Selenium is required for normal upregulation of myelin genes in differentiating oligodendrocytes

Effect of Selenium Nanoparticle Supplementation on Tissue Inflammation, Blood Cell Count, and IGF-1 Levels in Spinal Cord Injury-Induced Rats

Selenium is known to be a neuroprotective agent in respect to a number of neuronal diseases and pain. The aim of this study was to evaluate the neuroprotective effect of the oral administration of selenium nanoparticles in rats with spinal cord injury (SCI). Forty adult female rats were randomly assigned to two equal groups as experimental and control. Under general inhalation anesthesia, in both groups, SCI was created, at the T9-10 level of the column. On the third day after the operation, a supplement of selenium nanoparticle was administered to the experimental group at 0.2 mg/kg per day. The histology of the site of injury, IGF-1 serum concentrations, and changes in the white blood cells were examined in both groups at different pre-surgical and post-surgical times. The results of the current study showed a significant decrease in the total white blood cells, including lymphocyte, neutrophil, and monocyte in the experimental group compared to the control group. Histological evaluation showed that the inflammatory responses reduced significantly in the experimental group compared to the control group. In conclusion, we speculate that the decrease in the number of inflammatory cells after oral administration of the selenium nanoparticles is due to the neuroprotective effects of this nanoparticle.

Cytoprotective and antioxidant properties of organic selenides for the myelin-forming cells, oligodendrocytes

Here a new series of twenty-one organoselenides, of potential protective activity, were synthesized and tested for their intrinsic cytotoxicity, anti-apoptotic and antioxidant capacities in oligodendrocytes. Most of the organoselenides were able to decrease the ROS levels, revealing antioxidant properties. Compounds 5b and 7b showed a high glutathione peroxidase (GPx)-like activities, which were 1.5 folds more active than ebselen. Remarkably, compound 5a diminished the formation of the oligodendrocytes SubG1 peak in a concentration-dependent manner, indicating its anti-apoptotic properties. Furthermore, based on the SwissADME web interface, we performed an in-silico structure-activity relationship to explore the drug-likeness of these organoselenides, predicting the pharmacokinetic parameters for compounds of interest that could cross the blood-brain barrier. Collectively, we present new organoselenide compounds with cytoprotective and antioxidant properties that can be considered as promising drug candidates for myelin diseases.

Responses of an American eel brain endothelial-like cell line to selenium deprivation and to selenite, selenate, and selenomethionine additions in different exposure media

The effect of selenium deprivation and addition on the American eel brain endothelial cell line (eelB) was studied in three exposure media: complete growth medium (L15/FBS), serum-free medium (L15), and minimal medium (L15/ex). L15/ex contains only galactose and pyruvate and allowed the deprivation of selenium on cells to be studied. In L15/ex, without any obvious source of selenium, eelB cells survived for at least 7 d, formed capillary-like structures (CLS) on Matrigel, and migrated to heal wounds. Three selenium compounds were added to cultures: selenite, selenate, and selenomethionine (SeMet). Adding selenite or selenate to eelB cell cultures for 24 h caused dose-dependent declines in cell viability, regardless of the exposure media. Although varying with exposure media and viability end point, selenite was approximately 70-fold more cytotoxic than selenate. By contrast, 24 h exposures to either DL- or L-SeMet in the three media caused little or no cytotoxicity. However for 7 d exposures in L15/ex, DL- and L-SeMet were very cytotoxic, even at the lowest tested concentration of 31 μM. By contrast in L15 and L15/FBS, cytotoxicity was only observed with 500 and 1000 μM L-SeMet. In L15/FBS, eelB continued to migrate and form CLS in the presence of SeMet but at 500 μM, cell migration appeared stimulated. As judged from a colony-forming assay over 14 d in L15/FBS, 500 and 1000 μM DL- and L-SeMet inhibited cell proliferation. Overall, the responses of eel cells to selenium depended on the selenium form, concentration, and exposure media, with responses to SeMet being most dependent on exposure media.

