Reconstitution of human immunodeficiency virus-induced neurodegeneration using isolated populations of human neurons, astrocytes, and microglia and neuroprotection mediated by insulin-like growth factors

Primary human neuron cultures are an important in vitro model system for studies on mechanisms involved in human immunodeficiency virus (HIV)-associated dementia (HAD) and other neurological disorders. Here, more than 80 cell surface antigens were screened to identify a marker that could readily distinguish between neurons and astrocytes and found that neurons lack CD44 surface expression, whereas astrocytes and other cell types in brain are CD44⁺. Neurons and astrocytes were isolated from human fetal brain based on differential expression of CD44. Using purified neurons cocultured with astrocytes and/or microglia, it was demonstrated that HIV infection of microglia induces cellular activation and production of soluble factors that activate uninfected microglia and astrocytes and induce neuronal cell death. Activated astrocytes promoted HIV replication in microglia, thereby amplifying HIV-induced neurotoxicity. A screen for 120 cytokine/proteins detected upregulation of insulin-like growth factor (IGF)-binding protein (IGFBP)-2, interleukin (IL)-6, and CCL8/MCP-2 (monocyte chemoattractant protein 2) in supernatants of HIV-infected brain cell cultures. IGF-1 and -2 increased neuronal survival in HIV-infected brain cell cultures, whereas IGFBP-2 inhibited prosurvival effects of these growth factors. These findings identify CD44 as a marker that can be used to sort neurons from other cell types in brain, suggest the importance of microglia-astrocyte interactions in neurodegenerative mechanisms associated with HIV infection, and indicate a role for insulin-like growth factors in neuroprotection from HIV-induced neurodegeneration. The ability to reconstitute brain cultures using isolated populations of neurons, astrocytes, and microglia will be valuable for studies on pathogenic mechanisms in HAD and other neurological disorders, and will also facilitate neuroactive drug discovery.     

Cultures of astrocytes and microglia express interleukin 18

Interleukin 18 (IL-18 or interferon-gamma inducing factor) is a recently discovered pro-inflammatory cytokine and powerful stimulator of the cell-mediated immune response. IL-18 is produced by several sources including monocytes/macrophages, keratinocytes and the zona reticularis and zona fasciculata of the adrenal cortex. IL-18 occurs in brain but its cellular source in the CNS has never been investigated. The presence of IL-18 and its response to stimulation in the brain was tested with primary cultures of microglia, astrocytes and hippocampal neurons. IL-18 mRNA was present in astrocytes and microglia, but not in neurons. The endotoxin lipopolysaccharide (LPS) did not affect IL-18 in astrocytes, but LPS robustly increased IL-18 mRNA in microglia. IL-18 protein was constitutively expressed in astrocytes and induced in microglia by LPS. The levels of interleukin-1beta converting enzyme (ICE), an activating enzyme, and caspase 3 (CPP32), an inactivating enzyme, were assessed to investigate the presence of the appropriate processing enzymes in the cultured cells. ICE was present at constitutive levels in microglia and astrocytes suggesting that these cell types may produce and secrete matured IL-18. Active forms of CPP32 were not detectable in either cell type indicating the absence of a degradative pathway of IL-18. The present results demonstrate that microglia and astrocytes are sources of brain IL-18 and add a new member to the family of cytokines produced in the brain.     

S100b counteracts effects of the neurotoxicant trimethyltin on astrocytes and microglia

Central nervous system degenerative diseases are often characterized by an early, strong reaction of astrocytes and microglia. Both these cell types can play a double role, protecting neurons against degeneration through the synthesis and secretion of trophic factors or inducing degeneration through the secretion of toxic molecules. Therefore, we studied the effects of S100B and trimethyltin (TMT) on human astrocytes and microglia with two glial models, primary cultures of human fetal astrocytes and a microglia cell line. After treatment with 10(-5) M TMT, astrocytes showed morphological alterations associated with an increase in glial fibrillary acidic protein (GFAP) expression and changes in GFAP filament organization. Administration of S100B before TMT treatment prevented TMT-induced changes in morphology and GFAP expression. A decrease in inducible nitric oxide synthase expression was observed in astrocytes treated with TMT, whereas the same treatment induced iNOS expression in microglia. In both cases, S100B prevented TMT-induced changes. Tumor necrosis factor-alpha mRNA expression in astrocytes was not modified by TMT treatment, whereas it was increased in microglia cells. S100B pretreatment blocked the TMT-induced increase in TNF-alpha expression in microglia. To trace the mechanisms involved in S100B activity, the effect of BAY 11-7082, an inhibitor of nuclear factor-kappaB (NF-kappaB) activation, and of PD98059, an inhibitor of MEK-ERK1/2, were investigated. Results showed that the protective effects of S100B against TMT toxicity in astrocytes depend on NF-kappaB, but not on ERK1/2 activation. These results might help in understanding the role played by glial cells in brain injury after exposure to chemical neurotoxicants and support the view that S100B may protect brain cells in case of injury. (c) 2005 Wiley-Liss, Inc.     

