Center for Environmental Medicine, Asthma, and Lung Biology, University of North Carolina Chapel Hill, North Carolina, United States of America.
PLoS One. 2012;7(4):e35108. doi: 10.1371/journal.pone.0035108. Epub 2012 Apr 9.
Exposure to oxidant air pollution is associated with increased respiratory morbidities and susceptibility to infections. Ozone is a commonly encountered oxidant air pollutant, yet its effects on influenza infections in humans are not known. The greater Mexico City area was the primary site for the spring 2009 influenza A H1N1 pandemic, which also coincided with high levels of environmental ozone. Proteolytic cleavage of the viral membrane protein hemagglutinin (HA) is essential for influenza virus infectivity. Recent studies suggest that HA cleavage might be cell-associated and facilitated by the type II transmembrane serine proteases (TTSPs) human airway trypsin-like protease (HAT) and transmembrane protease, serine 2 (TMPRSS2), whose activities are regulated by antiproteases, such as secretory leukocyte protease inhibitor (SLPI). Based on these observations, we sought to determine how acute exposure to ozone may modulate cellular protease/antiprotease expression and function, and to define their roles in a viral infection. We utilized our in vitro model of differentiated human nasal epithelial cells (NECs) to determine the effects of ozone on influenza cleavage, entry, and replication. We show that ozone exposure disrupts the protease/antiprotease balance within the airway liquid. We also determined that functional forms of HAT, TMPRSS2, and SLPI are secreted from human airway epithelium, and acute exposure to ozone inversely alters their expression levels. We also show that addition of antioxidants significantly reduces virus replication through the induction of SLPI. In addition, we determined that ozone-induced cleavage of the viral HA protein is not cell-associated and that secreted endogenous proteases are sufficient to activate HA leading to a significant increase in viral replication. Our data indicate that pre-exposure to ozone disrupts the protease/antiprotease balance found in the human airway, leading to increased influenza susceptibility.
暴露于氧化剂空气污染与呼吸道发病率增加和易感染有关。臭氧是一种常见的氧化剂空气污染物，但它对人类流感感染的影响尚不清楚。2009 年春季，墨西哥城地区是甲型 H1N1 流感大流行的主要地点，同时也是环境臭氧水平较高的时候。病毒膜蛋白血凝素（HA）的蛋白水解裂解对于流感病毒的感染力至关重要。最近的研究表明，HA 裂解可能与细胞相关，并由 II 型跨膜丝氨酸蛋白酶（TTSPs）人呼吸道胰蛋白酶样蛋白酶（HAT）和跨膜蛋白酶丝氨酸 2（TMPRSS2）辅助，其活性受抗蛋白酶如分泌白细胞蛋白酶抑制剂（SLPI）调节。基于这些观察结果，我们试图确定急性暴露于臭氧如何调节细胞蛋白酶/抗蛋白酶的表达和功能，并定义它们在病毒感染中的作用。我们利用体外分化的人鼻上皮细胞（NEC）模型来确定臭氧对流感病毒裂解、进入和复制的影响。我们发现臭氧暴露会破坏气道液中的蛋白酶/抗蛋白酶平衡。我们还确定，功能性 HAT、TMPRSS2 和 SLPI 形式从人呼吸道上皮分泌出来，急性暴露于臭氧会反向改变它们的表达水平。我们还表明，添加抗氧化剂通过诱导 SLPI 可显著减少病毒复制。此外，我们确定臭氧诱导的病毒 HA 蛋白裂解与细胞无关，并且分泌的内源性蛋白酶足以激活 HA，导致病毒复制显著增加。我们的数据表明，臭氧预处理会破坏人呼吸道中发现的蛋白酶/抗蛋白酶平衡，导致流感易感性增加。
