Peripheral circadian clock rhythmicity is retained in the absence of adrenergic signaling

Hypertension disrupts the vascular clock in both sexes

Blood pressure (BP) displays a circadian rhythm and disruptions in this pattern elevate cardiovascular risk. Although both central and peripheral clock genes are implicated in these processes, the importance of vascular clock genes is not fully understood. BP, vascular reactivity, and the renin-angiotensin-aldosterone system display overt sex differences, but whether changes in circadian patterns underlie these differences is unknown. Therefore, we hypothesized that circadian rhythms and vascular clock genes would differ across sex and would be blunted by angiotensin II (ANG II)-induced hypertension. ANG II infusion elevated BP and disrupted circadian patterns similarly in both males and females. In females, an impact on heart rate (HR) and locomotor activity was revealed, whereas in males hypertension suppressed baroreflex sensitivity (BRS). A marked disruption in the vascular expression patterns of period circadian regulator 1 (Per1) and brain and muscle aryl hydrocarbon receptor nuclear translocator like protein 1 (Bmal1) was noted in both sexes. Vascular expression of the G protein-coupled estrogen receptor (Gper1) also showed diurnal synchronization in both sexes that was similar to that of Per1 and Per2 and disrupted by hypertension. In contrast, vascular expression of estrogen receptor 1 (Esr1) showed a diurnal rhythm and hypertension-induced disruption only in females. This study shows a strikingly similar impact of hypertension on BP rhythmicity, vascular clock genes, and vascular estrogen receptor expression in both sexes. We identified a greater impact of hypertension on locomotor activity and heart rate in females and on baroreflex sensitivity in males and also revealed a diurnal regulation of vascular estrogen receptors. These insights highlight the intricate ties between circadian biology, sex differences, and cardiovascular regulation.NEW & NOTEWORTHY This study reveals that ANG II-induced hypertension disrupts the circadian rhythm of blood pressure in both male and female mice, with parallel effects on vascular clock gene and estrogen receptor diurnal patterns. Notably, sex-specific responses to hypertension in terms of locomotor activity, heart rate, and baroreflex sensitivity are revealed. These findings pave the way for chronotherapeutic strategies tailored to mitigate cardiovascular risks associated with disrupted circadian rhythms in hypertension.

Role of Neurotransmitters in Steady State Hematopoiesis, Aging, and Leukemia

Haematopoiesis within the bone marrow (BM) represents a complex and dynamic process intricately regulated by neural signaling pathways. This delicate orchestration is susceptible to disruption by factors such as aging, diabetes, and obesity, which can impair the BM niche and consequently affect haematopoiesis. Genetic mutations in Tet2, Dnmt3a, Asxl1, and Jak2 are known to give rise to clonal haematopoiesis of intermediate potential (CHIP), a condition linked to age-related haematological malignancies. Despite these insights, the exact roles of circadian rhythms, sphingosine-1-phosphate (S1P), stromal cell-derived factor-1 (SDF-1), sterile inflammation, and the complement cascade on various BM niche cells remain inadequately understood. Further research is needed to elucidate how BM niche cells contribute to these malignancies through neural regulation and their potential in the development of gene-corrected stem cells. This literature review describes the updated functional aspects of BM niche cells in haematopoiesis within the context of haematological malignancies, with a particular focus on neural signaling and the potential of radiomitigators in acute radiation syndrome. Additionally, it underscores the pressing need for technological advancements in stem cell-based therapies to alleviate the impacts of immunological stressors. Recent studies have illuminated the microheterogeneity and temporal stochasticity of niche cells within the BM during haematopoiesis, emphasizing the updated roles of neural signaling and immunosurveillance. The development of gene-corrected stem cells capable of producing blood, immune cells, and tissue-resident progeny is essential for combating age-related haematological malignancies and overcoming immunological challenges. This review aims to provide a comprehensive overview of these evolving insights and their implications for future therapeutic strategies.

Circadian and Diurnal Regulation of Cerebral Blood Flow

Circadian and diurnal variation in cerebral blood flow directly contributes to the diurnal variation in the risk of stroke, either through factors that trigger stroke or due to impaired compensatory mechanisms. Cerebral blood flow results from the integration of systemic hemodynamics, including heart rate, cardiac output, and blood pressure, with cerebrovascular regulatory mechanisms, including cerebrovascular reactivity, autoregulation, and neurovascular coupling. We review the evidence for the circadian and diurnal variation in each of these mechanisms and their integration, from the detailed evidence for mechanisms underlying the nocturnal nadir and morning surge in blood pressure to identifying limited available evidence for circadian and diurnal variation in cerebrovascular compensatory mechanisms. We, thus, identify key systemic hemodynamic factors related to the diurnal variation in the risk of stroke but particularly identify the need for further research focused on cerebrovascular regulatory mechanisms.

Circadian Biology and the Neurovascular Unit

Mammalian physiology and cellular function are subject to significant oscillations over the course of every 24-hour day. It is likely that these daily rhythms will affect function as well as mechanisms of disease in the central nervous system. In this review, we attempt to survey and synthesize emerging studies that investigate how circadian biology may influence the neurovascular unit. We examine how circadian clocks may operate in neural, glial, and vascular compartments, review how circadian mechanisms regulate cell-cell signaling, assess interactions with aging and vascular comorbidities, and finally ask whether and how circadian effects and disruptions in rhythms may influence the risk and progression of pathophysiology in cerebrovascular disease. Overcoming identified challenges and leveraging opportunities for future research might support the development of novel circadian-based treatments for stroke.

Circadian Disruption and the Molecular Clock in Atherosclerosis and Hypertension

Circadian rhythms are crucial for maintaining vascular function and disruption of these rhythms are associated with negative health outcomes including cardiovascular disease and hypertension. Circadian rhythms are regulated by the central clock within the suprachiasmatic nucleus of the hypothalamus and peripheral clocks located in nearly every cell type in the body, including cells within the heart and vasculature. In this review, we summarize the most recent preclinical and clinical research linking circadian disruption, with a focus on molecular circadian clock mechanisms, in atherosclerosis and hypertension. Furthermore, we provide insight into potential future chronotherapeutics for hypertension and vascular disease. A better understanding of the influence of daily rhythms in behaviour, such as sleep/wake cycles, feeding, and physical activity, as well as the endogenous circadian system on cardiovascular risk will help pave the way for targeted approaches in atherosclerosis and hypertension treatment/prevention.

The circadian clock remains intact, but with dampened hormonal output in heart failure

BACKGROUND

Circadian (24-h) rhythms are important regulators in physiology and disease, but systemic disease may disrupt circadian rhythmicity. Heart failure (HF) is a systemic disease affecting hormonal regulation. We investigate whether HF affects the rhythmic expression of melatonin and cortisol, main endocrine products of the central clock, and cardiac-specific troponin in patients. We corroborate the functionality of the peripheral clock directly in the organs of translational models, inaccessible in human participants.

