Neutrophil-Derived Extracellular Vesicles Activate Platelets after Pneumolysin Exposure.

Eleftheria Letsiou,Matthias Felten,Holger C Müller-Redetzky,Timothy J Mitchell,Martin Witzenrath,Steven M Dudek,Luiz Gustavo Teixeira Alves

doi:10.3390/cells10123581

Abstract

Pneumolysin (PLY) is a pore-forming toxin of Streptococcus pneumoniae that contributes substantially to the inflammatory processes underlying pneumococcal pneumonia and lung injury. Host responses against S. pneumoniae are regulated in part by neutrophils and platelets, both individually and in cooperative interaction. Previous studies have shown that PLY can target both neutrophils and platelets, however, the mechanisms by which PLY directly affects these cells and alters their interactions are not completely understood. In this study, we characterize the effects of PLY on neutrophils and platelets and explore the mechanisms by which PLY may induce neutrophil–platelet interactions. In vitro studies demonstrated that PLY causes the formation of neutrophil extracellular traps (NETs) and the release of extracellular vesicles (EVs) from both human and murine neutrophils. In vivo, neutrophil EV (nEV) levels were increased in mice infected with S. pneumoniae. In platelets, treatment with PLY induced the cell surface expression of P-selectin (CD62P) and binding to annexin V and caused a significant release of platelet EVs (pl-EVs). Moreover, PLY-induced nEVs but not NETs promoted platelet activation. The pretreatment of nEVs with proteinase K inhibited platelet activation, indicating that the surface proteins of nEVs play a role in this process. Our findings demonstrate that PLY activates neutrophils and platelets to release EVs and support an important role for neutrophil EVs in modulating platelet functions in pneumococcal infections.

Highlights

Streptococcus pneumoniae is a Gram-positive bacterium that represents a major causative pathogen of community-acquired pneumonia [1]
The present study aims to characterize the effects of PLY on neutrophils and platelets and explores the hypothesis that PLY-induced neutrophil extracellular products (EVs and neutrophil extracellular traps (NETs)) contribute to platelet activation
We initially assessed the activation tein alteration, the release of granule content, the production of reactive oxygen species status of isolated human neutrophils following pneumolysin (PLY) treatment

Summary

Introduction

Streptococcus pneumoniae (or pneumococcus) is a Gram-positive bacterium that represents a major causative pathogen of community-acquired pneumonia [1]. When pneumococcal lung infections are severe, they result in a series of events that include the dysregulation of the innate immune system and failure of the lung barrier [2]. These events cause invasive disease and life-threatening complications, with sepsis and acute respiratory distress syndrome (ARDS) being among the most important ones [2]. PLY has a range of biological functions that contribute to key disease processes. These include direct cytotoxicity through cell lysis, the activation of multiple pro-inflammatory pathways, the promotion of extrapulmonary dissemination of

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