P2RX7 Protein

P2RX7 Protein — P2X Purinoceptor 7

<div class="infobox infobox-protein">
<table>
<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">P2RX7 Protein</th></tr>
<tr><td><strong>Protein Name</strong></td><td>P2X Purinoceptor 7 (P2X7)</td></tr>
<tr><td><strong>Gene</strong></td><td>[P2RX7](/entities/p2rx7-gene)</td></tr>
<tr><td><strong>UniProt ID</strong></td><td>[Q99572](https://www.uniprot.org/uniprot/Q99572)</td></tr>
<tr><td><strong>PDB IDs</strong></td><td>5U1L, 5U1U, 5U1V, 5U1W, 5U1X, 6U9V</td></tr>
<tr><td><strong>Molecular Weight</strong></td><td>~68.6 kDa (monomer)</td></tr>
<tr><td><strong>Subcellular Localization</strong></td><td>Plasma membrane, lipid rafts</td></tr>
<tr><td><strong>Protein Family</strong></td><td>P2X purinergic receptor family</td></tr>
<tr><td><strong>Oligomeric State</strong></td><td>Homotrimer</td></tr>
<tr><td><strong>Chromosomal Location</strong></td><td>12q24.31</td></tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">ALS</a>, <a href="/wiki/aging" style="color:#ef9a9a">Aging</a>, <a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/alzheimer's-disease" style="color:#ef9a9a">Alzheimer's disease</a>, <a href="/wiki/anxiety" style="color:#ef9a9a">Anxiety</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">200 edges</a></td>
</tr>
</table>
</div>

Overview

P2RX7 Protein — P2X Purinoceptor 7

<div class="infobox infobox-protein">
<table>
<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">P2RX7 Protein</th></tr>
<tr><td><strong>Protein Name</strong></td><td>P2X Purinoceptor 7 (P2X7)</td></tr>
<tr><td><strong>Gene</strong></td><td>[P2RX7](/entities/p2rx7-gene)</td></tr>
<tr><td><strong>UniProt ID</strong></td><td>[Q99572](https://www.uniprot.org/uniprot/Q99572)</td></tr>
<tr><td><strong>PDB IDs</strong></td><td>5U1L, 5U1U, 5U1V, 5U1W, 5U1X, 6U9V</td></tr>
<tr><td><strong>Molecular Weight</strong></td><td>~68.6 kDa (monomer)</td></tr>
<tr><td><strong>Subcellular Localization</strong></td><td>Plasma membrane, lipid rafts</td></tr>
<tr><td><strong>Protein Family</strong></td><td>P2X purinergic receptor family</td></tr>
<tr><td><strong>Oligomeric State</strong></td><td>Homotrimer</td></tr>
<tr><td><strong>Chromosomal Location</strong></td><td>12q24.31</td></tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">ALS</a>, <a href="/wiki/aging" style="color:#ef9a9a">Aging</a>, <a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/alzheimer's-disease" style="color:#ef9a9a">Alzheimer's disease</a>, <a href="/wiki/anxiety" style="color:#ef9a9a">Anxiety</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">200 edges</a></td>
</tr>
</table>
</div>

Overview

The P2X7 receptor (P2X purinoceptor 7) is an ATP-gated cation channel that occupies a unique position among purinergic receptors due to its dual function as both a rapid ion channel and a macropore-forming complex[@surprenant1996]. Unlike other P2X family members, P2X7 requires millimolar concentrations of extracellular ATP for activation — concentrations typically reached only during cellular stress, injury, or death — making it a danger signal sensor in the central nervous system[@di2017]. P2X7 is predominantly expressed on [microglia](/entities/microglia-in-neurodegeneration), [astrocytes](/cell-types/astrocytes), and oligodendrocytes, with lower expression on [neurons](/entities/neurons), positioning it as a master regulator of neuroinflammation[@bhatt2020].

In the context of neurodegeneration, P2X7 activation triggers the [NLRP3 inflammasome](/mechanisms/nlrp3-inflammasome) assembly, leading to [caspase-1](/proteins/caspase-1-protein)-dependent maturation and release of pro-inflammatory cytokines IL-1β and IL-18, as well as pyroptotic cell death via gasdermin D pore formation[@swanson2019]. This pathway is critically implicated in [Alzheimer's disease](/diseases/alzheimers-disease), [Parkinson's disease](/diseases/parkinsons-disease), [amyotrophic lateral sclerosis](/diseases/amyotrophic-lateral-sclerosis), [multiple sclerosis](/diseases/multiple-sclerosis), and [Huntington's disease](/diseases/huntington-disease)[@burnstock2016].

