Airway Disease Section, National Heart and Lung Institute, Imperial College London, United Kingdom.
Am J Physiol Lung Cell Mol Physiol. 2011 Feb;300(2):L295-304. doi: 10.1152/ajplung.00134.2010. Epub 2010 Dec 3.
Reactive oxygen species (ROS) are generated as a result of normal cellular metabolism, mainly through the mitochondria and peroxisomes, but their release is enhanced by the activation of oxidant enzymes such as NADPH oxidases or downregulation of endogenous antioxidant enzymes such as manganese-superoxide dismutase (MnSOD) and catalase. Transforming growth factor-β (TGF-β), found to be overexpressed in airway smooth muscle (ASM) from asthmatic and chronic obstructive pulmonary disease patients, may be a pivotal regulator of abnormal ASM cell (ASMC) function in these diseases. An important effect of TGF-β on ASMC inflammatory responses is the induction of IL-6 release. TGF-β also triggers intracellular ROS release in ASMCs by upregulation of NADPH oxidase 4 (Nox4). However, the effect of TGF-β on the expression of key antioxidant enzymes and subsequently on oxidant/antioxidant balance is unknown. Moreover, the role of redox-dependent pathways in the mediation of the proinflammatory effects of TGF-β in ASMCs is unclear. In this study, we show that TGF-β induced the expression of Nox4 while at the same time inhibiting the expression of MnSOD and catalase. This change in oxidant/antioxidant enzymes was accompanied by elevated ROS levels and IL-6 release. Further studies revealed a role for Smad3 and phosphatidyl-inositol kinase-mediated pathways in the induction of oxidant/antioxidant imbalance and IL-6 release. The changes in oxidant/antioxidant enzymes and IL-6 release were reversed by the antioxidants N-acetyl-cysteine (NAC) and ebselen through inhibition of Smad3 phosphorylation, indicating redox-dependent activation of Smad3 by TGF-β. Moreover, these findings suggest a potential role for NAC in preventing TGF-β-mediated pro-oxidant and proinflammatory responses in ASMCs. Knockdown of Nox4 using small interfering RNA partially prevented the inhibition of MnSOD but had no effect on catalase and IL-6 expression. These findings provide novel insights into redox regulation of ASM function by TGF-β.
活性氧（ROS）是细胞正常代谢的结果，主要通过线粒体和过氧化物酶体产生，但氧化酶如 NADPH 氧化酶的激活或内源性抗氧化酶如锰超氧化物歧化酶（MnSOD）和过氧化氢酶的下调会增强其释放。转化生长因子-β（TGF-β）在哮喘和慢性阻塞性肺疾病患者的气道平滑肌（ASM）中过度表达，可能是这些疾病中异常 ASM 细胞（ASMC）功能的关键调节剂。TGF-β 对 ASMC 炎症反应的一个重要影响是诱导白细胞介素-6（IL-6）释放。TGF-β 还通过上调 NADPH 氧化酶 4（Nox4）在 ASMC 中引发细胞内 ROS 释放。然而，TGF-β 对关键抗氧化酶表达的影响以及随后对氧化还原平衡的影响尚不清楚。此外，氧化还原依赖途径在 TGF-β 介导的 ASMC 促炎作用中的作用尚不清楚。在这项研究中，我们表明 TGF-β 诱导了 Nox4 的表达，同时抑制了 MnSOD 和过氧化氢酶的表达。氧化还原酶的这种变化伴随着 ROS 水平和 IL-6 释放的升高。进一步的研究揭示了 Smad3 和磷脂酰肌醇激酶介导的途径在诱导氧化还原失衡和 IL-6 释放中的作用。抗氧化剂 N-乙酰半胱氨酸（NAC）和埃布森通过抑制 Smad3 磷酸化逆转了氧化还原酶和 IL-6 释放的变化，表明 TGF-β 通过依赖氧化还原的途径激活 Smad3。此外，这些发现表明 NAC 在预防 TGF-β 介导的 ASMC 促氧化剂和促炎反应中可能具有潜在作用。使用小干扰 RNA 敲低 Nox4 可部分阻止 MnSOD 的抑制，但对过氧化氢酶和 IL-6 表达没有影响。这些发现为 TGF-β 对 ASM 功能的氧化还原调节提供了新的见解。
