Effects of gangliosides on the in vitro development of neuroblastoma cells: An ultrastructural study

Neuronal differentiation of human neuroblastoma SH-SY5Y cells by gangliosides

Exogenous administration of gangliosides induced neuronal differentiation with prominent neuritogenesis in human neuroblastoma SH-SY5Y cells in vitro. Neuritogenesis was characterized by ruffling of the cell membrane, the development of lamellipodia and filopodia, and the subsequent elongation and branching of the neurites ultrastructurally. Both axons and neurites were identified. Increased numbers of cell organelles in the neurites and cell bodies were noted. Nonsynaptic contacts and gap junctions formed between neurites or between each neurite and cell body. These findings could be implicated in histopathologic changes from neuroblastoma to ganglioneuroblastoma.

Gangliosides have a bimodal effect on DNA synthesis in U-1242 MG human glioma cells

GM1, GD1a, and GT1b inhibit both PDGF-stimulated and serum-stimulated DNA synthesis in Swiss 3T3 cells and the human glioma cell line U-1242 MG in a dose-dependent manner. The ganglioside inhibitory effect is counteracted in a dose-responsive fashion by serum such that ganglioside-induced inhibition is essentially abolished in 10% serum. Because of the potentially important role that gangliosides play in growth regulation of human gliomas, this phenomenon was studied in detail using U-1242 MG cells. Stimulation of DNA synthesis by low doses of serum in U-1242 MG cells is inhibited in a dose-responsive fashion by ganglioside GM1. However, serum itself counteracts the inhibitory effect of ganglioside in a dose responsive way. Kinetic analyses demonstrate that GM1 competes with some components of serum for sites on U-1242 MG cells (Kb of GM1 = 12.5 microM). On the other hand, GM1, GD1a, and GT1b stimulate DNA synthesis in quiescent U-1242 MG cells in both sparse and confluent conditions, indicating that ganglioside-stimulated DNA synthesis is dependent on the phase of cellular growth rather than cellular density. This growth stimulatory effect of gangliosides is more potent on quiescent, confluent cells than quiescent, sparse cells. These results demonstrate that exogenously added gangliosides can have opposite (bimodal) effects on progression of human glioma cells through the cell cycle depending upon the growth phase of the cells.

Retinoic acid- and staurosporine-induced bidirectional differentiation of human neuroblastoma cell lines

The differentiation pattern of two related human neuroblastoma cell lines, SK-N-SHF and SK-N-SHN, induced by retinoic acid and staurosporine was studied. Immunohistochemical and electron microscopic examination of the cells indicated that the SHF variant could undergo differentiation along a melanocytic route when treated with retinoic acid and to neuronal cells when treated with retionic acid and staurosporine together. Treatment of SHN cells with either or both these agents caused neuronal differentiation. The melanocytic pathway was characterized in part by the flattening of the cells, the appearance of melanocytic antigens and various forms of melanosomes, an increase in tyrosinase activity, and the absence of neuronal marker proteins. The neuronal route was typified by the development of long neuritic processes containing microtubules and numerous neurosecretory granules as well as by immunohistochemical reactions for neural cell adhesion molecule, synaptophysin, and neurofilament proteins. The significance of these results is discussed in terms of the differentiation responses of neuroblastoma cells to chemical agents as well as some of the factors involved in the regulation of phenotype expressions of these cells.

Calcium regulation of neuronal differentiation: the role of calcium in GM1-mediated neuritogenesis

Cultures of mouse Neuro-2a neuroblastoma cells treated with 3-6 mM extracellular Ca2+ exhibited enhanced neurite extension characterized by increased neurite numbers and lengths. The ganglioside GM1 potentiated the effect of extracellular Ca2+ by increasing further the number and length of the neurites formed in response to exogenous Ca2+. Maximal neuritic numbers were achieved with 4 mM Ca2+ while the longest neurites were observed in medium containing 4-6 mM Ca2+. Stimulation of the Ca2+ influx with the ionophore A23187 or the amino acid taurine also enhanced neurite formation and GM1 potentiated these actions. Transmission electron microscopy revealed numerous microtubules and neurofilaments in neurites and microfilaments with the spine-like processes along fine neuritic branches and in the filopodia of growth cones. Neuritic varicosities and growth cones contained a variety of vesicles. All of these structures were increased in the presence of GM1 and were increased further by extracellular Ca2+ or A23187. The ability of GM1 to enhance neuritogenesis was diminished by EGTA or Ruthenium red. Similarly, the effect of GM1 was diminished or abolished by Ca2+ channel blockers such as CdCl2 or LaCl3. X-ray microprobe analysis revealed that GM1 alone enhanced intracellular levels of total ionic and membrane bound Ca2+, perhaps accounting for the increased neuritogenesis observed under conditions in which Ca2+ was manipulated. The present study suggest that the neuritogenic action of GM1 is Ca2+ dependent.

