FGF23 — Fibroblast Growth Factor 23

FGF23 — Fibroblast Growth Factor 23

Overview

Pathway Diagram

```mermaid
flowchart TD
FGF2["FGF2<br/>Fibroblast Growth Factor 2"]
EGR1["EGR1<br/>Early Growth Response 1"]
ANGPT1["ANGPT1<br/>Angiopoietin 1"]
PDGFRB["PDGFRB<br/>Platelet Derived Growth<br/>Factor Receptor Beta"]
VEGFB["VEGFB<br/>Vascular Endothelial<br/>Growth Factor B"]
TLR4["TLR4<br/>Toll-like Receptor 4"]
HSPA1A["HSPA1A<br/>Heat Shock Protein<br/>Family A Member 1A"]

Angiogenesis["Angiogenesis<br/>Pathway"]
Fibroblast_Activation["Fibroblast<br/>Activation"]

ALS["ALS<br/>Amyotrophic Lateral<br/>Sclerosis"]
Alzheimer["Alzheimer's<br/>Disease"]
Neurodegeneration["Neurodegeneration"]
Neuroinflammation["Neuroinflammation"]
MS["Multiple<br/>Sclerosis"]

EGR1 -->|"regulates"| FGF2
FGF2 -->|"activates"| EGR1
FGF2 -->|"activates"| ANGPT1
FGF2 -->|"activates"| PDGFRB
FGF2 -->|"activates"| VEGFB
FGF2 -->|"regulates"| TLR4
FGF2 -->|"regulates"| HSPA1A

FGF2 -->|"promotes"| Angiogenesis
FGF2 -->|"causes"| Fibroblast_Activation

FGF2 -->|"biomarker_for"| ALS
FGF2 -->|"biomarker_for"| Alzheimer
FGF2 -->|"biomarker_for"| Neurodegeneration
FGF2 -->|"biomarker_for"| Neuroinflammation
FGF2 -->|"inhibits"| MS

ANGPT1 --> Angiogenesis
VEGFB --> Angiogenesis
TLR4 --> Neuroinflammation

style FGF2 fill:#006494
style EGR1 fill:#4a1a6b
style ANGPT1 fill:#4a1a6b
style PDGFRB fill:#4a1a6b
style VEGFB fill:#4a1a6b
style TLR4 fill:#4a1a6b
style HS

FGF23 — Fibroblast Growth Factor 23

Overview

Pathway Diagram

FGF23 (Fibroblast Growth Factor 23) encodes a hormone-like growth factor that belongs to the FGF19 subfamily of fibroblast growth factors. Originally discovered for its critical role in regulating phosphate and vitamin D metabolism, FGF23 has emerged as a molecule of interest in neuroscience due to its expression in the brain and associations with cognitive function, white matter integrity, and neurodegenerative diseases["@ostrowski2015"]. This unique growth factor acts in an endocrine fashion, with circulating FGF23 affecting distant target tissues including kidney, bone, and potentially brain.

FGF23 is produced primarily by osteocytes in bone and, to a lesser extent, by other tissues. It acts on the kidney to promote phosphate excretion (phosphaturia) and suppress active vitamin D (1,25-dihydroxyvitamin D) synthesis, making it a key regulator of mineral homeostasis["@kurosu2006"]. This endocrine function ensures proper phosphate levels for bone mineralization while preventing hyperphosphatemia that could lead to vascular calcification and other complications.

In recent years, research has revealed that FGF23 crosses the blood-brain barrier and exerts effects on neural tissues["@ferenbach2014"]. Elevated circulating FGF23 levels have been associated with cognitive impairment, white matter abnormalities, and increased risk of neurodegenerative diseases["@kanaki2017"]. These findings suggest that FGF23 may represent a bridge between peripheral mineral metabolism and central nervous system function, potentially opening new therapeutic avenues for neurological conditions.

