Circadian clock and vascular disease

Clinical, Anamnestic, and Demographic Characteristics of Patients with Myocardial Infarction in Russian Federation According to the Russian Registry of Acute Myocardial Infarction - REGION-IM

AIM

Based on data from the Russian REGION-MI registry, to characterize patients with myocardial infarction (MI) hospitalized in Russian hospitals, describe their historical, demographic, and clinical characteristics, and compare the results with the data of previous Russian and international registries of acute coronary syndrome.

MATERIAL AND METHODS

REGION-MI is a multicenter prospective observational study. The follow-up period was divided into three stages: during the hospital stay, at 6 and 12 months after the inclusion in the registry. Demographic and historic data and information about the present case of MI were entered into the patient's individual record card.

RESULTS

The median age of all patients was 63 years; 68% of patients were men. The mean age of women was older than that of men. Among all MI cases, 70% were ST-segment elevation myocardial infarction (STEMI). Patients with non-ST-segment elevation myocardial infarction (NSTEMI) were older and had more comorbidities than patients with STEMI. The median time from the first symptoms to ECG recording was two hours, and from the first symptoms to CAG 7 hours. CAG was performed in 91% of patients with STEMI and 84% of patients with NSTEMI. Stenting was performed in 69% of patients. Although many patients had a complicated cardiovascular history, at the time of admission only 31.5% of patients were taking at least one drug from the groups of antiplatelets, oral anticoagulants, statins, and beta-blockers.

CONCLUSION

Patients with MI in the Russian Federation are younger than patients with MI in European countries. Among the clinical and historical characteristics, conspicuous is the presence of modifiable risk factors in many patients, as well as the presence of a previous diagnosis of ischemic heart disease. Furthermore, a small proportion of patients took statins, antiplatelet agents or anticoagulants at the outpatient stage, which indicates a great reserve of both primary and secondary prevention of cardiovascular diseases in the Russian Federation. The delayed seeking medical help is also noticeable, which indicates the need for increasing the public awareness of the symptoms of MI and the importance of timely hospitalization.

Hypoxia Induces Alterations in the Circadian Rhythm in Patients with Chronic Respiratory Diseases

The function of the circadian cycle is to determine the natural 24 h biological rhythm, which includes physiological, metabolic, and hormonal changes that occur daily in the body. This cycle is controlled by an internal biological clock that is present in the body's tissues and helps regulate various processes such as sleeping, eating, and others. Interestingly, animal models have provided enough evidence to assume that the alteration in the circadian system leads to the appearance of numerous diseases. Alterations in breathing patterns in lung diseases can modify oxygenation and the circadian cycles; however, the response mechanisms to hypoxia and their relationship with the clock genes are not fully understood. Hypoxia is a condition in which the lack of adequate oxygenation promotes adaptation mechanisms and is related to several genes that regulate the circadian cycles, the latter because hypoxia alters the production of melatonin and brain physiology. Additionally, the lack of oxygen alters the expression of clock genes, leading to an alteration in the regularity and precision of the circadian cycle. In this sense, hypoxia is a hallmark of a wide variety of lung diseases. In the present work, we intended to review the functional repercussions of hypoxia in the presence of asthma, chronic obstructive sleep apnea, lung cancer, idiopathic pulmonary fibrosis, obstructive sleep apnea, influenza, and COVID-19 and its repercussions on the circadian cycles.

Vascular dysfunction caused by loss of Brn-3b/POU4F2 transcription factor in aortic vascular smooth muscle cells is linked to deregulation of calcium signalling pathways

Phenotypic and functional changes in vascular smooth muscle cells (VSMCs) contribute significantly to cardiovascular diseases (CVD) but factors driving early adverse vascular changes are poorly understood. We report on novel and important roles for the Brn-3b/POU4F2 (Brn-3b) transcription factor (TF) in controlling VSMC integrity and function. Brn-3b protein is expressed in mouse aorta with localisation to VSMCs. Male Brn-3b knock-out (KO) aortas displayed extensive remodelling with increased extracellular matrix (ECM) deposition, elastin fibre disruption and small but consistent narrowing/coarctation in the descending aortas. RNA sequencing analysis showed that these effects were linked to deregulation of genes required for calcium (Ca2+) signalling, vascular contractility, sarco-endoplasmic reticulum (S/ER) stress responses and immune function in Brn-3b KO aortas and validation studies confirmed changes in Ca2+ signalling genes linked to increased intracellular Ca2+ and S/ER Ca2+ depletion [e.g. increased, Cacna1d Ca2+ channels; ryanodine receptor 2, (RyR2) and phospholamban (PLN) but reduced ATP2a1, encoding SERCA1 pump] and chaperone proteins, Hspb1, HspA8, DnaJa1 linked to increased S/ER stress, which also contributes to contractile dysfunction. Accordingly, vascular rings from Brn-3b KO aortas displayed attenuated contractility in response to KCl or phenylephrine (PE) while Brn-3b KO-derived VSMC displayed abnormal Ca2+ signalling following ATP stimulation. This data suggests that Brn-3b target genes are necessary to maintain vascular integrity /contractile function and deregulation upon loss of Brn-3b will contribute to contractile dysfunction linked to CVD.

When the clock ticks wrong with COVID-19

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a member of the coronavirus family that causes the novel coronavirus disease first diagnosed in 2019 (COVID-19). Although many studies have been carried out in recent months to determine why the disease clinical presentations and outcomes can vary significantly from asymptomatic to severe or lethal, the underlying mechanisms are not fully understood. It is likely that unique individual characteristics can strongly influence the broad disease variability; thus, tailored diagnostic and therapeutic approaches are needed to improve clinical outcomes. The circadian clock is a critical regulatory mechanism orchestrating major physiological and pathological processes. It is generally accepted that more than half of the cell-specific genes in any given organ are under circadian control. Although it is known that a specific role of the circadian clock is to coordinate the immune system's steady-state function and response to infectious threats, the links between the circadian clock and SARS-CoV-2 infection are only now emerging. How inter-individual variability of the circadian profile and its dysregulation may play a role in the differences noted in the COVID-19-related disease presentations, and outcome remains largely underinvestigated. This review summarizes the current evidence on the potential links between circadian clock dysregulation and SARS-CoV-2 infection susceptibility, disease presentation and progression, and clinical outcomes. Further research in this area may contribute towards novel circadian-centred prognostic, diagnostic and therapeutic approaches for COVID-19 in the era of precision health.

Skipping breakfast during pregnancy and hypertensive disorders of pregnancy in Japanese women: the Tohoku medical megabank project birth and three-generation cohort study

BACKGROUND

Hypertensive disorders of pregnancy (HDP) adversely affect the prognosis of mother and child, and the prognosis depends on the subtype of HDP. Skipping breakfast may be associated with increased blood pressure due to disruption of the circadian clock, but the association with the development of HDP has not been studied. The purpose of this study was to examine the association between skipping breakfast and the development of HDP and HDP subtypes in Japanese pregnant women.

