LONG-TERM REGULATION BY THEOPHYLLINE OF FATTY-ACID SYNTHETASE, ACETYL-COA CARBOXYLASE AND LIPID-SYNTHESIS IN CULTURED GLIAL CELLS

The long-term regulation of fatty acid synthetase and acetyl-CoA carboxylase and of fatty acid and sterol synthesis was studied in C-6 glial cells [from rat astrocytoma] in culture. When theophylline (10-3 M) was added to the culture medium, rates of lipid synthesis from acetate and activities of synthetase and carboxylase became distinctly lower than in cells that were untreated. This effect appeared after approximately 12 h, and after 48 h enzymatic activities were reduced approximately 2-fold, and rates of lipid synthesis from acetate were reduced 3 to 4-fold. The likelihood that the decrease in fatty acid synthesis from acetate was caused by the decrease in activities of fatty acid synthetase and acetyl-CoA carboxylase was established by several observations. The locus of the effect probably did not reside at the level of acetate uptake into the cell, alterations in acetate pool sizes or conversion of acetate to acetyl-CoA. De novo fatty acid synthesis was the predominant pathway in these glial cells, whether treated with theophylline or not. The mechanism of the effect of theophylline on fatty acid synthetase was shown by immunochemical techniques to involve an alteration in content of enzyme rather than in catalytic efficiency. The change in content of fatty acid synthetase was shown by isotopic-immunochemical experiments to involve a decrease in synthesis of the enzyme. The mechanism whereby theophylline leads to a decrease in lipogenesis and in the synthesis of fatty acid synthetase may not be mediated entirely by inhibition of phosphodiesterase and an increase in cyclic[c]AMP levels, because dibutyryl cAMP (10-3 M) only partially reproduced the effect. There is a role for theophylline and cAMP in the regulation of lipogenesis and the activities of fatty acid synthetase and acetyl-CoA carboxylase in C-6 glial cells, which have features of glia found in developing nervous tissue. The data may be of particular clinical importance in view of the recent interest in the use of theophylline in the therapy of apneic spells in human newborns.