Regulation of leukemia inhibitory factor synthesis in cultured human astrocytes

We have examined the ability of human astrocytes to synthesize and secrete leukemia inhibitory factor (LIF), which is a multifunctional cytokine that controls cell proliferation and differentiation in many tissues, including the nervous system. Astrocyte-enriched cultures, prepared from 8- to 9-wk- old embryonic brains, expressed LIF mRNA and secreted LIF protein. LIF synthesis was significantly increased by the cytokines IL-1β, TNF-α, and TGF-β₁, but not by IFN-γ, IL-6, or LPS. No major differences in basal and cytokine-inducible LIF production were detected among astrocyte populations obtained from different brain areas. LIF synthesis was lower in serum-free than in serum-containing astrocyte cultures. A role for protein kinase C in the regulation of astrocyte LIF production was suggested by the findings that phorbol esters induced both LIF mRNA and protein and that the cytokine- induced LIF increase was partially antagonized by relatively selective inhibitors of protein kinase C such as H7 and staurosporine. Human leptomeningeal fibroblasts also expressed LIF gene and protein. Astrocytes produced LIF and responded to cytokines with increased LIF synthesis only after being subcultured, and not when grown in primary cultures in close contact with neurons. Our findings suggest that in vivo induction of astrocyte LIF secretion might occur in pathologic conditions as a consequence of both alterations of neuronal-glial interactions and a local increase in the level of inflammatory cytokines.