X-linked adrenoleukodystrophy enigma: how does the ALD peroxisomal transporter mutation affect CNS glia?

Increased neurotoxicity of high-density lipoprotein secreted from murine reactive astrocytes deficient in a peroxisomal very-long-chain fatty acid transporter Abcd1

X-linked adrenoleukodystrophy (X-ALD) is a genetic neurodegenerative disorder caused by pathogenic variants in ABCD1, resulting in the accumulation of very-long-chain fatty acids (VLCFAs) in tissues. The etiology of X-ALD is unclear. Activated astrocytes play a pathological role in X-ALD. Recently, reactive astrocytes have been shown to induce neuronal cell death via saturated lipids in high-density lipoprotein (HDL), although how HDL from reactive astrocytes exhibits neurotoxic effects has yet to be determined. In this study, we obtained astrocytes from wild-type and Abcd1-deficient mice. HDL was purified from the culture supernatant of astrocytes, and the effect of HDL on neurons was evaluated in vitro. To our knowledge, this study shows for the first time that HDL obtained from Abcd1-deficient reactive astrocytes induces a significantly higher level of lactate dehydrogenase (LDH) release, a marker of cell damage, from mouse primary cortical neurons as compared to HDL from wild-type reactive astrocytes. Notably, HDL from Abcd1-deficient astrocytes contained significantly high amounts of VLCFA-containing phosphatidylcholine (PC) and LysoPC. Activation of Abcd1-deficient astrocytes led to the production of HDL containing decreased amounts of PC with arachidonic acid in sn-2 acyl moieties and increased amounts of LysoPC, presumably through cytosolic phospholipase A2 α upregulation. These results suggest that compositional changes in PC and LysoPC in HDL, due to Abcd1 deficiency and astrocyte activation, may contribute to neuronal damage. Our findings provide novel insights into central nervous system pathology in X-ALD.

Why does brain metabolism not favor burning of fatty acids to provide energy? Reflections on disadvantages of the use of free fatty acids as fuel for brain

It is puzzling that hydrogen-rich fatty acids are used only poorly as fuel in the brain. The long-standing belief that a slow passage of fatty acids across the blood-brain barrier might be the reason. However, this has been corrected by experimental results. Otherwise, accumulated nonesterified fatty acids or their activated derivatives could exert detrimental activities on mitochondria, which might trigger the mitochondrial route of apoptosis. Here, we draw attention to three particular problems: (1) ATP generation linked to β-oxidation of fatty acids demands more oxygen than glucose, thereby enhancing the risk for neurons to become hypoxic; (2) β-oxidation of fatty acids generates superoxide, which, taken together with the poor anti-oxidative defense in neurons, causes severe oxidative stress; (3) the rate of ATP generation based on adipose tissue-derived fatty acids is slower than that using blood glucose as fuel. Thus, in periods of extended continuous and rapid neuronal firing, fatty acid oxidation cannot guarantee rapid ATP generation in neurons. We conjecture that the disadvantages connected with using fatty acids as fuel have created evolutionary pressure on lowering the expression of the β-oxidation enzyme equipment in brain mitochondria to avoid extensive fatty acid oxidation and to favor glucose oxidation in brain.

Reductions in neuronal peroxisomes in multiple sclerosis grey matter

Background:

Peroxisomes are organelles in eukaryotic cells with multiple functions including the detoxification of reactive oxygen species, plasmalogen synthesis and β-oxidation of fatty acids. Recent evidence has implicated peroxisomal dysfunction in models of multiple sclerosis (MS) disease progression.

Objectives:

Our aims were to determine whether there are changes in peroxisomes in MS grey matter (GM) compared to control GM.

Methods:

We analysed cases of MS and control GM immunocytochemically to assess peroxisomal membrane protein (PMP70) and neuronal proteins. We examined the expression of ABCD3 (the gene that encodes PMP70) in MS and control GM. Analyses of very long chain fatty acid (VLCFA) levels in GM were performed.

Results:

PMP70 immunolabelling of neuronal somata was significantly lower in MS GM compared to control. Calibration of ABCD3 gene expression with reference to glyceraldehyde 3-phsophate dehydrogenase (GAPDH) revealed overall decreases in expression in MS compared to controls. Mean PMP70 counts in involved MS GM negatively correlated to disease duration. Elevations in C26:0 (hexacosanoic acid) were found in MS GM.

