Immature Myelin Research Articles

Olig2 Ablation in Immature Oligodendrocytes Does Not Enhance CNS Myelination and Remyelination.

The oligodendrocyte (OL) lineage transcription factor Olig2 is expressed throughout oligodendroglial development and is essential for oligodendroglial progenitor specification and differentiation. It was previously reported that deletion of Olig2 enhanced the maturation and myelination of immature OLs and accelerated the remyelination process. However, by analyzing multiple Olig2 conditional KO mouse lines (male and female), we conclude that Olig2 has the opposite effect and is required for OL maturation and remyelination. We found that deletion of Olig2 in immature OLs driven by an immature OL-expressing Plp1 promoter resulted in defects in OL maturation and myelination, and did not enhance remyelination after demyelination. Similarly, Olig2 deletion during premyelinating stages in immature OLs using Mobp or Mog promoter-driven Cre lines also did not enhance OL maturation in the CNS. Further, we found that Olig2 was not required for myelin maintenance in mature OLs but was critical for remyelination after lysolecithin-induced demyelinating injury. Analysis of genomic occupancy in immature and mature OLs revealed that Olig2 targets the enhancers of key myelination-related genes for OL maturation from immature OLs. Together, by leveraging multiple immature OL-expressing Cre lines, these studies indicate that Olig2 is essential for differentiation and myelination of immature OLs and myelin repair. Our findings raise fundamental questions about the previously proposed role of Olig2 in opposing OL myelination and highlight the importance of using Cre-dependent reporter(s) for lineage tracing in studying cell state progression.SIGNIFICANCE STATEMENT Identification of the regulators that promote oligodendrocyte (OL) myelination and remyelination is important for promoting myelin repair in devastating demyelinating diseases. Olig2 is expressed throughout OL lineage development. Ablation of Olig2 was reported to induce maturation, myelination, and remyelination from immature OLs. However, lineage-mapping analysis of Olig2-ablated cells was not conducted. Here, by leveraging multiple immature OL-expressing Cre lines, we observed no evidence that Olig2 ablation promotes maturation or remyelination of immature OLs. Instead, we find that Olig2 is required for immature OL maturation, myelination, and myelin repair. These data raise fundamental questions about the proposed inhibitory role of Olig2 against OL maturation and remyelination. Our findings highlight the importance of validating genetic manipulation with cell lineage tracing in studying myelination.

Elucidation of peripheral nerve myelination by bimodal waveform analysis

PurposeAs the myelin sheath of the peripheral nerves is immaturely developed in children, a bimodal waveform may be evoked when sensory nerve conduction studies are performed in them. However, there has been no study regarding the relationship between age and the frequency of appearance of the bimodal waveform or the inter-peak latency. Herein, we examined how the bimodal waveform changes with age. MethodsA total of 218 sensory nerves (109 median and 109 ulnar nerves) in 86 children (0 to 15 years old) were analyzed. The frequency of the bimodal waveform and the distance-corrected inter-peak latency were examined with antidromic sensory nerve conduction studies of the upper limbs on proximal stimulation. ResultsThe frequency of bimodal waveforms and distance-corrected inter-peak latency decreased with age. Analysis of the slope line of the scatter plot demonstrated that the bimodal waveform was present until the age of 15–16 years. ConclusionThe bimodal waveform of sensory nerves faded with growth. Given that development-associated temporal dispersion is considered to be the cause of the differences in the bimodal waveform, our findings suggest that the underlying cause of the bimodal waveform is an immature myelin sheath, which may not be fully developed until the age of 15–16 years.

Effect of swimming on oligodendrocytic cells and myelin tissue in corpus callosum of rat model of MS induced by Cuprizone

Background: Multiple Sclerosis is a myelin destroyer disease, which physical activity can be effective in improving it. Therefore, in the present study, the effect of swimming on oligodendrocytic cells and myelin tissue in rat brain of the Cuprizone model of MS disease is investigated. Methods: In this study, 21 male Wistar rats were randomly divided into Control groups, Cuprizone and Swim + Cuprizone. For the induction of MS, Cuprizone 0.6% were gavaged for one month. The group of Swim + Cuprizone swam at the same time with gavage. The training program included 4 weeks of swimming for 5 sessions per week and 30 minutes. Immunohistochemistry technique was used to determine the percentage of immature and mature oligodendrocytes and Luxol fast blue solution for evaluation of myelin density. Image j software and One-way ANOVA was used to analyze the findings. Results: The mean percentage of immature and mature oligodendrocytes and myelin density in the Swim+Cuprizone group was significantly higher than that of the Cuprizone group (p≤0.05). Conclusion: Swimming decreases destruction of the oligodendrocytes and myelin cells due to Cuprizone.

