Neuregulins and erbB receptor expression in adult human oligodendrocytes

Newly Identified Deficiencies in the Multiple Sclerosis Central Nervous System and Their Impact on the Remyelination Failure

The pathogenesis of multiple sclerosis (MS) remains enigmatic and controversial. Myelin sheaths in the central nervous system (CNS) insulate axons and allow saltatory nerve conduction. MS brings about the destruction of myelin sheaths and the myelin-producing oligodendrocytes (ODCs). The conundrum of remyelination failure is, therefore, crucial in MS. In this review, the roles of epidermal growth factor (EGF), normal prions, and cobalamin in CNS myelinogenesis are briefly summarized. Thereafter, some findings of other authors and ourselves on MS and MS-like models are recapitulated, because they have shown that: (a) EGF is significantly decreased in the CNS of living or deceased MS patients; (b) its repeated administration to mice in various MS-models prevents demyelination and inflammatory reaction; (c) as was the case for EGF, normal prion levels are decreased in the MS CNS, with a strong correspondence between liquid and tissue levels; and (d) MS cobalamin levels are increased in the cerebrospinal fluid, but decreased in the spinal cord. In fact, no remyelination can occur in MS if these molecules (essential for any form of CNS myelination) are lacking. Lastly, other non-immunological MS abnormalities are reviewed. Together, these results have led to a critical reassessment of MS pathogenesis, partly because EGF has little or no role in immunology.

Oligodendrocyte lineage cells and depression

Depression is a common mental illness, affecting more than 300 million people worldwide. Decades of investigation have yielded symptomatic therapies for this disabling condition but have not led to a consensus about its pathogenesis. There are data to support several different theories of causation, including the monoamine hypothesis, hypothalamic-pituitary-adrenal axis changes, inflammation and immune system alterations, abnormalities of neurogenesis and a conducive environmental milieu. Research in these areas and others has greatly advanced the current understanding of depression; however, there are other, less widely known theories of pathogenesis. Oligodendrocyte lineage cells, including oligodendrocyte progenitor cells and mature oligodendrocytes, have numerous important functions, which include forming myelin sheaths that enwrap central nervous system axons, supporting axons metabolically, and mediating certain forms of neuroplasticity. These specialized glial cells have been implicated in psychiatric disorders such as depression. In this review, we summarize recent findings that shed light on how oligodendrocyte lineage cells might participate in the pathogenesis of depression, and we discuss new approaches for targeting these cells as a novel strategy to treat depression.

High-mobility group box-1 as an autocrine trophic factor in white matter stroke

Maintenance of white matter integrity in health and disease is critical for a variety of neural functions. Ischemic stroke in the white matter frequently results in degeneration of oligodendrocytes (OLs) and myelin. Previously, we found that toll-like receptor 2 (TLR2) expressed in OLs provides cell-autonomous protective effects on ischemic OL death and demyelination in white matter stroke. Here, we identified high-mobility group box-1 (HMGB1) as an endogenous TLR2 ligand that promotes survival of OLs under ischemic stress. HMGB1 rapidly accumulated in the culture medium of OLs exposed to oxygen-glucose deprivation (OGD). This conditioned medium exhibited a protective activity against ischemic OL death that was completely abolished by immunodepletion of HMGB1. Knockdown of HMGB1 or application of glycyrrhizin, a specific HMGB1 inhibitor, aggravated OGD-induced OL death, and recombinant HMGB1 application reduced the extent of OL death in a TLR2-dependent manner. We confirmed that cytosolic translocation of HMGB1 and activation of TLR2-mediated signaling pathways occurred in a focal white matter stroke model induced by endothelin-1 injection. Animals with glycyrrhizin coinjection showed an expansion of the demyelinating lesion in a TLR2-dependent manner, accompanied by aggravation of sensorimotor behavioral deficits. These results indicate that HMGB1/TLR2 activates an autocrine trophic signaling pathways in OLs and myelin to maintain structural and functional integrity of the white matter under ischemic conditions.

