Small molecule modifiers of circadian clocks

Spatiotemporal Control Over Circadian Rhythms With Light

Circadian rhythms are endogenous biological oscillators that synchronize internal physiological processes and behaviors with external environmental changes, sustaining homeostasis and health. Disruption of circadian rhythms leads to numerous diseases, including cardiovascular and metabolic diseases, cancer, diabetes, and neurological disorders. Despite the potential to restore healthy rhythms in the organism, pharmacological chronotherapy lacks spatial and temporal resolution. Addressing this challenge, chrono-photopharmacology, the approach that employs small molecules with light-controlled activity, enables the modulation of circadian rhythms when and where needed. Two approaches-relying on irreversible and reversible drug activation-have been proposed for this purpose. These methodologies are based on photoremovable protecting groups and photoswitches, respectively. Designing photoresponsive bioactive molecules requires meticulous structural optimization to obtain the desired chemical and photophysical properties, and the design principles, detailed guidelines and challenges are summarized here. In this review, we also analyze all the known circadian modulators responsive to light and dissect the rationale following their construction and application to control circadian biology from the protein level to living organisms. Finally, we present the strength of a reversible approach in allowing the modulation of the circadian period and the phase.

Gut Microbiome-Produced Bile Acid Metabolite Lengthens Circadian Period in Host Intestinal Cells

Host circadian signaling, feeding, and the gut microbiome are tightly interconnected. Changes in the gut microbial community can affect the expression of core clock genes, but the specific metabolites and molecular mechanisms that mediate this relationship remain largely unknown. Here, we sought to identify gut microbial metabolites that impact circadian signaling. Through a phenotypic screen of a focused library of gut microbial metabolites, we identified a bile acid metabolite, lithocholic acid (LCA), as a circadian modulator. LCA lengthened the circadian period of core clock gene hPer2 transcription in a dose-responsive manner in human colonic cells. We found evidence that LCA modulates the casein kinase 1 δ/ε (CK1δ/ε)-protein phosphatase 1 (PP1) feedback loop and stabilizes core clock protein cryptochrome 2 (CRY2). Furthermore, we showed that LCA feeding alters circadian transcription in mouse distal ileum and colon. Taken together, our work identifies LCA as a molecular link between host circadian biology and the microbiome. Because bile acids are secreted in response to feeding, our work provides potential mechanistic insight into the molecular nature of the food-entrainable oscillator by which peripheral clocks adapt to the timing of food intake. Given the association between circadian rhythm, feeding, and metabolic disease, our insights may offer a new avenue for modulating host health.

Inflammation o'clock: interactions of circadian rhythms with inflammation-induced skeletal muscle atrophy

Circadian rhythms are ∼24 h cycles evident in behaviour, physiology and metabolism. The molecular mechanism directing circadian rhythms is the circadian clock, which is composed of an interactive network of transcription-translation feedback loops. The core clock genes include Bmal1, Clock, Rev-erbα/β, Per and Cry. In addition to keeping time, the core clock regulates a daily programme of gene expression that is important for overall cell homeostasis. The circadian clock mechanism is present in all cells, including skeletal muscle fibres, and disruption of the muscle clock is associated with changes in muscle phenotype and function. Skeletal muscle atrophy is largely associated with a lower quality of life, frailty and reduced lifespan. Physiological and genetic modification of the core clock mechanism yields immune dysfunction, alters inflammatory factor expression and secretion and is associated with skeletal muscle atrophy in multiple conditions, such as ageing and cancer cachexia. Here, we summarize the possible interplay between the circadian clock modulation of immune cells, systemic inflammatory status and skeletal muscle atrophy in chronic inflammatory conditions. Although there is a clear disruption of circadian clocks in various models of atrophy, the mechanism behind such alterations remains unknown. Understanding the modulatory potential of muscle and immune circadian clocks in inflammation and skeletal muscle health is essential for the development of therapeutic strategies to protect skeletal muscle mass and function of patients with chronic inflammation.

Circadian de(regulation) in physiology: implications for disease and treatment

Time plays a crucial role in the regulation of physiological processes. Without a temporal control system, animals would be unprepared for cyclic environmental changes, negatively impacting their survival. Experimental studies have demonstrated the essential role of the circadian system in the temporal coordination of physiological processes. Translating these findings to humans has been challenging. Increasing evidence suggests that modern lifestyle factors such as diet, sedentarism, light exposure, and social jet lag can stress the human circadian system, contributing to misalignment; i.e., loss of phase coherence across tissues. An increasing body of evidence supports the negative impact of circadian disruption on several human health parameters. This review aims to provide a comprehensive overview of how circadian disruption influences various physiological processes, its long-term health consequences, and its association with various diseases. To illustrate the relevant consequences of circadian disruption, we focused on describing the many physiological consequences faced by shift workers, a population known to experience high levels of circadian disruption. We also discuss the emerging field of circadian medicine, its founding principles, and its potential impact on human health.

A circadian clock regulates the blood-brain barrier across phylogeny

As the central regulatory system of an organism, the brain is responsible for overseeing a wide variety of physiological processes essential for an organism's survival. To maintain the environment necessary for neurons to function, the brain requires highly selective uptake and elimination of specific molecules through the blood-brain barrier (BBB). As an organism's activities vary throughout the day, how does the BBB adapt to meet the changing needs of the brain? A mechanism is through temporal regulation of BBB permeability via its circadian clock, which will be the focal point of this chapter. To comprehend the circadian clock's role within the BBB, we will first examine the anatomy of the BBB and the transport mechanisms enabling it to fulfill its role as a restrictive barrier. Next, we will define the circadian clock, and the discussion will encompass an introduction to circadian rhythms, the Transcription-Translation Feedback Loop (TTFL) as the mechanistic basis of circadian timekeeping, and the organization of tissue clocks found in organisms. Then, we will cover the role of the circadian rhythms in regulating the cellular mechanisms and functions of the BBB. We discuss the implications of this regulation in influencing sleep behavior, the progression of neurodegenerative diseases, and finally drug delivery for treatment of neurological diseases.

Pterostilbene targets the molecular oscillator RORγ to restore circadian rhythm oscillation and protect against sleep restriction induced metabolic disorders

BACKGROUND

Considerable researches have directed toward metabolic disorders caused by sleep restriction (SR). SR-induced disruption of circadian metabolic rhythmicity is identified as an important pathophysiological mechanism. The flavonoid pterostilbene (PTE) is abundant in the traditional Chinese medicine dragon's blood with protective efficacy against obesity-related metabolic dysfunctions. Our previous study found that PTE ameliorates exercise intolerance and clock gene oscillation in the skeletal muscles subjected to SR.

PURPOSE

This study aimed to explore whether PTE improves SR-induced metabolic disorders and delineate the relationship between PTE and the circadian clock.

