The air pollutant PM2.5 aggravates airway inflammation via NF-κB/NLRP3-induced pyroptosis: partially inhibited by the TLR4 inhibitor TAK242

Background

Ambient fine particulate matter (PM2.5) is believed to be closely connected to asthma severity. However, studies are needed to investigate the underlying mechanism of these findings. Our study attempted to confirm the role of NF-κB/NLRP3 pyroptosis in asthma exacerbation through in vivo and in vitro tests. We also analyzed the differentially expressed genes via RNA-Seq to investigate potential regulatory mechanisms.

Methods

We undertook in vivo and in vitro research to investigate the effects of PM2.5 on a mouse asthma model and the human bronchial epithelial cell line Beas-2b. Female BALB/c mice were sensitized with OVA to create a murine asthma model. HE staining and the EMAK system were used to assess airway inflammation and hyperresponsiveness in mouse lungs. We also measured IL-4, IL-5, IL-13, and OVA-specific IgE levels to assess the inflammatory effects of PM2.5 on both normal and OVA-induced asthmatic mice. Western blotting and immunohistochemistry were used to analyze the expression of major NF-κB and pyroptosis proteins. Human bronchial epithelial Beas-2b cells were treated with PM2.5, and the degree of pyroptosis was determined. RNA sequencing (RNA-Seq) was employed to identify differentially expressed genes and investigate potential regulatory mechanisms.

Results

In vivo exposure to PM2.5 significantly increased HE staining scores in a mouse model of asthma. The levels of acetylcholine associated with enhanced airway responsiveness were lower in the PM2.5-exposed asthmatic group than in the control group. Compared with the asthmatic group, the BALF group presented considerably greater levels of IL-1β and IL-18. Compared with those in the asthmatic group, the protein expression levels of NLRP3, Caspase-1, GSDMD-N, cleaved Caspase-1p10, IL-1β, and p-NF-κBp65/NF-κBp65 in the lung tissues of the mice in the PM2.5 group were significantly greater than those in the asthmatic group. In vitro, PM2.5 causes pyroptosis and inflammation in Beas-2B human bronchial epithelial cells via the NF-κB/NLRP3 pathway. The TLR4 inhibitor TAK242 can partially block this effect.

Conclusion

In the OVA-induced asthma mouse model, PM2.5 activates the NF-κB/NLRP3 pathway and induces pyroptosis, thereby exacerbating airway inflammation and hyperreactivity. It may activate the NF-κB signalling cascade through the TLR4/MyD88 pathway, upregulate critical proteins in the pyroptosis pathway, and induce pyroptosis and inflammation in respiratory epithelial Beas-2b cells, exacerbating asthma.