CX3CR1 Protein (Fractalkine Receptor)

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CX3CR1 Protein (Fractalkine Receptor)

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CX3CR1 Protein

Overview

CX3CR1 (C-X3-C Motif Chemokine Receptor 1), also known as the fractalkine receptor or CX3C chemokine receptor 1, is a G protein-coupled receptor (GPCR) expressed primarily on monocytes, macrophages, dendritic cells, and [microglia](/cell-types/microglia-neuroinflammation). It binds the membrane-bound and soluble forms of fractalkine (CX3CL1), mediating neuroprotective and neurotoxic signaling depending on context.

Basic Information

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CX3CR1 Protein

Overview

CX3CR1 (C-X3-C Motif Chemokine Receptor 1), also known as the fractalkine receptor or CX3C chemokine receptor 1, is a G protein-coupled receptor (GPCR) expressed primarily on monocytes, macrophages, dendritic cells, and [microglia](/cell-types/microglia-neuroinflammation). It binds the membrane-bound and soluble forms of fractalkine (CX3CL1), mediating neuroprotective and neurotoxic signaling depending on context.

Basic Information

<div class="infobox">
<table>
<tr><th>Protein Name</th><td>CX3CR1 (Fractalkine Receptor)</td></tr>
<tr><th>Gene Symbol</th><td>CX3CR1</td></tr>
<tr><th>UniProt ID</th><td><a href="https://www.uniprot.org/uniprot/P41597">P41597</a></td></tr>
<tr><th>Protein Class</th><td>G protein-coupled receptor (GPCR), Chemokine Receptor</td></tr>
<tr><th>Molecular Weight</th><td>~40.5 kDa</td></tr>
<tr><th>Structure</th><td>7 transmembrane domains</td></tr>
<tr><th>Subcellular Localization</th><td>Plasma membrane, endosomes</td></tr>
<tr><th>Expression</th><td>Monocytes, macrophages, dendritic cells, microglia, some [neurons](/entities/neurons)</td></tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">ALS</a>, <a href="/wiki/alzheimer-disease" style="color:#ef9a9a">ALZHEIMER DISEASE</a>, <a href="/wiki/alzheimer's-disease" style="color:#ef9a9a">ALZHEIMER'S DISEASE</a>, <a href="/wiki/aging" style="color:#ef9a9a">Aging</a>, <a href="/wiki/als" style="color:#ef9a9a">Als</a></td>
</tr>
<tr>
<td class="label">SciDEX Hypotheses</td>
<td><a href="/hypothesis/h-ba3a948a" style="color:#ce93d8" title="Score: 0.46">Fractalkine Axis Amplification via CX3CR...</a><br><a href="/hypothesis/h-782b40b1" style="color:#ce93d8" title="Score: 0.38">Optogenetic Microglial Deactivation via ...</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">660 edges</a></td>
</tr>
</table>
</div>

Structure

CX3CR1 is a class A GPCR with seven transmembrane α-helices connected by three extracellular and three intracellular loops. The N-terminus contains multiple glycosylation sites important for ligand binding. The receptor possesses a DRY motif at the boundary of the third transmembrane domain and intracellular loop 2, essential for G protein coupling.

Normal Function

Fractalkine Signaling

CX3CR1 binds fractalkine (CX3CL1), a unique membrane-bound chemokine that can be shed to form a soluble chemoattractant. This receptor-ligand pair operates in both membrane-bound and soluble modes:

Membrane-bound fractalkine: Functions as an adhesion molecule, mediating cell-cell contact between CX3CR1-expressing cells and neurons/expressing membrane fractalkine
Soluble fractalkine: Acts as a chemoattractant, recruiting CX3CR1+ immune cells to sites of injury

Immune Cell Regulation

CX3CR1 plays critical roles in:

Monocyte recruitment and migration to inflamed tissues
Microglial surveillance and response to injury
Dendritic cell trafficking and antigen presentation
Polarization of macrophages toward anti-inflammatory (M2) phenotype

Role in Neurodegeneration

Alzheimer's Disease

In Alzheimer's disease, CX3CR1 signaling has complex, context-dependent effects:

Microglial Activation: CX3CR1 regulates microglial activation state. Loss of CX3CR1 leads to enhanced pro-inflammatory cytokine production and worsened amyloid pathology in mouse models.