Quantitation of ATP-binding cassette subfamily-A transporter gene expression in primary human brain cells

Five ATP-binding cassette (ABC) subfamily-A transporters (ABCA1, ABCA2, ABCA3, ABCA7 and ABCA8) are expressed in the brain. These transporters may regulate brain lipid transport; however, their relative expression level in isolated human brain cells is unknown. We developed real-time polymerase chain reaction assays to quantify the expression of these genes in human neurons, astrocytes, oligodendrocytes, microglia and cell lines. Neurons expressed predominantly ABCA1 and ABCA3; astrocytes ABCA1, ABCA2 and ABCA3; microglia ABCA1 and oligodendrocytes ABCA2 and ABCA3. Although ABCA7 and ABCA8 expression was relatively low in all cells, the highest expression occurred in microglia and neurons, respectively. ABCA gene expression in the NTERA-2 and MO3.13 cell lines closely resembled the ABCA expression pattern of primary neurons and oligodendrocytes, respectively.     

Microglial reaction induced by noncytotoxic methylmercury treatment leads to neuroprotection via interactions with astrocytes and IL-6 release.

Microglial cells react early to a neurotoxic insult. However, the bioactive factors and the cell-cell interactions leading to microglial activation and finally to a neuroprotective or neurodegenerative outcome remain to be elucidated. Therefore, we analyzed the microglial reaction induced by methylmercury (MeHgCl) using cell cultures of different complexity. Isolated microglia were found to be directly activated by MeHgCl (10(-10) to 10(-6) M), as indicated by process retraction, enhanced lectin staining, and cluster formation. An association of MeHgCl-induced microglial clusters with astrocytes and neurons was observed in three-dimensional cultures. Close proximity was found between the clusters of lectin-stained microglia and astrocytes immunostained for glial fibrillary acidic protein (GFAP), which may facilitate interactions between astrocytes and reactive microglia. In contrast, immunoreactivity for microtubule-associated protein (MAP-2), a neuronal marker, was absent in the vicinity of the microglial clusters. Interactions between astrocytes and microglia were studied in cocultures treated for 10 days with MeHgCl. Interleukin-6 release was increased at 10(-7) M of MeHgCl, whereas it was decreased when each of these two cell types was cultured separately. Moreover, addition of IL-6 to three-dimensional brain cell cultures treated with 3 x 10(-7) M of MeHgCl prevented the decrease in immunostaining of the neuronal markers MAP-2 and neurofilament-M. IL-6 administered to three-dimensional cultures in the absence of MeHgCl caused astrogliosis, as indicated by increased GFAP immunoreactivity. Altogether, these results show that microglial cells are directly activated by MeHgCl and that the interaction between activated microglia and astrocytes can increase local IL-6 release, which may cause astrocyte reactivity and neuroprotection.     

Comparative study on the response of rat primary astrocytes and microglia to methylmercury toxicity

As the two major glial cell types in the brain, astrocytes and microglia play pivotal but different roles in maintaining optimal brain function. Although both cell types have been implicated as major targets of methylmercury (MeHg), their sensitivities and adaptive responses to this metal can vary given their distinctive properties and physiological functions. This study was carried out to compare the responses of astrocytes and microglia following MeHg treatment, specifically addressing the effects of MeHg on cell viability, reactive oxygen species (ROS) generation and glutathione (GSH) levels, as well as mercury (Hg) uptake and the expression of NF-E2-related factor 2 (Nrf2). Results showed that microglia are more sensitive to MeHg than astrocytes, a finding that is consistent with their higher Hg uptake and lower basal GSH levels. Microglia also demonstrated higher ROS generation compared with astrocytes. Nrf2 and its downstream genes were upregulated in both cell types, but with different kinetics (much faster in microglia). In summary, microglia and astrocytes each exhibit a distinct sensitivity to MeHg, resulting in their differential temporal adaptive responses. These unique sensitivities appear to be dependent on the cellular thiol status of the particular cell type.     

