Subset Of Glial Cells Research Articles

Overexpression of H3K36 methyltransferase NSD in glial cells affects brain development in Drosophila.

NSD1 is a histone methyltransferase that methylates the lysine 36 at histone H3. NSD duplication is associated with short stature, microcephaly, intellectual disability, and behavioral defects in humans. Ectopic overexpression of NSD, an NSD1 homolog in Drosophila, was shown to induce developmental abnormalities via apoptosis. In this study, to investigate the effects of NSD overexpression on Drosophila brain development, we first examined the typical NSD expression pattern in larval brains and found that endogenous NSD promoter activity was detected only in subsets of glial cells. Pan-glial, but not pan-neuronal, NSD overexpression induced apoptosis in larval brain cells. However, pan-glial NSD overexpression also induced caspase-3 cleavage in neuronal cells. Among the various glial cell types, NSD overexpression in only astrocytic glia induced apoptosis and abnormal learning defects in the larval stage. Furthermore, NSD overexpression downregulated the expression of various astrocyte-specific genes, including draper (drpr), possibly owing to an indirect effect of NSD overexpression-induced astrocytic apoptosis. Since drpr plays a role in axon pruning during mushroom body (MB) formation in Drosophila astrocytes, we examined the effect of astrocytic NSD overexpression on this process and found that it disrupted the clearance of γ-neurons in the MB, subsequently inducing arrhythmic locomotor activity of the fly. Thus, these results suggest that aberrant NSD overexpression may cause neurodevelopmental disorders by interfering with crucial functions of astrocytes in the brain, underlining the importance of the tightly controlled astrocytic NSD expression for proper neurodevelopment.

Taking the stress out of life

Life-Span Extension In the model organism Caenorhabditis elegans , a roundworm, it has been shown that neurons can communicate proteostasis to the periphery to affect aging. Frakes et al. have now identified astrocytelike glial cells that also act as central regulators of systemic protein homeostasis and aging (see the Perspective by Miklas and Brunet). They found that the life span of C. elegans can be extended by expression of a constitutively active version of the transcription factor XBP-1s, which mediates the unfolded protein response of the endoplasmic reticulum (UPRER), in a specific subset of glial cells. Glial XBP-1s initiates induction of the UPRER in distal intestinal cells, which makes the worms more resistant to chronic ER stress. Neuropeptide signaling was required for glial-mediated longevity and induction of the peripheral UPRER, suggesting a distinct mechanism from that initiated by neuronal XBP-1s. Thus, in this animal model of aging, a mere four cells can control organismal physiology and aging Science , this issue p. [436][1]; see also p. [365][2] [1]: /lookup/doi/10.1126/science.aaz6896 [2]: /lookup/doi/10.1126/science.aba4474

NG2 expression in microglial cells affects the expression of neurotrophic and proinflammatory factors by regulating FAK phosphorylation.

Neural/glial antigen 2 (NG2), a chondroitin sulfate proteoglycan, is significantly upregulated in a subset of glial cells in the facial motor nucleus (FMN) following CNS injury. NG2 is reported to promote the resulting inflammatory reaction, however, the mechanism by which NG2 mediates these effects is yet to be determined. In this study, we examined the changes in NG2 expressing microglial cells in the FMN in response to facial nerve axotomy (FNA) in mice. Our findings indicated that NG2 expression was progressively induced and upregulated specifically in the ipsilateral facial nucleus following FNA. To further investigate the effects of NG2 expression, in vivo studies in NG2-knockout mice and in vitro studies in rat microglial cells transfected with NG2 shRNAs were performed. Abolition of NG2 expression both in vitro and in vivo resulted in increased expression of neurotrophic factors (nerve growth factor and glial derived neurotrophic factor), decreased expression of inflammatory mediators (tumor necrosis factor-α and interleukin-1β) and decreased apoptosis in the ipsilateral facial nucleus in response to FNA. Furthermore, we demonstrated the role of FAK in these NG2-induced effects. Taken together, our findings suggest that NG2 expression mediates inflammatory reactions and neurodegeneration in microglial cells in response to CNS injury, potentially by regulating FAK phosphorylation.

Neural stem/progenitor cell properties of glial cells in the adult mouse auditory nerve.

