Project description:Maintenance of circadian alignment between an organism and its environment is essential to ensure metabolic homeostasis. Synchrony is achieved by cell autonomous circadian clocks. Despite a growing appreciation of the integral relation between clocks and metabolism, little is known regarding the direct influence of a peripheral clock on cellular responses to fatty acids. To address this important issue, we utilized a genetic model of disrupted clock function specifically in cardiomyocytes in vivo (termed cardiomyocyte clock mutant (CCM)). CCM mice exhibited altered myocardial response to chronic high fat feeding at the levels of the transcriptome and lipidome as well as metabolic fluxes, providing evidence that the cardiomyocyte clock regulates myocardial triglyceride metabolism. Time-of-day-dependent oscillations in myocardial triglyceride levels, net triglyceride synthesis, and lipolysis were markedly attenuated in CCM hearts. Analysis of key proteins influencing triglyceride turnover suggest that the cardiomyocyte clock inactivates hormone-sensitive lipase during the active/awake phase both at transcriptional and post-translational (via AMP-activated protein kinase) levels. Consistent with increased net triglyceride synthesis during the end of the active/awake phase, high fat feeding at this time resulted in marked cardiac steatosis. These data provide evidence for direct regulation of triglyceride turnover by a peripheral clock and reveal a potential mechanistic explanation for accelerated metabolic pathologies after prevalent circadian misalignment in Western society.
Project description:Disruption of the Circadian Clock within the Cardiomyocyte Influences Myocardial Contractie Function, Metabolism, and Gene Expression Virtually every mammalian cell, including cardiomyocytes, possesses an intrinsic circadian clock. The role of this transcriptionally-based molecular mechanism in cardiovascular biology is poorly understood. We hypothesized that the circadian clock within the cardiomyocyte influences diurnal variations in myocardial biology. We therefore generated a cardiomyocyte-specific circadian clock mutant (CCM) mouse, in order to test this hypothesis. At 12 weeks of age, CCM mice exhibit normal myocardial contractile function in vivo, as assessed by echocardiography. Radiotelemetry studies reveal attenuation of heart rate diurnal variations and bradycardia in CCM mice (in the absence of conduction system abnormalities). Reduced heart rate persisted in CCM hearts perfused ex vivo in the working mode, highlighting the intrinsic nature of this phenotype. Wild-type, but not CCM, hearts exhibited a marked diurnal variation in responsiveness to an elevation in workload (80mmHg plus 1 microM epinephrine) ex vivo, with a greater increase in cardiac power and efficiency during the dark (active) phase versus the light (inactive) phase. Moreover, myocardial oxygen consumption and fatty acid oxidation rates were increased, while cardiac efficiency was decreased, in CCM hearts. These observations were associated with no alterations in mitochondrial content or structure, and modest mitochondrial dysfunction, in CCM hearts. Gene expression microarray analysis identified 548 and 176 genes in atria and ventricles, respectively, whose normal diurnal expression patterns were altered in CCM mice. These studies suggest that the cardiomyocyte circadian clock influences myocardial contractile function, metabolism, and gene expression. Keywords: Comparison of circadian oscillations in gene expression in hearts taken from wildtype and transgenic animals
Project description:Circadian clocks are cell autonomous, transcriptionally-based, molecular mechanisms that confer the selective advantage of anticipation, enabling cells/organs to respond to environmental factors in a temporally appropriate manner. Critical to circadian clock function are two transcription factors, CLOCK and BMAL1. Previous studies in our laboratory have highlighted roles for CLOCK in cardiac physiology/pathophysiology. Here, we describe transcriptional, metabolic, and functional consequences of cardiomyocyte-specific Bmal1 knockout (CBK). Microarray analysis revealed 2037 differentially expressed genes in CBK hearts, many of which were previously identified in cardiomyocyte-specific Clock mutant (CCM) hearts. Subsequent analysis showed that Beta-hydroxybutyrate dehydrogenase 1 mRNA, protein, and enzymatic activity are markedly depressed in both CBK and CCM hearts, as is myocardial Beta-hydroxybutyrate oxidation, revealing a novel role for the circadian clock in ketone body utilization. A number of genes encoding for collagen isoforms were identified as oscillating in a time-of-day-dependent manner in wild-type, but not CBK, hearts, including col3a1, col4a1, and col4a2. Chronic induction of collagen isoform genes in CBK hearts was associated with severe age-dependent depression of cardiac function. Development of cardiomyopathy in CBK mice was associated with early mortality; all CBK mice die by one year of age. These studies highlight novel critical functions for BMAL1 in the heart, including regulation of ketone body metabolism and the extracellular matrix. RNA from whole hearts collected every 3 hours for 24 hours from wildtype and CBK mice was isolated and analyzed using MouseRef-8_V2 BeadChips (Illumina, Inc.). The 24-hour data were examined for rhythmicity using cosinor analysis and differences in rhythmicity between genotype groups were further examined for differences in the model fitting parameters.
