Helicobacter pylori infection stimulates intestinalization of endocrine cells in glandular stomach of Mongolian gerbils

Diversity in bacterium-host interactions within the species Helicobacter heilmannii sensu stricto

Helicobacter (H.) heilmannii sensu stricto (s.s.) is a zoonotic bacterium that naturally colonizes the stomach of dogs and cats. In humans, this microorganism has been associated with gastritis, peptic ulcer disease and mucosa associated lymphoid tissue (MALT) lymphoma. Little information is available about the pathogenesis of H. heilmannii s.s. infections in humans and it is unknown whether differences in virulence exist within this species. Therefore, a Mongolian gerbil model was used to study bacterium-host interactions of 9 H. heilmannii s.s. strains. The colonization ability of the strains, the intensity of gastritis and gene expression of various inflammatory cytokines in the stomach were determined at 9 weeks after experimental infection. The induction of an antrum-dominant chronic active gastritis with formation of lymphocytic aggregates was shown for 7 strains. High-level antral colonization was seen for 4 strains, while colonization of 4 other strains was more restricted and one strain was not detected in the stomach at 9 weeks post infection. All strains inducing a chronic active gastritis caused an up-regulation of the pro-inflammatory cytokine IL-1β in the antrum. A reduced antral expression of H⁺/K⁺ ATPase was seen in the stomach after infection with 3 highly colonizing strains and 2 highly colonizing strains caused an increased gastrin expression in the fundus. In none of the H. heilmannii s.s.-infected groups, IFN-γ expression was up-regulated. This study demonstrates diversity in bacterium-host interactions within the species H. heilmannii s.s. and that the pathogenesis of gastric infections with this microorganism is not identical to that of an H. pylori infection.

Helicobacter pylori induces malignant transformation of gastric epithelial cells in vitro

Epidemiologic studies have demonstrated that Helicobacter pylori infection is associated with increased risk for the development of gastric cancer. Animal studies have also shown that H. pylori infection leads to gastric carcinogenesis, especially intestinal phenotypes. However, no in vitro study has been carried out for cell transformation induced by H. pylori. The present study aimed to investigate whether 'chronic'H. pylori infection induces gastric epithelial cell transformation, and elucidate the underlying mechanisms of transformation induced by H. pylori. The immortalized 'normal' gastric epithelial cell line, GES-1, was co-cultured for 45 days with H. pylori strains B975 and L301. The cell proliferation was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, Ki-67 antigen, and colony formation assay. The cell transformation was determined by observing cell morphology and measuring the expression of E-cadherin, β-catenin, and transcription factor-4 (TCF-4) at both protein and mRNA levels. H. pylori induced morphologic changes in GES-1 cells and significantly increased the proliferation of GES-1 cells. Moreover, H. pylori up-regulated the expression of β-catenin and TCF-4, and also induced the nuclear accumulation of β-catenin. In addition, the diffusive gastric cancer-related gene, E-cadherin, was up-regulated at the protein level, but down-regulated at the mRNA level. H. pylori infection is capable of inducing GES-1 transformation to present with the characteristics of intestinal-type gastric cancers in vitro, likely through the β-catenin/TCF-4 signaling pathway.

Animal models to study the role of long-term hypergastrinemia in gastric carcinogenesis

Patients with chronic hypergastrinemia due to chronic atrophic gastritis or gastrinomas have an increased risk of developing gastric malignancy, and it has been questioned whether also patients with hypergastrinemia caused by long-term use of acid inhibiting drugs are at risk. Gastric carcinogenesis in humans is affected by numerous factors and progresses slowly over years. When using animal models with the possibility of intervention, a complex process can be dissected by studying the role of hypergastrinemia in carcinogenesis within a relatively short period of time. We have reviewed findings from relevant models where gastric changes in animal models of long-term hypergastrinemia have been investigated. In all species where long-term hypergastrinemia has been induced, there is an increased risk of gastric malignancy. There is evidence that hypergastrinemia is a common causative factor in carcinogenesis in the oxyntic mucosa, while other cofactors may vary in the different models.

In vitro differentiation of Runx3-/- p53-/- gastric epithelial cells into intestinal type cells

We have reported that a lack of RUNX3 function is causally associated with gastric carcinogenesis. We have also presented evidence that loss of Runx3 may be related to the genesis of intestinal metaplasia because expression of RUNX3 is reduced in some intestinal metaplasias, and some Runx3(-/-)p53(-/-) gastric epithelial cells differentiate into intestinal type cells in vivo. Recently several reports have indicated that blood cells play important roles in the gastric carcinogenesis. In the present study, we therefore examined whether Runx3(-/-)p53(-/-) gastric epithelial cells differentiate autonomously into intestinal type cells, or whether the presence of other cells is necessary for the differentiation in vitro. When Runx3(-/-)p53(-/-) gastric epithelial cells were cultured with collagen gels, they did not exhibit any morphogenesis and differentiated poorly. When cultured with fetal mouse gastric mesenchymes, the cells formed glandular structures and differentiated into surface mucous cells, but differentiation of intestinal type cells was never observed. When cultured with Matrigel, the cells formed glandular structures, and some cells differentiated into intestinal type cells in vitro. Reverse transcription-polymerase chain reaction analysis showed that the cells expressed stomach-specific genes, and their levels decreased gradually during the culture. The cells expressed some intestine-specific genes weakly at the start of culture, and their levels were increased with time in culture. We therefore conclude that Runx3(-/-)p53(-/-) gastric epithelial cells differentiate into intestinal type cells in combination with Matrigel in the absence of other cell types. Extracellular matrix, not blood cells, may play a role in the genesis of intestinal metaplasia.