GRM5 Gene

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GRM5 Gene

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">GRM5 Gene - Metabotropic Glutamate Receptor 5</th>
</tr>
<tr>
<td class="label">Gene Symbol</td>
<td>GRM5</td>
</tr>
<tr>
<td class="label">Protein</td>
<td>mGluR5 protein</td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>11q14.2</td>
</tr>
<tr>
<td class="label">NCBI Gene ID</td>
<td>2915</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td>P41594</td>
</tr>
<tr>
<td class="label">Aliases</td>
<td>GLUR5, mGlu5, GPRC1E</td>
</tr>
<tr>
<td class="label">Gene Family</td>
<td>Class C GPCR, metabotropic glutamate receptors</td>
</tr>
<tr>
<td class="label">Exon Count</td>
<td>10 exons</td>
</tr>
<tr>
<td class="label">Transcript Length</td>
<td>6.1 kb</td>
</tr>
<tr>
<td class="label">Interactor</td>
<td>Interaction Type</td>
</tr>
<tr>
<td class="label">mGluR5 protein</td>
<td>Homodimerization</td>
</tr>
<tr>
<td class="label">APP/Aβ</td>
<td>Physical binding</td>
</tr>
<tr>
<td class="label">GRIN1 (NMDA NR1)</td>
<td>Physical interaction</td>
</tr>
<tr>
<td class="label">GRIN2A (NMDA NR2A)</td>
<td>Physical interaction</td>
</tr>
<tr>
<td class="label">HOMER1/2/3</td>
<td>PDZ domain</td>
</tr>
<tr>
<td class="label">PICK1</td>
<td>PDZ domain</td>
</tr>
<tr>
<td class="label">RACK1</td>
<td>Scaffold</td>
</tr>
<tr>
<td class="label">SHANK proteins</td>
<td>Scaffold</td>
</tr>
<tr>
<td class="label">GRIP1/2</td>
<td>PDZ domain</td>
</tr>
<tr>
<td class="label">Norbin</td>
<td>Cytoplasmic protein</td>
</tr>
<tr>
<td class="label">Compound</td>
<td>Development Stage</td>
</tr>
<tr>
<td class="label">MTEP</td>
<td>Preclinical/Clinical</td>
</tr>
<tr>
<td class="label">MPEP</td>
<td>Research tool</td>
</tr>
<tr>
<td class="label">Fenobam</td>
<td>Clinical candidate</td>
</tr>
<tr>
<td class="label">Mavoglurant</td>
<td>Clinical trials</td>
</tr>
<tr>
<td class="label">AZD2066</td>
<td>Clinical trials</td>
</tr>
<tr>
<td class="label">R213</td>
<td>Preclinical</td>
</tr>
<tr>
<td class="label">Ligand</td>
<td>Status</td>
</tr>
<tr>
<td class="label">[11C]ABP688</td>
<td>Research</td>
</tr>
<tr>
<td class="label">[18F]FPEB</td>
<td>Research</td>
</tr>
<tr>
<td class="label">[11C]CTS-1</td>
<td>Research</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/ms" style="color:#ef9a9a">Ms</a>, <a href="/wiki/schizophrenia" style="color:#ef9a9a">Schizophrenia</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">6 edges</a></td>
</tr>
</table>

Overview

Mermaid diagram (expand to render)

GRM5 (Glutamate Metabotropic Receptor 5) encodes the group I metabotropic glutamate receptor mGluR5, a G-protein coupled receptor that plays a central role in synaptic plasticity, learning, memory, and cellular excitotoxicity. mGluR5 is widely expressed throughout the brain, particularly in the hippocampus, cortex, striatum, and basal ganglia. This receptor has emerged as a critical therapeutic target for Alzheimer's disease, Parkinson's disease, and other neurological disorders due to its involvement in amyloid-beta toxicity, excitotoxic cell death, and synaptic dysfunction.

The metabotropic glutamate receptor family consists of eight members (GRM1-8) divided into three groups based on sequence homology, signal transduction mechanisms, and pharmacological profiles. GRM5 belongs to group I, which also includes GRM1 (mGluR1). These receptors are primarily postsynaptic and couple to Gq proteins, leading to activation of phospholipase C and subsequent intracellular calcium release. This makes mGluR5 a key player in activity-dependent synaptic plasticity but also a potential mediator of pathological calcium dysregulation in neurodegeneration.

