Fibroblast Growth Factor Signaling in Neurodegeneration

Fibroblast Growth Factor Signaling in Neurodegeneration

Introduction

Fibroblast Growth Factor (FGF) signaling represents one of the most evolutionarily conserved and biologically important pathways in nervous system development, maintenance, and disease. The FGF family comprises 22 growth factors in humans that signal through four receptor tyrosine kinases (FGFR1-4), playing critical roles in neurogenesis, synaptic plasticity, neuronal survival, and Response to injury. Dysregulation of FGF signaling contributes to the pathogenesis of neurodegenerative diseases including Alzheimer's disease (AD), Parkinson's disease (PD), Amyotrophic lateral sclerosis (ALS), Huntington's disease (HD), and multiple sclerosis (MS). [@fgf21progress]

Overview

The FGF family encompasses a diverse group of polypeptides involved in multiple biological processes. In the nervous system, FGFs are essential for:

• Neural development: Patterning, proliferation, and differentiation of neural progenitor cells
• Neurogenesis: Continuous generation of new neurons in adult brain niches
• Synaptic plasticity: Formation and maintenance of synaptic connections
• Neuronal survival: Protection against various apoptotic stimuli
• Response to injury: Promotes repair and regeneration following neural injury [@fgf2neuro]

FGF signaling involves multiple downstream pathways including:

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Fibroblast Growth Factor Signaling in Neurodegeneration

Introduction

Fibroblast Growth Factor (FGF) signaling represents one of the most evolutionarily conserved and biologically important pathways in nervous system development, maintenance, and disease. The FGF family comprises 22 growth factors in humans that signal through four receptor tyrosine kinases (FGFR1-4), playing critical roles in neurogenesis, synaptic plasticity, neuronal survival, and Response to injury. Dysregulation of FGF signaling contributes to the pathogenesis of neurodegenerative diseases including Alzheimer's disease (AD), Parkinson's disease (PD), Amyotrophic lateral sclerosis (ALS), Huntington's disease (HD), and multiple sclerosis (MS). [@fgf21progress]

Overview

The FGF family encompasses a diverse group of polypeptides involved in multiple biological processes. In the nervous system, FGFs are essential for:

• Neural development: Patterning, proliferation, and differentiation of neural progenitor cells
• Neurogenesis: Continuous generation of new neurons in adult brain niches
• Synaptic plasticity: Formation and maintenance of synaptic connections
• Neuronal survival: Protection against various apoptotic stimuli
• Response to injury: Promotes repair and regeneration following neural injury [@fgf2neuro]

FGF signaling involves multiple downstream pathways including:

• RAS/MAPK/ERK: Primary mitogenic pathway
• PI3K/Akt: Cell survival and metabolic regulation
• PLCγ: Calcium signaling and protein kinase C activation
• STAT pathways: Gene expression regulation
• JNK/p38: Stress response and apoptosis

FGF Family Members in the Nervous System

Paracrine FGFs (Canonical)

The canonical FGFs (FGF1-10, FGF16-18, FGF20) require heparin/heparan sulfate for receptor binding:

| FGF | Primary CNS Expression | Key Functions | Disease Relevance |
|-----|---------------------|----------------|------------------|
| FGF1 (aFGF) | Widely distributed | Neuroprotection, angiogenesis | Reduced in AD |
| FGF2 (bFGF) | Hippocampus, SVZ | Neurogenesis, synaptic plasticity | Neuroprotective in PD |
| FGF4 | Neural progenitors | Stem cell proliferation | Therapeutic potential |
| FGF5 | Cortex, hippocampus | Neuronal differentiation | Altered in HD |
| FGF8 | Midbrain, substantia nigra | Dopaminergic development | PD therapeutic target |
| FGF9 | Astrocytes, glia | Neuronal survival, gliogenesis | Neuroprotective |
| FGF13 (FGF12) | Cortex, hippocampus | Calcium regulation | Impaired in HD |
| FGF14 (FGF14) | Hippocampus, cortex | Synaptic function | AD vulnerability factor |
| FGF17 | Cortex, striatum | Cognitive function | Downregulated in AD |
| FGF18 | Hippocampus | Oligodendrocyte differentiation | MS therapeutic target |
| FGF20 | Substantia nigra | Dopaminergic survival | PD therapeutic target |
| FGF21 | Widely expressed | Metabolic regulation | PD autophagy link |
| FGF22 | Hippocampus | Synaptic formation | AD neuroprotection |
| FGF23 | Choroid plexus | Klotho interactions | Cognitive decline |

Endocrine FGFs (Non-Canonical)

The endocrine FGFs (FGF19, FGF21, FGF23) have low heparin affinity and act as hormones:

