IDENTIFICATION OF A COLLAGEN POTENTIATED NEURITE-PROMOTING FACTOR ISOLATED FROM C6 GLIOMA-CELLS

The C6 glial cell line has been used as a model cell system for the in vestigation of new glial produced neurotrophic and neurotropic molecul es. By using the C6 cell line grown in a defined medium on collagen, t his laboratory has isolated a distinct neurite promoting factor (NPF) that is potentiated by the presence of collagen (CPNPF). We have obser ved that C6 cells cultured in a defined medium on collagen (rat type-I ) slowed their growth rate and expressed an astrocytic- or oligodendro cytic-like morphology. CPNPF, at this state of purity, appears to be a distinct NPF which induces neurite outgrowth (neurites of 1 or more s omal diameters) in PC12 cells. These neurite promotion effects, howeve r, appear to support the neuron morphology for only a short period (4 days) of time without the presence of neurotrophic factor (NTF). The n eurite promoting activity is ineffective in inducing neurite outgrowth using mouse neuroblastoma cells (neuro-2a). CPNPF appears to be a hea t stable protein whose activity does not depend on the presence of int act collagen, heparin sulfate proteoglycan (HSPG), or chondroitin sulf ate proteoglycan (CSPG). Exposure to dissociative conditions results i n a loss of neurite promoting activity. CPNPF is not a glycoprotein th at contains an accessible alpha-D-mannopyranosyl, alpha-D-glucopyranos yl, or a sterically related residue (hydroxyl groups in the C-3,4, and 5 positions). Although these residues are not present on all glycopro teins, it does indicate that CPNPF is most likely not a glucoprotein. CPNPF activity is not blocked by neutralizing antibodies directed towa rd NGF, beta-FGF, IL-1beta, IL-6, TGF-beta2, TGF-beta1.2, TGF-beta3, T GF-beta5, or EGF. CPNPF appears to either be oligomeric protein or a c omplex of proteins. On the basis of indirect evidence, it does not app ear to be glial derived protease nexin-I. The alteration in morphology of the C6 glial cell line by serum-free conditions in the presence of collagen may have induced the production of a potentially new NPF not seen by previous investigators.