Abstract / Summary
Abstract Chronic coexposure to fine particulate matter (PM2.5) and house dust mite (HDM) allergen worsens allergic asthma outcomes, yet the stromal cell mechanisms linking combined environmental and allergic risk factors remain incompletely defined. Airway fibroblasts are traditionally viewed as structural matrix-producing cells, with limited published data describing their capacity to acquire antigen-presenting (APC) features after dual pollutant-allergen stimulation. Bronchoalveolar lavage fluid (BALF) fibroblasts represent a less invasive alternative to endobronchial biopsy tissue for primary stromal cell research, reducing procedural risks and sampling limitations in human asthma studies. BALF fibroblasts were isolated from 8 HDM-sensitized asthmatic participants and 8 HDM-sensitized nonasthmatic control subjects. An in vitro costimulation model was established to mimic concurrent PM2.5 and HDM exposure, with matched single-stimulus, vehicle, and TLR4 inhibitor control groups. We applied paired RNA-seq and ATAC-seq multiomics, antigen-specific CD4+ T cell coculture assays, CRISPR-Cas9 genetic editing, lentiviral complement, and humanized NSG mouse intervention experiments to characterize fibroblast functional shifts linked to air pollution. BALF fibroblasts from HDM-sensitized asthmatics displayed elevated HLA-DR, CD80, and CD86 surface markers alongside enhanced IL-33 secretion, and supported robust antigen-specific CD4+ T cell proliferation. Fibroblasts cultured with PM2.5 and HDM together acquired persistent memory-like functional alterations not observed under single-agent treatment. Integrated multiomic profiling identified FAM45A as the top transcript selectively upregulated only under dual exposure. In vitro assays demonstrated FAM45A interacts with V-ATPase complexes to slow lysosomal allergen degradation and amplifies NF-κB/AP-1 inflammatory signaling. CRISPR knockout and lentiviral rescue experiments support that FAM45A is required for the dual-stimulation-induced fibroblast phenotype. Neutralizing anti-FAM45A antibody reversed APC-like fibroblast activity in vitro and alleviated PM2.5/HDM-triggered airway inflammation in humanized mice. In a power-calculated expanded clinical cohort, fibroblast FAM45 protein levels positively correlated with residential PM2.5 exposure duration, serum HDM IgE, and GINA asthma severity. Concurrent PM2.5 and HDM exposure drives persistent memory-like functional and chromatin remodeling of human airway fibroblasts. FAM45A acts as a key molecular mediator of pollution-amplified allergic inflammation. BALF fibroblast FAM45A levels may serve as a correlative tissue marker reflecting combined environmental and allergic disease burden. Targeted FAM45A inhibition may offer a more tissue-restricted intervention relative to broad corticosteroid therapy, though comprehensive preclinical safety assessment across systemic immune compartments is needed to clarify off-target risks.