Induced NG2 expressing microglia in the facial motor nucleus after facial nerve axotomy

Diminished Ventral Oligodendrocyte Precursor Generation Results in the Subsequent Over-production of Dorsal Oligodendrocyte Precursors of Aberrant Morphology and Function

Oligodendrocyte precursor cells (OPCs) arise sequentially first from a ventral and then from a dorsal precursor domain at the end of neurogenesis during spinal cord development. Whether the sequential production of OPCs is of physiological significance has not been examined. Here we show that ablating Shh signaling from nascent ventricular zone derivatives and partially from the floor plate results in a severe diminishment of ventral derived OPCs but normal numbers of motor neurons in the postnatal spinal cord. In the absence of ventral vOPCs, dorsal dOPCs populate the entire spinal cord resulting in an increased OPC density in the ventral horns. These OPCs take on an altered morphology, do not participate in the removal of excitatory vGlut1 synapses from injured motor neurons, and exhibit morphological features similar to those found in the vicinity of motor neurons in the SOD1 mouse model of Amyotrophic Lateral Sclerosis (ALS). Our data indicate that vOPCs prevent dOPCs from invading ventral spinal cord laminae and suggest that vOPCs have a unique ability to communicate with injured motor neurons.

Protective Effects of Fucoxanthin on Ultraviolet B-Induced Corneal Denervation and Inflammatory Pain in a Rat Model

Fucoxanthin is a carotenoid with many pharmaceutical properties that is found in brown seaweed. However, the effects of fucoxanthin on corneal innervation and intense eye pain have not been extensively examined. To clarify the protective roles and underlying mechanisms of fucoxanthin on ocular lesions, we investigated the beneficial effects and mechanisms by which fucoxanthin ameliorates ultraviolet B (UVB)-induced corneal denervation and trigeminal pain. Treatment with fucoxanthin enhanced the expression of nuclear factor erythroid 2-related factor 2 in the cornea. Inhibition of typical denervation and epithelial exfoliation in the cornea were observed in rats treated with fucoxanthin following UVB-induced nerve disorders. Moreover, the active phosphorylated form of p38 MAP kinase (pp38) and the number of glial fibrillary acidic protein (GFAP)-positive neural cells were significantly reduced. Decreased expression of neuron-selective transient receptor potential vanilloid type 1 (TRPV1) in the trigeminal ganglia neurons was also demonstrated in rats treated with fucoxanthin after UVB-induced keratitis. Symptoms of inflammatory pain, including difficulty in opening the eyes and eye wipe behaviour, were also reduced in fucoxanthin-treated groups. Pre-treatment with fucoxanthin may protect the eyes from denervation and inhibit trigeminal pain in UVB-induced photokeratitis models.

Neuron-Glia Crosstalk and Neuropathic Pain: Involvement in the Modulation of Motor Activity in the Orofacial Region

Neuropathic orofacial pain (NOP) is a debilitating condition. Although the pathophysiology remains unclear, accumulating evidence suggests the involvement of multiple mechanisms in the development of neuropathic pain. Recently, glial cells have been shown to play a key pathogenetic role. Nerve injury leads to an immune response near the site of injury. Satellite glial cells are activated in the peripheral ganglia. Various neural and immune mediators, released at the central terminals of primary afferents, lead to the sensitization of postsynaptic neurons and the activation of glia. The activated glia, in turn, release pro-inflammatory factors, further sensitizing the neurons, and resulting in central sensitization. Recently, we observed the involvement of glia in the alteration of orofacial motor activity in NOP. Microglia and astroglia were activated in the trigeminal sensory and motor nuclei, in parallel with altered motor functions and a decreased pain threshold. A microglial blocker attenuated the reduction in pain threshold, reduced the number of activated microglia, and restored motor activity. We also found an involvement of the astroglial glutamate–glutamine shuttle in the trigeminal motor nucleus in the alteration of the jaw reflex. Neuron–glia crosstalk thus plays an important role in the development of pain and altered motor activity in NOP.

Expression of NG2 and platelet-derived growth factor receptor alpha in the developing neonatal rat brain

Platelet-derived growth factor receptor alpha (PDGFRα) is a marker of oligodendrocyte precursor cells in the central nervous system. NG2 is also considered a marker of oligodendrocyte precursor cells. However, whether there are differences in the distribution and morphology of oligodendrocyte precursor cells labeled by NG2 or PDGFRα in the developing neonatal rat brain remains unclear. In this study, by immunohistochemical staining, NG2 positive (NG²⁺) cells were ubiquitous in the molecular layer, external pyramidal layer, internal pyramidal layer, and polymorphic layer of the cerebral cortex, and corpus callosum, external capsule, piriform cortex, and medial septal nucleus. NG²⁺ cells were stellate or fusiform in shape with long processes that were progressively decreased and shortened over the course of brain development. The distribution and morphology of PDGFRα positive (PDGFRα⁺) cells were coincident with NG²⁺ cells. The colocalization of NG2 and PDGFRα in the cell bodies and processes of some cells was confirmed by double immunofluorescence labeling. Moreover, cells double-labeled for NG2 and PDGFRα were predominantly in the early postnatal stage of development. The numbers of NG²⁺/PDGFRα⁺ cells and PDGFRα⁺ cells decreased, but the number of NG²⁺ cells increased from postnatal days 3 to 14 in the developing brain. In addition, amoeboid microglial cells of the corpus callosum, newborn brain macrophages in the normal developing brain, did not express NG2 or PDGFRα, but NG2 expression was detected in amoeboid microglia after hypoxia. The present results suggest that NG2 and PDGFRα are specific markers of oligodendrocyte precursor cells at different stages during early development. Additionally, the NG2 protein is involved in inflammatory and pathological processes of amoeboid microglial cells.

Progenitor/Stem Cell Markers in Brain Adjacent to Glioblastoma: GD3 Ganglioside and NG2 Proteoglycan Expression

Characterization of tissue surrounding glioblastoma (GBM) is a focus for translational research because tumor recurrence invariably occurs in this area. We investigated the expression of the progenitor/stem cell markers GD3 ganglioside and NG2 proteoglycan in GBM, peritumor tissue (brain adjacent to tumor, BAT) and cancer stem-like cells (CSCs) isolated from GBM (GCSCs) and BAT (PCSCs). GD3 and NG2 immunohistochemistry was performed in paired GBM and BAT specimens from 40 patients. Double-immunofluorescence was carried out to characterize NG2-positive cells of vessel walls. GD3 and NG2 expression was investigated in GCSCs and PCSCs whose tumorigenicity was also evaluated in Scid/bg mice. GD3 and NG2 expression was higher in tumor tissue than in BAT. NG2 decreased as the distance from tumor margin increased, regardless of the tumor cell presence, whereas GD3 correlated with neoplastic infiltration. In BAT, NG2 was coexpressed with a-smooth muscle actin (a-SMA) in pericytes and with nestin in the endothelium. Higher levels of NG2 mRNA and protein were found in GCSCs while GD3 synthase was expressed at similar levels in the 2 CSC populations. PCSCs had lower tumorigenicity than GCSCs. These data suggest the possible involvement of GD3 and NG2 in pre/pro-tumorigenic events occurring in the complex microenvironment of the tissue surrounding GBM.

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.

Alternatively activated microglia and macrophages in the central nervous system

Macrophages are important players in the fight against viral, bacterial, fungal and parasitic infections. From a resting state they may undertake two activation pathways, the classical known as M1, or the alternative known as M2. M1 markers are mostly mediators of pro-inflammatory responses whereas M2 markers emerge for resolution and cleanup. Microglia exerts in the central nervous system (CNS) a function similar to that of macrophages in the periphery. Microglia activation and proliferation occurs in almost any single pathology affecting the CNS. Often microglia activation has been considered detrimental and drugs able to stop microglia activation were considered for the treatment of a variety of diseases. Cumulative evidence shows that microglia may undergo the alternative activation pathway, express M2-type markers and contribute to neuroprotection. This review focuses on details about the role of M2 microglia and in the approaches available for its identification. Approaches to drive the M2 phenotype and data on its potential in CNS diseases are also reviewed.

The activation of NG2 expressing cells is downstream to microglial reaction and mediated by the transforming growth factor beta 1

In the present study, we investigated the mechanism of activation of NG2 expressing cells. Application of microglial inhibitors not only attenuated morphological changes but also significantly retarded increase in the number of NG2 expressing cells. Intracerebral injection of TGF-β1 led to a profound activation of NG2 glia as well as an earlier accumulation of NG2(+)-microglia, whilst inhibition of TGF-β1 Smad2/3 signalling pathway eventually attenuated their active responses. We conclude that the activation of NG2 expressing cells is an event downstream to microglial reaction and TGF-β1 secreted from microglia might play an important role in modulation of the function of NG2 expressing cells.

Role of NG2 expressing cells in addiction: a new approach for an old problem

Neuron-glial antigen 2 (NG2) is a proteoglycan expressed predominantly in oligodendrocyte progenitor cells (OPCs). NG2-expressing OPCs (NG2-OPCs) are self-renewing cells that are widely distributed in the gray and white matter areas of the central nervous system. NG2-OPCs can mature into premyelinating oligodendrocytes and myelinating oligodendroglia which serve as the primary source of myelin in the brain. This review characterizes NG2-OPCs in brain structure and function, conceptualizes the role of NG2-OPCs in brain regions associated with negative reinforcement and relapse to drug seeking and discusses how NG2-OPCs are regulated by neuromodulators linked to motivational withdrawal. We hope to provide the readers with an overview of the role of NG2-OPCs in brain structure and function in the context of negative affect state in substance abuse disorders and to integrate our current understanding of the physiological significance of the NG2-OPCs in the adult brain.

Chondroitin sulfate proteoglycans in the nervous system: inhibitors to repair

Chondroitin sulfate proteoglycans (CSPGs) are widely expressed in the normal central nervous system, serving as guidance cues during development and modulating synaptic connections in the adult. With injury or disease, an increase in CSPG expression is commonly observed close to lesioned areas. However, these CSPG deposits form a substantial barrier to regeneration and are largely responsible for the inability to repair damage in the brain and spinal cord. This review discusses the role of CSPGs as inhibitors, the role of inflammation in stimulating CSPG expression near site of injury, and therapeutic strategies for overcoming the inhibitory effects of CSPGs and creating an environment conducive to nerve regeneration.

Activated microglia in a rat stroke model express NG2 proteoglycan in peri-infarct tissue through the involvement of TGF-β1

We investigated activated microglia in ischemic brain lesions from rats that had been subjected to transient middle cerebral artery occlusion. Activated microglia expressing NG2 chondroitin sulfate proteoglycan (NG2) were found only in the narrow zone (demarcation zone) that demarcated the peri-infarct tissue and ischemic core. NG2(-) activated microglia were abundantly distributed in the peri-infarct tissue outside the demarcation zone. NG2(+) microglia but not NG2(-) microglia expressed both CD68 and a triggering receptor expressed on myeloid cells 2 (TREM-2), suggesting that NG2(+) microglia eliminated apoptotic neurons. In fact, NG2(+) microglia often attached to degenerating neurons and sometimes internalized NeuN(+) or neurofilament protein(+) material. Kinetic studies using quantitative real-time RT-PCR revealed that expression of transforming growth factor-β1 (TGF-β1) was most evident in the ischemic core; with this marker produced mainly by macrophages located in this region. TGF-β receptor mRNA expression peaked at 3 days post reperfusion (dpr) in the peri-infarct tissue, including the demarcation zone. Primary cultured rat microglia also expressed the receptor mRNA. In response to TGF-β1, primary microglia enhanced the expression of NG2 protein and TREM-2 mRNA as well as migratory activity. A TGF-β1 inhibitor, SB525334, abolished these effects. The present results suggest that TGF-β1 produced in the ischemic core diffused toward the peri-infarct tissue, driving activated microglial cells to eliminate degenerating neurons. Appropriate control of NG2(+) microglia in the demarcation zone might be a novel target for the suppression of secondary neurodegeneration in the peri-infarct tissue.

Oligodendroglial alterations and the role of microglia in white matter injury: relevance to schizophrenia

Schizophrenia is a chronic and debilitating mental illness characterized by a broad range of abnormal behaviors, including delusions and hallucinations, impaired cognitive function, as well as mood disturbances and social withdrawal. Due to the heterogeneous nature of the disease, the causes of schizophrenia are very complex; its etiology is believed to involve multiple brain regions and the connections between them, and includes alterations in both gray and white matter regions. The onset of symptoms varies with age and severity, and there is some debate over a degenerative or developmental etiology. Longitudinal magnetic resonance imaging studies have detected progressive gray matter loss in the first years of disease, suggesting neurodegeneration; but there is also increasing recognition of a temporal association between clinical complications at birth and disease onset that supports a neurodevelopmental origin. Presently, neuronal abnormalities in schizophrenia are better understood than alterations in myelin-producing cells of the brain, the oligodendrocytes, which are the predominant constituents of white matter structures. Proper white matter development and its structural integrity critically impacts brain connectivity, which affects sensorimotor coordination and cognitive ability. Evidence of defective white matter growth and compromised white matter integrity has been found in individuals at high risk of psychosis, and decreased numbers of mature oligodendrocytes are detected in schizophrenia patients. Inflammatory markers, including proinflammatory cytokines and chemokines, are also associated with psychosis. A relationship between risk of psychosis, white matter defects and prenatal inflammation is being established. Animal models of perinatal brain injury are successful in producing white matter damage in the brain, typified by hypomyelination and/or dysmyelination, impaired motor coordination and prepulse inhibition of the acoustic startle reflex, recapitulating structural and functional characteristics observed in schizophrenia. In addition, elevated expression of inflammation-related genes in brain tissue and increased production of cytokines by blood cells from patients with schizophrenia indicate immunological dysfunction and abnormal inflammatory responses, which are also important underlying features in experimental models. Microglia, resident immune defenders of the central nervous system, play important roles in the development and protection of neural cells, but can contribute to injury under pathological conditions. This article discusses oligodendroglial changes in schizophrenia and focuses on microglial activity in the context of the disease, in neonatal brain injury and in various experimental models of white matter damage. These include disorders associated with premature birth, and animal models of perinatal bacterial and viral infection, oxygen deprivation (hypoxia) and excess (hyperoxia), and elevated systemic proinflammatory cytokine levels. We briefly review the effects of treatment with antipsychotic and anti-inflammatory agents in models of perinatal brain injury, and comment on the therapeutic potential of these strategies. By understanding the neurobiological basis of oligodendroglial abnormalities in schizophrenia, it is hoped that patients will benefit from the availability of targeted and more efficacious treatment options.

Microglia/monocytes with NG2 expression have no phagocytic function in the cortex after LPS focal injection into the rat brain

While OX42(+) microglia/macrophages have been considered as a scavenger in the brain, NG2(+) cells are generally considered as oligodendrocyte progenitor cells or function-unknown glial cells. Recent evidence showed that under some pathological conditions, certain cells have become positive for both anti-NG2 and anti-OX42 antibodies. Our results suggested that some OX42(+) microglia or macrophages were induced to express NG2 proteins 3 and 5 days later after focal injection of lipopolysaccharide into the brain cortex of Sprague-Dawley rats. In consideration of the induction of NG2 expression may associate with gaining or losing functions of microglia/macrophages, we further showed that, while OX42(+) or ED1(+) microglia/macrophages presented active phagocytic function, NG2(+) /OX42(+) cells failed to engulf latex beads. The induced expression of NG2 protein may possibly indicate the functional diversity of activated microglia/macrophages in the brain.

Polydendrocytes display large lineage plasticity following focal cerebral ischemia

Polydendrocytes (also known as NG2 glial cells) constitute a fourth major glial cell type in the adult mammalian central nervous system (CNS) that is distinct from other cell types. Although much evidence suggests that these cells are multipotent in vitro, their differentiation potential in vivo under physiological or pathophysiological conditions is still controversial.

To follow the fate of polydendrocytes after CNS pathology, permanent middle cerebral artery occlusion (MCAo), a commonly used model of focal cerebral ischemia, was carried out on adult NG2creBAC:ZEG double transgenic mice, in which enhanced green fluorescent protein (EGFP) is expressed in polydendrocytes and their progeny. The phenotype of the EGFP⁺ cells was analyzed using immunohistochemistry and the patch-clamp technique 3, 7 and 14 days after MCAo. In sham-operated mice (control), EGFP⁺ cells in the cortex expressed protein markers and displayed electrophysiological properties of polydendrocytes and oligodendrocytes. We did not detect any co-labeling of EGFP with neuronal, microglial or astroglial markers in this region, thus proving polydendrocyte unipotent differentiation potential under physiological conditions. Three days after MCAo the number of EGFP⁺ cells in the gliotic tissue dramatically increased when compared to control animals, and these cells displayed properties of proliferating cells. However, in later phases after MCAo a large subpopulation of EGFP⁺ cells expressed protein markers and electrophysiological properties of astrocytes that contribute to the formation of glial scar. Importantly, some EGFP⁺ cells displayed membrane properties typical for neural precursor cells, and moreover these cells expressed doublecortin (DCX) – a marker of newly-derived neuronal cells. Taken together, our data indicate that polydendrocytes in the dorsal cortex display multipotent differentiation potential after focal ischemia.

The effect of minocycline on the masticatory movements following the inferior alveolar nerve transection in freely moving rats

Background

To determine the effects of inferior alveolar nerve transection (IAN-X) on masticatory movements in freely moving rats and to test if microglial cells in the trigeminal principal sensory nucleus (prV) or motor nucleus (motV) may be involved in modulation of mastication, the effects of microglial cell inhibitor minocycline (MC) on masticatory jaw movements, microglia (Iba1) immunohistochemistry and the masticatory jaw movements and related masticatory muscle EMG activities were studied in IAN-X rats.

Results

The number of Iba1-immunoreactive (IR) cells both in prV and motV was significantly larger in IAN-X rats compared with sham rats on day 3 after IAN-X. The intraperitoneal (i.p.) administration of MC caused a significant reduction of the number of Iba1-IR cells both in prV and motV that was evident on day 14 after IAN-X. Furthermore, a significant reduction of the number of Iba1-IR cells could be observed in motV but not in prV after microinjection (m.i.) of MC into the motV of IAN-X rats. The rats also exhibited a significant decrease in the head-withdrawal threshold on the side ipsilateral to the IAN-X compared to the threshold before IAN-X and it lasted to day 14. In addition, IAN-X markedly affected the ability to rat to carry out mastication. The number of complete masticatory sequences was significantly decreased. Furthermore, the total masticatory sequence time and food preparatory (PP) period duration was significantly elongated in compared to sham rats. Although IAN-X significantly affected the total number of chewing cycles within the RC period of a masticatory sequence, it had no effect on the duration of the chewing cycles. On the other hand, systemic administration of MC (both i.p. and m.i.) in IAN-X rats significantly improved decreased head-withdrawal threshold and the impaired masticatory jaw movements.

Conclusions

The present findings reveal that the strong modulation of masticatory jaw movements occurs following microglial cell activation after IAN-X, and the modulation recovers after inhibition of the microglial cell activation by MC, suggesting that microglial cell activation in the motV as well as in the prV has a pivotal role in modulating mastication following trigeminal nerve injury associated with orofacial neuropathic pain.

Increased p75 neurotrophin receptor expression in the canine distemper virus model of multiple sclerosis identifies aldynoglial Schwann cells that emerge in response to axonal damage

Gliogenesis under pathophysiological conditions is of particular clinical relevance since it may provide regeneration-promoting cells recruitable for therapeutic purposes. There is accumulating evidence that aldynoglial cells with Schwann cell-like growth-promoting properties emerge in the lesioned CNS. However, the characterization of these cells and the signals triggering their in situ generation have remained enigmatic. In the present study, we used the p75 neurotrophin receptor (p75(NTR) ) as a marker for Schwann cells to study gliogenesis in the well-defined canine distemper virus (CDV)-induced demyelination model. White matter lesions of CDV-infected dogs contained bi- to multipolar, p75(NTR) -expressing cells that neither expressed MBP, GFAP, BS-1, or P0 identifying oligodendroglia, astrocytes, microglia, and myelinating Schwann cells nor CDV antigen. Interestingly, p75(NTR) -expression became apparent prior to the onset of demyelination in parallel to the expression of β-amyloid precursor protein (β-APP), nonphosphorylated neurofilament (n-NF), BS-1, and CD3, and peaked in subacute lesions with inflammation. To study the role of infiltrating immune cells during differentiation of Schwann cell-like glia, organotypic slice cultures from the normal olfactory bulb were established. Despite the absence of infiltrating lymphocytes and macrophages, a massive appearance of p75(NTR) -positive Schwann-like cells and BS-1-positive microglia was noticed at 10 days in vitro. It is concluded that axonal damage as an early signal triggers the differentiation of tissue-resident precursor cells into p75(NTR) -expressing aldynoglial Schwann cells that retain an immature pre-myelin state. Further studies have to address the role of microglia during this process and the regenerative potential of aldynoglial cells in CDV infection and other demyelinating diseases.

FABP7 expression in normal and stab-injured brain cortex and its role in astrocyte proliferation

Reactive gliosis, in which astrocytes as well as other types of glial cells undergo massive proliferation, is a common hallmark of all brain pathologies. Brain-type fatty acid-binding protein (FABP7) is abundantly expressed in neural stem cells and astrocytes of developing brain, suggesting its role in differentiation and/or proliferation of glial cells through regulation of lipid metabolism and/or signaling. However, the role of FABP7 in proliferation of glial cells during reactive gliosis is unknown. In this study, we examined the expression of FABP7 in mouse cortical stab injury model and also the phenotype of FABP7-KO mice in glial cell proliferation. Western blotting showed that FABP7 expression was increased significantly in the injured cortex compared with the contralateral side. By immunohistochemistry, FABP7 was localized to GFAP⁺ astrocytes (21% of FABP7⁺ cells) and NG2⁺ oligodendrocyte progenitor cells (62%) in the normal cortex. In the injured cortex there was no change in the population of FABP7⁺/NG2⁺ cells, while there was a significant increase in FABP7⁺/GFAP⁺ cells. In the stab-injured cortex of FABP7-KO mice there was decrease in the total number of reactive astrocytes and in the number of BrdU⁺ astrocytes compared with wild-type mice. Primary cultured astrocytes from FABP7-KO mice also showed a significant decrease in proliferation and omega-3 fatty acid incorporation compared with wild-type astrocytes. Overall, these data suggest that FABP7 is involved in the proliferation of astrocytes by controlling cellular fatty acid homeostasis.

A cytokine mixture of GM-CSF and IL-3 that induces a neuroprotective phenotype of microglia leading to amelioration of (6-OHDA)-induced Parkinsonism of rats

Dopamine (DA) agonists are widely used as primary treatments for Parkinson's disease. However, they do not prevent progressive degeneration of dopaminergic neurons, the central pathology of the disease. In this study, we found that subcutaneous injection of a cytokine mixture containing granulocyte macrophage colony-stimulating factor and interleukin-3 (IL-3) markedly suppressed dopaminergic neurodegeneration in 6-hydroxydopamine-lesioned rats, an animal model of Parkinson's disease. The cytokine mixture suppressed the decrease of DA content in the striatum, and ameliorated motor function in the lesioned rats. In response to the cytokine injection, dopaminergic neurons in the substantia nigra pars compacta increased expression of the antiapoptotic protein Bcl-xL. Microglial activation in the pars compacta was evident in both the saline- and cytokine-injected rats. However, the cytokine mixture suppressed expression of the proinflammatory cytokines IL-1β and tumor necrosis factors α, and upregulated the neuroprotective factors insulin-like growth factor-1 and hepatocyte growth factor. Similar responses were observed in cultured microglia. Detailed morphometric analyses revealed that NG2 proteoglycan-expressing glial cells increased in the cytokine-injected rats, while astrocytic activation with increased expression of antioxidative factors was evident only in the saline-injected rats. Thus, the present findings show that the cytokine mixture was markedly effective in suppressing neurodegeneration. Its neuroprotective effects may be mediated by increased expression of Bcl-xL in dopaminergic neurons, and the activation of beneficial actions of microglia that promote neuronal survival. Furthermore, this cytokine mixture may have indirect actions on NG2 proteoglycan-expressing glia, whose role may be implicated in neuronal survival.

