Identification of a novel endocannabinoid-hydrolyzing enzyme expressed by microglial cells.
The endocannabinoids (eCBs) anandamide and 2-arachidonoyl glycerol (2-AG) are inactivated by a two-step mechanism. First, they are carried into cells, and then anandamide is hydrolyzed by fatty acid amide hydrolase (FAAH) and 2-AG by monoacylglycerol lipase (MGL). Here we provide evidence for a previously undescribed MGL activity expressed by microglial cells. We found that the mouse microglial cell line BV-2 does not express MGL mRNA and yet efficiently hydrolyzes 2-AG. URB597 (3'-carbamoyl-biphenyl-3-yl-cyclohexylcarbamate) reduces this hydrolysis by 50%, suggesting the involvement of FAAH. The remaining activity is blocked by classic MGL inhibitors [[1,1-biphenyl]-3-yl-carbamic acid, cyclohexyl ester (URB602) and MAFP (methylarachidonyl fluorophosphate)] and is unaffected by inhibitors of COXs (cyclooxygenases), LOXs (lipooxygenases), and DGLs (diacylglycerol lipases), indicating the involvement of a novel MGL activity. Accordingly, URB602 leads to selective accumulation of 2-AG in intact BV-2 cells. Although MGL expressed in neurons is equally distributed between the cytosolic, mitochondrial, and nuclear fractions, the novel MGL activity expressed by BV-2 cells is enriched in mitochondrial and nuclear fractions. A screen for novel inhibitors of eCB hydrolysis identified several compounds that differentially block MGL, FAAH, and the novel MGL activity. Finally, we provide evidence for expression of the novel MGL by mouse primary microglia in culture. Our results suggest the presence of a novel, pharmacologically distinct, MGL activity that controls 2-AG levels in microglia.
Muccioli
Giulio G
GG
Department of Pharmacology, University of Washington, Seattle, Washington 98195-7280, USA.
Xu
Cong
C
Odah
Emma
E
Cudaback
Eiron
E
Cisneros
Jose Antonio
JA
Lambert
Didier M
DM
López Rodríguez
María Luz
ML
Bajjalieh
Sandra
S
Stella
Nephi
N
D000818:Animals; D001095:Arachidonic Acids / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D063385:Cannabinoid Receptor Modulators / Q000378:metabolism*; D002478:Cells, Cultured; D063388:Endocannabinoids; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000502:physiology; D005989:Glycerides / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D006868:Hydrolysis / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D017628:Microglia / Q000187:drug effects / Q000201:enzymology*; D008994:Monoacylglycerol Lipases / Q000037:antagonists & inhibitors / Q000096:biosynthesis
D001095:Arachidonic Acids; D063385:Cannabinoid Receptor Modulators; D063388:Endocannabinoids; D004791:Enzyme Inhibitors; D005989:Glycerides; C094503:glyceryl 2-arachidonate; D008994:Monoacylglycerol Lipases