Purinergic Signaling In Neurodegeneration is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.
Purinergic signaling refers to the signaling pathways mediated by purine nucleotides and nucleosides (ATP, ADP, adenosine) through activation of purinergic receptors (P1, P2X, P2Y). This ancient signaling system plays crucial roles in neural development, synaptic transmission, glial function, and neuroinflammation. Dysregulation of purinergic signaling contributes to neurodegenerative processes through multiple mechanisms.
Key aspects include:
- ATP release: Activity-dependent ATP release from [neurons[/entities/[neurons[/entities/[neurons[/entities/[neurons--TEMP--/entities)--FIX-- and [astrocytes[/cell-types/[astrocytes[/cell-types/[astrocytes[/cell-types/[astrocytes--TEMP--/cell-types)--FIX--
- Receptor activation: P2X (ionotropic) and P2Y (metabotropic) receptors mediate fast and modulatory signaling
- Adenosine signaling: A1, A2A, A2B, A3 receptors modulate neuronal excitability and inflammation
- neuroinflammation: P2X7 and A2A receptors regulate microglial activation and cytokine release
See also: [neuroinflammation[/mechanisms/[neuroinflammation[/mechanisms/[neuroinflammation[/mechanisms/[neuroinflammation--TEMP--/mechanisms)--FIX--, [Glial Activation], [Adenosine Signaling]
P2X receptors are ligand-gated ion channels activated by extracellular ATP. Seven subtypes (P2X1–P2X7) form trimeric assemblies that permit cation influx (Na+, Ca2+, K+). In the CNS, the most relevant are:
| Receptor |
Primary CNS Expression |
Key Functions |
| P2X4 |
[microglia[/cell-types/[microglia[/cell-types/[microglia[/cell-types/[microglia--TEMP--/cell-types)--FIX--/cell-types/microglia, [neurons[/entities/[neurons[/entities/[neurons[/entities/[neurons--TEMP--/entities)--FIX-- |
Microglial activation, BDNF release, neuropathic pain |
| P2X7 |
[Microglia[/entities/microglia/[neurons[/entities/microglia/[neurons[/entities/microglia/[neurons--TEMP--/entities/microglia)--FIX-- |
Nociception, neurotransmission |
| P2X1 |
Smooth muscle, platelets |
Vasoconstriction, platelet aggregation |
P2Y receptors are G-protein-coupled receptors activated by ATP, ADP, UTP, or UDP. Eight subtypes (P2Y1, 2, 4, 6, 11, 12, 13, 14) signal through Gq/11, Gi/o, or Gs pathways:
| Receptor |
Primary CNS Expression |
Key Functions |
| P2Y1 |
[astrocytes[/cell-types/[astrocytes[/cell-types/[astrocytes[/cell-types/[astrocytes--TEMP--/cell-types)--FIX--, [neurons[/entities/[neurons[/entities/[neurons[/entities/[neurons--TEMP--/entities)--FIX-- |
Calcium waves, glutamate release |
| P2Y6 |
[microglia[/cell-types/[microglia[/cell-types/[microglia[/cell-types/[microglia--TEMP--/cell-types)--FIX--/cell-types/microglia |
UDP-activated phagocytosis |
| P2Y12 |
Homeostatic [microglia/cell-types/microglia |
Chemotaxis, surveillance, synaptic monitoring |
| P2Y13 |
[Microglia, oligodendrocytes |
Process extension, ADP sensing |
Adenosine receptors are G-protein-coupled receptors activated by adenosine, the breakdown product of ATP via ectonucleotidases (CD39 and CD73):
| Receptor |
Coupling |
Key Functions |
| A1 |
Gi/o (inhibitory) |
Neuroprotection, presynaptic inhibition, anti-inflammatory |
| A2A |
Gs (excitatory) |
Pro-inflammatory microglial activation, synaptic modulation |
| A2B |
Gs |
Astrocyte activation, vascular regulation |
| A3 |
Gi/o |
Microglial process motility, mixed effects |
In the healthy brain, ATP is released in a controlled manner from synaptic vesicles and through pannexin channels during normal neurotransmission. In neurodegenerative diseases, pathological ATP release occurs through multiple mechanisms (Progress et al., 2024):
- Neuronal injury and death: Cytoplasmic ATP (~5 mM) floods the extracellular space upon membrane damage from excitotoxicity, oxidative stress, or mechanical trauma
- [amyloid-beta[/entities/[amyloid-beta[/entities/[amyloid-beta[/entities/[amyloid-beta--TEMP--/entities)--FIX-- stimulation: [Aβ[/entities/[amyloid-beta[/entities/[amyloid-beta[/entities/[amyloid-beta--TEMP--/entities)--FIX-- oligomers and plaques stimulate ATP release from [astrocytes[/cell-types/[astrocytes[/cell-types/[astrocytes[/cell-types/[astrocytes--TEMP--/cell-types)--FIX-- and [neurons[/entities/[neurons[/entities/[neurons[/entities/[neurons--TEMP--/entities)--FIX-- through pannexin-1 hemichannels and connexin-43 hemichannels (Illes et al., 2024)
- [α-synuclein/proteins/alpha release: Extracellular α-synuclein induces ATP release via the P2X7-pannexin-1 interaction (Jiang et al., 2015 (Purinergic et al., 2015
- **[Microglial/lysosomal] compartments
Extracellular ATP is rapidly metabolized by ectonucleotidases:
ATP → (CD39/NTPDase1) → ADP → (CD39) → AMP → (CD73/ecto-5'-nucleotidase) → Adenosine → (adenosine deaminase) → Inosine
This cascade determines the balance between ATP-driven inflammation (via P2 receptors) and adenosine-mediated neuroprotection (via A1 receptors). In neurodegeneration, changes in ectonucleotidase expression alter this balance, often favoring sustained ATP signaling (Calovi et al., 2019) (Activation et al., 2009).
