The cardiomyocyte molecular clock, regulation of Scn5a, and arrhythmia susceptibility

Abstract

The molecular clock mechanism underlies circadian rhythms and is defined by a transcription-translation feedback loop. Bmal1 encodes a core molecular clock transcription factor. Germline Bmal1 knockout mice show a loss of circadian variation in heart rate and blood pressure, and they develop dilated cardiomyopathy. We tested the role of the molecular clock in adult cardiomyocytes by generating mice that allow for the inducible cardiomyocyte-specific deletion of Bmal1 (iCS⌬Bmal1). ECG telemetry showed that cardiomyocyte-specific deletion of Bmal1 (iCS⌬Bmal1 Ϫ/Ϫ ) in adult mice slowed heart rate, prolonged RR and QRS intervals, and increased episodes of arrhythmia. Moreover, isolated iCS⌬Bmal1 Ϫ/Ϫ hearts were more susceptible to arrhythmia during electromechanical stimulation. Examination of candidate cardiac ion channel genes showed that Scn5a, which encodes the principle cardiac voltage-gated Na ϩ channel (NaV1.5), was circadianly expressed in control mouse and rat hearts but not in iCS⌬Bmal1 Ϫ/Ϫ hearts. In vitro studies confirmed circadian expression of a human Scn5a promoter-luciferase reporter construct and determined that overexpression of clock factors transactivated the Scn5a promoter. Loss of Scn5a circadian expression in iCS⌬Bmal1 Ϫ/Ϫ hearts was associated with decreased levels of NaV1.5 and Na ϩ current in ventricular myocytes. We conclude that disruption of the molecular clock in the adult heart slows heart rate, increases arrhythmias, and decreases the functional expression of Scn5a. These findings suggest a potential link between environmental factors that alter the cardiomyocyte molecular clock and factors that influence arrhythmia susceptibility in humans. cardiac excitability; circadian; heart; ion channels; Scn5a; Na ϩ current CIRCADIAN RHYTHMS are approximate 24-h cycles in biology. These rhythms are present at the systems level, the tissue level, the single cell and molecular levels (16,33,34,38). There are several examples of circadian rhythms in the cardiovascular system, with heart rate, blood pressure, and substrate metabolism exhibiting distinct oscillations over time of day (12,13,40,41). The mechanism that underlies circadian function is the molecular clock. The molecular clock is defined, in a simple way, by a transcription-translation feedback mechanism that is composed of the core clock genes Clock, Bmal1, Per1, Per2, Cry1, and Cry2. CLOCK and BMAL1 are transcription factors that heterodimerize and activate transcription of Per1, Per2, Cry1, and Cry2. PER1, PER2, CRY1, and CRY2 form multimers in the cytoplasm of the cell, translocate to the nucleus, and act to inhibit CLOCK:BMAL1 function. This cycle takes ϳ24 h and is the fundamental mechanism underlying circadian rhythms. Components of the core clock have also been shown to regulate the expression of genes outside the clock mechanism, and these genes are designated as clock-controlled genes (CCGs). CCGs often encode transcription factors or proteins that control rate-limiting steps in cell physiology (42).In the last 8 years, resear...

Circadian rhythm and cardiovascular disorders

“…Further, the same group identified Scn5a, which encodes the principal cardiac voltage-gated sodium (+) channel (Na [V] 1.5) and mediates the circadian variation in susceptibility to arrhythmia in humans, as a potential target. 17 Interestingly, as mentioned, patients with LQT3 due to SCN5a mutations show a significant prolongation of QTc interval at night as well as increased adverse events during sleep.…”

“…[5][6][7][8] In addition, disruption of the circadian rhythm either in the brain (central clock) or in the peripheral tissues (peripheral clock) leads to cardiovascular disease in both human and animal models. [9][10][11][12][13][14][15][16][17][18][19] In this review, we summarize our current understanding of the interplay between circadian regulation and cardiovascular disease, as well as future directions in development of therapy.…”

Bone Morphogenetic Protein 9 and 13 Induce C3H10T1/2 Cell Differentiation to Cardiomyocyte-Like Cells in Vitro

“…1D) in the cells transfected with BMP13 vector was significantly increased by 125-130 times over the controls (p < 0.05). (22,32,34,37) were examined using quantitative RT-PCR in the cells transfected with the vectors for BMP9 and BMP13. As shown in Figure 2A, the expression of Gata4 in the cells transfected with BMP9 or BMP13 vector was significantly increased by 2.5-3.5 times over the controls after 7 days of differentiation (p < 0.05).…”

Light phase-restricted feeding slows basal heart rate to exaggerate the type-3 long QT syndrome phenotype in mice

“…In vivo telemetry was used to measure core body temperature and ECGs. The method for RR interval analysis was done as previously described (25). We used two separate methods to assess the QT intervals.…”

“…The hourly averages for the RR and QT intervals for ϳ3 days were then fit with the nonlinear sinusoidal model: Interval ϭ A·cos[2 (t Ϫ )/T] ϩ m, to calculate the period (T), the time between the peak amplitudes; phase ( ), timing of the peak rhythm in reference to the onset of the light phase [Zeitgeber time (ZT) ϭ 0]; the amplitude (A), one-half of the peak to trough levels, and midline mean (m), a rhythm-adjusted mean halfway between the peak and trough amplitudes. Additionally, histograms were computed for RR intervals in bins of 5 ms similar to that previously reported (25). We also detected regions of bigeminy-like arrhythmia patterns by calculating the number of RR interval "flips" in one-min bins.…”