Mechanism of the circadian clock in physiology

Association between a large change between the minimum and maximum monthly values of solar insolation and a history of suicide attempts in bipolar I disorder

BACKGROUND

The rate of suicide attempts by patients with bipolar disorder is high. In addition to patient and country specific factors, environmental factors may contribute to suicidal behavior. Sunlight has multiple diverse impacts on human physiology and behavior. Solar insolation is defined as the electromagnetic energy from the sun striking a surface area on earth. We previously found that a large change in solar insolation between the minimum and maximum monthly values was associated with an increased risk of suicide attempts in patients with bipolar I disorder.

METHODS

The association between solar insolation and a history of suicide attempts in bipolar disorder was again investigated using an international database with 15% more data and more sites at diverse locations and countries.

RESULTS

Data were available from 5641 patients with bipolar I disorder living at a wide range of latitudes in 41 countries in both hemispheres. A large change in solar insolation between the minimum and maximum monthly values was associated with a history of suicide attempts in patients with bipolar I disorder, a replication of our prior analysis. The estimated model also associated state sponsored religion in the onset country, female gender, a history of alcohol or substance abuse, and being part of a younger birth cohort with a history of suicide attempts.

CONCLUSIONS

A large change between the minimum and maximum monthly values of solar insolation was associated with a history of suicide attempts in bipolar I disorder, replicating our prior research. Physicians should be aware that daylight has wide ranging physiological and psychiatric impacts, and that living with large changes in solar insolation may be associated with an increased suicide risk.

Circadian Influences on Brain Lipid Metabolism and Neurodegenerative Diseases

Circadian rhythms are intrinsic, 24 h cycles that regulate key physiological, mental, and behavioral processes, including sleep-wake cycles, hormone secretion, and metabolism. These rhythms are controlled by the brain's suprachiasmatic nucleus, which synchronizes with environmental signals, such as light and temperature, and consequently maintains alignment with the day-night cycle. Molecular feedback loops, driven by core circadian "clock genes", such as Clock, Bmal1, Per, and Cry, are essential for rhythmic gene expression; disruptions in these feedback loops are associated with various health issues. Dysregulated lipid metabolism in the brain has been implicated in the pathogenesis of neurological disorders by contributing to oxidative stress, neuroinflammation, and synaptic dysfunction, as observed in conditions such as Alzheimer's and Parkinson's diseases. Disruptions in circadian gene expression have been shown to perturb lipid regulatory mechanisms in the brain, thereby triggering neuroinflammatory responses and oxidative damage. This review synthesizes current insights into the interconnections between circadian rhythms and lipid metabolism, with a focus on their roles in neurological health and disease. It further examines how the desynchronization of circadian genes affects lipid metabolism and explores the potential mechanisms through which disrupted circadian signaling might contribute to the pathophysiology of neurodegenerative disorders.

Courtship Behavior of Adult Spodoptera frugiperda (Lepidoptera: Noctuidae) Observed Using Track 3D Trajectory Tracking

Spodoptera frugiperda, also known as the fall armyworm (FAW), is classified by the Food and Agriculture Organization of the United Nations (FAO) as a major agricultural pest. By gaining a more nuanced understanding of the fall armyworm's courtship behavior, simpler and more environmentally friendly methods of controlling this pest can be developed. This study used the Track 3D system to meticulously record and describe the activity characteristics and patterns of adult males and females during courtship. The results show that adult FAWs engaged in a variety of activities during courtship that were either discrete (flying, flapping, moving, and crawling), continuous (flapping + flying, flapping + crawling, and flying + crawling), or combined (flapping + touching + flapping; flying + touching + flying). Flying and flapping were the most common activities, with observed flight patterns consisting of parabolic, circular, and zigzag trajectories. The peak activity times for adult FAWs are mainly concentrated at 11:00 p.m., 3:00 a.m., and 5:00 a.m., providing fundamental data for the precise attraction and control of adult FAWs at later stages.

The circadian clock in enamel development

Circadian rhythms are self-sustaining oscillations within biological systems that play key roles in a diverse multitude of physiological processes. The circadian clock mechanisms in brain and peripheral tissues can oscillate independently or be synchronized/disrupted by external stimuli. Dental enamel is a type of mineralized tissue that forms the exterior surface of the tooth crown. Incremental Retzius lines are readily observable microstructures of mature tooth enamel that indicate the regulation of amelogenesis by circadian rhythms. Teeth enamel is formed by enamel-forming cells known as ameloblasts, which are regulated and orchestrated by the circadian clock during amelogenesis. This review will first examine the key roles of the circadian clock in regulating ameloblasts and amelogenesis. Several physiological processes are involved, including gene expression, cell morphology, metabolic changes, matrix deposition, ion transportation, and mineralization. Next, the potential detrimental effects of circadian rhythm disruption on enamel formation are discussed. Circadian rhythm disruption can directly lead to Enamel Hypoplasia, which might also be a potential causative mechanism of amelogenesis imperfecta. Finally, future research trajectory in this field is extrapolated. It is hoped that this review will inspire more intensive research efforts and provide relevant cues in formulating novel therapeutic strategies for preventing tooth enamel developmental abnormalities.

Mechanisms of oxidative stress in interstitial cystitis/bladder pain syndrome

Interstitial cystitis/bladder pain syndrome (IC/BPS) is characterized by bladder and/or pelvic pain, increased urinary urgency and frequency and nocturia. The pathophysiology of IC/BPS is poorly understood, and theories include chronic inflammation, autoimmune dysregulation, bacterial cystitis, urothelial dysfunction, deficiency of the glycosaminoglycan (GAG) barrier and urine cytotoxicity. Multiple treatment options exist, including behavioural interventions, oral medications, intravesical instillations and procedures such as hydrodistension; however, many clinical trials fail, and patients experience an unsatisfactory treatment response, likely owing to IC/BPS phenotype heterogeneity and the use of non-targeted interventions. Oxidative stress is implicated in the pathogenesis of IC/BPS as reactive oxygen species impair bladder function via their involvement in multiple molecular mechanisms. Kinase signalling pathways, nociceptive receptors, mast-cell activation, urothelial dysregulation and circadian rhythm disturbance have all been linked to reactive oxygen species and IC/BPS. However, further research is necessary to fully uncover the role of oxidative stress in the pathways driving IC/BPS pathogenesis. The development of new models in which these pathways can be manipulated will aid this research and enable further investigation of promising therapeutic targets.

Chronobioethics: Symphony of biological clocks observed by 7-day/24-hour ambulatory blood pressure monitoring and cardiovascular health

BACKGROUND

The high prevalence of desynchronized biological rhythms is becoming a primary public health concern. We assess complex and diverse inter-modulations among multi-frequency rhythms present in blood pressure (BP) and heart rate (HR).

SUBJECTS

and Methods: We performed 7-day/24-hour Ambulatory BP Monitoring in 220 (133 women) residents (23 to 74 years) of a rural Japanese town in Kochi Prefecture under everyday life conditions.

RESULTS

A symphony of biological clocks contributes to the preservation of a synchronized circadian system. (1) Citizens with an average 12.02-h period had fewer vascular variability disorders than those with shorter (11.37-h) or longer (12.88-h) periods (P<0.05), suggesting that the circasemidian rhythm is potentially important for human health. (2) An appropriate BP-HR coupling promoted healthier circadian profiles than a phase-advanced BP: lower 7-day nighttime SBP (106.8 vs. 112.9 mmHg, P=0.0469), deeper nocturnal SBP dip (20.5% vs. 16.8%, P=0.0101), and less frequent incidence of masked non-dipping (0.53 vs. 0.86, P=0.0378), identifying the night as an important time window.

CONCLUSION

Adaptation to irregular schedules in everyday life occurs unconsciously at night, probably initiated from the brain default mode network, in coordination with the biological clock system, including a reinforced about 12-hour clock, as "a biological clock-guided core integration system".

