Myeloperoxidase Negatively Regulates Neutrophil-Endothelial Cell Interactions by Impairing αMβ2 Integrin Function in Sterile Inflammation.

Alan Tseng,Kyungho Kim,Jaehyung Cho,Jing Li

doi:10.3389/fmed.2018.00134

Abstract

Interactions of neutrophils with endothelial cells (ECs) and platelets contribute to tissue damage and vascular occlusion under sterile inflammatory conditions. However, the molecular mechanisms regulating the cell–cell interactions remain poorly understood. Previous studies suggest that reactive oxygen species, such as hydrogen peroxide (H2O2), produced from NADPH oxidase 2 play a critical role in platelet–neutrophil interactions by regulating the function of neutrophil αMβ2 integrin during sterile inflammation. In this study, we further demonstrate a crucial role for myeloperoxidase (MPO) in regulating the adhesive function of neutrophils through αMβ2 integrin. Using real-time fluorescence intravital microscopy and in vitro assays, we showed that loss of MPO promoted neutrophil–EC interactions and neutrophil emigration but did not affect neutrophil–platelet interactions under inflammatory conditions. Using genetic and pharmacologic approaches, we found that following agonist stimulation, MPO knockout (KO) neutrophils exhibited a significant increase in extracellular H2O2 and surface level of αMβ2 integrin and that these effects were dependent on MPO activity. Our in vivo studies using an ischemia/reperfusion-induced hepatic inflammation model revealed that compared to wild-type mice, neutrophils from MPO KO mice—displayed a pro-migratory phenotype while ameliorating tissue damage. These results suggest that MPO plays a negative role in the adhesive and migratory function of neutrophils by impairing αMβ2 integrin function under sterile inflammatory conditions.

Highlights

Since deletion of hematopoietic cell NADPH oxidase 2 (NOX2) results in a remarkable decrease in platelet–neutrophil interactions without affecting neutrophil adhesion to activated endothelial cells (ECs) [3], these results indicate that neutrophil MPO plays a distinct role in neutrophil recruitment and platelet–neutrophil interactions during vascular inflammation
As quantified by the fluorescence intensity of anti-CD42c antibodies in the R1 gate, deletion of neutrophil MPO did not affect neutrophil–platelet aggregation (Figures 2A,B). These results suggest that the decreased platelet–neutrophil interaction seen in intravital microscopy was likely derived from a significant decrease in the number of adherent neutrophils remaining in the vessel due to increased emigration
We have found that MPO negatively regulates neutrophil adhesive function by consuming extracellular H2O2 and that loss or inhibition of MPO elevates extracellular H2O2 levels and enhances αMβ2 integrin function, facilitating neutrophil–EC interactions and subsequent neutrophil transmigration under sterile inflammatory conditions

Summary

Introduction

Their excessive recruitment to sites of inflammation causes severe and progressive tissue damage [1]. Neutrophils are the first responders of host-defense against invading micropathogens. For the innate immune response, neutrophils are recruited to the site of infection. Initial neutrophil rolling over the inflamed endothelium is mediated by the interaction between selectins and their ligands [1]. Activated integrins, mainly αLβ2 and αMβ2, bind to their ligands such as intercellular adhesion molecule 1, leading to neutrophil adhesion, crawling, and transmigration. Neutrophil transmigration across the endothelial cell (EC) barrier is regulated by the interactions of neutrophil integrins and other surface

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Conclusion