ADAPTATION OF C6 GLIOMA-CELLS TO SERUM-FREE CONDITIONS LEADS TO THE EXPRESSION OF A MIXED ASTROCYTE-OLIGODENDROCYTE PHENOTYPE AND INCREASEDPRODUCTION OF NEURITE-PROMOTING ACTIVITY

C6 cells were adapted to proliferate in defined culture medium to allo w the study of long-term effects of serum-free growth conditions on th eir phenotypic antigen expression and production of neurite promoting factors (NPFs), Cultures were grown in either Ham's F-12 or supplement ed Opti-MEM-I containing 15% heat-inactivated horse serum and 2.5% fet al calf serum (serum-containing) or in supplemented Opti-MEM-I alone ( serum-free), Immunocytochemical and immunofluorescence techniques were used to determine the antigenic expression of A2B5, galactocerebrosid e (GalC), and glial fibrillary acidic protein (GFAP) in passage matche d and sister cultures of serum and serum-free grown C6 cells, When C6 cells were grown under serum-containing conditions, two populations of cells were seen: young oligodendrocytes (A2B5(+), GFAP(-), GalC(+)), and mixed astrocyte-oligodendrocyte phenotype (A2B5(+), GFAP(+), GalC( +)), After adaptation of the C6 cells to serum-free conditions over 2- 3 passages, only one population of cells was observed, the mixed astro cyte-oligodendrocyte phenotype, The serum-free conditions also resulte d in greater staining of the C6 cells, Conditioned media from the two growth conditions were fractionated by ultrafiltration into two fracti ons: components >50 kDa and components of 10-50 kDa, The amount of neu rite promoting activity seen between the two culture conditions result ed in a 3-fold increase in NPF activity under serum-free conditions in the >50 kDa fraction, The 10-50 kDa fraction only expressed NPF activ ity if obtained from the serum-grown C6 cells, This alteration in NPF activity appears to be the result of the phenotypical alteration of th e C6 cells, and may suggest that the NPF activities from the two cultu re conditions may not be identical. (C) 1995 Wiley-Liss, Inc.