METHODS

We included 46 HF patients (71.7% male, median age of 60 years, NYHA class II (32.6%) or III (67.4%), ischemic cardiomyopathy (43.5%), comorbidities: diabetes 21.7%, atrial fibrillation 30.4%), and 24 matched controls. Blood was collected at seven time-points during a 24-h period (totalling 320 HF and 167 control samples) for melatonin, cortisol, and cardiac troponin T (cTnT) measurements after which circadian rhythms were assessed through cosinor analyses, both on the individual and the group level. Next, we analysed peripheral circadian clock functionality using cosinor analysis in male animal HF models: nocturnal mice and diurnal zebrafish, based on expression of core clock genes in heart, kidneys, and liver, every 4 h during a 24-h period in a light/darkness synchronised environment.

FINDINGS

Melatonin and cortisol concentrations followed a physiological 24-h pattern in both patients and controls. For melatonin, acrophase occurred during the night for both groups, with significantly decreased amplitude (median 5.2 vs 8.8, P = 0.0001) and circadian variation ([maximum]/[minimum]) in heart failure patients. For cortisol, mesor showed a significant increase for HF patients (mean 331.9 vs 275.1, P = 0.017) with a difference of 56.8 (95% CI 10.3-103.3) again resulting in a relatively lower variation: median 3.9 vs 6.3 (P = 0.0058). A nocturnal blood pressure dip was absent in 77.8% of HF patients. Clock gene expression profiles (Bmal, Clock, Per, Cry) were similar and with expected phase relations in animal HF models and controls, demonstrating preserved peripheral clock functionality in HF. Furthermore, oscillations in diurnal zebrafish were expectedly in opposite phases to those of nocturnal mice. Concordantly, cTnT concentrations in HF patients revealed significant circadian oscillations.

INTERPRETATION

Central clock output is dampened in HF patients while the molecular peripheral clock, as confirmed in animal models, remains intact. This emphasises the importance of taking timing into account in research and therapy for HF, setting the stage for another dimension of diagnostic, prognostic and therapeutic approaches.

FUNDING

Hartstichting.

Glucocorticoids coordinate the bladder peripheral clock and diurnal micturition pattern in mice

Peripheral clocks function to regulate each organ and are synchronized though various molecular and behavioral signals. However, signals that entrain the bladder clock remain elusive. Here, we show that glucocorticoids are a key cue for the bladder clock in vitro and in vivo. A pBmal1-dLuc human urothelial cell-line showed significant shifts in gene expression after cortisol treatment. In vivo, rhythmic bladder clock gene expression was unchanged by bilateral adrenalectomy but shifted 4 h forward by corticosterone administration at the inactive phase. Moreover, the bladder clock shifted 8-12 h in mice that underwent both bilateral adrenalectomy and corticosterone administration at the inactive phase. These mice showed decreases in the diurnal rhythm of volume voided per micturition, while maintaining diurnal activity rhythms. These results indicate that the diurnal rhythm of glucocorticoid signaling is a zeitgeber that overcomes other bladder clock entrainment factors and coordinates the diurnal rhythm of volume voided per micturition.

The Circadian Biology of Heart Failure

Driven by autonomous molecular clocks that are synchronized by a master pacemaker in the suprachiasmatic nucleus, cardiac physiology fluctuates in diurnal rhythms that can be partly or entirely circadian. Cardiac contractility, metabolism, and electrophysiology, all have diurnal rhythms, as does the neurohumoral control of cardiac and kidney function. In this review, we discuss the evidence that circadian biology regulates cardiac function, how molecular clocks may relate to the pathogenesis of heart failure, and how chronotherapeutics might be applied in heart failure. Disrupting molecular clocks can lead to heart failure in animal models, and the myocardial response to injury seems to be conditioned by the time of day. Human studies are consistent with these findings, and they implicate the clock and circadian rhythms in the pathogenesis of heart failure. Certain circadian rhythms are maintained in patients with heart failure, a factor that can guide optimal timing of therapy. Pharmacologic and nonpharmacologic manipulation of circadian rhythms and molecular clocks show promise in the prevention and treatment of heart failure.

Diurnal cardio-respiratory changes in ambulatory individuals deciphered using a multi-parameter wearable device

Background

Recent technological developments enable big data-driven insights on diurnal changes. This study aimed to describe the trajectory of multiple and advanced parameters using a medical-grade wearable remote patient monitor.

Methods

Parameters were monitored for 24 h in 256 ambulatory participants who kept living their normal life. Parameters included heart rate, blood pressure, stroke volume, cardiac index, systemic vascular resistance, blood oxygen saturation, and respiratory rate. Diurnal variations were evaluated, and analyses were stratified based on sex, age, and body mass index.

Results

All parameters showed diurnal changes (p < 0.001). Females demonstrated higher heart rate and cardiac index with lower systemic vascular resistance. Obese participants had a higher blood pressure, and lower stroke volume and cardiac index. Systemic vascular resistance was higher among the elderly. Diurnal changes corresponded with awake-sleep hours and differed between sex, age, and body mass index groups.

Conclusion

Wearable monitoring platforms could decipher hemodynamic changes in subgroups of individuals, and might help with efforts to provide personalized medicine, pre-symptomatic diagnosis and prevention, and drug development.

The Effect of Diet on the Cardiac Circadian Clock in Mice: A Systematic Review

Circadian rhythms play important roles in regulating physiological and behavioral processes. These are adjusted by environmental cues, such as diet, which acts by synchronizing or attenuating the circadian rhythms of peripheral clocks, such as the liver, intestine, pancreas, white and brown adipose tissue, lungs, kidneys, as well as the heart. Some studies point to the influence of diet composition, feeding timing, and dietary restriction on metabolic homeostasis and circadian rhythms at various levels. Therefore, this systematic review aimed to discuss studies addressing the effect of diet on the heart clock in animal models and, additionally, the chronodisruption of the clock and its relation to the development of cardiovascular disorders in the last 15 years. A search was conducted in the PubMed, Scopus, and Embase databases. The PRISMA guide was used to construct the article. Nineteen studies met all inclusion and exclusion criteria. In summary, these studies have linked the circadian clock to cardiovascular health and suggested that maintaining a robust circadian system may reduce the risks of cardiometabolic and cardiovascular diseases. The effect of time-of-day-dependent eating on the modulation of circadian rhythms of the cardiac clock and energy homeostasis is notable, among its deleterious effects predominantly in the sleep (light) phase and/or at the end of the active phase.