The Relationship between Circadian Rhythm and Cancer Disease

The circadian clock regulates biological cycles across species and is crucial for physiological activities and biochemical reactions, including cancer onset and development. The interplay between the circadian rhythm and cancer involves regulating cell division, DNA repair, immune function, hormonal balance, and the potential for chronotherapy. This highlights the importance of maintaining a healthy circadian rhythm for cancer prevention and treatment. This article investigates the complex relationship between the circadian rhythm and cancer, exploring how disruptions to the internal clock may contribute to tumorigenesis and influence cancer progression. Numerous databases are utilized to conduct searches for articles, such as NCBI, MEDLINE, and Scopus. The keywords used throughout the academic archives are "circadian rhythm", "cancer", and "circadian clock". Maintaining a healthy circadian cycle involves prioritizing healthy sleep habits and minimizing disruptions, such as consistent sleep schedules, reduced artificial light exposure, and meal timing adjustments. Dysregulation of the circadian clock gene and cell cycle can cause tumor growth, leading to the need to regulate the circadian cycle for better treatment outcomes. The circadian clock components significantly impact cellular responses to DNA damage, influencing cancer development. Understanding the circadian rhythm's role in tumor diseases and their therapeutic targets is essential for treating and preventing cancer. Disruptions to the circadian rhythm can promote abnormal cell development and tumor metastasis, potentially due to immune system imbalances and hormonal fluctuations.

Traumatic brain injury-induced disruption of the circadian clock

Disturbances in the circadian rhythm have been reported in patients following traumatic brain injury (TBI). However, the rhythmic expression of circadian genes in peripheral blood leukocytes (PBL) following TBI has not yet been studied. The messenger ribonucleic acid (mRNA) expression of period 1 (Per1), Per2, Per3, cryptochrome 1 (Cry1), Cry2, brain and muscle aryl hydrocarbon receptor nuclear translocator-like 1 (Bmal1), and circadian locomotor output cycles kaput (Clock) was quantified in PBLs from sham-operated rats and rats with acute subdural hematoma (ASDH) over a 48-h period. The rectal temperature of the animals was measured every 4 h over 2 days. The mesor, rhythm, amplitude, and acrophase were estimated using cosinor analysis. Cosinor analysis revealed that Per2, Cry1, and Bmal1 mRNAs were rhythmically expressed in the PBLs of sham-operated rats. In contrast, fluctuations in rhythmic expression were not observed following ASDH. The rectal temperature of sham-operated rats also exhibited rhythmicity. ASDH rats had a disrupted rectal temperature rhythm, a diminished amplitude, and an acrophase shift. TBI with ASDH results in dysregulated expression of some circadian genes and changes in body temperature rhythm. Further research is required to understand the pathophysiology of altered circadian networks following TBI. KEY MESSAGES: First to investigate the mRNA expression of circadian genes in PBLs of ASDH rats. ASDH rats had disrupted rhythmicity of Per2, Cry1, and Bmal1 mRNA expression. Cosinor analysis showed that ASDH rats had a disrupted rectal temperature rhythm.

PER2 gene and its association with sleep-related disorders: A review

The natural circadian rhythm in an individual governs the sleep-wake cycle over 24 h. Disruptions in this internal cycle can lead to major health hazards and sleep disorders. Reports suggest that at least 50 % of people worldwide suffer from sleep-related disorders. An increase in screen time, especially in the wake of the COVID-19 pandemic, is one of the external causative factors for this condition. While many factors govern the circadian clock and its aberrance, the PER2 gene has been strongly linked to chronotypes by many researchers. The current paper provides an extensive examination of key Single Nucleotide Polymorphisms within the PER2 gene and their potential connection to four major types of sleep disorders. This study investigates whether these SNPs play a causative role in sleep disorders or if they are solely associated with these conditions. Additionally, we explore whether these genetic variations exert a lifelong influence on these sleep patterns or if external triggers contribute to the development of sleep disorders. This gene is a crucial regulator of the circadian cycle responsible for the transcription of other clock genes. It regulates a variety of physiological systems such as metabolism, sleep, body temperature, blood pressure, endocrine, immunological, cardiovascular, and renal function. We aim to establish some clarity to the multifaceted nature of this gene, which is often overlooked, and seek to establish the mechanistic role of PER2 gene mutations in sleep disorders. This will improve further understanding, assessment, and treatment of these conditions in future.

Transcriptomic changes in glomeruli in response to a high salt challenge in the Dahl SS rat

Salt sensitivity impacts a significant portion of the population and is an important contributor to the development of chronic kidney disease. One of the significant early predictors of salt-induced damage is albuminuria, which reflects the deterioration of the renal filtration barrier: the glomerulus. Despite significant research efforts, there is still a gap in knowledge regarding the molecular mechanisms and signaling networks contributing to instigating and/or perpetuating salt-induced glomerular injury. To address this gap, we used 8-wk-old male Dahl salt-sensitive rats fed a normal-salt diet (0.4% NaCl) or challenged with a high-salt diet (4% NaCl) for 3 wk. At the end of the protocol, a pure fraction of renal glomeruli obtained by differential sieving was used for next-generation RNA sequencing and comprehensive semi-automatic transcriptomic data analyses, which revealed 149 differentially expressed genes (107 and 42 genes were downregulated and upregulated, respectively). Furthermore, a combination of predictive gene correlation networks and computational bioinformatic analyses revealed pathways impacted by a high salt dietary challenge, including renal metabolism, mitochondrial function, apoptotic signaling and fibrosis, cell cycle, inflammatory and immune responses, circadian clock, cytoskeletal organization, G protein-coupled receptor signaling, and calcium transport. In conclusion, we report here novel transcriptomic interactions and corresponding predicted pathways affecting glomeruli under salt-induced stress.NEW & NOTEWORTHY Our study demonstrated novel pathways affecting glomeruli under stress induced by dietary salt. Predictive gene correlation networks and bioinformatic semi-automatic analysis revealed changes in the pathways relevant to mitochondrial function, inflammatory, apoptotic/fibrotic processes, and cell calcium transport.

Male kidney-specific BMAL1 knockout mice are protected from K+-deficient, high-salt diet-induced blood pressure increases

The circadian clock protein basic helix-loop-helix aryl hydrocarbon receptor nuclear translocator-like protein 1 (BMAL1) is a transcription factor that impacts kidney function, including blood pressure (BP) control. Previously, we have shown that male, but not female, kidney-specific cadherin Cre-positive BMAL1 knockout (KS-BMAL1 KO) mice exhibit lower BP compared with littermate controls. The goal of this study was to determine the BP phenotype and immune response in male KS-BMAL1 KO mice in response to a low-K+ high-salt (LKHS) diet. BP, renal inflammatory markers, and immune cells were measured in male mice following an LKHS diet. Male KS-BMAL1 KO mice had lower BP following the LKHS diet compared with control mice, yet their circadian rhythm in pressure remained unchanged. Additionally, KS-BMAL1 KO mice exhibited lower levels of renal proinflammatory cytokines and immune cells following the LKHS diet compared with control mice. KS-BMAL1 KO mice were protected from the salt-sensitive hypertension observed in control mice and displayed an attenuated immune response following the LKHS diet. These data suggest that BMAL1 plays a role in driving the BP increase and proinflammatory environment that occurs in response to an LKHS diet.NEW & NOTEWORTHY We show here, for the first time, that kidney-specific BMAL1 knockout mice are protected from blood pressure (BP) increases and immune responses to a salt-sensitive diet. Other kidney-specific BMAL1 knockout models exhibit lower BP phenotypes under basal conditions. A salt-sensitive diet exacerbates this genotype-specific BP response, leading to fewer proinflammatory cytokines and immune cells in knockout mice. These data demonstrate the importance of distal segment BMAL1 in BP and immune responses to a salt-sensitive environment.

Modulating glucocorticoid receptor actions in physiology and pathology: Insights from coregulators

Glucocorticoids (GCs) are a class of steroid hormones that regulate key physiological processes such as metabolism, immune function, and stress responses. The effects of GCs are mediated by the glucocorticoid receptor (GR), a ligand-dependent transcription factor that activates or represses the expression of hundreds to thousands of genes in a tissue- and physiological state-specific manner. The activity of GR is modulated by numerous coregulator proteins that interact with GR in response to different stimuli assembling into a multitude of DNA-protein complexes and facilitate the integration of these signals, helping GR to communicate with basal transcriptional machinery and chromatin. Here, we provide a brief overview of the physiological and molecular functions of GR, and discuss the roles of GR coregulators in the immune system, key metabolic tissues and the central nervous system. We also present an analysis of the GR interactome in different cells and tissues, which suggests tissue-specific utilization of GR coregulators, despite widespread functions shared by some of them.

