CGAS Gene

CGAS Gene

Introduction

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">CGAS Gene</th>
</tr>
<tr>
<td class="label">Tissue</td>
<td>Expression Level</td>
</tr>
<tr>
<td class="label">Spleen</td>
<td>High</td>
</tr>
<tr>
<td class="label">Lymph nodes</td>
<td>High</td>
</tr>
<tr>
<td class="label">Bone marrow</td>
<td>High</td>
</tr>
<tr>
<td class="label">Brain</td>
<td>Moderate</td>
</tr>
<tr>
<td class="label">Lung</td>
<td>Moderate</td>
</tr>
<tr>
<td class="label">Liver</td>
<td>Moderate</td>
</tr>
<tr>
<td class="label">Kidney</td>
<td>Low-Moderate</td>
</tr>
<tr>
<td class="label">Variant</td>
<td>Location</td>
</tr>
<tr>
<td class="label">R255H</td>
<td>NTase domain</td>
</tr>
<tr>
<td class="label">G387R</td>
<td>Regulatory region</td>
</tr>
<tr>
<td class="label">Splice variant</td>
<td>Exon 4</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">ALS</a>, <a href="/wiki/alzheimer" style="color:#ef9a9a">ALZHEIMER</a>, <a href="/wiki/alzheimer's" style="color:#ef9a9a">ALZHEIMER'S</a>, <a href="/wiki/alzheimer's-disease" style="color:#ef9a9a">ALZHEIMER'S DISEASE</a>, <a href="/wiki/amyotrophic-lateral-sclerosis" style="color:#ef9a9a">AMYOTROPHIC LATERAL SCLEROSIS</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1403 edges</a></td>
</tr>
</table>

CGAS Gene

Introduction

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">CGAS Gene</th>
</tr>
<tr>
<td class="label">Tissue</td>
<td>Expression Level</td>
</tr>
<tr>
<td class="label">Spleen</td>
<td>High</td>
</tr>
<tr>
<td class="label">Lymph nodes</td>
<td>High</td>
</tr>
<tr>
<td class="label">Bone marrow</td>
<td>High</td>
</tr>
<tr>
<td class="label">Brain</td>
<td>Moderate</td>
</tr>
<tr>
<td class="label">Lung</td>
<td>Moderate</td>
</tr>
<tr>
<td class="label">Liver</td>
<td>Moderate</td>
</tr>
<tr>
<td class="label">Kidney</td>
<td>Low-Moderate</td>
</tr>
<tr>
<td class="label">Variant</td>
<td>Location</td>
</tr>
<tr>
<td class="label">R255H</td>
<td>NTase domain</td>
</tr>
<tr>
<td class="label">G387R</td>
<td>Regulatory region</td>
</tr>
<tr>
<td class="label">Splice variant</td>
<td>Exon 4</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">ALS</a>, <a href="/wiki/alzheimer" style="color:#ef9a9a">ALZHEIMER</a>, <a href="/wiki/alzheimer's" style="color:#ef9a9a">ALZHEIMER'S</a>, <a href="/wiki/alzheimer's-disease" style="color:#ef9a9a">ALZHEIMER'S DISEASE</a>, <a href="/wiki/amyotrophic-lateral-sclerosis" style="color:#ef9a9a">AMYOTROPHIC LATERAL SCLEROSIS</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1403 edges</a></td>
</tr>
</table>

Pathway Diagram

The CGAS (Cyclic GMP-AMP Synthase) gene encodes a crucial DNA sensor protein that plays a central role in the innate immune response to cytosolic DNA. Originally discovered in the context of antiviral immunity, cGAS has emerged as a critical player in the pathogenesis of Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and other neurodegenerative disorders. This gene provides a molecular link between genomic instability, mitochondrial dysfunction, and chronic neuroinflammation that characterizes these devastating conditions["@sun2013"][@wu2013].

Official Symbol: CGAS Official Full Name: Cyclic GMP-AMP Synthase Previous Names: MB21D1, cGAS Location: Chromosome 6q15 Gene ID: 115004 Ensemble ID: ENSG00000154122 OMIM ID: 617561

Gene Structure and Organization

The CGAS gene spans approximately 24 kilobases and consists of 8 exons encoding a protein of 522 amino acids with a molecular weight of approximately 57 kDa. The gene structure has been conserved throughout evolution, reflecting its fundamental importance in cellular immunity[@du2013].

