FPR2 (FPRL1 / ALX)

Formyl-peptide receptor 2 is a class A GPCR expressed on neutrophils, monocytes/macrophages, microglia, and epithelial cells that occupies a paradoxical dual role in inflammation: the same receptor mediates both pro-inflammatory signaling (in response to formyl peptides, serum amyloid A, and LL-37 in some contexts) and pro-resolving signaling (in response to lipoxin A4, resolvin D1, and annexin A1). This biased agonism — where different ligands stabilize distinct receptor conformations to produce opposing functional outcomes — places FPR2 at the pivot of the acute-to-chronic inflammation transition. In aging, dysregulation of pro-resolving FPR2 ligands (specialized pro-resolving mediators / SPMs) is implicated in the failure of inflammation resolution known as inflammaging.

Identity

UniProt: P25090 (FPR2_HUMAN)
NCBI Gene ID: 2358
HGNC: 3827
Ensembl: ENSG00000171049
Chromosome: 19q13.41 (gene cluster with FPR1, FPR3)
Protein length: 351 amino acids
Mouse ortholog: Fpr2 / Fpr-rs1 (one-to-one; conserved Gαi coupling and biased agonism)
MIM: 136538

Gene/protein family

FPR2 belongs to the formyl-peptide receptor family, a sub-family of class A (rhodopsin-like) GPCRs. Three human family members:

Gene	NCBI Gene ID	Primary agonist class
FPR1	2357	fMet-Leu-Phe (fMLF); high-affinity
FPR2	2358	Diverse: formyl peptides, SAA, LL-37, lipoxin A4, resolvins, annexin A1
FPR3	2359	Mitochondria-derived peptides; no LXA4 response

FPR2 was originally cloned as FPRH1/FPRL1 (formyl-peptide receptor-like 1); it was subsequently identified as the human lipoxin A4 receptor (LXA4R / ALX) ¹. The dual naming reflects independent characterization from the pro-inflammatory and pro-resolving directions before their convergence on a single gene.

Structure and signal transduction

FPR2 is a 7-transmembrane GPCR (TM1–TM7 spanning residues 28–304) that couples principally to Gαi/GNAI1, inhibiting adenylate cyclase and reducing intracellular cAMP. Key features:

N-linked glycosylation at Asn4 (extracellular N-terminus)
Disulfide bond Cys98–Cys176 (stabilizes extracellular loop 2)
Heterodimerization with FPR1 documented; functional consequence under investigation

Downstream effectors activated by Gαi signaling: phospholipase C-β → IP3/DAG → intracellular Ca2+ mobilization; PI3Kγ → Akt; ERK1/2 → gene expression; p38 MAPK. The precise effector profile is ligand-dependent (biased agonism — see below).

Biased agonism: the pro-inflammatory / pro-resolving switch

The canonical mechanistic feature of FPR2 is ligand-specific receptor conformational change producing divergent downstream signaling ²:

Ligand class	Representative ligand	Outcome	Dimerization state
Formyl peptides	fMet-Leu-Phe analogues	Chemotaxis, ROS burst	—
Acute-phase / DAMPs	Serum amyloid A (SAA)	Pro-inflammatory cytokines, NET formation	Monomer / FPR1-ALX heterodimer; does NOT promote ALX homodimerization (decreases ALX homodimer BRET signal)
Host AMPs	LL-37 / CAMP protein	Context-dependent: chemotactic at low dose, resolution-promoting in some models	—
Specialized pro-resolving mediators	Lipoxin A4 (LXA4), Resolvin D1 (RvD1)	Anti-inflammatory, PMN stop-signals, efferocytosis promotion	—
Endogenous protein ligands	Annexin A1 (ANXA1)	Pro-resolving, IL-10 production, p38/MK2/HSP27 axis	Homodimer

Cooray et al. 2013 (PNAS) demonstrated that annexin A1 preferentially activates FPR2 homodimers signaling through p38 MAPK → MK2 → HSP27 → IL-10 production, while SAA does not promote ALX homodimerization (it decreases the ALX homodimer BRET signal) and instead drives pro-inflammatory outputs through a distinct conformational state, with FPR1/ALX heterodimers mediating pro-apoptotic JNK pathway activation ². IL-10 production by AnxA1 was confirmed in primary human monocytes and in vivo in C57BL/6 mice (i.p. injection of 1 µg AnxA1); the effect was absent in Alx-Fpr2/3 KO mice. This structural basis for biased agonism is clinically relevant because the ratio of pro-resolving to pro-inflammatory FPR2 ligands — rather than receptor expression alone — determines tissue inflammatory tone.

