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. The purpose of the present study was to reveal novel physiologic functions of BMAL1 in the heart, as well as determine the pathologic consequences of chronic disruption of this circadian clock component. In order to address this goal, we generated cardiomyocyte-specific Bmal1 knockout (CBK) mice. Following validation of the CBK model, combined microarray and in silico analyses were performed, identifying 19 putative direct BMAL1 target genes, which included a number of metabolic (e.g., β-hydroxybutyrate dehydrogenase 1 [Bdh1]) and signaling (e.g., the p85α regulatory subunit of phosphatidylinositol 3-kinase [Pik3r1]) genes. Results from subsequent validation studies were consistent with regulation of Bdh1 and Pik3r1 by BMAL1, with predicted impairments in ketone body metabolism and signaling observed in CBK hearts. Furthermore, CBK hearts exhibited depressed glucose utilization, as well as a differential response to a physiologic metabolic stress (i.e., fasting). Consistent with BMAL1 influencing critical functions in the heart, echocardiographic, gravimetric, histologic, and molecular analyses revealed age-onset development of dilated cardiomyopathy in CBK mice, which was associated with a severe reduction in lifespan. Collectively, our studies reveal that BMAL1 influences metabolism, signaling, and contractile function of the heart.

Genome biology approaches have made enormous contributions to our understanding of biological rhythms, particularly in identifying outputs of the clock, including RNAs, proteins, and metabolites, whose abundance oscillates throughout the day. These methods hold significant promise for future discovery, particularly when combined with computational modeling. However, genome-scale experiments are costly and laborious, yielding “big data” that are conceptually and statistically difficult to analyze. There is no obvious consensus regarding design or analysis. Here we discuss the relevant technical considerations to generate reproducible, statistically sound, and broadly useful genome-scale data. Rather than suggest a set of rigid rules, we aim to codify principles by which investigators, reviewers, and readers of the primary literature can evaluate the suitability of different experimental designs for measuring different aspects of biological rhythms. We introduce CircaInSilico, a web-based application for generating synthetic genome biology data to benchmark statistical methods for studying biological rhythms. Finally, we discuss several unmet analytical needs, including applications to clinical medicine, and suggest productive avenues to address them.

Sleep deprivation, shift work, and jet lag all disrupt normal biological rhythms and have major impacts on health; however, circadian disorganization has never been shown as a causal risk factor in organ disease. We now demonstrate devastating effects of rhythm disorganization on cardiovascular and renal integrity and that interventions based on circadian principles prevent disease pathology caused by a short-period mutation (tau) of the circadian system in hamsters. The point mutation in the circadian regulatory gene, casein kinase-1epsilon, produces early onset circadian entrainment with fragmented patterns of behavior in +/tau heterozygotes. Animals die at a younger age with cardiomyopathy, extensive fibrosis, and severely impaired contractility; they also have severe renal disease with proteinuria, tubular dilation, and cellular apoptosis. On light cycles appropriate for their genotype (22 h), cyclic behavioral patterns are normalized, cardiorenal phenotype is reversed, and hearts and kidneys show normal structure and function. Moreover, hypertrophy does not develop in animals whose suprachiasmatic nucleus was ablated as young adults. Circadian organization therefore is critical for normal health and longevity, whereas chronic global asynchrony is implicated in the etiology of cardiac and renal disease.

