Volume 17, Number 24,
Issue of December 15, 1997
pp. 9624-9633
Macrophage/Microglia Regulation of Astrocytic Tenascin:
Synergistic Action of Transforming Growth Factor-
and Basic
Fibroblast Growth Factor
Received July 16, 1997; revised Sept. 12, 1997; accepted Sept. 26, 1997.
George M. Smith and
Jason H. Hale
Department of Anesthesiology and Pain Management, University of
Texas Southwestern Medical Center, Dallas, Texas 75235-9068
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-
1 (TGF-
1) 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-
1 but not bFGF; however, the
TGF-
1 concentration in supernatants was lower than that expected to
induce an increase in astrocytic tenascin similar to that seen with
recombinant TGF-
1. 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-
1 and bFGF. A similar synergistic effect was observed after the
addition of either TGF-
1 or bFGF to macrophage-conditioned medium.
Northern analysis also showed concomitant increases in TGF-
1, 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-
1 and bFGF in
vitro and after injury in vivo.
Key words:
microglia;
extracellular matrix;
astrocyte;
growth
factors;
cytokines;
glial-scar formation;
wound healing