Fibroblast-derived Spondin-2 promotes dysplastic transition in metaplastic gastric epithelial cells

Fibroblasts are increasingly recognized as active drivers of early gastric carcinogenesis, yet the specific fibroblast-derived factors that promote the transition from metaplasia to dysplasia remain unknown. We have recently found that coculture of metaplasia or cancer-derived fibroblasts with gastroids dominated by spasmolytic polypeptide-expressing metaplasia (SPEM) lineages leads to a decrease of metaplastic markers and a concomitant up-regulation of dysplasia markers. We have now identified the matricellular protein Spondin-2 (SPON2) as a key fibroblast-secreted mediator of this transition.

Single-cell RNA-sequencing of patient-derived fibroblast populations and proteomic profiling of conditioned media were used to identify fibroblast-secreted factors. Spatial transcriptomics was used to evaluate localization of SPON2+ fibroblasts in human gastric tissue. Knockdown of SPON2 in cancer-derived fibroblasts was performed in coculture with SPEM lineage gastroids, and recombinant SPON2 treatment was applied to metaplastic gastroids.

Single-cell RNA-sequencing and proteomic profiling revealed SPON2 as the most upregulated and selectively secreted protein in metaplasia- and cancer-derived fibroblasts compared to normal fibroblasts. Spatial transcriptomics demonstrated PDGFRA/SPON2 co-expressing fibroblasts localized adjacent to metaplastic glands in human gastric tissue. Knockdown of SPON2 in cancer-derived fibroblasts abrogated induction of dysplastic promotion in cocultured SPEM lineage gastroids, while preserving metaplastic markers. Conversely, recombinant SPON2 treatment promoted down-regulation of metaplastic markers and upregulation of dysplasia-associated proteins in metaplastic gastroids. Following cessation of SPON2 treatment, gastroid cells lost their dysplastic markers and regained metaplastic markers.

These findings identify fibroblast-derived SPON2 as a potent secreted factor driving the metaplasia-to-dysplasia transition in gastric epithelium. Therefore, SPON2 represents the first fibroblast-derived secreted factor that can promote pre-neoplastic progression.