Temporal expression of osteopontin and CD44 in rat brains with experimental cryolesions

Expression of osteopontin and CD44 in the brain was studied after cryolesioning to understand how osteopontin and its receptor, CD44, are involved in processes in the brains of rats with cryolesions. Western blot analysis showed that osteopontin increased significantly at days 4 and 7 post-injury and declined slightly thereafter in cryolesioned brains in comparison with levels in sham-operated controls. An immunohistochemical study localized osteopontin in activated microglia/macrophages in the core lesions, where the majority of macrophages proliferate. Osteopontin was also detected temporarily in some neurons and a few astrocytes in the lesion periphery on days 4 and 7 post-injury, but the immunoreactivity in macrophages, neurons, and astrocytes disappeared by day 14 post-injury. There was some CD44, a receptor for osteopontin, in the brain cells of sham-operated rats. After injury, intense CD44 immunostaining was seen in the majority of macrophages and in reactive astrocytes, but not in neurons, in the ipsilateral lesions after day 4 post-injury, and this immunoreactivity remained on day 14 post-injury. These findings suggest that activated microglia/macrophages and some neurons are major sources of osteopontin during the early stage of brain damage induced by a cryolesion and that osteopontin interacts with CD44 expressed on astrocytes and activated microglia/macrophages in the damaged cerebral cortex, possibly mediating cell migration after cryolesioning in the rat brain.     

Robust expression of TNF-alpha, IL-1beta, RANTES, and IP-10 by human microglial cells during nonproductive infection with herpes simplex virus

Cytokine (TNF-alpha/beta, IL-1beta, IL-6, IL-18, IL-10, and IFN-alpha/beta/gamma) and chemokine (IL-8, IP-10, MCP-1, MIP-1alpha/beta, and RANTES) production during herpes simplex virus (HSV) 1 infection of human brain cells was examined. Primary astrocytes as well as neurons were found to support HSV replication, but neither of these fully permissive cell types produced cytokines or chemokines in response to HSV. In contrast, microglia did not support extensive viral replication; however, ICP4 was detected by immunochemical staining, demonstrating these cells were infected. Late viral protein (nucleocapsid antigen) was detected in <10% of infected microglial cells. Microglia responded to nonpermissive viral infection by producing considerable amounts of TNF-alpha, IL-1beta, IP-10, and RANTES, together with smaller amounts of IL-6, IL-8, and MIP-1alpha as detected by RPA and ELISA. Surprisingly, no interferons (alpha, beta, or gamma) were detected in response to viral infection. Pretreatment of fully permissive astrocytes with TNF-alpha prior to infection with HSV was found to dramatically inhibit replication, resulting in a 14-fold reduction of viral titer. In contrast, pretreatment of astrocytes with IL-1beta had little effect on viral replication. When added to neuronal cultures, exogenous TNF-alpha or IL-1beta did not suppress subsequent HSV replication. Exogenously added IP-10 inhibited HSV replication in neurons (with a 32-fold reduction in viral titer), however, similar IP-10 treatment did not affect viral replication in astrocytes. These results suggest that IP-10 possesses direct antiviral activity in neurons and support a role for microglia in both antiviral defense of the brain as well as amplification of immune responses during neuroinflammation.     

Frequency of nuclear mutant huntingtin inclusion formation in neurons and glia is cell‐type‐specific