STUDY DESIGN AND METHODS

Two hundred male C57/B6J mice were kept awake for 20 h/d over five consecutive days and concurrently gavaged with 50, 100, or 200 mg/kg·bw/d PTE. Food consumption and body weight were monitored, and the metabolic status of the mice was evaluated by performing OGTT and ITT, measuring the serum lipid profiles and liver histopathology in response to SR. Daily behavior was analyzed by Clocklab™. The circadian rhythms of the liver clock genes and metabolic output genes were evaluated by cosine analysis. Binding between PTE and RORα/γ or NR1D1/2 was investigated by molecular docking. A luciferase reporter assay was used to determine the impact of PTE on Bmal1 transcription in SR-exposed mice co-transfected with Ad-BMAL1-LUC plus Ad-RORγ-mCherry or Ad-NR1D1-EGFP.

RESULTS

PTE significantly ameliorated abnormal glucose and lipid metabolism (p < 0.05) in SR-exposed mice. PTE improved circadian behavior (p < 0.05) and rescued the circadian rhythm oscillation of the liver clock (p < 0.05) and metabolic output genes (p < 0.05) under SR condition. Molecular docking disclosed that PTE might interact with RORs, and PTE was found to increase Bmal1 promoter luciferase activity with RORE elements in the presence of Ad-RORγ-mCherry (p < 0.05).

CONCLUSIONS

PTE may protect against SR-induced metabolic disorders by directly modulating RORγ to maintain circadian metabolic rhythm. The findings provide valuable insights into the potential use of PTE in the treatment of metabolic disorders associated with disruptions in the circadian rhythm.

Targeting sleep and the circadian system as a novel treatment strategy for Parkinson's disease

There is a growing appreciation of the wide range of sleep-wake disturbances that occur frequently in Parkinson's disease. These are known to be associated with a range of motor and non-motor symptoms and significantly impact not only on the quality of life of the patient, but also on their bed partner. The underlying causes for fragmented sleep and daytime somnolence are no doubt multifactorial but there is clear evidence for circadian disruption in Parkinson's disease. This appears to be occurring not only as a result of the neuropathological changes that occur across a distributed neural network, but even down to the cellular level. Such observations indicate that circadian changes may in fact be a driver of neurodegeneration, as well as a cause for some of the sleep-wake symptoms observed in Parkinson's disease. Thus, efforts are now required to evaluate approaches including the prescription of precision medicine to modulate photoreceptor activation ratios that reflect daylight inputs to the circadian pacemaker, the use of small molecules to target clock genes, the manipulation of orexin pathways that could help restore the circadian system, to offer novel symptomatic and novel disease modifying strategies.

Small-molecule CEM3 strengthens single-cell oscillators in the suprachiasmatic nucleus

A robust endogenous clock is required for proper function of many physiological processes. The suprachiasmatic nucleus (SCN) constitutes our central circadian clock and allows us to adapt to daily changes in the environment. Aging can cause a decline in the amplitude of circadian rhythms in SCN and peripheral clocks, which contributes to increased risk of several chronic diseases. Strengthening clock function would therefore be an effective strategy to improve health. A high-throughput chemical screening has identified clock-enhancing molecule 3 (CEM3) as small molecule that increases circadian rhythm amplitude in cell lines and SCN explants. It is, however, currently not known whether CEM3 acts by enhancing the amplitude of individual single-cell oscillators or by enhancing synchrony among neurons. In view of CEM3's potential, it is of evident importance to clarify the mode of action of CEM3. Here, we investigated the effects of CEM3 on single-cell PERIOD2::LUCIFERASE rhythms in mouse SCN explants. CEM3 increased the amplitude in approximately 80%-90% of the individual cells in the SCN without disrupting the phase and/or period of their rhythms. Noticeably, CEM3's effect on amplitude is independent of the cell's initial amplitude. These findings make CEM3 a potential therapeutic candidate to restore compromised amplitude in circadian rhythms and will boost the development of other molecular approaches to improve health.

Identification of Cyclocybe erebia metabolites that affect the circadian rhythm of Eluc expression under control of Bmal1 promoter in mouse fibroblast cells

Pharmacological intervention of circadian rhythms is a potentially useful approach for ameliorating various health problems caused by disturbed circadian rhythms including sleep disorder and metabolic diseases. To find compounds that affect circadian rhythms, we screened mushroom extracts using mouse cells expressing the luciferase gene under the control of the mouse Bmal1 promoter. The culture filtrate extract from the basidiomycete Cyclocybe erebia enhanced the oscillation of bioluminescence caused by the expression of the luciferase gene and prolonged the period of bioluminescence. Bioassay-guided fractionation of the extract resulted in purification of compounds 1 and 2. Spectroscopic analyses along with single-crystal X-ray diffraction analysis, revealed that these compounds were diterpenoids with a unique skeleton and a fused ring system comprising 3-, 7-, and 5-membered rings. Compounds 1 and 2 were named cyclocircadins A and B, respectively. These findings suggested that natural diterpenoids could be a source of compounds with the activity affecting circadian rhythms.

Chronotherapy in dentistry: A scoping review

The circadian clock modulates almost all vital aspects of our physiology and metabolism, including processes relevant to dentistry, such as healing, inflammation and nociception. Chronotherapy is an emerging field aiming to improve therapeutic efficacy and decrease adverse effects on health outcomes. This scoping review aimed to systematically map the evidence underpinning chronotherapy in dentistry and to identify gaps in knowledge. We conducted a systematic scoping search using four databases (Medline, Scopus, CINAHL and Embase). We identified 3908 target articles screened by two blinded reviewers, and only original animal and human studies investigating the chronotherapeutic use of drugs or interventions in dentistry were included. Of the 24 studies included, 19 were human studies and five were animal studies. Chrono-radiotherapy and chrono-chemotherapy reduced treatment side effects and improved therapeutic response, leading to higher survival rates in cancer patients. Animal studies reported that tooth movement and periodontal tissue response to orthodontic forces follow a diurnal rhythm that might influence bone metabolism. Profound and prolonged local anesthesia could be achieved when injected in the evening. Although the overall quality of the included studies was low, chronotherapy applications in dentistry seem to have favourable outcomes, especially in head and neck cancer treatments.

Circadian disruption: from mouse models to molecular mechanisms and cancer therapeutic targets

The circadian clock is a timekeeping system for numerous biological rhythms that contribute to the regulation of numerous homeostatic processes in humans. Disruption of circadian rhythms influences physiology and behavior and is associated with adverse health outcomes, especially cancer. However, the underlying molecular mechanisms of circadian disruption-associated cancer initiation and development remain unclear. It is essential to construct good circadian disruption models to uncover and validate the detailed molecular clock framework of circadian disruption in cancer development and progression. Mouse models are the most widely used in circadian studies due to their relatively small size, fast reproduction cycle, easy genome manipulation, and economic practicality. Here, we reviewed the current mouse models of circadian disruption, including suprachiasmatic nuclei destruction, genetic engineering, light disruption, sleep deprivation, and other lifestyle factors in our understanding of the crosstalk between circadian rhythms and oncogenic signaling, as well as the molecular mechanisms of circadian disruption that promotes cancer growth. We focused on the discoveries made with the nocturnal mouse, diurnal human being, and cell culture and provided several circadian rhythm-based cancer therapeutic strategies.