Gene Information

<div class="infobox infobox-gene">
<table>
<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">Fibroblast Growth Factor 23</th></tr>
<tr><td><strong>Gene Symbol</strong></td><td>FGF23</td></tr>
<tr><td><strong>Full Name</strong></td><td>Fibroblast Growth Factor 23</td></tr>
<tr><td><strong>Chromosome</strong></td><td>12p13</td></tr>
<tr><td><strong>NCBI Gene ID</strong></td><td><a href="https://www.ncbi.nlm.nih.gov/gene/79581" target="_blank">79581</a></td></tr>
<tr><td><strong>OMIM</strong></td><td>605380</td></tr>
<tr><td><strong>Ensembl ID</strong></td><td>ENSG00000166575</td></tr>
<tr><td><strong>UniProt ID</strong></td><td><a href="https://www.uniprot.org/uniprot/Q9GZV9" target="_blank">Q9GZV9</a></td></tr>
<tr><td><strong>Protein Length</strong></td><td>251 amino acids</td></tr>
<tr><td><strong>Molecular Weight</strong></td><td>28.6 kDa</td></tr>
<tr><td><strong>Associated Diseases</strong></td><td>[Alzheimer's Disease](/diseases/alzheimers-disease), [Parkinson's Disease](/diseases/parkinsons-disease), Chronic Kidney Disease</td></tr>
</table>
</div>

Protein Structure and Function

FGF23 Properties

FGF23 is a member of the FGF19 subfamily, which includes:

• FGF19: Enteroendocrine hormone regulating bile acid metabolism
• FGF21: Regulator of metabolic stress
• FGF23: Phosphate and vitamin D regulator

Structural Features

FGF23 has distinctive structural elements[@kurosu2006]:

• N-terminal signal peptide: Enables secretion
• FGF core domain: Receptor binding
• C-terminal tail: Contains alpha-Klotho binding site
• Cleavage site: Regulated proteolytic processing

Cleavage and Regulation

FGF23 activity is regulated through proteolytic cleavage:

• Intact FGF23: Full-length, biologically active
• Cleaved FGF23: Inactive fragments
• Regulated by: Phosphate status, vitamin D, PTH

Expression and Regulation

Peripheral Expression

FGF23 is primarily expressed in:

• Osteocytes: Bone-producing cells (major source)
• Osteoblasts: Bone-forming cells
• Dentin: Tooth tissue
• Thymus: Low expression

Central Nervous System Expression

FGF23 is expressed in brain regions[@ferenbach2014]:

• Hippocampus: Neuronal expression
• Cerebral cortex: Cortical neurons
• Cerebellum: Purkinje cells
• Hypothalamus: Neuroendocrine regions

Regulation by Phosphate and Vitamin D

FGF23 expression is regulated by:

• Serum phosphate: High phosphate induces FGF23
• 1,25(OH)2D: Active vitamin D stimulates expression
• PTH: Parathyroid hormone affects expression
• FGF23 itself: Negative feedback

Receptor Signaling

FGFR and Alpha-Klotho

FGF23 signals through FGFRs complexed with alpha-Klotho[@kurosu2006]:

• Alpha-Klotho: Essential co-receptor
• FGFR1c: Primary signaling receptor in kidney
• FGFR3c: Alternative receptor
• FGFR4: Some tissue expression

Signaling Pathways

FGF23 activates multiple downstream pathways:

• MAPK/ERK: Cell proliferation and survival
• PI3K/AKT: Metabolic regulation
• PLCγ: Calcium signaling

Blood-Brain Barrier Crossing

FGF23 can cross the blood-brain barrier[@leonard2018]:

• Transport mechanism: Saturable transport system
• Brain regions: Areas with permeable BBB
• Functional significance: May affect neural function

Mineral Metabolism and the Brain

Phosphate and Neuronal Function

Phosphate is essential for neuronal function:

• Membrane phospholipids: Structural component
• DNA/RNA: Genetic material
• ATP: Energy currency
• Second messengers: Signaling molecules

Vitamin D and the Brain

Vitamin D has important brain functions:

• Neuroprotection: Antioxidation and anti-inflammation
• Neurogenesis: Supports new neuron formation
• Calcium homeostasis: Regulates calcium signaling
• Neurotransmitter synthesis: Dopamine, serotonin

Cognitive Function

