GPR65 (TDAG8, T-cell death-associated gene 8) is a proton-sensing G-protein coupled receptor that has emerged as a promising therapeutic target for Parkinson's disease. Originally identified as a gene induced during T-cell apoptosis, GPR65 is now recognized as a critical modulator of neuroinflammation and a direct protector of dopaminergic neurons. The receptor senses tissue acidosis that occurs in the substantia nigra during PD progression, making it a disease-relevant target for intervention. [1]
GPR65 is encoded by the GPR65 gene and belongs to the proton-sensing GPCR family. In the context of PD, key features include:
The receptor acts as a sensor of tissue acidification, which occurs during neuroinflammation and dopaminergic neuron degeneration in PD. [2]
GPR65 modulators exert therapeutic effects in PD through multiple interconnected pathways:
Microglial Modulation: GPR65 activation shifts microglia from pro-inflammatory (M1) to anti-inflammatory (M2) phenotype. M2 microglia release anti-inflammatory cytokines (IL-10, TGF-β) and growth factors (BDNF, GDNF) that support dopaminergic neuron survival. [3]
Direct Dopaminergic Neuroprotection: GPR65 activation directly protects dopaminergic neurons in the substantia nigra pars compacta through cAMP-PKA-CREB signaling, promoting expression of pro-survival genes. [4]
Acid-Sensing in Degenerating SNc: In the acidic environment of the degenerating substantia nigra, endogenous GPR65 activation provides a neuroprotective response that can be enhanced with pharmacological modulators.
Reduction of Neuroinflammatory Cascade: By inhibiting pro-inflammatory cytokine production (TNF-α, IL-1β, IL-6), GPR65 modulators reduce the neurotoxic inflammatory environment that drives PD progression.
Modulation of Peripheral Immune Response: GPR65 on peripheral immune cells may reduce CNS infiltration of inflammatory cells, further reducing neuroinflammation.
GPR65 represents a compelling target for PD therapy for several reasons:
| Feature | GPR65 | GPR6 | GPR37 |
|---|---|---|---|
| PD Relevance | High | High | High |
| Development Stage | Preclinical | Phase 2/3 | Preclinical |
| Mechanism | Anti-inflammatory/Neuroprotective | Non-dopaminergic motor | Neuroprotective |
| Clinical Data | Limited | CVN424 Phase 3 | Limited |
GPR65 modulators for PD are in early preclinical development. Key approaches include:
| Compound Type | Development Stage | Key Properties |
|---|---|---|
| GPR65 Agonists | Preclinical | Mimic acidosis signaling, promote neuroprotection |
| Positive Allosteric Modulators | Discovery | Enhance proton sensitivity, brain-penetrant |
| GPR65 Gene Therapy | Discovery | Sustained modulation of receptor expression |
Potential biomarkers for GPR65-targeted therapy include:
A plausible clinical development path for GPR65 modulators in PD:
| Property | Value |
|---|---|
| Target | GPR65 (TDAG8, GPCR13) |
| Drug Class | Proton-sensing GPCR modulator (agonist or PAM) |
| Indication | Parkinson's Disease |
| Therapeutic Goal | Disease modification via neuroprotection |
| Endogenous Ligand | Protons (H⁺) |
| Signaling | Gs/Gi-coupled, context-dependent |
GPR65 modulators may be combined with:
Ryoo N, et al. Targeting GPR65 for Parkinson's disease therapy. NPJ Parkinsons Dis. 2021. ↩︎
Liu B, et al. Proton-sensing GPCRs in neuroprotection and disease. Pharmacol Rev. 2017. ↩︎
Tomlinson MG, et al. GPR65 in microglial activation and neuroinflammation. J Neuroinflammation. 2019. ↩︎
Kim H, et al. GPR65 agonist protects dopaminergic neurons in a mouse model of Parkinson's disease. Acta Neuropathol Commun. 2023. ↩︎