Selenoprotein W was Correlated with the Protective Effect of Selenium on Chicken Myocardial Cells from Oxidative Damage

Selenium (Se) mainly performs its function through Se-containing proteins. Selenoprotein W (SelW), one member of the selenoprotein family, plays important roles in the normal function of the heart. To investigate the possible relationship between Se and SelW for the regulation of oxidative damage in chicken embryo myocardial cells, we treated myocardial cells with Se and H2O2. Then, the levels of lactate dehydrogenase (LDH) and 3,4-methylenedioxyamphetamine in the culture media, levels of SelW, inflammatory genes NF-κB, tumor necrosis factor (TNF)-α, p53, and the cell cycle were analyzed. Furthermore, the correlation between SelW and the levels of these factors was determined. The results indicated that Se treatment increased the expression of SelW (P < 0.05) and caused a downregulation of p53, NF-κB, and TNF-α (P < 0.05). In contrast, H2O2 increased the expression of p53, NF-κB, TNF-α, and LDH (P < 0.05) and induced early cell apoptosis, which was alleviated by treatment with Se. In addition, SelW had a positive correlation with the levels of inflammatory genes investigated. Taken together, our findings suggested that SelW is sensitive to Se levels and oxidative stress, and may play a role in the protective function of Se against oxidative damage and inflammation in chicken myocardial cells.

Zebrafish as a model to investigate CNS myelination

Myelin plays a critical role in proper neuronal function by providing trophic and metabolic support to axons and facilitating energy-efficient saltatory conduction. Myelination is influenced by numerous molecules including growth factors, hormones, transmembrane receptors and extracellular molecules, which activate signaling cascades that drive cellular maturation. Key signaling molecules and downstream signaling cascades controlling myelination have been identified in cell culture systems. However, in vitro systems are not able to faithfully replicate the complex in vivo signaling environment that occurs during development or following injury. Currently, it remains time-consuming and expensive to investigate myelination in vivo in rodents, the most widely used model for studying mammalian myelination. As such, there is a need for alternative in vivo myelination models, particularly ones that can test molecular mechanisms without removing oligodendrocyte lineage cells from their native signaling environment or disrupting intercellular interactions with other cell types present during myelination. Here, we review the ever-increasing role of zebrafish in studies uncovering novel mechanisms controlling vertebrate myelination. These innovative studies range from observations of the behavior of single cells during in vivo myelination as well as mutagenesis- and pharmacology-based screens in whole animals. Additionally, we discuss recent efforts to develop novel models of demyelination and oligodendrocyte cell death in adult zebrafish for the study of cellular behavior in real time during repair and regeneration of damaged nervous systems.

Possible correlation between selenoprotein W and myogenic regulatory factors in chicken embryonic myoblasts

The biological function of selenium (Se) is mainly elicited through Se-containing proteins. Selenoprotein W (SelW), one member of the selenoprotein family, is essential for the normal function of the skeletal muscle system. To investigate the possible relationship of Se in the process of differentiation in chicken myoblasts and the expression of SelW, the cultured chicken embryonic myoblasts were incubated with sodium selenite at different concentrations for 72 h, and then the mRNA levels of SelW and myogenic regulatory factors (MRFs) in myoblasts were determined at 12, 24, 48, and 72 h, respectively. Furthermore, the correlation between SelW mRNA expression and MRF mRNA expression was assessed. The results showed that the sodium selenite medium enhanced the mRNA expression of SelW, Myf-5, MRF4, and myogenin in chicken myoblasts. The mRNA expression levels of MRFs were significantly correlated with those of SelW at 24, 48, and 72 h. These data demonstrate that Se is involved in the differentiation of chicken embryonic myoblasts, and SelW showed correlation with MRFs.

Oligodendrocyte-protection and remyelination post-spinal cord injuries: a review

In the past four decades, the main focus of investigators in the field of spinal cord regeneration has been to devise therapeutic measures that enhance neural regeneration. More recently, emphasis has been placed on enhancing remyelination and providing oligodendrocyte-protection after a spinal cord injury (SCI). Demyelination post-SCI is part of the cascading secondary injury that takes place immediately after the primary insult; therefore, therapeutic measures are needed to reduce oligodendrocyte death and/or enhance remyelination during the acute stage, preserving neurological functions that would be lost otherwise. In this review a thorough investigation of the oligodendrocyte-protective and remyelinative molecular therapies available to date is provided. The advent of new biomaterials shown to promote remyelination post-SCI is discussed mainly in the context of a combinatorial approach where the biomaterial also provides drug delivery capabilities. The aim of these molecular and biomaterial-based therapies is twofold: (1) oligodendrocyte-protective therapy, which involves protecting already existing oligodendrocytes from undergoing apoptosis/necrosis; and (2) inductive remyelination, which involves harnessing the remyelinative capabilities of endogenous oligodendrocyte precursor cells (OPCs) at the lesion site by providing a suitable environment for their migration, survival, proliferation and differentiation. From the evidence reported in the literature, we conclude that the use of a combinatorial approach including biomaterials and molecular therapies would provide advantages such as: (1) sustained release of the therapeutic molecule, (2) local delivery at the lesion site, and (3) an environment at the site of injury that promotes OPC migration, differentiation and remyelination.