Crosstalk between cerebral endothelium and oligodendrocyte

It is now relatively well accepted that the cerebrovascular system does not merely provide inert pipes for blood delivery to the brain. Cerebral endothelial cells may compose an embedded bunker of trophic factors that contribute to brain homeostasis and function. Recent findings suggest that soluble factors from cerebral endothelial cells nourish neighboring cells, such as neurons and astrocytes. Although data are strongest in supporting mechanisms of endothelial-neuron and/or endothelial-astrocyte trophic coupling, it is likely that similar interactions also exist between cerebral endothelial cells and oligodendrocyte lineage cells. In this mini-review, we summarize current advances in the field of endothelial-oligodendrocyte trophic coupling. These endothelial-oligodendrocyte interactions may comprise the oligovascular niche to maintain their cellular functions and sustain ongoing angiogenesis/oligodendrogenesis. Importantly, it should be noted that the cell-cell interactions are not static-the trophic coupling is disturbed under acute phase after brain injury, but would be recovered in the chronic phase to promote brain remodeling and repair. Oligodendrocyte lineage cells play critical roles in white matter function, and under pathological conditions, oligodendrocyte dysfunction lead to white matter damage. Therefore, a deeper understanding of the mechanisms of endothelial-oligodendrocyte trophic coupling may lead to new therapeutic approaches for white matter-related diseases, such as stroke or vascular dementia.

Therapeutic effect of co-transplantation of neuregulin-1-transfected Schwann cells and bone marrow stromal cells on spinal cord hemisection syndrome

The aim of this present study is to evaluate the therapeutic effect of co-transplantation of neuregulin-1-transfected Schwann cells (SCs) and bone marrow stromal cells (BMSCs) on a rat model of spinal cord hemi-section injuries (Brown-Séquard syndrome), which is relevant to human clinical spinal cord injury. Both in vivo and in vitro data we received demonstrated that co-transplantation BMSCs with NRG1-transfected SCs reduced the size of cystic cavities, promoted axonal regeneration and hind limb functional recovery in comparison with SCs or BMSCs transplantation alone or together, and this treatment could provide important insights into potential therapies of spinal cord hemi-section injuries.

Neuregulin-1, the fetal endothelium, and brain damage in preterm newborns

OBJECTIVE

To assess the potential role for Neuregulin-1 (NRG1) as a systemic endogenous protector in the setting of perinatal inflammatory brain damage.

METHODS

We measured NRG1-protein and mRNA levels in human umbilical venous endothelial cells (HUVECs) of different gestational ages at various durations of exposure to lipopolysaccharide (LPS). In parallel, we genotyped the donor individuals for SNP8NRG221533, a disease-related single nucleotide polymorphism in the 5' region upstream of the NRG1 sequence. Intracellular NRG1 localization was visualized by confocal microscopy. Furthermore we analyzed the relationship between SNP8NRG221533 genotype and neurodevelopmental outcome in children born preterm.

RESULTS

We observed a positive dose-response-relationship between NRG1-mRNA and intracellular protein levels with both advancing gestational age and duration of LPS exposure in HUVECs. The presence of allele C at the SNP8NRG221533 locus was associated with an increased cellular production of NRG1 in HUVECs, and with a significantly reduced risk for cerebral palsy and developmental delay in children born preterm.

INTERPRETATION

In conclusion, our data indicate that gestational age, duration of LPS exposure, and the SNP8NRG221533 genotype affect NRG1 levels. Our results support the hypothesis that NRG1 may qualify as an endogenous protector during fetal development.

The NRG1 gene is frequently silenced by methylation in breast cancers and is a strong candidate for the 8p tumour suppressor gene

Neuregulin-1 (NRG1) is both a candidate oncogene and candidate tumour suppressor gene. It encodes the heregulins and other mitogenic ligands for the ERBB family, but it also causes apoptosis in NRG1-expressing cells. We found that most breast cancer cell lines had reduced or undetectable expression of NRG1. This included cell lines that had translocation breaks in the gene. Similarly, expression in cancers was generally comparable to or less than various normal breast samples. Many non-expressing cell lines had extensive methylation of the CpG island at the principal transcription start site at exon 2 of NRG1. Expression was reactivated by demethylation. Many tumours also showed methylation, while normal mammary epithelial fragments had none. Lower NRG1 expression correlated with higher methylation. siRNA-mediated depletion of NRG1 increased net proliferation, in a normal breast cell line and a breast cancer cell line that expressed NRG1. The short arm of chromosome 8 is frequently lost in epithelial cancers, and NRG1 is the most centromeric gene that is always affected. NRG1 may therefore be the major tumour suppressor gene postulated to be on 8p: it is in the correct location, is anti-proliferative, and is silenced in many breast cancers.

