Abstract 275: The Intrinsic Circadian Clock within the Cardiomyocyte Regulates Myocardial Efficiency and Mitochondrial Function
Marked circadian rhythms in myocardial metabolism are mediated by as yet unidentified mechanism(s). Virtually every mammalian cell possesses an intrinsic circadian clock, a transcriptionally-based molecular mechanism capable of regulating multiple cellular functions. Recent studies suggest that the transcriptional co-activator, PGC1α, is an integral component of the mammalian circadian clock, which links this molecular mechanism to oxidative metabolism. To test the hypothesis that the circadian clock directly influences myocardial metabolism, a cardiomyocyte-specific circadian clock mutant (CCM) mouse was generated. Wild-type (WT) and CCM hearts were isolated and perfused in the working mode, for simultaneous assessment of myocardial contractile function and metabolism. Compared to WT, CCM hearts exhibited decreased cardiac efficiency independent of the time of day (13% lower; p<0.05), with greatest differences observed during the middle of the dark (awake) phase (29% lower; p<0.01). Subsarcolemmal (SSM) and interfibrillar (IFM) mitochondria were next isolated from the non-perfused WT and CCM hearts. Total SSM protein yields were significantly decreased in the CCM mice compared to WT (5.11 ± 0.95 vs 8.99 ± 1.43 mg/gww, p<0.05) with no differences in IFM proteins. State 3 respiration and respiratory control ratio (RCR, an indicator of mitochondrial coupling), were significantly depressed in SSM of CCM mice using glutamate, pyruvate, palmitoylcarnitine and palmitoyl CoA as respiratory substrates (See Table⇓). Microarray analysis revealed differential expression of multiple genes involved in mitochondrial biogenesis (e.g. pgc1α, mrpl49) and function (e.g. ucp3, uqcrb, suclgl, atp5f1, slc25a29) in CCM versus WT hearts. In conclusion, we report that disruption of the circadian clock within the cardiomyocyte decreases mitochondrial biogenesis and increases mitochondrial uncoupling, resulting in decreased myocardial efficiency.