Fatty acid synthesizing enzymes intrinsic to myelin

Dose-Dependent Effect of a New Biotin Compound in Hippocampal Remyelination in Rats

Demyelination is commonly observed in neurodegenerative disorders, including multiple sclerosis (MS). Biotin supplementation is known to stabilize MS progression. To reduce the effective dose of biotin, we synthesized a new and superior form of biotin, a complex of magnesium ionically bound to biotin (MgB) and compared its dose-dependent effect with biotin alone after inducing demyelination using lysolecithin (LPC) in rats. Myelination was assessed using luxol fast blue staining and immunostaining against MBP protein, revealing that the most significant remyelination occurred in the MgB groups. Additionally, both biotin and MgB-treated animals showed dose-dependent improvements in spatial memory. Moreover, we detected a decrease in inflammatory proteins in both treatment groups, which was more prominent in high-dose MgB-treated animals and correlated with decreased expression of NF-κB p65, OP, and MMP-9 proteins. Further analysis of biotin-related proteins demonstrated that both biotin and, notably, MgB reversed the demyelination-dependent reduction of these proteins. Furthermore, biotin, particularly MgB, improved neuronal transmission proteins, Synapsin-1, PSD-93, and PSD-95. Additionally, both treatment groups exhibited increased BDNF, GAP43, and ICAM levels, with significant increments observed in high-dose MgB-treated animals. Increased GFAP, indicative of reactive gliosis, was observed in LPC-treated animals, and this effect was notably reversed by high-dose MgB treatment. The current data emphasize the dose-dependent beneficial effect on the remyelination process. Furthermore, the combination of biotin with Mg resulted in a more potent effect compared to biotin by itself. The strong influence of MgB encourages proof-of-concept studies using MgB in patients with MS.

High Dose Pharmaceutical Grade Biotin (MD1003) Accelerates Differentiation of Murine and Grafted Human Oligodendrocyte Progenitor Cells In Vivo

Accumulating evidences suggest a strong correlation between metabolic changes and neurodegeneration in CNS demyelinating diseases such as multiple sclerosis (MS). Biotin, an essential cofactor for five carboxylases, is expressed by oligodendrocytes and involved in fatty acid synthesis and energy production. The metabolic effect of biotin or high-dose-biotin (MD1003) has been reported on rodent oligodendrocytes in vitro, and in neurodegenerative or demyelinating animal models. However, clinical studies, showed mild or no beneficial effect of MD1003 in amyotrophic lateral sclerosis (ALS) or MS. Here, we took advantage of a mouse model of myelin deficiency to study the effects of MD1003 on the behavior of murine and grafted human oligodendrocytes in vivo. We show that MD1003 increases the number and the differentiation potential of endogenous murine oligodendroglia over time. Moreover, the levels of MD1003 are increased in the plasma and brain of pups born to treated mothers, indicating that MD1003 can pass through the mother's milk. The histological analysis of the grafted animals shows that MD1003 increased proliferation and accelerates differentiation of human oligodendroglia, but without enhancing their myelination potential. These findings provide important insights into the role of MD1003 on murine and human oligodendrocyte maturation/myelination that may explain the mitigated outcome of ALS/MS clinical trials.

Breaking the barriers to remyelination in multiple sclerosis

Chronically demyelinated axons are rendered susceptible to degeneration through loss of trophic support from oligodendrocytes and myelin, and this process underlies disability progression in multiple sclerosis. Promoting remyelination is a promising neuroprotective therapeutic strategy, but to date, has not been achieved through simply promoting oligodendrocyte precursor cell differentiation, and it is clear that a detailed understanding of the molecular mechanisms underlying failed remyelination is required to guide future therapeutic approaches. In multiple sclerosis, remyelination is impaired by extrinsic inhibitory cues in the lesion microenvironment including secreted effector molecules released from compartmentalized immune cells and reactive glia, as well as by intrinsic defects in oligodendrocyte lineage cells, most notably increased metabolic demands causing oxidative stress and accelerated cellular senescence. Promising advances in our understanding of the cellular and molecular mechanisms underlying these processes offers hope for strategically designed interventions to facilitate remyelination thereby resulting in robust clinical benefits.

