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

Temporal dynamics of cells expressing NG2 and platelet-derived growth factor receptor-β in the fibrotic scar formation after 3-nitropropionic acid-induced acute brain injury

Neuron-glia antigen 2 (NG2) proteoglycan and platelet-derived growth factor receptor beta (PDGFR-β) are widely used markers of pericytes, which are considered cells that form fibrotic scars in response to central nervous system insults. However, the exact phenotypes of NG2- and PDGFR-β-expressing cells, as well as the origin of the fibrotic scar after central nervous system insults, are still elusive. In the present study, we directly examined the identities and distributions of NG2- and PDGFR-β-positive cells in the control and lesioned striatum injured by the mitochondrial toxin 3-nitropropionic acid. Immunoelectron microscopy and correlative light and electron microscopy clearly distinguished NG2 and PDGFR-β expression in the vasculature during the post-injury period. Vascular smooth muscle cells and pericytes expressed NG2, which was prominently increased after the injury. NG2 expression was restricted to these vascular mural cells until 14 days post-lesion. By contrast, PDGFR-β-positive cells were perivascular fibroblasts located abluminal to smooth muscle cells or pericytes. These PDGFR-β-expressing cells formed extravascular networks associated with collagen fibrils at 14 days post-lesion. We also found that in the injured striatal parenchyma, PDGFR-β could be used as a complementary marker of resting and reactive NG2 glia because activated microglia/macrophages shared only the NG2 expression with NG2 glia in the lesioned striatum. These data indicate that NG2 and PDGFR-β label different vascular mural and parenchymal cells in the healthy and injured brain, suggesting that fibrotic scar-forming cells most likely originate in PDGFR-β-positive perivascular fibroblasts rather than in NG2-positive pericytes.

Myelin Debris Stimulates NG2/CSPG4 Expression in Bone Marrow-Derived Macrophages in the Injured Spinal Cord

Although the increased expression of members of the chondroitin sulfate proteoglycan family, such as neuron-glial antigen 2 (NG2), have been well documented after an injury to the spinal cord, a complete picture as to the cellular origins and function of this NG2 expression has yet to be made. Using a spinal cord injury (SCI) mouse model, we describe that some infiltrated bone marrow-derived macrophages (BMDMΦ) are early contributors to NG2/CSPG4 expression and secretion after SCI. We demonstrate for the first time that a lesion-related form of cellular debris generated from damaged myelin sheaths can increase NG2/CSPG4 expression in BMDMΦ, which then exhibit enhanced proliferation and decreased phagocytic capacity. These results suggest that BMDMΦ may play a much more nuanced role in secondary spinal cord injury than previously thought, including acting as early contributors to the NG2 component of the glial scar.

Pericyte migration and proliferation are tightly synchronized to endothelial cell sprouting dynamics

Pericytes are critical for microvascular stability and maintenance, among other important physiological functions, yet their involvement in vessel formation processes remains poorly understood. To gain insight into pericyte behaviors during vascular remodeling, we developed two complementary tissue explant models utilizing 'double reporter' animals with fluorescently-labeled pericytes and endothelial cells (via Ng2:DsRed and Flk-1:eGFP genes, respectively). Time-lapse confocal imaging of active vessel remodeling within adult connective tissues and embryonic skin revealed a subset of pericytes detaching and migrating away from the vessel wall. Vessel-associated pericytes displayed rapid filopodial sampling near sprouting endothelial cells that emerged from parent vessels to form nascent branches. Pericytes near angiogenic sprouts were also more migratory, initiating persistent and directional movement along newly forming vessels. Pericyte cell divisions coincided more frequently with elongating endothelial sprouts, rather than sprout initiation sites, an observation confirmed with in vivo data from the developing mouse brain. Taken together, these data suggest that (i) pericyte detachment from the vessel wall may represent an important physiological process to enhance endothelial cell plasticity during vascular remodeling, and (ii) pericyte migration and proliferation are highly synchronized with endothelial cell behaviors during the coordinated expansion of a vascular network.