The Alteration of Brain Interstitial Fluid Drainage with Myelination Development

The integrity of myelination is crucial for maintaining brain interstitial fluid (ISF) drainage in adults; however, the mechanism of ISF drainage with immature myelin in the developing brain remains unknown. In the present study, the ISF drainage from the caudate nucleus (Cn) to the ipsilateral cortex was studied at different developmental stages of the rat brain (P 10, 20, 30, 40, 60, 80, 10-80). The results show that the traced ISF drained to the cortex from Cn and to the thalamus in an opposite direction before P30. From P40, we found impeded drainage to the thalamus due to myelin maturation. This altered drainage was accompanied by enhanced cognitive and social functions, which were consistent with those in the adult rats. A significant difference in diffusion parameters was also demonstrated between the extracellular space (ECS) before and after P30. The present study revealed the alteration of ISF drainage regulated by myelin at different stages during development, indicating that a regional ISF homeostasis may be essential for mature psychological and cognitive functions.

Oligodendrogenesis increases in hippocampal grey and white matter prior to locomotor or memory impairment in an adult mouse model of tauopathy.

Myelin and axon losses are associated with cognitive decline in healthy ageing but are worse in people diagnosed with tauopathy. To determine whether tauopathy is also associated with enhanced myelin plasticity, we evaluated the behaviour of OPCs in mice that expressed a human pathological variant of microtubule‐associated protein tau (MAPTP301S ). By 6 months of age (P180), MAPTP301S mice overexpressed hyperphosphorylated tau and had developed reactive gliosis in the hippocampus but had not developed overt locomotor or memory impairment. By performing cre‐lox lineage tracing of adult OPCs, we determined that the number of newborn oligodendrocytes added to the hippocampus, entorhinal cortex and fimbria was equivalent in control and MAPTP301S mice prior to P150. However, between P150 and P180, significantly more new oligodendrocytes were added to these regions in the MAPTP301S mouse brain. This large increase in new oligodendrocyte number was not the result of increased OPC proliferation, nor did it alter oligodendrocyte density in the hippocampus, entorhinal cortex or fimbria, which was equivalent in P180 wild‐type and MAPTP301S mice. Furthermore, the proportion of hippocampal and fimbria axons with myelin was unaffected by tauopathy. However, the proportion of myelinated axons that were ensheathed by immature myelin internodes was significantly increased in the hippocampus and fimbria of P180 MAPTP301S mice, when compared with their wild‐type littermates. These data suggest that MAPTP301S transgenic mice experience significant oligodendrocyte turnover, with newborn oligodendrocytes compensating for myelin loss early in the development of tauopathy.

A case report of reversible generalized seizures in a patient with Waardenburg syndrome associated with a novel nonsense mutation in the penultimate exon of SOX10

BackgroundWaardenburg syndrome type 1 (WS1) can be distinguished from Waardenburg syndrome type 2 (WS2) by the presence of dystopia canthorum. About 96% of WS1 are due to PAX3 mutations, and SOX10 mutations have been reported in 15% of WS2.Case presentationThis report describes a patient with WS1 who harbored a novel SOX10 nonsense mutation (c.652G > T, p.G218*) in exon 3 which is the penultimate exon. The patient had mild prodromal neurological symptoms that were followed by severe attacks of generalized seizures associated with delayed myelination of the brain. The immature myelination recovered later and the neurological symptoms could be improved. This is the first truncating mutation in exon 3 of SOX10 that is associated with neurological symptoms in Waardenburg syndrome. Previous studies reported that the neurological symptoms that associate with WS are congenital and irreversible. These findings suggest that the reversible neurological phenotype may be associated with the nonsense mutation in exon 3 of SOX10.ConclusionsWhen patients of WS show mild prodromal neurological symptoms, the clinician should be aware of the possibility that severe attacks of generalized seizures may follow, which may be associated with the truncating mutation in exon 3 of SOX10.

