FNDC5 — Fibronectin Type III Domain Containing 5
<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">FNDC5 — Fibronectin Type III Domain Containing 5</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td><strong>FNDC5</strong></td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>Fibronectin Type III Domain Containing 5</td>
</tr>
<tr>
<td class="label">Chromosome</td>
<td>1p36.22</td>
</tr>
<tr>
<td class="label">NCBI Gene</td>
<td><a href="https://www.ncbi.nlm.nih.gov/gene/56852" target="_blank">56852</a></td>
</tr>
<tr>
<td class="label">Ensembl</td>
<td><a href="https://ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000100597" target="_blank">ENSG00000100597</a></td>
</tr>
<tr>
<td class="label">UniProt</td>
<td><a href="https://www.uniprot.org/uniprot/Q8IZF6" target="_blank">Q8IZF6</a></td>
</tr>
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<td class="label">Protein Product</td>
<td>[FNDC5/Irisin](/proteins/fndc5-protein)</td>
</tr>
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<td class="label">Expression</td>
<td>[Skeletal muscle](/brain-regions/skeletal-muscle) (primary), [hippocampus](/brain-regions/hippocampus), [cortex](/brain-regions/cortex), [heart](/brain-regions/heart)</td>
</tr>
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<td class="label">Related Diseases</td>
<td>[Alzheimer's Disease](/diseases/alzheimers), [Parkinson's Disease](/diseases/parkinsons-disease), [ALS](/diseases/als), [Type 2 Diabetes](/diseases/type-2-diabetes)</td>
</tr>
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<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">ALS</a>, <a href="/wiki/aging" style="color:#ef9a9a">Aging</a>, <a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/alzheimer" style="color:#ef9a9a">Alzheimer</a>, <a href="/wiki/ataxia" style="color:#ef9a9a">Ataxia</a></td>
</tr>
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<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">139 edges</a></td>
</tr>
</table>
FNDC5 — Fibronectin Type III Domain Containing 5
Overview
FNDC5 (Fibronectin Type III Domain Containing 5) is a gene located on chromosome 1p36.22 that encodes a type I membrane protein primarily expressed in skeletal muscle. FNDC5 is the precursor protein for irisin, a circulation myokine that is cleaved and secreted in response to exercise[@fndc]. Irisin has garnered significant attention for its pleiotropic effects on energy metabolism and, more recently, for its neuroprotective properties in neurodegenerative disease models[@irisin2012].
The discovery of irisin in 2012 established FNDC5 as a critical mediator of exercise-induced systemic effects, linking physical activity to benefits in distant organs including the brain[@pgc2013]. This positions FNDC5 as a compelling therapeutic target for neurodegenerative disorders where exercise has shown beneficial effects.
Gene Structure and Expression
Genomic Location
- Chromosome: 1p36.22
- Genomic coordinates: ~10,000 bp coding region
- Orientation: Plus strand
- Isoforms: Multiple splice variants identified
Tissue Expression
FNDC5 exhibits tissue-specific expression patterns:
| Tissue | Expression Level | Notes |
|--------|-----------------|-------|
| Skeletal muscle | High | Primary source of circulating irisin |
| Heart | Moderate | Cardiac expression |
| Brain | Low-Moderate | [Hippocampus](/brain-regions/hippocampus), [cortex](/brain-regions/cortex), cerebellum |
| Brown adipose tissue | Moderate | Involved in thermogenesis |
| Liver | Low | Minor contribution |
Transcriptional Regulation
FNDC5 expression is primarily regulated by:
PGC-1α: Peroxisome proliferator-activated receptor gamma coactivator 1-alpha is the master regulator of exercise-induced FNDC5 expression[@irisin2019]
PPARγ: Nuclear receptor that can induce FNDC5
MyoD: Muscle differentiation factor
AMP-activated protein kinase (AMPK): Energy sensor that promotes FNDC5 expression during exercise
Protein: FNDC5/Irisin
Protein Structure
The FNDC5 protein consists of:
- N-terminal signal peptide: Targets for secretion
- Fibronectin type III domain: The characteristic domain giving the protein its name
- C-terminal hydrophobic region: Membrane anchor
- Cleavage site: Proteolytic processing releases irisin
Processing and Secretion
The cleavage of FNDC5 to produce irisin is mediated by:
- Tumor necrosis factor-alpha converting enzyme (TACE/ADAM17): Primary protease responsible for irisin release[@fndcirisin2019]
- Proteolytic processing: Generates the soluble irisin fragment (~112 amino acids)
Irisin Circulation
- Half-life: ~1 hour in circulation
- Levels: 10-100 ng/mL in human serum
- Induction: Exercise increases irisin 2-3 fold
- BBB penetration: Partial penetration of the [blood-brain barrier](/entities/blood-brain-barrier) reported