In situ dividing and phagocytosing retinal microglia express nestin, vimentin, and NG2 in vivo

Background

Following injury, microglia become activated with subsets expressing nestin as well as other neural markers. Moreover, cerebral microglia can give rise to neurons in vitro. In a previous study, we analysed the proliferation potential and nestin re-expression of retinal macroglial cells such as astrocytes and Müller cells after optic nerve (ON) lesion. However, we were unable to identify the majority of proliferative nestin⁺ cells. Thus, the present study evaluates expression of nestin and other neural markers in quiescent and proliferating microglia in naïve retina and following ON transection in adult rats in vivo.

Methodology/Principal Findings

For analysis of cell proliferation and cells fates, rats received BrdU injections. Microglia in retinal sections or isolated cells were characterized using immunofluorescence labeling with markers for microglia (e.g., Iba1, CD11b), cell proliferation, and neural cells (e.g., nestin, vimentin, NG2, GFAP, Doublecortin etc.). Cellular analyses were performed using confocal laser scanning microscopy. In the naïve adult rat retina, about 60% of resting ramified microglia expressed nestin. After ON transection, numbers of nestin⁺ microglia peaked to a maximum at 7 days, primarily due to in situ cell proliferation of exclusively nestin⁺ microglia. After 8 weeks, microglia numbers re-attained control levels, but 20% were still BrdU⁺ and nestin⁺, although no further local cell proliferation occurred. In addition, nestin⁺ microglia co-expressed vimentin and NG2, but not GFAP or neuronal markers. Fourteen days after injury and following retrograde labeling of retinal ganglion cells (RGCs) with Fluorogold (FG), nestin⁺NG2⁺ microglia were positive for the dye indicating an active involvement of a proliferating cell population in phagocytosing apoptotic retinal neurons.

Conclusions/Significance

The current study provides evidence that in adult rat retina, a specific resident population of microglia expresses proteins of immature neural cells that are involved in injury-induced cell proliferation and phagocytosis while transdifferentiation was not observed.

NG2 expressed by macrophages and oligodendrocyte precursor cells is dispensable in experimental autoimmune encephalomyelitis

Increased expression of the chondroitin proteoglycan NG2 is a prominent feature in central nervous system injury with unknown cellular source and biological relevance. Here, we describe the first detailed analysis of experimental autoimmune encephalomyelitis in NG2 knockout mice and NG2 knockout bone marrow chimeras. We show that both macrophages and oligodendrocyte progenitor cells express and secrete NG2 in response to transforming growth factor-β. A subpopulation of macrophages expresses NG2 within leucocyte infiltrates in the central nervous system, but only oligodendrocyte progenitor cells contribute to NG2 accumulation. Notably, NG2 plays no role in experimental autoimmune encephalomyelitis initiation, progression or recuperation. In concurrence, the immune response is unaltered in NG2-deficient mice as are the extent of central nervous system damage and degree of remyelination.

Restoration of microglial function by granulocyte-colony stimulating factor in ALS model mice

We studied the effects of G-CSF on microglial reactions in mutant SOD1 (mSOD1)-Tg (G93A) ALS model mice. Following hypoglossal axotomy, the numbers of neurons and microglia expressing GDNF were significantly lower in mSOD1-Tg mice than in non-transgenic (NTG) littermates. This decrease in the number of neurons after axotomy and a decrease in the number of large myelinated axons in mSOD1-Tg mice over the disease course were improved by G-CSF, which also increased microglial recruitment. Impaired migration of cultured mSOD1-Tg microglia to MCP-1 was recovered following G-CSF treatment. Restoration of microglial responses by G-CSF may contribute to its neuroprotective effects.