Activation of sirtuin 1 as therapy for the peroxisomal disease adrenoleukodystrophy

Mitochondrial Dysfunction as a Signaling Target for Therapeutic Intervention in Major Neurodegenerative Disease

Neurodegenerative diseases (NDD) are incurable and the most prevalent cognitive and motor disorders of elderly. Mitochondria are essential for a wide range of cellular processes playing a pivotal role in a number of cellular functions like metabolism, intracellular signaling, apoptosis, and immunity. A plethora of evidence indicates the central role of mitochondrial functions in pathogenesis of many aging related NDD. Considering how mitochondria function in neurodegenerative diseases, oxidative stress, and mutations in mtDNA both contribute to aging. Many substantial reports suggested the involvement of numerous contributing factors including, mitochondrial dysfunction, oxidative stress, mitophagy, accumulation of somatic mtDNA mutations, compromised mitochondrial dynamics, and transport within axons in neurodegenerative disorders including Alzheimer's disease, Parkinson's disease, Huntington's disease, and Amyotrophic Lateral Sclerosis. Therapies therefore target fundamental mitochondrial processes such as energy metabolism, free-radical generation, mitochondrial biogenesis, mitochondrial redox state, mitochondrial dynamics, mitochondrial protein synthesis, mitochondrial quality control, and metabolism hold great promise to develop pharmacological based therapies in NDD. By emphasizing the most efficient pharmacological strategies to target dysfunction of mitochondria in the treatment of neurodegenerative diseases, this review serves the scientific community engaged in translational medical science by focusing on the establishment of novel, mitochondria-targeted treatment strategies.

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.

Activating cannabinoid receptor 2 preserves axonal health through GSK-3β/NRF2 axis in adrenoleukodystrophy

Aberrant endocannabinoid signaling accompanies several neurodegenerative disorders, including multiple sclerosis. Here, we report altered endocannabinoid signaling in X-linked adrenoleukodystrophy (X-ALD), a rare neurometabolic demyelinating syndrome caused by malfunction of the peroxisomal ABCD1 transporter, resulting in the accumulation of very long-chain fatty acids (VLCFAs). We found abnormal levels of cannabinoid receptor 2 (CB2r) and related endocannabinoid enzymes in the brain and peripheral blood mononuclear cells (PBMCs) of X-ALD patients and in the spinal cord of a murine model of X-ALD. Preclinical treatment with a selective agonist of CB2r (JWH133) halted axonal degeneration and associated locomotor deficits, along with normalization of microgliosis. Moreover, the drug improved the main metabolic disturbances underlying this model, particularly in redox and lipid homeostatic pathways, including increased lipid droplets in motor neurons, through the modulation of the GSK-3β/NRF2 axis. JWH133 inhibited Reactive Oxygen Species elicited by excess VLCFAs in primary microglial cultures of Abcd1-null mice. Furthermore, we uncovered intertwined redox and CB2r signaling in the murine spinal cords and in patient PBMC samples obtained from a phase II clinical trial with antioxidants (NCT01495260). These findings highlight CB2r signaling as a potential therapeutic target for X-ALD and perhaps other neurodegenerative disorders that present with dysregulated redox and lipid homeostasis.

The Role of Oxidative Stress and Inflammation in X-Link Adrenoleukodystrophy

X-linked adrenoleukodystrophy (X-ALD) is an inherited disease caused by a mutation in the ABCD1 gene encoding a peroxisomal transmembrane protein. It is characterized by the accumulation of very-long-chain fatty acids (VLCFAs) in body fluids and tissues, leading to progressive demyelination and adrenal insufficiency. ALD has various phenotypes, among which the most common and severe is childhood cerebral adrenoleukodystrophy (CCALD). The pathophysiological mechanisms of ALD remain unclear, but some in vitro/in vivo research showed that VLCFA could induce oxidative stress and inflammation, leading to damage. In addition, the evidence that oxidative stress and inflammation are increased in patients with X-ALD also proves that it is a potential mechanism of brain and adrenal damage. Therefore, normalizing the redox balance becomes a critical therapeutic target. This study focuses on the possible predictors of the severity and progression of X-ALD, the potential mechanisms of pathogenesis, and the promising targeted drugs involved in oxidative stress and inflammation.