FGF23 and Cognition

Clinical studies have linked FGF23 to cognitive function[@ravi2015]:

• Elevated FGF23: Associated with cognitive impairment
• Cross-sectional studies: Correlations with test scores
• Prospective studies: Predictive of decline

Mechanism of Cognitive Effects

Potential mechanisms include:

• Direct neural effects: FGF23 action on neurons
• Vitamin D suppression: Reduced neuroprotective vitamin D
• Vascular effects: Cerebral blood flow
• White matter: Myelin integrity

White Matter Integrity

White Matter Abnormalities

FGF23 has been associated with white matter changes[@kanaki2017]:

• White matter hyperintensities: On MRI
• Microstructural damage: Diffusion tensor imaging changes
• Myelin integrity: Altered myelin basic protein

Oligodendrocyte Function

FGF23 may affect oligodendrocytes:

• Expression: FGFR in oligodendrocyte lineage
• Myelination: Potential role in myelination
• Survival: Effects on oligodendrocyte survival

Alzheimer's Disease

FGF23 in AD

FGF23 alterations have been reported in AD[@dagdag2018]:

• Elevated levels: Increased circulating FGF23
• Brain expression: Altered brain FGF23
• Disease association: Correlates with severity

Mechanisms in AD

Potential mechanisms include:

• Amyloid processing: Effects on APP metabolism
• Tau pathology: May influence phosphorylation
• Synaptic dysfunction: Calcium dysregulation
• Neuroinflammation: Microglial activation

Vitamin D Connection

The vitamin D-FGF23 relationship is relevant to AD:

• Vitamin D deficiency: Common in AD
• Supplementation studies: Mixed results
• Combined approach: May need to address both

Parkinson's Disease

FGF23 in PD

FGF23 has been studied in PD:

• Elevated levels: Reported in some PD cohorts
• Clinical correlations: With disease severity
• Mechanism: Possible dopaminergic effects

Dopaminergic Neurons

FGF23 may affect dopaminergic neurons:

• Vulnerability: Unique calcium handling
• Metabolic requirements: High energy demand
• Oxidative stress: Susceptibility to ROS

Chronic Kidney Disease and the Brain

CKD and Neurological Complications

Chronic kidney disease (CKD) is associated with neurological complications:

• Cognitive impairment: Increased risk
• White matter disease: Common finding
• Accelerated aging: Brain changes

FGF23 as a Mediator

FGF23 may mediate kidney-brain connections:

• Elevated in CKD: Due to reduced clearance
• Crosses BBB: Into the brain
• Direct effects: On neural tissues

Neuroinflammation

FGF23 and Glial Cells

FGF23 may affect neuroinflammation[@chen2019]:

• Microglial activation: Reported in some studies
• Cytokine production: Effects on inflammatory mediators
• Astrocyte function: Potential regulation

Inflammatory Signaling

FGF23 may interact with inflammatory pathways:

• NF-κB: Central inflammatory pathway
• MAPK pathways: Inflammatory kinase cascades
• Cytokine receptors: Cross-talk with inflammatory signals

Cardiovascular Connections

Cerebrovascular Disease

FGF23 affects cardiovascular function[@ouwens2010]:

• Cardiac hypertrophy: Direct cardiac effects
• Vascular calcification: Arterial stiffening
• Blood pressure: Hypertension development

Stroke Risk

FGF23 may influence stroke risk:

• Atrial fibrillation: Association with AF
• Cardioembolic stroke: Possible risk factor
• Small vessel disease: White matter effects

Genetic Variants

FGF23 Variants and Disease

Genetic studies have explored FGF23 variants[@yamasaki2019]:

• Missense variants: Rare pathogenic mutations
• Common polymorphisms: Some disease associations
• Functional effects: Altered protein function

Familial Hypophosphatemia

FGF23 gain-of-function causes:

• Tumor-induced osteomalacia: FGF23-secreting tumors
• Autosomal dominant hypophosphatemic rickets: FGF23 mutations
