Comparative study of the effects of PM1-induced oxidative stress on autophagy and surfactant protein B and C expressions in lung alveolar type II epithelial MLE-12 cells.

There is a strong link between smaller air pollution particles and a range of serious health conditions. Thus, there is a need for understanding the impacts of airborne fine particulate matter (PM) with an aerodynamic diameter of <1μm (PM1) on lung alveolar epithelial cells. In the present study, mouse lung epithelial type II cell MLE-12 cells were used to examine the intracellular oxidative responses and the surfactant protein expressions after exposure to various concentrations of PM1 collected from an urban site and a steel-factory site (referred as uPM1 and sPM1 hereafter, respectively). Physicochemical characterization of PM1 was performed by using scanning electron microscopy and transmission electron microscopy. Cytotoxicity and autophagy induced by PM1 were assessed by using comprehensive approaches after MLE-12 cells were exposed to different concentrations of PM1 for various times. Expression of surfactant proteins B and C in MLE-12 cells was determined by Western blotting. All of the tested PM1 induced cytotoxicity evidenced by significant decrease of cell viability and increase of lactate dehydrogenase (LDH) release in a time- and concentration-dependent manner in the exposed cells compared with the unexposed cells. A similar pattern of increase of intercellular reactive oxygen species (ROS) generation and decrease of superoxide dismutase (SOD) and catalase (CAT) activities was also observed. PM1-induced autophagy was evidenced by an increase in microtubule-associated protein light chain-3 (LC3) puncta, accumulation of LC3II, and increased levels of beclin1. Data from Western blotting showed significant decrease of surfactant protein B and C expressions. Relatively high concentrations of transition metals, including Fe, Cu and Mn, may be responsible for the higher toxicity of sPM1 compared with uPM1. Moreover, pretreatment with N-acetylcysteine (NAC) or Chelex (a metal chelating agent, which removes a large suite of metals from PM1) prevented the increase of PM1-inudced ROS generation and autophagy, and down-regulated the expression of surfactant proteins B and C. PM1, particularly PM1 with high concentrations of transition metals, such as Fe, Cu and Mn, induces oxidative damage and autophagy, as well as inhibits surfactant protein B and C expressions in lung alveolar type II epithelial cells. This study will help to understand the mechanism underlying the toxicological effects of PM1 in lung alveolar type II epithelial cells. This article is part of a Special Issue entitled Air Pollution, edited by Wenjun Ding, Andrew J. Ghio and Weidong Wu. Copyright © 2016 Elsevier B.V. All rights reserved.

Citation

Ru Bai, Longfei Guan, Wei Zhang, Jinxia Xu, Wei Rui, Fang Zhang, Wenjun Ding. Comparative study of the effects of PM1-induced oxidative stress on autophagy and surfactant protein B and C expressions in lung alveolar type II epithelial MLE-12 cells. Biochimica et biophysica acta. 2016 Dec;1860(12):2782-92

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PMID: 27208422

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