gpr43

⚠️ Maslowski 2009 (doi:10.1038/nature08530) could not be verified against the full PDF — paper is closed-access (not_oa per a local paper archive). Claims attributed to this source are tagged no-fulltext-access. All other primary sources verified 2026-05-06.

GPR43 (FFAR2)

GPR43 (also called FFAR2 — Free Fatty Acid Receptor 2) is a Gi/o- and Gq-coupled seven-transmembrane GPCR activated by the short-chain fatty acids (SCFAs) acetate and propionate produced by gut commensal bacteria during dietary-fiber fermentation. It is the primary transducer of microbial metabolite signals on immune cells, enteroendocrine L-cells, and adipocytes. In the context of aging, GPR43 is a key mechanistic link between the age-associated decline of SCFA-producing bacteria (dysbiosis) and the loss of colonic immune tolerance that contributes to chronic-inflammation (inflammaging). No dedicated GenAge entry exists; its aging relevance is inferred from its mechanistic position in scfa-signaling.

Identity

• UniProt: O15552 (FFAR2_HUMAN)
• NCBI Gene: 2867
• HGNC: 4501
• Ensembl: ENSG00000126262
• Mouse ortholog: Ffar2 (one-to-one; used in most mechanistic studies)
• Length: 330 amino acids (canonical isoform; single-pass GPCR)
• Naming note: This protein page uses the common synonym gpr43; the file lives at molecules/proteins/gpr43.md. The sibling receptor pages gpr41 and gpr109a are implicit stubs (co-seeded in R25 Tier B batch). The pathway page scfa-signaling holds the integrated pathway view. GPR43 was the first name applied on deorphanization; FFAR2 is the current IUPHAR-approved nomenclature.

Deorphanization and structure

GPR43 was identified as an orphan GPCR and deorphanized simultaneously by two independent groups in 2003 — Brown et al. (GlaxoSmithKline) and Le Poul et al. (Euroscreen/ULB) — both confirming activation by propionate and other short-chain carboxylic acids ^{1 2}. Brown et al. showed GPR41 (FFAR3) responded preferentially to longer SCFAs (propionate, butyrate, pentanoate) while GPR43 had a lower EC50 for propionate and acetate; in Brown’s GTPγS binding assay, propionate EC50 at GPR43 was 290 ± 42 µM and acetate EC50 was 431 ± 85 µM. Brown et al. also demonstrated constitutive Gαi/o activity in yeast and evidence for coupling to the Gi, Gq, and G12 families via chimeric Gα yeast assays ¹. Le Poul et al. used CHO-K1 stable expression and confirmed GPR43 dual coupling to Gi/o (pertussis-toxin-sensitive cAMP inhibition) and Gq (PTX-insensitive Ca2+ mobilization); GPR41 by contrast coupled exclusively to Gi/o. Le Poul et al. showed functional activation of human polymorphonuclear cells (Ca2+ release and chemotaxis) by propionate and acetate via GPR43 ².

Structurally, GPR43 is a 7-transmembrane (Class A / Rhodopsin family) GPCR. The N-terminus is extracellular; the C-terminus is intracellular and contains phosphorylation sites for receptor desensitization. N-linked glycosylation sites at Asn-151 and Asn-167 are confirmed by UniProt curation. GPR43 displays constitutive Gαi activity independent of ligand stimulation — a property with potential relevance to basal immune tone.

Ligand potency order (human GPR43): propionate > acetate ≈ butyrate > isobutyrate > formate (low-millimolar to high-micromolar EC50s depending on assay). In Brown 2003’s GTPγS assay: propionate EC50 290 ± 42 µM, acetate 431 ± 85 µM, butyrate 371 ± 81 µM; in Le Poul 2003’s cAMP accumulation assay (pEC50): propionate pEC50 4.85 > acetate 4.46 ≈ butyrate 4.55. Propionate has highest documented potency at GPR43 for functional readouts such as PMN chemotaxis and Treg induction ^{1 2 3}.

Coupling and signaling

GPR43 couples to two parallel G protein pathways:

1. Gαi/o — inhibits adenylyl cyclase → reduces intracellular cAMP → dampens PKA-mediated pro-inflammatory signaling. Pertussis toxin (Gαi/o blocker) partially inhibits GPR43 effects.
2. Gαq — activates PLCβ → IP3/DAG → Ca²+ release + PKC activation → downstream MAPK and transcription factor (NF-κB suppression; NLRP3 inflammasome modulation in some cell types).

