor) 29 , whereas DAG-lipases cleave 1,2-DAG to yield monoacylglycerol 30,31 , which is further hydrolysed by 2-acyl-sn-glycerol lipases to produce fatty acid and glycerol 32 (fIG. 4).…”

“…The fidelity of this signalling sequence appears to depend on the precise anatomical localization of DGl-α, a major biosynthetic enzyme for 2-AG in neural cells 30,31 . Immunogold electron-microscopy studies of hippocampal and cerebellar neurons have shown that this lipid hydrolase is primarily localized in a subdivision of the dendritic spine, called the perisynapse, which forms a thin border (100-200 nm thick) around the postsynaptic density 63,64 .…”