Cross-links: ll-37 · camp (LL-37 / CAMP protein) are documented FPR2 ligands; their interaction with FPR2 is context-sensitive and may vary by tissue and local concentration.

Role in aging and inflammaging

SPM decline with age

Specialized pro-resolving mediators (lipoxins, resolvins, protectins, maresins) are biosynthesized from omega-3 and omega-6 polyunsaturated fatty acids via lipoxygenase and COX-2 pathways. Their circulating and tissue levels have been reported to decline with advancing age in multiple studies, with functional consequences for acute inflammation resolution. This decline, combined with maintained or elevated pro-inflammatory FPR2 agonist loads (SAA rises in chronic low-grade inflammation), may shift the FPR2 ligand environment toward chronic pro-inflammatory signaling.

needs-replication — Population-level data on SPM decline across the human lifespan are limited; most studies are cross-sectional or use surrogate tissues (cerebrospinal fluid, adipose biopsy).

Alzheimer’s disease as an aging-relevant resolution-failure model

Resolution of neuroinflammation is impaired in Alzheimer’s disease (AD), an aging-associated condition. Wang et al. (2015, Alzheimer’s & Dementia, online Feb 2014) found:

Reduced LXA4 levels in AD hippocampal tissue (n=7 AD vs n=7 controls; Mann-Whitney U z=−2.236, p=0.026) and CSF (AD n=15 significantly lower than MCI n=20 and SCI n=21 groups; ANCOVA Bonferroni p=0.006 vs MCI, p<0.001 vs SCI)
Hippocampal tissue RvD1 did not differ significantly between AD and controls (z=−0.575, p=0.62)
SPM receptor expression changes in AD: FPRL1/FPR2 immunohistochemistry showed stronger glial labeling in AD, but Western blot showed no statistically significant difference in LXA4R/FPR2 protein between AD (n=7) and controls (n=9; z=−0.053, p=0.958); ChemR23 was significantly elevated in AD (z=−2.593, p=0.008); the biosynthetic enzyme 15-LOX-2 was higher in AD (z=−2.382, p=0.016)
CSF LXA4 correlated positively with MMSE cognitive scores (Spearman r=0.475, p<0.0005); CSF RvD1 also correlated with MMSE (r=0.343, p<0.05) ³

The same receptor axis (FPR2/ALX) mediates microglial responses to amyloid-beta: FPRL1/FPR2 on microglial cells drives chemotaxis toward Aβ and participates in its internalization, linking FPR2 biology to neuroinflammation and amyloid clearance ⁴.

A 2025 review (Molecular Neurodegeneration) synthesized evidence that n-3-derived SPMs — acting via FPR2 and related receptors — regulate microglial mitochondrial respiration and inflammation resolution in AD, reinforcing the aging-disease-resolution failure link ⁵. needs-human-replication

Obesity and metabolic inflammaging

Clária et al. (2012, J Immunology) showed that RvD1 and RvD2 reduce local inflammatory tone in obese adipose tissue — increasing adiponectin expression and suppressing pro-inflammatory cytokines (TNF-α, IL-6, IL-1β) and monocyte accumulation ⁶. RvD1 acts via ALX/FPR2 and ChemR23; RvD2 acts primarily via GPR32 and ChemR23. Obesity-associated low-grade inflammation (a form of inflammaging) is thus mechanistically linked to insufficient pro-resolving SPM signaling, with ALX/FPR2 as a key receptor node for RvD1. needs-replication — full text of this paper was not available for quantitative claim verification (PDF download failed; partially verified via Crossref abstract only).

COPD and chronic airway inflammation

In COPD, pro-resolving FPR2 agonists (LXA4, RvD1, annexin A1) are insufficient to suppress inflammation. Bozinovski, Anthony, and Vlahos (2014) attribute this to agonist-biased ALX/FPR2 receptor conformations within a COPD airway environment rich in competing pro-inflammatory FPR2 agonists (SAA, LL-37/hCAP-18, mitochondrial hexapeptides released from damaged tissue), which drive pro-inflammatory receptor conformations and override pro-resolving signaling ⁷. SAA also promotes FPR2 homodimerization and pro-survival signaling in neutrophils. COPD is highly age-associated, and this resolution-failure mechanism is a candidate contributor to the aging-inflammation link.

