Alaoui-El-Azher Mounia, Wu Yongzheng, Havet Nathalie, Israël Alain, Lilienbaum Alain, Touqui Lhousseine
Unité de Défense Innée et Inflammation and Unité de Biologie Moléculaire de l'Expression Génique, Institut Pasteur, Paris, France.
Mol Pharmacol. 2002 Apr;61(4):786-94. doi: 10.1124/mol.61.4.786.
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.
分泌型IIA磷脂酶A2（sPLA(2)-IIA）是一种参与炎症性疾病的关键酶。我们之前在豚鼠急性肺损伤（ALI）模型中已确定肺泡巨噬细胞（AMs）是脂多糖（LPS）诱导的sPLA(2)-IIA表达的主要肺部来源。在此，我们研究了花生四烯酸（AA）在调节AMs中基础和LPS诱导的sPLA(2)-IIA表达中的作用。我们发现AA及其不可代谢类似物5,8,11,14-二十碳四烯酸（ETYA）均抑制未刺激AMs中sPLA(2)-IIA的合成。然而，只有AA抑制LPS刺激细胞中sPLA(2)-IIA的表达，这表明该效应需要AA的代谢转化。事实上，环氧合酶抑制剂消除了这种下调作用。前列腺素PGE(2)、PGA(2)和15d-PGJ(2)也抑制LPS诱导的sPLA(2)-IIA表达。发现核因子-κB（NF-κB）调节AMs中sPLA(2)-IIA的表达。AA和ETYA均抑制NF-κB的基础激活，但对LPS诱导的NF-κB易位无影响，这表明在LPS刺激的细胞中AA对sPLA(2)-IIA合成的抑制是通过一条不依赖NF-κB的途径发生的。15-脱氧-Δ(12,14)-PGJ(2)和噻唑烷二酮，分别是过氧化物酶体增殖物激活受体-γ（PPAR-γ）的天然和合成配体，抑制LPS诱导的sPLA(2)-IIA合成，而过氧化物酶体增殖物激活受体-α（PPAR-α）配体则无效。此外电泳迁移率变动分析显示在LPS刺激的AMs中AA和PPAR-γ配体激活了PPAR。我们的结果表明基础sPLA(2)-IIA表达的下调与AA的代谢转化无关，但依赖于NF-κB激活的受损。相反，LPS刺激的sPLA(2)-IIA表达受抑制是由AA的环氧合酶衍生代谢产物介导的，且涉及一条PPAR-γ依赖的途径。这些发现为ALI的治疗提供了新的见解。
