Astrocyte cell lineage. II. Mouse fibrous astrocytes and reactive astrocytes in cultures have vimentin- and GFP-containing intermediate filaments

Heterogeneous astrocytes: Active players in CNS

Astrocytes, the predominant cell type that are broadly distributed in the brain and spinal cord, play key roles in maintaining homeostasis of the central nerve system (CNS) in physiological and pathological conditions. Increasing evidence indicates that astrocytes are a complex colony with heterogeneity on morphology, gene expression, function and many other aspects depending on their spatio-temporal distribution and activation level. In pathological conditions, astrocytes differentially respond to all kinds of insults, including injury and disease, and participate in the neuropathological process. Based on current studies, we here give an overview of the roles of heterogeneous astrocytes in CNS, especially in neuropathologies, which focuses on biological and functional diversity of astrocytes. We propose that a precise understanding of the heterogeneous astrocytes is critical to unlocking the secrets about pathogenesis and treatment of the mazy CNS.

Crown of Microfilaments in the Extending Cytoplasmic Processes of Medulloblastoma Glial Progenitors

Microfilaments and microtubules play a part in the extension of neuronal processes but their roles in the formation of glial processes have not yet been determined. The objectives of this study were to determine the organization of microfilaments in differentiating glial progenitors (RB2 cells) and to study the effects of microfilament or microtubule disruption on process extension. Intense F-actin staining (crown of microfilaments) was observed at the leading edge of a small extending conical tip in differentiating RB2 cells, but was absent in process-bearing TE671 rhabdomyosarcoma cells. No significant difference was noted in the mean number of TE671 cells with processes treated with a microfilament disrupter from that of similarly treated controls. In contrast, a significant difference was noted in the mean number of RB2 cells with processes after microfilament disruption treatment from that of similarly treated controls. Microtubule disruption arrested extension and caused process retraction in both cell types. The results of this study demonstrate that microtubules play an equally important part in the extension and stabilization of the RB2 and TE671 processes. Moreover, the crown of microfilaments concentrated in the glial RB2 process (and not in the TE671 process) may be critical to its extension during differentiation.

Aging, the metabolic syndrome, and ischemic stroke: redefining the approach for studying the blood-brain barrier in a complex neurological disease

The blood-brain barrier (BBB) has many important functions in maintaining the brain's immune-privileged status. Endothelial cells, astrocytes, and pericytes have important roles in preserving vasculature integrity. As we age, cell senescence can contribute to BBB compromise. The compromised BBB allows an influx of inflammatory cytokines to enter the brain. These cytokines lead to neuronal and glial damage. Ultimately, the functional changes within the brain can cause age-related disease. One of the most prominent age-related diseases is ischemic stroke. Stroke is the largest cause of disability and is third largest cause of mortality in the United States. The biggest risk factors for stroke, besides age, are results of the metabolic syndrome. The metabolic syndrome, if unchecked, quickly advances to outcomes that include diabetes, hypertension, cardiovascular disease, and obesity. The contribution from these comorbidities to BBB compromise is great. Some of the common molecular pathways activated include: endoplasmic reticulum stress, reactive oxygen species formation, and glutamate excitotoxicity. In this chapter, we examine how age-related changes to cells within the central nervous system interact with comorbidities. We then look at how comorbidities lead to increased risk for stroke through BBB disruption. Finally, we discuss key molecular pathways of interest with a focus on therapeutic targets that warrant further investigation.

Astrocyte phenotypes and their relationship to myelination

Astrocytes are one of the major glial cell types that maintain homeostasis in the undamaged CNS. After injury and disease, astrocytes become reactive and prevent regeneration; however, it has also been suggested that astrocytes can become activated and promote regeneration. Thus, it is hypothesised that astrocytes have an important role in modulating CNS repair. This review will focus on the variable phenotypic state of astrocytes that range from inactive/quiescent to reactive, and relate these to their ability to influence myelination. Using myelinating cultures plated on astrocytes we propose a possible mechanism for oligodendrocyte precursor cell interaction with the axon, leading to myelination. The phenotypic status of astrocytes is an intriguing and widely discussed issue, which is critical for understanding the mechanisms involved in CNS injury and its subsequent repair.

Differentiation and migration of astrocyte precursor cells and astrocytes in human fetal retina: relevance to optic nerve coloboma

The presence of astrocyte precursor cells (APCs) and time course and topography of astrocyte differentiation during development were investigated by triple-label immunohistochemistry with intact fetal and adult human retinas. Throughout retinal development and adulthood, expression of Pax2 was restricted to cells of the astrocytic lineage. Three distinct stages of astrocytic differentiation were identified during development: i) Pax2+/vimentin+/GFAP- APCs; ii) Pax2+/vimentin+/GFAP+ immature perinatal astrocytes; and iii) Pax2+/vimentin-/GFAP+ mature perinatal astrocytes. In adult, cells with the antigenic phenotype of mature perinatal astrocytes were restricted to a region surrounding the optic nerve head (ONH), whereas cells at a fourth stage of differentiation, adult astrocytes (Pax2-/vimentin-/GFAP+), were apparent throughout the vascularized retina. APC appearance was centered around the ONH and preceded the appearance of perinatal astrocytes. A cluster of Pax2+ somas was also present in a small region surrounding the ONH at the ventricular surface of the developing retina, which suggests the existence of two distinct sites of astrocytic differentiation. The coincidence in the location of APCs and perinatal astrocytes at the ventricular zone with that of optic nerve colobomas, together with the association of Pax2 gene mutations with this condition, suggests that coloboma formation may result from impaired astrocyte differentiation during development.

Re-evaluation of nestin as a marker of oligodendrocyte lineage cells

Maturation of oligodendrocyte progenitors (O2A) is characterized by morphological changes and the sequential expression of specific antigens leading to the formation of myelin membrane. Monoclonal antibodies A2B5, A007, anti-vimentin, and anti-galactocerebroside, recognize oligodendroglia at different stages of development. The neuroepithelial precursor marker nestin is also expressed by the oligodendroglial lineage; we have used enriched populations of progenitors isolated from neonatal rat brain cultures to further examine the cellular distribution of this intermediate filament protein. The phenotypic distribution of nestin positive cells among the oligodendrocyte lineage showed that 65% reacted with A2B5, whereas only 5% were A007(+), and 4% galactocerebroside(+). The remaining 25% of the cells were not labeled and had small cellular bodies devoid of processes, characteristic of the pre-O2A progenitor. Further analysis of the nestin(+) population showed that the majority of the cells were also vimentin(+). Antibody-dependent complement mediated cytolysis of A2B5(+) (O2A cells) and galactocerebroside(+) (mature oligodendrocytes) cells left a population of nestin(+) cells that were induced to proliferate in the presence of growth factors and to differentiate into A2B5(+) and galactocerebroside(+) cells. Proliferating cells maintained in the presence of platelet-derived growth factor or basic fibroblast growth factor retained nestin expression along with A2B5. By contrast, in serum-free medium nestin expression decreased while postmitotic cells acquired A007 and galactocerebroside. Our results suggest that nestin expression is a marker of pre-O2A cells that is maintained in proliferating glial progenitors, but is quickly down-regulated in postmitotic oligodendrocytes (A007(+)/galacto-cerebroside(+)) along with A2B5 and vimentin. However, other glial cells including type 2 astrocytes and some amoeboid microglia also share nestin expression.