Conclusions:

Collectively, these observations provide evidence that there is an overall reduction in peroxisomal gene expression and peroxisomal proteins in GM neurons in MS. Changes in peroxisomal function may contribute to neuronal dysfunction and degeneration in MS.

Histone deacetylase inhibitor upregulates peroxisomal fatty acid oxidation and inhibits apoptotic cell death in abcd1-deficient glial cells

In X-ALD, mutation/deletion of ALD gene (ABCD1) and the resultant very long chain fatty acid (VLCFA) derangement has dramatically opposing effects in astrocytes and oligodendrocytes. While loss of Abcd1 in astrocytes produces a robust inflammatory response, the oligodendrocytes undergo cell death leading to demyelination in X-linked adrenoleukodystrophy (X-ALD). The mechanisms of these distinct pathways in the two cell types are not well understood. Here, we investigated the effects of Abcd1-knockdown and the subsequent alteration in VLCFA metabolism in human U87 astrocytes and rat B12 oligodendrocytes. Loss of Abcd1 inhibited peroxisomal β-oxidation activity and increased expression of VLCFA synthesizing enzymes, elongase of very long chain fatty acids (ELOVLs) (1 and 3) in both cell types. However, higher induction of ELOVL's in Abcd1-deficient B12 oligodendrocytes than astrocytes suggests that ELOVL pathway may play a prominent role in oligodendrocytes in X-ALD. While astrocytes are able to maintain the cellular homeostasis of anti-apoptotic proteins, Abcd1-deletion in B12 oligodendrocytes downregulated the anti-apototic (Bcl-2 and Bcl-xL) and cell survival (phospho-Erk1/2) proteins, and upregulated the pro-apoptotic proteins (Bad, Bim, Bax and Bid) leading to cell loss. These observations provide insights into different cellular signaling mechanisms in response to Abcd1-deletion in two different cell types of CNS. The apoptotic responses were accompanied by activation of caspase-3 and caspase-9 suggesting the involvement of mitochondrial-caspase-9-dependent mechanism in Abcd1-deficient oligodendrocytes. Treatment with histone deacetylase (HDAC) inhibitor suberoylanilide hydroxamic acid (SAHA) corrected the VLCFA derangement both in vitro and in vivo, and inhibited the oligodendrocytes loss. These observations provide a proof-of principle that HDAC inhibitor SAHA may have a therapeutic potential for X-ALD.

The importance of ether-phospholipids: a view from the perspective of mouse models

Ether-phospholipids represent an important group of phospholipids characterized by an alkyl or an alkenyl bond at the sn-1 position of the glycerol backbone. Plasmalogens are the most abundant form of alkenyl-glycerophospholipids, and their synthesis requires functional peroxisomes. Defects in the biosynthesis of plasmalogens are the biochemical hallmark of the human peroxisomal disorder Rhizomelic Chondrodysplasia Punctata (RCDP), which is characterized by defects in eye, bone and nervous tissue. The generation and characterization of mouse models with defects in plasmalogen levels have significantly advanced our understanding of the role and importance of plasmalogens as well as pathogenetic mechanisms underlying RCDP. A review of the current mouse models and the description of the combined knowledge gathered from the histopathological and biochemical studies is presented and discussed. Further characterization of the role and functions of plasmalogens will contribute to the elucidation of disease pathogenesis in peroxisomal and non-peroxisomal disorders. This article is part of a Special Issue entitled: Metabolic Functions and Biogenesis of Peroxisomes in Health and Disease.

Mammalian peroxisomal ABC transporters: from endogenous substrates to pathology and clinical significance

Peroxisomes are indispensable organelles in higher eukaryotes. They are essential for a number of important metabolic pathways, including fatty acid α- and β-oxidation, and biosynthesis of etherphospholipids and bile acids. However, the peroxisomal membrane forms an impermeable barrier to these metabolites. Therefore, peroxisomes need specific transporter proteins to transfer these metabolites across their membranes. The mammalian peroxisomal membrane harbours three ATP-binding cassette (ABC) transporters. In recent years, significant progress has been made in unravelling the functions of these ABC transporters. There is ample evidence that they are involved in the transport of very long-chain fatty acids, pristanic acid, di- and trihydroxycholestanoic acid, dicarboxylic acids and tetracosahexaenoic acid (C24:6ω3). Surprisingly, only one disease is associated with a deficiency of a peroxisomal ABC transporter. Mutations in the ABCD1 gene encoding the peroxisomal ABC transporter adrenoleukodystrophy protein are the cause for X-linked adrenoleukodystrophy, an inherited metabolic storage disorder. This review describes the current state of knowledge on the mammalian peroxisomal ABC transporters with a particular focus on their function in metabolite transport.

