Regulation of the production of oligodendrocytes, that subsequently myelinated axons, is a fundamental aspect of normal development and may also play a role in demyelinating disorders and recovery from trauma or radiation damage. Mature oligodendrocytes have limited if any capacity to divide. During development they arise from glial progenitors, and the origin of slowly turning over mature oligodendrocytes may be progenitors that are now known to be present in the adult stage. In pathological conditions when the number of oligodendrocytes is diminished, e.g., multiple sclerosis, there is inadequate replacement of oligodendrocytes nd impaired remyelination in the central nervous system (CNS). This could result from decreased number of progenitors, lack of sufficient growth promoting factors for these cells, and/or inability of progenitors to respond to such factors. We hypothesize that neurons play a major role in the optimal development of oligodendrocytes. We have identified a novel growth factor activity in the conditioned medium of the B104 rat CNS neuronal cell line. It is target to biopotential )-2A glial progenitor cells that give rise to oligodendrocytes and type 2 astrocytes. Both neonatal and mature rat brain progenitors in culture have a dose-dependent response to growth factors contained in the serum- free conditioned medium of this neuronal cell line as well as of neuron- enriched neonatal cortical cultures. We have partially purified and characterized this oligodendrocyte progenitor growth factor activity and find it does not have identity with known growth factors based on apparent molecular weight, physicochemical properties, target cells, and/or immunoreactivity. We have generated monoclonal antibodies that neutralize this growth factor activity and recognize a 45-47 kD antigen in metabolically radiolabelled immunoprecipitates of both B104 cell- derived CM and neonatal rat cortex cytosol. The antigens are localized primarily in neurons and some subentricular cells, but not astrocytes or oligodendrocytes, in embryonic and neonatal, but not mature, rat brain tissue sections.
Our specific aims are to (1) isolate a novel oligodendrocyte progenitor growth factor activity from the CNS neuronal cell line using immunoaffinity and/or other chromatographic methods and (2) test the hypothesis that growth factors identical to B104 cell- derived factors are present in developing rat brain at the time of peak production of oligodendrocyte progenitors. Our long term goals are to understand the molecular mechanisms involved in the developmental expression of and response to neuron-derived growth factors that promote increases in oligodendrocytes of neonatal and mature progenitor origin. Future directions include cDNA cloning, determination of sites of synthesis, receptor binding studies, receptor isolation (if unique), and analysis of signal transduction mechanisms. The data generated will be relevant not only to normal development but may provide insight into new therapies for demyelinating and other pathological conditions in the central nervous system.