• X-linked hypophosphatemic rickets: PHEX mutations affecting FGF23

Biomarker Potential

Clinical Biomarkers

FGF23 has biomarker potential:

• Kidney disease: Used in CKD prognosis
• Cardiovascular disease: Risk stratification
• Bone disease: Phosphate disorders

Neurological Applications

Potential neurological applications include:

• Cognitive decline: Risk stratification
• White matter disease: Biomarker
• Disease progression: Tracking

Therapeutic Implications

Targeting FGF23

Therapeutic strategies targeting FGF23 include:

• Inhibitors: Blocking antibody approaches
• Neutralizing agents: Decoy receptors
• Metabolic modulators: Reducing production

Neurological Considerations

For neurological applications:

• Blood-brain barrier: Delivery challenges
• Peripheral vs. central: Which pool matters
• Combination therapy: With vitamin D

Signaling Pathways

FGF23 Signaling Cascade

FGF23 + alpha-Klotho → FGFR complex activation
↓
Receptor autophosphorylation
↓
Adapter protein recruitment
↓
MAPK/ERK, PI3K/AKT, PLCγ pathways
↓
Cellular response: phosphate handling, cell survival, gene transcription

Integration with Neurodegeneration

FGF23 connects to neurodegeneration through:

• Vitamin D suppression: Reduced neuroprotection
• Calcium dysregulation: Altered neuronal calcium
• White matter effects: Oligodendrocyte function
• Vascular effects: Cerebrovascular health

Clinical Translation and Therapeutic Approaches

Targeting FGF23 in Neurology

Given the associations between elevated FGF23 and neurodegenerative diseases, several therapeutic strategies are being explored. The primary approaches include reducing FGF23 production, blocking its action, and mitigating its downstream effects. Each strategy has distinct advantages and challenges that are actively being investigated in preclinical and clinical studies.

The most advanced therapeutic approach involves neutralizing circulating FGF23 with monoclonal antibodies. These antibodies bind FGF23 and prevent it from interacting with its receptor complex, effectively blocking all downstream signaling. Clinical trials in chronic kidney disease have demonstrated that this approach can successfully lower phosphate levels, and similar approaches are being developed for neurological applications.

Small molecule inhibitors of FGF23 signaling represent an alternative approach. These compounds target the FGFR-alpha-Klotho complex or downstream signaling pathways. While less advanced than antibody approaches, small molecules offer advantages in terms of oral bioavailability and tissue penetration, which may be important for achieving effects in the brain.

Vitamin D Supplementation Strategies

Since FGF23 suppresses vitamin D synthesis, one therapeutic approach involves vitamin D supplementation to overcome this suppression. This strategy is particularly relevant given the well-documented vitamin D deficiency in many patients with neurodegenerative diseases and the neuroprotective effects of vitamin D.

However, simple vitamin D supplementation may be insufficient in the context of elevated FGF23, as the hormone actively suppresses vitamin D production and can override supplementation efforts. More sophisticated approaches may be needed, including vitamin D analogs that are resistant to FGF23-mediated suppression or combination therapies that target both FGF23 and vitamin D metabolism.

The timing of vitamin D intervention may also be critical. Studies suggest that vitamin D supplementation is most effective in early disease stages or even prophylactically, before significant neurodegeneration has occurred. This highlights the importance of early identification of at-risk individuals who might benefit from intervention.

