title: Clock gene expression in human and mouse hepatic models shows similar periodicity but different dynamics of variation.
abstract: The biological hard-wiring of 24-hour rhythmicity relies on the circadian clock circuitry, made of peripheral oscillators operated by molecular clockworks and synchronized through humoral and neural outputs by central oscillators located in the hypothalamic suprachiasmatic nuclei. Metabolically active tissues, such as the liver, are entrained also by local cues represented by metabolic flux related to feeding. The mechanics of the molecular clockwork have been explored by studies using cell lines and wild type or genetically engineered mouse models. There is a compelling need to reduce the use of animals in experimental settings. The aim of our study was to evaluate the periodicity and dynamics of functioning of the hepatic clock gene machinery in human and mouse hepatic models. We compared the results obtained in human hepatoma cells (HepG2 cells) and in mouse liver, and a significant 24-hour rhythmic component was found for five clock genes in the HepG2 cells (Bmal1, Cry1, Per1, Per2, NR1D1) and for six clock genes in the mouse liver (Bmal1, Clock, Cry1, Per1, Per2, NR1D1). The amplitude of oscillation rendered by the cosine curve and the dynamics of expression rendered by the rate of change (the derivative of gene expression level with respect to time) were greater in the mouse liver than in the HepG2 cells for Bmal1, Per1, Per2 and NR1D1, and the cosine curve phase was different for many of them. In conclusion, the periodicity of expression of the clock genes showed similar patterns when the two experimental models were compared, whereas the dynamics of transcription in human hepatoma cells cultured in vitro were less vigorous and phased in a different way when compared to mouse hepatic tissue. The results support the reliability of the human hepatic in vitro model as an alternative to animal models only to study the periodicity of function of the molecular clockwork, but not to evaluate the dynamics of clock gene expression.
authors.affiliation: a Division of Internal Medicine and Chronobiology Unit , IRCCS Scientific Institute and Regional General Hospital "Casa Sollievo della Sofferenza," San Giovanni Rotondo (FG) , Italy.
authors.forename: Gianluigi
authors.initials: G
authors.lastname: Mazzoccoli
authors.affiliation: a Division of Internal Medicine and Chronobiology Unit , IRCCS Scientific Institute and Regional General Hospital "Casa Sollievo della Sofferenza," San Giovanni Rotondo (FG) , Italy.
authors.forename: Rosa
authors.initials: R
authors.lastname: Rubino
authors.affiliation: a Division of Internal Medicine and Chronobiology Unit , IRCCS Scientific Institute and Regional General Hospital "Casa Sollievo della Sofferenza," San Giovanni Rotondo (FG) , Italy.
authors.forename: Cristiana
authors.initials: C
authors.lastname: Tiberio
authors.affiliation: b Computing Unit, IRCCS Scientific Institute and Regional General Hospital "Casa Sollievo della Sofferenza," San Giovanni Rotondo (FG) , Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Giuliani
authors.affiliation: a Division of Internal Medicine and Chronobiology Unit , IRCCS Scientific Institute and Regional General Hospital "Casa Sollievo della Sofferenza," San Giovanni Rotondo (FG) , Italy.|c Euro-Mediterranean Institute of Sciences and Technology (IEMEST) , Palermo , Italy.|d School of Science and Technology , Nottingham Trent University , Nottingham , United Kingdom.|e University College London, Institute for Liver and Digestive Health, Division of Medicine , Royal Free Campus , London , United Kingdom.
authors.forename: Manlio
authors.initials: M
authors.lastname: Vinciguerra
authors.affiliation: e University College London, Institute for Liver and Digestive Health, Division of Medicine , Royal Free Campus , London , United Kingdom.
authors.forename: Jude
authors.initials: J
authors.lastname: Oben
authors.affiliation: a Division of Internal Medicine and Chronobiology Unit , IRCCS Scientific Institute and Regional General Hospital "Casa Sollievo della Sofferenza," San Giovanni Rotondo (FG) , Italy.
authors.forename: Angelo
authors.initials: A
authors.lastname: De Cata
authors.affiliation: f Department of Clinical and Experimental Medicine , University of Florence , Florence , Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Tarquini
authors.affiliation: a Division of Internal Medicine and Chronobiology Unit , IRCCS Scientific Institute and Regional General Hospital "Casa Sollievo della Sofferenza," San Giovanni Rotondo (FG) , Italy.
authors.forename: Salvatore
authors.initials: S
authors.lastname: De Cosmo
authors.affiliation: g Department of Clinical Research , MSD R&D , Beijing , P.R. China.
authors.forename: Shu
authors.initials: S
authors.lastname: Liu
authors.affiliation: h Department of Neurology and Neurobiology , Xuanwu Hospital of Capital Medical University, Key Laboratory for Neurodegenerative Diseases of Ministry of Education , Beijing , P. R. China.
authors.forename: Yanning
authors.initials: Y
authors.lastname: Cai
mesh_terms: D000818:Animals; D056926:CLOCK Proteins / Q000235:genetics*; D002478:Cells, Cultured; D057906:Circadian Clocks / Q000235:genetics*; D002940:Circadian Rhythm / Q000235:genetics* / Q000502:physiology; D015870:Gene Expression / Q000502:physiology*; D005786:Gene Expression Regulation; D006801:Humans; D008099:Liver / Q000378:metabolism*; D008297:Male; D008810:Mice, Inbred C57BL; D012333:RNA, Messenger / Q000378:metabolism; D015203:Reproducibility of Results; D013493:Suprachiasmatic Nucleus / Q000378:metabolism*
chemical_list: D012333:RNA, Messenger; D056926:CLOCK Proteins
keywords: Chronobiology; clock genes; hepatocytes; liver