Neuroinflammation, Sleep, and Circadian Rhythms

Molecules involved in innate immunity affect sleep and circadian oscillators and vice versa. Sleep-inducing inflammatory molecules are activated by increased waking activity and pathogens. Pathologies that alter inflammatory molecules, such as traumatic brain injury, cancer, cardiovascular disease, and stroke often are associated with disturbed sleep and electroencephalogram power spectra. Moreover, sleep disorders, such as insomnia and sleep disordered breathing, are associated with increased dysregulation of inflammatory processes. Inflammatory molecules in both the central nervous system and periphery can alter sleep. Inflammation can also modulate cerebral vascular hemodynamics which is associated with alterations in electroencephalogram power spectra. However, further research is needed to determine the interactions of sleep regulatory inflammatory molecules and circadian clocks. The purpose of this review is to: 1) describe the role of the inflammatory cytokines interleukin-1 beta and tumor necrosis factor-alpha and nucleotide-binding domain and leucine-rich repeat protein-3 inflammasomes in sleep regulation, 2) to discuss the relationship between the vagus nerve in translating inflammatory signals between the periphery and central nervous system to alter sleep, and 3) to present information about the relationship between cerebral vascular hemodynamics and the electroencephalogram during sleep.

A wrinkle in time: circadian biology in pulmonary vascular health and disease

An often overlooked element of pulmonary vascular disease is time. Cellular responses to time, which are regulated directly by the core circadian clock, have only recently been elucidated. Despite an extensive collection of data regarding the role of rhythmic contribution to disease pathogenesis (such as systemic hypertension, coronary artery, and renal disease), the roles of key circadian transcription factors in pulmonary hypertension remain understudied. This is despite a large degree of overlap in the pulmonary hypertension and circadian rhythm fields, not only including shared signaling pathways, but also cell-specific effects of the core clock that are known to result in both protective and adverse lung vessel changes. Therefore, the goal of this review is to summarize the current dialogue regarding common pathways in circadian biology, with a specific emphasis on its implications in the progression of pulmonary hypertension. In this work, we emphasize specific proteins involved in the regulation of the core molecular clock while noting the circadian cell-specific changes relevant to vascular remodeling. Finally, we apply this knowledge to the optimization of medical therapy, with a focus on sleep hygiene and the role of chronopharmacology in patients with this disease. In dissecting the unique relationship between time and cellular biology, we aim to provide valuable insight into the practical implications of considering time as a therapeutic variable. Armed with this information, physicians will be positioned to more efficiently use the full four dimensions of patient care, resulting in improved morbidity and mortality of pulmonary hypertension patients.

Potential Effect of the Circadian Clock on Erectile Dysfunction

The circadian rhythm is an internal timing system, which is generated by circadian clock genes. Because the circadian rhythm regulates numerous cellular, behavioral, and physiological processes, organisms have evolved with intrinsic biological rhythms to adapt the daily environmental changes. A variety of pathological events occur at specific times, while disturbed rhythms can lead to metabolic syndrome, vascular dysfunction, inflammatory disorders, and cancer. Therefore, the circadian clock is considered closely related to various diseases. Recently, accumulated data have shown that the penis is regulated by the circadian clock, while erectile function is impaired by an altered sleep-wake cycle. The circadian rhythm appears to be a novel therapeutic target for preventing and managing erectile dysfunction (ED), although research is still progressing. In this review, we briefly summarize the superficial interactions between the circadian clock and erectile function, while focusing on how disturbed rhythms contribute to risk factors of ED. These risk factors include NO/cGMP pathway, atherosclerosis, diabetes mellitus, lipid abnormalities, testosterone deficiency, as well as dysfunction of endothelial and smooth muscle cells. On the basis of recent findings, we discuss the potential role of the circadian clock for future therapeutic strategies on ED, although further relevant research needs to be performed.

Molecular basis of Period 1 regulation by adrenergic signaling in the heart

The cardiac circadian clock is responsible for the modulation of different myocardial processes, and its dysregulation has been linked to disease development. How this clock machinery is regulated in the heart remains an open question. Because noradrenaline (NE) can act as a zeitgeber in cardiomyocytes, we tested the hypothesis that adrenergic signaling resets cardiac clock gene expression in vivo. In its anti-phase with Clock and Bmal1, cardiac Per1 abundance increased during the dark phase, concurrent with the rise in heart rate and preceded by an increase in NE levels. Sympathetic denervation altered Bmal1 and Clock amplitude, while Per1 was affected in both amplitude and oscillatory pattern. We next treated mice with a β-adrenergic receptor (β-AR) blocker. Strikingly, the β-AR blockade during the day suppressed the nocturnal increase in Per1 mRNA, without altering Clock or Bmal1. In contrast, activating β-AR with isoproterenol (ISO) promoted an increase in Per1 expression, demonstrating its responsiveness to adrenergic input. Inhibitors of ERK1/2 and CREB attenuated ISO-induced Per1 expression. Upstream of ERK1/2, PI3Kγ mediated ISO induction of Per1 transcription, while activation of β2-AR, but not β1-AR induced increases in ERK1/2 phosphorylation and Per1 expression. Consistent with the β2-induction of Per1 mRNA, ISO failed to activate ERK1/2 and elevate Per1 in the heart of β2-AR-/- mice, whereas a β2-AR antagonist attenuated the nocturnal rise in Per1 expression. Our study established a link between NE/β2-AR signaling and Per1 oscillation via the PI3Ky-ERK1/2-CREB pathway, providing a new framework for understanding the physiological mechanism involved in resetting cardiac clock genes.

The impact of stress and stress hormones on endogenous clocks and circadian rhythms

In mammals, daily rhythms in physiology and behavior are under control of a circadian pacemaker situated in the suprachiasmatic nucleus (SCN). This master clock receives photic input from the retina and coordinates peripheral oscillators present in other tissues, maintaining all rhythms in the body synchronized to the environmental light-dark cycle. In line with its function as a master clock, the SCN appears to be well protected against unpredictable stressful stimuli. However, available data indicate that stress and stress hormones at certain times of day are capable of shifting peripheral oscillators in, e.g., liver, kidney and heart, which are normally under control of the SCN. Such shifts of peripheral oscillators may represent a temporary change in circadian organization that facilitates adaptation to repeated stress. Alternatively, these shifts of internal rhythms may represent an imbalance between precisely orchestrated physiological and behavioral processes that may have severe consequences for health and well-being.

