Beyond Vacuolation: Helicobacter Pylori Vaca Toxin Activity In Vitro and In Vivo

Abstract

Colonization of the human stomach with Helicobacter pylori strains producing active forms of a secreted toxin, VacA, is associated with an increased risk of peptic ulcer disease and gastric cancer compared to colonization with strains producing hypoactive forms of VacA. The goals of my project were to define cellular metabolic consequences of VacA intoxication and define consequences of VacA activity in vivo. Untargeted metabolomics analyses revealed that several hundred metabolites were significantly altered in VacA-treated gastroduodenal cells (AGS and AZ-521) compared with control cells. Pathway analysis indicated that VacA caused alterations in numerous metabolic pathways, including taurine and hypotaurine metabolism, purine metabolism, pyrimidine metabolism, and alanine, aspartate, and glutamate metabolism. Supplementation of the tissue culture medium with taurine or hypotaurine protected AZ-521 cells against VacA-induced cell death. Treatment of cells with purified active s1m1 forms of VacA, but not hypoactive s2m1 or Δ6-27 VacA-mutant proteins (defective in membrane channel formation), caused reductions in intracellular taurine and hypotaurine concentrations. VacA treatment also resulted in increased levels of lysophospholipids within cells and the release of lysophospholipids into the extracellular space. Comparative studies of an H. pylori wild-type strain and a vacA insertion mutant in the Mongolian gerbil model did not reveal significant differences in gastric colonization or gastric inflammation. However, detected numerous VacA-dependent metabolic changes in gastric tissues. These discoveries, described in my thesis, provide new insights into the effects of VacA on gastric epithelial cells and the gastric environment.