The Effect And Mechanism Of Real-ambient PM_2.5 Exposure On Lung Damage Modulated By Nrf2

Objective:PM_2.5 exposure can lead to respiratory diseases,including asthma,chronic obstructive pulmonary disease and lung cancer.The heavy metals and polycyclic aromatic hydrocarbons（PAHs）in PM_2.5 can induce oxidative stress and inflammatory response in cells,which are the main mechanisms of respiratory damage by PM_2.5.Nrf2 can regulate the expression of antioxidant and anti-inflammatory genes and play a key role in defense against oxidative stress and inflammation caused by PM_2.5 exposure.This study used Nrf2^-/-and wild-type mice to simulate real atmospheric particulate matter exposure using IVC system to explore the mechanism of Nrf2 in lung injury caused by PM_2.5 exposure.Methods:The KO mice and WT mice were divided into PM and FA groups（20 mice per group）.The mice were exposed to PM_2.5 in real-ambient system for 6 weeks,and sustained exposure for 16 hours per day.The exposure system was located in Shijiazhuang city,Hebei province.We detected the concentration of PM in the IVC system and the external environment.After exposure,the lung function and oxidative stress indexes were tested after PM_2.5 exposure.And the potential molecular pathways were explored by RNA-sequence analysis.Results:1.During six weeks of exposure,the average concentration of PM in IVC cage and outside atmosphere was 89.95μg/m³ and 151.40μg/m³,respectively.The lowest concentrations in IVC cage and outside atmosphere were 24.00μg/m³and 38.33μg/m³,respectively.The maximum concentrations in IVC cage and outside atmosphere were307.67μg/m³ and 588.33μg/m³,respectively.Days of severe pollution（over 150μg/m³）were 12 days.2.During PM exposure,no significant changes were observed in the body weight of the four groups mice.After PM_2.5 exposure,no remarkable difference was observed in the lung weight or the ratio of the lung weight between the WT-FA and WT-PM groups or the KO-FA and KO-PM groups.The forced vital capacity（FVC）and forced expiratory volume in the first 0.2 seconds（FEV0.2）were significantly decreased in the WT-PM group relative to the WT-FA group,while no remarkable difference was detected between the KO-FA and KO-PM groups.In WT mice,the pathological tests suggested serious alveolar congestion and alveolar wall thickening after PM exposure.The typical manifestations of lung damage were alveolar congestion and alveolar wall thickening.Interestingly,there was no significant pathological change between the KO-FA and KO-PM groups.3.In the KO mice,the expression of Nrf2,HO-1,NQO1 and GCLC was significantly down-regulated compared with WT mice.The expression levels of IL-6,MDA and SOD were significantly increased in WT and KO mice after exposure to PM_2.5.4.RNA-sequence analysis revealed that CYP450 pathways were associated with PM_2.5 metabolism.And we observed a remarkable decrease in the protein levels of CYP2E1expression in the PM_2.5-treated lungs of Nrf2-knockout mice,but not in WT mice.CYP2E1is closely related to endoplasmic reticulum stress.In our results,a significant decrease of GRP94 and CHOP expression was observed in the KO-PM mice compared to the KO-FA mice.Conclusion:1.In WT mice,the levels of inflammation,oxidative stress and endoplasmic reticulum stress were increased in the lung after exposure to PM_2.5.The lung function indicators and lung pathological sections were changed,suggesting that PM_2.5exposure affects lung function and causes lung injury.2.In the KO mice,the level of inflammation and oxidative stress were increased under PM_2.5 exposure.However,the ER stress was decreased significantly in KO-PM mice compared with KO-FA mice.3.Nrf2 knockdown altered the expression levels of CYP2E1 in lung tissue of mice after exposure to PM_2.5.According to our study,the decrease of ER stress in KO-PM mice may be due to the down-regulated of CYP2E1 expression by Nrf2.This may explain the lack of changes in lung function and pathology in the KO-FA group and the specific mechanism needs further study.