The auditory nerve is the primary conveyor of hearing information from sensory hair cells to the brain. It has been believed that loss of the auditory nerve is irreversible in the adult mammalian ear, resulting in sensorineural hearing loss. We examined the regenerative potential of the auditory nerve in a mouse model of auditory neuropathy. Following neuronal degeneration, quiescent glial cells converted to an activated state showing a decrease in nuclear chromatin condensation, altered histone deacetylase expression and up-regulation of numerous genes associated with neurogenesis or development. Neurosphere formation assays showed that adult auditory nerves contain neural stem/progenitor cells (NSPs) that were within a Sox2-positive glial population. Production of neurospheres from auditory nerve cells was stimulated by acute neuronal injury and hypoxic conditioning. These results demonstrate that a subset of glial cells in the adult auditory nerve exhibit several characteristics of NSPs and are therefore potential targets for promoting auditory nerve regeneration.

Upregulation of alphaB-crystallin expression in the substantia nigra of patients with Parkinson's disease

Parkinson's disease (PD) is one of the most devastating neurodegenerative disorders. The underlying mechanisms of the characteristic neurodegeneration in the substantia nigra (SN) are still not fully understood. To better understand the molecular events occurring in the SN of PD brain, we used the culture-derived isotope tag–based quantitative proteomics to compare the protein expression profiles in the nigral tissue of PD patients and control subjects. We identified a total of 11 differentially expressed proteins, including alphaB-crystallin (Cryab). Both the levels and pattern of Cryab expression in the SN were validated. It was revealed that Cryab was markedly upregulated in the SN of PD brain. Cryab expression was also upregulated in reactive astrocytes and microglia in a neurotoxin-induced mouse PD model. Moreover, we showed increased expression of Cryab in cytoplasmic inclusions in a subset of glial cells in Parkinsonian brain. Thus, we identified Cryab that is highly expressed in the SN of PD brain and may be involved in the glial pathology during dopaminergic neuron degeneration in PD.

The Power and Pitfalls of Strategies for Selective Ablation of Oligodendrocytes in the Vertebrate CNS

Normal functioning of the mammalian Central Nervous System (CNS) depends on a high degree of interaction between its constitutive cell types. Although neurons represent the fundamental units of information processing in the CNS, a number of different glial cell types dynamically coordinate and modulate the final neuronal outputs. As a result, it is difficult to identify the relative contributions of individual cell types in the execution of complex CNS functions. Novel experimental tools for eliminating selected populations of glial cells are shedding light on the mechanisms underlying complex cell-to-cell interactions that influence the ultimate functionality of the brain and spinal cord. In particular, in vivo models of targeted cell death are making it possible to determine changes in natural phenomena in the absence of distinct subsets of glial cells, providing clues about the roles of those cells in neurophysiology. Distinct but complementary models of oligodendrocyte ablation, the topic of this review, are not only uncovering novel physiological roles for this subclass of glia in maintaining tissue homeostasis but also in the pathogenesis of demyelinating diseases. The goal of the current review is two-fold: to discuss various strategies developed to ablate populations of oligodendrocytes from awake, behaving animals and to identify the key contributions as well as the limitations of each model moving forward. Topics discussed include 1) whether primary oligodendrocyte death is sufficient to drive an autoimmune response that resembles multiple sclerosis, 2) the concept of a homeostatic mechanism for regulating the number of myelinating oligodendrocytes in the adult CNS, and 3) the copper-dependency of oligodendrocytes and its potential implications for demyelinating diseases. In the future, analyses of the data being generated both between and within these various animal models will be key to discovering novel roles for oligodendrocytes in both normal physiology and disease.

Lipopolysaccharide enhances asymmetrical production of cytokines and nitric oxide by left and right cerebral cortical microglial cells in BALB/C mice

Lipopolysaccharide (LPS)-induced inflammatory factors production by the cerebral cortical glial cells in two sides of the murine brain are different. To determine if microglial cells, a subset of glial cells, are involved in asymmetric production, interleukin-6 (IL-6), interleukin-1β (IL-1β) and nitric oxide (NO) responses to LPS by microglial cells in the right and left cerebral cortices were examined. Primary microglial cells were isolated from BALB/C neonatal mice, treated with LPS (10 µg ml(-1) ) for 24 h and examined for IL-6, IL-1β and NO production. At untreated state, the levels of IL-6, IL-1β and NO showed no statistical difference between left and right. However, after LPS treatment, the levels of IL-6, IL-1β and NO for the right microglial cells was statistically significant higher than the left (P < 0·05). Our results denote that enhanced production of IL-6, IL-1β and NO after LPS treatment in microglia is directly proportional to their basal-state levels, and right cortical microglia produce higher levels of IL-6, IL-1β and NO than left cortical microglia.

