Adenosine A3 Receptor Protein
Overview
The adenosine A3 receptor (ADORA3), also known as the A3 adenosine receptor, is a G-protein coupled receptor (GPCR) encoded by the ADORA3 gene located on chromosome 1q32.1 in humans. This seven-transmembrane domain receptor belongs to the adenosine receptor family, which includes four subtypes (A1, A2A, A2B, and A3) that mediate the physiological effects of adenosine, a purine nucleoside present throughout the body. ADORA3 is particularly notable for its high selectivity for adenosine compared to other adenosine receptor subtypes and shows distinct tissue-specific expression patterns, with particularly high levels in immune cells, mast cells, and certain brain regions including the hippocampus and cortex. The receptor's distinctive pharmacological profile and distribution pattern have made it an emerging target for understanding neuroinflammation and neuroprotection in neurodegenerative diseases.
PMID: 41148800
Function and Biology
...Adenosine A3 Receptor Protein
Overview
The adenosine A3 receptor (ADORA3), also known as the A3 adenosine receptor, is a G-protein coupled receptor (GPCR) encoded by the ADORA3 gene located on chromosome 1q32.1 in humans. This seven-transmembrane domain receptor belongs to the adenosine receptor family, which includes four subtypes (A1, A2A, A2B, and A3) that mediate the physiological effects of adenosine, a purine nucleoside present throughout the body. ADORA3 is particularly notable for its high selectivity for adenosine compared to other adenosine receptor subtypes and shows distinct tissue-specific expression patterns, with particularly high levels in immune cells, mast cells, and certain brain regions including the hippocampus and cortex. The receptor's distinctive pharmacological profile and distribution pattern have made it an emerging target for understanding neuroinflammation and neuroprotection in neurodegenerative diseases.
PMID: 41148800
Function and Biology
ADORA3 functions as a cell surface receptor that initiates intracellular signaling cascades upon adenosine binding. Like other adenosine receptors, ADORA3 is coupled to inhibitory G-proteins (Gi/o), leading to decreased cAMP production and activation of alternative downstream pathways including phospholipase C, calcium mobilization, and mitogen-activated protein kinase (MAPK) signaling. However, ADORA3 exhibits unique signaling capabilities compared to other adenosine receptor subtypes. The receptor can activate both Gi and Gq proteins, enabling activation of phospholipase C and subsequent release of intracellular calcium stores, a property less prominent in A1 and A2A receptors. This dual G-protein coupling allows ADORA3 to modulate diverse cellular responses including gene expression, cell proliferation, and apoptosis. In neural tissue, ADORA3 is expressed on both neurons and glia, with particularly important roles on microglial cells and astrocytes where it regulates inflammatory mediator release. The receptor's activation generally promotes anti-inflammatory and potentially neuroprotective effects through suppression of pro-inflammatory cytokine production and enhancement of anti-inflammatory signaling pathways.
PMID: 39680577
Role in Neurodegeneration
ADORA3 has emerged as a significant player in multiple neurodegenerative disease pathologies. In Alzheimer's disease, adenosine signaling through ADORA3 on microglial cells modulates the neuroinflammatory response to amyloid-beta accumulation, with evidence suggesting that ADORA3 activation suppresses microglial-mediated neuroinflammation. Studies have demonstrated that ADORA3 signaling can reduce the release of pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) from activated microglia. In Parkinson's disease, adenosine A3 receptor signaling has shown protective effects against dopaminergic neuron degeneration, potentially through both direct neuroprotective mechanisms and indirect immunomodulatory pathways. In neuroinflammatory conditions and models of neurodegeneration, ADORA3 activation has been associated with reduced glial activation and decreased neuronal death. The receptor's expression levels and signaling efficiency may be altered in neurodegenerative disease contexts, contributing to disease progression through compromised neuroprotection.
PMID: 38236582
Molecular Mechanisms
ADORA3-mediated neuroprotection involves multiple converging mechanisms. Upon adenosine binding, ADORA3 activates Gi proteins, suppressing cAMP and reducing pro-inflammatory transcription factor activation. Simultaneously, ADORA3 can activate phospholipase C through Gq coupling, generating inositol-1,4,5-trisphosphate and diacylglycerol, leading to calcium mobilization and activation of calcium-dependent anti-inflammatory pathways. In microglial cells, ADORA3 activation inhibits NF-κB signaling, a master regulator of pro-inflammatory gene expression. The receptor also modulates ERK1/2 and p38 MAPK pathways, which can suppress or enhance inflammatory responses depending on cellular context. ADORA3 signaling may enhance neuroprotective autophagy pathways and promote apoptosis of activated pro-inflammatory glia while preserving neuronal viability.
PMID: 37531576
Clinical and Research Significance
ADORA3 represents a promising therapeutic target for neurodegenerative diseases, with selective ADORA3 agonists under investigation for neuroprotective potential. The receptor's prominent role in restraining neuroinflammation makes it particularly attractive for conditions where microglial overactivation contributes to pathology. Research continues to elucidate optimal ADORA3-selective pharmacology and delivery strategies for central nervous system penetration.
- ADORA1, ADORA2A, ADORA2B: Other adenosine receptor subtypes with distinct tissue distributions and functions
- Adenosine: Endogenous ligand for all adenosine receptors
- Microglia: Primary cellular source of ADORA3 effects in neuroinflammation
- **NF
AlphaFold Structure
AlphaFold DB provides a predicted structure for ADORA3 / UniProt P0DMS8 (model version 6): https://alphafold.ebi.ac.uk/entry/P0DMS8.
AlphaFold reports a mean pLDDT confidence score of 91.31, indicating very high average confidence.
InterPro annotations highlight G protein-coupled receptor, rhodopsin-like family (14-297); Adenosine A3 receptor family (6-18); Adenosine receptor family (13-22).
PDB coordinates: https://alphafold.ebi.ac.uk/files/AF-P0DMS8-F1-model_v6.pdb mmCIF coordinates: https://alphafold.ebi.ac.uk/files/AF-P0DMS8-F1-model_v6.cif.
Use the prediction as structural context for target assessment; local low-pLDDT segments may reflect disorder, flexible linkers, or unresolved domain orientation rather than a stable fold.