We have discovered that N-acetyl-L-cysteine (NAC) protects cells against death induced by exposure to noxious stimuli and against programed cell death (apoptosis) associated with exposure to inadequate amounts of trophic factors. NAC prevented glutamate-induced death of oligodendrocytes and tumor necrosis factor a (TNF-a)-induced death of oligodendrocytes and L929 fibroblasts. Moreover, suboptimal doses of NAC plus ciliary neurotrophic factor (which also protects oligodendrocytes against TNF-a-mediated killing)

The transplantation of well defined populations of precursor cells offers a means of repairing damaged tissue and of delivering therapeutic compounds to sites of injury or degeneration. For example, a functional immune system can be reconstituted by transplantation of purified haematopoietic stem cells, and transplanted skeletal myoblasts and keratinocytes can participate in the formation of normal tissue in host animals. Cell transplantation in the central nervous system (CNS) has been proposed as a means of correcting neuronal dysfunction in diseases associated with neuronal loss; it might also rectify glial cell dysfunction, with transplanted oligodendrocyte precursor cells eventually allowing repair of demyelinating damage in the CNS. Here we use co-operating growth factors to expand purified populations of oligodendrocyte type-2 astrocyte (O-2A) progenitor cells for several weeks in vitro. When injected into demyelinating lesions in spinal cords of adult rats, created in such a way as to preclude host-mediated remyelination, these expanded populations are capable of producing extensive remyelination. In addition, transplantation of O-2A progenitor cells genetically modified to express the bacterial beta-galactosidase gene gives rise to beta-galactosidase-positive oligodendrocytes which remyelinate demyelinated axons within the lesion. These results offer a viable strategy for the manipulation of neural precursor cells which is compatible with attempts to repair damaged CNS tissue by precursor transplantation.

The inhibition of differentiation of oligodendrocyte-type-2 astrocyte (O-2A) progenitors into oligodendrocytes caused by basic fibroblast growth factor (bFGF) can be overcome by non-O-2A lineage cells present in the optic nerve and by astrocytes purified from cerebral cortices. Although purified O-2A progenitors grown in the presence of bFGF for up to 6 days were inhibited from differentiating into oligodendrocytes, O-2A progenitors growing in heterogeneous optic nerve cultures did not show a similar inhibition of differentiation. The factor(s) responsible for overriding the inhibitory effects of bFGF appeared to be secreted by astrocytes, as extensive generation of oligodendrocytes was seen in cultures of purified O-2A progenitors exposed to bFGF+ medium conditioned by purified astrocytes (ACM). In addition, purified O-2A progenitors displayed a remarkable sensitivity to bFGF, which extended at least down to concentrations of 0.03 ng/ml, a concentration of < 2 x 10(-12) M. At a bFGF concentration of just 0.1 ng/ml, this mitogen still promoted DNA synthesis in as many O-2A progenitors as in cultures exposed to 1-30 ng/ml of this growth factor, but exhibited a reduced ability to promote DNA synthesis in oligodendrocytes. In addition, although concentrations of bFGF as low as 0.03 ng/ml were a potent stimulator of DNA synthesis in O-2A progenitors, application of this amount of bFGF no longer inhibited the differentiation of progenitors into oligodendrocytes as effectively as application of higher bFGF concentrations. Thus, the induction of DNA synthesis by bFGF can be uncoupled from the inhibition of differentiation.(ABSTRACT TRUNCATED AT 250 WORDS)

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We have found that CNTF and LIF are pleiotropic modulators of development in the O-2A lineage. Both molecules enhanced the generation of oligodendrocytes in cultures of dividing O-2A progenitors. CNTF and LIF also promoted oligodendrocyte maturation, as determined by expression of myelin basic protein, and could promote oligodendrocyte survival to an extent comparable with insulin-like growth factor-1 or insulin. In addition, LIF and CNTF both promoted the differentiation of O-2A progenitors into type-2 astrocytes but only when applied in the presence of extracellular matrix (EnMx) derived from cultures of endothelial cells. The ability of CNTF and LIF to enhance differentiation of O-2A progenitors along either of the alternative pathways of oligodendrocyte and astrocyte differentiation suggests that these proteins are able to enhance the process of differentiation per se, while the actual path of differentiation promoted is determined by the presence or absence of additional molecules in the extracellular environment.