The crosstalk between reactive oxygen species and noncoding RNAs: from cancer code to drug role

Oxidative stress (OS), characterized by the excessive accumulation of reactive oxygen species (ROS), is an emerging hallmark of cancer. Tumorigenesis and development driven by ROS require an aberrant redox homeostasis, that activates onco-signaling and avoids ROS-induced programmed death by orchestrating antioxidant systems. These processes are revealed to closely associate with noncoding RNAs (ncRNAs). On the basis of the available evidence, ncRNAs have been widely identified as multifarious modulators with the involvement of several key redox sensing pathways, such as NF-κB and Nrf2 signaling, therefore potentially becoming effective targets for cancer therapy. Furthermore, the vast majority of ncRNAs with property of easy detected in fluid samples (e.g., blood and urine) facilitate clinicians to monitor redox homeostasis, indicating a novel method for cancer diagnosis. Herein, focusing on carcinoma initiation, metastasis and chemoradiotherapy resistance, we aimed to discuss the ncRNAs-ROS network involved in cancer progression, and the potential clinical application as biomarkers and therapeutic targets.

The brain penetrant PPARγ agonist leriglitazone restores multiple altered pathways in models of X-linked adrenoleukodystrophy

X-linked adrenoleukodystrophy (X-ALD), a potentially fatal neurometabolic disorder with no effective pharmacological treatment, is characterized by clinical manifestations ranging from progressive spinal cord axonopathy [adrenomyeloneuropathy (AMN)] to severe demyelination and neuroinflammation (cerebral ALD-cALD), for which molecular mechanisms are not well known. Leriglitazone is a recently developed brain penetrant full PPARγ agonist that could modulate multiple biological pathways relevant for neuroinflammatory and neurodegenerative diseases, and particularly for X-ALD. We found that leriglitazone decreased oxidative stress, increased adenosine 5'-triphosphate concentration, and exerted neuroprotective effects in primary rodent neurons and astrocytes after very long chain fatty acid-induced toxicity simulating X-ALD. In addition, leriglitazone improved motor function; restored markers of oxidative stress, mitochondrial function, and inflammation in spinal cord tissues from AMN mouse models; and decreased the neurological disability in the EAE neuroinflammatory mouse model. X-ALD monocyte-derived patient macrophages treated with leriglitazone were less skewed toward an inflammatory phenotype, and the adhesion of human X-ALD monocytes to brain endothelial cells decreased after treatment, suggesting the potential of leriglitazone to prevent the progression to pathologically disrupted blood-brain barrier. Leriglitazone increased myelin debris clearance in vitro and increased myelination and oligodendrocyte survival in demyelination-remyelination in vivo models, thus promoting remyelination. Last, leriglitazone was clinically tested in a phase 1 study showing central nervous system target engagement (adiponectin increase) and changes on inflammatory biomarkers in plasma and cerebrospinal fluid. The results of our study support the use of leriglitazone in X-ALD and, more generally, in other neuroinflammatory and neurodegenerative conditions.

Modulation of mitochondrial and inflammatory homeostasis through RIP140 is neuroprotective in an adrenoleukodystrophy mouse model

AIMS

Mitochondrial dysfunction and inflammation are at the core of axonal degeneration in several multifactorial neurodegenerative diseases, including multiple sclerosis, Alzheimer's disease, and Parkinson's disease. The transcriptional coregulator RIP140/NRIP1 (receptor-interacting protein 140) modulates these functions in liver and adipose tissue, but its role in the nervous system remains unexplored. Here, we investigated the impact of RIP140 in the Abcd1^- mouse model of X-linked adrenoleukodystrophy (X-ALD), a genetic model of chronic axonopathy involving the convergence of redox imbalance, bioenergetic failure, and chronic inflammation.

