Long-term cultured astrocytes inhibit myelin formation, but not axonal growth in the co-cultured nerve tissue

The chronic demyelinated plaque of multiple sclerosis (MS) is characterised by a loss of oligodendrocytes, astrogliosis, and incomplete or no remyelination which probably results in part from the suppressive effects of gliotic astrocytes on myelin formation. We explanted mouse cerebella on astrocyte cultures which had been maintained for 2 to 12 weeks and assessed the myelination in the cerebellar tissue at 18 days after explanation. Myelination occurred vigorously in the tissue explanted on 2- to 4-week-old astrocytes, but was poorer in the tissue explanted on astrocytes older than 4 weeks. No myelin sheath was formed on 12-week-old astrocytes, although axons developed equally as well as those in the tissues explanted on 2-week-old astrocytes. As astrocytes were maintained longer, they became fibrous and immunostained more deeply with anti-glial fibrillary acidic protein antibody, being analogous to astrogliosis. These findings imply that astrogliosis in chronic demyelinated lesions of MS may potentially block remyelination.