Role of Bmal1 and Gut Microbiota in Alzheimer's Disease and Parkinson's Disease Pathophysiology: The Probable Effect of Melatonin on Their Association

In recent years, the role of new factors in the pathophysiology of neurodegenerative diseases has been investigated. Alzheimer's disease (AD) and Parkinson's disease (PD) are the most common neurodegenerative diseases worldwide. Although pathological changes such as the accumulation of aggregated proteins in the brain and inflammatory responses are known as the main factors involved in the development of these diseases, new studies show the role of gut microbiota and circadian rhythm in the occurrence of these changes. However, the association between circadian rhythm and gut microbiota in AD and PD has not yet been investigated. Recent results propose that alterations in circadian rhythm regulators, mainly Bmal1, may regulate the abundance of gut microbiota. This correlation has been linked to the regulation of the expression of immune-related genes and Bmal-1 mediated oscillation of IgA and hydrogen peroxide production. These data seem to provide new insight into the molecular mechanism of melatonin inhibiting the progression of AD and PD. Therefore, this manuscript aims to review the role of the gut microbiota and circadian rhythm in health and AD and PD and also presents a hypothesis on the effect of melatonin on their communication.

Measuring light regularity: sleep regularity is associated with regularity of light exposure in adolescents

STUDY OBJECTIVES

Light is the main time cue for the human circadian system. Sleep and light are intrinsically linked; light exposure patterns can influence sleep patterns and sleep can influence light exposure patterns. However, metrics for quantifying light regularity are lacking, and the relationship between sleep and light regularity is underexplored. We developed new metrics for light regularity and demonstrated their utility in adolescents, across school term and vacation.

METHODS

Daily sleep/wake and light patterns were measured using wrist actigraphy in 75 adolescents (54% male, 17.17 ± 0.83 years) over 2 weeks of school term and a subsequent 2-week vacation. The Sleep Regularity Index (SRI) and social jetlag were computed for each 2-week block. Light regularity was assessed using (1) variation in mean daily light timing (MLiT); (2) variation in daily photoperiod; and (3) the Light Regularity Index (LRI). Associations between SRI and each light regularity metric were examined, and within-individual changes in metrics were examined between school and vacation.

RESULTS

Higher SRI was significantly associated with more regular LRI scores during both school and vacation. There were no significant associations of SRI with variation in MLiT or daily photoperiod. Compared to school term, all three light regularity metrics were less variable during the vacation.

CONCLUSIONS

Light regularity is a multidimensional construct, which until now has not been formally defined. Irregular sleep patterns are associated with lower LRI, indicating that irregular sleepers also have irregular light inputs to the circadian system, which likely contributes to circadian disruption.

The Self-Simulational Theory of temporal extension

Subjective experience is experience in time. Unfolding in a continuous river of moments, our experience, however, consists not only in the changing phenomenological content per se but, further, in additional retrodiction and prospection of the moments that immediately preceded and followed it. It is in this way that William James's 'specious present' presents itself as extending between the past and future. While the phenomenology of temporality always happens, in normal waking states, to someone, and the notions of self-representation and temporal experience have continuously been associated with each other, there has not yet been an explicit account of their relationship. In this paper, the emergence of the subjective experience of temporal extension will be conceived of as arising out of a difference-relation between counterfactual and actual self-representations. After presenting the proposed relationship on both a conceptual level and a formalized and neuronally realistic level of description using information theory, convergent empirical evidence from general findings about temporal experience and inference, altered states of consciousness, and mental illness is examined. The Self-Simulational Theory of temporal extension is able to explain systematic variations in the subjectively experienced length of the temporal Now across numerous domains and holds potentially wide implications for the neuroscience of consciousness, as well as for a deeper understanding of different forms of mental illness.

Circadian regulation of mTORC1 signaling via Per2 dependent mechanism disrupts folliculogenesis and oocyte maturation in female mice

mTOR (mammalian target of Rapamycin) is an important signaling pathway involved in several crucial ovarian functions including folliculogenesis and oocyte maturation. The circadian rhythm regulates multiple physiological processes and PER2 is one of the core circadian rhythm components. mTOR is regulated by the circadian clock and in turn, the rhythmic mTOR activities strengthen the clock function. Our current study aims to investigate a possible interconnection between the circadian clock and the mTORC1 signaling pathway in folliculogenesis and oocyte maturation. Here we demonstrate that the circadian system regulates mTORC1 signaling via Per2 dependent mechanism in the mouse ovary. To investigate the effect of constant light on ovarian and oocyte morphology, animals were housed 12:12 h L:D group in standard lightening conditions and the 12:12 h L:L group in constant light for one week. Food intake and body weight changes were measured. Ovarian morphology, follicle counting, and oocyte aging were evaluated. Afterward, western blot for mTOR, p-mTOR, p70S6K, p-p70S6K, PER2, and Caspase-3 protein levels was performed. The study demonstrated that circadian rhythm disruption caused an alteration in their food intake and decrease in primordial follicle numbers and an increase in the number of atretic follicles. It caused an increase in oxidative stress and a decrease in ZP3 expression in oocytes. Decreased protein levels of mTOR, p-mTOR, p70S6K, and PER2 were shown. The results showed that the circadian clock regulates mTORC1 through PER2 dependent mechanism and that decreased mTORC1 activity can contribute to premature aging of mouse ovary. In conclusion, these results suggest that the circadian clock may control ovarian aging by regulating mTOR signaling pathway through Per2 expression.

Gut microbiota and circadian rhythm in Alzheimer's disease pathophysiology: a review and hypothesis on their association

Alzheimer's disease (AD) is the most common neurodegenerative disease and the leading cause of dementia worldwide. Different pathologic changes have been introduced to be involved in its progression. Although amyloid-β (Aβ) deposition and tau hyperphosphorylation and aggregation are mainly considered the main characterizations of AD, several other processes are involved. In recent years, several other changes, including alterations in gut microbiota proportion and circadian rhythms, have been noticed due to their role in AD progression. However, the exact mechanism indicating the association between circadian rhythms and gut microbiota abundance has not been investigated yet. This paper aims to review the role of gut microbiota and circadian rhythm in AD pathophysiology and introduces a hypothesis to explain their association.

Aryl hydrocarbon receptor (AhR) impairs circadian regulation: impact on the aging process

Circadian clocks control the internal sleep-wake rhythmicity of 24hours which is synchronized by the solar cycle. Circadian regulation of metabolism evolved about 2.5 billion years ago, i.e., the rhythmicity has been conserved from cyanobacteria and Archaea through to mammals although the mechanisms utilized have developed with evolution. While the aryl hydrocarbon receptor (AhR) is an evolutionarily conserved defence mechanism against environmental threats, it has gained many novel functions during evolution, such as the regulation of cell cycle, proteostasis, and many immune functions. There is robust evidence that AhR signaling impairs circadian rhythmicity, e.g., by interacting with the core BMAL1/CLOCK complex and disturbing the epigenetic regulation of clock genes. The maintenance of circadian rhythms is impaired with aging, disturbing metabolism and many important functions in aged organisms. Interestingly, it is known that AhR signaling promotes an age-related tissue degeneration, e.g., it is able to inhibit autophagy, enhance cellular senescence, and disrupt extracellular matrix. These alterations are rather similar to those induced by a long-term impairment of circadian rhythms. However, it is not known whether AhR signaling enhances the aging process by impairing circadian homeostasis. I will examine the experimental evidence indicating that AhR signaling is able to promote the age-related degeneration via a disruption of circadian rhythmicity.

Skeletal muscle gene expression dysregulation in long-term spaceflights and aging is clock-dependent

The circadian clock regulates cellular and molecular processes in mammals across all tissues including skeletal muscle, one of the largest organs in the human body. Dysregulated circadian rhythms are characteristic of aging and crewed spaceflight, associated with, for example, musculoskeletal atrophy. Molecular insights into spaceflight-related alterations of circadian regulation in skeletal muscle are still missing. Here, we investigated potential functional consequences of clock disruptions on skeletal muscle using published omics datasets obtained from spaceflights and other clock-altering, external (fasting and exercise), or internal (aging) conditions on Earth. Our analysis identified alterations of the clock network and skeletal muscle-associated pathways, as a result of spaceflight duration in mice, which resembles aging-related gene expression changes observed in humans on Earth (e.g., ATF4 downregulation, associated with muscle atrophy). Furthermore, according to our results, external factors such as exercise or fasting lead to molecular changes in the core-clock network, which may compensate for the circadian disruption observed during spaceflights. Thus, maintaining circadian functioning is crucial to ameliorate unphysiological alterations and musculoskeletal atrophy reported among astronauts.

