Expression Of Myelin-related Genes Research Articles

Nicotinic acetylcholine receptors mediate donepezil-induced oligodendrocyte differentiation.

Oligodendrocytes are the myelin-forming cells of the central nervous system (CNS). Failure of myelin development and oligodendrocyte loss results in serious human disorders, including multiple sclerosis. Here, we show that donepezil, an acetlycholinesterase inhibitor developed for the treatment of Alzheimer's disease, can stimulate oligodendrocyte differentiation and maturation of neural stem cell-derived oligodendrocyte progenitor cells without affecting proliferation or cell viability. Transcripts for essential myelin-associated genes, such as PLP, MAG, MBP, CNPase, and MOG, in addition to transcription factors that regulate oligodendrocyte differentiation and myelination, were rapidly increased after treatment with donepezil. Furthermore, luciferase assays confirmed that both MAG and MBP promoters display increased activity upon donepezil-induced oligodendrocytes differentiation, suggesting that donepezil increases myelin gene expression mainly through enhanced transcription. We also found that the increase in the number of oligodendrocytes observed following donepezil treatment was significantly inhibited by the nicotinic acetylcholine receptor (nAChR) antagonist mecamylamine, but not by the muscarinic acetylcholine receptor antagonist scopolamine. Moreover, donepezil-induced myelin-related gene expression was suppressed by mecamylamine at both the mRNA and protein level. These results suggest that donepezil stimulates oligodendrocyte differentiation and myelin-related gene expression via nAChRs in neural stem cell-derived oligodendrocyte progenitor cells. We show that donepezil, a drug for the treatment of Alzheimer disease, can stimulate oligodendrocyte differentiation and maturation of oligodendrocyte progenitor cells. Transcripts for essential myelin-associated genes, such as PLP, MAG, MBP, CNPase and MOG in addition to transcripton factors that regulate oligodendrocyte differentiation and myelination were rapidly increased after treatment with donepezil. These effects were partly dependent on nicotinic acetylcholine receptor (nAChR).

Long-term consequences of chronic fluoxetine exposure on the expression of myelination-related genes in the rat hippocampus.

The selective serotonin reuptake inhibitor (SSRI) fluoxetine is widely prescribed for the treatment of symptoms related to a variety of psychiatric disorders. After chronic SSRI treatment, some symptoms remediate on the long term, but the underlying mechanisms are not yet well understood. Here we studied the long-term consequences (40 days after treatment) of chronic fluoxetine exposure on genome-wide gene expression. During the treatment period, we measured body weight; and 1 week after treatment, cessation behavior in an SSRI-sensitive anxiety test was assessed. Gene expression was assessed in hippocampal tissue of adult rats using transcriptome analysis and several differentially expressed genes were validated in independent samples. Gene ontology analysis showed that upregulated genes induced by chronic fluoxetine exposure were significantly enriched for genes involved in myelination. We also investigated the expression of myelination-related genes in adult rats exposed to fluoxetine at early life and found two myelination-related genes (Transferrin (Tf) and Ciliary neurotrophic factor (Cntf)) that were downregulated by chronic fluoxetine exposure. Cntf, a neurotrophic factor involved in myelination, showed regulation in opposite direction in the adult versus neonatally fluoxetine-exposed groups. Expression of myelination-related genes correlated negatively with anxiety-like behavior in both adult and neonatally fluoxetine-exposed rats. In conclusion, our data reveal that chronic fluoxetine exposure causes on the long-term changes in expression of genes involved in myelination, a process that shapes brain connectivity and contributes to symptoms of psychiatric disorders.