Structure

Domain Architecture

P2X7 is a 595-amino-acid protein with a distinctive topology consisting of:

• Intracellular N-terminus (26 residues): Contains a conserved protein kinase C phosphorylation site (T18) that modulates channel gating
• First transmembrane domain (TM1): Contributes to the ion conduction pathway and intersubunit contacts
• Large extracellular loop (~280 residues): Contains the ATP-binding site at subunit interfaces, stabilized by five conserved disulfide bonds (C119–C168, C130–C159, C149–C163, C217–C227, C260–C267), and houses N-glycosylation sites at N187, N202, N213, N241, and N284
• Second transmembrane domain (TM2): Lines the ion pore; critical residues include T339 and S342 for ion selectivity
• Extended C-terminal tail (~240 residues): The longest among P2X family members, essential for macropore formation, protein-protein interactions, and signaling scaffold function[@mccarthy2019]

Homotrimeric Assembly

P2X7 functions as a homotrimer, with three ATP-binding sites located at subunit interfaces. The crystal structure of the panda P2X7 ectodomain (PDB: 5U1L) revealed a chalice-shaped architecture with each subunit resembling a dolphin, consistent with other P2X receptor structures[@karasawa2016]. Upon ATP binding, the receptor undergoes conformational changes that open a cation-selective channel within milliseconds; sustained ATP application (seconds to minutes) induces a secondary dilation to a macropore permeable to molecules up to ~900 Da[@bhatt2008].

Post-Translational Modifications

• Palmitoylation: C-terminal cysteines (C371, C373, C374, C477, C479, C482, C498, C499, C506, C572, C573) are palmitoylated, anchoring the C-terminus to the membrane and enabling macropore formation
• Phosphorylation: T18 (PKC), Y343 (Src family kinases) regulate channel activity
• ADP-ribosylation: In murine P2X7, ecto-ART2.2 modifies R125, providing an alternative NAD-dependent activation pathway[@danquah2016]

Normal Function in the Nervous System

Microglial Surveillance

P2X7 is the most abundantly expressed purinergic receptor on [microglia](/entities/microglia-in-neurodegeneration). At resting state, low-level P2X7 signaling contributes to:

• Phagocytic activity: Moderate P2X7 activation enhances microglial phagocytosis of apoptotic debris and synaptic material
• Process motility: ATP gradients detected through P2X7 (and [P2Y12](/entities/p2ry12-gene)) guide microglial surveillance processes toward sites of neuronal activity or damage
• Cytokine homeostasis: Tonic P2X7 signaling maintains baseline IL-1β processing for synaptic plasticity[@bhatt2012]

Synaptic Modulation

Although neuronal P2X7 expression remains debated, functional evidence supports roles in:

• Presynaptic glutamate release: P2X7 activation at hippocampal mossy fiber terminals enhances glutamate release
• GABA release modulation: P2X7 on GABAergic terminals in the cerebellum modulates inhibitory transmission
• [Long-term potentiation](/mechanisms/long-term-potentiation) (LTP): P2X7 knockout mice show enhanced LTP at CA1 synapses, suggesting tonic P2X7-mediated suppression of synaptic plasticity[@bhatt2012a]

Oligodendrocyte Biology

P2X7 activation on oligodendrocyte precursor cells (OPCs) promotes differentiation at low ATP concentrations but triggers [apoptosis](/entities/apoptosis) at sustained high concentrations, creating a concentration-dependent switch between myelination and demyelination[@matute2007].

Role in Neurodegenerative Disease

Alzheimer's Disease

P2X7 is critically implicated in [Alzheimer's disease](/diseases/alzheimers-disease) pathogenesis through multiple converging mechanisms:

• Amyloid-β-induced activation: Soluble amyloid-β oligomers stimulate ATP release from [astrocytes](/entities/astrocytes) and neurons, creating a feed-forward loop of P2X7 activation on [microglia](/cell-types/microglia-neuroinflammation)[@sanz2009]
• [NLRP3 inflammasome](/entities/nlrp3-inflammasome) activation: P2X7→K⁺ efflux→NLRP3→caspase-1→IL-1β/IL-18 is the primary pathway linking amyloid pathology to neuroinflammation. P2X7 knockout in [APP](/entities/app-protein)/PS1 mice reduces amyloid plaque burden by ~50% and rescues spatial memory deficits[@martin2019]
• [Tau](/proteins/tau) phosphorylation: IL-1β released via P2X7/NLRP3 activates neuronal [GSK-3β](/proteins/gsk3b) and [CDK5](/proteins/cdk5) pathways, promoting [tau](/proteins/tau) hyperphosphorylation
• Microglial M1 polarization: Chronic P2X7 activation shifts microglia toward a pro-inflammatory (disease-associated) phenotype with impaired amyloid phagocytosis
• Genetic association: The P2RX7 rs208294 (H155Y) gain-of-function variant is associated with increased AD risk in European populations[@sanz2014]

Parkinson's Disease

In [Parkinson's disease](/diseases/parkinsons-disease), P2X7 contributes to dopaminergic neuron loss:

• Substantia nigra inflammation: P2X7 expression is upregulated on microglia surrounding degenerating dopaminergic neurons in both MPTP mouse models and human PD brain tissue
• α-Synuclein-mediated activation: Extracellular [α-synuclein](/proteins/alpha-synuclein) aggregates trigger microglial ATP release and subsequent P2X7 activation, creating a neuroinflammatory amplification loop
• Pyroptosis: P2X7-dependent [caspase-1](/proteins/caspase-1-protein) activation in microglia promotes pyroptotic cell death, releasing DAMPs that further propagate inflammation[@bhatt2019]