Murata R, Pereira LJ. Association between Chronotype and Nutritional, Clinical and Sociobehavioral Characteristics of Adults Assisted by a Public Health Care System in Brazil

Chronotype (CT) has been associated with predisposition to chronic noncommunicable diseases (CNCDs), such as diabetes mellitus and obesity. However, the effects of CT on individuals assisted by public health systems (PHSs) in middle-up economies are still poorly explored. The objective of this study was to evaluate the relationship between CT and clinical, sociobehavioral and nutritional aspects in adults assisted by a PHS in Brazil. This is a population-based cross-sectional study. The sample consisted of 380 individuals, selected through probabilistic sampling by clusters, in all health units in a city of approximately 100 thousand inhabitants. Data collection was performed during home visits, by means of general and nutritional interviews, anthropometric measurements and the Morningness-Eveningness Questionnaire (MEQ). Statistical analysis comprised chi-square test and principal component analysis (CPA) followed by Fisher's discriminant analysis to determine aspects associated with each CT (morning, evening or intermediate). With the aim of explaining the variation in the CT scores, the consumption of micronutrients (corrected to the total energy intake) and other individual and sociodemographic variables were used as explanatory factors in the adjustment of a linear regression model. The morning group was characterized by older men, with less than eight years of schooling, with low body mass index (BMI) and with low intake of omega-6, omega-3, sodium, zinc, thiamine, pyridoxine and niacin. The evening group, on the other hand, was composed of younger individuals, with a high consumption of these same nutrients, with high BMI and a higher frequency of heart diseases (p < 0.05). It was concluded that most morning CT individuals were elderly thin males with lower consumption of omega-6 and -3, sodium, zinc, thiamine, pyridoxine and niacin, whereas evening individuals were younger, had higher BMI and had higher consumption of the studied micronutrients. The identification of circadian and behavioral risk groups can help to provide preventive and multidisciplinary health promotion measures.

The Autonomic Nervous System Pulls the Strings to Coordinate Circadian HSC Functions

As for many other adult stem cells, the behavior of hematopoietic stem and progenitor cells (HSPCs) is subjected to circadian regulatory patterns. Multiple HSPC functions, such as proliferation, differentiation or trafficking exhibit time-dependent patterns that require a tight coordination to ensure daily blood cell production. The autonomic nervous system, together with circulating hormones, relay circadian signals from the central clock-the suprachiasmatic nucleus in the brain-to synchronize HSC niche physiology according to light/darkness cycles. Research over the last 20 years has revealed how specific neural signals modulate certain aspects of circadian HSC biology. However, only recently some studies have started to decipher the cellular and molecular mechanisms that orchestrate this complex regulation in a time-dependent fashion. Here we firstly review some of the recent key findings illustrating how different neural signals (catecholaminergic or cholinergic) regulate circadian HSC egress, homing, maintenance, proliferation, and differentiation. In particular, we highlight the critical role of different neurotransmitter receptors in the bone marrow microenvironment to channel these neural signals and regulate antagonistic processes according to circadian cues and organismal demands. Then, we discuss the potential biological meaning of HSC circadian regulation and its possible utility for clinical purposes. Finally, we offer our perspective on emerging concepts in HSC chronobiology.

Artery-Associated Sympathetic Innervation Drives Rhythmic Vascular Inflammation of Arteries and Veins

BACKGROUND

The incidence of acute cardiovascular complications is highly time-of-day dependent. However, the mechanisms driving rhythmicity of ischemic vascular events are unknown. Although enhanced numbers of leukocytes have been linked to an increased risk of cardiovascular complications, the role that rhythmic leukocyte adhesion plays in different vascular beds has not been studied.

METHODS

We evaluated leukocyte recruitment in vivo by using real-time multichannel fluorescence intravital microscopy of a tumor necrosis factor-α-induced acute inflammation model in both murine arterial and venous macrovasculature and microvasculature. These approaches were complemented with genetic, surgical, and pharmacological ablation of sympathetic nerves or adrenergic receptors to assess their relevance for rhythmic leukocyte adhesion. In addition, we genetically targeted the key circadian clock gene Bmal1 (also known as Arntl) in a lineage-specific manner to dissect the importance of oscillations in leukocytes and components of the vessel wall in this process.

RESULTS

In vivo quantitative imaging analyses of acute inflammation revealed a 24-hour rhythm in leukocyte recruitment to arteries and veins of the mouse macrovasculature and microvasculature. Unexpectedly, although in arteries leukocyte adhesion was highest in the morning, it peaked at night in veins. This phase shift was governed by a rhythmic microenvironment and a vessel type-specific oscillatory pattern in the expression of promigratory molecules. Differences in cell adhesion molecules and leukocyte adhesion were ablated when disrupting sympathetic nerves, demonstrating their critical role in this process and the importance of β₂-adrenergic receptor signaling. Loss of the core clock gene Bmal1 in leukocytes, endothelial cells, or arterial mural cells affected the oscillations in a vessel type-specific manner. Rhythmicity in the intravascular reactivity of adherent leukocytes resulted in increased interactions with platelets in the morning in arteries and in veins at night with a higher predisposition to acute thrombosis at different times as a consequence.

CONCLUSIONS

Together, our findings point to an important and previously unrecognized role of artery-associated sympathetic innervation in governing rhythmicity in vascular inflammation in both arteries and veins and its potential implications in the occurrence of time-of-day-dependent vessel type-specific thrombotic events.

Time-of-Day-Dependent Trafficking and Function of Leukocyte Subsets

The number of leukocytes circulating in blood in mammals is under circadian control (i.e., ∼24h). We summarize here latest findings on the mechanisms governing leukocyte migration from the blood into various organs, focusing on the distinct leukocyte subtype- and tissue-specific molecules involved. We highlight the oscillatory expression patterns of adhesion molecules, chemokines, and their receptors that are expressed on endothelial cells and leukocytes, and which are crucial regulators of rhythmic leukocyte recruitment. We also discuss the relevance of clock genes for leukocyte function and migration. Finally, we compare immune cell rhythms under steady-state conditions as well as during inflammation and disease, and we postulate how these findings provide potential new avenues for therapeutic intervention.

Coupling the Circadian Clock to Homeostasis: The Role of Period in Timing Physiology

A plethora of physiological processes show stable and synchronized daily oscillations that are either driven or modulated by biological clocks. A circadian pacemaker located in the suprachiasmatic nucleus of the ventral hypothalamus coordinates 24-hour oscillations of central and peripheral physiology with the environment. The circadian clockwork involved in driving rhythmic physiology is composed of various clock genes that are interlocked via a complex feedback loop to generate precise yet plastic oscillations of ∼24 hours. This review focuses on the specific role of the core clockwork gene Period1 and its paralogs on intra-oscillator and extra-oscillator functions, including, but not limited to, hippocampus-dependent processes, cardiovascular function, appetite control, as well as glucose and lipid homeostasis. Alterations in Period gene function have been implicated in a wide range of physical and mental disorders. At the same time, a variety of conditions including metabolic disorders also impact clock gene expression, resulting in circadian disruptions, which in turn often exacerbates the disease state.