Function in Neurodegeneration
Exercise-Induced Neuroprotection
FNDC5/irisin mediates several exercise-induced beneficial effects in the brain:
Neurogenesis: Promotes hippocampal neurogenesis
Synaptic plasticity: Enhances [long-term potentiation](/mechanisms/long-term-potentiation) (LTP)
Mitochondrial function: Increases mitochondrial biogenesis
Neuroinflammation: Reduces inflammatory responses
Amyloid clearance: Facilitates Aβ clearanceAlzheimer's Disease
In [Alzheimer's disease](/diseases/alzheimers-disease) models, FNDC5/irisin has shown:
- [Amyloid-beta](/proteins/amyloid-beta) reduction: Decreased Aβ accumulation and plaque formation[@adammediated2016]
- [Tau](/proteins/tau) pathology: Reduced tau phosphorylation and aggregation
- Synaptic protection: Preserved synaptic markers and function
- Cognitive improvement: Enhanced memory and learning in mouse models
- Neurogenesis: Promoted adult hippocampal neurogenesis
Parkinson's Disease
Evidence for FNDC5/irisin in PD includes:
- Dopaminergic neuron protection: Preserved tyrosine hydroxylase (TH)-positive [neurons](/entities/neurons)[^7]
- Mitochondrial enhancement: Increased PGC-1α and mitochondrial DNA content
- [Alpha-synuclein](/proteins/alpha-synuclein): Reduced aggregation and toxicity
- Motor function: Improved behavioral outcomes in models
Amyotrophic Lateral Sclerosis (ALS)
In ALS models:
- Motor neuron protection: Reduced motor neuron degeneration
- Neuromuscular junction: Improved stability of neuromuscular junctions
- Muscle-nerve connection: Maintained muscle innervation
Therapeutic Targeting
Exercise Mimetics
Given the therapeutic potential of FNDC5/irisin, several strategies are being explored:
| Approach | Mechanism | Status | Challenges |
|----------|-----------|--------|------------|
| Recombinant irisin | Direct protein administration | Preclinical | BBB penetration, half-life |
| FNDC5 overexpression | Gene therapy | Preclinical | Delivery, expression control |
| Small molecule agonists | PGC-1α activators | Research | Specificity |
| Exercise mimetics | Pharmacological PGC-1α induction | Research | Off-target effects |
Pharmacological Modulation
Compounds being investigated:
- PGC-1α agonists: Activate FNDC5 expression
- AMPK activators: Indirect FNDC5 induction
- [HDAC](/entities/hdac-enzymes) inhibitors: Epigenetic upregulation
- ADAM17 enhancers: Increase irisin release
Clinical Relevance
Biomarker Potential
Serum irisin levels have been studied as:
- Exercise compliance marker: Tracks physical activity levels
- Disease biomarker: Altered levels in AD, PD, diabetes
- Therapeutic response indicator: Monitors treatment efficacy
Clinical Trials
Current clinical investigations include:
- Exercise interventions and irisin measurement
- Recombinant irisin safety studies
- FNDC5 gene therapy trials (preclinical)
Cross-Links
- [PGC-1α Signaling](/mechanisms/pgc1-alpha-neurodegeneration)
- [Mitochondrial Biogenesis](/mechanisms/mitochondrial-dysfunction-neurodegeneration)
- [AMPK Signaling](/mechanisms/ampk-signaling)
- [BDNF Neuroprotection](/mechanisms/bdnf-neuroprotection)
- [Irisin Neuroprotective Pathways](/mechanisms/irisin-neuroprotection)
- [Irisin (FNDC5 cleavage product)](/proteins/irisin-protein) — Coming soon
- [Alzheimer's Disease](/diseases/alzheimers-disease)
- [Parkinson's Disease](/diseases/parkinsons-disease)
- [ALS](/diseases/als)
See Also
- [ Protein](/proteins/irisin-protein)
- [PGC-1α Signaling](/mechanisms/pgc1-alpha-neurodegeneration)
- [Mitochondrial Biogenesis](/mechanisms/mitochondrial-dysfunction-neurodegeneration)
- [AMPK Signaling](/mechanisms/ampk-signaling)
- [BDNF Neuroprotection](/mechanisms/bdnf-neuroprotection)
- [Irisin Neuroprotective Pathways](/mechanisms/irisin-neuroprotection)
- [Alzheimer's Disease](/diseases/alzheimers-disease)
- [Parkinson's Disease](/diseases/parkinsons-disease)
External Links
- [Ensembl: ENSG00000100597](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000100597)
References
Unknown, FNDC5 gene (NCBI) (n.d.)
[Irisin: The exercise hormone (Boström et al., 2012) (2012)](https://doi.org/10.1038/nature10753)
[PGC-1α regulates FNDC5 expression (Wrann et al., 2013) (2013)](https://doi.org/10.1152/japplphysiol.00028.2013)
[Irisin and Alzheimer's disease (Lourenco et al., 2019) (2019)](https://doi.org/10.1093/brain/awz291)
[FNDC5/irisin in Parkinson's disease (Liu et al., 2019) (2019)](https://doi.org/10.1007/s12035-019-1580-6)
[ADAM17-mediated irisin release (Wei et al., 2016) (2016)](https://doi.org/10.1038/nm.4475)Pathway Context
Mermaid diagram (expand to render)
Pathway Diagram
The following diagram shows the key molecular relationships involving FNDC5 — Fibronectin Type III Domain Containing 5 discovered through SciDEX knowledge graph analysis:
Mermaid diagram (expand to render)