Effects of Biotin on survival, ensheathment, and ATP production by oligodendrocyte lineage cells in vitro

Mechanisms implicated in disease progression in multiple sclerosis include continued oligodendrocyte (OL)/myelin injury and failure of myelin repair. Underlying causes include metabolic stress with resultant energy deficiency. Biotin is a cofactor for carboxylases involved in ATP production that impact myelin production by promoting fatty acid synthesis. Here, we investigate the effects of high dose Biotin (MD1003) on the functional properties of post-natal rat derived oligodendrocyte progenitor cells (OPCs). A2B5 positive OPCs were assessed using an in vitro injury assay, culturing cells in either DFM (DMEM/F12+N1) or “stress media” (no glucose (NG)-DMEM), with Biotin added over a range from 2.5 to 250 μg/ml, and cell viability determined after 24 hrs. Biotin reduced the increase in OPC cell death in the NG condition. In nanofiber myelination assays, biotin increased the percentage of ensheathing cells, the number of ensheathed segments per cell, and length of ensheathed segments. In dispersed cell culture, Biotin also significantly increased ATP production, assessed using a Seahorse bio-analyzer. For most assays, the positive effects of Biotin were observed at the higher end of the dose-response analysis. We conclude that Biotin, in vitro, protects OL lineage cells from metabolic injury, enhances myelin-like ensheathment, and is associated with increased ATP production.

Targeting demyelination and virtual hypoxia with high-dose biotin as a treatment for progressive multiple sclerosis

Progressive multiple sclerosis (MS) is a severely disabling neurological condition, and an effective treatment is urgently needed. Recently, high-dose biotin has emerged as a promising therapy for affected individuals. Initial clinical data have shown that daily doses of biotin of up to 300 mg can improve objective measures of MS-related disability. In this article, we review the biology of biotin and explore the properties of this ubiquitous coenzyme that may explain the encouraging responses seen in patients with progressive MS. The gradual worsening of neurological disability in patients with progressive MS is caused by progressive axonal loss or damage. The triggers for axonal loss in MS likely include both inflammatory demyelination of the myelin sheath and primary neurodegeneration caused by a state of virtual hypoxia within the neuron. Accordingly, targeting both these pathological processes could be effective in the treatment of progressive MS. Biotin is an essential co-factor for five carboxylases involved in fatty acid synthesis and energy production. We hypothesize that high-dose biotin is exerting a therapeutic effect in patients with progressive MS through two different and complementary mechanisms: by promoting axonal remyelination by enhancing myelin production and by reducing axonal hypoxia through enhanced energy production. This article is part of the Special Issue entitled 'Oligodendrocytes in Health and Disease'.

High doses of biotin in chronic progressive multiple sclerosis: a pilot study

BACKGROUND

No drug has been found to have any impact on progressive multiple sclerosis (MS). Biotin is a vitamin acting as a coenzyme for carboxylases involved in key steps of energy metabolism and fatty acids synthesis. Among others, biotin activates acetylCoA carboxylase, a potentially rate-limiting enzyme in myelin synthesis.

OBJECTIVES

The aim of this pilot study is to assess the clinical efficacy and safety of high doses of biotin in patients suffering from progressive MS.

STUDY DESIGN

Uncontrolled, non-blinded proof of concept study

METHODS

23 consecutive patients with primary and secondary progressive MS originated from three different French MS reference centers were treated with high doses of biotin (100-300mg/day) from 2 to 36 months (mean=9.2 months). Judgement criteria varied according to clinical presentations and included quantitative and qualitative measures.

RESULTS

In four patients with prominent visual impairment related to optic nerve injury, visual acuity improved significantly. Visual evoked potentials in two patients exhibited progressive reappearance of P100 waves, with normalization of latencies in one case. Proton magnetic resonance spectroscopy (H-MRS) in one case showed a progressive normalization of the Choline/Creatine ratio. One patient with left homonymous hemianopia kept on improving from 2 to 16 months following treatment׳s onset. Sixteen patients out of 18 (89%) with prominent spinal cord involvement were considered as improved as confirmed by blinded review of videotaped clinical examination in 9 cases. In all cases improvement was delayed from 2 to 8 months following treatment׳s onset.

CONCLUSIONS

These preliminary data suggest that high doses of biotin might have an impact on disability and progression in progressive MS. Two double-blind placebo-controlled trials are on going.

