PM2.5 Causes Increased Bacterial Invasion by Affecting HBD1 Expression in the Lung

Our research addresses the critical environmental issue of a fine particulate matter (PM2.5), focusing on its association with the increased infection risks. We explored the influence of PM2.5 on human beta-defensin 1 (HBD1), an essential peptide in mucosal immunity found in the airway epithelium. Using C57BL/6J mice and human bronchial epithelial cells (HBE), we examined the effects of PM2.5 exposure followed by Pseudomonas aeruginosa (P. aeruginosa) infection on HBD1 expression at both mRNA and protein levels. The study revealed that PM2.5's toxicity to epithelial cells and animals varies with time and concentration. Notably, HBE cells exposed to PM2.5 and P. aeruginosa showed increased bacterial invasion and decreased HBD1 expression compared to the cells exposed to P. aeruginosa alone. Similarly, mice studies indicated that combined exposure to PM2.5 and P. aeruginosa significantly reduced survival rates and increased bacterial invasion. These harmful effects, however, were alleviated by administering exogenous HBD1. Furthermore, our findings highlight the activation of MAPK and NF-κB pathways following PM2.5 exposure. Inhibiting these pathways effectively increased HBD1 expression and diminished bacterial invasion. In summary, our study establishes that PM2.5 exposure intensifies P. aeruginosa invasion in both HBE cells and mouse models, primarily by suppressing HBD1 expression. This effect can be counteracted with exogenous HBD1, with the downregulation mechanism involving the MAPK and NF-κB pathways. Our study endeavors to elucidate the pathogenesis of lung infections associated with PM2.5 exposure, providing a novel theoretical basis for the development of prevention and treatment strategies, with substantial clinical significance.