Extrapolation table

Dimension	Status	Notes
Pathway conserved in humans?	yes	GPCR class A; Gαi coupling conserved; SPM receptor function validated in primary human leukocytes
Phenotype conserved in humans?	partial	Resolution failure in aging and AD documented in humans; causal directionality (SPM decline → inflammaging) not formally established
Replicated in humans?	partial	SPM-FPR2 resolution axis replicated across multiple disease models; direct aging-specific RCT data lacking

Pharmacology and druggability

Druggability tier: 2 (aging context). Multiple selective FPR2 agonists have reached clinical development for inflammatory indications (not aging per se):

BMS-986235 (LAR-1219) — potent selective FPR2 agonist (J Med Chem 2020); clinical development for cardiovascular / inflammatory indications
Lipoxin A4 analogues — synthetic mimetics in early clinical investigation; anti-inflammatory without immunosuppression
Resolvin D1 (RvD1) — endogenous agonist; not clinical-stage as drug per se but used as pharmacological tool
Compound 17b — biased FPR2 agonist (Nat Commun 2018); evidence of conformationally selective agonism

No FPR2-targeting drug is FDA-approved or in a registered aging-indication clinical trial as of 2026-05-09. Tier 2 reflects high-quality pharmacological probes + multiple clinical-stage agonists for inflammatory indications. needs-aging-trial

Note on LXA4/FPR2 controversy: Hanson et al. (2013, Biochemical Pharmacology) reported that heterologously expressed FPR2 does not respond to LXA4 in some assay systems, suggesting the receptor pharmacology may be cell-context-dependent or require specific membrane lipid environments. This is an active area of debate in the field. contradictory-evidence

Pathway membership

nf-kb — pro-inflammatory FPR2 activation feeds into NF-κB via PI3Kγ → IKK
lps-tlr4-nfkb — SAA-mediated FPR2 signaling amplifies TLR-driven NF-κB responses
SPM-pathway — gap/needs-canonical-id no dedicated wiki page yet; FPR2 is the canonical receptor node for lipoxin A4, resolvin D1 class SPMs; implicit stub: spm-pathway

Key interactors and ligands

camp (LL-37) — endogenous antimicrobial peptide ligand; context-dependent pro- or anti-inflammatory via FPR2
ll-37 — LL-37 compound page
Annexin A1 (ANXA1) — endogenous glucocorticoid-regulated pro-resolving ligand; activates FPR2 homodimers → IL-10
Serum amyloid A (SAA) — acute-phase DAMP; pro-inflammatory FPR2 agonist
Resolvin D1 (RvD1) — omega-3 metabolite; potent pro-resolving FPR2 agonist; structural basis for selectivity elucidated by molecular dynamics ⁸
FPR1 — heterodimerization partner; may modify FPR2 signaling

Limitations and gaps

#gap/needs-canonical-id — SPM-pathway has no dedicated wiki page. Implicit stub: spm-pathway.
#gap/needs-aging-trial — No registered clinical trial tests FPR2 agonism in a human aging or inflammaging indication as of 2026-05-09.
#gap/needs-human-replication — SPM decline with aging as causal driver of inflammaging is biologically plausible but not established by RCT or MR evidence.
#gap/contradictory-evidence — LXA4 / FPR2 pharmacological coupling is disputed (Hanson 2013 vs multiple functional studies); cell-context dependence likely.
#gap/no-fulltext-access — Le 2002 (Trends Immunol, 10.1016/s1471-4906(02)02316-5) and Iribarren 2005 (Immunol Res, 10.1385/ir:31:3:165) are closed-access (not_oa per a local paper archive); framing claims attributed to these reviews cannot be fully verified against primary source text. Claria 2012 (J Immunol, 10.4049/jimmunol.1201272) PDF download failed repeatedly; body claims partially verified from Crossref abstract.
gtex-aging-correlation: not populated — requires GTEx v2 API query per sops/finding-tissue-expression.md.
mr-causal-evidence: not-tested — no GWAS instruments or MR studies identified for FPR2 and aging outcomes.
genage-id: null — FPR2 does not appear in GenAge Human; aging relevance is indirect (through SPM axis). needs-canonical-id if relevant.