Vitamin-regulated cytokines and growth factors in the CNS and elsewhere

There is a growing awareness that natural vitamins (with the only exception of pantothenic acid) positively or negatively modulate the synthesis of some cytokines and growth factors in the CNS, and various mammalian cells and organs. As natural vitamins are micronutrients in the human diet, studying their effects can be considered a part of nutritional genomics or nutrigenomics. A given vitamin selectively modifies the synthesis of only a few cytokines and/or growth factors, although the same cytokine and/or growth factor may be regulated by more than one vitamin. These effects seem to be independent of the effects of vitamins as coenzymes and/or reducing agents, and seem to occur mainly at genomic and/or epigenetic level, and/or by modulating NF-kappaB activity. Although most of the studies reviewed here have been based on cultured cell lines, but their findings have been confirmed by some key in vivo studies. The CNS seems to be particularly involved and is severely affected by most avitaminoses, especially in the case of vitamin B(12). However, the vitamin-induced changes in cytokine and growth factor synthesis may initiate a cascade of events that can affect the function, differentiation, and morphology of the cells and/or structures not only in the CNS, but also elsewhere because most natural vitamins, cytokines, and growth factors cross the blood-brain barrier. As cytokines are essential to CNS-immune and CNS-hormone system communications, natural vitamins also interact with these circuits. Further studies of such vitamin-mediated effects could lead to vitamins being used for the treatment of diseases which, although not true avitaminoses, involve an imbalance in cytokine and/or growth factor synthesis.

Deficit of perineuronal oligodendrocytes in the prefrontal cortex in schizophrenia and mood disorders

OBJECTIVE

A deficit of oligodendrocytes has been reported in the prefrontal cortex (PFC) in schizophrenia (SCH), bipolar disorder (BPD) and major depression (MDD). Also, a decreased size of pyramidal neurons has been detected in layer III in SCH and in mood disorders. Since oligodendrocytes have a trophic influence on neurons, reduced neuronal size reported in these disorders might be associated with the deficit in subpopulation of perineuronal oligodendrocytes. We hypothesized that deficit of perineuronal oligodendrocytes might occur in SCH and mood disorders.

METHOD

We estimated the number of oligodendroglial satellites of pyramidal neurons and the size of pyramidal neurons in layer III (Brodmann's area 9) in Nissl stained sections in SCH, BPD, MDD and normal controls. The Stanley Foundation Neuropathology Consortium brain collection consisted of 15 cases in each of four groups was used.

RESULTS

We detected a prominent and significant reduction in the number of perineuronal oligodendrocytes in the sublayers IIIa, IIIb and IIIc in SCH, BPD and MDD as compared to controls. The BPD group differed significantly from SCH group and from MDD group. There were no significant differences in somal sizes of pyramidal neurons in the sublayers IIIa, IIIb, IIIc between each of the psychiatric groups and the control group. Only BPD group showed significantly smaller neuronal size in sublayer IIIc as compared to controls.

CONCLUSIONS

Our data provide evidence for a deficit of perineuronal oligodendrocytes in severe mental disorders that may play a key role in the pathophysiology of SCH, BPD and MDD.

Neuregulins: Versatile growth and differentiation factors in nervous system development and human disease

The neuregulins are a family of growth and differentiation factors with a wide range of functions in the nervous system. The power and diversity of the neuregulin signaling system comes in part from a large number of alternatively-spliced forms of the NRG1 gene that can produce both soluble and membrane-bound forms. The soluble forms of neuregulin are unique from other factors in that they have a structurally distinct heparin-binding domain that targets and potentiates its actions. In addition, a finely tuned, bidirectional mechanism regulates when and where neuregulin is released from neurons in response to neurotrophic factors produced by both neuronal targets and supporting glial cells. Together, this produces a balanced intercellular signaling system that can be localized to distinct regions for both normal development and maintenance of the mature nervous system. Recent evidence suggests that neuregulin signaling plays important roles in many neurological disorders including multiple sclerosis, traumatic brain and spinal cord injury, peripheral neuropathy, and schizophrenia. Here, we review the basic biology of neuregulins and relate this to research suggesting their involvement with and potential therapeutic uses for neurological disorders.

