NLRP3 inflammasome activation determines the fibrogenic potential of PM_(2.5) air pollution particles in the lung

Airborne fine particulate matter(PM_(2.5))is known to cause respiratory inflammation such as chronic obstructive pulmonary disease and lung fibrosis.NLRP3 inflammasome activation has been implicated in these diseases;however,due to the complexity in PM_(2.5)compositions,it is difficult to differentiate the roles of the components in triggering this pathway.We collected eight real-life PM_(2.5)samples for a comparative analysis of their effects on NLRP3 inflammasome activation and lung fibrosis.In vitro assays showed that although the PM_(2.5)particles did not induce significant cytotoxicity at the dose range of 12.5to 100μg/m L,they induced potent TNF-αand IL-1βproduction in PMA differentiated THP-1 human macrophages and TGF-β1 production in BEAS-2B human bronchial epithelial cells.At the dose of 100μg/m L,PM_(2.5)induced NLRP3 inflammasome activation by inducing lysosomal damage and cathepsin B release,leading to IL-1βproduction.This was confirmed by using NLRP3-and ASC-deficient cells as well as a cathepsin B inhibitor,ca-074 ME.Administration of PM_(2.5)via oropharyngeal aspiration at 2 mg/kg induced significant TGF-β1 production in the bronchoalveolar lavage fluid and collagen deposition in the lung at 21days post-exposure,suggesting PM_(2.5)has the potential to induce pulmonary fibrosis.The ranking of in vitro IL-1βproduction correlates well with the in vivo total cell count,TGF-β1 production,and collagen deposition.In summary,we demonstrate that the PM_(2.5)is capable of inducing NLRP3 inflammasome activation,which triggers a series of cellular responses in the lung to induce fibrosis.