PEX13 deficiency in mouse brain as a model of Zellweger syndrome: abnormal cerebellum formation, reactive gliosis and oxidative stress

Metabolic Determinants of Cerebellar Circuit Formation and Maintenance

Cells configure their metabolism in a synchronized and timely manner to meet their energy demands throughout development and adulthood. Transitions of developmental stages are coupled to metabolic shifts, such that glycolysis is highly active during cell proliferation, whereas oxidative phosphorylation prevails in postmitotic states. In the cerebellum, metabolic transitions are remarkable given its protracted developmental timelines. Such distinctive feature, along with its high neuronal density and metabolic demands, make the cerebellum highly vulnerable to metabolic insults. Despite the expansion of metabolomic approaches to uncover biological mechanisms, little is known about the role of metabolism on cerebellar development and maintenance. To illuminate the intricate connections between metabolism, physiology, and cerebellar disorders, we examined here the impact of metabolism on cerebellar growth, maturation, and adulthood through the lens of inborn errors of metabolism.

Case Report: Identification of microduplication in the chromosomal 2p16.1p15 region in an infant suffering from pulmonary arterial hypertension

This study reports the first case of a patient with chromosomal 2p16.1p15 microduplication syndrome complicated by pulmonary arterial hypertension (PAH). A female infant was admitted to the hospital suffering from dyskinesia and developmental delay, and conventional echocardiography revealed an atrial septal defect (ASD), which was not taken seriously or treated at that time. Two years later, preoperative right heart catheterization for ASD closure revealed a mean pulmonary artery pressure (mPAP) of 45 mmHg. The mPAP was reduced, and the condition was stabilized after drug therapy. A genomic copy number duplication (3×) of at least 2.58 Mb in the 2p16.1p15 region on the paternal chromosome was revealed. Multiple Online Mendelian Inheritance in Man (OMIM) genes are involved in this genomic region, such as BCL11A, EHBP1, FAM161A, PEX13, and REL. EHBP1 promotes a molecular phenotypic transformation of pulmonary vascular endothelial cells and is thought to be involved in the rapidly developing PAH of this infant. Collectively, our findings contribute to the knowledge of the genes involved and the clinical manifestations of the 2p16.1p15 microduplication syndrome. Moreover, clinicians should be alert to the possibility of PAH and take early drug intervention when facing patients with 2p16.1p15 microduplications.

Lipidomics-Paving the Road towards Better Insight and Precision Medicine in Rare Metabolic Diseases

Even though the application of Next-Generation Sequencing (NGS) has significantly facilitated the identification of disease-associated mutations, the diagnostic rate of rare diseases is still below 50%. This causes a diagnostic odyssey and prevents specific treatment, as well as genetic counseling for further family planning. Increasing the diagnostic rate and reducing the time to diagnosis in children with unclear disease are crucial for a better patient outcome and improvement of quality of life. In many cases, NGS reveals variants of unknown significance (VUS) that need further investigations. The delineation of novel (lipid) biomarkers is not only crucial to prove the pathogenicity of VUS, but provides surrogate parameters for the monitoring of disease progression and therapeutic interventions. Lipids are essential organic compounds in living organisms, serving as building blocks for cellular membranes, energy storage and signaling molecules. Among other disorders, an imbalance in lipid homeostasis can lead to chronic inflammation, vascular dysfunction and neurodegenerative diseases. Therefore, analyzing lipids in biological samples provides great insight into the underlying functional role of lipids in healthy and disease statuses. The method of choice for lipid analysis and/or huge assemblies of lipids (=lipidome) is mass spectrometry due to its high sensitivity and specificity. Due to the inherent chemical complexity of the lipidome and the consequent challenges associated with analyzing it, progress in the field of lipidomics has lagged behind other omics disciplines. However, compared to the previous decade, the output of publications on lipidomics has increased more than 17-fold within the last decade and has, therefore, become one of the fastest-growing research fields. Combining multiple omics approaches will provide a unique and efficient tool for determining pathogenicity of VUS at the functional level, and thereby identifying rare, as well as novel, genetic disorders by molecular techniques and biochemical analyses.

Mouse Models to Study Peroxisomal Functions and Disorders: Overview, Caveats, and Recommendations

During the last three decades many mouse lines were created or identified that are deficient in one or more peroxisomal functions. Different methodologies were applied to obtain global, hypomorph, cell type selective, inducible, and knockin mice. Whereas some models closely mimic pathologies in patients, others strongly deviate or no human counterpart has been reported. Often, mice, apparently endowed with a stronger transcriptional adaptation, have to be challenged with dietary additions or restrictions in order to trigger phenotypic changes. Depending on the inactivated peroxisomal protein, several approaches can be taken to validate the loss-of-function. Here, an overview is given of the available mouse models and their most important characteristics.

The physiological functions of human peroxisomes

Peroxisomes are subcellular organelles that play a central role in human physiology by catalyzing a range of unique metabolic functions. The importance of peroxisomes for human health is exemplified by the existence of a group of usually severe diseases caused by an impairment in one or more peroxisomal functions. Among others these include the Zellweger spectrum disorders, X-linked adrenoleukodystrophy, and Refsum disease. To fulfill their role in metabolism, peroxisomes require continued interaction with other subcellular organelles including lipid droplets, lysosomes, the endoplasmic reticulum, and mitochondria. In recent years it has become clear that the metabolic alliance between peroxisomes and other organelles requires the active participation of tethering proteins to bring the organelles physically closer together, thereby achieving efficient transfer of metabolites. This review intends to describe the current state of knowledge about the metabolic role of peroxisomes in humans, with particular emphasis on the metabolic partnership between peroxisomes and other organelles and the consequences of genetic defects in these processes. We also describe the biogenesis of peroxisomes and the consequences of the multiple genetic defects therein. In addition, we discuss the functional role of peroxisomes in different organs and tissues and include relevant information derived from model systems, notably peroxisomal mouse models. Finally, we pay particular attention to a hitherto underrated role of peroxisomes in viral infections.

Molecular insights into peroxisome homeostasis and peroxisome biogenesis disorders

Peroxisomes are single-membrane organelles essential for cell metabolism including the β-oxidation of fatty acids, synthesis of etherlipid plasmalogens, and redox homeostasis. Investigations into peroxisome biogenesis and the human peroxisome biogenesis disorders (PBDs) have identified 14 PEX genes encoding peroxins involved in peroxisome biogenesis and the mutation of PEX genes is responsible for the PBDs. Many recent findings have further advanced our understanding of the biology, physiology, and consequences of a functional deficit of peroxisomes. In this Review, we discuss cell defense mechanisms that counteract oxidative stress by 1) a proapoptotic Bcl-2 factor BAK-mediated release to the cytosol of H₂O₂-degrading catalase from peroxisomes and 2) peroxisomal import suppression of catalase by Ser232-phosphorylation of Pex14, a docking protein for the Pex5-PTS1 complex. With respect to peroxisome division, the important issue of how the energy-rich GTP is produced and supplied for the division process was recently addressed by the discovery of a nucleoside diphosphate kinase-like protein, termed DYNAMO1 in a lower eukaryote, which has a mammalian homologue NME3. In regard to the mechanisms underlying the pathogenesis of PBDs, a new PBD model mouse defective in Pex14 manifests a dysregulated brain-derived neurotrophic factor (BDNF)-TrkB pathway, an important signaling pathway for cerebellar morphogenesis. Communications between peroxisomes and other organelles are also addressed.

