Glia maturation factor in bovine brain: partial purification and physicochemical characterization

Differential gene expression of multiple chondroitin sulfate modification enzymes among neural stem cells, neurons and astrocytes

Chondroitin sulfate/dermatan sulfate (CS/DS) polysaccharides have been reported to play a crucial role in the proliferation and maintenance of neural stem cells (NSCs). However, little is known about the structural changes and functional role of CS/DS chains in the differentiation of NSCs. Western blots of NSCs, neurons and astrocytes in culture, with three CS-polysaccharide antibodies of different specificities, revealed marked differences in CS structure among the three cell types. To confirm this finding, we measured gene expression levels of CS sulfotransferases and C5-epimerase in these cell types, as these are responsible for producing the high structural diversity of CS/DS. Expressions of chondroitin 4-O-sulfotransferase, chondroitin 6-O-sulfotransferase, and N-acetylgalactosamine 4-sulfate 6-O-sulfotransferase mRNAs were low in cultures of differentiated neural cells, such as neurons and astrocytes, in comparison to NSCs. In contrast, expressions of uronyl 2-O-sulfotransferase and C5-epimerase mRNAs were higher in the differentiated neural cells than NSCs. Thus, we first provide evidence to support the hypothesis that CS/DS undergoes structural changes during NSC differentiation. The structural changes in CS/DS may be implicated in the regulation of NSC differentiation through interactions with growth/neurotrophic factors and cytokines.

Activin increases the number of synaptic contacts and the length of dendritic spine necks by modulating spinal actin dynamics

Long-lasting modifications in synaptic transmission depend on de novo gene expression in neurons. The expression of activin, a member of the transforming growth factor beta (TGF-beta) superfamily, is upregulated during hippocampal long-term potentiation (LTP). Here, we show that activin increased the average number of presynaptic contacts on dendritic spines by increasing the population of spines that were contacted by multiple presynaptic terminals in cultured neurons. Activin also induced spine lengthening, primarily by elongating the neck, resulting in longer mushroom-shaped spines. The number of spines and spine head size were not significantly affected by activin treatment. The effects of activin on spinal filamentous actin (F-actin) morphology were independent of protein and RNA synthesis. Inhibition of cytoskeletal actin dynamics or of the mitogen-activated protein (MAP) kinase pathway blocked not only the activin-induced increase in the number of terminals contacting a spine but also the activin-induced lengthening of spines. These results strongly suggest that activin increases the number of synaptic contacts by modulating actin dynamics in spines, a process that might contribute to the establishment of late-phase LTP.

Human neuroblastoma growth inhibitory factor (h-NGIF), derived from human astrocytoma conditioned medium, has neurotrophic properties

Investigations on the general characteristics of human astrocytoma cell line NAC-1 revealed neuroblastoma growth inhibitory activity in conditioned medium. Neuroblastoma growth inhibitory factor (NGIF) was partially purified by Econo Q, Econo CM, and Superose 12 column chromatography. The protein is weakly basic with an estimated M(r) of 120,000, possibly having an M(r) 60,000 dimeric structure. NGIF inhibits the growth of human neuroblastoma cell lines but has no effect on morphology nor does it produce any change in the growth of human glioblastoma cell lines. Interestingly, NGIF appears to promote survival and neurite outgrowth of embryonal rat cortical neurons. These neurotrophic properties suggest a role for NGIF in the development of the nervous system.

Neurotropism of mouse-adapted haemagglutinating encephalomyelitis virus

The propagation of a mouse-adapted strain (67N) of haemagglutinating encephalomyelitis virus in infected mice and murine cells was examined by viral re-isolation and immunostaining. Viral propagation was strictly limited to the neurons and to an established line of neuroblastoma cells in in-vivo and in-vitro experiments. These results provide adequate evidence that this virus is neurotropic.

A novel glial growth inhibitory factor, gliostatin, derived from neurofibroma

Neurofibroma tissue was investigated for the presence of glial growth modulators that would suppress the proliferation of glial cells. A novel endogenous polypeptide inhibitor of proliferation and DNA synthesis in glial cells, gliostatin, was purified from the extracts of neurofibroma by a procedure comprising dye and anion-exchange column chromatography, and HPLC. A monoclonal antibody raised against partially purified gliostatin showed no cross-reactivity with known cytokines, but adsorbed the growth inhibitory activity of gliostatin and immunochemically visualized the putative gliostatin bands on western blot analyses. Although the product showed an apparent M(r) of 100,000 accompanied by an inhibitory activity on gel filtration column chromatography, it migrated at a lower apparent M(r) of 50,000 under the reducing conditions on western blotting, indicating that a homodimeric structure of native gliostatin consisted of 50-kDa subcomponents. Gliostatin was a potent growth inhibitor acting at nanomolar concentrations against all glial tumor cells and glia maturation factor-stimulated astroblasts, but not neuronal cells.

Brain interstitial fluid collected through implanted tissue cages

The physicochemical properties of the whole-brain interstitial fluid (IF) are unknown. A volume of whole-brain IF sufficient for analysis was obtained through a small, hollow, multiperforated polypropylene sphere implanted for 4-5 weeks into the dog brain parenchyma. The main physicochemical properties of the whole-brain IF were characterized, in comparison with the physicochemical properties of cerebrospinal fluid and blood/serum.

