Interactions between fibroblasts and monocyte-derived cells in chronic lung injuries induced by real-ambient particulate matter exposure

Long-term exposure to fine particulate matter (PM_2.5) can lead to chronic lung injury, including inflammation, idiopathic pulmonary fibrosis, and cancer. Mesenchymal cells, such as fibroblasts, myeloid-derived suppressor cells (MDSCs), and interstitial macrophages (IMs), contribute to immune regulation in lung, yet their diversity and functions upon long-term exposure to particulate matter (PM) remain inadequately characterized. In this study, we conducted a 16-week real-ambient PM exposure experiment on C57BL/6 J male mice in Shijiazhuang, China. We used single-cell RNA sequencing to analyze the cellular and molecular changes in lung tissues. Notably, we revealed a significant increase in specific fibroblast (ATX⁺, Col5a1⁺Meg3⁺, universal fibroblasts) and monocyte-derived cell subpopulations (monocytic-MDSCs (M-MDSCs), Lyve1^loMHC-Ⅱ^hi IMs, Lyve1^hiMHC-Ⅱ^lo IMs) that exhibited pro-inflammatory and pro-fibrotic functions. These cell subpopulations engaged in immunosuppressive signaling pathways and interactions with various cytokines, shaping a pulmonary microenvironment similar to those associated with cancer-associated fibroblasts (CAFs) and tumor-associated macrophages (TAMs). This altered immune environment may promote the development of pulmonary fibrosis caused by PM exposure, underscoring the intricate roles of mesenchymal cells in chronic lung injury and highlighting the cancer-causing potential of PM_2.5 exposure.