Control of mitochondrial dynamics and apoptotic pathways by peroxisomes

Peroxisomes are organelles containing different enzymes that catalyze various metabolic pathways such as β-oxidation of very long-chain fatty acids and synthesis of plasmalogens. Peroxisome biogenesis is controlled by a family of proteins called peroxins, which are required for peroxisomal membrane formation, matrix protein transport, and division. Mutations of peroxins cause metabolic disorders called peroxisomal biogenesis disorders, among which Zellweger syndrome (ZS) is the most severe. Although patients with ZS exhibit severe pathology in multiple organs such as the liver, kidney, brain, muscle, and bone, the pathogenesis remains largely unknown. Recent findings indicate that peroxisomes regulate intrinsic apoptotic pathways and upstream fission-fusion processes, disruption of which causes multiple organ dysfunctions reminiscent of ZS. In this review, we summarize recent findings about peroxisome-mediated regulation of mitochondrial morphology and its possible relationship with the pathogenesis of ZS.

Dysfunctional peroxisomal lipid metabolisms and their ocular manifestations

Retina is rich in lipids and dyslipidemia causes retinal dysfunction and eye diseases. In retina, lipids are not only important membrane component in cells and organelles but also fuel substrates for energy production. However, our current knowledge of lipid processing in the retina are very limited. Peroxisomes play a critical role in lipid homeostasis and genetic disorders with peroxisomal dysfunction have different types of ocular complications. In this review, we focus on the role of peroxisomes in lipid metabolism, including degradation and detoxification of very-long-chain fatty acids, branched-chain fatty acids, dicarboxylic acids, reactive oxygen/nitrogen species, glyoxylate, and amino acids, as well as biosynthesis of docosahexaenoic acid, plasmalogen and bile acids. We also discuss the potential contributions of peroxisomal pathways to eye health and summarize the reported cases of ocular symptoms in patients with peroxisomal disorders, corresponding to each disrupted peroxisomal pathway. We also review the cross-talk between peroxisomes and other organelles such as lysosomes, endoplasmic reticulum and mitochondria.

Association of Oxidative Stress with Neurological Disorders

BACKGORUND

Oxidative stress is one of the main contributing factors involved in cerebral biochemical impairment. The higher susceptibility of the central nervous system to reactive oxygen species mediated damage could be attributed to several factors. For example, neurons use a greater quantity of oxygen, many parts of the brain have higher concentraton of iron, and neuronal mitochondria produce huge content of hydrogen peroxide. In addition, neuronal membranes have polyunsaturated fatty acids, which are predominantly vulnerable to oxidative stress (OS). OS is the imbalance between reactive oxygen species generation and cellular antioxidant potential. This may lead to various pathological conditions and diseases, especially neurodegenerative diseases such as, Parkinson's, Alzheimer's, and Huntington's diseases.

OBJECTIVES

In this study, we explored the involvement of OS in neurodegenerative diseases.

METHODS

We used different search terms like "oxidative stress and neurological disorders" "free radicals and neurodegenerative disorders" "oxidative stress, free radicals, and neurological disorders" and "association of oxidative stress with the name of disorders taken from the list of neurological disorders. We tried to summarize the source, biological effects, and physiologic functions of ROS.

RESULTS

Finally, it was noted that more than 190 neurological disorders are associated with oxidative stress.

CONCLUSION

More elaborated studies in the future will certainly help in understanding the exact mechanism involved in neurological diseases and provide insight into revelation of therapeutic targets.

Fluoxetine in the environment may interfere with the neurotransmission or endocrine systems of aquatic animals

Antidepressants are extensively used to treat the symptoms of depression in humans, and the environmentally discharged drugs potentially threaten aquatic organisms. In this study, the acute toxic effects of fluoxetine (FLX) were investigated in two aquatic organisms, the freshwater polyp (Hydra magnipapillata) and Javanese medaka (Oryzias javanicus). The median lethal concentration (LC₅₀) of FLX in H. magnipapillata was 3.678, 3.082, and 2.901 mg/L after 24, 48, and 72 h, respectively. Morphological observations of the FLX-exposed H. magnipapillata showed that 1.5 mg/L FLX induced the contraction of the tentacles and body column. The LC₅₀ of FLX in O. javanicus was 2.046, 1.936, 1.532, and 1.237 mg/L after 24, 48, 72, and 96 h, respectively. Observation of the behavior of the FLX-exposed fish showed that FLX reduced their swimming performance at a minimum concentration of 10 µg/L. The half-maximal effective concentration (EC₅₀) of FLX for swimming behavior in O. javanicus was 0.135, 0.108, and 0.011 mg/L after 12, 24, and 96 h, respectively. Transcriptomic analyses indicated that FLX affects various physiological and metabolic processes in both species. FLX exposure induced oxidative stress, reproductive deficiency, abnormal pattern formation, DNA damage, and neurotransmission disturbance in H. magnipapillata, whereas it adversely affected O. javanicus by inducing oxidative stress, DNA damage, endoplasmic reticulum stress, and mRNA instability. Neurotransmission-based behavioral changes and endocrine disruption were strongly suspected in the FLX-exposed fish. These results suggest that FLX affects the behavior and metabolic regulation of aquatic organisms.

Celia's Encephalopathy (BSCL2-Gene-Related): Current Understanding

Seipin, encoded by the BSCL2 gene, is a protein that in humans is expressed mainly in the central nervous system. Uniquely, certain variants in BSCL2 can cause both generalized congenital lipodystrophy type 2, upper and/or lower motor neuron diseases, or progressive encephalopathy, with a poor prognosis during childhood. The latter, Celia's encephalopathy, which may or may not be associated with generalized lipodystrophy, is caused by the c.985C >T variant. This cytosine to thymine transition creates a cryptic splicing zone that leads to intronization of exon 7, resulting in an aberrant form of seipin, Celia seipin. It has been proposed that the accumulation of this protein, both in the endoplasmic reticulum and in the nucleus of neurons, might be the pathogenetic mechanism of this neurodegenerative condition. In recent years, other variants in BSCL2 associated with generalized lipodystrophy and progressive epileptic encephalopathy have been reported. Interestingly, most of these variants could also lead to the loss of exon 7. In this review, we analyzed the molecular bases of Celia's encephalopathy and its pathogenic mechanisms, the clinical features of the different variants, and a therapeutic approach in order to slow down the progression of this fatal neurological disorder.