Comparative anatomy of the cerebellar cortex in mice lacking vimentin, GFAP, and both vimentin and GFAP

In the cerebellum of adult mammals, glial fibrillary acidic protein (GFAP) and vimentin (VIM) are coexpressed in Golgi epithelial cells (GEC), also known as Bergmann glia. In this study we used three transgenic knockout mice (GFAP, VIM and double GFAP and VIM) to analyze the involvement of these proteins in the building of glial filaments and in neuron-glia interactions. The cerebella of VIM, GFAP, and GFAP/VIM mutant mice were processed by the rapid Golgi method and also for electron microscopy. In VIM mutant mice, Bergmann fibers are hypertrophic with thickened appendages. In the electron microscope they appear as large glial profiles devoid of glial filaments, with embedded dendritic thorns and parallel fiber boutons. In addition, signs of degeneration are observed in Purkinje cells. In GFAP mutant mice, GEC exhibit fine, delicate processes, as those seen in wild-type animals, however, a large accumulation of lamellae and granular appendages was observed along their surfaces, which came into contact with each other. The electron microscope exhibited fine and scarce astroglial profiles containing some glial filaments, a stunted glia limitans, and the presence of large extracellular spaces. In double mutant mice, the two phenotypes are expressed but appear attenuated, with a total absence of glial filaments and the general appearance of immaturity for GEC. In conclusion, it appears that the absence of each of the proteins yields a specific phenotype and that the defects are not necessarily additive.

Establishment of astrocyte cell lines from sheep genetically susceptible to scrapie

Primary cultures of the brain from sheep embryos were used to establish cell lines after transfection by the simian virus 40 (SV40) large T gene. Two of the lines (A15 and 4A6) displayed astroglial properties. They expressed the glial fibrillary acidic protein (GFAP), intermediate filament protein vimentin, and S-100 (beta-subunit) protein. While numerous rodent and human glial cell lines are available, this is to our knowledge the first description of ovine cell lines with astrocyte features. In addition, these cell lines were derived from sheep embryos chosen for their genetic susceptibility to scrapie (PrP genotype: VV136, QQ171). Therefore, they could be attractive tissue culture models for the study of propagation and pathogenesis of the scrapie agent ex vivo.

Alterations in temporal/spatial distribution of GFAP- and vimentin-positive astrocytes after spinal cord contusion with the New York University spinal cord injury device

Astrocytes become reactive as a result of various types of lesions and upregulate 2 intermediate filaments, glial fibrillary acidic protein (GFAP), and the developmentally regulated protein vimentin. Young female Sprague-Dawley rats were subjected to a spinal cord contusion at segment T10 using the New York University injury device. Animals were killed at 1, 2, 7, 14, and 30 days postinjury. Horizontal spinal cord sections spanning segments T7-T13 were assessed with antibodies to both intermediate filament proteins. The number of gray matter GFAP-positive astrocytes increased by 2 days postinjury, with segments adjacent (proximal) to the injury site showing greater responses than areas several segments away (distal). By 30 days following injury, astroglial cell numbers returned to normal levels. Vimentin-positive astrocytes also showed a graded proximal/distal response by 2 days following injury. Proximal regions remained significantly higher at 30 days following injury than control animals. Rostral/caudal changes were also evident, with regions caudal to the injury showing significantly higher numbers of vimentin positive astrocytes than those rostral, indicating that gray matter areas caudal to spinal cord injury may undergo more stress following spinal cord injury.

Spatio-temporal patterns of ensheathing cell differentiation in the rat olfactory system during development

An immunocytochemical approach with specific glial markers was used to investigate the temporal and spatial patterns of differentiation of ensheathing glia wrapping axon fascicles along the primary olfactory pathway of the rat during development. The two glial markers tested, the proteins S-100 and glial fibrillary acidic protein, are known to be expressed at different stages of maturation in glial cells. The S-100 protein was first weakly expressed in cells accompanying the olfactory axons at embryonic day 14 (E14), while a first faint glial fibrillary acidic protein staining was detected along the olfactory axons at E15 and along the vomeronasal nerves at E16. A strong S-100 immunoreactivity was already present from E16 onwards along the axon fascicles through their course in both the nasal mesenchyme and the subarachnoid space before entering the olfactory nerve layer of the olfactory bulb. A gradual increase in glial fibrillary acidic protein expression was observed along this part of the developing olfactory pathway from E16 up to E20, when an adult-like pattern of staining intensity was seen. By contrast, most of the ensheathing cells residing in the olfactory nerve layer exhibited some delay in their differentiation timing and also a noticeable delayed maturation. It was only from E20 onwards that a weak to moderate S-100 expression was detected in an increasing number of cells throughout this layer, and only few of them appeared weakly glial fibrillary acidic protein positive at postnatal days 1 and 5. The immunocytochemical data indicate that there is a proximodistal gradient of differentiation of ensheathing cells along the developing olfactory pathway. The prolonged immaturity of ensheathing cells in the olfactory nerve layer, which coincides with the formation of the first glomeruli, might facilitate the sorting out of olfactory axons leading to a radical reorganization of afferents before they end in specific glomeruli.

Spatial patterns of Ca2+ signals define intracellular distribution of a signaling by Ca2+/Calmodulin-dependent protein kinase II

Ca2+ plays a central role in cell signaling, and Ca2+/calmodulin-dependent protein kinase II (CaMKII) is a major mediator of Ca2+ actions. The spatial distribution of intracellular Ca2+ signaling is not homogenous, rather it is dynamically organized, and it has been speculated that spatial patterns of Ca2+ signals may function as a form of cellular information transmitted to downstream molecules. To address this issue, we studied the intracellular distributions of the signalings by CaMKII and Ca2+ in the same astrocytes. The former was visualized by monitoring site-specific phosphorylation of a cytoskeletal protein vimentin, using site- and phosphorylation-specific antibodies, while the latter was examined by fura-2-based Ca2+ microscopy. Local Ca2+ signals induced vimentin phosphorylation by CaMKII localized in the same area. On the other hand, Ca2+ waves in astrocytes induced global phosphorylation of vimentin by CaMKII. A small population of vimentin filaments highly phosphorylated by CaMKII underwent structural alteration into short filaments at electron microscopic level. These results indicate that CaMKII transmits spatial patterns of Ca2+ signals to vimentin as cellular information. The possibility is discussed that spatial patterns of vimentin phosphorylation may be important for intracellular organization of vimentin filament networks.

Immunocytochemical localization of a novel radial glial intermediate filament protein

We have examined by immunocytochemistry the subcellular localization of a chick radial glial protein, named transitin, that by molecular cloning has been shown to be a novel member of the intermediate filament protein superfamily. In astrocytes cultured from E10 chick brain, transitin is localized to the intermediate filament network in accordance with its structural properties. Using confocal microscopy we examined the expression of transitin, vimentin and glial fibrillary acidic protein (GFAP) in cultured astrocytes, and show that transitin co-distributes with these other glial intermediate filament proteins. The expression of transitin, vimentin and GFAP was also compared in embryonic chick spinal cord and brain radial glia, with these studies showing that these intermediate filament proteins display distinct expression patterns during CNS development. Of particular note is the absence of vimentin and GFAP in spinal cord midline radial glia that express transitin protein, and a transient expression of transitin in brain midline radial glia that continue to express vimentin. Our studies presented here therefore indicate that transitin, a novel radial glial intermediate filament protein, may have functions that are unrelated to GFAP or vimentin during CNS development, since transitin is localized to the processes of midline radial glia and is transiently expressed during chick CNS development.