The PEX7-mediated peroxisomal import system is required for fungal development and pathogenicity in Magnaporthe oryzae

In eukaryotes, microbodies called peroxisomes play important roles in cellular activities during the life cycle. Previous studies indicate that peroxisomal functions are important for plant infection in many phytopathogenic fungi, but detailed relationships between fungal pathogenicity and peroxisomal function still remain unclear. Here we report the importance of peroxisomal protein import through PTS2 (Peroxisomal Targeting Signal 2) in fungal development and pathogenicity of Magnaporthe oryzae. Using an Agrobacterium tumefaciens-mediated transformation library, a pathogenicity-defective mutant was isolated from M. oryzae and identified as a T-DNA insert in the PTS2 receptor gene, MoPEX7. Gene disruption of MoPEX7 abolished peroxisomal localization of a thiolase (MoTHL1) containing PTS2, supporting its role in the peroxisomal protein import machinery. ΔMopex7 showed significantly reduced mycelial growth on media containing short-chain fatty acids as a sole carbon source. ΔMopex7 produced fewer conidiophores and conidia, but conidial germination was normal. Conidia of ΔMopex7 were able to develop appressoria, but failed to cause disease in plant cells, except after wound inoculation. Appressoria formed by ΔMopex7 showed a defect in turgor generation due to a delay in lipid degradation and increased cell wall porosity during maturation. Taken together, our results suggest that the MoPEX7-mediated peroxisomal matrix protein import system is required for fungal development and pathogenicity M. oryzae.

Pathomechanisms underlying X-adrenoleukodystrophy: a three-hit hypothesis

X-adrenoleukodystrophy (X-ALD) is a complex disease where inactivation of ABCD1 gene results in clinically diverse phenotypes, the fatal disorder of cerebral ALD (cALD) or a milder disorder of adrenomyeloneuropathy (AMN). Loss of ABCD1 function results in defective beta oxidation of very long chain fatty acids (VLCFA) resulting in excessive accumulation of VLCFA, the biochemical "hall mark" of X-ALD. At present, the ABCD1-mediated mechanisms that determine the different phenotype of X-ALD are not well understood. The studies reviewed here suggest for a "three-hit hypothesis" for neuropathology of cALD. An improved understanding of the molecular mechanisms associated with these three phases of cALD disease should facilitate the development of effective pharmacological therapeutics for X-ALD.

Adrénoleucodystrophie liée à l'X☆☆Cet article est publié en partenariat avec Orphanet et disponible sur le site www.orpha.net. © 2007 Orphanet. Publié par Elsevier Masson SAS. Tous droits réservés