Gliatrophic and gliatropic roles of PVF/PVR signaling during axon guidance

Evidence of molecular and functional homology between vertebrate and Drosophila glia is limited, restricting the power of Drosophila as a model system to unravel the molecular basis of glial function. Like in vertebrates, in the Drosophila central nervous system glial cells are produced in excess and surplus glia are eliminated by apoptosis adjusting final glial number to axons. The underlying molecular mechanisms are largely unknown, as the only gliatrophic pathway known to date in flies is the EGFR and its ligands. The PDGFR signaling pathway plays a major role in regulating oligodendrocyte migration and number in vertebrates. Here, we show that the Drosophila PDGFR/VEGFR homologue PVR is required in midline glia during axon guidance for glial survival and migration, ultimately enabling axonal enwrapment. The midline glia migrate aided by the VUM and the MP1 midline neurons--sources of PVF ligands--and concomitantly interactions with neurons maintain midline glia survival. Upon loss of function for PVF/PVR signaling midline glia apoptosis increases, and gain of function induces supernumerary midline glia. Midline glial cells are displaced towards ectopic sources of PVF ligands. PVR signaling promotes midline glia survival through AKT and ERK pathways. This work shows that the PVR/PDGFR pathway plays conserved gliatrophic and gliatropic roles in subsets of glial cells in flies and vertebrates.

Ocular Pathologic Findings of Neurofibromatosis Type 2

To gain insight into the pathogenesis of neurofibromatosis type 2 (NF2) by investigating the ocular manifestations of this disease. Using standard histologic techniques, immunohistochemistry, and electron microscopy, we described the ocular pathologic findings of a 34-year-old woman who died from complications of NF2. We identified 3 types of NF2-associated lesions: juvenile posterior subcapsular cataracts, epiretinal membranes, and an intrascleral schwannoma. Our analysis indicated that dysplastic lens cells accumulate just anterior to the posterior lens capsule in juvenile posterior subcapsular cataracts and that dysplastic Müller cells may be a major component of NF2-associated epiretinal membranes. Clinical Relevance Our findings suggest that a subset of glial cells with epithelial features (Schwann cells, ependymal cells, and Müller cells) may be particularly sensitive to loss of the NF2 gene. Understanding the molecular basis for this sensitivity may lead to novel strategies for treating NF2.

TROY, a Novel Member of the Tumor Necrosis Factor Receptor Superfamily in the Central Nervous System

Using a signal sequence trap method, we isolated TROY, a novel member of the tumor necrosis factor receptor superfamily (TNFRSF), from a mouse brain cDNA library. TROY mRNA is strongly expressed in brain and embryo. In situ hybridization analysis of the embryo showed that TROY mRNA was exclusively expressed in the epithelium of many tissues, including neuroepithelium. In the developing central nervous system, TROY mRNA was strongly expressed in the ventricular and subventricular zones, which contain neuronal and glial precursors during mouse embryogenesis that are both region-specific and stagedependent. In addition, TROY mRNA was expressed in the developing olfactory bulb from embryonic day (E) 13.5 to neonate. Next, we focused on the detailed cellular characterization of TROY-expressing cells in the developing olfactory system.TROYmRNAwas first detected in the olfactory nerve layer (ONL) of the olfactory bulb at E13.5 and was expressed most intensely in the inner ONL (ONL-i) during late embryogenesis. In the postnatal olfactory bulb, TROY-expressing cells were also detected in the glomerular layer (GL) and ONL-i. TROY was intensely expressed in olfactory ensheathing cells (OECs) of the ONL-i, which are positive for neuropeptide Y (NPY), but negative for S-100 or p75 low-affinity nerve growth factor receptor. Furthermore, TROY was also detected in glial fibrillary acidic protein (GFAP)-positive glial cells of the ONL-i and GL. Thus, TROY was expressed in some specific subsets of glial cells in the olfactory bulb, including OECs, and may play some roles in the developing and adult olfactory system.

Expression profiling of glial genes during Drosophila embryogenesis

In the central nervous system of Drosophila, the induction of the glial cell fate is dependent on the transcription factor glial cells missing ( gcm). Though a considerable number of other genes have been shown to be expressed in all or in subsets of glial cells, the course of glial cell differentiation and subtype specification is only poorly understood. This prompted us to design a whole genome microarray approach comparing gcm gain-of-function and, for the first time, gcm loss-of-function genetics to wildtype in time course experiments along embryogenesis. The microarray data were analyzed with special emphasis on the temporal profile of differential regulation. A comparison of both experiments enabled us to identify more than 300 potential gcm target genes. Validation by in situ hybridization revealed expression in glial cells, macrophages, and tendon cells (all three cell types depend on gcm) for 70 genes, of which more than 50 had been unknown to be under gcm control. Eighteen genes are exclusively expressed in glial cells, and their dependence on gcm was confirmed in situ. Initial considerations regarding the role of the newly discovered glial genes are discussed based on gene ontology and the temporal profile and subtype specificity of their expression. This collection of glial genes provides an important basis for the clarification of the genetic network controlling various aspects of glial development and function.

Cellular prion protein/laminin receptor: distribution in adult central nervous system and characterization of an isoform associated with a subtype of cortical neurons

The 67-kDa LR protein was originally discovered as a non-integrin laminin receptor. Several more recent in vitro studies demonstrated the function of 67-kDa LR and its related 'precursor' form 37-kDa LRP as receptors of cellular prion protein and their implication in abnormal prion protein propagation in vitro. In addition, expression of both proteins was shown to increase considerably in the brain of scrapie-infected mice and hamsters. While LRP/LR are thus likely to play important roles in neuronal cell adhesion, survival and homeostasis and during pathological disorders, little is known so far about their fine cellular distribution in adult central nervous system. Using immunocytochemistry and western blotting, we show here that the 67-kDa LR is the major receptor form in adult rat brain and spinal cord, expressed within the cytoplasm and at the plasma membrane of most neurons and in a subset of glial cells. The overall distribution of LR correlates well with that reported for laminin-1 but also with brain regions classically associated with prion-related neurodegeneration. In contrast to LR, the 37-kDa LRP form is much less abundant in adult than in postnatal central nervous system. Characterization of a novel antibody allowed us to study the distribution across tissues of cell membrane-associated LRP. Interestingly, this form is almost exclusively found on a subclass of parvalbumin-immunoreactive cortical interneurons known to degenerate during the early stages of Creutzfeldt-Jakob disease. Our demonstration of local differences in the expression of particular LRP/LR isoforms may be a first step towards unraveling their specific molecular interactions.

Migration and Function of a Glial Subtype in the Vertebrate Peripheral Nervous System

Glia-axon interactions are essential for the development and function of the nervous system. We combine in vivo imaging and genetics to address the mechanism by which the migration of these cells is coordinated during embryonic development. Using stable transgenic lines, we have followed the migration of one subset of glial cells and their target axons in living zebrafish embryos. These cells coalesce at an early stage and remain coupled throughout migration, with axons apparently pathfinding for glia. Mutant analysis demonstrates that axons provide instructive cues that are sufficient to control glial guidance. Furthermore, mutations in the transcription factor Sox10/ cls uncouple the migration of axons and glia. Finally, genetic ablation of this glial subtype reveals an essential role in nerve fasciculation.

Synucleins in glaucoma: implication of gamma-synuclein in glaucomatous alterations in the optic nerve.