Taurine-induced neuronal differentiation: the influence of calcium and the ganglioside GM1

Taurine-induced differentiation was examined in the murine neuroblastoma Neuro-2a cell line in the presence or absence of the monosialoganglioside GM1 and under conditions in which Ca2+ levels were manipulated. Taurine (4 mM), GM1 (200 micrograms/ml), or taurine with GM1 were applied to culture media that contained either various concentrations of Ca2+ or the Ca2+ ionophore A23187. Taurine or GM1 and taurine with GM1 increased the number of cells emitting neurites above that found for controls. A significant interaction was found between treatment (taurine, GM1 or taurine + GM1) and the manipulations of Ca2+ levels, affecting the number of neurites and producing changes on the neuritic and perikaryal surfaces. Treatment with both taurine and taurine + GM1 and the various concentrations of Ca2+ resulted in a significant increase in neurite elongation. The Ca2+ ionophore A23187 in the presence of taurine or taurine + GM1 caused neurites to grow longer than observed in media containing Ca2+, either in a low concentration (about 125 microM) or at 1-2 mM. Taurine-treated cultures in the presence of extracellular Ca2+ or A23187 were characterized by surfaces with numerous microvillar, spine-like projections. This effect was enhanced with GM1 and was less pronounced in the medium containing low levels of Ca2+. Transmission electron microscopy of the taurine-stimulated neurons revealed an excessive number of clear-core vesicles (40-200 nm in diameter) in perikarya, neurites and neuritic varicosities and growth cones. In addition, numerous aggregates of intermediate filaments were seen. They were most abundant in the taurine + GM1 treated cultures. The taurine + A23187 cultures also exhibited numerous microtubules within the elongated processes. The different neuritic patterns induced by taurine under conditions in which Ca2+ levels were manipulated and/or when cells were exposed to exogenous GM1 suggest that taurine's actions depend in part on Ca2+ flux.

Ganglioside potentiation of NGF-independent trophic agents on sensory ganglia

The ability of gangliosides to potentiate nerve growth factor (NGF)-independent trophic agents was determined by examining the capacity of an exogenous mixture of bovine brain gangliosides (BBG) and the monosialoganglioside GM1 to enhance the neuritogenic action of conditioned media (CM). CM were prepared with cultures of C6 glioma cells, neonatal rat astroglial cells, rat L6 myoblasts and chick embryonic skeletal muscle. Chick embryonic (9 day) dorsal root ganglia (DRG) were cultured on collagen-coated surfaces. The nutrient media with serum added or serum-free N1 medium were supplemented with 50% of one of the CM with or without BBG (150 micrograms/ml) or GM1 (150 micrograms/ml). The neuritogenic responses of DRG 48 h in vitro were evaluated microscopically on the basis of neurite length and number. The neurite promoting action of the factor(s) present in the various CM was potentiated by BBG or GM1 and resulted in increased neurite length and number.

Inhibition of conditioned media-mediated neuritogenesis of sensory ganglia by monoclonal antibodies to GM1 ganglioside