Enterovirus 71 induces neural cell apoptosis and autophagy through promoting ACOX1 downregulation and ROS generation

Enterovirus 71 (EV71) infection causes hand, foot, and mouth disease (HFMD), and even fatal neurological complications. However, the mechanisms underlying EV71 neurological pathogeneses are largely unknown. This study reveals a distinct mechanism by which EV71 induces apoptosis and autophagy in neural cells. EV71 non-structure protein 3D (also known as RNA-dependent RNA polymerase, RdRp) interacts with the peroxisomal protein acyl-CoA oxidase 1 (ACOX1), and contributes to ACOX1 downregulation. Further studies demonstrate that EV71 reduces peroxisome numbers. Additionally, knockdown of ACOX1 or peroxin 19 (PEX19) induces apoptosis and autophagy in neural cells including human neuroblastoma (SK-N-SH) cells and human astrocytoma (U251) cells, and EV71 infection induces neural cell death through attenuating ACOX1 production. Moreover, EV71 infection and ACOX1 knockdown facilitate reactive oxygen species (ROS) production and attenuate the cytoprotective protein deglycase (DJ-1)/Nuclear factor erythroid 2-related factor 2 (NRF2)/Heme oxygenase 1 (HO-1) pathway (DJ-1/NRF2/HO-1), which collectively result in ROS accumulation in neural cells. In conclusion, EV71 downregulates ACOX1 protein expression, reduces peroxisome numbers, enhances ROS generation, and attenuates the DJ-1/NRF2/HO-1 pathway, thereby inducing apoptosis and autophagy in neural cells. These findings provide new insights into the mechanism underlying EV71-induced neural pathogenesis, and suggest potential treatments for EV71-associated diseases.

Peroxisomes of the Brain: Distribution, Functions, and Associated Diseases

Peroxisomes are versatile cell organelles that exhibit a repertoire of organism and cell-type dependent functions. The presence of oxidases and antioxidant enzymes is a characteristic feature of these organelles. The role of peroxisomes in various cell types in human health and disease is under investigation. Defects in the biogenesis of the organelle and its function lead to severe debilitating disorders. In this manuscript, we discuss the distribution and functions of peroxisomes in the nervous system and especially in the brain cells. The important peroxisomal functions in these cells and their role in the pathology of associated disorders such as neurodegeneration are highlighted in recent studies. Although the cause of the pathogenesis of these disorders is still not clearly understood, emerging evidence supports a crucial role of peroxisomes. In this review, we discuss research highlighting the role of peroxisomes in brain development and its function. We also provide an overview of the major findings in recent years that highlight the role of peroxisome dysfunction in various associated diseases.

Peroxisome Deficiency Impairs BDNF Signaling and Memory

Peroxisome is an intracellular organelle that functions in essential metabolic pathways including β-oxidation of very-long-chain fatty acids and biosynthesis of plasmalogens. Peroxisome biogenesis disorders (PBDs) manifest severe dysfunction in multiple organs including central nervous system (CNS), whilst the pathogenic mechanisms are largely unknown. We recently reported that peroxisome-deficient neural cells secrete an increased level of brain-derived neurotrophic factor (BDNF), resulting in the cerebellar malformation. Peroxisomal functions in adulthood brain have been little investigated. To induce the peroxisome deficiency in adulthood brain, we here established tamoxifen-inducible conditional Pex2-knockout mouse. Peroxisome deficiency in the conditional Pex2-knockout adult mouse brain induces the upregulated expression of BDNF and its inactive receptor TrkB-T1 in hippocampus, which notably results in memory disturbance. Our results suggest that peroxisome deficiency gives rise to the dysfunction of hippocampal circuit via the impaired BDNF signaling.

Growth cone repulsion to Netrin-1 depends on lipid raft microdomains enriched in UNC5 receptors

During brain development, Uncoordinated locomotion 5 (UNC5) receptors control axonal extension through their sensing of the guidance molecule Netrin-1. The correct positioning of receptors into cholesterol-enriched membrane raft microdomains is crucial for the efficient transduction of the recognized signals. However, whether such microdomains are required for the appropriate axonal guidance mediated by UNC5 receptors remains unknown. Here, we combine the use of confocal microscopy, live-cell FRAP analysis and single-particle tracking PALM to characterize the distribution of UNC5 receptors into raft microdomains, revealing differences in their membrane mobility properties. Using pharmacological and genetic approaches in primary neuronal cultures and brain cerebellar explants we further demonstrate that disrupting raft microdomains inhibits the chemorepulsive response of growth cones and axons against Netrin-1. Together, our findings indicate that the distribution of all UNC5 receptors into cholesterol-enriched raft microdomains is heterogeneous and that the specific localization has functional consequences for the axonal chemorepulsion against Netrin-1.

SYPL1 Inhibits Apoptosis in Pancreatic Ductal Adenocarcinoma via Suppression of ROS-Induced ERK Activation

Synaptophysin-like 1 (SYPL1) is a neuroendocrine-related protein. The role of SYPL1 in pancreatic ductal adenocarcinoma (PDAC) and the underlying molecular mechanism remain unclarified. Here, after analyzing five datasets (GSE15471, GSE16515, GSE28735, TCGA, and PACA-AU) and 78 PDAC patients from Sun Yat-sen University Cancer Center, we demonstrated that SYPL1 was upregulated in PDAC and that a high level of SYPL1 indicated poor prognosis. Bioinformatics analysis implied that SYPL1 was related to cell proliferation and cell death. To validate these findings, gain-of-function and loss-of-function experiments were carried out, and we found that SYPL1 promoted cell proliferation in vitro and in vivo and that it protected cells from apoptosis. Mechanistic studies revealed that sustained extracellular-regulated protein kinase (ERK) activation was responsible for the cell death resulting from knockdown of SYPL1. In addition, bioinformatics analysis showed that the expression of SYPL1 positively correlated with antioxidant activity. Reactive oxygen species (ROS) were upregulated in cells with SYPL1 knockdown and vice versa. Upregulated ROS led to ERK activation and cell death. These results suggest that SYPL1 plays a vital role in PDAC and promotes cancer cell survival by suppressing ROS-induced ERK activation.

Maintaining social contacts: The physiological relevance of organelle interactions

Membrane-bound organelles in eukaryotic cells form an interactive network to coordinate and facilitate cellular functions. The formation of close contacts, termed "membrane contact sites" (MCSs), represents an intriguing strategy for organelle interaction and coordinated interplay. Emerging research is rapidly revealing new details of MCSs. They represent ubiquitous and diverse structures, which are important for many aspects of cell physiology and homeostasis. Here, we provide a comprehensive overview of the physiological relevance of organelle contacts. We focus on mitochondria, peroxisomes, the Golgi complex and the plasma membrane, and discuss the most recent findings on their interactions with other subcellular organelles and their multiple functions, including membrane contacts with the ER, lipid droplets and the endosomal/lysosomal compartment.

