DIFFERENTIATION OF OLIGODENDROCYTES CULTURED FROM DEVELOPING RAT-BRAIN IS ENHANCED BY EXOGENOUS GM3 GANGLIOSIDE

Cultures consisting primarily of O-2A progenitor cells and immature ol igodendrocytes with a few microglia and astrocytes were obtained by sh aking primary cultures from neonatal rat brain after 12-14 days in vit ro. Addition of 50 mu g/ml exogenous NeuNAc alpha 2-3Gal beta 1-4Glc b eta 1-1'ceramide (GM3 ganglioside) to the cultures resulted in an incr ease in the number and thickness of cell processes that stained intens ely for sulfatide and galactocerebroside (galC) in comparison to contr ol cultures without added GM3. The treated cultures also contained few er astrocytes than control cultures as revealed by immunostaining for glial fibrillary acidic protein (GFAP). Cells that immunostained for b oth GFAP and sulfatide/galC were very rare in control cultures but wer e frequently seen in the GM3-treated cultures, suggesting that these m ay represent cells changing their direction of differentiation away fr om type II astrocytes toward oligodendrocytes under the influence of G M3. These effects on the developing rat oligodendrocytes were specific for GM3 ganglioside and were not produced by adding GM1, GM2, GD3, or GD1a to the cultures. Lactosyl ceramide and neuraminyl lactose were a lso ineffective. When control cultures were initially plated on polyly sine and incubated with [C-14]galactose, GD3 was the principal labeled ganglioside. However, as the control cells differentiated over time i n culture without the addition of exogenous GM3 and produced increasin g amounts of myelin-related components, the incorporation of [C-14]gal actose into endogenous GM3 increased to become the predominant labeled ganglioside by 6 days after plating. Metabolic labeling of the GM3-tr eated oligodendrocytes with [C-14]galactose revealed increased incorpo ration into galC and sulfatide in comparison to control cultures, but a decreased labeling of endogenous GM3. Similarly, incorporation of an amino acid precursor into the myelin-associated glycoprotein (MAG) wa s increased by GM3 treatment, but incorporation into myelin basic prot ein (MBP) was not affected. Although the overall effect of added GM3 w as to decrease the phosphorylation of most proteins in the oligodendro cytes, including MBP, GM3 enhanced the phosphorylation of MAG. These f indings indicate that GM3 ganglioside has an important role in the dif ferentiation of cells of the O-2A lineage toward myelin production, si nce differentiation is associated with increased metabolic labeling of endogenous GM3 in control cultures and is enhanced by the addition of exogenous GM3. (C) 1994 Wiley-Liss, Inc.