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

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.

ChemR23, the Receptor for Chemerin and Resolvin E1, Is Expressed and Functional on M1 but Not on M2 Macrophages

“…This is in line with the IL-4-mediated reduction in cell-surface expression for both receptors (Fig. 2D) (30). Repolarization of primary human macrophages with 10 nM RvE1 reduced but not totally ablated migration toward chemerin and did not influence migration toward fMLF.…”

“…To investigate whether RvE1 causes a repolarization of inflammatory M1 macrophages, we sequentially stimulated primary human macrophages with LPS followed by the stimulation with RvE1, and characterized the polarization phenotype of these macrophages. As expected, LPS-stimulated M1 macrophages exhibited an increased transcription of IL-1b, TNF-a, and cell-surface expression of CD80 and CD206 (mannose receptor) (30,35), which returned to levels comparable with untreated macrophages upon removal of the stimulus for 4 d (data not shown). Sequential stimulation of these M1 macrophages with 10 nM RvE1 at day 1 of the 4-d incubation did not alter transcription for IL-1b and TNF-a, or cell-surface expression for ChemR23 and CD206 (Fig.…”

“…As expected, M1 macrophages migrated toward chemerin and toward the macro- Relative mRNA expression of ChemR23 after stimulation of primary human macrophages with different stimuli for 24 h (IL-4 10 ng/ml, IL-13 10 ng/ml, TGF-b 1 ng/ml, IL-1b 1 ng/ml, IL-6 10 ng/ml, IFN-g 50 ng/ml, TNF-a 1 ng/ml, CpG 100 ng/ml, LPS 100 ng/ml, poly I:C 1 ng/ml, 3M001 3 mM, 3M002 3 mM). phage chemoattractant fMLF (30), whereas IL-4 repolarized macrophages lost the ability to migrate toward both chemoattractants (Fig. 6A).…”

FAM19A4 is a novel cytokine ligand of formyl peptide receptor 1 (FPR1) and is able to promote the migration and phagocytosis of macrophages

“…When searching for such a chemotactic receptor that can promote phagocytosis as well, we focused on FPR1, which has been reported to be a non-classical chemokine receptor highly expressed on stimulated macrophages that also regulates phagocytosis. 22,23 To test our hypothesis, we overexpressed FPR1 on the HEK293 cells and observed the effects of FAM19A4 on the cells. The chemotaxis assays showed that FAM19A4 was able to recruit FPR1-expressing HEK293 cells in a dose-dependent manner (Figure 4a).…”

“…In addition, FPR1 is thought to play a role in sensing the endogenous signals of dysfunctional cells, which should attract leukocytes to the sites of inflammation and tissue damage. 11,22,23,25,26 As the ligand with the highest affinity for FPR1, fMLF has a Kd of 0.04 nM. 27 According to the ratio of Ki for fMLF (Ki50.08139 pM) and FAM19A4 (Ki558.81 pM) from the competition binding analysis, the Kd of FAM19A4 is 722 times that of fMLF.…”