β-Adrenergic receptors control brown adipose UCP-1 tone and cold response without affecting its circadian rhythmicity

Brown adipose tissue (BAT) thermogenic functions are primarily mediated by uncoupling protein (UCP)-1. Ucp1 gene expression is highly induced by cold temperature, via sympathetic nervous system and β-adrenergic receptors (βARs). Ucp1 is also repressed by the clock gene Rev-erbα, contributing to its circadian rhythmicity. In this study, we investigated mice lacking βARs (β-less mice) to test the relationship between βAR signaling and the BAT molecular clock. We found that in addition to controlling the induction of Ucp1 and other key BAT genes at near freezing temperatures, βARs are essential for the basal expression of BAT Ucp1 at room temperature. Remarkably, although basal Ucp1 expression is low throughout day and night in β-less mice, the circadian rhythmicity of Ucp1 and clock genes in BAT is maintained. Thus, the requirement of βAR signaling for BAT activity is independent of the circadian rhythmicity of Ucp1 expression and circadian oscillation of the molecular clock genes. On the other hand, we found that βARs are essential for the normal circadian rhythms of locomotor activity. Our results demonstrate that in addition to controlling the BAT response to extreme cold, βAR signaling is necessary to maintain basal Ucp1 tone and to couple BAT circadian rhythmicity to the central clock.-Razzoli, M., Emmett, M. J., Lazar, M. A., Bartolomucci, A. β-Adrenergic receptors control brown adipose UCP-1 tone and cold response without affecting its circadian rhythmicity.

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.

A Selective Bombesin Receptor Subtype 3 Agonist Promotes Weight Loss in Male Diet-Induced-Obese Rats With Circadian Rhythm Change

Bombesin receptor subtype 3 (BRS-3) is an orphan G protein-coupled receptor. Based on the obese phenotype of male BRS-3-deficient mice, BRS-3 has been considered an attractive target for obesity treatment. Here, we developed a selective BRS-3 agonist (compound-A) and evaluated its antiobesity effects. Compound-A showed anorectic effects and enhanced energy expenditure in diet-induced-obese (DIO)-F344 rats. Moreover, repeated oral administration of compound-A for 7 days resulted in a significant body weight reduction in DIO-F344 rats. We also evaluated compound-A for cardiovascular side effects using telemeterized Sprague-Dawley (SD) rats. Oral administration of compound-A resulted in transient blood pressure increases in SD rats. To investigate the underlying mechanisms of BRS-3 agonist effects, we focused on the suprachiasmatic nucleus (SCN), the main control center of circadian rhythms in the hypothalamus, also regulating sympathetic nervous system. Compound-A significantly increased the messenger RNA expression of Brs-3, c-fos, and circadian rhythm genes in SCN of DIO-F344 rats. Because SCN also controls the hypothalamic-pituitary-adrenal (HPA) axis, we evaluated the relationship between BRS-3 and the HPA axis. Oral administration of compound-A caused a significant increase of plasma corticosterone levels in DIO-F344 rats. On this basis, energy expenditure enhancement by compound-A may be due to a circadian rhythm change in central and peripheral tissues, enhancement of peripheral lipid metabolism, and stimulation of the sympathetic nervous system. Furthermore, the blood pressure increase by compound-A could be associated with sympathetic nervous system stimulation via SCN and elevation of plasma corticosterone levels through activation of the HPA axis.

Circadian Influence on Metabolism and Inflammation in Atherosclerosis

Many aspects of human health and disease display daily rhythmicity. The brain's suprachiasmic nucleus, which interprets recurring external stimuli, and autonomous molecular networks in peripheral cells together, set our biological circadian clock. Disrupted or misaligned circadian rhythms promote multiple pathologies including chronic inflammatory and metabolic diseases such as atherosclerosis. Here, we discuss studies suggesting that circadian fluctuations in the vessel wall and in the circulation contribute to atherogenesis. Data from humans and mice indicate that an impaired molecular clock, disturbed sleep, and shifting light-dark patterns influence leukocyte and lipid supply in the circulation and alter cellular behavior in atherosclerotic lesions. We propose that a better understanding of both local and systemic circadian rhythms in atherosclerosis will enhance clinical management, treatment, and public health policy.

Effects of Intracerebroventricular Administration of Neuropeptide Y on Metabolic Gene Expression and Energy Metabolism in Male Rats

Neuropeptide Y (NPY) is an important neurotransmitter in the control of energy metabolism. Several studies have shown that obesity is associated with increased levels of NPY in the hypothalamus. We hypothesized that the central release of NPY has coordinated and integrated effects on energy metabolism in different tissues, resulting in increased energy storage and decreased energy expenditure (EE). We first investigated the acute effects of an intracerebroventricular (ICV) infusion of NPY on gene expression in liver, brown adipose tissue, soleus muscle, and sc and epididymal white adipose tissue (WAT). We found increased expression of genes involved in gluconeogenesis and triglyceride secretion in the liver already 2-hour after the start of the NPY administration. In brown adipose tissue, the expression of thermogenic genes was decreased. In sc WAT, the expression of genes involved in lipogenesis was increased, whereas in soleus muscle, the expression of lipolytic genes was decreased after ICV NPY. These findings indicate that the ICV infusion of NPY acutely and simultaneously increases lipogenesis and decreases lipolysis in different tissues. Subsequently, we investigated the acute effects of ICV NPY on locomotor activity, respiratory exchange ratio, EE, and body temperature. The ICV infusion of NPY increased locomotor activity, body temperature, and EE as well as respiratory exchange ratio. Together, these results show that an acutely increased central availability of NPY results in a shift of metabolism towards lipid storage and an increased use of carbohydrates, while at the same time increasing activity, EE, and body temperature.

Obtaining Human Ischemic Stroke Gene Expression Biomarkers from Animal Models: A Cross-species Validation Study

Recent studies have revealed the systematic altering of gene expression in human peripheral blood during the early stages of ischemic stroke, which suggests a new potential approach for the rapid diagnosis or prediction of stroke onset. Nevertheless, due to the difficulties of collecting human samples during proper disease stages, related studies are rather restricted. Many studies have instead been performed on manipulated animal models for investigating the regulation patterns of biomarkers during different stroke stages. An important inquiry is how well the findings of animal models can be replicated in human cases. Here, a method is proposed based on PageRank scores of miRNA-mRNA interaction network to select ischemic stroke biomarkers derived from rat brain samples, and biomarkers are validated with two human peripheral blood gene expression datasets. Hierarchical clustering results revealed that the achieved biomarkers clearly separate the blood gene expression of stroke patients and healthy people. Literature searches and functional analyses further validated the biological significance of these biomarkers. Compared to the traditional methods, such as differential expression, the proposed approach is more stable and accurate in detecting cross-species biomarkers with biological relevance, thereby suggesting an efficient approach of re-using gene biomarkers obtained from animal-model studies for human diseases.

