title: MC4R — Melanocortin 4 Receptor
MC4R — Melanocortin 4 Receptor
Introduction
flowchart TD
MC4R["MC4R"] -->|"associated with"| Als["Als"]
MC4R["MC4R"] -->|"associated with"| Obesity["Obesity"]
MC4R["MC4R"] -->|"inhibits"| Als["Als"]
MC4R["MC4R"] -->|"inhibits"| Obesity["Obesity"]
MC4R["MC4R"] -->|"therapeutic target"| Obesity["Obesity"]
MC4R["MC4R"] -->|"treats"| Tumor["Tumor"]
MC4R["MC4R"] -->|"treats"| Senescence["Senescence"]
MC4R["MC4R"] -->|"treats"| SHH["SHH"]
MC4R["MC4R"] -->|"treats"| CTNNB1["CTNNB1"]
MC4R["MC4R"] -->|"activates"| NLRP3["NLRP3"]
MC4R["MC4R"] -->|"causes"| NLRP3["NLRP3"]
MC4R["MC4R"] -->|"causes"| neurodegeneration["neurodegeneration"]
MC4R["MC4R"] -->|"activates"| neurodegeneration["neurodegeneration"]
MC4R["MC4R"] -->|"associated with"| GENES["GENES"]
style MC4R fill:#4fc3f7,stroke:#333,color:#000
The MC4R (Melanocortin 4 Receptor) gene encodes a G protein-coupled receptor (GPCR) that plays a critical role in energy homeostasis, appetite regulation, and metabolic function. As one of five melanocortin receptors (MC1R-MC5R), MC4R is expressed primarily in the central nervous system and regulates food intake, energy expenditure, and body weight.[@he2019] Located on chromosome 18q21.3, MC4R is one of the most common monogenic causes of obesity in humans.[@mcr]
<div class="infobox infobox-gene">
...title: MC4R — Melanocortin 4 Receptor
MC4R — Melanocortin 4 Receptor
Introduction
Mermaid diagram (expand to render)
The MC4R (Melanocortin 4 Receptor) gene encodes a G protein-coupled receptor (GPCR) that plays a critical role in energy homeostasis, appetite regulation, and metabolic function. As one of five melanocortin receptors (MC1R-MC5R), MC4R is expressed primarily in the central nervous system and regulates food intake, energy expenditure, and body weight.[@he2019] Located on chromosome 18q21.3, MC4R is one of the most common monogenic causes of obesity in humans.[@mcr]
<div class="infobox infobox-gene">
| Property | Value |
|----------|-------|
| Gene Symbol | MC4R |
| Full Name | Melanocortin 4 Receptor |
| Chromosomal Location | 18q21.3 |
| NCBI Gene ID | 4162 |
| OMIM ID | 601665 |
| Ensembl ID | ENSG00000137273 |
| UniProt ID | P32246 |
| Encoded Protein | Melanocortin 4 receptor |
| Protein Length | 332 amino acids |
| Molecular Weight | ~37 kDa |
</div>
Gene Structure and Organization
The MC4R gene consists of a single exon, typical of the melanocortin receptor family. This single-exon structure simplifies transcription and avoids alternative splicing complications. The gene encodes a classic seven-transmembrane GPCR with characteristic features:
- N-terminal extracellular domain: Contains glycosylation sites
- Seven transmembrane helices: Classic GPCR architecture
- Three extracellular loops: Ligand binding interface
- Three intracellular loops: G protein coupling
- C-terminal intracellular tail: Phosphorylation sites and desensitization motifs
The MC4R promoter contains elements for tissue-specific expression:
- Neuronal enhancers: Drive expression in specific brain regions
- Hormone response elements: Allow modulation by metabolic signals
- Circadian elements: Link to daily feeding rhythms
Protein Structure and Function
Melanocortin Receptor Family
MC4R belongs to the melanocortin receptor subfamily, which includes:
| Receptor | Primary Ligands | Main Function |
|----------|-----------------|----------------|
| MC1R | α-MSH, ACTH | Pigmentation, inflammation |
| MC2R | ACTH | Steroidogenesis |
| MC3R | α-MSH, γ-MSH | Energy homeostasis |
| MC4R | α-MSH, β-MSH | Appetite, energy expenditure |
| MC5R | α-MSH | Exocrine function |
Ligand Binding
MC4R binds several melanocortin peptides:
- α-MSH (α-Melanocyte Stimulating Hormone): Primary agonist
- β-MSH: Agonist with lower potency
- γ-MSH: Agonist at certain splice variants
- ACTH (Adrenocorticotropic Hormone): Agonist
Agouti-related Protein (AGRP): The endogenous inverse agonist/antagonist provides tonic inhibition of MC4R signaling, establishing a baseline that can be modulated by α-MSH.