Circadian Oscillations in Skin and Their Interconnection with the Cycle of Life

Periodically oscillating biological processes, such as circadian rhythms, are carefully concerted events that are only beginning to be understood in the context of tissue pathology and organismal health, as well as the molecular mechanisms underlying these interactions. Recent reports indicate that light can independently entrain peripheral circadian clocks, challenging the currently prevalent hierarchical model. Despite the recent progress that has been made, a comprehensive overview of these periodic processes in skin is lacking in the literature. In this review, molecular circadian clock machinery and the factors that govern it have been highlighted. Circadian rhythm is closely linked to immunological processes and skin homeostasis, and its desynchrony can be linked to the perturbation of the skin. The interplay between circadian rhythm and annual, seasonal oscillations, as well as the impact of these periodic events on the skin, is described. Finally, the changes that occur in the skin over a lifespan are presented. This work encourages further research into the oscillating biological processes occurring in the skin and lays the foundation for future strategies to combat the adverse effects of desynchrony, which would likely have implications in other tissues influenced by periodic oscillatory processes.

BMAL1 regulates MUC1 overexpression in ovalbumin-induced asthma

Asthma often presents with a daily rhythm; however, the underlying mechanisms remain unclear. Circadian rhythm genes have been proposed to regulate inflammation and mucin expression. Here, ovalbumin (OVA)-induced mice and serum shock human bronchial epidermal cells (16HBE) were used in in vivo and in vitro models, respectively. We constructed a brain and muscle ARNT-like 1 (BMAL1) knockdown 16HBE cell line to analyze the effects of rhythmic fluctuations on mucin expression. Serum immunoglobulin E (IgE) and circadian rhythm genes in asthmatic mice showed rhythmic fluctuation amplitude. Mucin (MUC) 1 and MUC5AC expression was increased in the lung tissue of the asthmatic mice. MUC1 expression was negatively correlated with that of the circadian rhythm genes, particularly BMAL1 (r = -0.546, P = 0.006). There was also a negative correlation between BMAL1 and MUC1 expression (r = -0.507, P = 0.002) in the serum shock 16HBE cells. BMAL1 knockdown negated the rhythmic fluctuation amplitude of MUC1 expression and upregulated MUC1 expression in the 16HBE cells. These results indicate that the key circadian rhythm gene, BMAL1, causes periodic changes in airway MUC1 expression in OVA-induced asthmatic mice. Targeting BMAL1 to regulate periodic changes in MUC1 expression may, therefore, improve asthma treatments.

Dapagliflozin Treatment Augments Bioactive Phosphatidylethanolamine Concentrations in Kidney Cortex Membrane Fractions of Hypertensive Diabetic db/db Mice and Alters the Density of Lipid Rafts in Mouse Proximal Tubule Cells

In addition to inhibiting renal glucose reabsorption and allowing for glucose excretion, the sodium/glucose cotransporter 2 (SGLT2) inhibitor dapagliflozin may be efficacious in treating various comorbidities associated with type 2 diabetes mellitus (T2DM). The molecular mechanisms by which dapagliflozin exerts its beneficial effects are largely unknown. We hypothesized dapagliflozin treatment in the diabetic kidney alters plasma membrane lipid composition, suppresses extracellular vesicle (EV) release from kidney cells, and disrupts lipid rafts in proximal tubule cells. In order to test this hypothesis, we treated diabetic db/db mice with dapagliflozin (N = 8) or vehicle (N = 8) and performed mass spectrometry-based lipidomics to investigate changes in the concentrations of membrane lipids in the kidney cortex. In addition, we isolated urinary EVs (uEVs) from urine samples collected during the active phase and the inactive phase of the mice and then probed for changes in membrane proteins enriched in the EVs. Multiple triacylglycerols (TAGs) were enriched in the kidney cortex membrane fractions of vehicle-treated diabetic db/db mice, while the levels of multiple phosphatidylethanolamines were significantly higher in similar mice treated with dapagliflozin. EV concentration and size were lesser in the urine samples collected during the inactive phase of dapagliflozin-treated diabetic mice. In cultured mouse proximal tubule cells treated with dapagliflozin, the lipid raft protein caveolin-1 shifted from less dense fractions to more dense sucrose density gradient fractions. Taken together, these results suggest dapagliflozin may regulate lipid-mediated signal transduction in the diabetic kidney.

Effect of a hyaluronic acid-based mesotherapeutic injectable on the gene expression of CLOCK and Klotho proteins, and environmentally induced oxidative stress in human skin cells

OBJECTIVE

Normal circadian rhythms are essential to the repair mechanisms of oxidative stress implicated in skin aging. Given reports that hyaluronic acid (HA) homeostasis exhibits a different profile in chronological skin aging, as compared to environmental or extrinsic aging, an improved understanding of the way HA interacts with its surroundings, and the impact of HA injectables in replacing lost HA and encouraging rejuvenation, is of key benefit to skin aging treatments. The objectives of these current studies were twofold. Firstly, to demonstrate the in vitro effects of two lightweight hyaluronic-based injectables on the expression of CLOCK protein in human skin fibroblasts, and their effects on Klotho protein expression as a marker for circadian rhythms in a combined human keratinocyte and Merkel cell model. Secondly, to ascertain whether these findings could be correlated with in vitro effects on various environmental oxidative stress aging markers (blue light, UVA/UVB, Urban Dust, and IR exposures).

METHODS

Oxidative stress studies were aimed to highlight possible protective effects through different challenge conditions in two models, ex vivo human skin explants and in vitro monolayer cultures of normal human dermal fibroblasts (NHDF). The protective effects of the test products were evaluated against an increase of cyclobutene pyrimidine dimers (CPDs) abundance within epidermal section of ex vivo skin explants after UVA/UVB radiation; effects of blue light on gene expression from NHDFs fibroblasts; effects of pollutants (Urban dust, UbD) on gene expression in NHDFs fibroblasts; and an increase of reactive oxygen species (ROS) production by NHDFs fibroblasts after infrared-A radiation. Gene expression was assayed and analyzed utilizing microfluidic TaqMan qPCR arrays. CLOCK expression was measured in young and senescing NHDFs by immunostaining, and Klotho and melatonin expression by immunostaining in Merkel cell-enriched normal adult human epidermal cell cultures.

RESULTS

In an aging culture of mixed keratinocyte and Merkel skin cells, activation of Klotho expression was induced by the application of both HA test products. Moreover, the HA products increase Klotho protein expression in both Merkel cells and keratinocytes. The observed positive effect of the tested products on melatonin receptors 1A and 1B expression in aging Merkel cell culture and keratinocytes is also interesting. HA-Y (developed for patients 25+ years old) stimulated melatonin receptors type 1B expression in aging cell cultures more strongly than HA-S (developed for patients 35-65 years old). In age (stressed) cells, a lower expression of Klotho protein and melatonin receptors 1A and 1B is apparent. The addition of HA-Y and HA-S stimulates their expression thus providing a "protective" effect. The blue light irradiation at 40 J/cm² performed in NHDF fibroblast cultures led to a modification of the expression of several genes, all involved in mechanisms known to be modulated in case of solar radiation stress.

CONCLUSIONS

Although these are preliminary findings, they are the first we know of that demonstrate HA facial injectables having a benefit and possibilities beyond the "physical filling" of the skin. As regards the beneficial effects against blue light-induced oxidative stress, and a return to cellular homeostasis, there is a need to conduct further and more precise investigations into HA-S. Furthermore, the benefit of these HA injectables (Novacutan®) in the modulation of oxidative stressed circadian rhythms widens their potential benefit.

PPARG agonist pioglitazone influences diurnal kidney medulla mRNA expression of core clock, inflammation-, and metabolism-related genes disrupted by reverse feeding in mice

This study examined the influence of PPARG activation by pioglitazone (PG) on the mRNA of core clock, inflammation- and metabolism-related genes in the mouse kidney medulla as well as urinary sodium/potassium excretion rhythms disrupted by reverse feeding. Mice were assigned to daytime feeding and nighttime feeding groups. PG 20 mg/kg was administered at 7 am or 7 pm. On day 8 of the feeding intervention, mice were killed at noon and midnight. Kidney medulla expression of Arntl, Clock, Nr1d1, Cry1, Cry2, Per1, Per2, Nfe2l2, Pparg, and Scnn1g was determined by qRT PCR. We measured urinary K+ , Na+ , urine volume, food, and H2 O intake. The reverse feeding uncoupled the peripheral clock gene rhythm in mouse kidney tissues. It was accompanied by a decreased expression of Nfe2l2 and Pparg as well as an increased expression of Rela and Scnn1g. These changes in gene expressions concurred with an increase in urinary Na+ , K+ , water excretion, microcirculation disorders, and cell loss, especially in distal tubules. PG induced the restoration of diurnal core clock gene expression as well as Nfe2l2, Pparg, Scnn1g mRNA, and decreased Rela expressions, stimulating Na+ reabsorption and inhibiting K+ excretion. PG intake at 7 pm was more effective than at 7 am.