Circadian clocks, obesity and cardiometabolic function

Life on earth is governed by the continuous 24-h cycle of light and dark. Organisms have adapted to this environment with clear diurnal rhythms in their physiology and metabolism, enabling them to anticipate predictable environmental fluctuations over the day and to optimize the timing of relevant biological processes to this cycle. These rhythms are regulated by molecular circadian clocks, and current evidence suggests that interactions between the central and peripheral molecular clocks are important in metabolic and vascular functions. Disrupting this process through mutations in the core clock genes or by interfering with the environmental zeitgebers that entrain the clock appear to modulate the function of cells and tissues, leading to an increased risk for cardiometabolic disease.

Evaluation of mouse urinary bladder smooth muscle for diurnal differences in contractile properties

Most physiological systems show daily variations in functional output, entrained to the day–night cycle. Humans exhibit a daily rhythm in urinary voiding (micturition), and disruption of this rhythm (nocturia) has significant clinical impact. However, the underlying mechanisms are not well-understood. Recently, a circadian rhythm in micturition was demonstrated in rodents, correlated with functional changes in urodynamics, providing the opportunity to address this issue in an animal model. Smooth muscle cells from mouse bladder have been proposed to express a functional and autonomous circadian clock at the molecular level. In this study, we addressed whether a semi-intact preparation of mouse urinary bladder smooth muscle (UBSM) exhibited measurable differences in contractility between day and night. UBSM tissue strips were harvested at four time points over the diurnal cycle, and spontaneous (phasic) and nerve-evoked contractions were assessed using isometric tension recordings. During the active period (ZT12-24) when micturition frequency is higher in rodents, UBSM strips had no significant differences in maximal- (high K⁺) or nerve-evoked contractions compared to strips harvested from the resting period (ZT0-12). However, a diurnal rhythm in phasic contraction was observed, with higher amplitudes at ZT10. Consistent with the enhanced phasic amplitudes, expression of the BK K⁺ channel, a key suppressor of UBSM excitability, was lower at ZT8. Higher expression of BK at ZT20 was correlated with an enhanced effect of the BK antagonist paxilline (PAX) on phasic amplitude, but PAX had no significant time-of-day dependent effect on phasic frequency or nerve-evoked contractions. Overall, these results identify a diurnal difference for one contractile parameter of bladder muscle. Taken together, the results suggest that autonomous clocks in UBSM make only a limited contribution to the integrated control of diurnal micturition patterns.

The rhythmic expression of clock genes attenuated in human plaque-derived vascular smooth muscle cells

BACKGROUND

Acute myocardial infarction and stroke are more likely to occur in the early morning. Circadian pacemakers are considered to be involved in the process. Many peripheral tissues and cells also contain clock systems. In this study, we examined whether the primary cultured human plaque-derived vascular smooth muscle cells (VSMCs) process circadian rhythmicity; furthermore, we investigated the expression difference of clock genes between normal human carotid VSMCs and human plaque-derived VSMCs.

METHODS

Fifty-six human carotid plaques provided the atherosclerotic tissue, and 21 samples yielded viable cultured primary VSMCs. The normal carotid VSMCs were cultured from donors' normal carotids. The mRNA levels of the target genes were measured by Quantitative Real-Time Polymerase Chain Reaction (qRT-PCR).

RESULTS

After serum shock, both types of cells showed clear circadian expressions of Bmal1, Cry1, Cry2, Per1, Per2, Per3 and Rev-erbα mRNA; meanwhile the Clock mRNA show a rhythmic expression in plaque-derived SMCs but not in normal carotid VSMCs. The expression levels of these main clock genes were significantly attenuated in human plaque-derived VSMCs compared with normal human carotid VSMCs. The rhythm of Bmal1 mRNA in plaque-derived VSMCs was changed.

CONCLUSION

The present results demonstrate that the human plaque-derived VSMCs possess different circadian rhythmicity from that of normal carotid VSMCs. The rhythm changes of clock genes in plaque-derived VSMCs may be involved in the process of atherosclerosis and finally promote the rupture of plaque.

Influence of menopause on adipose tissue clock gene genotype and its relationship with metabolic syndrome in morbidly obese women

Menopausal women exhibit a loss of circadian coordination, a process that runs parallel with a redistribution of adipose tissue. However, the specific genetic mechanisms underlying these alterations have not been studied. Thus, the aim of the present study was to determine whether the development of menopause induces an alteration of the genes that control biological rhythms in human subcutaneous (SAT) and visceral (VAT) adipose tissue, and whether changes in clock gene expression are involved in the increased risk of developing metabolic syndrome (MetS), which is frequently associated with menopause. To this end, VAT and SAT biopsies were taken in pre- (n = 7) and postmenopausal (n = 7) women at similar hours in the morning. RNA was extracted, and a microarray analysis was made. Data were confirmed by quantitative real-time polymerase chain reaction. Western blot and immunohistochemical analysis were also performed. When clock gene expression was compared between both groups of women, data in SAT showed that expression of the core clock gene period3 was significantly higher in postmenopausal women, while casein kinase-1δ, E1A-binding protein and cAMP-responsive element were preferentially expressed in the premenopausal group. In VAT, period2 (PER2) and v-myc myelocytomatosis viral oncogene expressions were significantly higher in the postmenopausal group. Western blot analysis indicated that PER2 and PER3 protein expression was also increased in postmenopausal women. In addition, several genes, including PER2, were differentially expressed depending on whether or not the patient met the MetS criteria. We conclude that menopause transition induces several changes in the genotype of the adipose tissue chronobiological machinery related to an increased risk of developing MetS.

Secretory patterns of catecholamines in Indo-Pacific bottlenose dolphins

Catecholamines (CAs), namely adrenaline (A), noradrenaline (NA), and dopamine (DA), are secreted by the sympathoadrenal system and participate in a diverse array of functions, e.g., heat production, cardiovascular regulation, stress response and so on. However, little is known regarding peripheral CA fluctuations in cetaceans; nevertheless aquatic animals like them have needed to modify their physiological response especially for thermoregulation in water and oxygen economy during diving. To understand CA dynamism in cetaceans, diurnal changes in serum A, NA, and DA concentrations were measured during the winter and summer solstices in four Indo-Pacific bottlenose dolphins (Tursiops aduncus). The average serum NA concentration was much higher than the average A and DA concentrations, and all concentrations were higher than those reported in other cetacean species. No distinct diurnal fluctuations were observed in CA concentrations in either solstice, suggesting inhibition of the decrease in CA concentrations during nocturnal periods by the unique sleep pattern of dolphins. All the serum CA concentrations were negatively correlated with water temperature as body temperatures were, indicating that the sympathoadrenal system might be more active during winter than in summer season, suggesting a role of CA in thermoregulation.

Metabolic cycles are linked to the cardiovascular diurnal rhythm in rats with essential hypertension

Background

The loss of diurnal rhythm in blood pressure (BP) is an important predictor of end-organ damage in hypertensive and diabetic patients. Recent evidence has suggested that two major physiological circadian rhythms, the metabolic and cardiovascular rhythms, are subject to regulation by overlapping molecular pathways, indicating that dysregulation of metabolic cycles could desynchronize the normal diurnal rhythm of BP with the daily light/dark cycle. However, little is known about the impact of changes in metabolic cycles on BP diurnal rhythm.

Methodology/Principal Findings

To test the hypothesis that feeding-fasting cycles could affect the diurnal pattern of BP, we used spontaneously hypertensive rats (SHR) which develop essential hypertension with disrupted diurnal BP rhythms and examined whether abnormal BP rhythms in SHR were caused by alteration in the daily feeding rhythm. We found that SHR exhibit attenuated feeding rhythm which accompanies disrupted rhythms in metabolic gene expression not only in metabolic tissues but also in cardiovascular tissues. More importantly, the correction of abnormal feeding rhythms in SHR restored the daily BP rhythm and was accompanied by changes in the timing of expression of key circadian and metabolic genes in cardiovascular tissues.

Conclusions/Significance

These results indicate that the metabolic cycle is an important determinant of the cardiovascular diurnal rhythm and that disrupted BP rhythms in hypertensive patients can be normalized by manipulating feeding cycles.

Cardiovascular disease, chronopharmacotherapy, and the molecular clock

Cardiovascular functions such as heart rate and blood pressure show 24h variation. The incidence of cardiovascular diseases including acute myocardial infarction and arrhythmia also exhibits diurnal variation. The center of this circadian clock is located in the suprachiasmatic nucleus in the hypothalamus. However, recent findings revealed that each organ, including cardiovascular tissues, has its own internal clock, which has been termed a peripheral clock. The functional roles played by peripheral clocks have been reported recently. Since the peripheral clock is considered to play considerable roles in the processes of cardiac tissues, the identification of genes specifically regulated by this clock will provide insights into its role in the pathogenesis of cardiovascular disorders. In addition, the discovery of small compounds that modulate the peripheral clock will help to establish chronotherapeutic approaches. Understanding the biological relevance of the peripheral clock will provide novel approaches to the prevention and treatment of cardiovascular diseases.

Circadian clocks and vascular function

The circadian clock regulates many aspects of physiology, including cardiovascular function. Internal oscillators exist in endothelial, smooth muscle cells, and fibroblasts of the vasculature. Vascular tone and thrombus formation, 2 key elements of vascular function with regard to adverse cardiovascular events, exhibit diurnal rhythmicity. In this review, we describe changes in vascular function that result from genetic disruption of discrete elements of the circadian clock.

Postnatal ontogenesis of clock genes in mouse suprachiasmatic nucleus and heart

BACKGROUND

The master clock within the hypothalamic suprachiasmatic nucleus (SCN) synchronizing clocks in peripheral tissues is entrained by the environmental condition, such as the light-dark (LD) cycle. The mechanisms of circadian clockwork are similar in both SCN and peripheral tissues. The aim of the present work was to observe the profiles of clock genes expression in mouse central and peripheral tissues within postnatal day 5 (P5). The daily expression of four clock genes mRNA (Bmal1, Per2, Cry1 and Rev-erb alpha) in mouse SCN and heart was measured at P1, P3 and P5 by real-time PCR.

RESULTS

All the studied mice clock genes began to express in a circadian rhythms manner in heart and SCN at P3 and P5 respectively. Interestingly, the daily rhythmic phase of some clock genes shifted during the postnatal days. Moreover, the expressions of clock genes in heart were not synchronized with those in SCN until at P5.

CONCLUSION

The data showed the gradual development of clock genes in SCN and a peripheral tissue, and suggested that development of clock genes differed between in the SCN and the heart. Judging from the mRNA expression, it was possible that the central clock synchronized the peripheral clock as early as P5.

VMH lesions downregulate the expression of Per2 gene in the pancreas in the rat

The mammalian circadian system contains both central and peripheral oscillators. It was reported that the rhythmic expressions of period homolog 2 (per2) mRNA in peripheral tissues were abolished by the suprachiasmatic nucleus (SCN) lesions. However, there are no reports that ventromedial hypothalamic (VMH) lesions can directly affect the expression of clock genes in pancreas and liver. In the present study, we examined whether VMH lesions can affect the expression of the clock gene, per2 in these organs. Total RNA was extracted from rat pancreas and liver tissues, and differences in the gene expression profiles between rats at day 3 after VMH lesioning and sham-VMH-lesioned rats were investigated using DNA microarray and real-time quantitative analysis. These results showed that VMH lesions downregulated the expression of the clock gene, per2 in the pancreas, but not the liver in the morning. There is a possibility that VMH lesions may affect the expression of the clock gene, per2 in the pancreas.

Role of mutation of the circadian clock gene Per2 in cardiovascular circadian rhythms

Alterations in the circadian blood pressure pattern are frequently observed in hypertension and lead to increased cardiovascular morbidity. However, there are no studies that have investigated a possible implication of the Period2 gene, a key component of the molecular circadian clock, on the circadian rhythms of blood pressure and heart rate. To address this question, we monitored blood pressure, heart rate, and locomotor activity 24 h a day by telemetry in mice carrying a mutation in the Period2 gene and in wild-type control mice. Under a standard 12:12-h light-dark cycle, mutant mice showed a mild cardiovascular phenotype with an elevated 24-h heart rate, a decreased 24-h diastolic blood pressure, and an attenuation of the dark-light difference in blood pressure and heart rate. Locomotor activity was similar in both groups and did not appear to explain the observed hemodynamic differences. When mice were placed under constant darkness during eight consecutive days, wild-type mice maintained 24-h rhythms, whereas there was an apparent progressive loss of 24-h rhythm of blood pressure, heart rate, and locomotor activity in mutant mice. However, a chi square periodogram revealed that circadian rhythms were preserved under complete absence of any light cue, but with shorter periods by approximately 40 min, leading to a cumulative phase shift toward earlier times of approximately 5 h and 20 min by the end of the 8th day. When heart rate, mean arterial pressure, and activity were recalculated according to the endogenous circadian periods of each individual mouse, the amplitudes of the circadian rhythms ("subjective night"-"subjective day" differences) were maintained for all variables studied. Our data show that mutation of the Period2 gene results in an attenuated dipping of blood pressure and heart rate during both light-dark cycles and constant darkness, and in shorter circadian periods during constant darkness.