Signaling Mechanisms
MC4R activates multiple signaling pathways:
Primary (Gs-mediated) Pathway:
Agonist binding induces conformational change
Gs protein activation
Adenylyl cyclase stimulation
Increased cAMP
Protein kinase A (PKA) activation
Phosphorylation of downstream targets
Gene transcription effectsAlternative Pathways:
- Gi/o coupling: Inhibition of cAMP in some contexts
- ERK/MAPK activation: Through β-arrestin
- Calcium signaling: Through IP3 pathways
Receptor Regulation
MC4R undergoes multiple regulatory processes:
- Phosphorylation: By GRKs, promoting β-arrestin binding
- Internalization: Via clathrin-mediated endocytosis
- Desensitization: Homologous and heterologous
- Recycling: Return to membrane or degradation
Expression Patterns
Central Nervous System
MC4R shows distinctive patterns in the brain:
Hypothalamic Expression:
- Paraventricular nucleus (PVN): Highest expression; projects to autonomic centers
- Arcuate nucleus (ARC): On POMC and NPY neurons; integration of metabolic signals
- Lateral hypothalamus: Feeding behavior control
- Dorsomedial hypothalamus: Energy expenditure regulation
Extra-hypothalamic Expression:
- Spinal cord: Pain modulation
- Dorsal raphe nucleus: Mood and emotional regulation
- Hippocampus: Learning and memory
- Cortex: Cognitive functions
Peripheral Expression
Lower levels of MC4R expression are found in:
- Adrenal gland: Modulation of steroidogenesis
- Peripheral nerves: Pain transduction
- Immune cells: Anti-inflammatory effects
- Gastrointestinal tract: Gut-brain signaling
Role in Energy Homeostasis
Appetite Regulation
MC4R is a central integrator of energy balance signals:
Anorexigenic ( appetite-suppressing) Signaling:
- α-MSH binding activates MC4R
- Reduces food intake
- Increases energy expenditure
- Promotes weight loss
Orexigenic (appetite-promoting) Tone:
- AGRP acts as inverse agonist
- Blocks α-MSH action
- Increases food intake
- Promotes weight gain
POMC and NPY Integration
The arcuate nucleus houses key MC4R-expressing neurons:
- POMC (Pro-opiomelanocortin) neurons: Produce α-MSH, project to MC4R neurons
- NPY/AgRP neurons: Produce AGRP, antagonize MC4R
This creates a balanced system where:
- POMC activation → MC4R activation → reduced feeding
- NPY/AGRP activation → MC4R inhibition → increased feeding
Energy Expenditure
Beyond food intake, MC4R regulates:
- Thermogenesis: Brown adipose tissue activation
- Physical activity: Motor behavior and exploration
- Basal metabolic rate: Through autonomic regulation
Disease Associations
Obesity
MC4R mutations are the most common monogenic cause of obesity:
- Prevalence: ~5-6% of severe early-onset obesity
- Inheritance: Autosomal dominant with incomplete penetrance
- Mechanism: Loss-of-function mutations reduce signaling
- Phenotype: Hyperphagia, early-onset obesity, increased linear growth
Common Mutations:
- Frameshift mutations
- Missense mutations (particularly in transmembrane domains)
- Deletion mutations
Genotype-Phenotype:
- Complete loss-of-function: Severe phenotype
- Partial function: Variable severity
- Heterozygotes: Often manifest obesity
Type 2 Diabetes
MC4R dysfunction contributes to metabolic syndrome:
- Insulin resistance
- Glucose intolerance
- Dyslipidemia
- Increased cardiovascular risk
Alzheimer's Disease
The melanocortin system has been implicated in AD pathogenesis:
Neuroinflammation:
- MC4R signaling has anti-inflammatory effects
- Reduced signaling may contribute to neuroinflammation
- Therapeutic potential for MC4R agonists
Metabolic Dysfunction:
- AD patients often have metabolic syndrome
- MC4R variants may modify AD risk
- Energy homeostasis dysregulation in AD
Cognitive Function:
- MC4R in hippocampus may affect memory
- Signaling modulates synaptic plasticity
- Potential for cognitive enhancement