Genomic Organization:

• Exon 1: Encodes the N-terminal structured domain
• Exons 2-4: Encode the central regulatory region
• Exons 5-8: Encode the C-terminal nucleotidyltransferase domain

Protein Structure and Function

cGAS adopts a unique fold distinct from other nucleotidyltransferases, consisting of two primary structural domains[@civril2013][@kato2013]:

N-Terminal Domain (Residues 1-160)

• Multiple serine/threonine residues subject to phosphorylation
• A zinc ribbon motif involved in DNA binding
• Regulatory sequences controlling enzymatic activity
• An autoinhibitory element that maintains basal inactivity

C-Terminal Nucleotidyltransferase Domain (Residues 161-522)

• Catalytic core with conserved Asp-Asp-Glu (DDE) motif
• DNA-binding surfaces on the outer face
• STING interaction interface
• ATP/GTP binding pocket
• Zinc-dependent DNA binding module

Catalytic Mechanism

cGAS catalyzes the synthesis of cyclic GMP-AMP (cGAMP) from ATP and GTP through a two-step reaction:

The resulting 2',3'-cGAMP contains mixed phosphodiester bonds (one 3',5' and one 2',5' linkage), distinguishing it from other cyclic nucleotides. This unique structure enables high-affinity binding to STING with dissociation constants in the nanomolar range[@ablasser2013].

Molecular Mechanisms of Activation

DNA Binding and Oligomerization

cGAS binds double-stranded DNA (dsDNA) in a sequence-independent manner, with binding affinity enhanced by DNA length and higher-order structure. Key activation steps include[@liu2019]:

Liquid-Liquid Phase Separation

cGAS undergoes liquid-liquid phase separation (LLPS) upon DNA binding, forming biomolecular condensates that concentrate cGAS molecules and enhance catalytic activity. This process is mediated by:

• Multivalent interactions between cGAS and DNA
• π-π stacking interactions between aromatic residues
• Electrostatic interactions with the DNA phosphate backbone

STING Activation and Downstream Signaling

Activated cGAS produces cGAMP, which binds to STING (encoded by TMEM173) in the endoplasmic reticulum. This triggers:

Expression Pattern and Cellular Distribution

Tissue Distribution

cGAS is ubiquitously expressed across tissues, with highest levels in immune organs:

Cellular Expression in the Brain

Within the central nervous system, cGAS is expressed in[@motwani2019]:

Neurons:

• Constitutively expressed in most neuronal populations
• Particularly high in cortical and hippocampal neurons
• Upregulated during neurodegeneration

• Astrocytes: Moderate constitutive expression
• Microglia: High expression, increases with activation
• Oligodendrocytes: Lower baseline expression

Subcellular Localization

cGAS localizes primarily to the cytosol, but can also be found:

• Associated with nuclear envelope (proximity to genomic DNA)
• In mitochondrial periphery (mitochondrial DNA sensing)
• In stress granules during cellular stress

Role in Neurodegenerative Diseases

Alzheimer's Disease

cGAS-STING pathway activation is a hallmark of AD pathophysiology[@xie2022][@hu2022]:

Evidence:

• Elevated cGAS expression in AD brain tissue
• Increased cGAMP levels in AD patient cerebrospinal fluid
• cGAS colocalization with amyloid plaques and neurofibrillary tangles
• Type I interferon signature in AD brain transcriptomes
• cGAS activation in microglia surrounding amyloid deposits

• Amyloid-β (Aβ) deposition triggers mitochondrial dysfunction
• Mitochondrial DNA released into cytosol activates cGAS
• Nuclear envelope dysfunction allows genomic DNA leakage
• DNA damage accumulation from oxidative stress
• Microglial cGAS activated by phagocytosed debris

• Chronic type I interferon response
• Enhanced microglial activation and cytokine release
• Synaptic pruning acceleration
• Neuronal dysfunction and death

Parkinson's Disease

The cGAS-STING pathway contributes to PD through multiple mechanisms[@zhou2022]:

Evidence:

• Elevated STING expression in dopaminergic neurons
• cGAS activation in PD substantia nigra
• Increased cGAMP in PD patient CSF
• IFN-responsive genes upregulated in PD brain

• Mitochondrial dysfunction in dopaminergic neurons leads to mtDNA release
• α-Synuclein aggregation induces DNA damage
• Environmental toxins (MPTP, rotenone) cause DNA damage
• Lysosomal dysfunction promotes nuclear DNA leakage

• Neuroinflammation in substantia nigra
• Accelerated dopaminergic neuron loss
• Enhanced α-synuclein aggregation through impaired autophagy

Amyotrophic Lateral Sclerosis

cGAS-STING activation in ALS involves[@yu2022]:

Evidence:

• STING upregulation in motor neurons
• cGAS activation in astrocytes and microglia
• IFN signature in ALS spinal cord

• TDP-43 pathology triggers DNA damage
• Mitochondrial dysfunction is prevalent
• FUS mutations cause DNA repair impairment
• Oxidative stress contributes to DNA damage

• Motor neuron inflammation
• Glial activation and toxicity
• Accelerated disease progression

Other Neurodegenerative Conditions

cGAS-STING involvement has been reported in:

Multiple Sclerosis:

• Demyelination triggers cGAS activation
• Oligodendrocyte vulnerability

• Mutant huntingtin causes DNA damage
• cGAS contributes to neuroinflammation

• TDP-43 pathology linked to cGAS
• Similar mechanisms to ALS

Genetic Variants and Disease Risk

Known CGAS Variants

Several CGAS variants have been associated with disease:

GWAS Findings

While no common CGAS variants have reached genome-wide significance in neurodegenerative diseases, pathway analyses suggest involvement of cGAS-STING pathway genes in AD and PD genetic risk scores.

