Die in vivo Funktion der gamma-glutamyltransferase, eines essentiellen Virulenzfaktors von Helicobacter pylori, während der Besiedlung und der Immunantwort.
Zusammenfassung der Projektergebnisse
H. pylori gGT is a virulence factor that is correlated with the development of gastric cancer and ulcers. Enzymatic gGT-activity was shown to dampen T-cell responses, to tolerize dendritic cells and to induce cell damage and inflammatory responses in gastric epithelial cells. However, the role of gGT during persistent infection has never been systematically studied. Moreover, the metabolic role of gGT for the bacterium during gastric colonization was unclear. Using a H. pylori mouse infection model, we found that gGT is important for initial colonization. Only 50% of mice were successfully infected with the gGT-deficient mutant and bacterial loads in infected animals were significantly reduced at the beginning of the infection. However, bacterial loads adapted over time and after 1 month of infection no difference between mice infected with H. pylori wt or ∆ggt was observed anymore. We confirmed that gGT is important for acid survival at low pH in conditions similar to the human stomach,which at least in part, can be explained by a reduced urease activity in the absence of gGT. GGT-deficient H. pylori profited from an elevated pH in the murine stomach indicating that an impaired acid survival is one explanation for the initial colonization difference. A comparison of the proteome of gGT-deficient strains before and after infection revealed that all gGT-deficient re-isolates compensate for the loss of the enzyme and maintain some of these compensatory mechanisms during infection. An increased expression of ammonium producing enzymes, of flagellar proteins, of adhesion factors, metabolite transporters and nucleic acid modifying proteins was detected in the gGT-deficient strains. An enhanced motility, adhesion, and activity of the enzymes AmiF and AmiE was confirmed in further experiments. Moreover, iron acquisition was hampered without gGT and is compensated by a higher expression of iron uptake proteins. During infection H. pylori gGT induces a strong innate immune response that is characterized by neutrophil infiltration and production of cytokines and chemokines associated with the innate immune response. The T-helper cell response is similar in the presence or absence of gGT. But CD8 T-cell infiltration is strongly reduced in the absence of gGT. Feeding additional glutamine to mice revealed that CD8 T-cells infiltrate the infected tissue in a glutaminedependent manner. More CD8 T-cells were found in human tissue infected with H. pylori strains with a high gGT-activity. Moreover, glutamine supplementation reverted the gGT-induced production of pro-inflammatory cytokines and chemokines. Taken together, our results confirm a central function of H. pylori gGT in the metabolism of the bacterium and during the host`s immune response to the infection.