METHODS

Of the pregnant women who participated in the Tohoku Medical Megabank Project Three-Generation Cohort Study, 18,839 who answered the required questions were included in the analysis. This study had a cross-sectional design. The breakfast intake frequency from pre-pregnancy to early pregnancy was classified into four groups: daily, 5-6 times per week, 3-4 times per week, and 0-2 times per week. HDP was classified into gestational hypertension (GH), chronic hypertension (CH), preeclampsia (PE), and severe preeclampsia (SuPE). Multiple logistic regression analysis and multinomial logistic analysis were used to calculate odds ratios (ORs) and 95% confidence intervals (CIs) for breakfast intake frequency and development of HDP or HDP subtypes. We performed a stratified analysis based on energy intake.

RESULTS

Of the participants, 74.3% consumed breakfast daily, and 11.1% developed HDP. Women who consumed breakfast 0-2 times per week had a higher risk of HDP (OR: 1.33, 95% CI: 1.14-1.56), CH (OR: 1.63, 95% CI: 1.21-2.19), and PE (OR: 1.68, 95% CI: 1.27-2.21) than those who consumed breakfast daily. No association was found between skipping breakfast and the risk of developing GH (OR: 1.26, 95% CI: 0.99-1.61) and SuPE (OR: 0.91, 95% CI: 0.55-1.49). Stratified analysis showed that the risk of developing HDP due to skipping breakfast was highest in the group with the highest daily energy intake.

CONCLUSIONS

Skipping breakfast during pre-to early pregnancy is associated with the development of HDP. Further longitudinal studies are required to clarify the causal association between skipping breakfast and HDP.

Clock Gene Bmal1 Disruption in Vascular Smooth Muscle Cells Worsens Carotid Atherosclerotic Lesions

BACKGROUND

Clock system disruptions are associated with cardiovascular diseases. We previously demonstrated Bmal1 (brain muscle aryl nuclear translocase like-1) expression is significantly attenuated in plaque-derived vascular smooth muscle cells (VSMCs). However, the influence of Bmal1 disruption in VSMCs and its molecular targets are still unclear. Here, we aim to define how Bmal1 disruption in VSMCs influences the atherosclerosis lesions.

METHODS

The relationship among Bmal1, neurological symptoms, and plaque stability was investigated. VSMC Bmal1^-/- and VSMC Bmal1^+/+mice were generated and injected with adeno associated virus encoding mutant proprotein convertase subtilisin/kexin type 9 to induce atherosclerosis. Carotid artery ligation and cuff placement were performed in these mice to confirm the role of Bmal1 in atherosclerosis progression. The relevant molecular mechanisms were then explored.

RESULTS

Bmal1 expression in the carotid plague was significantly lower in symptomatic patients as well as in unstable plaques. Moreover, Bmal1 reduction is an independent risk factor for neurological symptoms and plaque instability. Besides, VSMC Bmal1^-/- mice exhibit aggravated atherosclerotic lesions. Further study demonstrated that Bmal1 downregulation in VSMCs increased VSMC migration, monocyte transmigration, reactive oxygen species levels, and VSMCs apoptosis. As for the mechanism, we revealed that Bmal1 suppresses VSMCs migration by inhibiting RAC1 activity in 2 ways: by activating the transcription of RhoGDIα and by interacting with RAC1. Besides, Bmal1 was shown to preserve antioxidant function in VSMCs by activating Nrf2 (nuclear factor erythroid 2-related factor 2) and Bcl-2 transcription.

CONCLUSIONS

Bmal1 disruption in VSMCs worsens atherosclerosis by promoting VSMC migration and monocyte transmigration and impairing antioxidant function. Therefore, Bmal1 may be a potential therapeutic target and biomarker of atherosclerosis in the future.

Estimating nocturnal stroke onset times by magnetic resonance imaging in the WAKE-UP trial

BACKGROUND

Fluid-attenuated inversion recovery (FLAIR) sequences have gained a role to guide treatment of patients with unknown time of stroke symptom onset. Evolution of signal intensities in FLAIR is associated with time since stroke onset with continuous linear increases.

AIMS

Estimating symptom onset during night-sleep in patients from the WAKE-UP trial based on relative signal intensities FLAIR (FLAIR-rSI) from acute stroke lesions an independent dataset (PRE-FLAIR study).

METHODS

FLAIR-rSI was quantified in stroke lesions in PRE-FLAIR and WAKE-UP. The PRE-FLAIR study was a multicenter observational trial establishing FLAIR as a surrogate parameter for time since stroke onset. WAKE-UP was a randomized controlled trial that revealed a benefit for alteplase in patients selected based on a DWI-FLAIR mismatch. Stroke onset times were recorded in PRE-FLAIR and used to fit a linear regression model with FLAIR-rSI, adjusted for patient age and lesion volume. The model was applied to FLAIR-rSI of stroke lesions to estimate onset times in those patients enrolled in WAKE-UP who had symptom onset during night-sleep.

RESULTS

FLAIR-rSI was quantified in 399 patients from PRE-FLAIR. Linear regression indicated a significant association of age (p = 0.001), lesion volume (p = 0.005) and FLAIR-rSI (p < 0.001) with time since symptom onset (adjusted R²= 0.179). In 813 patients from WAKE-UP, distribution of times of last seen well, symptom recognition and MRI examination were recorded. Median times of last seen well were 1 h before midnight (IQR 2.4 h) and symptom recognition 7 h after midnight (IRQ 2.2 h). Based on the FLAIR-rSI profiles, we estimated median stroke onset 6.1 h after midnight (IQR 2.7 h).

CONCLUSION

Nocturnal strokes during night-sleep may predominantly occur during the early morning hours. Our results are in line with evidence of characteristic diurnal patterns of cardiovascular events.

Impact of the circadian clock on fibrinolysis and coagulation in healthy individuals and cardiovascular patients - A systematic review

INTRODUCTION

Human body functions exhibit a circadian rhythm generated in peripheral cells and synchronized by the suprachiasmatic nucleus (SCN), which mostly is entrained by the daily light/dark cycles. Activity, meals and posture are capable of interfering with the endogenous circadian rhythm of coagulation parameters. An increasing number of human disorders show a circadian component, and epidemiological studies find cardiovascular events to peak in the morning hours. The aim was to review the circadian rhythms impact on fibrinolysis and coagulation in healthy individuals and cardiovascular patients.

MATERIALS AND METHODS

A total number of 25 studies were identified where 8 enrolled cardiovascular patients with or without healthy individuals. Using a MeSH-search in MEDLINE PubMed. Only original peer-reviewed papers were included.

RESULTS

Results showed substantial variance with respect to exhibition of circadian rhythms and/or peak/trough times. Circadian rhythms of fibrinolysis were less pronounced in cardiovascular patients than in healthy individuals with decreased levels in the morning hours compared to healthy inducing higher risk of blood clotting.

