FASLG - Fas Ligand
Overview
<table class="infobox infobox-gene">
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<th class="infobox-header" colspan="2">FASLG - Fas Ligand</th>
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<td class="label">Symbol</td>
<td><strong>FASLG</strong></td>
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<td class="label">Full Name</td>
<td>FASLG - Fas Ligand</td>
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<td class="label">Type</td>
<td>Gene</td>
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<td class="label">NCBI</td>
<td><a href="https://www.ncbi.nlm.nih.gov/gene/?term=FASLG" target="_blank">Search NCBI</a></td>
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<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">2 edges</a></td>
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Pathway Diagram
Mermaid diagram (expand to render)
FASLG (Fas Cell Surface Death Receptor Ligand) is a gene encoding the Fas ligand (FasL/CD95L), a Type II transmembrane protein belonging to the tumor necrosis factor (TNF) superfamily. FasL is a critical effector of [apoptosis](/entities/apoptosis) (programmed cell death) and plays a significant role in immune privilege, tumor immune evasion, and neuronal cell death in neurodegenerative diseases. [@ethell2002]
- Gene Symbol: FASLG
- Official Name: Fas ligand (TNF superfamily, member 6)
- Chromosomal Location: 1q24.3
- NCBI Gene ID: 3564
- Uniprot ID: P48023
Protein Structure and Function
The Fas ligand protein is a Type II transmembrane protein with the following structural features: [@mattson2000]
- N-terminal intracellular domain: Contains a proline-rich region important for protein-protein interactions
- Transmembrane domain: Anchors the protein to the cell membrane
- C-terminal extracellular domain: The functional domain that binds to Fas receptors
FasL functions as a trimer and triggers apoptosis by binding to its cognate receptor Fas (CD95), forming the Fas-FasL death-inducing signaling complex (DISC). This activation leads to the recruitment of adaptor proteins (FADD) and initiator caspases (caspase-8), ultimately activating executioner caspases (caspase-3, -6, -7) that cleave cellular substrates and lead to cell death. [@combs2001]
Alternative Functions
Beyond apoptosis, FasL signaling can also: [@rohn2001]
- Induce [necroptosis](/entities/necroptosis) (programmed necrosis) under certain conditions
- Trigger inflammatory responses through [NF-κB](/entities/nf-kb) activation
- Promote IL-1β release from glial cells
- Modulate synaptic plasticity and neuronal excitability
Expression Patterns
FasL is expressed in various tissues with notable patterns relevant to neurodegeneration: [@yang2006]
- Brain: Expressed in [neurons](/entities/neurons), [astrocytes](/entities/astrocytes), and [microglia](/cell-types/microglia-neuroinflammation)
- Immune system: High expression in activated T lymphocytes and natural killer (NK) cells
- Testis: High expression in Sertoli cells (immune privileged site)
- Eye: Expressed in corneal and retinal cells (immune privileged sites)
In the brain, both neurons and glial cells can express FasL, creating a system for regulated cell death and immune modulation. [@jellinger2003]
Role in Neurodegenerative Diseases
Alzheimer's Disease
In [Alzheimer's disease](/diseases/alzheimers-disease) (AD), FasL plays a complex role in [amyloid-beta](/proteins/amyloid-beta) (Aβ)-induced neurotoxicity: [@wang2006]
- Aβ-mediated FasL upregulation: Amyloid-beta peptides upregulate FasL expression in neurons and astrocytes, creating a pro-apoptotic environment [1]
- Synaptic dysfunction: FasL signaling contributes to synaptic loss through caspase activation [2]
- Microglial activation: Aβ can induce FasL expression in microglia, promoting neuroinflammation [3]
- [Tau](/proteins/tau) pathology: FasL-mediated apoptosis may accelerate [tau](/proteins/tau) phosphorylation and spread [4]
Parkinson's Disease
In [Parkinson's disease](/diseases/parkinsons-disease) (PD), FasL is implicated in dopaminergic neuron loss: [@liu2010]
- Mitochondrial dysfunction: Environmental toxins (e.g., MPTP, rotenone) upregulate FasL and trigger dopaminergic neuron apoptosis [5]
- [α-Synuclein](/proteins/alpha-synuclein) aggregation: FasL expression is elevated in PD brains and may be induced by α-synuclein oligomers [6]
- Microglial neurotoxicity: Activated microglia express FasL and can kill neurons through Fas-FasL interactions [7]
- Genetic associations: Certain FASLG polymorphisms may increase PD risk [8]
Amyotrophic Lateral Sclerosis (ALS)
FasL contributes to motor neuron degeneration in ALS: [@guegan2003]
