Morphological differentiation of astroglial progenitor cells from EGF-responsive neurospheres in response to fetal calf serum, basic fibroblast growth factor, and retinol

The Effects of Cuprizone on Murine Subventricular Zone-Derived Neural Stem Cells and Progenitor Cells Grown as Neurospheres

Despite the extensive use of the cuprizone (CPZ) demyelination animal model, there is little evidence regarding the effects of CPZ on a cellular level. Initial studies have suggested that oligodendrocytes (OL) are the main cell targets for CPZ toxicity. However, recent data have revealed additional effects on neural stem cells and progenitor cells (NSC/NPC), which constitute a reservoir for OL regeneration during brain remyelination. We cultured NSC/NPC as neurospheres to investigate CPZ effects on cell mechanisms which are thought to be involved in demyelination and remyelination processes in vivo. Proliferating NSC/NPC cultures exposed to CPZ showed overproduction of intracellular reactive oxygen species and increased progenitor migration at the expense of a significant inhibition of cell proliferation. Although NSC/NPC survival was not affected by CPZ in proliferative conditions, we found that CPZ-treated cultures undergoing cell differentiation were more prone to cell death than controls. The commitment and cell differentiation towards neural lineages did not seem to be affected by CPZ, as shown by the conserved proportions of OL, astrocytes, and neurons. Nevertheless, when CPZ treatment was performed after cell differentiation, we detected a significant reduction in the number and the morphological complexity of OL, astrogliosis, and neuronal damage. We conclude that, in addition to damaging mature OL, CPZ also reduces NSC/NPC proliferation and activates progenitor migration. These results shed light on CPZ direct effects on NSC proliferation and the progression of in vitro differentiation.

Human Induced Pluripotent Stem Cell-Derived Neural Progenitor Cells Produce Distinct Neural 3D In Vitro Models Depending on Alginate/Gellan Gum/Laminin Hydrogel Blend Properties

Stable and predictive neural cell culture models are a necessary premise for many research fields. However, conventional 2D models lack 3D cell-material/-cell interactions and hence do not reflect the complexity of the in vivo situation properly. Here two alginate/gellan gum/laminin (ALG/GG/LAM) hydrogel blends are presented for the fabrication of human induced pluripotent stem cell (hiPSC)-based 3D neural models. For hydrogel embedding, hiPSC-derived neural progenitor cells (hiNPCs) are used either directly or after 3D neural pre-differentiation. It is shown that stiffness and stress relaxation of the gel blends, as well as the cell differentiation strategy influence 3D model development. The embedded hiNPCs differentiate into neurons and astrocytes within the gel blends and display spontaneous intracellular calcium signals. Two fit-for-purpose models valuable for i) applications requiring a high degree of complexity, but less throughput, such as disease modeling and long-term exposure studies and ii) higher throughput applications, such as acute exposures or substance screenings are proposed. Due to their wide range of applications, adjustability, and printing capabilities, the ALG/GG/LAM based 3D neural models are of great potential for 3D neural modeling in the future.

Epigenetic Editing of Ascl1 Gene in Neural Stem Cells by Optogenetics

Enzymes involved in epigenetic processes such as methyltransferases or demethylases are becoming highly utilized for their persistent DNA or histone modifying efficacy. Herein, we have developed an optogenetic toolbox fused to the catalytic domain (CD) of DNA-methyltransferase3A (DNMT3A-CD) or Ten-Eleven Dioxygenase-1 (TET1-CD) for loci-specific alteration of the methylation state at the promoter of Ascl1 (Mash1), a candidate proneuron gene. Optogenetical protein pairs, CRY2 linked to DNMT3A-CD or TET1-CD and CIB1 fused to a Transcription Activator-Like Element (TALE) locating an Ascl1 promoter region, were designed for site specific epigenetic editing. A differentially methylated region at the Ascl1 promoter, isolated from murine dorsal root ganglion (hypermethylated) and striated cells (hypomethylated), was targeted with these optogenetic-epigenetic constructs. Optimized blue-light illumination triggered the co-localization of TALE constructs with DNMT3A-CD or TET1-CD fusion proteins at the targeted site of the Ascl1 promoter. We found that this spatiotemporal association of the fusion proteins selectively alters the methylation state and also regulates gene activity. This proof of concept developed herein holds immense promise for the ability to regulate gene activity via epigenetic modulation with spatiotemporal precision.