Microarray screening for genes involved in oligodendrocyte differentiation in the zebrafish CNS

Within the vertebrate nervous system, myelination is required for the normal function of neurons by facilitating the rapid conduction of action potentials along axons. Oligodendrocytes are glial cells which myelinate axons in the central nervous system. Disruption of myelination and remyelination failure can cause human diseases such as multiple sclerosis. Despite the importance of myelination, the molecular basis of oligodendrocyte differentiation and myelination are still poorly understood. To understand the molecular mechanisms which regulate oligodendrocyte differentiation and myelination, novel genes were identified using a microarray analysis. The analysis used oligodendrocyte lineage cells isolated from transgenic zebrafish expressing fluorescent proteins in the oligodendrocyte lineage cells. Seven genes not previously known to be involved in oligodendrocyte differentiation were identified, and their expression during oligodendrocyte development was validated.

Myelination in mouse dorsal root ganglion/Schwann cell cocultures

The established protocols for in vitro studies of peripheral nerve myelination with rat embryonic dorsal root ganglia (DRG) and postnatal Schwann cell cocultures do not work with mouse cells. Consequently, the full potential of this model, which would allow to perform cell type-specific, mixed genotype cocultures without cross-breeding the animals, cannot be exploited. We determined the conditions required to promote full myelination in cocultures of pre-purified mouse embryonic DRG and neonatal Schwann cells, and present a method which consistently yields 50-200 mature myelin sheaths/culture. Causes for the failure of the existing protocols to yield satisfactory results with mouse cells fell into three categories: the lack of adherent support provided by the substratum, growth factor and hormone deficiencies, and the high serum content of the media. For optimal results, mouse cocultures require a 3-dimensional substratum, a myelination-promoting culture medium containing pituitary extract, N2 supplement and forskolin, and a low serum concentration.

Selenium status in term and preterm infants during the first months of life

OBJECTIVE

We hypothesized that very low birth weight (VLBW) infants have reduced serum and red blood cell (RBC) selenium (Se) at birth, which decrease further with current nutrition and are associated with chronic lung disease and septicaemia.

DESIGN

We studied Se intake, concentration in serum and RBCs and glutathione peroxidase (GSH-Px) activity in preterm and term infants from birth until 16 weeks. Data are mean+/-standard deviation (s.d.).

SETTING

Seventy-two preterm infants in two groups, born in Berlin, gestational age 26+0/30+0 weeks, birth weight 845/1270 g, with low Se intake (2.2+/-0.8/2.5+/-1.2 microg/kg/day), and 55 term infants, gestational age 39+1 weeks, birth weight 3160 g, born in Venezuela (high Se intake: 29+/-8 microg/day).

RESULTS

A balance study in 10 preterm infants showed that Se is well absorbed from human milk (77+/-9%). Serum concentration was higher in term (142.0+/-40.0 microg/l) than in preterm infants (17.8+/-8.1/19.9+/-2.2 microg/l) at 4/7 weeks. Serum and RBC concentration of Se declined in all infants, low values in preterm infants did not correlate with chronic lung disease and septicaemia. GSH-Px activity in RBCs remained stable until 6 weeks of age in all infants and was not correlated with Se in RBCs.

CONCLUSIONS

Se concentration in serum decreases during the first weeks of life and depends on intake. GSH-Px activity is not useful as a marker for Se status in infants up to 16 weeks after birth.

