Peroxisomes are small, membrane-bound compartments found in virtually every cell of your body, and they handle a surprisingly wide range of metabolic tasks, from breaking down certain fats to neutralizing toxic byproducts of normal cell chemistry. For decades after their discovery in the 1960s, they were treated as minor players compared to mitochondria or the endoplasmic reticulum. That reputation has shifted dramatically. Research over the past two decades has revealed that peroxisomes are deeply wired into cellular communication networks, that they physically dock with other organelles to exchange molecules, and that their decline with age may contribute to neurodegenerative disease.
What Peroxisomes Actually Do
Peroxisomes earned their name from hydrogen peroxide. Many of the enzymes packed inside them are oxidases, which produce hydrogen peroxide as a byproduct while carrying out their primary chemical reactions. To keep this reactive molecule from damaging the cell, peroxisomes also contain catalase, an enzyme that rapidly converts hydrogen peroxide into water and oxygen.1PubMed Central. Effects of peroxisomal catalase inhibition on mitochondrial function This built-in cleanup system makes the peroxisome a controlled environment for reactions that would be dangerous if they happened freely in the cell’s interior.
Beyond managing reactive oxygen species, peroxisomes are central to lipid metabolism. They carry out a specialized form of fatty acid breakdown that handles very-long-chain fatty acids, molecules too large for mitochondria to process directly. Peroxisomes shorten these chains, then pass the products along to mitochondria for further energy extraction. They also participate in the synthesis of bile acids, which are essential for digesting dietary fats in the gut, and of plasmalogens, a class of ether-linked phospholipids that make up a substantial fraction of the lipid content in brain and heart tissue.2PubMed Central. Peroxisomes: a nexus for lipid metabolism and cellular signaling
Plasmalogens and the Brain
Plasmalogen synthesis begins inside the peroxisome and finishes in the endoplasmic reticulum. These lipids are not obscure biochemical curiosities. They account for a large share of the phospholipids in nervous tissue and play roles in membrane fluidity, signaling, and protection against oxidative damage. When plasmalogen production fails, the consequences are severe. In patients who lack functional peroxisomes, plasmalogens are absent from multiple organs, and in animal models, the loss of plasmalogens disrupts cholesterol synthesis in the brain and reduces the expression of myelin basic protein, a molecule critical for insulating nerve fibers.3Brain Research Bulletin. Regulation of plasmalogen biosynthesis in mammalian cells and tissues
This connection between peroxisomes and myelin health is one reason researchers have grown increasingly interested in peroxisomal function as a factor in neurological disease. Myelin sheaths wrap around nerve fibers and allow electrical signals to travel quickly. When myelin breaks down, the result is the kind of progressive neurological deterioration seen in conditions like multiple sclerosis and certain inherited metabolic diseases.
Talking to Mitochondria and the Endoplasmic Reticulum
Peroxisomes do not operate in isolation. They form physical contact sites with mitochondria and the endoplasmic reticulum, and these contacts are not just incidental bumps between neighboring structures. They are held together by specific tethering proteins and serve as highways for molecular exchange.
The peroxisome-mitochondria contact has attracted particular attention. A 2025 study in Science identified a direct mechanism by which peroxisomes help maintain mitochondrial health. The researchers found that two proteins, ACBD5 and PTPIP51, form a bridge between the two organelles. During periods of mitochondrial oxidative stress, more of these contacts form, and reactive oxygen species are transferred from the mitochondria into the peroxisome, where catalase can neutralize them. In other words, peroxisomes act as a kind of overflow antioxidant system for mitochondria.4PubMed. ROS transfer at peroxisome-mitochondria contact regulates mitochondrial redox
The metabolic cooperation runs both ways. When cells rely heavily on fatty acid breakdown for energy, peroxisomes move closer to mitochondria, and the transfer of acetyl-CoA (the shortened fatty acid product) from peroxisomes into mitochondria accelerates. Researchers have shown that genetically expanding these contact sites in yeast boosted the rate of complete fatty acid burning, as measured by carbon dioxide production.5Nature Communications. Systematic mapping of contact sites reveals tethers and a function for the peroxisome-mitochondria contact
Peroxisomes also maintain contact with the endoplasmic reticulum through a tethering complex identified in human cells, involving proteins called VAPA/B on the ER side and ACBD5 on the peroxisome side.6PubMed Central. Incredibly close-A newly identified peroxisome-ER contact site in humans One function of this connection is lipid transfer. Peroxisomes lack the ability to make their own membrane lipids from scratch, so the ER supplies them. This transfer happens through a direct, nonvesicular pathway, meaning lipids move across contact sites without being packaged into tiny transport bubbles. The process does not even require energy in the form of ATP.7PubMed Central. Nonvesicular phospholipid transfer between peroxisomes and the endoplasmic reticulum
How Peroxisomes Are Born and Destroyed
Cells maintain their population of peroxisomes through two main routes. The primary method is growth and division: an existing peroxisome enlarges, imports new proteins and lipids, then pinches in half. This is broadly similar to how mitochondria reproduce and is the more efficient way to keep peroxisome numbers steady. But cells also have a backup. When the normal fission-and-inheritance pathway fails, new peroxisomes can form from scratch, budding off from the endoplasmic reticulum. Studies in yeast show that this backup route works, but it is slower and less efficient than simple division.8PubMed Central. Peroxisome Maintenance Depends on De Novo Peroxisome Formation in Yeast Mutants Defective in Peroxisome Fission and Inheritance
Getting proteins into an already-formed peroxisome requires a specialized import system. Most peroxisomal enzymes are made on ribosomes in the cytoplasm and carry a short targeting signal that flags them for delivery. Two main types of signal exist, and cells use receptor proteins (Pex5p and Pex7p) to recognize them and escort the cargo to a docking site on the peroxisome membrane.9PubMed. Molecular mechanisms of import of peroxisome-targeting signal type 2 (PTS2) proteins by PTS2 receptor Pex7p and PTS1 receptor Pex5pL This import machinery is a common target of mutations in inherited peroxisomal diseases.
On the destruction side, cells selectively remove peroxisomes that are damaged or no longer needed through a process called pexophagy. This is a specialized branch of autophagy, the cell’s broader recycling program, and it is tightly regulated to avoid eliminating too many peroxisomes at once.10PubMed Central. Pexophagy: the selective degradation of peroxisomes Getting the balance right matters. When pexophagy is artificially ramped up in experiments, the cell’s autophagy system becomes overwhelmed. Cells forced into high rates of peroxisome degradation struggled to clear protein aggregates through a separate autophagy pathway, failing to eliminate the aggregates even after a five-hour clearance window.11Nature Communications. Upregulated pexophagy limits the capacity of selective autophagy This finding has implications for neurodegenerative diseases, where the buildup of protein aggregates is a hallmark feature.
When Peroxisomes Fail: Zellweger Spectrum Disorders
The most dramatic illustration of why peroxisomes matter comes from people born without functional ones. Zellweger spectrum disorders are a group of inherited conditions caused by mutations in PEX genes, the very genes that encode the machinery for building peroxisomes and importing proteins into them. The clinical picture spans a wide range. At the severe end, infants present at birth with profound muscle weakness, seizures, hearing and vision loss, distinctive facial features, and liver dysfunction. At the milder end, patients may not develop symptoms until adolescence or adulthood.12PubMed Central. Zellweger spectrum disorders: clinical overview and management approach
In the most severe form, historically called Zellweger syndrome, the absence of functional peroxisomes leads to a cascade of metabolic failures. Very-long-chain fatty acids accumulate because there is no peroxisomal machinery to shorten them. Plasmalogens are absent. Bile acid production is abnormal. The combined effect is devastating to the developing brain and other organs, and the condition is typically fatal in the first year of life.13PubMed. Zellweger syndrome – a lethal peroxisome biogenesis disorder The metabolic abnormalities can be detected through blood and urine tests, and genetic testing can confirm which PEX gene is affected.14PubMed Central. Peroxisome biogenesis disorders in the Zellweger spectrum: An overview of current diagnosis, clinical manifestations, and treatment guidelines
X-Linked Adrenoleukodystrophy
Not all peroxisomal diseases involve the complete failure of the organelle. X-linked adrenoleukodystrophy (X-ALD) is caused by mutations in a single gene, ABCD1, which encodes a transporter protein embedded in the peroxisome membrane. This transporter is responsible for moving very-long-chain fatty acids into the peroxisome so they can be broken down. When it is defective, those fatty acids accumulate in the brain, spinal cord, adrenal glands, and body fluids.15PubMed Central. Pathophysiology of X-Linked Adrenoleukodystrophy: Updates on Molecular Mechanisms
X-ALD is the most common peroxisomal disorder. Because the gene sits on the X chromosome, the disease predominantly affects males. It can manifest in childhood as a rapidly progressive form that destroys the white matter of the brain, or it may appear in adulthood as a slower condition affecting the spinal cord and peripheral nerves. Adrenal insufficiency, where the adrenal glands fail to produce enough hormones, is another frequent feature. The link between fatty acid accumulation and the inflammatory destruction of myelin is complex and not fully understood, though reduced peroxisomal beta-oxidation is clearly the upstream trigger.16PubMed. X-linked adrenoleukodystrophy: very long-chain fatty acid metabolism, ABC half-transporters and the complicated route to treatment Treatments include dietary management, hormone replacement for adrenal insufficiency, and in some cases hematopoietic stem cell transplantation, though the evidence around each approach has evolved over time.
Peroxisomes and Aging
Outside of rare inherited conditions, peroxisomal function appears to decline gradually as people age. Catalase activity drops, fatty acid oxidation slows, and plasmalogen levels fall. The combined effect is a shift in which peroxisomes go from being net protectors of the cell to potential contributors to chronic oxidative stress and lipid imbalance.17PubMed Central. Peroxisomes in Aging: Guardians of Cellular Resilience and Function
This decline has been linked to an earlier onset of several age-related diseases, including neurodegenerative conditions such as Alzheimer’s and Parkinson’s disease.18PubMed. Peroxisomal dysfunction in neurodegenerative diseases The connection is plausible on several levels. Falling plasmalogen levels reduce the antioxidant capacity of cell membranes. Declining fatty acid oxidation could lead to toxic lipid accumulation. And if peroxisomes are less able to absorb excess reactive oxygen species from mitochondria, the burden on the cell’s overall stress-response systems increases. Whether interventions that restore peroxisomal function could slow neurodegeneration is an open and actively researched question, though no clinical therapies targeting peroxisomes specifically for age-related disease exist yet.
Immune Signaling and Cancer
One of the more surprising recent findings is that peroxisomes participate in immune defense. They serve as platforms for antiviral signaling, hosting components of the cell’s innate immune detection system. When a virus enters a cell, sensors on the peroxisome membrane can activate signaling cascades that trigger the production of interferons and other defensive molecules. There is also emerging evidence that peroxisomes play a role in the immune response to bacterial infections.19PubMed Central. Peroxisomes and Innate Immunity: Antiviral Response and Beyond This makes sense from an evolutionary standpoint: peroxisomes sit at a crossroads of lipid and reactive oxygen species metabolism, both of which are deeply involved in immune signaling.
In cancer biology, peroxisomes occupy a complicated position. Their roles in fatty acid oxidation, ether lipid synthesis, and redox balance are all processes that cancer cells may co-opt or disrupt to support their own growth. Some tumor types show altered peroxisomal activity, and researchers have proposed that the metabolic flexibility peroxisomes provide could either suppress or promote tumor progression depending on the context. The field is still in its early stages, and no consensus has emerged on whether targeting peroxisomes therapeutically would help or hinder cancer treatment.
Specialized Peroxisomes in Other Organisms
Peroxisomes are not unique to animals. They appear across nearly all eukaryotic life, and in some organisms, they have been adapted for specialized tasks that go well beyond what happens in human cells.
In plants, specialized peroxisomes called glyoxysomes carry out the glyoxylate cycle, a metabolic pathway that converts stored fats into sugars. This is especially important during seed germination, when the seedling needs to mobilize fat reserves before it can photosynthesize. The interaction between glyoxysomes, mitochondria, and the cytoplasm during this process has been revised in recent years. One enzyme long assumed to reside inside glyoxysomes, aconitase, was found roughly 25 years ago to actually operate outside them, though some textbooks still get this wrong.20PubMed Central. Aconitase: To Be or not to Be Inside Plant Glyoxysomes, That Is the Question
In filamentous fungi, peroxisomes give rise to an entirely different kind of organelle: the Woronin body. These dense-core structures are found only in filamentous fungi and act as emergency plugs. Fungal cells are connected by small pores in their cross-walls, and when a cell is wounded, Woronin bodies rush to the pore and seal it, preventing the cell’s contents from leaking out and protecting the rest of the organism.21PubMed Central. Making two organelles from one: Woronin body biogenesis by peroxisomal protein sorting The protein that forms the core of a Woronin body is sorted through the peroxisomal import pathway before the organelle buds off and matures into its final form.22PubMed Central. Woronin body-based sealing of septal pores
The sheer variety of peroxisomal specializations across the tree of life reinforces how versatile these organelles are. Their core machinery, a single-membrane compartment with an oxidase-and-catalase pairing, has been repurposed again and again by evolution to meet different metabolic demands. That same versatility is part of what makes them so difficult to study in any single organism and so consequential when they malfunction in humans.