Summary

Haute résolution microscopie électronique de la<em> Helicobacter pylori</em> Cag sécrétion de type IV Système Pili Produit dans différentes conditions de Fer Disponibilité

Published: November 21, 2014
doi:

Summary

Here we describe a method to visualize the oncogenic bacterial organelle known as the Cag Type IV Secretion System (Cag-T4SS). We find that the Cag-T4SS is differentially produced on the surface of H. pylori in response to varying conditions of iron availability.

Abstract

Helicobacter pylori is a helical-shaped, gram negative bacterium that colonizes the human gastric niche of half of the human population1,2. H. pylori is the primary cause of gastric cancer, the second leading cause of cancer-related deaths worldwide3. One virulence factor that has been associated with increased risk of gastric disease is the Cag-pathogenicity island, a 40-kb region within the chromosome of H. pylori that encodes a type IV secretion system and the cognate effector molecule, CagA4,5. The Cag-T4SS is responsible for translocating CagA and peptidoglycan into host epithelial cells5,6. The activity of the Cag-T4SS results in numerous changes in host cell biology including upregulation of cytokine expression, activation of proinflammatory pathways, cytoskeletal remodeling, and induction of oncogenic cell-signaling networks5-8. The Cag-T4SS is a macromolecular machine comprised of sub-assembly components spanning the inner and outer membrane and extending outward from the cell into the extracellular space. The extracellular portion of the Cag-T4SS is referred to as the “pilus”5. Numerous studies have demonstrated that the Cag-T4SS pili are formed at the host-pathogen interface9,10. However, the environmental features that regulate the biogenesis of this important organelle remain largely obscure. Recently, we reported that conditions of low iron availability increased the Cag-T4SS activity and pilus biogenesis. Here we present an optimized protocol to grow H. pylori in varying conditions of iron availability prior to co-culture with human gastric epithelial cells. Further, we present the comprehensive protocol for visualization of the hyper-piliated phenotype exhibited in iron restricted conditions by high resolution scanning electron microscopy analyses.

Introduction

H. pylori infection is a significant risk factor for gastric cancer1. However, disease outcomes vary and depend on numerous factors such as host genetics, genetic diversity of H. pylori strains, and environmental elements such as host diet11. Previous reports have established that a correlation exists between H. pylori infection, iron deficiency (as measured by decreased blood ferritin and hemoglobin concentrations), and increased proinflammatory cytokine production, including IL-8 secretion, which ultimately leads to increased gastric disease progression12. Acute H. pylori infection is also associated with hypochlorhydria which impairs the host’s ability to absorb nutrient iron, and ultimately leads to changes in iron homeostasis13. These clinical findings suggest that iron availability within the gastic niche could be an important factor in disease outcome. In fact, animal models of H. pylori infection have demonstrated that low dietary iron consumption exacerbates gastric disease14. The reduced iron levels in these animals necessitate that H. pylori induce an iron-acquisition response in order to obtain the iron needed for bacterial replication. H. pylori has the capacity to perturb iron trafficking within host cells to facilitate bacterial replication in a CagA-dependent fashion15. Interestingly, the cag-pathogenicity island has been shown to be regulated by the iron-responsive transcription factor Fur16,17. Furthermore, Cag+ strains are associated with increased inflammation and gastric diseases such as cancer1. These findings support a model whereby H. pylori alters Cag-T4SS expression in an effort to obtain iron from host cells that reside in an iron deplete environment resulting in exacerbated disease outcomes.

Two factors that increase inflammation and morbidity are Cag expression and low dietary iron intake. These facts support the hypothesis that reduced iron availability increases the production of Cag-T4SS pili at the host pathogen interface resulting in worse gastric disease11-14. The goal of the method provided in this manuscript is to establish the role of the micronutrient iron in the regulation of the Cag-T4SS pilus biogenesis. In previous work, we utilized two approaches to observe an iron-dependent increase in Cag-T4SS expression. First, output strains from animals maintained on high and low iron diets were analyzed and revealed that low-iron diet output strains produced more Cag-T4SS pili than high-iron diet strains14. Second, growing the H. pylori 7.13 strain in vitro in iron replete conditions resulted in reduced pili formation while cells grown in the presence of an iron chelator produced significantly more pili.

