Matrix metalloproteinase-7 and premalignant host responses in Helicobacter pylori-infected mice

Abstract

Helicobacter pylori-induced gastritis is the strongest singular risk factor for gastric adenocarcinoma. Matrix metalloproteinase-7 (MMP-7) is a proteolytic enzyme that can modify the intestinal microbial replicative niche as well as affect tumorigenesis, and H. pylori stimulates expression of MMP-7 in gastric epithelial cells in vitro. Utilizing a transgenic murine model of H. pylori-mediated injury, our experiments now show that gastric inflammation is increased within the context of MMP-7 deficiency, which involves both Th1- and Th17-mediated pathways. Enhanced gastritis in H. pylori-infected mmp-7-/- mice is strongly linked to accelerated epithelial cellular turnover. However, more severe inflammation and heightened proliferation and apoptosis are not dependent on MMP-7-mediated bacterial eradication. Collectively, these studies indicate that H. pylori-mediated induction of MMP-7 may serve to protect the gastric mucosa from pathophysiologic processes that promote carcinogenesis.

Figure 1. Infection of wild-type mice with H. pylori increases MMP-7 expression while MMP-7 deficiency augments H. pylori-mediated inflammation

Wild-type mice were inoculated with Brucella broth (broth control, Panel A) or H. pylori (Panel B). Twelve weeks post-infection, stomachs were analyzed for MMP-7 expression by immunohistochemistry. Arrows indicate MMP-7. 400× magnification. Panels C, D: acute and chronic inflammatory scores for H. pylori-infected mice. Data are shown as vertical scatterplots with mean values. +/+, wild-type; −/−, mmp-7^−/−. A=antrum, C=corpus. *, P≤0.05; **, P≤0.01 mmp-7^−/− versus wild-type. For 3 mmp-7^−/− mice infected with H. pylori for 12 weeks, antral tissues were not available for pathologic evaluation.

Figure 2. H. pylori challenge of mmp-7^−/− mice results in enhanced inflammation

Representative images of H&E stained sections from antrum (A, C) and corpus (B, D) of wild-type (A, B) and mmp-7^−/− mice (C, D) infected for 12 weeks. +/+, wild-type; −/−, mmp-7^−/−. 100× magnification.

Figure 3. MMP-7 deficiency augments T and B cell responses to H. pylori independent of colonization density

Panel A) Immunohistochemical analysis for T cells and B cells was performed on sections from all mice infected for 36 weeks. Data represent the average number of cells per high-powered field in corpus plus antrum for each mouse. *, P<0.05; **, P<0.01 infected mmp-7^−/− versus wild-type. Panel B) Comparison of IFN-γ, IL-17, and IL-10 mRNA levels in gastric tissue harvested from wild-type or mmp-7^−/− mice infected with H. pylori for 36 weeks. Results are normalized to cytokine levels in uninfected wild-type mice. **, P<0.01; ***, P<0.001 infected versus uninfected wild-type. §, P<0.05; §§, P<0.01 infected mmp-7^−/− versus infected wild-type. Panel C) Immunohistochemical analysis for H. pylori was performed on sections from mice infected for 12 and 36 weeks and colonization density was scored on an ordinal scale from 0 to 4. +/+, wild-type; −/−, mmp-7^−/−. For one mmp-7^−/− mouse infected for 36 weeks, tissue was not available for analysis.

Figure 4. H. pylori challenge of mmp-7^−/− mice increases levels of cellular turnover

Representative images of anti-Ki67 (A) or anti-active caspase-3 (C) staining in H. pylori-infected wild-type and mmp-7^−/− mice. The percentage of cells positive for Ki67 (B) or active caspase-3 (D) was calculated for 10 high-powered fields for each mouse. The average of these 10 fields is represented by a single dot in the vertical scatterplot. +/+, wild-type; −/−, mmp-7^−/−. ***, P<0.001; ****, P<0.0001 infected mmp-7^−/− versus infected wild-type; ##, P<0.01; ###, P<0.001; ####, P<0.0001 infected mmp-7^−/− versus uninfected mmp-7^−/−. Bar, 100 μM. 400× magnification.