title: The intrinsic circadian clock within the cardiomyocyte.
abstract: Circadian clocks are intracellular molecular mechanisms that allow the cell to anticipate the time of day. We have previously reported that the intact rat heart expresses the major components of the circadian clock, of which its rhythmic expression in vivo is consistent with the operation of a fully functional clock mechanism. The present study exposes oscillations of circadian clock genes [brain and arylhydrocarbon receptor nuclear translocator-like protein 1 (bmal1), reverse strand of the c-erbaalpha gene (rev-erbaalpha), period 2 (per2), albumin D-element binding protein (dbp)] for isolated adult rat cardiomyocytes in culture. Acute (2 h) and/or chronic (continuous) treatment of cardiomyocytes with FCS (50% and 2.5%, respectively) results in rhythmic expression of circadian clock genes with periodicities of 20-24 h. In contrast, cardiomyocytes cultured in the absence of serum exhibit dramatically dampened oscillations in bmal1 and dbp only. Zeitgebers (timekeepers) are factors that influence the timing of the circadian clock. Glucose, which has been previously shown to reactivate circadian clock gene oscillations in fibroblasts, has no effect on the expression of circadian clock genes in adult rat cardiomyocytes, either in the absence or presence of serum. Exposure of adult rat cardiomyocytes to the sympathetic neurotransmitter norephinephrine (10 microM) for 2 h reinitiates rhythmic expression of circadian clock genes in a serum-independent manner. Oscillations in circadian clock genes were associated with 24-h oscillations in the metabolic genes pyruvate dehydrogenase kinase 4 (pdk4) and uncoupling protein 3 (ucp3). In conclusion, these data suggest that the circadian clock operates within the myocytes of the heart and that this molecular mechanism persists under standard cell culture conditions (i.e., 2.5% serum). Furthermore, our data suggest that norepinephrine, unlike glucose, influences the timing of the circadian clock within the heart and that the circadian clock may be a novel mechanism regulating myocardial metabolism.
authors.affiliation: Brown Foundation Institute of Molecular Medicine, University of Texas Health Science Ctr. at Houston, 2121 W. Holcombe Blvd., IBT 1011, Houston, TX 77030, USA.
authors.forename: David J
authors.initials: DJ
authors.lastname: Durgan
authors.forename: Margaret A
authors.initials: MA
authors.lastname: Hotze
authors.forename: Tara M
authors.initials: TM
authors.lastname: Tomlin
authors.forename: Oluwaseun
authors.initials: O
authors.lastname: Egbejimi
authors.forename: Christophe
authors.initials: C
authors.lastname: Graveleau
authors.forename: E Dale
authors.initials: ED
authors.lastname: Abel
authors.forename: Chad A
authors.initials: CA
authors.lastname: Shaw
authors.forename: Molly S
authors.initials: MS
authors.lastname: Bray
authors.forename: Paul E
authors.initials: PE
authors.lastname: Hardin
authors.forename: Martin E
authors.initials: ME
authors.lastname: Young
mesh_terms: D056930:ARNTL Transcription Factors; D000367:Age Factors; D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins; D002352:Carrier Proteins / Q000235:genetics; D018797:Cell Cycle Proteins; D002478:Cells, Cultured; D002940:Circadian Rhythm / Q000187:drug effects / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics; D005786:Gene Expression Regulation / Q000502:physiology*; D005947:Glucose / Q000494:pharmacology; D007473:Ion Channels; D008297:Male; D024101:Mitochondrial Proteins; D032383:Myocytes, Cardiac / Q000166:cytology / Q000502:physiology*; D009638:Norepinephrine / Q000494:pharmacology; D009687:Nuclear Proteins / Q000235:genetics; D056953:Nuclear Receptor Subfamily 1, Group D, Member 1; D056950:Period Circadian Proteins; D010507:Periodicity; D011494:Protein Kinases / Q000235:genetics; D051381:Rats; D017208:Rats, Wistar; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics; D013566:Sympathomimetics / Q000494:pharmacology; D014157:Transcription Factors / Q000235:genetics; D000071247:Uncoupling Protein 3
chemical_list: D056930:ARNTL Transcription Factors; D051792:Basic Helix-Loop-Helix Proteins; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D005947:Glucose; D007473:Ion Channels; D024101:Mitochondrial Proteins; D009638:Norepinephrine; D009687:Nuclear Proteins; D056953:Nuclear Receptor Subfamily 1, Group D, Member 1; D056950:Period Circadian Proteins; D011494:Protein Kinases; D018160:Receptors, Cytoplasmic and Nuclear; D013566:Sympathomimetics; D014157:Transcription Factors; D000071247:Uncoupling Protein 3; C485975:DBP protein, rat; C498263:Nr1d1 protein, rat; C513311:Per2 protein, rat; C000604394:Ucp3 protein, rat; C403287:pyruvate dehydrogenase kinase 4