X-linked adrenoleukodystrophy (ALD) is a severe neurodegenerative disorder. ALD is characterized by progressive demyelination within the central and peripheral nervous system, adrenal insufficiency (Addison's disease) and accumulation of very-long-chain fatty acids (VLCFA) in plasma, fibroblasts and tissues. The overall incidence of ALD is 1:17,000 including hemizygotes and heterozygotes who are frequently symptomatic. There are two main ALD phenotypes: 1) a cerebral demyelinating form which affects boys between 5-12 years, but also 35% of adult males; 2) a form that mainly involves the spinal cord (adrenomyeloneuropathy, AMN) in adult males between 20-50 years and 50% of heterozygous women after the age of 40 years. AMN presents with progressive spastic paraparesis. Addison's disease may be the first symptom of ALD in boys and adult males. These patients are at risk to develop cerebral ALD or AMN for life. ALD results from mutations in the ABCD1 gene without correlation between genotype and phenotype. The diagnosis of ALD relies upon the measurement of plasma VLCFA levels that allows the identification of 100% affected males and of 80-95% heterozygous women. Because of these false-negative, it is therefore mandatory to search for a mutation in the ABCD1 gene in all women at risk to be heterozygous for ALD. The ABCD1 gene encodes a peroxisomal transmembrane protein (ALD protein) with the structure of an half ATP-binding cassette transporter. It is possible that ALD protein imports VLCFA or VLCFA-CoA into peroxisomes in which they are degraded by a peroxisomal beta-oxidation system. Elongation of VLCFAs is enhanced in fibroblasts from ALD patients and likely contributes to the load of VLCFA in tissues. The underlying mechanisms that lead to cerebral demyelination, axonal degeneration in spinal cord and adrenal insufficiency are unknown. The "toxic" role of VLCFA accumulation remains to be demonstrated. The mechanisms that lead to the inflammatory reaction in cerebral ALD might involve abnormal acylation of gangliosides and phospholipids by VLCFA that would result in immune reaction of brain macrophages and astrocytes bearing CD1 molecules that recognize lipid antigens. De novo mutation of ABCD1 occurs in less than 8% of ALD patients. The genetic counseling aims to identify: 1) women who are at risk to be heterozygous; 2) neurologically asymptomatic boys. It is only at this stage that allogeneic bone marrow transplantation has clinical benefit; 3) ALD patients who have Addison's disease that can lead to sudden death. Prenatal diagnosis (chorionic villus samples, cultured amniotic fluid cells) relies upon DNA based mutation detection techniques, expression of ALD protein and measurement of VLCFA levels. Allogeneic bone marrow transplantation is the only treatment that provides a permanent cure when the procedure is performed at an early stage of cerebral demyelination, i.e when the patients are asymptomatic despite abnormal brain MRI. Treatment of Addison's disease is mandatory but does not modify the course of neurological symptoms. Dietary therapy failed to halt the neurologic progression in cerebral ALD and AMN. It might have a partial preventive effect in boys treated before 6 years of age.

Live cell FRET microscopy: homo- and heterodimerization of two human peroxisomal ABC transporters, the adrenoleukodystrophy protein (ALDP, ABCD1) and PMP70 (ABCD3)

The adrenoleukodystrophy protein (ALDP) and the 70-kDa peroxisomal membrane protein (PMP70) are half-ATP-binding cassette (ABC) transporters in the mammalian peroxisome membrane. Mutations in the gene encoding ALDP result in a devastating neurodegenerative disorder, X-linked adrenoleukodystrophy (X-ALD) that is associated with elevated levels of very long chain fatty acids because of impaired peroxisomal beta-oxidation. The interactions of peroxisomal ABC transporters, their role in the peroxisomal membrane, and their functions in disease pathogenesis are poorly understood. Studies on ABC transporters revealed that half-transporters have to dimerize to gain functionality. So far, conflicting observations are described for ALDP. By the use of in vitro methods (yeast two-hybrid and immunoprecipitation assays) on the one hand, it was shown that ALDP can form homodimers as well as heterodimers with PMP70 and ALDR, while on the other hand, it was demonstrated that ALDP and PMP70 exclusively homodimerize. To circumvent the problems of artificial interactions due to biochemical sample preparation in vitro, we investigated protein-protein interaction of ALDP in its physiological environment by FRET microscopy in intact living cells. The statistical relevance of FRET data was determined in two different ways using probability distribution shift analysis and Kolmogorov-Smirnov statistics. We demonstrate in vivo that ALDP and PMP70 form homodimers as well as ALDP/PMP70 heterodimers where ALDP homodimers predominate. Using C-terminal deletion constructs of ALDP, we demonstrate that the last 87 C-terminal amino acids harbor the most important protein domain mediating these interactions, and that the N-terminal transmembrane region of ALDP has an additional stabilization effect on ALDP homodimers. Loss of ALDP homo- or heterodimerization is highly relevant for understanding the disease mechanisms of X-ALD.

