Ichikawa Tomonaga, Zhang Jifeng, Chen Kai, Liu Yusen, Schopfer Francisco J, Baker Paul R S, Freeman Bruce A, Chen Yuqing E, Cui Taixing
Cardiovascular Medicine, University of Michigan Medical Center, Ann Arbor, Michigan 48109, USA.
Endocrinology. 2008 Aug;149(8):4086-94. doi: 10.1210/en.2007-1639. Epub 2008 May 8.
Nitration products of unsaturated fatty acids are formed via NO-dependent oxidative reactions and appear to be a new class of endogenous antiinflammatory mediators. Nitroalkene derivatives of nitrated linoleic acid (LNO(2)) and nitrated oleic acid (OA-NO(2)) alleviate inflammatory responses in macrophages, but the underlying mechanisms remain to be fully defined. Herein we report that LNO(2) and OA-NO(2) suppress proinflammatory signal transducer and activator of transcription (STAT) signaling in macrophages. In RAW264.7 cells, a murine macrophage cell line, LNO(2) and OA-NO(2) inhibited the lipopolysaccharide (LPS)-induced STAT1 phosphorylation and the STAT1-dependent transcriptional activity, thereby suppressing expression of its target gene such as iNOS and MCP-1. The nitroalkene-mediated inhibition of STAT1 activity was not affected by 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (a NO scavenger), GW9662 (a peroxisome proliferator-activated receptor-gamma-specific antagonist) or glutathione (an antioxidant), suggesting an underlying mechanism independent of NO, peroxisome proliferator-activated receptor-gamma, or thio-nitralkylation. In contrast, LNO(2) or OA-NO(2) alone up-regulated both mRNA and protein levels of MAPK phosphatase 1 (MKP-1) and strongly augmented the LPS-induced MKP-1 protein expression. Knockdown of MKP-1 by MKP-1 small interfering RNA enhanced the LPS-induced STAT1 phosphorylation, suggesting that MKP-1 acts as a negative regulator for LPS-induced STAT signaling. In addition, the nitroalkene-mediated inhibitory effects on STAT1 phosphorylation, iNOS expression, and MCP-1 secretion were also largely attenuated by the MKP-1 small interfering RNA approach. Taken together, our data demonstrate that nitroalkenes inhibit proinflammatory STAT signaling through inducting MKP-1 in macrophages.
不饱和脂肪酸的硝化产物通过一氧化氮（NO）依赖的氧化反应形成，似乎是一类新的内源性抗炎介质。硝化亚油酸（LNO₂）和硝化油酸（OA-NO₂）的硝基烯烃衍生物可减轻巨噬细胞中的炎症反应，但其潜在机制仍有待充分明确。在此我们报告，LNO₂和OA-NO₂可抑制巨噬细胞中促炎信号转导和转录激活因子（STAT）信号传导。在小鼠巨噬细胞系RAW264.7细胞中，LNO₂和OA-NO₂抑制脂多糖（LPS）诱导的STAT1磷酸化和STAT1依赖的转录活性，从而抑制其靶基因如诱导型一氧化氮合酶（iNOS）和单核细胞趋化蛋白-1（MCP-1）的表达。硝基烯烃介导的对STAT1活性的抑制不受2-（4-羧基苯基）-4,4,5,5-四甲基咪唑啉-1-氧基3-氧化物（一种NO清除剂）、GW9662（一种过氧化物酶体增殖物激活受体-γ特异性拮抗剂）或谷胱甘肽（一种抗氧化剂）的影响，提示其潜在机制独立于NO、过氧化物酶体增殖物激活受体-γ或硫代硝基烷基化。相反，单独的LNO₂或OA-NO₂上调丝裂原活化蛋白激酶磷酸酶1（MKP-1）的mRNA和蛋白水平，并强烈增强LPS诱导的MKP-1蛋白表达。用MKP-1小干扰RNA敲低MKP-1增强了LPS诱导的STAT1磷酸化,表明MKP-1作为LPS诱导的STAT信号的负调节因子。此外，MKP-1小干扰RNA方法也大大减弱了硝基烯烃介导的对STAT1磷酸化、iNOS表达和MCP-1分泌的抑制作用。综上所述，我们的数据证明硝基烯烃通过在巨噬细胞中诱导MKP-1来抑制促炎STAT信号传导。