Klotho-Based Therapies

The alpha-Klotho co-receptor is essential for FGF23 signaling, and modulation of Klotho expression or function represents another therapeutic approach. Increasing alpha-Klotho expression can potentially enhance FGF23 sensitivity, which may be beneficial in conditions where phosphate handling is impaired, but could also potentially enhance the negative effects of elevated FGF23 in the brain.

Alternatively, strategies to reduce alpha-Klotho expression in the brain could be explored to make neural tissues less responsive to circulating FGF23. However, alpha-Klotho has important brain functions beyond FGF23 signaling, and global reduction of its expression may have unintended consequences.

Gene therapy approaches to deliver Klotho or modulate its expression are also under investigation. These approaches aim to achieve sustained changes in Klotho expression that could provide long-term benefits, though the same concerns about specificity and timing apply.

FGF23 and Peripheral-Brain Interactions

The Kidney-Brain Axis

The relationship between kidney function and brain health represents an important emerging area of research, with FGF23 potentially serving as a key mediator. Chronic kidney disease (CKD) is associated with increased risk of cognitive impairment and cerebrovascular disease, and FGF23 elevation in CKD may contribute to these neurological complications.

The mechanisms underlying the kidney-brain connection involve multiple pathways. Beyond the direct effects of FGF23 on the brain, renal dysfunction leads to accumulation of uremic toxins, electrolyte imbalances, and cardiovascular complications that can all affect brain function. FGF23 may therefore serve as a biomarker that reflects the overall burden of renal dysfunction on the brain.

Studies have demonstrated that individuals with CKD show accelerated brain aging, with white matter hyperintensities, reduced hippocampal volume, and cognitive decline that exceeds what would be expected from age alone. The contribution of FGF23 to these changes is an active area of investigation.

Cardiovascular Intermediary

FGF23's effects on the cardiovascular system may indirectly affect brain health. Left ventricular hypertrophy, arterial stiffness, and heart failure associated with elevated FGF23 can lead to cerebral hypoperfusion, increasing the risk of vascular cognitive impairment and contributing to the progression of neurodegenerative diseases.

The relationship is bidirectional, as cerebrovascular disease can also affect kidney function through mechanisms such as reduced renal perfusion and atherosclerotic nephropathy. This creates a potential vicious cycle in which brain and kidney disease mutually reinforce each other, with FGF23 serving as a circulating mediator of this relationship.

Understanding these cardiovascular中介 effects is important for designing therapeutic strategies. Interventions that improve cardiovascular health may have beneficial effects on both kidney and brain function, potentially in part through reducing FGF23-related pathology.

FGF23 in Specific Clinical Contexts

Stroke and Cerebrovascular Disease

FGF23 has been associated with stroke risk and post-stroke outcomes. Elevated FGF23 levels predict incident stroke in some population studies, potentially through the cardiovascular effects discussed above. After stroke, FGF23 levels may increase further due to acute kidney injury or stress-related mechanisms.

The relationship between FGF23 and stroke is complicated by the fact that stroke itself can affect kidney function, creating feedback loops that may be difficult to disentangle. Nevertheless, FGF23 represents a potentially modifiable risk factor that could be targeted in stroke prevention strategies.

Post-stroke rehabilitation may be affected by FGF23, given its roles in neuroplasticity and neural repair. Understanding these relationships could inform rehabilitation strategies and help identify patients who might benefit from specific interventions targeting FGF23 or its downstream pathways.

Vascular Cognitive Impairment

Vascular cognitive impairment (VCI) represents the second most common cause of dementia after Alzheimer's disease and is closely linked to cardiovascular risk factors. FGF23 may contribute to VCI through multiple mechanisms, including direct effects on the brain, cardiovascular effects leading to cerebral hypoperfusion, and interactions with other risk factors.

The white matter abnormalities associated with VCI are particularly relevant to FGF23, given the associations between FGF23 and white matter health discussed earlier. These connections suggest that FGF23-lowering strategies might be particularly beneficial for patients with VCI or those at risk for the condition.

