Involvement of nitric oxide in the pathogenesis of adult respiratory syndrome (ARDS) and the regulation of ARDS by osteopontin

成人呼吸窘迫综合征（ARDS）是一种非心源性肺水肿。近年来的研究表明，活化的巨噬细胞中诱导型一氧化氮合酶（iNOS）介导的一氧化氮（NO）参与了ARDS的发病过程。骨桥蛋白（OPN）是一种磷酸化糖蛋白，由包括巨噬细胞在内的多种细胞产生。OPN抑制iNOS表达的最新发现使我们验证了OPN可能是ARDS发展中iNOS的反调节剂的假设。为了解决这一假设，我们检测了内源性OPN和iNOS在ARDS小鼠模型（ARDS小鼠）肺和鼠巨噬细胞系RAW 264.7细胞中的表达，通过用脂多糖（LPS）和干扰素-γ（IFN-γ）处理细胞。腹腔注射LPS制备ARDS小鼠模型。在ARDS小鼠肺组织中观察到iNOS和OPN mRNA的共诱导表达。有趣的是，OPN mRNA的诱导比iNOS mRNA慢。用LPS和IFN-γ刺激RAW 264.7细胞，12 h后iNOS mRNA表达最高。相反，OPN mRNA的诱导比iNOS mRNA慢，这在ARDS小鼠的肺中也可以看到。诱导的OPN mRNA与增加的iNOS mRNA密切相关，因为在RAW 264.7细胞中OPN和iNOS mRNA的表达被加入特异性iNOS抑制剂或NOS抑制剂显著抑制。此外，NO释放剂精胺NONOate可增强OPN mRNA的表达，提示iNOS产生的NO可上调LPS和IFN-γ刺激的巨噬细胞内源性OPN的表达。内源性OPN的这种上调可能代表了一种负反馈系统，其作用是减少iNOS表达，并且可能至少部分地有助于保护肺免受LPS介导的组织损伤。

Adult respiratory distress syndrome (ARDS) is a noncardiogenic lung edema. Recent studies suggest that nitric oxide (NO) mediated by inducible NO synthase (iNOS) in activated macrophages is involved in the pathogenesis of ARDS. Osteopontin (OPN) is a phosphorylated glycoprotein produced by a variety of cells including macrophages. Recent findings that OPN inhibits iNOS expression led us to test the hypothesis that OPN may be a counter-regulator for iNOS in development of ARDS. To address this hypothesis, we examined expression of endogenous OPN and iNOS in the lung of a mouse model of ARDS (ARDS mice) and in a murine macrophage cell line, RAW 264.7 cells, by treatment of cells with lipopolysaccharide (LPS) and interferon-γ (IFN-γ). Mice were given LPS intratracheally to produce ARDS mice. Coinduction of iNOS and OPN mRNA was observed in the lung of ARDS mice. Interestingly, OPN mRNA was induced more slowly than iNOS mRNA. Stimulation of RAW 264.7 cells with LPS and IFN-γresulted in an increase of iNOS mRNA to maximum at 12 h after stimulation. In contrast, OPN mRNA was induced more slowly than iNOS mRNA, as was also seen in the lung of ARDS mice. Induced OPN mRNA is closely associated with increased iNOS mRNA because expression of both OPN and iNOS mRNA in RAW 264.7 cells was markedly suppressed by addition of the specific iNOS inhibitor or the NOS inhibitor. In addition, the No-releasing agent spermine NONOate enhanced induction of OPN mRNA, suggesting that NO generated by iNOS up-regulates the endogenous OPN in macrophages stimulated with LPS and IFN-γ. This up-regulation of endogenous OPN may represent a negative feedback system acting to reduce iNOS expression and may contribute, at least in part, to protect the lungs from LPS-mediated tissue injury.