Aged median eminence glial cell cultures promote survival and neurite outgrowth of cocultured neurons

We have recently shown that tanycytes, a particular type of glial cell that has morphological and biochemical similarities with radial glial cells, constitute a preferential support for the regeneration of lesioned neurohypophysial axons. The present study was designed to explore the possible neurotrophic role of tanycytes in vitro. Glial cells derived from the median eminence or from the cerebral cortex of 10-day-old rats were cultured for 4-7 weeks. At these times the majority of the cells identified in the median eminence cultures exhibited immunostaining patterns of tanycytes, as detected in the mediobasal hypothalamus of 10-day-old and adult rats, i.e., they were immunoreactive to vimentin (VIM), to DARPP-32 (a dopamine- and adenosine 3':5'-monophosphate-regulated phosphoprotein), and to a lesser extent to glial fibrillary acidic protein (GFAP) antibodies. On the other hand, the majority of cells in cortex cultures showed immunostaining patterns of astrocytes, i.e., they were intensely immunoreactive to GFAP and VIM antibodies but negative to DARPP-32. Cells obtained from the dissociation of 3-day-old rat mesencephalon, cortex, and hypothalamus were cocultured on these glial monolayers, and the number of surviving neurons and their neurite length were quantified after 8 days. Our data showed that, when compared with astrocytes, tanycytes greatly improved both survival (six-to ten-fold higher) and neurite outgrowth (two- to five-fold longer) of cocultured neurons whatever their origin. Experiments performed by coculturing neurons on millicell inserts placed above the glial monolayers showed that diffusible factors from median eminence glial cells slightly increased survival (1.7-fold higher) of cocultured neurons but had no significant effect on neurite outgrowth. These observations indicate: 1) that aged tanycytes have a capacity to support survival and neurite outgrowth for a variety of postnatal neurons; and 2) that this neurotrophic effect is exerted mainly by means of specific molecules bound to the tanycytic plasmalemma limiting membrane and/or to the extracellular matrix.

Targeted deletion in astrocyte intermediate filament (Gfap) alters neuronal physiology

Glial fibrillary acidic protein (GFAP) is a member of the family of intermediate filament structural proteins and is found predominantly in astrocytes of the central nervous system (CNS). To assess the function of GFAP, we created GFAP-null mice using gene targeting in embryonic stem cells. The GFAP-null mice have normal development and fertility, and show no gross alterations in behavior or CNS morphology. Astrocytes are present in the CNS of the mutant mice, but contain a severely reduced number of intermediate filaments. Since astrocyte processes contact synapses and may modulate synaptic function, we examined whether the GFAP-null mice were altered in long-term potentiation in the CA1 region of the hippocampus. The GFAP-null mice displayed enhanced long-term potentiation of both population spike amplitude and excitatory post-synaptic potential slope compared to control mice. These data suggest that GFAP is important for astrocyte-neuronal interactions, and that astrocyte processes play a vital role in modulating synaptic efficacy in the CNS. These mice therefore represent a direct demonstration that a primary defect in astrocytes influences neuronal physiology.

Glial cells in transected optic nerves of immature rats. II. An immunohistochemical study

The glia response to Wallerian degeneration was studied in optic nerves 21 days after unilateral enucleation (PED21) of immature rats, 21 days old (P21), using immunohistochemical labelling. Nerves from normal P21 and P42 nerves were also studied for comparison. At PED21, there was a virtual loss of axons apart from a few solitary fibres of unknown origin. The nerve comprised a homogeneous glial scar tissue formed by dense astrocyte processes, oriented parallel to the long axis of the nerve along the tracks of degenerated axons. Astrocytes were almost perfectly co-labelled by antibodies to glial fibrillary acid protein and vimentin in both normal and transected nerves. However, there was a small population of VIM+GFAP- cells in normal P21 and P42 nerves, and we discuss the possibility that they correspond to O-2A progenitor cells described in vitro. Significantly, double immunofluorescence labelling in transected nerves revealed a distinct population of hypertrophic astrocytes which were GFAP+VIM-. These cells represented a novel morphological and antigenic subtype of reactive astrocyte. It was also noted that the number of oligodendrocytes in transected nerves did not appear to be less than in normal nerves, on the basis of double immunofluorescence staining for carbonic anhydrase II, myelin oligodendrocyte glycoprotein, myelin basic protein, glial fibrillary acid protein and ED-1 (for macrophages), although it was not excluded that a small proportion may have been microglia. A further prominent feature of transected nerves was that they contained a substantial amount of myelin debris, notwithstanding that OX-42 and ED1 immunostaining showed that there were abundant microglia and macrophages, sufficient for the rapid and almost complete removal of axonal debris. In conclusion, glial cells in the immature P21 rat optic nerve reacted to Wallerian degeneration in a way equivalent to the adult CNS, i.e. astrocytes underwent pronounced reactive changes and formed a dense glial scar, oligodendrocytes persisted and were not dependent on axons for their continued survival, and there was ineffective phagocytosis of myelin possibly due to incomplete activation of microglia/macrophages.

Disrupted glial fibrillary acidic protein network in astrocytes from vimentin knockout mice

Glial fibrillary acidic protein (GFAP) is an intermediate filament protein expressed predominantly in astrocytes. The study of its expression in the astrocyte lineage during development and in reactive astrocytes has revealed an intricate relationship with the expression of vimentin, another intermediate filament protein widely expressed in embryonic development. these findings suggested that vimentin could be implicated in the organization of the GFAP network. To address this question, we have examined GFAP expression and network formation in the recently generated vimentin knockout (Vim-) mice. We show that the GFAP network is disrupted in astrocytes that normally coexpress vimentin and GFAP, e.g., those of the corpus callosum or the Bergmann glia of cerebellum. Furthermore, Western blot analysis of GFAP protein content in the cerebellum suggests that posttranslational mechanisms are implicated in the disturbance of GFAP network formation. The role of vimentin in this process was further suggested by transfection of Vim-cultured astrocytes with a vimentin cDNA, which resulted in the normal assembly of the GFAP network. Finally, we examined GFAP expression after stab wound-induced astrogliosis. We demonstrate that in Vim- mice, reactive astrocytes that normally express both GFAP and vimentin do not exhibit GFAP immunoreactivity, whereas those that normally express GFAP only retain GFAP immunoreactivity. Taken together, these results show that in astrocytes, where vimentin is normally expressed with GFAP fails to assemble into a filamentous network in the absence of vimentin. In these cells, therefore, vimentin appears necessary to stabilize GFAP filaments and consequently the network formation.

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

Procurement of multipotential neuroglial stem cells is possible with the addition of epidermal growth factor (EGF). Stem cells will differentiate into neurons and glia upon the removal of EGF from the culture medium. We have previously characterized the neuronal differentiation of stem cells derived from long-term cultured nonpassage neurospheres. In the current study, we (1) characterize the morphological differentiation of the astroglial progenitor cell from 3-mo-old neurospheres, (2) examine whether the astroglial progenitor cells from neurospheres of different brain areas exhibit different differentiation responses to the same exogenous signals, and (3) test the effects of basic fibroblast growth factor (bFGF) and retinol on differentiation. Cerebral cortex, striatum, and mesencephalon cells were obtained from Embryonic Day 14 (E-14) rat fetuses and were dissociated for the procurement of neurospheres in chemically defined medium supplemented with EGF. After 3 mo in culture, the neurospheres, derived from each of the three brain areas, were subcultured into three groups on chamber slides: (1) basal medium, (2) the basal medium plus 20 ng/mL bFGF, and (3) the basal medium plus 10 muM retinol. Phenotypic expression of astroglial cells was examined after 14 days subculture. Our findings indicate that the 3-mo-old cultured nonpassage neurospheres contained numerous multipotential stem cells that stained positive with nestin, and that environmental factors played an important role in influencing the differentiation of astroglial progenitor cells. As detected by glial fibrillary acid protein (GFAP), astroglial progenitor cells turned into protoplasmic astrocytes in the FCS-containing basal medium, fibrous astrocytes in the presence of bFGF, and spindle-shaped astrocytes in the presence of retinol. There were no noticeable differences in differentiation among astroglial progenitor cells of the various brain region-derived neurospheres in any of the three medium conditions. Peculiar varicosity-and growth cone-like structures on the long slender GFAP-positive processes suggest that neuroblasts and glioblast may share common morphologies, features, or common progenitor cells during initial differentiation in vitro.

