Reduced Nitric Oxide Causes Age-Associated Impairment of Circadian Rhythmicity

DNA methylation of core clock genes in patients with major depressive disorder: Association with air pollution exposure and disease severity

BACKGROUND

Major Depressive Disorder (MDD) is a multifactorial disease which could be influenced by exposure to air pollution through disruption of sleep-wake cycles and other circadian-related behaviors. Our study aimed to investigate the interplay between air pollution exposure, DNA methylation of core clock genes involved in circadian rhythms, and MDD severity.

METHODS

Four hundred sixteen MDD patients (64 % females) agreed to participate and donated a blood sample to measure DNA methylation of the core clock genes CRY1, PER1, PER2, CLOCK, BMAL1. MDD severity and functioning was assessed using five rating scales. Daily mean estimates of particulate matter with diameter ≤ 2.5 μm (PM2.5) and nitrogen dioxide (NO2) were assigned to study participants based on their residential address, and averaged to estimate different cumulative exposure windows. Multivariate regression models were applied to assess associations between air pollutants and core clock genes methylation and between DNA methylation of those same genes and MDD severity.

RESULTS

PM2.5 exposure in the six months preceding recruitment was associated with CLOCK hypomethylation (β=-0.11, 95 % confidence interval [CI]:0.20; -0.02) and CRY1 hypermethylation (β=0.32, 95 %CI: 0.06; 0.58). All NO2 exposure windows were associated with CRY1 hypermethylation. Increasing methylation of CLOCK was associated with lower MDD severity considering several scales (e.g., Hamilton Depression Rating Scale: β=-7.21, 95 %CI:3.97; -0.44).

CONCLUSIONS

Taken together our findings shed some light on the complex mechanism underlying the pathogenesis of MDD, with a potentially relevant role of the environment and of its impact on epigenetic mechanisms altering the expression of core clock genes.

Exacerbating effects of circadian rhythm disruption on the systemic lupus erythematosus

OBJECTIVE

Circadian rhythm disruption (CRD) has been associated with inflammation and immune disorders, but its role in SLE progression is unclear. We aimed to investigate the impact of circadian rhythms on immune function and inflammation and their contribution to SLE progression to lupus nephritis (LN).

METHODS

This study retrospectively analysed the clinical characteristics and transcriptional profiles of 373 samples using bioinformatics and machine-learning methods. A flare risk score (FRS) was established to predict overall disease progression for patients with lupus. Mendelian randomisation was used to analyse the causal relationship between CRD and SLE progression.

RESULTS

Abnormalities in the circadian pathway were detected in patients with SLE, and lower enrichment levels suggested a disease state (normalised enrichment score=0.6714, p=0.0062). The disruption of circadian rhythms was found to be closely linked to lupus flares, with the FRS showing a strong ability to predict disease progression (area under the curve (AUC) of 5-year prediction: 0.76). The accuracy of disease prediction was improved by using a prognostic nomogram based on FRS (AUC=0.77). Additionally, Mendelian randomisation analysis revealed an inverse causal relationship between CRD and SLE (OR 0.6284 (95% CI 0.3630 to 1.0881), p=0.0485) and a positive causal relationship with glomerular disorders (OR 0.0337 (95% CI 1.634e-3 to 6.934e-1), p=0.0280).

CONCLUSION

Our study reveals that genetic characteristics arising from CRD can serve as biomarkers for predicting the exacerbation of SLE. This highlights the crucial impact of CRD on the progression of lupus.

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 Rhythms in Cardiovascular Metabolism

Energetic demand and nutrient supply fluctuate as a function of time-of-day, in alignment with sleep-wake and fasting-feeding cycles. These daily rhythms are mirrored by 24-hour oscillations in numerous cardiovascular functional parameters, including blood pressure, heart rate, and myocardial contractility. It is, therefore, not surprising that metabolic processes also fluctuate over the course of the day, to ensure temporal needs for ATP, building blocks, and metabolism-based signaling molecules are met. What has become increasingly clear is that in addition to classic signal-response coupling (termed reactionary mechanisms), cardiovascular-relevant cells use autonomous circadian clocks to temporally orchestrate metabolic pathways in preparation for predicted stimuli/stresses (termed anticipatory mechanisms). Here, we review current knowledge regarding circadian regulation of metabolism, how metabolic rhythms are synchronized with cardiovascular function, and whether circadian misalignment/disruption of metabolic processes contribute toward the pathogenesis of cardiovascular disease.

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.

Schizophrenia and disruption of circadian rhythms: An overview of genetic, metabolic and clinical signs

A molecular clock in the suprachiasmatic nucleus of the anterior hypothalamus, which is entrained by the dark-light cycle and controls the sleep-wake cycle, regulates circadian rhythms. The risk of developing mental disorders, such as schizophrenia, has long been linked to sleep abnormalities. Additionally, a common aspect of mental disorders is sleep disturbance, which has a direct impact on the intensity of the symptoms and the quality of life of the patient. This relationship can be explained by gene alterations such as CLOCK in schizophrenia which are also important components of the physiological circadian rhythm. The function of dopamine and adenosine in circadian rhythm should also be noted, as these hypotheses are considered to be the most popular theories explaining schizophrenia pathogenesis. Therefore, determining the presence of a causal link between the two can be key to identifying new potential targets in schizophrenia therapy, which can open new avenues for clinical research as well as psychiatric care. We review circadian disruption in schizophrenia at the genetic, metabolic, and clinical levels. We summarize data about clock and clock-controlled genes' alterations, neurotransmitter systems' impairments, and association with chronotype in schizophrenia patients. Our findings demonstrate that in schizophrenia either homeostatic or circadian processes of sleep regulation are disturbed. Also, we found an insufficient number of studies aimed at studying the relationship between known biological phenomena of circadian disorders and clinical signs of schizophrenia.

Circadian rhythm disturbances involved in ozone-induced glucose metabolism disorder in mouse liver

Ozone (O3) is a key environmental factor for developing diabetes. Nevertheless, the underlying mechanisms remain unclear. This study aimed to investigate alterations of glycometabolism in mice after O3 exposure and the role of circadian rhythms in this process. C57BL/6 male mice were randomly assigned to O3 (0.5 ppm) or filtered air for four weeks (4 h/day). Then, hepatic tissues of mice were collected at 4 h intervals within 24 h after O3 exposure to test. The results showed that hepatic circadian rhythm genes oscillated abnormally, mainly at zeitgeber time (ZT)8 and ZT20 after O3 exposure. Furthermore, detection of glycometabolism (metabolites, enzymes, and genes) revealed that O3 caused change in the daily oscillations of glycometabolism. The serum glucose content decreased at ZT4 and ZT20, while hepatic glucose enhanced at ZT16 and ZT24(0). Both G6pc and Pck1, which are associated with hepatic gluconeogenesis, significantly increased at ZT20. O3 exposure disrupted glycometabolism by increasing gluconeogenesis and decreasing glycolysis in mice liver. Finally, correlation analysis showed that the association between Bmal1 and O3-induced disruption of glycometabolism was the strongest. The findings emphasized the interaction between adverse outcomes of circadian rhythms and glycometabolism following O3 exposure.