MTORC1 promotes proliferation of immature Schwann cells and myelin growth of differentiated Schwann cells

The myelination of axons in peripheral nerves requires precisely coordinated proliferation and differentiation of Schwann cells (SCs). We found that the activity of the mechanistic target of rapamycin complex 1 (mTORC1), a key signaling hub for the regulation of cellular growth and proliferation, is progressively extinguished as SCs differentiate during nerve development. To study the effects of different levels of sustained mTORC1 hyperactivity in the SC lineage, we disrupted negative regulators of mTORC1, including TSC2 or TSC1, in developing SCs of mutant mice. Surprisingly, the phenotypes ranged from arrested myelination in nerve development to focal hypermyelination in adulthood, depending on the level and timing of mTORC1 hyperactivity. For example, mice lacking TSC2 in developing SCs displayed hyperproliferation of undifferentiated SCs incompatible with normal myelination. However, these defects and myelination could be rescued by pharmacological mTORC1 inhibition. The subsequent reconstitution of SC mTORC1 hyperactivity in adult animals resulted in focal hypermyelination. Together our data suggest a model in which high mTORC1 activity promotes proliferation of immature SCs and antagonizes SC differentiation during nerve development. Down-regulation of mTORC1 activity is required for terminal SC differentiation and subsequent initiation of myelination. In distinction to this developmental role, excessive SC mTORC1 activity stimulates myelin growth, even overgrowth, in adulthood. Thus, our work delineates two distinct functions of mTORC1 in the SC lineage essential for proper nerve development and myelination. Moreover, our studies show that SCs retain their plasticity to myelinate and remodel myelin via mTORC1 throughout life.

“As Little as Possible, As Much as Required”: Epilepsy Surgery in Children and Adults

Extensive, multilobar or hemispheric epileptogenic zones are usually associated with early epilepsy onset, a catastrophic course and, eventually, with the urgent need for early surgical intervention. The prevalent underlying etiologies of drug-resistant epilepsy in infants and young children are focal cortical dysplasia and glioneuronal tumors. The completeness of resection is the best predictor of postoperative seizure freedom, due to the intrinsic epileptogenicity of these lesions. Presurgical workup in the first years of life is challenging, due to the limitations of MRI diagnostics at an age of yet immature myelination. Infants and young children with a focal brain lesion may be favorable candidates for epilepsy surgery despite the prevalence of generalized EEG seizures and a diffuse pattern of hypsarrhythmia with multifocal bilateral interictal epileptiform discharges. Seizure semiology in focal epilepsies manifesting in the first years of life is rarely lateralizing and hardly ever localizing. Focal epileptogenic lesions in infancy may present with infantile spasms in the context of West syndrome. Young children undergo mostly multilobar and hemispheric procedures, in stark contrast to adults undergoing temporal lobe resections. Younger children require more extensive procedures, but have the potential to compensate neurological deficits due to increased brain plasticity in early life. Postoperative seizure freedom and anticonvulsant tapering are expected to have a positive effect on cognitive development, considering the devastating effects of seizures and anticonvulsants on the developing brain. This very young pediatric population differs to a great extent from adult cohorts with later epilepsy onset, due to a more limited epileptogenic zone, and later epilepsy surgery.

Development and characterization of a human embryonic stem cell-derived 3D neural tissue model for neurotoxicity testing

Alternative models for more rapid compound safety testing are of increasing demand. With emerging techniques using human pluripotent stem cells, the possibility of generating human in vitro models has gained interest, as factors related to species differences could be potentially eliminated. When studying potential neurotoxic effects of a compound it is of crucial importance to have both neurons and glial cells. We have successfully developed a protocol for generating in vitro 3D human neural tissues, using neural progenitor cells derived from human embryonic stem cells. These 3D neural tissues can be maintained for two months and undergo progressive differentiation. We showed a gradual decreased expression of early neural lineage markers, paralleled by an increase in markers specific for mature neurons, astrocytes and oligodendrocytes. At the end of the two-month culture period the neural tissues not only displayed synapses and immature myelin sheaths around axons, but electrophysiological measurements also showed spontaneous activity. Neurotoxicity testing – comparing non-neurotoxic to known neurotoxic model compounds – showed an expected increase in the marker of astroglial reactivity after exposure to known neurotoxicants methylmercury and trimethyltin. Although further characterization and refinement of the model is required, these results indicate its potential usefulness for in vitro neurotoxicity testing.

