GPR37 Protein

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GPR37 Protein

<div class="infobox infobox-protein">
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<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">GPR37 Protein</th></tr>
<tr><td><strong>Protein Name</strong></td><td>GPR37 (Parmethin)</td></tr>
<tr><td><strong>Gene Symbol</strong></td><td>[GPR37](/genes/gpr37)</td></tr>
<tr><td><strong>UniProt ID</strong></td><td>[O00163](https://www.uniprot.org/uniprot/O00163)</td></tr>
<tr><td><strong>Molecular Weight</strong></td><td>~70 kDa (predicted from sequence)</td></tr>
<tr><td><strong>Subcellular Localization</strong></td><td>Endoplasmic reticulum, Plasma membrane</td></tr>
<tr><td><strong>Protein Family</strong></td><td>GPCR Class A (Orphan, D6 subfamily)</td></tr>
<tr><td><strong>Ligand</strong></td><td>Orphan (no confirmed endogenous ligand)</td></tr>
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<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/bacterial-infection" style="color:#ef9a9a">Bacterial Infection</a>, <a href="/wiki/cancer" style="color:#ef9a9a">Cancer</a>, <a href="/wiki/demyelinating-disorders" style="color:#ef9a9a">Demyelinating Disorders</a></td>
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<td class="label">SciDEX Hypotheses</td>
<td><a href="/hypothesis/h-f71a9791" style="color:#ce93d8" title="Score: 0.42">Oligodendrocyte Protectin D1 Mimetic for...</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">187 edges</a></td>
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GPR37 Protein

Overview

GPR37 (G protein-coupled receptor 37), also known as Parmethin, is an orphan G-protein-coupled receptor primarily expressed in the central nervous system[@imai2004]. GPR37 is a well-characterized substrate of the E3 ubiquitin ligase [parkin](/genes/park2), and its accumulation in parkin-deficient conditions has been directly implicated in [Parkinson's Disease](/diseases/parkinsons-disease) pathogenesis[@mandrik2022]. GPR37 also shows pathology in other tauopathies including Progressive Supranuclear Palsy (PSP) and is being investigated as a potential biomarker and therapeutic target[@yang2023].

Gene

The [GPR37 gene](/genes/gpr37) is located on chromosome 7q31 and encodes a 613-amino acid protein. The gene is highly expressed in brain, particularly in dopaminergic neurons of the substantia nigra pars compacta, cerebellar Purkinje cells, and pyramidal neurons of the hippocampus and cortex. Alternative splicing generates multiple transcript variants, though the full functional significance of isoform diversity remains under investigation.

Structure

GPR37 adopts the canonical seven-transmembrane (7TM) alpha-helical fold of Class A GPCRs[@mandrik2022]:

N-terminal extracellular domain: Contains a signal peptide directing ER translocation, followed by a short extracellular region with potential N-linked glycosylation sites
Seven transmembrane helices (TM1-TM7): Form the characteristic GPCR barrel structure with three extracellular and three intracellular loops
Extracellular loops (ECL1-ECL3): ECL2 contains a disulfide bond important for structural stability; ECL3 is relatively short
Intracellular loops (ICL1-ICL3): ICL2 and ICL3 contain signatures for G-protein coupling
C-terminal tail: Cytoplasmic tail with sorting motifs (di-lysine ER retention signal, dileucine trafficking motifs)

The lack of a confirmed endogenous ligand classifies GPR37 as an orphan receptor. However, structural studies suggest it may be capable of ligand binding if an appropriate agonist is identified.

Normal Function

Parkin Substrate and Proteostasis

GPR37 is a paradigmatic substrate of [parkin](/genes/park2), the E3 ubiquitin ligase mutated in autosomal recessive juvenile-onset Parkinson's disease[@imai2004]:

Parkin monoubiquitinates GPR37 at multiple sites
This monoubiquitination does not target GPR37 for proteasomal degradation but rather regulates its trafficking and function
Under normal conditions, parkin maintains GPR37 homeostasis — excess GPR37 is removed and potentially targeted for lysosomal degradation
Polyubiquitination (via K63-linked chains) can occur under certain conditions, marking GPR37 for autophagic clearance

Neuroprotective Signaling

Despite its characterization as an orphan receptor, GPR37 appears to signal through Gi/o-type G proteins[@mandrik2022]:

Gi/o coupling leads to inhibition of adenylate cyclase and decreased cAMP levels
Pro-survival signaling through this pathway may protect neurons against various stressors
Some studies suggest GPR37 can activate pro-survival kinase pathways including AKT and ERK
The orphan status means ligand-independent (constitutive) activity may be physiologically relevant

ER Function and Stress Response

GPR37 is predominantly localized to the endoplasmic reticulum in many cell types[@mandrik2022]:

Acts as an ER stress sensor — accumulating GPR37 triggers unfolded protein response (UPR) signaling
ER stress response activation can be protective (adaptive UPR) or pro-apoptotic (maladaptive UPR)
GPR37 may help couple ER proteostasis status to broader cellular stress responses

Interaction Network

| Partner | Interaction Type | Functional Consequence |
|---------|----------------|------------------------|
| [Parkin](/genes/park2) | E3 ligase substrate | Monoubiquitination, trafficking regulation |
| GPR37L1 | Heterodimerization | May modulate ligand binding and signaling |
| Necdin | Protein interaction | Neuronal survival regulation |
| CDCrel-1 | Co-purification | Possible role in dopamine release |
| PAWR/PRKC | Protein interaction | Apoptosis regulation pathway |

Role in Disease

Parkinson's Disease

GPR37 dysfunction is strongly linked to PD pathogenesis[@imai2004]:

Parkin Deficiency and GPR37 Accumulation: In the absence of functional parkin (loss-of-function mutations cause autosomal recessive juvenile PD), GPR37 accumulates in neurons:

Loss of parkin E3 ligase activity

GPR37 fails to be properly ubiquitinated and cleared

Accumulated GPR37 forms detergent-insoluble aggregates

GPR37-positive inclusions appear in post-mortem PD brain

Pathogenic Mechanisms:

Impaired ER-associated degradation: GPR37 accumulates when parkin-dependent ERAD pathways fail
ER stress and UPR activation: Accumulated GPR37 triggers chronic ER stress, which in dopaminergic neurons can activate pro-apoptotic pathways
Synaptic dysfunction: GPR37 may regulate presynaptic function through interactions with release machinery (e.g., CDCrel-1)
Aggregation and inclusions: GPR37 can form ubiquitinated inclusions that may be directly toxic or mark other pathogenic proteins

Lewy Body Pathology: GPR37 has been detected in Lewy bodies in PD substantia nigra neurons, suggesting it is part of the pathologic inclusions that define this disease.

Therapeutic Implications: Enhancing parkin activity, promoting GPR37 clearance, or developing GPR37 agonists are all being explored as PD therapeutic strategies[@yang2023].

Tauopathies

GPR37 immunoreactivity is observed in other neurodegenerative conditions beyond PD[@marui2009]:

Progressive Supranuclear Palsy (PSP): GPR37-positive inclusions are found in PSP brains, colocalizing with tau pathology. This suggests GPR37 dysfunction may be part of broader proteostasis failure in tauopathies.

Multiple System Atrophy (MSA): Some GPR37 pathology reported, though less prominent than in PD/PSP.

Huntington's Disease: Altered GPR37 expression patterns observed in HD models, suggesting involvement in multiple neurodegenerative conditions.

GPR37L1

GPR37L1 is the closest relative of GPR37 and shares similar structural features. GPR37L1 is primarily expressed in the brain and has been linked to:

Cerebellar function and ataxia
Demyelination and oligodendrocyte biology
Some neurodegeneration contexts

GPR37 and GPR37L1 can form heterodimers, potentially modulating each other's function.

Biomarker Potential

GPR37 is being investigated as a Parkinson's disease biomarker[@yang2023]:

Cerebrospinal Fluid (CSF) GPR37: Studies have detected GPR37 in CSF, with levels potentially altered in PD patients compared to controls. CSF GPR37 could serve as:

Diagnostic marker to distinguish PD from other parkinsonisms
Disease progression indicator
Surrogate marker for therapeutic response

Technical considerations: Reliable quantification of GPR37 in CSF requires validated immunoassays; standardization across studies is needed.

Therapeutic Targeting

Small Molecule Agonists

Given GPR37's apparent Gi/o signaling and neuroprotective effects:

Identification of GPR37 agonists could activate pro-survival pathways
Brain-penetrant compounds would be required for CNS applications
Agonist approach may be challenging given lack of known endogenous ligand

Parkin Activation

Rather than targeting GPR37 directly:

Small molecules that enhance parkin E3 ligase activity could restore GPR37 clearance
Proteostasis enhancement broadly beneficial beyond GPR37

Gene Therapy

AAV-mediated expression of functional GPR37 or parkin
CRISPR approaches to correct GPR37 regulatory variants
All approaches require careful dose optimization to avoid GPR37 accumulation

Animal Models

Gpr37 knockout mice: Viable with relatively mild phenotypes — subtle behavioral deficits, reduced dopamine release
Gpr37/parkin double mutants: Show more pronounced neurodegeneration than either single mutant, supporting the interaction model
zebrafish models: Gpr37 morphants show developmental abnormalities including dopaminergic neuron defects

Key Publications

[Imai Y et al. GPR37 as a parkin substrate (2004)](https://pubmed.ncbi.nlm.nih.gov/15316217/) — Original identification of GPR37 as parkin substrate

[Mandrik N et al. GPR37 in neurodegeneration (2022)](https://doi.org/10.3389/fncel.2022.1009128) — Comprehensive review of GPR37 biology

[Yang J et al. GPR37 in Parkinson's disease (2023)](https://doi.org/10.1038/s41531-023-00543-8) — Current therapeutic perspective

[Marui W et al. GPR37 in tauopathies (2009)](https://pubmed.ncbi.nlm.nih.gov/19189862/) — GPR37 pathology in PSP and related disorders

External Links

[UniProt O00163](https://www.uniprot.org/uniprot/O00163)
[NCBI Gene: GPR37](https://www.ncbi.nlm.nih.gov/gene/2862)
[AlphaFold Structure Prediction](https://alphafold.ebi.ac.uk/entry/O00163)
[IUPHAR Database: GPR37](https://www.guidetopharmacology.org/GTP/GPR37)
[GeneCards: GPR37](https://www.genecards.org/cgi-bin/carddisp.pl?gene=GPR37)

From the [SciDEX Exchange](/exchange) — scored by multi-agent debate

[Oligodendrocyte Protectin D1 Mimetic for Myelin Resolution](/hypothesis/h-f71a9791) — <span style="color:#ffd54f;font-weight:600">0.42</span> · Target: GPR37

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GPR37 Protein

GPR37 Protein

GPR37 Protein

Overview

Gene

Structure

Normal Function

Parkin Substrate and Proteostasis

Neuroprotective Signaling

ER Function and Stress Response

Interaction Network

Role in Disease

Parkinson's Disease

Tauopathies

GPR37L1

Biomarker Potential

Therapeutic Targeting

Small Molecule Agonists

Parkin Activation

Gene Therapy

Animal Models

Key Publications

See Also

External Links

Related Hypotheses