Constitutive neuregulin-1/ErbB signaling contributes to human vestibular schwannoma proliferation

Vestibular schwannomas (VSs) are benign tumors that arise from the Schwann cells (SCs) lining the vestibular nerve. VS cells survive and proliferate far from neurons and axonally derived growth factors. We have previously shown that VSs produce the glial growth factor, neuregulin-1 (NRG1), and its receptors, ErbB2 and ErbB3. In the present work, we explore the contribution of constitutive NRG1:ErbB signaling to human VS cell proliferation. We confirm that human VSs, which express markers of immature and denervated SCs, also express endogenous NRG1 and activated ErbB2. We find that a blocking anti-NRG1 antibody and trastuzumab (Herceptin, HCN), a humanized anti-ErbB2 inhibitory monoclonal antibody, effectively inhibit NRG1 induced SC proliferation. Treatment of primary VS cultures with anti-NRG1 or HCN reduces cell proliferation in the absence of exogenous NRG1. Furthermore, conditioned medium from VS cell cultures contains NRG1 and stimulates SC proliferation in SC cultures, an effect that is inhibited by anti-NRG1 and HCN. These data suggest an autocrine pathway of VS growth stimulation involving NRG and ErbB receptors. Inhibition of constitutive NRG:ErbB signaling reduces VS cell proliferation in vitro and may have therapeutic potential for patients with VSs.

Localization of neuregulin-1α (heregulin-α) and one of its receptors, ErbB-4 tyrosine kinase, in developing and adult human brain

Using immunohistochemistry, Western blot analysis, and RT-polymerase chain reaction, we studied the distribution of neuregulin-1 splice variant alpha (NRG-1alpha) and one of its putative receptors, ErbB-4 tyrosine kinase, in human brain. In the pre- and perinatal human brain immunoreactivity was confined to numerous neurons, with the highest cell density found in cortical gray matter, hypothalamus and cerebellum. In the adult brain, single cortical gray and white matter neurons showed NRG-1alpha immunoreactivity. Occasionally, immunoreactive oligodendrocytes were observed. NRG-1alpha-expressing neurons were also found in the hypothalamus, hippocampus, basal ganglia and brain stem. Application of two antibodies recognizing alpha and beta isoforms revealed a different distribution pattern in that many cortical and hippocampal pyramidal neurons were labeled. ErbB-4 immunoreactivity was expressed in both neurons and oligodendrocytes. Our data show that NRG-1alpha expression is lower in the adult human brain than in the developing brain, and, therefore, support a role for NRG-1alpha in brain development.

Integrin-growth factor interactions as regulators of oligodendroglial development and function

Central nervous system (CNS) development requires mechanisms for the regulation of cell number. Although growth factors are essential determinants of the proliferation and apoptosis that determine final numbers, the long-range nature of signals from diffusible growth factors makes them insufficient for the provision of the precise and localized signals required. Integration of integrin and growth factor receptor signaling in controlling cell behavior has been an important theme of research over the past several years. The focus of this review is on the mechanisms by which integrin-growth factor interactions regulate the development of oligodendrocytes and provide a mechanism for controlling, both in space and in time, oligodendrocyte numbers in the developing CNS.

A real-time quantitative PCR comparative study between rat optic and sciatic nerves: determination of neuregulin-1 mRNA levels

Injured axons from peripheral nervous system (PNS) possess the ability to regenerate. In contrast, regeneration of injured axons does not occur in the central nervous system (CNS) or occurs to a limited extent. Previous works have shown that rat sciatic nerve conditioned medium (CM) produced PC12 cells neuronal-like differentiation and neurite outgrowth. In the present work, we compared the expression of neuregulin-1s (NRG-1s) from rat sciatic and optic nerves as members of the PNS and CNS, respectively. Sciatic nerve CM showed a higher neurotrophic activity on PC12 cells than rat optic nerve CM. RT-PCR analysis verified the presence of all three types of NRG-1 mRNAs and their receptors in both types of nerves. Real-time quantitative PCR (QPCR) assays showed that the relative expression levels of all three types of NRG-1 mRNAs were higher in optic nerves than in sciatic nerves. Eleven-day cultured optic nerves showed an increased in NDF and SMDF when compared to freshly isolated optic nerves, whereas GGF decreased. However, 11-day-cultured sciatic nerves only showed an increase in SMDF mRNA. Western blots corroborated the differences in NRG-1 expression profile for both types of nerves and their CMs. Incubation of both CMs with the anti-pan-NRG-1 antibody showed that the neurotrophic activity of the optic nerve CM increased, whereas the sciatic nerve CM remained unchanged. These results indicated that different NRG-1 levels are expressed upon nerve degeneration and the balance between those levels and other neurotrophic factors could have an important role on nerve regeneration.

