Publication date: Jul 14, 2025

To examine the role of ETS domain containing protein ELK4 in macrophage polarization and pulmonary fibrosis in connective tissue disease-related interstitial lung disease(CTD-ILD). This study analyzed gene expression datasets (SSc-ILD, ALI, COVID-19) to identify target genes in CTD-ILD. We performed RT-qPCR, Western blot, and immunohistochemistry to assess macrophage polarization and epithelial-mesenchymal transition (EMT) both in vitro and in a mouse model of pulmonary fibrosis. Non-invasive lung function testing was also conducted. Bioinformatics analysis demonstrated that reduced ELK4 expression is associated with ILD. In CTD-ILD patients, lower ELK4 levels correlated with higher KL-6 and ferritin, and lower DLCO. In vitro, ELK4 down-regulation increased macrophage markers (CD86 and iNOS) and p38/JNK phosphorylation, while promoting mesenchymal markers (N-cadherin, Vimentin) and inhibiting E-cadherin. In the bleomycin-induced fibrosis model, ELK4 overexpression reversed these changes, improved lung function, and reduced IL-6 and TNF-α levels in bronchoalveolar lavage fluid (BALF). The reduced expression of ELK4 activates the p38 and ERK signaling pathways in the MAPK signaling pathway, promoting macrophage polarization toward the M1 phenotype. These findings demonstrate that ELK4 plays a crucial role in the pathogenesis of CTD-ILD.