CONCLUSIONS

Because of small studied group sizes and failure to control for entraining factors, larger studies are needed to fully establish the effects of the circadian rhythm on especially coagulation. The findings of chronobiologic rhythms in coagulation and fibrinolysis could suggest a need for a chrono-pharmacological approach when treating/preventing cardiovascular diseases.

Circadian Pattern of Acute Myocardial Infarction and Atrial Fibrillation in a Mediterranean Country: A study in Diabetic Patients

Background and objectives: The circadian pattern seems to play a crucial role in cardiovascular events and arrhythmias. Diabetes mellitus is a complex metabolic disorder associated with autonomic nervous system alterations and increased risk of microvascular and macrovascular disease. We sought to determine whether acute myocardial infarction (AMI) and atrial fibrillation (AF) follow a circadian pattern in diabetic patients in a Mediterranean country. Materials and Methods: This retrospective study included 178 diabetic patients (mean age: 67.7) with AMI or AF who were admitted to the coronary care unit. The circadian pattern of AMI and AF was identified in the 24-h period (divided in 3-h and 1-h intervals). Patients were also divided in 3 groups according to age; 40-65 years, 66-79 years and patients older than 80 years. A chi-square goodness-of-fit test was used for the statistical analysis. Results: AMI seems to occur more often in the midnight hours (21:00-23:59) (p < 0.001). Regarding age distribution, patients between 40 and 65 years were more likely to experience an AMI compared to other age groups (p < 0.001). Autonomic alterations, working habits, and social reasons might contribute to this phenomenon. AF in diabetic patients occurs more frequently at noon (12:00-14:59) (p = 0.019). Conclusions: Diabetic patients with AMI and AF seem to follow a specific circadian pattern in a Mediterranean country, with AMI occurring most often at midnight hours and AF mostly at noon. Autonomic dysfunction, glycemic fluctuations, intense anti-diabetic treatment before lunch, and patterns of insulin secretion and resistance may explain this pattern. More studies are needed to elucidate the circadian pattern of AMI and AF in diabetic patients to contribute to the development of new therapeutic approaches in this setting.

BMAL1 regulates mitochondrial fission and mitophagy through mitochondrial protein BNIP3 and is critical in the development of dilated cardiomyopathy

Dysregulation of circadian rhythms associates with cardiovascular disorders. It is known that deletion of the core circadian gene Bmal1 in mice causes dilated cardiomyopathy. However, the biological rhythm regulation system in mouse is very different from that of humans. Whether BMAL1 plays a role in regulating human heart function remains unclear. Here we generated a BMAL1 knockout human embryonic stem cell (hESC) model and further derived human BMAL1 deficient cardiomyocytes. We show that BMAL1 deficient hESC-derived cardiomyocytes exhibited typical phenotypes of dilated cardiomyopathy including attenuated contractility, calcium dysregulation, and disorganized myofilaments. In addition, mitochondrial fission and mitophagy were suppressed in BMAL1 deficient hESC-cardiomyocytes, which resulted in significantly attenuated mitochondrial oxidative phosphorylation and compromised cardiomyocyte function. We also found that BMAL1 binds to the E-box element in the promoter region of BNIP3 gene and specifically controls BNIP3 protein expression. BMAL1 knockout directly reduced BNIP3 protein level, causing compromised mitophagy and mitochondria dysfunction and thereby leading to compromised cardiomyocyte function. Our data indicated that the core circadian gene BMAL1 is critical for normal mitochondria activities and cardiac function. Circadian rhythm disruption may directly link to compromised heart function and dilated cardiomyopathy in humans.

Intense light as anticoagulant therapy in humans

Blood coagulation is central to myocardial ischemia and reperfusion (IR) injury. Studies on the light elicited circadian rhythm protein Period 2 (PER2) using whole body Per2-/- mice found deficient platelet function and reduced clotting which would be expected to protect from myocardial IR-injury. In contrast, intense light induction of PER2 protected from myocardial IR-injury while Per2 deficiency was detrimental. Based on these conflicting data, we sought to evaluate the role of platelet specific PER2 in coagulation and myocardial ischemia and reperfusion injury. We demonstrated that platelets from mice with tissue-specific deletion of Per2 in the megakaryocyte lineage (Per2loxP/loxP-PF4-CRE) significantly clot faster than platelets from control mice. We further found increases in infarct sizes or plasma troponin levels in Per2loxP/loxP-PF4-CRE mice when compared to controls. As intense light increases PER2 protein in human tissues, we also performed translational studies and tested the effects of intense light therapy on coagulation in healthy human subjects. Our human studies revealed that intense light therapy repressed procoagulant pathways in human plasma samples and significantly reduced the clot rate. Based on these results we conclude that intense light elicited PER2 has an inhibitory function on platelet aggregation in mice. Further, we suggest intense light as a novel therapy to prevent or treat clotting in a clinical setting.

Circadian Rhythm of Cardiovascular Disease: The Potential of Chronotherapy With Aspirin

Almost all the systems in our body adhere to a daily 24 h rhythm. The cardiovascular system is also affected by this 24 h rhythm. In the morning there is a change in various cardiovascular processes, including platelet aggregability. These changes may play a role in the relative excess of early morning cardiovascular events. The number of recurrent cardiovascular diseases (CVD) could, in theory, be reduced by responding to this 24 h rhythm with timed medication intake (chronotherapy), which also applies to aspirin. Multiple studies on chronotherapy with low-dose aspirin are promising, showing a decrease in early morning platelet activity with evening intake compared with morning intake. However, in order to further demonstrate its clinical impact, randomized trials with cardiovascular events as a primary outcome are needed. This review discusses the available evidence of the effects of circadian rhythm on CVD and the potential positive effect of chronotherapy with aspirin.

Circadian clock genes and myocardial infarction in patients with type 2 diabetes mellitus

Disruption of circadian clock may trigger the onset of diabetes mellitus and myocardial infarction. Type 2 diabetes mellitus (T2DM) is well-known risk factors for cardiovascular diseases and myocardial infarction. We performed a case-control study, where we explored the possible association between single nucleotide polymorphisms in three circadian rhythm genes (ARNTL, CLOCK, and PER2) and myocardial infarction in 657 patients with T2DM. The study group consisted of 231 patients with myocardial infarction and T2DM and a control group of 426 T2DM patients. We hypothesized that variations in the circadian rhythm genes in patients with T2DM could be an additional risk factor for myocardial infarction. The statistically significant difference was found in allelic (p = 1.1 × 10-5) and genotype distribution (p = 1.42 × 10-4) between two groups of the rs12363415 at the ARNTL gene locus. We provide evidence that genetic variability in the ARNTL gene might be associated with myocardial infarction in patients with T2DM.

