Relation of cholesterol to oligodendroglial differentiation in C-6 glial cells

The relation of cellular cholesterol content of a biochemical expression of oligodendroglial differentiation was studied in cultured C-6 glial cells. Induction of the oligodendroglial marker enzyme 2':3'-cyclic nucleotide 3'-phosphohydrolase (CNP) was determined after alteration of the sterol content of cellular membranes by exposure to compactin, a specific inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase and cholesterol synthesis. The sterol content and, as a consequence, the sterol/phospholipid molar ratio of C-6 glial cells were decreased by treating the cells, in 10% lipoprotein-poor serum, with various concentrations of compactin for 24 h. The degrees of sterol depletion thus produced were maintained for 48 h after removal of the compactin if the cells were maintained in serum-free medium, the culture conditions necessary for induction of CNF in untreated cells. Forty-eight hours after removal of serum, no induction of CNP occurred in cells previously treated with 0.5 micrograms/ml of compactin, whereas untreated cells exhibited a three- to fourfold increase in CNP activity. Intermediate degree of sterol depletion resulted in intermediate degrees of inhibition of the CNP induction. Moreover, the morphological expressions of glial differentiation observed in the untreated cells did not occur in the sterol-depleted cells. That the effect of compactin on the induction of CNP relates to depletion of sterol was indicated by the finding that when low-density lipoprotein was added to the compactin-treated cells, the induction of CNP, the morphological expressions of differentiation, and the sterol/phospholipid molar ratios were preserved. The degree of sterol depletion that totally prevented the induction of CNP had no effect on (Na+ R K+)-activated ATPase activity, total protein synthesis, and cell viability. The data define a critical role for sterol in oligodendroglial differentiation in this model system.