Expression of an acyl-CoA synthetase, lipidosin, in astrocytes of the murine brain and its up-regulation during remyelination following cuprizone-induced demyelination

Lipidosin is an 80-kDa protein with long-chain acyl-CoA synthetase activity expressed in the brain, adrenal gland, testis, and ovary, which are selectively damaged in X-linked adrenoleukodystrophy (X-ALD). Western blot analysis of the cerebrum and cerebellum revealed a gradual increase in the expression of lipidosin postnatally. Light microscopic immunohistochemistry using a panel of specific monoclonal antibodies showed that the lipidosin-immunopositive cells were ubiquitously distributed in the brain and were denser in the gray matter than in the white matter. Lipidosin immunoreactivity was colocalized with GFAP immunoreactivity but not with ubiquitin C-terminal hydrolase 1 (= PGP9.5) immunoreactivity, a neuronal marker, and lipidosin-producing cells detected by an antisense probe specific for lipidosin mRNA were also GFAP immunopositive. These data together with Western blot analysis of primary cultured astrocytes indicate that lipidosin is expressed in astrocytes. Immunoelectron microscopic analysis revealed that lipidosin immunoreactivity was widely distributed from perivascular endfeet to perisynaptic processes without being limited to peroxisomes. Lipidosin immunoreactivity was greatly increased in astrocytes in the area of remyelination following experimental demyelination induced by the administration of cuprizone to mice. These data suggest that lipidosin was involved in fatty acid metabolism during reconstruction of the myelin sheath.

[Adult onset hereditary leukoencephalopathies]

In clinical practice, the term "genetic leukoencephalopathy" refers to a group of genetic diseases whose common point is to give an aspect of diffuse leukoencephalopathy on MRI. With progress in diagnostic techniques including radiology, biochemistry or genetics, a large number of hereditary diseases causing leukoencephalopathy have been identified. Although generally beginning in childhood, these diseases often have more insidious clinical forms which can begin in adulthood. These forms remain poorly known. Some are accessible to treatment so their diagnosis appears essential. The diagnostic steps must be guided by clinical examination (neurological, ophthalmological and systemic), electromyography and MRI. The purpose of this review is to propose a classification of the genetic leukoencephalopathies and to give a progress report applicable in neurological practice.

Probing substrate-induced conformational alterations in adrenoleukodystrophy protein by proteolysis

The adrenoleukodystrophy protein (ALDP) is a half-ABC (ATP-binding cassette) transporter localized in the peroxisomal membrane. Dysfunction of this protein is the cause of the human genetic disorder X-linked adrenoleukodystrophy (X-ALD), which is characterized by accumulation of saturated, very-long-chain fatty acids (VLCFAs). This observation suggests that ALDP is involved in the metabolism of these compounds. Whether ALDP transports VLCFAs or their derivatives across the peroxisomal membrane or some cofactors essential for the efficient peroxisomal beta-oxidation of these fatty acids is still unknown. In this work, we used a protease-based approach to search for substrate-induced conformational alterations on ALDP. Our results suggest that ALDP is directly involved in the transport of long- and very-long-chain acyl-CoAs across the peroxisomal membrane.

Mouse liver PMP70 and ALDP: homomeric interactions prevail in vivo

ALDP, ALDPR, PMP70 and PMP70R are half ATP-binding cassette (ABC) transporters of the mammalian peroxisomal membrane. By analogy with other members of this family, it is assumed that peroxisomal ABC transporters must dimerize to become functional units. However, not much is known regarding the type of dimers (i.e., homodimers and/or heterodimers) that are formed in vivo under normal expression conditions. In this work, we have characterized the quaternary structure of mouse liver PMP70 and ALDP. The PMP70 protein complex was purified to apparent homogeneity using a two-step purification protocol. The ALDP-containing protein complex was characterized by preparative immunoprecipitation experiments. In both cases, no evidence for the existence of heteromeric interactions or for the presence of accessory proteins in these ABC transporter protein complexes could be obtained. Our data indicate that the majority (if not all) of mouse liver PMP70 and ALDP are homomeric proteins.

Similarity to peroxisomal-membrane protein family reveals that Sinorhizobium and Brucella BacA affect lipid-A fatty acids

Sinorhizobium meliloti, a legume symbiont, and Brucella abortus, a phylogenetically related mammalian pathogen, both require the bacterial-encoded BacA protein to establish chronic intracellular infections in their respective hosts. We found that the bacterial BacA proteins share sequence similarity with a family of eukaryotic peroxisomal-membrane proteins, including the human adrenoleukodystrophy protein, required for the efficient transport of very-long-chain fatty acids out of the cytoplasm. This insight, along with the increased sensitivity of BacA-deficient mutants to detergents and cell envelope-disrupting agents, led us to discover that BacA affects the very-long-chain fatty acid (27-OHC28:0 and 29-OHC30:0) content of both Sinorhizobium and Brucella lipid A. We discuss models for how BacA function affects the lipid-A fatty-acid content and why this activity could be important for the establishment of chronic intracellular infections.