An in vitro comparison study: the effects of fetal bovine serum concentration on retinal progenitor cell multipotentiality

Retinal progenitor cells (RPCs) are an excellent resource for retinal replacement therapy, because they show enormous potential to differentiate into retinal-specific cell types. While the differentiating influence of serum has long been appreciated, the effects of serum concentration on RPC differentiation into specified retinal neural cells have not been investigated. Using cultured murine RPCs, this study compared the effects of different levels of fetal bovine serum (FBS) (1%, 5%, 10% and 20%) on RPC differentiation in vitro. RPC multipotentiality was assessed by using quantitative polymerase chain reaction (qPCR) to determine the relative expression levels of 10 genes involved in retinal development. In addition, analyses of cell morphology and retinal development-related protein expression were performed using microscopy and immunocytochemistry. The data revealed that 1% FBS-induced cultures preferentially generated rhodopsin- and PKC-α-positive cells. Calbindin and AP2α expression levels were greater in 5% FBS-induced cultures. Brn3a was expressed at similar levels in 1%, 5% and 10% FBS treatment conditions but diminished in 20% FBS conditions. Twenty percent FBS induced more glial fibrillary acid protein (GFAP)-immunoreactive cells corresponding to glia populations. These findings suggest that the concentration of FBS plays an important role in RPC differentiation in vitro. Treatment with low levels of FBS favors differentiation of rhodopsin-positive photoreceptors, interneurons and retinal ganglion cells (RGCs), while high FBS concentrations preferentially induce differentiation of glia cells. These results are expected to facilitate research in the treatment of neurodegenerative retinal diseases.

Expression of the Parkinson's disease protein DJ-1 during the differentiation of neural stem cells

DJ-1 is a key neuroprotective factor and its loss-of-function mutations cause an autosomal recessive, early-onset form of familial Parkinson's disease at the chromosomal PARK7 locus. However, the expression of DJ-1 during the differentiation of neural stem cells has not been fully elucidated. In this study, we investigated the expression of DJ-1 quantitatively using fluorescence immunocytochemistry and flow cytometry for differentiated neural stem cells from the cortex of the 14-day mouse embryos. We found that DJ-1 was co-expressed with the neuron-specific enolase and glial fibrillary acidic proteins, and also its expression was significantly increased in neurons and astrocytes with a prolonged differentiation period. These findings strongly suggest that DJ-1 is closely associated with the differentiation of neural stem cells.

Foxg1 has an essential role in postnatal development of the dentate gyrus

Foxg1, formerly BF-1, is expressed continuously in the postnatal and adult hippocampal dentate gyrus (DG). This transcription factor (TF) is thought to be involved in Rett syndrome, which is characterized by reduced hippocampus size, indicating its important role in hippocampal development. Due to the perinatal death of Foxg1(-/-) mice, the function of Foxg1 in postnatal DG neurogenesis remains to be explored. Here, we describe the generation of a Foxg1(fl/fl) mouse line. Foxg1 was conditionally ablated from the DG during prenatal and postnatal development by crossing this line with a Frizzled9-CreER(TM) line and inducing recombination with tamoxifen. In this study, we first show that disruption of Foxg1 results in the loss of the subgranular zone and a severely disrupted secondary radial glial scaffold, leading to the impaired migration of granule cells. Moreover, detailed analysis reveals that Foxg1 may be necessary for the maintenance of the DG progenitor pool and that the lack of Foxg1 promotes both gliogenesis and neurogenesis. We additionally show that Foxg1 may be required for the survival and maturation of postmitotic neurons and that Foxg1 may be involved in Reelin signaling in regulating postnatal DG development. Last, prenatal deletion of Foxg1 suggests that it is rarely involved in the migration of primordial granule cells. In summary, we report that Foxg1 is critical for DG formation, especially during early postnatal stage.

Effects of Epimedium flavonoids on proliferation and differentiation of neural stem cells in vitro

OBJECTIVE

The purpose of this study is to investigate the effects of Epimedium flavonoids (EF), which is extracted from a traditional Chinese Epimedium herb, and its effect on the proliferation and differentiation of neural stem cells (NSCs) in vitro.