Morphological Differentiation of Astroglial Progenitor Cells from Egf-Responsive Neurospheres in Response to Fetal Calf Serum, Basic Fibroblast Growth Factor, and Retinol

Procurement of multipotential neuroglial stem cells is possible with the addition of epidermal growth factor (EGF). Stem cells will differentiate into neurons and glia upon the removal of EGF from the culture medium. We have previously characterized the neuronal differentiation of stem cells derived from long-term cultured nonpassage neurospheres. In the current study, we (1) characterize the morphological differentiation of the astroglial progenitor cell from 3-mo-old neurospheres, (2) examine whether the astroglial progenitor cells from neurospheres of different brain areas exhibit different differentiation responses to the same exogenous signals, and (3) test the effects of basic fibroblast growth factor (bFGF) and retinol on differentiation. Cerebral cortex, striatum, and mesencephalon cells were obtained from Embryonic Day 14 (E-14) rat fetuses and were dissociated for the procurement of neurospheres in chemically defined medium supplemented with EGF. After 3 mo in culture, the neurospheres, derived from each of the three brain areas, were subcultured into three groups on chamber slides: (1) basal medium, (2) the basal medium plus 20 ng/mL bFGF, and (3) the basal medium plus 10 μM retinol. Phenotypic expression of astroglial cells was examined after 14 days subculture. Our findings indicate that the 3-mo-old cultured nonpassage neurospheres contained numerous multipotential stem cells that stained positive with nestin, and that environmental factors played an important role in influencing the differentiation of astroglial progenitor cells. As detected by glial fibrillary acid protein (GFAP), astroglial progenitor cells turned into protoplasmic astrocytes in the FCS-containing basal medium, fibrous astrocytes in the presence of bFGF, and spindle-shaped astrocytes in the presence of retinol. There were no noticeable differences in differentiation among astroglial progenitor cells of the various brain region-derived neurospheres in any of the three medium conditions. Peculiar varicosity-and growth cone-like structures on the long slender GFAP-positive processes suggest that neuroblasts and glioblast may share common morphologies, features, or common progenitor cells during initial differentiation in vitro.

Developmental study in the circadian clock of the golden hamster: a putative role of astrocytes

The hypothalamic suprachiasmatic nuclei (SCN) house the circadian clock in the mammalian brain. A glial fibrillary acidic protein immunoreactivity (GFAP-ir) distribution rhythm has been observed in the SCN of adult Syrian hamster. The implication of astrocytes in photic entrainment was analyzed through developmental studies of the photic pathway and of SCN astrocytes appearance. Using anterograde tracing we studied the timing of penetration of the retinohypothalamic tract (RHT) fibers into the SCN. Using c-fos induction by light we followed the maturation of RHT synapses in the SCN. When RHT terminals reach the SCN, c-fos induction can be obtained. Using GFAP immunoreactivity we demonstrated that the number of astrocytes increased in parallel with RHT development from PN5 to PN15. At PN15, a time when pups can shift from maternal to photic entrainment, RHT terminals and GFAP-ir exhibit an adult-like pattern. One demonstrated role of astrocytes is to control extracellular glutamate concentration. Glutamate is the neurotransmitter released at RHT terminals; its content fluctuates according to a circadian rhythm within the SCN. Thus the present data tend to indicate that SCN astrocytes are participating in the circadian rhythm of SCN glutamate content.

Astrocytes: form, functions, and roles in disease

Astrocytes, once relegated to a mere supportive role in the central nervous system, are now recognized as a heterogeneous class of cells with many important and diverse functions. Major astrocyte functions can be grouped into three categories: guidance and support of neuronal migration during development, maintenance of the neural microenvironment, and modulation of immune reactions by serving as antigen-presenting cells. The concept of astrocytic heterogeneity is critical to understanding the functions and reactions of these cells in disease. Astrocytes from different regions of the brain have diverse biochemical characteristics and may respond in different ways to a variety of injuries. Astrocytic swelling and hypertrophy-hyperplasia are two common reactions to injury. This review covers the morphologic and pathophysiologic findings, time course, and determinants of these two responses. In addition to these common reactions, astrocytes may play a primary role in certain diseases, including epilepsy, neurological dysfunction in liver disease, neurodegenerative disorders such as Parkinson's and Huntington's diseases, and demyelination. Evidence supporting primary involvement of astrocytes in these diseases will be considered.

Molecular profile of reactive astrocytes--implications for their role in neurologic disease

The central nervous system responds to diverse neurologic injuries with a vigorous activation of astrocytes. While this phenomenon is found in many different species, its function is obscure. Understanding the molecular profile characteristic of reactive astrocytes should help define their function. The purpose of this review is to provide a summary of molecules whose levels of expression differentiate activated from resting astrocytes and to use the molecular profile of reactive astrocytes as the basis for speculations on the functions of these cells. At present, reactive astrocytosis is defined primarily as an increase in the number and size of cells expressing glial fibrillary acidic protein. In vivo, this increase in glial fibrillary acidic protein-positive cells reflects predominantly phenotypic changes of resident astroglia rather than migration or proliferation of such cells. Upon activation, astrocytes upmodulate the expression of a large number of molecules. From this molecular profile it becomes apparent that reactive astrocytes may benefit the injured nervous system by participating in diverse biological processes. For example, upregulation of proteases and protease inhibitors could help remodel the extracellular matrix, regulate the concentration of different proteins in the neuropil and clear up debris from degenerating cells. Cytokines are key mediators of immunity and inflammation and could play a critical role in the regulation of the blood-central nervous system interface. Neurotrophic factors, transporter molecules and enzymes involved in the metabolism of excitotoxic amino acids or in the antioxidant pathway may help protect neurons and other brain cells by controlling neurotoxin levels and contributing to homeostasis within the central nervous system. Therefore, an impairment of astroglial performance has the potential to exacerbate neuronal dysfunction. Based on the synopsis of studies presented, a number of issues become apparent that deserve a more extensive analysis. Among them are the relative contribution of microglia and astrocytes to early wound repair, the characterization of astroglial subpopulations, the specificity of the astroglial response in different diseases as well as the analysis of reactive astrocytes with techniques that can resolve fast physiologic processes. Differences between reactive astrocytes in vivo and primary astrocytes in culture are discussed and underline the need for the development and exploitation of models that will allow the analysis of reactive astrocytes in the intact organism.