Traumatic brain injuries: structural changes

A host of complications and consequences may follow a contusion or other brain injury of any sort. An appreciation of the temporal evolution of the contusion from a microscopic standpoint is useful to a full understanding of the process by which physical force damages the brain and how the brain reacts to this damage. Some disruptions of the blood brain barrier quite early will result in extracellular edema. The microscopic appearance of an edematous area is usually spongy with numerous vacuoles. The neuropil may appear bubbly, and glial cells may be swollen. If edema has been long standing, the vacuoles may be larger and in fact a small cyst may appear in the white matter. If focal cerebral edema is not present for long periods of time and the underlying cause has been corrected, residual fluid and electrolytes are eventually removed, restoring the neuropil to a normal state, leaving no sign of its presence. However, in longer standing lesions, myelin pallor and some reactive gliosis may remain indefinitely. Neurons may show swelling very early and for a short period of time, which gives way to shrinkage, eosinophilia, and nuclear pyknosis. These changes may be observed at the periphery of lesions for as long as 5 or 6 months after the initial event. Before dissolution, nuclear pyknosis may remain in the tissue for many days and possibly longer, and may even become mineralized in situ (ferruginated neurons) to remain for years. In a traumatic lesion, swollen and ballooned axons may be found in and around the contusion but also at great distances from it (diffuse axonal injury). Axonal ballooning may be observed between 24 and 48 h postinjury and may persist wherever found for many years. Selective axonal calcification has been observed in humans as well as in experimental trauma. At about 7-10 days postinjury increased numbers of astroglia probably are present. Over the ensuing weeks and months, and probably years, astrocytes increase in number and in fibrillary appearance, eventually resulting in a glial scar in and about the injured area. It is thought that this reactive gliosis results in restoration of the blood-brain barrier in the damaged area.

Astrocytic reaction predominance in chronic encephalitis of Junin virus-infected rats

Junin virus antigen distribution and astrocytic reaction to prolonged infection were characterized in rat brain by the PAP technique. During the acute stage of neurologic disease following intracerebral inoculation, Junin antigen was detected in 100% of animals, strongly in most neurons but also to a much lesser degree in scattered astrocytes, dropping to 20% of rats at 540 days postinfection. Initially labeled in all brain areas, viral antigen gradually disappeared from hippocampus but persisted irregularly in cerebral cortex, basal ganglia, Purkinje cells, pons, and medulla oblongata. Such a pattern suggests that specific neuronal subpopulations, in spite of apparently unaltered cell morphology, may persistently harbor the virus, leading on occasion to a delayed neurologic syndrome. During both the acute and chronic stages of disease, a mild inflammatory exudate was observed, characterized by the presence of T and B lymphocytes, as well as macrophages and unidentified round cells. GFAP immunostaining showed increased astrocytic reaction as infection lapsed into chronicity. Corpus callosum, hippocampus, and cerebellum exhibited the sharpest reactive astrocytosis, followed by basal ganglia, pons, and medulla oblongata, whereas in cerebral cortex it was considerably less. Astrocyte activation, which failed to correlate with viral antigen presence in neurons, seems to result from a generalized condition, possibly including diffusible brain factors triggered by viral infection. Such widespread astroglial reaction may thus contribute to the outcome of the late neurologic syndrome.

Enhancement of both intracellular uptake and antitumor action of cisplatinum on human neuroblastoma cells by encapsulation in liposomes

Phospholipid vesicles (phosphatidylcholine:phosphatidylserine:cholesterol = 6:2:3 in molar ratio) with a small unilamellar structure were used as drug carriers for introducing cis-diamminedichloroplatinum (CDDP) into human neuroblastoma cells, IMR-32, GOTO, Nagai, and TGW. DNA synthesis of IMR-32 cells among the human neuroblastoma cell lines was inhibited most strongly by CDDP-liposomes. CDDP-liposomes dose-dependently inhibited the DNA synthesis of IMR-32 in a similar fashion to that observed with free CDDP, but the drug concentration required to induce 50% inhibition of DNA synthesis for CDDP-liposomes (IC50: 0.7 micrograms CDDP/ml) was 1/3 of the IC50 for free CDDP (2.0 micrograms CDDP/ml). In support of the marked growth-inhibitory action of CDDP-liposomes, the intracellular incorporation rate of CDDP-liposomes was 3-fold higher when liposomes were used as carriers than when free CDDP was directly applied. CDDP-liposomes showed a stronger growth inhibition on IMR-32 cells at a high cell density than at a low density in culture. CDDP-liposomes were rapidly incorporated by IMR-32 cells within 5 min, resulting in the inhibition of DNA synthesis to 40% of the control. Swiss albino mouse 3T3 cells were less inhibited by CDDP-liposomes than by free CDDP, suggesting that encapsulation of CDDP in liposomes decreases cytotoxicity to normal cells.