Accelerated remyelination during inflammatory demyelination prevents axonal loss and improves functional recovery.

Demyelination in MS disrupts nerve signals and contributes to axon degeneration. While remyelination promises to restore lost function, it remains unclear whether remyelination will prevent axonal loss. Inflammatory demyelination is accompanied by significant neuronal loss in the experimental autoimmune encephalomyelitis (EAE) mouse model and evidence for remyelination in this model is complicated by ongoing inflammation, degeneration and possible remyelination. Demonstrating the functional significance of remyelination necessitates selectively altering the timing of remyelination relative to inflammation and degeneration. We demonstrate accelerated remyelination after EAE induction by direct lineage analysis and hypothesize that newly formed myelin remains stable at the height of inflammation due in part to the absence of MOG expression in immature myelin. Oligodendroglial-specific genetic ablation of the M1 muscarinic receptor, a potent negative regulator of oligodendrocyte differentiation and myelination, results in accelerated remyelination, preventing axonal loss and improving functional recovery. Together our findings demonstrate that accelerated remyelination supports axonal integrity and neuronal function after inflammatory demyelination.

Normal Molecular Repair Mechanisms in Regenerative Peripheral Nerve Interfaces Allow Recording of Early Spike Activity Despite Immature Myelination

Clinical use of neurally controlled prosthetics has advanced in recent years, but limitations still remain, including lacking fine motor control and sensory feedback. Indwelling multi-electrode arrays, cuff electrodes, and regenerative sieve electrodes have been reported to serve as peripheral neural interfaces, though long-term stability of the nerve-electrode interface has remained a formidable challenge. We recently developed a regenerative multi-electrode interface (REMI) that is able to record neural activity as early as seven days post-implantation. While this activity might represent normal neural depolarization during axonal regrowth, it can also be the result of altered nerve regeneration around the REMI. This study evaluated high-throughput expression levels of 84 genes involved in nerve injury and repair, and the histological changes that occur in parallel to this early neural activity. Animals exhibiting spike activity increased from 29% to 57% from 7 to 14 days following REMI implantation with a corresponding increase in firing rate of 113%. Two weeks after implantation, numbers of neurofilament-positive axons in the control and REMI implanted nerves were comparable, and in both cases the number of myelinated axons was low. During this time, expression levels of genes related to nerve injury and repair were similar in regenerated nerves, both in the presence or absence of the electrode array. Together, these results indicate that the early neural activity is intrinsic to the regenerating axons, and not induced by the REMI neurointerface.

Death receptor 6 negatively regulates oligodendrocyte survival, maturation and myelination

Survival and differentiation of oligodendrocytes are important for the myelination of central nervous system (CNS) axons during development and crucial for myelin repair in CNS demyelinating diseases such as multiple sclerosis. Here we show that death receptor 6 (DR6) is a negative regulator of oligodendrocyte maturation. DR6 is expressed strongly in immature oligodendrocytes and weakly in mature myelin basic protein (MBP)-positive oligodendrocytes. Overexpression of DR6 in oligodendrocytes leads to caspase 3 (casp3) activation and cell death. Attenuation of DR6 function leads to enhanced oligodendrocyte maturation, myelination and downregulation of casp3. Treatment with a DR6 antagonist antibody promotes remyelination in both lysolecithin-induced demyelination and experimental autoimmune encephalomyelitis (EAE) models. Consistent with the DR6 antagoinst antibody studies, DR6-null mice show enhanced remyelination in both demyelination models. These studies reveal a pivotal role for DR6 signaling in immature oligodendrocyte maturation and myelination that may provide new therapeutic avenues for the treatment of demyelination disorders such as multiple sclerosis.