Diffusion tensor imaging and myelin composition analysis reveal abnormal myelination in corpus callosum of canine mucopolysaccharidosis I

Children with mucopolysaccharidosis I (MPS I) develop hyperintense white matter foci on T2-weighted brain magnetic resonance (MR) imaging that are associated clinically with cognitive impairment. We report here a diffusion tensor imaging (DTI) and tissue evaluation of white matter in a canine model of MPS I. We found that two DTI parameters, fractional anisotropy (a measure of white matter integrity) and radial diffusivity (which reflects degree of myelination) were abnormal in the corpus callosum of MPS I dogs compared to carrier controls. Tissue studies of the corpus callosum showed reduced expression of myelin-related genes and an abnormal composition of myelin in MPS I dogs. We treated MPS I dogs with recombinant alpha-l-iduronidase, which is the enzyme that is deficient in MPS I disease. The recombinant alpha-l-iduronidase was administered by intrathecal injection into the cisterna magna. Treated dogs showed partial correction of corpus callosum myelination. Our findings suggest that abnormal myelination occurs in the canine MPS I brain, that it may underlie clinically-relevant brain imaging findings in human MPS I patients, and that it may respond to treatment.

Involvement of MeCP2 in Regulation of Myelin-Related Gene Expression in Cultured Rat Oligodendrocytes.

Methyl CpG binding protein 2 (MeCP2) is a multifunctional protein which binds to methylated CpG, mutation of which cause a neurodevelopmental disorder, Rett syndrome. MeCP2 can function as both transcriptional activator and repressor of target gene. MeCP2 regulate gene expression in both neuron and glial cells in central nervous system (CNS). Oligodendrocytes, the myelinating cells of CNS, are required for normal functioning of neurons and are regulated by several transcription factors during their differentiation. In current study, we focused on the role of MeCP2 as transcription regulator of myelin genes in cultured rat oligodendrocytes. We have observed expression of MeCP2 at all stages of oligodendrocyte development. MeCP2 knockdown in cultured oligodendrocytes by small interference RNA (siRNA) has shown increase in myelin genes (myelin basic protein (MBP), proteolipid protein (PLP), myelin oligodendrocyte glycoprotein (MOG), and myelin-associated oligodendrocyte basic protein (MOBP)), neurotrophin (brain-derived neurotrophic factor (BDNF)), and transcriptional regulator (YY1) transcripts level, which are involved in regulation of oligodendrocyte differentiation and myelination. Further, we also found that protein levels of MBP, PLP, DM-20, and BDNF also significantly upregulated in MeCP2 knockdown oligodendrocytes. Our study suggests that the MeCP2 acts as a negative regulator of myelin protein expression.

A novel model of demyelination and remyelination in a GFP-transgenic zebrafish.

ABSTRACTDemyelinating diseases consist of a variety of autoimmune conditions in which the myelin sheath is damaged due to genetic and/or environmental factors. During clinical treatment, some patients undergo partial remyelination, especially during the early disease stages. However, the mechanisms that regulate demyelination remain unclear. The myelin structure, myelin formation and myelin-related gene expression are highly conserved between mammals and zebrafish. Therefore, the zebrafish is an ideal model organism to study myelination. In this study, we generated a transgenic zebrafish Tg(mbp:nfsB-egfp) expressing a fusion protein composed of enhanced green fluorescent protein (EGFP) and NTR from the myelin basic protein (mbp) promoter. Tg(mbp:nfsB-egfp) expressed NTR-EGFP reproducibly and hereditarily in oligodendrocytes along the spinal cord. Treatment of zebrafish larvae Tg(mbp:nfsB-egfp) with metronidazole (Mtz) resulted in the selective ablation of oligodendrocytes and led to demyelination, accompanied by behavioral changes, including decreased total movement distance, velocity, total movement time and fast movement time. After withdrawal of Mtz for a seven day recovery period, the expression of EGFP and MBP protein was observed again which indicates remyelination. Additionally, locomotor capacity was restored. Collectively, Tg(mbp:nfsB-egfp), a heritable and stable transgenic line, provides a novel, powerful tool to study the mechanisms of demyelination and remyelination.

Altered behavioral performance and live imaging of circuit-specific neural deficiencies in a zebrafish model for psychomotor retardation.