- SOD1 mutations: Mutant SOD1 proteins upregulate FasL in motor neurons and astrocytes [9]
- Non-cell autonomous toxicity: FasL expression in astrocytes mediates motor neuron death [10]
- [TDP-43](/mechanisms/tdp-43-proteinopathy) pathology: TDP-43 aggregates are associated with increased FasL expression [11]
Other Neurodegenerative Disorders
- Huntington's disease: FasL-mediated apoptosis contributes to striatal neuron loss [12]
- Multiple sclerosis: FasL on autoreactive T cells and microglia contributes to demyelination [13]
- Prion diseases: Prion protein aggregation induces FasL expression [14]
Therapeutic Implications
Targeting the Fas-FasL pathway represents a therapeutic strategy for neurodegenerative diseases: [@nagai2007]
FasL Inhibitors
- Fas/Fc decoy receptors: Soluble Fas-Fc can block FasL signaling
- Small molecule inhibitors: Various compounds are being developed to block DISC formation
- Neutralizing antibodies: Anti-FasL antibodies can prevent apoptosis
Challenges
- Immune suppression risk: Blocking FasL globally can increase cancer risk and autoimmune reactions
- [Blood-brain barrier](/entities/blood-brain-barrier): Therapeutic agents must penetrate the BBB
- Timing: Inhibiting apoptosis may be most effective in early disease stages
Current Research
- Nanoparticle-delivered FasL inhibitors
- Gene therapy approaches using AAV vectors
- Combination therapies with other neuroprotective agents
Genetics
Polymorphisms
- -844T>C polymorphism: Associated with altered FasL expression levels
- -672A>G polymorphism: May influence autoimmune disease risk
Disease Associations
- Certain FASLG variants have been linked to increased risk of:
- Sporadic Parkinson's disease
- Multiple sclerosis
- ALS with autoimmune features
Interacting Proteins
FasL interacts with several proteins relevant to neurodegeneration: [@pasinelli2006]
- FAS (CD95): Primary receptor mediating apoptosis
- FADD: Adaptor protein in death receptor signaling
- Caspase-8: Initiator caspase in extrinsic apoptosis
- Caspase-3: Executioner caspase
- DR5: Can also bind FasL in some contexts
- X-linked inhibitor of apoptosis (XIAP): Regulated by FasL signaling
Diagnostic and Prognostic Potential
Biomarkers
- Soluble FasL (sFasL) in cerebrospinal fluid (CSF) as a potential biomarker
- Peripheral blood FasL levels correlate with disease progression in some studies
Research Applications
- FasL expression as a marker for neuroinflammation
- Tracking apoptosis in animal models of neurodegeneration
Additional evidence sources: [@trettel2000] [@sabelko1999] [@schultz2004]
See Also
- [FAS Gene (Fas Receptor)](/genes/fas)
- [Apoptosis Pathways](/mechanisms/apoptosis-parkinsons-disease)
- [Alzheimer's Disease](/diseases/alzheimers-disease)
- [Parkinson's Disease](/diseases/parkinsons-disease)
- [Amyotrophic Lateral Sclerosis (ALS)](/diseases/amyotrophic-lateral-sclerosis)
- [Neuroinflammation](/mechanisms/neuroinflammation-pathway)
- [Caspase Pathways](/mechanisms/caspase-pathways)
External Links
- [NCBI Gene: FASLG](https://www.ncbi.nlm.nih.gov/gene/3564)
- [Uniprot: FASLG](https://www.uniprot.org/uniprotkb/P48023)
- [OMIM: FASLG](https://www.omim.org/entry/134638)
References
[Ethell et al., Amyloid-beta-induced FasL upregulation (2002) (2002)](https://pubmed.ncbi.nlm.nih.gov/11862280/)
[Unknown, Mattson, Synaptic apoptosis in Alzheimer's disease (2000) (2000)](https://pubmed.ncbi.nlm.nih.gov/10774721/)
[Combs et al., Microglial FasL in Aβ toxicity (2001) (2001)](https://pubmed.ncbi.nlm.nih.gov/11292687/)
[Rohn et al., Caspase activation in tau pathology (2001) (2001)](https://pubmed.ncbi.nlm.nih.gov/11595185/)
[Yang et al., MPTP-induced FasL in dopaminergic neurons (2006) (2006)](https://pubmed.ncbi.nlm.nih.gov/16629778/)
[Unknown, Jellinger, Alpha-synuclein and cell death in PD (2003) (2003)](https://pubmed.ncbi.nlm.nih.gov/14569015/)
[Wang et al., Microglial FasL-mediated neurotoxicity (2006) (2006)](https://pubmed.ncbi.nlm.nih.gov/16439995/)
[Liu et al., FASLG polymorphisms and PD risk (2010) (2010)](https://pubmed.ncbi.nlm.nih.gov/20628659/)
[Guegan et al., SOD1 and FasL in ALS (2003) (2003)](https://pubmed.ncbi.nlm.nih.gov/14637012/)
[Nagai et al., Astrocyte-mediated motor neuron death (2007) (2007)](https://pubmed.ncbi.nlm.nih.gov/17329282/)
[Pasinelli et al., TDP-43 in ALS (2006) (2006)](https://pubmed.ncbi.nlm.nih.gov/17023659/)
[Trettel et al., FasL in Huntington's disease (2000) (2000)](https://pubmed.ncbi.nlm.nih.gov/11094147/)
[Sabelko et al., FasL in multiple sclerosis (1999) (1999)](https://pubmed.ncbi.nlm.nih.gov/10408856/)
[Schultz et al., Prion protein and apoptosis (2004) (2004)](https://pubmed.ncbi.nlm.nih.gov/15512880/)