Free radical release in C6 glial cells enriched in hexacosanoic acid: implication for X-linked adrenoleukodystrophy pathogenesis

Free radicals have been implicated in the etiopathology of some neurological and demyelinating diseases. To evaluate their involvement in the cerebral form of X-linked adrenoleukodystrophy (cerALD) disorder, characterised by very long chain fatty acid (VLCFA) accumulation, we utilised an in vitro model using rat C6 glial cells, enriched in hexacosenoic acid (C26:0, HA). Modified cells were incubated in presence of oxidative stressors, such as bacterial endotoxin lipopolisaccharides (LPS) and human oxidised low-density lipoprotein (ox-LDL), and the production of proinflammatory cytokines, nitrite, nitrate and superoxide was determined in the supernatants. The results show that modified cells produce higher amounts of nitric oxide (NO) products and superoxide compared to native C6 cells, supporting the role of free radicals as important pathophysiological modulator of the neuroinflammatory response in ALD. This hypothesis suggests that the cerebral damage in ALD could be due to intracellular signalling activated by interaction of exogenous factors with the particular membrane fatty acid composition.

Correlation of very long chain fatty acid accumulation and inflammatory disease progression in childhood X-ALD:

This study was designed to understand the role of inflammatory mediators involved in the neurobiology of childhood adrenoleukodystrophy (cALD) by comparing the differential expression of the inflammatory mediators with metabolite very long chain fatty acids that accumulate in this disease. Histopathological examinations indicated extensive demyelination and accumulation of infiltrates in perivascular cuffs in plaque area (PA) and inflammatory area (IA) compared to normal looking area (NLA) of the cALD brain and controls. The PA had excessive accumulation of cholesterol ester (25-30-fold), VLC fatty acids (8-12-fold), and exhaustive depletion of cholesterol (60-70%) and sphingomyelin (50-55%) in comparison to controls. The mRNA expression of cytokines (IL-1alpha, IL-2, IL-3, IL-6, TNF-alpha, and GM-CSF), chemokines (CCL2, -4, -7, -11, -16, -21, -22, CXCL1, CX3CL1, and SDF-2) and iNOS in IA was significantly increased compared to NLA of the cALD and controls determined by gene array, semiquantitative RT-PCR, and immunohistochemistry. These results indicate that accumulation of VLC fatty acid contents in membrane domains associated with signal transduction pathways may trigger the inflammatory process through activation of resident glial cells (microglia and astrocytes) resulting in loss of myelin and oligodendrocytes.

Genetic variations and humoral immune responses to myelin oligodendroglia glycoprotein in adult phenotypes of X-linked adrenoleukodystrophy

The lack of phenotype/genotype association in X-linked adrenoleukodystrophy (X-ALD) has prompted the search for disease modifying factors. We previously demonstrated increased serum antibody responses against myelin oligodendrocyte glycoprotein (MOG) in various clinical phenotypes of X-ALD allowing speculations that myelin specific humoral immune responses might be involved in phenotype generation of X-ALD. In the present study, we investigated the possible association of (1) a naturally occurring variable number tandem repeat (vntr) polymorphism (C allele) in the 3' flanking region of the interleukin-6 gene (IL-6), previously demonstrated to modify the course of Alzheimer's disease, systemic lupus erythematodes and Multiple Sclerosis (MS), (2) a tetranucleotide repeat polymorphism (TAAA)(n) in the 3' flanking region of the MOG gene and (3) HLA class II alleles with adult clinical phenotypes and serum antibody responses to MOG in 70 adult X-ALD patients. HLA class II alleles, (TAAA)(n) MOG gene polymorphisms, and IL-6 C allele were not associated with clinical phenotypes. Anti-MOG antibodies were detectable in 17/54 X-ALD patients (31.5%). Anti-MOG antibodies were associated with the 226 bp (TAAA)(n) MOG gene polymorphism but not with distinct clinical phenotypes.

