NADPH Oxidase-dependent Generation of Lysophosphatidylserine Enhances Clearance of Activated and Dying Neutrophils via G2A

Christina Leslie,Robert C Murphy,S Courtney Frasch,Donna L Bratton,Hyun-Sun Jin,Karin Zemski Berry,Ruby Fernandez-Boyanapalli,Peter M Henson

doi:10.1074/jbc.m807047200

Christina Leslie, Robert C Murphy + Show 6 more

Open Access

https://doi.org/10.1074/jbc.m807047200

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Abstract

Exofacial phosphatidylserine (PS) is an important ligand mediating apoptotic cell clearance by phagocytes. Oxidation of PS fatty acyl groups (oxPS) during apoptosis reportedly mediates recognition through scavenger receptors. Given the oxidative capacity of the neutrophil NADPH oxidase, we sought to identify oxPS signaling species in stimulated neutrophils. Using mass spectrometry analysis, only trace amounts of previously characterized oxPS species were found. Conversely, 18:1 and 18:0 lysophosphatidylserine (lyso-PS), known bioactive signaling phospholipids, were identified as abundant modified PS species following activation of the neutrophil oxidase. NADPH oxidase inhibitors blocked the production of lyso-PS in vitro, and accordingly, its generation in vivo by activated, murine neutrophils during zymosan-induced peritonitis was absent in mice lacking a functional NADPH oxidase (gp91phox-/-). Treatment of macrophages with lyso-PS enhanced the uptake of apoptotic cells in vitro, an effect that was dependent on signaling via the macrophage G2A receptor. Similarly, endogenously produced lyso-PS also enhanced the G2A-mediated uptake of activated PS-exposing (but non-apoptotic) neutrophils, raising the possibility of non-apoptotic mechanisms for removal of inflammatory cells during resolution. Finally, antibody blockade of G2A signaling in vivo prolonged zymosan-induced neutrophilia in wild-type mice, whereas having no effect in gp91phox-/- mice where lyso-PS are not generated. Taken together, we show that lyso-PS are modified PS species generated following activation of the NADPH oxidase and lyso-PS signaling through the macrophage G2A functions to enhance existing receptor/ligand systems for optimal resolution of neutrophilic inflammation.

Highlights

Phosphatidylserine (PS)2 exposed in the plasma membrane outer leaflet of apoptotic cells has long been known as a key ligand important for their recognition and removal
Our studies demonstrate that lyso-PS are modified PS species that signal via the macrophage G2A receptor to enhance existing receptor/ligand systems for the engulfment of PS exposing activated and apoptotic cells in vitro and in vivo
Lyso-PS Are Abundant Modified PS Species Generated in Neutrophils Stimulated to Activate the NADPH Oxidase—The signaling potential of lyso-PS was first recognized in its description as a potent mast cell secretagogue, and it has subsequently been given signaling roles in other settings [20, 21, 39, 55, 56]

Summary

Introduction

Phosphatidylserine (PS)2 exposed in the plasma membrane outer leaflet of apoptotic cells has long been known as a key ligand important for their recognition and removal. Our studies demonstrate that lyso-PS are modified PS species that signal via the macrophage G2A receptor to enhance existing receptor/ligand systems for the engulfment of PS exposing activated and apoptotic cells in vitro and in vivo.

Results

Conclusion