title: O-GlcNAcylation as a novel ammonia-induced posttranslational protein modification in cultured rat astrocytes.
abstract: Hepatic encephalopathy (HE) is a clinical manifestation of a low grade cerebral edema with a mutual interrelationship between osmotic- and oxidative stress. This leads to RNA oxidation and posttranslational protein modifications such as protein tyrosine nitration with pathophysiological relevance. Here, we report on O-GlcNAcylation as another ammonia-induced posttranslational protein modification in cultured rat astrocytes. NH4Cl induced O-GlcNAcylation of distinct proteins (25-250 kDa) in astrocytes in a dose- and time-dependent manner. Exposure of astrocytes to NH4Cl (5 mmol/l) for 48 h and 72 h significantly increased protein O-GlcNAcylation by about 2-fold and 4-fold, respectively. NH4Cl at a concentration of 1 mmol/l was sufficient to double protein O-GlcNAcylation in astrocytes after 72 h as compared to untreated controls. Ammonia-induced protein O-GlcNAcylation was sensitive towards glutamine-synthetase inhibition by methionine sulfoximine (MSO), but was not induced by hypoosmolarity (205 mosmol/l) or CH3NH3Cl (5 mmol/l). Increased protein O-GlcNAcylation in NH4Cl (5 mmol/l, 48 h)-treated astrocytes was fully reversible within 24 h after withdrawal of NH4Cl from culture medium. Amongst the proteins which are O-GlcNAcylated in response to ammonia, GAPDH was identified. It is concluded that ammonia induces reversible protein O-GlcNAcylation in astrocytes that depends on glutamine synthesis but not on astrocyte swelling per se or ammonia-induced pH-changes. In view of the complex involvement of O-GlcNAcylation in cell regulation, such as energy metabolism, apoptosis and circadian rhythmicity and in pathologies, such as neurodegenerative diseases, O-GlcNAcylation might contribute to the pathophysiology of hepatic encephalopathy.
authors.affiliation: Clinic for Gastroenterology, Hepatology and Infectiology, Heinrich-Heine University, 40225, Düsseldorf, Germany.
authors.forename: Ayşe
authors.initials: A
authors.lastname: Karababa
authors.forename: Boris
authors.initials: B
authors.lastname: Görg
authors.forename: Freimut
authors.initials: F
authors.lastname: Schliess
authors.forename: Dieter
authors.initials: D
authors.lastname: Häussinger
mesh_terms: D000117:Acetylglucosamine / Q000378:metabolism*; D000643:Ammonium Chloride / Q000494:pharmacology*; D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000378:metabolism*; D002478:Cells, Cultured; D005973:Glutamine / Q000378:metabolism; D024581:Glyceraldehyde-3-Phosphate Dehydrogenase (Phosphorylating) / Q000378:metabolism; D006031:Glycosylation; D006863:Hydrogen-Ion Concentration; D008744:Methylamines / Q000494:pharmacology; D017351:N-Acetylglucosaminyltransferases / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009994:Osmolar Concentration; D061251:Primary Cell Culture; D011499:Protein Processing, Post-Translational; D051381:Rats; D017208:Rats, Wistar
chemical_list: D008744:Methylamines; D009419:Nerve Tissue Proteins; D000643:Ammonium Chloride; D005973:Glutamine; C027451:methylamine; D024581:Glyceraldehyde-3-Phosphate Dehydrogenase (Phosphorylating); D017351:N-Acetylglucosaminyltransferases; C449880:O-GlcNAc transferase; D000117:Acetylglucosamine