| Gene Symbol | GRM5 |
|---|---|
| Full Name | Glutamate Metabotropic Receptor 5 |
| Chromosomal Location | 11q14.2 |
| NCBI Gene ID | 2915 |
| OMIM | 604474 |
| Ensembl ID | ENSG00000169040 |
| UniProt | P41594 |
| Protein | mGluR5 Protein |
| Protein Family | Class C GPCR, Group I mGluRs |
| Expression | Striatum, Hippocampus, Cortex, Thalamus |
The GRM5 gene (Glutamate Metabotropic Receptor 5) encodes the mGluR5 receptor, a member of the Group I metabotropic glutamate receptor family within the Class C G protein-coupled receptor (GPCR) superfamily. mGluR5 is widely expressed throughout the brain with particularly high levels in the striatum, hippocampus, and cerebral cortex. It plays critical roles in synaptic plasticity, learning, memory, motor control, pain perception, and emotional processing.
mGluR5 has emerged as a key therapeutic target in Alzheimer's disease due to its function as a receptor for amyloid-beta (Aβ) oligomers, which drive synaptic dysfunction. The receptor is also central to the pathophysiology of Parkinson's disease, Fragile X syndrome, schizophrenia, and addiction disorders. Recent advances in PET imaging have enabled visualization of mGluR5 in the living human brain, providing new insights into its role in disease and therapeutic response monitoring[1][2][3].
mGluR5 shares the characteristic Class C GPCR architecture with GRM1, but exhibits distinct expression patterns and functional properties:
Extracellular
┌─────────────────────────────────────────┐
│ │
┌─┴───────────────────────────────────────┴─┐
│ Venus Flytrap Domain (VFTD) │
│ Residues: 1-600 │
│ Glutamate binding, dimer formation │
└───────────────────────────────────────────┘
┌───────────────────────────────────────────┐
│ Cysteine-Rich Domain (CRD) │
│ Residues: 600-800 │
│ Signal transduction │
└───────────────────────────────────────────┘
┌───────────────────────────────────────────┐
│ 7-TM Domain (Transmembrane) │
│ Residues: 800-1100 │
│ G protein coupling │
└───────────────────────────────────────────┘
┌───────────────────────────────────────────┐
│ C-terminal Tail │
│ Residues: 1100- 1212 │
│ PDZ motifs, phosphorylation sites │
└───────────────────────────────────────────┘
Intracellular
Venus Flytrap Domain (VFTD):
Cysteine-Rich Domain (CRD):
Seven Transmembrane Domain (7TM):
C-terminal Tail:
Like mGluR1, mGluR5 couples to Gq/11 proteins, activating the PLCβ signaling cascade:
mGluR5 activity is modulated by:
| Brain Region | Expression Level | Cell Types |
|---|---|---|
| Striatum | Very High | Medium spiny neurons |
| Hippocampus | High | CA1-CA3 pyramidal, dentate gyrus granule |
| Cortex | High | Layer 2/3, 5 pyramidal neurons |
| Thalamus | Medium-High | Relay neurons |
| Olfactory Bulb | Medium | Mitral cells |
| Nucleus Accumbens | Medium-High | Medium spiny neurons |
| Amygdala | Medium | Principal neurons |
| Cerebellum | Low | Granule cells (minor) |
mGluR5 has emerged as a critical player in Alzheimer's disease pathophysiology:
Recent PET studies have visualized mGluR5 in living AD patients:
| Study | Tracer | Finding |
|---|---|---|
| Petersen 2024[1:1] | [(18)F]PSS232 | mGluR5 associated with amyloid deposition and neurodegeneration |
| Lucas 2024[2:1] | Multiple | SV2A-mGluR5 correlation independent of amyloid |
| Song 2024[3:1] | Multi-tracer | Synaptic density and mGluR5 changes in early AD |
The mGluR5 theory of FXS remains a dominant framework:
| Agent | Phase | Status | Notes |
|---|---|---|---|
| Mavoglurant (AFQ056) | Phase 2 | Completed | Mixed results |
| Basimglurant (RO5186526) | Phase 2 | Completed | Some benefit |
| ADX-71149 | Phase 1 | Completed | Safety established |
Recent trials continue to explore mGluR5 NAMs for FXS with refined patient selection[5].
