| Attribute |
Value |
Sources |
| Symbol |
FGF22 |
|
| Name |
Fibroblast Growth Factor 22 |
|
| Chromosome |
19p13.3 |
|
| NCBI Gene ID |
27006 |
|
| UniProt ID |
Q9ULL0 |
|
| Gene Type |
Protein coding |
|
| Alternative Names |
FGF22 |
|
FGF22 (Fibroblast Growth Factor 22) is a secreted FGF family member with critical roles in synapse formation and presynaptic differentiation. Discovered as a synapse-organizing molecule, FGF22 is strategically localized at synaptic sites where it provides retrograde signals to presynaptic neurons, promoting synaptic vesicle recruitment, active zone assembly, and proper neurotransmitter release [@f gf22-synapse].
Unlike intracellular FGFs (FGF13, FGF14), FGF22 is a classical secreted growth factor that signals through FGFR receptors on adjacent neurons. This positions FGF22 at the synaptic cleft, where it orchestrates the coordinated development of both pre- and postsynaptic compartments. The synaptic specificity of FGF22 makes it particularly relevant to neurodegenerative diseases where synaptic failure is a cardinal early feature .
FGF22 functions as a synaptic organizer:
1. Presynaptic Differentiation
- Secreted by postsynaptic neurons
- Binds to FGFRs on presynaptic terminals
- Induces:
- Synaptic vesicle clustering
- Active zone assembly
- Cytoskeletal reorganization
- Synaptic protein recruitment
2. Receptor Interactions
- Primary receptors: FGFR1, FGFR2
- Heparan sulfate proteoglycans (HSPGs) as co-receptors
- downstream signaling through:
- MAPK/ERK pathway
- PI3K/Akt pathway
- PLCγ pathway
3. Synaptic Vesicle Organization
- Recruits synaptic vesicles to active zones
- Organizes vesicle pools (readily releasable, reserve)
- Regulates vesicle cycling dynamics
- Maintains synaptic homeostasis
FGF22 exemplifies trans-synaptic signaling:
| Signal Source |
Target |
Effect |
| Postsynaptic spine |
Presynaptic terminal |
Differentiation |
| Dendrite |
Axon terminal |
Maturation |
| Synaptic cleft |
Presynaptic FGFR |
Vesicle recruitment |
FGF22 contributes to AD through synaptic mechanisms [@f gf-ad]:
1. Synaptic Loss in AD
- Synaptic failure is the earliest feature of AD
- FGF22 levels decline in AD brains
- Loss of synaptic organizing signals contributes to:
- Synaptic vesicle depletion
- Active zone disruption
- Neurotransmitter release failure
2. Amyloid-Induced Synaptic Dysfunction
- Amyloid-β oligomers disrupt synaptic function
- FGF22 signaling is impaired
- This exacerbates synaptic degeneration
- Therapeutic potential for FGF22 restoration
3. Tau Pathology
- Hyperphosphorylated tau affects synaptic function
- FGF22-dependent synaptic maintenance is impaired
- Tau-mediated synaptic loss compounds FGF22 deficits
4. Synaptic Plasticity
- Long-term potentiation (LTP) requires proper synaptic organization
- FGF22 supports synaptic plasticity mechanisms
- Impaired signaling contributes to memory deficits
FGF22 contributes to PD through :
1. Dopaminergic Synaptic Function
- FGF22 is expressed in striatal neurons
- Regulates glutamatergic synapses onto medium spiny neurons
- Dysregulation affects motor circuit function
2. Synuclein and Synaptic Function
- Alpha-synuclein affects synaptic vesicles
- FGF22 signaling may interact with α-syn pathology
- Combined dysfunction accelerates synaptic loss
3. Axonal Terminal Vulnerability
- Dopaminergic terminals are early targets in PD
- FGF22 supports axonal terminal integrity
- Loss contributes to terminal degeneration
FGF22 has significant potential for nerve regeneration :
1. Peripheral Nerve Injury
- FGF22 is upregulated after nerve injury
- Promotes axonal regeneration
- Schwann cell responses
2. CNS Repair
- Limited regeneration in CNS
- FGF22 may enhance repair
- Promotes synaptic re-establishment
3. Axonal Guidance
- Guides regenerating axons
- Helps form appropriate synaptic connections
- Supports functional recovery
FGF22-based therapeutic approaches:
- FGF22 protein therapy: Deliver exogenous FGF22
- Gene therapy: Express FGF22 in target neurons
- Small molecule FGFR agonists: Activate downstream signaling
- Synaptic protection: Prevent synaptic loss
- Regeneration support: Enhance repair after injury
FGF22 shows synapse-enriched expression:
- Hippocampus: CA1-CA3 pyramidal neurons, dentate granule cells
- Cerebral cortex: Layer V pyramidal neurons
- Cerebellum: Purkinje cells
- Striatum: Medium spiny neurons
- Olfactory bulb: Mitral and tufted cells
Cellular localization:
- Dendritic shafts and spines
- Postsynaptic densities
- Axon terminals (lower levels)
- FGFR1
- FGFR2
- FGFR3 (lower affinity)
- HSPGs (syndecan, glypican)
- FRS2
- GRB2
- SPRY
- MAPK pathway
- PI3K/Akt pathway
- Synapsin
- Synaptophysin
- SV2
- Bassoon
- Piccolo
- RIM
- Munc13
- APP (amyloid precursor)
- Alpha-synuclein
- Tau
flowchart TD
subgraph FGF22_Synapse_Function
A["FGF22 Gene"] --> B["FGF22 Protein"]
B --> C["Secreted at<br/>Synapse"]
C --> D["Presynaptic<br/>Differentiation"]
D --> E["Synaptic Vesicle<br/>Clustering"]
D --> F["Active Zone<br/>Assembly"]
end
subgraph Normal_Synapse
E --> G["Normal<br/>Transmission"]
F --> G
G --> H["Synaptic<br/>Plasticity"]
end
subgraph AD_Pathology
I["AD Pathology"] --> J["FGF22<br/>Downregulation"]
J --> K["Synaptic Vesicle<br/>Depletion"]
J --> L["Active Zone<br/>Disruption"]
K --> M["Neurotransmitter<br/>Release Failure"]
L --> M
M --> N["Synaptic<br/>Failure"]
end
subgraph PD_Pathology
O["PD Pathology"] --> P["FGF22<br/>Dysregulation"]
P --> Q["Dopaminergic<br/>Synapse Dysfunction"]
Q --> R["Motor Circuit<br/>Abnormalities"]
end
subgraph Regeneration
S["Nerve Injury"] --> T["FGF22<br/>Upregulation"]
T --> U["Axonal<br/>Regeneration"]
U --> V["Synaptic<br/>Reformation"]
end
style A fill:#e3f2fd
style I fill:#ffcdd2
style O fill:#ffcdd2
style N fill:#b71c1c
- FGF13 — Intracellular neuronal FGF
- FGF14 — Related neuronal FGF
- FGF2 — Classic neurotrophic FGF