Amyloid and Tau Interactions

The relationships between FGF23 and the hallmark proteinopathies of Alzheimer's disease are complex and not fully understood. Some studies suggest that amyloid pathology may affect FGF23 regulation, while others explore whether FGF23 can influence amyloid processing or tau phosphorylation.

One proposed mechanism involves the crosstalk between mineral metabolism and amyloid processing. Phosphate ions can influence amyloid-beta aggregation and toxicity, and FGF23's effects on phosphate homeostasis may therefore indirectly affect amyloid pathology. Additionally, vitamin D suppression by FGF23 may reduce the neuroprotective effects of vitamin D against amyloid toxicity.

Tau pathology may also be influenced by FGF23 through effects on neuronal calcium handling and kinase/phosphatase balance. These interactions are less well-characterized but represent an important area for future research.

Biomarker Development

Cerebrospinal Fluid FGF23

Cerebrospinal fluid represents the most direct window into brain biochemistry, and CSF FGF23 measurements may provide clinically useful information. Studies have demonstrated that CSF FGF23 can be detected and quantified, with some differences observed between patients with neurodegenerative diseases and healthy controls.

The interpretation of CSF FGF23 is complicated by the multiple potential sources of the protein, including production in the brain and transport from the periphery. Nevertheless, CSF FGF23 may prove useful for diagnosis, prognosis, or treatment monitoring in specific contexts.

Blood-Based Biomarkers

Peripheral blood FGF23 measurements are more commonly available and have been extensively studied in kidney disease. The translation of these measurements to neurological applications is an active area of research, with the goal of developing accessible biomarkers that could aid in diagnosis or risk stratification.

Blood FGF23 shows correlations with cognitive function in some studies, though the strength of these associations varies. The utility of blood FGF23 as a biomarker may be enhanced when combined with other measures, creating multi-analyte panels that more accurately reflect brain health.

Research Models and Future Directions

Animal Models

Transgenic and knockout mouse models have provided important insights into FGF23 biology. FGF23 transgenic mice show phenotypes including hypophosphatemia and growth retardation, while FGF23 knockout mice develop hyperphosphatemia and soft tissue calcification. These models have been used to study the systemic effects of FGF23 and to test therapeutic interventions.

More recently, models with brain-specific manipulation of FGF23 or its receptor have been developed. These models allow the study of direct CNS effects without the confounding systemic effects, helping to clarify the brain-specific biology of FGF23.

Human Studies

Large-scale human studies are needed to clarify the relationships between FGF23 and neurological diseases. These include prospective studies that track FGF23 levels and neurological outcomes over time, as well as intervention studies that test whether modifying FGF23 levels affects neurological outcomes.

The development of biomarkers and therapies for neurological applications will require careful attention to the differences between the well-characterized systemic effects of FGF23 and its less-understood brain-specific actions.

Research Models

Animal Models

Key models for studying FGF23:

• Transgenic mice: FGF23 overexpression
• Knockout mice: FGF23 deficiency
• Klotho mice: Alpha-Klotho deficiency

Clinical Studies

Human studies include:

• Cross-sectional: Patient populations
• Prospective: Longitudinal cohorts
• Intervention: Treatment effects

Cross-links

• [Fibroblast Growth Factors](/proteins/fibroblast-growth-factors)
• [FGF Signaling](/mechanisms/fgfr-signaling)
• [Phosphate Metabolism](/mechanisms/phosphate-metabolism)
• [Vitamin D and Neurodegeneration](/mechanisms/vitamin-d-neurodegeneration)
• [White Matter Disease](/mechanisms/white-matter-disease)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)

See Also

• [Genes Index](/genes)
• [Growth Factors](/proteins/growth-factors)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)

References

Pathway Diagram

The following diagram shows the key molecular relationships involving FGF23 — Fibroblast Growth Factor 23 discovered through SciDEX knowledge graph analysis: