Arachidonic acid differentially affects basal and lipopolysaccharide-induced sPLA(2)-IIA expression in alveolar macrophages through NF-kappaB and PPAR-gamma-dependent pathways.
Secretory type IIA phospholipase A(2) (sPLA(2)-IIA) is a critical enzyme involved in inflammatory diseases. We have previously identified alveolar macrophages (AMs) as the major pulmonary source of lipopolysaccharide (LPS)-induced sPLA(2)-IIA expression in a guinea pig model of acute lung injury (ALI). Here, we examined the role of arachidonic acid (AA) in the regulation of basal and LPS-induced sPLA(2)-IIA expression in AMs. We showed that both AA and its nonmetabolizable analog, 5,8,11,14-eicosatetraynoic acid (ETYA), inhibited sPLA(2)-IIA synthesis in unstimulated AMs. However, only AA inhibited sPLA(2)-IIA expression in LPS-stimulated cells, suggesting that this effect requires metabolic conversion of AA. Indeed, cyclooxygenase inhibitors abolished this down-regulation. Prostaglandins PGE(2), PGA(2), and 15d-PGJ(2) also inhibited the LPS-induced sPLA(2)-IIA expression. Nuclear factor-kappaB (NF-kappaB) was found to regulate sPLA(2)-IIA expression in AMs. Both AA and ETYA inhibited basal activation of NF-kappaB but had no effect on LPS-induced NF-kappaB translocation, suggesting that suppression of sPLA(2)-IIA synthesis by AA in LPS-stimulated cells occurs via a NF-kappaB-independent pathway. 15-Deoxy-Delta(12,14)-PGJ(2) and ciglitazone, which are, respectively, natural and synthetic ligands for peroxisome proliferator-activated receptor-gamma (PPAR-gamma), inhibited LPS-induced sPLA(2)-IIA synthesis, whereas PPAR-alpha ligands were ineffective. Moreover, electrophoretic mobility shift assay showed PPAR activation by AA and PPAR-gamma ligands in LPS-stimulated AMs. Our results suggest that the down-regulation of basal sPLA(2)-IIA expression is unrelated to the metabolic conversion of AA but is dependent on the impairment of NF-kappaB activation. In contrast, the inhibition of LPS-stimulated sPLA(2)-IIA expression is mediated by cyclooxygenase-derived metabolites of AA and involves a PPAR-gamma-dependent pathway. These findings provide new insights for the treatment of ALI.
Alaoui-El-Azher
Mounia
M
Unité de Défense Innée et Inflammation and Unité de Biologie Moléculaire de l'Expression Génique, Institut Pasteur, Paris, France.
Wu
Yongzheng
Y
Havet
Nathalie
N
Israël
Alain
A
Lilienbaum
Alain
A
Touqui
Lhousseine
L
D015117:5,8,11,14-Eicosatetraynoic Acid / Q000494:pharmacology; D000818:Animals; D016718:Arachidonic Acid / Q000494:pharmacology*; D002478:Cells, Cultured; D004347:Drug Interactions; D015870:Gene Expression / Q000187:drug effects*; D054501:Group II Phospholipases A2; D006168:Guinea Pigs; D008070:Lipopolysaccharides / Q000494:pharmacology*; D016676:Macrophages, Alveolar / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D016328:NF-kappa B / Q000378:metabolism*; D010741:Phospholipases A / Q000096:biosynthesis* / Q000235:genetics / Q000276:immunology; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D012703:Serotyping; D014157:Transcription Factors / Q000378:metabolism*
D008070:Lipopolysaccharides; D016328:NF-kappa B; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; D015117:5,8,11,14-Eicosatetraynoic Acid; D016718:Arachidonic Acid; D011451:Prostaglandin-Endoperoxide Synthases; D010741:Phospholipases A; D054501:Group II Phospholipases A2