Huntington's disease (HD) is an autosomal dominant inherited neurodegenerative disorder that is caused by a CAG expansion in the Huntingtin (HTT) gene, leading to HTT inclusion formation in the brain. The mutant huntingtin protein (mHTT) is ubiquitously expressed and therefore nuclear inclusions could be present in all brain cells. The effects of nuclear inclusion formation have been mainly studied in neurons, while the effect on glia has been comparatively disregarded. Astrocytes, microglia, and oligodendrocytes are glial cells that are essential for normal brain function and are implicated in several neurological diseases. Here we examined the number of nuclear mHTT inclusions in both neurons and various types of glia in the two brain areas that are the most affected in HD, frontal cortex, and striatum. We compared nuclear mHTT inclusion body formation in three HD mouse models that express either full‐length HTT or an N‐terminal exon1 fragment of mHTT, and we observed nuclear inclusions in neurons, astrocytes, oligodendrocytes, and microglia. When studying the frequency of cells with nuclear inclusions in mice, we found that half of the population of neurons contained nuclear inclusions at the disease end stage, whereas the proportion of GFAP‐positive astrocytes and oligodendrocytes having a nuclear inclusion was much lower, while microglia hardly showed any nuclear inclusions. Nuclear inclusions were also present in neurons and all studied glial cell types in human patient material. This is the first report to compare nuclear mHTT inclusions in glia and neurons in different HD mouse models and HD patient brains. GLIA 2016;65:50–61     

Transient expression of the NG2 proteoglycan by a subpopulation of activated macrophages in an excitotoxic hippocampal lesion

Cells that express the NG2 proteoglycan (NG2+ cells) constitute a large glial population in the normal mature rodent brain. They can differentiate into oligodendrocytes but are distinct from mature oligodendrocytes, astrocytes, microglia, and neurons. Changes in NG2+ cells were examined in kainic acid-induced excitotoxic lesions of the hippocampus, and the relationship between NG2+ cells and reactive astrocytes and microglia was investigated between 1 and 90 days after lesioning. Two types of reactive NG2+ cells with altered morphology and increased NG2 immunoreactivity were observed in the lesion. Early changes, consisting of an increase in NG2 immunoreactivity and the number of processes, were apparent 24 h after lesioning and persisted through 3 months. These cells were distinct from reactive astrocytes or activated microglia/macrophages. A second type of reactive NG2+ cells appeared 2 weeks after injection, following an influx of macrophages. They had large, round cell bodies with short processes and expressed the microglia/macrophage antigens OX42 and ED1. Single cells coexpressing NG2 and macrophage/microglial antigens could be isolated from the lesion. The number of NG2+/OX42+ cells gradually declined and disappeared by 3 months after injection. They did not express glial fibrillary acidic protein or the alpha receptor for platelet-derived growth factor, indicating that they are distinct from astrocytes or oligodendrocyte progenitor cells. Cells that coexpressed NG2 and OX42 were never observed in hippocampal slice cultures treated with kainic acid, suggesting that NG2+/OX42+ cells are not derived from endogenous resident brain cells. These findings demonstrate that NG2 expression is transiently upregulated on activated macrophages/microglia that appear during the chronic stage in an excitotoxic lesion in the adult CNS.     

Accumulation of Non-Transferrin-Bound Iron by Neurons, Astrocytes, and Microglia

Neurodegenerative conditions such as Alzheimer’s disease, Parkinson’s disease, and hemorrhagic stroke are associated with increased levels of non-transferrin-bound iron (NTBI) in the brain, which can promote Fenton chemistry. While all types of brain cells can take up NTBI, their efficiency of accumulation and capacity to withstand iron-mediated toxicity has not been directly compared. The present study assessed NTBI accumulation in cultures enriched in neurons, astrocytes, or microglia after exposure to ferric ammonium citrate (FAC). Microglia were found to be the most efficient in accumulating iron, followed by astrocytes, and then neurons. Exposure to 100 μM FAC for 24 h increased the specific iron content of cultured neurons, astrocytes, and microglial cells by 30-, 80-, and 100-fold, respectively. All cell types accumulated iron against the concentration gradient, resulting in intracellular iron concentrations that were several orders of magnitude higher than the extracellular iron concentrations. Accumulation of these large amounts of iron did not affect the viability of the cell cultures, indicating a high resistance to iron-mediated toxicity. These findings show that neurons, astrocytes and microglia cultured from neonatal mice all have the capacity to accumulate and safely store large quantities of iron, but that glial cells do this more efficiently than neurons. It is concluded that neurodegenerative conditions involving iron-mediated toxicity may be due to a failure of iron transport or storage mechanisms, rather than to the presence of high levels of NTBI.     