Synucleins are small proteins associated with neurodegenerative diseases and some forms of cancer. They are studied predominantly in the brain; information about their presence and functions in ocular tissues is scarce. Here we describe the localization of three members of the synuclein family in the optic nerve of donors with different types of glaucoma compared with control samples from donors without ocular diseases. We did not find significant differences in the localization of alpha- and beta-synucleins in the optic nerve or retina of glaucoma patients compared with controls, whereas considerable redistribution of gamma-synuclein occurred in the glaucomatous optic nerve compared with control eye without glaucoma. In the optic nerve from control and glaucomatous individuals, nerve bundles are immunopositive for gamma-synuclein; however, a strong gamma-synuclein-immunopositive staining in a subset of glial cells was observed in the lamina and postlamina cribrosa regions of the optic nerve only in glaucoma patients. In the optic nerve of rats with episcleral vein cauterization used as an animal model of glaucoma, the quantity of both gamma-synuclein mRNA and protein was decreased compared with the optic nerves of control animals. Incubation of rat astrocyte culture at elevated hydrostatic pressure reduced the amount of gamma-synuclein but did not affect the quantities of actin and glial fibrillary acidic protein. These data suggest that significant changes in the pattern of expression and/or localization occur in the glaucomatous optic nerve for gamma-synuclein but not for alpha- and beta-members of the synuclein family.

Carnosine-like immunoreactivity in the central nervous system of rats during postnatal development.

In the nervous system of adult rodents, the aminoacylhistidine dipeptides (carnosine and/or homocarnosine) have been shown to be expressed in three main populations of cells: the mature olfactory receptor neurons, a subset of glial cells, and the neuroblasts of the rostral migratory stream. The current study analyzed the distribution of these dipeptides during postnatal development within the rat brain and spinal cord focusing on their pattern of appearance in the glial cells. Double staining methods using antibodies against carnosine and some markers specific for immature (vimentin) and mature (glial fibrillary acidic protein and Rip) glial cell types were used. Glial immunostaining for the aminoacylhistidine dipeptides appears starting from postnatal day 6 and reaches the final distribution in 3-week-old animals. The occurrence of carnosine-like immunoreactivity in astrocytes lags behind that in oligodendrocytes suggesting that, as previously demonstrated by in vitro studies, oligodendrocytes are also able to synthesize carnosine and/or homocarnosine in vivo. Furthermore, the spatiotemporal patterns observed support the hypothesis that the production of these dipeptides coincides with the final stages of glia differentiation. In addition, a strong carnosine-like immunoreactivity is transiently seen in a small population of cells localized in the hypothalamus and in the subfornical organ from birth to postnatal day 21. In these cells, carnosine-like immunoreactivity was not colocalized with any of the glial specific markers used. Moreover, no evidence for colocalization of carnosine and gonadotropin-releasing hormone (GnRH) has been observed.

Gliarin and macrolin, two novel intermediate filament proteins specifically expressed in sets and subsets of glial cells in leech central nervous system.

Using monoclonal antibodies, we have identified two novel intermediate filament (IF) proteins, Gliarin and Macrolin, which are specifically expressed in the central nervous system of an invertebrate. The two proteins both contain the coiled-coil rod domain typical of the superfamily of IF proteins flanked by unique N- and C-terminal domains. Gliarin was found in all glial cells including macro- and microglial cells, whereas Macrolin was expressed in only a single pair of giant connective glial cells. The identification of Macrolin and Gliarin together with the characterization of the strictly neuronal IF protein Filarin in leech central nervous system demonstrate that multiple neuron- and glial-specific IFs are not unique to the vertebrate nervous system but are also found in invertebrates. Interestingly, phylogenetic analysis based on maximum parsimony indicated that the presence of neuron- and glial cell-specific IFs in coelomate protostomes as well as in vertebrates is not of monophyletic origin, but rather represents convergent evolution and appears to have arisen independently.

Metabolic labeling of a subset of glial cells by UDP-galactose: implication for astrocyte lineage diversity.

Astrocytes are implicated in many aspects of brain function; however, it remains unclear whether astrocytes arise from a single cell lineage. It is therefore important to obtain new markers for the astrocyte cell lineage. We show that exogenously added UDP-galactose (UDP-Gal) can be used to metabolically label a subset of glial fibrillary acidic protein-positive (GFAP+) cells. UDP-Gal was incorporated into the cultured embryonic mouse brain slices in a time-dependent manner. Surprisingly, the transferred sugar moiety was no longer Gal but was mainly glucose. Most of the radioactivity was transferred to a polymer of glucose, most likely to be glycogen, and also to glucosyl ceramide. In the slice culture, the reaction products were distributed densely in the ventricular zone and also on process-like structures extending to the pial surface. In dissociation culture, UDP-Gal labeled some of the GFAP+ cells and some of the vimentin+ cells. Because radial glial cells (RGCs) contain glycogen and change from vimentin+ to GFAP+, it is strongly suggested that UDP-Gal labeled RGCs and their descendants. Only 27% of the GFAP+ cells were labeled with UDP-Gal, which suggests that only a subset of astrocytes are derived from RGCs and that there is a discrete group of GFAP+ cells that is not generated from RGCs.