Time for Exercise? Exercise and Its Influence on the Skeletal Muscle Clock

Circadian rhythms drive our daily behaviors to coincide with the earth's rotation on an approximate 24-h cycle. The circadian clock mechanism present in nearly every cell is responsible for our circadian rhythms and is comprised of a transcriptional-translational feedback loop in mammals. The central clock resides in the hypothalamus responding to external light cues, whereas peripheral clocks receive signals from the central clock and are also sensitive to cues from feeding and activity. Of the peripheral clocks, the skeletal muscle clock is particularly sensitive to exercise which has shown to be an important time-cue with the ability to influence and adjust the muscle clock phase in response to exercise timing. Since the skeletal muscle clock is also involved in the expression of tissue-specific gene expression-including glucoregulatory genes-this might suggest a role for exercise timing as a therapeutic strategy in metabolic diseases, like type 2 diabetes. Notably, those with type 2 diabetes have accompanied disruptions in their skeletal muscle clock mechanism which may also be related to the increased risk of type 2 diabetes seen among shift workers. Therefore, the direct influence of exercise on the skeletal muscle clock might support the use of exercise timing to provide disease-mitigating effects. Here, we highlight the potential use of time-of-day exercise as a chronotherapeutic tool within circadian medicine to improve the metabolic profile of type 2 diabetes and support long-term glycemic control, potentially working through the skeletal muscle clock and circadian physiology.

When the clock ticks wrong with COVID-19

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

Androgen-mediated Perturbation of the Hepatic Circadian System Through Epigenetic Modulation Promotes NAFLD in PCOS Mice

In women, excess androgen causes polycystic ovary syndrome (PCOS), a common fertility disorder with comorbid metabolic dysfunctions including diabetes, obesity, and nonalcoholic fatty liver disease. Using a PCOS mouse model, this study shows that chronic high androgen levels cause hepatic steatosis while hepatocyte-specific androgen receptor (AR)-knockout rescues this phenotype. Moreover, through RNA-sequencing and metabolomic studies, we have identified key metabolic genes and pathways affected by hyperandrogenism. Our studies reveal that a large number of metabolic genes are directly regulated by androgens through AR binding to androgen response element sequences on the promoter region of these genes. Interestingly, a number of circadian genes are also differentially regulated by androgens. In vivo and in vitro studies using a circadian reporter [Period2::Luciferase (Per2::LUC)] mouse model demonstrate that androgens can directly disrupt the hepatic timing system, which is a key regulator of liver metabolism. Consequently, studies show that androgens decrease H3K27me3, a gene silencing mark on the promoter of core clock genes, by inhibiting the expression of histone methyltransferase, Ezh2, while inducing the expression of the histone demethylase, JMJD3, which is responsible for adding and removing the H3K27me3 mark, respectively. Finally, we report that under hyperandrogenic conditions, some of the same circadian/metabolic genes that are upregulated in the mouse liver are also elevated in nonhuman primate livers. In summary, these studies not only provide an overall understanding of how hyperandrogenism associated with PCOS affects liver gene expression and metabolism but also offer insight into the underlying mechanisms leading to hepatic steatosis in PCOS.

Importance of Bmal1 in Alzheimer's disease and associated aging-related diseases: Mechanisms and interventions

With the aging world population, the prevalence of aging-related disorders is on the rise. Diseases such as Alzheimer's, type 2 diabetes mellitus (T2DM), Parkinson's, atherosclerosis, hypertension, and osteoarthritis are age-related, and most of these diseases are comorbidities or risk factors for AD; however, our understandings of molecular events that regulate the occurrence of these diseases are still not fully understood. Brain and muscle Arnt-like protein-1 (Bmal1) is an irreplaceable clock gene that governs multiple important physiological processes. Continuous research of Bmal1 in AD and associated aging-related diseases is ongoing, and this review picks relevant studies on a detailed account of its role and mechanisms in these diseases. Oxidative stress and inflammation turned out to be common mechanisms by which Bmal1 deficiency promotes AD and associated aging-related diseases, and other Bmal1-dependent mechanisms remain to be identified. Promising therapeutic strategies involved in the regulation of Bmal1 are provided, including melatonin, natural compounds, metformin, d-Ser2-oxyntomodulin, and other interventions, such as exercise, time-restricted feeding, and adiponectin. The establishment of the signaling pathway network for Bmal1 in aging-related diseases will lead to advances in the comprehension of the molecular and cellular mechanisms, shedding light on novel treatments for aging-related diseases and promoting aging-associated brain health.

A potential role of p75NTR in the regulation of circadian rhythm and incremental growth lines during tooth development

Objective: Tooth morphogenesis and the formation of hard tissues have been reported to be closely related to circadian rhythms. This study investigates the spatiotemporal expression and relationship of p75NTR with core clock genes, mineralization-related or odontogenesis-related genes, and aims to derive the potential role of p75NTR in regulating circadian rhythm and incrementality growth line formation during tooth development.

Materials and methods: The dynamic morphology of the rat dental germ was observed at seven stages (E14.5 d, E16.5 d, E18.5 d, P.N. 4 d, P.N. 7 d, P.N. 10 d, and P.N. 15 d). Next, the expressions of p75NTR and other target factors were traced. The ectomesenchymal stem cells (EMSCs) were isolated from the E18.5d rat dental germs and synchronized using 50% of fetal bovine serum. Then, they were cultured in light/light (L.L.), dark/dark (D.D.), and light/dark (L.D.) conditions for 48 h. The total RNA was collected every 4 h, and the circadian rhythm dynamics of target factors were observed. To reveal the mechanism further, p75NTR was down-regulated in p75NTR^ExIII−/− mice and up-regulated in immortalized mouse dental apical papilla progenitor cells. The change tendencies of other target factors were also detected.

Results: The clock genes Bmal1, Clock, Per1, and Per2 were all expressed in tooth germs before the formation of dental hard tissues and demonstrated a regular oscillating expression pattern in EMSCs from dental germs. Their expression was affected by the L.D. stimulus, and most of them were promoted by D.D. conditions. p75NTR presented a similar expression pattern and a positive or negative relationship with most clock genes, mineralization-related and odontogenesis-related factors, such as brain and muscle ARNT-like protein-1 (Bmal1), runt-related transcription factor 2 (Runx2), alkaline phosphatase (ALP), MSH-like 1 (MSX1), dentin matrix acidic phosphoprotein 1 (Dmp1), and dentin sialophosphoprotein (Dspp). Moreover, the arrangement, morphology, and even boundary in pre-odontoblast/pre-ameloblast layers were disordered in the p75NTR^ExIII−/− mice.

Conclusion: Circadian rhythm was found to affect tooth development. p75NTR might play a crucial role in regulating clock genes in the mineralization and formation of the dental hard tissues. p75NTR is actively involved in the odontoblast-ameloblast junction and cell polarity establishment during tooth morphogenesis.

Dysregulation of Circadian Clock Genes Associated with Tumor Immunity and Prognosis in Patients with Colon Cancer

Early research shows that disrupting the circadian rhythm increases the risk of various cancers. However, the roles of circadian clock genes in colorectal cancer, which is becoming more common and lethal in China, remained to be unclear. In conclusion, the present study has demonstrated that multiple CCGs were dysregulated and frequently mutated in CRC samples by analyzing the TCGA database. The higher expression levels of REV1, ADCYAP1, CSNK1D, NR1D1, CSNK1E, and CRY2 had a strong link with shorter DFS time in CRC patients, demonstrating that CCGs had an important regulatory role in CRC development. Moreover, 513 CRC tumor samples were divided into 3 categories, namely, cluster1 (n = 428), cluster2 (n = 83), and cluster 3 (n = 109), based on the expression levels of the CCGs. Clinical significance analysis showed that the overall survival and disease-free survival of cluster 2 and cluster 3 were significantly shorter than those of cluster 1. The stemness scores in cluster 1 and cluster 2 were significantly higher than those of cluster 3 CRC samples. Clinically, we found that the C3 subtype had significantly higher percentage of T3/T4, N1/N2, and grades III and IV than groups C1 or C2. In addition, we reported that different CRC clusters had significantly different tumor-infiltrating immune cell signatures. Finally, pancancer analysis showed that higher expression of CSNK1D was correlated with shorter DFS time in multiple cancer types, such as COAD and LIHC, and was dysregulated in various cancers. In conclusion, we effectively developed a CCG-related predictive model and opened up new avenues for research into immune regulatory mechanisms and the development of immunotherapy for CRC.