The role of circadian clock in astrocytes: From cellular functions to ischemic stroke therapeutic targets

Accumulating evidence suggests that astrocytes, the abundant cell type in the central nervous system (CNS), play a critical role in maintaining the immune response after cerebral infarction, regulating the blood-brain barrier (BBB), providing nutrients to the neurons, and reuptake of glutamate. The circadian clock is an endogenous timing system that controls and optimizes biological processes. The central circadian clock and the peripheral clock are consistent, controlled by various circadian components, and participate in the pathophysiological process of astrocytes. Existing evidence shows that circadian rhythm controls the regulation of inflammatory responses by astrocytes in ischemic stroke (IS), regulates the repair of the BBB, and plays an essential role in a series of pathological processes such as neurotoxicity and neuroprotection. In this review, we highlight the importance of astrocytes in IS and discuss the potential role of the circadian clock in influencing astrocyte pathophysiology. A comprehensive understanding of the ability of the circadian clock to regulate astrocytes after stroke will improve our ability to predict the targets and biological functions of the circadian clock and gain insight into the basis of its intervention mechanism.

Effect of the Citrus Flavone Nobiletin on Circadian Rhythms and Metabolic Syndrome

The importance of the circadian clock in maintaining human health is now widely acknowledged. Dysregulated and dampened clocks may be a common cause of age-related diseases and metabolic syndrome Thus, circadian clocks should be considered as therapeutic targets to mitigate disease symptoms. This review highlights a number of dietary compounds that positively affect the maintenance of the circadian clock. Notably the polymethoxyflavone nobiletin has shown some encouraging results in pre-clinical experiments. Although many more experiments are needed to fully elucidate its exact mechanism of action, it is a promising candidate with potential as a chronotherapeutic agent.

Tangeretin prevents cognitive deficit in delirium through activating RORα/γ-E4BP4 axis in mice

Delirium is a common and serious neuropsychiatric syndrome characterized with acute cognitive and attentional deficits, however, the effective therapies are lacking. Here, using mouse models of delirium, we investigated the effects of tangeretin (TAN, a natural flavonoid) on cognitive impairment by assessing object preference with novel object recognition (NOR) test and spontaneous alternation with Y maze test. We found that TAN, as a RORα/γ agonist, prevented cognitive decline in delirious mice as evidenced by a normal novel object preference and increased spontaneous alternation. This was accompanied by decreased expression of ERK1/2, TNFα and IL-1β as well as diminished microglial activation in delirious mice. The protective effect of TAN on delirium was mainly attributed to increased hippocampal E4BP4 expression (a known target of RORs and a regulator of cognition in delirium through modulating the ERK1/2 cascade and microglial activation) via activation of RORα/γ. In addition, TAN treatment modulated the expression of RORα/γ target genes (such as E4bp4 and Bmal1) and inhibited the expression of TNFα and IL-1β in lipopolysaccharide (LPS)-stimulated cells, supporting a beneficial effect of TAN on delirium. In conclusion, TAN is identified as a RORα/γ agonist which promotes E4BP4 expression to prevent cognitive decline in delirious mice. Our findings may have implications for drug development of TAN for prevention and treatment of various diseases associated with cognitive deficiency.

New insight into ischemic stroke: Circadian rhythm in post-stroke angiogenesis

The circadian rhythm is an endogenous clock system that coordinates and optimizes various physiological and pathophysiological processes, which accord with the master and the peripheral clock. Increasing evidence indicates that endogenous circadian rhythm disruption is involved in the lesion volume and recovery of ischemic stroke. As a critical recovery mechanism in post-stroke, angiogenesis reestablishes the regional blood supply and enhances cognitive and behavioral abilities, which is mainly composed of the following processes: endothelial cell proliferation, migration, and pericyte recruitment. The available evidence revealed that the circadian governs many aspects of angiogenesis. This study reviews the mechanism by which circadian rhythms regulate the process of angiogenesis and its contribution to functional recovery in post-stroke at the aspects of the molecular level. A comprehensive understanding of the circadian clock regulating angiogenesis in post-stroke is expected to develop new strategies for the treatment of cerebral infarction.

ISX-9 potentiates CaMKIIδ-mediated BMAL1 activation to enhance circadian amplitude

Circadian dysregulation associates with numerous diseases including metabolic dysfunction, sleep disorder, depression and aging. Given that declined circadian amplitude is a trait commonly found with compromised health, interventions that design in precluding circadian amplitude from dampening will aid to mitigate complex, circadian-related diseases. Here we identify a neurogenic small molecule ISX-9 that is able to support persistent and higher amplitude of circadian oscillations. ISX-9 improves diurnal metabolic rhythms in middle-aged mice. Moreover, the ISX-9-treated mice show better sleep homeostasis with increased delta power during the day time and higher locomotive activity in the dark period. ISX-9 augments CaMKIIδ expression and increases BMAL1 activity via eliciting CaMKIIδ-mediated phosphorylation on BMAL1 residues S513/S515/S516, accordingly composes a positive feedback effect on enhancing circadian amplitude. CaMKIIδ-targeting, and the use of ISX-9 may serve as decent choices for treating circadian-related disorders.

Circadian clock dysfunction of epithelial cells in pulmonary diseases

Highly-differentiated pulmonary epithelial cells are essential for maintaining lung homeostasis by exerting various physiological functions, which are regulated by circadian clock consisted of an autoregulatory feedback loop of clock genes, including Brain-Muscle Aryl-hydrocarbon Receptor Nuclear Translocator-Like 1 (BMAL1) and Nuclear Heme Receptor Reverse Erythroblastosis Virus α (REV-ERB-α). The circadian clock dysfunction of epithelial cells has been increasingly associated with the pulmonary diseases: BMAL1 and REV-ERB-α regulates inflammatory response of club cells induced by lipopolysaccharide and cigarette smoke (CS) respectively; the clock disfunction in alveolar epithelial type2 cells (AEC-II) has been implicated in CS-induced airway inflammation and early-life hyperoxia-related susceptibility to influenza infection; the ciliary beat frequency of ciliated cells also shows circadian rhythms. Here, we review the current knowledge on the circadian regulation of different epithelial-cell subtypes, attempting to provide insights into how clock dysfunction contributes to pulmonary diseases, and explore possible pharmacological therapies and future directions for fundamental studies.

Chronobiotics KL001 and KS15 Extend Lifespan and Modify Circadian Rhythms of Drosophila melanogaster

Chronobiotics are a group of drugs, which are utilized to modify circadian rhythms targeting clock-associated molecular mechanisms. The circadian clock is known as a controller of numerous processes in connection with aging. Hypothesis: KL001 and KS15 targeting CRY, affect lifespan, locomotor activity and circadian rhythm of Drosophila melanogaster. We observed a slight (2%, p < 0.001) geroprotective effect on median lifespan (5 µM solution of KL001 in 0.1% DMSO) and a 14% increase in maximum lifespan in the same group. KS15 10 µM solution extended males’ median lifespan by 8% (p < 0.05). The statistically significant positive effects of KL001 and KS15 on lifespan were not observed in female flies. KL001 5 µM solution improved locomotor activity in young male imagoes (p < 0.05), elevated morning activity peak in aged imagoes and modified robustness of their circadian rhythms, leaving the period intact. KS15 10 µM solution decreased the locomotor activity in constant darkness and minimized the number of rhythmic flies. KL001 5 µM solution improved by 9% the mean starvation resistance in male flies (p < 0.01), while median resistance was elevated by 50% (p < 0.0001). This phenomenon may suggest the presence of the mechanism associated with improvement of fat body glucose depos’ utilization in starvation conditions which is activated by dCRY binding KL001.