Bmal1 in Perivascular Adipose Tissue Regulates Resting-Phase Blood Pressure Through Transcriptional Regulation of Angiotensinogen

BACKGROUND

The perivascular adipose tissue (PVAT) surrounding vessels constitutes a distinct functional integral layer of the vasculature required to preserve vascular tone under physiological conditions. However, there is little information on the relationship between PVAT and blood pressure regulation, including its potential contributions to circadian blood pressure variation.

METHODS

Using unique brown adipocyte-specific aryl hydrocarbon receptor nuclear translocator-like protein 1 (Bmal1) and angiotensinogen knockout mice, we determined the vasoactivity of homogenized PVAT in aortic rings and how brown adipocyte peripheral expression of Bmal1 and angiotensinogen in PVAT regulates the amplitude of diurnal change in blood pressure in mice.

RESULTS

We uncovered a peripheral clock in PVAT and demonstrated that loss of Bmal1 in PVAT reduces blood pressure in mice during the resting phase, leading to a superdipper phenotype. PVAT extracts from wild-type mice significantly induced contractility of isolated aortic rings in vitro in an endothelium-independent manner. This property was impaired in PVAT from brown adipocyte-selective Bmal1-deficient (BA-Bmal1-KO) mice. The PVAT contractile properties were mediated by local angiotensin II, operating through angiotensin II type 1 receptor-dependent signaling in the isolated vessels and linked to PVAT circadian regulation of angiotensinogen. Indeed, angiotensinogen mRNA and angiotensin II levels in PVAT of BA-Bmal1-KO mice were significantly reduced. Systemic infusion of angiotensin II, in turn, reduced Bmal1 expression in PVAT while eliminating the hypotensive phenotype during the resting phase in BA-Bmal1-KO mice. Angiotensinogen, highly expressed in PVAT, shows circadian expression in PVAT, and selective deletion of angiotensinogen in brown adipocytes recapitulates the phenotype of selective deletion of Bmal1 in brown adipocytes. Furthermore, angiotensinogen is a transcriptional target of Bmal1 in PVAT.

CONCLUSIONS

These data indicate that local Bmal1 in PVAT regulates angiotensinogen expression and the ensuing increase in angiotensin II, which acts on smooth muscle cells in the vessel walls to regulate vasoactivity and blood pressure in a circadian fashion during the resting phase. These findings will contribute to a better understanding of the cardiovascular complications of circadian disorders, alterations in the circadian dipping phenotype, and cross-talk between systemic and peripheral regulation of blood pressure.

Genetic variations in circadian rhythm genes and susceptibility for myocardial infarction

Disruption of endogenous circadian rhythms has been shown to increase the risk of developing myocardial infarction (MI), suggesting that circadian genes might play a role in determining disease susceptibility. We conducted a case-control study on 200 patients hospitalized due to MI and 200 healthy controls, investigating the association between MI and single nucleotide polymorphisms (SNPs) in four circadian genes (ARNTL, CLOCK, CRY2, and PER2). The variants of all four genes were chosen based on their previously reported association with cardiovascular risk factors, which have a major influence on the occurrence of myocardial infarction. Statistically significant differences, assessed through Chi-square analysis, were found in genotype distribution between cases and controls of the PER2 gene rs35333999 (p=0.024) and the CRY2 gene rs2292912 (p=0.028); the corresponding unadjusted odds ratios, also significant, were respectively OR=0.49 (95% CI 0.26-0.91) and OR=0.32 (95% CI 0.11-0.89). Our data suggest that genetic variability in the CRY2 and PER2 genes might be associated with myocardial infarction.

Altered Circadian Timing System-Mediated Non-Dipping Pattern of Blood Pressure and Associated Cardiovascular Disorders in Metabolic and Kidney Diseases

The morning surge in blood pressure (BP) coincides with increased cardiovascular (CV) events. This strongly suggests that an altered circadian rhythm of BP plays a crucial role in the development of CV disease (CVD). A disrupted circadian rhythm of BP, such as the non-dipping type of hypertension (i.e., absence of nocturnal BP decline), is frequently observed in metabolic disorders and chronic kidney disease (CKD). The circadian timing system, controlled by the central clock in the suprachiasmatic nucleus of the hypothalamus and/or by peripheral clocks in the heart, vasculature, and kidneys, modulates the 24 h oscillation of BP. However, little information is available regarding the molecular and cellular mechanisms of an altered circadian timing system-mediated disrupted dipping pattern of BP in metabolic disorders and CKD that can lead to the development of CV events. A more thorough understanding of this pathogenesis could provide novel therapeutic strategies for the management of CVD. This short review will address our and others' recent findings on the molecular mechanisms that may affect the dipping pattern of BP in metabolic dysfunction and kidney disease and its association with CV disorders.

The rat cerebral vasculature exhibits time-of-day-dependent oscillations in circadian clock genes and vascular function that are attenuated following obstructive sleep apnea

Circadian clock components oscillate in cells of the cardiovascular system. Disruption of these oscillations has been observed in cardiovascular diseases. We hypothesized that obstructive sleep apnea, which is associated with cerebrovascular diseases, disrupts the cerebrovascular circadian clock and rhythms in vascular function. Apneas were produced in rats during sleep. Following two weeks of sham or obstructive sleep apnea, cerebral arteries were isolated over 24 h for mRNA and functional analysis. mRNA expression of clock genes exhibited 24-h rhythms in cerebral arteries of sham rats (p < 0.05). Interestingly, peak expression of clock genes was significantly lower following obstructive sleep apnea (p < 0.05). Obstructive sleep apnea did not alter clock genes in the heart, or rhythms in locomotor activity. Isolated posterior cerebral arteries from sham rats exhibited a diurnal rhythm in sensitivity to luminally applied ATP, being most responsive at the beginning of the active phase (p < 0.05). This rhythm was absent in arteries from obstructive sleep apnea rats (p < 0.05). Rhythms in ATP sensitivity in sham vessels were absent, and not different from obstructive sleep apnea, following treatment with L-NAME and indomethacin. We conclude that cerebral arteries possess a functional circadian clock and exhibit a diurnal rhythm in vasoreactivity to ATP. Obstructive sleep apnea attenuates these rhythms in cerebral arteries, potentially contributing to obstructive sleep apnea-associated cerebrovascular disease.

Regulation of Clock Genes by Adrenergic Receptor Signaling in Osteoblasts

The clock system has been identified as one of the major mechanisms controlling cellular functions. Circadian clock gene oscillations also actively participate in the functions of various cell types including bone-related cells. Previous studies demonstrated that clock genes were expressed in bone tissue and also that their expression exhibited circadian rhythmicity. Recent findings have shown that sympathetic tone plays a central role in biological oscillations in bone. Adrenergic receptor (AR) signaling regulates the expression of clock genes in cancellous bone. Furthermore, α₁-AR signaling in osteoblasts is known to negatively regulate the expression of bone morphogenetic protein-4 (Bmp4) by up-regulating nuclear factor IL-3 (Nfil3)/e4 promoter-binding protein 4 (E4BP4). The ablation of α_1B-AR signaling also increases the expression of the Bmp4 gene in bone. The findings of transient overexpression and siRNA experiments have supported the involvement of the transcription factor CCAAT/enhancer-binding protein delta (C/EBPδ, Cebpd) in Nfil3 and Bmp4 expression in MC3T3-E1 cells. These findings suggest that the effects of Cebpd are due to the circadian regulation of Bmp4 expression, at least in part, by the up-regulated expression of the clock gene Nfil3 in response to α_1B-AR signaling in osteoblasts. Therefore, AR signaling appears to modulate cellular functionality through the expression of clock genes that are circadian rhythm regulators in osteoblasts. The expression of clock genes regulated by the sympathetic nervous system and clock-controlled genes that affect bone metabolism are described herein.

