Activation of Cytosolic Phospholipase A2α in Resident Peritoneal Macrophages by Listeria monocytogenes Involves Listeriolysin O and TLR2

Saritha Suram,David L. Williams,Christina C. Leslie,Milena Girotti,Joseph V. Bonventre,Kevin Breuel,Satoshi Uematsu,Shahid Noor,Shizuo Akira,Laurel L. Lenz,Howard Goldfine,Dawn E. Tucker

doi:10.1074/jbc.m709956200

Abstract

Eicosanoid production by macrophages is an early response to microbial infection that promotes acute inflammation. The intracellular pathogen Listeria monocytogenes stimulates arachidonic acid release and eicosanoid production from resident mouse peritoneal macrophages through activation of group IVA cytosolic phospholipase A2 (cPLA2alpha). The ability of wild type L. monocytogenes (WTLM) to stimulate arachidonic acid release is partially dependent on the virulence factor listeriolysin O; however, WTLM and L. monocytogenes lacking listeriolysin O (DeltahlyLM) induce similar levels of cyclooxygenase 2. Arachidonic acid release requires activation of MAPKs by WTLM and DeltahlyLM. The attenuated release of arachidonic acid that is observed in TLR2-/- and MyD88-/- macrophages infected with WTLM and DeltahlyLM correlates with diminished MAPK activation. WTLM but not DeltahlyLM increases intracellular calcium, which is implicated in regulation of cPLA2alpha. Prostaglandin E2, prostaglandin I2, and leukotriene C4 are produced by cPLA2alpha+/+ but not cPLA2alpha-/- macrophages in response to WTLM and DeltahlyLM. Tumor necrosis factor (TNF)-alpha production is significantly lower in cPLA2alpha+/+ than in cPLA2alpha-/- macrophages infected with WTLM and DeltahlyLM. Treatment of infected cPLA2alpha+/+ macrophages with the cyclooxygenase inhibitor indomethacin increases TNFalpha production to the level produced by cPLA2alpha-/- macrophages implicating prostaglandins in TNFalpha down-regulation. Therefore activation of cPLA2alpha in macrophages may impact immune responses to L. monocytogenes.

Highlights

The human pathogen Listeria monocytogenes promotes disease through ingestion of contaminated food, and primarily affects individuals with a suppressed immune system [1]
Arachidonic acid release induced by wild type L. monocytogenes (WTLM) was inhibited by the cPLA2␣ inhibitor pyrrolidine-2 (Fig. 1B) and was reduced by 85% in cPLA2␣Ϫ/Ϫ macrophages infected with WTLM and was near background levels in cPLA2␣Ϫ/Ϫ macrophages infected with ⌬hlyLM (Fig. 1C)
The results of this study demonstrate that L. monocytogenes stimulates cPLA2␣ activation and eicosanoid production in resident peritoneal macrophages and occurs in the absence of serum with un-opsonized bacteria

Summary

Introduction

The human pathogen Listeria monocytogenes promotes disease through ingestion of contaminated food, and primarily affects individuals with a suppressed immune system [1]. In this study we demonstrate that nonopsonized L. monocytogenes activates group IVA cytosolic phospholipase A2 (cPLA2␣) in resident peritoneal macrophages resulting in arachidonic acid release and eicosanoid production. An L. monocytogenes mutant strain lacking LLO (⌬hlyLM) induced ϳ60% less arachidonic acid release than WTLM at 60 min after infection.

Results

Conclusion