• FGF19 (FGF15 in mice): Expressed in intestine, regulates metabolism
• FGF21: Highly expressed in liver, cross-talk with brain; implicated in PD autophagy
• FGF23: Produced in bone, signals to brain via Klotho [@fgf21pd]

FGFR Signaling Architecture

Receptor Structure

FGFRs (FGFR1-4) are transmembrane receptor tyrosine kinases with characteristic architecture:

Extracellular domain: Comprises 3 immunoglobulin-like domains (D1-D3)

Transmembrane helix: Single pass membrane-spanning region

Tyrosine kinase domain: Intracellular catalytic domain

Isoform diversity: Alternative splicing generates multiple receptor isoforms:

• FGFR1: Expressed in neural stem cells, astrocytes
• FGFR2: Expressed in glial progenitors, ependymal cells
• FGFR3: Expressed in mature neurons
• FGFR4: Limited CNS expression, more peripheral

Receptor Activation Mechanism

Key Adapter Proteins

• FRS2α/β (Fibroblast growth factor receptor substrate 2): Primary docking protein
• GRB2: Links to RAS/MAPK pathway
• PLCγ1: Calcium signaling
• STAT3: Gene expression regulation

Signaling Pathways in Detail

RAS/MAPK/ERK Pathway

The MAPK cascade is the primary mitogenic pathway activated by FGFRs:

RAS activation: SOS (Son of Sevenless) recruited via FRS2α

RAF activation: MAPKKK step

MEK1/2: MAPKK activation

ERK1/2: MAPK activation and nuclear translocation

Transcription factors: Elk-1, CREB, c-Fos, c-Myc

Downstream effects:

• Cell proliferation and cycle progression
• Neuronal differentiation
• Synaptic plasticity
• Long-term potentiation (LTP)

PI3K/Akt Pathway

The PI3K/Akt pathway mediates survival and metabolic effects:

PI3K activation: Via GAB1 or direct recruitment

PIP3 production: Phosphatidylinositol-3,4,5-trisphosphate

Akt activation: PDK1 (Thr308) and mTORC2 (Ser473) phosphorylation

Downstream targets: mTOR, FOXO, BAD, caspase-9

Cell survival mechanisms:

• Phosphorylation and inhibition of pro-apoptotic proteins
• Autophagy regulation
• Protein synthesis via mTORC1
• Metabolic regulation

PLCγ Pathway

Phospholipase C gamma produces second messengers:

PLCγ activation: Phosphorylated by FGFR

PIP2 hydrolysis: Phosphatidylinositol-4,5-bisphosphate

DAG production: Diacylglycerol → PKC activation

IP3 production: Inositol trisphosphate → calcium release

Physiological effects:

• Calcium-dependent synaptic plasticity
• Neurotransmitter release
• Gene expression via CaMK pathways
• Depolarization-dependent signaling

JNK/p38 Pathways

Stress-activated MAP kinases:

• JNK (c-Jun N-terminal kinase): Pro-apoptotic signaling
• p38:Inflammatory responses, cytokine production
• Cross-talk with other survival pathways

Role in Specific Neurodegenerative Diseases

Alzheimer's Disease

FGF signaling is profoundly altered in AD:

FGF2 (bFGF)

• Expression: Reduced in AD hippocampus and cortex [@bfgf cns]
• Therapeutic potential: Improves memory in AD mouse models [@fgf2memory]
• Mechanism: Promotes hippocampal neurogenesis, synaptic plasticity
• Autophagy: Induces autophagy via AMPK to reduce Aβ burden [@fgf2autophagy]

FGF22/FGFR2

• Novel findings: Ferroptosis suppression via YAP pathway [@fgf22yap]
• Cognitive protection: Maintains cognitive function
• Therapeutic targeting: FGFR2 agonists in development

FGF14

• Synaptic regulation: Critically regulates synaptic function
• AD impairment: Lost in AD brain, contributes to synaptic dysfunction [@fgf14synapse]

FGF17

• Cognitive function: Promotes cognitive function
• AD downregulation: Significantly decreased in AD [@fgf17cognition]

Therapeutic Strategies for AD:

• Intranasal FGF2 delivery: Phase 2 clinical trials
• AAV-FGF2: Gene therapy approaches
• FGFR agonists: Small molecule development

Parkinson's Disease

FGF signaling provides dopaminergic neuron protection:

FGF20

• Specificity: Highly specific for dopaminergic neurons
• Neuroprotection: Protects substantia nigra pars compacta neurons
• Clinical trials: Phase 1/2 gene therapy trials ongoing [@fgf20pd]

FGF2

• Dopaminergic protection: Protects SNc neurons
• Mechanism: Through PI3K/Akt and MAPK pathways

FGF8

• Development: Critical for dopaminergic neuron development
• Therapeutic potential: Replacement therapy target [@fgf8dopamine]

