E-prostanoid 2 receptor signaling suppresses lung innate immunity against Streptococcus pneumoniae

https://doi.org/10.1016/j.prostaglandins.2012.03.002Get rights and content

Abstract

Pneumonia is a major global health problem. Prostaglandin (PG) E2 is an immunomodulatory lipid with anti-inflammatory, immunosuppressive, and pro-resolving actions. Data suggest that the E-prostanoid (EP) 2 receptor mediates immunomodulatory effects of PGE2, but the extent to which this occurs in Streptococcus pneumoniae infection is unknown. Intratracheal lung infection of C57BL/6 mice possessing (EP2+/+) or lacking (EP2−/−) the EP2 receptor was performed, as were in vitro studies of alveolar macrophage (AM) host defense functions. Bacterial clearance and survival were significantly improved in vivo in EP2−/− mice and it correlated with greater neutrophilic inflammation and higher lung IL-12 levels. Upon ex vivo challenge with pneumococcus, EP2−/−cells expressed greater amounts of TNF-α and MIP-2 than did EP2+/+ AMs, and had improved phagocytosis, intracellular killing, and reactive oxygen intermediate generation. These data suggest that PGE2-EP2 signaling may provide a novel pharmacological target for treating pneumococcal pneumonia in combination with antimicrobials.

Highlights

► EP2 receptor-deficient mice are protected from death from pneumococcal pneumonia. ► EP2 null mice have enhanced inflammatory responses to S. pneumoniae in the lungs. ► Alveolar macrophage phagocytosis of S. pneumoniae is suppressed by PGE2-EP2 signaling. ► PGE2 restricts pneumococcal killing by alveolar macrophages via the EP2 receptor. ► The EP2 receptor limits inflammatory mediator production by infected macrophages.

Introduction

Pneumonia is the leading cause of infectious mortality in the United States [1] and therapeutic options are limited by emerging antimicrobial resistance [2]. Streptococcus pneumoniae is the most frequently isolated pathogen in community-acquired pneumonia [3] and accounts for more deaths (nearly 1.6 million per year [4]) than any other bacterium [5]. An improved understanding of immune defenses against S. pneumoniae is important to the discovery of improved targets for preventive and therapeutic strategies.

A critical innate immune barrier to bacterial pneumonia is the alveolar macrophage (AM) [6], which patrols gas-exchanging alveoli and removes potential pathogens through phagocytosis and intracellular killing. Furthermore, AMs alert the host to the presence of invading microbes by releasing lipid and protein mediators that activate resident cells and recruit polymorphonuclear leukocytes (neutrophils) to the focus of infection [7]. This response is highly regulated, to limit self-inflicted damage to host cells and tissues [8]. Emerging evidence suggests that lipid mediators are major regulators of both the amplitude and duration of infection-triggered inflammatory responses [9]. For example, leukotriene (LT) B4 has potent proinflammatory effects that augment innate immune functions of the AM [10], [11] and recruit/activate neutrophils, while prostaglandins (PGs) such as PGE2 and PGI2 have opposite, anti-inflammatory actions in the context of pneumonia [12], [13]. The recently-described resolvins and protectins are lipids that have been postulated to drive the resolution phase of inflammation [14].

The cyclooxygenase (COX)-derived eicosanoid PGE2 primarily down-regulates AM defense functions [12], [15], [16]. PGE2 binds to four distinct G protein-coupled E-prostanoid (EP) receptors, termed EP1-4. The inhibitory effects of PGE2 primarily result from cAMP-dependent signaling processes, triggered by EP2 and/or EP4 activation [17] and likely evolved to prevent inflammatory tissue damage and promote the resolution of inflammation [18], [19], [20]. Sadikot et al. demonstrated that PGE2-EP2 signaling suppressed bacterial clearance from the lungs of mice infected with Pseudomonas aeruginosa [21]. In addition, Stables et al. used ex vivo human whole blood assays to demonstrate that inhibiting either PGE2 synthesis or EP2 signaling significantly improved innate immune defenses against S. pneumoniae, including antimicrobial-resistant strains [22]. That important study shed new light on the potential for targeting PGE2 synthesis or signaling systems as adjunctive therapy against pneumonia. However, those studies were not designed to examine pneumococcal pneumonia in vivo [22]. Thus, mechanistic details of how PGE2 regulates pulmonary host defense during pneumococcal infection remain undefined.

We hypothesized that the EP2 receptor would play a potentially maladaptive, anti-inflammatory role in severe pneumococcal pneumonia, suppressing innate host defenses to allow infection to progress. A combination of pharmacological and genetic experiments were conducted to test this hypothesis, revealing a novel and critical role for PGE2-EP2 signaling in regulating pulmonary innate immunity during pneumococcal respiratory tract infection. These data add support and understanding to the idea of targeting prostaglandin synthesis and signaling as adjunctive treatments against pneumonia.

Section snippets

Animals

Mice harboring a targeted deletion of both alleles of the Ptger2 encoding the EP2 receptor were originally generated by Dr. Richard Breyer (Vanderbilt University). These six-to-eight week old female EP2-deficient (EP2−/−) mice, bred on a C57BL/6 background, and age-matched, female C57BL/6 wild type (WT) animals (EP2+/+ mice) were purchased from The Jackson Laboratory (Bar Harbor, ME) and bred in the University of Michigan Unit for Laboratory Animal Medicine. The genotypes of mouse strains were

The absence of PGE2-EP2 signaling is protective in pneumococcal pneumonia

Similar to our previous study of PGE2-EP3 signaling [23], female C57BL/6 mice were noted to be susceptible to pneumococcal pneumonia, exhibiting 92% mortality after intratracheal inoculation of 1 × 105 CFU of S. pneumoniae (Fig. 1A). We have previously reported that PGE2 is an abundant mediator in the lungs of C57BL/6 mice infected with pneumococcus [28], [29]. Mice unable to sense this PGE2 via the EP2 receptor (EP2−/− mice) were significantly protected from infection-related death (59.3%

