AIM2 Protein — Absent in Melanoma 2

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AIM2 Protein — Absent in Melanoma 2

<div class="infobox infobox-protein">
<table>
<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">AIM2 Protein</th></tr>
<tr><td><strong>Protein Name</strong></td><td>AIM2 (Absent in Melanoma 2)</td></tr>
<tr><td><strong>Gene</strong></td><td>[AIM2](https://www.ncbi.nlm.nih.gov/gene/9447)</td></tr>
<tr><td><strong>UniProt ID</strong></td><td>[Q9UBR9](https://www.uniprot.org/uniprot/Q9UBR9)</td></tr>
<tr><td><strong>Molecular Weight</strong></td><td>~37 kDa</td></tr>
<tr><td><strong>Subcellular Localization</strong></td><td>Cytoplasm, nucleus</td></tr>
<tr><td><strong>Protein Family</strong></td><td>HIN-200 family (Pyrin/ AIM2-like receptors)</td></tr>
<tr><td><strong>Ligand</strong></td><td>Double-stranded DNA (dsDNA)</td></tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/aging" style="color:#ef9a9a">Aging</a>, <a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/atherosclerosis" style="color:#ef9a9a">Atherosclerosis</a>, <a href="/wiki/autoimmune" style="color:#ef9a9a">Autoimmune</a>, <a href="/wiki/bacterial-infection" style="color:#ef9a9a">Bacterial Infection</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">218 edges</a></td>
</tr>
</table>
</div>

Overview

...

AIM2 Protein — Absent in Melanoma 2

Overview

AIM2 (Absent in Melanoma 2) is a critical cytosolic DNA sensor that plays a central role in the innate immune response by forming the AIM2 inflammasome. Discovered as a tumor suppressor whose loss contributes to melanoma progression, AIM2 has emerged as a key player in neuroinflammation and neurodegenerative diseases [1]. The AIM2 inflammasome detects foreign and endogenous double-stranded DNA in the cytosol, triggering a pro-inflammatory cascade that contributes to the chronic neuroinflammation observed in Alzheimer's disease (AD), Parkinson's disease (PD), and other neurodegenerative conditions [2].

The AIM2 protein is expressed in various cell types within the central nervous system (CNS), including [neurons](/entities/neurons), [astrocytes](/cell-types/astrocytes), [microglia](/cell-types/microglia-neuroinflammation), and oligodendrocytes. Its activation in these cell types contributes to the neuroinflammatory milieu that drives disease progression in multiple neurodegenerative disorders [3]. Understanding the AIM2 inflammasome pathway has become a major focus for developing therapeutic interventions aimed at modulating neuroinflammation in these devastating diseases.

Structure

AIM2 possesses a distinctive bipartite structure that enables its dual function as both a DNA sensor and an inflammasome scaffold:

Pyrin Domain (PYD)

The N-terminal Pyrin Domain (approximately 90 amino acids) belongs to the death domain fold family and is responsible for homotypic protein-protein interactions:

Interaction with ASC: The PYD recruits the adaptor protein ASC (PYCARD) through PYD-PYD interactions
Oligomerization: AIM2 PYD mediates the formation of the inflammasome complex
Signal integration: Serves as a platform for integrating upstream activation signals

HIN-200 Domain

The C-terminal HIN-200 domain (approximately 200 amino acids) is the DNA-binding component:

Oligosaccharide-binding (OB) folds: Two OB folds form a DNA-binding pocket
dsDNA recognition: Binds double-stranded DNA of various lengths without sequence specificity
Charge-dependent binding: DNA binding is mediated by electrostatic interactions with positively charged residues

Linker Region

The flexible linker between PYD and HIN-200 domains:

Conformational flexibility: Allows the protein to adapt to different DNA binding scenarios
Auto-inhibition: May contribute to keeping AIM2 in an inactive state in the absence of DNA

Normal Function

DNA Sensing and Inflammasome Assembly

AIM2 functions as a pattern recognition receptor (PRR) for cytosolic double-stranded DNA:

DNA binding: Cytosolic dsDNA binds to the HIN-200 domain of AIM2

Conformational change: DNA binding induces oligomerization of AIM2

Adaptor recruitment: The PYD recruits ASC adapter protein

Caspase-1 activation: ASC recruits pro-caspase-1 to the complex

Proteolytic cleavage: Active caspase-1 cleaves pro-IL-1β and pro-IL-18

Cytokine release: Mature IL-1β and IL-18 are secreted

Physiological Roles

In the normal CNS, AIM2-mediated inflammasome activation serves protective functions:

Defense against pathogens: Detects viral and bacterial DNA in infected cells
Tumor surveillance: Recognizes DNA from abnormal cells
DNA damage response: May sense genomic instability
Cell death regulation: Controls pyroptotic cell death pathways

Expression Pattern

AIM2 is expressed throughout the body with particular relevance to immune cells:

Microglia: High expression in brain-resident macrophages
Neurons: Moderate expression, increases with cellular stress
Astrocytes: Constitutive expression, upregulated in inflammation
Peripheral immune cells: B cells, dendritic cells, macrophages

Role in Neurodegeneration

Alzheimer's Disease

AIM2 plays a significant role in Alzheimer's disease pathogenesis through multiple mechanisms [4]:

Amyloid-β-Induced Inflammasome Activation:

Aβ plaques contain DNA that can activate AIM2
Aβ directly interacts with microglia to increase AIM2 expression
AIM2 inflammasome activation contributes to chronic neuroinflammation

IL-1β-Mediated Pathology:

Elevated IL-1β in AD brain correlates with disease severity
IL-1β promotes tau phosphorylation and aggregation
Sustained IL-1β release drives synaptic dysfunction

Neuroinflammation Amplification:

AIM2 activation creates a feed-forward inflammatory loop
Cytokine release attracts additional immune cells
Contributes to the chronic inflammatory microenvironment

Therapeutic Implications:

AIM2 inhibitors under development for AD
Targeting inflammasome components may reduce neuroinflammation

Parkinson's Disease

AIM2 contributes to Parkinson's disease through several pathways [5]:

α-Synuclein-Induced Activation:

α-Synuclein aggregates can trigger AIM2 inflammasome
Microglial activation by α-synuclein increases AIM2 expression
Inflammasome activation contributes to dopaminergic neuron loss

Neuroinflammation in PD:

Post-mortem studies show increased AIM2 in PD substantia nigra
IL-1β levels elevated in PD cerebrospinal fluid
Inflammasome activation exacerbates motor symptoms

Mitochondrial DNA Sensing:

Damaged mitochondria release mitochondrial DNA
AIM2 may sense mitochondrial DNA in stressed neurons
Contributes to inflammatory responses in PD

Multiple Sclerosis

AIM2 has been implicated in multiple sclerosis (MS):

Demyelination: Inflammasome activation in oligodendrocytes
Blood-brain barrier: Disruption through inflammatory mediators
Lesion formation: Contributes to chronic demyelinating lesions

Amyotrophic Lateral Sclerosis (ALS)

In ALS, AIM2 contributes to motor neuron degeneration:

Motor neuron vulnerability: High AIM2 expression in affected neurons
Glial inflammation: Microglial AIM2 drives progressive inflammation
Disease progression: Inflammasome activation correlates with progression

Inflammasome Signaling Pathway

Activation Triggers

AIM2 inflammasome can be activated by:

Viral DNA: Herpesviruses, adenoviruses, retroviruses

Bacterial DNA: Intracellular bacterial pathogens

Endogenous DNA: Genomic DNA, mitochondrial DNA

DNA-containing aggregates: Amyloid, pathological proteins

Genomic instability: DNA damage, micronuclei

Signaling Cascade

dsDNA → AIM2 → ASC → Pro-caspase-1
↓
Active caspase-1
↓
┌───────────────────┴───────────────────┐
↓ ↓
Pro-IL-1β → IL-1β Pro-IL-18 → IL-18
↓ ↓
Pyroptosis Inflammation
Cell death Immune recruitment

Regulatory Mechanisms

AIM2 activity is tightly regulated:

Post-translational modifications: Phosphorylation, ubiquitination
Negative regulators: ASC antagonists, caspase inhibitors
Cellular localization: Sequestration prevents inappropriate activation
Epigenetic control: Transcriptional regulation of AIM2 expression

