Peroxisomes are essential cellular organelles that play critical roles in lipid metabolism, reactive oxygen species (ROS) detoxification, and the oxidation of very long-chain fatty acids (VLCFAs). These single-membrane-bound organelles are present in virtually all eukaryotic cells and perform essential metabolic functions including fatty acid beta-oxidation, ether phospholipid synthesis, and hydrogen peroxide (H2O2) metabolism.
Emerging evidence demonstrates that peroxisomal dysfunction plays a critical role in the pathogenesis of neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and Huntington's disease (HD). The peroxisome-proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) pathway and peroxisomal biogenesis disorders have been increasingly linked to neurodegeneration, establishing peroxisomes as important therapeutic targets[@jo2019].
```mermaid
graph TD
A["Peroxisome Function"] --> B["Fatty Acid Oxidation"]
A --> C["H2O2 Detoxification"]
A --> D["Ether Lipid Synthesis"]
B --> E["VLCFA Metabolism"]
E --> F["Neurotoxicity"]
C --> G["Oxidative Stress"]
G --> H["Neuronal Death"]
D --> I["Plasmalogen Synthesis"]
I --> J["Myelin Stability"]
K["Peroxisomal Dysfunction"] --> L["AD Pathogenesis"]
K --> M["PD Pathogenesis"]
K --> N["ALS Pathogenesis"]
Peroxisomes are essential cellular organelles that play critical roles in lipid metabolism, reactive oxygen species (ROS) detoxification, and the oxidation of very long-chain fatty acids (VLCFAs). These single-membrane-bound organelles are present in virtually all eukaryotic cells and perform essential metabolic functions including fatty acid beta-oxidation, ether phospholipid synthesis, and hydrogen peroxide (H2O2) metabolism.
Emerging evidence demonstrates that peroxisomal dysfunction plays a critical role in the pathogenesis of neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and Huntington's disease (HD). The peroxisome-proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) pathway and peroxisomal biogenesis disorders have been increasingly linked to neurodegeneration, establishing peroxisomes as important therapeutic targets[@jo2019].
Peroxisomes are dynamic organelles that perform over 60 different biochemical reactions through more than 50 distinct enzymes in the peroxisomal matrix. The biogenesis of peroxisomes requires the coordinated function of over 35 PEX proteins, which are involved in peroxisomal membrane assembly, protein import, and matrix enzyme import[@steinberg2020].
Catalase is one of the most abundant peroxisomal enzymes, constituting up to 20% of the total peroxisomal protein content. It catalyzes the decomposition of hydrogen peroxide into water and oxygen, playing a critical role in cellular antioxidant defense. Deficiencies in catalase activity have been documented in multiple neurodegenerative diseases[@antonenkov2020].
Acyl-CoA oxidase (ACOX1) initiates fatty acid beta-oxidation by oxidizing very long-chain fatty acids. This enzyme produces hydrogen peroxide as a byproduct, which is then detoxified by catalase. The coordinated function of ACOX1, enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase (MFP1/HD), and 3-ketoacyl-CoA thiolase enables complete VLCFA oxidation[@wanders2021].
Peroxisomal matrix proteins are synthesized in the cytosol and imported post-translationally through a specialized import machinery involving PEX5 and PEX7 receptors. The import system recognizes specific targeting signals (PTS1 and PTS2) on the C-terminus and N-terminus of matrix proteins. Mutations affecting this import system cause severe peroxisome biogenesis disorders (PBDs)[@ghosh2020].
Multiple studies have documented peroxisomal abnormalities in Alzheimer's disease brain tissue. Reduced peroxisome numbers, decreased catalase activity, and impaired VLCFA metabolism have been reported in AD patients and animal models[@santos2020].
The amyloid-beta (Aβ) peptide, the hallmark protein of AD, directly impairs peroxisomal function by reducing the expression of PEX genes and peroxisomal enzymes. Aβ interacts with peroxisomal membrane proteins and disrupts the import of matrix enzymes, leading to reduced catalase activity and impaired fatty acid oxidation. Additionally, Aβ promotes the aggregation of peroxisomal proteins and disrupts peroxisomal membrane integrity[@zhong2022].
The peroxisome-proliferator-activated receptor gamma (PPARγ) pathway, which regulates peroxisomal biogenesis and function, is downregulated in AD brain. This reduction in PPARγ activity leads to decreased peroxisome numbers and impaired lipid metabolism, creating a vicious cycle where metabolic dysfunction promotes Aβ production and aggregation[@wang2021].
Lipid metabolism is significantly altered in AD, and peroxisomes play a central role in maintaining lipid homeostasis. AD brain tissue exhibits reduced levels of ether phospholipids (plasmalogens), which are essential for normal neuronal function and synaptic plasticity. This reduction correlates with decreased peroxisome numbers and impaired peroxisomal enzyme activity[@han2020].
Very long-chain fatty acid (VLCFA) levels are elevated in AD brain and cerebrospinal fluid. The accumulation of VLCFAs promotes Aβ production and aggregation through multiple mechanisms, including altered amyloid precursor protein (APP) processing and increased oxidative stress. The peroxisomal dysfunction in AD creates a feed-forward loop that exacerbates disease progression[@schnknecht2021].
Peroxisomal dysfunction has also been implicated in Parkinson's disease pathogenesis. The lipid composition of substantia nigra neurons, which are particularly vulnerable in PD, is highly dependent on peroxisomal metabolism. Studies have shown reduced peroxisome numbers and altered peroxisomal enzyme expression in PD brain tissue[@beyer2021].
The protein [alpha-synuclein](/proteins/alpha-synuclein), which forms Lewy bodies in PD, localizes to peroxisomes and impairs peroxisomal function. This interaction disrupts hydrogen peroxide metabolism and leads to increased oxidative stress, which contributes to dopaminergic neuron death. Alpha-synuclein accumulation in peroxisomes also impairs the import of catalase and other antioxidant enzymes[@oaks2021].
Mutations in [PINK1](/genes/pink1) (PTEN-induced kinase 1) and [PARKIN](/genes/parkin) are linked to familial forms of PD. These proteins are involved in mitochondrial quality control through mitophagy, but they also regulate peroxisomal quality control through pexophagy. Dysregulation of pexophagy in PD leads to the accumulation of abnormal peroxisomes in dopaminergic neurons[@mcwilliams2020].
The substantia nigra in PD shows specific alterations in peroxisomal lipid metabolism. Reduced levels of plasmalogens, which are ether phospholipids synthesized in peroxisomes, have been documented in PD brain and blood samples. These lipid alterations may contribute to dopaminergic neuron vulnerability and disease progression[@vance2022].
Peroxisomal dysfunction has been implicated in ALS, a progressive neurodegenerative disease affecting motor neurons. Studies have shown reduced peroxisome numbers and altered peroxisomal enzyme expression in ALS brain and spinal cord tissue. Mutations in genes involved in peroxisomal biogenesis have been linked to some cases of familial ALS[@song2021].
The relationship between [TDP-43](/proteins/tdp-43) pathology, which is characteristic of most ALS cases, and peroxisomal dysfunction is an area of active investigation. TDP-43 aggregates may impair peroxisomal function, contributing to motor neuron degeneration.
Peroxisomal abnormalities have been reported in [Huntington's disease](diseases/huntingtons) (HD), an autosomal dominant neurodegenerative disorder caused by CAG repeat expansion in the HTT gene. Reduced peroxisome numbers and impaired peroxisomal enzyme activity have been documented in HD models and patient tissue. The mutant huntingtin protein interferes with peroxisome biogenesis and function through multiple mechanisms[@kim2021].
Studies in AD mouse models have demonstrated that pharmacological activation of PPARγ or PGC-1α can improve peroxisomal function, reduce Aβ burden, and ameliorate cognitive deficits. Thiazolidinediones (TZDs), which are PPARγ agonists such as pioglitazone and rosiglitazone, have shown promise in preclinical models and are being evaluated in clinical trials for AD[@pedersen2020].
PGC-1α activation through exercise, caloric restriction, or pharmacological agents promotes peroxisomal biogenesis and protects against neurodegeneration. The [AMPK](/mechanisms/ampk-neurodegeneration)-PGC-1α axis represents a promising therapeutic target for maintaining peroxisomal function in aging and disease. Pharmacological activation of AMPK using compounds such as metformin and AICAR has been shown to promote peroxisomal biogenesis[@hardie2021].
Targeting peroxisomal antioxidant enzymes, particularly catalase and peroxiredoxin 5 (PRDX5), may reduce oxidative stress in neurodegenerative diseases. Gene therapy approaches to increase catalase expression have shown neuroprotective effects in animal models[@liu2021].
Peroxisomal dysfunction interacts with multiple other pathological pathways in neurodegeneration:
The formation of functional peroxisomes requires the coordinated assembly of over 35 PEX proteins, each playing specific roles in membrane assembly, protein import, and proliferation. Mutations in PEX genes cause severe peroxisome biogenesis disorders (PBDs), with Zellweger spectrum disorders representing the most severe phenotype[@steinberg2020a].
PEX3 is essential for peroxisomal membrane assembly and serves as a docking site for PMP import. PEX3 deficiency leads to complete loss of peroxisomes in cells and severe developmental abnormalities in humans[@fujiki2021].
PEX5 mediates the import of peroxisomal matrix proteins containing the PTS1 signal (serine-lysine-leucine motif). PEX5 binds cargo proteins in the cytosol and translocates them through the peroxisomal translocon, then is recycled back to the cytosol via monoubiquitination[@francisco2020].
PEX6 participates in the import of matrix proteins and is required for the extraction of PEX5 from the peroxisomal membrane. Mutations in PEX6 cause peroxisome biogenesis disorders and have been linked to certain cases of familial ALS[@steinberg2021].
PEX10 functions as a ubiquitin ligase involved in peroxisomal quality control. PEX10 mutations cause a subset of peroxisome biogenesis disorders with neurological involvement[@wang2021a].
Peroxisomes proliferate in response to metabolic demands through a process involving elongation, constriction, and fission. The dynamin-related protein 1 (DRP1) mediates peroxisomal fission, while proliferation is regulated by PPARα-mediated transcriptional activation of genes involved in peroxisome biogenesis[@koch2020].
Peroxisomes are the primary site of ether phospholipid biosynthesis in mammalian cells. These unique lipids, characterized by an ether bond at the sn-1 position of the glycerol backbone, are essential components of neuronal membranes and myelin sheaths[@braverman2021].
The synthesis of plasmalogens begins in the peroxisome with the formation of alkyl-dihydroxyacetonephosphate (alkyl-DHAP) from dihydroxyacetonephosphate (DHAP). This reaction is catalyzed by alkyl-DHAP synthase (AGPS), a peroxisomal enzyme. Subsequent steps in the ER produce the various plasmalogen species found in brain tissue[@nagan2021].
Plasmalogens constitute approximately 20% of phospholipids in the human brain and are particularly enriched in synaptic membranes and myelin. They play critical roles in membrane fluidity, signal transduction, and antioxidant defense[@farooqui2020].
Reduced plasmalogen levels have been documented in AD, PD, and other neurodegenerative diseases. The decrease correlates with disease severity and may contribute to synaptic dysfunction and neuronal vulnerability. Therapeutic approaches to increase plasmalogen levels through dietary supplementation or pharmacological activation of peroxisomal synthesis are being investigated[@goodenowe2022].
Peroxisomes are major producers and consumers of hydrogen peroxide (H2O2), making them central to cellular redox balance. The peroxisomal antioxidant system maintains low H2O2 concentrations while allowing controlled signaling functions[@nordgren2021].
Catalase is a tetrameric enzyme with four identical subunits, each containing a heme prosthetic group. The enzyme exhibits ping-pong kinetics, with hydrogen peroxide serving as both substrate and electron donor. Catalase deficiency in brain tissue contributes to increased oxidative stress in AD and PD[@gumpricht2020].
Peroxiredoxin 5 (PRDX5) is a unique peroxiredoxin that localizes to peroxisomes, mitochondria, and cytosol. It reduces hydrogen peroxide, peroxynitrite, and lipid hydroperoxides, providing broad antioxidant protection. PRDX5 expression is upregulated in neurodegenerative diseases as a compensatory response[@knoops2022].
When peroxisomal catalase activity is impaired, accumulated hydrogen peroxide diffuses to the cytosol and mitochondria, contributing to widespread oxidative damage. Lipid peroxidation, protein oxidation, and DNA damage are elevated in neurodegenerative diseases, partly due to peroxisomal dysfunction[@diazvillanueva2023].
Peroxisomes are the primary site of VLCFA (C22 or longer) oxidation in mammalian cells. The accumulation of VLCFAs due to peroxisomal dysfunction is neurotoxic and contributes to the pathogenesis of neurodegenerative diseases[@liu2022].
VLCFAs enter peroxisomes via ABC transporters and are oxidized by the peroxisomal β-oxidation system. ACOX1 initiates the first oxidation step, producing acetyl-CoA and H2O2. Subsequent steps generate shorter chain fatty acids that can be further metabolized in mitochondria[@wanders2021a].
Elevated VLCFA levels in neurodegenerative disease brain tissue result from both increased dietary intake and impaired peroxisomal oxidation. The accumulation disrupts membrane fluidity and lipid raft function, impairing synaptic signaling and neuronal communication[@zhang2022].
VLCFAs promote amyloid-β production and α-synuclein aggregation through multiple mechanisms. They alter APP processing by affecting γ-secretase activity and increase oxidative stress. The peroxisomal dysfunction thus contributes to both amyloid and synuclein pathology[@sharon2020].
Dietary VLCFA restriction and pharmacological approaches to enhance peroxisomal VLCFA oxidation are being investigated. Lorenzo's oil, a 4:1 mixture of oleic and erucic acids, has been used to reduce VLCFA levels in peroxisomal disorders and is being evaluated in neurodegenerative diseases[@ferdinandusse2021].
PPARγ coactivator-1α (PGC-1α) is a master regulator of mitochondrial and peroxisomal biogenesis. PGC-1α activates PPARα and PPARγ, promoting the expression of genes involved in fatty acid oxidation and antioxidant defense[@ronatas2021].
The AMP-activated protein kinase (AMPK)-PGC-1α axis is a central regulator of cellular energy metabolism and peroxisomal biogenesis. Activation of AMPK in response to energy stress promotes PGC-1α activity and stimulates peroxisome proliferation. This pathway is impaired in neurodegenerative diseases[@herzig2024].
Exercise, caloric restriction, and pharmacological agents activate PGC-1α and promote peroxisomal biogenesis. Natural compounds including resveratrol, quercetin, and sulforaphane activate AMPK-PGC-1α signaling and have shown neuroprotective effects in preclinical models[@marinangeli2022].
Emerging evidence suggests sex differences in peroxisomal function that may contribute to the differential susceptibility to neurodegenerative diseases. Women demonstrate higher baseline catalase activity in certain brain regions, while men show greater peroxisomal proliferative responses to metabolic challenges. These differences may relate to the estrogen-mediated regulation of peroxisome biogenesis[@vasko2021].
Estrogen receptor α (ERα) interacts with PGC-1α to regulate peroxisomal biogenesis. Estrogen treatment increases peroxisome numbers in cellular models, providing a potential mechanism for the protective effects of estrogen in neurodegenerative diseases. The decline in estrogen during menopause may contribute to increased vulnerability to oxidative stress[@zhou2021].
Polymorphisms in PEX genes influence susceptibility to neurodegenerative diseases. Genetic variants in PEX5 and PEX10 have been associated with increased risk for AD and PD in genome-wide association studies. These variants may affect peroxisomal import efficiency or response to cellular stress[@matsuda2021].
Peroxisomal gene expression is regulated through epigenetic mechanisms including DNA methylation and histone modification. Hypomethylation of PEX gene promoters has been observed in AD brain tissue, potentially reflecting altered transcriptional regulation in disease states[@chen2021].
Aging is associated with reduced peroxisome numbers and impaired peroxisomal function in multiple tissues, including brain. The age-related decline in peroxisomal function contributes to increased oxidative stress, altered lipid metabolism, and cellular senescence[@ipsiroglu2020].
Electron microscopy studies reveal decreased peroxisome density in aged brain tissue. Catalase activity declines with age, while VLCFA levels increase. These changes may contribute to age-related cognitive decline and increased susceptibility to neurodegenerative diseases[@tofaris2022].
Plasma VLCFA levels, plasmalogen ratios, and catalase activity serve as peripheral markers of peroxisomal function. Reduced plasmalogen levels in blood have been documented in AD and PD patients and correlate with disease severity. These biomarkers may aid in early diagnosis and disease monitoring[@kaddoumi2022].
Positron emission tomography (PET) using peroxisome-targeted probes is being developed to visualize peroxisomal function in vivo. These imaging agents may allow non-invasive assessment of peroxisomal integrity in patient brains[@shao2023].
Understanding peroxisomal dysfunction in neurodegeneration has opened new therapeutic avenues:
Thiazolidinediones (TZDs) such as pioglitazone and rosiglitazone activate PPARγ and promote peroxisomal biogenesis. These drugs have shown neuroprotective effects in animal models of AD and PD and are being evaluated in clinical trials[@nicolakakis2021].
Compounds that activate PGC-1α, including AMPK activators (metformin, AICAR) and natural compounds (resveratrol, quercetin), enhance peroxisome and mitochondria biogenesis. These approaches may restore cellular energy metabolism and antioxidant defense[@owens2022].
Targeting peroxisomal antioxidant enzymes, particularly catalase and PRDX5, may reduce oxidative stress in neurodegenerative diseases. Gene therapy approaches to deliver functional catalase or enhance peroxiredoxin expression are being investigated[@chen2022].
Approaches to deliver functional PEX genes or enhance peroxisomal biogenesis are being investigated for peroxisome-related neurodegeneration. CRISPR-based gene editing may correct peroxisomal biogenesis defects in the future[@ebberink2024].
Peroxisomes are essential organelles that play critical roles in lipid metabolism, reactive oxygen species (ROS) detoxification, and cellular homeostasis[@van2020]. In recent years, peroxisomal dysfunction has emerged as a significant contributor to the pathogenesis of neurodegenerative diseases including Alzheimer's Disease (AD) and Parkinson's Disease (PD)[@jo2019]. The bidirectional relationship between peroxisome function and neuronal health makes this pathway a promising therapeutic target.
Peroxisomes are single-membrane organelles found in all eukaryotic cells, with particularly high abundance in the brain[@steinberg2020]. They perform essential functions including:
Peroxisomes are delimited by a single membrane and contain over 50 enzymes involved in various metabolic pathways[@antonenkov2020]. Their biogenesis involves two major pathways:
De novo formation:
Fatty acid oxidation:
Multiple lines of evidence connect peroxisomal dysfunction to AD pathogenesis Lipid abnormalities:
peroxisomal dysfunction contributes to PD through multiple mechanismsFatty acid metabolism:
Peroxisomes play crucial roles in maintaining lipid homeostasis- Peroxisomes are the primary site for VLCFA β-oxidation
Peroxisomes are both sources and targets of oxidative stress- Catalase is the- Peroxisomes generate H2O2 as a byproduct of oxidation
Peroxisomal dysfunction contributes to neuroinflammation- Pe- Leuko- Inflammatory mediator production
Cytokine regulation:
Peroxisomes are essential for synaptic health- Provide - Support vesicle recycl- Maintain ion gradients
**Lipid- Determine membrane properties at synapses
Multiple therapeutic approaches are being explored- Fibrates activatAntioxidant approaches:
Nutritional approaches to support peroxisome function
Existing drugs with peroxisome eff
Peroxisome biogenesis disorders cause severe neurological symptoms### Implicati
Sporadic AD and PD share features with peroxisome disorders:
In Alzheimer's disease, peroxisomal dysfunction creates a multi-hit pathology- Peroxi**Tau - Multiple tau kinases activated
Neuroinflammation interactions:
In Parkinson's disease, peroxisomal dysfunction contributes to alpha-synuclein pathology- Perox- PEX5 deficiency leads to i**Mitochondrial-peroxis- Both orga- Shared fission/fusion machinery
Peroxisome proliferator-activated receptor alpha (PPARα) agonists show promise- I- Enhanced fatty ac- Reduced inflammation
Targeting peroxisomal oxidative stress*- Catalase + superox- Mitochondrial-targeted antiox- Plasmalogen precursors
Potential peroxisome-related biomarkers
Gene var
Research tools for studying peroxisomes:
Peroxisomal dysfunction represents a significant yet underappreciated contributor to neurodegenerative diseases. The roles of peroxisomes in lipid metabolism, antioxidant defense, and inflammation make them critical for neuronal health. Understanding peroxisome biology in the context of AD and PD offers opportunities for therapeutic intervention.
Key therapeutic strategies include:
Further research into peroxisome-neurodegeneration connections may reveal novel diagnostic and therapeutic approaches for these devastating diseases.