Growth factor and cytokine regulation of the beta gene in rat astrocytes

Abstract

Basic fibroblast growth factor (FGF-2) and interleukin-l{dollar}\beta{dollar} (IL-1{dollar}\beta{dollar}) stimulate reactive gliosis and regulate neurotrophic factor expression in astrocytes. S100{dollar}\beta{dollar} is a putative neurotrophic factor which is over-expressed in reactive astrocytes. Therefore, we tested the hypothesis that FGF-2 and/or IL-1{dollar}\beta{dollar} would stimulate S100{dollar}\beta{dollar} gene expression. FGF-2 decreased S100{dollar}\beta{dollar} mRNA after 12 and 24 hours of treatment in cultured rat cortical astrocytes, but increased its levels after 7 days. IL-1{dollar}\beta{dollar} suppressed S100{dollar}\beta{dollar} mRNA levels after 24 and 48 hours, and continued to inhibit after 7 days of exposure. In combination, the effect of these two factors appeared synergistic. In C6 glioma cells, only FGF-2 suppressed gene expression. To assess indirectly whether alterations in transcriptional rate could explain the changes in mRNA, we measured levels of S100{dollar}\beta{dollar} primary transcript. FGF-2 decreased S100{dollar}\beta{dollar} nuclear primary transcript levels after 6 and 12 hours, but increased its levels after 48 hours. IL-1{dollar}\beta{dollar} decreased nuclear primary transcript after 48 hours. We further measured intracellular S100{dollar}\beta{dollar} protein levels to determine whether the alterations in mRNA were translated into parallel changes in the level of protein. FGF-2 did not suppress S100{dollar}\beta{dollar} protein levels after 1, 2, or 3 days of treatment, but increased it after 5 and 8 days. IL-1{dollar}\beta{dollar} and combination treatment did not significantly alter protein levels. Our results clearly demonstrate that FGF-2 and IL-1{dollar}\beta{dollar} influence the expression of the S100{dollar}\beta{dollar} gene, that this regulation appears to occur at the level of transcription, and that changes in mRNA are sometimes, but not always, reflected in changes at the level of protein. In a second study we determined whether the changes observed in vitro would also be seen in a lesion model for reactive gliosis in which both FGF-2 and IL-1{dollar}\beta{dollar} are elevated: the cortical contusion. Mild contusion bilaterally elevated S100{dollar}\beta{dollar} mRNA over sham levels in both the cortex and hippocampus of young adult, male rats. However, mRNA levels in sham animals decreased with time, making it unclear whether the contusions stimulated S100{dollar}\beta{dollar} or mitigated the inhibitory effect of sham. The contusion stimulated a robust elevation in GFAP mRNA, a "marker" of reactive gliosis, in both brain regions. Our data clearly demonstrate that contusion produces a vigorous glial response, and suggest that the mechanisms involved in the regulation of S100{dollar}\beta{dollar} and GFAP are different. This hypothesis is further supported by our in vitro finding that GFAP and S100{dollar}\beta{dollar} are differentially regulated in astrocytes by FGF-2 and IL-1{dollar}\beta.{dollar}* ftn*Originally published in DAI vol. 56, no. 9. Reprinted here with corrected author name.