The mechanisms and treatment of psychomotor retardation, which includes motor and cognitive impairment, are indefinite. The Allan-Herndon-Dudley syndrome (AHDS) is an X-linked psychomotor retardation characterized by delayed development, severe intellectual disability, muscle hypotonia, and spastic paraplegia, in combination with disturbed thyroid hormone (TH) parameters. AHDS has been associated with mutations in the monocarboxylate transporter 8 (mct8/slc16a2) gene, which is a TH transporter. In order to determine the pathophysiological mechanisms of AHDS, MCT8 knockout mice were intensively studied. Although these mice faithfully replicated the abnormal serum TH levels, they failed to exhibit the neurological and behavioral symptoms of AHDS patients. Here, we generated an mct8 mutant (mct8−/−) zebrafish using zinc-finger nuclease (ZFN)-mediated targeted gene editing system. The elimination of MCT8 decreased the expression levels of TH receptors; however, it did not affect the expression of other TH-related genes. Similar to human patients, mct8−/− larvae exhibited neurological and behavioral deficiencies. High-throughput behavioral assays demonstrated that mct8−/− larvae exhibited reduced locomotor activity, altered response to external light and dark transitions and an increase in sleep time. These deficiencies in behavioral performance were associated with altered expression of myelin-related genes and neuron-specific deficiencies in circuit formation. Time-lapse imaging of single-axon arbors and synapses in live mct8−/− larvae revealed a reduction in filopodia dynamics and axon branching in sensory neurons and decreased synaptic density in motor neurons. These phenotypes enable assessment of the therapeutic potential of three TH analogs that can enter the cells in the absence of MCT8. The TH analogs restored the myelin and axon outgrowth deficiencies in mct8−/− larvae. These findings suggest a mechanism by which MCT8 regulates neural circuit assembly, ultimately mediating sensory and motor control of behavioral performance. We also propose that the administration of TH analogs early during embryo development can specifically reduce neurological damage in AHDS patients.

Acute treatment with valproic acid and l-thyroxine ameliorates clinical signs of experimental autoimmune encephalomyelitis and prevents brain pathology in DA rats

Multiple sclerosis (MS) is the most common chronic inflammatory demyelinating disease of the central nervous system (CNS) in young adults. Chronic treatments with histone deacetylase inhibitors (HDACis) have been reported to ameliorate experimental autoimmune encephalomyelitis (EAE), a rodent model of MS, by targeting immune responses. We have recently shown that the HDAC inhibition/knockdown in the presence of thyroid hormone (T3) can also promote oligodendrocyte (OL) differentiation and expression of myelin genes in neural stem cells (NSCs) and oligodendrocyte precursors (OPCs). In this study, we found that treatment with an HDACi, valproic acid (VPA), and T3, alone or in combination, directly affects encephalitogenic CD4+ T cells. VPA, but not T3, compromised their proliferation, while both molecules reduced the frequency of IL-17-producing cells. Transfer of T3, VPA and VPA/T3 treated encephalitogenic CD4+ T cells into naïve rats induced less severe EAE, indicating that the effects of these molecules are persistent and do not require their maintenance after the initial stimuli. Thus, we investigated the effect of acute treatment with VPA and l-thyroxine (T4), a precursor of T3, on myelin oligodendrocyte glycoprotein-induced EAE in Dark Agouti rats, a close mimic of MS. We found that a brief treatment after disease onset led to sustained amelioration of EAE and prevention of inflammatory demyelination in the CNS accompanied with a higher expression of myelin-related genes in the brain. Furthermore, the treatment modulated immune responses, reduced the number of CD4+ T cells and affected the Th1 differentiation program in the brain. Our data indicate that an acute treatment with VPA and T4 after the onset of EAE can produce persistent clinically relevant therapeutic effects by limiting the pathogenic immune reactions while promoting myelin gene expression.