Co-expression of GFAP and vimentin in astrocytes proliferating in response to injury in the mouse cerebral hemisphere. A combined autoradiographic and double immunocytochemical study

Changes in the distribution of proliferating astrocytes expressing glial fibrillary acidic protein (GFAP) and/or vimentin were examined in the injured cerebral hemisphere in adult mice. The injury was followed by [3H]thymidine injections at different time intervals. The brain sections were doubly immunostained for GFAP and vimentin and subjected to autoradiography. In that way three cell types were distinguished immunocytochemically: (1) astrocytes co-expressing glial fibrillary acidic protein (GFAP) and vimentin, (2) astrocytes expressing only GFAP and (3) astrocyte-like cells expressing vimentin. Thereafter, numbers of immunopositive and autoradiographically labelled cells and their locations within the region of injury were recorded at each stage of the experiment. Two hours as well as 1 day after the injury proliferation of GFAP-positive astrocytes and of those co-expressing GFAP and vimentin could only be seen as statistically insignificant phenomena. On day 2 the reactive proliferation of each immunocytochemically defined cell type was already maximal, then gradually decreased and its last signs were recorded on day 8. On day 2, among all the proliferating GFAP-positive astrocytes, 67.2% were also vimentin-positive. Later, the proportion declined to 50.7% and 38.5% on days 4 and 8, respectively. The labelled astrocyte-like vimentin-positive cells were located closest to the lesion margins. In comparison, the astrocytes co-expressing GFAP and vimentin and those expressing exclusively GFAP, occupied regions progressively farther from the lesion site. At the initial stages of the response to injury, vimentin expression in cells starting their reactive proliferation did not precede the expression of GFAP.(ABSTRACT TRUNCATED AT 250 WORDS)

Reactive astrocytes in explant cultures of glial scars derived from lesioned rat optic nerve: an ultrastructural study

Explant cultures of glial scars generated by surgical removal of the retina in 3-60-day-old rats were used to determine if reactive astrocytes survive in vitro and how closely reactive astrocytes in culture resemble their in vivo counterparts. Characterization of the composition of age matched glial scars in vivo and in vitro showed that reactive astrocytes survived in glial scar explants even after several weeks in culture. Reactive astrocytes in both neonatal and adult glial scars retained ultrastructural features characteristic of reactive astrocytes in vivo. However, fewer reactive astrocytes survived in culture when explants were prepared from adult rat glial scars. The results of this study demonstrate that tissue culture is a viable model for the study of reactive astrocytes. A critical factor in the survival of reactive astrocytes in culture was the complete removal of myelin debris prior to the establishment of the culture. This outcome suggests that it will be important to clarify why myelin debris persists in culture and how it affects the survival of reactive astrocytes.

Phagocytosis of myelin by astrocytes in explants of adult rabbit cerebral white matter maintained on Gelfoam matrix

The role of astrocytes in the process of demyelination has been controversial. A culture system in which explants of adult cerebral rabbit white matter were maintained on a Gelfoam matrix was used for evaluating the phagocytosis of myelin by astrocytes without an influx of phagocytic cells derived from actively circulating blood-borne cells. Adult neurons were not viable for more than a few days in these explant cultures, thus resulting in empty myelin sheaths following loss of their axons. After 7 days in vitro, astrocytes, recognized by positivity for glial fibrillary acidic protein by electron microscopic immunocytochemistry, contained numerous membrane-bound vesicles filled with myelin in various stages of degradation. Although the majority of macrophage-like cells were negative for glial fibrillary acidic protein, a minority were positive, in spite of the lack of bundles of intermediate filaments, and were interpreted as astrocytic. Astrocytes were also often positive for glutamine synthetase. This study presents evidence suggesting that astrocytes may actively participate in the phagocytosis and degradation of myelin, a function generally attributed to reactive macrophages.

Age-related immunoreactivity pattern in medulloblastoma

Thirty-five paraffin-embedded medulloblastomas (19 from children and 16 from adults; 24 classic medulloblastomas, 10 desmoplastic medulloblastomas, 1 tumor with neuronal differentiation) were examined for reactions with antibodies against glial fibrillary acidic protein (GFAP), cytokeratins KL1 and MNF116, desmin, and vimentin. Only the tumor from the youngest patient, a 152-day-old boy, showed a positive immunoreaction for cytokeratins. Because of this age-related expression of cytokeratins in medulloblastomas primarily in very young children, cytokeratin positivity was interpreted as a sign of tumor immaturity. Five medulloblastomas showed scattered GFAP-positive reactive astrocytes and/or other positive, probably neoplastic, cells. Only two tumors showed GFAP immunoreactivity in unequivocally neoplastic cells. Of six tumors that reacted with vimentin, three showed strong reactivity throughout, one being the tumor from the 152-day-old boy. The remaining three demonstrated nests of vimentin-positive cells with weak or intense somatic immunoreactivity for vimentin. None of the 35 cases showed positivity for desmin; indicating that mesenchymal differentiation is restricted to the rare so-called medullomyoblastomas.

The topoisomerase II inhibitor teniposide (VM-26) induces apoptosis in unstimulated mature murine lymphocytes

This study shows that not only concanavalin A-stimulated proliferating lymphocytes but also unstimulated mouse splenic lymphocytes are sensitive to the topoisomerase II (topo II) inhibitor teniposide (VM-26). When unstimulated lymphocytes are pretreated with VM-26 for a 2-h period and are then incubated in drug-free medium, cell viability, as determined by trypan blue exclusion, decreases to 40% of the control by 6 h. The drug-treated cultures show two to three times the level of detergent soluble DNA than the control cultures and agarose gel electrophoresis of the soluble DNA shows the presence of oligonucleosomal-sized fragments, a feature considered to be a hallmark of apoptosis. Phase contrast microscopy, Hoechst staining for DNA, and immunofluorescence microscopy of various nuclear and cytoplasmic antigens (nucleolar fibrillarin, snRNP, ubiquitin, vimentin, tubulin) in the VM-26-treated cells characterize the morphological changes during apoptosis of these cells. The role of topo II as the mediator of the VM-26 effects is supported by pulsed field gel electrophoresis, which shows the typical topo II-induced cleavage of supercoiled DNA into loop-sized 300- and 50-kbp fragments. We conclude that the cancer chemotherapeutic agent VM-26 interacts with topo II and induces apoptosis in unstimulated lymphocytes.

The role of swollen astrocytes in human brain lesions after edema--an immunohistochemical study using formalin-fixed paraffin-embedded sections

Swollen astrocytes (SAs) in the white matter after brain edema were immunohistochemically studied in cases with cerebral vascular events, brain tumor and protracted non-missile head injury. SAs showed a decrease in reactivity to glial fibrillary acidic protein (GFAP) and, on the other hand, were positive for laminin, an extracellular matrix glycoprotein known to be secreted by astrocytes. SAs in protracted lesions were strongly positive for both vimentin and plasma proteins including IgG, IgM, C3d and C4d. Remarkable vimentin expression in SAs, instead of GFAP, strongly suggests that SAs are not going to degenerate but are bearing up to regenerate in such circumstances. A number of vimentin-positive buttons also appeared in such protracted lesions, demonstrating disintegration of the processes of SAs. Immunohistochemical detection of plasma proteins in SAs are believed to indicate a facilitated activation in SAs to transform to macrophage-like cells and to act as phagocytes. In addition, demonstration of laminin may suggest hyperactivity of laminin production in SAs after both axonal injury and concomitant edema in order to stimulate neuritic regeneration.

Neonatal host astrocyte migration into xenogeneic cerebral cortical grafts

Migration of host astrocytes into grafts was investigated by transplantation of rat cortex (E16) into the cortex or midbrain of neonatal mice. Host astrocytes, visualized by the mouse astrocyte-specific antibody, began to invade the grafted cortex during the first week post-transplantation and sequentially migrated substantial distances throughout the graft. Host cells in the grafts which were undergoing immune rejection became hypertrophic. These results have important implications when assessing interactions between host and graft cells.

