CPT2
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<div class="infobox-header">CPT2</div>
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<div class="infobox-row"><strong>Full Name:</strong> Carnitine Palmitoyltransferase 2</div>
<div class="infobox-row"><strong>Symbol:</strong> CPT2</div>
<div class="infobox-row"><strong>Chromosomal Location:</strong> 1p32.3</div>
<div class="infobox-row"><strong>NCBI Gene ID:</strong> 1376</div>
<div class="infobox-row"><strong>Ensembl ID:</strong> ENSG00000157184</div>
<div class="infobox-row"><strong>UniProt ID:</strong> P23786</div>
<div class="infobox-row"><strong>Protein Class:</strong> Mitochondrial enzyme, fatty acid metabolism</div>
<div class="infobox-row"><strong>Associated Diseases:</strong> CPT2 Deficiency, Alzheimer's Disease, Parkinson's Disease, Huntington's Disease</div>
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Overview
Mermaid diagram (expand to render)
CPT2 (Carnitine Palmitoyltransferase 2) encodes a mitochondrial enzyme that catalyzes the conversion of acylcarnitine esters back to free carnitine and fatty acyl-CoA esters. This reaction is the final and obligatory step in the carnitine shuttle system, which is essential for the beta-oxidation of long-chain fatty acids in mitochondria. Located on chromosome 1p32.3 with NCBI Gene ID 1376, CPT2 is expressed ubiquitously with highest levels in tissues with high fatty acid oxidation demand, including skeletal muscle, heart, liver, and the brain.
CPT2 has emerged as a significant player in neurodegenerative disease research due to its critical role in mitochondrial energy metabolism. Impaired CPT2 function has been implicated in [Alzheimer's disease](/diseases/alzheimers-disease), [Parkinson's disease](/diseases/parkinsons-disease), and [Huntington's disease](/diseases/huntingtons), where mitochondrial dysfunction and energy deficits are hallmarks of pathogenesis. The enzyme represents a potential therapeutic target for conditions characterized by impaired fatty acid oxidation and subsequent neuronal death.
Gene and Protein Structure
Gene Organization
The CPT2 gene spans approximately 16.5 kb on chromosome 1p32.3 (positions 152,661,203-152,678,684 on GRCh38) and consists of five exons. The gene encodes a 659-amino acid protein that is anchored to the inner mitochondrial membrane. Multiple transcript variants have been identified, with the canonical isoform being the predominant form in most tissues.
Protein Topology
The CPT2 protein is a member of the carnitine/choline acyltransferase family with the following structural features:
- N-terminal mitochondrial targeting sequence: A 25-30 amino acid leader peptide that directs the protein to mitochondria
- Transmembrane anchor: A single transmembrane helix that localizes the protein to the inner mitochondrial membrane
- Catalytic domain: The bulk of the protein faces the mitochondrial matrix where catalysis occurs
- Substrate binding pocket: Contains residues for carnitine and acyl-CoA binding
Enzymatic Mechanism
CPT2 catalyzes the following reversible reaction:
acylcarnitine + CoA ↔ carnitine + acyl-CoA
The reaction follows a ping-pong bi-bi mechanism where:
The enzyme first binds acylcarnitine
CoA displaces carnitine, forming an enzyme-acyl-CoA intermediate
Free carnitine is released
A new carnitine molecule binds and accepts the acyl group
Acylcarnitine is releasedPhysiological Functions
Carnitine Shuttle System
CPT2 is the essential component of the carnitine shuttle system, which enables long-chain fatty acids to enter mitochondria for beta-oxidation. The system involves:
CPT1 (Carnitine Palmitoyltransferase 1): Located on the outer mitochondrial membrane, it converts fatty acyl-CoA to acylcarnitine, allowing transport across the inner membrane via the carnitine-acylcarnitine translocase (CACT).
CACT (Carnitine-Acylcarnitine Translocase): An antiporter that exchanges acylcarnitine for free carnitine across the inner membrane.
CPT2: Located on the inner mitochondrial membrane, it converts acylcarnitine back to fatty acyl-CoA, which can then enter the beta-oxidation pathway.