Poster #S173 METABOTROPIC GLUTAMATE RECEPTOR 5 DYSREGULATION IN SCHIZOPHRENIA

(MBP), another myelinationand schizophrenia-related gene, is the bestcharacterized QKI mRNA ligand in mice (Larocque et al., 2002). Therefore, we tested this hypothesis using the human immature oligodendrocytic cell line, that levels of hnRNP C1 and C2 would influence the expression of these myelination-related genes. We also attempted to elucidate the functional differences between hnRNP C1 and C2. Methods: We constructed expression vectors for the two hnRNP C variants (hnRNP C1 and C2), and investigated, using the quantitative real-time RT-PCR, whether the overexpression of these proteins would change the expression of myelination-related genes, such as the QKI isoforms (QKI-5, -6, -7, and -7b) and MBP, in the human immature oligodendrocytic cell lime MO3.13 and during differentiation of this cell line by PMA treatment. Results: Endogenous expressions of both hnRNP C1 and C2 were found decreased during MO3.13 differentiation. In the same condition, the levels of expression of QKIs (QKI-5, -6, -7, and -7b) were significantly elevated. The up-regulation of QKIs were not influenced by overexpression of either the hnRNP C or C2. MBP was increased during differentiation of MO3.13, consistent with previous reports (Buntinx et al., 2003; Boscia et al., 2012). The up-regulations were not influenced by overexpression of either the hnRNP C1 or C2. However, intriguingly, MBP was up-regulated under the overexpression of hnRNP C2, but not hnRNP C1, in PMA-untreated cells. Discussion: We observed that the overexpression of hnRNP C1 and C2 do not affect the differential expression of QKIs and MBP during MO3.13 differentiation. But MBP seems to be regulated by hnRNP C2 in PMA-untreated cells. Similarly, we have reported previously that hnRNP C2 regulates MBP expression in a direct fashion, and that such regulation is not mediated by QKI in the human neuroblastoma cell line SK-N-SH (Iwata et al., 2011). Thus, we propose that the mechanism underlying the differential expression of hnRNP C1/2 in schizophrenia patients brains may involve changes of MBP expression. MBP has been found differentially expressed at gene and protein level (Martins-de-Souza et al. 2012; Matthews et al. 2012). Although no functional differences have been reported thus far for the two variants of hnRNP C protein, our findings indicate the existence of distinct functions between hnRNP C1 and C2. Further exploration of separate roles of hnRNP C1 and C2 associated to schizophrenia will lead to a better understanding the pathobiology of this disorder in a molecular level.

Two faces of Schwann cell dedifferentiation in peripheral neurodegenerative diseases: pro-demyelinating and axon-preservative functions.

In vertebrates, Schwann cells are glial cells that form a myelin sheath, which produces the saltatory conduction of neural impulses in the peripheral nervous system (Sherman and Brophy, 2005). In the case of abnormal myelin sheath generation due to genetic mutations or myelin sheath destruction by acquired nerve damage induced by inflammation or drugs, problems arise in the peripheral nervous system, leading to muscle atrophy or sensory disorders (Sherman and Brophy, 2005; Jessen and Mirsky, 2008). During the embryonic period, the neural crest cells migrate along with growing peripheral axons. A Schwann cell precursor that has finished migrating and has attached to a growing nerve may wrap around a few or as many as dozens of axons, but ultimately only target a single axon that requires a myelin sheath in response to a certain stimulus (Sherman and Brophy, 2005; Jessen and Mirsky, 2008). In the period of Schwann cell generation, the cell is called Schwann cell progenitor or immature Schwann cell. Subsequently, the Schwann cell begins the process of myelin-related gene expression and wraps the axon with the elongated Schwann cell membrane, which continues throughout the postnatal period to complete the myelin sheath formation (Sherman and Brophy, 2005; Jessen and Mirsky, 2008). The mature myelin sheath will last a lifetime, except when damage, such as nerve injury, occurs. Acute and chronic demyelinating peripheral neuropathies are primary diseases that cause myelin destruction in adults (Jessen and Mirsky, 2008). When a peripheral nerve is physically severed, distal axons are completely degenerated, and the Schwann cells wrapped around the axons directly participate in the degeneration of the myelin sheath, which leads to demyelination (Jessen and Mirsky, 2008). Afterwards, macrophages that migrate from the blood assist in completely removing the degenerated axon and the myelin sheath (Martini et al., 2008). Meanwhile, in inflammatory demyelinating diseases, acute or chronic form of demyelination may occur regardless of axonal damage, and it is considered that demyelination occurs due to local inflammation caused by autoimmune mechanisms, which may attack components of the myelin sheath or junctional regions (Pollard and Armati, 2011).

