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[1][2].
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
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[3].
Genomic Organization:
The promoter region contains interferon-stimulated response elements (ISRE), allowing for transcriptional upregulation in response to type I interferons. This creates a positive feedback loop that can amplify cGAS expression during chronic inflammation.
cGAS adopts a unique fold distinct from other nucleotidyltransferases, consisting of two primary structural domains[4][5]:
The N-terminal region contains:
This domain contains:
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[6].
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[7]:
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:
Activated cGAS produces cGAMP, which binds to STING (encoded by TMEM173) in the endoplasmic reticulum. This triggers:
cGAS is ubiquitously expressed across tissues, with highest levels in immune organs:
| Tissue | Expression Level |
|---|---|
| Spleen | High |
| Lymph nodes | High |
| Bone marrow | High |
| Brain | Moderate |
| Lung | Moderate |
| Liver | Moderate |
| Kidney | Low-Moderate |
Within the central nervous system, cGAS is expressed in[8]:
Glial Cells:
cGAS localizes primarily to the cytosol, but can also be found:
cGAS-STING pathway activation is a hallmark of AD pathophysiology[9][10]:
Evidence:
Mechanisms:
Consequences:
The cGAS-STING pathway contributes to PD through multiple mechanisms[11]:
Evidence:
Mechanisms:
Consequences:
cGAS-STING activation in ALS involves[12]:
Evidence:
Mechanisms:
Consequences:
cGAS-STING involvement has been reported in:
Multiple Sclerosis:
Huntington's Disease:
Frontotemporal Dementia:
Several CGAS variants have been associated with disease:
| Variant | Location | Association |
|---|---|---|
| R255H | NTase domain | Reduced catalytic activity |
| G387R | Regulatory region | Altered DNA binding |
| Splice variant | Exon 4 | Impaired protein function |
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.
Several cGAS targeting approaches are under development[13][14]:
Direct cGAS Inhibitors:
Mechanism of Action:
STING inhibition shows benefit in AD models: Mathavarajan et al. (2024) demonstrated that STING inhibition reduces neuroinflammation and improves cognitive function in AD mouse models[16].
Existing drugs with cGAS-STING effects:
cGAS Knockout Mice (cGAS-/-):
STING Knockout Mice (STING-/-):
cGAMP serves as a potential biomarker for cGAS-STING activation:
Type I interferon-stimulated genes (ISGs) serve as downstream markers:
Cyclic GMP-AMP synthase is a cytosolic DNA sensor that activates the type I interferon pathway. ↩︎
Cyclic GMP-AMP is an endogenous second messenger in innate immune signaling by cytosolic DNA. ↩︎
Structure of human cGAS reveals a conserved catalytic core. ↩︎
Structure of the human cGAS-DNA complex reveals the basis for immune activation. ↩︎
cGAS produces a 2',3'-cGAMP second messenger that enables STING to bind and activate transcription. ↩︎
DNA sensing by the cGAS-STING pathway in innate immunity. ↩︎
cGAS-STING regulates neuroinflammation in Alzheimer's disease. ↩︎
The cGAS-STING pathway as a therapeutic target in inflammatory diseases. ↩︎
cGAS-STING pathway inhibition: a new therapeutic strategy for neurodegenerative diseases. ↩︎
cGAS inhibitor RU.521 reduces pathological tau-induced inflammation. ↩︎