Affinage

FGF22

Fibroblast growth factor 22 · UniProt Q9HCT0

Length
170 aa
Mass
19.7 kDa
Annotated
2026-04-28
18 papers in source corpus 13 papers cited in narrative 13 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

FGF22 is a secreted fibroblast growth factor that functions as a target-derived presynaptic organizer, signaling through FGFR2 to induce synaptic vesicle clustering and excitatory presynaptic differentiation in the mammalian brain. It is selectively trafficked to excitatory postsynaptic sites via a KIF3A/KIF17/SAP102-dependent microtubule transport system and presented to presynaptic terminals by syndecan-2, where CaMKII-dependent positive feedback coordinates pre- and postsynaptic maturation (PMID:15260994, PMID:25431136, PMID:27627962). FGF22 also acts retrogradely on presynaptic axons to induce IGF2 expression, which stabilizes presynaptic terminals in an activity-dependent manner, and CA3-specific deletion reduces excitatory synapse number and produces depression-like behavior (PMID:27083047, PMID:29311892). Beyond central synapses, FGF22 maintains cochlear ribbon synapses by sustaining vesicle pools and exocytosis efficiency, with its loss causing hidden hearing loss through downregulation of SNAP-25/Gipc3 and upregulation of MEF2D (PMID:26639016, PMID:35966010).

Mechanistic history

Synthesis pass · year-by-year structured walk · 9 steps
  1. 2004 High

    The fundamental question of what molecules organize presynaptic differentiation was addressed by identifying FGF22 as a target-derived signal that clusters synaptic vesicles and signals through FGFR2 on presynaptic neurons.

    Evidence Biochemical purification from mouse brain, synaptic vesicle clustering assay, in vivo antibody neutralization, and FGFR2 conditional knockout in cerebellum

    PMID:15260994

    Open questions at the time
    • Downstream signaling cascade from FGFR2 to vesicle clustering machinery not defined
    • Whether FGF22 acts alone or requires co-factors at the synapse not resolved
  2. 2005 Medium

    How FGF22 bioavailability is regulated extracellularly was partially answered by showing that FGF-binding protein (FGF-BP/FGFBP1) physically interacts with FGF22 and enhances its activity at low concentrations.

    Evidence Co-immunoprecipitation/pulldown and functional enhancement assay with wound injury model

    PMID:15806171

    Open questions at the time
    • No reciprocal binding validation with purified proteins
    • Mechanism of FGF-BP enhancement of FGF22 activity not elucidated
    • Relevance to synaptic versus epithelial contexts unclear
  3. 2013 Medium

    Whether FGF22 functions in brain patterning beyond synaptogenesis was established by showing that zebrafish Fgf22 acts downstream of Fgf3/Fgf8 through Fgfr2b to regulate midbrain-hindbrain boundary morphogenesis and cell proliferation.

    Evidence Morpholino knockdown, genetic epistasis with double morphants, and partial rescue in zebrafish

    PMID:23789101

    Open questions at the time
    • Morpholino approach lacks genetic mutant confirmation
    • Direct binding of Fgf22 to Fgfr2b not biochemically demonstrated in this system
  4. 2014 High

    How FGF22 achieves specificity for excitatory synapses was resolved by demonstrating its selective intracellular transport to excitatory postsynaptic sites via KIF3A/KIF17 motors and the SAP102 adaptor.

    Evidence Live-cell time-lapse imaging, motor/adaptor protein knockdown, co-immunoprecipitation, and immunofluorescence co-localization

    PMID:25431136

    Open questions at the time
    • How SAP102 recognizes FGF22-containing vesicles molecularly undefined
    • Whether similar trafficking applies in vivo not tested
  5. 2015 Medium

    FGF22's role was extended beyond central synapses by showing it maintains cochlear ribbon synapses in inner hair cells, with exogenous FGF22 rescuing gentamicin-induced synapse loss partly through MEF2D suppression.

    Evidence Immunohistochemistry, recombinant FGF22 cochlear infusion, auditory brainstem response, RT-PCR for MEF2D

    PMID:26639016

    Open questions at the time
    • No genetic loss-of-function in this study
    • MEF2D as direct or indirect target of FGF22 signaling not distinguished
  6. 2016 High

    Two critical steps in FGF22's synaptic mechanism were established: (1) postsynaptic syndecan-2 presents FGF22 to presynaptic FGFR with CaMKII-dependent positive feedback through KIF17, and (2) FGF22 retrogradely induces IGF2 in presynaptic neurons for activity-dependent synapse stabilization, distinguishing initial differentiation from stabilization.