Induction of astroglial growth inhibition and differentiation by sialosyl cholesterol

Normal rat astroblasts in culture were exposed to 11 sialosyl or cholesterol derivatives at concentrations lower than 20 microM. Synthesized sialosyl cholesterols (alpha- and beta-D-N-acetyl neuraminyl cholesterols) and cholesterol sulfate showed a marked growth inhibitory action. Sialosyl cholesterol uniquely evoked an astroglia-like stellation resembling that induced by glia maturation factor (GMF) as well as a suppression of GMF-induced mitogenesis of astroblasts. The minimal incubation period of sialosyl cholesterol for the initiation of growth inhibition was as short as one hour. The inhibitory effect retained an irreversibility even after removal of the drug. Cytosolic protein with 58 kDa Mr in size was specifically phosphorylated by sialosyl cholesterol through a certain protein kinase dependent on neither Ca2+ nor cyclic AMP. The competition experiment of sialosyl cholesterol action revealed that sialosyl and cholesterol moieties were indispensable for the phenomena. These results most likely imply that sialosyl cholesterol alters the membrane microenvironment to affect the affinity of growth factor receptor, protein kinase activity, and/or cytoskeletal anchorages.

Cyclic nucleotides and the activity of glia maturation factor in the hypoplastic cerebellum of developing jaundiced Gunn rats

Developmental changes of cyclic nucleotides were studied in the hypoplastic cerebellum of jaundiced Gunn rats over the period of postnatal days 8 to 30. The mitogenic activity of glia maturation factor was also measured at day 15. In jaundiced homozygotes (jj), the amount of cyclic GMP on a protein basis was not significantly different from that in control heterozygotes (j+) at either day 8 or 15, but at day 30 it was reduced to about 19% of the control. On the other hand, a lowered nucleotide level on a wet weight basis in jj rats was already statistically significant at day 15. In contrast to cyclic GMP, the rates of increase of cyclic AMP on a wet weight basis were almost the same in the two groups of rats, but the nucleotide levels on a protein basis at days 15 and 30 were a little, but significantly, higher in jj rats than in j+ rats. The activity of glia maturation factor in jj rats was found to be 1.5-3 times as high as that in j+ rats. Possible implications of the present results are discussed.

Sialosyl cholesterol induces morphological and biochemical differentiations of glioblasts without intracellular cyclic AMP level rise

Synthesized sialosyl cholesterols, alpha- and beta-D-N-acetylneuraminyl cholesterols (alpha-SC and beta-SC), induced the morphological conversion of normal rat glioblasts from a flat epithelioid morphology to an astrocytic process-bearing (stellate) morphology resembling the conversion by glia maturation factor (GMF). The stellogenic effects were rapid and detectable within 1 h after drug stimulation, and irrelevant to the intracellular cyclic adenosine monophosphate (cAMP) levels. The morphological alteration was ascertained by the fluorescence-visualization of cytoskeletons: alpha-SC elicited the reorganization of GFA protein network to the formation of bundles, the destruction of stress fiber, and the redistribution as plasmalemmal constituents. alpha-SC also evoked biological differentiations represented by an elevation of glial marker proteins, S-100 protein and GFA protein. The results provide a possibility that SC incorporated into plasma membrane may cause morphologically and biochemically astrocyte-like differentiations of glioblast through the alteration of membrane characteristics, the cytoskeletal anchorages to the membrane, the affinity of receptors, and/or the postreceptor responses distinct from cAMP-production system.

Gradient isolation of glial cells: evidence that flat epithelial cells are astroglial cell precursors

Discontinuous gradients of metrizamide were used to separate the cell components of monolayers of primary cultures of embryonic rat brains. These primary cell cultures were of two types: long-term cultures (more than a year) of embryonic rat brain, which contained several glial cell types, and monolayers of cell cultures (several weeks old), which contained a complex population of cells, including neuronal elements. The gradient separation produces fractions of pure flat epithelial cells that are able to survive and proliferate. After a few days, all flat epithelial cells become confluent and show a positive reaction to glial fibrillary acidic protein (GFAP); this indicates that these cells astroglial precursor cells. Following their maintenance in vitro for several months, all cultures give rise to a pure population of astrocytes identified not only by their characteristic morphology, but also by their content of GFAP. It is proposed that the differentiation controls are dependent on cell interactions that are influenced by the composition of the cell population and/or the molecular growth and differentiation factors released by these cells into the medium.

Functional dissociation of dual activities of glia maturation factor: inhibition of glial proliferation and preservation of differentiation by glial growth inhibitory factor

Glial growth inhibitory factor (GGIF), derived from the culture medium of mouse neuroblastoma cell (NAs-1), lowered the DNA synthesis and cell multiplication of normal rat glioblasts induced by glia maturation factor (GMF). The inhibitory action of GGIF depended on the concentration of GMF in the culture medium, and was of an uncompetitive type on kinetic analysis. GGIF showed the inhibitory activity at a late stage of the G1 phase or early stage of the S phase. The factor, however, failed to inhibit the differentiation-promoting activity of GMF. The data strongly suggest that the dual activities of GMF, the promotion of glial proliferation and differentiation, may be elicited by mutually independent intracellular processes.

