Response of gastric epithelial progenitors to H. pylori isolates from Swedish patients with chronic atrophic gastritis 1

Helicobacter pylori infection is associated with development of gastric adenocarcinoma in a subset of infected humans, especially those that develop an antecedent condition, chronic atrophic gastritis (ChAG) characterized by loss of acid-producing parietal cells. Studies in a gnotobiotic transgenic mouse model of ChAG, with an engineered ablation of parietal cells and an associated expansion of gastric epithelial progenitors (GEPs), have shown that a subset of GEPs is able to harbor intracellular collections of H. pylori. To better understand H. pyloris adaptation to ChAG, we sequenced the genomes of 24 isolates, obtained from 6 individuals, each sampled over a 4-year interval, as they maintained normal gastric histology, or progressed from normal histology to ChAG, or experienced worsening ChAG, or proceeded from ChAG to cancer. Analyses of gene content and single nucleotide polymorphisms (SNPs) demonstrated that H. pylori populations within study participants were largely clonal, and remarkably stable over the 4-year interval, regardless of disease state. Because they exhibited such broad inter-host variation (38.64.7 SNPs/1000bp of genome), and did not cluster according to host pathology, we sought to identify common functional properties by performing GeneChip studies of the responses of a cultured mouse gastric stem cell-like line (mGEPs) to infection with sequenced strains. The results yielded a shared 695-member set of genes differentially expressed after infection with ChAG-associated, but not normal or heat killed strains: 434 of these genes were also represented in dataset of responses to the cancer-associated strain. Ingenuity Pathway Analysis revealed that ChAG- and ChAG/cancer- associated responses were significantly enriched in genes associated with tumorigenesis in general, and gastric carcinogenesis in specific cases. Whole genome transcriptional profiling of a sequenced ChAG strain during mGEP infection disclosed a set of responses that included upregulation of hopZ, an adhesin belonging to a family of outer membrane proteins. Expression profiles of wild-type and hopZ strains revealed a number of pH-regulated genes affected by loss of HopZ, including HopP which binds sialylated glycans produced by GEPs in vivo. Genetic inactivation of hopZ produces a fitness defect in gnotobiotic transgenic mice but not their wild-type littermates. This study illustrates an approach for identifying GEP responses specific to ChAG, and bacterial genes important for survival in a gastric ecosystem that lacks parietal cells.

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Giannakis M, Bäckhed HK, Chen SL, Faith JJ, Wu M, Guruge JL, Engstrand L, Gordon JI