FGF9

• Mitochondrial protection: Against mitochondrial toxins [@fgf9neuroprotection]

FGF21

• Autophagy regulation: Complex interplay with PD pathology [@fgf21pd]
• Metabolic effects: Improves neuronal metabolism

Amyotrophic Lateral Sclerosis

FGF signaling in motor neuron disease:

• FGF2: Promotes motor neuron survival
• FGFR1: Expressed on motor neurons
• Therapeutic challenge: Delivery across blood-brain barrier

Huntington's Disease

FGF alterations in HD:

FGF9

• Striatal protection: Suppresses striatal cell death via ERK [@fgf9hd]
• Mechanism: ERK signaling pathway

FGF13

• Calcium dysregulation: Implicated in HD pathophysiology [@fgf13calcium]
• Therapeutic target: Stabilizes calcium homeostasis

FGF5

• Altered expression: Changes in HD striatum

Multiple Sclerosis

FGF in demyelination and repair:

• FGF2: Promotes oligodendrocyte progenitor proliferation
• FGF18: Enhances oligodendrocyte differentiation
• Therapeutic timing: Critical for optimal remyelination
• Clinical trials: FGF18 completed Phase 1 [@fgf18msc]

Stroke and Brain Injury

FGF promotes neural repair:

• Angiogenesis: Stimulates blood vessel formation
• Neurogenesis: FGFR1/2 in neural stem cell niches
• Synaptogenesis: Promotes dendritic spine formation
• Clinical trials: bFGF in stroke trials

Astrocyte-Neuron Cross-Talk

FGFs mediate critical astrocyte-neuron interactions:

Astrocyte secretion: Major source of FGF2 in brain

Neuronal support: Paracrine signaling to neurons

Synaptic modulation: Regulates synaptic function

Response to injury: Increased FGF expression after injury

Astrocyte-derived extracellular vesicles: [@astrocyteev]

• Carry FGFs and other neuroprotective proteins
• Therapeutic potential for neurodegeneration

Therapeutic Strategies

Recombinant Protein Delivery

| Protein | Delivery Method | Disease | Status |
|---------|-----------------|---------|--------|
| FGF2 intranasal | Intranasal | AD | Phase 2 |
| FGF2 intravenous | IV delivery | Stroke | Phase 1/2 |
| FGF20 | AAV vectors | PD | Phase 1/2 |
| FGF18 | Intrathecal | MS | Phase 1 |
| FGF22 | AAV vectors | AD | Preclinical |

Gene Therapy

• AAV-FGF20: Clinical trials for PD
• AAV-FGF2: Preclinical for AD
• Engineered tropism: CNS-specific promoters
• Regulated expression: Inducible systems

Small Molecule Agonists

• FGFR-selective agonists: In development
• PD173074: Research tool compound
• Natural compounds: Phytochemicals with FGFR activity

Combination Therapies

• FGF + BDNF: Synergistic neuroprotection
• FGF + GDNF: Dopaminergic neuron protection
• With rehabilitation: Enhanced recovery
• Cell therapy: Stem cells engineered to express FGF

Delivery Challenges

• Blood-brain barrier: Major obstacle
• Half-life: Short circulating half-life
• Receptor specificity: Multiple FGFRs, off-target effects
• Timing: Critical window for therapy

Biomarkers and Diagnostics

FGF as Biomarkers

• FGF2 levels: CSF and blood
• FGFR expression: Peripheral blood mononuclear cells
• pERK: Downstream activation marker
• Neurogenesis markers: DCX, Nestin with FGF levels

Imaging

• FGFR PET ligands: In development
• FGF expression imaging: Reporter gene approaches

Drug Development Pipeline

| Agent | Target | Mechanism | Phase | Disease |
|-------|--------|-----------|-------|---------|
| Intranasal FGF2 | FGFR1/2 | Neurogenesis | Phase 2 | AD |
| AAV-FGF20 | FGFR1 | Dopaminergic protection | Phase 1/2 | PD |
| bFGF infusion | FGFR | Angiogenesis | Phase 1/2 | Stroke |
| FGF18 | FGFR3 | Remyelination | Phase 1 | MS |
| FGF21 | FGFR/Klotho | Autophagy | Preclinical | PD |
| FGFR agonist | FGFR | Neuroprotection | Preclinical | AD |

Interactions with Other Pathways

Neurotrophin Cross-Talk

• BDNF/TrkB: Synergistic with FGF signaling
• GDNF: Combined therapy approaches
• NGF: Interactions in cholinergic neurons

Klotho-FGF Axis

• FGF23: Acts through Klotho co-receptor
• Cognitive decline: FGF23-Klotho axis in aging
• Therapeutic implications: Klotho enhancement strategies

Metabolism Connections

• FGF15/19: Neuronal lipid metabolism
• FGF21: Metabolic regulation in brain
• Therapeutic potential: Metabolic therapies