Abstract-Day/night rhythms are recognized as important to normal cardiovascular physiology and timing of adverse cardiovascular events; however, their significance in disease has not been determined. We demonstrate that day/night rhythms play a critical role in compensatory remodeling of cardiovascular tissue, and disruption exacerbates disease pathophysiology. We use a murine model of pressure overload cardiac hypertrophy (transverse aortic constriction) in a rhythm-disruptive 20-hour versus 24-hour environment. Echocardiography reveals increased left ventricular end-systolic and -diastolic dimensions and reduced contractility in rhythm-disturbed transverse aortic constriction animals. Furthermore, cardiomyocytes and vascular smooth muscle cells exhibit reduced hypertrophy, despite increased pressure load. Microarray and real-time PCR demonstrate altered gene cycling in transverse aortic constriction myocardium and hypothalamic suprachiasmatic nucleus. With rhythm disturbance, there is a consequent altered cellular clock mechanism ( per2 and bmal), whereas key genes in hypertrophic pathways (ANF, BNP, ACE, and collagen) are downregulated paradoxical to the increased pressure. Phenotypic rescue, including reversal/attenuation of abnormal pathology and genes, only occurs when the external rhythm is allowed to correspond with the animals' innate 24-hour internal rhythm. Our study establishes the importance of diurnal rhythm as a vital determinant in heart disease. Disrupted rhythms contribute to progression of organ dysfunction; restoration of normal diurnal schedules appears to be important for effective treatment of disease. Key Words: cardiac hypertrophy Ⅲ renin-angiotensin-aldosterone system pathway Ⅲ remodeling Ⅲ gene expression microarrays Ⅲ circadian C ardiovascular disease is a major and increasing cause of death worldwide. Epidemiological studies suggest an important role for day/night rhythms in the cyclic variation of heart rate and blood pressure, 1,2 timing of endocrine hormone secretion, 3,4 temporal variations of cardiac vulnerability, 5 and susceptibility to adverse cardiovascular events (including myocardial infarction, 6,7 stroke, 8 angina, 9 ventricular arrhythmias, 10 dissection/rupture of aortic aneurysm, 11 and sudden cardiac death 12 ). Shift workers and patients with sleep disorders are at increased risk of adverse cardiovascular events and poorer prognosis. 13,14 However, there are no experimental data actually linking disturbed diurnal rhythms with cardiovascular pathophysiology and remodeling postinjury. Thus, relevance of diurnal rhythms is routinely ignored in clinical medicine; for example, diurnal rhythms are disturbed when multibedded rooms are used in intensive care units, and time of day is infrequently considered relevant for drug treatment or the efficacy of contemporary interventional procedures.Daily behavioral and physiological rhythms in mammals are driven by the circadian pacemaker in the suprachiasmatic nucleus (SCN) of the hypothalamus, 15,16 which orchestrates a hierarch...

O ver the years the management of patients in intensive care units (ICUs) after myocardial infarction (MI) has become increasingly intensive in an attempt to anticipate events and allow early intervention. These management strategies inadvertently increase noise, light, and multiple other well-established stimuli in the ICU environment. This has resulted in a generally clinically unappreciated disruption of the endogenous circadian rhythms and sleep in acutely ill patients. 1,2 Editorial, see p 1675Maintaining normal circadian rhythms is important because these are fundamental determinants of healthy cardiac physiology (eg, the cyclic variation in heart rate, blood pressure, and sympathovagal balance of the autonomic nervous system). [3][4][5][6] Although circadian rhythms in timing of onset and tolerance to MIs are well established, 7-11 the consequences of rhythm disturbance early after MI have not been reported. The heart is relatively incapable of myocyte regeneration, and early healing after MI relies on coordinated removal of dead tissue through an early inflammatory phase, 12 followed by replacement and remodeling of the myocardium and extracellular matrix. 13 As remodeling progresses toward the maturation phase, the heart changes size, shape, and structure, and these processes can lead to ventricular dilation, dysfunction, and ultimately failure.14 Whether short-term diurnal rhythm disruption after MI would impair the critical, orderly, temporal Objective: Short-term diurnal rhythm disruption immediately after MI impairs remodeling and adversely affects long-term cardiac structure and function in a murine model. Methods and Results: Mice were infarcted by left anterior descending coronary artery ligation (MI model) withina 3-hour time window, randomized to either a normal diurnal or disrupted environment for 5 days, and then maintained under normal diurnal conditions. Initial infarct size was identical. Short-term diurnal disruption adversely affected body metabolism and altered early innate immune responses. In the first 5 days, crucial for scar formation, there were significant differences in cardiac myeloperoxidase, cytokines, neutrophil, and macrophage infiltration. Homozygous clock mutant mice exhibited altered infiltration after MI, consistent with circadian mechanisms underlying innate immune responses crucial for scar formation. In the proliferative phase, 1 week after MI, this led to significantly less blood vessel formation in the infarct region of disrupted mice; by day 14, echocardiography showed increased left ventricular dilation and infarct expansion. These differences continued to evolve with worse cardiac structure and function by 8 weeks after MI. Conclusions: