Regulation of an oligodendrocyte progenitor cell line by the interleukin-6 family of cytokines

We report pleiotropic actions of the interleukin‐6 family of cytokines on a rat cerebral cortical oligodendrocyte cell line, Central Glia‐4 (CG‐4). This is a bipotential oligodendrocyte type‐2 astrocyte (O‐2A) progenitor cell line that can be manipulated in vitro to become either a type‐2 astrocyte or to follow a linear sequence of events into becoming a mature oligodendrocyte. Using Northern and Western analyses in conjunction with immunocytochemistry we have demonstrated that ciliary neurotrophic factor (CNTF), leukemia inhibitory factor (LIF), and interleukin‐6 (IL‐6) cause a transient increase in glial fibrillary acidic protein (GFAP) in oligodendrocyte type‐2 astrocyte (O‐2A) progenitor cells. At maximal cytokine concentrations, the largest increase in GFAP protein levels were observed for CNTF and LIF; albeit, IL‐6 did increase GFAP but the order of magnitude was 6‐7 times less. Moreover, in trophic factor deprived medium, CNTF and LIF protected immature (O4+/MBP−) and mature (MBP+) oligodendrocytes from the apoptotic mode of cell death, while IL‐6 had no effect in enhancing oligodendrocyte cell survival. Analysis of the cytokine‐induced early response genes (ERGs) revealed a strong degree of overlap for CNTF and LIF. The effect of IL‐6 was different in the degree to which the ERGs were up‐regulated and in their temporal patterns of expression. These findings suggest that ERGs may be important, at least in part, for determining the extent of functional overlap observed within this cytokine family. Our findings clearly demonstrate differential regulation of oligodendrocyte survival and differentiation by the IL‐6 family of cytokines.