Phenotypic manipulation of normal and malignant brain cells

Frame, Margaret C (1983) Phenotypic manipulation of normal and malignant brain cells. PhD thesis, University of Glasgow.

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In this investigation several questions were posed about expression of differentiated and malignancy-associated properties in cell cultures derived from grades III and IV anaplastic astrocytomas. For comparison, cells derived from normal adult post-mortem brain and foetal brain, were also investigated. Characterisation studies were complicated by the absence of the astrocyte-specific protein, GFAP from the normal adult cultures and many of the gliomas. Other groups of workers have demonstrated that both normal glia-(278) and glioma-(110) derived cultures can lose GFAP as a result of in vitro growth. In the case of the malignant cells, the loss of cellular differentiation could also be the result of in vitro neoplasia. GFAP positive glioma cultures were presumed to contain highly differentiated astrocytoma cells, whereas GFAP negative cultures probably contained less well differentiated or more anaplastic cells. Biochemical investigation led to the hypothesis that the flat polygonal cells obtained in cultures from normal adult brain tissue were percursor glial cells or glioblasts. The malignant cell lines represented a gradation in states of biochemical, astroglial differentiation. The degree of differentiation exhibited by a particular cell line was not related to the pathological state of the tumour from which it was derived. The foetal cultures contained apparently mature, highly differentiated astroglia and were found to be pheno-typically stable, relative to the normal adult and malignant cultures, in response to environmental changes. The accumulation of immunological and biochemical data for many cell lines led to the postulation of a possible astroglial precursor pathway. Investigating the relationship between differentiated and malignancy-associated properties, required the development of assays to represent marker properties. GFAP, high affinity GABA uptake and glutamine synthetase were chosen to represent expression of the differentiated astroglial phenotype and plasminogen activator and tumour angiogenesis factor (or endothelial cell mitogenesis), the malignancy associated phenotype. The effects of varying the microenvironment of the cells in culture were investigated in a number of ways. Increasing cell density, dramatically increased the expression of GFAP in C6 cultures and high affinity GABA uptake in many cell lines, at the onset of confluence. As these differentiated properties were stimulated, the production of PA in malignant cell lines was dramatically reduced; possible explanations for the observed effects with changing cell density were put forward in terms of the proliferative state of cells and the formation of cell-cell contacts. Experiments with heterologous co-cultures and high density perfusion cultures, further demonstrated the importance of cell-cell contacts in the expression of differentiation. The effects of exposing neoplastic cells to various chemical agents were also investigated. Some of the agents upset the balance between differentiated and malignancy-associated properties. In particular dexamethasone, pig brain extract and interferon pushed the phenotypic expression of malignant cells in the direction of more mature, differentiated astroglia, at the same time reducing expression of the malignancy- associated properties. The tumour promoting phorbol ester, TPA, effectively pushed the balance of phenotypic expression in the direction of malignancy, as determined by in vitro criteria. The differentiated properties were unaffected by this agent. The DNA-alkylating carcinogens,mitomycin C and methylnitrosourea, both used clinically in the treatment of cancer, stimulated expression of both differentiated and malignancy-associated properties. The relevance of these findings in considering the growth and spread of tumours after chemotherapy, and possible new treatment procedures for malignant disease, are discussed.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Ian Freshney
Keywords: Neurosciences
Date of Award: 1983
Depositing User: Enlighten Team
Unique ID: glathesis:1983-72788
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 11 Jun 2019 11:06
Last Modified: 11 Jun 2019 11:06

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