Human circadian variations

Circadian rhythms, present in most phyla across life, are biological oscillations occurring on a daily cycle. Since the discovery of their molecular foundations in model organisms, many inputs that modify this tightly controlled system in humans have been identified. Polygenic variations and environmental factors influence each person's circadian rhythm, contributing to the trait known as chronotype, which manifests as the degree of morning or evening preference in an individual. Despite normal variation in chronotype, much of society operates on a "one size fits all" schedule that can be difficult to adjust to, especially for certain individuals whose endogenous circadian phase is extremely advanced or delayed. This is a public health concern, as phase misalignment in humans is associated with a number of adverse health outcomes. Additionally, modern technology (such as electric lights and computer, tablet, and phone screens that emit blue light) and lifestyles (such as shift or irregular work schedules) are disrupting circadian consistency in an increasing number of people. Though medical and lifestyle interventions can alleviate some of these issues, growing research on endogenous circadian variability and sensitivity suggests that broader social changes may be necessary to minimize the impact of circadian misalignment on health.

Importance of circadian timing for aging and longevity

Dietary restriction (DR) decreases body weight, improves health, and extends lifespan. DR can be achieved by controlling how much and/or when food is provided, as well as by adjusting nutritional composition. Because these factors are often combined during DR, it is unclear which are necessary for beneficial effects. Several drugs have been utilized that target nutrient-sensing gene pathways, many of which change expression throughout the day, suggesting that the timing of drug administration is critical. Here, we discuss how dietary and pharmacological interventions promote a healthy lifespan by influencing energy intake and circadian rhythms.

Circadian clocks link physiologic processes to environmental conditions and a mismatch between internal and external rhythms has negative effects on organismal health. In this review, the authors discuss the interactions between circadian clocks and dietary interventions targeted to promote healthy aging.

Circadian Effects of Drug Responses

Circadian rhythms describe physiological systems that repeat themselves with a cycle of approximately 24 h. Our understanding of the cellular and molecular origins of these oscillations has improved dramatically, allowing us to appreciate the significant role these oscillations play in maintaining physiological homeostasis. Circadian rhythms allow living organisms to predict and efficiently respond to a dynamically changing environment, set by repetitive day/night cycles. Since circadian rhythms underlie almost every aspect of human physiology, it is unsurprising that they also influence the response of a living organism to disease, stress, and therapeutics. Therefore, not only do the mechanisms that maintain health and disrupt homeostasis depend on our internal circadian clock, but also the way drugs are perceived and function depends on these physiological rhythms. We present a holistic view of the therapeutic process, discussing components such as disease state, pharmacokinetics, and pharmacodynamics, as well as adverse reactions that are critically affected by circadian rhythms. We outline challenges and opportunities in moving toward personalized medicine approaches that explore and capitalize on circadian rhythms for the benefit of the patient.

Small-molecule modulators of the circadian clock: Pharmacological potentials in circadian-related diseases

Disruption of circadian oscillations has a wide-ranging impact on health, with the potential to induce the development of clock-related diseases. Small-molecule modulators of the circadian clock (SMMCC) target core or noncore clock proteins, modulating physiological effects as a consequence of agonist, inverse agonist, or antagonist interference. These pharmacological modulators are usually identified using chemical screening of large libraries of active compounds. However, target-based screens, chemical optimization, and circadian crystallography have recently assisted in the identification of these compounds. In this review, we focus on established and novel SMMCCs targeting both core and noncore clock proteins, identifying their circadian targets, detailed circadian effects, and specific physiological effects. In addition, we discuss their therapeutic potential for the treatment of diverse clock-related disorders (such as metabolic-associated disorders, autoimmune diseases, mood disorders, and cancer) and as chronotherapeutics. Future perspectives are also considered, such as clinical trials, and potential safety hazards, including those in the absence of clinical trials.

Circadian control of hepatitis B virus replication

Chronic hepatitis B virus (HBV) infection is a major cause of liver disease and cancer worldwide for which there are no curative therapies. The major challenge in curing infection is eradicating or silencing the covalent closed circular DNA (cccDNA) form of the viral genome. The circadian factors BMAL1/CLOCK and REV-ERB are master regulators of the liver transcriptome and yet their role in HBV replication is unknown. We establish a circadian cycling liver cell-model and demonstrate that REV-ERB directly regulates NTCP-dependent hepatitis B and delta virus particle entry. Importantly, we show that pharmacological activation of REV-ERB inhibits HBV infection in vitro and in human liver chimeric mice. We uncover a role for BMAL1 to bind HBV genomes and increase viral promoter activity. Pharmacological inhibition of BMAL1 through REV-ERB ligands reduces pre-genomic RNA and de novo particle secretion. The presence of conserved E-box motifs among members of the Hepadnaviridae family highlight an evolutionarily conserved role for BMAL1 in regulating this family of small DNA viruses.

Circadian rhythm as a therapeutic target

The circadian clock evolved in diverse organisms to integrate external environmental changes and internal physiology. The clock endows the host with temporal precision and robust adaptation to the surrounding environment. When circadian rhythms are perturbed or misaligned, as a result of jet lag, shiftwork or other lifestyle factors, adverse health consequences arise, and the risks of diseases such as cancer, cardiovascular diseases or metabolic disorders increase. Although the negative impact of circadian rhythm disruption is now well established, it remains underappreciated how to take advantage of biological timing, or correct it, for health benefits. In this Review, we provide an updated account of the circadian system and highlight several key disease areas with altered circadian signalling. We discuss environmental and lifestyle modifications of circadian rhythm and clock-based therapeutic strategies, including chronotherapy, in which dosing time is deliberately optimized for maximum therapeutic index, and pharmacological agents that target core clock components and proximal regulators. Promising progress in research, disease models and clinical applications should encourage a concerted effort towards a new era of circadian medicine.

Molecular regulation of brain metabolism underlying circadian epilepsy

Extensive study has demonstrated that epilepsy occurs with greater frequency at certain times in the 24-h cycle. Although these findings implicate an overlap between the circadian rhythm and epilepsy, the molecular and cellular mechanisms underlying this circadian regulation are poorly understood. Because the 24-h rhythm is generated by the circadian molecular system, it is not surprising that this system comprised of many circadian genes is implicated in epilepsy. We summarized evidence in the literature implicating various circadian genes such as Clock, Bmal1, Per1, Rev-erb⍺, and Ror⍺ in epilepsy. In various animal models of epilepsy, the circadian oscillation and the steady-state level of these genes are disrupted. The downstream pathway of these genes involves a large number of metabolic pathways associated with epilepsy. These pathways include pyridoxal metabolism, the mammalian target of rapamycin pathway, and the regulation of redox state. We propose that disruption of these metabolic pathways could mediate the circadian regulation of epilepsy. A greater understanding of the cellular and molecular mechanism of circadian regulation of epilepsy would enable us to precisely target the circadian disruption in epilepsy for a novel therapeutic approach.