Environmental changes induced by growth-associated triggering factors in injured optic nerve of adult rabbit

Central nervous system (CNS) neurons of mammals regenerate poorly after axonal injury. However, if an injured CNS neuron (rabbit optic nerve) is supplied with appropriate soluble substances ("growth-associated triggering factors") derived from medium conditioned by regenerating fish optic nerve or newborn rabbit optic nerve, it can express regeneration-associated characteristics. Such characteristics include a general increase in protein synthesis, changes in synthesis of specific polypeptides, and sprouting of nerve fibers in culture. The present study of rabbit optic nerves demonstrates that such active substances affect the neuronal environment (i.e., the non-neuronal cells), thereby perhaps causing a shift in the environment from an inhibitory to a regenerative supportive one. Apparently, such an environment is spontaneously achieved in injured CNS nerves of lower vertebrates (e.g., fish optic nerves), which are regenerable. Treatment of injured rabbit optic nerve with soluble factors from medium conditioned by regenerating carp optic nerve resulted in a selective increase in proliferation ([3H]thymidine incorporation) of perineural cells and the appearance of a 12-kDa polypeptide in a homogenate derived from the nerve and its associated cells. This polypeptide may be related to growth, since it comigrates in NaDodSO4/polyacrylamide gel electrophoresis with a 12-kDa polypeptide that is continuously present in a regenerative system. In addition, there were injury-induced changes in the polypeptides of the nerve that were independent of treatment with conditioned medium and were correlated with nerve maturation. The most prominent changes of this type were in 18-kDa and 25-kDa polypeptides whose levels were reduced after injury and were found to be correlated with the nerve maturation (myelination) state.

Molecular and cellular aspects of nerve regeneration

Injury of an axon leads to at least four independent events, summarized in Figure 1: first, deprivation of the nerve cell body from target-derived or mediated substances, which leads to a derepressed or a permissive state; second, disruption of anterograde transport, with a resultant accumulation of anterogradely transported molecules; third, environmental response with possible consequent changes in constituents of the extracellular matrix and substances secreted from the surrounding cells; and fourth, appearance of growth inhibitors and modified protease activity. It seems that the first three of these events are obligatory, but not sufficient, i.e., they lead to a growth state only if the cell body is able to respond to the injury-induced signals from the environment (a and b). The regenerative state is characterized by alterations in protein synthesis and axonal transport and by sprouting activity. The subsequent elongation of the growing fibers depends on a continuous supply of appropriate growth factors. These factors are presumably anchored to the appropriate extracellular matrix that serves as a substratum for elongating fibers. It should be mentioned that the proliferating nonneuronal cells have a conducive effect on regeneration by forming a scaffold for the growing fibers. Accordingly, the lack of regeneration may stem from a deficiency in the ability of glial cells to provide the appropriate soluble components or from insufficient formation of extracellular matrix. In this respect, one may consider regeneration of an injured axon as a process which involves regeneration of both the nonneuronal cells and the supported axons. The regeneration of glial cells may fulfill the rules which are applied to regeneration of any other proliferating tissue. Furthermore, the processes of regeneration in the axon and the glial cells are mutually dependent. Perhaps the triggering factors provided by the nonneuronal cells affect the nonneuronal cells themselves by modulating their postlesion gliosis and thereby inducing their appropriate activation. In such a case, regeneration of nonneuronal cells may resemble an autocrine type of regulation that exists also during ontogeny. The growth regulation is shifted back to the paracrine type upon neuronal maturation or cessation of axonal growth. When the elongating fibers reach the vicinity of the target organ, they are under the influence of the target-derived factors, which guide the fibers and eventually cease their elongation.

Possible association of platelet-derived growth factor (PDGF) with the appearance of reactive astrocytes following brain injury in situ

The association of platelet-derived growth factor (PDGF) with the appearance of reactive astrocytes following injury was investigated by using a specific antagonist of PDGF, Trapidil. The cerebral cortex of 4-week-old male rats was unilaterally injured with a 22-gauge needle. Immunohistochemical staining with antiserum to glial fibrillary acidic protein revealed that reactive astrocytes had increased in number around the wound by 2 days following the injury and had spread to the ipsilateral areas distant from the wound by 3 days. The appearance of reactive astrocytes in areas distant from the wound was dramatically suppressed by the administration of Trapidil. This finding indicates that PDGF might play a role in gliosis following injury.

A neurotrophic factor derived from goldfish brain: characterization and purification

Previous studies carried out in our laboratory have demonstrated that goldfish brain contains substances that promote neurite extension from regenerating retinae in culture. Fractionation of the brain extract by molecular sieving chromatography revealed the presence of several molecular species, including two peaks that have neurotrophic activity, representing low-molecular-weight substances. One peak was eluted (P-a) with an apparent molecular weight of about 13 kDa and was designated substratum neurite extension factor (SNEF) because it retained its neurotrophic activity when adsorbed onto the substratum. This recovered Sephadex fraction (P-a) when applied in vivo intraocularly caused an earlier capacity of the corresponding retinae to sprout in vitro. Thus, at 3 and 5 days after injury the neuritic growth indices from the factor-treated retinae were of 0.9 +/- 0.2 and 2.8 +/- 0.5, respectively, as compared with indices of 0.3 +/- 0.1 and 0.9 +/- 0.2, respectively, in retinae of injured but nontreated nerves. The factor was further purified by two steps of HPLC (ion exchange followed by reversed phase). The results showed that it is an acidic glycoprotein with an apparent molecular weight of 10 kDa.

