Control of glial number: purification from mammalian brain extracts of an inhibitor of astrocyte division.

Inhibitors of astrocyte cell division, immunologically related to the sugar moiety of epidermal growth factor receptor and to blood group antigens, have been purified from mammalian brain extracts. Mass spectra, high resolution proton magnetic resonance spectra, and chemical and enzymic analysis of the purified fraction indicated that the compounds isolated were glycosphingolipids, although signals compatible with the presence of aminoacid residues were also observed. Lectin binding indicated the presence of NAc-Neuraminic acid, NAc-glucosamine, fucose, galactose, and glucose. The inhibitor was cytostatic for astrocytes, C6 glioma cells, and endothelial cells, with approximate ID50 of 250 nM. Primary cultures of fibroblasts or 3T3 cells were not affected up to concentrations of 800 nM. Concentrations of the inhibitor of 800 nM or higher, caused non-specific cytotoxicity. The biological and immunological properties of this brain inhibitor were identical to those of the EGF receptor-related inhibitor previously described with the acronym ERI. Because of its source and cytostatic action, the glial inhibitor has been renamed neurostatin. Rabbit antibodies to neurostatin immunostained astrocytes and neurons, both in culture and in tissue sections.