    Evidence SDC2–FGF22 co-immunoprecipitation with domain deletions and filopodial targeting assays; local FGF22 application on axons, Fgf22 knockout cultures, IGF2 rescue experiments

    PMID:27083047 PMID:27627962

    Open questions at the time
    • Whether SDC2 is required in vivo for FGF22-mediated synaptogenesis not shown
    • How FGF22 retrograde signal reaches the nucleus to induce IGF2 transcription unknown
    • Relative contributions of FGFR1 versus FGFR2 in retrograde signaling untested
  7. 2017 High

    The in vivo behavioral relevance of FGF22's synaptogenic function was demonstrated by showing that CA3-specific FGF22 knockout reduces excitatory synapses and produces depression-like behavior without affecting dentate neurogenesis.

    Evidence Conditional CA3-specific Cre knockout mice, synapse quantification, forced swim and sucrose preference behavioral assays

    PMID:29311892

    Open questions at the time
    • Whether behavioral phenotype is reversible by synapse restoration not tested
    • Contribution of FGF22 from other brain regions to affective behavior unknown
  8. 2022 Medium

    The molecular mechanism of FGF22 in cochlear ribbon synapses was refined by showing that Fgf22 knockout reduces vesicle number and exocytosis efficiency at IHC synapses, with SNAP-25 and Gipc3 downregulation and MEF2D upregulation as downstream effectors.

    Evidence Fgf22 knockout mice, patch-clamp capacitance recordings, immunofluorescence, auditory brainstem response, qRT-PCR

    PMID:35966010

    Open questions at the time
    • Whether SNAP-25/Gipc3 are direct transcriptional targets of FGFR2 signaling not established
    • Single lab finding not independently replicated
  9. 2023 Medium

    FGF22-FGFR2b signaling was shown to promote neurogenesis of glutamatergic and GABAergic neurons while suppressing oligodendrocyte differentiation in zebrafish forebrain, extending its developmental role beyond midbrain patterning.

    Evidence Morpholino knockdown and overexpression of fgf22, epistasis with fgfr2b knockdown, cell-type marker analysis in zebrafish

    PMID:37783119

    Open questions at the time
    • Morpholino-based approach not confirmed with stable genetic mutants
    • Whether this neurogenic function is conserved in mammals unknown

Open questions

Synthesis pass · forward-looking unresolved questions
  • The intracellular signaling cascade downstream of FGFR2 activation that leads to synaptic vesicle clustering, the structural basis of the FGF22-FGFR2 interaction, and whether FGF22's synaptogenic and neuroprotective roles share common effector pathways remain unresolved.
  • No structural model of FGF22-FGFR2 complex exists
  • Downstream signaling effectors from FGFR2 to vesicle clustering not identified
  • Whether FGF22 synaptogenic function is relevant to human neurological disease not established through direct genetic evidence

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0048018 receptor ligand activity 5
Localization
GO:0005576 extracellular region 4 GO:0031410 cytoplasmic vesicle 1
Pathway
R-HSA-162582 Signal Transduction 4 R-HSA-112316 Neuronal System 3 R-HSA-1266738 Developmental Biology 2
Partners
FGFBP1FGFR2IGF2KIF17KIF3ASAP102SDC2

