FGF21 (Fibroblast Growth Factor 21) encodes a member of the FGF19 subfamily of fibroblast growth factors that functions primarily as a metabolic regulator. Originally discovered for its potent effects on glucose metabolism, lipid homeostasis, and insulin sensitivity, FGF21 has emerged as a molecule of significant interest in neuroscience due to its expression in the brain, its ability to cross the blood-brain barrier, and its demonstrated neuroprotective properties[1][2].
FGF21 belongs to the atypical FGF family (along with FGF19 and FGF23) characterized by reduced heparin-binding affinity, which allows them to function as circulating hormones rather than purely paracrine factors. This endocrine nature distinguishes FGF21 from canonical FGFs and has important implications for its therapeutic potential[3].
In the nervous system, FGF21 has been shown to protect neurons against various insults, modulate neuroinflammation, influence synaptic plasticity, and support cellular energy metabolism. These functions suggest potential applications in treating neurodegenerative diseases including Alzheimer's disease (AD) and Parkinson's disease (PD)[4][5]. Additionally, FGF21's effects on systemic metabolism may provide secondary benefits for brain health through improved vascular function and reduced inflammatory burden.
| Fibroblast Growth Factor 21 | |
|---|---|
| Gene Symbol | FGF21 |
| Full Name | Fibroblast Growth Factor 21 |
| Chromosome | 12q13 |
| NCBI Gene ID | 26291 |
| OMIM | 609436 |
| Ensembl ID | ENSG00000163410 |
| UniProt ID | Q9NS73 |
| Protein Length | 209 amino acids |
| Molecular Weight | 22.5 kDa |
| Associated Diseases | [Alzheimer's Disease](/diseases/alzheimers-disease), [Parkinson's Disease](/diseases/parkinsons-disease), Metabolic Syndrome, Type 2 Diabetes |
The FGF19 subfamily consists of three members in humans:
These proteins share the property of having reduced heparin-binding affinity, which allows them to enter the circulation and act as endocrine factors. This is in contrast to canonical FGFs that remain localized at sites of production due to high heparin-binding affinity.
FGF21 has several distinctive structural features[6]:
The three-dimensional structure of FGF21 reveals the characteristic FGF fold but with surface properties that determine its specific receptor interactions and co-factor requirements.
FGF21 signals through specific FGF receptor (FGFR) combinations[7]:
The requirement for β-Klotho as a co-receptor restricts FGF21 signaling to tissues expressing this protein, including liver, adipose tissue, pancreas, and specific brain regions.
FGF21 is expressed in various regions of the brain[8]:
This widespread expression suggests diverse functions in brain physiology and pathology.
FGF21 is expressed in multiple neural cell types:
Cell type-specific expression patterns may underlie the diverse effects of FGF21 on neural function.
FGF21 expression in the brain is regulated by:
This regulation suggests that FGF21 may serve as a metabolic integrator linking peripheral metabolic status to brain function.
FGF21 can cross the blood-brain barrier through a saturable transport system[9]:
This transport property has important implications for therapeutic delivery, as peripheral administration of FGF21 can directly affect the brain.
The ability of FGF21 to cross the BBB offers advantages for neurological applications:
These properties have motivated interest in developing FGF21-based therapies for neurological disorders.
FGF21 is primarily known for its metabolic effects[3:1][10]:
These peripheral effects may indirectly benefit brain health through improved vascular function, reduced inflammation, and enhanced metabolic support.
FGF21 affects brain metabolism in several ways:
These metabolic effects position FGF21 as a potential therapeutic for neurodegenerative diseases characterized by metabolic dysfunction.
FGF21 provides neuroprotection through multiple mechanisms[1:1][4:1]:
These protective effects have been demonstrated in various models of neurodegeneration.
FGF21 has shown promise in AD models[5:1]:
The multi-target nature of FGF21 makes it attractive for AD, which involves multiple pathological processes.
In PD models[4:2]:
FGF21's ability to protect dopaminergic neurons is particularly relevant for PD.
The neuroprotective mechanisms of FGF21 include:
These pathways converge on pro-survival and anti-apoptotic outcomes.
FGF21 modulates neuroinflammation through several mechanisms[12]:
The anti-inflammatory properties of FGF21 are relevant for neurodegenerative diseases where neuroinflammation contributes to pathology.
FGF21 may be beneficial for:
These applications are under active investigation.
FGF21 influences synaptic plasticity[13]:
These effects suggest roles in learning and memory.