The P2X7 receptor (P2X7R) has several properties that distinguish it from other P2X family members and make it particularly important in neurodegeneration:
- Low ATP affinity: Requires high (>100 μM) ATP concentrations for activation, meaning it is primarily activated under pathological conditions
- Pore formation: Sustained activation opens a large non-selective pore (permeant to molecules up to ~900 Da), enabling release of pro-inflammatory mediators
- [NLRP3[/mechanisms/[nlrp3-inflammasome[/mechanisms/[nlrp3-inflammasome[/mechanisms/[nlrp3-inflammasome--TEMP--/mechanisms)--FIX-- inflammasome activation: P2X7R is the canonical trigger of the [NLRP3[/mechanisms/[nlrp3-inflammasome[/mechanisms/[nlrp3-inflammasome[/mechanisms/[nlrp3-inflammasome--TEMP--/mechanisms)--FIX-- inflammasome assembly, leading to [caspase]-1 activation, IL-1β and IL-18 maturation and release
- Absence of desensitization: Unlike other P2X receptors, P2X7R does not desensitize during sustained stimulation, enabling persistent inflammatory signaling
¶ P2X7R and the NLRP3 Inflammasome
The P2X7R–[NLRP3[/mechanisms/[nlrp3-inflammasome[/mechanisms/[nlrp3-inflammasome[/mechanisms/[nlrp3-inflammasome--TEMP--/mechanisms)--FIX-- axis represents a critical link between purinergic signaling and neuroinflammation (Mechanisms et al., 2021):
- ATP binds P2X7R on [microglia[/cell-types/[microglia[/cell-types/[microglia[/cell-types/[microglia--TEMP--/cell-types)--FIX--
- Released IL-1β amplifies neuroinflammation and causes neuronal damage
In [Alzheimer's disease[/diseases/[alzheimers[/diseases/[alzheimers[/diseases/[alzheimers--TEMP--/diseases)--FIX--, [Aβ[/entities/[amyloid-beta[/entities/[amyloid-beta[/entities/[amyloid-beta--TEMP--/entities)--FIX-- aggregates activate P2X7R on peripaque [microglia[/cell-types/[microglia[/cell-types/[microglia[/cell-types/[microglia--TEMP--/cell-types)--FIX--, driving chronic IL-1β release and creating a self-amplifying neuroinflammatory cycle (Illes et al., 2024).
- Extracellular [α-synuclein/proteins/alpha activates microglial P2X7R, inducing oxidative stress and [NLRP3[/mechanisms/[nlrp3-inflammasome[/mechanisms/[nlrp3-inflammasome[/mechanisms/[nlrp3-inflammasome--TEMP--/mechanisms)--FIX---mediated inflammation
- P2X7R activation contributes to [dopaminergic] neuron loss in the substantia nigra
- P2X7R-pannexin-1 interaction mediates α-synuclein-induced ATP release from neuroblastoma cells (Jiang et al., 2015
- P2X7R activation on oligodendrocytes contributes to [demyelination[/mechanisms/[demyelination[/mechanisms/[demyelination[/mechanisms/[demyelination--TEMP--/mechanisms)--FIX--
- Chronic P2X7R stimulation on [microglia[/cell-types/[microglia[/cell-types/[microglia[/cell-types/[microglia--TEMP--/cell-types)--FIX--/entities/microgliahttps://doi.org/10.3389/fneur.2021.654850)).
