Formyl peptide receptor 2

N-formyl peptide receptor 2 (FPR2) is a

Confusingly, there are two "standard" nomenclatures for FPR receptors and their genes, the first used, FPR, FPR1, and FPR2 and its replacement, FPR1, FPR2, and FPR3. The latter nomenclature is recommended by the International Union of Basic and Clinical Pharmacology[17] and is used here. Other previously used names for FPR1 are NFPR, and FMLPR; for FPR2 are FPRH1, FPRL1, RFP, LXA4R, ALXR, FPR2/ALX, HM63, FMLPX, and FPR2A; and for FPR3 are FPRH2, FPRL2, and FMLPY.^[17]

Genes

Human

The human FPR2 gene encodes the 351 amino acid receptor, FPR2, within an intronless

Mice have no less than 7 FPR receptors encoded by 7 genes that localize to chromosome 17A3.2 in the following order: Fpr1, Fpr-rs2 (or fpr2), Fpr-rs1 (or LXA4R), Fpr-rs4, Fpr-rs7, Fpr-rs7, Fpr-rs6, and Fpr-rs3; this locus also contains Pseudogenes ψFpr-rs2 and ψFpr-rs3 (or ψFpr-rs5) which lie just after Fpr-rs2 and Fpr-rs1, respectively. The 7 mouse FPR receptors have ≥50% amino acid sequence identity with each other as well as with the three human FPR receptors.^[20] Fpr2 and mFpr-rs1 bind with high affinity and respond to lipoxins but have little or no affinity for, and responsiveness to, formyl peptides; they thereby share key properties with human FPR2;^[21][22][23]

Gene knockout studies

The large number of mouse compared to human FPR receptors makes it difficult to extrapolate human FPR functions based on genetic (e.g. gene knockout or forced overexpression) or other experimental manipulations of the FPR receptors in mice. In any event, combined disruption of the Fpr2 and Fpr3 genes causes mice to mount enhanced acute inflammatory responses as evidenced in three models, intestine inflammation caused by mesenteric artery ischemia-reperfusion, paw swelling caused by carrageenan injection, and arthritis caused by the intraperatoneal injection of arthritis-inducing serum.^[24] Since Fpr2 gene knockout mice exhibit a faulty innate immune response to intravenous listeria monocytogenes injection,^[25] these results suggest that the human FPR2 receptor and mouse Fpr3 receptor have equivalent functions in dampening at least certain inflammatory response.

Other species

Rats express an ortholog of FPR2 (74% amino acid sequence identity) with high affinity for

FPR2 is also known as the LXA4 or ALX/FPR2 receptor based on studies finding that is a high affinity receptor for the arachidonic acid metabolite, lipoxin A4 (LXA4), and thereafter for a related arachidonic acid metabolite, the Epi-lipoxin, aspirin-triggered lipoxin A4 (i.e. ATL, 15-epi-LXA4) and a docosahexaenoic acid metabolite, resolvin D1 (i.e. RvD1); these three cell-derived fatty acid metabolites act to inhibit and resolve inflammatory responses.^{[30][31][32][33][34]} This receptor was previously known as an orphan receptor, termed RFP, obtained by screening myeloid cell-derived libraries with a FMLP-like probe.^[35][36][37] In addition to LXA4, LTA, RvD1, and FMLP, FPR2 binds a wide range of polypeptides, proteins, and products derived from these polypeptides and proteins. One or more of these various ligands may be involved not only in regulating inflammation but also be involved in the development of obesity, cognitive decline, reproduction, neuroprotection, and cancer.^[38] However, the most studied and accepted role for FPR2 receptors is in mediating the actions of the cited lipoxins and resolvins in dampening and resolving a wide range of inflammatory reactions (see lipoxin, Epi-lipoxin, and resolvin).^[39][40]

The following is a list of FPR2/ALX ligands and in parentheses their suggested pro-inflammatory or anti-inflammatory actions base on in vitro and animal model studies: a) bacterial and mitochondrial N-formyl peptides such as FMLP (pro-inflammatory but perhaps less significant or insignificant compared to the actions of LXA4, ATL, and RvD1 on FPR2);

b) Hp(2-20), a non-formyl peptide derived from Helicobacter pylori (pro-inflammatory by promoting inflammatory responses against this stomach ulcer-causing pathogen);

c) T21/DP107 and N36, which are N-acetylated polypeptides derived from the gp41 envelope protein of the

d) the N-terminally truncated form of the chemotactic chemokine, CCL23, termed CCL23 splice variant CCL23β(amino acids 22–137) and SHAAGtide, which is a product of CCL23β cleavage by pro-inflammatory proteases (pro-inflammatory); e) two N-acetyl peptides, Ac2–26 and Ac9–25 of Annexin A1 (ANXA1 or lipocortin 1), which at high concentrations fully stimulate neutrophil functions but at lower concentrations leave neutrophils desensitized (i.e. unresponsive) to the chemokine IL-8 (CXCL8) (pro-inflammatory and anti-inflammatory, respectively, highlighting the duality of FPR2/ALX functions in inflammation);

f) Amyloid beta(1–42) fragment and prion protein fragment PrP(106–126) (pro-inflammatory, suggesting a role for FPR2/ALX in the inflammatory components of diverse amyloid-based diseases including Alzheimer's disease, Parkinson's disease, Huntington's disease, prion-based diseases such as Transmissible spongiform encephalopathy, Creutzfeldt–Jakob disease, and Kuru), and numerous other neurological and non-neurological diseases [see amyloid]);

g) the neuroprotective peptide, Humanin (anti-inflammatory by inhibiting the pro-inflammatory effects of Amalyoid beta(1-42) in promoting Alzheimer's disease-related inflammation);

h) two cleaved soluble fragments of

i) LL-37 and CRAMP, which are enzymatic cleavage products of human and rat, respectively,

j) Pituitary adenylate cyclase-activating polypeptide 27 (pro-inflammatory).[17]^[41]

See also

• Eicosanoid receptor
• Formyl peptide receptor
• Lipoxin
• Resolvin
• Formyl peptide receptor 1
• Formyl peptide receptor 3

References