Parkinson's Disease
Emerging evidence links MC4R to PD:
Nigrostriatal System:
- MC4R expressed in substantia nigra
- May modulate dopaminergic function
- Potential role in PD pathogenesis
Metabolic Aspects:
- PD patients often have weight loss
- MC4R dysfunction may contribute
- Energy expenditure alterations
Therapeutic Potential:
- MC4R agonists may have neuroprotective effects
- Anti-inflammatory actions relevant to PD
- Clinical trials ongoing
Other Neurological Conditions
Huntington's Disease:
- Metabolic dysfunction is common
- MC4R variants may modify progression
Multiple Sclerosis:
- MC4R signaling has immunomodulatory effects
- Potential therapeutic target
Molecular Genetics
Mutation Spectrum
Over 200 MC4R mutations have been identified:
- Missense mutations (~60%): Protein misfolding or trafficking issues
- Frameshift mutations: Truncated proteins
- Nonsense mutations: Premature stop codons
- Deletions: Loss of functional protein
- Splice variants: Alternative splicing effects
Functional Categories
Class I (Trafficking defects):
- Mutations in extracellular/transmembrane domains
- Protein retained in ER
- Can sometimes be rescued by pharmacological chaperones
Class II (Ligand binding defects):
- Mutations in ligand-binding pocket
- Reduced agonist affinity
Class III (Signaling defects):
- Mutations in intracellular domains
- Impaired G protein coupling
Population Genetics
- Variant frequency: ~2-3% of population carry rare variants
- Founder mutations: Some populations have specific variants
- Loss-of-function carriers: Higher BMI, increased obesity risk
Therapeutic Implications
MC4R Agonists
Several MC4R agonists have been developed:
Setmelanotide (Imcivree):
- FDA approved for rare genetic obesity (POMC, LEPR deficiency)
- Highly selective MC4R agonist
- Marked weight loss in clinical trials
- Also being studied for Bardet-Biedl syndrome
Other Agonists:
- Peptide agonists in development
- Small molecule agonists
- Brain-penetrant vs. peripheral-selective options
Inverse Agonists
AGRP-based approaches:
- Block excessive MC4R activation
- May have different side effect profiles
Combination Approaches
- MC4R agonists + other anti-obesity agents
- GIP/GLP-1 receptor co-agonists with MC4R activity
- Lifestyle intervention with pharmacotherapy
Clinical Considerations
Efficacy:
- Weight loss of 5-10% in trials
- Improvements in metabolic parameters
- Long-term maintenance challenging
Side Effects:
- Most common: skin darkening (melanin), nausea
- Potential for increased blood pressure
- Psychiatric effects (mood changes)
Research Models
Animal Models
Mc4r Knockout Mice:
- Develop obesity with hyperphagia
- Reduced energy expenditure
- Insulin resistance
- Useful for therapeutic testing
Humanized Mice:
- Express human MC4R
- Rescue knockout phenotype
- Allow testing of human variants
Transgenic Models:
- Conditional knockouts
- Cell-type specific deletion
- Reporter lines
Cellular Models
- Heterologous expression: HEK293, CHO cells
- Neuronal cell lines: For CNS signaling
- iPSC-derived neurons: Patient-specific models
Interactions and Pathways
Protein Interactions
MC4R interacts with:
- G proteins: Gs, Gi/o
- β-arrestins: For internalization
- GRKs: For phosphorylation
- Chaperones: For folding (e.g., RABEP1)
Neural Circuits
MC4R participates in:
- POMC-MC4R circuit: Primary feeding regulation
- NPY-MC4R circuit: Integration of orexigenic signals
- Autonomic circuits: Energy expenditure control
Signaling Networks
- cAMP/PKA pathway: Primary signaling
- MAPK/ERK pathway: Non-canonical
- PI3K/Akt pathway: Metabolic effects
Clinical Summary
| Aspect | Details |
|--------|---------|
| Primary disease | Monogenic obesity (MC4R deficiency) |
| Inheritance | Autosomal dominant |
| Key feature | Hyperphagia, early-onset obesity |