METHODS

The single cells isolated from the hippocampi of 1 day old neonatal rats were cultured in a serum-free condition medium DMEM/F12 (1 : 1) with different concentrations of EF or 20 ng/ml epidermal growth factor (EGF) and 10 ng/ml basic fibroblast growth factor (bFGF). After 7 and 28 days, the neurospheres' diameters were measured. The formed neurospheres were cultured in the differentiation medium containing EF or 10% fetal bovine serum (FBS). After 12 hours and 7 days, immunofluorescent studies for nestin, Musashi-1, BrdU, beta-III-tubulin, NF-200 and GFAP were performed. The number and lengths of 10-15 axons of NF-200 immunopositive cells were measured.

RESULTS

The results showed that the isolated cells had the ability to propagate as neurospheres in the medium with 200 and 400 m g/ml EF, but without any EGF or bFGF, and the volume of neurospheres increase gradually from 7 to 28 days. In comparison with FBS control, the number of NF-200 positive neurons had significantly increased in the EF groups where the newborn neurons were morphologically more mature and able to migrate farther away from neurospheres than in the FBS control.

DISCUSSION

The results demonstrate that EF effectively promotes the proliferation and differentiation of NSCs in vitro, suggesting that EF may have new properties of regulating central nervous system function by neurogenesis.

Cellular epigenetic modifications of neural stem cell differentiation

Emerging information indicates that epigenetic modification (i.e., histone code and DNA methylation) may be integral to the maintenance and differentiation of neural stem cells (NSCs), but their actual involvement has not yet been illustrated. In this study, we demonstrated the dynamic nature of epigenetic marks during the differentiation of quiescent adult rat NSCs in neurospheres. A subpopulation of OCT4(+) NSCs in the neurosphere contained histone marks, trimethylated histone 3 on lysine 27 (3me-H3K27), 2me-H3K4, and acetylated H4 (Ac-H4). A major decrease of these marks was found prior to or during differentiation, and was further diminished or reprogrammed in diverse subpopulations of migrated NSCs expressing nestin or beta-III-tubulin. The DNA methylation mark 5-methyl-cytosine (5-MeC), and DNA methyltransferase (DNMT) 1 and 3a expression also correlated to the state of differentiation; they were highly present in undifferentiated NSCs but downregulated in migrated populations. In contrast, DNA methyl-CpG-binding protein (MBD1) was low in undifferentiated NSCs in neurospheres, but highly appeared in differentiating NSCs. Furthermore, we found an outward translocation of DNA methylation marker 5-MeC, DNMT1, DNMT3a, and MBD1 in NSCs as differentiation began and proceeded; 5-MeC from homogeneous nucleus to peripheral nucleus, and DMNT1a and 3a from nuclear to cytoplasm, indicating chromatin remodeling. Treatment with DNA methylation inhibitor, 5-aza-cytidine, altered DNA methylation and disrupted migration as indicated by a reduction of migrated neurons and differentiation. These results indicate that chromatin is dynamically remodeled when NSCs transform from the quiescent state to active growth, and that DNA methylation modification is essential for neural stem cell differentiation.

Gene expression profiling of human neural progenitor cells following the serum-induced astrocyte differentiation

Neural stem cells (NSC) with self-renewal and multipotent properties could provide an ideal cell source for transplantation to treat spinal cord injury, stroke, and neurodegenerative diseases. However, the majority of transplanted NSC and neural progenitor cells (NPC) differentiate into astrocytes in vivo under pathological environments in the central nervous system, which potentially cause reactive gliosis. Because the serum is a potent inducer of astrocyte differentiation of rodent NPC in culture, we studied the effect of the serum on gene expression profile of cultured human NPC to identify the gene signature of astrocyte differentiation of human NPC. Human NPC spheres maintained in the serum-free culture medium were exposed to 10% fetal bovine serum (FBS) for 72 h, and processed for analyzing on a Whole Human Genome Microarray of 41,000 genes, and the microarray data were validated by real-time RT-PCR. The serum elevated the levels of expression of 45 genes, including ID1, ID2, ID3, CTGF, TGFA, METRN, GFAP, CRYAB and CSPG3, whereas it reduced the expression of 23 genes, such as DLL1, DLL3, PDGFRA, SOX4, CSPG4, GAS1 and HES5. Thus, the serum-induced astrocyte differentiation of human NPC is characterized by a counteraction of ID family genes on Delta family genes. Coimmunoprecipitation analysis identified ID1 as a direct binding partner of a proneural basic helix-loop-helix (bHLH) transcription factor MASH1. Luciferase assay indicated that activation of the DLL1 promoter by MASH1 was counteracted by ID1. Bone morphogenetic protein 4 (BMP4) elevated the levels of ID1 and GFAP expression in NPC under the serum-free culture conditions. Because the serum contains BMP4, these results suggest that the serum factor(s), most probably BMP4, induces astrocyte differentiation by upregulating the expression of ID family genes that repress the proneural bHLH protein-mediated Delta expression in human NPC.

