ERFE

ERFE (erythroferrone/myonectin/CTRP15/FAM132B) is a secreted C1q/TNF-family protein that couples erythropoietic and metabolic demand to systemic iron homeostasis by acting as an extracellular BMP pathway antagonist (PMID:31846624, PMID:30287465). Its central iron-regulatory function is to suppress liver hepcidin: acting downstream of EPO, ERFE interferes with the engagement of specific BMP ligands by their receptors, blocking BMP/SMAD signaling in the liver (PMID:30287465, PMID:37413927), and this BMP-inhibitory activity is independent of the conserved C1q domain (PMID:31846624). ERFE is produced by multiple cell types under erythropoietic stress, including osteocytes, where EPO/EPOR signaling drives its expression and contributes to systemic hepcidin suppression after phlebotomy [PMID:bio_10.1101_2024.09.27.615409]. The gain-of-function ERFE-A260S variant raises ERFE protein, impairs hepatic BMP/SMAD signaling, and causes iron overload, establishing ERFE as a modifier of human iron regulation (PMID:31400017). Beyond iron metabolism, ERFE has documented roles in lipid handling—promoting fatty acid uptake in adipocytes and hepatocytes via induction of CD36, FATP1, Fabp1, and Fabp4 (PMID:22351773)—and its mRNA is stabilized post-transcriptionally by METTL14-deposited m6A marks read by IGF2BP3 (PMID:41205320).

1. 2012 Medium

   Before its iron role was known, the protein was characterized as a muscle-secreted myokine, establishing it as a circulating C1q/TNF-family factor that influences peripheral lipid handling.

   Evidence Recombinant protein administration in mice plus in vitro fatty acid uptake assays in adipocytes/hepatocytes

   PMID:22351773

   Open questions at the time

   • No receptor or direct binding partner identified for the fatty-acid-uptake effect
   • Link between lipid metabolism and later iron/BMP functions not established
2. 2018 Medium

   Defined the iron-regulatory mechanism, showing ERFE acts downstream of EPO to suppress hepcidin by interfering with BMP ligand–receptor binding rather than acting as a conventional hormone on a dedicated receptor.

   Evidence Commentary summarizing experimental EPO→ERFE→BMP receptor interference data

   PMID:30287465

   Open questions at the time

   • Identity of the specific BMP ligands trapped not resolved here
   • Source is a commentary, not the primary dataset
3. 2019 High

   Established mechanistically that ERFE is an extracellular BMP antagonist acting by direct ligand binding, and mapped the activity to a region outside the conserved C1q domain.

   Evidence Gain-of-function and morpholino knockdown in Xenopus embryos, ectodermal explant assays, domain-deletion experiments, RNAseq

   PMID:31846624

   Open questions at the time

   • Which BMP ligands are bound with what affinity not quantified
   • Structural basis of ligand sequestration unknown
4. 2019 Medium

   Connected ERFE function to human disease by showing a gain-of-function variant raises ERFE, impairs hepatic BMP/SMAD signaling, and drives iron overload.

   Evidence Functional characterization of ERFE-A260S in hepatic cells with BMP/SMAD readout plus patient cohort genotyping

   PMID:31400017

   Open questions at the time

   • Mechanism by which A260S elevates protein level unclear
   • Penetrance and modifier interactions in patients not defined
5. 2020 Medium

   Extended ERFE biology to the heart, identifying an anti-fibrotic action mediated through IR/IRS-1/Akt signaling that antagonizes TGF-β1/Smad3, distinct from its extracellular BMP-trap mechanism.

   Evidence AAV9 overexpression in pressure-overloaded mice, recombinant protein and conditioned-medium treatment of cardiac fibroblasts, pathway inhibitor rescue

   PMID:32424654

   Open questions at the time

   • Direct ERFE–IR binding not demonstrated
   • Reconciliation with BMP-trap mechanism unaddressed
6. 2022 Medium

   Defined a vascular/metabolic role in which ERFE promotes macrophage cholesterol efflux through a T-cadherin/miR-101-3p/ABCA1 axis.

   Evidence Lentiviral CTRP15 overexpression in apoE-/- mice plus in vitro macrophage cholesterol efflux and miRNA/gene expression assays

   PMID:35286626

   Open questions at the time

   • Direct interaction between ERFE and T-cadherin not shown biochemically
   • Relevance to iron/BMP signaling unknown
7. 2022 Low

   Implicated ERFE in glucose homeostasis, with overexpression improving insulin resistance and knockdown impairing adipose epinephrine response, though candidate receptors were only computationally predicted.

   Evidence AAV9 gene delivery and shRNA knockdown in high-fat-diet mice with metabolic phenotyping; structural prediction of ADRB2/insulin-receptor interaction

   PMID:35922561

   Open questions at the time

   • Receptor interactions (ADRB2, insulin receptor) are in silico predictions only, not experimentally validated
   • Mutant construct (A136T/P159A) confounds interpretation of native function
8. 2023 Low

   Provided in vivo correlative support that EPO/STAT5 governs ERFE expression and that this axis tunes hepatic hepcidin via BMP/SMAD in a metabolic-disease context.

   Evidence Rat metabolic syndrome model with/without CIHH, protein and mRNA quantification of STAT5/ERFE/hepcidin/BMP-SMAD components

   PMID:37413927

   Open questions at the time

   • No direct manipulation of ERFE; pathway linkage is correlative
   • STAT5 control of ERFE shown by association, not genetic perturbation
9. 2024 Medium

   Identified osteocytes as an additional EPO-responsive cellular source of ERFE that contributes to systemic hepcidin suppression during stress erythropoiesis.

   Evidence Osteocyte RNAseq, bone marrow transplant into Erfe-/- mice, osteocyte-specific Epor knockout (Dmp1-Cre), phlebotomy stress model with liver hepcidin readout (preprint)

   PMID:bio_10.1101_2024.09.27.615409

   Open questions at the time

   • Quantitative contribution of osteocyte vs erythroid ERFE not resolved
   • Preprint, not yet peer-reviewed
10. 2025 Medium

    Revealed post-transcriptional control of ERFE, showing METTL14-deposited m6A marks read by IGF2BP3 stabilize ERFE mRNA, with functional consequences for renal tubular ferroptosis.

    Evidence MeRIP-PCR, IGF2BP3 RIP, actinomycin D mRNA stability assay, siRNA/overexpression and epistasis rescue in HK-2 cells

    PMID:41205320

    Open questions at the time

    • Whether m6A regulation operates in erythroid/osteocyte ERFE sources untested
    • Mechanism linking ERFE level to ferroptosis not defined

• The molecular identity of the specific BMP ligands ERFE traps and a structural model of the ligand-binding interface remain undefined, as does how ERFE's multiple receptor-coupled effects (IR/IRS-1, T-cadherin, predicted ADRB2) relate to its extracellular BMP-antagonist mode.
• No structural model of ERFE–BMP ligand complex
• No validated cell-surface receptor for the metabolic effects
• Tissue-specific selectivity among ERFE functions unexplained