Matrix metalloproteinases in Helicobacter inducedgastritis
Abstract: Helicobacter pylori infects the stomach and areas of gastric metaplasia in the duodenum. Theinfection leads to peptic ulcers or gastric cancers in 10-20% of infected individuals, while themajority are more or less asymptomatic. However, active chronic gastritis develops in all infectedindividuals, often in association with atrophic gastritis. Matrix metalloproteinases (MMPs) are afamily of proteases that have been shown to be important in the pathogenesis of a range ofinflammatory diseases and bacterial infections. MMPs are also required for many normalfunctions, ranging from tissue remodeling, cell migration, diapedesis and wound healing.The aim of this thesis was to elucidate the possible role of MMPs, and their specific inhibitorsthe tissue inhibitors of matrix metalloproteinases (TIMPs), during H. pylori associated gastritis.To this end methods were established to examine MMP and TIMP production in small biopsiesfrom human volunteers, following in vitro stimulations with H. pylori of cells isolated from thegastric mucosa and blood, and finally during acute gastritis in a murine Helicobacter felis infectionmodel.Using these methods we demonstrated a large, on average 19-fold, increase of MMP-9 in theantrum of H. pylori infected volunteers, compared to the uninfected. We also found acorresponding, although smaller, 3-fold increase in MMP-2. In parallel to the protein increase wefound a 12-fold increase in the generation of MMP-9 mRNA in the infected individuals. Incontrast, there was no difference in the levels of TIMP-1 or -2 between the groups. Usingimmunohistochemistry we also found a 3-fold increase in tissue resident macrophages in theantrum of the infected individuals, compared to the uninfected volunteers, andimmunofluorescence co-localised MMP-9 to these tissue resident macrophages. Furthermore,stimulation of isolated macrophages from gastric tissue indicated that they were capable ofresponding to H. pylori to produce MMP-9.In vitro stimulation of monocyte derived macrophages indicated that both live H. pylori andpurified protein factors were capable of inducing increased MMP-9 secretion from macrophages.As several protein factors could induce this secretion, there was no significant difference betweenany strains used, independent of their individual expression of H. pylori virulence factors. Indeed,inhibition experiments showed that several different, independent, pathways contributed to theH. pylori induced MMP-9 secretion.We then used H. felis infected mice to study the acute response to Helicobacter infection, andshowed that MMP-9 increased only a few days after infection, before any cell influx. MMP-9levels then continued to increase as new cells entered the lamina propria. As the number ofmacrophages in the tissue rose so did the amount of MMP-9. Using MMP-9 knockout mice weappeared to delay the onset of gastritis slightly.In conclusion, our results show that MMP-9 is strongly associated with H. pylori induced gastritis.MMP-9 is present immediately before the initial influx of inflammatory cells, and the levelscontinue to rise as the gastritis increases. The majority of gastric MMP-9 is likely to come frommacrophages, although there may be some component from other cell types. The MMP-9 islikely to help cells getting into the tissue, and at late stages of disease to be involved in the localtissue damage.
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