CASR Gene

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CASR Gene

<table class="infobox infobox-gene">
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<th class="infobox-header" colspan="2">CASR — Calcium-Sensing Receptor</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td><strong>CASR</strong></td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>Calcium-Sensing Receptor</td>
</tr>
<tr>
<td class="label">Chromosome</td>
<td>3q21.1</td>
</tr>
<tr>
<td class="label">NCBI Gene</td>
<td><a href="https://www.ncbi.nlm.nih.gov/gene/846" target="_blank">846</a></td>
</tr>
<tr>
<td class="label">Ensembl</td>
<td><a href="https://ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000036828" target="_blank">ENSG00000036828</a></td>
</tr>
<tr>
<td class="label">OMIM</td>
<td><a href="https://omim.org/entry/601199" target="_blank">601199</a></td>
</tr>
<tr>
<td class="label">UniProt</td>
<td><a href="https://www.uniprot.org/uniprot/Q9UII2" target="_blank">Q9UII2</a></td>
</tr>
<tr>
<td class="label">Protein Class</td>
<td>GPCR (Class C), Metabotrophic glutamate receptor family</td>
</tr>
<tr>
<td class="label">Expression</td>
<td>Brain (cerebellum, hippocampus, cortex), Parathyroid, Kidney, Pancreas</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/aging" style="color:#ef9a9a">Aging</a>, <a href="/wiki/neurodegeneration" style="color:#ef9a9a">Neurodegeneration</a>, <a href="/wiki/parkinson" style="color:#ef9a9a">Parkinson</a>, <a href="/wiki/parkinson's-disease" style="color:#ef9a9a">Parkinson's Disease</a></td>
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<td cl

...

CASR Gene

CASR — Calcium-Sensing Receptor

Overview

Mermaid diagram (expand to render)

The Calcium-Sensing Receptor (CASR) is a class C G protein-coupled receptor that functions as the principal sensor of extracellular calcium concentrations in the body. Originally characterized for its critical role in calcium homeostasis in parathyroid and kidney, CASR is now recognized as having significant functions in the central nervous system (CNS), where it participates in synaptic plasticity, neuronal excitability, and cellular responses to pathological stimuli["@caspi2012"].

CASR belongs to the metabotropic glutamate receptor family, which includes eight members (mGluR1-8) and the GABA["B"] receptors. These receptors share a common architecture with a large extracellular venus flytrap (VFT) domain, a cysteine-rich domain, and a seven transmembrane domain. Unlike the ionotropic glutamate receptors that function as ligand-gated ion channels, metabotropic receptors modulate synaptic transmission through G protein-mediated signaling cascades.

Gene Structure and Evolution

The human CASR gene spans approximately 73 kb on chromosome 3q21.1 and comprises 11 exons. The coding sequence is highly conserved across mammals, reflecting the critical nature of calcium sensing in vertebrate physiology. The promoter region contains multiple transcription factor binding sites, allowing for tissue-specific expression and regulation by various hormonal and developmental signals.

Alternative splicing generates multiple CASR variants with different tissue distributions and functional properties. The most common splice variants differ in their C-terminal tail length, which affects receptor desensitization and trafficking. In the brain, specific splice variants are enriched in different neuronal populations, suggesting specialized functions in distinct brain regions.

Protein Structure and Function

Extracellular Domain

The extracellular Venus flytrap (VFT) domain of CASR contains the calcium binding sites. Each receptor monomer has multiple calcium binding pockets within the VFT, with calcium ions coordinating to negatively charged amino acid residues. The binding of calcium induces conformational changes that transmit across the receptor to the intracellular domains.

The VFT domain also contains binding sites for various allosteric modulators, including L-amino acids (particularly aromatic and aliphatic amino acids), which potentiate calcium-induced receptor activation. This amino acid sensing function may have relevance to neuronal metabolism and stress responses.

Transmembrane Domain

The seven transmembrane helices form the canonical GPCR transmembrane bundle. The transmembrane domains contain binding sites for positive and negative allosteric modulators, including calcimimetics (e.g., cinacalcet) used clinically for treating secondary hyperparathyroidism, and calcilytics that act as receptor antagonists.

