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Iron influences the expression of Helicobacter pylori outer membrane vesicle-associated virulence factors
1Department of Surgery, Christchurch School of Medicine, New Zealand. jacqui.keenan@chmeds.ac.nz
Background:
Helicobacter pylori shed outer membrane vesicles (OMV) in vitro and in vivo. These OMV, which contain active VacA, provide a potential vehicle for the delivery of H. pylori virulence factors to the gastric mucosa.
Objective:
To assess the influence of environmental iron levels on H. pylori OMV VacA and protease expression in vitro.
Methods:
Three well-characterized H. pylori type-strains were grown for 72 h under normal (Brucella broth, 5% fetal calf serum) and iron-limiting (Brucella broth, 5% fetal calf serum, 50 micromol/l deferoxamine) conditions. Following harvesting by differential centrifugation, the ratio of whole cells to OMV was determined. OMV VacA levels in response to iron availability were determined by ELISA and immunolabelling of washed bacteria. Protease activity was detected by zymography of OMV in the presence and absence of enzyme inhibitors and activators. HEp-2 cells were used to assay for OMV-associated cytopathogenic toxins.
Results:
Decreased iron availability, which limited bacterial growth but not OMV release, also influenced the expression of OMV-associated virulence factors. VacA levels were reduced, whereas two new proteolytic enzymes were expressed on these OMV. When an iron salt was added to counteract the effect of the deferoxamine, VacA levels were restored in the outer membrane and the proteolytic activity disappeared.
Conclusions:
These results suggest that OMV release by H. pylori is influenced by environmental iron levels, and that the qualitative changes that occur in outer membrane composition may contribute to the clinical patterns of H. pylori-associated disease.
Insights
Environmental iron levels impact Helicobacter pylori outer membrane vesicles (OMV). Lower iron reduces VacA but increases protease expression on OMV, potentially influencing disease. Supplementing iron restores VacA and removes proteases.
Area of Science:
- Microbiology
- Molecular Biology
- Pathogenesis
Background:
- Helicobacter pylori releases outer membrane vesicles (OMV) containing virulence factors like VacA.
- These OMV are implicated in delivering bacterial toxins to the gastric mucosa.
Purpose of the Study:
- To investigate how environmental iron availability affects the expression of VacA and proteases in H. pylori OMV.
- To understand the role of iron in modulating bacterial virulence factor delivery via OMV.
Main Methods:
- H. pylori strains were cultured under normal and iron-limiting conditions.
- OMV were isolated, and VacA levels were quantified using ELISA and immunolabelling.
- Protease activity in OMV was assessed by zymography.
- Cytotoxicity assays were performed on HEp-2 cells.
Main Results:
- Reduced iron availability decreased bacterial growth but not OMV production.
- VacA levels in OMV were lower under iron limitation, while two new proteases were detected.
- Restoring iron levels reversed these changes, increasing VacA and eliminating protease activity.
Conclusions:
- Environmental iron significantly influences H. pylori OMV composition and virulence factor expression.
- Changes in OMV content due to iron availability may contribute to the varied clinical presentations of H. pylori infections.