We have continued to investigate the iron-dependent regulation of Cag-T4SS pili phenotype and offer the following optimized protocol and representative results performed with an additional Helicobacter pylori strain, PMSS1. The rationale behind the development of this technique was to correlate increased Cag-T4SS activity in conditions of iron-limitation with increased Cag-T4SS pilus formation. The broader implication and use of this technique will provide optimized culture conditions that result in elevated production of the Cag-T4SS pili. This assay will be useful to researchers seeking to determine the composition and architecture of the Cag-T4SS by enriching for this important bacterial surface feature. The sample preparation and visualization by field-emission gun electron microscopy has numerous advantages over alternative techniques such as light-microscopy methods to visualize the Cag-T4SS and will be appropriate to investigators interested in studying the regulation of this organelle10.

Protocol

1. H. pylori croissance dans différentes conditions de Fer Disponibilité et co-culture avec des cellules humaines épithéliales gastriques Sélectionnez H. pylori souche PMSS1 pour ces études car il a une île de pathogénicité cag intact et exprime un système IV de sécrétion de type fonctionnement. Utiliser également un mutant de la cage isogéniques (PMSSI Δ cage) comme contrôle négatif. Cultiver les bactéries sur des plaques de TSA complétées avec…

Representative Results

Dans ce rapport, nous avons démontré que les conditions de disponibilité est variable de fer ont la capacité de moduler H. pylori Cag-T4SS pili biogenèse à l'interface hôte-pathogène. Lorsqu'elle est cultivée dans le milieu seul, H. pylori constitue un moyen de pili 3 / cellule. Lorsque H. pylori est cultivé en fer épuiser conditions (à l'aide du chélateur dipyridyle synthétique) qui sont sous-inhibitrice pour la croissance des bactéries (Figure 1), …

Discussion

Le fer est un oligo-élément essentiel pour la plupart des formes de vie, y compris les bactéries pathogènes. Dans un effort pour limiter la viabilité des micro-organismes envahisseurs, les hôtes vertébrés séquestrent fer éléments nutritifs dans un processus connu sous le nom "immunité nutritionnelle» 18. En réponse à cela, les bactéries pathogènes ont évolué à utiliser le fer comme une molécule de signalisation mondiale de sentir leur environnement et de réglementer l'élaborati…

Disclosures

The authors have nothing to disclose.

Acknowledgements

This research was supported by the Department of Veterans Affairs Career Development Award 1IK2BX001701 and the CTSA award UL1TR000445 from the National Center for Advancing Translational Sciences. Its contents are solely the responsibility of the authors and do not necessarily represent official views of the National Center for Advancing Translational Sciences or the National Institutes of Health. Scanning electron microscopy experiments were performed in part through the use of the VUMC Cell Imaging Shared Resource, supported by NIH grants CA68485, DK20593, DK58404, DK59637 and EY08126.

Materials

Name of Material/ Equipment Company Catalog Number
Modified brucella broth
Peptone from casein (10g/L) Sigma 70172
Peptic digest of animal tissue (10g/L) Sigma 70174
Yeast extract (2g/L) Sigma 92144
Dextrose (1g/L) Sigma D9434
Sodium chloride (5g/L) Thermo Fisher S271-10
Cholesterol (250X) (4mL/L) Life Technologies 12531018
Ferric chloride (100 or 250 uM) Sigma 157740-100G
Dipyridyl (200 uM) Sigma D216305-100G
Modified RPMI
RPMI+HEPES (1X) Life Technologies 22400-121
Fetal bovine serum (100 mL/L) Life Technologies 10438-026
Electron Microscopy Preparation
Paraformaldehyde (2.0% aqueous) Electron Microscopy Sciences 15713
Gluteraldehyde (2.5% aqueous) Electron Microscopy Sciences 16220
Sodium cacodylate (0.05 M) Electron Microscopy Sciences 12300
Osmium tetroxide (0.1% aqueous) Electron Microscopy Sciences 19150
Ethanol (absolute) Sigma E7023
Colloidal silver paint Electron Microscopy Sciences 12630
SEM sample stubs Electron Microscopy Sciences 75220
Coverslips Thermo Fisher 08-774-383
IL-8 Secretion Evaluation
Quantikine IL-8 ELISA kit R&D Systems D8000C

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Cite This Article
Haley, K. P., Blanz, E. J., Gaddy, J. A. High Resolution Electron Microscopy of the Helicobacter pylori Cag Type IV Secretion System Pili Produced in Varying Conditions of Iron Availability. J. Vis. Exp. (93), e52122, doi:10.3791/52122 (2014).

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