Functional expression of the seven-transmembrane HIV-1 co-receptor APJ in neural cells

APJ is a recently described seven-transmembrane (7TM) receptor that is abundantly expressed in the central nervous system (CNS). This suggests an important role for APJ in neural development and/or function, but neither its cellular distribution nor its function have been defined. APJ can also serve as a co-receptor with CD4 for fusion and infection by some strains of human immunodeficiency virus (HIV-1) in vitro, suggesting a role in HIV neuropathogenesis if it were expressed on CD4-positive CNS cells. To address this, we examined APJ expression in cultured neurons, astrocytes, oligodendrocytes, microglia and monocyte-derived macrophages utilizing both immunocytochemical staining with a polyclonal anti-APJ antibody and RT - PCR. We also analyzed the ability of a recently identified APJ peptide ligand, apelin, to induce calcium elevations in cultured neural cells. APJ was expressed at a high level in neurons and oligodendrocytes, and at lower levels in astrocytes. In contrast, APJ was not expressed in either primary microglia or monocyte-derived macrophages. Several forms of the APJ peptide ligand induced calcium elevations in neurons. Thus, APJ is selectively expressed in certain CNS cell types and mediates intracellular signals in neurons, suggesting that APJ may normally play a role in signaling in the CNS. However, the absence of APJ expression in microglia and macrophages, the prinicpal CD4-positive cell types in the brain, indicates that APJ is unlikely to mediate HIV-1 infection in the CNS.     

Evaluation of the expression pattern of rAAV2/1, 2/5, 2/7, 2/8, and 2/9 serotypes with different promoters in the mouse visual cortex

This study compared the expression pattern, laminar distribution, and cell specificity of several rAAV serotypes (2/1, 2/5, 2/7, 2/8, and 2/9) injected in the primary visual cortex (V1) of adult C57Bl/6J mice. In order to obtain specific expression in certain neuron subtypes, different promoter sequences were evaluated for excitatory cell specificity: a universal cytomegalovirus (CMV) promoter, and two versions of the excitatory neuron‐specific Ca²⁺/calmodulin‐dependent kinase subunit α (CaMKIIα) promoter, CaMKIIα 0.4 and CaMKIIα 1.3. The spatial distribution as well as the cell type specificity was immunohistochemically verified. Depending on the rAAV serotype used, the transduced volume expressing reporter protein differed substantially (rAAV2/5 ? 2/7 ≈ 2/9 ≈ 2/8 ? 2/1). Excitatory neuron‐specific targeting was promoter‐dependent, with a surprising difference between the 1.3 kb and 0.4 kb CaMKIIα promoters. While CaMKIIα 1.3 and CMV carrying vectors were comparable, with 78% of the transduced neurons being excitatory for CMV and 82% for CaMKIIα 1.3, the shorter CaMKIIα 0.4 version resulted in 95% excitatory specificity. This study therefore puts forward the CaMKIIα 0.4 promoter as the best choice to target excitatory neurons with rAAVs. Together, these results can be used as an aid to select the most optimal vector system to deliver transgenes into specific rodent neocortical circuits, allowing further elucidation of their functions. J. Comp. Neurol. 523:2019–2042, 2015. © 2015 Wiley Periodicals, Inc.     

Microglia expressing interleukin-13 undergo cell death and contribute to neuronal survival in vivo

How to minimize brain inflammation is pathophysiologically important, since inflammation induced by microglial activation can exacerbate brain damage. In the present report, we show that injection of lipopolysaccharide (LPS) into the rat cortex led to increased levels of interleukin-13 (IL-13) and to IL-13 immunoreactivity, followed by the substantial loss of microglia at 3 days post-LPS. IL-13 levels in LPS-injected cortex reached a peak at 12 h post-injection, remained elevated at 24 h, and returned to basal levels at day 4. In parallel, IL-13 immunoreactivity was detected as early as 12 h post-LPS and maintained up to 24 h; it disappeared at 4 days. Surprisingly, IL-13 immunoreactivity was detected exclusively in microglia, but not in neurons or astrocytes. Following treatment with LPS in vitro, IL-13 expression was also induced in microglia in the presence of neurons, but not in the presence of astrocytes or in cultured pure microglia alone. In experiments designed to determine the involvement of IL-13 in microglia cell death, IL-13-neutralizing antibodies significantly increased survival of activated microglia at 3 days post-LPS. Consistent with these results, the expression of inducible nitric oxide synthase (iNOS) and tumor necrosis factor-alpha (TNF-alpha) was sustained in activated microglia and neuronal cell death was consequently increased. Taken together, the present study is the first to demonstrate the endogenous expression of IL-13 in LPS-activated microglia in vivo, and to demonstrate that neurons may be required for IL-13 expression in microglia. Our data strongly suggest that IL-13 may control brain inflammation by inducing the death of activated microglia in vivo, resulting in an enhancement of neuronal survival.     

