Arachidonic Acid Differentially Affects Basal and Lipopolysaccharide-Induced sPLA₂-IIA Expression in Alveolar Macrophages through NF-κB and PPAR-γ–Dependent Pathways

Abstract

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 LPSinduced sPLA 2 -IIA expression. Nuclear factor-B (NF-B) was found to regulate sPLA 2 -IIA expression in AMs. Both AA and ETYA inhibited basal activation of NF-B but had no effect on LPS-induced NF-B translocation, suggesting that suppression of sPLA 2 -IIA synthesis by AA in LPS-stimulated cells occurs via a NF-B-independent pathway. 15-Deoxy-⌬ 12,14 -PGJ 2 and ciglitazone, which are, respectively, natural and synthetic ligands for peroxisome proliferator-activated receptor-␥ (PPAR-␥), inhibited LPS-induced sPLA 2 -IIA synthesis, whereas PPAR-␣ ligands were ineffective. Moreover, electrophoretic mobility shift assay showed PPAR activation by AA and PPAR-␥ 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-B activation. In contrast, the inhibition of LPS-stimulated sPLA 2 -IIA expression is mediated by cyclooxygenase-derived metabolites of AA and involves a PPAR-␥-dependent pathway. These findings provide new insights for the treatment of ALI.

Suppression of endothelial or lipoprotein lipase in THP-1 macrophages attenuates proinflammatory cytokine secretion

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A role for 12R-lipoxygenase in MUC5AC expression by respiratory epithelial cells

“…Electrophoretic mobility shift assay Nuclear proteins were extracted from 2610 6 cells as described previously [27]. The double-stranded oligonucleotide containing a Sp1 binding site consensus sequence (59-attcgatcggggcggggcgagc-39) was labelled with [c- ) and purified using a ProbeQuant G-50 micro column (GE Healthcare).…”

Inhibitory Effect of FXa on Secretory Group IIA Phospholipase A2

“…It is well known that LPS and other inflammatory cytokines upregulate the transcription of sPLA 2 -IIA and its protein level in a variety of cells including macrophage [23], fibroblast [24], endothelial cells [25], and astrocytes [15]. Analysis of the expression level of sPLA 2 -IIA by primary HUVECs in response to varying concentrations of LPS for 24 h indicated that the induction level reaches plateau in cell culture supernatants at 100 ng/mL LPS (data not shown).…”