CPT2

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CPT2

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CPT2

<div class="infobox infobox-gene">
<div class="infobox-header">CPT2</div>
<div class="infobox-content">
<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>
</div>
</div>

Overview

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CPT2

<div class="infobox infobox-gene">
<div class="infobox-header">CPT2</div>
<div class="infobox-content">
<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>
</div>
</div>

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 released

Physiological 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.

Metabolic Roles

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)

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