Autocrine regulation of glial proliferation and differentiation: the induction of cytodifferentiation of postmitotic normal glioblast by growth-promoting factor from astrocytoma cell

A growth-promoting factor (GPF) from astrocytoma cells (GA-1) cultured in serum-free medium (N2) exerted on normal glioblasts proliferative and differentiation-promoting effects, which have been observed in glia maturation factor (GMF) stimulation. The serum-free conditioned media of GA-1 provoked DNA synthesis of glioblasts, and subsequently elicited a morphological differentiation characterized by the extrusion of processes as well as biochemical changes including an increased cellular level of glia fibrillary acidic protein (GFA protein), S-100 protein, and alpha-enolase. The transforming growth factor activity was also found in the media. Partially purified GPF had a molecular weight range of 7100-10,000 Mr and acidic isoelectric point (pH 4.6), and showed a susceptibility to heat treatment and denaturation at low and high pHs. The present results and the findings accumulated from our previous studies on gliotrophic growth factors provide a general concept of the growth and differentiation regulations of normal or neoplastic glial cells by growth factors through autocrine systems.

Septal deafferentation enhances the neurotrophic effects of rat hippocampus on cultured neural cells from the central nervous system

Neurotrophic effects (NTEs) of various brain regions of 4-week-old rats were examined in primary culture of rat embryonic cerebral hemispheres. Extracts of the hippocampus, brainstem and septal nucleus highly enhanced the survivability of neuronal cells and the division of non-neuronal cells by 9 days. The septohippocampal tract (fimbria fornix) was cut and the effect on the neurotrophic activity in the hippocampus was examined. The NTEs of hippocampal extracts remained unchanged 3 days after septal deafferentation, was significantly increased by 7 days, peaked at 14 days and returned to the basal level by 21 days.

Stimulative effect of glia maturation factor and acetylcholine on active amino acid uptake and Ca2+,Mg2+-ATPase activity in nodose ganglia excised from adult rats

During aerobic incubation at 37 degrees C, active uptake of labeled non-metabolizable alpha-aminoisobutyric acid (AIB) into isolated nodose ganglia (NG) excised from adult rats was accelerated to nearly twice that of the control, by the addition of glia maturation factor (GMF, 5 micrograms/ml) in a dose-dependent manner. A similar but moderate stimulative effect on ganglionic AIB uptake was caused by the addition of acetylcholine (ACh, 1 mM) plus eserine (0.1 mM). This effect, however, was not antagonized by nicotinic (hexamethonium, C6, 0.1 mM) or muscarinic (atropine, 0.1 mM) blockers. The GMF-induced amino acid uptake seemed to be inhibited by further addition of ACh. On the other hand, ganglionic Ca2+,Mg2+-ATPase activity was greatly stimulated by either GMF or ACh. These results suggest that the increase in AIB uptake induced by GMF or ACh is possibly linked to Ca2+,Mg2+-ATPase activity in NG cell membranes.

Primary glial cells and brain fibroblasts: interactions in culture

Primary glial-enriched cultures were prepared from newborn mouse cerebral hemispheres. The cultures were grown in Dulbecco's Modified Eagle Medium in which L-valine was substituted with D-valine; this medium selectively inhibits the growth of fibroblasts. Using glutamine synthetase and glial fibrillary acidic protein as immunocytochemical markers, cultures in D-valine medium were characterized as being over 80% astrocytic. However, these cultures exhibited a suppressed growth rate and lagged behind in their differentiation as assessed biochemically using DNA content and glutamine synthetase activity as markers for growth and differentiation. Growth was restored when D-valine cultures were grown in medium containing conditioned medium derived from brain fibroblast cultures when grown on matrix or killed substrata derived from brain fibroblast cultures. This in vitro approach offers the possibility of purifying factors and developing immunological probes to investigate the possible role of brain fibroblasts in influencing glial cell function.

Astrocyte growth enhanced by culture supernatant of a cloned rat thymic myoid cell

A conditioned medium (CM) from a cloned rat thymic myoid cell (IT-45R92) was used to investigate a possible relationship between the thymus and brain. CM stimulated the DNA synthesis of the cultured perinatal rat brain cells and spleen myelo-lymphoid cells but not that of the other types of cells including dorsal root ganglia, spinal cord, heart muscle, skeletal muscle, kidney, liver, skin, and thymic fibroblasts. CM appeared to stimulate glioblasts to differentiate into mature astrocytes that have a characteristic intracellular fibrous structure and a glial fibrillary acidic protein. These results indicated that thymic myoid cells release (a) 'cytokine(s)' for the astrocytes and myelo-lymphoid cells, similar to a 'lymphokine' (glia cell stimulating factor, GSF) produced by murine and human lymphocytes stimulated with mitogens.

Acquisition of glial fibrillary acidic protein-containing fibres by astroglial cells in primary culture is orchestrated by a communicable factor

In a previous study we discovered that primary cultures initiated from the whole brain of 21-day foetal rats contained astroblasts that concertedly acquired glial fibrillary acidic protein (GFAP) fibres. The mechanism of this burst of cytoskeletal differentiation could not be investigated in these cultures because it occurred too quickly (completed within 2 h). We report that cultures initiated from the region of the third ventricle display an extended burst of GFAP acquisition whose rate could be markedly reduced by medium changing. Temporary medium deprivation or the addition of cytosine arabinoside to the growth medium had no effect. Our findings suggest that an as yet uncharacterised communicable factor is involved in the orchestration of cytoskeletal differentiation in culture. This factor may be responsible for synchronising the appearance of GFAP-positive cells in the periventricular regions of the foetal brain.