Acute brain injuries trigger microglia as an additional source of the proteoglycan NG2

NG2 is a type I transmembrane glycoprotein known as chondroitin sulfate proteoglycan 4 (CSPG4). In the healthy central nervous system, NG2 is exclusively expressed by oligodendrocyte progenitor cells and by vasculature pericytes. A large body of immunohistochemical studies showed that under pathological conditions such as acute brain injuries and experimental autoimmune encephalomyelitis (EAE), a number of activated microglia were NG2 immuno-positive, suggesting NG2 expression in these cells. Alternative explanations for the microglial NG2 labeling consider the biochemical properties of NG2 or the phagocytic activity of activated microglia. Reportedly, the transmembrane NG2 proteoglycan can be cleaved by a variety of proteases to deposit the NG2 ectodomain into the extracellular matrix. The ectodomain, however, could also stick to the microglial surface. Since microglia are phagocytic cells engulfing debris of dying cells, it is difficult to identify a genuine expression of NG2. Recent studies showing (1) pericytes giving rise to microglial after stroke, and (2) immune cells of NG2-EYFP knock-in mice lacking NG2 expression in an EAE model generated doubts for the de novo expression of NG2 in microglia after acute brain injuries. In the current study, we took advantage of three knock-in mouse lines (NG2-CreERT2, CX₃CR₁-EGFP and NG2-EYFP) to study NG2 expression indicated by transgenic fluorescent proteins in microglia after tMCAO (transient middle cerebral artery occlusion) or cortical stab wound injury (SWI). We provide strong evidence that NG2-expressing cells, including OPCs and pericytes, did not differentiate into microglia after acute brain injuries, whereas activated microglia did express NG2 in a disease-dependent manner. A subset of microglia continuously activated the NG2 gene at least within the first week after tMCAO, whereas within 3 days after SWI a limited number of microglia at the lesion site transiently expressed NG2. Immunohistochemical studies demonstrated that these microglia with NG2 gene activity also synthesized the NG2 protein, suggesting activated microglia as an additional source of the NG2 proteoglycan after acute brain injuries.

The induction of Neuron-Glial2 (NG2) expressing cells in methamphetamine toxicity-induced neuroinflammation in rat brain are averted by melatonin

Neuron-Glial2 (NG2) expressing cells are described as the oligodendrocyte precursor cells in the brain. This study aimed to investigate the possible involvement of NG2 cells under the methamphetamine (METH)-induced neurotoxicity and neuroprotective capacity of melatonin. The results showed that the levels of NG2 in rat brain gradually increase from postnatal day 0 to postnatal day 8 and then the lower levels of NG2 are shown in adults. In adult rats, the levels of NG2 and COX-2 in the brain were significantly increased in lipopolysaccharide treatment. Pretreatment of 10 mg/kg melatonin prior to treating with METH was able to reduce an increase in the levels of NG2 and activation in astrocyte and microglia. These findings would extend the contribution of NG2 expressing cells in the adult brain during pathological conditions such as neuroinflammation.

Spatiotemporal Profile and Morphological Changes of NG2 Glia in the CA1 Region of the Rat Hippocampus after Transient Forebrain Ischemia