Intracellular high cholesterol content disorders the clock genes, apoptosis-related genes and fibrinolytic-related genes rhythmic expressions in human plaque-derived vascular smooth muscle cells

Background

The clock genes are involved in regulating cardiovascular functions, and their expression disorders would lead to circadian rhythm disruptions of clock-controlled genes (CCGs), resulting in atherosclerotic plaque formation and rupture. Our previous study revealed the rhythmic expression of clock genes were attenuated in human plaque-derived vascular smooth muscle cells (PVSMCs), but failed to detect the downstream CCGs expressions and the underlying molecular mechanism. In this study, we examined the difference of CCGs rhythmic expression between human normal carotid VSMCs (NVSMCs) and PVSMCs. Furthermore, we compared the cholesterol and triglycerides levels between two groups and the link to clock genes and CCGs expressions.

Methods

Seven health donors’ normal carotids and 19 carotid plaques yielded viable cultured NVSMCs and PVSMCs. The expression levels of target genes were measured by quantitative real-time PCR and Western-blot. The intracellular cholesterol and triglycerides levels were measured by kits.

Result

The circadian expressions of apoptosis-related genes and fibrinolytic-related genes were disordered. Besides, the cholesterol levels were significant higher in PVSMCs. After treated with cholesterol or oxidized low density lipoprotein (ox-LDL), the expressions of clock genes were inhibited; and the rhythmic expressions of clock genes, apoptosis-related genes and fibrinolytic-related genes were disturbed in NVSMCs, which were similar to PVSMCs.

Conclusion

The results suggested that intracellular high cholesterol content of PVSMCs would lead to the disorders of clock genes and CCGs rhythmic expressions. And further studies should be conducted to demonstrate the specific molecular mechanisms involved.

Hypothalamic and inflammatory basis of hypertension

Hypertension is a major health problem with great consequences for public health. Despite its role as the primary cause of significant morbidity and mortality associated with cardiovascular disease, the pathogenesis of essential hypertension remains largely unknown. The central nervous system (CNS) in general, and the hypothalamus in particular, are intricately involved in the development and maintenance of hypertension. Over the last several decades, the understanding of the brain's role in the development of hypertension has dramatically increased. This brief review is to summarize the neural mechanisms of hypertension with a focus on neuroendocrine and neurotransmitter involvement, highlighting recent findings that suggest that hypothalamic inflammation disrupts key signalling pathways to affect the central control of blood pressure, and therefore suggesting future development of interventional strategies that exploit recent findings pertaining to the hypothalamic control of blood pressure as well as the inflammatory-sympathetic mechanisms involved in hypertension.

Central and peripheral clocks are coupled by a neuropeptide pathway in Drosophila

Animal circadian clocks consist of central and peripheral pacemakers, which are coordinated to produce daily rhythms in physiology and behaviour. Despite its importance for optimal performance and health, the mechanism of clock coordination is poorly understood. Here we dissect the pathway through which the circadian clock of Drosophila imposes daily rhythmicity to the pattern of adult emergence. Rhythmicity depends on the coupling between the brain clock and a peripheral clock in the prothoracic gland (PG), which produces the steroid hormone, ecdysone. Time information from the central clock is transmitted via the neuropeptide, sNPF, to non-clock neurons that produce the neuropeptide, PTTH. These secretory neurons then forward time information to the PG clock. We also show that the central clock exerts a dominant role on the peripheral clock. This use of two coupled clocks could serve as a paradigm to understand how daily steroid hormone rhythms are generated in animals.

Differential Regulation of BMAL1, CLOCK, and Endothelial Signaling in the Aortic Arch and Ligated Common Carotid Artery

The circadian clock is rhythmically expressed in blood vessels, but the interaction between the circadian clock and disturbed blood flow remains unclear. We examined the relationships between BMAL1 and CLOCK and 2 regulators of endothelial function, AKT1 and endothelial nitric oxide synthase (eNOS), in vascular regions of altered blood flow. We found that the aortic arch from WT mice exhibited reduced sensitivity to acetylcholine (Ach)-mediated relaxation relative to the thoracic aorta. In Clock-mutant (mut) mice the aorta exhibited a reduced sensitivity to Ach. In WT mice, the phosphorylated forms of eNOS and AKT were decreased in the aortic arch, while BMAL1 and CLOCK expression followed a similar pattern of reduction in the arch. In conditions of surgically induced flow reduction, phosphorylated-eNOS (serine 1177) increased, as did p-AKT in the ipsilateral left common carotid artery (LC) of WT mice. Similarly, BMAL1 and CLOCK exhibited increased expression after 5 days in the remodeled LC. eNOS expression was increased at 8 p.m. versus 8 a.m. in WT mice, and this pattern was abolished in mut and Bmal1-KO mice. These data suggest that the circadian clock may be a biomechanical and temporal sensor that acts to coordinate timing, flow dynamics, and endothelial function.

Circadian clock and the onset of cardiovascular events

The onset of cardiovascular diseases often shows time-of-day variation. Acute myocardial infarction or ventricular arrhythmia such as ventricular tachycardia occurs mainly in the early morning. Multiple biochemical and physiological parameters show circadian rhythm, which may account for the diurnal variation of cardiovascular events. These include the variations in blood pressure, activity of the autonomic nervous system and renin-angiotensin axis, coagulation cascade, vascular tone and the intracellular metabolism of cardiomyocytes. Importantly, the molecular clock system seems to underlie the circadian variation of these parameters. The center of the biological clock, also known as the central clock, exists in the suprachiasmatic nucleus. In contrast, the molecular clock system is also activated in each cell of the peripheral organs and constitute the peripheral clock. The biological clock system is currently considered to have a beneficial role in maintaining the homeostasis of each organ. Discoordination, however, between the peripheral clock and external environment could potentially underlie the development of cardiovascular events. Therefore, understanding the molecular and cellular pathways by which cardiovascular events occur in a diurnal oscillatory pattern will help the establishment of a novel therapeutic approach to the management of cardiovascular disorders.