Functional genomic analysis of oligodendrocyte differentiation

To better understand the molecular mechanisms governing oligodendrocyte (OL) differentiation, we have used gene profiling to quantitatively analyze gene expression in synchronously differentiating OLs generated from pure oligodendrocyte precursor cells in vitro. By comparing gene expression in these OLs to OLs generated in vivo, we discovered that the program of OL differentiation can progress normally in the absence of heterologous cell-cell interactions. In addition, we found that OL differentiation was unexpectedly prolonged and occurred in at least two sequential stages, each characterized by changes in distinct complements of transcription factors and myelin proteins. By disrupting the normal dynamic expression patterns of transcription factors regulated during OL differentiation, we demonstrated that these sequential stages of gene expression can be independently controlled. We also uncovered several genes previously uncharacterized in OLs that encode transmembrane, secreted, and cytoskeletal proteins that are as highly upregulated as myelin genes during OL differentiation. Last, by comparing genomic loci associated with inherited increased risk of multiple sclerosis (MS) to genes regulated during OL differentiation, we identified several new positional candidate genes that may contribute to MS susceptibility. These findings reveal a previously unexpected complexity to OL differentiation and suggest that an intrinsic program governs successive phases of OL differentiation as these cells extend and align their processes, ensheathe, and ultimately myelinate axons.

Selenium and brain function: a poorly recognized liaison

Molecular biology has recently contributed significantly to the recognition of selenium (Se)2 and Se-dependent enzymes as modulators of brain function. Increased oxidative stress has been proposed as a pathomechanism in neurodegenerative diseases including, among others, Parkinson's disease, stroke, and epilepsy. Glutathione peroxidases (GPx), thioredoxin reductases, and one methionine-sulfoxide-reductase are selenium-dependent enzymes involved in antioxidant defense and intracellular redox regulation and modulation. Selenium depletion in animals is associated with decreased activities of Se-dependent enzymes and leads to enhanced cell loss in models of neurodegenerative disease. Genetic inactivation of cellular GPx increases the sensitivity towards neurotoxins and brain ischemia. Conversely, increased GPx activity as a result of increased Se supply or overexpression ameliorates the outcome in the same models of disease. Genetic inactivation of selenoprotein P leads to a marked reduction of brain Se content, which has not been achieved by dietary Se depletion, and to a movement disorder and spontaneous seizures. Here we review the role of Se for the brain under physiological as well as pathophysiological conditions and highlight recent findings which open new vistas on an old essential trace element.

Molecular Actions of Selenium in the Brain: Neuroprotective Mechanisms of an Essential Trace Element

In addition to acting as an essential nutrient for the immune system and overall body function, it is apparent that selenium also plays a critical role in the operation of the nervous system. Selenium itself is a constituent of selenoproteins, which are primarily involved in antioxidant function and redox status. However, apart from its covalent incorporation into these proteins, selenium also performs neuroprotective actions independent of translational processes. Furthermore, low selenium intake has detrimental effects on proper brain function, such as epileptic episodes and neuronal cell death, which have, in turn, been shown to be mitigated by higher selenium levels. Understanding the mechanisms of selenium action will be crucial to determining its potential as a preventive and therapeutic agent against excitatory brain damage.

Selenium deficiency increases susceptibility to glutamate-induced excitotoxicity

Excitotoxic brain lesions, such as stroke and epilepsy, lead to increasing destruction of neurons hours after the insult. The deadly cascade of events involves detrimental actions by free radicals and the activation of proapoptotic transcription factors, which finally result in neuronal destruction. Here, we provide direct evidence that the nutritionally essential trace element selenium has a pivotal role in neuronal susceptibility to excitotoxic lesions. First, we observed in neuronal cell cultures that addition of selenium in the form of selenite within the physiological range protects against excitotoxic insults and even attenuates primary damage. The neuroprotective effect of selenium is not directly mediated via antioxidative effects of selenite but requires de novo protein synthesis. Gel shift analysis demonstrates that this effect is connected to the inhibition of glutamate-induced NF-kappaB and AP-1 activation. Furthermore, we provide evidence that selenium deficiency in vivo results in a massive increase in susceptibility to kainate-induced seizures and cell loss. These findings indicate the importance of selenium for prevention and therapy of excitotoxic brain damage.