A peroxisome deficiency-induced reductive cytosol state up-regulates the brain-derived neurotrophic factor pathway

The peroxisome is a subcellular organelle that functions in essential metabolic pathways, including biosynthesis of plasmalogens, fatty acid β-oxidation of very-long-chain fatty acids, and degradation of hydrogen peroxide. Peroxisome biogenesis disorders (PBDs) manifest as severe dysfunction in multiple organs, including the central nervous system (CNS), but the pathogenic mechanisms in PBDs are largely unknown. Because CNS integrity is coordinately established and maintained by neural cell interactions, we here investigated whether cell-cell communication is impaired and responsible for the neurological defects associated with PBDs. Results from a noncontact co-culture system consisting of primary hippocampal neurons with glial cells revealed that a peroxisome-deficient astrocytic cell line secretes increased levels of brain-derived neurotrophic factor (BDNF), resulting in axonal branching of the neurons. Of note, the BDNF expression in astrocytes was not affected by defects in plasmalogen biosynthesis and peroxisomal fatty acid β-oxidation in the astrocytes. Instead, we found that cytosolic reductive states caused by a mislocalized catalase in the peroxisome-deficient cells induce the elevation in BDNF secretion. Our results suggest that peroxisome deficiency dysregulates neuronal axogenesis by causing a cytosolic reductive state in astrocytes. We conclude that astrocytic peroxisomes regulate BDNF expression and thereby support neuronal integrity and function.

A Mouse Model System to Study Peroxisomal Roles in Neurodegeneration of Peroxisome Biogenesis Disorders

Fourteen PEX genes are currently identified as genes responsible for peroxisome biogenesis disorders (PBDs). Patients with PBDs manifest as neurodegenerative symptoms such as neuronal migration defect and malformation of the cerebellum. To address molecular mechanisms underlying the pathogenesis of PBDs, mouse models for the PBDs have been generated by targeted disruption of Pex genes. Pathological phenotypes and metabolic abnormalities in Pex-knockout mice well resemble those of the patients with PBDs. The mice with tissue- or cell type-specific inactivation of Pex genes have also been established by using a Cre-loxP system. The genetically modified mice reveal that pathological phenotypes of PBDs are mediated by interorgan and intercellular communications. Despite the illustrations of detailed pathological phenotypes in the mutant mice, mechanistic insights into pathogenesis of PBDs are still underway. In this chapter, we overview the phenotypes of Pex-inactivated mice and the current understanding of the pathogenesis underlying PBDs.

Lipidomics unveils lipid dyshomeostasis and low circulating plasmalogens as biomarkers in a monogenic mitochondrial disorder

Mitochondrial dysfunction characterizes many rare and common age-associated diseases. The biochemical consequences, underlying clinical manifestations, and potential therapeutic targets, remain to be better understood. We tested the hypothesis that lipid dyshomeostasis in mitochondrial disorders goes beyond mitochondrial fatty acid β-oxidation, particularly in liver. This was achieved using comprehensive untargeted and targeted lipidomics in a case-control cohort of patients with Leigh syndrome French-Canadian variant (LSFC), a mitochondrial disease caused by mutations in LRPPRC, and in mice harboring liver-specific inactivation of Lrpprc (H-Lrpprc-/-). We discovered a plasma lipid signature discriminating LSFC patients from controls encompassing lower levels of plasmalogens and conjugated bile acids, which suggest perturbations in peroxisomal lipid metabolism. This premise was reinforced in H-Lrpprc-/- mice, which compared with littermates recapitulated a similar, albeit stronger peroxisomal metabolic signature in plasma and liver including elevated levels of very-long-chain acylcarnitines. These mice also presented higher transcript levels for hepatic markers of peroxisome proliferation in addition to lipid remodeling reminiscent of nonalcoholic fatty liver diseases. Our study underscores the value of lipidomics to unveil unexpected mechanisms underlying lipid dyshomeostasis ensuing from mitochondrial dysfunction herein implying peroxisomes and liver, which likely contribute to the pathophysiology of LSFC, but also other rare and common mitochondrial diseases.

Epigenetically dysregulated genes and pathways implicated in the pathogenesis of non-syndromic high myopia

Myopia, commonly referred to as nearsightedness, is one of the most common causes of visual disability throughout the world. It affects more people worldwide than any other chronic visual impairment condition. Although the prevalence varies among various ethnic groups, the incidence of myopia is increasing in all populations across globe. Thus, it is considered a pressing public health problem. Both genetics and environment play a role in development of myopia. To elucidate the epigenetic mechanism(s) underlying the pathophysiology of high-myopia, we conducted methylation profiling in 18 cases and 18 matched controls (aged 4–12 years), using Illumina MethylationEPIC BeadChips array. The degree of myopia was variable among subjects, ranging from −6 to −15D. We identified 1541 hypermethylated CpGs, representing 1745 genes (2.0-fold or higher) (false discovery rate (FDR) p ≤ 0.05), multiple CpGs were p < 5 × 10⁻⁸ with a receiver operating characteristic area under the curve (ROC-AUC) ≥ 0.75 in high-myopia subjects compared to controls. Among these, 48 CpGs had excellent correlation (AUC ≥ 0.90). Herein, we present the first genome-wide DNA methylation analysis in a unique high-myopia cohort, showing extensive and discrete methylation changes relative to controls. The genes we identified hold significant potential as targets for novel therapeutic intervention either alone, or in combination.

Redox Signaling from and to Peroxisomes: Progress, Challenges, and Prospects

SIGNIFICANCE

Peroxisomes are organelles that are best known for their role in cellular lipid and hydrogen peroxide (H₂O₂) metabolism. Emerging evidence suggests that these organelles serve as guardians and modulators of cellular redox balance, and that alterations in their redox metabolism may contribute to aging and the development of chronic diseases such as neurodegeneration, diabetes, and cancer. Recent Advances: H₂O₂ is an important signaling messenger that controls many cellular processes by modulating protein activity through cysteine oxidation. Somewhat surprisingly, the potential involvement of peroxisomes in H₂O₂-mediated signaling processes has been overlooked for a long time. However, recent advances in the development of live-cell approaches to monitor and modulate spatiotemporal fluxes in redox species at the subcellular level have opened up new avenues for research in redox biology and boosted interest in the concept of peroxisomes as redox signaling platforms.

