Effects of transforming growth factor-beta on murine astrocyte glutamine synthetase activity. Implications in neuronal injury.
Cytokines have been implicated in the pathogenesis of a number of brain diseases in which neurological dysfunction has been attributed to a change in amino acid neurotransmitter metabolism. In the present in vitro study, we investigated the effects of cytokines on astrocyte glutamine synthetase (GS) activity and subsequently on N-methyl-D-aspartate (NMDA) receptor-mediated neurotoxicity. Proinflammatory cytokines IL-1 alpha, IL-1 beta, and IL-6 at a concentration of 20 ng/ml did not affect GS activity; however, tumor necrosis factor-alpha inhibited this activity by 20% in mixed neuronal/astrocyte cultures. Treatment for 24 h with transforming growth factor (TGF)-beta 1 or -beta 2 inhibited up to 60% GS activity. TGF-beta 2 also inhibited GS in enriched astrocyte cultures with an ED50 of 10 pg/ml. Antibodies specific to TGF-beta 2 blocked this effect. Treatment of astrocytes with TGF-beta 2 (250 pg/ml) resulted in markedly dilated rough endoplasmic reticulum. Since astrocyte GS may play a protective role in NMDA receptor-mediated neurotoxicity, we treated mixed neuronal/astrocyte cultures with TGF-beta 2 (250 pg/ml) and found a threefold potentiation of NMDA receptor-mediated neurotoxicity. These data suggest that TGF-beta impairs astrocyte GS function and enhances neurotoxicity, thus providing insight into understanding one mechanism of cytokine-mediated central nervous system disease.
Chao
C C
CC
Neuroimmunobiology and Host Defense Laboratory, Minneapolis Medical Research Foundation, Minnesota 55404.
Hu
S
S
Tsang
M
M
Weatherbee
J
J
Molitor
T W
TW
Anderson
W R
WR
Peterson
P K
PK
D000818:Animals; D001253:Astrocytes / Q000187:drug effects* / Q000201:enzymology* / Q000648:ultrastructure; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D005974:Glutamate-Ammonia Ligase / Q000037:antagonists & inhibitors*; D005971:Glutamates / Q000378:metabolism / Q000633:toxicity; D018698:Glutamic Acid; D051379:Mice; D009474:Neurons / Q000187:drug effects*; D016194:Receptors, N-Methyl-D-Aspartate / Q000502:physiology; D016212:Transforming Growth Factor beta / Q000633:toxicity*
D005971:Glutamates; D016194:Receptors, N-Methyl-D-Aspartate; D016212:Transforming Growth Factor beta; D018698:Glutamic Acid; D005974:Glutamate-Ammonia Ligase