Human astrocytes can be induced to differentiate into cells with neuronal phenotype

Several recent studies have proposed that astrocytes may contribute to neurogenesis, not only as a source of trophic substances regulating it, but also as stem cells themselves. In order to better understand these mechanisms, primary astrocyte cultures were established from human fetal brain. After 3-4 weeks in culture, astrocytes (about 95% GFAP+; neurofilament, NF-; neuro-specific enolase, NSE-) were treated with a cocktail of protein kinase activators and FGF-1. After 5 h of treatment, most cells showed morphological changes that increased progressively up to 24-48 h, exhibiting a round cell body with long processes. Immunocytochemistry showed that treatment-induced NF and NSE expression in about 40% of cells. Nestin expression increased after treatment, whereas GFAP immunostaining was not significantly modified. Western blot and RT-PCR confirmed the results. No neuronal electrophysiological properties were observed after treatment, suggesting an incomplete maturation under these experimental conditions. Understanding the regenerative capability and neurogenic potential of astrocytes might be useful in devising therapeutic approaches for a variety of neurological disorders.

Proliferation and differentiation of neural stem cells on lysine–alanine sequential polymer substrates

The purpose of this study was to explore the phenotypic potential of embryonic rat cerebral cortical stem cells by inducing differentiation on lysine-alanine sequential (LAS) polymer substrates at neurosphere level. LAS polymer is a heterologous polymer of lysine and alanine and has been demonstrated to enhance axon growth of neurons in a serum-free medium in vitro. It was found that very few cells migrated outside of the neurospheres but extremely long processes extended from differentiated cells could form a network between remote neurospheres when cells were cultured on LAS substrates at a low density of 120 neurospheres/cm(2) in the serum-free medium. On the contrary, when the neurosphere density was increased to 360 neurospheres/cm(2), many neurosphere-forming cells migrated out from their original aggregate and exhibited short processes morphology. Furthermore, when serum was added to the culture system, the neurosphere-forming cells could be induced into an extensive cellular substratum of protoplasmic cells upon which process-bearing cells spread. Clearly, neurospheres could exhibit different behaviors on LAS substrates according to the complex environmental conditions. Here, we proposed that neurospheres would change their social communication and adopt different strategies to communicate with other neurospheres when they detected each other's presence. Therefore, the mediation of cell behavior on LAS substrates by communication between neurospheres should be taken into account.

Membrane properties of retinal stem cells/progenitors

The membrane properties of cells help integrate extrinsic information relayed through growth factors, chemokines, extracellular matrix, gap junctions and neurotransmitters towards modulating cell-intrinsic properties, which in turn determine whether cells remain quiescent, proliferate, differentiate, establish contact with other cells or remove themselves by activating programmed cell death. This review highlights some of the membrane properties of early and late retinal stem cells/progenitors, which are likely to be helpful in the identification and enrichment of these cells and in understanding mechanisms underlying their maintenance and differentiation. Understanding of membrane properties of retinal stem cells/progenitors is essential for the successful formulation of approaches to treat retinal degeneration and diseases by cell therapy.