Epidermal growth factor promotes oligodendrocyte process formation and regrowth after injury

Oligodendrocytes (OLs) form myelin within the central nervous system and are targets in numerous demyelinating diseases and injuries. OLs grown in culture maintain the developmental timetable which occurs in vivo and mature into cells with a relatively normal phenotype. In this study, cultured cells are used to test whether EGF can modulate process formation in OLs both before and after transection injury. EGF had no effect on the formation of new processes by OLs at any stage of development. To test the effect of EGF on process outgrowth after injury, mature OLs were selected and injured by laser transection of a single process, then imaged at 24-h intervals for 120 h. EGF promoted the recovery and regrowth of injured processes and also significantly increased outgrowth in uninjured processes. As well, it increased the number of new sprouts formed by OLs after injury. Results suggest that the effects of EGF on process outgrowth are a consequence of EGF interaction with a signaling pathway that is specifically activated within injured OLs. The potent effect of EGF on OL process formation after an injury suggests that modulation of the signaling pathways involved might provide a mechanism to promote remyelination.

Localization of neuregulin isoforms and erbB receptors in myelinating glial cells

Neuregulins (NRGs) are growth factors present in neurons and glial cells of the central and peripheral nervous systems and play a role in the survival, proliferation, and differentiation of these cells. We now report the localization of the two major isoforms of NRG (alpha and beta) and their receptors (erbB) in cultured Schwann cells and oligodendrocytes isolated from neonatal rat pups. Immunocytochemistry and Western blots for NRG and erbB receptors in defined subcellular fractions were utilized to assess cellular localization. Less differentiated oligodendrocytes contain both NRG isoforms in the cell bodies but not the processes, while only NRG-1beta was found in the nucleus. In contrast, more differentiated oligodendrocytes contained neither isoform in the nucleus while both isoforms were colocalized in the cytoplasm and cell processes. In Schwann cells, both NRG-1beta and NRG-1alpha were colocalized in the cytoplasm and processes. The Schwann cell nucleus had weak immunoreactivity for both NRG-1 isoforms, although NRG-1beta was predominant. ErbB2 and erbB3 receptors, which transduce the NRG-1 signal in Schwann cells, were found throughout the cytoplasm and in the processes and were also localized in the cell nucleus. The nuclear localization of NRG-1 isoforms and/or erbB receptors in both cell types was confirmed by Western blotting of nuclear and cytoplasmic extracts. Stimulation of Schwann cells with mitotic agents increased NRG-1beta expression in the nucleus and dramatically suppressed NRG-1alpha expression throughout the cell. The functional implications of this differential localization in myelinating cells are discussed.

Multiple sclerosis: Cytokine receptors on oligodendrocytes predict innate regulation

Multiple sclerosis (MS) is an immune-mediated demyelinating condition in which numerous soluble mediators have been implicated. We have extended the repertoire of cytokines studied in MS tissue by examining interleukin (IL-4), IL-6, IL-10, IL-12, IL-18, interferon (IFNgamma), and their receptors and have compared patterns with those seen in normal subjects and other neurological diseases (OND). Expression was evaluated by immunocytochemistry and Western blots. Remarkably, oligodendrocytes expressed all the cytokine receptors examined, particularly Th2-type, constitutively in normal subjects and upregulated in disease. Microglial cells also expressed cytokine receptors at similar levels. Cytokine expression was invariably a feature of microglial cells, except for IL-10, which was exclusively astrocytic. Oligodendrocytes did not display cytokines, except for low levels of IL-18. Although no pattern was specific for MS, most molecules were upregulated in MS and OND. Downstream JAK/STAT molecules were correspondingly upregulated. Cytokine receptors on oligodendrocytes (and microglia), and their corresponding ligands on microglia (and astrocytes), may implicate paracrine/autocrine regulation and may bespeak innate immunity in the central nervous system.

Oligodendrocytes as providers of growth factors

Glial cells recently are being appreciated as supporters of brain neurons. This review addresses their role as growth factor providers. While the function of astrocytes in this capacity is known, new data indicate that oligodendrocytes, the myelinating cells of the brain, exhibit similar abilities. Oligodendrocytes provide trophic signals to nearby neurons and synthesize defined growth factors. Expression of growth factors is influenced by neural signals. The review summarizes these roles and their implications in brain function.