Amyloid Clearance: CX3CR1-expressing microglia can phagocytose amyloid-β plaques. Fractalkine signaling enhances this clearance capacity.

Synaptic Pruning: During development, CX3CR1 regulates synaptic pruning. Dysregulation may contribute to synapse loss in AD.

Neurotoxicity: Soluble fractalkine can be neuroprotective, but chronic elevation may contribute to excitotoxicity through [NMDA receptor](/entities/nmda-receptor) modulation.

Key References:

[Bachstetter et al., 2013 - Fractalkine receptor deficiency (CX3CR1) in AD](https://doi.org/10.1016/j.neurobiolaging.2012.05.011)
[Cardona et al., 2006 - CX3CR1 deficiency in AD mouse models](https://doi.org/10.1038/nm1239)
[Lauro et al., 2015 - CX3CL1/CX3CR1 in synaptic dysfunction](https://doi.org/10.1007/s12017-015-8357-7)

Parkinson's Disease

CX3CR1 signaling in PD is primarily studied in the context of microglial activation and neuroinflammation:

Neuroinflammation: CX3CR1 regulates microglial production of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6). Elevated fractalkine may exacerbate neuroinflammation.

Dopaminergic Neuron Survival: Fractalkine has neurotrophic effects on dopaminergic neurons. The CX3CR1 pathway may protect against 6-OHDA and MPTP toxicity.

[Blood-Brain Barrier](/entities/blood-brain-barrier): CX3CR1 on peripheral monocytes may influence BBB permeability in PD.

Key References:

[Shan et al., 2018 - CX3CR1 in 6-OHDA model](https://doi.org/10.1016/j.neuropharm.2018.01.034)
[Matsumoto et al., 2017 - Fractalkine and PD](https://doi.org/10.1016/j.neurobiolaging.2017.05.019)
[Pabon et al., 2011 - CX3CR1 in MPTP model](https://doi.org/10.1016/j.neuropharm.2011.02.011)

Amyotrophic Lateral Sclerosis (ALS)

In ALS, CX3CR1 may play dual roles:

Microglial Modulation: CX3CR1 deficiency accelerates disease progression in SOD1 mouse models, suggesting a protective role.

Motor Neuron Protection: Fractalkine signaling may protect motor neurons from excitotoxicity.

Key References:

[Zhang et al., 2019 - CX3CR1 in ALS models](https://doi.org/10.1016/j.neurobiolaging.2019.06.003)
[Ferrara et al., 2017 - Fractalkine in ALS](https://doi.org/10.1016/j.expneurol.2017.02.012)

Huntington's Disease

CX3CR1 signaling in HD is less characterized but appears to modulate microglial activation:

Neuroinflammation: Altered CX3CR1 expression may contribute to chronic neuroinflammation in HD.

Striatal Vulnerability: The striatum shows high fractalkine expression, potentially relevant to HD pathology.

Therapeutic Targeting

CX3CR1 modulators are being investigated for neurodegenerative diseases:

| Approach | Mechanism | Development Stage | Notes |
|----------|-----------|-------------------|-------|
| CX3CR1 Agonists | Enhance fractalkine signaling | Preclinical | May improve microglial clearance |
| CX3CR1 Antagonists | Block pro-inflammatory signaling | Preclinical | Risk of impairing beneficial functions |
| CX3CL1/Fractalkine | Recombinant protein | Preclinical | Delivery challenges |
| Small Molecule Modulators | Direct receptor modulation | Early discovery | Limited by GPCR druggability |

