title: Phospholipase A2 regulates eicosanoid class switching during inflammasome activation.
abstract: Initiation and resolution of inflammation are considered to be tightly connected processes. Lipoxins (LX) are proresolution lipid mediators that inhibit phlogistic neutrophil recruitment and promote wound-healing macrophage recruitment in humans via potent and specific signaling through the LXA4 receptor (ALX). One model of lipoxin biosynthesis involves sequential metabolism of arachidonic acid by two cell types expressing a combined transcellular metabolon. It is currently unclear how lipoxins are efficiently formed from precursors or if they are directly generated after receptor-mediated inflammatory commitment. Here, we provide evidence for a pathway by which lipoxins are generated in macrophages as a consequence of sequential activation of toll-like receptor 4 (TLR4), a receptor for endotoxin, and P2X7, a purinergic receptor for extracellular ATP. Initial activation of TLR4 results in accumulation of the cyclooxygenase-2-derived lipoxin precursor 15-hydroxyeicosatetraenoic acid (15-HETE) in esterified form within membrane phospholipids, which can be enhanced by aspirin (ASA) treatment. Subsequent activation of P2X7 results in efficient hydrolysis of 15-HETE from membrane phospholipids by group IVA cytosolic phospholipase A2, and its conversion to bioactive lipoxins by 5-lipoxygenase. Our results demonstrate how a single immune cell can store a proresolving lipid precursor and then release it for bioactive maturation and secretion, conceptually similar to the production and inflammasome-dependent maturation of the proinflammatory IL-1 family cytokines. These findings provide evidence for receptor-specific and combinatorial control of pro- and anti-inflammatory eicosanoid biosynthesis, and potential avenues to modulate inflammatory indices without inhibiting downstream eicosanoid pathways.
authors.affiliation: Departments of Chemistry/Biochemistry and Pharmacology, and.
authors.forename: Paul C
authors.initials: PC
authors.lastname: Norris
authors.affiliation: Cellular and Molecular Medicine, University of California, San Diego, La Jolla, CA 92093.
authors.forename: David
authors.initials: D
authors.lastname: Gosselin
authors.affiliation: Cellular and Molecular Medicine, University of California, San Diego, La Jolla, CA 92093.
authors.forename: Donna
authors.initials: D
authors.lastname: Reichart
authors.affiliation: Cellular and Molecular Medicine, University of California, San Diego, La Jolla, CA 92093.
authors.forename: Christopher K
authors.initials: CK
authors.lastname: Glass
authors.affiliation: Departments of Chemistry/Biochemistry and Pharmacology, and edennis@ucsd.edu.
authors.forename: Edward A
authors.initials: EA
authors.lastname: Dennis
mesh_terms: D000818:Animals; D001241:Aspirin / Q000494:pharmacology; D000068579:Celecoxib; D002461:Cell Line, Transformed; D052246:Cyclooxygenase 2 Inhibitors / Q000494:pharmacology; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D015777:Eicosanoids / Q000276:immunology / Q000378:metabolism*; D054513:Group IV Phospholipases A2 / Q000276:immunology / Q000378:metabolism*; D006893:Hydroxyeicosatetraenoic Acids / Q000276:immunology / Q000378:metabolism; D058847:Inflammasomes / Q000276:immunology / Q000378:metabolism*; D007375:Interleukin-1 / Q000276:immunology / Q000378:metabolism; D008064:Lipidoses / Q000276:immunology; D008264:Macrophages / Q000166:cytology / Q000201:enzymology* / Q000276:immunology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D011720:Pyrazoles / Q000494:pharmacology; D058486:Receptors, Purinergic P2X7 / Q000276:immunology / Q000378:metabolism; D015398:Signal Transduction / Q000276:immunology*; D013449:Sulfonamides / Q000494:pharmacology; D051197:Toll-Like Receptor 4 / Q000276:immunology / Q000378:metabolism
chemical_list: D052246:Cyclooxygenase 2 Inhibitors; D016861:Cyclooxygenase Inhibitors; D015777:Eicosanoids; D006893:Hydroxyeicosatetraenoic Acids; D058847:Inflammasomes; D007375:Interleukin-1; D011720:Pyrazoles; D058486:Receptors, Purinergic P2X7; D013449:Sulfonamides; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; C027356:11-hydroxy-5,8,12,14-eicosatetraenoic acid; C025984:15-hydroxy-5,8,11,13-eicosatetraenoic acid; D054513:Group IV Phospholipases A2; D000068579:Celecoxib; D001241:Aspirin
keywords: enzyme coupling; lipidomics; membrane remodeling