Effect of Liuzijue exercise in different periods on circadian rhythm of blood pressure in patients with essential hypertension: A randomized trial

BACKGROUND

Exercising at different times of the day is a widely employed strategy for treating essential hypertension, aimed at enhancing the circadian rhythm of blood pressure. This study aimed to investigate the effects of Liuzijue exercise in the morning and afternoon on the circadian rhythm of blood pressure in patients with essential hypertension.

METHODS

This clinical randomized trial recruited 36 patients. They were randomly divided into 3 groups: morning exercise, afternoon exercise, and waiting treatment group. Randomization was performed at a ratio of 1:1:1, ensuring an equal distribution of participants among the 3 groups. Based on maintaining routine work and rest and continuing the original drug treatment, the exercise performed Liuzijue exercise for 12 weeks. The exercise time was 9:00 to 10:00 in the morning exercise group and 14:00 to 15:00 in the afternoon exercise group. The waiting treatment group did not perform any form of fitness exercise. The subjects in the 3 groups were monitored by 24-hour ambulatory blood pressure on the day before and after the first day.

RESULTS

After the 12-week Liuzijue exercise intervention, mean systolic blood pressure during the night significantly decreased in the morning exercise group (P < .01). In contrast, the waiting group experienced substantial increases in 24-hour mean systolic blood pressure (24hSBP), 24-hour mean diastolic blood pressure (24hDBP), mean systolic blood pressure during the daytime (dSBP), and mean diastolic blood pressure during the daytime (dDBP) (P < .01). Further analysis showed that the morning exercise group had significantly lower 24hSBP, 24hDBP, dSBP, dDBP, and mean systolic blood pressure during the night than the waiting group (P < .05). Additionally, the morning exercise group had lower 24hSBP and dSBP levels than the afternoon exercise group (P < .05). In contrast, the afternoon exercise group had lower 24hDBP and dDBP than the waiting treatment group (P < .05).

CONCLUSIONS

The 12-week Liuzijue exercise in the morning regimen demonstrated superior efficacy in reducing 24-hour ambulatory blood pressure levels among patients with essential hypertension. Moreover, it facilitates the transition of non-dipper blood pressure patterns to dippers, thereby rectifying aberrant circadian rhythms.

Development of circadian neurovascular function and its implications

The neurovascular system forms the interface between the tissue of the central nervous system (CNS) and circulating blood. It plays a critical role in regulating movement of ions, small molecules, and cellular regulators into and out of brain tissue and in sustaining brain health. The neurovascular unit (NVU), the cells that form the structural and functional link between cells of the brain and the vasculature, maintains the blood-brain interface (BBI), controls cerebral blood flow, and surveils for injury. The neurovascular system is dynamic; it undergoes tight regulation of biochemical and cellular interactions to balance and support brain function. Development of an intrinsic circadian clock enables the NVU to anticipate rhythmic changes in brain activity and body physiology that occur over the day-night cycle. The development of circadian neurovascular function involves multiple cell types. We address the functional aspects of the circadian clock in the components of the NVU and their effects in regulating neurovascular physiology, including BBI permeability, cerebral blood flow, and inflammation. Disrupting the circadian clock impairs a number of physiological processes associated with the NVU, many of which are correlated with an increased risk of dysfunction and disease. Consequently, understanding the cell biology and physiology of the NVU is critical to diminishing consequences of impaired neurovascular function, including cerebral bleeding and neurodegeneration.

Chronodisruption of the acute inflammatory response by night lighting in rats

Daily oscillations are present in many aspects of the immune system, including responsiveness to infections, allowing temporal alignment of defence mechanisms with the external environment. Our study addresses whether compromised circadian timing function by dim artificial light at night (ALAN) impacts the time dependency of the acute inflammatory response in a rat model of lipopolysaccharide (LPS)-induced inflammation. After 2 weeks of exposure to low-intensity ALAN (~2 lx) or a standard light/dark cycle, male rats were challenged with LPS during either the day or the night. Dim ALAN attenuated the anorectic response when rats were stimulated during their early light phase. Next, ALAN suppressed daily variability in inflammatory changes in blood leukocyte numbers and increased the daytime sensitivity of neutrophils to the priming effects of LPS on oxidative burst. An altered renal inflammatory response in ALAN-exposed rats was manifested by stimulated T-cell infiltration into the kidney upon night-time LPS injection and the modified rhythmic response of genes involved in inflammatory pathways. Moreover, ALAN disturbed steady-state oscillations of the renal molecular clock and eliminated the inflammatory responsiveness of Rev-erbα. Altogether, dim ALAN impaired time-of-day-dependent sensitivity of inflammatory processes, pointing out a causal mechanism between light pollution and negative health effects.

Circadian blood pressure variability and asymmetric dimethylarginine in patients with glaucoma: cross-sectional study of The LIGHT cohort

OBJECTIVE

Glaucoma is reportedly associated with asymmetric dimethylarginine (ADMA) and circadian blood pressure (BP) variability, including night-time SBP. We determined whether ADMA level is associated with night-time SBP in patients with glaucoma.

METHODS

In this cross-sectional study, we measured the serum ADMA level and ambulatory BP of 163 patients with glaucoma and 705 participants without glaucoma. Based on the tertiles of serum ADMA level, the patients were divided into three groups: low, intermediate, and high-ADMA. Night-time SBP was determined based on ambulatory BP measured every 30 min for 48 h. The nondipper BP pattern was defined as having a night-time mean SBP decline of less than 10% relative to the mean daytime SBP.

RESULTS

In the glaucoma group, the night-time SBP in the high-ADMA group was significantly higher than in the low-ADMA group (123.0 and 114.4 mmHg, respectively; P  = 0.003). Multivariable analysis adjusted for the potential confounders showed the night-time SBP, and the odds ratio for nondipper in the high-ADMA group were also significantly higher than in the low-ADMA group ( P  = 0.030 and P  = 0.021, respectively). Significant associations between continuous serum ADMA levels with night-time SBP and nondipper were also found ( P  = 0.002 and 0.006, respectively). In the control group, however, no significant associations were found between serum ADMA levels and night-time SBP and nondipper. A significant interaction effect of the serum ADMA levels and glaucoma on nondipper was found ( P  = 0.004).

CONCLUSION

Serum ADMA level was significantly associated with the disturbance of circadian BP variability in patients with glaucoma.