Therapeutic Implications

cGAS Inhibitors in Development

Several cGAS targeting approaches are under development[@decout2021][@decout2024]:

Direct cGAS Inhibitors:

• RU.521: Selective cGAS inhibitor, reduces tau-induced inflammation[@wang2024]
• Compound 3: Blocks cGAS catalytic activity
• PF-069: Brain-penetrant cGAS inhibitor

• Competitive inhibition of DNA binding
• Allosteric modulation of catalytic site
• Prevention of phase separation

STING Inhibitors (Downstream Target)

• H-151: Covalent STING antagonist, blocks palmitoylation
• C-176/C-178: STING trafficking inhibitors

Repurposing Opportunities

Existing drugs with cGAS-STING effects:

• Hydroxychloroquine: Blocks STING activation
• Metformin: Modulates mitochondrial cGAS signaling
• Aspirin: Inhibits NF-κB downstream of STING

Gene Therapy Approaches

• AAV-mediated cGAS knockdown
• CRISPR-based cGAS inactivation
• Soluble STING decoy proteins

Animal Models

Genetic Knockout Models

cGAS Knockout Mice (cGAS-/-):

• Viable and fertile
• Defective in cytosolic DNA sensing
• Protected from DNA damage-induced senescence
• Reduced neuroinflammation in disease models

• Impaired type I interferon response
• Protected from neuroinflammation
• Used to confirm cGAS-STING pathway involvement

Disease Models

• 5xFAD mice: Show elevated cGAS-STING activation
• MPTP model: cGAS activation in substantia nigra
• Tauopathy models: cGAS responds to pathological tau

Biomarker Potential

cGAMP as Biomarker

cGAMP serves as a potential biomarker for cGAS-STING activation:

• Elevated in AD and PD cerebrospinal fluid
• Correlates with disease severity
• Can be measured by mass spectrometry

Interferon Signature

Type I interferon-stimulated genes (ISGs) serve as downstream markers:

• Elevated in neurodegenerative disease brain
• Detectable in peripheral blood
• Potential for disease monitoring

Future Directions

Research Priorities

Outstanding Questions

• What initiates cGAS activation in sporadic neurodegeneration?
• Can cGAS inhibition provide neuroprotection in human patients?
• What determines the cell-type specific pattern of cGAS-STING activation?
• How does cGAS-STING interact with other inflammatory pathways?

Cross-Links to Related Pages

• [STING Gene](/genes/tmem173) - Downstream partner of cGAS
• [TBK1 Gene](/genes/tbk1) - Key signaling kinase
• [IRF3 Gene](/genes/irf3) - Transcription factor
• [cGAS-STING Pathway in Neurodegeneration](/mechanisms/cgas-sting-neurodegeneration)
• [cGAS-STING Signaling in Parkinson's Disease](/mechanisms/cgas-sting-parkinsons)
• [Mitochondrial Dysfunction in Neurodegeneration](/mechanisms/mitochondrial-dysfunction-neurodegeneration)
• [Neuroinflammation](/mechanisms/neuroinflammation-neurodegeneration)
• [Cellular Senescence](/mechanisms/cellular-senescence)

External Links

• [NCBI Gene: CGAS](https://www.ncbi.nlm.nih.gov/gene/115004)
• [UniProt: cGAS](https://www.uniprot.org/uniprot/Q8N884)
• [OMIM: CGAS](https://www.omim.org/entry/617561)
• [Ensembl: CGAS](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000154122)
• [PubMed Central - cGAS-STING in AD](https://pubmed.ncbi.nlm.nih.gov/35892789/)
• [PubMed Central - cGAS-STING in PD](https://pubmed.ncbi.nlm.nih.gov/35081756/)

References

Related Hypotheses

From the [SciDEX Exchange](/exchange) — scored by multi-agent debate

• [Senescent Cell Mitochondrial DNA Release](/hypothesis/h-1a34778f) — <span style="color:#ffd54f;font-weight:600">0.54</span> · Target: CGAS/STING1/DNASE2

Pathway Diagram

The following diagram shows the key molecular relationships involving CGAS Gene discovered through SciDEX knowledge graph analysis: