FPR2/ALX receptor expression and internalization are critical for lipoxin A4 and annexin-derived peptide-stimulated phagocytosis

FASEB J. 2010 Nov;24(11):4240-9. doi: 10.1096/fj.10-159913. Epub 2010 Jun 22.

Abstract

Lipoxins (LXs) are endogenously produced eicosanoids with well-described anti-inflammatory and proresolution activities, stimulating nonphlogistic phagocytosis of apoptotic cells by macrophages. LXA(4) and the glucocorticoid-derived annexin A1 peptide (Ac2-26) bind to a common G-protein-coupled receptor, termed FPR2/ALX. However, direct evidence of the involvement of FPR2/ALX in the anti-inflammatory and proresolution activity of LXA(4) is still to be investigated. Here we describe FPR2/ALX trafficking in response to LXA(4) and Ac2-26 stimulation. We have transfected cells with HA-tagged FPR2/ALX and studied receptor trafficking in unstimulated, LXA(4) (1-10 nM)- and Ac2-26 (30 μM)-treated cells using multiple approaches that include immunofluorescent confocal microscopy, immunogold labeling of cryosections, and ELISA and investigated receptor trafficking in agonist-stimulated phagocytosis. We conclude that PKC-dependent internalization of FPR2/ALX is required for phagocytosis. Using bone marrow-derived macrophages (BMDMs) from mice in which the FPR2/ALX ortholog Fpr2 had been deleted, we observed the nonredundant function for this receptor in LXA(4) and Ac2-26 stimulated phagocytosis of apoptotic neutrophils. LXA(4) stimulated phagocytosis 1.7-fold above basal (P<0.001) by BMDMs from wild-type mice, whereas no effect was found on BMDMs from Fpr2(-/-) mice. Similarly, Ac2-26 stimulates phagocytosis by BMDMs from wild-type mice 1.5-fold above basal (P<0.05). However, Ac2-26 failed to stimulate phagocytosis by BMDMs isolated from Fpr2(-/-) mice relative to vehicle. These data reveal novel and complex mechanisms of the FPR2/ALX receptor trafficking and functionality in the resolution of inflammation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Annexins / pharmacology*
  • Gene Expression Regulation / drug effects
  • HeLa Cells
  • Humans
  • Lipoxins / pharmacology*
  • Mice
  • Microscopy, Confocal
  • Peptides / pharmacology*
  • Phagocytosis / drug effects
  • Protein Transport / drug effects
  • Receptors, Formyl Peptide / genetics
  • Receptors, Formyl Peptide / metabolism*
  • Receptors, Lipoxin / genetics
  • Receptors, Lipoxin / metabolism*

Substances

  • Annexins
  • FPR2 protein, human
  • Lipoxins
  • Peptides
  • Receptors, Formyl Peptide
  • Receptors, Lipoxin
  • lipoxin A4