METHODS AND RESULTS

We provide evidence that RIP140 is modulated through a redox-dependent mechanism driven by very long-chain fatty acids (VLCFAs), the levels of which are increased in X-ALD. Genetic inactivation of RIP140 prevented mitochondrial depletion and dysfunction, bioenergetic failure, inflammatory dysregulation, axonal degeneration and associated locomotor disabilities in vivo in X-ALD mouse models.

CONCLUSIONS

Together, these findings show that aberrant overactivation of RIP140 promotes neurodegeneration in X-ALD, underscoring its potential as a therapeutic target for X-ALD and other neurodegenerative disorders that present with metabolic and inflammatory dyshomeostasis.

The pleiotropic neuroprotective effects of resveratrol in cognitive decline and Alzheimer's disease pathology: From antioxidant to epigenetic therapy

While the elderly segment of the population continues growing in importance, neurodegenerative diseases increase exponentially. Lifestyle factors such as nutrition, exercise, and education, among others, influence ageing progression, throughout life. Notably, the Central Nervous System (CNS) can benefit from nutritional strategies and dietary interventions that prevent signs of senescence, such as cognitive decline or neurodegenerative diseases such as Alzheimer's disease and Parkinson's Disease. The dietary polyphenol Resveratrol (RV) possesses antioxidant and cytoprotective effects, producing neuroprotection in several organisms. The oxidative stress (OS) occurs because of Reactive oxygen species (ROS) accumulation that has been proposed to explain the cause of the ageing. One of the most harmful effects of ROS in the cell is DNA damage. Nevertheless, there is also evidence demonstrating that OS can produce other molecular changes such as mitochondrial dysfunction, inflammation, apoptosis, and epigenetic modifications, among others. Interestingly, the dietary polyphenol RV is a potent antioxidant and possesses pleiotropic actions, exerting its activity through various molecular pathways. In addition, recent evidence has shown that RV mediates epigenetic changes involved in ageing and the function of the CNS that persists across generations. Furthermore, it has been demonstrated that RV interacts with gut microbiota, showing modifications in bacterial composition associated with beneficial effects. In this review, we give a comprehensive overview of the main mechanisms of action of RV in different experimental models, including clinical trials and discuss how the interconnection of these molecular events could explain the neuroprotective effects induced by RV.

Pharmacological advances in mitochondrial therapy

Mitochondria play a vital role in cellular metabolism and are central mediator of intracellular signalling, cell differentiation, morphogenesis and demise. An increasingly higher number of pathologies is linked with mitochondrial dysfunction, which can arise from either genetic defects affecting core mitochondrial components or malfunctioning pathways impairing mitochondrial homeostasis. As such, mitochondria are considered an important target in several pathologies spanning from neoplastic to neurodegenerative diseases as well as metabolic syndromes. In this review we provide an overview of the state-of-the-art in mitochondrial pharmacology, focusing on the novel compounds that have been generated in the bid to correct mitochondrial aberrations. Our work aims to serve the scientific community working on translational medical science by highlighting the most promising pharmacological approaches to target mitochondrial dysfunction in disease.

