Induction of cell death by L-alpha-aminoadipic acid exposure in cultured rat astrocytes: relationship to protein synthesis.
The excitotoxin, L-alpha-aminoadipic acid (L-AAA), kills primary astrocytes in the brain. The mechanism underlying the induction of cell death is not well understood although many possible mechanisms are theorized. Previous studies have reported that astrocytes die after prolonged exposure to L-AAA suggesting a delayed programmed cell death and apoptosis. In this study rat cortical astrocytes exposed to continuous 1 mM L-AAA exposure for 24-, 48-, or 72 hours demonstrated increased DNA laddering, a characteristic of apoptosis. Unexpectedly, this was not ameliorated by the presence of cycloheximide at 0.1 microg/ml medium. Because of our interest in cytoprotective heat shock proteins induced by excitoxic stress, we studied the effect of prolonged exposure of L-AAA on the synthesis of stress proteins and protein synthesis in rat cortical astrocytes. Protein synthesis as measured by [35S]-methionine labeling showed a marked and significant decrease in incorporation of radiolabel after 24 hours of exposure to L-AAA and prior to induction of significant cell death noted at 48- and 72 hours of L-AAA exposure. The inhibition of protein synthesis was partially reversible at 24 hours if cells were labeled in medium without L-AAA during the radiolabeling period. Heat shock or stress proteins, HSP70 and heme oxygenase-1 (HO-1), were analyzed after a 24 hour exposure to L-AAA and showed no significant induction of HSP70 or HO-1. The findings suggest that the prolonged inhibition of protein synthesis and associated lack of induction of HSP70 and HO-1 synthesis contributed to apoptotic cell death induced by the excitoxin L-AAA.
Nishimura
R N
RN
Department of Neurology, VA Greater Los Angeles Healthcare System, Sepulveda, California, 91343 USA. rnishimu@ucla.edu
Santos
D
D
Fu
S T
ST
Dwyer
B E
BE
D015074:2-Aminoadipic Acid / Q000494:pharmacology*; D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D001253:Astrocytes / Q000187:drug effects* / Q000502:physiology; D016923:Cell Death / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D018840:HSP70 Heat-Shock Proteins / Q000187:drug effects* / Q000378:metabolism; D006419:Heme Oxygenase (Decyclizing) / Q000187:drug effects* / Q000378:metabolism; D051547:Heme Oxygenase-1; D051381:Rats; D017208:Rats, Wistar
D018691:Excitatory Amino Acid Antagonists; D018840:HSP70 Heat-Shock Proteins; D015074:2-Aminoadipic Acid; D006419:Heme Oxygenase (Decyclizing); D051547:Heme Oxygenase-1