Cellular Plasmalogen Content Does Not Influence Arachidonic Acid Levels or Distribution in Macrophages: A Role for Cytosolic Phospholipase A2γ in Phospholipid Remodeling.

Patricia Lebrero,Julio M Rubio,Lidia Fernández-Caballero,Jesús Balsinde,George Kokotos,Alma M Astudillo,María A Balboa

doi:10.3390/cells8080799

Abstract

Availability of free arachidonic acid (AA) constitutes a rate limiting factor for cellular eicosanoid synthesis. AA distributes differentially across membrane phospholipids, which is largely due to the action of coenzyme A-independent transacylase (CoA-IT), an enzyme that moves the fatty acid primarily from diacyl phospholipid species to ether-containing species, particularly the ethanolamine plasmalogens. In this work, we examined the dependence of AA remodeling on plasmalogen content using the murine macrophage cell line RAW264.7 and its plasmalogen-deficient variants RAW.12 and RAW.108. All three strains remodeled AA between phospholipids with similar magnitude and kinetics, thus demonstrating that cellular plasmalogen content does not influence the process. Cell stimulation with yeast-derived zymosan also had no effect on AA remodeling, but incubating the cells in AA-rich media markedly slowed down the process. Further, knockdown of cytosolic-group IVC phospholipase A2γ (cPLA2γ) by RNA silencing significantly reduced AA remodeling, while inhibition of other major phospholipase A2 forms such as cytosolic phospholipase A2α, calcium-independent phospholipase A2β, or secreted phospholipase A2 had no effect. These results uncover new regulatory features of CoA-IT-mediated transacylation reactions in cellular AA homeostasis and suggest a hitherto unrecognized role for cPLA2γ in maintaining membrane phospholipid composition via regulation of AA remodeling.

Highlights

IntroductionArachidonic acid (cis-5,8,11,14-eicosatetraenoic acid; arachidonic acid (AA)) is the precursor of the eicosanoids, a large family of compounds with key roles in the initiation and resolution of inflammation [1].Since AA is not found in free fatty acid form in cells but esterified into the sn-2 position of membrane glycerophospholipids, the participation of phospholipase A2 enzymes that liberate the fatty acid constitutes a limiting step for the synthesis of eicosanoids, a process which depends on the expression levels and activity of the AA-metabolizing enzymes cyclooxygenases and lipoxygenases [2,3,4,5].AA, which is usually the major polyunsaturated fatty acid in the membranes of innate immune cells, is not uniformly distributed among membrane glycerophospholipids
Arachidonic acid is the precursor of the eicosanoids, a large family of compounds with key roles in the initiation and resolution of inflammation [1].Since arachidonic acid (AA) is not found in free fatty acid form in cells but esterified into the sn-2 position of membrane glycerophospholipids, the participation of phospholipase A2 enzymes that liberate the fatty acid constitutes a limiting step for the synthesis of eicosanoids, a process which depends on the expression levels and activity of the AA-metabolizing enzymes cyclooxygenases and lipoxygenases [2,3,4,5].AA, which is usually the major polyunsaturated fatty acid in the membranes of innate immune cells, is not uniformly distributed among membrane glycerophospholipids
Since AA is not found in free fatty acid form in cells but esterified into the sn-2 position of membrane glycerophospholipids, the participation of phospholipase A2 enzymes that liberate the fatty acid constitutes a limiting step for the synthesis of eicosanoids, a process which depends on the expression levels and activity of the AA-metabolizing enzymes cyclooxygenases and lipoxygenases [2,3,4,5]

Summary

Introduction

Arachidonic acid (cis-5,8,11,14-eicosatetraenoic acid; AA) is the precursor of the eicosanoids, a large family of compounds with key roles in the initiation and resolution of inflammation [1].Since AA is not found in free fatty acid form in cells but esterified into the sn-2 position of membrane glycerophospholipids, the participation of phospholipase A2 enzymes that liberate the fatty acid constitutes a limiting step for the synthesis of eicosanoids, a process which depends on the expression levels and activity of the AA-metabolizing enzymes cyclooxygenases and lipoxygenases [2,3,4,5].AA, which is usually the major polyunsaturated fatty acid in the membranes of innate immune cells, is not uniformly distributed among membrane glycerophospholipids. Since AA is not found in free fatty acid form in cells but esterified into the sn-2 position of membrane glycerophospholipids, the participation of phospholipase A2 enzymes that liberate the fatty acid constitutes a limiting step for the synthesis of eicosanoids, a process which depends on the expression levels and activity of the AA-metabolizing enzymes cyclooxygenases and lipoxygenases [2,3,4,5]. Cells 2019, 8, 799 differences exist in the distribution of AA across several different phospholipid molecular species. Among particular molecular species within phospholipid classes, the ethanolamine plasmalogens are markedly enriched with AA [6,7,8,9,10,11]

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