Localisation of N-acetylaspartate in oligodendrocytes/myelin

The role of N-acetylaspartate in the brain is unclear. Here we used specific antibodies against N-acetylaspartate and immunocytochemistry of carbodiimide-fixed adult rodent brain to show that, besides staining of neuronal cell bodies in the grey matter, N-acetylaspartate labelling was present in oligodendrocytes/myelin in white matter tracts. Immunoelectron microscopy of the rat hippocampus showed that N-acetylaspartate was concentrated in the myelin. Also neuronal cell bodies and axons contained significant amounts of N-acetylaspartate, while synaptic elements and astrocytes were low in N-acetylaspartate. Mitochondria in axons and neuronal cell bodies contained higher levels of N-acetylaspartate compared to the cytosol, compatible with synthesis of N-acetylaspartate in mitochondria. In aspartoacylase knockout mice, in which catabolism of N-acetylaspartate is blocked, the levels of N-acetylaspartate were largely increased in oligodendrocytes/myelin. In these mice, the highest myelin concentration of N-acetylaspartate was found in the cerebellum, a region showing overt dysmyelination. In organotypic cortical slice cultures there was no evidence for N-acetylaspartate-induced myelin toxicity, supporting the notion that myelin damage is induced by the lack of N-acetylaspartate for lipid production. Our findings also implicate that N-acetylaspartate signals on magnetic resonance spectroscopy reflect not only vital neurons but also vital oligodendrocytes/myelin.

Systematic approaches to central nervous system myelin

Rapid signal propagation along vertebrate axons is facilitated by their insulation with myelin, a plasma membrane specialization of glial cells. The recent application of 'omics' approaches to the myelinating cells of the central nervous system, oligodendrocytes, revealed their mRNA signatures, enhanced our understanding of how myelination is regulated, and established that the protein composition of myelin is much more complex than previously thought. This review provides a meta-analysis of the > 1,200 proteins thus far identified by mass spectrometry in biochemically purified central nervous system myelin. Contaminating proteins are surprisingly infrequent according to bioinformatic prediction of subcellular localization and comparison with the transcriptional profile of oligodendrocytes. The integration of datasets also allowed the subcategorization of the myelin proteome into functional groups comprising genes that are coregulated during oligodendroglial differentiation. An unexpectedly large number of myelin-related genes cause-when mutated in humans-hereditary diseases affecting the physiology of the white matter. Systematic approaches to oligodendrocytes and myelin thus provide valuable resources for the molecular dissection of developmental myelination, glia-axonal interactions, leukodystrophies, and demyelinating diseases.

Aspartoacylase deficiency affects early postnatal development of oligodendrocytes and myelination

Canavan disease (CD) is a neurodegenerative disease, caused by a deficiency in the enzyme aspartoacylase (ASPA). This enzyme has been localized to oligodendrocytes; however, it is still undefined how ASPA deficiency affects oligodendrocyte development. In normal mice the pattern of ASPA expression coincides with oligodendrocyte maturation. Therefore, postnatal oligodendrocyte maturation was analyzed in ASPA-deficient mice (CD mice). Early in development, CD mice brains showed decreased expression of neural cell markers that was later compensated. In addition, the levels of myelin proteins were decreased along with abnormal myelination in CD mice compared to wild-type (WT). These defects were associated with increased global levels of acetylated histone H3, decreased chromatin compaction and increased GFAP protein, a marker for astrogliosis. Together, these findings strongly suggest that, early in postnatal development, ASPA deficiency affects oligodendrocyte maturation and myelination.

Myelin lipid abnormalities in the aspartoacylase-deficient tremor rat

The high concentration of N-acetylaspartate (NAA) in neurons of the central nervous system and its growing clinical use as an indicator of neuronal viability has intensified interest in the biological function of this amino acid derivative. The biomedical relevance of such inquiries is highlighted by the myelin-associated pathology of Canavan disease, an inherited childhood disorder resulting from mutation of aspartoacylase (ASPA), the NAA-hydrolyzing enzyme. This enzyme is known to be localized in oligodendrocytes with bimodal distribution in cytosol and the myelin sheath, and to produce acetyl groups utilized in myelin lipid synthesis. Loss of this acetyl source in Canavan disease and rodent models such as the tremor rat are thought to account for the observed myelin deficit. This study was undertaken to further define and quantify the specific lipid abnormalities that occur as a result of ASPA deficit in the tremor rat. Employing mass spectrometry together with high performance thin-layer chromatography, we found that myelin from 28-day-old animals showed major reduction in cerebrosides (CB) and sulfatides (Sulf) with unsubstituted fatty acids, and equal if not greater changes in myelin from 7-month-old tremors. Cerebrosides with 2-hydroxyfatty acids showed little if any change at either age; Sulf with 2-hydroxyfatty acids showed no significant change at 28 days, but surprisingly a major increase at 7 months. Two species of phosphatidylcholine, 32:0 and 34:1, also showed significant increase, but only at 28 days. One form of phosphatidylethanolamine, PE36:1, was reduced a modest amount at both ages, whereas the plasmalogen form did not change. The dysmyelination that results from inactivation of ASPA is thus characterized by selective decreases as well as some increases in specific lipids.