Neuron-glial antigen-2 (NG2) glia undergo proliferation and morphological changes following brain insults. Here, we show that NG2 glia is activated in a characteristic time- and layer-specific manner in the ischemia-vulnerable CA1 region of the rat hippocampus. Resting NG2 glia of the pyramidal cell layer (somatic region) shared morphological features with those of the neighboring dendritic stratum radiatum. During the postischemic period, reactive NG2 glia of the pyramidal cell layer exhibited shortened, scarcely branched processes, while those of the stratum radiatum had multiple branching processes with their arborization being almost indiscernible 7~14 days after reperfusion. Immunoelectron microscopy demonstrated that NG2 immunoreactivity was specifically associated with the plasma membrane and the adjacent extracellular matrix of NG2 glia in the stratum radiatum at 14 days. NG2 glia also exhibited differences in their numbers and proliferation profiles in the two examined hippocampal strata after ischemia. In addition, induced NG2 expression in activated microglia/macrophages exhibited a characteristic strata-dependent pattern in the ischemic CA1 hippocampus. NG2 induction was prominent in macrophage-like phenotypes which were predominantly localized in the pyramidal cell layer, compared with activated stellate microglial cells in the stratum radiatum. Thus, our data demonstrate that activation of NG2 glia and the induction of NG2 expression in activated microglia/macrophages occur in a distinct time- and layer-specific manner in the ischemic CA1 hippocampus. These characteristic profiles of reactive NG2 glia could be secondary to the degeneration processes occurring in the cell bodies or dendritic domains of hippocampal CA1 pyramidal neurons after ischemic insults.

Transforming growth factor-beta renders ageing microglia inhibitory to oligodendrocyte generation by CNS progenitors

It is now well-established that the macrophage and microglial response to CNS demyelination influences remyelination by removing myelin debris and secreting a variety of signaling molecules that influence the behaviour of oligodendrocyte progenitor cells (OPCs). Previous studies have shown that changes in microglia contribute to the age-related decline in the efficiency of remyelination. In this study, we show that microglia increase their expression of the proteoglycan NG2 with age, and that this is associated with an altered micro-niche generated by aged, but not young, microglia that can divert the differentiation OPCs from oligodendrocytes into astrocytes in vitro. We further show that these changes in ageing microglia are generated by exposure to high levels of TGFβ. Thus, our findings suggest that the rising levels of circulating TGFβ known to occur with ageing contribute to the age-related decline in remyelination by impairing the ability of microglia to promote oligodendrocyte differentiation from OPCs, and therefore could be a potential therapeutic target to promote remyelination.

Methods to label, image, and analyze the complex structural architectures of microvascular networks

Microvascular networks play key roles in oxygen transport and nutrient delivery to meet the varied and dynamic metabolic needs of different tissues throughout the body, and their spatial architectures of interconnected blood vessel segments are highly complex. Moreover, functional adaptations of the microcirculation enabled by structural adaptations in microvascular network architecture are required for development, wound healing, and often invoked in disease conditions, including the top eight causes of death in the Unites States. Effective characterization of microvascular network architectures is not only limited by the available techniques to visualize microvessels but also reliant on the available quantitative metrics that accurately delineate between spatial patterns in altered networks. In this review, we survey models used for studying the microvasculature, methods to label and image microvessels, and the metrics and software packages used to quantify microvascular networks. These programs have provided researchers with invaluable tools, yet we estimate that they have collectively attained low adoption rates, possibly due to limitations with basic validation, segmentation performance, and nonstandard sets of quantification metrics. To address these existing constraints, we discuss opportunities to improve effectiveness, rigor, and reproducibility of microvascular network quantification to better serve the current and future needs of microvascular research.

Macrophage Populations and Expression of Regulatory Inflammatory Factors in Hepatic Macrophage-depleted Rat Livers under Lipopolysaccharide (LPS) Treatment

To investigate the significance of the appearance of hepatic macrophages and expression of inflammatory factors in normal and macrophage-depleted livers, hepatic macrophages were depleted with liposome (Lipo)-encapsulated clodronate (CLD; 50 mg/kg, i.v.) followed by lipopolysaccharide (LPS) administration (0.1 mg/kg, i.p.) in F344 rats (CLD + LPS). Vehicle control rats (Lipo + LPS) received empty-Lipo before LPS. The low dose of LPS did not result in microscopic changes in the liver in either treatment group but did modulate M1 and M2 macrophage activity in Lipo + LPS rats without altering repopulating hepatic macrophages in CLD + LPS rats. LPS treatment in Lipo + LPS rats dramatically increased the M1 (IL-1β, IL-6, TNF-α, and MCP-1) but not M2 macrophage-related factors (IL-4 and CSF-1) compared to CLD + LPS rats. In the CLD + LPS rats, the M2 macrophage-related factors IL-4 and CSF-1 were elevated. In conclusion, low-dose LPS activated hepatic macrophages in rat livers without causing liver injury or stimulating repopulating hepatic macrophages. These data suggest that LPS may alter the liver microenvironment by modulating M1 or M2 macrophage-related inflammatory mediators and macrophage-based hepatotoxicity.