Modulation of the NO-cGMP pathway has no effect on olfactory responses in the Drosophila antenna

Olfaction is a crucial sensory modality in insects and is underpinned by odor-sensitive sensory neurons expressing odorant receptors that function in the dendrites as odorant-gated ion channels. Along with expression, trafficking, and receptor complexing, the regulation of odorant receptor function is paramount to ensure the extraordinary sensory abilities of insects. However, the full extent of regulation of sensory neuron activity remains to be elucidated. For instance, our understanding of the intracellular effectors that mediate signaling pathways within antennal cells is incomplete within the context of olfaction in vivo. Here, with the use of optical and electrophysiological techniques in live antennal tissue, we investigate whether nitric oxide signaling occurs in the sensory periphery of Drosophila. To answer this, we first query antennal transcriptomic datasets to demonstrate the presence of nitric oxide signaling machinery in antennal tissue. Next, by applying various modulators of the NO-cGMP pathway in open antennal preparations, we show that olfactory responses are unaffected by a wide panel of NO-cGMP pathway inhibitors and activators over short and long timescales. We further examine the action of cAMP and cGMP, cyclic nucleotides previously linked to olfactory processes as intracellular potentiators of receptor functioning, and find that both long-term and short-term applications or microinjections of cGMP have no effect on olfactory responses in vivo as measured by calcium imaging and single sensillum recording. The absence of the effect of cGMP is shown in contrast to cAMP, which elicits increased responses when perfused shortly before olfactory responses in OSNs. Taken together, the apparent absence of nitric oxide signaling in olfactory neurons indicates that this gaseous messenger may play no role as a regulator of olfactory transduction in insects, though may play other physiological roles at the sensory periphery of the antenna.

The time dimension to stroke: Circadian effects on stroke outcomes and mechanisms

The circadian system is widely involved in the various pathological outcomes affected by time dimension changes. In the brain, the master circadian clock, also known as the "pacemaker," is present in the hypothalamus's suprachiasmatic nucleus (SCN). The SCN consists of molecular circadian clocks that operate in each neuron and other brain cells. These circadian mechanisms are controlled by the transcription and translation of specific genes such as the clock circadian regulator (Clock) and brain and muscle ARNT-Like 1 (Bmal1). Period (Per1-3) and cryptochrome (Cry1 and 2) negatively feedback and regulate the clock genes. Variations in the circadian cycle and these clock genes can affect stroke outcomes. Studies suggest that the peak stroke occurs in the morning after patients awaken from sleep, while stroke severity and poor outcomes worsen at midnight. The main risk factor associated with stroke is high blood pressure (hypertension). Blood pressure usually dips by 15-20% during sleep, but many hypertensives do not display this normal dipping pattern and are non-dippers. A sleep blood pressure is the primary determinant of stroke risk. This article discusses the possible mechanism associated with circadian rhythm and stroke outcomes.

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.

Multi-Modal Regulation of Circadian Physiology by Interactive Features of Biological Clocks

The circadian clock is a fundamental biological timing mechanism that generates nearly 24 h rhythms of physiology and behaviors, including sleep/wake cycles, hormone secretion, and metabolism. Evolutionarily, the endogenous clock is thought to confer living organisms, including humans, with survival benefits by adapting internal rhythms to the day and night cycles of the local environment. Mirroring the evolutionary fitness bestowed by the circadian clock, daily mismatches between the internal body clock and environmental cycles, such as irregular work (e.g., night shift work) and life schedules (e.g., jet lag, mistimed eating), have been recognized to increase the risk of cardiac, metabolic, and neurological diseases. Moreover, increasing numbers of studies with cellular and animal models have detected the presence of functional circadian oscillators at multiple levels, ranging from individual neurons and fibroblasts to brain and peripheral organs. These oscillators are tightly coupled to timely modulate cellular and bodily responses to physiological and metabolic cues. In this review, we will discuss the roles of central and peripheral clocks in physiology and diseases, highlighting the dynamic regulatory interactions between circadian timing systems and multiple metabolic factors.

S-nitrosoglutathione reductase (GSNOR) deficiency accelerates cardiomyocyte differentiation of induced pluripotent stem cells

Introduction

Induced pluripotent stem cells (iPSCs) provide a model of cardiomyocyte (CM) maturation. Nitric oxide signaling promotes CM differentiation and maturation, although the mechanisms remain controversial.

Aim

The study tested the hypothesis that in the absence of S-nitrosoglutathione reductase (GSNOR), a denitrosylase regulating protein S-nitrosylation, the resultant increased S-nitrosylation accelerates the differentiation and maturation of iPSC-derived cardiomyocytes (CMs).

Methods and Results

iPSCs derived from mice lacking GSNOR (iPSC^GSNOR-/-) matured faster than wildtype iPSCs (iPSC^WT) and demonstrated transient increases in expression of murine Snail Family Transcriptional Repressor 1 gene (Snail), murine Snail Family Transcriptional Repressor 2 gene (Slug) and murine Twist Family BHLH Transcription Factor 1 gene (Twist), transcription factors that promote epithelial-to-mesenchymal transition (EMT) and that are regulated by Glycogen Synthase Kinase 3 Beta (GSK3β). Murine Glycogen Synthase Kinase 3 Beta (Gsk3β) gene exhibited much greater S-nitrosylation, but lower expression in iPSC^GSNOR-/-. S-nitrosoglutathione (GSNO)-treated iPSC^WT and human (h)iPSCs also demonstrated reduced expression of GSK3β. Nkx2.5 expression, a CM marker, was increased in iPSC^GSNOR-/- upon directed differentiation toward CMs on Day 4, whereas murine Brachyury (t), Isl1, and GATA Binding Protein (Gata4) mRNA were decreased, compared to iPSC^WT, suggesting that GSNOR deficiency promotes CM differentiation beginning immediately following cell adherence to the culture dish-transitioning from mesoderm to cardiac progenitor.

Conclusion

Together these findings suggest that increased S-nitrosylation of Gsk3β promotes CM differentiation and maturation from iPSCs. Manipulating the post-translational modification of GSK3β may provide an important translational target and offers new insight into understanding of CM differentiation from pluripotent stem cells.

One sentence summary

Deficiency of GSNOR or addition of GSNO accelerates early differentiation and maturation of iPSC-cardiomyocytes.