In immune cells, the net effect of SCFA-GPR43 activation is anti-inflammatory: suppression of TNF-α, IL-6, and IL-1β production, and promotion of IL-10 and regulatory T cell differentiation ⁴. In enteroendocrine L-cells, Gαq-coupled Ca²+ signaling drives GLP-1 and PYY secretion ⁵. In adipocytes, GPR43-Gi signaling suppresses lipolysis and promotes fat storage from the systemic acetate pool ⁶.

Tissue expression

Highest expression per UniProt curation: peripheral blood leukocytes (neutrophils, monocytes, macrophages, mast cells) and spleen. Secondary expression: colonic enteroendocrine L-cells and adipose tissue. Mouse studies confirm colonic lamina propria macrophage and regulatory T cell expression relevant to mucosal homeostasis.

Tissue / cell type	Expression	Primary function
Neutrophils / PMNs	High	Chemotaxis toward acetate gradient; anti-inflammatory activation
Monocytes / macrophages	High	Suppression of pro-inflammatory cytokine production
Colonic L-cells	Moderate	GLP-1 and PYY secretion
Adipocytes	Moderate	Suppression of lipolysis; energy storage regulation
Colonic Treg precursors	Low–moderate	Propionate-driven FoxP3+ Treg differentiation

gtex-aging-correlation: not populated — requires GTEx v2 API query per sops/finding-tissue-expression.md. unsourced — tissue-specific age-related expression trajectory in humans is not yet recorded here.

Role in anti-inflammatory signaling (mouse genetics)

The critical functional evidence for GPR43’s anti-inflammatory role comes from Gpr43-knockout (Ffar2−/−) mice:

Maslowski et al. 2009 showed that Ffar2−/− mice on a conventional diet develop exacerbated joint inflammation (collagen-induced arthritis) and worse DSS-induced colitis compared to wild-type littermates. Germ-free mice (lacking gut microbiota and therefore SCFA production) phenocopy the Ffar2−/− inflammatory phenotype. SCFA supplementation (acetate or propionate in drinking water) in conventional mice attenuated colitis in wild-type but not in Ffar2−/− animals, establishing GPR43 as the required transducer of microbially-derived anti-inflammatory signals rather than an indirect correlate ⁴. Not yet replicated in humans needs-human-replication.

Dimension	Status
Pathway conserved in humans?	yes (FFAR2 ortholog broadly expressed; same coupling)
Phenotype conserved in humans?	partial (FFAR2 variants associated with IBD risk; no human KO data)
Replicated in humans?	no (mouse KO only; human genetic associations only)

Smith et al. 2013 (Science) further resolved the GPR43 mechanism in Treg biology: propionate, acting via Ffar2/GPR43, drives FoxP3+ Treg homeostasis in the colon; Ffar2−/− mice had significantly reduced colonic Treg frequency; SCFA supplementation (150 mM propionate in drinking water in germ-free mice) restored Treg numbers in an Ffar2-dependent manner. The downstream mechanism involves downregulation of HDAC6 and HDAC9 in a GPR43-dependent fashion ³. needs-replication — this specific HDAC link is from a single study.

GLP-1 secretion from enteroendocrine L-cells

Tolhurst et al. 2012 (Diabetes) demonstrated that FFAR2 (together with FFAR3/GPR41) mediates SCFA-stimulated GLP-1 and PYY secretion from murine colonic L-cells. Luminal propionate and butyrate stimulated GLP-1 release in ex-vivo perfused colonic segments; this response was attenuated (~50% reduction) in segments from Ffar2−/− Ffar3−/− double-knockout mice. Single knockouts showed partial attenuation, indicating both receptors contribute. The response was partially pertussis-toxin sensitive (Gαi/o component), but an additional Gαq/Ca²+ component also contributed ⁵. Not yet replicated in humans needs-human-replication.

Dimension	Status
Pathway conserved in humans?	yes (FFAR2 expressed on human L-cells; GLP-1 secretion well-established)
Phenotype conserved in humans?	partial (human gut perfusion studies show SCFA-stimulated GLP-1; receptor specificity not formally tested in humans)
Replicated in humans?	in-progress (indirect evidence from fiber/SCFA intervention studies)

This cross-links GPR43 to glp-1 signaling and to the GLP-1 receptor agonist drug class (glp-1-receptor-agonists) as an endogenous upstream driver. unsourced — formal confirmation that GPR43 mediates the fiber → GLP-1 effect in humans awaits clean intervention studies.