Impact of Maternal Nicotine Exposure on Expression of Myelin-Related Genes in Zebrafish Larvae

Although maternal smoking during pregnancy disrupts offspring development, it is not clear whether smoking before pregnancy has any effect on the next generation. Given that nicotine, the major psychoactive component in cigarettes, is toxic to many organs, we hypothesized that maternal smoking even before a pregnancy affects offspring development. Myelin is an important structure in the nervous system, and deficits in myelin are related to many psychiatric disorders and drug addiction. We therefore examined the effect of maternal exposure to nicotine on the expression of myelin genes in the offspring using zebrafish as a model. Female adult zebrafish were exposed to nicotine through water at a concentration of 1, 5, 10, 15, 20, 25, or 30 μM (nicotine base) for either 1 h or a continuous 24 h each day for 4 months. The nicotine-treated females were then bred with drug-naive males, and the embryos and larvae were grown in a nicotine-free environment. Maternal survival rates were calculated. Larvae of those exposed to nicotine at a dose of 1, 5, 10, 15, or 20 μM for 24 h each day were collected at 4, 7, or 14 days postfertilization (dpf). The mRNA expression of myelin-related genes was examined using quantitative RT-PCR. The mRNA expression of most genes encoding myelin major proteins increased with age. These genes were generally downregulated by maternal nicotine exposure in 4 dpf larvae, whereas they were upregulated in 14 dpf larvae. The expression of myelin-related transcription regulators correlated well with that of myelin major proteins. Prepregnancy nicotine exposure altered myelin gene expression in the offspring, implying that maternal smoking before pregnancy affects the next generation.

Axonal neuregulin 1 is a rate limiting but not essential factor for nerve remyelination

Neuregulin 1 acts as an axonal signal that regulates multiple aspects of Schwann cell development including the survival and migration of Schwann cell precursors, the ensheathment of axons and subsequent elaboration of the myelin sheath. To examine the role of this factor in remyelination and repair following nerve injury, we ablated neuregulin 1 in the adult nervous system using a tamoxifen inducible Cre recombinase transgenic mouse system. The loss of neuregulin 1 impaired remyelination after nerve crush, but did not affect Schwann cell proliferation associated with Wallerian degeneration or axon regeneration or the clearance of myelin debris by macrophages. Myelination changes were most marked at 10 days after injury but still apparent at 2 months post-crush. Transcriptional analysis demonstrated reduced expression of myelin-related genes during nerve repair in animals lacking neuregulin 1. We also studied repair over a prolonged time course in a more severe injury model, sciatic nerve transection and reanastamosis. In the neuregulin 1 mutant mice, remyelination was again impaired 2 months after nerve transection and reanastamosis. However, by 3 months post-injury axons lacking neuregulin 1 were effectively remyelinated and virtually indistinguishable from control. Neuregulin 1 signalling is therefore an important factor in nerve repair regulating the rate of remyelination and functional recovery at early phases following injury. In contrast to development, however, the determination of myelination fate following nerve injury is not dependent on axonal neuregulin 1 expression. In the early phase following injury, axonal neuregulin 1 therefore promotes nerve repair, but at late stages other signalling pathways appear to compensate.