Serum autoantibody responses to myelin oligodendrocyte glycoprotein and myelin basic protein in X-linked adrenoleukodystrophy and multiple sclerosis

We analyzed the sera of 51 patients with various phenotypes of X-linked adrenoleukodystrophy (X-ALD), 20 patients with multiple sclerosis (MS) and 22 healthy volunteers for the presence of autoantibodies specific for the recombinant extracellular immunoglobulin-like domain of human myelin oligodendrocyte glycoprotein (rhMOG(Igd)) and myelin basic protein (MBP). Anti-rhMOG(Igd) autoantibodies were significantly more frequent in X-ALD and MS patients as opposed to healthy individuals (p<0.05). Anti-MBP autoantibodies were present in about one-fourth of X-ALD and MS patients but in less than 10% of healthy individuals. Anti-rhMOG(Igd) autoantibody responses were not accompanied by increased T cell reactivity against rhMOG(Igd). These findings may have important implications for the understanding of humoral anti-myelin immunoreactivity in demyelinating diseases of the central nervous system such as X-ALD and MS.

Biology of oligodendrocyte and myelin in the mammalian central nervous system

Oligodendrocytes, the myelin-forming cells of the central nervous system (CNS), and astrocytes constitute macroglia. This review deals with the recent progress related to the origin and differentiation of the oligodendrocytes, their relationships to other neural cells, and functional neuroglial interactions under physiological conditions and in demyelinating diseases. One of the problems in studies of the CNS is to find components, i.e., markers, for the identification of the different cells, in intact tissues or cultures. In recent years, specific biochemical, immunological, and molecular markers have been identified. Many components specific to differentiating oligodendrocytes and to myelin are now available to aid their study. Transgenic mice and spontaneous mutants have led to a better understanding of the targets of specific dys- or demyelinating diseases. The best examples are the studies concerning the effects of the mutations affecting the most abundant protein in the central nervous myelin, the proteolipid protein, which lead to dysmyelinating diseases in animals and human (jimpy mutation and Pelizaeus-Merzbacher disease or spastic paraplegia, respectively). Oligodendrocytes, as astrocytes, are able to respond to changes in the cellular and extracellular environment, possibly in relation to a glial network. There is also a remarkable plasticity of the oligodendrocyte lineage, even in the adult with a certain potentiality for myelin repair after experimental demyelination or human diseases.

Th 1 cytokine production by peripheral blood mononuclear cells in X-linked adrenoleukodystrophy

Cerebral adrenoleukodystrophy (ALD) and adrenomyeloneuropathy (AMN) are the two most frequent clinical phenotypes of the same genetic defect leading to the accumulation of very long chain fatty acids (VLCFA). Previous studies have suggested that inflammatory cytokines may play a role in the cerebral demyelination and in phenotype expression of the disease. We analyzed cytokine production by stimulated peripheral blood mononuclear cells (PBMC) from 17 patients (four asymptomatic subjects, eight AMN and five ALD). Our results show that lipopolysaccarides (LPS) stimulated PBMC from both symptomatic and asymptomatic patients have an increased production of IL-12 and TNFalpha compared to controls, while after phitoemoagglutinin (PHA) stimulation we observed a decreased production of IL-6 and IL-10. These data indicate that, following an immunological stimulus, PBMC from patients have an increased production of cytokines typical of a Th1 cell response which is able to promote the inflammatory process. This characteristic profile of cytokine production could be related to the biochemical defect and could have a role in central nervous system (CNS) pathogenesis.

Apoptosis in the central nervous system of cerebral adrenoleukodystrophy patients

The childhood cerebral form of adrenoleukodystrophy (ALD) is a fatal demyelinating disease, yet mice deficient in the ALD gene do not show such clinicopathological phenotype. We have therefore investigated in human autopsy tissues whether the ALD gene mutation results in apoptosis of CNS cells. Specimens from telencephalic and brainstem regions of four patients, and three controls were examined for internucleosomal DNA fragmentation, in situ detection of DNA breaks by the TUNEL method, and caspase-3 immunostaining. None of the controls showed significant apoptosis in white matter, while apoptotic nuclei with chromatin alterations were detected in areas of active demyelination in three ALD patients. A large proportion of apoptotic cells were oligodendrocytes and some express activated caspase-3. TUNEL-positive nuclei and/or caspase-3 staining were also detected in perivascular infiltrates and, occasionally, in neurons. We conclude that apoptosis of oligodendrocytes may account, at least in part, for the demyelinating process in the ALD brain.