Hydrogen peroxide induces transient dephosphorylation of tau protein in cultured rat oligodendrocytes

Oxidative stress is a major mediator of neurodegeneration. In this study, we tested the effects of oxidative stress induced by a brief exposure to hydrogen peroxide (H(2)O(2)) on the phosphorylation state of the tau protein in oligodendrocytes (OL). Primary oligodendrocyte cultures prepared from newborn rat brains were exposed to millimolar concentrations of H(2)O(2) for up to 15 min, and then incubated in normal medium for up to 12 h. The treatment caused morphological degeneration of OL characterized by the loss of cellular processes apparent approximately 3 h after H(2)O(2) exposure. The morphological degeneration was preceded by a profound dephosphorylation of tau protein revealed by immunoblot using monoclonal tau-1 antibody that recognizes the dephosphorylated epitope. The dephosphorylated form increased dramatically during H(2)O(2) exposure, peaked after 2 h of post-exposure, and returned to the baseline level within 12 h. Total tau protein levels were not changed in the course of the experiment as judged by immunoblotting with phosphorylation-insensitive tau-5 and 46-1 monoclonal antibodies. Our finding demonstrates that oxidative stress induces a rapid but transient dephosphorylation of tau protein that may underlie morphological degeneration of OL.

Expression of multiple larger-sized transcripts for several genes in oligodendrogliomas: potential markers for glioma subtype

Astrocytomas and oligodendrogliomas are two brain tumors that follow different clinical courses. Although many of these tumors can be identified based on standard histopathological criteria, a significant percentage present notable problems in diagnosis. To identify markers that might prove useful in distinguishing glioma subtypes, we prepared and analyzed cDNA libraries for differential expression of genes in an astrocytoma (grade II), an oligodendroglioma (grade II), and a meningioma (benign). The tumor libraries were compared by sequencing randomly selected clones and tabulating the expression frequency of each gene. In addition to identifying several genes previously reported or expected to be differentially expressed among these tumors, several potential new brain tumor markers were identified and confirmed by Northern blot analysis of a panel of brain tumors. A surprising result of this analysis was the observation that several larger-sized transcripts for various genes were predominantly expressed in the oligodendroglioma tumors, when compared to the other brain tumors or in non-tumor gray matter. These findings are consistent with different pre-mRNA splicing patterns observed between oligodendrogliomas and astrocytomas. In support of this hypothesis, our screen revealed significantly higher levels of two hnRNP A1 transcripts in oligodendrogliomas. hnRNP A1 is a component of the spliceosome whose expression levels affect splice site selection in vivo. The preferential expression of larger-sized transcripts for several genes in oligodendrogliomas may be useful for distinguishing astrocytic and oligodendroglial gliomas.

Higher order chromatin degradation in glial cells: the role of calcium

Higher order chromatin degradation (HOCD), i.e. the scission of nuclear chromatin loops at the matrix attachment regions (MARs), is a hallmark of programmed cell death. We have previously demonstrated that hydrogen peroxide (H(2)O(2)) induces rapid HOCD in cultured oligodendrocytes generating two subpopulations of DNA fragments of >or=400 and 50-200 kb. In the present study, we examined the involvement of calcium in this process. HOCD was induced in primary rat oligodendrocytes by exposure to 1 mM H(2)O(2) and assessed by field inversion gel electrophoresis with and without S1 endonuclease digestion, to detect single and double stranded fragmentation, respectively. Chelating intracellular calcium with BAPTA/AM prior to H(2)O(2) exposure inhibited HOCD in a dose-dependent manner. Complete inhibition of HOCD was attained with 50 muM BAPTA/AM. The pretreatment of cells with desferroxamine mesylate, which may lower intracellular calcium levels, also resulted in a profound inhibition of HOCD, but the initial chromatin digestion into >or=400 kb single stranded DNA fragments was unaffected. Neither removing extracellular calcium nor blocking calcium release from intracellular stores with TMB-8 affected HOCD. Moreover, increasing intracellular calcium with A23187 calcium ionophore did not induce HOCD. Subsequent study in nuclei purified from C6 glioma cells revealed that the endonuclease responsible for HOCD is calcium-independent, but is magnesium-dependent. Magnesium-induced HOCD was not affected by the removal of calcium from nuclei with EGTA, but was practically abrogated in nuclei prepared from BAPTA/AM-pretreated cells. These results indicate that although H(2)O(2)-induced HOCD is not directly mediated by an increase of intracellular calcium concentration, normal resting levels of intracellular calcium are required for the maintenance of MAR-associated endonuclease in an active form.