EEG gamma-band synchronization in visual coding from childhood to old age: Evidence from evoked power and inter-trial phase locking

To investigate lifespan age differences in neuronal mechanisms of visual coding in the context of perceptual discrimination. We recorded EEG from 17 children (10-12 years), 16 younger adults (20-26 years), and 17 older adults (70-76 years) during a simple choice-reaction task requiring discrimination of squares and circles of different sizes. We examined age-group differences in the effect of stimulus size on early ERP components, evoked gamma-band power, and inter-trial phase-stability in the gamma band as assessed by the phase-locking index (PLI). In the absence of age differences in discrimination accuracy, we observed reliable age differences in patterns of ERP, evoked gamma power, and PLI. P1 and N1 peak amplitudes were larger and the peak latencies longer in children than in adults. Children also showed lower levels of evoked power and PLI than adults. Older adults showed smaller increments in evoked power with increasing stimulus size than younger adults, but similar amounts of phase locking for small- and medium-sized stimuli as younger adults. The relative importance of different coding mechanisms in early visual areas changes from childhood to old age. Due to synaptic overproduction and immature myelination, the visual system of children is less entrained by incoming information, resulting in less synchronized neuronal responses. Adults primarily rely on sparse representations formed through experience-dependent temporally synchronized neuronal interactions. In old age, senescent decline in neuronal density and neurotransmitter availability further increase the reliance on temporally synchronized processing. Findings from this study defy the notion that sensory aging consists in a reversal of sensory development in childhood, and point to a high degree of age specificity in mechanisms of visual coding.

Another Case of Paroxysmal Tonic Downgaze in Infancy

Two years ago, Wolsey and Warner (1) reported in this journal on two healthy infants with brief episodes of downgaze followed by abnormal body movements. They called this condition “paroxysmal tonic downgaze” and considered it idiopathic and transient. We extend their report by describing a 2-month-old healthy boy presenting with an episodic downward gaze disturbance (Fig. 1).FIG. 1: Downward eye deviation in a 2-month-old boy. The downward eye deviation occurred many times per day, lasted from 10 to 90 seconds, and resolved spontaneously within 3 months.Born at term after an uneventful delivery and normal development, he was transferred for possible “seizures” from another hospital. The spells had started 7 days before presentation, coincident with a diagnosis of a new upper respiratory tract infection. We observed many spells per day that lasted between 10 and 90 seconds without any impairment in consciousness and seemed to occur more frequently when he was supine or upon awakening but never in an upright position or during sleep. They did not appear to follow touching or shaking. Longer spells were associated with stiffening of the right upper extremities. Ophthalmologic examination disclosed that he fixed and followed equally with each eye. He had normal alignment and full extraocular movements without nystagmus. Neurologic examination showed slightly reduced muscle tone but normal muscle strength and deep tendon reflexes. There was no ataxia. The child underwent MRI and an electroencephalogram (EEG) because of a report of hydrocephalus and seizures in very similar downgaze episodes in children aged 2 to 8 months (2) who later showed severe developmental disabilities. Results of these studies were normal. Because we could not entirely exclude opsoclonus-myoclonus syndrome, we undertook evaluation for neuroblastoma with ultrasound of the abdomen, urine for vanillylmandelic acid levels, and iodine-131 metaiodobenzylguanidine (MIBG) scanning (3). Results of all studies were negative. The episodes began to decrease in frequency spontaneously 1.5 months after they began and resolved within 3 months. He did not develop any neurologic problems in the subsequent 18 months and has had normal development except for a slight delay in expressive language and a mild attention deficit. The pathogenesis of this transient gaze disturbance is not understood. Some observers have hypothesized that it may be the result of immature myelination of the corticomesencephalic vertical gaze pathways (4). Its transient nature, especially in older infants, may result from temporary failure of cortical compensation when a stressor such an illness is present (5). Our experience reinforces the idiopathic and transient nature of this condition. Even so, this manifestation is frightening. Because more serious conditions cannot be entirely excluded, imaging and an EEG cannot be avoided. Meropi Tzoufi, MD Polyxeni Sixlimiri, MD Alexandros Makis, MD Antigone Siamopoulou-Mavridou, MD Child Health Department Medical School of the University of Ioannina Ioannina, Greece E-mail: [email protected]

