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，活化巨噬细胞中诱导型NO合成酶（iNOS）介导的一氧化氮（NO）参与了ARDS的发病机制。骨桥蛋白（Osteopontin， OPN）是一种由包括巨噬细胞在内的多种细胞产生的磷酸化糖蛋白。最近的研究发现，OPN抑制iNOS表达，这使我们验证了OPN可能是ARDS发展中iNOS的反调节因子的假设。为了验证这一假设，我们通过脂多糖（LPS）和干扰素-γ (IFN-γ)处理小鼠巨噬细胞系RAW 264.7细胞，检测了ARDS小鼠模型肺中内源性OPN和iNOS的表达。小鼠气管内注射LPS产生ARDS小鼠。在ARDS小鼠肺中观察到iNOS和OPN mRNA的共诱导。有趣的是，OPN mRNA的诱导速度比iNOS mRNA慢。LPS和IFN-γ刺激RAW 264.7细胞后，iNOS mRNA在刺激后12 h达到最大值。相比之下，OPN mRNA的诱导速度比iNOS mRNA慢，这在ARDS小鼠的肺中也可以看到。由于添加特异性iNOS抑制剂或NOS抑制剂可显著抑制RAW 264.7细胞中OPN和iNOS mRNA的表达，因此诱导的OPN mRNA与iNOS mRNA的增加密切相关。此外，NO释放剂精胺NONOate增强了对OPN mRNA的诱导，提示iNOS产生的NO上调LPS和IFN-γ刺激的巨噬细胞内源性OPN。内源性OPN的上调可能代表了一个负反馈系统，其作用是减少iNOS的表达，并可能至少在一定程度上保护肺部免受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.