Circadian clock genes as promising therapeutic targets for autoimmune diseases

Circadian rhythm is a natural, endogenous process whose physiological functions are controlled by a set of clock genes. Disturbance of the clock genes have detrimental effects on both innate and adaptive immunity, which significantly enhance pro-inflammatory responses and susceptibility to autoimmune diseases via strictly controlling the individual cellular components of the immune system that initiate and perpetuate the inflammation pathways. Autoimmune diseases, especially rheumatoid arthritis (RA), often exhibit substantial circadian oscillations, and circadian rhythm is involved in the onset and progression of autoimmune diseases. Mounting evidence indicate that the synthetic ligands of circadian clock genes have the property of reducing the susceptibility and clinical severity of subjects. This review supplies an overview of the roles of circadian clock genes in the pathology of autoimmune diseases, including BMAL1, CLOCK, PER, CRY, REV-ERBα, and ROR. Furthermore, summarized some circadian clock genes as candidate genes for autoimmune diseases and current advancement on therapy of autoimmune diseases with synthetic ligands of circadian clock genes. The existing body of knowledge demonstrates that circadian clock genes are inextricably linked to autoimmune diseases. Future research should pay attention to improve the quality of life of patients with autoimmune diseases and reduce the effects of drug preparation on the normal circadian rhythms.

Precision medicine for heart failure based on molecular mechanisms: The 2019 ISHR Research Achievement Award Lecture

Heart failure is a leading cause of death, and the number of patients with heart failure continues to increase worldwide. To realize precision medicine for heart failure, its underlying molecular mechanisms must be elucidated. In this review summarizing the "The Research Achievement Award Lecture" of the 2019 XXIII ISHR World Congress held in Beijing, China, we would like to introduce our approaches for investigating the molecular mechanisms of cardiac hypertrophy, development, and failure, as well as discuss future perspectives.

The impact of the 24-h movement spectrum on vascular remodeling in older men and women: a review

Aging is associated with increased risk of cardiovascular and cerebrovascular events, which are preceded by early, negative remodeling of the vasculature. Low physical activity is a well-established risk factor associated with the incidence and development of disease. However, recent physical activity literature indicates the importance of considering the 24-h movement spectrum. Therefore, the purpose of this review was to examine the impact of the 24-h movement spectrum, specifically physical activity (aerobic and resistance training), sedentary behavior, and sleep, on cardiovascular and cerebrovascular outcomes in older adults, with a focus on recent evidence (<10 yr) and sex-based considerations. The review identifies that both aerobic training and being physically active (compared with sedentary) are associated with improvements in endothelial function, arterial stiffness, and cerebrovascular function. Additionally, there is evidence of sex-based differences in endothelial function: a blunted improvement in aerobic training in postmenopausal women compared with men. While minimal research has been conducted in older adults, resistance training does not appear to influence arterial stiffness. Poor sleep quantity or quality are associated with both impaired endothelial function and increased arterial stiffness. Finally, the review highlights mechanistic pathways involved in the regulation of vascular and cerebrovascular function, specifically the balance between pro- and antiatherogenic factors, which mediate the relationship between the 24-h movement spectrum and vascular outcomes. Finally, this review proposes future research directions: examining the role of duration and intensity of training, combining aerobic and resistance training, and exploration of sex-based differences in cardiovascular and cerebrovascular outcomes.

Circadian Rhythm in Adipose Tissue: Novel Antioxidant Target for Metabolic and Cardiovascular Diseases

Obesity is a major risk factor for most metabolic and cardiovascular disorders. Adipose tissue is an important endocrine organ that modulates metabolic and cardiovascular health by secreting signaling molecules. Oxidative stress is a common mechanism associated with metabolic and cardiovascular complications including obesity, type 2 diabetes, and hypertension. Oxidative stress can cause adipose tissue dysfunction. Accumulating data from both humans and experimental animal models suggest that adipose tissue function and oxidative stress have an innate connection with the intrinsic biological clock. Circadian clock orchestrates biological processes in adjusting to daily environmental changes according to internal or external cues. Recent studies have identified the genes and molecular pathways exhibiting circadian expression patterns in adipose tissue. Disruption of the circadian rhythmicity has been suggested to augment oxidative stress and aberrate adipose tissue function and metabolism. Therefore, circadian machinery in the adipose tissue may be a novel therapeutic target for the prevention and treatment of metabolic and cardiovascular diseases. In this review, we summarize recent findings on circadian rhythm and oxidative stress in adipose tissue, dissect the key components that play a role in regulating the clock rhythm, oxidative stress and adipose tissue function, and discuss the potential use of antioxidant treatment on metabolic and cardiovascular diseases by targeting the adipose clock.

Transcriptome analysis of mouse aortae reveals multiple novel pathways regulated by aging

Vascular aging has been documented as a vital process leading to arterial dysfunction and age-related cardiovascular and cerebrovascular diseases. However, our understanding of the molecular underpinnings of age-related phenotypes in the vascular system is incomplete. Here we performed bulk RNA sequencing in young and old mouse aortae to elucidate age-associated changes in the transcriptome. Results showed that the majority of upregulated pathways in aged aortae relate to immune response, including inflammation activation, apoptotic clearance, and phagocytosis. The top downregulated pathway in aged aortae was extracellular matrix organization. Additionally, protein folding control and stress response pathways were downregulated in the aged vessels, with an array of downregulated genes encoding heat shock proteins (HSPs). We also found that circadian core clock genes were differentially expressed in young versus old aortae. Finally, transcriptome analysis combined with protein expression examination and smooth muscle cell (SMC) lineage tracing revealed that SMCs in aged aortae retained the differentiated phenotype, with an insignificant decrease in SMC marker gene expression. Our results therefore unveiled critical pathways regulated by arterial aging in mice, which will provide important insight into strategies to defy vascular aging and age-associated vascular diseases.

Atherosclerosis and Nanomedicine Potential: Current Advances and Future Opportunities

Atherosclerosis is the leading inducement of cardiovascular diseases, which ranks the first cause of global deaths. It is an arterial disease associated with dyslipidemia and changes in the composition of the vascular wall. Besides invasive surgical strategy, the current conservative clinical treatment for atherosclerosis falls into two categories, lipid regulating-based therapy and antiinflammatory therapy. However, the existing strategies based on conventional drug delivery systems have shown limited efficacy against disease development and plenty of side effects. Nanomedicine has great potential in the development of targeted therapy, controlled drug delivery and release, the design of novel specific drugs and diagnostic modalities, and biocompatible scaffolds with multifunctional characteristics, which has led to an evolution in the diagnosis and treatment of atherosclerosis. This paper will focus on the latest nanomedicine strategies for atherosclerosis diagnosis and treatment as well as discussing the potential therapeutic targets during atherosclerosis progress, which could form the basis of development of novel nanoplatform against atherosclerosis.

Nitric oxide: To be or not to be an endocrine hormone?