Chemotaxis of rat brain astrocytes to platelet derived growth factor

Using a purified population of rat brain astrocytes prepared from neonatal cortex, we investigated the chemotaxis of astroglia to several well characterized growth factors. Chemotactic activity for astrocytes was found for the platelet derived growth factor with a half maximal response occurring at 0.5 ng/ml as compared with a value of 2-3 ng/ml obtained for NIH/3T3 fibroblasts in control experiments. Other growth factors including epidermal growth factor, fibroblast growth factor and insulin were inactive as chemoattractants. Affinity purified fibronectin was also found to stimulate the migration of astroglia, with half maximal doses of approximately 1 microgram/ml relative to maximal responses to platelet derived growth factor.

The control of glial populations in brain: changes in astrocyte mitogenic and morphogenic factors in response to injury

Injury to rat brain induces a 3-10-fold increase in the activity of factors capable of stimulating astrocyte DNA synthesis and cell division in vitro. Maximum mitogenic activity was reached 10-15 days post-lesion in both the tissue surrounding the wound and in the gelfoam filling the wound cavity. Factors capable of transforming the astrocyte morphology from polygonal-flat to fibrous-like (morphogens) could also be observed in brain tissue and showed increased activity beginning at 10 days postlesion. On the other hand, morphogenic activity was very low or absent in gelfoam extracts until 15 days postlesion. Both mitogenic and morphogenic factors were nondiffusible and were partly temperature and trypsin sensitive, i.e. they had the properties of protein-like substances, but seemed different from both epidermal and fibroblast growth factors. As judged by their filtration behavior on Amicon membranes, the molecular weight of mitogens and morphogens ranged from lower than 30,000 to greater than 100,000. Inhibitors of both mitogenic and morphogenic activities with molecular weight lower than 30,000 seemed to be also present in the brain extracts. The factors described here can account for the processes of astrocytosis and astrogliosis observed in vivo in response to CNS injury.

Purification of two astroglial growth factors from bovine brain

The astroglial growth factor (AGF), which induces a characteristic morphological change in cultured rat astroglial cells and stimulates their proliferation, was purified to homogeneity from bovine brain. Two different methods were used, the second one including heparin-Sepharose affinity chromatography. AGF is actually composed of two factors, AGF1 and AGF2, which both modify the morphology and stimulate the proliferation of the astroglial cells. Several data suggest that the AGFs are similar or possibly identical to the fibroblast growth factors (FGFs) isolated from brain [(1984) Proc. Natl. Acad. Sci. USA 81, 357-361; and 6963-6967]. A specific antiserum against AGFs was raised in mouse.

Observations on cell growth and regulation of glutamine synthetase by dexamethasone in primary cultures of forebrain and cerebellar astrocytes

Cell growth, development of glutamine synthetase and its regulation by glucocorticoids, were studied in primary cultures of two types of astrocytes derived from rat brain, one from newborn forebrain and another from either newborn or 8-day-old cerebellum. Cell number per dish increased linearly following an initial decrease due to removal of non-astrocytic cells, and after the second week reached a stationary phase in both types of cultures at more or less the same time, although the cell number in cerebellar cultures was about 35% lower than in forebrain cultures of the same age. At all ages, irrespective of cell density, the cerebellar astrocytes were larger in size than the forebrain astroglial cells. The developmental curves for glutamine synthetase activity were similar in vitro and in vivo; however, the increase in enzyme activity in vitro was significantly greater than in vivo and this difference was more marked in forebrain than in cerebellar cultures. Throughout the period studied the specific activity of glutamine synthetase was significantly higher in forebrain astrocytes than in cerebellar astroglial cells. Treatment with dexamethasone caused a marked increase in the specific activity of glutamine synthetase. However, in agreement with our previous in vivo findings, the steroid induction in forebrain astrocytes was significantly less than that in cerebellar astrocytes. In culture, both types of astrocytes remain responsive to the hormone for longer than in vivo. The differences in the biochemical properties of the forebrain and cerebellar astrocytes seem to be intrinsic, and not related to the cell density or to the purity of the cultures.

Mitogenic growth factors and nerve dependence of limb regeneration

Regeneration of the amphibian limb after amputation depends on division of blastemal cells, the progenitor cells of the regenerate. This division is controlled, at least in the early stages of regeneration, by the nerve supply to the blastema. A monoclonal antibody to newt blastema cells has provided evidence that Schwann cells and muscle fibers contribute to the blastema, and identifies blastemal cells whose division is persistently dependent on the nerve. Glial growth factor, a molecule identified by its action on rat Schwann cells, is present in the newt blastema and is lost on denervation.

Glia maturation factor promotes proliferation and morphologic expression of rat Schwann cells

Glia maturation factor (GMF) is an acidic protein with a molecular weight of about 20,000 daltons, found in the adult brain of many species. Previously GMF was observed to stimulate the proliferation and subsequent maturation of rat astroblasts in culture. We investigated the effects of GMF on Schwann cells. Schwann cells were dissociated from rat sciatic nerve and purified by means of antimitotic agents and by selective immunoadsorption of contaminating fibroblasts. Cultured Schwann cells after 3 passages assumed a flat polygonal shape. Exposure of the cells to GMF converted the cells to the elongated, spindle morphology typical of Schwann cells. GMF also stimulated a 7-fold increase in DNA synthesis when compared with control cultures grown in F10 medium containing 5% fetal calf serum. The mitogenic activity of GMF was still detectable at 5 ng protein/ml medium. The maximal effect on DNA synthesis occurred 72 h after the initial exposure to GMF. Although the cells were positive for the Schwann cell marker Ran-1, GMF failed to induce the production of myelin-associated glycolipids (galactocerebroside) and proteins (Po) nor did it induce the astrocytic marker glial fibrillary acidic protein (GFAP). The effects of GMF on Schwann cells extend its biological role beyond the central nervous system.

