Helicobacter Pylori Urease Induces Pro-inflammatory Effects and Differentiation of Human Endothelial Cells: Cellular and Molecular Mechanism

Background: Helicobacter pylori urease (HPU) is a key virulence factor that enables bacteria to colonize and survive in the stomach. We early demonstrated that HPU, independent of its catalytic activity, induced inflammatory and angiogenic responses in vivo and directly activated human neutrophils to produce reactive oxygen species (ROS). We have investigated the effects of HPU on endothelial cells, focusing on the signaling mechanism involved.

Methods: Monolayers of human microvascular endothelial cells (HMEC-1) were stimulated with HPU (up to 10 nmol/L): Paracellular permeability was accessed through dextran-FITC passage. NO and ROS production was evaluated using intracellular probes. Proteins or mRNA expressions were detected by Western blotting and fluorescence microscopy or qPCR assays, respectively.

Results: Treatment with HPU enhanced paracellular permeability of HMEC-1, preceded by VE-cadherin phosphorylation and its dissociation from cell-cell junctions. This caused profound alterations in actin cytoskeleton dynamics and focal adhesion kinase (FAK) phosphorylation. HPU triggered ROS and nitric oxide (NO) production by endothelial cells. Increased intracellular ROS resulted in nuclear factor kappa B (NF-κB) activation and upregulated expression of cyclooxygenase-2 (COX-2), hemeoxygenase-1 (HO-1), interleukin-1β (IL-1β), and intercellular adhesion molecule-1 (ICAM-1). Higher ICAM-1 and E-selectin expression was associated with increased neutrophil adhesion on HPU-stimulated HMEC monolayers. The effects of HPU on endothelial cells were dependent on ROS production and lipoxygenase pathway activation, being inhibited by esculetin. Additionally, HPU improved vascular endothelial growth factor receptor 2 (VEGFR-2) expression.

Conclusion: The data suggest that the pro-inflammatory properties of HPU drive endothelial cell to a ROS-dependent program of differentiation that contributes to the progression of H pylori infection.