CRITICAL ISSUES

This review first introduces the reader to what is known about the role of peroxisomes in cellular H₂O₂ production and clearance, with a focus on mammalian cells. Next, it briefly describes the benefits and drawbacks of current strategies used to investigate the complex interplay between peroxisome metabolism and cellular redox state. Furthermore, it integrates and critically evaluates literature dealing with the interrelationship between peroxisomal redox metabolism, cell signaling, and human disease.

FUTURE DIRECTIONS

As the precise molecular mechanisms underlying many of these associations are still poorly understood, a key focus for future research should be the identification of primary targets for peroxisome-derived H₂O₂.

Peroxisome biogenesis deficiency attenuates the BDNF-TrkB pathway-mediated development of the cerebellum

Peroxisome biogenesis disorders (PBDs) manifest as neurological deficits in the central nervous system, including neuronal migration defects and abnormal cerebellum development. However, the mechanisms underlying pathogenesis remain enigmatic. Here, to investigate how peroxisome deficiency causes neurological defects of PBDs, we established a new PBD model mouse defective in peroxisome assembly factor Pex14p, termed Pex14 ^ΔC/ΔC mouse. Pex14 ^ΔC/ΔC mouse manifests a severe symptom such as disorganization of cortical laminar structure and dies shortly after birth, although peroxisomal biogenesis and metabolism are partially defective. The Pex14 ^ΔC/ΔC mouse also shows malformation of the cerebellum including the impaired dendritic development of Purkinje cells. Moreover, extracellular signal-regulated kinase and AKT signaling are attenuated in this mutant mouse by an elevated level of brain-derived neurotrophic factor (BDNF) together with the enhanced expression of TrkB-T1, a dominant-negative isoform of the BDNF receptor. Our results suggest that dysregulation of the BDNF-TrkB pathway, an essential signaling for cerebellar morphogenesis, gives rise to the pathogenesis of the cerebellum in PBDs.

The peroxisome: an update on mysteries 2.0

Peroxisomes are key metabolic organelles, which contribute to cellular lipid metabolism, e.g. the β-oxidation of fatty acids and the synthesis of myelin sheath lipids, as well as cellular redox balance. Peroxisomal dysfunction has been linked to severe metabolic disorders in man, but peroxisomes are now also recognized as protective organelles with a wider significance in human health and potential impact on a large number of globally important human diseases such as neurodegeneration, obesity, cancer, and age-related disorders. Therefore, the interest in peroxisomes and their physiological functions has significantly increased in recent years. In this review, we intend to highlight recent discoveries, advancements and trends in peroxisome research, and present an update as well as a continuation of two former review articles addressing the unsolved mysteries of this astonishing organelle. We summarize novel findings on the biological functions of peroxisomes, their biogenesis, formation, membrane dynamics and division, as well as on peroxisome-organelle contacts and cooperation. Furthermore, novel peroxisomal proteins and machineries at the peroxisomal membrane are discussed. Finally, we address recent findings on the role of peroxisomes in the brain, in neurological disorders, and in the development of cancer.

Impaired neurogenesis and associated gliosis in mouse brain with PEX13 deficiency

Zellweger syndrome (ZS), a neonatal lethal disorder arising from defective peroxisome biogenesis, features profound neuroanatomical abnormalities and brain dysfunction. Here we used mice with brain-restricted inactivation of the peroxisome biogenesis gene PEX13 to model the pathophysiological features of ZS, and determine the impact of peroxisome dysfunction on neurogenesis and cell maturation in ZS. In the embryonic and postnatal PEX13 mutant brain, we demonstrate key regions with altered brain anatomy, including enlarged lateral ventricles and aberrant cortical, hippocampal and hypothalamic organization. To characterize the underlying mechanisms, we show a significant reduction in proliferation, migration, differentiation, and maturation of neural progenitors in embryonic E12.5 through to P3 animals. An increasing reactive gliosis in the PEX13 mutant brain started at E14.5 in association with the pathology. Together with impaired neurogenesis and associated gliosis, our data demonstrate increased cell death contributing to the hallmark brain anatomy of ZS. We provide unique data where impaired neurogenesis and migration are shown as critical events underlying the neuropathology and altered brain function of mice with peroxisome deficiency.

Plasmalogen homeostasis - regulation of plasmalogen biosynthesis and its physiological consequence in mammals

Plasmalogens, mostly ethanolamine-containing alkenyl ether phospholipids, are a major subclass of glycerophospholipids. Plasmalogen synthesis is initiated in peroxisomes and completed in the endoplasmic reticulum. The absence of plasmalogens in several organs of peroxisome biogenesis-defective patients suggests that the de novo synthesis of plasmalogens plays a pivotal role in its homeostasis in tissues. Plasmalogen synthesis is regulated by modulating the stability of fatty acyl-CoA reductase 1 on peroxisomal membranes, a rate-limiting enzyme in plasmalogen synthesis, by sensing plasmalogens in the inner leaflet of plasma membranes. Dysregulation of plasmalogen homeostasis impairs cholesterol biosynthesis by altering the stability of squalene monooxygenase, a key enzyme in cholesterol biosynthesis, implying physiological consequences of plasmalogen homeostasis with respect to cholesterol metabolism in cells, as well as in organs such as the liver.

Mitochondrial changes and oxidative stress in a mouse model of Zellweger syndrome neuropathogenesis

Zellweger syndrome (ZS) is a peroxisome biogenesis disorder that involves significant neuropathology, the molecular basis of which is still poorly understood. Using a mouse model of ZS with brain-restricted deficiency of the peroxisome biogenesis protein PEX13, we demonstrated an expanded and morphologically modified brain mitochondrial population. Cultured fibroblasts from PEX13-deficient mouse embryo displayed similar changes, as well as increased levels of mitochondrial superoxide and membrane depolarization; this phenotype was rescued by antioxidant treatment. Significant oxidative damage to neurons in brain was indicated by products of lipid and DNA oxidation. Similar overall changes were observed for glial cells. In toto, these findings suggest that mitochondrial oxidative stress and aberrant mitochondrial dynamics are associated with the neuropathology arising from PEX13 deficiency.

Peroxisomes in brain development and function

Peroxisomes contain numerous enzymatic activities that are important for mammalian physiology. Patients lacking either all peroxisomal functions or a single enzyme or transporter function typically develop severe neurological deficits, which originate from aberrant development of the brain, demyelination and loss of axonal integrity, neuroinflammation or other neurodegenerative processes. Whilst correlating peroxisomal properties with a compilation of pathologies observed in human patients and mouse models lacking all or individual peroxisomal functions, we discuss the importance of peroxisomal metabolites and tissue- and cell type-specific contributions to the observed brain pathologies. This enables us to deconstruct the local and systemic contribution of individual metabolic pathways to specific brain functions. We also review the recently discovered variability of pathological symptoms in cases with unexpectedly mild presentation of peroxisome biogenesis disorders. Finally, we explore the emerging evidence linking peroxisomes to more common neurological disorders such as Alzheimer’s disease, autism and amyotrophic lateral sclerosis. This article is part of a Special Issue entitled: Peroxisomes edited by Ralf Erdmann.

