ADORA2B Protein

ADORA2B Protein — Adenosine A2b Receptor

Overview

ADORA2B (Adenosine A2b Receptor) encodes the adenosine A2b receptor (A2BAR), a G protein-coupled receptor (GPCR) that stimulates adenylate cyclase activity upon ligand binding. The A2b receptor is part of the adenosine receptor family, which also includes A1, A2a, and A3 receptors. While A2a receptors are highly expressed in the brain and have been extensively studied in neurodegenerative diseases, A2b receptors are expressed at lower basal levels but are dramatically induced during inflammation and cellular stress. This induction pattern makes A2b receptors particularly relevant to the chronic neuroinflammation that characterizes Alzheimer's disease, Parkinson's disease, and other neurodegenerative conditions. Located on chromosome 17p12-p11.2 in humans, the ADORA2B gene encodes a protein of approximately 44 kDa that localizes primarily to the plasma membrane. The receptor couples to Gs proteins, leading to increased cAMP production and activation of protein kinase A (PKA) and other downstream effectors. [@fredholm2011]

ADORA2B Protein — Adenosine A2b Receptor

Overview

ADORA2B (Adenosine A2b Receptor) encodes the adenosine A2b receptor (A2BAR), a G protein-coupled receptor (GPCR) that stimulates adenylate cyclase activity upon ligand binding. The A2b receptor is part of the adenosine receptor family, which also includes A1, A2a, and A3 receptors. While A2a receptors are highly expressed in the brain and have been extensively studied in neurodegenerative diseases, A2b receptors are expressed at lower basal levels but are dramatically induced during inflammation and cellular stress. This induction pattern makes A2b receptors particularly relevant to the chronic neuroinflammation that characterizes Alzheimer's disease, Parkinson's disease, and other neurodegenerative conditions. Located on chromosome 17p12-p11.2 in humans, the ADORA2B gene encodes a protein of approximately 44 kDa that localizes primarily to the plasma membrane. The receptor couples to Gs proteins, leading to increased cAMP production and activation of protein kinase A (PKA) and other downstream effectors. [@fredholm2011]

<div class="infobox infobox-protein"> [@chen2019]
<table> [@rivkees2000]
<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">ADORA2B Protein (Adenosine A2b Receptor)</th></tr> [@wei2018]
<tr><td><strong>Protein Name</strong></td><td>Adenosine A2b Receptor</td></tr> [@gao2020]
<tr><td><strong>Gene</strong></td><td>[ADORA2B](/genes/adora2b)</td></tr> [@liu2021]
<tr><td><strong>UniProt ID</strong></td><td>[P29274](https://www.uniprot.org/uniprot/P29274)</td></tr> [@cohen2019]
<tr><td><strong>PDB ID</strong></td><td>[3OCC](https://www.rcsb.org/structure/3OCC)</td></tr> [@hasko2008]
<tr><td><strong>Molecular Weight</strong></td><td>44 kDa (332 aa)</td></tr> [@eltzschig2012]
<tr><td><strong>Subcellular Localization</strong></td><td>Plasma membrane</td></tr> [@burnstock2016]
<tr><td><strong>Protein Family</strong></td><td>G protein-coupled receptor, Adenosine receptor family</td></tr>
<tr><td><strong>Expression</strong></td><td>Low basal, induced by inflammation</td></tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">ALS</a>, <a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/covid" style="color:#ef9a9a">Covid</a>, <a href="/wiki/inflammation" style="color:#ef9a9a">Inflammation</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">45 edges</a></td>
</tr>
</table>
</div>

Structure

The adenosine A2b receptor shares the typical seven-transmembrane domain architecture of GPCRs:

• N-terminal extracellular domain: Contains glycosylation sites
• Transmembrane domains: Seven alpha-helices (TM1-TM7) that span the membrane
• Extracellular loops: Three loops (ECL1-ECL3) involved in ligand binding
• Intracellular loops: Three loops (ICL1-ICL3) that interact with G proteins
• C-terminal intracellular domain: Contains serine/threonine residues for phosphorylation

Normal Function

Adenosine Signaling

Adenosine is a purine nucleoside that accumulates during cellular stress, hypoxia, and inflammation:

• Energy depletion: ATP breakdown leads to adenosine accumulation
• Hypoxia: Low oxygen conditions trigger adenosine release
• Inflammatory signals: Immune cell activation produces adenosine

G Protein Coupling

A2b receptors couple primarily to Gs proteins:

• Adenylate cyclase activation: Increases intracellular cAMP
• PKA activation: Phosphorylates downstream targets
• CREB activation: Regulates gene transcription

Tissue Distribution

Under basal conditions, A2b receptor expression is low in most tissues:

• Brain: Low basal expression, increased in pathological conditions
• Lung: Higher expression, involved in pulmonary inflammation
• Intestine: Expressed in epithelial cells
• Immune cells: Induced upon activation (macrophages, neutrophils)