mGluR5 dysfunction contributes to schizophrenia pathophysiology:
mGluR5 plays a key role in reward processing and addiction[6]:
| Approach | Mechanism | Status | Examples |
|---|---|---|---|
| NAMs | Allosteric inhibition | Clinical | Mavoglurant, Basimglurant |
| Antagonists | Orthosteric block | Preclinical | LY-341495 |
| PAMs | Allosteric enhancement | Preclinical | CDPPB, VU0360172 |
| PET Tracers | Imaging | Clinical | [(18)F]PSS232, [(11)C]ABP-688 |
Clinical Candidates:
Mavoglurant (AFQ056)
Basimglurant (RO5186526)
RO5429083
Rationale: Enhance mGluR5 function for cognitive enhancement
| Tracer | Status | Applications |
|---|---|---|
| [(11)C]ABP-688 | Clinical | Baseline mGluR5 mapping |
| [(18)F]PSS232 | Clinical | AD, PD, FXS studies |
| [(18)F]FPEB | Clinical | Receptor occupancy |
Three landmark 2024 studies have advanced our understanding of mGluR5 in AD:
Petersen et al. (2024): [(18)F]PSS232 PET/MRI demonstrates mGluR5 association with amyloid deposition and neurodegeneration in AD patients[1:2]
Lucas et al. (2024): SV2A presynaptic density correlates with postsynaptic mGluR5 availability, independent of amyloid pathology in early cognitive impairment[2:2]
Song et al. (2024): Multi-tracer PET approach reveals synaptic density and mGluR5 changes in early AD, suggesting biomarker potential[3:2]
A groundbreaking 2025 study demonstrates:
Research from 2023-2024 reveals:
Recent work reveals:
Renner MC, et al. mGluR5 functions as a receptor for amyloid-beta oligomers. Nat Neurosci. 2012
Bear MF, et al. The mGluR theory of fragile x syndrome. Trends Neurosci. 2004
Petersen C, et al. mGluR5 and amyloid deposition in AD. Alzheimers Res Ther. 2024
Lucas EK, et al. SV2A and mGluR5 correlation. J Nucl Med. 2024
Song Y, et al. Multi-tracer PET in early AD. Neuroimage. 2024
Chen L, et al. mGluR5 modulator rescues connectivity in AD model. Mol Psychiatry. 2025
Thompson A, et al. mGluR5 and D2 receptor interactions. Brain. 2024
| Model | Key Phenotypes | Utility |
|---|---|---|
| GRM5⁻/⁻ | Reduced anxiety, altered learning | Basic biology |
| Fmr1 KO | Enhanced mGluR5 signaling | FXS studies |
| AD Tg | amyloid pathology | Drug testing |
| Partner | Interaction Type | Function |
|---|---|---|
| Homer | PDZ binding | Scaffolding, signaling |
| PSD-95 | PDZ binding | Synaptic localization |
| Shank | Multiple | Dendritic spine structure |
| D2 Receptor | Heteromer | Signal integration |
| NMDA Receptor | Functional | Synaptic plasticity |
Petersen C, et al. mGluR5 is associated with neurodegeneration and amyloid deposition in AD: A [(18)F]PSS232 PET/MRI study. Alzheimers Res Ther. 2024. ↩︎ ↩︎ ↩︎
Lucas EK, et al. SV2A density correlates with mGluR5 availability in early cognitive impairment. J Nucl Med. 2024. ↩︎ ↩︎ ↩︎
Song Y, et al. Multi-tracer PET assessment of synaptic density and metabotropic glutamate receptors in early AD. Neuroimage. 2024. ↩︎ ↩︎ ↩︎
Thompson A, et al. mGluR5 and dopamine D2 receptor interactions in basal ganglia. Brain. 2024. ↩︎ ↩︎
Hamilton LM, et al. mGluR5 negative allosteric modulators in fragile x syndrome clinical trials. 2024. ↩︎
Kumar R, et al. mGluR5 in addiction and reward learning. 2024. ↩︎
Davies C, et al. Novel mGluR5 positive allosteric modulator for cognitive enhancement. 2024. ↩︎
Chen L, et al. Aging-dependent loss of functional connectivity in AD mouse model and reversal by mGluR5 modulator. Mol Psychiatry. 2025. ↩︎
Yang J, et al. mGluR5 in neuroinflammation and microglial activation. Glia. 2023. ↩︎