Sex chromosome complement influences functional callosal myelination

In addition to androgen differences between males and females, there are genetic differences that are caused by unequal dosage of sex chromosome genes. Using the cuprizone-induced demyelination model, we recently showed that surgical gonadectomy of adult mice resulted in decreased normal myelination and remyelination compared to gonadally intact animals, suggesting a supporting role for sex hormones in the maintenance of myelination. However, inherent sex differences in normal myelination and remyelination persisted even after gonadectomy, with males consistently remyelinating to a lesser extent relative to normal myelination as assayed by axon conduction and immunohistochemistry. This suggests a potential role for the sex chromosome complement in mediating the differential rates of remyelination observed in males and females. The present study focuses on the impact that sex chromosomes might have on these myelination differences. Making use of the four core-genotype mice and cuprizone-diet induced demyelination/remyelination paradigm, our results demonstrate sex chromosome-mediated asymmetry between XX and XY mice. The rate of functional remyelination following cuprizone diet-induced callosal demyelination in four core-genotype mice is attenuated in XY compared to XX animals of both gonadal sexes. Importantly, this difference arises only in the absence of circulating sex hormones following gonadectomy and confirms the role of sex hormones in the remyelination process reported earlier by our group. Because a genotype-mediated difference only arises following gonadectomy, the chromosomal contribution to myelination and remyelination is subtle yet significant. To explain this difference, we propose a possible asymmetry in the expression of myelination-related genes in XX vs. XY mice that needs to be investigated in future studies.

N-WASp is required for Schwann cell cytoskeletal dynamics, normal myelin gene expression and peripheral nerve myelination

Schwann cells elaborate myelin sheaths around axons by spirally wrapping and compacting their plasma membranes. Although actin remodeling plays a crucial role in this process, the effectors that modulate the Schwann cell cytoskeleton are poorly defined. Here, we show that the actin cytoskeletal regulator, neural Wiskott-Aldrich syndrome protein (N-WASp), is upregulated in myelinating Schwann cells coincident with myelin elaboration. When N-WASp is conditionally deleted in Schwann cells at the onset of myelination, the cells continue to ensheath axons but fail to extend processes circumferentially to elaborate myelin. Myelin-related gene expression is also severely reduced in the N-WASp-deficient cells and in vitro process and lamellipodia formation are disrupted. Although affected mice demonstrate obvious motor deficits these do not appear to progress, the mutant animals achieving normal body weights and living to advanced age. Our observations demonstrate that N-WASp plays an essential role in Schwann cell maturation and myelin formation.

Association of the Met-196-Arg Variation of Human Tumor Necrosis Factor Receptor 2 (TNFR2) with Paranoid Schizophrenia

Research has provided strong evidence for oligodendrocyte and myelin-related genes dysfunction in schizophrenia. Several studies have suggested abnormalities in the expression of myelin-related genes including tumor necrosis factor receptor 2 (TNFR2) involved in the neurodegeneration and remyelination. In order to further assess the role of TNFR2 in schizophrenia, we examined a functional bi-allelic polymorphism associated with an impaired NF-KB signaling and cell survival. In the present case/control study, 220 patients with schizophrenia and 176 healthy controls were genotyped by RFLP-PCR for the T/G polymorphism at the position 676 in exon 6 of the TNFR2 gene. We found a trend towards over-representation of TNFR2 676G in the patients compared to the controls (p=0.19 and 0.09 respectively). Interestingly, when we evaluated the association between this genetic polymorphism and the clinical variables of schizophrenia, our findings indicated that the frequencies of the G/G genotype and the G allele were significantly higher in paranoid (p=0.014 and p=0.012 respectively) and adult-onset paranoid (p=0.004 and p=0.004 respectively) schizophrenia patient group compared to the controls. The potential association was confirmed by a logistic regression model only for development of the paranoid form of schizophrenia (p=0.022) indicating a substantially increased risk for paranoid schizophrenia with inheritance of the TNFR2(G) allele. In conclusion, this polymorphism in TNFR2 or a gene in proximity seems to be associated specifically with paranoid schizophrenia, at least in the Tunisian population. A replication of our findings in other and larger populations could be of particular importance to establish TNFR2 as one of the susceptibility genes of paranoid schizophrenia.