Evidence

Reading pass · 13 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2004 FGF22 is a target-derived presynaptic organizing molecule that induces clustering of synaptic vesicles in cultured neurons. FGF22 is expressed by cerebellar granule cells (postsynaptic) and its receptor FGFR2 is expressed by pontine and vestibular neurons (presynaptic mossy fibers). Neutralization of FGF7, -10, and -22 or inactivation of FGFR2 inhibits presynaptic differentiation of mossy fibers at granule cell contact sites in vivo. Biochemical purification from mouse brain, synaptic vesicle clustering assay, in vivo antibody neutralization, FGFR2 genetic inactivation Cell High 15260994
2005 FGF-binding protein (FGF-BP) physically interacts with FGF-22 (as well as FGF-7 and FGF-10) and enhances FGF-22 activity at low ligand concentrations. FGF-BP expression is upregulated after skin injury, suggesting it mobilizes FGF-22 to promote epithelial repair. Co-immunoprecipitation/pulldown binding assay, functional activity enhancement assay, wound injury model in vivo Oncogene Medium 15806171
2014 FGF22 is selectively targeted to excitatory postsynaptic sites via intracellular microtubule transport requiring motor proteins KIF3A and KIF17 and the adaptor protein SAP102 (DLG3). Time-lapse imaging shows FGF22 co-moves with SAP102 vesicles. This selective targeting underlies FGF22's specific role in excitatory (vs. inhibitory) presynaptic differentiation. Live-cell time-lapse imaging, knockdown of motor/adaptor proteins, immunofluorescence co-localization, co-immunoprecipitation Journal of cell science High 25431136
2016 FGF22 released from CA3 pyramidal neurons acts retrogradely on axons of dentate granule cells (presynaptic) to induce IGF2 expression in those neurons. IGF2 then localizes to presynaptic terminals and stabilizes them in an activity-dependent manner. IGF2 application rescues presynaptic defects in Fgf22−/− cultures, placing this FGF22→IGF2 feedback loop as required for presynaptic stabilization but not initial differentiation. Local FGF22 application on axons, Fgf22 knockout cultures, IGF2 rescue experiment, in vivo genetic analysis eLife High 27083047
2016 Postsynaptic syndecan-2 (SDC2) uses its ectodomain to interact with FGF22 and facilitate its dendritic filopodial targeting, thereby triggering presynaptic maturation via FGF22 presentation to presynaptic FGFR. CaMKII (activated downstream of NMDAR) further regulates FGF22 targeting via the KIF17 motor, forming a positive feedback loop coordinating pre- and postsynaptic differentiation. Co-immunoprecipitation of SDC2 and FGF22, domain deletion experiments, imaging of filopodial targeting, pharmacological and genetic perturbations Scientific reports Medium 27627962
2013 In zebrafish, Fgf22 acts downstream of Fgf3/Fgf8 signaling at the midbrain-hindbrain boundary, and its signaling is mediated through Fgfr2b. Fgf22 morphants show defective MHB constriction, decreased cell proliferation, and altered midbrain patterning. Partial rescue of fgf3/fgf8 double morphant phenotype by fgf22 places it genetically downstream in this pathway. Morpholino knockdown, genetic epistasis via double morphants and rescue, in situ hybridization, marker gene expression analysis Biology open Medium 23789101
2015 FGF22 protein is expressed in inner hair cells (IHCs) of the cochlea. Gentamicin reduces FGF22 expression and ribbon synapse number; cochlear infusion of recombinant FGF22 preserves ribbon synapses, restores hearing function, and inhibits MEF2D expression, suggesting FGF22 maintains ribbon synapse integrity partly by suppressing MEF2D. Immunohistochemistry, recombinant protein infusion, auditory brainstem response, RT-PCR Hearing research Medium 26639016
2017 CA3 pyramidal neuron-specific FGF22 knockout reduces excitatory synapses on CA3 neurons and produces depression-like behavior, without affecting dentate neurogenesis. This demonstrates that CA3-derived FGF22 acts as a target-derived excitatory synaptic organizer in vivo and that its synaptogenic role (not neurogenic role) in CA3 links to affective behavior. Conditional (CA3-specific Cre) knockout mice, synapse quantification by immunofluorescence, behavioral assays (forced swim, sucrose preference), dentate neurogenesis quantification Frontiers in synaptic neuroscience High 29311892
2022 FGF22 deletion in mice causes hidden hearing loss by reducing vesicle number at IHC ribbon synapses and decreasing exocytosis efficiency (reduced membrane capacitance change). Mechanistically, Fgf22 deletion downregulates SNAP-25 and Gipc3 and upregulates MEF2D, implicating these molecules in FGF22-dependent ribbon synapse maintenance. Fgf22 knockout mice, patch-clamp capacitance recording of exocytosis, immunofluorescence, auditory brainstem response, quantitative RT-PCR Frontiers in molecular neuroscience Medium 35966010
2021 In pancreatic cancer, FGFBP1 produced by cancer-associated fibroblasts (CAFs) promotes FGF22 release into the co-culture medium. FGF22 signals through FGFR2 on pancreatic cancer cells to facilitate their migration and invasion; FGFR2 silencing abrogates FGF22-driven invasion. Co-culture system, ELISA for FGF22, siRNA knockdown of FGFBP1/FGF22/FGFR2, invasion assay Acta biochimica et biophysica Sinica Medium 34117747
2023 In zebrafish forebrain development, Fgf22 signals through Fgfr2b to promote neurogenesis (glutamatergic neurons, GABAergic interneurons, astrocytes) and suppress oligodendrocyte differentiation; fgfr2b morphant phenotype mirrors fgf22 morphant phenotype, establishing Fgf22-Fgfr2b as the operative ligand-receptor axis. Morpholino knockdown, fgf22 overexpression, marker gene analysis, epistasis between fgf22 and fgfr2b knockdowns Biochemical and biophysical research communications Medium 37783119
2025 FGF22 ameliorates cognitive deficits in an Aβ1-42 AD mouse model by activating the FGFR2/YAP signaling pathway, reducing ferroptosis and neuronal apoptosis, and attenuating synaptic impairments. Aβ1-42 injection AD model, biochemical pathway analysis (FGFR2/YAP), FGF22 treatment in vivo and in vitro (HT22 cells), ferroptosis and apoptosis assays Experimental neurology Low 41482107
2025 FGF22 secreted by dermal papilla cells (DPCs) promotes hair follicle stem cell (HFSC) proliferation and differentiation by upregulating FGFR1/FGFR2 on HFSCs and activating Wnt/β-catenin, Sonic Hedgehog, and Notch signaling while inhibiting BMP signaling. DPC-HFSC co-culture system, FGF22 overexpression and knockout, EdU proliferation assay, CCK-8 viability, pathway inhibitor analysis, qPCR Biomolecules Low 41301478

