Requirement of the inducible nitric oxide synthase pathway for IL-1-induced osteoclastic bone resorption

Nitric oxide has been suggested to be involved in the regulation of bone turnover, especially in pathological conditions characterized by release of bone-resorbing cytokines. The cytokine IL-1 is thought to act as a mediator of periarticular bone loss and tissue damage in inflammatory diseases such as rheumatoid arthritis. IL-1 is a potent stimulator of both osteoclastic bone resorption and expression of inducible nitric oxide synthase (iNOS) in bone cells and other cell types. In this study, we investigated the role that the iNOS pathway plays in mediating the bone-resorbing effects of IL-1 by studying mice with targeted disruption of the iNOS gene. Studies in vitro and in vivo showed that iNOS-deficient mice exhibited profound defects of IL-1-induced osteoclastic bone resorption but responded normally to calciotropic hormones such as 1,25 dihydroxyvitamin D3 and parathyroid hormone. Immunohistochemical studies and electrophoretic mobility shift assays performed on bone marrow cocultures from iNOS-deficient mice showed abnormalities in IL-1-induced nuclear translocation of the p65 component of NFκB and in NFκB-DNA binding, which were reversed by treatment with the NO donor S-nitroso-acetyl penicillamine. These results show that the iNOS pathway is essential for IL-1-induced bone resorption and suggest that the effects of NO may be mediated by modulating IL-1-induced nuclear activation of NFκB in osteoclast precursors.

一氧化氮（nitric oxide）被认为参与骨转换的调控，尤其在以骨吸收细胞因子释放为特征的病理状态中。细胞因子IL-1被认为是类风湿关节炎（rheumatoid arthritis）等炎症性疾病中关节周围骨丢失与组织损伤的介导因子。IL-1是破骨细胞性骨吸收以及骨细胞与其他细胞类型中诱导型一氧化氮合酶（inducible nitric oxide synthase，iNOS）表达的强效刺激剂。本研究通过构建iNOS基因靶向敲除小鼠，探究了iNOS通路在介导IL-1诱导的骨吸收效应中的作用。体外与体内实验结果显示，iNOS缺陷小鼠在IL-1诱导的破骨细胞性骨吸收方面存在显著缺陷，但对1,25-二羟维生素D3、甲状旁腺激素（parathyroid hormone）等促钙激素的应答正常。对iNOS缺陷小鼠骨髓共培养体系开展的免疫组织化学研究与电泳迁移率变动分析表明，IL-1诱导的核因子κB（NFκB）p65亚基的核转位以及NFκB与DNA的结合均出现异常，而一氧化氮供体S-亚硝基乙酰青霉胺可逆转该异常。上述结果证实，iNOS通路是IL-1诱导骨吸收所必需的，且提示一氧化氮的效应可能通过调控破骨细胞前体中IL-1诱导的NFκB核激活来实现。