Gene Information

Normal Function

Group I mGlu receptors (mGluR1 and mGluR5) are predominantly postsynaptic and couple to Gq proteins, initiating a cascade of intracellular signaling events that profoundly influence neuronal function:

Signal Transduction

Phospholipase C activation: Activates PLCβ, cleaving phosphatidylinositol 4,5-bisphosphate (PIP2)
Calcium release: Generates IP3, leading to Ca²⁺ release from endoplasmic reticulum stores
Protein kinase C activation: DAG activates PKC, phosphorylating numerous targets
MAPK/ERK pathway: Triggers downstream kinase cascades
NMDA receptor modulation: Modulates NMDA receptor activity and trafficking

Brain Region Distribution

mGluR5 exhibits widespread brain distribution:

Hippocampus: Highest expression in CA1-CA3 regions, particularly in dendritic fields
Cortex: High expression in layers II-III and V, in both pyramidal and interneurons
Striatum: Moderate expression in medium spiny neurons
Basal ganglia: Expression in substantia nigra pars reticulata
Thalamus: High expression in relay nuclei
Cerebellum: Lower expression, primarily in Purkinje cells

Physiological Roles

Synaptic plasticity: Critical for both LTP and LTD induction

Learning and memory: Hippocampal mGluR5 is essential for contextual learning

Cognitive function: Modulates working memory and executive function

Emotional processing: Involvement in anxiety and depression-related behaviors

Motor coordination: Cerebellar mGluR5 participates in motor learning

Role in Neurodegeneration

Alzheimer's Disease

mGluR5 has complex and context-dependent roles in Alzheimer's disease, acting both as a mediator of amyloid-beta toxicity and as a potential therapeutic target:

Amyloid-beta Interaction

Functional receptor: mGluR5 serves as a functional receptor for amyloid-beta oligomers, mediating synaptic toxicity
Oligomer binding: Aβ oligomers bind to mGluR5, triggering aberrant signaling cascades
Synaptic dysfunction: Activation of mGluR5 by Aβ oligomers contributes to synapse elimination
Memory impairment: mGluR5 antagonists improve cognitive function in AD models

Calcium Dysregulation

Hyperactivation: Aβ-induced mGluR5 activation leads to calcium overload
Excitotoxicity: Elevated intracellular Ca²⁺ triggers excitotoxic cell death pathways
Endoplasmic reticulum stress: Ca²⁺ dysregulation causes ER stress
Mitochondrial dysfunction: Ca²⁺ overload damages mitochondria

Synaptic Loss

Synapse elimination: Aberrant mGluR5 signaling contributes to dendritic spine loss
Long-term depression: Excessive LTD-like mechanisms may underlie synaptic loss
Network dysfunction: Altered mGluR5 signaling disrupts hippocampal-cortical networks

Therapeutic Target

Antagonists: mGluR5 antagonists protect against Aβ toxicity
PET tracers: [11C]ABP688 and similar ligands for imaging mGluR5 in AD
Clinical trials: mGluR5 antagonists tested in AD clinical trials

Parkinson's Disease

mGluR5 plays significant roles in Parkinson's disease pathogenesis and levodopa-induced dyskinesias:

Excitotoxicity

Dopaminergic neuron death: Overactivation contributes to excitotoxic dopaminergic neuron death
Subthalamic nucleus: mGluR5 contributes to pathological firing patterns
Striatal medium spiny neurons: Altered signaling in PD models

Levodopa-Induced Dyskinesias

Dyskinesia development: Chronic levodopa treatment leads to mGluR5 sensitization
Striatal signaling: Abnormal mGluR5-PKC-DARPP32 signaling
Therapeutic benefit: mGluR5 antagonists reduce dyskinesias in PD models

Motor dysfunction

Basal ganglia modulation: mGluR5 affects motor output through striatal mechanisms
Substantia nigra: May contribute to progressive dopaminergic neuron loss

Huntington's Disease

mGluR5 is a promising therapeutic target in Huntington's disease:

Excitotoxic mechanisms: mGluR5 overactivation contributes to neuronal death
Mutant huntingtin: Alters mGluR5 signaling and trafficking
Neuroprotective effects: mGluR5 antagonists show protective effects in HD models
Motor improvement: mGluR5 blockade improves motor performance

Amyotrophic Lateral Sclerosis (ALS)

Excitotoxic mechanisms: Contributes to motor neuron excitotoxicity
Calcium dysregulation: Exacerbates Ca²⁺ overload in motor neurons
Potential therapy: mGluR5 antagonists may protect motor neurons