The monosialoganglioside GM1 can potentiate the neuritogenic activity of media conditioned by several cell types: neonatal glia, C6 glioma, embryonic chick heart or skeletal muscle and the rat myogenic line L6. To probe further the neuritogenic activity of conditioned media (CM), 5 mouse monoclonal antibodies (mAbs) against GM1, designated B6, C3, C4h2, D1 and D3 were incorporated individually into nutrient medium (NM) supplemented with CM prior to incubation with sensory ganglia. Nine-day embryonic chick dorsal root ganglia were explanted onto collagen-coated coverslips and incubated at 35 degrees C for 5 h in NM supplemented with 150 micrograms/ml GM1. After washing with NM, the explants were re-fed with NM + CM containing 20% mAb and cultured for an additional 43 h. The resultant neuritogenesis was evaluated microscopically by determining mean neurite number and length of randomly mixed cultures. The 5 antibodies differed in their capacities to inhibit CM-mediated neuritogenesis of these primed target cells. D1 and D3 were most effective in reducing neurite length and number produced by all sources of the CM, while C3 and C4h2 were intermediate in their inhibition of neurite initiation (number). The effect of B6 on neurite initiation and elongation was the least. The ability of these mAbs to inhibit neuritogenic activity of CM derived from both glial and myogenic tissue suggests that gangliosides play a basic role in neuronal development. The differing responses elicited by the individual mAbs may reflect a relationship between the structural complexity of the GM1 molecule and the neuritogenic mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurotrophic effects of GABA in cultures of embryonic chick brain and retina

The present study examined whether GABA treatments would affect the growth and development of embryonic chick cortical and retinal neurons in culture. Incubation of these cells in the presence of 10(-5) M GABA produced several responses. It promoted the proliferation and the differentiation of the neurons studied by affecting the length and branching of the neurites as well as synaptogenesis, as revealed by morphometric measures. At the ultrastructural level, GABA treatment also led to an increased density of neurotubules, rough endoplasmic reticulum (RER), Golgi apparatus, coated vesicles, and other vesicles. These data support the hypothesis that GABA functions as a trophic or regulatory factor of at least certain neuron types.

GM1 ganglioside accelerates neurite outgrowth from primary peripheral and central neurons under selected culture conditions

Neurons from chick embryonic day 8 (E8) ciliary ganglia, E8 and E15 dorsal root ganglia, E8 forebrain, and from rat E18 hippocampus and striatum were cultured as monolayers in the presence or absence of GM1 ganglioside. All of the primary neurons tested were susceptible to an effect of GM1 on their neuritic outgrowth, resulting in a 2- to 3-fold stimulation over control, the recognition of which depended on selecting culture conditions appropriate to each case. The response of E8 ciliary ganglionic neurons required a serum-free medium containing ciliary neuronotrophic factor, and was most pronounced by 8 h at 3 X 10(-8) M GM1. The neuritic response by either E8 or E15 dorsal root ganglionic neurons required serum (greater than or equal to 0.3%), their appropriate neuronotrophic factor, and 100-fold higher GM1 concentrations (presumably reflecting the serum presence), with optimal response times of 12-24 h. For E8 chick forebrain and E18 rat central neurons, GM1 substantially increased the proportion of neurite-bearing neurons in a serum-free pyruvate-containing medium between 7 and 24 h, with an optimal GM1 concentration of 10(-7) M. In all cases, the response to GM1 was a time-related gain, i.e. an earlier onset of neuritic regeneration rather than permanent increase in the number of neurite-bearing neurons.

Ultrastructural features of a human neuroblastoma cell line treated with retinoic acid

This report examines the morphological changes that occur in a line of human neuroblastoma cells (LA-N-5) following treatment with retinoic acid, in vitro. The results demonstrate that retinoic acid induces pronounced differentiation of these cells. Perikarya aggregate into tight clusters and extend long processes that are frequently fasciculated. Growth cones appear at the ends of these processes. Transmission electron microscopy reveals that after 10 days of treatment these long neurites give rise to varicosities which contain clusters of large dense-core vesicles and smaller clear vesicles. After 18 days of treatment the cultures cease to differentiate further. The pattern of neurite outgrowth is very complex by this point and the frequency of growth cones and vesicle-containing varicosities is greatly increased compared with shorter treatments. Most of these varicosities contain a mix of large dense-core vesicles and smaller clear vesicles and in some profiles the clear vesicles are round while in others they are pleomorphic. Despite this increase in the number of vesicle-containing profiles no membrane specializations were seen that resemble mature synapses. The present results demonstrate that retinoic acid can produce morphological changes in these cells in culture, and that these changes closely mimic those of normal differentiating neurons in culture. Considered with previous studies, these findings suggest that this cell line might provide a useful model system for studying neural differentiation.

