Regulation of the Formyl Peptide Receptor 1 (FPR1) Gene in Primary Human Macrophages

Claudio Gemperle,Mattia Schmid,Magdalena Herova,Martin Hersberger,Sophia J A Wuest,Jacqueline Marti-Jaun,Christa Loretz,Jörn Coers

doi:10.1371/journal.pone.0050195

Abstract

The formyl peptide receptor 1 (FPR1) is mainly expressed by mammalian phagocytic leukocytes and plays a role in chemotaxis, killing of microorganisms through phagocytosis, and the generation of reactive oxygen species. A large number of ligands have been identified triggering FPR1 including formylated and non-formylated peptides of microbial and endogenous origin. While the expression of FPR1 in neutrophils has been investigated intensively, knowledge on the regulation of FPR1 expression in polarized macrophages is lacking. In this study we show that primary human neutrophils, monocytes and resting macrophages do express the receptor on their cell surface. Polarization of macrophages with IFNγ, LPS and with the TLR8 ligand 3M-002 further increases FPR1 mRNA levels but does not consistently increase protein expression or chemotaxis towards the FPR1 ligand fMLF. In contrast, polarization of primary human macrophages with IL-4 and IL-13 leading to the alternative activated macrophages, reduces FPR1 cell surface expression and abolishes chemotaxis towards fMLF. These results show that M2 macrophages will not react to triggering of FPR1, limiting the role for FPR1 to chemotaxis and superoxide production of resting and pro-inflammatory M1 macrophages.

Highlights

The formyl peptide receptor 1 (FPR1) belongs to a family of G protein-coupled pattern recognition receptors, which are mainly expressed by mammalian phagocytic leukocytes and are key players in innate immunity and host defence [1,2,3]
To investigate the regulation of the FPR1 gene in leukocytes, primary human macrophages were stimulated with different pro- and antiinflammatory cytokines or Toll-Like Receptor (TLR) agonists for 24 hours and the relative mRNA expression was measured by Quantitative Real-Time PCR (qPCR)
We studied the regulation of FPR1 receptor expression in primary human macrophages and observed that neutrophils, monocytes and resting macrophages express the receptor on their cell surface

Summary

Introduction

The formyl peptide receptor 1 (FPR1) belongs to a family of G protein-coupled pattern recognition receptors, which are mainly expressed by mammalian phagocytic leukocytes and are key players in innate immunity and host defence [1,2,3]. The first ligands identified for FPR1 were the N-formylated peptides from bacteria, later it was found that such Nformylated peptides could derive endogenously from mitochondria, released as a result of severe cell dysfunction or cell death [1]. It is currently not clear whether these mitochondria derived N-formylated peptides are produced in vivo [2]. A large number of microbial and endogenous peptides of various compositions have been identified as agonists for FPR1. These include formylated and non-formylated peptides of microbial and endogenous origin, like the GP-41 envelope protein of the human immuno-deficiency virus (HIV), annexin-1, and a list of peptides from peptide libraries [2,4]

Methods

Results

Conclusion