An improved procedure for the isolation of glia maturation factor

A procedure for the bulk isolation of glia maturation factor (GMF) in high yield and high purity from bovine brains is outlined. The method involves extraction by homogenization and centrifugation, followed by ammonium sulfate precipitation and column chromatography with diethylaminoethyl (DEAE) Sephacel, Sephadex G-75, and hydroxylapatite. The method results in a 10,000-fold purification, a purity exceeding that of previously published procedures, and enables us to handle as much as 2.8 kg brain tissue or eight brains/week. The ability to mass-produce GMF with this method greatly facilitates its biological studies, further purification, and chemical characterization. The isolated GMF shows a molecular weight of 13,000 on Bio-gel P-30 column and an isoelectric point of about 5.4 on isoelectric focusing. The isolated GMF is heat labile and susceptible to papain and ficin but relatively resistant to trypsin, neuraminidase, and endoglycosidase.

The absence of differentiation-promoting response of astroglioma cells to glia maturation factor

The effects of glia maturation factor (GMF) on cell proliferation and differentiation were investigated with 3 astroglioma cells (GE-12, C6, and GA-1), Schwannoma-like cells (354A), and mixed glioma cells (LRM-55). In the exponentially growing phase the growth rates of all glioma cells were enhanced by GMF regardless of the presence or absence of serum, but the factor failed to make the saturation density surpass the control level observed in the medium without GMF even in the chemically defined medium (N2 medium). GMF markedly lowered the saturation density of Schwannoma-like cells in N2 medium. Although GMF increased the intracellular content of S-100 protein 10-fold and 2',3'-cyclic nucleotide phosphohydrolase activity 1.5-fold in Schwannoma-like cells, GMF conversely decreased the S-100 contents and glycerol phosphate dehydrogenase activity in astroglioma cells. All the astroglioma cells secreted into the culture medium large quantities of a growth-promoting factor(s) which had similar chemical properties to those of GMF and stimulated the proliferation of normal glioblasts; but Schwannoma-like cells did not, although they produced a small amount of such a factor(s). These findings imply that astroglioma cells are deprived of the differentiation-promoting response to GMF while Schwannoma-like cells still preserve the response in addition to the proliferative response to GMF.

Cerebellar astroglial cells in primary culture: expression of different morphological appearances and different ability to take up [3H]D-aspartate and [3H]GABA

In non-neuronal cultures of cells dissociated from postnatal rat cerebellum astrocytes, identified by the presence of the marker protein glial fibrillary acidic protein (GFAP), displayed two distinct morphological forms. One class was stellate in shape with radially distributed fine processes, while the other class was more varied in shape being polygonal or elongate. [3H]thymidine incorporation experiments revealed that cells of both morphologies were able to incorporate this nucleoside, suggesting the capacity for both cell types to undergo cell division. An autoradiographic study of the uptake of [3H]D-aspartate and [3H]GABA revealed that whilst the two classes of astrocytes took up the aspartate to apparently the same extent, only the stellate cells were found to be heavily labeled following incubation with [3H]GABA. A study of the cultures over a 12-day period showed that there was a disappearance of the stellate astrocytes. The time of disappearance was found to be dependent upon the initial plating density; the stellate morphology was apparent longer in lower density cultures. Time lapse studies suggested that one of the reasons for the disappearance of the stellate cells might be that in fact they underwent a change in shape following certain cell-cell interactions, but cell death also has to be considered as a further possibility. The relationships between the two classes of astroglial cells in these cultures is not yet clear. The possibilities are that they represent two different types of astrocytes, or just one type at different stages of differentiation, or maybe a combination of the two possibilities.

Differentiation of purified astrocytes in a chemically defined medium

Homogeneous cultures of astrocytes and oligodendrocytes provide an excellent model system for studying the regulation of glial structure and function. Recently, a chemically defined (CD) medium was developed for purified cultures of astrocytes, thus eliminating the requirement for serum and providing a controlled system for the study of astroglial properties. Due to the widespread use of astrocyte cultures and the potential benefits to be gained from using a defined medium, astrocyte cultures raised in CD medium were analyzed for purity as well as morphological and biochemical properties. Purity was assessed using immunocytochemical staining for glial fibrillary acidic protein (GFAP) and fibronectin. Astrocytes raised in CD medium are 95% pure using the expression of GFAP as a criterion. Fewer than 1% of the cells in CD medium stained positive for fibronectin eliminating the possibility that CD medium is selective for meningeal or endothelial cells. Astrocytes raised in CD medium exhibit a striking degree of morphological differentiation as seen in scanning electron micrographs. They also exhibit a high degree of biochemical differentiation illustrated by increases in the specific activity of S-100 protein and the induction of glutamine synthetase by glucocorticoids. A defined medium that supports the proliferation of rat astrocytes and enhances numerous morphological and biochemical properties should greatly facilitate the study of factors controlling glial proliferation and differentiation.