The Changing Face of Adrenoleukodystrophy

Adrenoleukodystrophy (ALD) is a rare X-linked disorder of peroxisomal oxidation due to mutations in ABCD1. It is a progressive condition with a variable clinical spectrum that includes primary adrenal insufficiency, myelopathy, and cerebral ALD. Adrenal insufficiency affects over 80% of ALD patients. Cerebral ALD affects one-third of boys under the age of 12 and progresses to total disability and death without treatment. Hematopoietic stem cell transplantation (HSCT) remains the only disease-modifying therapy if completed in the early stages of cerebral ALD, but it does not affect the course of adrenal insufficiency. It has significant associated morbidity and mortality. A recent gene therapy clinical trial for ALD reported short-term MRI and neurological outcomes comparable to historical patients treated with HSCT without the associated adverse side effects. In addition, over a dozen states have started newborn screening (NBS) for ALD, with the number of states expecting to double in 2020. Genetic testing of NBS-positive neonates has identified novel variants of unknown significance, providing further opportunity for genetic characterization but also uncertainty in the monitoring and therapy of subclinical and/or mild adrenal insufficiency or cerebral involvement. As more individuals with ALD are identified at birth, it remains uncertain if availability of matched donors, transplant (and, potentially, gene therapy) centers, and specialists may affect the timely treatment of these individuals. As these promising gene therapy trials and NBS transform the clinical management and outcomes of ALD, there will be an increasing need for the endocrine management of presymptomatic and subclinical adrenal insufficiency. (Endocrine Reviews 41: 1 - 17, 2020).

High-dose biotin restores redox balance, energy and lipid homeostasis, and axonal health in a model of adrenoleukodystrophy

Biotin is an essential cofactor for carboxylases that regulates the energy metabolism. Recently, high-dose pharmaceutical-grade biotin (MD1003) was shown to improve clinical parameters in a subset of patients with chronic progressive multiple sclerosis. To gain insight into the mechanisms of action, we investigated the efficacy of high-dose biotin in a genetic model of chronic axonopathy caused by oxidative damage and bioenergetic failure, the Abcd1^- mouse model of adrenomyeloneuropathy. High-dose biotin restored redox homeostasis driven by NRF-2, mitochondria biogenesis and ATP levels, and reversed axonal demise and locomotor impairment. Moreover, we uncovered a concerted dysregulation of the transcriptional program for lipid synthesis and degradation in the spinal cord likely driven by aberrant SREBP-1c/mTORC1signaling. This resulted in increased triglyceride levels and lipid droplets in motor neurons. High-dose biotin normalized the hyperactivation of mTORC1, thus restoring lipid homeostasis. These results shed light into the mechanism of action of high-dose biotin of relevance for neurodegenerative and metabolic disorders.

The peroxisomal fatty acid transporter ABCD1/PMP-4 is required in the C. elegans hypodermis for axonal maintenance: A worm model for adrenoleukodystrophy

Adrenoleukodystrophy is a neurometabolic disorder caused by a defective peroxisomal ABCD1 transporter of very long-chain fatty acids (VLCFAs). Its pathogenesis is incompletely understood. Here we characterize a nematode model of X-ALD with loss of the pmp-4 gene, the worm orthologue of ABCD1. These mutants recapitulate the hallmarks of X-ALD: i) VLCFAs accumulation and impaired mitochondrial redox homeostasis and ii) axonal damage coupled to locomotor dysfunction. Furthermore, we identify a novel role for PMP-4 in modulating lipid droplet dynamics. Importantly, we show that the mitochondria targeted antioxidant MitoQ normalizes lipid droplets size, and prevents axonal degeneration and locomotor disability, highlighting its therapeutic potential. Moreover, PMP-4 acting solely in the hypodermis rescues axonal and locomotion abnormalities, suggesting a myelin-like role for the hypodermis in providing essential peroxisomal functions for the nematode nervous system.

SIRT1 activation alleviates brain microvascular endothelial dysfunction in peroxisomal disorders

Peroxisomal disorders are genetically heterogeneous metabolic disorders associated with a deficit of very long chain fatty acid β-oxidation that commonly manifest as early-onset neurodegeneration. Brain microvascular endothelial dysfunction with increased permeability to monocytes has been described in X-linked adrenoleukodystrophy, one of the most common peroxisomal disorders caused by mutations of the ATP binding cassette subfamily D member 1 (ABCD1) gene. The present study demonstrated that dysregulation of sirtuin 1 (SIRT1) in human brain microvascular endothelial cells (HBMECs) mediates changes in adhesion molecules and tight-junction protein expression, as well as increased adhesion to monocytes associated with peroxisomal dysfunction due to ABCD1 or hydroxysteroid 17-β dehydrogenase 4 silencing. Furthermore, enhancement of the function of SIRT1 by resve-ratrol attenuated this molecular and functional dysregulation of HBMECs via modulation of the nuclear factor-κB and Krüppel-like factor 4 signaling pathways.

