title: The bile acid receptor TGR5 (Gpbar-1) acts as a neurosteroid receptor in brain.
abstract: TGR5 (Gpbar-1) is a membrane-bound bile acid receptor in the gastrointestinal tract and immune cells with pleiotropic actions. As shown in the present study, TGR5 is also expressed in astrocytes and neurons. Here, TGR5 may act as a neurosteroid receptor, which is activated by nanomolar concentrations of 5β-pregnan-3α-ol-20-one and micromolar concentrations of 5β-pregnan-3α-17α-21-triol-20-one and 5α-pregnan-3α-ol-20-one (allopregnanolone). TGR5 stimulation in astrocytes and neurons is coupled to adenylate cyclase activation, elevation of intracellular Ca(2+) and the generation of reactive oxygen species. In cultured rat astrocytes, TGR5 mRNA is downregulated in the presence of neurosteroids and ammonia already at concentrations of 0.5 mmol L(-1). Furthermore, TGR5 protein levels are significantly reduced in isolated rat astrocytes after incubation with ammonia. A marked downregulation of TGR5 mRNA is also found in cerebral cortex from cirrhotic patients dying with hepatic encephalopathy (HE) when compared with brains from noncirrhotic control subjects. It is concluded that TGR5 is a novel neurosteroid receptor in brain with implications for the pathogenesis of HE.
authors.affiliation: Clinic for Gastroenterology, Hepatology, and Infectiology, Heinrich-Heine-University, Moorenstrasse 5, 40225 Düsseldorf, Germany.
authors.forename: Verena
authors.initials: V
authors.lastname: Keitel
authors.forename: Boris
authors.initials: B
authors.lastname: Görg
authors.forename: Hans J
authors.initials: HJ
authors.lastname: Bidmon
authors.forename: Irina
authors.initials: I
authors.lastname: Zemtsova
authors.forename: Lina
authors.initials: L
authors.lastname: Spomer
authors.forename: Karl
authors.initials: K
authors.lastname: Zilles
authors.forename: Dieter
authors.initials: D
authors.lastname: Häussinger
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D001921:Brain / Q000166:cytology / Q000378:metabolism*; D050882:CREB-Binding Protein / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D002756:Cholagogues and Choleretics / Q000494:pharmacology; D018920:Coculture Techniques; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D006801:Humans; D008164:Luminescent Proteins; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D018377:Neurotransmitter Agents / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D017382:Reactive Oxygen Species / Q000378:metabolism; D043562:Receptors, G-Protein-Coupled / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D018709:Statistics, Nonparametric; D013658:Taurolithocholic Acid / Q000494:pharmacology; D014162:Transfection / Q000379:methods
chemical_list: D002756:Cholagogues and Choleretics; D005904:Glial Fibrillary Acidic Protein; C518268:Gpbar1 protein, rat; D008164:Luminescent Proteins; C489787:MAP2 protein, rat; D008869:Microtubule-Associated Proteins; D018377:Neurotransmitter Agents; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; D043562:Receptors, G-Protein-Coupled; D005576:Colforsin; D013658:Taurolithocholic Acid; D000242:Cyclic AMP; D050882:CREB-Binding Protein; C494365:Crebbp protein, rat; D002118:Calcium