| Summary: | The gastric pathogen Helicobacter pylori is linked to gastritis, leading to gastric cancer but the mechanisms are unclear. Gastritis is characterised by remodelling of the gastric mucosa, which requires degradation of the extracellular matrix (ECM). Proteases such as matrix metalloproteinases (MMPs) and urokinase plasminogen activator (uPA), as well as proteases inhibitors such as plasminogen activator inhibitor (PAI)-1 play an important role in this process. Since members of the uPA system (namely PAI-2, uPA and its receptor, uPAR) have been shown to be increased by H pylori, it was hypothesised that PAI-1 expression is also increased in the gastric mucosa during infection, which could playa role in the tissue remodelling observed during the development of gastritis. The aim of this study was to investigate the effect of H pylori on PAI-1 expression in the gastric mucosa, to examine the consequences of this protease inhibitor on human primary gastric epithelial cell proliferation and to determine its initial contribution to gastric mucosal protection during epithelial injury. Real-time quantitative polymerase chain reaction (Q-PCR) of biopsies from gastric corpus, but not antrum, showed significantly increased PAl-1 expression in H pylori positive patients which was further increased in gastric cancer patients compared to controls. Using immunohistochemistry, it was found that H pylori significantly increased the expression of PAI-1 in primary gastric epithelial cells, particularly in the acid-secreting parietal cells. Expression of PAI-I in gastric cancer patients was also found in epithelial cells. A transgenic mouse model of gastric remodelling (INS-GAS) infected with H felis showed an increase in PAI-1 expression six months post-infection. Proliferation assays showed that both H. pylori and exogenous uPA stimulated human primary gastric epithelial cell proliferation, which was further increased after PAI-I knockdown using anti-sense oligonucleotides treatment, consistent with PAI-l inhibition of endogenous uPA. Transfection of human primary gastric epithelial cells with uPA, PAl-lor uPAR promoters, in luciferase reporter constructs, revealed expression of all three in H+, K+-ATPase- and VMAT-2-expressing cells; uPA-Iuciferase was also expressed in pepsinogen-containing cells and uPAR in TFF-l-expressing cells. In each case, expression patterns of the luciferase reporter constructs were similar to that of the endogenously expressed proteins, and all were increased in response to H. pylori. However, the virulence factor CagE was required for the stimulation ofuPA, but not PAI-lor uPAR. The production and use of uPA system transgenic. mice in an acute model of gastric mucosal injury revealed that PAI-l plays a protective role during gastric epithelial damage. Mice in which this gene is deleted displayed a more severe phenotype after challenge compared to wild-type mice, as did uPA overexpressing mice. However, this phenotype was reversed when PAI-l was overexpressed, consistent with the idea that expression of PAl-1 is vital for the restraint of uPA in order for the initial formation and stabilisation of a haemostatic fibrin plug at the site of epithelial injury to occur. Together these data indicate that the initial induction of PAI-l expreSSIOn 111 acute H. pylori infection is part of a defensive mechanism as it has been demonstrated that PAI-l plays a pivotal role in the protection of the gastric epithelium after injur y. However, PAI-l also acts to restrain uPA, therefore controlling epithelial cell proliferation which IS a key characteristic of a preneoplastic, H pylori infected epithelium. During prolonged H pylori infection it can be suggested that sustained increased levels of anti-fibrinolytic PAI-I contribute to the process of fibrosis, increased proliferation favours the acquisition of mutations which influences tissue remodelling leading to gastric cancer.
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