Previous studies in this and other laboratories have shown that interl
eukin-1 beta (IL-1 beta) is a selective and potent activator of human
astrocytes with respect to induction of cytokines and hematopoietic gr
owth factors. To study the effect of recombinant human IL-1 beta (rhlL
-1 beta) on astrocyte morphology, glial fibrillary acidic protein (GFA
P) and vimentin expression, and actin organization, we conducted a sys
tematic survey using dissociated human fetal astrocyte cultures. Withi
n hours of stimulation with IL-1 beta, the majority of astrocytes conv
erted from flat, polygonal cells to small, contracted, highly branched
cells. This change in morphology was more striking when serum was eli
minated from the medium. Complete dissolution of filamentous actin occ
urred simultaneously with the change in cell shape, as demonstrated by
fluorescein-phalloidin binding. These ''activated'' astrocytes displa
yed intense GFAP and vimentin immunoreactivity in the small perikarya
and processes. in contrast, the large, flat astrocytes in control cult
ures showed diffuse pale immunoreactivity for GFAP and vimentin. To qu
antify the changes in GFAP and vimentin content with IL-1 beta stimula
tion, densitometric analyses of northern and western blots were perfor
med. Northern blot analysis of IL-1 beta-stimulated astrocytes reveale
d a transient, marked decrease in steady-state levels of mRNA for GFAP
, vimentin, and microtubule-associated protein 4. The decrease in mRNA
levels was evident by 4-8 h and fell to the lowest level at 16-24 h (
80-98% decrease by densitometry) with partial recovery by 72 h. By imm
unoblotting, a significant decrease in both GFAP and vimentin protein
content was observed after IL-1 beta stimulation. Furthermore, metabol
ic labeling studies revealed an almost total loss of GFAP synthesis fo
llowing stimulation with IL-1 beta for 16 h. These observations are co
nsistent with the idea that increases in immunoreactivity were related
to factors such as redistribution of epitope, rather than increases i
n total protein content. We hypothesize that in IL-1 beta-stimulated a
strocytes, synthesis of other proteins, e.g., inflammatory cytokines,
occurs at the expense of structural proteins and that the decrease in
content of cytoskeletal proteins may reflect an ''activated'' state of
astrocytes.