Anticipating anticipation: pursuing identification of cardiomyocyte circadian clock function

Diurnal rhythms in myocardial physiology (e.g., metabolism, contractile function) and pathophyiology (e.g., sudden cardiac death) are well establish and have classically been ascribed to time-of-day-dependent alterations in the neurohumoral milieu. Existence of an intramyocellular circadian clock has recently been exposed. Circadian clocks enable the cell to anticipate environmental stimuli, facilitating a timely and appropriate response. Generation of genetically modified mice with a targeted disruption of the cardiomyocyte circadian clock has provided an initial means for deciphering the functions of this transcriptionally based mechanism and allowed predictions regarding which environmental stimuli the heart anticipates (i.e., "anticipating anticipation"). Recent studies show that the cardiomyocyte circadian clock influences myocardial gene expression, beta-adrenergic signaling, transcriptional responsiveness to fatty acids, triglyceride metabolism, heart rate, and cardiac output, as well as ischemia-reperfusion tolerance. In addition to reviewing current knowledge regarding the roles of the cardiomyocyte circadian clock, this article highlights putative frontiers in this field. The latter includes establishing molecular links between the cardiomyocyte circadian clock with identified functions, understanding the pathophysiological consequences of disruption of this mechanism, targeting resynchronization of the cardiomyocyte circadian clock for prevention/treatment of cardiovascular disease, linking the circadian clock with the cardiobeneficial effects of caloric restriction, and determining whether circadian clock genes are subject to epigenetic regulation. Information gained from studies investigating the cardiomyocyte circadian clock will likely translate to extracardiac tissues, such as skeletal muscle, liver, and adipose tissue.

Expression of cortisol metabolism-related genes shows circadian rhythmic patterns in human adipose tissue

OBJECTIVE

To analyze, in morbid obese patients, the expression of several human genes regulating cortisol metabolism, such as glucocorticoid receptor (GR), 11beta-hydroxysteroid dehydrogenase type 1 (11betaHSD1), 11beta-hydroxysteroid dehydrogenase type 2 (11betaHSD2), stearoyl-acute regulatory protein (StAR), 5alpha-reductase type I (5alpha-R) and peroxisome proliferator-activated receptor-gamma (PPARgamma) in two different adipose depots. A second objective was to characterize the circadian rhythmicity of these genes in both adipose tissue (AT) regions.

DESIGN

Visceral and subcutaneous abdominal AT biopsies were obtained from obese patients (body mass index >or=40 kg m(-2)). To carry out rhythmic expression analysis, AT explants were cultured for 24 h and gene expression at times (T) 0, 6, 12 and 18 h, was performed with quantitative real-time PCR.

RESULT

GR, 11betaHSD1 and PPARgamma genes were highly expressed in both subcutaneous and visceral depots. StAR and 5alpha-R genes were detected at lower levels. The expression of 11betaHSD2 was quantified in both AT depots with a higher expression in the visceral depot (P=0.032). Both sexes had similar gene expression levels, except for 5alpha-R (P=0.002). The genes studied showed circadian rhythmicity being more robust in visceral than in subcutaneous AT. Genes ranged in anti-phase between both depots (P=0.002). This rhythmicity was maintained in an AT culture.

CONCLUSION

We have shown for the first time circadian rhythmicity in glucocorticoid-related gene expression in human AT ex vivo. These results may have potential therapeutic implications with respect to the pathogenesis and treatment of diseases, such as obesity, type 2 diabetes and cardiovascular diseases.

Hypertension and disrupted blood pressure circadian rhythm in type 2 diabetic db/db mice

Human Type 2 diabetes is associated with increased incidence of hypertension and disrupted blood pressure (BP) circadian rhythm. Db/db mice have been used extensively as a model of Type 2 diabetes, but their BP is not well characterized. In this study, we used radiotelemetry to define BP and the circadian rhythm in db/db mice. We found that the systolic, diastolic, and mean arterial pressures were each significantly increased by 11, 8, and 9 mmHg in db/db mice compared with controls. In contrast, no difference was observed in pulse pressure or heart rate. Interestingly, both the length of time db/db mice were active (locomotor) and the intensity of locomotor activity were significantly decreased in db/db mice. In contrast to controls, the 12-h light period average BP in db/db mice did not dip significantly from the 12-h dark period. A partial Fourier analysis of the continuous 72-h BP data revealed that the power and the amplitude of the 24-h period length rhythm were significantly decreased in db/db mice compared with the controls. The acrophase was centered at 0141 in control mice, but became scattered from 1805 to 0236 in db/db mice. In addition to BP, the circadian rhythms of heart rate and locomotor activity were also disrupted in db/db mice. The mean arterial pressure during the light period correlates with plasma glucose, insulin, and body weight. Moreover, the oscillations of the clock genes DBP and Bmal1 but not Per1 were significantly dampened in db/db mouse aorta compared with controls. In summary, our data show that db/db mice are hypertensive with a disrupted BP, heart rate, and locomotor circadian rhythm. Such changes are associated with dampened oscillations of clock genes DBP and Bmal1 in vasculature.

Sympathetic input modulates, but does not determine, phase of peripheral circadian oscillators

The circadian clock in the suprachiasmatic nucleus (SCN) maintains phase synchrony among circadian oscillators throughout the organism. Environmental light signals entrain the SCN, but timed, limited meal access acts as an overriding time cue for several peripheral tissues. We present data from a peripheral oscillator, the submaxillary salivary gland, in which temporal restriction of meals fails to entrain gene expression. In day-fed rats, submaxillary gland rhythms in expression of the clock gene Period1 (Per1) stay entrained to the light cycle (peaking at night) or become arrhythmic. This result suggests that feeding cues compete weakly with light cycle cues to set the phase of clock genes in this tissue. Since the submaxillary glands receive sympathetic innervation originating in the SCN, which relays light cycle cues to other oscillators, we attempted to assess the role of this neural input in phase control of submaxillary Per1 expression. We sympathetically denervated the submaxillary glands before subjecting rats to daytime-restricted feeding. After denervation, Per1 rhythms in all submaxillary glands shifted phase 180 degrees and entrained to daytime feeding. These results support the hypothesis that peripheral oscillators may receive multiple signals contributing to their phase of entrainment. Sympathetic efferents from the SCN can relay light cycle information, while other external cues may reach tissues through other efferents or nonneural pathways. In an abnormal, disruptive regimen such as daytime-restricted feeding, these different signals compete. Arrhythmicity may result if one signal is not clearly dominant. Elimination of the dominant signal (e.g., surgical sympathectomy) may allow a secondary signal to control phase.