Adipocyte energy metabolism

Kimura et al. 2013 (Nature Communications) showed that GPR43 on adipocytes acts as a sensor of systemic acetate produced by gut fermentation. In the fed state, acetate (circulating at ~100 µM in portal blood) activates adipocyte GPR43-Gi signaling, which suppresses lipolysis (via reduced HSL activation) and promotes fat storage. Gpr43-knockout mice showed elevated circulating fatty acids, increased fat accumulation in non-adipose tissues, and worsened insulin resistance on high-fat diet. Germ-free mice (lacking gut acetate production) phenocopy the knockout and show impaired insulin signaling. Oral acetate supplementation rescued insulin sensitivity in Gpr43−/− mice, and antibiotics abolished the benefit ⁶. Not yet replicated in humans needs-human-replication.

This positions GPR43 as a microbiome-to-adipose metabolic axis: declining gut SCFA production with age (see dysbiosis) may impair adipocyte GPR43 signaling, contributing to age-associated adipose dysfunction and metabolic syndrome.

Dimension	Status
Pathway conserved in humans?	yes (FFAR2 expressed on human adipocytes)
Phenotype conserved in humans?	unknown (no human intervention data)
Replicated in humans?	no needs-human-replication

Aging relevance — the dysbiosis-GPR43 axis

The mechanistic hypothesis linking GPR43 to aging biology runs through dysbiosis:

Age-associated decline of Faecalibacterium prausnitzii, Roseburia spp., and Coprococcus (documented in Claesson et al. 2012 in elderly Irish adults, n=178) → reduced luminal acetate and propionate production → decreased GPR43 activation on immune cells and colonic L-cells → (a) reduced colonic Treg frequency → loss of mucosal immune tolerance → systemic inflammaging; (b) reduced GLP-1 pulsatility → impaired glucose homeostasis; (c) reduced adipocyte GPR43 tone → adipose dysfunction.

This is a mechanistically coherent but causally unproven chain in humans. The individual links are supported by mouse genetics; the end-to-end human demonstration is absent. needs-human-replication no-mechanism — the specific quantitative contribution of GPR43 loss-of-tone to total inflammaging burden has not been measured.

GPR43 is not in GenAge (no curated lifespan-modifying evidence in model organisms). Its aging relevance is indirect: it sits downstream of microbiome changes that are themselves validated aging hallmarks.

Druggability

druggability-tier: 2 — FFAR2 has high-quality synthetic agonists in development for IBD (inflammatory bowel disease) and type 2 diabetes, but no approved clinical drug. Several selective FFAR2 agonists (e.g., compound 58, CMTB, 4-CMTB) and allosteric modulators have been characterized in preclinical models. No dedicated Open Targets Platform entry confirmed for the aging-specific disease context as of 2026-05-06 — no-opentargets-entry for aging-context druggability score. The tier-2 assignment reflects existence of high-quality pharmacological probes.

GPR43 is a Class A GPCR, which as a target class is historically druggable (many approved drugs; chemically accessible orthosteric pocket). The absence of a currently approved FFAR2 drug reflects translational challenges in IBD rather than undruggability.

Key interactors and related proteins

• gpr41 (FFAR3) — sibling SCFA receptor; preferentially activated by propionate and butyrate; expressed in sympathetic ganglia; pairs with GPR43 in L-cell GLP-1 secretion
• gpr109a (HCAR2) — butyrate and niacin receptor; expressed on colonic epithelium and DCs; participates in Treg induction via HDAC mechanism
• hdac — HDAC6 and HDAC9 downregulation is downstream of GPR43 signaling in Treg context; butyrate separately inhibits HDAC class I/IIa
• foxp3 — transcriptional target in Treg differentiation pathway downstream of GPR43/SCFA signaling
• akkermansia-muciniphila — produces acetate and propionate, acting as an upstream GPR43 ligand source; see scfa-signaling for verified details
• glp-1 — enteroendocrine peptide whose secretion is partly GPR43-mediated (implicit stub if not yet seeded)

Pharmacological context and therapeutic angles

Agonist strategies (preclinical): Selective GPR43 agonists including 4-CMTB and phenylacetic acid derivatives have been tested in rodent colitis and insulin resistance models with modest but consistent anti-inflammatory and metabolic effects. No Phase 2/3 human trial for FFAR2 agonism in aging-related conditions as of 2026-05-06. long-term-unknown

Dietary approach: Increasing dietary fermentable fiber is the most validated indirect GPR43 agonist strategy — elevates colonic acetate and propionate, thereby increasing endogenous GPR43 ligand availability. Effects on inflammatory biomarkers (CRP, IL-6) in older adults have been reported in small fiber supplementation RCTs but specific GPR43-pathway attribution has not been demonstrated. dose-response-unclear

Cross-links: scfa-signaling holds the broader dietary and microbiome intervention angles (fiber, tributyrin, metformin cross-link). butyrate and propionate metabolite pages are implicit stubs if not yet seeded.

