Anti-Inflammatory Role of the Murine Formyl-Peptide Receptor 2: Ligand-Specific Effects on Leukocyte Responses and Experimental Inflammation

Abstract

The human formyl-peptide receptor (FPR)-2 is a G protein-coupled receptor that transduces signals from lipoxin A4, annexin A1, and serum amyloid A (SAA) to regulate inflammation. In this study, we report the creation of a novel mouse colony in which the murine FprL1 FPR2 homologue, Fpr2, has been deleted and describe its use to explore the biology of this receptor. Deletion of murine fpr2 was verified by Southern blot analysis and PCR, and the functional absence of the G protein-coupled receptor was confirmed by radioligand binding assays. In vitro, Fpr2−/− macrophages had a diminished response to formyl-Met-Leu-Phe itself and did not respond to SAA-induced chemotaxis. ERK phosphorylation triggered by SAA was unchanged, but that induced by the annexin A1-derived peptide Ac2–26 or other Fpr2 ligands, such as W-peptide and compound 43, was attenuated markedly. In vivo, the antimigratory properties of compound 43, lipoxin A4, annexin A1, and dexamethasone were reduced notably in Fpr2−/− mice compared with those in wild-type littermates. In contrast, SAA stimulated neutrophil recruitment, but the promigratory effect was lost following Fpr2 deletion. Inflammation was more marked in Fpr2−/− mice, with a pronounced increase in cell adherence and emigration in the mesenteric microcirculation after an ischemia–reperfusion insult and an augmented acute response to carrageenan-induced paw edema, compared with that in wild-type controls. Finally, Fpr2−/− mice exhibited higher sensitivity to arthrogenic serum and were completely unable to resolve this chronic pathology. We conclude that Fpr2 is an anti-inflammatory receptor that serves varied regulatory functions during the host defense response. These data support the development of Fpr2 agonists as novel anti-inflammatory therapeutics.

A formyl peptide receptor agonist suppresses inflammation and bone damage in arthritis

“…Based on the known anti-inflammatory effects of AnxA1, and exacerbation of K/BxN serum transferinduced arthritis in FPR2 −/− mice (Dufton et al, 2010), we hypothesized that Cpd43 might act as a potent inhibitor of inflammatory arthritis. We have shown here that treatment of mice with Cpd43 at a dose of 30 mg·kg −1 , either before or after the onset of disease, almost completely inhibited arthri- overnight.…”

“…FPR2 is activated by lipoxin A4, AnxA1 or AnxA1-derived peptides, as well as by the acute phase reactant serum amyloid A. Mice deficient in FPR2/3, which is homologous to human FPR2, exhibit exacerbated disease in carrageenan-induced paw oedema and K/BxN serum transferinduced arthritis (Dufton et al, 2010), indicating that FPR2 mediates anti-inflammatory effects. Thus, the antiinflammatory effects of AnxA1 in arthritis may be receptordependent, raising the possibility that synthetic ligands of FPR2 could have therapeutic potential.…”

“…In vivo, Cpd43 exerts anti-inflammatory effects in murine ear inflammation and air-pouch models, which require FPR2 (Burli et al, 2006;Dufton et al, 2010;Sogawa et al, 2011). Mutation studies have identified specific domains in FPR2, which are required for the action of Cpd43 (Bena et al, 2012), but in human neutrophils, Cpd43 has also been reported to interact with FPR1 (Forsman et al, 2011).…”

Inhibition of neutrophil migration in mice by mouse formyl peptide receptors 1 and 2 dual agonist: indication of cross-desensitization in vivo

“…13,33,34 It is reasonable to speculate that FPR2/ALX is also capable of inducing cross-desensitization in neutrophils, because it has been reported that some FPR2/ALX selective agonists induced cross-desensitization of CCR5 and CXCR4 in human monocytes and cells transfected with FPR2/ALX in combination with CCR5 or CXCR4. 31,32,35 In addition, the Fpr2-dependent inhibitory effect of Cpd43 on neutrophil migration in the IL-1b-induced air pouch assay described in a study using Fpr2-deficient mice 12 implies that Fpr2-mediated cross-desensitization is operative in vivo as a mechanism of inhibition by Cpd43, although induction of cross-desensitization by Cpd43 was not investigated in that study. Obtaining highly selective ligands/antibody for each receptor and/or receptor-deficient mice will help to answer the question regarding the roles of Fpr1 and Fpr2 in the induction of cross-desensitization.…”

“…11 However, in terms of neutrophil migration in interleukin (IL)-1b-induced air pouch or zymosan peritonitis assays, no difference was observed between Fpr2-deficient mice and wild-type mice. 12 Thus, the biological roles of Fpr1 and Fpr2 in neutrophil migration in vivo remain elusive.…”