title: A phosphatidylinositol species acutely generated by activated macrophages regulates innate immune responses.
abstract: Activation of macrophages with stimuli of the innate immune response results in the intense remodeling of arachidonate-containing phospholipids, leading to the mobilization of large quantities of this fatty acid for conversion into biologically active eicosanoids. As a consequence of this process, the arachidonate levels in membrane phospholipids markedly decrease. We have applied mass spectrometry-based lipid profiling to study the levels of arachidonate-containing phospholipids under inflammatory activation of macrophages. We identify an unusual inositol phospholipid molecule, PI(20:4/20:4), the levels of which do not decrease but actually increase by 300% after activation of the macrophages. PI(20:4/20:4) is formed and degraded rapidly, suggesting a role for this molecule in regulating cell signaling events. Using a metabolipidomic approach consisting in exposing the cells to deuterium-labeled arachidonate at the time they are exposed to stimuli, we show that PI(20:4/20:4) biosynthesis occurs via the sequential incorporation of arachidonate, first into the sn-2 position of a preformed phosphatidylinositol (PI) molecule, followed by the rapid introduction of a second arachidonate moiety into the sn-1 position. Generation requires the participation of cytosolic phospholipase A2α and CoA-dependent acyltransferases. PI(20:4/20:4) formation is also detected in vivo in murine peritonitis exudates. Elevating the intracellular concentration of PI(20:4/20:4) by introducing the lipid into the cells results in enhancement of the microbicidal capacity of macrophages, as measured by reactive oxygen metabolite production and lysozyme release. These findings suggest that PI(20:4/20:4) is a novel bioactive inositol phospholipid molecule that regulates innate immune responses in macrophages.
authors.affiliation: Instituto de Biología y Genética Molecular, Consejo Superior de Investigaciones Científicas, 47003 Valladolid, Spain.
authors.forename: Luis
authors.initials: L
authors.lastname: Gil-de-Gómez
authors.forename: Alma M
authors.initials: AM
authors.lastname: Astudillo
authors.forename: Clara
authors.initials: C
authors.lastname: Meana
authors.forename: Julio M
authors.initials: JM
authors.lastname: Rubio
authors.forename: Carlos
authors.initials: C
authors.lastname: Guijas
authors.forename: María A
authors.initials: MA
authors.lastname: Balboa
authors.forename: Jesús
authors.initials: J
authors.lastname: Balsinde
mesh_terms: D000818:Animals; D016718:Arachidonic Acid / Q000737:chemistry / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry; D002478:Cells, Cultured; D002853:Chromatography, Liquid; D007113:Immunity, Innate; D008262:Macrophage Activation; D008264:Macrophages / Q000276:immunology* / Q000378:metabolism*; D008297:Male; D013058:Mass Spectrometry; D051379:Mice; D010538:Peritonitis / Q000276:immunology; D010716:Phosphatidylinositols / Q000378:metabolism*; D010743:Phospholipids / Q000737:chemistry; D017382:Reactive Oxygen Species; D015398:Signal Transduction
chemical_list: D010716:Phosphatidylinositols; D010743:Phospholipids; D017382:Reactive Oxygen Species; D016718:Arachidonic Acid