In vitro analysis of the oligodendrocyte lineage in mice during demyelination and remyelination

C57B1/6N mice by intracranial injection of a coronavirus (murine hepatitis virus strain A59) is followed by functional recovery and efficient CNS myelin repair. To study the biological properties of the cells involved in this repair process, glial ceils were isolated and cultured from spinal cords of these young adult mice during demyelination and remyelination. Using three-color immunofluorescence combined with [3H]thymidine autoradiography, we have analyzed the antigenic phenotype and mitotic potential of individual glial cells. We identified oligodendrocytes with an antibody to galactocerebroside, astrocytes with an antibody to glial fibrillary acidic protein, and oligodendrocyte-type 2 astrocyte (O-2A) progenitor cells with the 04 antibody. Cultures from demyelinated tissue differed in several ways from those of agematched controls: first, the total number of O-2A lin-cage cells was strikingly increased; second, the O-2A population consisted of a higher proportion of 04positive astrocytes and cells of mixed oligodendrocyteastrocyte phenotype; and third, all the cell types within the O-2A lineage showed enhanced proliferation. This proliferation was not further enhanced by adding PDGF, basic fibroblast growth factor (bFGF), or insulin-like growth factor I (IGF-I) to the defined medium. However, bFGF and IGF-I seemed to influence the fate of O-2A lineage cells in cultures of demyelinated tissue. Basic FGF decreased the percentage of cells expressing galactocerebroside. In contrast, IGF-I increased the relative proportion of oligodendrocytes. Thus, O-2A lineage cells from adult mice display greater phenotypic plasticity and enhanced mitotic potential in response to an episode of demyelination. These properties may be linked to the efficient remyelination achieved in this demyelinating disease. I ~ demyelinating diseases, damage to myelin sheaths disrupts conduction of electrical impulses along axonal processes of neurons. Typically, damaged myelin is not efficiently repaired in the human CNS (Perier and Gregoire, 1965; Prineas et al., 1984) . Thus patients with CNS demyelinating diseases, such as multiple sclerosis, frequently experience prolonged neurological dysfunction. In contrast, efficient remyelination and functional recovery is achieved in rodents in certain experimental models of CNS demyelination (reviewed in Ludwin, 1981) . One such model is produced by infecting C57B1/6N mice with a coronavirus (murine hepatitis virus strain A59; MHV-A59), which leads to the development of multiple CNS demyelinating lesions (Lavi et al., 1984; Jordan et al., 1989) . This coronavirus replicates in glial cells during an early phase of the disease and is subsequently cleared from the CNS (Jordan et al., 1989) . Infected mice exhibit clinical signs of CNS demyelin-ation within the first week post infection (wpi)? By 3-5 wpi, focal areas of demyelination are present throughout the CNS, with prominent lesions in the spinal cord. In the following weeks, remyelination is paralleled by functional recovery. Using this model, we can analyze the processes involved in regeneration of the cells that form CNS myelin.