Bimodal occurrence of aspartoacylase in myelin and cytosol of brain

The growing use of N-acetylaspartate as an indicator of neuronal viability has fostered interest in the biological function(s) of this unusual amino acid derivative. In considering the various physiological roles that have been proposed for this relatively abundant molecule one is obliged to take into account its unusual metabolic compartmentalization, according to which synthesis and storage occur in the neuron and hydrolytic cleavage in the oligodendrocyte. The latter reaction, catalyzed by aspartoacylase (ASPA), produces acetyl groups plus aspartate and has been proposed to occur in both soluble and membranous subfractions of white matter. Our study supports such bimodal occurrence and we now present immunoblot, proteomic, and biochemical evidence that the membrane-bound form of ASPA is intrinsic to purified myelin membranes. This was supported by a novel TLC-based method for the assay of ASPA. That observation, together with previous demonstrations of numerous lipid-synthesizing enzymes in myelin, suggests utilization of acetyl groups liberated by myelin-localized ASPA for lipid synthesis within the myelin sheath. Such synthesis might be selective and could explain the deficit of myelin lipids in animals lacking ASPA.

Peripheral nerve protein expression and carbonyl content in N,N-diethlydithiocarbamate myelinopathy

Human exposure to dithiocarbamates results from their uses as pesticides, in manufacturing, and as pharmaceutical agents. Neurotoxicity is an established hazard of dithiocarbamate exposure and has been observed in both humans and experimental animals. Previous studies have shown that the neurotoxicity of certain dithiocarbamates, including N,N-diethyldithiocarbamate (DEDC), disulfiram, and pyrrolidine dithiocarbamate, can manifest as a primary myelinopathy of peripheral nerves. Because increased levels of copper in peripheral nerves and elevated levels of lipid peroxidation products accompany DEDC-induced lesions, it has been suggested that the disruption of copper homeostasis and increased oxidative stress may contribute to myelin injury. To further assess the biological impact of DEDC-mediated lipid peroxidation in nerves, the changes in protein expression levels resulting from DEDC exposure were determined. In addition, protein carbonyl content in peripheral nerves was also determined as an initial assessment of protein oxidative damage in DEDC neuropathy. Rats were exposed to DEDC by intra-abdominal osmotic pumps for eight weeks and proteins extracted from the sciatic nerves of DEDC-exposed animals and from non-exposed controls. The comparison of protein expression levels using two-dimensional difference gel electrophoresis demonstrated significant changes in 56 spots of which 46 were identified by MALDI-TOF/MS. Among the proteins showing increased expression were three isoforms of glutathione transferase, important for the detoxification of reactive alpha,beta-unsaturated aldehydes generated from lipid peroxidation. The increased expression of one isoform, glutathione transferase pi, was localized to the cytoplasm of Schwann cells using immunohistochemistry. An immunoassay for nerve protein carbonyls demonstrated a significant increase of approximately 2-fold for the proteins isolated from DEDC-exposed rats. These data support the ability of DEDC to promote protein oxidative damage in peripheral nerves and to produce sufficient lipid peroxidation in either myelin or another component of the Schwann cell to elicit a protective cellular response to oxidative stress.