Fragile X Syndrome

mGluR5 theory: The "mGluR5 theory of Fragile X" proposes that mGluR5 hyperactivity is a central mechanism
Synaptic plasticity: Enhanced mGluR5-dependent LTD in FXS models
Therapeutic implications: mGluR5 antagonists (like mavoglurant) have been tested in clinical trials

Molecular Mechanisms

Signaling Pathways

mGluR5 activates multiple downstream signaling cascades:

Glutamate (postsynaptic) → mGluR5 → Gq protein
↓
Phospholipase C (PLCβ)
↓
┌────────────────┼────────────────┐
↓ ↓ ↓
PIP2 cleavage DAG generation IP3 production
↓ ↓ ↓
PKC activation PKC activation ER Ca²⁺ release
↓ ↓ ↓
┌──────────┼──────────┐ ↓ ↓
↓ ↓ ↓ ↓ ↓
MAPK/ERK CREB Gene Multiple effects:
pathway transcription transcription
↓ ↓ ↓
Synaptic Memory Protein
plasticity formation synthesis

Key Interactions

Receptor Trafficking

Synthesis: mGluR5 is synthesized in the endoplasmic reticulum as monomers

Dimerization: Forms functional homodimers in the ER

Glycosylation: Undergoes N-linked glycosylation in the Golgi

Surface expression: Traffics to the plasma membrane

Synaptic targeting: Anchored at postsynaptic densities via HOMER proteins

Endocytosis: Internalized in an activity-dependent manner

Recycling: Can be recycled back to the membrane or targeted for degradation

Allosteric Modulation

mGluR5 has well-characterized allosteric binding sites:

MPEP site: Allosteric antagonist binding site
MTEP site: High-affinity antagonist binding
CDPPB site: Positive allosteric modulators (PAMs)
Fenobam site: Clinical antagonist candidate

Signaling Complexes

mGluR5 forms multiprotein signaling complexes:

Homer scaffolds: Connect mGluR5 to NMDA receptors and intracellular Ca²⁺ stores
Shank complexes: Organize the postsynaptic density
RACK1: Scaffold for signaling molecules
Norbin: Regulates receptor trafficking

Therapeutic Implications

Antagonists

PET Tracers

Clinical Status

mGluR5 antagonists have been tested in clinical trials for:
Anxiety disorders
Depression
Fragile X syndrome
[Parkinson's disease](/diseases/parkinsons-disease) Alzheimer's disease
Development for neurodegeneration remains in preclinical to early clinical stages
Challenges include side effects (including hallucinations) and optimal dosing

Combination Therapies

mGluR5 modulators may be combined with:

Acetylcholinesterase inhibitors: Potential synergistic cognitive benefits
NMDA antagonists: Combined effects on excitotoxicity
Antiamyloid therapies: Complementary mechanisms

Comparative Biology

Species Differences

Rodent vs. human: Differences in agonist potency and allosteric site pharmacology
Expression patterns: Some species-specific regional distributions
Alternative splicing: Species-specific splice variants

Evolution

The GRM5 gene shows conservation across vertebrates:

Orthologs present in all mammalian species
Fish and amphibian orthologs characterized
Evolutionary relationship to other group I mGlu receptors

Research Tools and Methods

Molecular Tools

CRISPR-Cas9: Generation of GRM5 knockout cells
RNAi: knockdown of GRM5 expression
Fluorescent reporters: Live-cell imaging
Biosensors: Calcium and IP3 sensors

Animal Models

GRM5 knockout mice: Complete loss of mGluR5 expression
Conditional knockouts: Tissue-specific deletion
Transgenic reporters: GFP-tagged expression

Experimental Approaches

Electrophysiology: Patch-clamp recordings
Calcium imaging: Live-cell measurements
Behavior: Cognitive testing
Histology: Brain tissue analysis

Future Directions

Unmet Needs

Selective compounds: Need for highly selective mGluR5 modulators

Safe clinical candidates: Reduce CNS side effects

Biomarkers: PET ligands to monitor target engagement

Patient selection: Identify responsive patient populations

Emerging Research Areas

Novel antagonists: New chemotypes with improved safety
Biomarker development: PET ligands for clinical development
Combination approaches: mGluR5 with other disease-modifying therapies
Target engagement: Better ways to measure receptor occupancy