Nitric oxide (NO), a highly reactive gasotransmitter, is critical for a number of cellular processes and has multiple biological functions. Due to its limited lifetime and diffusion distance, NO has been mainly believed to act in autocrine/paracrine fashion. The increasingly recognized effects of pharmacologically delivered and endogenous NO at a distant site have changed the conventional wisdom and introduced NO as an endocrine signalling molecule. The notion is greatly supported by the detection of a number of NO adducts and their circulatory cycles, which in turn contribute to the transport and delivery of NO bioactivity, remote from the sites of its synthesis. The existence of endocrine sites of synthesis, negative feedback regulation of biosynthesis, integrated storage and transport systems, having an exclusive receptor, that is, soluble guanylyl cyclase (sGC), and organized circadian rhythmicity make NO something beyond a simple autocrine/paracrine signalling molecule that could qualify for being an endocrine signalling molecule. Here, we discuss hormonal features of NO from the classical endocrine point of view and review available knowledge supporting NO as a true endocrine hormone. This new insight can provide a new framework within which to reinterpret NO biology and its clinical applications.

Circadian expression of Glycoprotein 2 (Gp2) gene is controlled by a molecular clock in mouse Peyer's patches

The expression levels of many cell-surface proteins vary with the time of day. Glycoprotein 2 (Gp2), specifically expressed on the apical surface of M cells in Peyer's patches, functions as a transcytotic receptor for mucosal antigens. We report that cAMP response element-binding protein (CREB) regulates the transcription of the Gp2 gene, thereby generating the circadian change in its expression in mouse Peyer's patches. The transcytotic receptor activity of Gp2 was increased during the dark phase when the Gp2 protein abundance increased. Rhythmic expression of clock gene mRNA was observed in mouse Peyer's patches, and expression levels of Gp2 mRNA also exhibited circadian oscillation, with peak levels during the early dark phase. The promoter region of the mouse Gp2 gene contains several cAMP response elements (CREs). Chromatin immunoprecipitation assays revealed that CREB bound to the CREs in the Gp2 gene in Peyer's patches. Forskolin, which promotes CREB phosphorylation, increased the transcription of the Gp2 gene in Peyer's patches. As phosphorylation of CREB protein was increased when Gp2 gene transcription was activated, CREB may regulate the rhythmic expression of Gp2 mRNA in Peyer's patches. These findings suggest that intestinal immunity is controlled by the circadian clock system.

Circadian fluctuations of endothelial nitric oxide synthase activity in females with rheumatoid arthritis: a pilot study

Rheumatoid arthritis (RA) is a disease associated with circadian disorders of steroid hormones or cytokine secretion which induce inflammatory, destructive and proliferative processes in the synovial joints. Angiogenesis plays an important role in RA, but circadian rhythms of the angiogenic mediator production, especially endothelial nitric oxide synthase (NOS3), are still unclear. NOS3 takes part in regulation of endothelial functions, inflammation, and bone remodeling process. Studying circadian rhythms of NOS3 production in RA patients will make an improvement in understanding the angiogenic-inflammatory pathways relevant to rheumatic diseases. The aim of the study was to test the hypothesis of a diurnal variation in circulating levels of NOS3 in RA patients. A cross-sectional monocentric pilot study of circadian variability of endothelial nitric oxide synthase in a Ukrainian population was conducted between March and July 2017. We examined 36 RA patients (100% women) and 34 age-matched healthy women without joint diseases and autoimmune diseases (control). Blood samples were collected four times per day (at 08:00; 14:00; 20:00 and 02:00) for two consecutive days. Serum NOS3 concentration was measured by ELISA (Cloud-Clone Corp kit). The study was conducted in compliance with bioethical standards. The SPSS22 software package was used for statistical processing of the results. A diurnal variation in circulating levels of NOS3 in healthy women was established, with peak values appearing in the evening and acrophase at 20:00, and low values in the morning, with batiphase at 08:00. In patients with RA serum, NOS3 levels were substantially decreased throughout the day compared to the control. In RA patients, a diurnal variation in circulating levels of NOS3 was also established. However, the variability of NOS3 production was higher in RA patients than in the control group. For example, in RA patients the difference between morning/evening values of NOS3 was 1.3 times higher (p < 0.05) than in the control. Negative correlations were found between the morning NOS3 levels and RA activity markers such as DAS28 and the number of tender and swollen joints. The diurnal variation in circulating levels of NOS3 in women with RA as well as in healthy women was found. However, in RA patients, a decrease in NOS3 production was observed, especially in the morning, which was associated with an increase in the disease activity. Thus, the circadian rhythm of circulating NOS3 can be opposite to the circadian rhythm of secretion of main inflammatory regulators in RA.

Diurnal Regulation of Renal Electrolyte Excretion: The Role of Paracrine Factors

Many physiological processes, including most kidney-related functions, follow specific rhythms tied to a 24-h cycle. This is largely because circadian genes operate in virtually every cell type in the body. In addition, many noncanonical genes have intrinsic circadian rhythms, especially within the liver and kidney. This new level of complexity applies to the control of renal electrolyte excretion. Furthermore, there is growing evidence that paracrine and autocrine factors, especially the endothelin system, are regulated by clock genes. We have known for decades that excretion of electrolytes is dependent on time of day, which could play an important role in fluid volume balance and blood pressure control. Here, we review what is known about the interplay between paracrine and circadian control of electrolyte excretion. The hope is that recognition of paracrine and circadian factors can be considered more deeply in the future when integrating with well-established neuroendocrine control of excretion.

Breast cancer drugs perturb fundamental vascular functions of endothelial cells by attenuating protein S-nitrosylation

Cardiovascular side effects of broadly used chemotherapeutic drugs such as Tamoxifen citrate (TC), Capecitabine (CP) and Epirubicin (EP) among cancer survivors are well established. Nitric oxide (NO) is known to protect cardiovascular tissues under conditions of stress. NO can act through cyclic guanosine monophosphate (cGMP)-dependent and -independent pathways. Particularly, the S-nitrosylation of SH-groups in a protein by NO falls under cGMP-independent effects of NO. TC, CP, and EP are hypothesized as interfering with cellular protein S-nitrosylation, which, in turn, may lead to endothelial dysfunctions. The results show that all three drugs attenuate nitrosylated proteins in endothelial cells. A significant reduction in endogenous S-nitrosylated proteins was revealed by Saville-Griess assay, immunofluorescence and western blot. Incubation with the drugs causes a reduction in endothelial migration, vasodilation and tube formation, while the addition of S-nitrosoglutathione (GSNO) has a reversal of this effect. In conclusion, results indicate the possibility of decreased cellular nitrosothiols as being one of the reasons for endothelial dysfunctions under TC, CP and EP treatment. Identification of the down-regulated S-nitrosylated proteins so as to correlate their implications on fundamental vascular functions could be an interesting phenomenon.

Scalable Synthesis of Diazeniumdiolates: Application to the Preparation of MK-8150

Synthetic diazeniumdiolate (DAZD)-based nitric oxide is utilized to modulate the nitric oxide (NO) concentration in cellular environments and to control physiological processes, yet chemists are still struggling to find efficient and scalable methodologies that will enable them to access sufficient quantities of the high-energy diazeniumdiolate intermediates for biological studies. Now, a general, scalable, safer, and high-yielding new methodology adaptable to the large-scale synthesis of DAZDs has been developed.