Aberrant regulation of the GSK-3β/NRF2 axis unveils a novel therapy for adrenoleukodystrophy

The nuclear factor erythroid 2‐like 2 (NRF2) is the master regulator of endogenous antioxidant responses. Oxidative damage is a shared and early‐appearing feature in X‐linked adrenoleukodystrophy (X‐ALD) patients and the mouse model (Abcd1 null mouse). This rare neurometabolic disease is caused by the loss of function of the peroxisomal transporter ABCD1, leading to an accumulation of very long‐chain fatty acids and the induction of reactive oxygen species of mitochondrial origin. Here, we identify an impaired NRF2 response caused by aberrant activity of GSK‐3β. We find that GSK‐3β inhibitors can significantly reactivate the blunted NRF2 response in patients’ fibroblasts. In the mouse models (Abcd1⁻ and Abcd1⁻/Abcd2^−/− mice), oral administration of dimethyl fumarate (DMF/BG12/Tecfidera), an NRF2 activator in use for multiple sclerosis, normalized (i) mitochondrial depletion, (ii) bioenergetic failure, (iii) oxidative damage, and (iv) inflammation, highlighting an intricate cross‐talk governing energetic and redox homeostasis in X‐ALD. Importantly, DMF halted axonal degeneration and locomotor disability suggesting that therapies activating NRF2 hold therapeutic potential for X‐ALD and other axonopathies with impaired GSK‐3β/NRF2 axis.

Epigenomic signature of adrenoleukodystrophy predicts compromised oligodendrocyte differentiation

Epigenomic changes may either cause disease or modulate its expressivity, adding a layer of complexity to mendelian diseases. X‐linked adrenoleukodystrophy (X‐ALD) is a rare neurometabolic condition exhibiting discordant phenotypes, ranging from a childhood cerebral inflammatory demyelination (cALD) to an adult‐onset mild axonopathy in spinal cords (AMN). The AMN form may occur with superimposed inflammatory brain demyelination (cAMN). All patients harbor loss of function mutations in the ABCD1 peroxisomal transporter of very‐long chain fatty acids. The factors that account for the lack of genotype‐phenotype correlation, even within the same family, remain largely unknown. To gain insight into this matter, here we compared the genome‐wide DNA methylation profiles of morphologically intact frontal white matter areas of children affected by cALD with adult cAMN patients, including male controls in the same age group. We identified a common methylomic signature between the two phenotypes, comprising (i) hypermethylation of genes harboring the H3K27me3 mark at promoter regions, (ii) hypermethylation of genes with major roles in oligodendrocyte differentiation such as MBP, CNP, MOG and PLP1 and (iii) hypomethylation of immune‐associated genes such as IFITM1 and CD59. Moreover, we found increased hypermethylation in CpGs of genes involved in oligodendrocyte differentiation, and also in genes with H3K27me3 marks in their promoter regions in cALD compared with cAMN, correlating with transcriptional and translational changes. Further, using a penalized logistic regression model, we identified the combined methylation levels of SPG20, UNC45A and COL9A3 and also, the combined expression levels of ID4 and MYRF to be good markers capable of discriminating childhood from adult inflammatory phenotypes. We thus propose the hypothesis that an epigenetically controlled, altered transcriptional program may drive an impaired oligodendrocyte differentiation and aberrant immune activation in X‐ALD patients. These results shed light into disease pathomechanisms and uncover putative biomarkers of interest for prognosis and phenotypic stratification.

