Oligodendroglial Differentiation in Glial Primary Cultures: Requirement for Mevalonate

Abstract: The oligodendroglial enzyme, 2′,3′‐cyclic nucleo‐tide 3′‐phosphohydrolase (CNP), is a valuable marker for expression of oligodendroglial differentiation in glial primary cultures, and the inducibility of this enzyme by dibu‐tyryl‐3′,5′‐cyclic AMP (dBcAMP) appears to be limited to immature or developing oligodendroglia. To investigate the relationship between the induction of CNP and the sterol biosynthetic pathway, primary cultures of glia dissociated from the brains of newborn rats were maintained in 10% fetal calf serum (FCS) and exposed to 1 mM dBcAMP on day 7 in culture. Cultures so treated for either 48 h or 72 h demonstrated a three‐ to fourfold induction of CNP specific activity. The magnitude of this induction was not affected when the cholesterol content of the culture medium was reduced by >95% by placing the cultures in 10% lipoprotein‐poor serum rather than 10% FCS during the exposure to dBcAMP. Mevinolin (10 μM), a specific inhibitor of 3‐hy‐droxy‐3‐methylglutaryl coenzyme A reductase, the rate‐limiting enzyme of the sterol biosynthetic pathway, completely inhibited the induction of CNP by dBcAMP, while not affecting either the accumulation of cellular protein per flask or rate of protein synthesis. Simultaneous addition of mevalonate (20 mM) prevented the inhibition of the induction of CNP by mevinolin. However, simultaneous addition of low‐density lipoprotein sufficient to increase the cholesterol content of the medium 80‐fold failed to correct mevi‐nolin's inhibition of the induction of CNP. Thus, these results demonstrate that the presence of mevalonate is obligatory for the induction of CNP in primary cultures of developing glia, and suggest that a critical nonsterol derivative of mevalonate is required for this expression of oligodendroglial differentiation.