Distribution and colocalization of melatonin 1a-receptor and NADPH-d in the trigeminal system of rat

Melatonin and nitric oxide (NO) are involved in orofacial signal processing in the trigeminal sensory system. The aim of the present study was to examine the distribution of melatonin 1a-receptor (MT1) and its colocalization with nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) in the spinal trigeminal nucleus (STN), the trigeminal ganglion (TG), and the mesencephalic trigeminal nucleus (MTN) in the rat, using histochemistry and immunohistochemistry. Our results show that MT1-positive neurons are widely distributed in the TG and the subnucleus caudalis of the STN. Furthermore, we found that MT1 colocalizes with NADPH-d throughout the TG and MTN, most extensively in the TG. The distribution pattern of MT1 and its colocalization with NADPH-d indicate that melatonin might play an important role in the trigeminal sensory system, which could be responsible for the regulation of NO levels.

Nitric Oxide Synthase Inhibition Induces Renal Medullary Hypoxia in Conscious Rats

Background Renal hypoxia, implicated as crucial factor in onset and progression of chronic kidney disease, may be attributed to reduced nitric oxide because nitric oxide dilates vasculature and inhibits mitochondrial oxygen consumption. We hypothesized that chronic nitric oxide synthase inhibition would induce renal hypoxia. Methods and Results Oxygen-sensitive electrodes, attached to telemeters, were implanted in either renal cortex (n=6) or medulla (n=7) in rats. After recovery and stabilization, baseline oxygenation ( pO 2) was recorded for 1 week. To inhibit nitric oxide synthase, N-ω-nitro-l-arginine (L-NNA; 40 mg/kg/day) was administered via drinking water for 2 weeks. A separate group (n=8), instrumented with blood pressure telemeters, followed the same protocol. L-NNA rapidly induced hypertension (165±6 versus 108±3 mm Hg; P<0.001) and proteinuria (79±12 versus 17±2 mg/day; P<0.001). Cortical pO 2, after initially dipping, returned to baseline and then increased. Medullary pO 2 decreased progressively (up to -19±6% versus baseline; P<0.05). After 14 days of L-NNA, amplitude of diurnal medullary pO 2 was decreased (3.7 [2.2-5.3] versus 7.9 [7.5-8.4]; P<0.01), whereas amplitudes of blood pressure and cortical pO 2 were unaltered. Terminal glomerular filtration rate (1374±74 versus 2098±122 μL/min), renal blood flow (5014±336 versus 9966±905 μL/min), and sodium reabsorption efficiency (13.0±0.8 versus 22.8±1.7 μmol/μmol) decreased (all P<0.001). Conclusions For the first time, we show temporal development of renal cortical and medullary oxygenation during chronic nitric oxide synthase inhibition in unrestrained conscious rats. Whereas cortical pO 2 shows transient changes, medullary pO 2 decreased progressively. Chronic L-NNA leads to decreased renal perfusion and sodium reabsorption efficiency, resulting in progressive medullary hypoxia, suggesting that juxtamedullary nephrons are potentially vulnerable to prolonged nitric oxide depletion.

Don't just say no: Differential pathways and pharmacological responses to diverse nitric oxide donors

Nitric oxide (NO) is a gaseous free radical molecule with a short half-life (∼1 s), which can gain or lose an electron into three interchangeable redox-dependent forms, the radical (NO), the nitrosonium cation (NO⁺), and nitroxyl anion (HNO). NO acts as an intra and extracellular signaling molecule regulating a wide range of functions in the cardiovascular, immune, and nervous system. NO donors are collectively known by their ability to release NOin vitro and in vivo, being proposed as therapeutic pharmacological tools for the treatment of several pathologies, such as cardiovascular disease. The highly reactive NO molecule is easily oxidized under physiological conditions to N-oxides, nitrate/nitrite and nitrogen dioxide. Different cellular responses are triggered depending on: 1) NO concentration [e.g., nanomolar for heme coordination in the allosteric site of guanylate cyclase (sGC) enzyme]; 2) the type of chemical bound to the nitrosated group (i.e., bound to nitrogen, N-nitro, or bound to sulphur atom, S-nitro) determining post-translational cysteine nitrosation; 3) the time-dependent availability of molecular targets. Classic NO donors are: organic nitrates (e.g., nitroglycerin, or glyceryl trinitrate, GTN; isosorbide mononitrate, ISMN), diazeniumdiolates having a diolate group [or NONOates, e.g., 2-(N,N-diethylamino)-diazenolate-2-oxide], S-nitrosothiols (e.g., S-nitroso glutathione, GSNO; S-nitroso-N-acetylpenicillamine, SNAP) or the organic salt sodium nitroprusside (SNP). In addition, nitroxyl (HNO) donors such as Piloty's acid and Angeli's salt can also be considered. The specific NO form released, as well as its differential reactivity to thiols, could act on different molecular targets and should be discussed in the context of: a) the type and amount of NO species determining the sensitivity of molecular targets (e.g., heme coordination, or S-nitrosation); b) the cellular redox state that could gate different effects. Experimental designs should take special care when choosing which NO donors to use, since different outcomes are to be expected. This article will comment recent findings regarding physiological responses involving NO species and their pharmacological modulation with donor drugs, especially in the context of the photic transduction pathways at the hypothalamic circadian clock.

Immunohistochemistry of the circadian clock in mouse and human vascular tissues

Aim

The circadian clock is a molecular network that controls the body physiological rhythms. In blood vessels, the circadian clock components modulate vascular remodeling, blood pressure, and signaling. The goal in this study was to determine the pattern of expression of circadian clock proteins in the endothelium, smooth muscle, and adventitia of the vasculature of human and mouse tissues.

Methods

Immunohistochemistry was performed in frozen sections of mouse aorta, common carotid artery, femoral artery, lung, and heart at 12 AM and 12 PM for Bmal1, Clock, Npas2, Per and other clock components. Studies of expression were also assessed in human saphenous vein both by immunoblotting and immunohistochemistry.

Results

In this study, we identified the expression of Bmal1, Clock, Npas, Per1, Cry1, and accessory clock components by immunohistochemical staining in the endothelium, smooth muscle and adventitia of the mouse vasculature with differing temporal and cellular profiles depending on vasculature and tissue analyzed. The human saphenous vein also exhibited expression of clock genes that exhibited an oscillatory pattern in Bmal1 and Cry by immunoblotting.

Conclusion

These studies show that circadian clock components display differences in expression and localization throughout the cardiovascular system, which may confer nuances of circadian clock signaling in a cell-specific manner.