Loss of SIRT2 leads to axonal degeneration and locomotor disability associated with redox and energy imbalance

Sirtuin 2 (SIRT2) is a member of a family of NAD⁺‐dependent histone deacetylases (HDAC) that play diverse roles in cellular metabolism and especially for aging process. SIRT2 is located in the nucleus, cytoplasm, and mitochondria, is highly expressed in the central nervous system (CNS), and has been reported to regulate a variety of processes including oxidative stress, genome integrity, and myelination. However, little is known about the role of SIRT2 in the nervous system specifically during aging. Here, we show that middle‐aged, 13‐month‐old mice lacking SIRT2 exhibit locomotor dysfunction due to axonal degeneration, which was not present in young SIRT2 mice. In addition, these Sirt2^−/− mice exhibit mitochondrial depletion resulting in energy failure, and redox dyshomeostasis. Our results provide a novel link between SIRT2 and physiological aging impacting the axonal compartment of the central nervous system, while supporting a major role for SIRT2 in orchestrating its metabolic regulation. This underscores the value of SIRT2 as a therapeutic target in the most prevalent neurodegenerative diseases that undergo with axonal degeneration associated with redox and energetic dyshomeostasis.

Tauroursodeoxycholic bile acid arrests axonal degeneration by inhibiting the unfolded protein response in X-linked adrenoleukodystrophy

The activation of the highly conserved unfolded protein response (UPR) is prominent in the pathogenesis of the most prevalent neurodegenerative disorders, such as Alzheimer’s disease (AD), Parkinson’s disease (PD) and amyotrophic lateral sclerosis (ALS), which are classically characterized by an accumulation of aggregated or misfolded proteins. This activation is orchestrated by three endoplasmic reticulum (ER) stress sensors: PERK, ATF6 and IRE1. These sensors transduce signals that induce the expression of the UPR gene programme. Here, we first identified an early activator of the UPR and investigated the role of a chronically activated UPR in the pathogenesis of X-linked adrenoleukodystrophy (X-ALD), a neurometabolic disorder that is caused by ABCD1 malfunction; ABCD1 transports very long-chain fatty acids (VLCFA) into peroxisomes. The disease manifests as inflammatory demyelination in the brain or and/or degeneration of corticospinal tracts, thereby resulting in spastic paraplegia, with the accumulation of intracellular VLCFA instead of protein aggregates. Using X-ALD mouse model (Abcd1⁻ and Abcd1⁻/Abcd2^−/− mice) and X-ALD patient’s fibroblasts and brain samples, we discovered an early engagement of the UPR. The response was characterized by the activation of the PERK and ATF6 pathways, but not the IRE1 pathway, showing a difference from the models of AD, PD or ALS. Inhibition of PERK leads to the disruption of homeostasis and increased apoptosis during ER stress induced in X-ALD fibroblasts. Redox imbalance appears to be the mechanism that initiates ER stress in X-ALD. Most importantly, we demonstrated that the bile acid tauroursodeoxycholate (TUDCA) abolishes UPR activation, which results in improvement of axonal degeneration and its associated locomotor impairment in Abcd1⁻/Abcd2^−/− mice. Altogether, our preclinical data provide evidence for establishing the UPR as a key drug target in the pathogenesis cascade. Our study also highlights the potential role of TUDCA as a treatment for X-ALD and other axonopathies in which similar molecular mediators are implicated.

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.

Altered glycolipid and glycerophospholipid signaling drive inflammatory cascades in adrenomyeloneuropathy