The functional recovery of damaged brain: the effect of GM1 monosialoganglioside

In the present study the topology and the biochemical mechanisms underlying the functional recovery of the dopaminergic nigrostriatal system is further analyzed. Rats with unilateral hemitransection were treated with 30 mg/kg GM1 monosialoganglioside or with its internal ester derivative for different periods of time. GM1 enhances 3H-dopamine uptake in striatal synaptosomes of the lesioned side, and the enhancement of dopamine uptake precedes that of striatal tyrosine hydroxylase activity. The above biochemical effects are accompanied by changes in behavioral- and electrophysiological-related parameters. The effect of GM1 on striatal tyrosine hydroxylase of the lesioned side disappears when the ascending dopaminergic fibers are extensively lesioned. This suggests that the source of regrowing dopaminergic nerve terminals in the striatum of partially lesioned rats resides mainly in the intact axons remaining in the ipsilateral side. When GM1 is injected into partially lesioned rats kept in darkness, no effect on tyrosine hydroxylase activity is observed. This indicates that the mechanism through which GM1 acts involves a normal light-dark cycle.

Biology of gangliosides: neuritogenic and neuronotrophic properties

Research on the biologic function of gangliosides has accelerated in recent years following discovery of their pronounced effects when administered exogenously to neurons in culture and in vivo. These effects are of two principal types: 1) neuronotrophic, concerned primarily with survival and maintenance of the neuron, and 2) neuritogenic, involving significant increase in the number, length, and/or branching of neuronal processes. Such neurite-promoting activity has been observed in primary cultures of neurons from brain and ganglia as well as transformed lines of neuronal origin. These phenomena may be related to the remarkable growth of aberrant secondary neurites, often accompanied by synaptogenesis, observed in the gangliosidoses. Several in vivo studies have shown exogenously administered gangliosides to aid nervous system repair in both the CNS and PNS, although it is not clear in some cases whether the observed effects should be attributed to neuronotrophic or neuritogenic effects (or both). This article attempts to briefly review the principal developments that have occurred in this area of ganglioside research over the past several years. It also presents for consideration some of the tentative hypotheses put forward concerning mechanism of action.

Dorsal root ganglia and nerve growth factor: a model for understanding the mechanism of GM1 effects on neuronal repair

The experimental strategy of adding monosialoganglioside GM1 to a culture medium of fetal chick dorsal root ganglia (DRG) was utilized as a model system in which to examine the potential role of GM1 in modulation of neuronal cell responsiveness to nerve growth factor (NGF). Data indicate that the addition of GM1 to DRG explants or to DRG dissociated neuronal cells in culture enhances NGF-induced neurite outgrowth, neurite complexity, and neuronal cell survival following NGF withdrawal. The GM1 molecule apparently facilitates the acquisition or maintenance of the NGF-induced specific neuronal properties. Results are consistent with the hypothesis that the presence of GM1 molecules on the neuronal cell surface, either endogenous or following stable insertion of exogenous molecules, plays a prominent role in the modulation of functional neuronal cell behavior in response to varying neuronotrophic signals. This may prove to be relevant for the comprehension of GM1 effects on the facilitation of central nervous system repair processes.

Reduction of cerebral edema with GM1 ganglioside

Administration of exogenous gangliosides has been reported to accelerate neurite outgrowth in vitro, and to enhance peripheral nerve regeneration and central nervous system recovery subsequent to damage. After injury, facilitation of CNS recovery with GM1 ganglioside treatment has been postulated to be due to enhanced neuronal regeneration. Since maximal recovery is achieved when experimental animals are treated before injury with GM1 ganglioside, an alternative or parallel mechanism is that gangliosides are "protecting" the CNS by limiting the extent of damage (ie, cell loss, process degeneration, membrane disruption). This may be due to a reduction in the edema subsequent to injury. In this study, rats were treated for 2 days with 20 mg/kg/day of GM1 ganglioside. On the third day they were subjected to a unilateral lesion (mechanical) of one cerebral hemisphere and given another 20 mg/kg of GM1. On the fourth day brains were removed for analysis of edema resulting from the injury. In treated animals there was a significant reduction in edema as measured either in the entire injured hemisphere (23%) or in the area of injury (33%). No effect was seen outside the damaged area. Since exogenous gangliosides can spontaneously "insert" into membranes, it is postulated that the effect of the GM1 may be due to alterations of membrane processes (eg, lipid hydrolysis, phospholipase activation, levels and membrane action of arachidonic acid, ionic permeation) that are characteristic of edema.