Regenerative potential of adult O1+ oligodendrocytes

Remyelination in the adult central nervous system (CNS) is preceded by the generation of new oligodendrocytes (ODCs) but the source of the new ODCs has not been resolved. Adult galactocerebroside positive (O1+)ODCs proliferate when cultured with purified sensory neurons (Wood and Bunge, Nature 320:756-758, 1999), implying that differentiated ODCs could be an important source of new myelinating ODCs. To test this possibility purified O1+ODCs (>96% purity) were plated at low density (20-50 cells/culture) into cultures of purified dorsal root ganglion neurons. Three days after plating, single O1+ODCs were located (209 ODCs/43 cultures) and sequentially observed for 4 weeks. The ODCs began to proliferate by the fifth day after plating and formed large colonies by the third week. Most cells in these colonies were 01- but positive for another ODC antigen, O4. A few O1+, myelin basic protein (MBP)+ODCs, and glial fibrillary acidic protein (GFAP)+cells with astrocytic morphology were observed in some colonies. In similar cultures plated with cell-sorted O1+ODCs (>99.5% purity), ciliary neurotrophic factor (CNTF, 1ng/ml) increased the number and size of colonies, the number of O1+MBP+ODCs (including ODCs producing myelin-like profiles in association with axons) and the number of GFAP+ astrocytes, relative to untreated controls. The results are evidence that CNTF exerts a trophic effect on adult O1+ODCs, and/or their progeny, and that cells generated by division of O1+ODCs can become either new myelin-producing ODC, or astrocytes. This plasticity in regenerative potential of adult O1+ODCs has not been previously demonstrated.