Alteration of the Secretome in Airway Epithelial Cells by Air Pollutants: Evidence from an Air-Liquid Interface Model

While the structural damage to the airway epithelium from ozone (O₃) or diesel exhaust particles (DEP) is known, the common regulatory mechanisms activated during mixed exposures, which mirror real-world scenarios, remain poorly understood. This study aimed to identify shared molecular pathways initiated by exposure to O₃ and DEP using an in vitro air-liquid interface (ALI) model to understand the initial cellular responses.

Polarized Calu-3 cell monolayers at the ALI were acutely exposed to non-cytotoxic O₃ or DEP. Barrier integrity was assessed via transepithelial electrical resistance (TEER) and FITC-dextran permeability. Gene expression of tight junctions and alarmin cytokines was quantified by qPCR, while the protein level of tight junctions was identified by immunofluorescence. The cellular secretome was comprehensively analyzed using label-free liquid chromatography-tandem mass spectrometry.

Both pollutants impaired barrier integrity, evidenced by decreased TEER and increased permeability, and induced a potent inflammatory response via upregulation of alarmin cytokines IL-25, IL-33, and TSLP. Critically, secretome analysis revealed that although O₃ and DEP initiated distinct upstream damage patterns, their responses converged on common downstream pathways, including the activation of Wnt signaling and antigen processing and presentation.

Exposure to O₃ and DEP compromises airway epithelial barrier function and triggers a robust alarmin-driven inflammatory response. Our identification of convergent downstream pathways, such as Wnt signaling, provides crucial mechanistic insights into the shared pathophysiology of mixed pollutant exposure. These findings highlight potential therapeutic targets for mitigating the adverse health effects of complex air pollution.