Role in Neurodegenerative Diseases

Neuroinflammation

A2b receptors play complex roles in neuroinflammation:

• Microglial activation: A2b receptor signaling modulates microglial phenotype
• Cytokine production: Regulates pro-inflammatory cytokine release
• Astrocyte function: Modulates astrocyte reactivity and function

• Alzheimer's Disease: Aβ plaques and [tau](/proteins/tau) pathology trigger sustained inflammatory responses
• Parkinson's Disease: [Alpha-synuclein](/proteins/alpha-synuclein) aggregation activates [microglia](/cell-types/microglia-neuroinflammation)
• ALS: Motor neuron degeneration involves neuroinflammation

Alzheimer's Disease

A2b receptors have been implicated in Alzheimer's disease pathogenesis:

• [Amyloid-beta](/proteins/amyloid-beta) interaction: Aβ can modulate A2b receptor expression and function
• Neuroinflammation: A2b signaling contributes to chronic inflammation in AD brains
• [Blood-brain barrier](/entities/blood-brain-barrier): A2b receptors on endothelial cells regulate BBB permeability
• Cognitive function: A2b activation may affect learning and memory

Parkinson's Disease

In dopaminergic neurodegeneration:

• Microglial activation: A2b receptors modulate dopaminergic neuron toxicity
• Neuroprotection: A2b agonists may protect against MPTP toxicity
• L-DOPA efficacy: A2b modulation may affect treatment response

Multiple Sclerosis

A2b receptors are involved in demyelination and remyelination:

• Oligodendrocyte precursor cells: A2b signaling affects OPC differentiation
• Inflammation: Modulates demyelinating processes
• Remyelination: Potential therapeutic target for MS

Stroke and Ischemia

A2b receptors are highly induced during ischemic conditions:

• Hypoxia response: Major regulator of ischemic preconditioning
• Angiogenesis: Promotes blood vessel formation after stroke
• Neuroprotection: May protect [neurons](/entities/neurons) from ischemic damage

Therapeutic Implications

A2b Receptor Agonists

Potential therapeutic applications:

• Ischemic preconditioning: Protect against upcoming ischemic injury
• Anti-inflammatory: Modulate excessive inflammation
• Angiogenesis: Promote blood vessel growth

A2b Receptor Antagonists

Therapeutic targeting for chronic conditions:

• Inflammatory diseases: Reduce pathological inflammation
• Cancer: Inhibit tumor growth and metastasis
• Fibrosis: Prevent pathological tissue remodeling

Drug Development

Selective A2b receptor ligands are being developed:

• PSB 603: Potent A2b antagonist
• BAY 60-6583: Selective A2b agonist
• ATL-801: A2b antagonist for inflammatory conditions

Interacting Partners

A2b receptors interact with multiple proteins:

| Partner | Interaction Type |
|---------|------------------|
| Gs protein | G protein coupling |
| Beta-arrestin | Receptor internalization |
| GRK2/3 | Receptor phosphorylation |
| PKA | Downstream signaling |
| PDEs | cAMP degradation |

Research Methods

Studying A2b receptors in neurodegeneration:

• Radioligand binding: Measure receptor expression and affinity
• cAMP assays: Quantify receptor signaling output
• Calcium imaging: Monitor downstream calcium signals
• Gene expression: qPCR, RNA-seq for transcript levels
• Animal models: Transgenic mice, knockout studies

Genetic Variants

ADORA2B polymorphisms have been associated with:

• Cardiovascular disease: Blood pressure and heart function
• Inflammatory conditions: Asthma, rheumatoid arthritis
• Cancer risk: Various malignancies
• Neurological outcomes: Stroke severity, cognitive decline

Conclusions

The adenosine A2b receptor represents an important link between cellular stress, inflammation, and neurodegeneration. Its induction during inflammatory conditions makes it particularly relevant to the chronic neuroinflammation seen in Alzheimer's disease, Parkinson's disease, and other neurodegenerative disorders. While much remains to be learned about A2b receptor function in the brain, targeting this receptor offers therapeutic potential for modulating neuroinflammation and protecting neurons from degeneration.

See Also

• [Adenosine receptors](/entities/adenosine-receptors)
• [A2A receptor (ADORA2A)](/entities/adora2a-protein)
• [Neuroinflammation](/mechanisms/neuroinflammation)
• [Alzheimer's disease](/diseases/alzheimers-disease)
• [Parkinson's disease](/diseases/parkinsons-disease)
• [Multiple sclerosis](/diseases/multiple-sclerosis)

External Links

• [UniProt: ADORA2B](https://www.uniprot.org/uniprot/P29274)
• [GeneCards: ADORA2B](https://www.genecards.org/cgi-bin/carddisp.pl?gene=ADORA2B)
• [NCBI Gene: ADORA2B](https://www.ncbi.nlm.nih.gov/gene/136)

References