Mild cognitive impairment and subjective cognitive impairment

Mild cognitive impairment and subjective cognitive impairment

Iron in the Brain

After completing this article, readers should be able to: 1. Describe the role of iron in proteins involved in neuronal and glial energy metabolism, myelin production, and monoamine neurotransmitter metabolism. 2. Indicate the neonates who are at risk for iron deficiency. 3. Explain how iron deficiency affects the biochemistry, structure, signaling molecules, and electrophysiology of the hippocampus. 4. Describe the primary causes of iron overload in the neonate. 5. Explain why the preterm infant is at particular risk for iron deficiency. This article is designed to acquaint readers with the role of iron in early brain development. Several important principles that govern the effects of nutrients on the immature brain are discussed, followed by an explanation of the roles of iron during development. Because the developing brain is sensitive to iron overload as well as iron deficiency, both are discussed in the context of human studies and in model systems. The first guiding principle of nutrient-brain interactions during development is the concept of timing, dose, and duration. (1) The positive or negative effects of any nutrient depend on which brain regions or processes are developing at the time that nutrient status is altered and the requirements of those regions for the nutrient during that time of development. Generally, the more rapidly an area is developing, the more vulnerable it is. Dependence on specific nutrients during phases of rapid proliferation or differentiation results in the second principle, a regionalization of brain effects during periods of nutrient deficiency. In the case of iron deficiency, certain brain areas that are dependent on iron for proper development are more vulnerable than areas that are less dependent on iron. Additionally, these same brain areas are likely to be more vulnerable at certain time points than at others. To exert a maximal effect on regional brain development, the timing of iron …

Neuronal differentiation of stem cells isolated from adult muscle.

Lineage uncommitted pluripotent stem cells reside in the connective tissue of skeletal muscle. The present study was carried out with pluripotent stem cells (PPSCs) isolated from 6-month old rat muscle. Before differentiation, these cells were vimentin+, CD90+, CD45-, and varied in their expression of CD34. The PPSCs were expanded as non-adherent aggregates under similar conditions to those used to generate neurospheres from embryonic or neural stem cells. The PPSC-derived neurospheres were positive for nestin, an early marker present in neuronal precursors, and expressed the two alternative mRNA forms of the neuroectodermal marker Pax-6, as well as mRNA for Oct-4, a gene related to the pluripotentiality of stem cells. To confirm their neural potential, PPSC-derived neurospheres were plated on coated coverslips under varying conditions: Neurobasal medium with N2 or B27, and either NT3 or BDNF. After 4-6 days the cells expressed neuronal (Tuj1+, NF68), astrocytic (GFAP) and oligodendrocytic (MOSP+, MBP+) markers, both by immunocytochemistry and RT-PCR. In addition, PPSCs were cultured as monolayers under adherent conditions, exposed to growth factors and defined differentiating conditions for 5 hr, and subsequently kept for 2 days in a maturation medium. At this point they gave rise to a mixed population of early neural progenitors (Nestin+ or NG2+), immature and mature neurons (Tuj1+ and NF145+) and myelin producing oligodendrocytes (CNPase + and MOSP+). Our study shows that PPSCs present in adult muscle can overcome germ lineage restrictions and express the molecular characteristics of brain cells. Therefore, PPSCs isolated from adult muscle could provide a novel source for autologous cell replacement in neurodegenerative and demyelinating diseases.

Enhanced T cell responsiveness to citrulline-containing myelin basic protein in multiple sclerosis patients.

Myelin basic protein (MBP), a candidate autoantigen in multiple sclerosis (MS), exists in different isoforms and charge isomers generated by differential splicing of exons and by a combination of posttranslational modifications, respectively. These various isoforms and charge isomers of MBP vary in abundance and most likely serve different functions during myelinogenesis and remyelination. The least cationic among the charge isomers of MBP is citrullinated and is referred to as MBP-C8. MBP-C8 is relatively increased in the population of MBP isomers in more developmentally immature myelin and in MS brain tissue. In a previous study, we found that MBP-C8-reactive T cells could be detected in CD4+ T cell lines (TCL) generated with MBP from both MS patients and normal controls. Here, we examined the frequency and peptide specificity of MBP-C8-specific TCL generated with MBP-C8 in MS patients and controls. Ten subjects grouped in five sets, each an MS patient and a control, were studied. In all cases, the MS patient had either a higher overall number of MBP-C8-responding lines, responded with greater sensitivity to the MBP-C8 antigen or both. Few lines responded to the MBP-C8 peptides but, if they did, they appeared to be specific to the carboxyl-half of the MBP-C8 molecule. Given the large amounts of citrullinated MBP in MS brain tissue, a preferential T cell response to MBP-C8 may be involved in the induction and perpetuation of this disease. Multiple Sclerosis (2000) 6 220 - 225

Highly deiminated isoform of myelin basic protein from multiple sclerosis brain causes fragmentation of lipid vesicles