α1B-Adrenergic receptor signaling controls circadian expression of Tnfrsf11b by regulating clock genes in osteoblasts

Circadian clocks are endogenous and biological oscillations that occur with a period of <24 h. In mammals, the central circadian pacemaker is localized in the suprachiasmatic nucleus (SCN) and is linked to peripheral tissues through neural and hormonal signals. In the present study, we investigated the physiological function of the molecular clock on bone remodeling. The results of loss-of-function and gain-of-function experiments both indicated that the rhythmic expression of Tnfrsf11b, which encodes osteoprotegerin (OPG), was regulated by Bmal1 in MC3T3-E1 cells. We also showed that REV-ERBα negatively regulated Tnfrsf11b as well as Bmal1 in MC3T3-E1 cells. We systematically investigated the relationship between the sympathetic nervous system and the circadian clock in osteoblasts. The administration of phenylephrine, a nonspecific α1-adrenergic receptor (AR) agonist, stimulated the expression of Tnfrsf11b, whereas the genetic ablation of α_1B-AR signaling led to the alteration of Tnfrsf11b expression concomitant with Bmal1 and Per2 in bone. Thus, this study demonstrated that the circadian regulation of Tnfrsf11b was regulated by the clock genes encoding REV-ERBα (Nr1d1) and Bmal1 (Bmal1, also known as Arntl), which are components of the core loop of the circadian clock in osteoblasts.

Summary: This study demonstrates that the circadian regulation of TNFRSF11B is regulated by the clock genes Nr1d1 and Arntl, which are components of the core loop of the circadian clock in osteoblasts, providing a molecular mechanism for the control of bone remodelling by circadian rhythms.

The role of clock genes and circadian rhythm in the development of cardiovascular diseases

The time of onset of cardiovascular disorders such as myocardial infarctions or ventricular arrhythmias exhibits a circadian rhythm. Diurnal variations in autonomic nervous activity, plasma cortisol level or renin-angiotensin activity underlie the pathogenesis of cardiovascular diseases. Transcriptional-translational feedback loop of the clock genes constitute a molecular clock system. In addition to the central clock in the suprachiasmatic nucleus, clock genes are also expressed in a circadian fashion in each organ to make up the peripheral clock. The peripheral clock seems to be beneficial for anticipating external stimuli and thus contributes to the maintenance of organ homeostasis. Loss of synchronization between the central and peripheral clocks also augments disease progression. Moreover, accumulating evidence shows that clock genes affect inflammatory and intracellular metabolic signaling. Elucidating the roles of the molecular clock in cardiovascular pathology through the identification of clock controlled genes will help to establish a novel therapeutic approach for cardiovascular disorders.

Involvement of adenosine monophosphate-activated protein kinase in the influence of timed high-fat evening diet on the hepatic clock and lipogenic gene expression in mice

A high-fat diet may result in changes in hepatic clock gene expression, but potential mechanisms are not yet elucidated. Adenosine monophosphate-activated protein kinase (AMPK) is a serine/threonine protein kinase that is recognized as a key regulator of energy metabolism and certain clock genes. Therefore, we hypothesized that AMPK may be involved in the alteration of hepatic clock gene expression under a high-fat environment. This study aimed to examine the effects of timed high-fat evening diet on the activity of hepatic AMPK, clock genes, and lipogenic genes. Mice with hyperlipidemic fatty livers were induced by orally administering high-fat milk via gavage every evening (19:00-20:00) for 6 weeks. Results showed that timed high-fat diet in the evening not only decreased the hepatic AMPK protein expression and activity but also disturbed its circadian rhythm. Accordingly, the hepatic clock genes, including clock, brain-muscle-Arnt-like 1, cryptochrome 2, and period 2, exhibited prominent changes in their expression rhythms and/or amplitudes. The diurnal rhythms of the messenger RNA expression of peroxisome proliferator-activated receptorα, acetyl-CoA carboxylase 1α, and carnitine palmitoyltransferase 1 were also disrupted; the amplitude of peroxisome proliferator-activated receptorγcoactivator 1α was significantly decreased at 3 time points, and fatty liver was observed. These findings demonstrate that timed high-fat diet at night can change hepatic AMPK protein levels, activity, and circadian rhythm, which may subsequently alter the circadian expression of several hepatic clock genes and finally result in the disorder of hepatic lipogenic gene expression and the formation of fatty liver.

Recent advances in circadian rhythms in cardiovascular system

Growing evidence shows that intrinsic circadian clocks are tightly related to cardiovascular functions. The diurnal changes in blood pressure and heart rate are well known circadian rhythms. Endothelial function, platelet aggregation and thrombus formation exhibit circadian changes as well. The onset of many cardiovascular diseases (CVDs) or events, such as myocardial infarction, stroke, arrhythmia, and sudden cardiac death, also exhibits temporal trends. Furthermore, there is strong evidence from animal models and epidemiological studies showing that disruption of circadian rhythms is a significant risk factor for many CVDs, and the intervention of CVDs may have a time dependent effect. In this mini review, we summarized recent advances in our understanding of the relationship between circadian rhythm and cardiovascular physiology and diseases including blood pressure regulation and myocardial infarction.

Weaker circadian activity rhythms are associated with poorer executive function in older women

STUDY OBJECTIVES

Older adults and patients with dementia often have disrupted circadian activity rhythms (CARs). Disrupted CARs are associated with health declines and could affect cognitive aging. We hypothesized that among older women, weaker CARs would be associated with poorer cognitive function 5 y later.

DESIGN

Prospective observational study.

SETTING

Three US clinical sites.

PARTICIPANTS

There were 1,287 community-dwelling older women (82.8 ± 3.1 y) participating in an ongoing prospective study who were free of dementia at the baseline visit.

MEASUREMENTS AND RESULTS

Baseline actigraphy was used to determine CAR measures (amplitude, mesor, and rhythm robustness, analyzed as quartiles; acrophase analyzed by peak activity time < 13:34 and > 15:51). Five years later, cognitive performance was assessed with the Modified Mini-Mental Status Examination (3MS), California Verbal Learning Task (CVLT), digit span, Trail Making Test B (Trails B), categorical fluency, and letter fluency. We compared cognitive performance with CARs using analyses of covariance adjusted for a number of health factors and comorbidities. Women in the lowest quartile for CAR amplitude performed worse on Trails B and categorical fluency compared to women in the highest quartile (group difference (d) = 30.42 sec, d = -1.01 words respectively, P < 0.05). Women in the lowest quartile for mesor performed worse on categorical fluency (d = -0.86 words, P < 0.05). Women with a later acrophase performed worse on categorical fluency (d = -0.69 words, P < 0.05). Controlling for baseline Mini-Mental State Examination and sleep factors had little effect on our results.

CONCLUSION

Weaker circadian activity rhythm patterns are associated with worse cognitive function, especially executive function, in older women without dementia. Further investigation is required to determine the etiology of these relationships.