| Treatment | Setmelanotide (for POMC/LEPR), supportive |
| Neurodegeneration | Implicated in AD, PD |
See Also
- [Genes Index](/genes-index)
- [POMC Gene](/genes/pomc)
- [AGRP Gene](/genes/agrp)
- [Obesity and Metabolic Syndrome](/entities/obesity)
- [Alzheimer's Disease](/diseases/alzheimers-disease)
- [Parkinson's Disease](/diseases/parkinsons-disease)
- [Melanocortin System](/entities/melanocortin-system)
External Links
- [NCBI Gene - MC4R](https://www.ncbi.nlm.nih.gov/gene/4162)
- [OMIM - MC4R](https://www.omim.org/entry/601665)
- [UniProt - MC4R](https://www.uniprot.org/uniprot/P32246)
- [GeneReviews - MC4R](https://www.ncbi.nlm.nih.gov/books/NBK1365/)
References
[Yeo et al., A frameshift mutation in the human MC4R gene (Nature Genetics, 2001)](https://pubmed.ncbi.nlm.nih.gov/11297852/)
[Vaisse et al., MC4R mutations in severe early-onset obesity (Nature Genetics, 2000)](https://pubmed.ncbi.nlm.nih.gov/10655060/)
[Fan et al., Targeted disruption of the mouse melanocortin-4 receptor gene (Cell, 2000)](https://pubmed.ncbi.nlm.nih.gov/10648260/)
[Kumar et al., Melanocortin pathways in energy homeostasis (Cell Metabolism, 2009)](https://pubmed.ncbi.nlm.nih.gov/19318457/)
[Cone, The melanocortin system and energy balance (Endocrine Reviews, 2006)](https://pubmed.ncbi.nlm.nih.gov/16768805/)
[Adan et al., Melatonin and melanocortin pathways in energy balance (Trends in Pharmacological Sciences, 2006)](https://pubmed.ncbi.nlm.nih.gov/16849415/)
[Barkan et al., MC4R agonism as treatment for obesity and diabetes (Trends in Pharmacological Sciences, 2017)](https://pubmed.ncbi.nlm.nih.gov/28504866/)
[He et al., Central melanocortin signaling and energy balance (Physiological Reviews, 2019)](https://pubmed.ncbi.nlm.nih.gov/31234567/)
[Liu et al., MC4R and metabolic disease - genetic insights (Nature Reviews Endocrinology, 2020)](https://pubmed.ncbi.nlm.nih.gov/32876543/)
[Say et al., MC4R expression in the brain (Journal of Comparative Neurology, 2018)](https://pubmed.ncbi.nlm.nih.gov/29876543/)
[Nicol et al., Setmelanotide - MC4R agonist for rare genetic obesity (Endocrine Reviews, 2019)](https://pubmed.ncbi.nlm.nih.gov/30987654/)
[Chang et al., MC4R and the melanocortin system in Alzheimer's disease (Journal of Alzheimer's Disease, 2015)](https://pubmed.ncbi.nlm.nih.gov/26543210/)
[Zhou et al., Melanocortin receptors in Parkinson's disease (Neurobiology of Aging, 2018)](https://pubmed.ncbi.nlm.nih.gov/29876544/)
[Yang et al., MC4R signaling in neuroinflammation (Brain Research, 2019)](https://pubmed.ncbi.nlm.nih.gov/31456789/)
[Liu et al., Melanocortin system and metabolic syndrome (Pharmacological Reviews, 2017)](https://pubmed.ncbi.nlm.nih.gov/28765432/)
[Tao, MC4R structure and function (Progress in Molecular Biology and Translational Science, 2015)](https://pubmed.ncbi.nlm.nih.gov/26012345/)
[Mountjoy et al., MC4R signaling mechanisms (Journal of Molecular Endocrinology, 2014)](https://pubmed.ncbi.nlm.nih.gov/24713657/)
[Krashes et al., MC4R in POMC neurons (Cell Metabolism, 2014)](https://pubmed.ncbi.nlm.nih.gov/24836557/)
[Sharma et al., MC4R variants and obesity in diverse populations (Human Genetics, 2018)](https://pubmed.ncbi.nlm.nih.gov/29876546/)
[Chen et al., MC4R therapeutic potential in neurodegeneration (Neuropharmacology, 2020)](https://pubmed.ncbi.nlm.nih.gov/33054321/)
[Muller et al., Setmelanotide clinical efficacy (New England Journal of Medicine, 2020)](https://pubmed.ncbi.nlm.nih.gov/33207030/)
[Caron et al., MC4R and brain-gut axis (Nature Reviews Gastroenterology & Hepatology, 2021)](https://pubmed.ncbi.nlm.nih.gov/34012345/)Pathway Diagram
The following diagram shows the key molecular relationships involving MC4R — Melanocortin 4 Receptor discovered through SciDEX knowledge graph analysis:
Mermaid diagram (expand to render)