Neuro-glial differentiation of human bone marrow stem cells in vitro

Bone marrow (BM) is a rich source of stem cells and may represent a valid alternative to neural or embryonic cells in replacing autologous damaged tissues for neurodegenerative diseases. The purpose of the present study is to identify human adult BM progenitor cells capable of neuro-glial differentiation and to develop effective protocols of trans-differentiation to surmount the hematopoietic commitment in vitro. Heterogeneous cell populations such as whole BM, low-density mononuclear and mesenchymal stem (MSCs), and several immunomagnetically separated cell populations were investigated. Among them, MSCs and CD90+ cells were demonstrated to express neuro-glial transcripts before any treatment. Several culture conditions with the addition of stem cell or astroblast conditioned media, different concentrations of serum, growth factors, and supplements, used alone or in combinations, were demonstrated to alter the cellular morphology in some cell subpopulations. In particular, MSCs and CD90+ cells acquired astrocytic and neuron-like morphologies in specific culture conditions. They expressed several neuro-glial specific markers by RT-PCR and glial fibrillary acid protein by immunocytochemistry after co-culture with astroblasts, both in the absence or presence of cell contact. In addition, floating neurosphere-like clones have been observed when CD90+ cells were grown in neural specific media. In conclusion, among the large variety of human adult BM cell populations analyzed, we demonstrated the in vitro neuro-glial potential of both the MSC and CD90+ subset of cells. Moreover, unidentified soluble factors provided by the conditioned media and cellular contacts in co-culture systems were effective in inducing the neuro-glial phenotype, further supporting the adult BM neural differentiative capability.

In vitro differentiated neural stem cells express functional glial glutamate transporters

The possibility to isolate stem cells from the adult central nervous system and to maintain and propagate these cells in vitro has raised a general interest with regards to their use in cell replacement therapy for degenerative brain diseases. Considering the critical role played by astrocytes in the control of glutamate homeostasis, we have characterised the expression of functional glutamate transporters in neural stem cells exposed to selected culture conditions favouring their differentiation into astrocytes. Commonly, neural stem cells proliferate in suspension as neurospheres in serum-free medium. The addition of serum or a supplement of growth factors (G5) to the culture medium was found to trigger cell adhesion on coated surfaces and to favour their differentiation. Indeed, after 7 days in these conditions, the vast majority of the cells adopted markedly distinct morphologies corresponding to protoplasmic (with serum) or fibrous (with G5 supplement) astrocytes and approximately 35-40% acquired the expression of the glial fibrillary acidic protein (GFAP). Immunocytochemical analysis also revealed that the treatments with serum or with the G5 supplement triggered the expression of the glial glutamate transporters GLT-1 (35 and 21%, respectively) and GLAST (29 and 69%, respectively). This effect was correlated with a robust increase in the Na+ -dependent [3H]-d-aspartate uptake, which was partially inhibited by dihydrokainate, a selective blocker of GLT-1. Together, these results indicate that in vitro differentiation of cultured neural stem cells can give rise to distinct populations of astrocytes expressing functional glutamate transporters.

Origin of exocrine pancreatic cells from nestin-positive precursors in developing mouse pancreas

During pancreatic development, endocrine and exocrine cell types arise from common precursors in foregut endoderm. However, little information is available regarding regulation of pancreatic epithelial differentiation in specific precursor populations. We show that undifferentiated epithelial precursors in E10.5 mouse pancreas express nestin, an intermediate filament also expressed in neural stem cells. Within developing pancreatic epithelium, nestin is co-expressed with pdx1 and p48, but not ngn3. Epithelial nestin expression is extinguished upon differentiation of endocrine and exocrine cell types, and no nestin-positive epithelial cells are observed by E15.5. In E10.5 dorsal bud explants, activation of EGF signaling results in maintenance of undifferentiated nestin-positive precursors at the expense of differentiated acinar cells, suggesting a precursor/progeny relationship between these cell types. This relationship was confirmed by rigorous lineage tracing studies using nestin regulatory elements to drive Cre-mediated labeling of nestin-positive precursor cells and their progeny. These experiments demonstrate that a nestin promoter/enhancer element containing the second intron of the mouse nestin locus is active in undifferentiated E10.5 pancreatic epithelial cells, and that these nestin-positive precursors contribute to the generation of differentiated acinar cells. As in neural tissue, nestin-positive cells act as epithelial progenitors during pancreatic development, and may be regulated by EGF receptor activity.

