Abstract Rationale Pulmonary fibrosis is a progressive interstitial lung disease characterized by the replacement of normal parenchyma with fibrotic tissue, ultimately leading to chronic respiratory failure. Idiopathic pulmonary fibrosis (IPF) represents its most common and severe form. Fibroblasts expressing secreted frizzled-related protein 2 (SFRP2) have been reported to be increased in IPF lungs, yet their biological function remains unclear. This study aimed to elucidate the role and underlying mechanisms of SFRP2 in lung fibroblasts. Methods To investigate the characteristics of SFRP2, we reanalyzed a publicly available single-cell RNA sequencing (scRNA-seq) dataset of lung tissues from patients with IPF and healthy controls. Immunofluorescence staining was conducted to assess the protein-level localization of SFRP2 in fibrotic lungs. In vitro, primary human lung fibroblasts from healthy donors were stimulated with transforming growth factor-β (TGF-β), and SFRP2 expression was examined by quantitative polymerase chain reaction (qPCR). SFRP2 was also overexpressed or silenced, or exogenous recombinant SFRP2 was applied, and effects on TGF-β-induced myofibroblast differentiation were evaluated by qPCR and Western blotting (WB). To further elucidate the molecular mechanisms of SFRP2, transcriptomic profiling by RNA sequencing was performed on lung fibroblasts overexpressing SFRP2, followed by gene set enrichment analysis and pathway analysis, with key signaling changes validated by WB. Results scRNA-seq analysis revealed the emergence of a distinct subset of fibroblasts with high SFRP2 expression along the trajectory from resting fibroblasts to myofibroblasts. Immunofluorescence demonstrated that SFRP2 was predominantly localized adjacent to fibroblastic foci in IPF lungs. TGF-β stimulation increased SFRP2 mRNA expression in primary human lung fibroblasts. Functionally, SFRP2 overexpression and recombinant SFRP2 attenuated TGF-β-induced myofibroblast differentiation, whereas SFRP2 knockdown enhanced it. Transcriptomic and pathway analyses revealed that SFRP2 modulated both canonical and non-canonical Wnt signaling pathways. Notably, SFRP2 overexpression or recombinant SFRP2 administration suppressed the TGF-β-induced upregulation of AXIN2 and reduced JNK/ROCK and Ca²+ signaling, suggesting that SFRP2 inhibits myofibroblast differentiation through Wnt pathway modulation. Conclusions SFRP2 is upregulated in lung fibroblasts upon TGF-β stimulation and functions as an inhibitory modulator of fibroblast-to-myofibroblast differentiation by regulating Wnt signaling, thereby counteracting progression of fibrosis. SFRP2 may therefore represent an intrinsic antifibrotic factor and a potential therapeutic target in pulmonary fibrosis. This abstract is funded by: None
Yamamoto et al. (Fri,) studied this question.