Ammonia induces MK‐801‐sensitive nitration and phosphorylation of protein tyrosine residues in rat astrocytes

• Published in: The FASEB journal 2002-05, Vol.16 (7), p.739-741
• Main Authors: Schliess, Freimut, Görg, Boris, Fischer, Richard, Desjardins, Paul, Bidmon, Hans J., Herrmann, Andreas, Butterworth, Roger F., Zilles, Karl, Häussinger, Dieter
• Format: Article
• Language: English
• Subjects: Ammonia - pharmacology; Animals; Astrocytes - drug effects; Astrocytes - metabolism; calcium; Cells, Cultured; Dizocilpine Maleate - pharmacology; Drug Synergism; encephalopathy; Glutamate-Ammonia Ligase - metabolism; glutamine synthetase; Glyceraldehyde-3-Phosphate Dehydrogenases - metabolism; hepatic; liver; MAP kinases; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinases - metabolism; Models, Neurological; nitric oxide; Nitric Oxide - biosynthesis; Nitric Oxide Synthase - biosynthesis; Nitric Oxide Synthase Type II; NMDA receptor; Phosphoproteins - chemistry; Phosphoproteins - metabolism; Phosphorylation; Phosphotyrosine - metabolism; Rats; Receptors, GABA-A - metabolism; Receptors, N-Methyl-D-Aspartate - antagonists & inhibitors; Tyrosine - analogs & derivatives; Tyrosine - metabolism
• ISSN: 0892-6638; 1530-6860
• DOI: 10.1096/fj.01-0862fje

Astrocytes play a key role in the pathogenesis of ammonia‐induced neurotoxicity and hepatic encephalopathy. As shown here, ammonia induces protein tyrosine nitration in cultured rat astrocytes, which is sensitive to the N‐methyl‐D‐aspartate (NMDA) receptor antagonist MK‐801. A similar pattern of nitrated proteins is produced by NMDA. Ammonia‐induced tyrosine nitration depends on a rise in [Ca2+]i, IκB degradation, and NO synthase (iNOS) induction, which are prevented by MK‐801 and the intracellular Ca2+ chelator 1,2‐bis(oaminophenoxy)ethane‐N,N,N',N'‐tetraacetic acid (BAPTA‐AM). Moreover, the increase in tyrosine nitration is blunted by L‐NMMA, 1400W, uric acid, Cu, Zn‐superoxide dismutase/catalase treatment, and methionine‐sulfoximine, which indicate the involvement of reactive nitrogen intermediates and intracellular glutamine accumulation. Such reactive nitrogen intermediates additionally mediate ammonia‐induced phosphorylation of the MAP‐kinases Erk1/Erk‐2 and p38MAPK. Among the proteins, which are tyrosine‐nitrated by ammonia, glyceraldehyde‐3‐phosphate dehydrogenase, the peripheral‐type benzodiazepine receptor, Erk‐1, and glutamine synthetase are identified. Ammonia‐induced nitration of glutamine synthetase is associated with a loss of enzymatic activity. Astroglial protein tyrosine nitration is found in brains from rats after acute ammonia‐intoxication or after portacaval anastomosis, indicating the in vivo relevance of the present findings. The production of reactive nitrogen intermediates and protein tyrosine nitration may alter astrocyte function and contribute to ammonia neurotoxicity.