High-throughput measurement of fibroblast rhythms reveals genetic heritability of circadian phenotypes in diversity outbred mice and their founder strains

Circadian variability is driven by genetics and Diversity Outbred (DO) mice is a powerful tool for examining the genetics of complex traits because their high genetic and phenotypic diversity compared to conventional mouse crosses. The DO population combines the genetic diversity of eight founder strains including five common inbred and three wild-derived strains. In DO mice and their founders, we established a high-throughput system to measure cellular rhythms using in vitro preparations of skin fibroblasts. Among the founders, we observed strong heritability for rhythm period, robustness, phase and amplitude. We also found significant sex and strain differences for these rhythms. Extreme differences in period for molecular and behavioral rhythms were found between the inbred A/J strain and the wild-derived CAST/EiJ strain, where A/J had the longest period and CAST/EiJ had the shortest. In addition, we measured cellular rhythms in 329 DO mice, which displayed far greater phenotypic variability than the founders—80% of founders compared to only 25% of DO mice had periods of ~ 24 h. Collectively, our findings demonstrate that genetic diversity contributes to phenotypic variability in circadian rhythms, and high-throughput characterization of fibroblast rhythms in DO mice is a tractable system for examining the genetics of circadian traits.

Oligostilbenes extracts from Iris lactea Pall. var. chinensis (Fisch.) Koidz improve lipid metabolism in HFD/STZ-induced diabetic mice and inhibit adipogenesis in 3T3-L1 cells

The present study investigated the anti-diabetic effects of Oligostilbenes extracts (Olie) from Iris lactea Pall. var. chinensis (Fisch.) Koidz (I. lactea) and the potential mechanisms, in high-fat-diet (HFD)-induced diabetic mice and 3T3-L1 adipocytes. Olie are a group of major active extracts from I. lactea that have been used as nutraceutical because of their antioxidant activity. Six-week Olie treatment improved fasting blood glucose levels, as well as blood lipid profiles in HFD/streptozocin (STZ)-induced diabetic mice, compared with non-treated mice. Olie treatment upregulated the levels of phosphorylated of AMPK and lipolysis-related proteins, while the hepatic expression of ACC and FAS in diabetic mice was inhibited. In cultured 3T3-L1 cells, Olie (2-15 μg/mL) treatment dose-dependently suppressed the differentiation into mature adipocytes and lowered cellular lipid accumulation. Consistently, Olie reduced expression of adipogenic transcription factors including CCAAT/enhancer-binding protein β (C/EBPβ) and peroxisome proliferator-activated receptor γ (PPARγ). In addition, mitochondrial function in 3T3-L1 adipocytes was improved after Olie treatment. Taken together, our findings indicate that a lipid-lowering effect of Olie in HFD/STZ-induced diabetic mice and adipogenesis/ lipogenesis suppressing effect in 3T3-L1 cells, via regulating the expression of lipid metabolism-related proteins.

Small Molecules Targeting Biological Clock; A Novel Prospective for Anti-Cancer Drugs

The circadian rhythms are an intrinsic timekeeping system that regulates numerous physiological, biochemical, and behavioral processes at intervals of approximately 24 h. By regulating such processes, the circadian rhythm allows organisms to anticipate and adapt to continuously changing environmental conditions. A growing body of evidence shows that disruptions to the circadian rhythm can lead to various disorders, including cancer. Recently, crucial knowledge has arisen regarding the essential features that underlie the overt circadian rhythm and its influence on physiological outputs. This knowledge suggests that specific small molecules can be utilized to control the circadian rhythm. It has been discovered that these small molecules can regulate circadian-clock-related disorders such as metabolic, cardiovascular, inflammatory, as well as cancer. This review examines the potential use of small molecules for developing new drugs, with emphasis placed on recent progress that has been made regarding the identification of small-molecule clock modulators and their potential use in treating cancer.

Therapeutics on the clock: Circadian medicine in the treatment of chronic inflammatory diseases

The circadian clock is a collection of endogenous oscillators with a periodicity of ~ 24 h. Recently, our understanding of circadian rhythms and their regulation at genomic and physiologic scales has grown significantly. Knowledge of the circadian influence on biological processes has provided new possibilities for novel pharmacological strategies. Directly targeting the biological clock or its downstream targets, and/or using timing as a variable in drug therapy are now important pharmacological considerations. The circadian machinery mediates many aspects of the inflammatory response and, reciprocally, an inflammatory environment can disrupt circadian rhythms. Therefore, intense interest exists in leveraging circadian biology as a means to treat chronic inflammatory diseases such as sepsis, asthma, rheumatoid arthritis, osteoarthritis, and cardiovascular disease, which all display some type of circadian signature. The purpose of this review is to evaluate the crosstalk between circadian rhythms, inflammatory diseases, and their pharmacological treatment. Evidence suggests that carefully rationalized application of chronotherapy strategies - alone or in combination with small molecule modulators of circadian clock components - can improve efficacy and reduce toxicity, thus warranting further investigation and use.

Circadian rhythm disorder: a potential inducer of vascular calcification?

Over the past decades, circadian rhythm has drawn a great attention in cardiovascular diseases. The expressions of rhythm genes fluctuate in accordance with the diurnal changes of vascular physiology, which highlights the pivotal effect of vascular clock. Recent researches show that the circadian clock can directly regulate the synthetic and secretory function of endothelial cells and phenotypic switch of vascular smooth muscle cells to adjust vascular relaxation and contraction. Importantly, dysfunction of vascular cells is involved in vascular calcification. Secretion of osteogenic cytokines and calcified vesicles in the vessel, osteogenic phenotype switch of vascular smooth muscle cells are all implicated in the calcification process. Moreover, circadian rhythm disorder can lead to abnormal hormone secretion, oxidative stress, inflammatory reaction, and autophagy, all of which should not be ignored in vascular calcification. Vascular senescence is another pathogenetic mechanism in vascular calcification. Accelerated vascular senescence may act as an important intermediate factor to promote vascular calcification in circadian rhythm disorders. In this review, we elaborate the potential effect of circadian rhythm disorder in vascular calcification and try to provide a new direction in the prevention of vascular calcification.

Therapeutic implications of circadian clocks in neurodegenerative diseases

Circadian clocks, endogenous oscillators generating daily biological rhythms, have important roles in the nervous system to control diverse cellular processes-not only in the suprachiasmatic nucleus (SCN), where the master clocks reside to synchronize all circadian clocks in the body but also in other non-SCN areas. Accumulating evidence has shown relationships between circadian abnormalities (e.g., sleep disturbances and abnormal rest-activity rhythms) and disease progressions in various neurodegenerative diseases, including Alzheimer's (AD) and Parkinson's (PD) disease. Although circadian abnormalities were frequently considered as consequences of disease onsets, recent studies suggest altered circadian clocks as risk factors to develop neurodegenerative diseases via altered production or clearance rates of toxic metabolites like amyloid β. In this review, we will summarize circadian clock-related pathologies in the most common neurodegenerative diseases in the central nervous system, AD and PD. Then, we will introduce the current clinical trials to rescue circadian abnormalities in AD and PD patients. Finally, a discussion about how to improve targeting circadian clocks to increase treatment efficiencies and specificities will be followed. This discussion will provide insight into circadian clocks as potential therapeutic targets to attenuate onsets and progressions of neurodegenerative diseases.