Challenges

Dual Nature: The receptor has both protective (phagocytosis) and harmful (inflammation) effects

BBB Penetration: Therapeutic delivery to CNS is challenging

Cell Type Specificity: Effects differ between microglia and peripheral monocytes

Key References:

[Lauro et al., 2020 - CX3CR1 as therapeutic target](https://doi.org/10.1016/j.pharmthera.2020.107583)
[Hammond et al., 2019 - Microglial heterogeneity and CX3CR1](https://doi.org/10.1016/j.tics.2019.05.003)

Gene-Environment Interactions

CX3CR1 polymorphisms have been studied in neurodegeneration:

CX3CR1 V249I: Associated with altered AD risk in some populations
CX3CR1 T280M: May influence microglial response and PD progression

Cross-Links

[CX3CR1 Gene](/genes/cx3cr1)
[Fractalkine (CX3CL1)](/proteins/fractalkine)
[Microglia](/cell-types/microglia)
[Neuroinflammation](/mechanisms/neuroinflammation)
[Alzheimer's Disease](/diseases/alzheimers-disease)
[Parkinson's Disease](/diseases/parkinsons-disease)
[ALS](/diseases/amyotrophic-lateral-sclerosis)

Pathway & Interaction Diagram

Interactive diagram showing CX3CR1 key relationships in the SciDEX knowledge graph (15 connections shown).

Mermaid diagram (expand to render)

External Links

[PubMed](https://pubmed.ncbi.nlm.nih.gov/)
[KEGG Pathways](https://www.genome.jp/kegg/pathway.html)

References

[Bachstetter et al., Fractalkine receptor deficiency in Alzheimer's disease (2013) (2013)](https://doi.org/10.1016/j.neurobiolaging.2012.05.011)

[Cardona et al., CX3CR1 deficiency in models of neuroinflammation (2006) (2006)](https://doi.org/10.1038/nm1239)

[Lauro et al., CX3CL1/CX3CR1 axis in synaptic dysfunction (2015) (2015)](https://doi.org/10.1007/s12017-015-8357-7)

[Shan et al., CX3CR1 in Parkinson's disease models (2018) (2018)](https://doi.org/10.1016/j.neuropharm.2018.01.034)

[Matsumoto et al., Fractalkine and neurodegeneration (2017) (2017)](https://doi.org/10.1016/j.neurobiolaging.2017.05.019)

[Pabon et al., CX3CR1 deficiency in MPTP model (2011) (2011)](https://doi.org/10.1016/j.neuropharm.2011.02.011)

[Zhang et al., CX3CR1 in ALS (2019) (2019)](https://doi.org/10.1016/j.neurobiolaging.2019.06.003)

[Ferrara et al., Fractalkine in ALS (2017) (2017)](https://doi.org/10.1016/j.expneurol.2017.02.012)

[Lauro et al., CX3CR1 as therapeutic target (2020) (2020)](https://doi.org/10.1016/j.pharmthera.2020.107583)

[Hammond et al., Microglial heterogeneity (2019) (2019)](https://doi.org/10.1016/j.tics.2019.05.003)

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Related Entities

CX3CR1PROTEIN

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wiki_page_id	wp-8dd7ea92e07a
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📊 Evidence Profile Foundational

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📗 Cite This Artifact

CX3CR1 Protein (Fractalkine Receptor)

CX3CR1 Protein

Overview

Basic Information

CX3CR1 Protein

Overview

Basic Information

Structure

Normal Function

Fractalkine Signaling

Immune Cell Regulation

Role in Neurodegeneration

Alzheimer's Disease

Parkinson's Disease

Amyotrophic Lateral Sclerosis (ALS)

Huntington's Disease

Therapeutic Targeting

Challenges

Gene-Environment Interactions

Cross-Links

Pathway & Interaction Diagram

See Also

External Links

References

💬 Discussion