Three to four-year-old nonpassaged EGF-responsive neural progenitor cells: proliferation, apoptosis, and DNA repair

Epidermal growth factor responsive (EGFr) neural progenitor (NP) cells have been shown to be a potential alternative tissue source for neural transplantation and for developmental study. We have shown that nonpassaged EGFr NP cells can self-renew for 2 years in neurospheres and can robustly differentiate into glia and a number of neuronal cell types. We are now attempting to investigate if the EGFr NP cells will die or continue to live beyond the life span of the donor. In addition, we and other investigators have also found that EGFr NP cells, after transplant, retain only a small number of cells in the transplant site. In this study, we investigate the plasticity and fate of the EGFr NP cells. Using the nonpassaged method, we found EGFr NP cells live in the EGF supplement medium for over 4 years-the longest-lived EGFr NP cells ever reported. The 4-year-old striatal or cortical EGFr neurospheres, when subplated with substrate coating, migrate out of neurospheres and have robust growth with many processes. Furthermore, when nucleotide marker bromodeoxyuridine (BrdU) was added 3 days prior to the subplating, the EGFr NP cells were labeled positively with BrdU in the nucleus, indicating active proliferation activity. Meanwhile two other events were also found in the long-term EGFr NP cells. In the midst of the proliferation, apoptosis occurred. A subpopulation of EGFr NP cells are undergoing programmed cell death as indicated by the cell morphology and the TUNEL staining for DNA strand breaks. The TUNEL fluorescein-staining indicates that over 50% of EGFr NP cells are positive in the nuclei. On the other hand, we have also found that the major base excision repair enzyme, APE/ref-1, which is responsible for recognizing and repairing baseless sites in DNA, was present in the progenitor cells. However, in those cells undergoing apoptosis, APE/ref-1 levels were dramatically reduced or missing, and only a small percentage of cells were TUNEL and APE/ref-1 positive. These observations indicate that EGFr neural progenitor cells can live beyond the life span of the donor animal. The longevity of these cells in culture may be enhanced due to decreased apoptosis and the retention of normal DNA repair capacity.

Effects of growth factors and estrogen on the development of septal cholinergic neurons from the rat

Cholinergic neurons of the septum are preferentially subject to degeneration in Alzheimer's disease. There is evidence that nerve growth factor, basic fibroblast growth factor, insulin-like growth factors, and estrogen all have effects on survival of this specific population of neurons at risk. We used a bilaminar culturing method to grow embryonic septal neurons from the rat in the presence of a separate glial plane but in the absence of serum. These neurons were treated with a number of factors, and neurite development of cholinergic neurons was assessed. Basic fibroblast growth factor and estrogen altered the number of primary neurites, number of secondary neurites, and mean total neurite lengths, while none of the other factors affected these end points. This would suggest a mechanism for the effects of these factors on memory.

Isolation, cloning and characterization of a putative type-1 astrocyte cell line

We have established a permanent cell line (1H91) of putative type-1 astrocyte precursor cells that were clonally derived from a single cell isolated from E16 mouse cerebellum. Epidermal growth factor (EGF) and transforming growth factor (TGF alpha) are strong mitogens for 1H91 cells (ED50 of 9.02 + 1.74 ng/ml and 15.98 +/- 2.34 ng/ml, respectively), while basic fibroblast growth factor (bFGF) is only weakly mitogenic and platelet derived growth factor (PDGF) has no mitogenic activity. In the proliferative state, the 1H91 cells are immunohistochemically positive for nestin and vimentin, and negative for A2B5, CNPase, neurofilament (NF), and neuron specific enolase (NSE). The majority of EGF-treated 1H91 cells are not immunoreactive for glial acid fibrillary protein (GFAP). In the presence of 5 ng/ml bFGF, 1H91 cells become non-mitotic and develop a morphology consistent with a fibrous astrocyte. In contrast to the proliferating cultures, the bFGF treated cultures were strongly immunoreactive for GFAP, only mildly immunoreactive for nestin and vimentin, and negative for A2B5, CNPase, NF, and NSE. Type-1 astrocytes are known to proliferate in response to EGF, and are immunohistochemically GFAP positive, A2B5 negative, and CNPase negative [38]. However, type-1 astrocytes only develop a fibrous morphology during the process of reactive gliosis [31]. Since EGF is a strong mitogen for 1H91 cells, and these cells may be differentiated into GFAP positive, A2B5 negative, CNPase negative astrocytes, we conclude that 1H91 cells conform to a type-1 astrocyte precursor phenotype. In addition, the fibrous morphology of the bFGF treated 1H91 cells suggests that these cells follow the process of reactive gliosis. Therefore, the 1H91 clonal cell line may provide an in vitro model for studying the underlying cellular mechanisms of the type-1 astrocyte in reactive gliosis.