Circadian Sensitivity of Noise Trauma-Induced Hearing Loss and Tinnitus in Mongolian Gerbils

Noise-induced hearing loss (HL) has a circadian component: In nocturnal mice, hearing thresholds (HT) have a significantly stronger effect to acoustic trauma when induced during the night compared to rather mild effects on hearing when induced during daytime. Here, we investigate whether such effects are also present in diurnal Mongolian gerbils and determined whether trauma-induced HL correlated with the development of a tinnitus percept in these animals. In particular, we investigated the effects of acoustic trauma (2 kHz, 115 dB SPL, 75 min) on HT and tinnitus development in 34 male gerbils exposed either at 9 AM, 1 PM, 5 PM, or 12 PM. HT was measured by acoustic brainstem response audiometry at defined times 1 day before and 1 week after the trauma. Possible tinnitus percepts were assessed behaviorally by the gap prepulse inhibition of the acoustic startle response at defined times 1 day before and 1 week after the trauma. We found daytime-dependent changes due to trauma in mean HT in a frequency-dependent manner comparable to the results in mice, but the results temporally shifted according to respective activity profiles. Additionally, we found linear correlations of these threshold changes with the strength of the tinnitus percept, with the most prominent correlations in the 5 PM trauma group. Taken together, circadian sensitivity of the HT to noise trauma can also be found in gerbils, and tinnitus strength correlates most strongly with HL only when the trauma is applied at the most sensitive times, which seem to be the evening.

Transcriptional Feedback Loops in the Caprine Circadian Clock System

The circadian clock system is based on interlocked positive and negative transcriptional and translational feedback loops of core clock genes and their encoded proteins. The mammalian circadian clock system has been extensively investigated using mouse models, but has been poorly investigated in diurnal ruminants. In this study, goat embryonic fibroblasts (GEFs) were isolated and used as a cell model to elucidate the caprine circadian clock system. Real-time quantitative PCR analysis showed that several clock genes and clock-controlled genes were rhythmically expressed in GEFs over a 24 h period after dexamethasone stimulation. Immunofluorescence revealed that gBMAL1 and gNR1D1 proteins were expressed in GEFs, and western blotting analysis further verified that the proteins were expressed with circadian rhythmic changes. Diurnal changes in clock and clock-controlled gene expression at the mRNA and protein levels were also observed in goat liver and kidney tissues at two representative time points in vivo. Amino acid sequences and tertiary structures of goat BMAL1 and CLOCK proteins were found to be highly homologous to those in mice and humans. In addition, a set of goat representative clock gene orthologs and the promoter regions of two clock genes of goats and mice were cloned. Dual-luciferase reporter assays showed that gRORα could activate the promoter activity of the goat BMAL1, while gNR1D1 repressed it. The elevated pGL4.10-gNR1D1-Promoter-driven luciferase activity induced by mBMAL1/mCLOCK was much higher than that induced by gBMAL1/gCLOCK, and the addition of gCRY2 or mPER2 repressed it. Real-time bioluminescence assays revealed that the transcriptional activity of BMAL1 and NR1D1 in goats and mice exhibited rhythmic changes over a period of approximately 24 h in NIH3T3 cells or GEFs. Notably, the amplitudes of gBMAL1 and gNR1D1 promoter-driven luciferase oscillations in NIH3T3 cells were higher than those in GEFs, while mBMAL1 and mNR1D1 promoter-driven luciferase oscillations in NIH3T3 cells had the highest amplitude. In sum, transcriptional and translational loops of the mammalian circadian clock system were found to be broadly conserved in goats and not as robust as those found in mice, at least in the current experimental models. Further studies are warranted to elucidate the specific molecular mechanisms involved.

Apparent Absence of BMAL1-Dependent Skeletal Muscle-Kidney Cross Talk in Mice

BMAL1 is a core mammalian circadian clock transcription factor responsible for the regulation of the expression of thousands of genes. Previously, male skeletal-muscle-specific BMAL1-inducible-knockout (iMS-BMAL1 KO) mice have been described as a model that exhibits an aging-like phenotype with an altered gait, reduced mobility, muscle weakness, and impaired glucose uptake. Given this aging phenotype and that chronic kidney disease is a disease of aging, the goal of this study was to determine if iMS-BMAL1 KO mice exhibit a renal phenotype. Male iMS-BMAL1 KO and control mice were challenged with a low potassium diet for five days. Both genotypes responded appropriately by conserving urinary potassium. The iMS-BMAL1 KO mice excreted less potassium during the rest phase during the normal diet but there was no genotype difference during the active phase. Next, iMS-BMAL1 KO and control mice were used to compare markers of kidney injury and assess renal function before and after a phase advance protocol. Following phase advance, no differences were detected in renal mitochondrial function in iMS-BMAL1 KO mice compared to control mice. Additionally, the glomerular filtration rate and renal morphology were similar between groups in response to phase advance. Disruption of the clock in skeletal muscle tissue activates inflammatory pathways within the kidney of male mice, and there is evidence of this affecting other organs, such as the lungs. However, there were no signs of renal injury or altered function following clock disruption of skeletal muscle under the conditions tested.

Understanding the Emerging Link Between Circadian Rhythm, Nrf2 Pathway, and Breast Cancer to Overcome Drug Resistance

The levels of different molecules in the cell are rhythmically cycled by the molecular clock present at the cellular level. The circadian rhythm is closely linked to the metabolic processes in the cells by an underlying mechanism whose intricacies need to be thoroughly investigated. Nevertheless, Nrf2 has been identified as an essential bridge between the circadian clock and cellular metabolism and is activated by the by-product of cellular metabolism like hydrogen peroxide. Once activated it binds to the specific DNA segments and increases the transcription of several genes that play a crucial role in the normal functioning of the cell. The central clock located in the suprachiasmatic nucleus of the anterior hypothalamus synchronizes the timekeeping in the peripheral tissues by integrating the light-dark input from the environment. Several studies have demonstrated the role of circadian rhythm as an effective tumor suppressor. Tumor development is triggered by the stimulation or disruption of signaling pathways at the cellular level as a result of the interaction between cells and environmental stimuli. Oxidative stress is one such external stimulus that disturbs the prooxidant/antioxidant equilibrium due to the loss of control over signaling pathways which destroy the bio-molecules. Altered Nrf2 expression and impaired redox balance are associated with various cancers suggesting that Nrf2 targeting may be used as a novel therapeutic approach for treating cancers. On the other hand, Nrf2 has also been shown to enhance the resistance of cancer cells to chemotherapeutic agents. We believe that maximum efficacy with minimum side effects for any particular therapy can be achieved if the treatment strategy regulates the circadian rhythm. In this review, we discuss the various molecular mechanisms interlinking the circadian rhythm with the Nrf2 pathway and contributing to breast cancer pathogenesis, we also talk about how these two pathways work in close association with the cell cycle which is another oscillatory system, and whether this interplay can be exploited to overcome drug resistance during chemotherapy.

NF-κB modifies the mammalian circadian clock through interaction with the core clock protein BMAL1

In mammals, the circadian clock coordinates cell physiological processes including inflammation. Recent studies suggested a crosstalk between these two pathways. However, the mechanism of how inflammation affects the clock is not well understood. Here, we investigated the role of the proinflammatory transcription factor NF-κB in regulating clock function. Using a combination of genetic and pharmacological approaches, we show that perturbation of the canonical NF-κB subunit RELA in the human U2OS cellular model altered core clock gene expression. While RELA activation shortened period length and dampened amplitude, its inhibition lengthened period length and caused amplitude phenotypes. NF-κB perturbation also altered circadian rhythms in the master suprachiasmatic nucleus (SCN) clock and locomotor activity behavior under different light/dark conditions. We show that RELA, like the clock repressor CRY1, repressed the transcriptional activity of BMAL1/CLOCK at the circadian E-box cis-element. Biochemical and biophysical analysis showed that RELA binds to the transactivation domain of BMAL1. These data support a model in which NF-kB competes with CRY1 and coactivator CBP/p300 for BMAL1 binding to affect circadian transcription. This is further supported by chromatin immunoprecipitation analysis showing that binding of RELA, BMAL1 and CLOCK converges on the E-boxes of clock genes. Taken together, these data support a significant role for NF-κB in directly regulating the circadian clock and highlight mutual regulation between the circadian and inflammatory pathways.