Inhibition of glia maturation factor-induced mitogenesis in glioblasts by calmodulin antagonists

The growth inhibitory activity of calmodulin antagonist, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7) and trifluoperazine (TFP), was analyzed by the use of rat fetal glioblasts stimulated by glia maturation factor (GMF) or rat astrocytoma cells (C6). The inhibitory effect of W-7 on GMF-induced DNA synthesis of glioblasts was apparent when the drug was added within 10 h after the stimulation by GMF (late G1 phase), but was not shown when W-7 was added at 12 h or later (S phase). The intracellular calmodulin content was built up concurrently with the increase in the DNA synthesis in S phase. The half-maximal inhibition (ID50) of GMF-induced DNA synthesis in glioblasts was observed at 16.5 microM of W-7 or 9.0 microM of TFP. ID50 of DNA synthesis in exponentially growing C6 cells was approximately 3 times higher than that in glioblasts: 24 microM of TFP and as high as 40 microM of W-7. ID50 of growth rate of C6 cells was 15 microM of TFP which was comparable to the ID50 dose for the inhibition of DNA synthesis. Both calmodulin antagonists and W-5, a dechlorinated analog of W-7, however, elicited a curious activation of DNA synthesis of glioblasts at low concentrations (lower than 10 microM of W-7 and W-5, or lower than 5 microM of TFP), indicating non-specific effects of calmodulin antagonists on DNA synthesis. These results suggest that calmodulin antagonists have two conflicting effects on DNA synthesis: the stimulation of DNA synthesis at lower concentrations, and inhibition at higher concentrations.

Characterization and partial purification of neuroblastoma growth inhibitory factor from the culture medium of glioblasts

Neuroblastoma growth inhibitory factor (NGIF) exists in the conditioned medium of normal rat glioblasts. When neuroblastoma cells (Neuro2a, NS-20Y, and N1E-115) were cultured in the presence of the factor, the cell growth rates and DNA synthesis were markedly inhibited and the morphological differentiation including neural process formation was induced. However, the factor neither altered the growth rate nor the morphology of non-neuronal cells such as glial cell lines (C6 and 354A) or fibroblast (3T3). The molecular weight of the factor was estimated to be 75,000 Mr by gel filtration with Bio-Gel P-200, and the isoelectric point was 5.8. The factor was devoid of esteropeptidase activity, and susceptible to protease and thermal treatment. The growth inhibitory action of the factor was unrelated to the intracellular contents of cyclic AMP and GMP. The ability of NGIF to suppress preferentially the neural growth suggests its regulatory role in normal brain development.

The induction of glial proliferation by an astrocytoma-derived growth factor resembling glia maturation factor

Glia maturation factor (GMF)-like activity which induces DNA synthesis and morphological differentiation of density-inhibited glioblasts was detected in various glial tumor cells. A polypeptide from C6 cells (rat astrocytoma) which has a molecular weight range of 40,000-50,000 showed the highest activity. This factor also induced DNA synthesis in glioma cells (354A and LRM55) and fibroblast (Swiss 3T3). The activity was susceptible to heat treatment at 70 degrees C for 5 min, or to proteases such as trypsin, chymotrypsin, papain, and subtilisin, but it was devoid of esteropeptidase activity. The isoelectric point was found to be 5.3. Subcellular fractionation localized the activity in cytosomal and microsomal fractions. These properties closely resemble those of GMF from pig and bovine brain.

Effect of glia maturation factor on glial fibrillary acidic protein and fibronectin: a comparative study on glioblasts and fibroblasts using immunofluorescence

Glia maturation factor (GMF) was tested on separate cultures of glioblasts and fibroblasts isolated from the same rate fetuses. The astrocytic marker glial fibrillary acidic (GFA) protein and the fibroblast marker fibronectin were visualized with immunofluorescence. Before GMF stimulation, glioblasts showed only background fluorescence for GFA protein and fibronectin. After GMF stimulation, glioblasts showed intense fluorescence for GFA protein, especially in the processes and end-feet. GMF-stimulated glioblasts also showed a slight increase in intracellular fluorescence for fibronectin, mainly in the perinuclear cytoplasm but never in the process terminals. At no time was extracellular fibronectin observed in glioblast cultures. In contrast, fibroblast cultures formed an extensive extracellular network of fibronectin whether or not they were exposed to GMF. GFA protein never showed up in fibroblast cultures regardless of stimulation by GMF. The results indicate that GMF stimulates an increase of GFA protein in glial processes and confirms the astrocytic nature of these glioblasts.

Interaction of glia maturation factor with the glial cell membrane

Glia maturation factor (GMF) immobilized on agarose beads retained the same mitogenic and morphological transforming activities as free GMF when tested on glioblasts. The exposure of glioblasts to immobilized GMF for 5 min provoked the initiation of DNA synthesis and maximal stimulation was obtained within 30 min. Thiol-reducing agents, such as dithiothreitol and cysteine, increased the biological activity of GMF. These data suggest the presence of a surface receptor to GMF on the glioblasts, while the reduction of the thiol group(s) in GMF promotes the binding to its receptor. Repeated use of immobilized GMF decreased both the mitogenic and the morphological transforming activities. Immobilized GMF used for the third time lost its biological activity. This implies the existence of a certain kind of degradation system such as a proteolytic enzyme located close to the GMF receptor on the glial cell surface.