Footnotes

doi:10.1016/s1471-4906(02)02316-5 · Le Y, Murphy PM, Wang JM · Trends Immunol 2002;23(11):541–548 · review · cited_by 604 · Formyl-peptide receptors revisited: characterization of FPR and FPRL1 (FPR2) as receptors for structurally diverse pro- and anti-inflammatory ligands ↩
doi:10.1073/pnas.1308253110 · Cooray SN, Gobbetti T, Montero-Melendez T, McArthur S, Thompson D, Clark AJL, Flower RJ, Perretti M · PNAS 2013;110(45):18232–18237 · in-vitro + in-vivo · model: transfected HEK293 cells (BRET/co-IP), primary human monocytes and neutrophils, C57BL/6 and Alx-Fpr2/3 KO mice (i.p. AnxA1 1 µg; LPS 10 mg/kg) · AnxA1 selectively promotes ALX homodimerization (BRET signal enhanced; co-IP confirmed); SAA does NOT promote homodimerization (decreases BRET signal); AnxA1 → p38/MAPKAPK/Hsp27 pathway → IL-10 in monocytes and mice; FPR1/ALX heterodimer → JNK pathway → pro-apoptotic signaling in neutrophils; biased agonism established mechanistically ↩ ↩²
doi:10.1016/j.jalz.2013.12.024 · Wang X, Zhu M, Hjorth E, Cortés-Toro V, Eyjolfsdottir H, Graff C, et al. · Alzheimer’s & Dementia 2015;11(4):405–419 (online Feb 2014) · observational · n=postmortem hippocampal tissue (AD n=7–10, controls n=7–10) + CSF (AD n=15, MCI n=20, SCI n=21) · LXA4 reduced in AD hippocampus (p=0.026) and CSF (p<0.001 vs SCI); hippocampal RvD1 not significantly reduced (p=0.62); FPR2/LXA4R protein not significantly different by Western blot (p=0.958); ChemR23 significantly elevated in AD (p=0.008); CSF LXA4 correlates with MMSE (r=0.475, p<0.0005); CSF RvD1 correlates with MMSE (r=0.343, p<0.05) ↩
doi:10.1385/ir:31:3:165 · Iribarren P, Le Y, Wang JM · Immunol Res 2005;31(3):165–176 · review · cited_by 105 · FPRL1/FPR2 on microglia mediates Aβ chemotaxis and internalization in Alzheimer disease ↩
doi:10.1186/s13024-025-00824-1 · Slayo M, Rummel C, Singhaarachchi PH, Feldotto M, Spencer SJ · Mol Neurodegener 2025;20:35 · review · n-3-derived SPMs (lipoxins, D-series resolvins, protectins, maresins) regulate microglial mitochondrial bioenergetics (AMPK → SIRT1 → PGC-1α → oxidative phosphorylation) and inflammation resolution in AD; SPM bioavailability proposed as sustaining pro-resolving microglial phenotype and amyloid-β phagocytosis; FPR2/ALX and related receptors (ChemR23, RORα/LGR6) as therapeutic targets; RvD4 receptor on microglia is currently unknown ↩
doi:10.4049/jimmunol.1201272 · Clária J, Dalli J, Yacoubian S, Gao F, Serhan CN · J Immunol 2012;189(5):2597–2605 · in-vivo + ex-vivo · model: obese mouse adipose / human adipocytes · RvD1 (via ALX/FPR2 and ChemR23) and RvD2 (via GPR32 and ChemR23) rescue adiponectin expression and reduce monocyte accumulation and pro-inflammatory cytokines in obese adipose tissue · no-fulltext-access PDF download failed; body claims partially verified from Crossref abstract only ↩
doi:10.3978/j.issn.2072-1439.2014.08.08 · Bozinovski S, Anthony D, Vlahos R · J Thorac Dis 2014;6(11):1548–1556 · review · COPD resolution failure attributed to imbalance between pro-inflammatory FPR2 agonists (SAA, LL-37/hCAP-18, mitochondrial hexapeptides) and pro-resolving agonists (LXA4, RvD1, annexin A1); agonist-biased ALX/FPR2 conformations proposed as mechanism; SAA shown to promote FPR2 homodimerisation and pro-survival neutrophil pathways ↩
doi:10.1021/acs.jpcb.3c01787 · Nunes VS, Serhan CN · J Phys Chem B 2023 · in-silico (molecular dynamics) · Structural basis for RvD1 vs AT-RvD1 selectivity at FPR2; R201 and R205 as receptor hotspots; RvD1 maintains active state 74% of simulation time ↩

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