Chemical perturbations reveal that RUVBL2 regulates the circadian phase in mammals

Transcriptional regulation lies at the core of the circadian clockwork, but how the clock-related transcription machinery controls the circadian phase is not understood. Here, we show both in human cells and in mice that RuvB-like ATPase 2 (RUVBL2) interacts with other known clock proteins on chromatin to regulate the circadian phase. Pharmacological perturbation of RUVBL2 with the adenosine analog compound cordycepin resulted in a rapid-onset 12-hour clock phase-shift phenotype at human cell, mouse tissue, and whole-animal live imaging levels. Using simple peripheral injection treatment, we found that cordycepin penetrated the blood-brain barrier and caused rapid entrainment of the circadian phase, facilitating reduced duration of recovery in a mouse jet-lag model. We solved a crystal structure for human RUVBL2 in complex with a physiological metabolite of cordycepin, and biochemical assays showed that cordycepin treatment caused disassembly of an interaction between RUVBL2 and the core clock component BMAL1. Moreover, we showed with spike-in ChIP-seq analysis and binding assays that cordycepin treatment caused disassembly of the circadian super-complex, which normally resides at E-box chromatin loci such as PER1, PER2, DBP, and NR1D1. Mathematical modeling supported that the observed type 0 phase shifts resulted from derepression of E-box clock gene transcription.

Circadian Rhythms in the Pathogenesis and Treatment of Fatty Liver Disease

Circadian clock proteins are endogenous timing mechanisms that control the transcription of hundreds of genes. Their integral role in coordinating metabolism has led to their scrutiny in a number of diseases, including nonalcoholic fatty liver disease (NAFLD). Discoordination between central and peripheral circadian rhythms is a core feature of nearly every genetic, dietary, or environmental model of metabolic syndrome and NAFLD. Restricting feeding to a defined daily interval (time-restricted feeding) can synchronize the central and peripheral circadian rhythms, which in turn can prevent or even treat the metabolic syndrome and hepatic steatosis. Importantly, a number of proteins currently under study as drug targets in NAFLD (sterol regulatory element-binding protein [SREBP], acetyl-CoA carboxylase [ACC], peroxisome proliferator-activator receptors [PPARs], and incretins) are modulated by circadian proteins. Thus, the clock can be used to maximize the benefits and minimize the adverse effects of pharmaceutical agents for NAFLD. The circadian clock itself has the potential for use as a target for the treatment of NAFLD.

Chemical modulation of circadian rhythms and assessment of cellular behavior via indirubin and derivatives

Circadian rhythms are critical regulators of many physiological and behavioral functions. The use and abilities of small molecules to affect oscillations have recently received significant attention. These manipulations can be reversible and tunable, and have been used to study various biological mechanisms and molecular properties. Here, we outline procedures for assessment of cellular circadian changes following treatment with small molecules, using luminescent reporters. We describe reporter generation, luminometry experiments, and data analysis. Protocols for studies of accompanying effects on cells, including motility, viability, and anchorage-independent proliferation assays are also presented. As examples, we use indirubin-3'-oxime and two derivatives, 5-iodo-indirubin-3'-oxime and 5-sulfonic acid-indirubin-3'-oxime. In this case study, we analyze effects of these compounds on Bmal1 and Per2 (positive and negative core circadian elements) oscillations and provide step-by-step protocols for data analysis, including removal of trends from raw data, period estimations, and statistical analysis. The reader is provided with detailed protocols, and guidance regarding selection of and alternative approaches.

Therapeutic effects of hydro-alcoholic leaf extract of Withania somnifera on age-induced changes in daily rhythms of Sirt1, Nrf2 and Rev-erbα in the SCN of male Wistar rats

The temporal expression pattern of the circadian clock genes are known to be altered/attenuated with advance in age. Withania somnifera (WS) essentially consists of numerous active constituents including withanolides is known to have antioxidant, anti-inflammatory and adaptogenic properties. We have earlier demonstrated therapeutic effects of hydro-alcoholic leaf extract of WS on the age-induced alterations in the levels and daily rhythms of various clock genes such as rBmal1, rPer1, rPer2 and rCry1. We have now studied effects of hydro-alcoholic leaf extract of WS on the age-induced alterations in the levels and daily rhythms of expression of SIRT1 (an NAD⁺ dependent histone deacetylase and a modulator of clock) and NRF2 (a clock controlled gene and a master transcription factor regulating various endogenous antioxidant enzymes) in addition to rRev-erbα in SCN of adult [3 months (m)], middle-aged (12 m) and old-aged (24 m) male Wistar rats. The daily rhythms of rNrf2 expression showed 6 h phase delay in middle age and 12 h phase advance in old age. WS restored rSirt1 daily rhythms and phase in old age whereas it restored the phase of rNrf2 in the SCN of both middle and old aged animals. At protein level, SIRT1 expression showed phase advances in 12 m and 24 m whereas NRF2 daily rhythms were abolished in both the age groups. WS restored the phase and daily rhythms of SIRT1 as well as NRF2 in 12 m old rats. However, rRev-erbα expression was found insensitive to WS treatment in all the age groups studied. Pairwise correlation analysis demonstrated significant stoichiometric interactions among rSirt1, rNrf2 and rRev-erbα in 3 m which altered with aging significantly. WS treatment resulted in differential restorations of such interactions.

Circadian-Hypoxia Link and its Potential for Treatment of Cardiovascular Disease

Throughout the evolutionary time, all organisms and species on Earth evolved with an adaptation to consistent oscillations of sunlight and darkness, now recognized as 'circadian rhythm.' Single-cellular to multisystem organisms use circadian biology to synchronize to the external environment and provide predictive adaptation to changes in cellular homeostasis. Dysregulation of circadian biology has been implicated in numerous prevalent human diseases, and subsequently targeting the circadian machinery may provide innovative preventative or treatment strategies. Discovery of 'peripheral circadian clocks' unleashed widespread investigations into the potential roles of clock biology in cellular, tissue, and organ function in healthy and diseased states. Particularly, oxygen-sensing pathways (e.g. hypoxia inducible factor, HIF1), are critical for adaptation to changes in oxygen availability in diseases such as myocardial ischemia. Recent investigations have identified a connection between the circadian rhythm protein Period 2 (PER2) and HIF1A that may elucidate an evolutionarily conserved cellular network that can be targeted to manipulate metabolic function in stressed conditions like hypoxia or ischemia. Understanding the link between circadian and hypoxia pathways may provide insights and subsequent innovative therapeutic strategies for patients with myocardial ischemia. This review addresses our current understanding of the connection between light-sensing pathways (PER2), and oxygen-sensing pathways (HIF1A), in the context of myocardial ischemia and lays the groundwork for future studies to take advantage of these two evolutionarily conserved pathways in the treatment of myocardial ischemia.

