A single-cell perspective on polyethylene microplastic toxicity: linking fibroblast reprogramming to immune microenvironment alterations in the lung

BACKGROUND: Microplastics represent ubiquitous and persistent environmental contaminants, with growing evidence of their accumulation in human tissues including the lung. Chronic pulmonary exposure has been associated with tissue damage, fibrotic remodeling, and immune dysregulation; however, a systematic understanding of the underlying multicellular dynamics and transcriptional alterations remains limited. Polyethylene is a dominant component of airborne microplastics, yet its specific pathogenic mechanisms in the lung are poorly characterized. METHODS: We developed a rat model of chronic intranasal exposure to polyethylene microplastics (PE-MPs). Lung tissues from exposed and control animals were analyzed by histopathology and subjected to high-throughput single-cell RNA sequencing (scRNA-seq). Computational pipelines were employed to construct a comprehensive cellular atlas, characterize transcriptomic alterations, infer cellular communication, and map transcription factor regulatory networks. Cell populations were annotated based on canonical markers, and differential analyses compared PE-MPs-exposed and control groups. RESULTS: Histological analysis revealed enhanced collagen deposition and perivascular lymphocyte infiltration in PE-MPs-exposed lungs. scRNA-seq profiling of 25,625 cells delineated a remodeled cellular landscape, marked by expansion of fibroblasts and myofibroblasts alongside increased proportions of T cells, B cells, and dendritic cells, coupled with a contraction of specific epithelial and endothelial subsets. Fibroblasts exhibited an activated phenotype characterized by upregulation of extracellular matrix genes and inferred hyperactivation of TGF-β pathway transducers Smad3 and Smad4. Epithelial dysfunction was evident across populations: club cells displayed altered differentiation potential, ciliated cells showed impaired ciliogenesis, and alveolar type II cells downregulated surfactant homeostasis genes. Myeloid immune cells upregulated chemokines (Cxcl9, Cxcl10, Ccl3, Ccl4) and MHC molecules, indicating enhanced antigen-presenting capacity and chemotactic activity. Notably, Tgfb1 expression was significantly elevated in plasmacytoid dendritic cells, monocytes, macrophages, and NK/NKT cells. Ligand-receptor interaction analysis predicted heightened TGF-β1 signaling to fibroblasts and increased chemokine-mediated recruitment of immune cells, particularly plasmacytoid dendritic cells. CD123, TGF‑β1, and p‑Smad3 immunoreactivities co‑localized with Masson's trichrome‑stained collagen deposits in the perivascular spaces of small pulmonary arteries. CONCLUSION: This study provides a high-resolution single-cell transcriptomic atlas delineating the pulmonary response to chronic PE-MPs exposure. We identify a coordinated pathogenic network involving epithelial/endothelial dysfunction, immune microenvironment imbalance, and fibroblast activation via paracrine TGF-β signaling as central mechanisms driving microplastic-induced lung injury. These findings elucidate novel cellular and molecular pathways linking environmental plastic exposure to pulmonary fibrosis and immune dysregulation, offering potential targets for therapeutic intervention.