Project description:Circadian clocks are cell autonomous, transcriptionally-based, molecular mechanisms that confer the selective advantage of anticipation, enabling cells/organs to respond to environmental factors in a temporally appropriate manner. Critical to circadian clock function are two transcription factors, CLOCK and BMAL1. Previous studies in our laboratory have highlighted roles for CLOCK in cardiac physiology/pathophysiology. Here, we describe transcriptional, metabolic, and functional consequences of cardiomyocyte-specific Bmal1 knockout (CBK). Microarray analysis revealed 2037 differentially expressed genes in CBK hearts, many of which were previously identified in cardiomyocyte-specific Clock mutant (CCM) hearts. Subsequent analysis showed that Beta-hydroxybutyrate dehydrogenase 1 mRNA, protein, and enzymatic activity are markedly depressed in both CBK and CCM hearts, as is myocardial Beta-hydroxybutyrate oxidation, revealing a novel role for the circadian clock in ketone body utilization. A number of genes encoding for collagen isoforms were identified as oscillating in a time-of-day-dependent manner in wild-type, but not CBK, hearts, including col3a1, col4a1, and col4a2. Chronic induction of collagen isoform genes in CBK hearts was associated with severe age-dependent depression of cardiac function. Development of cardiomyopathy in CBK mice was associated with early mortality; all CBK mice die by one year of age. These studies highlight novel critical functions for BMAL1 in the heart, including regulation of ketone body metabolism and the extracellular matrix.
Project description:Circadian clocks temporally orchestrate biological processes critical for cellular/organ function. For example, the cardiomyocyte circadian clock modulates cardiac metabolism, signaling, and electrophysiology over the course of the day, such that, disruption of the clock leads to age-onset cardiomyopathy (through unknown mechanisms). Here, we report that genetic disruption of the cardiomyocyte clock results in chronic induction of the transcriptional repressor E4BP4. Importantly, E4BP4 deletion prevents age-onset cardiomyopathy following clock disruption. These studies also indicate that E4BP4 regulates both cardiac metabolism (eg, fatty acid oxidation) and electrophysiology (eg, QT interval). Collectively, these studies reveal that E4BP4 is a novel regulator of both cardiac physiology and pathophysiology.
Project description:Circadian clocks temporally orchestrate biological processes critical for cellular/organ function. For example, the cardiomyocyte circadian clock modulates cardiac metabolism, signaling, and electrophysiology over the course of the day, such that, disruption of the clock leads to age-onset cardiomyopathy (through unknown mechanisms). Here, we report that genetic disruption of the cardiomyocyte clock results in chronic induction of the transcriptional repressor E4BP4. Importantly, E4BP4 deletion prevents age-onset cardiomyopathy following clock disruption. These studies also indicate that E4BP4 regulates both cardiac metabolism (eg, fatty acid oxidation) and electrophysiology (eg, QT interval). Collectively, these studies reveal that E4BP4 is a novel regulator of both cardiac physiology and pathophysiology.