A new German Charité Jet Lag Scale for jet lag symptoms and application

Travelling across multiple time zones provokes adaptation of endogenous circadian rhythm to the new time zone. Within the context of previous studies, an English-language state-of-health questionnaire, the Columbia Jet Lag Scale, is the only sufficiently validated scale for jet lag and its symptoms. This study presents a new state-of-health questionnaire in German, one intended to achieve standardisation of surveys on jet lag. The questionnaire was applied to define the baseline for the prevalence of jet lag symptoms based on a reference group (n = 36). The jet lag score ascertained was subsequently applied to determine the frequency of jet lag in a group of 53 subjects. Systematic investigation of the frequency of jet lag symptoms had not been previously presented. Among the group of 53 travelling test subjects, 60% demonstrated moderate jet lag symptoms. Practitioner Summary: This introduction of the Charité Jet Lag Scale, the first German jet lag questionnaire, calls attention to this topic for the first time since a 2000 publication in Ergonomics. Our systematic investigation of jet lag frequency, with the new scale, determined moderate jet lag symptoms among 60% of subjects.

Time-of-day of energy intake: association with hypertension and blood pressure 10 years later in the 1946 British Birth Cohort

OBJECTIVES

The role of circadian rhythm of energy and macronutrient intake in influencing cardiometabolic risk factors is increasingly recognized. However, little is known of the association between time of energy intake and blood pressure. We examined the association between time-of-day of energy intake and subsequent hypertension and change in blood pressure.

METHODS

The analysis included 517 men and 635 women from the 1946 British birth cohort. Diet was assessed using 5-day estimated diaries. Diaries were divided into seven meal slots: breakfast, mid-morning, lunch, mid-afternoon, dinner, late evening and extras. Time-of-day of energy intake at age 43 years was related to hypertension prevalence at 43 years and incidence at age 53 years and 10-year changes in SBP and DBP using logistic regression and censored regression controlling for medication use.

RESULTS

Cohort members in the highest quintile of energy intake at breakfast at age 43 years had 30% lower odds of hypertension prevalence compared with those in the lowest. Cohort members in the highest quintile of energy intake at late evening had higher odds of incident hypertension at age 53 years [odds ratio = 1.55; 95% confidence interval (CI) 0.93-2.61; P for linear trend = 0.052]. Compared to the lowest quintile, the highest quintile of energy intake late in the evening was related to a greater rise in SBP (β = 5.09; 95% CI 1.25-8.93) and DBP (43-53 years) (β = 2.08; 95%CI 0.27-5.32).

CONCLUSION

Higher energy intake at breakfast is associated with lower hypertension prevalence. Greater energy intake late in the evening is associated with higher hypertension prevalence, incidence and greater increases in blood pressure.

Prospective study of breakfast eating and incident coronary heart disease in a cohort of male US health professionals

BACKGROUND

Among adults, skipping meals is associated with excess body weight, hypertension, insulin resistance, and elevated fasting lipid concentrations. However, it remains unknown whether specific eating habits regardless of dietary composition influence coronary heart disease (CHD) risk. The objective of this study was to prospectively examine eating habits and risk of CHD.

METHODS AND RESULTS

Eating habits, including breakfast eating, were assessed in 1992 in 26 902 American men 45 to 82 years of age from the Health Professionals Follow-up Study who were free of cardiovascular disease and cancer. During 16 years of follow-up, 1527 incident CHD cases were diagnosed. Cox proportional hazards models were used to estimate relative risks and 95% confidence intervals for CHD, adjusted for demographic, diet, lifestyle, and other CHD risk factors. Men who skipped breakfast had a 27% higher risk of CHD compared with men who did not (relative risk, 1.27; 95% confidence interval, 1.06-1.53). Compared with men who did not eat late at night, those who ate late at night had a 55% higher CHD risk (relative risk, 1.55; 95% confidence interval, 1.05-2.29). These associations were mediated by body mass index, hypertension, hypercholesterolemia, and diabetes mellitus. No association was observed between eating frequency (times per day) and risk of CHD.

CONCLUSIONS

Eating breakfast was associated with significantly lower CHD risk in this cohort of male health professionals.

Disruption of the Circadian Clock in Mice Increases Intestinal Permeability and Promotes Alcohol-Induced Hepatic Pathology and Inflammation

The circadian clock orchestrates temporal patterns of physiology and behavior relative to the environmental light:dark cycle by generating and organizing transcriptional and biochemical rhythms in cells and tissues throughout the body. Circadian clock genes have been shown to regulate the physiology and function of the gastrointestinal tract. Disruption of the intestinal epithelial barrier enables the translocation of proinflammatory bacterial products, such as endotoxin, across the intestinal wall and into systemic circulation; a process that has been linked to pathologic inflammatory states associated with metabolic, hepatic, cardiovascular and neurodegenerative diseases – many of which are commonly reported in shift workers. Here we report, for the first time, that circadian disorganization, using independent genetic and environmental strategies, increases permeability of the intestinal epithelial barrier (i.e., gut leakiness) in mice. Utilizing chronic alcohol consumption as a well-established model of induced intestinal hyperpermeability, we also found that both genetic and environmental circadian disruption promote alcohol-induced gut leakiness, endotoxemia and steatohepatitis, possibly through a mechanism involving the tight junction protein occludin. Circadian organization thus appears critical for the maintenance of intestinal barrier integrity, especially in the context of injurious agents, such as alcohol. Circadian disruption may therefore represent a previously unrecognized risk factor underlying the susceptibility to or development of alcoholic liver disease, as well as other conditions associated with intestinal hyperpermeability and an endotoxin-triggered inflammatory state.

24-hour intraocular pressure and ocular perfusion pressure in glaucoma

This review analyzes the currently available literature on circadian rhythms of intraocular pressure (IOP), blood pressure, and calculated ocular perfusion pressure (OPP) in patients with open-angle glaucoma. Although adequately powered, prospective trials are not available. The existing evidence suggests that high 24-hour IOP and OPP fluctuations can have detrimental effects in eyes with glaucoma. The currently emerging continuous IOP monitoring technologies may soon offer important contributions to the study of IOP rhythms. Once telemetric technologies become validated and widely available for clinical use, they may provide an important tool towards a better understanding of long- and short-term IOP fluctuations during a patient's daily routine. Important issues that need to be investigated further include the identification of appropriate surrogate measures of IOP and OPP fluctuation for patients unable to undergo 24-hour measurements, the determination of formulae that best describe the relationship between systemic blood pressure and IOP with OPP, and the exact clinical relevance of IOP and OPP fluctuation in individual patients. Despite the unanswered questions, a significant body of literature suggests that OPP assessment may be clinically relevant in a significant number of glaucoma patients.