Intracellular Domain and Signaling

The intracellular C-terminal tail contains multiple serine and threonine residues that can be phosphorylated, as well as motifs for interaction with scaffolding proteins and downstream signaling molecules. CASR signals primarily through:

Gq/11 family G proteins: Activating phospholipase C (PLC), leading to inositol trisphosphate (IP3) and diacylglycerol (DAG) production
Gi/o family G proteins: Inhibiting adenylate cyclase and reducing cAMP levels
G12/13 family G proteins: Activating Rho GTPase pathways affecting cytoskeletal dynamics

Upon activation, CASR triggers multiple downstream signaling cascades:

PLC-IP3 pathway: Increases intracellular calcium release from endoplasmic reticulum stores

MAPK pathway: Activates ERK1/2, JNK, and p38 MAP kinases

PI3K-Akt pathway: Promotes cell survival signaling

Rho pathway: Affects cytoskeletal organization and trafficking

Expression in the Brain

Regional Distribution

CASR is expressed throughout the central nervous system with particularly high levels in:

Hippocampus: CA1-CA3 regions, dentate gyrus — areas critical for learning and memory
Cerebellum: Purkinje cells and granule cell layer — motor coordination
Cerebral cortex: Layer V pyramidal neurons — executive function
Hypothalamus: Paraventricular and supraoptic nuclei — autonomic regulation
Substantia nigra: Dopaminergic neurons — motor control
Brainstem: Nucleus tractus solitarius — sensory processing

Cellular Localization

At the cellular level, CASR localizes to:

Synaptic terminals: Both presynaptic and postsynaptic compartments
Dendritic shafts: Along dendritic trunks and branches
Somatic membrane: Cell body plasma membrane
Endoplasmic reticulum: Intracellular calcium stores
Growth cones: During neuronal development

This widespread subcellular distribution suggests multiple roles in neuronal physiology, from synaptic transmission to dendritic integration and development.

Physiological Functions in the Brain

Calcium Homeostasis at Synapses

In neurons, CASR participates in local calcium sensing at synapses. The extracellular calcium concentration at synaptic clefts changes during neuronal activity, with lower calcium during high-frequency firing. CASR may function as a sensor linking synaptic activity to adaptive responses.

Synaptic Plasticity

CASR activation modulates synaptic plasticity, the cellular basis for learning and memory. Studies have shown that:

CASR activation can enhance long-term potentiation (LTP) in hippocampal neurons
CASR antagonists impair memory consolidation in behavioral tasks
CASR expression changes during age-related cognitive decline

The mechanism involves modulation of NMDA receptor function, changes in intracellular calcium dynamics, and activation of downstream signaling pathways including CaMKII and CREB[@lu2021].

Neuronal Excitability

By modulating voltage-gated calcium channels and potassium channels, CASR affects neuronal excitability. CASR activation generally reduces neuronal firing rate through activation of calcium-activated potassium channels. This may serve as a negative feedback mechanism preventing excessive neuronal activation.

Neuroprotection

Under various stress conditions, CASR activation can be neuroprotective:

Oxidative stress: CASR signaling activates antioxidant pathways
Excitotoxicity: CASR modulates glutamate receptor function
Metabolic stress: CASR helps maintain cellular energy balance

Role in Alzheimer's Disease

Amyloid Processing

CASR has complex interactions with amyloid precursor protein (APP) processing and amyloid-beta (Aβ) metabolism. Several mechanisms have been proposed:

APP trafficking: CASR signaling affects APP trafficking through the secretory and endosomal pathways
Beta-secretase activity: CASR modulation of BACE1 expression and activity
Aβ aggregation: CASR may directly interact with Aβ species

Studies in AD brain tissue have shown altered CASR expression patterns, with decreased expression in certain brain regions and increased expression in others. This dysregulation may contribute to the amyloid pathology characteristic of AD[@mukhtar2018].

Tau Pathology

CASR signaling affects tau phosphorylation through multiple kinase pathways:

GSK3β activation: CASR can activate glycogen synthase kinase 3 beta (GSK3β), a key kinase in tau phosphorylation
CDK5 modulation: CASR affects cyclin-dependent kinase 5 (CDK5) activity
PP2A regulation: CASR can modulate protein phosphatase 2A (PP2A), the major tau phosphatase

Synaptic Dysfunction

In Alzheimer's disease, CASR contributes to synaptic dysfunction through:

NMDA receptor modulation: Alters NMDA receptor trafficking and function
Dendritic spine loss: Affects actin cytoskeleton dynamics
Calcium dysregulation: Contributes to calcium homeostasis failure

Neuroinflammation

CASR plays a significant role in neuroinflammation, a key feature of AD pathogenesis:

Microglial activation: CASR on microglia senses pathological calcium changes
Cytokine production: CASR signaling modulates inflammatory cytokine release
NLRP3 inflammasome: CASR contributes to inflammasome activation

Role in Parkinson's Disease

Dopaminergic Neuron Survival

In the substantia nigra, CASR is expressed in dopaminergic neurons and affects their survival:

Mitochondrial function: CASR signaling modulates mitochondrial calcium handling
Oxidative stress: CASR activation can induce antioxidant responses
Apoptosis: CASR can be protective against apoptotic stimuli

Altered CASR expression has been documented in PD brain tissue, particularly in the substantia nigra. This dysregulation may contribute to the selective vulnerability of dopaminergic neurons in PD[@ye2019].

Alpha-Synuclein Aggregation

CASR may influence alpha-synuclein (α-syn) aggregation through:

Protein folding: CASR-mediated calcium changes affect protein folding quality control
Aggregation kinetics: Calcium can promote α-syn aggregation
Autophagy modulation: CASR affects autophagy pathways that clear aggregated proteins

Neuroinflammation in PD

Similar to AD, neuroinflammation plays a key role in PD pathogenesis, and CASR participates in:

Microglial activation: CNS immune cell responses
Peripheral inflammation: CASR in peripheral immune cells may affect CNS inflammation
Cytokine networks: Modulation of pro-inflammatory and anti-inflammatory cytokines

Role in Amyotrophic Lateral Sclerosis (ALS)

In ALS, CASR dysregulation has been observed in:

Motor neuron vulnerability: Altered calcium sensing in vulnerable motor neurons
Glial cells: CASR in astrocytes and microglia affects neuroinflammation
Muscle: CASR in neuromuscular junctions may affect transmission

The role of CASR in ALS is an emerging area of research with potential therapeutic implications.

Therapeutic Implications

Calcimimetics

Calcimimetic compounds that allosterically activate CASR have been developed for clinical use in secondary hyperparathyroidism. These compounds may have neuroprotective effects by:

Reducing parathyroid hormone (PTH) levels and associated secondary effects
Direct effects on neuronal CASR signaling
Modulation of systemic calcium homeostasis

However, CNS-penetrant calcimimetics are needed for direct central nervous system effects.

Calcilytics

Calcilytic compounds that antagonize CASR have been explored for:

Osteoporosis treatment (through PTH release)
Potential modulation of neuronal excitability

The therapeutic potential of calcilytics in neurodegenerative diseases remains to be explored.

Novel Therapeutic Strategies

Based on current understanding, several therapeutic approaches targeting CASR could be developed:

Brain-penetrant modulators: Designing calcimimetics or calcilytics that cross the blood-brain barrier

Allosteric modulators: Targeting specific allosteric sites for subtype-selective effects

Signal-biased ligands: Developing ligands that selectively activate beneficial signaling pathways

Gene therapy: Viral vector-mediated CASR expression modulation

Protein-protein interaction inhibitors: Disrupting pathological CASR interactions

Biomarker Potential

CASR expression or function may serve as a biomarker for:

Disease progression in AD and PD
Therapeutic response to calcium-modulating drugs
Neuronal injury and neurodegeneration

Research Challenges and Future Directions

Key Questions

Several fundamental questions about CASR in neurodegeneration remain:

Mechanistic understanding: What are the precise molecular mechanisms linking CASR to neurodegenerative processes?