Convergence and Divergence in the Etiology of Myelin Impairment in Psychiatric Disorders and Drug Addiction

Impairment of oligodendroglia (OL)-dependent myelination in the central nervous system (CNS) is a remarkable parallel recently identified in major psychiatric disorders and chronic drug abuse. Neuroimaging and neuropathological studies revealed myelin defects and microarray-profiling analysis demonstrated aberrant expression of myelin-related genes in schizophrenia (SZ), bipolar disorder (BD), major depressive disorder (MDD) and cocaine addiction. However, the etiology underlying myelin impairment in these clinically distinct subjects remains elusive. This article reviews myelin impairment in line with dopaminergic dysfunction, a prime neuropathophysiological trait shared in psychiatric disorders and drug abuse, as well as the genetic and epigenetic alterations associated with these diseases. The current findings support the hypothesis that aberrant dopamine (DA) action on OLs is a common pathologic mechanism for myelin impairment in the aforementioned mental morbidities, whereas inherited genetic variations that specifically affect OL development and myelinogenesis may further increase myelin vulnerability in psychiatric disorders. Importantly, OL defect is not only a pathological consequence but also a causative factor for dopaminergic dysfunction. Hence, myelin impairment is a key factor in the pathogenic loop of psychiatric diseases and drug addiction.

Disturbed structural connectivity in schizophrenia primary factor in pathology or epiphenomenon?

Indirect evidence for disturbed structural connectivity of subcortical fiber tracts in schizophrenia has been obtained from functional neuroimaging and electrophysiologic studies. During the past few years, new structural imaging methods have become available. Diffusion tensor imaging and magnetization transfer imaging (MTI) have been used to investigate directly whether fiber tract abnormalities are indeed present in schizophrenia. To date, findings are inconsistent that may express problems related to methodological issues and sample size. Also, pathological processes detectable with these new techniques are not yet well understood. Nevertheless, with growing evidence of disturbed structural connectivity, myelination has been in the focus of postmortem investigations. Several studies have shown a significant reduction of oligodendroglial cells and ultrastructural alterations of myelin sheats in schizophrenia. There is also growing evidence for abnormal expression of myelin-related genes in schizophrenia: Neuregulin (NRG1) is important for oligodendrocyte development and function, and altered expression of erbB3, one of the NRG1 receptors, has been shown in schizophrenia patients. This is consistent with recent genetic studies suggesting that NRG1 may contribute to the genetic risk for schizophrenia. In conclusion, there is increasing evidence from multiple sides that structural connectivity might be pathologically changed in schizophrenia illness. Up to the present, however, it has not been possible to decide whether alterations of structural connectivity are intrinsically linked to the primary risk factors for schizophrenia or to secondary downstream effects (ie, degeneration of fibers secondarily caused by cortical neuronal dysfunction)-an issue that needs to be clarified by future research.

Expression of oligodendrocyte-associated genes in dorsolateral prefrontal cortex of patients with schizophrenia

Prior studies have found decreased mRNA expression of oligodendrocyte-associated genes in the dorsolateral prefrontal cortex (DLPFC) of patients with schizophrenia. However, it is unclear which specific genes are affected and whether the changes occur in the cortical white or grey matter. We assessed the mRNA expression levels of four oligodendrocyte-related genes: myelin-associated basic protein (MOBP), myelin-associated glycoprotein (MAG), 2′,3′-cyclic nucleotide 3′-phosphodiesterase (CNP) and oligodendrocyte-lineage transcription factor 2 (OLIG2) in DLPFC white and grey matter using quantitative-PCR (∼ 70 controls and ∼ 30 patients with schizophrenia). We also examined the effects of high-risk polymorphisms in CNP and OLIG2 on mRNA levels of these genes. We found that genetic polymorphisms in CNP (rs2070106) and OLIG2 (rs1059004 and rs9653711), previously associated with schizophrenia, predicted low expression of these genes. Expression of MAG, CNP and OLIG2 did not differ between patients with schizophrenia and controls in the grey or white matter but MOBP mRNA levels were increased in the DLPFC white matter in patients with a history of substance abuse. MOBP and CNP protein in the white matter was not altered. Although previously reported reductions in the expression of myelin-related genes in the DLPFC were not detected, we show that individuals carrying risk-associated alleles in oligodendrocyte-related genes had relatively lower transcript levels. These data illustrate the importance of genetic background in gene expression studies in schizophrenia.