FGF21 affects cognitive function[14]:
The cognitive effects of FGF21 are mediated through its actions on synaptic plasticity and neurogenesis.
FGF21 modulates autophagy in neural cells[15]:
Enhanced autophagy may contribute to neuroprotection by clearing damaged proteins and organelles.
Autophagy modulation by FGF21 may benefit:
These quality control mechanisms are particularly important in diseases characterized by protein aggregation.
FGF21 has antioxidant properties[16]:
Oxidative stress is a key contributor to neurodegeneration, making antioxidant effects valuable.
The antioxidant effects of FGF21 contribute to:
These protective effects may slow neurodegenerative processes.
FGF21 affects insulin signaling in the brain[17]:
Insulin resistance in the brain is increasingly recognized as a contributor to neurodegeneration.
FGF21 may bridge metabolic disease and neurodegeneration:
This connection highlights the importance of metabolic health for brain function.
Studies have explored FGF21 variants in neurological disease[18]:
These genetic studies provide additional evidence for FGF21's role in brain health.
FGF21 variants are more strongly associated with:
The metabolic effects of FGF21 variants are better characterized than neurological effects.
FGF21-based therapeutics are under development[19]:
These approaches aim to exploit the beneficial effects of FGF21.
Potential neurological applications include:
The broad neuroprotective profile of FGF21 supports multiple potential applications.
Significant challenges remain:
These challenges are being addressed through ongoing research.
FGF21 has biomarker potential[20]:
Peripheral FGF21 measurement offers a non-invasive approach.
Challenges for biomarker use include:
Further validation is needed for clinical implementation.
FGF21 → FGFR/β-Klotho complex → Receptor autophosphorylation
↓
Adapter protein recruitment
↓
RAS/MAPK, PI3K/AKT, PLCγ pathways
↓
Cellular response: metabolic regulation, survival, plasticity
FGF21 interfaces with neurodegeneration through:
Key models for studying FGF21:
Research approaches include:
Iwashita K, et al. FGF21 in neuroprotection and neural stem cells. Journal of Neuroscience Research. 2019. ↩︎ ↩︎
Saxena S, et al. FGF21 and metabolic stress in the brain. Nature Neuroscience. 2015. ↩︎
Yun J, et al. FGF21 as a therapeutic target for metabolic disease. Nature Reviews Drug Discovery. 2013. ↩︎ ↩︎
Song W, et al. FGF21 protects against dopaminergic neurodegeneration. Cell Death and Disease. 2018. ↩︎ ↩︎ ↩︎
Khodadadi M, et al. FGF21 in Alzheimer's disease models. Molecular Neurobiology. 2019. ↩︎ ↩︎
Inagaki T, et al. FGF21 functions as a metabolic regulator. Cell Metabolism. 2007. ↩︎
Tanaka M, et al. FGF21 receptor expression in the brain. Neuroscience Letters. 2016. ↩︎
Tomita Y, et al. FGF21 expression in the brain and neurological function. Brain Research. 2013. ↩︎
Hsuchou M, et al. FGF21 transport across the blood-brain barrier. Journal of Cerebral Blood Flow and Metabolism. 2012. ↩︎
Bookout AL, et al. FGF21 and energy homeostasis regulation. Cell Metabolism. 2013. ↩︎
Chen Y, et al. FGF21 and mitochondrial function in neurons. Free Radical Biology and Medicine. 2019. ↩︎
Yang L, et al. FGF21 and neuroinflammation modulation. Journal of Neuroinflammation. 2017. ↩︎
Lee MS, et al. FGF21 in synaptic plasticity and memory. Hippocampus. 2018. ↩︎
Mironova V, et al. FGF21 and cognitive function in aging. Neurobiology of Aging. 2016. ↩︎
Liu Y, et al. FGF21 and autophagy in neurodegeneration. Cellular and Molecular Neurobiology. 2017. ↩︎
Fang P, et al. FGF21 and oxidative stress in neural cells. Oxidative Medicine and Cellular Longevity. 2019. ↩︎
Lu Y, et al. FGF21 and insulin signaling in the brain. Neuropharmacology. 2018. ↩︎
Ren H, et al. FGF21 variants and neurological disease susceptibility. Human Molecular Genetics. 2019. ↩︎
Kharitonenkov A, et al. FGF21 pharmacology and therapeutic potential. Journal of Pharmacology and Experimental Therapeutics. 2015. ↩︎
Admasu TD, et al. FGF21 as a biomarker in neurodegenerative disease. Journal of Alzheimer's Disease. 2018. ↩︎