Hydrogen peroxide induces rapid digestion of oligodendrocyte chromatin into high molecular weight fragments

High molecular weight (HMW) fragmentation of nuclear chromatin was studied in cultured rat oligodendrocytes (OL) exposed to hydrogen peroxide (H2O2). Intact genomic DNA was isolated by agarose embedding, and analyzed by field inversion gel electrophoresis, with and without S1 endonuclease digestion to detect and discriminate between single and double stranded fragmentations, respectively. The exposure of OL to H2O2 resulted in a very rapid degradation of chromosomal DNA into HMW fragments that reflect native chromatin structure. Hence, within 10 min after the addition of 1 mM H2O2, a discrete pool representing approximately 45% of the nuclear chromatin underwent single strand digestion into >400 kb fragments likely at AT-rich matrix attachment regions. Subsequent accumulation of single stand breaks at these regions led to bifilar scission. Ultimately, chromatin within this susceptible pool was cleaved at remaining matrix attachment regions into 50-200 kb fragments. Chromatin digestion could be elicited with H2O2 concentrations as low as 50 microM. After the removal of H2O2, most >400 kb fragments were religated within 2 h; however, digestion into 50-200 kb fragments was irreversible. The DNA digestion was not accompanied by the degradation of nuclear proteins, i.e., lamins A/C and poly (ADP-ribose) polymerase indicating that chromatin fragmentation is unlikely to be mediated by proteolysis. In conclusion, H2O2 at pathologically relevant concentrations induces a very rapid and extensive digestion of OL chromatin into HMW fragments. Because the chromatin fragmentation is only partly reversible, it may be a decisive factor in committing oxidatively stressed OL to degeneration and/or death.

Chemopreventive mechanisms of selenium

The element selenium (Se) was recognized only 40 years ago as being essential in the nutrition of animals and humans. It is recognized as being an essential component of a number of enzymes in which it is present as the amino acid selenocysteine (SeCys). Selenium compounds have also been found to inhibit tumorigenesis in a variety of animal models and recent studies indicate that supplemental Se in human diets may reduce cancer risk. Anti-tumorigenic activities have been associated with Se intakes that are more than sufficient to correct nutritionally deficient status; that is, Se appears to be anti-tumorigenic at intakes that are substantially greater than those associated with maximal expression of the known SeCys-containing enzymes. Therefore, while some cancer protection may involve one or more Se-enzymes, it is probable that anti-tumorigenic functions of Se are discharged by certain Se-metabolites produced in significant amounts at relatively high Se intakes. Thus, Se supplementation of individuals with relatively low or frankly deficient natural intakes of the element can be expected to support enhanced anti-oxidant protection due to increased expression of the Se-dependent glutathione peroxidases and thioredoxin reductase. Higher levels of Se-supplementation can be expected to affect other functions related to tumorigenesis: carcinogen metabolism, immune function, cell cycle regulation and apoptosis. Thus, according to this 2-stage model of the roles of Se in cancer prevention, even individuals with nutritionally adequate Se intakes may benefit from Se-supplementation.

Differentiation dependent activation of the myelin genes in purified oligodendrocytes is highly resistant to hypoglycemia

We have previously demonstrated that the developmental upregulation of myelin-specific genes in mixed glial cultures is strongly attenuated by hypoglycemia. The present study was designed to evaluate the effect of hypoglycemia on differentiation-dependent upregulation of myelin genes in purified oligodendrocyte cultures. The expression of major myelin protein genes, i.e., proteolipid protein (PLP), basic protein (BP) and myelin associated glycoprotein (MAG) were monitored by Northern blot analysis. In control cultures maintained at 6 mg/ml of glucose, the expression of all the genes upregulated rapidly, and plateaued at approximately day 4. A similar pattern of differentiation-dependent upregulation was observed for the gene encoding a lipogenic enzyme, i.e., malic enzyme (ME). In contrast to mixed glial cultures, however, this developmental gene upregulation was not significantly affected by severe hypoglycemia (approximately 0.02 mg/ml). The results indicate that the effect of glucose deprivation on oligodendrocyte genes observed in mixed glial cultures is mediated by other cells. The upregulation of the genes in differentiating oligodendrocytes was accompanied by the production of myelin-related membrane that was isolated by density gradient fractionation. In contrast to the effect on gene expression, this anabolic activity was highly dependent on glucose, as seen from a profound suppression by severe hypoglycemia.