Peroxisomal Disorders: A Review on Cerebellar Pathologies

Peroxisomes are organelles with diverse metabolic tasks including essential roles in lipid metabolism. They are of utmost importance for the normal functioning of the nervous system as most peroxisomal disorders are accompanied with neurological symptoms. Remarkably, the cerebellum exquisitely depends on intact peroxisomal function both during development and adulthood. In this review, we cover all aspects of cerebellar pathology that were reported in peroxisome biogenesis disorders and in diseases caused by dysfunction of the peroxisomal α-oxidation, β-oxidation or ether lipid synthesis pathways. We also discuss the phenotypes of mouse models in which cerebellar pathologies were recapitulated and search for connections with the metabolic abnormalities. It becomes increasingly clear that besides the most severe forms of peroxisome dysfunction that are associated with developmental cerebellar defects, milder impairments can give rise to ataxia later in life.

Oxidative stress, mitochondrial and proteostasis malfunction in adrenoleukodystrophy: A paradigm for axonal degeneration

Peroxisomal and mitochondrial malfunction, which are highly intertwined through redox regulation, in combination with defective proteostasis, are hallmarks of the most prevalent multifactorial neurodegenerative diseases-including Alzheimer's (AD) and Parkinson's disease (PD)-and of the aging process, and are also found in inherited conditions. Here we review the interplay between oxidative stress and axonal degeneration, taking as groundwork recent findings on pathomechanisms of the peroxisomal neurometabolic disease adrenoleukodystrophy (X-ALD). We explore the impact of chronic redox imbalance caused by the excess of very long-chain fatty acids (VLCFA) on mitochondrial respiration and biogenesis, and discuss how this impairs protein quality control mechanisms essential for neural cell survival, such as the proteasome and autophagy systems. As consequence, prime molecular targets in the pathogenetic cascade emerge, such as the SIRT1/PGC-1α axis of mitochondrial biogenesis, and the inhibitor of autophagy mTOR. Thus, we propose that mitochondria-targeted antioxidants; mitochondrial biogenesis boosters such as the antidiabetic pioglitazone and the SIRT1 ligand resveratrol; and the autophagy activator temsirolimus, a derivative of the mTOR inhibitor rapamycin, hold promise as disease-modifying therapies for X-ALD.

Hepatic dysfunction in peroxisomal disorders

The peroxisomal compartment in hepatocytes hosts several essential metabolic conversions. These are defective in peroxisomal disorders that are either caused by failure to import the enzymes in the organelle or by mutations in the enzymes or in transporters needed to transfer the substrates across the peroxisomal membrane. Hepatic pathology is one of the cardinal features in disorders of peroxisome biogenesis and peroxisomal β-oxidation although it only rarely determines the clinical fate. In mouse models of these diseases liver pathologies also occur, although these are not always concordant with the human phenotype which might be due to differences in diet, expression of enzymes and backup mechanisms. Besides the morphological changes, we overview the impact of peroxisome malfunction on other cellular compartments including mitochondria and the ER. We further focus on the metabolic pathways that are affected such as bile acid formation, and dicarboxylic acid and branched chain fatty acid degradation. It appears that the association between deregulated metabolites and pathological events remains unclear.

ABCD1 deletion-induced mitochondrial dysfunction is corrected by SAHA: implication for adrenoleukodystrophy

X-linked Adrenoleukodystrophy (X-ALD), an inherited peroxisomal metabolic neurodegenerative disorder, is caused by mutations/deletions in the ATP-binding cassette transporter (ABCD1) gene encoding peroxisomal ABC transporter adrenoleukodystrophy protein (ALDP). Metabolic dysfunction in X-ALD is characterized by the accumulation of very long chain fatty acids ≥ C22:0) in the tissues and plasma of patients. Here, we investigated the mitochondrial status following deletion of ABCD1 in B12 oligodendrocytes and U87 astrocytes. This study provides evidence that silencing of peroxisomal protein ABCD1 produces structural and functional perturbations in mitochondria. Activities of electron transport chain-related enzymes and of citric acid cycle (TCA cycle) were reduced; mitochondrial redox status was dysregulated and the mitochondrial membrane potential was disrupted following ABCD1 silencing. A greater reduction in ATP levels and citrate synthase activities was observed in oligodendrocytes as compared to astrocytes. Furthermore, most of the mitochondrial perturbations induced by ABCD1 silencing were corrected by treating cells with suberoylanilide hydroxamic acid, an Histone deacetylase inhibitor. These observations indicate a novel relationship between peroxisomes and mitochondria in cellular homeostasis and the importance of intact peroxisomes in relation to mitochondrial integrity and function in the cell types that participate in the pathobiology of X-ALD. These observations suggest suberoylanilide hydroxamic acid as a potential therapy for X-ALD. Schematic description of the effects of loss of peroxisomal ATP-binding cassette transporter D1 (ABCD1) gene on cellular Redox and mitochondrial activities and their correction by suberoylanilide hydroxamic acid (SAHA) treatment. Pathogenomic accumulation of very long chain fatty acids (VLCFA) as a result of loss of ABCD1 leads to dysfunctions of mitochondrial biogenesis and its activities. Treatment with SAHA corrects mitochondrial dysfunctions. These studies describe unique cooperation between mitochondria and peroxisome for cellular activities.

Deficits in cerebellar granule cell development and social interactions in CD47 knockout mice

CD47 is involved in neurite differentiation in cultured neurons, but the function of CD47 in brain development is largely unknown. We determined that CD47 mRNA was robustly expressed in the developing cerebellum, especially in granule cells. CD47 protein was mainly expressed in the inner layer of the external granule layer (EGL), molecular layer, and internal granule layer (IGL), where granule cells individually become postmitotic and migrate, leading to neurite fasciculation. At postnatal day 8 (P8), CD47 knockout mice exhibited an increased number of proliferating granule cells in the EGL, whereas the CD47 agonist peptide 4N1K increased the number of postmitotic cells in primary granule cells. Knocking out the CD47 gene and anti-CD47 antibody impaired the radial migration of granule cells from the EGL to the IGL individually in mice and slice cultures. In primary granule cells, knocking out CD47 reduced the number of axonal collaterals and dendritic branches; by contrast, overexpressing CD47 or 4N1K treatment increased the axonal length and numbers of axonal collaterals and dendritic branches. Furthermore, the length of the fissure between Lobules VI and VII was decreased in CD47 knockout mice at P21 and at 14 wk after birth. Lastly, CD47 knockout mice exhibited increased social interaction at P21 and depressive-like behaviors at 10 wk after birth. Our study revealed that the cell adhesion molecule CD47 participates in multiple phases of granule cell development, including proliferation, migration, and neurite differentiation implying that aberrations of CD47 are risk factors that cause abnormalities in cerebellar development and atypical behaviors.

