Macrophage/Microglia Regulation of Astrocytic Tenascin: Synergistic Action of Transforming Growth Factor-β and Basic Fibroblast Growth Factor

After injury to the CNS, extracellular matrix molecules such as tenascin are upregulated around the injury site and may be involved in inhibition of axon growth. In the present study, astrocytes were investigated to determine which cell types, growth factors, or cytokines are responsible for the injury-induced regulation of tenascin. The addition of activated macrophage- or microglial-conditioned medium increased astrocytic expression of tenascin 2.5-fold, as determined by Northern and Western blot analysis and ELISA. Of the cytokines and growth factors examined, only transforming growth factor-β1 (TGF-β1) and basic fibroblast growth factor (bFGF) significantly induced an increase in the production of astrocytic tenascin. Examination of macrophage and microglial supernatants showed the presence of TGF-β1 but not bFGF; however, the TGF-β1 concentration in supernatants was lower than that expected to induce an increase in astrocytic tenascin similar to that seen with recombinant TGF-β1. Western blot analysis of astrocytes showed only the presence of bFGF. Compared with the responses of the individual growth factors, tenascin production by astrocytes was dramatically potentiated when grown in the presence of a combination of both TGF-β1 and bFGF. A similar synergistic effect was observed after the addition of either TGF-β1 or bFGF to macrophage-conditioned medium. Northern analysis also showed concomitant increases in TGF-β1, bFGF, and tenascin after CNS injury to animals 14 d of age or older. These results show that the regulation of astrocytic tenascin is mediated by the synergistic action of TGF-β1 and bFGF in vitro and after injury in vivo .