Multihormonal control of proliferation and cytosolic glycerol phosphate dehydrogenase, lactate dehydrogenase and malic enzyme in glial cells in culture

Expression of thyroid hormone receptor isoforms in the oligodendrocyte lineage

Thyroid hormone (T3) regulates brain development and function and in particular ensures normal myelination. Animal models and in vitro systems have been employed to demonstrate the effects of T3, which acts via nuclear hormone receptors. T3 receptors (TRs) are transcription factors that activate or suppress target gene expression, such as myelin basic protein (MBP), in a hormone-dependent or -independent fashion. Two distinct genes, TR alpha and TR beta, encode several receptor isoforms with specific functions. This overview summarizes current knowledge on the cellular expression and the role of these isoforms and also examines the action of T3 on oligodendrocyte lineage cell types at defined developmental stages. Re-expression of TRs and also that of other transcription factors in oligodendrocytes may constitute some of the metabolic changes required for succesfull remyelination in the adult central nervous system after demyelinating lesions.

Sodium butyrate induces major morphological changes in C6 glioma cells that are correlated with increased synthesis of a spectrin-like protein

Butyrate induced flattening and development of cell processes in rat glioma (C6) cells and this change was correlated with an increase in the synthesis of a polypeptide doublet with an apparent molecular weight of about 200 kDa. Blot analysis revealed that at least one of these polypeptides was a spectrin-like protein. Indirect immunofluorescence studies with the spectrin antiserum indicated that the antigen was present in the cell bodies, and also in the cell processes. Thus fodrin may be one the major targets for the action of butyrate on C6 cells.

Proliferation and differentiation are not directly related to H1(0) accumulation in cultured glial cells

A basic nuclear chromatin protein with electrophoretic mobility of H1(0) histone is present in C6 rat glial cells and in primary cultures of rat brain astroglial cells. That this protein is identical to H1(0) is further demonstrated by the finding that it accumulates in C6 cells in a time- and dose-dependent manner in response to butyrate, an agent which is known to induce this protein in other cell types. Other short-chain fatty acids were found to influence H1(0) levels similarly although to a lesser extent than butyrate. There was a very close correlation between the induction of H1(0) and the inhibition of growth induced by different concentrations of short-chain fatty acids which supports the idea that the concentration of this protein is higher in non-proliferating cells. However, when cell growth was inhibited by dexamethasone or agents that increase intracellular cyclic adenosine monophosphate levels, H1(0) levels were not affected, even though these compounds also blocked DNA synthesis and induced morphologic changes in C6 cells. These observations suggest that, at least in glial cells, the accumulation of H1(0) is specifically caused by short-chain fatty acids and that suppression of cell division or commitment to differentiation are not sufficient 'per se' for the induction of this protein.