X-linked adrenomyeloneuropathy (AMN) is an inherited neurometabolic disorder caused by malfunction of the ABCD1 gene, characterized by slowly progressing spastic paraplegia affecting corticospinal tracts, and adrenal insufficiency. AMN is the most common phenotypic manifestation of adrenoleukodystrophy (X-ALD). In some cases, an inflammatory cerebral demyelination occurs associated to poor prognosis in cerebral AMN (cAMN). Though ABCD1 codes for a peroxisomal transporter of very long-chain fatty acids, the molecular mechanisms that govern disease onset and progression, or its transformation to a cerebral, inflammatory demyelinating form, remain largely unknown. Here we used an integrated -omics approach to identify novel biomarkers and altered network dynamic characteristic of, and possibly driving, the disease. We combined an untargeted metabolome assay of plasma and peripheral blood mononuclear cells (PBMC) of AMN patients, which used liquid chromatography coupled to quadrupole-time-of-flight mass spectrometry (LC-Q-TOF), with a functional genomics analysis of spinal cords of Abcd1(-) mouse. The results uncovered altered nodes in lipid-driven proinflammatory cascades, such as glycosphingolipid and glycerophospholipid synthesis, governed by the β-1,4-galactosyltransferase (B4GALT6), the phospholipase 2γ (PLA2G4C) and the choline/ethanolamine phosphotransferase (CEPT1) enzymes. Confirmatory investigations revealed a non-classic, inflammatory profile, consisting on the one hand of raised plasma levels of several eicosanoids derived from arachidonic acid through PLA2G4C activity, together with also the proinflammatory cytokines IL6, IL8, MCP-1 and tumor necrosis factor-α. In contrast, we detected a more protective, Th2-shifted response in PBMC. Thus, our findings illustrate a previously unreported connection between ABCD1 dysfunction, glyco- and glycerolipid-driven inflammatory signaling and a fine-tuned inflammatory response underlying a disease considered non-inflammatory.

Peroxisome biogenesis in mammalian cells: The impact of genes and environment

The initiation and progression of many human diseases are mediated by a complex interplay of genetic, epigenetic, and environmental factors. As all diseases begin with an imbalance at the cellular level, it is essential to understand how various types of molecular aberrations, metabolic changes, and environmental stressors function as switching points in essential communication networks. In recent years, peroxisomes have emerged as important intracellular hubs for redox-, lipid-, inflammatory-, and nucleic acid-mediated signaling pathways. In this review, we focus on how nature and nurture modulate peroxisome biogenesis and function in mammalian cells. First, we review emerging evidence that changes in peroxisome activity can be linked to the epigenetic regulation of cell function. Next, we outline how defects in peroxisome biogenesis may directly impact cellular pathways involved in the development of disease. In addition, we discuss how changes in the cellular microenvironment can modulate peroxisome biogenesis and function. Finally, given the importance of peroxisome function in multiple aspects of health, disease, and aging, we highlight the need for more research in this still understudied field.

Redox interplay between mitochondria and peroxisomes

Reduction-oxidation or “redox” reactions are an integral part of a broad range of cellular processes such as gene expression, energy metabolism, protein import and folding, and autophagy. As many of these processes are intimately linked with cell fate decisions, transient or chronic changes in cellular redox equilibrium are likely to contribute to the initiation and progression of a plethora of human diseases. Since a long time, it is known that mitochondria are major players in redox regulation and signaling. More recently, it has become clear that also peroxisomes have the capacity to impact redox-linked physiological processes. To serve this function, peroxisomes cooperate with other organelles, including mitochondria. This review provides a comprehensive picture of what is currently known about the redox interplay between mitochondria and peroxisomes in mammals. We first outline the pro- and antioxidant systems of both organelles and how they may function as redox signaling nodes. Next, we critically review and discuss emerging evidence that peroxisomes and mitochondria share an intricate redox-sensitive relationship and cooperate in cell fate decisions. Key issues include possible physiological roles, messengers, and mechanisms. We also provide examples of how data mining of publicly-available datasets from “omics” technologies can be a powerful means to gain additional insights into potential redox signaling pathways between peroxisomes and mitochondria. Finally, we highlight the need for more studies that seek to clarify the mechanisms of how mitochondria may act as dynamic receivers, integrators, and transmitters of peroxisome-derived mediators of oxidative stress. The outcome of such studies may open up exciting new avenues for the community of researchers working on cellular responses to organelle-derived oxidative stress, a research field in which the role of peroxisomes is currently highly underestimated and an issue of discussion.