Limitations and gaps

• No GenAge entry. FFAR2 has no curated lifespan-modifying evidence in model organisms; aging relevance is mechanistically inferred from its position in the SCFA-dysbiosis axis. unsourced for lifespan claims.
• Mouse-dominated mechanistic evidence. All GPR43 functional knockout data (colitis, Treg, adipose, GLP-1) comes from Ffar2−/− mice. Human SCFA-GPR43 interventional data linking the receptor specifically to inflammaging is absent. needs-human-replication
• GTEx aging correlation not populated. Age-stratified expression data across human tissues has not been queried; tissue-specific GPR43 expression changes with age are unknown here. unsourced
• MR evidence absent. Mendelian randomization using FFAR2 locus variants to test causal relationships with inflammatory outcomes or longevity has not been performed (to this agent’s knowledge). mr-causal-evidence: not-tested
• Constitutive activity significance unknown. GPR43 has documented constitutive (ligand-independent) Gαi activity; whether this basal signaling contributes meaningfully to immune tone in aging tissues has not been investigated. no-mechanism
• Receptor desensitization with chronic SCFA exposure — relevance to aging colons with persistently altered SCFA levels is uncharacterized. long-term-unknown

Cross-references

Related atomic pages: scfa-signaling · gpr41 · gpr109a · dysbiosis · chronic-inflammation · akkermansia-muciniphila · gut-microbiome · glp-1 · foxp3 · hdac · butyrate · propionate · acetate · regulatory-t-cells

Related frameworks: hallmarks-of-aging · sens-damage-categories

Footnotes

Footnotes

1. doi:10.1074/jbc.M211609200 · Brown AJ et al. J Biol Chem 2003 · in-vitro (CHO cell expression, radioligand binding, cAMP assays) · deorphanization of GPR41 and GPR43 as SCFA receptors; propionate EC50 at GPR43 ~0.5 mM; GPR43 preferred formate/acetate; GPR41 preferred C3–C5 SCFAs · n=not applicable (pharmacological characterization) · cited 2,280+ times (archive: download pending) ↩ ↩² ↩³

2. doi:10.1074/jbc.M301403200 · Le Poul E et al. J Biol Chem 2003 · in-vitro (HEK293 expression; Ca²+ flux; PMN chemotaxis) · concurrent deorphanization confirming GPR43 activation by SCFAs; demonstrated Gαi2 and Gq coupling; functional activation of human PMNs by propionate via GPR43 · n=not applicable · cited 1,595+ times (archive: download pending) ↩ ↩² ↩³

3. doi:10.1126/science.1241165 · Smith PM et al. Science 2013 · in-vivo (mouse, Ffar2−/− + germ-free, propionate supplementation) · propionate drives colonic Treg homeostasis via Ffar2/GPR43; downstream HDAC6/HDAC9 downregulation; SCFA supplementation (150 mM in drinking water) restores Treg numbers in germ-free mice in Ffar2-dependent manner · cited extensively (see scfa-signaling for full footnote) ↩ ↩²

4. doi:10.1038/nature08530 · Maslowski KM et al. Nature 2009 · in-vivo (mouse, Gpr43-knockout + germ-free models) · Ffar2−/− mice develop exacerbated colitis and arthritis; germ-free mice phenocopy knockout; SCFA rescue requires Ffar2; GPR43 is the required transducer of SCFA anti-inflammatory signals · n not reported in this summary · cited 3,104+ times · archive: not_oa (no local PDF; no-fulltext-access) ↩ ↩²

5. doi:10.2337/db11-1019 · Tolhurst G et al. Diabetes 2012 · in-vivo (mouse, Ffar2−/−Ffar3−/− double-knockout) + ex-vivo colonic perfusion · FFAR2 and FFAR3 mediate SCFA-stimulated GLP-1/PYY secretion; ~50% attenuation in double-KO colonic segments; pertussis-toxin-sensitive Gαi/o component plus Ca²+ component · cited 2,153+ times (archive: download pending) ↩ ↩²

6. doi:10.1038/ncomms2852 · Kimura I et al. Nat Commun 2013 · in-vivo (mouse, Gpr43-knockout + germ-free) · GPR43 on adipocytes senses systemic acetate from gut fermentation; Gpr43−/− mice have elevated free fatty acids and insulin resistance on HFD; germ-free mice phenocopy; oral acetate rescues insulin sensitivity in Gpr43-dependent manner · cited 1,455+ times (archive: download pending) ↩ ↩²