PLIN3 overexpression in lung adenocarcinoma promotes M2 macrophage–myofibroblast transition in the tumor microenvironment

Macrophage–myofibroblast transition (MMT) promotes tumor progression. Studies have primarily emphasized macrophage-intrinsic regulation; however, whether lung adenocarcinoma (LUAD) cells actively drive MMT in tumor-associated macrophages (TAMs) remains unclear. We integrated LUAD single-cell RNA sequencing (scRNA-seq) and bulk transcriptomic datasets, applying MMT-infiltration-stratified differential analysis to identify tumor cell-derived upstream regulators of MMT. Multiple machine learning algorithms were used to construct an MMT-related risk score. SHAP analysis prioritized key genes, and NicheNet inferred tumor–macrophage ligand–receptor–target axes. Tumor cell–conditioned medium (CM)–driven MMT induction in M2 macrophages was examined by dual immunofluorescence and in vitro experiments. Single-cell analysis showed that M2 macrophages in LUAD exhibit variable activation of an MMT-related transcriptional program. Tumor-level differential analysis across MMT infiltration strata identified tumor cell-derived candidate regulators of MMT. A 9-gene MMT prognostic risk model was established using univariate Cox regression and machine learning analyses. This model achieved a higher C-index than previously reported models, and high-risk tumors displayed an immunosuppressive infiltration pattern. SHAP analysis identified PLIN3 as a key driver. NicheNet analysis suggested that PLIN3-high tumor cells may induce MMT through TGF-β1-related signaling. Immunohistochemistry demonstrated PLIN3 upregulation in LUAD tissues, while immunofluorescence further revealed enrichment of CD68⁺α-SMA⁺ macrophages around tumor cells in PLIN3-high samples. LUAD cell-derived CM induced MMT in M2 macrophages. PLIN3 knockdown in LUAD cells attenuated CM-induced MMT, whereas PLIN3 overexpression enhanced it. PLIN3 knockdown also suppressed LUAD cell migration, invasion, and colony formation. High PLIN3 expression in LUAD promotes MMT through tumor–macrophage crosstalk in the tumor microenvironment.