Peroxisomes are required for lipid metabolism and muscle function in Drosophila melanogaster

Peroxisomes are ubiquitous organelles that perform lipid and reactive oxygen species metabolism. Defects in peroxisome biogenesis cause peroxisome biogenesis disorders (PBDs). The most severe PBD, Zellweger syndrome, is characterized in part by neuronal dysfunction, craniofacial malformations, and low muscle tone (hypotonia). These devastating diseases lack effective therapies and the development of animal models may reveal new drug targets. We have generated Drosophila mutants with impaired peroxisome biogenesis by disrupting the early peroxin gene pex3, which participates in budding of pre-peroxisomes from the ER and peroxisomal membrane protein localization. pex3 deletion mutants lack detectible peroxisomes and die before or during pupariation. At earlier stages of development, larvae lacking Pex3 display reduced size and impaired lipid metabolism. Selective loss of peroxisomes in muscles impairs muscle function and results in flightless animals. Although, hypotonia in PBD patients is thought to be a secondary effect of neuronal dysfunction, our results suggest that peroxisome loss directly affects muscle physiology, possibly by disrupting energy metabolism. Understanding the role of peroxisomes in Drosophila physiology, specifically in muscle cells may reveal novel aspects of PBD etiology.

Central serotonergic neuron deficiency in a mouse model of Zellweger syndrome

Zellweger syndrome (ZS) is a severe peroxisomal disorder caused by mutations in peroxisome biogenesis, or PEX, genes. A central hallmark of ZS is abnormal neuronal migration and neurodegeneration, which manifests as widespread neurological dysfunction. The molecular basis of ZS neuropathology is not well understood. Here we present findings using a mouse model of ZS neuropathology with conditional brain inactivation of the PEX13 gene. We demonstrate that PEX13 brain mutants display changes that reflect an abnormal serotonergic system - decreased levels of tryptophan hydroxylase-2, the rate-limiting enzyme of serotonin (5-hydroxytryptamine, 5-HT) synthesis, dysmorphic 5-HT-positive neurons, abnormal distribution of 5-HT neurons, and dystrophic serotonergic axons. The raphe nuclei region of PEX13 brain mutants also display increased levels of apoptotic cells and reactive, inflammatory gliosis. Given the role of the serotonergic system in brain development and motor control, dysfunction of this system would account in part for the observed neurological changes of PEX13 brain mutants.

Disruption of oxidative phosphorylation and synaptic Na(+), K(+)-ATPase activity by pristanic acid in cerebellum of young rats

AIMS

Peroxisomal biogenesis disorders (PBD) are inherited disorders clinically manifested by neurological symptoms and brain abnormalities, in which the cerebellum is usually involved. Biochemically, patients affected by these neurodegenerative diseases accumulate branched-chain fatty acids, including pristanic acid (Prist) in the brain and other tissues.

MAIN METHODS

In the present investigation we studied the in vitro influence of Prist, at doses found in PBD, on oxidative phosphorylation, by measuring the activities of the respiratory chain complexes I-IV and ATP production, as well as on creatine kinase and synaptic Na(+), K(+)-ATPase activities in rat cerebellum.

KEY FINDINGS

Prist significantly decreased complexes I-III (65%), II (40%) and especially II-III (90%) activities, without altering the activities of complex IV of the respiratory chain and creatine kinase. Furthermore, ATP formation and synaptic Na(+), K(+)-ATPase activity were markedly inhibited (80-90%) by Prist. We also observed that this fatty acid altered mitochondrial and synaptic membrane fluidity that may have contributed to its inhibitory effects on the activities of the respiratory chain complexes and Na(+), K(+)-ATPase.

SIGNIFICANCE

Considering the importance of oxidative phosphorylation for mitochondrial homeostasis and of Na(+), K(+)-ATPase for the maintenance of cell membrane potential, the present data indicate that Prist compromises brain bioenergetics and neurotransmission in cerebellum. We postulate that these pathomechanisms may contribute to the cerebellar alterations observed in patients affected by PBD in which Prist is accumulated.

Mitochondria are targets for peroxisome-derived oxidative stress in cultured mammalian cells

Many cellular processes are driven by spatially and temporally regulated redox-dependent signaling events. Although mounting evidence indicates that organelles such as the endoplasmic reticulum and mitochondria can function as signaling platforms for oxidative stress-regulated pathways, little is known about the role of peroxisomes in these processes. In this study, we employ targeted variants of the genetically encoded photosensitizer KillerRed to gain a better insight into the interplay between peroxisomes and cellular oxidative stress. We show that the phototoxic effects of peroxisomal KillerRed induce mitochondria-mediated cell death and that this process can be counteracted by targeted overexpression of a select set of antioxidant enzymes, including peroxisomal glutathione S-transferase kappa 1, superoxide dismutase 1, and mitochondrial catalase. We also present evidence that peroxisomal disease cell lines deficient in plasmalogen biosynthesis or peroxisome assembly are more sensitive to KillerRed-induced oxidative stress than control cells. Collectively, these findings confirm and extend previous observations suggesting that disturbances in peroxisomal redox control and metabolism can sensitize cells to oxidative stress. In addition, they lend strong support to the ideas that peroxisomes and mitochondria share a redox-sensitive relationship and that the redox communication between these organelles is not only mediated by diffusion of reactive oxygen species from one compartment to the other. Finally, these findings indicate that mitochondria may act as dynamic receivers, integrators, and transmitters of peroxisome-derived mediators of oxidative stress, and this may have profound implications for our views on cellular aging and age-related diseases.

Peroxisome deficient invertebrate and vertebrate animal models

Although peroxisomes are ubiquitous organelles in all animal species, their importance for the functioning of tissues and organs remains largely unresolved. Because peroxins are essential for the biogenesis of peroxisomes, an obvious approach to investigate their physiological role is to inactivate a Pex gene or to suppress its translation. This has been performed in mice but also in more primitive organisms including D. melanogaster, C. elegans, and D. rerio, and the major findings and abnormalities in these models will be highlighted. Although peroxisomes are generally not essential for embryonic development and organogenesis, a generalized inactivity of peroxisomes affects lifespan and posthatching/postnatal growth, proving that peroxisomal metabolism is necessary for the normal maturation of these organisms. Strikingly, despite the wide variety of model organisms, corresponding tissues are affected including the central nervous system and the testis. By inactivating peroxisomes in a cell type selective way in the brain of mice, it was also demonstrated that peroxisomes are necessary to prevent neurodegeneration. As these peroxisome deficient model organisms recapitulate pathologies of patients affected with peroxisomal diseases, their further analysis will contribute to the elucidation of still elusive pathogenic mechanisms.