Temporal dynamics: How does CASR dysfunction change across disease progression?

Cell-type specificity: What are the specific roles of CASR in different neural cell types?

Network effects: How does CASR dysfunction affect neural circuit function?

Therapeutic targeting: Can CASR be safely and effectively modulated for neuroprotection?

Research Tools Needed

Advancing the field requires:

Better animal models: Transgenic and conditional knockout models
Imaging tools: Live-cell calcium imaging and functional imaging
Cell-specific approaches: Cell-type-specific CASR manipulation
Clinical biomarkers: Peripheral and CSF markers of CASR function

Summary

The Calcium-Sensing Receptor (CASR) is a G protein-coupled receptor with emerging importance in neurodegenerative diseases. Originally characterized for its role in systemic calcium homeostasis, CASR is now recognized as having significant functions in the brain, where it affects synaptic plasticity, neuronal excitability, and neuroprotection.

In Alzheimer's disease, CASR contributes to amyloid processing, tau pathology, synaptic dysfunction, and neuroinflammation. In Parkinson's disease, CASR affects dopaminergic neuron survival, alpha-synuclein aggregation, and neuroinflammation. These connections make CASR an interesting therapeutic target, though significant research is needed to develop brain-penetrant modulators and understand the precise mechanistic connections.

External Links

[NCBI Gene: CASR](https://www.ncbi.nlm.nih.gov/gene/846)
[UniProt: CASR](https://www.uniprot.org/uniprot/Q9UII2)
[Ensembl: CASR](https://ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000036828)
[OMIM: CASR](https://omim.org/entry/601199)
[HGNC: CASR](https://www.genenames.org/data/hgnc_data.php?hgnc_id=1514)

References

[Caspi et al., Calcium-sensing receptor in brain (2012)](https://pubmed.ncbi.nlm.nih.gov/22480641/)

[Chaki et al., Calcium-sensing receptor and neurodegenerative diseases (2011)](https://pubmed.ncbi.nlm.nih.gov/22272122/)

[Mukhtar et al., Calcium-sensing receptor in Alzheimer's disease (2018)](https://pubmed.ncbi.nlm.nih.gov/30507367/)

[Ye et al., Calcium-sensing receptor dysfunction in Parkinson's disease (2019)](https://pubmed.ncbi.nlm.nih.gov/31176153/)

[Zhang et al., Calcium-sensing receptor-mediated neuroinflammation (2020)](https://pubmed.ncbi.nlm.nih.gov/32020475/)

[Lu et al., Calcium-sensing receptor and synaptic plasticity (2021)](https://pubmed.ncbi.nlm.nih.gov/33451984/)

Pathway Diagram

The following diagram shows the key molecular relationships involving CASR Gene discovered through SciDEX knowledge graph analysis:

Mermaid diagram (expand to render)

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CASR Gene

CASR Gene

CASR Gene

CASR — Calcium-Sensing Receptor

Overview

Gene Structure and Evolution

Protein Structure and Function

Extracellular Domain

Transmembrane Domain

Intracellular Domain and Signaling

Expression in the Brain

Regional Distribution

Cellular Localization

Physiological Functions in the Brain

Calcium Homeostasis at Synapses

Synaptic Plasticity

Neuronal Excitability

Neuroprotection

Role in Alzheimer's Disease

Amyloid Processing

Tau Pathology

Synaptic Dysfunction

Neuroinflammation

Role in Parkinson's Disease

Dopaminergic Neuron Survival

Alpha-Synuclein Aggregation

Neuroinflammation in PD

Role in Amyotrophic Lateral Sclerosis (ALS)

Therapeutic Implications

Calcimimetics

Calcilytics

Novel Therapeutic Strategies

Biomarker Potential

Research Challenges and Future Directions

Key Questions

Research Tools Needed

Summary

External Links

References

See Also

Pathway Diagram