Pancreatic ductal adenocarcinoma (PDAC) is characterized by its aggressive nature and dismal prognosis, largely attributed to its unique tumor microenvironment. However, the molecular mechanisms by which tumor-associated macrophages (TAMs) promote PDAC progression, particularly the role of β-catenin signaling in regulating TAM phenotype and function, remain incompletely understood. Initially, we performed comprehensive analyses of RNA-seq and single-cell RNA-seq (scRNA-seq) datasets to investigate OSM and LOXL2 expression patterns in PDAC. Subsequently, the regulatory relationship between β-catenin and OSM in TAMs was examined using THP-1-derived macrophages. Furthermore, the functional impact of TAM-derived OSM on PDAC progression was evaluated through in vitro co-culture systems and an in vivo Panc02 lung metastasis model. Additionally, mechanistic studies employed pharmacological inhibitors and genetic approaches targeting β-catenin, OSM, and STAT3 signaling. Notably, elevated expression of OSM and LOXL2 in PDAC specimens significantly correlated with poor patient survival. Intriguingly, scRNA-seq analysis revealed that β-catenin signaling was uniquely activated in TAMs among immune cells, which consequently regulated both TAM polarization and OSM expression. These OSM-expressing TAMs exhibited a distinct hybrid M1/M2 phenotype. Besides, our transcriptional profiling of TAMs revealed concurrent activation of both pro- and anti-inflammatory programs, with enrichment in Wnt signaling pathways. RNA-seq analysis of PDAC cells exposed to TAM-derived factors demonstrated enhanced mesenchymal transition and stemness properties, with direct enrichment of OSM signaling and extracellular matrix remodeling pathways. Mechanistically, β-catenin activation directly regulated both TAM phenotype and OSM expression, while TAM-conditioned medium enhanced PDAC cell migration, invasion, and lung metastasis. Importantly, inhibition of β-catenin signaling simultaneously altered TAM polarization and reduced OSM expression, which substantially attenuated epithelial-mesenchymal transition (EMT) in co-cultured PDAC cells. Moreover, STAT3 inhibition abolished OSM-induced LOXL2 expression and subsequent EMT programming. Collectively, we identified a novel β-catenin/OSM-STAT3/LOXL2 signaling axis mediating TAM-induced PDAC progression. This pathway not only elucidates a previously unrecognized mechanism of β-catenin-mediated regulation of TAM function and phenotype but also presents potential therapeutic targets for intervention.
