Background
Pyloric metaplasia or spasmolytic polypeptide-expressing metaplasia (SPEM) routinely develops in the setting of oxyntic atrophy, where parietal and chief lineages are lost. While a number of cellular sources have been postulated for the origins of SPEM, the contribution by spasmolytic polypeptide/trefoil family factor 2 (SP/TFF2)- expressing neck progenitor cells has not been investigated.
Methods
We performed lineage tracing of Tff2+ progenitors in homeostasis using Tff2-CreERT knockin mice. Mucous neck cells were stained with TFF2 antibodies and GSII lectin; gastric chief cells were identified by GIF staining. To study the cell fate of Tff2-CreERT+ cells during regeneration, Tff2-CreERT; LSL-tdTomato or Tff2-CreERT; Lgr5-DTR-eGFP; LSL-tdTomato mice were treated with high doses of tamoxifen (HDT) or diphtheria toxin (DT). Proliferation and cell migration were assessed with Ki67 and EdU staining. Mouse and human tissues were subjected to single-cell RNA sequencing and spatial transcriptome analysis.
Results
Tff2-CreERT positive cells, reflecting Tff2 mRNA transcription, are found to be highly proliferative and reside in the lower corpus isthmus, just above TFF2 peptide positive mucous neck cells, as previously reported in Tff2-CreERT BAC transgenic mice. In the lineage tracing experiments, Tff2-CreERT+ isthmus progenitors first give rise to mucous neck cells labeled by TFF2 antibody or GSII, as well as parietal cells. While migrating downward, the Tff2-derived clones first transition from a GIF-GSII+ state to next becoming GIF+GSII+ intermediate cells, and subsequently evolving into GIF+GSII- mature chief cells, thus defining them as a source of the downward transdifferentiation from neck to chief lineage. HDT or DT-treatment of Lgr5-DTR mice leads to rapid loss of GIF⁺ chief cells, followed by more rapid expansion of Tff2⁺ progenitor-derived clones covering the GIF+GSII+ SPEM cells near the gland base. The downward migration of isthmus progenitors was confirmed by Edu labeling. Notably, Tff2-labeled cells migrate down to replace the lost chief cells, but these traced cells decline over time, reflecting their short-term progenitor nature. Analysis of murine and human scRNA-seq datasets using CytoTRACE showed that isthmus progenitors have the greatest cell potency while chief cells have the lowest, with spatial transcriptomics indicated a trajectory from isthmus cells to GIF⁺GS-II⁺progenitors/SPEM and finally to chief cells.
Conclusions.
Tff2-CreERT⁺ specifically labels corpus isthmus progenitors, which normally give rise to parietal cells, mucous neck cells, SPEM-like intermediate cells, and chief cells. However, after acute injury and chief cell loss, they rapidly expand and give rise to more numerous SPEM cells, which eventually reconstitute the chief cell lineage.

Yoku Hayakawa

Appearances