Optimized protocols for isolation of primary motor neurons, astrocytes and microglia from embryonic mouse spinal cord

Neuron-glial interactions are important in development of the nervous system and pathogenesis of disease. Primary cell cultures prepared from nervous tissue are often used to study the properties of individual cell types and how they interact with each other. Isolation of pure populations of cells and their culture is challenging, particularly from murine spinal cord. The purpose of this study was to optimize various protocols to achieve efficient, parallel isolation and purification of primary motor neurons, microglia and astrocytes from the same mouse embryonic spinal cord sample. Following dissociation of E12 embryonic spinal cords, motor neurons were isolated at 97% purity by a single step centrifugation of the cell suspension through multiple discontinuous density gradients of NycoPrep. The residual mixed cell pellet was resuspended and cultured for 2 weeks. Mixed cultures were then shaken to release microglia, which were then harvested from the medium and subjected to another round of differential adhesion to achieve 99% purity. The astrocytes remaining in the mixed cultures were culled to 98% purity by treatment with leucine methyl ester and a subsequent vigorous shaking step to remove any remaining microglia and neurons. Furthermore, no cross contamination was observed in the glial cultures. This technique provides a simple, convenient, and reliable method of obtaining highly purified preparations of motor neurons, microglia and astrocytes from embryonic spinal cord for the study of spinal cord cell biology and motor neuron diseases.     

FGF-18 is a neuron-derived glial cell growth factor expressed in the rat brain during early postnatal development

We examined the expression of fibroblast growth factor-18 (FGF-18) in the rat brain during postnatal development by in situ hybridization. FGF-18 was transiently expressed at the early postnatal stages in various regions of the rat brain including the cerebral cortex and hippocampus. FGF-18 in the brain was preferentially expressed in neurons but not in glial cells. To elucidate the role of FGF-18 in the brain, we examined the ligand-specificity of FGF-18 by the BIAcore system. FGF-18 was found to bind to FGF receptors (FGFRs)-3c and -2c but not to FGFR-1c, suggesting that FGF-18 acts on glial cells but not on neurons. Therefore, we examined the mitogenic activity of FGF-18 for cultured rat astrocytes and microglia. FGF-18 was found to have mitogenic activity for both astrocytes and microglia. We also examined the neurotrophic activity of FGF-18 for cultured rat cortical neurons. FGF-18 was found to have no neurotrophic activity. The present findings indicated that FGF-18 is a unique FGF that plays a role as a neuron-derived glial cell growth factor in early postnatal development when gliogenesis occurs.     

Expression and localization of absent in melanoma 2 in the injured spinal cord

In traumatic brain injury, absent in melanoma 2(AIM2) has been demonstrated to be involved in pyroptotic neuronal cell death. Although the pathophysiological mechanism of spinal cord injury is similar to that of brain injury, the expression and cellular localization of AIM2 after spinal cord injury is still not very clear. In the present study, we used a rat model of T9 spinal cord contusive injury, produced using the weight drop method. The rats were randomly divided into 1-hour, 6-hour, 1-day, 3-day and 6-day(post-injury time points) groups. Sham-operated rats only received laminectomy at T9 without contusive injury. Western blot assay revealed that the expression levels of AIM2 were not significantly different among the 1-hour, 6-hour and 1-day groups. The expression levels of AIM2 were markedly higher in the 1-hour, 6-hour and 1-day groups compared with the sham, 3-day and 7-day groups. Double immunofluorescence staining demonstrated that AIM2 was expressed by NeuN+(neurons), GFAP+(astrocytes), CNPase+(oligodendrocytes) and CD11 b+(microglia) cells in the sham-operated spinal cord. In rats with spinal cord injury, AIM2 was also found in CD45+(leukocytes) and CD68+(activated microglia/macrophages) cells in the spinal cord at all time points. These findings indicate that AIM2 is mainly expressed in neurons, astrocytes, microglia and oligodendrocytes in the normal spinal cord, and that after spinal cord injury, its expression increases because of the infiltration of leukocytes and the activation of astrocytes and microglia/macrophages.