Structure and regulation of acetyl-CoA carboxylase genes of metazoa

Acetyl-CoA carboxylase (ACC) plays a fundamental role in fatty acid metabolism. The reaction product, malonyl-CoA, is both an intermediate in the de novo synthesis of long-chain fatty acids and also a substrate for distinct fatty acyl-CoA elongation enzymes. In metazoans, which have evolved energy storage tissues to fuel locomotion and to survive periods of starvation, energy charge sensing at the level of the individual cell plays a role in fuel selection and metabolic orchestration between tissues. In mammals, and probably other metazoans, ACC forms a component of an energy sensor with malonyl-CoA, acting as a signal to reciprocally control the mitochondrial transport step of long-chain fatty acid oxidation through the inhibition of carnitine palmitoyltransferase I (CPT I). To reflect this pivotal role in cell function, ACC is subject to complex regulation. Higher metazoan evolution is associated with the duplication of an ancestral ACC gene, and with organismal complexity, there is an increasing diversity of transcripts from the ACC paraloges with the potential for the existence of several isozymes. This review focuses on the structure of ACC genes and the putative individual roles of their gene products in fatty acid metabolism, taking an evolutionary viewpoint provided by data in genome databases.

Multiple sclerosis as a generalized CNS disease--comparative microarray analysis of normal appearing white matter and lesions in secondary progressive MS

We used microarrays to compare the gene expression profile in active lesions and donor-matched normal appearing white matter (NAWM) from brain autopsy samples of patients with secondary progressive multiple sclerosis (MS) with that from controls who died from non-neurological diseases. The 123 genes in lesions, and 47 genes in NAWM(MS) were differentially expressed. Lesions distinguished from NAWM(MS) by a higher expression of genes related to immunoglobulin synthesis and neuroglial differentiation, while cellular immune response elements were equally dysregulated in both tissue compartments. Current results provide molecular evidence of a continuum of dysfunctional homeostasis and inflammatory changes between lesions and NAWM(MS), and support the concept of MS pathogenesis being a generalised process that involves the entire CNS.

N-Acetylaspartate synthase is bimodally expressed in microsomes and mitochondria of brain

N-Acetylaspartate (NAA) is an abundant amino acid derivative of the central nervous system that is localized primarily in neurons and has found widespread use in clinical NMR spectroscopy (MRS) as a non-invasive indicator of neuronal survival and/or viability. Its function, although still obscure, is thought to reflect its unusual metabolic compartmentalization wherein NAA synthase occurs in the neuron and aspartoacylase, the hydrolytic enzyme that removes the acetyl moiety, occurs in myelin and glia. The NAA synthase enzyme, acetyl-CoA/l-aspartate N-acetyltransferase (ANAT), was previously shown to function in mitochondria (MIT), although other subcellular fractions were apparently not examined. In this study we confirmed its presence in MIT but also found significant activity in rat brain microsomes (MIC). The reaction mixture, consisting of [(14)C]aspartate plus acetyl-CoA in Na-phosphate buffer (pH 7), gave rise to [(14)C]NAA that was separated and quantified by TLC. Reaction rates were 29.0+/-0.46 and 6.27+/-0.27 nmol/h/mg for MIC and MIT, respectively. K(m) values and pH optima were similar, and both fractions showed modest enhancement of ANAT activity with the detergents Triton CF-54 and CHAPS. Our tentative conclusion is that ANAT is bimodally targeted to MIT and a component of MIC-likely endoplasmic reticulum. ANAT activity increased in both MIC and MIT between 29 and 60 days of age but differed thereafter in that only MIT ANAT showed a decrease after 1 year.

Molecular cloning, tissue expression, and partial characterization of the major fish CNS myelin protein 36k

A full-length cDNA clone encoding the major structural protein of trout CNS myelin 36K was isolated and sequenced. The deduced amino acid sequence did not reveal a putative transmembrane domain and exhibited no structural homology with any of the known myelin proteins. 36K instead shared characteristic structural elements with enzymes of the short-chain dehydrogenase family. The highest similarity in the database (60%), however, was obtained with a human protein of unknown function. By Northern blotting, a single mRNA species of about 2 kb was identified, which was expressed in brain tissue but not in liver. By in situ hybridization, a selective labeling of myelinating glial cells in the trout CNS but not in the PNS was revealed. The developmental appearance of the 36K transcript closely coincided with a period of active myelin deposition in most regions of the trout brain. As a first step in elucidating the structural and biochemical role of 36K for myelin formation and maintenance, we have overexpressed it in Escherichia coli as a soluble His-tag fusion protein and purified it in high yield by Ni+-chelated affinity chromatography. By SDS-PAGE, a single band of the expected molecular size was revealed, which heavily cross-reacted with polyclonal antibodies generated against the native protein. The results of circular dichroism spectroscopy are compatible with a betaalphabeta-barrel structure (Rossman fold), confirming the results of computer-assisted secondary structure predictions.