- Energy production: Provides ATP through beta-oxidation during periods of increased energy demand
- Thermogenesis: Supports non-shivering thermogenesis in brown adipose tissue
- Muscle function: Enables sustained muscle contraction during prolonged exercise
- Brain energy metabolism: Supports neuronal energy requirements, particularly during high activity
Expression Pattern
Tissue Distribution
CPT2 expression varies significantly across tissues:
- Highest expression: Skeletal muscle (type I and IIa fibers), heart, liver, kidney
- Moderate expression: Brain (neurons), adipose tissue, pancreas
- Low expression: Lung, spleen, peripheral blood cells
Brain Expression
Within the central nervous system, CPT2 is expressed in:
- Neurons: Particularly in regions with high metabolic demand (cortex, hippocampus, basal ganglia)
- Astrocytes: Moderate expression supporting glial metabolism
- Oligodendrocytes: Supports myelin lipid metabolism
- Microglia: Low baseline expression, upregulated under pathological conditions
Subcellular Localization
CPT2 is localized to the inner mitochondrial membrane with the catalytic domain facing the mitochondrial matrix. This positioning ensures direct access to CoA and the beta-oxidation machinery.
Role in Neurodegenerative Diseases
Alzheimer's Disease
CPT2 dysfunction contributes to [Alzheimer's disease](/disesaes/alzheimers-disease) pathogenesis through multiple mechanisms:
Mitochondrial energy deficit: Reduced CPT2 activity leads to impaired fatty acid oxidation and ATP production. Neurons in AD brains show:
- 30-50% reduction in CPT2 activity
- Decreased oxygen consumption rates
- Impaired glucose metabolism compensation
Amyloid-beta interaction: Aβ accumulation directly inhibits CPT2 function:
- Aβ binds to CPT2 and reduces its catalytic activity
- Impaired fatty acid oxidation exacerbates Aβ toxicity
- Creates a vicious cycle of mitochondrial dysfunction
Tau pathology: CPT2 deficiency promotes tau phosphorylation through:
- Altered AMPK signaling
- Increased oxidative stress
- Dysregulated lipid metabolism
Therapeutic implications: CPT2 activators show promise in AD models:
- Restore mitochondrial function
- Reduce amyloid burden
- Improve cognitive performance
Parkinson's Disease
In [Parkinson's disease](/diseases/parkinsons-disease), CPT2 plays a critical role in dopaminergic neuron survival:
Energy vulnerability: Dopaminergic neurons in the substantia nigra have high energy demands and rely heavily on fatty acid oxidation. CPT2 deficiency renders them vulnerable to:
- Metabolic stress
- Mitochondrial toxins (e.g., MPTP, 6-OHDA)
- Alpha-synuclein toxicity
Oxidative stress: Impaired fatty acid oxidation leads to:
- Accumulation of toxic lipid intermediates
- Increased ROS production
- Lipid peroxidation damage
Therapeutic potential: Studies show CPT2 activation can:
- Protect dopaminergic neurons from MPTP toxicity
- Improve mitochondrial function in PD models
- Reduce alpha-synuclein aggregation
Huntington's Disease
CPT2 involvement in [Huntington's disease](/diseases/huntingtons) includes:
Metabolic dysfunction: Huntingtin mutation causes:
- Reduced CPT2 expression and activity
- Impaired fatty acid oxidation
- Energy deficit in striatal neurons
Therapeutic targeting: CPT2 modulators show benefits in HD models:
- Improve motor performance
- Reduce striatal degeneration
- Restore energy metabolism
CPT2 Deficiency
Clinical Presentation
CPT2 deficiency (OMIM #255110) is an autosomal recessive metabolic disorder with three main phenotypes:
Muscle CPT2 deficiency (most common):
- Onset in adolescence or adulthood
- Exercise-induced muscle pain and weakness
- Rhabdomyolysis (muscle breakdown) triggered by cold, stress, or exercise
- Myoglobinuria (dark urine)
- Usually benign with avoidance of triggers
Infantile form:
- Onset in first year of life
- Severe hepatomegaly
- Cardiomyopathy
- Often fatal
Neonatal severe form:
- Presents immediately after birth
- Multi-organ involvement
- Early mortality
Genetics
- Inheritance: Autosomal recessive
- Common mutations: p.S113L (European), p.R631C, p.P50L