Morphological characterization of NG2 glia and their association with neuroglial cells in the 3-nitropropionic acid-lesioned striatum of rat

Our aim was to examine the spatiotemporal profiles and phenotypic characteristics of neuron-glia antigen 2 (NG2) glia and their associations with neuroglial cells in striatal lesions due to the mitochondrial toxin 3-nitropropionic acid (3-NP). In control striatum, weak NG2 immunoreactivity was restricted to resting NG2 glia with thin processes, but prominent NG2 expression was noted on activated microglia/macrophages, and reactive NG2 glia in the lesion core after 3-NP injection. Activation of NG2 glia, including enhanced proliferation and morphological changes, had a close spatiotemporal relationship with infiltration of activated microglia into the lesion core. Thick and highly branched processes of reactive NG2 glia formed a cellular network in the astrocyte-free lesion core and primarily surrounded developing cavities 2–4 weeks post-lesion. NG2 glia became associated with astrocytes in the lesion core and the border of cavities over the chronic interval of 4–8 weeks. Immunoelectron microscopy indicated that reactive NG2 glia had large euchromatic nuclei with prominent nucleoli and thick and branched processes that ramified distally. Thus, our data provide detailed information regarding the morphologies of NG2 glia in the lesion core, and support the link between transformation of NG2 glia to the reactive form and microglial activation/recruitment in response to brain insults.

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.

Lipopolysaccharide Upregulates the Expression of CINC-3 and LIX in Primary NG2 Cells

Numerous NG2 cells, also called oligodendrocyte progenitor cells (OPCs), exist ubiquitously in the gray and white matter in the adult central nervous system (CNS). Although NG2 cells could become active by upregulation of NG2 expression and hypertrophy or extension of their processes under various neuropathological conditions, their actual role in the brain remains to be illustrated. In view of the fact that the synergy of cytokine and chemokine networks plays an important role in CNS inflammation and immunity, we have assumed that the NG2 cells might take part in brain inflammation and immunity by making a contribution to the pool of cytokines or chemokines. In the current study, NG2-expressing OPCs were prepared from cerebral hemispheres of postnatal day 0 or 1 Sprague-Dawley rats. Our results showed that NG2-expressing OPCs, verified by immunohistological staining of anti-NG2 antibody and anti-platelet-derived growth factor receptor alpha (PDGFRα) antibody, presented binding affinity to lipopolysaccharide (LPS), a commonly used stimulator in a neuroinflammatory model. Using cytokine antibody array, QPCR and ELISA, we have further shown that LPS could upregulate the expression of cytokine induced neutrophil chemoattractant-3 (CINC-3) and LPS induced CXC chemokine (LIX) in primary NG2-expressing OPCs, without the alteration in cell number of NG2-expressing OPCs. In addition, the cells bearing the receptor for these two cytokines included microglia and OPCs. Taken together, our results suggest that NG2-expressing OPCs could response to LPS and may take part in neuroinflammatory process, through secreting cytokines and chemokines to exert an effect on target cells (OPCs and microglia).

After Intracerebral Hemorrhage, Oligodendrocyte Precursors Proliferate and Differentiate Inside White-Matter Tracts in the Rat Striatum

Damage to myelinated axons contributes to neurological deficits after acute CNS injury, including ischemic and hemorrhagic stroke. Potential treatments to promote re-myelination will require fully differentiated oligodendrocytes, but almost nothing is known about their fate following intracerebral hemorrhage (ICH). Using a rat model of ICH in the striatum, we quantified survival, proliferation, and differentiation of oligodendrocyte precursor cells (OPCs) (at 1, 3, 7, 14, and 28 days) in the peri-hematoma region, surrounding striatum, and contralateral striatum. In the peri-hematoma, the density of Olig2⁺ cells increased dramatically over the first 7 days, and this coincided with disorganization and fragmentation of myelinated axon bundles. Very little proliferation (Ki67⁺) of Olig2⁺ cells was seen in the anterior subventricular zone from 1 to 28 days. However, by 3 days, many were proliferating in the peri-hematoma region, suggesting that local proliferation expands their population. By 14 days, the density of Olig2⁺ cells declined in the peri-hematoma region, and, by 28 days, it reached the low level seen in the contralateral striatum. At these later times, many surviving axons were aligned into white-matter bundles, which appeared less swollen or fragmented. Oligodendrocyte cell maturation was prevalent over the 28-day period. Densities of immature OPCs (NG2⁺Olig2⁺) and mature (CC-1⁺Olig2⁺) oligodendrocytes in the peri-hematoma increased dramatically over the first week. Regardless of the maturation state, they increased preferentially inside the white-matter bundles. These results provide evidence that endogenous oligodendrocyte precursors proliferate and differentiate in the peri-hematoma region and have the potential to re-myelinate axon tracts after hemorrhagic stroke.

The role of the NG2 proteoglycan in OPC and CNS network function

In the normal mammalian CNS, the NG2 proteoglycan is expressed by oligodendrocyte precursor cells (OPC) but not by any other neural cell-type. NG2 is a type-1 membrane protein, exerting multiple roles in the CNS including intracellular signaling within the OPC, with effects on migration, cytoskeleton interaction and target gene regulation. It has been recently shown that the extracellular region of NG2, in addition to an adhesive function, acts as a soluble ECM component with the capacity to alter defined neuronal network properties. This region of NG2 is thus endowed with neuromodulatory properties. In order to generate biologically active fragments yielding these properties, the sequential cleavage of the NG2 protein by α- and γ-secretases occurs. The basal level of constitutive cleavage is stimulated by neuronal network activity. This processing leads to 4 major NG2 fragments which all have been associated with distinct biological functions. Here we summarize these functions, focusing on recent discoveries and their implications for the CNS. This article is part of a Special Issue entitled SI:NG2-glia(Invited only).

Alteration of synaptic connectivity of oligodendrocyte precursor cells following demyelination

Oligodendrocyte precursor cells (OPCs) are a major source of remyelinating oligodendrocytes in demyelinating diseases such as Multiple Sclerosis (MS). While OPCs are innervated by unmyelinated axons in the normal brain, the fate of such synaptic contacts after demyelination is still unclear. By combining electrophysiology and immunostainings in different transgenic mice expressing fluorescent reporters, we studied the synaptic innervation of OPCs in the model of lysolecithin (LPC)-induced demyelination of corpus callosum. Synaptic innervation of reactivated OPCs in the lesion was revealed by the presence of AMPA receptor-mediated synaptic currents, VGluT1+ axon-OPC contacts in 3D confocal reconstructions and synaptic junctions observed by electron microscopy. Moreover, 3D confocal reconstructions of VGluT1 and NG2 immunolabeling showed the existence of glutamatergic axon-OPC contacts in post-mortem MS lesions. Interestingly, patch-clamp recordings in LPC-induced lesions demonstrated a drastic decrease in spontaneous synaptic activity of OPCs early after demyelination that was not caused by an impaired conduction of compound action potentials. A reduction in synaptic connectivity was confirmed by the lack of VGluT1+ axon-OPC contacts in virtually all rapidly proliferating OPCs stained with EdU (50-ethynyl-20-deoxyuridine). At the end of the massive proliferation phase in lesions, the proportion of innervated OPCs rapidly recovers, although the frequency of spontaneous synaptic currents did not reach control levels. In conclusion, our results demonstrate that newly-generated OPCs do not receive synaptic inputs during their active proliferation after demyelination, but gain synapses during the remyelination process. Hence, glutamatergic synaptic inputs may contribute to inhibit OPC proliferation and might have a physiopathological relevance in demyelinating disorders.

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.

Finding degrees of separation: experimental approaches for astroglial and oligodendroglial cell isolation and genetic targeting

The study of CNS glial cell function requires experimental methods to detect, purify, and manipulate each cell population with fidelity and specificity. With the identification and cloning of cell- and stage-specific markers, glial cell analysis techniques have grown beyond physical methods of tissue dissociation and cell culture, and become highly specific with immunoselection of cell cultures in vitro and genetic targeting in vivo. The unique plasticity of glial cells offers the potential for cell replacement therapies in neurological disease that utilize neural cells derived from transplanted neural stem and progenitor cells. In this mini-review, we outline general physical and genetic approaches for macroglial cell generation. We summarize cell culture methods to obtain astrocytes and oligodendrocytes and their precursors, from developing and adult tissue, as well as approaches to obtain human neural progenitor cells through the establishment of stem cells. We discuss popular targeting rodent strains designed for cell-specific detection, selection and manipulation of neuroglial cell progenitors and their committed progeny. Based on shared markers between astrocytes and stem cells, we discuss genetically modified mouse strains with overlapping expression, and highlight SOX-expressing strains available for targeting of stem and progenitor cell populations. We also include recently established mouse strains for detection, and tag-assisted RNA and miRNA analysis. This discussion aims to provide a brief overview of the rapidly expanding collection of experimental approaches and genetic resources for the isolation and targeting of macroglial cells, their sources, progeny and gene products to facilitate our understanding of their properties and potential application in pathology.

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.

Microglial regulation of immunological and neuroprotective functions of astroglia

Microglia and astroglia play critical roles in the development, function, and survival of neurons in the CNS. However, under inflammatory conditions the role of astrogliosis in the inflammatory process and its effects on neurons remains unclear. Here, we used several types of cell cultures treated with the bacterial inflammogen LPS to address these questions. We found that the presence of astroglia reduced inflammation-driven neurotoxicity, suggesting that astrogliosis is principally neuroprotective. Neutralization of supernatant glial cell line-derived neurotrophic factor (GDNF) released from astroglia significantly reduced this neuroprotective effect during inflammation. To determine the immunological role of astroglia, we optimized a highly-enriched astroglial culture protocol and demonstrated that LPS failed to induce the synthesis and release of TNF-α and iNOS/NO. Instead we found significant enhancement of TNF-α and iNOS expression in highly-enriched astroglial cultures required the presence of 0.5-1% microglia, respectively. Thus suggesting that microglial-astroglial interactions are required for LPS to induce the expression of pro-inflammatory factors and GDNF from astroglia. Specifically, we found that microglia-derived TNF-α plays a pivotal role as a paracrine signal to regulate the neuroprotective functions of astrogliosis. Taken together, these findings suggest that astroglia may not possess the ability to directly recognize the innate immune stimuli LPS, but rather depend on crosstalk with microglia to elicit release of neurotrophic factors as a counterbalance to support neuronal survival from the collateral damage generated by activated microglia during neuroinflammation.

The glial scar in spinal cord injury and repair

Glial scarring following severe tissue damage and inflammation after spinal cord injury (SCI) is due to an extreme, uncontrolled form of reactive astrogliosis that typically occurs around the injury site. The scarring process includes the misalignment of activated astrocytes and the deposition of inhibitory chondroitin sulfate proteoglycans. Here, we first discuss recent developments in the molecular and cellular features of glial scar formation, with special focus on the potential cellular origin of scar-forming cells and the molecular mechanisms underlying glial scar formation after SCI. Second, we discuss the role of glial scar formation in the regulation of axonal regeneration and the cascades of neuro-inflammation. Last, we summarize the physical and pharmacological approaches targeting the modulation of glial scarring to better understand the role of glial scar formation in the repair of SCI.

Early proliferation does not prevent the loss of oligodendrocyte progenitor cells during the chronic phase of secondary degeneration in a CNS white matter tract

Partial injury to the central nervous system (CNS) is exacerbated by additional loss of neurons and glia via toxic events known as secondary degeneration. Using partial transection of the rat optic nerve (ON) as a model, we have previously shown that myelin decompaction persists during secondary degeneration. Failure to repair myelin abnormalities during secondary degeneration may be attributed to insufficient OPC proliferation and/or differentiation to compensate for loss of oligodendrocyte lineage cells (oligodendroglia). Following partial ON transection, we found that sub-populations of oligodendroglia and other olig2+ glia were differentially influenced by injury. A high proportion of NG2+/olig2-, NG2+/olig2+ and CC1-/olig2+ cells proliferated (Ki67+) at 3 days, prior to the onset of death (TUNEL+) at 7 days, suggesting injury-related cues triggered proliferation rather than early loss of oligodendroglia. Despite this, a high proportion (20%) of the NG2+/olig2+ OPCs were TUNEL+ at 3 months, and numbers remained chronically lower, indicating that proliferation of these cells was insufficient to maintain population numbers. There was significant death of NG2+/olig2- and NG2-/olig2+ cells at 7 days, however population densities remained stable, suggesting proliferation was sufficient to sustain cell numbers. Relatively few TUNEL+/CC1+ cells were detected at 7 days, and no change in density indicated that mature CC1+ oligodendrocytes were resistant to secondary degeneration in vivo. Mature CC1+/olig2- oligodendrocyte density increased at 3 days, reflecting early oligogenesis, while the appearance of shortened myelin internodes at 3 months suggested remyelination. Taken together, chronic OPC decreases may contribute to the persistent myelin abnormalities and functional loss seen in ON during secondary degeneration.

Existence of glioma stroma mesenchymal stemlike cells in Korean glioma specimens

PURPOSE

It was presented that mesenchymal stem cells (MSCs) can be isolated from western glioma specimens. However, whether MSCs exist in glioma specimens of different ethnicities is unknown. To verify the existence of MSCs in an independent cohort, we undertook studies to isolate MSCs from a group of Korean patients. We hypothesized that cells resembling MSCs that were deemed mesenchymal stemlike cells (MSLCs) exist in an independent cohort of Korean gliomas.

METHODS

We cultured fresh glioma specimens using the protocols used for culturing MSCs. The cultured cells were analyzed with fluorescence-activated cell sorting (FACS) for surface markers associated with MSCs. Cultured cells were exposed to mesenchymal differentiation conditions. To presume possible locations of MSLCs in the glioma, sections of glioma were analyzed by immunofluorescent labeling for CD105, CD31, and NG2.

RESULTS

From nine of 31 glioma specimens, we isolated cells resembling MSCs, which were deemed Korean glioma stroma MSLCs (KGS-MSLCs). KGS-MSLCs were spindle shaped and adherent to plastic. KGS-MSLCs had similar surface markers to MSCs (CD105(+), CD90(+), CD73(+), and CD45(-)). KGS-MSLCs were capable of mesenchymal differentiation and might be located around endothelial cells, pericytes, and in a disorganized perivascular area inside glioma stroma.

CONCLUSIONS

We found that cells resembling MSCs indeed exist in an independent cohort of glioma patients, as presented in western populations. We could presume that the possible location of KGS-MSLCs was in perivascular area or in glioma stroma that was a disorganized vascular niche. It might be possible that KGS-MSLCs could be one of constituent of stroma of glioma microenvironment.