Source papers

Stage 0 corpus · 18 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2004 FGF22 and its close relatives are presynaptic organizing molecules in the mammalian brain. Cell 230 15260994
2005 The fibroblast growth factor binding protein is a novel interaction partner of FGF-7, FGF-10 and FGF-22 and regulates FGF activity: implications for epithelial repair. Oncogene 80 15806171
2001 Identification of a novel fibroblast growth factor, FGF-22, preferentially expressed in the inner root sheath of the hair follicle. Biochimica et biophysica acta 63 11342227
2016 Retrograde fibroblast growth factor 22 (FGF22) signaling regulates insulin-like growth factor 2 (IGF2) expression for activity-dependent synapse stabilization in the mammalian brain. eLife 39 27083047
2014 Selective synaptic targeting of the excitatory and inhibitory presynaptic organizers FGF22 and FGF7. Journal of cell science 25 25431136
2015 FGF22 protects hearing function from gentamycin ototoxicity by maintaining ribbon synapse number. Hearing research 23 26639016
2013 Suppression of epileptogenesis-associated changes in response to seizures in FGF22-deficient mice. Frontiers in cellular neuroscience 23 23616746
2016 Postsynaptic SDC2 induces transsynaptic signaling via FGF22 for bidirectional synaptic formation. Scientific reports 22 27627962
2005 Comparative genomics on FGF7, FGF10, FGF22 orthologs, and identification of fgf25. International journal of molecular medicine 19 16142419
2023 Synaptogenic gene therapy with FGF22 improves circuit plasticity and functional recovery following spinal cord injury. EMBO molecular medicine 17 36601738
2021 FGFBP1-mediated crosstalk between fibroblasts and pancreatic cancer cells via FGF22/FGFR2 promotes invasion and metastasis of pancreatic cancer. Acta biochimica et biophysica Sinica 17 34117747
2013 Fgf22 regulated by Fgf3/Fgf8 signaling is required for zebrafish midbrain development. Biology open 16 23789101
2017 Selective Inactivation of Fibroblast Growth Factor 22 (FGF22) in CA3 Pyramidal Neurons Impairs Local Synaptogenesis and Affective Behavior Without Affecting Dentate Neurogenesis. Frontiers in synaptic neuroscience 12 29311892
2022 FGF22 deletion causes hidden hearing loss by affecting the function of inner hair cell ribbon synapses. Frontiers in molecular neuroscience 7 35966010
2018 Expression of fibroblast growth factor 22 (FGF22) and its receptor, FGFR1B, during development and regression of bovine corpus luteum. Theriogenology 6 30366151
2023 Fgf22 and Fgfr2b are required for neurogenesis and gliogenesis in the zebrafish forebrain. Biochemical and biophysical research communications 4 37783119
2025 FGF22 Secreted by Hair Papilla Cells Regulates Hair Follicle Stem Cell Proliferation and Differentiation. Biomolecules 0 41301478
2025 FGF22/FGFR2/YAP modulates ferroptosis to suppress neurodegeneration and cognitive impairment in Alzheimer's disease. Experimental neurology 0 41482107