267 Macrophages Promote the Progression of Metaplasia in the Stomach Following Acute Parietal Cell Loss

Abstract

Adenocarcinoma in the human stomach evolves in the setting of Helicobacter pylori-induced oxyntic atrophy and chronic mucous cell metaplasia. Two types of metaplasia associated with development of intestinal-type cancers are observed in the human stomach: intestinal metaplasia (IM; intestinal type goblet cells in the stomach) and Spasmolytic Polypeptide (TFF2) Expressing Metaplasia (SPEM; with the presence of antral type TFF2-expressing mucous cells in the oxyntic region). Our previous study showed that SPEM developed from transdifferentiation of mature chief cells, rather than originating from aberrant differentiation of resident progenitor cells. Recent investigations have noted evidence for increased Ras activity in up to a third of gastric cancers. Thus, we have hypothesized that activated Ras, specifically induced in mature chief cells, elicits transdifferentiation of chief cells into SPEM and progression of SPEM to more intestinalized metaplasia. To test this hypothesis, we have examined a novel mouse model of metaplasia in the stomach in Mist1-CreERT2Tg/+;LSLK-Ras(G12D)Tg/+;mT/mGTg/+ mice. Tamoxifen (TAM) treatment induces the expression of activated K-Ras specifically in mature chief cells and marks the K-Ras-induced chief cells with GFP as a lineage tracer. This mouse model rapidly develops SPEM and IM within 3 months, following TAM induction of activated K-Ras expression in mature chief cells. At 1 week post TAM treatment, we found several groups of metaplastic glands between normal oxyntic glands that were positive for SPEM markers. At 3 months post TAM treatment, oxyntic glands were replaced withmetaplastic glands that showed highly proliferative mucous cell populations at the bases and the cells in the metaplastic glands were strongly positive for clusterin and TFF3 with distinct goblet cell morphologies, and also positive for Pdx1. Some glands were positive for IM markers such as villin and Cdx1. The mice at 4 months post TAM treatment developed severe inflammation, metaplasia, dysplasia and the invasive adenocarcinoma. Consistent with active K-Ras expression, cells with nuclear expression of phospho-ERK1/2 were also observed at the bases of metaplastic glands. Interestingly, we observed that the metaplastic glands were positive for GFP, indicating that they were derived from transdifferentiation of Cre-induced chief cells. Therefore, the induction of activated Ras specifically in mature chief cells initially leads to transdifferentiation of chief cells into SPEM followed by evolution of goblet cell IM and eventual neoplastic lesions. These studies demonstrate that expression of activated Ras in Chief cells can lead to the development of the entire spectrum of metaplastic and neoplastic lineages leading to gastric cancer.