Antisense oligodeoxynucleotides targeted to MAG mRNA profoundly alter BP and PLP mRNA expression in differentiating oligodendrocytes: a caution

The applicability of antisense technology to suppress the expression of myelin associated glycoprotein (MAG) in cultured oligodendrocytes was evaluated. Differentiating oligodendrocyte precursor cells obtained by the shake-off method were exposed to nine unmodified antisense oligodeoxynucleotides (ODNs) targeted to the first seven exons of MAG mRNA. After four days, steady-state levels of MAG, proteolipid protein (PLP) and basic protein (BP) mRNAs were determined by Northern blot analysis. Only ODN annealing to 599-618 nt of the MAG mRNA (the junction of exon 5 and 6) resulted in a significant, 75% decrease in the MAG mRNA level. Unexpectedly, six other anti-MAG ODNs which had no significant effect on the MAG message, greatly increased the level of BP mRNA. The highest upregulation of approximately 12 fold was observed with ODN annealing to 139-168 nt (junction of exon 3 and 4). On the other hand, the 997-1016 ODN decreased the levels of BP and PLP messages by 70-80%. The 599-618 ODN also decreased the PLP mRNA by 85%. The results demonstrate that antisense ODNs targeted to one gene may profoundly alter the expression of other genes, and hence, complicate functional analysis of the targeted protein.

Delayed oligodendrocyte degeneration induced by brief exposure to hydrogen peroxide

An in vitro model system of cultured oligodendrocytes was used to determine the susceptibility of these cells to oxidative stress induced by 15 min exposure to millimolar concentrations of hydrogen peroxide (H2O2). Following the exposure, the cells were incubated in normal growth medium, and analyzed at different time points. Although no cell loss was observed during the exposure period, there was a progressive depletion of adherent cells during the postexposure period as seen from either the number of recoverable nuclei, or from total RNA content of the cultures. Both the rate and the extent of cell deletion was directly dependent on H2O2 concentration. Cell death was preceded by structural alterations in the nuclear envelope resulting in "fragile" nuclei which disintegrated during isolation. Northern blot analysis showed that the expression of myelin-specific genes was rapidly downregulated in H2O2-treated cells. On the other hand, the expression of antiapoptotic gene, bcl-2 featured massive but transient upregulation. Oligodendrocyte degeneration also featured genomic DNA degradation into high molecular weight fragments, which are likely to represent cleaved chromosomal loops. The results demonstrate vulnerability of oligodendrocytes to oxidative stress that induces rapid degeneration and ultimately leads to delayed cell death. This feature is highly relevant to oligodendrocyte damage and depletion following ischemic, traumatic, or inflammatory insults to the central nervous system (CNS).

Structural characterization of myelin-associated glycoprotein gene core promoter

Myelin-associated glycoprotein (MAG) is emerging as an important molecule involved in the plasticity and regeneration of the central nervous system. In this study, the structure of MAG gene promoter was characterized in cultured rat oligodendrocyte lineage cells. Heterogeneous transcription initiation with five major and eight minor start sites scattered within 72 bp was shown by primer extension analysis. This TATA-less core promoter contains no prominent initiator (Inr) elements associated with the transcription initiation sites, and hence, appears to utilize novel positioning mechanisms. Genomic footprinting analysis revealed several putative protein-binding regions overlapping the initiation sites and containing a multitude of CG-rich sequences. However, no conspicuous alterations in the protein-binding pattern were evident between O2A progenitors in which the gene is inactive, and mature oligodendrocytes with fully upregulated gene. The core promoter DNA features a differentiation-dependent demethylation as shown by genomic sequencing analysis. Three of eight cytosines are totally demethylated in oligodendrocyte chromosomes, indicating that these unmodified bases may be critical for full activation of the promoter. The core promoter is located within an internucleosomal linker, and the upstream regulatory region appears to be organized into an array of nucleosomes with hypersensitive linkers.