Abstract 1231: Identification of Genes Directly Regulated by the Intrinsic Circadian Clock Within the Cardiomyocyte
Circadian rhythms in cardiovascular physiology (e.g. heart rate, cardiac output) and patho-physiology (e.g. arrhythmias) are firmly established. These phenomena have been attributed primarily to circadian rhythms in neurohumoral influences (e.g. sympathetic activity). Nevertheless, cardiomyocytes possess an intrinsic circadian clock, a transcriptionally-based molecular mechanism capable of influencing myocardial gene expression (and ultimately function) over the course of the day. At least 13% of myocardial genes exhibit significant circadian rhythmicity in expression. This may be due to neurohumoral factors and/or the circadian clock within the cardiomyocyte. To investigate the role of the circadian clock within the cardiomyocyte, we generated a transgenic mouse in which this molecular mechanism was specifically impaired within the cardiomyocyte, through targeted overexpression of a dominant negative CLOCK mutant protein; circadian rhythms in expression of known clock genes are severely attenuated in transgenic hearts (but not in extra-cardiac tissues). Microarray analysis revealed extensive differential expression between wild-type and transgenic hearts, with 605 genes induced (p<0.05) and 650 genes repressed (p<0.05). For a sub-set of genes (25), microarray data were confirmed through qRT-PCR. Based on gene ontology analysis, the differentially expressed genes could be classified into the following categories: ion homeostasis (e.g. kcne1, a voltage-gated K+ channel), mitochondrial function (e.g. uqcr, ubiquinol-cytochrome c reductase), transcription (e.g. mef2a, myocyte enhancer factor 2A), G-protein coupled signaling (e.g. p2ry1, purinergic receptor P2Y1), phosphorylation/dephosphorylation (e.g. phkγ1, phosphorylase kinase γ1), substrate utilization (e.g. bdh, 3-hydroxybutarate dehydrogenase), contraction (e.g. mylc2b, myosin light chain 2b), and protein turnover (e.g. usp2, ubiquitin specific protease 2). These data suggest that the circadian clock within the cardiomyocyte may regulate myocardial metabolism, excitation-contraction coupling, signaling, and transcription/translation, strengthening a role for this molecular mechanism in both cardiovascular physiology and pathophysiology.