Amyotrophic Lateral Sclerosis

P2X7 is upregulated in the spinal cord of ALS patients and SOD1-G93A mice:

• Motor neuron vulnerability: P2X7 activation on spinal cord microglia and astrocytes releases toxic factors (TNFα, glutamate, ROS) that damage motor neurons
• Presymptomatic upregulation: P2X7 expression increases before motor neuron degeneration becomes apparent, suggesting a causative role rather than reactive response
• Genetic modifiers: P2RX7 loss-of-function variants are associated with later disease onset in some ALS cohorts[@apolloni2014]

Multiple Sclerosis

P2X7 mediates oligodendrocyte death and demyelination:

• Excitotoxic oligodendrocyte damage: Sustained P2X7 activation causes Ca²⁺ overload and mitochondrial dysfunction in oligodendrocytes
• EAE models: P2X7 knockout mice show reduced demyelination and clinical scores in experimental autoimmune encephalomyelitis
• Macropore-mediated antigen release: P2X7 macropore formation facilitates release of myelin antigens, potentially driving autoimmune responses[@bhatt2007]

Huntington's Disease

In [Huntington's disease](/diseases/huntington-disease), mutant [huntingtin](/proteins/huntingtin-protein) aggregates sensitize cells to P2X7 activation:

• Mutant [huntingtin](/proteins/huntingtin) expression lowers the ATP threshold for P2X7 macropore formation
• P2X7 antagonism reduces striatal neuron vulnerability in R6/2 mice[@diazhernandez2009]

Therapeutic Targeting

P2X7 Antagonists in Development

| Compound | Developer | Stage | Notes |
|----------|-----------|-------|-------|
| JNJ-54175446 | Janssen | Phase II (depression) | Brain-penetrant, selective P2X7 antagonist |
| JNJ-55308942 | Janssen | Phase I | Second-generation P2X7 antagonist |
| AZD9056 | AstraZeneca | Phase II (RA) | Limited CNS penetration; discontinued for inflammation |
| CE-224535 | Pfizer | Phase II (RA) | Discontinued |
| GSK1482160 | GSK | Phase I | High CNS penetration; PET tracer developed |
| Lu AF27139 | Lundbeck | Preclinical | Optimized for neuroinflammation |

PET Imaging

¹¹CGSK1482160 and ¹⁸FJNJ-64413739 are P2X7-specific PET tracers enabling in vivo quantification of P2X7 expression in neuroinflammatory conditions. Studies in AD patients show elevated P2X7 binding in temporal and parietal cortices correlating with amyloid burden[@janssen2018].

Therapeutic Strategies

Key Interactions

• [NLRP3](/genes/nlrp3): P2X7-mediated K⁺ efflux is the primary upstream trigger for NLRP3 inflammasome assembly
• [Pannexin-1](/entities/panx1-gene): Forms large-pore channels that amplify ATP release downstream of P2X7 activation
• [Caspase-1](/proteins/caspase-1-protein): Effector protease activated by the P2X7→NLRP3 inflammasome axis
• [IL-1β](/entities/il1b-gene): Primary pro-inflammatory cytokine matured by P2X7/NLRP3/caspase-1 signaling
• [TREM2](/entities/trem2-protein): Counter-regulatory receptor; [TREM2](/proteins/trem2) signaling opposes P2X7-driven inflammation
• [CD39](/entities/cd39) / [CD73](/entities/cd73): Ectonucleotidases that degrade extracellular ATP, reducing P2X7 activation
• [P2Y12](/entities/p2ry12-gene): Complementary purinergic receptor on microglia; P2Y12 mediates chemotaxis while P2X7 mediates inflammation

See Also

• [NLRP3 Inflammasome](/mechanisms/nlrp3-inflammasome)
• [Caspase-1 Protein](/proteins/caspase-1-protein)
• [Microglia in Neurodegeneration](/entities/microglia-in-neurodegeneration)
• [Neuroinflammation](/mechanisms/neuroinflammation)
• [Pannexin-1](/entities/panx1-gene)
• [P2RX7 Gene](/p2rx7-gene)

External Links

• [UniProt: Q99572](https://www.uniprot.org/uniprot/Q99572)
• [NCBI Gene: P2RX7](https://www.ncbi.nlm.nih.gov/gene/5027)
• [PDB: 5U1L](https://www.rcsb.org/structure/5U1L)
• [OMIM: 602566](https://www.omim.org/entry/602566)

Brain Atlas Resources

• [Allen Human Brain Atlas - P2RX7 Expression](https://human.brain-map.org/microarray/search/show?search_term=P2RX7)
• [Allen Cell Type Atlas](https://celltypes.brain-map.org/)
• [BrainSpan Atlas of the Developing Human Brain](https://brainspan.org/)

References