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Involvement of EGF receptor signaling and NLRP12 inflammasome in fine particulate matter‐induced lung inflammation in mice

Epidemiological studies have shown that exposure to ambient fine particulate matter (PM2.5) is associated with respiratory diseases. Lung inflammation is a central feature of many pulmonary diseases, which can be induced by PM2.5 exposure. However, the mechanisms underlying PM2.5‐induced lung inflammation remain unclear. To characterize the role of epidermal growth factor receptor (EGFR) and inflammasome in PM2.5‐induced lung inflammation in mice, 30 BALB/c mice were intrabroncheally instilled with saline and PM2.5 suspension (4.0 mg/kg b.w.) for 5 consecutive days, respectively. Bronchoalveolar lavage (BAL) was conducted and BAL fluid (BALF) was collected. The levels of reactive oxygen species (ROS), inducible nitric oxide synthase (iNOS), epidermal growth factor (EGF), CXCL1, interleukin (IL)−1β, and IL‐18 in BALF were determined using ELISA. mRNA levels of IL‐6, IL‐1β, IL‐18, CXCL1, IL‐10, NLRP3, Caspase‐1, and NLRP12 in lung tissues were determined by RT‐PCR. Phospho‐EGFR (Tyr1068) and phospho‐Akt (Thr308) in lung tissues were examined using immunohistochemical staining and Western blotting, respectively. Protein levels of Caspase‐1, NLRP3, NF‐κB‐p52/p100, and NF‐κB‐p65 in bronchial epithelium were examined using immunohistochemical staining. It was shown that PM2.5 exposure induced lung inflammation. Levels of total protein, ROS, iNOS, EGF, and CXCL1 and cell number in the BALF of mice exposed to PM2.5 were markedly elevated relative to the control. mRNA levels of CXCL1, IL‐1β, and IL‐18 in lung tissues of PM2.5‐exposed mice were increased in comparison with the control. However, level of NLRP12 mRNA in lung tissues of PM2.5‐exposed mice was reduced. Phospho‐EGFR (Tyr1068) and phospho‐Akt (Thr308) levels in the lungs of PM2.5‐instilled mice were higher than those in the lungs of the control. The protein levels of NF‐κB‐p52/p100 and NF‐κB‐p65 in bronchial epithelium of PM2.5‐exposed mice were also increased compared with the control. This study suggests that EGF‐EGFR‐Akt‐NF‐κB signaling and NLRP12 inflammasome may be associated with PM2.5‐induced lung inflammation in mice. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1121–1134, 2017.