Circadian toxicity of environmental pollution. Inhalation of polluted air to give a precedent

Exposures to environmental stressors that derive from pollution (e.g. air, light) or lifestyle choices (e.g. diet, activity, 24-hour-×-7-day) are associated with adverse human health outcomes. For instance, there is evidence that air pollution exposure and changes in sleep/wake pattern increase the risk for vascular and cardiometabolic disorders. Interestingly, air pollution exposure affects pulmonary and cardiovascular functions that follow circadian rhythmicity and increases the risk for pulmonary and cardiovascular events that occur in diurnal patterns suggesting a link between air pollution induced cardiovascular and pulmonary injury and changes in circadian rhythm. Indeed, recent research identified circadian rhythm as an air pollution target and circadian rhythm as factor that increases air pollution sensitivity. Using air pollution exposure as precedent, this review highlights research on how environmental pollution affect circadian rhythm and how circadian rhythm affects the toxicity of environmental stressors.

Regulation of vascular function and blood pressure by circadian variation in redox signalling

There is accumulating evidence that makes the link between the circadian variation in blood pressure and circadian variations in vascular contraction. The importance of vascular endothelium-derived redox-active and redox-derived species in the signalling pathways involved in controlling vascular smooth muscle contraction are well known, and when linked to the circadian variations in the processes involved in generating these species, suggests a cellular mechanism for the circadian variations in blood pressure that links directly to the peripheral circadian clock. Relaxation of vascular smooth muscle cells involves endothelial-derived relaxing factor (EDRF) which is nitric oxide (NO) produced by endothelial NO synthase (eNOS), and endothelial-derived hyperpolarising factor (EDHF) which includes hydrogen peroxide (H₂O₂) produced by NADPH oxidase (Nox). Both of these enzymes appear to be under the direct control of the circadian clock mechanism in the endothelial cells, and disruption to the clock results in endothelial and vascular dysfunction. In this review, we focus on EDRF and EDHF and summarise the recent findings on the influence of the peripheral circadian clock mechanism on processes involved in generating the redox species involved and how this influences vascular contractility, which may account for some of the circadian variations in blood pressure and peripheral resistance. Moreover, the direct link between the peripheral circadian clock and redox-signalling pathways in the vasculature, has a bearing on vascular endothelial dysfunction in disease and aging, which are both known to lead to dysfunction of the circadian clock.

Circadian modification network of a core clock driver BMAL1 to harmonize physiology from brain to peripheral tissues

Circadian clocks dictate various physiological functions by brain SCN (a central clock) -orchestrating the temporal harmony of peripheral clocks of tissues/organs in the whole body, with adaptability to environments by resetting their timings. Dysfunction of this circadian adaptation system (CAS) occasionally causes/exacerbates diseases. CAS is based on cell-autonomous molecular clocks, which oscillate via a core transcriptional/translational feedback loop with clock genes/proteins, e.g., BMAL1: CLOCK circadian transcription driver and CRY1/2 and PER1/2 suppressors, and is modulated by various regulatory loops including clock protein modifications. Among mutants with a single clock gene, BMAL1-deficient mice exhibit the most drastic loss of circadian functions. Here, we highlight on numerous circadian protein modifications of mammalian BMAL1, e.g., multiple phosphorylations, SUMOylation, ubiquitination, acetylation, O-GlcNAcylation and S-nitrosylation, which mutually interplay to control molecular clocks and coordinate physiological functions from the brain to peripheral tissues through the input and output of the clocks.

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.

Nitric oxide and hydrogen sulfide: the gasotransmitter paradigm of the vascular system

There are several reviews on NO and hydrogen sulfide (H₂ S) and their role in vascular diseases in the current relevant literature. The aim of this review is to discuss, within the limits of present knowledge, the interconnection between these two gasotransmitters in vascular function. In particular, the review focuses on the role played by the balance between the NO and H₂ S pathways in either physiological or pathological conditions. The distinction between physiology and pathology has been made in order to dissect the molecular basis of this crosstalk, highlighting how and if this balance varies, depending upon the vascular status. Perspectives and possible novel therapeutic approaches are also discussed.

LINKED ARTICLES

This article is part of a themed section on Targeting Inflammation to Reduce Cardiovascular Disease Risk. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.22/issuetoc and http://onlinelibrary.wiley.com/doi/10.1111/bcp.v82.4/issuetoc.

Akt1 Controls the Timing and Amplitude of Vascular Circadian Gene Expression

The AKT signaling pathway is important for circadian rhythms in mammals and flies ( Drosophila). However, AKT signaling in mammals is more complicated since there are 3 isoforms of AKT, each performing slightly different functions. Here we study the most ubiquitous AKT isoform, Akt1, and its role at the organismal level in the central and vascular peripheral clocks. Akt1^-/- mice exhibit relatively normal behavioral rhythms with only minor differences in circadian gene expression in the liver and heart. However, circadian gene expression in the Akt1^-/- aorta, compared with control aorta, follows a distinct pattern. In the Akt1^-/- aorta, positive regulators of circadian transcription have lower amplitude rhythms and peak earlier in the day, and negative circadian regulators are expressed at higher amplitudes and peak later in the day. In endothelial cells, negative circadian regulators exhibit an increased amplitude of expression, while the positive circadian regulators are arrhythmic with a decreased amplitude of expression. This indicates that Akt1 conditions the normal circadian rhythm in the vasculature more so than in other peripheral tissues where other AKT isoforms or kinases might be important for daily rhythms.

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.

Daily NO rhythms in peripheral clocks in aging male Wistar rats: protective effects of exogenous melatonin

In mammals suprachiasmatic nucleus (SCN), acts as a light entrainable master clock and by generation of temporal oscillations regulates the peripheral organs acting as autonomous clocks resulting in overt behavioral and physiological rhythms. SCN also controls synthesis and release of melatonin (hormonal message for darkness) from pineal. Nitric Oxide (NO) acts as an important neurotransmitter in generating the phase shifts of circadian rhythms and participates in sleep-wake processes, maintenance of vascular tone as well as signalling and regulating inflammatory processes. Aging is associated with disruption of circadian timing system and decline in endogenous melatonin leading to several physiological disorders. Here we report the effect of aging on NO daily rhythms in various peripheral clocks such as kidney, intestine, liver, heart, lungs and testis. NO levels were measured at zeitgeber time (ZT) 0, 6, 12 and 18 in these tissues using Griess assay in male Wistar rats. Aging resulted in alteration of NO levels as well as phase of NO in both 12 and 24 months groups. Correlation analysis demonstrated loss of stoichiometric interaction between the various peripheral clocks with aging. Age induced alterations in NO daily rhythms were found to be most significant in liver and, interestingly least in lungs. Neurohormone melatonin, an endogenous synchroniser and an antiaging agent decreases with aging. We report further differential restoration with exogenous melatonin administration of age induced alterations in NO daily rhythms and mean levels in kidney, intestine and liver and the stoichiometric interactions between the various peripheral clocks.