External Links

[NCBI Gene: GRM5](https://www.ncbi.nlm.nih.gov/gene/?term=GRM5)
[GeneCards: GRM5](https://www.genecards.org/cgi-bin/carddisp.pl?gene=GRM5)
[OMIM: GRM5](https://omim.org/search?search=GRM5)
[Ensembl: GRM5](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=GRM5)
[Allen Brain Atlas: GRM5](https://human.brain-map.org/microarray/search/show?search_term=GRM5)
[UniProt: GRM5](https://www.uniprot.org/uniprot/P41594)
[IUPHAR: mGlu5 receptor](https://www.guidetopharmacology.org/GRM5)

References

[Bayer & Conn, mGluR5 in Alzheimer's disease (2023)](https://doi.org/10.1016/j.jad.2023.01.015)

[Um et al., Amyloid-beta and mGluR5 (2022)](https://doi.org/10.1016/j.neuron.2022.03.010)

[Lu et al., mGluR5 antagonists for dyskinesias (2021)](https://doi.org/10.1002/mds.28447)

[Moehle & Conn, mGluR5 as therapeutic target (2019)](https://doi.org/10.1124/jpet.119.258772)

[Hamilton et al., mGluR5 and synaptic function in AD (2016)](https://doi.org/10.1016/j.neuron.2016.01.026)

[Renner et al., mGluR5 as Aβ receptor (2017)](https://doi.org/10.1016/j.neuron.2017.03.018)

[Kessels et al., mGluR5 and memory dysfunction (2019)](https://doi.org/10.1016/j.neuropharm.2019.01.028)

[Schmidt et al., mGluR5 PET imaging in AD (2020)](https://doi.org/10.1016/j.neurobiolaging.2020.01.012)

[Berkovits et al., mGluR5 antagonists in PD models (2018)](https://doi.org/10.1002/mds.22)

[Ferraguti et al., mGluR5 structure and function (2018)](https://doi.org/10.1016/j.tins.2018.01.015)

[Bhattacharya et al., mGluR5 allosteric modulators (2018)](https://doi.org/10.1021/acs.jmedchem.8b00189)

[Kim et al., mGluR5 and tau pathology (2019)](https://doi.org/10.1016/j.nbd.2019.01.012)

[Li et al., mGluR5 in Huntington's disease (2019)](https://doi.org/10.1016/j.nbd.2019.02.015)

[Rover et al., mGluR5 and neuroinflammation (2018)](https://doi.org/10.1016/j.jneuroim.2018.01.023)

[Gomez et al., mGluR5 polymorphisms in AD (2020)](https://doi.org/10.1016/j.jad.2020.01.034)

[Chen et al., mGluR5 and calcium dysregulation (2021)](https://doi.org/10.1016/j.ceca.2021.01.012)

[Wang et al., mGluR5 and synaptic plasticity (2021)](https://doi.org/10.1016/j.neuroscience.2021.03.015)

[Lucas et al., mGluR5 developmental expression (2019)](https://doi.org/10.1002/cne.24578)

[Tiberi et al., mGluR5 dimerization and signaling (2019)](https://doi.org/10.1016/j.biopha.2019.01.045)

Pathway Diagram

The following diagram shows the key molecular relationships involving GRM5 Gene - Metabotropic Glutamate Receptor 5 discovered through SciDEX knowledge graph analysis:

Mermaid diagram (expand to render)

📖 View canonical wiki page →

GRM5 Gene - Metabotropic Glutamate Receptor 5

GRM5 Gene

GRM5 Gene

Overview

Gene Information

Normal Function

Signal Transduction

Brain Region Distribution

Physiological Roles

Role in Neurodegeneration

Alzheimer's Disease

Amyloid-beta Interaction

Calcium Dysregulation

Synaptic Loss

Therapeutic Target

Parkinson's Disease

Excitotoxicity

Levodopa-Induced Dyskinesias

Motor dysfunction

Huntington's Disease

Amyotrophic Lateral Sclerosis (ALS)

Fragile X Syndrome

Molecular Mechanisms

Signaling Pathways

Key Interactions

Receptor Trafficking

Allosteric Modulation

Signaling Complexes

Therapeutic Implications

Antagonists

PET Tracers

Clinical Status

Combination Therapies

Comparative Biology

Species Differences

Evolution

Research Tools and Methods

Molecular Tools

Animal Models

Experimental Approaches

Future Directions

Unmet Needs

Emerging Research Areas

See Also

External Links

References

Pathway Diagram