Relationships between endogenous circadian period, physiological and cognitive parameters and sex in aged gray mouse lemurs (Microcebus murinus)

The biological clock generates circadian rhythms, with an endogenous period tau close to 24 h. The circadian resonance theory proposes that lifespan is reduced when endogenous period goes far from 24 h. It has been suggested that daily resetting of the circadian clock to the 24 h external photoperiod might induce marginal costs that would accumulate over time and forward accelerate aging and affect fitness. In this study, we aimed to evaluate the link between the endogenous period and biomarkers of aging in order to investigate the mechanisms of the circadian resonance theory. We studied 39 middle-aged and aged Microcebus murinus, a nocturnal non-human primate whose endogenous period is about 23.1 h, measuring the endogenous period of locomotor activity, as well as several physiological and behavioral parameters (rhythm fragmentation and amplitude, energetic expenditure, oxidative stress, insulin-like growth factor-1 (IGF-1) concentrations and cognitive performances) in both males and females. We found that aged males with tau far from 24 h displayed increased oxidative stress. We also demonstrated a positive correlation between tau and IGF-1 concentrations, as well as learning performances, in males and females. Together these results suggest that a great deviation of tau from 24 h leads to increased biomarkers of age-related impairments.

Circadian Control of Sodium and Blood Pressure Regulation

The attention for the control of dietary risk factors involved in the development of hypertension, includes a large effort on dietary salt restrictions. Ample studies show the beneficial role of limiting dietary sodium as a lifestyle modification in the prevention and management of essential hypertension. Not until the past decade or so have studies more specifically investigated diurnal variations in renal electrolyte excretion, which led us to the hypothesis that timing of salt intake may impact cardiovascular health and blood pressure regulation. Cell autonomous molecular clocks as the name implies, function independently to maintain optimum functional rhythmicity in the face of environmental stressors such that cellular homeostasis is maintained at all times. Our understanding of mechanisms influencing diurnal patterns of sodium excretion and blood pressure has expanded with the discovery of the circadian clock genes. In this review, we discuss what is known about circadian regulation of renal sodium handling machinery and its influence on blood pressure regulation, with timing of sodium intake as a potential modulator of the kidney clock.

Diurnal Cortisol Rhythm in Female Flight Attendants

The work of flight attendants is associated with exposure to long-term stress, which may cause increased secretion of cortisol. The aim of the study is to determine the circadian rhythm of cortisol and to seek factors of potential influence on the secretion of cortisol in female flight attendants working within one time zone as well as on long-distance flights. The prospective study covers 103 women aged 23-46. The study group (I) was divided into two subgroups: group Ia, comprising female flight attendants flying within one flight zone, and group Ib, comprising female flight attendants working on long-distance flights. The control group (II) are women of reproductive age who sought medical assistance due to marital infertility in whom the male factor was found to be responsible for problems with conception in the course of the diagnostic process. The assessment included: age, BMI, menstrual cycle regularity, the length of service, the frequency of flying, diurnal profile of the secretion of cortisol, testosterone, estradiol, 17-OH progesterone, SHBG, androstenedione, and progesterone concentration. Descriptive methods and inferential statistics methods were used to compile the data. Comparing the profile of flight attendants from groups Ia and Ib shows that the curve flattened among women flying within one time zone. The secretion curve is also more flattened in women with less years worked and in flight attendants working less than 60 h per month. Due to the character of work, the female flights attendants do not have hypersecretion of cortisol. Frequency of flying and length of work affect the dysregulation of HPA axis.

The association of polymorphisms in related circadian rhythm genes and clopidogrel resistance susceptibility

Previous studies have confirmed that a dynamic change in circadian rhythm will affect platelet activity, resulting in clopidogrel resistance (CR). We attempted to evaluate whether polymorphisms of related circadian rhythm genes are involved in CR in stable coronary artery disease (SCAD) patients. A sum of 204 SCAD patients met our requirements and were recruited, and 96 patients were considered to have CR. After clinical data collection and platelet function evaluation, genomic DNA was isolated from human peripheral blood, and 23 tagSNPs from related circadian rhythm genes were genotyped by GenomeLab SNPstream Genotyping System. After RNA isolation, relative expression of related gene mRNAs (CLOCK, CRY1, CACNA1C and PRKCG) was measured by real-time PCR. The results showed that polymorphisms in CRY1, CACNA1C and PRKCG changed the response to clopidogrel. And then, the rs1801260 polymorphism might lead to higher mRNA expression in CLOCK and potentially induce the occurrence of CR. Additionally, the TC genotype of rs3745406 might lower mRNA expression of PRKCG, resulting in CR. These findings support the hypothesized role of circadian rhythm genes in CR and indicate probable biomarkers for CR susceptibility, providing new insight into individualized medicine for coronary heart disease.

Light cycle phase advance as a model for jet lag reprograms the circadian rhythms of murine extraorbital lacrimal glands

PURPOSE

Jet lag causes a disruption in physiological rhythms in humans. This study aims to explore the extent to which jet lag affects the circadian rhythmicity in the lacrimal glands.

METHODS

C57BL/6J mice were subjected to a 12-h light/12-h dark (LD) cycle and an 8-h advanced LD schedule as a model for jet lag. On day 5 after the LD advance, the extraorbital lacrimal glands (ELGs) were collected at 3-h intervals during a 24-h cycle. Total mRNA was extracted from normal and advanced LD-treated ELGs and assayed using high-throughput RNA sequencing. The rhythmic transcripts were identified, analyzed, and visualized by bioinformatics techniques. Finally, (i) animal behavior; (ii) the mass, cell size, and secretion response of ELGs; and (iii) circadian migration of immune cells to ELGs were also assayed.

RESULTS

Jet lag treatment drastically altered the phase and composition of the rhythmic transcripts compared to that of normal ELGs. The key biological processes, signaling pathways, and protein-protein association networks were also dramatically altered in a spatiotemporal pattern. Furthermore, the circadian migration of neutrophils, T cells, B cells, and macrophages to the ELGs increased and shifted later by 6-h. Finally, the circadian rhythms of the ELGs with respect to mass, cell size, and secretion response were also impaired in jet lag-treated animals.

CONCLUSIONS

Jet lag impairs the circadian rhythm of the transcriptomic profile, structure, and secretion function of the lacrimal glands. This information provides novel insight into the negative effects of jet lag on ELGs.

Evaluation of Cardiac Circadian Rhythm Deconditioning Induced by 5-to-60 Days of Head-Down Bed Rest

Head-down tilt (HDT) bed rest elicits changes in cardiac circadian rhythms, generating possible adverse health outcomes such as increased arrhythmic risk. Our aim was to study the impact of HDT duration on the circadian rhythms of heart beat (RR) and ventricular repolarization (QTend) duration intervals from 24-h Holter ECG recordings acquired in 63 subjects during six different HDT bed rest campaigns of different duration (two 5-day, two 21-day, and two 60-day). Circadian rhythms of RR and QTend intervals series were evaluated by Cosinor analysis, resulting in a value of midline (MESOR), oscillation amplitude (OA) and acrophase (φ). In addition, the QTc (with Bazett correction) was computed, and day-time, night-time, maximum and minimum RR, QTend and QTc intervals were calculated. Statistical analysis was conducted, comparing: (1) the effects at 5 (HDT5), 21 (HDT21) and 58 (HDT58) days of HDT with baseline (PRE); (2) trends in recovery period at post-HDT epochs (R) in 5-day, 21-day, and 60-day HDT separately vs. PRE; (3) differences at R + 0 due to bed rest duration; (4) changes between the last HDT acquisition and the respective R + 0 in 5-day, 21-day, and 60-day HDT. During HDT, major changes were observed at HDT5, with increased RR and QTend intervals' MESOR, mostly related to day-time lengthening and increased minima, while the QTc shortened. Afterward, a progressive trend toward baseline values was observed with HDT progression. Additionally, the φ anticipated, and the OA was reduced during HDT, decreasing system's ability to react to incoming stimuli. Consequently, the restoration of the orthostatic position elicited the shortening of RR and QTend intervals together with QTc prolongation, notwithstanding the period spent in HDT. However, the magnitude of post-HDT changes, as well as the difference between the last HDT day and R + 0, showed a trend to increase with increasing HDT duration, and 5/7 days were not sufficient for recovering after 60-day HDT. Additionally, the φ postponed and the OA significantly increased at R + 0 compared to PRE after 5-day and 60-day HDT, possibly increasing the arrhythmic risk. These results provide evidence that continuous monitoring of astronauts' circadian rhythms, and further investigations on possible measures for counteracting the observed modifications, will be key for future missions including long periods of weightlessness and gravity transitions, for preserving astronauts' health and mission success.

