The Circadian Clock within the Cardiomyocyte Is Essential for Responsiveness of the Heart to Fatty Acids

Abstract

Cells/organs must respond both rapidly and appropriately to increased fatty acid availability; failure to do so is associated with the development of skeletal muscle and hepatic insulin resistance, pancreatic ␤-cell dysfunction, and myocardial contractile dysfunction. Here we tested the hypothesis that the intrinsic circadian clock within the cardiomyocytes of the heart allows rapid and appropriate adaptation of this organ to fatty acids by investigating the following: 1) whether circadian rhythms in fatty acid responsiveness persist in isolated adult rat cardiomyocytes, and 2) whether manipulation of the circadian clock within the heart, either through light/dark (L/D) cycle or genetic disruptions, impairs responsiveness of the heart to fasting in vivo. We report that both the intramyocellular circadian clock and diurnal variations in fatty acid responsiveness observed in the intact rat heart in vivo persist in adult rat cardiomyocytes. Reversal of the 12-h/12-h L/D cycle was associated with a re-entrainment of the circadian clock within the rat heart, which required 5-8 days for completion. Fasting rats resulted in the induction of fatty acid-responsive genes, an effect that was dramatically attenuated 2 days after L/D cycle reversal. Similarly, a targeted disruption of the circadian clock within the heart, through overexpression of a dominant negative CLOCK mutant, severely attenuated induction of myocardial fatty acid-responsive genes during fasting. These studies expose a causal relationship between the circadian clock within the cardiomyocyte with responsiveness of the heart to fatty acids and myocardial triglyceride metabolism.

A sincronização noradrenérgica e o papel da insulina na modulação da síntese da melatonina pela glândula pineal de ratos.

“…As such, both intracellular and extracellular factors should be considered as important mediators of circadian rhythms in cardiovascular function. We speculate that impairment of this molecular mechanism may contribute toward myocardial contractile dysfunction associated with pressure overload, diabetes mellitus, myocardial infarction, and/or shift work (conditions in which the circadian clock within the heart is known to be altered) (9,18,43,45,46). Future studies should focus on addressing this important hypothesis.…”

“…In our CCM mice, the circadian clock within the heart is severely attenuated in a sex-independent manner, as demonstrated by attenuation of clock component and output gene circadian oscillations, without affecting circadian clocks within extracardiac tissues (9). Using this model, our laboratory has recently shown that the circadian clock within the cardiomyocyte is essential for responsiveness of the heart to fatty acids (9).…”

“…Isolated working mouse heart perfusions were utilized to investigate diurnal variations in myocardial metabolism and contractile function ex vivo, as described previously (10). Hearts were perfused in the working mode in a non-recirculating manner with Krebs-Henseleit bicarbonate buffer containing 5 mM glucose, 0.4 mM oleate conjugated to 3% BSA (fraction V, fatty acid free; dialyzed), 10 U/ml insulin, and tracer amounts of [U- 14 C]glucose (40 Ci/l) and [9, H]oleate (60 Ci/l). After 30 min of normal workload perfusion conditions (11.5 mmHg preload, 50 mmHg afterload), hearts were perfused for an additional 30 min under high workload conditions (11.5 mmHg H 2O preload, 80 mmHg afterload plus 1 M epinephrine).…”

“…Specific quantitative assays were designed from mouse sequences available in GenBank. Primer and probe sequences for bmal1, dbp, per3, dgat2, and adpn Taqman assays have been published previously (9,45), whereas those for dec1, e4bp4, mcip1, pbef1, pik3r1, and prkar1a are presented in Supplemental Table 1. (The online version of this article contains supplemental data.)…”

“…The most extensively characterized of these models is the Clock mutant mouse, in which chemical mutagenesis-induced truncation of the native Clock gene resulted in a dominant-negative CLOCK (dnCLOCK) mutant protein lacking the transactivation domain of this transcription factor (termed CLOCK ⌬19 , due to loss of exon 19). We recently generated a cardiomyocyte-specific circadian clock mutant (CCM) mouse, through MHC-␣ promoter-driven expression of the CLOCK ⌬19 protein within cardiomyocytes (9). We employed this dominant-negative approach, in contrast to a tissue-specific CLOCK knockout approach, due to the marked redundancy within the mammalian circadian clock mechanism.…”