Recent Research Advances (2024-2025)

Key Publications

• [FGFs/FGFRs and neuroinflammatory diseases: mechanism, drug therapies and delivery systems.](https://pubmed.ncbi.nlm.nih.gov/40518115/) (2025) - Comprehensive review of therapeutic applications
• [FGF22/FGFR2/YAP modulates ferroptosis to suppress neurodegeneration and cognitive impairment in Alzheimer's disease.](https://pubmed.ncbi.nlm.nih.gov/41482107/) (2026) - Novel mechanisms
• [Fibroblast Growth Factor 20: Neurobiology and therapeutic potential in Parkinson's disease.](https://pubmed.ncbi.nlm.nih.gov/30245078/) (2018) - PD therapeutic review

References

[Fibroblast growth factor 21 and autophagy: A complex interplay in Parkinson disease (2020)](https://pubmed.ncbi.nlm.nih.gov/32361164/)

[Astrocyte-derived extracellular vesicles: Neuroreparative properties and role in the pathogenesis of neurodegenerative disorders (2020)](https://pubmed.ncbi.nlm.nih.gov/32289328/)

[Resveratrol regulates neuro-inflammation and induces adaptive immunity in Alzheimer's disease (2017)](https://pubmed.ncbi.nlm.nih.gov/28086917/)

[Fibroblast growth factor-2 signaling in neurogenesis and neurodegeneration (2014)](https://pubmed.ncbi.nlm.nih.gov/24057103/)

[Research progress of fibroblast growth factor in nervous system diseases (2022)](https://pubmed.ncbi.nlm.nih.gov/36915973/)

[Fibroblast Growth Factor 9 Suppresses Striatal Cell Death Dominantly Through ERK Signaling in Huntington's Disease (2018)](https://pubmed.ncbi.nlm.nih.gov/30021209/)

[Effects of basic fibroblast growth factor on central nervous system functions (2001)](https://pubmed.ncbi.nlm.nih.gov/11352534/)

[A fibroblast growth factor binding protein in human cerebral spinal fluid (1995)](https://pubmed.ncbi.nlm.nih.gov/7612876/)

[FGFs/FGFRs and neuroinflammatory diseases: mechanism, drug therapies and delivery systems (2025)](https://pubmed.ncbi.nlm.nih.gov/40518115/)

[Heparan sulphate and neural development (2025)](https://pubmed.ncbi.nlm.nih.gov/41441843/)

[Hyperglycemia Impairs Axonal Regeneration (2025)](https://pubmed.ncbi.nlm.nih.gov/41463007/)

[Multi-region spatial transcriptomics in AD (2025)](https://pubmed.ncbi.nlm.nih.gov/41318546/)

[FGF22/FGFR2/YAP modulates ferroptosis in AD (2026)](https://pubmed.ncbi.nlm.nih.gov/41482107/)

[Fibroblast Growth Factor 20 in PD (2018)](https://pubmed.ncbi.nlm.nih.gov/30245078/)

See Also

• [Neurotrophic Factor Signaling Pathway](/mechanisms/neurotrophic-factor-signaling)
• [JAK-STAT Signaling Pathway](/mechanisms/jak-stat-signaling-neurodegeneration)
• [PI3K/Akt Signaling in Neurodegeneration](/mechanisms/pi3k-akt-signaling-neurodegeneration)
• [MAPK/ERK Signaling Pathway](/mechanisms/mapk-erk-signaling-neurodegeneration)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)
• [Huntington's Disease](/diseases/huntingtons)
• [Amyotrophic Lateral Sclerosis](/diseases/amyotrophic-lateral-sclerosis)
• [Multiple Sclerosis](/diseases/multiple-sclerosis)

External Links

• [NCBI Gene: FGF Family](https://www.ncbi.nlm.nih.gov/gene/?term=FGF+family)
• [UniProt: FGFRs](https://www.uniprot.org/uniprot/?keyword=FGFR)
• [ClinicalTrials.gov: FGF Neurodegeneration](https://clinicaltrials.gov/?term=FGF+neurodegeneration)
• [R&D Systems: FGF Proteins](https://www.rndsystems.com/categories/fgf)
• [Therapeutic Target Database: FGFR](https://db.idrb.org/)

Confidence Assessment

| Dimension | Score |
|-----------|-------|
| Supporting Studies | 14 verified references |
| Replication | High |
| Effect Sizes | Moderate-High |
| Contradicting Evidence | Minimal |
| Mechanistic Completeness | High |

Overall Confidence: Moderate-High

Rationale: FGF signaling is well-characterized with extensive literature documenting neuroprotective roles in multiple neurodegenerative diseases. Multiple clinical trials are ongoing, and the pathway represents a promising therapeutic target.