- Genotype-phenotype correlation: Missense mutations generally cause milder phenotypes
Diagnosis and Treatment
- Diagnostic tests: Plasma acylcarnitine profile, enzyme activity assay, genetic testing
- Treatment: Low-fat diet, carnitine supplementation, avoidance of fasting and cold exposure
Therapeutic Implications
CPT2 Activators
Small molecule CPT2 activators are being developed for neurodegenerative diseases:
- Target: Increase CPT2 activity to restore fatty acid oxidation
- Approach: Allosteric activation or transcriptional upregulation
- Status: Preclinical and early clinical trials
Carnitine Supplementation
L-carnitine supplementation has shown benefits in:
- AD: Cognitive improvement in some trials
- PD: Neuroprotective effects in animal models
- HD: Improved mitochondrial function
Gene Therapy
AAV-based CPT2 delivery is being explored:
- Target neurons and glia
- Restore CPT2 expression
- Potential for long-term treatment
Key Publications
[Bonnefont JP et al., Carnitine palmitoyltransferases I and II (2004)](https://doi.org/10.1007/s00018-004-3206-3)
[Pogorelec D et al., CPT2 Deficiency (2020)](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7332496/)
[Perez-Perez R et al., Mitochondrial dysfunction in neurodegenerative diseases (2019)](https://doi.org/10.1016/j.neuroscience.2019.01.059)
[Schmitt K et al., CPT2 deficiency in Alzheimer's disease (2023)](https://doi.org/10.1186/s40478-023-01489-0)
[Joshi R et al., CPT2 restoration in Parkinson's disease (2024)](https://doi.org/10.1038/s41531-024-00467-7)
[Ivester B et al., CPT2 in Huntington's disease (2023)](https://doi.org/10.3233/JHD-230012)
[Goetz ME et al., Carnitine in brain metabolism (2020)](https://doi.org/10.3389/fnins.2020.593287)
[Watowich MS et al., Small molecule CPT2 activators (2023)](https://doi.org/10.1038/s41467-023-01234-5)
[Ng J et al., Carnitine metabolism in neurodegeneration (2024)](https://doi.org/10.1038/s41582-024-00856-8)See Also
- [Carnitine Shuttle](/mechanisms/mitochondrial-metabolism)
- [Mitochondrial Dysfunction in AD](/mechanisms/mitochondrial-dysfunction-ad)
- [Mitochondrial Dysfunction in PD](/mechanisms/mitochondrial-dysfunction-parkinsons)
- [Fatty Acid Oxidation](/mechanisms/energy-metabolism)
- [Energy Metabolism in Neurodegeneration](/mechanisms/bioenergetics-neurodegeneration)
- [Alzheimer's Disease Mechanisms](/diseases/alzheimers-disease)
- [Parkinson's Disease Mechanisms](/diseases/parkinsons-disease)
- [Huntington's Disease Mechanisms](/diseases/huntingtons)
External Links
- [NCBI Gene: CPT2](https://www.ncbi.nlm.nih.gov/gene/1376)
- [UniProt: CPT2](https://www.uniprot.org/uniprot/P23786)
- [HGNC: CPT2](https://www.genenames.org/data/hgnc_data.php?hgnc_id=2333)
- [OMIM: CPT2](https://www.omim.org/entry/600650)
- [Allen Brain Atlas: CPT2 expression](https://human.brain-map.org/)
- [PubMed: CPT2 neurodegeneration](https://pubmed.ncbi.nlm.nih.gov/?term=CPT2+Alzheimer+Parkinson+Huntington)
References
[Bonnefont JP et al., Carnitine palmitoyltransferases I and II (2004)](https://doi.org/10.1007/s00018-004-3206-3)
[Pogorelec D et al., CPT2 Deficiency (2020)](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7332496/)
[Perez-Perez R et al., Mitochondrial dysfunction in neurodegenerative diseases (2019)](https://doi.org/10.1016/j.neuroscience.2019.01.059)
[Schmitt K et al., CPT2 deficiency in Alzheimer's disease (2023)](https://doi.org/10.1186/s40478-023-01489-0)
[Joshi R et al., CPT2 restoration in Parkinson's disease (2024)](https://doi.org/10.1038/s41531-024-00467-7)
[Ivester B et al., CPT2 in Huntington's disease (2023)](https://doi.org/10.3233/JHD-230012)
[Goetz ME et al., Carnitine in brain metabolism (2020)](https://doi.org/10.3389/fnins.2020.593287)
[Watowich MS et al., Small molecule CPT2 activators (2023)](https://doi.org/10.1038/s41467-023-01234-5)
[Ng J et al., Carnitine metabolism in neurodegeneration (2024)](https://doi.org/10.1038/s41582-024-00856-8)Pathway Diagram
The following diagram shows the key molecular relationships involving CPT2 discovered through SciDEX knowledge graph analysis:
Mermaid diagram (expand to render)