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Impairment of apoptotic cell engulfment by pyocyanin, a toxic metabolite of Pseudomonas aeruginosa

Research output: Contribution to journalArticlepeer-review

  • Stephen M. Bianchi
  • Lynne R. Prince
  • Kathleen McPhillips
  • Lucy Allen
  • Helen M. Marriott
  • Graham W. Taylor
  • Paul G. Hellewell
  • Ian Sabroe
  • David Dockrell
  • Peter W. Henson
  • Moira K. B. Whyte

Related Edinburgh Organisations

Original languageEnglish
Pages (from-to)35-43
Number of pages9
JournalAmerican Journal of Respiratory and Critical Care Medicine
Volume177
Issue number1
Publication statusPublished - 1 Jan 2008

Abstract

Rationale: Cystic fibrosis lung disease is characterized by accumulation of apoptotic neutrophils, indicating impaired clearance of dying cells. Pseudomonas aeruginosa, the principal microbial pathogen in cystic fibrosis, manipulates apoptosis induction via production of toxic metabolites. Whether these metabolites, particularly pyocyanin, can also modulate apoptotic cell engulfment is unknown.

Objectives: To assess the effects of pyocyanin on apoptotic cell engulfment by macrophages in vitro and in vivo and to investigate potential mechanisms of the observed effects.

Methods: Human monocyte-derived macrophages were treated with pyocyanin before challenge with apoptotic neutrophils, apoptotic Jurkat cells, or latex beads, and phagocytosis was assessed by light microscopy and flow cytometry. Effects of pyocyanin production on apoptotic cell clearance in vivo were assessed in a murine model, comparing infection by wild-type or pyocyanin-deficient P. aeruginosa. Oxidant production was investigated using fluorescent probes and pharmacologic inhibition and Rho GTPase signaling by immunoblotting and inhibitor studies.

Measurements and Main Results: Pyocyanin treatment impaired macrophage engulfment of apoptotic cells in vitro, without inducing significant macrophage apoptosis, whereas latex bead uptake was preserved. Macrophage ingestion of apoptotic cells was reduced and late apoptotic/necrotic cells were increased in mice infected with pyocyanin-producing P. aeruginosa compared with the pyocyanin-deficient strain. Inhibition of apoptotic cell uptake involved intracellular generation of reactive oxygen species (ROS) and effects on Rho GTPase signaling. Antioxidants or blockade of Rho signaling substantially restored apoptotic cell engulfment.

Conclusions: These studies demonstrate that P. aeruginosa can manipulate the inflammatory microenvironment through inhibition of apoptotic cell engulfment, and suggest potential strategies to limit pulmonary inflammation in cystic fibrosis.

    Research areas

  • macrophages, phagocytosis, apoptosis, inflammation, cystic fibrosis, CYSTIC-FIBROSIS, NEUTROPHIL APOPTOSIS, OXIDATIVE STRESS, GRANULOCYTE APOPTOSIS, EPITHELIAL-CELLS, DOUBLE-BLIND, RHO GTPASES, HUMAN LUNG, MACROPHAGES, CLEARANCE

ID: 17166067