DDAH1 plays dual roles in PM2.5 induced cell death in A549 cells

BACKGROUND: Dimethylarginine dimethylaminohydrolase 1 (DDAH1) is an enzyme that can degrade asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase (NOS) inhibitor. Emerging evidence suggests that alterations in the ADMA-DDAH1 pathway are involved in environmental pollution induced airway inflammation. However, the role of DDAH1 in protection against cytotoxicity of ambient airborne particulate matter is unclear.METHODS: We examined the influence of DDAH1 expression on oxidative stress and cell apoptosis in human type II alveolar epithelial A549 cells exposed to PM2.5 (particulate matter with an aerodynamic diameter less than 2.5 mu M).RESULTS: We found that PM2.5 exposure for 48h significantly decreased DDAH1 expression. However, knockdown of DDAH1 prior to PM2.5 exposure actually attenuated the cytotoxicity of PM2.5. Cytoprotection in DDAH1 deficient cells was due to increased reactive oxygen species, activation of PI3K-AKT and mitogen-activated protein kinase (MAPK) pathways, subsequent activation of nuclear factor erythroid-2-related factor 2 (Nrf2) and this caused a subsequent reduction in PM2.5 induced oxidative stress relative to control. DDAH1 depletion also repressed the induction of inducible NOS (iNOS) in PM2.5-exposed cells and knockdown of iNOS protected cells against PM2.5 induced cell death. Interestingly, overexpression of DDAH1 also exerted a protective effect against the cytotoxicity of PM2.5 and this was associated with a reduction in oxidative stress and upregulation of the anti-apoptotic protein Bcl-2.CONCLUSIONS: Our data indicate that DDAH1 plays dual roles in protection against cytotoxicity of PM2.5 exposure, apparently by limiting PM2.5 induced oxidative stress.GENERAL SIGNIFICANCE: Our findings reveal new insights into the role(s) of the DDAH1/ADMA in pulmonary protection against airborne pollutants. (C) 2016 Elsevier B.V. All rights reserved.

背景：二甲基精氨酸二甲胺水解酶1（DDAH1）是一种能够降解不对称二甲基精氨酸（ADMA）的酶，ADMA是一种内源性一氧化氮合酶（NOS）抑制剂。新出现的证据表明，ADMA - DDAH1通路的改变与环境污染诱导的气道炎症有关。然而，DDAH1在抵御环境空气悬浮颗粒物细胞毒性方面的作用尚不清楚。 方法：我们研究了DDAH1表达对暴露于PM2.5（空气动力学直径小于2.5微米的颗粒物）的人II型肺泡上皮A549细胞氧化应激和细胞凋亡的影响。 结果：我们发现暴露于PM2.5达48小时显著降低了DDAH1的表达。然而，在暴露于PM2.5之前敲低DDAH1实际上减轻了PM2.5的细胞毒性。DDAH1缺陷细胞中的细胞保护作用是由于活性氧增加、PI3K - AKT和丝裂原活化蛋白激酶（MAPK）通路激活，随后核因子红细胞2相关因子2（Nrf2）激活，这导致相对于对照，PM2.5诱导的氧化应激随后降低。DDAH1缺失还抑制了暴露于PM2.5的细胞中诱导型NOS（iNOS）的诱导，并且敲低iNOS可保护细胞免受PM2.5诱导的细胞死亡。有趣的是，DDAH1的过表达也对PM2.5的细胞毒性产生保护作用，这与氧化应激降低和抗凋亡蛋白Bcl - 2上调有关。 结论：我们的数据表明，DDAH1在抵御PM2.5暴露的细胞毒性方面具有双重作用，显然是通过限制PM2.5诱导的氧化应激。 一般意义：我们的研究结果为DDAH1/ADMA在肺部抵御空气污染物中的作用提供了新的见解。（C）2016爱思唯尔B.V.保留所有权利。