STIMULATION OF IN-VITRO MYELIN SYNTHESIS BY MICROGLIA

Central nervous system myelin is elaborated by oligodendrocytes, which have been studied extensively in cell culture. Dissociated brain cult ures allow in vitro analysis of events in myelinogenesis, including ce ll-cell interactions. Microglia, the primary phagocytic cell of the ce ntral nervous system, appear in developing fiber tracts prior to the o nset of myelination in vivo. To gain insight into potential oligodendr ocyte-microglial interactions during development, these cells were co- cultured and various parameters of myelin synthesis were measured. In co-culture, microglia stimulated the synthesis of sulfatide, a myelin- specific galactolipid, in oligodendrocytes, as well as the expression of the myelin-specific proteins myelin basic protein and proteolipid p rotein. Activity of the oligodendrocyte cytoplasm-specific enzyme 2',3 '-cyclic nucleotide 3'-phosphohydrolase was not elevated, suggesting t hat the effects of microglia were not due to stimulation of oligodendr ocyte proliferation. This was confirmed by the inability of microglia to induce significant DNA synthesis. Conditioned medium from cultured microglia provided a similar stimulatory activity, suggesting that the increase in myelin synthesis does not require contact between oligode ndrocytes and microglia. These findings suggest a stimulatory role for microglia during myelinogenesis. (C) 1994 Wiley-Liss, Inc.