The adenosine A1 receptor provides constitutive neuroprotection through:
- Presynaptic inhibition of glutamate release, opposing excitotoxicity
- Reduction of neuronal metabolic demand
- Anti-inflammatory effects on [microglia/dopamine] signaling — A2A antagonists (istradefylline) are approved for [Parkinson's disease[/diseases/[parkinsons[/diseases/[parkinsons[/diseases/[parkinsons--TEMP--/diseases)--FIX--
- In [microglia[/cell-types/[microglia[/cell-types/[microglia[/cell-types/[microglia--TEMP--/cell-types)--FIX-- to reduced AD and PD risk (Calovi et al., 2019)
[astrocytes[/cell-types/[astrocytes[/cell-types/[astrocytes[/cell-types/[astrocytes--TEMP--/cell-types)--FIX-- are major participants in purinergic signaling:
- Calcium waves: ATP released from [astrocytes[/cell-types/[astrocytes[/cell-types/[astrocytes[/cell-types/[astrocytes--TEMP--/cell-types)--FIX-- activates P2Y1 receptors on neighboring [astrocytes[/cell-types/[astrocytes[/cell-types/[astrocytes[/cell-types/[astrocytes--TEMP--/cell-types)--FIX--, propagating calcium waves across astrocyte networks — a form of gliotransmission that can modulate neuronal activity over large distances
- Glutamate release: Astrocytic P2X7R and P2Y1 activation triggers glutamate release, potentially contributing to excitotoxicity
- Reactive astrogliosis: P2Y1 and P2X7 signaling drives [astrocytes[/cell-types/[astrocytes[/cell-types/[astrocytes[/cell-types/[astrocytes--TEMP--/cell-types)--FIX-- reactivity in neurodegeneration
- [BBB[/entities/[blood-brain-barrier[/entities/[blood-brain-barrier[/entities/[blood-brain-barrier--TEMP--/entities)--FIX-- regulation: Astrocytic purinergic signaling modulates [Blood-Brain Barrier[/entities/[blood-brain-barrier[/entities/[blood-brain-barrier[/entities/[blood-brain-barrier--TEMP--/entities)--FIX-- permeability
Multiple P2X7R antagonists are being developed for neurological indications:
JNJ-54175446 (Janssen)
- Brain-penetrant P2X7R antagonist with favorable pharmacokinetics
- Completed Phase 1 clinical trials demonstrating safety and CNS target engagement
- Reduced neuroinflammation biomarkers and modulated mood in healthy volunteers
- Dose-dependent inhibition of IL-1β release in the [hippocampus[/brain-regions/[hippocampus[/brain-regions/[hippocampus[/brain-regions/[hippocampus--TEMP--/brain-regions)--FIX-- (Recourt et al., 2020; Bhatt et al., 2019
Other P2X7R antagonists in development:
- CE-224,535 (Pfizer): Tested in rheumatoid arthritis
- AZD9056 (AstraZeneca): Tested in inflammatory conditions
- GSK1482160 (GSK: Brain-penetrant PET ligand and potential therapeutic
- Istradefylline (Nourianz): FDA-approved as adjunctive therapy for [Parkinson's disease[/diseases/[parkinsons[/diseases/[parkinsons[/diseases/[parkinsons--TEMP--/diseases)--FIX--; may have disease-modifying potential through anti-neuroinflammatory effects
- Preladenant, tozadenant: Additional A2A antagonists evaluated in PD clinical trials
- Caffeine: Epidemiologically associated with reduced AD and PD risk; mechanisms include A2A antagonism and adenosine A1 agonism
Targeting ectonucleotidases to shift the ATP/adenosine balance represents a newer therapeutic approach. Enhancing CD39 activity could reduce pro-inflammatory ATP levels while increasing neuroprotective adenosine.
Strategies to maintain or restore microglial P2Y12 expression in disease states could help preserve homeostatic surveillance and neuroprotection.