Immuno-electron microscopical localization of vimentin and glial fibrillary acidic protein in mouse astrocytes and their precursor cells in culture

Immuno-electron microscopy was used to localize the distribution of vimentin and glial fibrillary acidic protein (GFAP) in mouse astrocytes and their precursor cells in primary cultures. In astroblasts and astrocytes, vimentin and GFAP form intermediate filaments (IF), which are heteropolymers, as previously observed in gliomas. Astrocytes and their precursor cells may have IF composed of GFAP-vimentin heteropolymer or vimentin alone, but IF composed of GFAP only were not seen. It seems that the formation of IF that are GFAP-vimentin heteropolymers is a feature of normal astroglia development and that the ratio of GFAP to vimentin in these IF reflects the degree of differentiation and functional state of the cell.

Sexual dimorphism in the hamster cerebellum demonstrated by glial fibrillary acidic protein (GFAP) and vimentin immunoreactivity

Male and female hamsters aged 1, 4, and 10 postnatal weeks were used to study the distribution of vimentin and glial fibrillary acidic protein (GFAP) in the cerebellum. Vimentin immunoreactivity exceeded that of GFAP during the first postnatal week, although GFAP was also observed in all cerebellar layers. Immunoperoxidase analysis revealed that by the fourth postnatal week vimentin was only detected in Bergmann fibers and the very scarce fibrous astrocytes located in the inner white matter. The Purkinje cell bodies were only coated with GFAP-immunopositive processes. At 10 weeks, vimentin immunoreactivity was reduced to thin Bergmann glial processes, whereas GFAP immunoreactivity had greatly increased in the whole cerebellum. The GFAP immunostaining was denser in males than in females; however, in females, the Bergmann fibers were heavily immunostained with anti-vimentin in contrast to the males. The results described in the present paper indicate a sex difference in vimentin and GFAP immunoreactivities in the cerebellar astrocytes at 4 weeks of age, which persisted in the oldest hamsters in this study. The existence of sexual dimorphism might suggest that the expression of both gliofilament proteins could be influenced by circulating sex steroids.

The neuronal cytoskeleton

In this paper we have described the organization of F-actin and actin-binding proteins (ABP): alpha-actinin, myosin, tropomyosin, caldesmon, vinculin, talin, and spectrin, in differentiating astroglia in colony cultures. We observed that the microfilament (MF) network arrangements differ at various stages of astroglia development, but the composition of MF bundles and stress fibers is the same at all developmental stages. F-actin is closely colocalized with myosin, tropomyosin, caldesmon, and alpha-actinin. The striated pattern of myosin, tropomyosin, and caldesmon are superimposable. Tropomyosin and caldesmon extend along F-actin but are interrupted for short periods, whereas myosin is interrupted for longer periods. alpha-actinin colocalizes with tropomyosin and caldesmon but not with myosin. In astroglia at different stages of development spectrin is arranged in the form of fine networks spreading through the cell and does not follow the arrangement of MF bundles. Only F-actin, alpha-actinin, and vinculin can be detected at cell-cell junctions. In the areas of the focal contacts, F-actin, alpha-actinin, vinculin, and talin are present. They overlap each other, although talin and vinculin extend toward the cell membrane beyond F-actin and alpha-actinin. Astroglia undergo well-defined states of nonmotility, motility, and nonmotility again during differentiation. The changes in motility are paralleled by changes in the organization of F-actin and ABP: as GFAP-containing intermediate filaments increase in differentiating astroglia, the F-actin and ABP are down-regulated, leading to non motility.

Replacement of glucose by sorbitol in growth medium causes selection of astroglial cells from heterogeneous primary cultures derived from newborn mouse brain

Primary cultures derived from the brains of newborn mice are quantitatively dominated by astroglial cells, but contain also oligodendroglial, phagocytic and ependymal cells. When confluent cultures are fed with glucose-free growth medium containing 25 mM sorbitol for 14 days, oligodendroglial, phagocytic and ependymal cells are eliminated from the culture, as judged by morphological and immunocytochemical criteria. The remaining cells stain positively for vimentin and glial fibrillary acidic protein and, therefore, can be considered as astroglial cells. Inoculation of freshly dissociated mouse brain cells in the absence of glucose in a sorbitol-containing medium is not possible; however, feeding of the cultures from day 2 on with sorbitol instead of glucose results in a pure astroglial culture at confluency. Therefore glucose-free growth medium supplemented with sorbitol can be considered a selective medium for astroglial cells in primary mouse glial cultures.

Expression of glial fibrillary acidic protein by Müller cells in rd chick retina

Accumulation of glial fibrillary acidic protein (GFAP) in Müller cells has been observed in retinas of several mammalian species secondary to genetically induced degeneration and neuronal injury. In the present series of experiments, I have examined the effects of the rd (retinal degeneration) mutation on the expression of GFAP in retinas of chicks homozygous for the mutation (rd/rd) prior to and following the onset of photoreceptor degeneration, which first appears approximately 7 days posthatch (7 dph). Carrier (+/rd) and wild-type (+/+) retinas served as controls. Retinas taken from 1, 7, 21, and 33 dph rd/rd, +/rd, and +/+ chicks were analyzed for the presence of GFAP by immunocytochemical and SDS-PAGE/Western blot techniques. The following immunocytochemical observations were made: (1) GFAP immunostaining was limited to and located throughout the Müller cells. (2) The intensity of GFAP immunostaining increased with age in all three retina types in tissue sections, as well as on immunoblots. (3) The distribution of GFAP staining within rd/rd Müller cells following the onset of degeneration was slightly different from that observed in +/+ and +/rd retinas and was distinguished by increased staining of the cell bodies and the cell processes forming the outer limiting membrane. The results of these experiments show that Müller cells in chick retina contain GFAP. In addition, they suggest that, in contrast to Müller cells in degenerating mammalian retina, Müller cells in rd chick retina do not accumulate large amounts of GFAP in response to degeneration.

Cell cycling of astrocytes and their precursors in primary cultures: a mevalonate requirement identified in late G1, but before the G1/S transition, involves polypeptides

The relationship between mevalonate and cell cycling was investigated in developing glial cells. Primary cultures of newborn rat brains were serum-depleted (0.1%, vol/vol) for 48 h on days 4-6 in vitro, then returned to 10% calf serum (time 0). After 48 h, 70-80% of the cells were glial fibrillary acidic protein (GFAP)-negative by indirect immunofluorescence; 79 +/- 7% were GFAP-positive after an additional 3 days. Serum shift-up resulted in 12 h of quiescence, and then by 20 h (S phase) in increased proportions of cells synthesizing DNA (from 15 +/- 6% to 75 +/- 4% by bromodeoxyuridine immunofluorescence at 12 h and 20 h, respectively) and rates of DNA synthesis (42 +/- 6 versus 380 +/- 32 cpm/micrograms of protein/h of [3H]thymidine uptake). Additional mevalonate (25 mM) for 30 min at 10 h reversed the inhibition of DNA synthesis apparent with mevinolin (150 microM), an inhibitor of mevalonate synthesis, present from time 0. Cycloheximide added simultaneously with mevalonate prevented this reversal of inhibition. To cause arrest at G1/S, cultures were exposed to hydroxyurea between 10 and 22 h. By 3 h after hydroxyurea removal, bromodeoxyuridine-labeled nuclei increased from 0% to 75 +/- 9%, and DNA synthesis increased 10-fold. Mevinolin failed to inhibit these increases. Thus, primary astroglial precursors stimulated to progress through the cell cycle express a mevalonate requirement in late G1, but before the G1/S transition. The effect of mevalonate was characterized further as being brief (30 min) and as requiring polypeptides.