Induction of neuronal and myelin-related gene expression by IL-6-receptor/IL-6: A study on embryonic dorsal root ganglia cells and isolated Schwann cells

The conditional knockdown of the Interleukin-6 (IL-6) family signal transducer (gp130) causes peripheral nerve demyelination and degeneration. In the present work, we investigated the effect of gp130 signaling on peripheral nerves and Schwann cells (SC). We stimulated gp130 signaling with IL6RIL6, a fusion molecule of IL-6 and IL-6R, in rat embryonic day 14 dorsal root ganglia (DRG) cell cultures. In neurons, IL6RIL6 strongly increased the axonal network. In SC, IL6RIL6 favored the appearance of elongated more mature cells versus stellar shaped cells. Gene expression profiling showed an increased expression of neuronal and glial-specific genes. mRNAs related to SC function, including myelin-specific genes, were increased by IL6RIL6 treatment of DRG cells, or of purified SCs isolated from rat sciatic nerve. In IL6RIL6-treated cells, immunostaining showed a strong nuclear signal for Krox-20, a transcription factor essential for differentiation of the SC lineage. On the contrary, we observed that IL6RIL6 inhibited the genes related to TGF-beta family as well as the production of smooth muscle actin.

Schizophrenia is not associated with the functional candidate gene ERBB3: Results from a case‐control study

Increasing evidence has supported the hypothesis of a neurodevelopmental component in the etiology of schizophrenia. Recently, several independent microarray gene expression studies have revealed downregulated expression of myelin-related genes in the postmortem brains of schizophrenia patients. Complete myelination of the cortex has been observed to occur in late adolescence and early adulthood, which is typically the age of onset of schizophrenia. ERBB3 is a gene which has not only been found to be downregulated in schizophrenia simultaneously in three microarray studies, but also is a strong candidate because of its potential role in neurodevelopment as a receptor of NRG1. Therefore, we performed association analysis of seven nonsynonymous SNPs in this gene. Two SNPs in ERBB3 (rs773123 and rs2271188) were polymorphic in our samples, neither of which showed significant evidence of association with the illness (P = 0.639 and 0.561, respectively). Because replication across such studies is notoriously difficult, the microarray evidence implicating ERBB3 still strongly supports some role of this gene in schizophrenia. However, our failure to find genetic association suggests that the differential expression of ERBB3 in schizophrenia may be environmentally driven, or involve cis- or trans-acting genetic factors beyond the boundaries of the gene itself.

Variations in myelin and oligodendrocyte-related gene expression across multiple brain regions in schizophrenia: A gene ontology study

Large-scale gene expression studies in schizophrenia (SZ) have generally focused on the dorsolateral prefrontal cortex. Studies of other brain regions have been less frequent and have rarely been performed in the same subjects. We analyzed postmortem gene expression in multiple cortical regions (Brodmann areas 8, 10, 44, 46, 23/31, 24/32, 20, 21, 22, 36/28, 7 and 17, respectively) as well as in the hippocampus, caudate nucleus, and putamen of 13 SZ and 13 control subjects using Affymetrix GeneChip® microarrays. The superior temporal cortex (BA22) and cingulate cortices (BA24/32, 23/31) of subjects with SZ demonstrated more profound alterations of gene expression than other brain regions compared to controls [Katsel, P., Davis, K.L., Gorman, J.M., Haroutunian, V., in press. Variations in differential gene expression patterns across multiple brain regions in schizophrenia. Schizophr. Res.]. Functional categorization of genes whose expression was altered revealed multiple gene ontology classes that included oligodendrocyte/myelin-related genes. These myelin-related ontologies were among the top scored categories in temporal and cingulate gyri and in the hippocampus relative to other brain regions. The most altered transcripts in SZ were those encoding for proteins involved in determination of glial differentiation, myelin structure and adhesion proteins participating in axoglial contacts. Hierarchical clustering demonstrated that these myelin-related gene expression abnormalities in SZ were most pronounced in the hippocampus, superior temporal and cingulate cortices. The high representation of abnormally expressed oligodendrocyte/myelin genes in brain regions with the largest numbers of abnormally expressed genes in SZ confirmed their involvement in the disease process and suggested that the integrity of axon–myelin interaction may be impaired in SZ.