Tumor-derived WNT7A reprograms pulmonary fibroblasts to remodel the metastatic niche and promote bladder cancer lung metastasis.

The mechanisms underlying lung metastases in bladder cancer (BLCA) remain poorly understood. Cancer-associated fibroblasts (CAFs) are key modulators of the metastatic microenvironment, but how they are activated and contribute to BLCA lung metastases remains unclear. Single-nucleus RNA sequencing was conducted on metastatic lung lesions from patients with BLCA to characterize the tumor microenvironment. Functional and molecular biology experiments, including co-culture assays, luciferase reporter assays, chromatin immunoprecipitation and in vivo lung metastasis models, were performed to explore the mechanisms by which tumor-derived factors and CAFs-secreted exosomes contribute to metastasis. The results revealed that CAFs were enriched in metastatic lung lesions and activated by tumor-derived WNT7A via the Wnt/β-catenin pathway. These activated CAFs promoted BLCA cell proliferation, stemness and migration through the exosomal delivery of miR-1910-5p, which directly suppressed CTDNEP1 expression and activated MYC signaling. Mechanistically, RBMX was identified as a regulator of miR-1910-5p packaging into CAFs-derived exosomes. In vivo, inhibition of CAFs-derived exosomes secretion reduced lung metastasis, highlighting their critical role in metastasis formation. In conclusion, this study uncovers a novel reciprocal activation loop between tumor cells and CAFs in BLCA lung metastases, where tumor-secreted WNT7A activates resident pulmonary CAFs, which in turn enhance tumor malignancy through exosomal delivery of miR-1910-5p. This exosome-mediated crosstalk promotes metastatic progression via the CTDNEP1/MYC signaling pathway. These findings provide potential therapeutic targets for mitigating metastatic progression in BLCA.