The type 2 iodothyronine deiodinase is expressed primarily in glial cells in the neonatal rat brain.

Thyroid hormone plays an essential role in mammalian brain maturation and function, in large part by regulating the expression of specific neuronal genes. In this tissue, the type 2 deiodinase (D2) appears to be essential for providing adequate levels of the active thyroid hormone 3,5,3'-triiodothyronine (T3) during the developmental period. We have studied the regional and cellular localization of D2 mRNA in the brain of 15-day-old neonatal rats. D2 is expressed in the cerebral cortex, olfactory bulb, hippocampus, caudate, thalamus, hypothalamus, and cerebellum and was absent from the white matter. At the cellular level, D2 is expressed predominantly, if not exclusively, in astrocytes and in the tanycytes lining the third ventricle and present in the median eminence. These results suggest a close metabolic coupling between subsets of glial cells and neurons, whereby thyroxine is taken up from the blood and/or cerebrospinal fluid by astrocytes and tanycytes, is deiodinated to T3, and then is released for utilization by neurons.

Neurotransmitter‐mediated signaling between axons and glial cells

Neurotransmitter-mediated signaling is not restricted to the synaptic regions of the nervous system but also takes places along fiber tracts lacking vesicular means of releasing neuroactive substances. The first demonstration for dynamic signaling of this type came in the early 1970s from studies by Villegas and co-workers in squid axons and their satellite Schwann cells. In this invertebrate system, glutamate has been identified as the mediator of this signaling in being first released from the active axons thus setting off a series of cascades, leading to a cholinergic activation of the Schwann cell membrane. Recent evidence suggests that receptor-mediated signaling also exists between glial cells and axons in vertebrates. In the frog optic nerve, axonal activity facilitated the activity of glial ion channels. In the neonatal rat optic nerve, electrical activity of axons triggered oscillations in intracellular calcium in a subset of glial cells. These observations have been postulated to reflect receptor-mediated signaling, including a mechanism in which glutamate is released from axons via the reversal of a transporter and induces intracellular calcium spiking in glial cells via metabotropic glutamate receptors. The efficacy of "axon-to-glia" transmission may, like that in "neuron-to-neuron" transmission, be modulated by co-release of multiple neuroactive substances. One possibility is that adenosine, which is known to be released from fiber tracts, can modulate glutamate signaling in white matter by modulating the periaxonal glutamate concentration through an effect on the glial glutamate uptake system.

PDGF receptors in the rat CNS: during late neurogenesis, PDGF alpha-receptor expression appears to be restricted to glial cells of the oligodendrocyte lineage.

Using in situ hybridization, we have visualized cells in the rat central nervous system (CNS) that contain mRNA encoding the platelet-derived growth factor alpha receptor (PDGF-alpha R). After embryonic day 16 (E16), PDGF-alpha R mRNA appears to be expressed by a subset of glial cells, but not by neurons. The temporal and spatial distribution of PDGF-alpha R+ cells, together with 125I-PDGF binding studies on subsets of glial cells in vitro, suggests that PDGF-alpha R may be expressed predominantly, or exclusively, by cells of the oligodendrocyte-type-2 astrocyte (O-2A) lineage. This conclusion is supported by the fact that the numbers of PDGF-alpha R+ cells in developing and adult optic nerves correlate well with independent estimates of the number of O-2A progenitor cells in the nerve at equivalent ages. Small numbers of PDGF-alpha R+ cells are present in the brain at E16, at which time they are found outside the subventricular germinal zones, suggesting that these cells do not express PDGF-alpha R until after, or shortly before they start to migrate away from the subventricular layer towards their final destinations. Reduced numbers of PDGF-alpha R+ cells persist in the adult CNS. PDGF-alpha R is also expressed strongly in the meningeal membranes and choroid plexus, and in the inner limiting membrane of the retina.