SRY-Box 9-Driven Spasmolytic Polypeptide-Expressing Metaplasia Cell Lineage Plasticity Is a Potential Therapeutic Target That Mitigates Risk of Metaplastic Progression to Gastric Cancer.

Gastric cancer develops through a sequential carcinogenic process beginning with pyloric metaplasia, a key feature of which is the transdifferentiation of gastric chief cells into spasmolytic polypeptide-expressing metaplastic (SPEM) cells. We found that SRY-Box 9 (SOX9), a transcription factor, is highly expressed in SPEM cells in both human and murine metaplasia. We therefore investigated the impact of SOX9-mediated SPEM cell plasticity and function on metaplasia development and progression during gastric carcinogenesis. We used 2 Sox9 knockout mouse models, GIFrtTA/+;TetO-CreTg/+;Sox9flox/flox (GCS) and GIFrtTA/+;TetO-CreTg/+;LSL-KrasG12DTg/+;Sox9flox/flox (GCKS) to examine the effects of SOX9 loss on metaplasia development after mucosal injury and carcinogenesis by immunofluorescence and single-cell RNA sequencing. We also confirmed our findings in human patient tissue microarrays and used SPEM organoids to identify genes regulated by SOX9. Sox9 knockout in chief cells resulted in the failure of metaplasia development in both acute and chronic injury because chief cells were unable to transdifferentiate into SPEM cells. The GCKS mouse failed to progress through carcinogenesis due to lack of a SPEM cell subpopulation responsible for metaplasia progression and fibroblast recruitment to gland bases. Instead, homeostatic gastric cell lineages were repopulated in the glands. We also identified a DNA topoisomerase II-α-expressing SPEM cell subpopulation that contributes to metaplasia progression, and putative SOX9 downstream genes associated with lineage plasticity. These results demonstrate that SOX9 is a master regulator of SPEM cell lineage evolution and metaplasia progression. Therefore, SOX9-mediated SPEM cell plasticity is a central mechanism in carcinogenesis.