title: Ghrelin induces clock gene expression in the liver of goldfishin vitrovia protein kinase C and protein kinase A pathways.
abstract: The liver is the most important link between the circadian system and metabolism. As a food-entrainable oscillator, the hepatic clock needs to be entrained by food-related signals. The objective of the present study was to investigate the possible role of ghrelin (an orexigenic peptide mainly synthesized in the gastrointestinal tract) as an endogenous synchronizer of the liver oscillator in teleosts. To achieve this aim, we first examined the presence of ghrelin receptors in the liver of goldfish. Then, the ghrelin regulation of clock gene expression in the goldfish liver was studied. Finally, the possible involvement of the phospholipase C/protein kinase C (PLC/PKC) and adenylate cyclase/protein kinase A (AC/PKA) intracellular signalling pathways was investigated. Ghrelin receptor transcripts,ghs-r1a, are present in the majority of goldfish hepatic cells. Ghrelin induced the mRNA expression of the positive (gbmal1a,gclock1a) and negative (gpergenes) elements of the main loop of the molecular clock machinery, as well asgrev-erbα(auxiliary loop) in cultured liver. These effects were blocked, at least in part, by a ghrelin antagonist. Incubation of liver with a PLC inhibitor (U73122), a PKC activator (phorbol 12-myristate 13-acetate) and a PKC inhibitor (chelerythrine chloride) demonstrated that the PLC/PKC pathway mediates such ghrelin actions. Experiments with an AC activator (forskolin) and a PKA inhibitor (H89) showed thatgrev-erbαregulation could be due to activation of PKA. Taken together, the present results show for the first time in vertebrates a direct action of ghrelin on hepatic clock genes and support a role for this hormone as a temporal messenger in the entrainment of liver circadian functions.
authors.affiliation: Animal Physiology Department, Faculty of Biology, Complutense University of Madrid, Madrid 28040, Spain.
authors.forename: Aída
authors.initials: A
authors.lastname: Sánchez-Bretaño
authors.affiliation: Animal Physiology Department, Faculty of Biology, Complutense University of Madrid, Madrid 28040, Spain.
authors.forename: Ayelén M
authors.initials: AM
authors.lastname: Blanco
authors.affiliation: Animal Physiology Department, Faculty of Biology, Complutense University of Madrid, Madrid 28040, Spain.
authors.forename: Ángel L
authors.initials: ÁL
authors.lastname: Alonso-Gómez
authors.affiliation: Animal Physiology Department, Faculty of Biology, Complutense University of Madrid, Madrid 28040, Spain.
authors.forename: María J
authors.initials: MJ
authors.lastname: Delgado
authors.affiliation: Neuroendocrine Effects of Endocrine Disruptors, Inserm (Research Institute for Health, Environment and Occupation, IRSET, INSERM U1085), SFR Biosit Université de Rennes 1, 35000 Rennes, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Kah
authors.affiliation: Animal Physiology Department, Faculty of Biology, Complutense University of Madrid, Madrid 28040, Spain eisornaa@bio.ucm.es.
authors.forename: Esther
authors.identifier: 0000-0002-2387-0119
authors.initials: E
authors.lastname: Isorna
mesh_terms: D000818:Animals; D056926:CLOCK Proteins / Q000235:genetics*; D002478:Cells, Cultured; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D029941:Fish Proteins / Q000235:genetics* / Q000378:metabolism*; D005786:Gene Expression Regulation; D054439:Ghrelin / Q000378:metabolism*; D006054:Goldfish / Q000235:genetics / Q000502:physiology*; D008099:Liver / Q000166:cytology / Q000502:physiology; D011493:Protein Kinase C / Q000378:metabolism*; D054440:Receptors, Ghrelin / Q000378:metabolism; D015398:Signal Transduction; D010738:Type C Phospholipases / Q000378:metabolism
chemical_list: D029941:Fish Proteins; D054439:Ghrelin; D054440:Receptors, Ghrelin; D056926:CLOCK Proteins; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D010738:Type C Phospholipases
keywords: Circadian system; Hepatic clock; Orexigenic peptides; Protein kinase A; Protein kinase C; Teleost