A molecular clock regulates angiopoietin-like protein 2 expression

Various physiological and behavioral processes exhibit circadian rhythmicity. These rhythms are usually maintained by negative feedback loops of core clock genes, namely, CLOCK, BMAL, PER, and CRY. Recently, dysfunction in the circadian clock has been recognized as an important foundation for the pathophysiology of lifestyle-related diseases, such as obesity, cardiovascular disease, and some cancers. We have reported that angiopoietin-like protein 2 (ANGPTL2) contributes to the pathogenesis of these lifestyle-related diseases by inducing chronic inflammation. However, molecular mechanisms underlying regulation of ANGPTL2 expression are poorly understood. Here, we assess circadian rhythmicity of ANGPTL2 expression in various mouse tissues. We observed that ANGPTL2 rhythmicity was similar to that of the PER2 gene, which is regulated by the CLOCK/BMAL1 complex. Promoter activity of the human ANGPTL2 gene was significantly induced by CLOCK and BMAL1, an induction markedly attenuated by CRY co-expression. We also identified functional E-boxes in the ANGPTL2 promoter and observed occupancy of these sites by endogenous CLOCK in human osteosarcoma cells. Furthermore, Cry-deficient mice exhibited arrhythmic Angptl2 expression. Taken together, these data suggest that periodic expression of ANGPTL2 is regulated by a molecular clock.

The Angiotensin-melatonin axis

Accumulating evidence indicates that various biological and neuroendocrine circadian rhythms may be disrupted in cardiovascular and metabolic disorders. These circadian alterations may contribute to the progression of disease. Our studies direct to an important role of angiotensin II and melatonin in the modulation of circadian rhythms. The brain renin-angiotensin system (RAS) may modulate melatonin synthesis, a hormone with well-established roles in regulating circadian rhythms. Angiotensin production in the central nervous system may not only influence hypertension but also appears to affect the circadian rhythm of blood pressure. Drugs acting on RAS have been proven effective in the treatment of cardiovascular and metabolic disorders including hypertension and diabetes mellitus (DM). On the other hand, since melatonin is capable of ameliorating metabolic abnormalities in DM and insulin resistance, the beneficial effects of RAS blockade could be improved through combined RAS blocker and melatonin therapy. Contemporary research is evidencing the existence of specific clock genes forming central and peripheral clocks governing circadian rhythms. Further research on the interaction between these two neurohormones and the clock genes governing circadian clocks may progress our understanding on the pathophysiology of disease with possible impact on chronotherapeutic strategies.

The role of the circadian clock system in nutrition and metabolism

Mammals have an endogenous timing system in the suprachiasmatic nuclei (SCN) of the hypothalamic region of the brain. This internal clock system is composed of an intracellular feedback loop that drives the expression of molecular components and their constitutive protein products to oscillate over a period of about 24 h (hence the term 'circadian'). These circadian oscillations bring about rhythmic changes in downstream molecular pathways and physiological processes such as those involved in nutrition and metabolism. It is now emerging that the molecular components of the clock system are also found within the cells of peripheral tissues, including the gastrointestinal tract, liver and pancreas. The present review examines their role in regulating nutritional and metabolic processes. In turn, metabolic status and feeding cycles are able to feed back onto the circadian clock in the SCN and in peripheral tissues. This feedback mechanism maintains the integrity and temporal coordination between various components of the circadian clock system. Thus, alterations in environmental cues could disrupt normal clock function, which may have profound effects on the health and well-being of an individual.

Digital clocks: simple Boolean models can quantitatively describe circadian systems

The gene networks that comprise the circadian clock modulate biological function across a range of scales, from gene expression to performance and adaptive behaviour. The clock functions by generating endogenous rhythms that can be entrained to the external 24-h day–night cycle, enabling organisms to optimally time biochemical processes relative to dawn and dusk. In recent years, computational models based on differential equations have become useful tools for dissecting and quantifying the complex regulatory relationships underlying the clock's oscillatory dynamics. However, optimizing the large parameter sets characteristic of these models places intense demands on both computational and experimental resources, limiting the scope of in silico studies. Here, we develop an approach based on Boolean logic that dramatically reduces the parametrization, making the state and parameter spaces finite and tractable. We introduce efficient methods for fitting Boolean models to molecular data, successfully demonstrating their application to synthetic time courses generated by a number of established clock models, as well as experimental expression levels measured using luciferase imaging. Our results indicate that despite their relative simplicity, logic models can (i) simulate circadian oscillations with the correct, experimentally observed phase relationships among genes and (ii) flexibly entrain to light stimuli, reproducing the complex responses to variations in daylength generated by more detailed differential equation formulations. Our work also demonstrates that logic models have sufficient predictive power to identify optimal regulatory structures from experimental data. By presenting the first Boolean models of circadian circuits together with general techniques for their optimization, we hope to establish a new framework for the systematic modelling of more complex clocks, as well as other circuits with different qualitative dynamics. In particular, we anticipate that the ability of logic models to provide a computationally efficient representation of system behaviour could greatly facilitate the reverse-engineering of large-scale biochemical networks.

Abnormalities in circadian blood pressure variability and endothelial function: pragmatic markers for adverse cardiometabolic profiles in asymptomatic obese adults

Background

Cardiovascular disease (CVD) risk, although perceived to be high, is often difficult to demonstrate in disease free (healthy) obese adults.

Hypothesis

Changes in circadian blood pressure variability (CBPV) and endothelial function (EF) may be early correlates of cardiometabolic disorders.

Methods

Asymptomatic men and women in 3 groups: normal weight (n = 10), overweight (n = 10) and obese (n = 15) were evaluated. Blood pressure and heart rate were recorded over 7 days: every 30 minutes during the day and every 60 minutes during the night, by automatic ambulatory monitoring. Resting EF was assessed in a fasting state between 8-10 AM by brachial ultrasound. Anthropometric and cardiometabolic indicators were measured and correlations with CBPV and EF were investigated.

Results

The 3 groups had (Mean(SD)) BMI: 22.6(1.6), 27(3) and 34(5) kg/m², respectively, weight: 64(16), 79(14), 95(16) kg and waist circumference: 79(9), 93(10), 107(13) cm. None in normal-weight or overweight groups had abnormal CBPV, while 8 of 15 obese adults had one or more CBPV abnormities (p < 0.05). Obese adults with CBPV abnormalities had elevated hs-CRP (15.3(9.3) mg/L), fibrinogen (593(97) mg/dl), fasting serum glucose (102(16) mg/dL), and cardiac risk ratios (Total-C/HDL-C: 5.2(1.9), LDL-C/HDL-C: 3.1(1.4)). Adults in the 3 respective groups who did not have CBPV abnormalities had flow-mediated brachial artery dilatation (FMD) of 0.22(0.06); 0.20(0.04), 0.23(0.02) mm over resting diameter. Obese participants with CBPV abnormalities (Mesor-hypotension, circadian hyper amplitude tension, elevated pulse pressure), had attenuated FMD at 78, 52, and 56% of resting reference diameter (means 0.18(0.07), 0.12(0.08), and 0.13(0.05) mm; p < 0.05), respectively.

Conclusions

Asymptomatic obese adults with abnormal CBPV and EF exhibit unfavorable cardiometabolic profiles.