Peroxisomes: the neuropathological consequences of peroxisomal dysfunction in the developing brain

Peroxisomes are intracellular organelles that perform vital metabolic functions. They have been extensively studied in the hepatic and renal systems, yet their pivotal roles in facilitating central nervous system patterning and in disease pathogenesis are only recently being firmly established by the neuroscience community. Peroxisomal functions including the break-down of long chain fatty acids, the removal of H2O2, and the biosynthesis of ether lipids. The build up of long chain fatty acids and H2O2 is detrimental to cellular function, and ether lipids play roles in maintaining cell membrane structure. These findings have major implications for treatments for the full spectrum of peroxisomal disorders. Here, we provide a timely review highlighting the most important data in recent times linking peroxisomal functions to brain formation, and we describe how peroxisomal deficiency and pathway dysfunction results in neurological deficits, the more severe of which result in life changing disabilities and death.

Aging, age-related diseases and peroxisomes

Human aging is considered as one of the biggest risk factors for the development of multiple diseases such as cancer, type-2 diabetes, and neurodegeneration. In addition, it is widely accepted that these age-related diseases result from a combination of various genetic, lifestyle, and environmental factors. As biological aging is a complex and multifactorial phenomenon, the molecular mechanisms underlying disease initiation and progression are not yet fully understood. However, a significant amount of evidence supports the theory that oxidative stress may act as a primary etiologic factor. Indeed, many signaling components like kinases, phosphatases, and transcription factors are exquisitely sensitive to the cellular redox status, and a chronic or severe disturbance in redox homeostasis can promote cell proliferation or trigger cell death. Now, almost 50 years after their discovery, there is a wealth of evidence that peroxisomes can function as a subcellular source, sink, or target of reactive oxygen and nitrogen molecules. Yet, the possibility that these organelles may act as a signaling platform for a variety of age-related processes has so far been underestimated and largely neglected. In this review, we will critically discuss the possible role of peroxisomes in the human aging process in light of the available data.

Peroxisome deficiency but not the defect in ether lipid synthesis causes activation of the innate immune system and axonal loss in the central nervous system

BACKGROUND

Mice with peroxisome deficiency in neural cells (Nestin-Pex5-/-) develop a neurodegenerative phenotype leading to motor and cognitive disabilities and early death. Major pathologies at the end stage of disease include severe demyelination, axonal degeneration and neuroinflammation. We now investigated the onset and progression of these pathological processes, and their potential interrelationship. In addition, the putative role of oxidative stress, the impact of plasmalogen depletion on the neurodegenerative phenotype, and the consequences of peroxisome elimination in the postnatal period were studied.

METHODS

Immunohistochemistry in association with gene expression analysis was performed on Nestin-Pex5-/- mice to document demyelination, axonal damage and neuroinflammation. Also Gnpat-/- mice, with selective plasmalogen deficiency and CMV-Tx-Pex5-/- mice, with tamoxifen induced generalized loss of peroxisomes were analysed.

RESULTS

Activation of the innate immune system is a very early event in the pathological process in Nestin-Pex5-/- mice which evolves in chronic neuroinflammation. The complement factor C1q, one of the earliest up regulated transcripts, was expressed on neurons and oligodendrocytes but not on microglia. Transcripts of other pro- and anti-inflammatory genes and markers of phagocytotic activity were already significantly induced before detecting pathologies with immunofluorescent staining. Demyelination, macrophage activity and axonal loss co-occurred throughout the brain. As in patients with mild peroxisome biogenesis disorders who develop regressive changes, demyelination in cerebellum and brain stem preceded major myelin loss in corpus callosum of both Nestin-Pex5-/- and CMV-Tx-Pex5-/- mice. These lesions were not accompanied by generalized oxidative stress throughout the brain. Although Gnpat-/- mice displayed dysmyelination and Purkinje cell axon damage in cerebellum, confirming previous observations, no signs of inflammation or demyelination aggravating with age were observed.

CONCLUSIONS

Peroxisome inactivity triggers a fast neuroinflammatory reaction, which is not solely due to the depletion of plasmalogens. In association with myelin abnormalities this causes axon damage and loss.

Deletion of a single allele of the Pex11β gene is sufficient to cause oxidative stress, delayed differentiation and neuronal death in mouse brain

Impaired neuronal migration and cell death are commonly observed in patients with peroxisomal biogenesis disorders (PBDs), and in mouse models of this diseases. In Pex11β-deficient mice, we observed that the deletion of a single allele of the Pex11β gene (Pex11β^+/− heterozygous mice) caused cell death in primary neuronal cultures prepared from the neocortex and cerebellum, although to a lesser extent as compared with the homozygous-null animals (Pex11β^−/− mice). In corresponding brain sections, cell death was rare, but differences between the genotypes were similar to those found in vitro. Because PEX11β has been implicated in peroxisomal proliferation, we searched for alterations in peroxisomal abundance in the brain of heterozygous and homozygous Pex11β-null mice compared with wild-type animals. Deletion of one allele of the Pex11β gene slightly increased the abundance of peroxisomes, whereas the deletion of both alleles caused a 30% reduction in peroxisome number. The size of the peroxisomal compartment did not correlate with neuronal death. Similar to cell death, neuronal development was delayed in Pex11β^+/− mice, and to a further extent in Pex11β^−/− mice, as measured by a reduced mRNA and protein level of synaptophysin and a reduced protein level of the mature isoform of MAP2. Moreover, a gradual increase in oxidative stress was found in brain sections and primary neuronal cultures from wild-type to heterozygous to homozygous Pex11β-deficient mice. SOD2 was upregulated in neurons from Pex11β^+/− mice, but not from Pex11β^−/− animals, whereas the level of catalase remained unchanged in neurons from Pex11β^+/− mice and was reduced in those from Pex11β^−/− mice, suggesting a partial compensation of oxidative stress in the heterozygotes, but a failure thereof in the homozygous Pex11β^−/− brain. In conclusion, we report the alterations in the brain caused by the deletion of a single allele of the Pex11β gene. Our data might lead to the reconsideration of the clinical treatment of PBDs and the common way of using knockout mouse models for studying autosomal recessive diseases.

Plasmalogens the neglected regulatory and scavenging lipid species

Plasmalogens are a class of phospholipids carrying a vinyl ether bond in sn-1 and an ester bond in sn-2 position of the glycerol backbone. Although they are widespread in all tissues and represent up to 18% of the total phospholipid mass in humans, their physiological function is still poorly understood. The aim of this review is to give an overview over the current knowledge in plasmalogen biology and pathology with an emphasis on neglected aspects of their involvement in neurological and metabolic diseases. Furthermore a better understanding of plasmalogen biology in health and disease could also lead to the development of better diagnostic and prognostic biomarkers for vascular and metabolic diseases such as obesity and diabetes mellitus, inflammation, neuro-degeneration and cancer.