CLOCK-BMAL1 Governs Ventricular Arrhythmogenesis In Chronic Heart Failure

Background:Circadian rhythm influences the incidence of sudden cardiac death in chronic heart failure (CHF),the underlying mechanism of circadian VA in CHF is mediated by circadian sympathic activity. Recently, cardiac circadian systerm is proved to regulate cardiac ion channels and ventricular arrhythmias. However, no study has reported the role of core circadian genes in circadian ventricular arrhythmia (VA) of CHF.Objective:We aimed to demonstrate the role of core circadian genes in circadian VA of CHF.Methods:(1) The guinea pig CHF model was created by transaortic constriction. And circadian expressions of circadian clock genes were examined by RT-PCR.(2) The electrocardiograms of Langendorff-perfused hearts were recorded and VAs were induced by programmed electrical stimulation with isoprenaline (ISO), ISO +CGP-20712A (CGP) and ISO+ICI118551 (ICI) at circadian time 3 (CT3) and CT15.(3) Circadian expressions of β-ARs were examined by RT-PCR and Western blotting.(4) Adenovirus infections were applied to overexpress CLOCK and/or BMAL1 in the guinea pig ventricular cardiomyocytes, then the occurence of arrhythmia and the action potential durations were measured.(5) Luciferase and chromatin immunoprecipitation assay(ChIP) were applied to determine whether CLOCK-BMAL1 transcriptionally regulate β1-AR expression.Results:(1) Circadian oscillations of core clock genes were maintained in CHF.(2) During ISO and ISO+ICI infusion, the circadian variations in response to β-AR activation translated to a greater incidence of VA at CT3 (P<0.05; ISO group HF-CT3:HF-CT15=100%:60%; ISO+ICI group HF-CT3:HF-CT15=80%: 40%), whereas ISO+CGP infusion did not lead to circadian variations of VA (P>0.05; HF-CT3:HF-CT15=26.7%:26.7%).(3) Circadian oscillations of β1-AR (P<0.05, Period=24, Phase=20, Amplitude=0.18) were maitained in CHF. However, the mean expression of β1-AR was significantly attenuated in CHF (P<0.05).(4) Over-expression of CLOCK-BMALl resulted in prolonged APDs and greater incidences of arrhythmia in myocytes and up-regulation of β1-AR (P<0.05).(5) Luciferase and ChIP-RT PCR analysis revealed that BMAL1 could bind to the enhancer of β1-AR(located at-741bp and -806bp).Conclusions:(1) Cardiac circadian system was maintained in CHF guinea pigs.(2) BMAL1 might bind to the enhancer of β1-AR to modulate ventricular arrhythmias severity in CHF.