Therapeutic Targeting

Drug Development

Several approaches target AIM2 inflammasome:

| Approach | Mechanism | Status | Example |
|----------|-----------|--------|---------|
| AIM2 inhibitors | Block DNA binding | Preclinical | Small molecule inhibitors |
| ASC inhibitors | Prevent inflammasome assembly | Preclinical | MCC950 |
| Caspase-1 inhibitors | Block cytokine cleavage | Clinical | VX-765 |
| IL-1R antagonists | Block cytokine signaling | Approved | Anakinra, Canakinumab |

Clinical Applications

Alzheimer's Disease:

Ongoing trials with NLRP3 inflammasome inhibitors
IL-1β targeting strategies in early trials
Gene therapy approaches to reduce AIM2 expression

Parkinson's Disease:

Inflammasome inhibitors in preclinical models
IL-1β blockade shows neuroprotective effects
Targeting microglial AIM2 activation

Challenges

Specificity: Ensuring AIM2 selectivity over other inflammasomes
Delivery: Crossing the blood-brain barrier
Timing: Optimal intervention point in disease course
Safety: Balancing inflammation suppression with host defense

Animal Models

Transgenic Models

AIM2 knockout mice: Reduced inflammation in disease models
AIM2 overexpression: Increased susceptibility to inflammatory damage
Humanized models: AIM2 expressed in human cells

Disease Models

AD models: 5xFAD, APP/PS1 mice with AIM2 modulation
PD models: MPTP, α-synuclein transgenic mice
MS models: EAE (Experimental Autoimmune Encephalomyelitis)

Genetic Variation

Polymorphisms in the AIM2 gene have been associated with:

Autoimmune diseases: SLE, rheumatoid arthritis
Infectious disease susceptibility: Viral infections
Cancer risk: Melanoma, other malignancies
Neurological disease: Potential modifiers of AD/PD risk

Biomarkers

AIM2-related biomarkers under investigation:

IL-1β levels: Peripheral and CSF measurements
ASC specks: Circulating inflammasome components
AIM2 expression: Gene expression in immune cells
Genetic markers: SNP associations with disease

External Links

[UniProt Q9UBR9](https://www.uniprot.org/uniprot/Q9UBR9)
[NCBI Gene AIM2](https://www.ncbi.nlm.nih.gov/gene/9447)
[IUPHAR Database](https://www.guidetopharmacology.org/)
[Human Protein Atlas](https://www.proteinatlas.org/)

References

[Schattauer et al., AIM2 Inflammasome in CNS Diseases (Front Immunol, 2019)](https://pubmed.ncbi.nlm.nih.gov/31749763/)

[Chen et al., AIM2 in Neuroinflammation and Neurodegeneration (Cell Mol Neurobiol, 2022)](https://pubmed.ncbi.nlm.nih.gov/35039953/)

[Walsh et al., Inflammasome Activation in Alzheimer's Disease (Nat Neurosci, 2021)](https://pubmed.ncbi.nlm.nih.gov/34079914/)

[Kaae et al., AIM2 and the Innate Immune Response (Nat Rev Immunol, 2022)](https://pubmed.ncbi.nlm.nih.gov/35173167/)

[Haidar et al., AIM2 Inflammasome in Parkinson's Disease (J Neuroinflammation, 2022)](https://pubmed.ncbi.nlm.nih.gov/35642075/)

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AIM2 Protein — Absent in Melanoma 2

AIM2 Protein — Absent in Melanoma 2

Overview

AIM2 Protein — Absent in Melanoma 2

Overview

Structure

Pyrin Domain (PYD)

HIN-200 Domain

Linker Region

Normal Function

DNA Sensing and Inflammasome Assembly

Physiological Roles

Expression Pattern

Role in Neurodegeneration

Alzheimer's Disease

Parkinson's Disease

Multiple Sclerosis

Amyotrophic Lateral Sclerosis (ALS)

Inflammasome Signaling Pathway

Activation Triggers

Signaling Cascade

Regulatory Mechanisms

Therapeutic Targeting

Drug Development

Clinical Applications

Challenges

Animal Models

Transgenic Models

Disease Models

Genetic Variation

Biomarkers

See Also

External Links

References