Several purinergic components are being investigated as biomarkers:
- CSF ATP levels: Elevated in AD patients, correlating with disease severity
- P2X7R PET ligands: Radioligands like [11C]JNJ-54173717 enable in vivo imaging of P2X7R expression, providing a biomarker of neuroinflammation
- Plasma adenosine: Altered adenosine metabolism may serve as a peripheral biomarker
- CD39/CD73 expression: Changes in ectonucleotidase activity on circulating immune cells may reflect CNS purinergic dysfunction
- Cell-type-specific purinergic atlas: Single-cell RNA sequencing and spatial transcriptomics are mapping purinergic receptor expression across brain cell types in health and disease
- P2X7R splice variants: Alternative splicing generates functionally distinct P2X7R isoforms with different sensitivities to ATP and antagonists — understanding these variants is critical for drug development (Illes et al., 2024)
- Purinergic-mitochondrial crosstalk: P2X7R-mediated calcium influx directly impacts [mitochondrial] function and may contribute to ferroptosis and metabolic dysfunction
- Gut-brain purinergic axis: Purinergic signaling in the [enteric nervous system[/brain-regions/[enteric-nervous-system[/brain-regions/[enteric-nervous-system[/brain-regions/[enteric-nervous-system--TEMP--/brain-regions)--FIX-- may influence CNS neurodegeneration through the [Gut-Brain Axis[/mechanisms/[gut-brain-axis[/mechanisms/[gut-brain-axis[/mechanisms/[gut-brain-axis--TEMP--/mechanisms)--FIX--
- Purinergic control of [glymphatic] clearance: ATP and adenosine may regulate [glymphatic system[/entities/[glymphatic-system[/entities/[glymphatic-system[/entities/[glymphatic-system--TEMP--/entities)--FIX-- function and [Aβ[/entities/[amyloid-beta[/entities/[amyloid-beta[/entities/[amyloid-beta--TEMP--/entities)--FIX-- clearance during sleep
- Combination approaches: P2X7R blockade combined with [anti-amyloid] or [anti-tau]tau] therapies for synergistic neuroprotection
- [Microglia
- [Disease-Associated [Microglia (DAM)
The study of Purinergic Signaling In Neurodegeneration has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.
- [Burnstock, G. (2020]. "Role of purinergic receptors in Alzheimer's Disease." Purinergic Signalling, 14, 371–382. DOI
- [Calovi, S., Mut-Arbona, P., & Sperlágh, B. (2021]. "Glial Purinergic Signaling in Neurodegeneration." Frontiers in Neurology, 12, 654850. DOI
- [Illes, P., et al. (2024]. "Unlocking the therapeutic potential of P2X7 receptor: a comprehensive review of its role in neurodegenerative disorders." Frontiers in Pharmacology, 15, 1450704. DOI
- [Bhatt, D. P., et al. (2019]. "Targeting neuroinflammation with brain penetrant P2X7 antagonists as novel therapeutics for neuropsychiatric disorders." Neuropsychopharmacology, 44, 229–236. DOI
- [Recourt, K., et al. (2020]. "Characterisation of the pharmacodynamic effects of the P2X7 receptor antagonist JNJ-54175446 using an oral dexamphetamine challenge model in healthy males." Journal of Psychopharmacology, 34(9], 1013–1023. DOI
- Jiang, T., et al. (2015]. "P2X7 receptor-pannexin 1 interaction mediates extracellular [ alpha-synuclein )]-induced ATP release in neuroblastoma SH-SY5Y cells." Purinergic Signalling, 11, 439–449. DOI:10.1007/s11302-017-9567-2https://doi.org/10.1007/s11302-017-9567-2
- [Sanz, J. M., et al. (2009]. "Activation of [microglia[/entities/[microglia[/entities/[microglia[/entities/[microglia--TEMP--/entities)--FIX-- by amyloid β requires P2X7 receptor expression." Journal of Immunology, 182(7], 4378–4385. DOI
- [Deussing, J. M., & Bhatt, D. P. (2022]. "P2X7 receptor and purinergic signaling: orchestrating mitochondrial dysfunction in neurodegenerative diseases." eNeuro, 9(6], ENEURO.0092-22.2022. DOI
- [Sperlágh, B., & Illes, P. (2014]. "P2X7 receptor: an emerging target in central nervous system diseases." Trends in Pharmacological Sciences, 35(10], 537–547. DOI
- [Faroni, A., & Bhatt, D. P. (2024]. "Purinergic-associated immune responses in neurodegenerative diseases." Progress in Neurobiology, 241, 102672. DOI
- [Ribeiro, D. E., et al. (2021]. "Mechanisms of astrocytic and microglial purinergic signaling in homeostatic regulation and implications for neurological disease." Exploration of Neuroscience, 3, 100676. DOI
- [Zarrinmayeh, H., & Territo, P. R. (2020]. "Purinergic Receptors of the Central Nervous System: Biology, PET Ligands, and Their Applications." Molecular Imaging, 19, 1536012120927609. DOI
🔴 Low Confidence
| Dimension |
Score |
| Supporting Studies |
12 references |
| Replication |
0% |
| Effect Sizes |
25% |
| Contradicting Evidence |
33% |
| Mechanistic Completeness |
50% |
Overall Confidence: 39%