Myelin basic protein (MBP) occurs as a number of charge isomers due to phosphorylation, deamidation, and deimination of arginine to citrulline. All of these modifications decrease the net positive charge of the protein and its ability to cause aggregation of negatively charged lipid vesicles. This is used as a model system for the ability of MBP to cause adhesion of the cytosolic surfaces of myelin. Therefore, the effect of two deiminated forms of MBP on lipid vesicles was compared with that of the unmodified, most positively charged isomer, C1, to determine how loss of positively charged arginines would affect the function of MBP. The deiminated forms were the isomer isolated from normal human brains, in which only 6 Arg are deiminated to citrulline (MBP-Cit(6)), and an isomer isolated from the brain of a patient who died with acute, fulminating multiple sclerosis (Marburg type), in which 18 of the 19 Arg were deiminated (MBP-Cit(18)). Whereas C1 caused aggregation of lipid vesicles, resulting in an increase in absorbance due to light scattering, MBP-Cit(18) caused a decrease in absorbance of the lipid vesicles. Size exclusion chromatography and negative staining electron microscopy showed that this was due to fragmentation of the large multilayered vesicles into much smaller vesicles. MBP-Cit(6) caused less aggregation of lipid vesicles than did C1. However, no fragmentation of the vesicles into smaller ones in the presence of C1 and MBP-Cit(6) was detected by size exclusion chromatography or electron microscopy. The membrane fragmentation caused by MBP-Cit(18) is dramatically different from the effects of other forms of MBP from normal brain and may indicate a pathogenic effect of this charge isomer, which may have contributed to the severity of the Marburg type of multiple sclerosis. Alternatively, the deimination may have been a secondary effect resulting from the disease process. Regardless of the role of MBP-Cit(18) in multiple sclerosis, the effect of this modification indicates that, when most of the arginines of MBP are modified to an uncharged amino acid, the protein acquires properties similar to an apolipoprotein; thus, it may take up an amphipathic structure when bound to lipid. A partly amphipathic character may also be related to the role of MBP-Cit(6) in normal immature myelin, where it is the predominant charge isomer.

Highly deiminated isoform of myelin basic protein from multiple sclerosis brain causes fragmentation of lipid vesicles

Myelin basic protein (MBP) occurs as a number of charge isomers due to phosphorylation, deamidation, and deimination of arginine to citrulline. All of these modifications decrease the net positive charge of the protein and its ability to cause aggregation of negatively charged lipid vesicles. This is used as a model system for the ability of MBP to cause adhesion of the cytosolic surfaces of myelin. Therefore, the effect of two deiminated forms of MBP on lipid vesicles was compared with that of the unmodified, most positively charged isomer, C1, to determine how loss of positively charged arginines would affect the function of MBP. The deiminated forms were the isomer isolated from normal human brains, in which only 6 Arg are deiminated to citrulline (MBP-Cit6), and an isomer isolated from the brain of a patient who died with acute, fulminating multiple sclerosis (Marburg type), in which 18 of the 19 Arg were deiminated (MBP-Cit18). Whereas C1 caused aggregation of lipid vesicles, resulting in an increase in absorbance due to light scattering, MBP-Cit18 caused a decrease in absorbance of the lipid vesicles. Size exclusion chromatography and negative staining electron microscopy showed that this was due to fragmentation of the large multilayered vesicles into much smaller vesicles. MBP-Cit6 caused less aggregation of lipid vesicles than did C1. However, no fragmentation of the vesicles into smaller ones in the presence of C1 and MBP-Cit6 was detected by size exclusion chromatography or electron microscopy. The membrane fragmentation caused by MBP-Cit18 is dramatically different from the effects of other forms of MBP from normal brain and may indicate a pathogenic effect of this charge isomer, which may have contributed to the severity of the Marburg type of multiple sclerosis. Alternatively, the deimination may have been a secondary effect resulting from the disease process. Regardless of the role of MBP-Cit18 in multiple sclerosis, the effect of this modification indicates that, when most of the arginines of MBP are modified to an uncharged amino acid, the protein acquires properties similar to an apolipoprotein; thus, it may take up an amphipathic structure when bound to lipid. A partly amphipathic character may also be related to the role of MBP-Cit6 in normal immature myelin, where it is the predominant charge isomer. J. Neurosci. Res. 57:529–535, 1999. © 1999 Wiley-Liss, Inc.