Macrophage-like cells originate from neuroepithelium in culture: characterization and properties of the macrophage-like cells

Cultures of astroglia from C3H/HeJ mice, which are resistant to bacterial cell wall polysaccharide (LPS), initiated from embryos of Theiler stage 14 (9 days of gestation) up to Theiler stage 25 (17 days of gestation) as well as newborn animals, when subjected to nutritional deprivation, i.e. non-feeding of cultures, form large numbers of macrophage-like cells. These cells express Mac-1, Mac-3, F4/80 and Fc antigens. The cells are negative for GFAP, positive for vimentin, express Ia antigen and take up DiL-Ac-LDL. They are positive to non-specific esterase, secrete lysozyme and are phagocytic. Their morphology and ultrastructure closely resemble those of macrophages. Cultures initiated from neuroepithelium of Theiler stage 13 (8.5 days of gestation), before vascularization, when subjected to nutritional deprivation, also produce macrophage-like cells. Using spleen colony assay and methyl cellulose cultures, we were unable to detect the presence of hemopoietic (macrophage) precursor cells in astroglia cultures. This supports the hypothesis that the macrophage-like cells are of neuroectodermal origin and probably correspond to resident microglia of the CNS. Using nutritionally deprived astroglia cultures, a procedure was developed for isolation of macrophage-like cells and production of highly enriched macrophage-like (microglia) cultures.

Intermediate filaments in the inner ear of normal and experimentally damaged guinea pigs

The hypothesis that proteins known to occur in glial cells in the central nervous system may be present in inner-ear supporting cells was investigated. Immunocytochemical techniques were used to look for the existence of two classes of intermediate filaments, vimentin and glial fibrillary acidic protein (GFAP), in cellular elements of the inner-ear epithelium in normal and experimentally damaged guinea-pig cochleas. Vimentin is present in two types of supporting cells in the normal organ of Corti: Deiters' cells and inner pillar cells. Differences in intensity and distribution of vimentin immunostaining are observed across the three rows of Deiters' cells. GFAP immunoreactivity was not detected in any supporting-cell type in the organ. Cochlear hair cells were not labeled for either GFAP or vimentin. Following hair-cell destruction by exposure to noise or the administration of aminoglycosides, GFAP and vimentin are not present in phalangeal scars replacing lost hair cells.

Thrombin and its inhibitors regulate morphological and biochemical differentiation of astrocytes in vitro

Flat, amorphous astroblasts in culture differentiate into rounded process-bearing cells after removal of serum from the media or following addition of dibutyryl cyclic-AMP (dbcAMP). We report here that addition of thrombin (10 nM) to rat primary astroglial cultures reversed both the spontaneous morphological differentiation of astroblasts caused by serum removal, and the more extensive morphological differentiation caused by pre-treatment with dbcAMP. The astroblasts retained the ability to differentiate upon removal of thrombin from the medium. Proteolytic activity of thrombin was required for the reversal of differentiation. Moreover, addition of serine protease inhibitors active against thrombin elicited a prolonged morphological differentiation rivaling that induced by dbcAMP, suggesting that inactivation of cell-associated thrombin might be sufficient for morphological differentiation to occur. Two other serine proteases with a cleavage specificity similar to thrombin were ineffective in reversing differentiation. Both the induction of morphological differentiation by dbcAMP and its reversal by thrombin were rapid, being essentially complete by 1 h. With more prolonged treatments, thrombin also reduced the dbcAMP-mediated increase in glutamine synthetase, a biochemical marker for astroglial differentiation. Thrombin also inhibited morphological differentiation in C6 glioma and altered the morphology of microglial cells; however, thrombin did not prevent neurite outgrowth in primary central neuronal cultures in contrast to its previously reported effects on the neuroblastoma 2a cell line. These findings indicate that a proteolytic mechanism mediated by thrombin and its inhibitors may underlie the regulation of astroglial differentiation.

Expression of microtubule-associated protein 2 by reactive astrocytes

After an injury to the central nervous system, a dramatic change in the astrocytes bordering the wound occurs. The most characteristic feature of this process, termed reactive gliosis, is the upregulation of the intermediate filament protein, glial fibrillary acidic protein. In the present study, we show that reactive astrocytes express high levels of microtubule-associated protein 2 (MAP-2), a protein normally found in the somatodendritic compartment of neurons. When sections of injured brain are double-stained with antibodies directed against MAP-2 and glial fibrillary protein, all of the reactive astrocytes are found to contain MAP-2. The high levels of this protein appear to represent a permanent change in reactive astrocytes. In parallel quantitative studies, an elevated level of MAP-2 in the injured brain is confirmed by an immunoblot analysis of injured and normal white matter. This report demonstrates the direct involvement of a microtubule protein in the process of reactive gliosis.

Changes in glial cell markers in recent and old demyelinated lesions in central pontine myelinolysis

An immunohistochemical study was performed to compare glial reactions in recent and old lesions of central pontine myelinolysis (CPM). Regions of demyelination and destruction of oligodendrocytes, showed reduced immunoreactivity of myelin basic protein (MBP), myelin-associated glycoprotein (MAG), transferrin, and carbonic anhydrase C (CA C). In addition, labeling of glial fibrillary acidic protein (GFAP) and S-100 protein revealed distinct dystrophic alterations of the astroglia. Remarkably, immunolabeling of GFAP was drastically reduced in astrocytic cytoplasm within freshly demyelinated lesions. Immunostaining of vimentin revealed a differential intracytoplasmic decoration of hypertrophic and dystrophic astrocytes in recent and old CPM lesions. Immunolabeling of desmin failed to stain glial cells. Monoclonal antibodies against HNK-1 exhibited greatly increased immunoreactivity both of persisting oligodendrocytes and of reactive fibrillary astrocytes in old CPM foci. In freshly demyelinated lesions, enhanced immunoreactivity of the X-hapten (3-fucosyl-N-acetyllactosamine) was prominent in astroglia and oligodendrocytes. Simultaneously, reactive astrocytes revealed intracytoplasmic labeling of laminin. Quantitation of GFAP+ astroglia in fresh CPM and control cases revealed an increase in the number of astrocytes within the demyelinated foci and in the surrounding non-demyelinated pontine tissue of CPM cases. The occurrence of astroglial alterations in the demyelinated foci of CPM could be interpreted as "astroglial dystrophy" which may represent a pathogenic factor in CPM. Furthermore, it is possible that changes of the glial microenvironment may influence the astroglia to revert transiently back to an immature phenotype as indicated by the enhanced expression of the X-hapten and HNK-1, and the de novo synthesis of vimentin and laminin.

Protein gene product (PGP) 9.5 as a reliable marker in primitive neuroectodermal tumours--an immunohistochemical study of 21 childhood cases

A number of antibodies to neural proteins have been used to demonstrate neuronal differentiation in primitive neuroectodermal tumours. One of them is protein gene product (PGP) 9.5, a neuronal protein isolated from brain, whose function is unknown at present. We have studied differentiation in 21 cases of primitive neuroectodermal tumours of the CNS in children. Immunocytochemical staining was performed for such neuronal markers as: PGP 9.5, neuron specific enolase and synaptophysin, a glycosylated protein associated with synaptic vesicles. Positive staining for PGP 9.5 was present in 16 cases (strong staining in 12), for neuron-specific enolase in 16 cases (strong staining in 10) and for synaptophysin in 10 cases (strong staining in six). Both PGP 9.5 and synaptophysin showed a clear staining pattern with less non-specific background than with neuron-specific enolase. Our findings demonstrate the value of using more than one antibody marker in assessing neuronal differentiation in tumours. The high incidence of positive staining with antibody to PGP 9.5 suggests that this is an essential marker in the panel of antibodies used for the identification of primitive neuroectodermal tumours.

