title: ATP induces a rapid and pronounced increase in 2-arachidonoylglycerol production by astrocytes, a response limited by monoacylglycerol lipase.
abstract: The cytoplasm of neural cells contain millimolar amounts of ATP, which flood the extracellular space after injury, activating purinergic receptors expressed by glial cells and increasing gliotransmitter production. These gliotransmitters, which are thought to orchestrate neuroinflammation, remain widely uncharacterized. Recently, we showed that microglial cells produce 2-arachidonoylglycerol (2-AG), an endocannabinoid known to prevent the propagation of harmful neuroinflammation, and that ATP increases this production by threefold at 2.5 min (Witting et al., 2004). Here we show that ATP increases 2-AG production from mouse astrocytes in culture, a response that is more rapid (i.e., significant within 10 sec) and pronounced (i.e., 60-fold increase at 2.5 min) than any stimulus-induced increase in endocannabinoid production reported thus far. Increased 2-AG production from astrocytes requires millimolar amounts of ATP, activation of purinergic P2X7 receptors, sustained rise in intracellular calcium, and diacylglycerol lipase activity. Furthermore, we show that astrocytes express monoacylglycerol lipase (MGL), the main hydrolyzing enzyme of 2-AG, the pharmacological inhibition of which potentiates the ATP-induced 2-AG production (up to 113-fold of basal 2-AG production at 2.5 min). Our results show that ATP greatly increases, and MGL limits, 2-AG production from astrocytes. We propose that 2-AG may function as a gliotransmitter, with MGL inhibitors potentiating this production and possibly restraining the propagation of harmful neuroinflammation.
authors.affiliation: Department of Pharmacology, University of Washington, Seattle, Washington 98195-7280, USA.
authors.forename: Lisa
authors.initials: L
authors.lastname: Walter
authors.forename: Thien
authors.initials: T
authors.lastname: Dinh
authors.forename: Nephi
authors.initials: N
authors.lastname: Stella
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000581:Amidohydrolases / Q000378:metabolism; D000818:Animals; D001095:Arachidonic Acids / Q000096:biosynthesis* / Q000502:physiology; D001253:Astrocytes / Q000187:drug effects* / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects; D063385:Cannabinoid Receptor Modulators / Q000096:biosynthesis*; D002478:Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D063388:Endocannabinoids; D004789:Enzyme Activation / Q000187:drug effects; D008401:Gas Chromatography-Mass Spectrometry; D020869:Gene Expression Profiling; D005989:Glycerides / Q000096:biosynthesis* / Q000502:physiology; D008071:Lipoprotein Lipase / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008994:Monoacylglycerol Lipases / Q000502:physiology*; D009419:Nerve Tissue Proteins / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D018048:Receptors, Purinergic P2 / Q000378:metabolism; D058486:Receptors, Purinergic P2X7; D013268:Stimulation, Chemical; D000099252:Fatty Acid Amide Hydrolases
chemical_list: D000255:Adenosine Triphosphate; D000581:Amidohydrolases; D001095:Arachidonic Acids; D063385:Cannabinoid Receptor Modulators; D063388:Endocannabinoids; D005989:Glycerides; D008071:Lipoprotein Lipase; D008994:Monoacylglycerol Lipases; D009419:Nerve Tissue Proteins; D018048:Receptors, Purinergic P2; D058486:Receptors, Purinergic P2X7; D000099252:Fatty Acid Amide Hydrolases; C546469:P2rx7 protein, mouse; C094503:glyceryl 2-arachidonate