LAUSR

BACKGROUND & AIMS Elements of field cancerization including atrophic gastritis, metaplasia and dysplasia promote gastric cancer development in association with chronic inflammation. However, it remains unclear how stroma changes during carcinogenesis and how the stroma contributes to progression of gastric preneoplasia. Here we investigated heterogeneity of fibroblasts, one of the most important elements in the stroma, and their roles in neoplastic transformation of metaplasia. METHODS We utilized single cell transcriptomics to evaluate the cellular heterogeneity of mucosal cells from human gastric cancer patients. Tissue sections from the same cohort and tissue microarrays were used to identify the geographical distribution of distinct fibroblast subsets. We further evaluated the role of fibroblasts from pathologic mucosa in dysplastic progression of metaplastic cells using patient-derived metaplastic gastroids and fibroblasts. RESULTS We identified four subsets of fibroblasts within stromal cells defined by the differential expression of PDGFRA, FBLN2, ACTA2 or PDGFRB. Each subset was distributed distinctively throughout stomach tissues with different proportions at each pathologic stage. The PDGFRα+ subset expanded in metaplasia and cancer compared with normal, maintaining a close proximity with the epithelial compartment. Co-culture of metaplasia- or cancer-derived fibroblasts with gastroids showing the characteristics of spasmolytic polypeptide-expressing metaplasia (SPEM) induced disordered growth, loss of metaplastic markers and increases in markers of dysplasia. Culture of metaplastic gastroids with conditioned media from metaplasia- or cancer-derived fibroblasts also promoted dysplastic transition. CONCLUSIONS These findings indicate that fibroblast associations with metaplastic epithelial cells can facilitate direct transition of metaplastic SPEM cell lineages into dysplastic lineages.