Differentiation potential of a monoclonal antibody-defined neural progenitor cell population isolated from prenatal rat brain by fluorescence-activated cell sorting

We have studied the differentiation potential in vitro of a subpopulation of neural progenitor cells from BDIX-rat brain. These cells transiently express a cell surface determinant (CSD) specified by monoclonal antibody (Mab) RB13-2 (Kindler-Röhrborn, A. et al., Differentiation 30 (1985) 53-60), and recently identified as a set of O-acetylated gangliosides (Reinhardt-Maelicke, S. et al., submitted) also recognized by Mab D1.1 (Levine, J.M. et al., J. Neurosci., 4 (1984) 826-831) and partly by Mab JONES (Schlosshauer, B. et al., J. Neurosci., 8 (1988) 580-592), respectively. As analyzed by immunofluorescence, Mab RB13-2 binding brain cells (prenatal days 11-22; postnatal days 7 and 89) were localized in different areas of the proliferative ventricular layer of the prenatal cerebrum and in the external granular layer of the early postnatal cerebellum. No Mab RB13-2 positive brain cells were found in adult brain. Following their isolation by fluorescence activated cell sorting on prenatal day 18, the differentiation potential of Mab RB13-2 binding brain cells was studied by double-immunofluorescence analysis under different conditions of monolayer culture. In the presence of 10% fetal calf serum (FCS), these cells differentiated into glial fibrillary acidic protein (GFAP) positive flat astrocytes, whereas neurons (neurofilament-positive) and a smaller number of stellate astrocytes (GFAP-positive) developed in a chemically defined medium containing 0.5% FCS. Neural progenitor cells binding Mab RB13-2 may thus either retain more than one option for differentiation into specific cell types, or the expression of the CSD specified by Mab RB13-2 may be common to more than one subset of neural progenitor cells (with or without predetermined unidirectional differentiation pathways) whose survival and/or proliferative behavior could be differentially affected by microenvironmental conditions.

Developmental expression of glial fibrillary acidic protein mRNA in the rat brain analyzed by in situ hybridization

Glial fibrillary acidic protein (GFAP) accumulates in astrocytes during development. We have characterized the increase in GFAP mRNA during development of the rat brain by using Northern blotting and in situ hybridization histochemistry and have found a caudal to rostral gradient of expression, consistent with overall brain maturation. GFAP mRNA was first observed at embryonic day 16 (E16) in the glial limitans of the ventral hindbrain. During brain development message levels increased rostrally and by postnatal day 5 (P5) the entire glial limitans showed a positive signal which persisted into adulthood. GFAP mRNA was also found to accumulate in a caudal to rostral direction within the Purkinje cell layer of cerebellum beginning shortly after birth. By P5 the entire layer was positive and signal in this region could be localized to Bergmann glia by P15. A transient elevation in GFAP mRNA was apparent during the second postnatal week in cerebellum and cerebrum. Using in situ hybridization, a peak in message levels was observed at P15 and could be localized primarily to the deep white matter of cerebellum, to the corpus callosum, and to certain hippocampal fiber tracts. The pattern of GFAP expression in these regions is consistent with the differentiation of interfascicular glia and the appearance of type-2 astrocytes during the initial events of myelination. GFAP mRNA levels in white matter were greatly reduced in the adult. The pronounced regional differences in GFAP mRNA expression during development may reflect the differentiation of subpopulations of astrocytes.

Region- and sex-related differences in maturation of astrocytes in dissociated cell cultures of embryonic rat brain

Previous studies using dissociated cell cultures of fetal rat brain have revealed considerable regional diversity as well as sex steroid-independent sex differences in developmental schedules of dopaminergic neurons. Because these phenomena might be related to glial heterogeneity, cultures of dissociated male and female diencephalon, mesencephalon, and rhombencephalon of gestational day 14 rats were investigated with respect to the development of astrocytic markers. Cultures were incubated for 3-8 days in vitro (DIV) in serum-supplemented or serum-free medium. Vimentin and glial fibrillary acidic protein (GFAP) were quantified by counting of immunolabeled cells and immunoblotting. Vimentin and GFAP content rose from DIV 3 to 6 in all cultures. Regional variation of vimentin content was low, but large differences occurred in amounts of GFAP. GFAP reached high levels in rhombencephalon, especially when supplemented with serum, but remained very low or not detectable in mesencephalon. Simultaneous immunostaining for both cytoskeletal proteins revealed the presence of large numbers of vimentin single-labeled and small numbers of vimentin/GFAP double-labeled cells. Numbers of cells expressing GFAP showed similar regional variations as GFAP contents in both serum-free and serum-supplemented medium. They rose steeply from DIV 3 to 8 in rhomb- and diencephalon but not in mesencephalon. Transiently, female diencephalic cultures contained slightly more GFAP-immunoreactive cells than male cultures. The results thus demonstrate considerable regional heterogeneity of astrocytic maturation. However, neither the regional nor the sex differences show a consistent correlation with previous data on development of dopaminergic and other monoaminergic neurons in vitro. It seems likely that the dependence of neurons on glial environment for realization of an inherent developmental program varies among neuronal phenotypes.

The modulation of astrocytic differentiation in cells derived from a medulloblastoma surgical specimen

Medulloblastomas are cerebellar tumors which are primarily composed of sheets of uniform, small malignant cells and may have astrocytic, neuronal or no features typical of these cell types. The assessment of astrocytic differentiation in medulloblastoma rests largely on the detection in malignant cells of glial fibrillary acidic protein (GFAP), a marker present in the later stages of normal astrocyte differentiation. It is still not known whether cells that do not contain GFAP in medulloblastomas with astrocytic differentiation correspond to highly proliferative astrocyte progenitors in maturation arrest at earlier stages of differentiation. The purpose of the current study was to examine whether cells in short term culture derived from a medulloblastoma tumor specimen with astrocytic differentiation were of the astrocytic lineage and if so, whether they represented proliferative astrocyte progenitors which would morphologically and antigenically mature in response to differentiating agents. A portion of tumor specimen from a 10-month-old child with recurrent posterior fossa medulloblastoma (RB2) that contained GFAP focally in tumor cells was grown in monolayer culture. We examined cellular structure and appearance of western immunoblotting and immunohistochemical studies for GFAP and neuron-specific enolase (NSE) in RB2 cells before and after treatment with retinoic acid (RA) and dibutyryl cyclic AMP (dBcAMP). RB2 in culture consisted of small polygonal cells (93%), large flat cells (3%), and polygonal cells with cytoplasmic processes (4%). In untreated RB2, 30% of cells expressed GFAP and staining for NSE was negative. RA treatment produced flattened cells and decreased GFAP. DBcAMP reversibly induced fine cytoplasmic processes containing GFAP in 85% of cells within 96 h. Neither agent induced NSE. The results suggest that cultured cells which are derived from a medulloblastoma with astrocytic differentiation do not spontaneously differentiate but that treatment with dBcAMP suppresses proliferation, enhances cytoplasmic process formation and increases cytoplasmic GFAP. Cells in culture and in medulloblastoma tumor specimens which do not contain GFAP may represent astrocyte progenitors in maturation arrest.