Direct Regulation of Myocardial Triglyceride Metabolism by the Cardiomyocyte Circadian Clock

Abstract

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.Striking time-of-day-dependent oscillations are observed in multiple cardiometabolic parameters in both animal models and humans. These parameters range from levels of circulating nutrients and endocrine factors, neural activity, glucose tolerance, insulin sensitivity, feeding behavior, and energy metabolism (both at the individual tissue and whole body levels) to cardiovascular function (1-5). Significant alterations in many of these oscillations are observed in metabolic disease states (e.g. obesity, diabetes mellitus, and cardiovascular disease), suggesting that circadian misalignment may play an important role in the etiology of multiple pathologies (5, 6). Recent molecular/ genetic-based studies reinforce such a concept and suggest that intrinsic cellular circadian clocks play a pivotal role in mediating many, if not all, biological rhythms. Circadian clocks are transcriptionally based molecular mechanisms that generate self-sustained positive and negative feedback loops with a free running period of ϳ24 h (7); this molecular mechanism has been identified within essentially all mammalian cells (both central and peripheral). Circadian clocks confer the selective advantage of anticipation. In doing so molecular clocks enable the cell to prepare for an external stimulus before its onset, thereby maintaining optimal synchrony with the environment. Given marked time-of-day-dependent rhythms in energy supply (e.g. dietary nutrient intake) and de...

Circadian variations of ischemic burden among patients with myocardial infarction undergoing primary percutaneous coronary intervention

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Circadian rhythms in glucose and lipid metabolism in nocturnal and diurnal mammals

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O-GlcNAcylation, Novel Post-Translational Modification Linking Myocardial Metabolism and Cardiomyocyte Circadian Clock

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