A Metastasis-Competent CAF Subpopulation Defined by MFAP5⁷THY1⁷ Co-expression Drives Prostate Cancer Metastasis via EMT Activation

Background: The tumor microenvironment, particularly cancer-associated fibroblasts (CAFs), contributes to prostate cancer (PCa) metastasis, however, the role of CAF heterogeneity remains incompletely characterized. The study aims to identify and functionally characterize a metastasis-competent CAF subpopulation in PCa and evaluate its potential as a biomarker for predicting metastatic progression. Methods: We integrated single-cell RNA sequencing data from 1,214 CAFs across 14 PCa specimens. Metastasis-derived CAFs were functionally validated in vitro. Stromal marker expression was assessed by multiplex immunofluorescence in 78 PCa tissues samples. Results: A 20-gene signature stratified CAFs into three subsets, with the MFAP5-expressing subset (CAFa) enriched in metastatic patients. Co-expression of MFAP5 and THY1 specifically identified CAFa with 96.2% specificity. MFAP5 secretion was associated with AKT phosphorylation, Slug upregulation, and epithelial-mesenchymal transition (EMT). Stromal MFAP5⁷THY1⁷ colocalization predicted postoperative metastasis risk independently of Gleason score (multivariate HR = 5.69, p < 0.001). Discussion: Our findings establish stromal MFAP5⁷THY1⁷ co-localization as a potential prognostic biomarker that could complement Gleason scoring. Further validation in multi-center cohorts is required to confirm its clinical independence. Conclusion: We identified a metastasis-competent CAF subpopulation defined by MFAP5⁷THY1⁷ co-expression, where THY1 serves as a spatial anchor for MFAP5 detection and MFAP5 secretion is functionally linked to AKT/EMT pathway activation.