A CLOCK-binding small molecule disrupts the interaction between CLOCK and BMAL1 and enhances circadian rhythm amplitude

Proper function of many physiological processes requires a robust circadian clock. Disruptions of the circadian clock can result in metabolic diseases, mood disorders, and accelerated aging. Therefore, identifying small molecules that specifically modulate regulatory core clock proteins may potentially enable better management of these disorders. In this study, we applied a structure-based molecular-docking approach to find small molecules that specifically bind to the core circadian regulator, the transcription factor circadian locomotor output cycles kaput (CLOCK). We identified 100 candidate molecules by virtual screening of ∼2 million small molecules for those predicted to bind closely to the interface in CLOCK that interacts with its transcriptional co-regulator, Brain and muscle Arnt-like protein-1 (BMAL1). Using a mammalian two-hybrid system, real-time monitoring of circadian rhythm in U2OS cells, and various biochemical assays, we tested these compounds experimentally and found one, named CLK8, that specifically bound to and interfered with CLOCK activity. We show that CLK8 disrupts the interaction between CLOCK and BMAL1 and interferes with nuclear translocation of CLOCK both in vivo and in vitro Results from further experiments indicated that CLK8 enhances the amplitude of the cellular circadian rhythm by stabilizing the negative arm of the transcription/translation feedback loop without affecting period length. Our results reveal CLK8 as a tool for further studies of CLOCK's role in circadian rhythm amplitude regulation and as a potential candidate for therapeutic development to manage disorders associated with dampened circadian rhythms.

Circadian rhythms and the molecular clock in cardiovascular biology and disease

The Earth turns on its axis every 24 h; almost all life on the planet has a mechanism - circadian rhythmicity - to anticipate the daily changes caused by this rotation. The molecular clocks that control circadian rhythms are being revealed as important regulators of physiology and disease. In humans, circadian rhythms have been studied extensively in the cardiovascular system. Many cardiovascular functions, such as endothelial function, thrombus formation, blood pressure and heart rate, are now known to be regulated by the circadian clock. Additionally, the onset of acute myocardial infarction, stroke, arrhythmias and other adverse cardiovascular events show circadian rhythmicity. In this Review, we summarize the role of the circadian clock in all major cardiovascular cell types and organs. Second, we discuss the role of circadian rhythms in cardiovascular physiology and disease. Finally, we postulate how circadian rhythms can serve as a therapeutic target by exploiting or altering molecular time to improve existing therapies and develop novel ones.

Resetting the Aging Clock: Implications for Managing Age-Related Diseases

Worldwide, individuals are living longer due to medical and scientific advances, increased availability of medical care and changes in public health policies. Consequently, increasing attention has been focused on managing chronic conditions and age-related diseases to ensure healthy aging. The endogenous circadian system regulates molecular, physiological and behavioral rhythms orchestrating functional coordination and processes across tissues and organs. Circadian disruption or desynchronization of circadian oscillators increases disease risk and appears to accelerate aging. Reciprocally, aging weakens circadian function aggravating age-related diseases and pathologies. In this review, we summarize the molecular composition and structural organization of the circadian system in mammals and humans, and evaluate the technological and societal factors contributing to the increasing incidence of circadian disorders. Furthermore, we discuss the adverse effects of circadian dysfunction on aging and longevity and the bidirectional interactions through which aging affects circadian function using examples from mammalian research models and humans. Additionally, we review promising methods for managing healthy aging through behavioral and pharmacological reinforcement of the circadian system. Understanding age-related changes in the circadian clock and minimizing circadian dysfunction may be crucial components to promote healthy aging.

At the Interface of Lifestyle, Behavior, and Circadian Rhythms: Metabolic Implications

Nutrient metabolism is under circadian regulation. Disruption of circadian rhythms by lifestyle and behavioral choices such as work schedules, eating patterns, and social jetlag, seriously impacts metabolic homeostasis. Metabolic dysfunction due to chronic misalignment of an organism's endogenous rhythms is detrimental to health, increasing the risk of obesity, metabolic and cardiovascular disease, diabetes, and cancer. In this paper, we review literature on recent findings on the mechanisms that communicate metabolic signals to circadian clocks and vice versa, and how human behavioral changes imposed by societal and occupational demands affect the physiological networks integrating peripheral clocks and metabolism. Finally, we discuss factors possibly contributing to inter-individual variability in response to circadian changes in the context of metabolic (dys)function.

The circadian clock and liver function in health and disease

Each day, all organisms are subjected to changes in light intensity because of the Earth's rotation around its own axis. To anticipate this geo-physical variability, and to appropriately respond biochemically, most species, including mammals, have evolved an approximate 24-hour endogenous timing mechanism known as the circadian clock (CC). The 'clock' is self-sustained, cell autonomous and present in every cell type. At the core of the clock resides the CC-oscillator, an exquisitely crafted transcriptional-translational feedback system. Remarkably, components of the CC-oscillator not only maintain daily rhythmicity of their own synthesis, but also generate temporal variability in the expression levels of numerous target genes through transcriptional, post-transcriptional and post-translational mechanisms, thus, ensuring proper chronological coordination in the functioning of cells, tissues and organs, including the liver. Indeed, a variety of physiologically critical hepatic functions and cellular processes are CC-controlled. Thus, it is not surprising that modern lifestyle factors (e.g. travel and jet lag, night and rotating shift work), which force 'circadian misalignment', have emerged as major contributors to global health problems including obesity, non-alcoholic fatty liver disease and steatohepatitis. Herein, we provide an overview of the CC-dependent pathways which play critical roles in mediating several hepatic functions under physiological conditions, and whose deregulation is implicated in chronic liver diseases including non-alcoholic steatohepatitis and alcohol-related liver disease.

Female ClockΔ19/Δ19 mice are protected from the development of age-dependent cardiomyopathy

Aims

Circadian rhythms are important for healthy cardiovascular physiology and they are regulated by the molecular circadian mechanism. Previously, we showed that disruption of the circadian mechanism factor CLOCK in male ClockΔ19/Δ19 mice led to development of age-dependent cardiomyopathy. Here, we investigate the role of biological sex in protecting against heart disease in aging female ClockΔ19/Δ19 mice.

Methods and results

Female ClockΔ19/Δ19 mice are protected from the development of cardiomyopathy with age, as heart structure and function are similar to 18 months of age vs. female WT mice. We show that female ClockΔ19/Δ19 mice maintain normal glucose tolerance as compared with female WT. Tissue metabolic profiling revealed that aging female ClockΔ19/Δ19 mice maintain normal cardiac glucose uptake, whereas the male ClockΔ19/Δ19 mice have increased cardiac glucose uptake consistent with pathological remodelling. Shotgun lipidomics revealed differences in phospholipids that were sex and genotype specific, including cardiolipin CL76:11 that was increased and CL72:8 that was decreased in male ClockΔ19/Δ19 mice. Additionally, female ClockΔ19/Δ19 mice show increased activation of AKT signalling and preserved cytochrome c oxidase activity compared with male ClockΔ19/Δ19 mice, which can help to explain why they are protected from heart disease. To determine how this protection occurs in females even with the Clock mutation, we examined the effects of ovarian hormones. We show that ovarian hormones protect female ClockΔ19/Δ19 mice from heart disease as ovariectomized female ClockΔ19/Δ19 mice develop cardiac dilation, glucose intolerance and reduced cardiac cytochrome c oxidase; this phenotype is consistent with the age-dependent decline observed in male ClockΔ19/Δ19 mice.

