Mechanisms and consequences of cytoskeletal control of Helicobacter pylori cell shape

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PROJECT SUMMARY/ABSTRACT Helicobacter pylori is a helical-shaped Gram-negative pathogen for which the only known niche is the human stomach. H. pylori infects 50% of the world’s population and causes chronic gastritis, which can progress to gastric cancers, or ulcers in a subset of patients [1]. How exactly H. pylori causes severe disease is not fully understood, but in general it occurs through eliciting inflammation. The bacterium’s helical cell shape is essential for multiple facets of early infection; helical strains of H. pylori more robustly colonize mice during acute (one week) infections than non-helical mutants that lack cell shape genes (curved or rod cells) [2-5]. Helical cell shape may promote colonization of the viscous mucous layer of the stomach through a corkscrewing mechanism [6] which allows H. pylori to reach the epithelium and colonize the epithelial surface [7]. Furthermore, additional evidence from mouse models suggests that in chronic infections (one or three months), helical H. pylori elicit higher levels of inflammation and hyperplasia than non-helical mutant strains [5]. How helical cell shape is determined and how it promotes colonization and inflammation of the stomach are two questions essential to our understanding of how H. pylori causes disease. Multiple proteins that are required for helical cell shape in H. pylori have been identified and proposed to form a “shapesome” complex that determines helical cell shape [2- 4, 8]. The hypothesis of this project is that the helical shape of H. pylori contributes to H. pylori’s ability to traverse the mucous layer and interact with the gastric mucosa to induce inflammation and is controlled by the “shapesome” which the cytoskeletal protein CcmA stabilizes and localizes to the inner membrane of H. pylori. The following aims will test this hypothesis: Aim 1 will characterize how each domain of CcmA contributes to polymerization and proper localization of CcmA, Aim 2 will determine whether proper intracellular localization of CcmA is modulated by its interaction partners and whether these interactions are impacted by cell shape-altering point mutations in CcmA, and Aim 3 will investigate whether localization to the epithelium through the mucous layer is impacted by alterations of helical parameters of H. pylori cells. This project will leverage advanced microscopy and organoid culture techniques to inform our understanding of how helical cell shape in H. pylori is determined and how helical cell shape impacts interactions with the gastric epithelium. The research fits the mission of the NIAID by providing knowledge that could advance the development of anti-virulence therapies for H. pylori infection considering clinical isolates of H. pylori increasingly show antibiotic resistance [13-15]. Additionally, this work will enhance understanding of how perturbation of helical cell shape impacts pathogenicity of H. pylori and could be applied to other helical rod-shaped gastrointestinal pathogens.