Alta resolução de Microscopia Eletrônica da<em> Helicobacter pylori</em> Cag Tipo IV Secreção Sistema Pili Produzido em diferentes condições de Ferro Disponibilidade

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 Fur^16,17. 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 disease^11-14. 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.