Helicobacter pylori Type IV Secretion System and Its Adhesin Subunit, CagL, Mediate Potent Inflammatory Responses in Primary Human Endothelial Cells.

Mona Tafreshi,Rebecca J Gorrell,Elizabeth M Davies,Manfred Rohde,Jyeswei Guan,Roger J Daly,Nicole Chew,Virginie Deswaerte,Terry Kwok,Brendan J Jenkins,Yue Xin,Richard M Peek

doi:10.3389/fcimb.2018.00022

Abstract

The Gram-negative bacterium, Helicobacter pylori, causes chronic gastritis, peptic ulcers, and gastric cancer in humans. Although the gastric epithelium is the primary site of H. pylori colonization, H. pylori can gain access to deeper tissues. Concurring with this notion, H. pylori has been found in the vicinity of endothelial cells in gastric submucosa. Endothelial cells play crucial roles in innate immune response, wound healing and tumorigenesis. This study examines the molecular mechanisms by which H. pylori interacts with and triggers inflammatory responses in endothelial cells. We observed that H. pylori infection of primary human endothelial cells stimulated secretion of the key inflammatory cytokines, interleukin-6 (IL-6) and interleukin-8 (IL-8). In particular, IL-8, a potent chemokine and angiogenic factor, was secreted by H. pylori-infected endothelial cells to levels ~10- to 20-fold higher than that typically observed in H. pylori-infected gastric epithelial cells. These inflammatory responses were triggered by the H. pylori type IV secretion system (T4SS) and the T4SS-associated adhesin CagL, but not the translocation substrate CagA. Moreover, in contrast to integrin α5β1 playing an essential role in IL-8 induction by H. pylori upon infection of gastric epithelial cells, both integrin α5β1 and integrin αvβ3 were dispensable for IL-8 induction in H. pylori-infected endothelial cells. However, epidermal growth factor receptor (EGFR) is crucial for mediating the potent H. pylori-induced IL-8 response in endothelial cells. This study reveals a novel mechanism by which the H. pylori T4SS and its adhesin subunit, CagL, may contribute to H. pylori pathogenesis by stimulating the endothelial innate immune responses, while highlighting EGFR as a potential therapeutic target for controlling H. pylori-induced inflammation.

Highlights

The microaerophilic Gram-negative bacterium, Helicobacter pylori, causes chronic gastritis, peptic ulcers, and gastric cancer in humans (Kusters et al, 2006)
After 24 h of stimulation by H. pylori, the level of IL-8 secreted by the endothelial cell line EA.Hy926 was more than double that observed with a gastric epithelial cell line (AGS) (Figure 1A)
This marked response was even more pronounced with the primary endothelial cells HUVECs (Figure 1A). These levels of IL-8 induction observed in H. pylori-infected endothelial cells at multiplicities of infection (MOI) of 1 are similar to or even higher than that previously observed with H. pylori infection of primary human gastric epithelial cells at MOI of 100 (Fischer, 2011; Mustapha et al, 2014)

Summary

Introduction

The microaerophilic Gram-negative bacterium, Helicobacter pylori, causes chronic gastritis, peptic ulcers, and gastric cancer in humans (Kusters et al, 2006). Almost all individuals infected by H. pylori develop active chronic inflammation in the stomach, characterized by infiltration of neutrophils and macrophages into the gastric mucosa (Sipponen, 1993). This inflammation is driven by various cytokines and chemokines secreted during H. pylori infection, including interleukin-1β, tumor necrosis factor alpha (TNF-α), IL-8, and IL-6. Upon H. pylori infection of gastric epithelial cells, the cag T4SS stimulates IL-8 release via a multipronged mechanism that involves both the T4SS translocation substrate, CagA, and the putative T4SS adhesin and minor pilin, CagL (Gorrell et al, 2013). The cag T4SS has been shown to contribute to IL-6 induction in gastric epithelial cells infected with H. pylori (Lu et al, 2005), but the corresponding roles of CagL and CagA remain to be examined

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Conclusion