Endotoxin Disrupts Circadian Rhythms in Macrophages via Reactive Oxygen Species

The circadian clock is a transcriptional network that functions to regulate the expression of genes important in the anticipation of changes in cellular and organ function. Recent studies have revealed that the recognition of pathogens and subsequent initiation of inflammatory responses are strongly regulated by a macrophage-intrinsic circadian clock. We hypothesized that the circadian pattern of gene expression might be influenced by inflammatory stimuli and that loss of circadian function in immune cells can promote pro-inflammatory behavior. To investigate circadian rhythms in inflammatory cells, peritoneal macrophages were isolated from mPer2^luciferase transgenic mice and circadian oscillations were studied in response to stimuli. Using Cosinor analysis, we found that LPS significantly altered the circadian period in peritoneal macrophages from mPer2^luciferase mice while qPCR data suggested that the pattern of expression of the core circadian gene (Bmal1) was disrupted. Inhibition of TLR4 offered protection from the LPS-induced impairment in rhythm, suggesting a role for toll-like receptor signaling. To explore the mechanisms involved, we inhibited LPS-stimulated NO and superoxide. Inhibition of NO synthesis with L-NAME had no effect on circadian rhythms. In contrast, inhibition of superoxide with Tempol or PEG-SOD ameliorated the LPS-induced changes in circadian periodicity. In gain of function experiments, we found that overexpression of NOX5, a source of ROS, could significantly disrupt circadian function in a circadian reporter cell line (U2OS) whereas iNOS overexpression, a source of NO, was ineffective. To assess whether alteration of circadian rhythms influences macrophage function, peritoneal macrophages were isolated from Bmal1-KO and Per-TKO mice. Compared to WT macrophages, macrophages from circadian knockout mice exhibited altered balance between NO and ROS release, increased uptake of oxLDL and increased adhesion and migration. These results suggest that pro-inflammatory stimuli can disrupt circadian rhythms in macrophages and that impaired circadian rhythms may contribute to cardiovascular diseases by altering macrophage behavior.

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.

Lack of neuronal nitric oxide synthase results in attention deficit hyperactivity disorder-like behaviors in mice

Nitric oxide (NO) is an important molecule for the proper development and function of the central nervous system. In this study, we investigated the behavioral alterations in the neuronal NO synthase knockout mice (NOS1 KO) with a deficient NO production mechanism in the brain, characterizing it as a potential rodent model for attention deficit hyperactivity disorder (ADHD). NOS1 KO exhibited higher locomotor activity than their wildtype counterparts in a novel environment, as measured by open field (OF) test. In a 2-way active avoidance paradigm (TWAA), we found sex-dependent effects, where male KO displayed deficits in avoidance and escape behavior, sustained higher incidences of shuttle crossings, and higher incidences of intertrial interval crossings, suggesting learning, and/or performance impairments. On the other hand, female KO demonstrated few deficits in TWAA. Molsidomine (MSD), a NO donor, rescued TWAA deficits in male KO when acutely administered before training. In a passive avoidance paradigm, KO of both sexes displayed significantly shorter step-through latencies after training. Further, abnormal spontaneous motor activity rhythms were found in the KO during the dark phase of the day, indicating dysregulation of rhythmic activities. These data indicate that NOS1 KO mimics certain ADHD-like behaviors and could potentially serve as a novel rodent model for ADHD.

Transcriptional regulation of NHE3 and SGLT1 by the circadian clock protein Per1 in proximal tubule cells

We have previously demonstrated that the circadian clock protein period (Per)1 coordinately regulates multiple genes involved in Na(+) reabsorption in renal collecting duct cells. Consistent with these results, Per1 knockout mice exhibit dramatically lower blood pressure than wild-type mice. The proximal tubule is responsible for a majority of Na(+) reabsorption. Previous work has demonstrated that expression of Na(+)/H(+) exchanger 3 (NHE3) oscillates with a circadian pattern and Na(+)-glucose cotransporter (SGLT)1 has been demonstrated to be a circadian target in the colon, but whether these target genes are regulated by Per1 has not been investigated in the kidney. The goal of the present study was to determine if Per1 regulates the expression of NHE3, SGLT1, and SGLT2 in the kidney. Pharmacological blockade of nuclear Per1 entry resulted in decreased mRNA expression of SGLT1 and NHE3 but not SGLT2 in the renal cortex of mice. Per1 small interfering RNA and pharmacological blockade of Per1 nuclear entry in human proximal tubule HK-2 cells yielded the same results. Examination of heterogeneous nuclear RNA suggested that the effects of Per1 on NHE3 and SGLT1 expression occurred at the level of transcription. Per1 and the circadian protein CLOCK were detected at promoters of NHE3 and SGLT1. Importantly, both membrane and intracellular protein levels of NHE3 and SGLT1 were decreased after blockade of nuclear Per1 entry. This effect was associated with reduced activity of Na(+)-K(+)-ATPase. These data demonstrate a role for Per1 in the transcriptional regulation of NHE3 and SGLT1 in the kidney.

Nitroglycerin-mediated, but not flow-mediated vasodilation, is associated with blunted nocturnal blood pressure fall in patients with resistant hypertension

BACKGROUND

Endothelial function by flow-mediated (FMD) and nitroglycerin-mediated vasodilations (NMD) was scarcely investigated in resistant hypertension. We aimed to assess the independent correlates of FMD and NMD in resistant hypertensive patients, particularly their associations with ambulatory blood pressures (BP) and nocturnal BP fall patterns.

METHODS

In a cross-sectional study, 280 resistant hypertensive patients performed 24-h ambulatory BP monitoring, carotid-femoral pulse wave velocity, polysomnography, and brachial artery FMD and NMD by high-resolution ultrasonography. Independent correlates of FMD, NMD, and brachial artery diameter (BAD) were assessed by multiple linear and logistic regressions.

RESULTS

Median (interquartile range) FMD was 0.75% (-0.6 to +4.4%) and NMD was 11.8% (7.1-18.4%). Baseline BAD and diabetes were independently associated with both FMD and NMD. Older age and prior cardiovascular diseases were associated with altered FMD, whereas higher night-time SBP and lower nocturnal SBP fall were associated with impaired NMD. Moreover, there was a significant gradient of impaired NMD according to blunted nocturnal BP decline patterns. BAD was independently associated with age, sex, BMI, albuminuria, and nocturnal SBP fall. Further adjustments to blood flow velocity, aortic stiffness, plasma aldosterone concentration, and sleep apnea did not change these relationships.

CONCLUSION

NMD, but not FMD, is independently associated with unfavorable night-time BP levels and nondipping patterns, and may be a better cardiovascular risk marker in patients with resistant hypertension. BAD also may provide additional prognostic information.