The Impact of Helicobacter pylori Urease upon Platelets and Consequent Contributions to Inflammation

Abstract

Gastric infection by Helicobacter pylori is considered a risk factor for gastric and duodenal cancer, and extragastric diseases. Previous data have shown that, in a non-enzymatic way, H. pylori urease (HPU) activates neutrophils to produce ROS and also induces platelet aggregation, requiring ADP secretion modulated by the 12-lipoxygenase pathway, a signaling cascade also triggered by the physiological agonist collagen. Here we investigated further the effects on platelets of recombinant versions of the holoenzyme HPU, and of its two subunits (HpUreA and HpUreB). Although HpUreA had no aggregating activity on platelets, it partially inhibited collagen-induced aggregation. HpUreB induced platelet aggregation in the nanomolar range, and also interfered dose-dependently on both collagen- and ADP-induced platelet aggregation. HPU-induced platelet aggregation was inhibited by antibodies against glycoprotein VI (GPVI), the main collagen receptor in platelets. Flow cytometry analysis revealed exposure of P-selectin in HPU-activated platelets. Anti-glycoprotein IIbIIIa (GPIIbIIIa) antibodies increased the binding of FITC-labeled HPU to activated platelets, whereas anti-GPVI did not. Evaluation of post-transcriptional events in HPU-activated platelets revealed modifications in the pre-mRNA processing of pro-inflammatory proteins, with increased levels of mRNAs encoding IL-1β and CD14. We concluded that HPU activates platelets probably through its HpUreB subunit. Activation of platelets by HPU turns these cells into a pro-inflammatory phenotype. Altogether, our data suggest that H. pylori urease, besides allowing bacterial survival within the gastric mucosa, may have an important, and so far overlooked, role in gastric inflammation mediated by urease-activated neutrophils and platelets.

Platelet TLR4 at the crossroads of thrombosis and the innate immune response

“…Therefore, if platelet activation triggered by LPS is performed in washed platelets, the addition of plasma or serum (containing microgram levels of soluble CD14) or recombinant CD14 is required. Interestingly, it was recently demonstrated that Helicobacter pylori urease (HPU) activates platelets and also increases the levels of mRNA encoding IL‐1β and CD14 . This finding may be crucial to explaining platelet activation during sepsis, as it indicates that although CD14 is not present under physiologic conditions, it can be up‐regulated during infection.…”

Helicobacter pylori urease induces pro‐inflammatory effects and differentiation of human endothelial cells: Cellular and molecular mechanism

“…Nevertheless, recent evidences have highlighted pathophysiologic properties of HPU unrelated to its ureolytic activity. We have previously reported that non‐catalytic HPU has pro‐inflammatory activity in mice and activates host cells, inducing blood platelet aggregation, chemotaxis, and ROS production by human neutrophils . More recently, it was demonstrated that HPU was internalized by epithelial gastric cells, triggering the expression of pro‐angiogenic mediators, and induced angiogenesis in vivo in the chicken chorioallantoic membrane model .…”

“…We have previously reported that non-catalytic HPU has pro-inflammatory activity in mice and activates host cells, inducing blood platelet aggregation, chemotaxis, and ROS production by human neutrophils. [11][12][13] More recently, it was demonstrated that HPU was internalized by epithelial gastric cells, triggering the expression of pro-angiogenic mediators, and induced angiogenesis in vivo in the chicken chorioallantoic membrane model. 14 We are now showing that HPU directly activates human microvasculature endothelial cells, modulating the molecular mechanisms that lead to their differentiation toward a pro-inflammatory profile.…”

“…HPU also induced in vitro platelet aggregation, human neutrophil chemotaxis, and production of reactive oxygen species (ROS) . Platelets activated by HPU display a pro‐inflammatory phenotype with modifications in the pre‐mRNA processing of pro‐inflammatory proteins, and increased levels of mRNAs encoding IL‐1β and CD14 . These results suggest that the inflammatory response triggered by HPU may contribute to amplify local inflammation, worsening mucosal damage during bacterial infection.…”

Helicobacter: Inflammation, immunology, and vaccines

“…For this purpose, they used recombinant versions of H. pylori urease and its two subunits, and they conducted platelet aggregation assays, flow cytometry and quantitative PCR to analyze how these proteins affect the platelets’ physiology. They demonstrated that the H. pylori urease, and notably its B subunit, activates platelet aggregation and that the activation of platelets by H. pylori urease appears to lead these cells to exhibit a proinflammatory phenotype . Therefore, platelets might possibly contribute to the development and/or the persistence of H. pylori ‐induced inflammation.…”