Conclusions

These data demonstrate that ovarian hormones protect female ClockΔ19/Δ19 mice from the development of age-dependent cardiomyopathy even though Clock function is disturbed. Understanding the interaction of biological sex and the circadian mechanism in cardiac growth, renewal and remodelling opens new doors for understanding and treating heart disease.

Sleep and circadian rhythm disruption and stress intersect in Alzheimer's disease

Alzheimer's disease (AD) was discovered and the pathological hallmarks were revealed more than a century ago. Subsequently, many remarkable discoveries and breakthroughs provided us with mechanistic insights into the pathogenesis of AD. The identification of the molecular underpinning of the disease not only provided the framework of AD pathogenesis but also targets for therapeutic inventions. Despite all the initial successes, no effective treatment for AD has emerged yet as all the late stages of clinical trials have failed. Many factors ranging from genetic to environmental factors have been critically appraised as the potential causes of AD. In particular, the role of stress on AD has been intensively studied while the relationship between sleep and circadian rhythm disruption (SCRD) and AD have recently emerged. SCRD has always been thought to be a corollary of AD pathologies until recently, multiple lines of evidence converge on the notion that SCRD might be a contributing factor in AD pathogenesis. More importantly, how stress and SCRD intersect and make their concerted contributions to AD phenotypes has not been reviewed. The goal of this literature review is to examine at multiple levels - molecular, cellular (e.g. microglia, gut microbiota) and holistic - how the interaction between stress and SCRD bi-directionally and synergistically exacerbate AD pathologies and cognitive impairment. AD, in turn, worsens stress and SCRD and forms the vicious cycle that perpetuates and amplifies AD.

Emerging relevance of circadian rhythms in headaches and neuropathic pain

Circadian rhythms of physiology are the keys to health and fitness, as dysregulation, by genetic mutations or environmental factors, increases disease risk and aggravates progression. Molecular and physiological studies have shed important light on an intrinsic clock that drives circadian rhythms and serves essential roles in metabolic homoeostasis, organ physiology and brain functions. One exciting new area in circadian research is pain, including headache and neuropathic pain for which new mechanistic insights have recently emerged. For example, cluster headache is an intermittent pain disorder with an exceedingly precise circadian timing, and preliminary evidence is emerging linking several circadian components (eg, Clock and Nr1d1) with the disease. In this review, we first discuss the broad metabolic and physiological relevance of the circadian timing system. We then provide a detailed review of the circadian relevance in pain disease and physiology, including cluster headache, migraine, hypnic headache and neuropathic pain. Finally, we describe potential therapeutic implications, including existing pain medicines and novel clock-modulating compounds. The physiological basis for the circadian rhythms in pain is an exciting new area of research with profound basic and translational impact.

Genome-Wide Association Study of Circadian Behavior in Drosophila melanogaster

Circadian rhythms influence physiological processes from sleep–wake cycles to body temperature and are controlled by highly conserved cycling molecules. Although the mechanistic basis of the circadian clock has been known for decades, the extent to which circadian rhythms vary in nature and the underlying genetic basis for that variation is not well understood. We measured circadian period (Ʈ) and rhythmicity index in the Drosophila Genetic Reference Panel (DGRP) and observed extensive genetic variation in both. Seven DGRP lines had sexually dimorphic arrhythmicity and one line had an exceptionally long Ʈ. Genome-wide analyses identified 584 polymorphisms in 268 genes. We observed differences among transcripts for nine genes predicted to interact among themselves and canonical clock genes in the long period line and a control. Mutations/RNAi knockdown targeting these genes also affected circadian behavior. Our observations reveal that complex genetic interactions influence high levels of variation in circadian phenotypes.

EGCG stimulates the recruitment of brite adipocytes, suppresses adipogenesis and counteracts TNF-α-triggered insulin resistance in adipocytes

The global rise in obesity and type 2 diabetes has precipitated the need for therapeutic intervention in the arsenal against adiposity. (-)-Epigallocatechin-3-gallate (EGCG), a major nutraceutical component of green tea, has been regarded as a nutraceutical that has powerful antioxidant and anti-obesity bioactivities. In the present study, we showed that EGCG alleviates intracellular lipid accumulation markedly, and the inhibitory effect was largely limited to the early stage of adipocyte differentiation. Consistently, EGCG notably evoked the phosphorylation of AMPK and ACC and blunted the key enzymes of de novo lipogenesis. Interestingly, EGCG elicited iWAT-preadipocyte-derived mature white adipocyte beiging via activating thermogenic gene Ucp1 expression and mitochondrial biogenesis. Furthermore, our results also revealed that EGCG attenuated insulin signaling pathway blockage induced by TNF-α through the abrogation of redox imbalance and mitochondrial dysfunction. These findings indicate that EGCG is capable of suppressing adipogenesis and evoking white adipocyte beiging and therefore it may potentially serve as a novel approach to combat obesity.

The cryptochrome inhibitor KS15 enhances E-box-mediated transcription by disrupting the feedback action of a circadian transcription-repressor complex

AIMS

We have previously identified a chemical scaffold possessing 2-ethoxypropanoic acid (designated as KS15) that directly binds to the C-terminal region of cryptochromes (CRYs: CRY1 and CRY2) and enhances E-box-mediated transcription. However, it is still unclear how KS15 impairs the feedback actions of the CRYs and which chemical moieties are functionally important for its actions.

MAIN METHODS

The E-box-mediated transcriptional activities were mainly used to examine the effects of KS15 and its derivatives. Co-immunoprecipitation assays accompanied by immunoblotting were employed to monitor protein-protein associations. We also examined the effects of KS15 and selected derivatives on circadian molecular rhythms in cultured cells.

KEY FINDINGS

The present study shows that KS15 inhibits the interaction between CRYs and Brain-Muscle-Arnt-Like protein 1 (BMAL1), thereby impairing the feedback actions of CRYs on E-box-dependent transcription by CLOCK:BMAL1 heterodimer, an indispensable transcriptional regulator of the mammalian circadian clock. Subsequent structure-activity relationship analyses using a well-designed panel of derivatives identified the structural requirements for the effects of KS15 on CRY-evoked regulation of E-box-mediated transcription. We found that KS15 and several derivatives significantly reduce the amplitude and delayed the phase of molecular circadian rhythms in fibroblast cultures.

SIGNIFICANCE

Taken together, our results provide valuable information on the molecular mode-of-action as well as the chemical components of the CRYs inhibitor that pharmacologically impact on the transcriptional activity of the CLOCK:BMAL1 heterodimer.