Immunocytochemical demonstration of glial-neuronal interactions and myelinogenesis in subcultures of rat brain cells

Astrocytes induce oligodendrocyte processes to align with and adhere to axons

In order to study the signals that control the onset of myelination, we cocultured highly purified postnatal retinal ganglion cells and optic nerve oligodendrocytes under serum-free conditions that promote their survival for at least a month and found that no myelination occurred. Although the addition of optic nerve astrocytes induced the oligodendrocyte processes to align with, and adhere to, axons, myelination still did not occur. The effect of astrocytes was mimicked by removal of polysialic acid from both cell types using neuroaminidase. These findings provide evidence for a novel role for astrocytes in controlling the onset of myelination by promoting adhesion of oligodendrocyte processes to axons. They also suggest that other, as yet unidentified, cell-cell interactions are necessary to induce the myelination process itself.

Ethanolamine is released from glial cells in primary culture on stimulation with foetal calf serum and phorbol ester

Ethanolamine is released to the external medium at increased rates over basal levels when [3H]ethanolamine-labelled glial cells in primary culture, subcultures of astrocytes and O-2A lineage glia or C6 glioma cells are treated with phorbol ester or foetal calf serum. On equilibrium labelling of mixed glial cultures 90-95% of incorporated [3H]ethanolamine was in ethanolamine-containing phospholipids and 2% in the phosphatidylcholine component. On stimulation of glia with phorbol ester or foetal calf serum ethanolamine, and not phosphoethanolamine or choline, was released to the medium suggesting that a phospholipase D-mediated turnover of lipid, perhaps partially linked to protein kinase C, is involved. The results show that cells in primary culture behave similarly to cell lines in that signal transduction pathways involve a stimulated turnover of ethanolamine-phospholipids with the external release of ethanolamine.

Multiplication of rubella and measles viruses in primary rat neural cell cultures: relevance to a postulated triggering mechanism for multiple sclerosis

Rubella virus multiplied to low titre and produced a partial cytopathic effect in rat glial cell cultures. Anti-galactocerebroside staining showed that this cytopathic effect involved the disintegration of oligodendrocytes. A similar effect was produced following infection of myelinating neural cell cultures with rubella virus, but virus multiplication could not be detected in pure neuron cultures. Measles virus was found to multiply and produce a cytopathic effect in primary cultures of both neurons and glial cells. These results are discussed in relation to the ability of measles and rubella viruses to trigger human multiple sclerosis.

RGD-containing peptides inhibit the synthesis of myelin-like membrane by cultured oligodendrocytes

A synthetic peptide derived from the fibronectin cell-binding domain, GRGDSP, inhibits the adhesion of rat oligodendrocytes to a number of substrates. However, while GRGDSP inhibited the adhesion of cells in a short term adhesion assay, the presence of the peptide did not prevent cells from adhering and thriving in longer term culture. The morphological characteristics of individual cells cultured with 0.1 mg/ml GRGDSP were similar to untreated cultures; small rounded cell bodies radiating numerous fine processes. Peptide-treated cultures were inhibited in their ability to produce myelin specific components. The characteristic developmental peak in sulfolipid synthesis which occurs both in vivo and in vitro was completely inhibited when cells were cultured with GRGDSP. In addition, the synthesis of myelin basic protein was inhibited. Ultrastructurally, cells treated with GRGDSP showed a greatly reduced number of multilamellar myelin-like membrane figures than cells grown without peptide or those grown with GRADSP. Cultured oligodendrocytes did not become sensitive to inhibition of sulfolipid synthesis by GRGDSP until a period immediately preceding the peak in sulfolipid biosynthesis. The effects of pretreatment with peptide for 5 d before this time were completely reversible. Pretreatment which extended into the time of peak myelin synthesis resulted in permanent impairment in the cell's ability to synthesize sulfolipid. The oligodendrocyte's ability to synthesize a myelin-like membrane in culture is, in part, inherent since it occurs in the absence of neurons. The present results indicate that myelin membrane production is also subject to external control since it appears that occupancy of an RGD-dependent cell surface receptor during a critical period of in vitro development is required for the oligodendrocyte to produce myelin-like membrane.

Stimulation of protein phosphorylation in mixed glial cell primary cultures and subcultures by the phorbol ester 12-O-tetradecanoylphorbol-13-acetate

Glial cell primary cultures consisting of protoplasmic and fibrous astrocytes, oligodendrocytes and progenitor glial cells incubated in medium containing 0.5% foetal calf serum and treated with 25 nM 12-o-tetradecanoylphorbol-13-acetate (TPA) for periods between 15 and 60 min showed a stimulation of protein phosphorylation which was most prominent in a polypeptide with a molecular weight of about 80,000 Da. Glial subcultures consisting mainly of Type 2 astrocytes, oligodendrocytes and progenitor glia showed a similar TPA stimulation of 80,000 Da protein phosphorylation detectable within 1 min of phorbol ester addition. TPA treatment of primary glial cultures led to an enhancement of phospholipid turnover but exposure of primary glial cultures to concentrations of TPA up to 250 nM caused no morphological change in protoplasmic astrocytes. 4-Phorbol (4-PH) or dimethylsulfoxide (DMSO) was without effect on protein phosphorylation or lipid turnover in glial cultures.

Protein kinase C activity in soluble fractions from glial cells in primary culture and subcultures

Protein kinase C (calcium + phospholipid-dependent kinase) activity has been measured in soluble 100,000 g fractions from mixed glial cells in primary culture; in 12 day cultures the specific activity (mean +/- S.D.) was 184 +/- 10 pmol 32P incorporated/10 min/mg protein. In glial cell subcultures lacking protoplasmic astrocytes protein kinase C specific activity was lower. An inhibitor of protein kinase C in 100,000 g supernatants was removed by chromatography through DE-52 anion exchange resin increasing the specific activity of the calcium + phospholipid-dependent kinase about 20 times. Protein kinase C was also associated with membrane fractions from glial cells; the membrane-associated enzyme had a higher specific activity than in the cytoplasm.