Discussion

S. pneumoniae is the most common bacterial cause of community-acquired pneumonia in the world and remains a significant source of morbidity and mortality [39]. This study newly defines the important contribution of PGE2-EP2 signaling to the regulation of innate pulmonary host defenses during pneumococcal pneumonia. Whereas PGE2 may serve a homeostatic function by promoting the resolution of inflammation when infection is moderate in degree [18], [40], its immunosuppressive actions might be

Funding

This work was supported by the National Institutes of Health [HL078727 to DMA, HL077417 to PM, HL058897 to MP-G, and T32ES007062 to EO] and the Flight Attendants Medical Research Institute [CIA-103071 to PM].

Disclosure statements

D.M. Aronoff contributed to planning experiments, analyzing data, making figures, and was the primary author of this manuscript. I.L. Bergin provided expertise in histopathology experiments, helped to analyze data, made figures, and assisted in writing the manuscript. C. Lewis, D. Goel and E. O’Brien conducted experiments, made figures, and assisted in writing the manuscript. M. Peters-Golden contributed to planning experiments, analyzing data, and editing the manuscript. P. Mancuso contributed

Acknowledgments

The authors wish to thank Dr. Carlos H. Serezani for his critical reading of this manuscript. We thank Joel Whitfield from the University of Michigan Cancer Center Cellular Immunology Core for technical assistance.

References (69)

  • Bernstein A, Bilheimer LT, Makuc DM, and National Center for Health, S. Dept. of Health and Human Services, Centers for...
  • J.A. Bosso et al.

    Application of antimicrobial stewardship to optimise management of community acquired pneumonia

    Int J Clin Pract

    (2011)
  • L.A. Mandell et al.

    Infectious Diseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults

    Clin Infect Dis

    (2007)
  • O.S. Levine et al.

    Pneumococcal vaccination in developing countries

    Lancet

    (2006)
  • H.M. Marriott et al.

    The role of the macrophage in lung disease mediated by bacteria

    Exp Lung Res

    (2007)
  • L.A. Pittet et al.

    Earliest innate immune responses require macrophage RelA during pneumococcal pneumonia

    Am J Respir Cell Mol Biol

    (2011)
  • C.N. Serhan et al.

    Resolution of inflammation: state of the art, definitions and terms

    FASEB J

    (2007)
  • P. Mancuso et al.

    Intrapulmonary administration of leukotriene B4 enhances pulmonary host defense against pneumococcal pneumonia

    Infect Immun

    (2010)
  • D.M. Aronoff et al.

    Prostaglandin E2 inhibits alveolar macrophage phagocytosis through an E-prostanoid 2 receptor-mediated increase in intracellular cyclic AMP

    J Immunol

    (2004)
  • D.M. Aronoff et al.

    Synthetic prostacyclin analogs differentially regulate macrophage function via distinct analog-receptor binding specificities

    J Immunol

    (2007)
  • T. Carlo et al.

    Molecular circuits of resolution in airway inflammation

    Sci World J

    (2010)
  • R.M. Strieter et al.

    Differential regulation of tumor necrosis factor-alpha in human alveolar macrophages and peripheral blood monocytes: a cellular and molecular analysis

    Am J Respir Cell Mol Biol

    (1989)
  • C.H. Serezani et al.

    Prostaglandin E2 suppresses bacterial killing in alveolar macrophages by inhibiting NADPH oxidase

    Am J Respir Cell Mol Biol

    (2007)
  • C.H. Serezani et al.

    Master regulator of innate immune cell function

    Am J Respir Cell Mol Biol

    (2008)
  • P.F. Gomez et al.

    Resolution of inflammation: prostaglandin E2 dissociates nuclear trafficking of individual NF-kappaB subunits (p65, p50) in stimulated rheumatoid synovial fibroblasts

    J Immunol

    (2005)
  • J.U. Scher et al.

    The anti-inflammatory effects of prostaglandins

    J Investig Med

    (2009)
  • M. St-Onge et al.

    Impact of anti-inflammatory agents on the gene expression profile of stimulated human neutrophils: unraveling endogenous resolution pathways

    PLoS ONE

    (2009)
  • R.T. Sadikot et al.

    Bacterial clearance of Pseudomonas aeruginosa is enhanced by the inhibition of COX-2

    Eur J Immunol

    (2007)
  • M.J. Stables et al.

    Priming innate immune responses to infection by cyclooxygenase inhibition kills antibiotic susceptible and resistant bacteria

    Blood

    (2010)
  • D.M. Aronoff et al.

    E-prostanoid 3 receptor deletion improves pulmonary host defense and protects mice from death in severe Streptococcus pneumoniae infection

    J Immunol

    (2009)
  • M.B. Bailie et al.

    Leukotriene-deficient mice manifest enhanced lethality from Klebsiella pneumoniae in association with decreased alveolar macrophage phagocytic and bactericidal activities

    J Immunol

    (1996)
  • M.S. Arredouani et al.

    The macrophage scavenger receptor SR-AI/II and lung defense against pneumococci and particles

    Am J Respir Cell Mol Biol

    (2006)
  • P. Mancuso et al.

    5-Lipoxygenase reaction products modulate alveolar macrophage phagocytosis of Klebsiella pneumoniae

    Infect Immun

    (1998)
  • A. Hsu et al.

    Leptin improves pulmonary bacterial clearance and survival in ob/ob mice during pneumococcal pneumonia

    Clin Exp Immunol

    (2007)
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