Environmental circadian disruption suppresses rhythms in kidney function and accelerates excretion of renal injury markers in urine of male hypertensive rats

Nontraditional work schedules, such as shift work, have been associated with numerous health issues, including cardiovascular and metabolic disease. These work schedules can chronically misalign environmental timing cues with internal circadian clock systems in the brain and in peripheral organs, leading to dysfunction of those systems and their associated biological processes. Environmental circadian disruption in the kidney may be an important factor in the increased incidence of hypertension and adverse health outcomes in human shift workers. The relationship between renal rhythmicity and injury resilience is not well understood, especially in the context of environmental, rather than genetic, manipulations of the circadian system. We conducted a longitudinal study to determine whether chronic shifting of the light cycle that mimics shift work schedules would disrupt output rhythms of the kidney and accelerate kidney injury in salt-loaded male spontaneously hypertensive, stroke-prone rats. We observed that chronic shifting of the light-dark (LD) cycle misaligned and decreased the amplitude of urinary volume rhythms as the kidney phase-shifted to match each new lighting cycle. This schedule also accelerated glomerular and tubular injury marker excretion, as quantified by nephrin and KIM-1 compared with rats kept in a static LD cycle. These data suggest that disrupted rhythms in the kidney may decrease resilience and contribute to disease development in systems dependent on renal and cardiovascular functions.

Elevated CLOCK and BMAL1 Contribute to the Impairment of Aerobic Glycolysis from Astrocytes in Alzheimer's Disease

Altered glucose metabolism has been implicated in the pathogenesis of Alzheimer's disease (AD). Aerobic glycolysis from astrocytes is a critical metabolic pathway for brain energy metabolism. Disturbances of circadian rhythm have been associated with AD. While the role of circadian locomotor output cycles kaput (CLOCK) and brain muscle ARNT-like1 (BMAL1), the major components in the regulation of circadian rhythm, has been identified in the brain, the mechanism by which CLOCK and BMAL1 regulates the dysfunction of astrocytes in AD remains unclear. Here, we show that the protein levels of CLOCK and BMAL1 are significantly elevated in impaired astrocytes of cerebral cortex from patients with AD. We demonstrate that the over-expression of CLOCK and BMAL1 significantly suppresses aerobic glycolysis and lactate production by the reduction in hexokinase 1 (HK1) and lactate dehydrogenase A (LDHA) protein levels in human astrocytes. Moreover, the elevation of CLOCK and BMAL1 induces functional impairment by the suppression of glial fibrillary acidic protein (GFAP)-positive filaments in human astrocytes. Furthermore, the elevation of CLOCK and BMAL1 promotes cytotoxicity by the activation of caspase-3-dependent apoptosis in human astrocytes. These results suggest that the elevation of CLOCK and BMAL1 contributes to the impairment of astrocytes by inhibition of aerobic glycolysis in AD.

Survival is reduced when endogenous period deviates from 24 h in a non-human primate, supporting the circadian resonance theory

Circadian rhythms are ubiquitous attributes across living organisms and allow the coordination of internal biological functions with optimal phases of the environment, suggesting a significant adaptive advantage. The endogenous period called tau lies close to 24 h and is thought to be implicated in individuals' fitness: according to the circadian resonance theory, fitness is reduced when tau gets far from 24 h. In this study, we measured the endogenous period of 142 mouse lemurs (Microcebus murinus), and analyzed how it is related to their survival. We found different effects according to sex and season. No impact of tau on mortality was found in females. However, in males, the deviation of tau from 24 h substantially correlates with an increase in mortality, particularly during the inactive season (winter). These results, comparable to other observations in mice or drosophila, show that captive gray mouse lemurs enjoy better fitness when their circadian period closely matches the environmental periodicity. In addition to their deep implications in health and aging research, these results raise further ecological and evolutionary issues regarding the relationships between fitness and circadian clock.

Neuronal Activity Regulates Blood-Brain Barrier Efflux Transport through Endothelial Circadian Genes

The blood vessels in the central nervous system (CNS) have a series of unique properties, termed the blood-brain barrier (BBB), which stringently regulate the entry of molecules into the brain, thus maintaining proper brain homeostasis. We sought to understand whether neuronal activity could regulate BBB properties. Using both chemogenetics and a volitional behavior paradigm, we identified a core set of brain endothelial genes whose expression is regulated by neuronal activity. In particular, neuronal activity regulates BBB efflux transporter expression and function, which is critical for excluding many small lipophilic molecules from the brain parenchyma. Furthermore, we found that neuronal activity regulates the expression of circadian clock genes within brain endothelial cells, which in turn mediate the activity-dependent control of BBB efflux transport. These results have important clinical implications for CNS drug delivery and clearance of CNS waste products, including Aβ, and for understanding how neuronal activity can modulate diurnal processes.

Transcriptome analysis of the uterus of hens laying eggs differing in cuticle deposition

Background

Avian eggs have a proteinaceous cuticle. The quantity of cuticle varies and the deposition of a good cuticle in the uterus (Shell-gland) prevents transmission of bacteria to the egg contents.

Results

To understand cuticle deposition, uterus transcriptomes were compared between hens with i) naturally good and poor cuticle and, ii) where manipulation of the hypothalamo-pituitary-gonadal-oviduct axis produced eggs with or without cuticle. The highest expressed genes encoded eggshell matrix and cuticle proteins, e.g. MEPE (OC-116), BPIFB3 (OVX-36), RARRES1 (OVX-32), WAP (OVX-25), and genes for mitochondrial oxidative phosphorylation, active transport and energy metabolism. Expression of a number of these genes differed between hens laying eggs with or without cuticle. There was also a high expression of clock genes. PER2, CRY2, CRY1, CLOCK and BMAL1 were differentially expressed when cuticle deposition was prevented, and they also changed throughout the egg formation cycle. This suggests an endogenous clock in the uterus may be a component of cuticle deposition control. Cuticle proteins are glycosylated and glycosaminoglycan binding genes had a lower expression when cuticle proteins were deposited on the egg. The immediate early genes, JUN and FOS, were expressed less when the cuticle had not been deposited and changed over the egg formation cycle, suggesting they are important in oviposition and cuticle deposition. The uterus transcriptome of hens with good and poor cuticle deposition did not differ.

Conclusions

We have gained insights into the factors that can affect the production of the cuticle especially clock genes and immediate early genes. We have demonstrated that these genes change their expression over the period of eggshell formation supporting their importance. The lack of differences in expression between the uterus of hens laying eggs with the best and worse cuticle suggest the genetic basis of the trait may lie outside the oviduct.

Deletion of astrocytic BMAL1 results in metabolic imbalance and shorter lifespan in mice

Disruption of the circadian cycle is strongly associated with metabolic imbalance and reduced longevity in humans. Also, rodent models of circadian arrhythmia, such as the constitutive knockout of the clock gene Bmal1, leads to metabolic disturbances and early death. Although astrocyte clock regulates molecular and behavioral circadian rhythms, its involvement in the regulation of energy balance and lifespan is unknown. Here, we show that astrocyte-specific deletion of Bmal1 is sufficient to alter energy balance, glucose homeostasis, and reduce lifespan. Mutant animals displayed impaired hypothalamic molecular clock, age-dependent astrogliosis, apoptosis of hypothalamic astrocytes, and increased glutamate and GABA levels. Importantly, modulation of GABAA-receptor signaling completely restored glutamate levels, delayed the reactive gliosis as well as the metabolic phenotypes and expanded the lifespan of the mutants. Our results demonstrate that the astrocytic clock can influence many aspects of brain function and neurological disease and suggest astrocytes and GABAA receptor as pharmacological targets to prevent the metabolic dysfunctions and shortened lifespan associated with alterations of circadian rhythms.