Rev-erbα and the circadian transcriptional regulation of metabolism

Development of radioligand binding assays for REV-ERBα and REV-ERBβ

REV-ERBα and REV-ERBβ are atypical nuclear receptors that function as ligand-dependent repressors of transcription. They play critical roles in the regulation of the circadian rhythm, inflammation, and metabolism. The natural ligand for the REV-ERBs is heme, and synthetic ligands (both agonists and antagonists) have been designed and utilized to probe the potential clinical utility of targeting REV-ERBs for drug development. Although biochemical assays that can detect REV-ERB ligands have been developed based on protein-protein interactions, no classical fluorescent- or radioligand-binding assay has yet been developed that directly detects ligand binding. Here, we describe the development of the first radioligand binding assay (RLBA) using scintillation proximity assay (SPA) technology for both REV-ERBα and REV-ERBβ using labeled STL1267, a potent REV-ERBα/β agonist we recently described. 3H-STL1267 displayed saturable binding to the ligand binding domains of both REV-ERBα and REV-ERBβ with equilibrium dissociation constants (Kds) of 392 nM and 202 nM, respectively. In competition radioligand binding assays, we used unlabeled STL1267 or the well-characterized first-generation REV-ERB agonist SR9009 as competitors to 3H-STL1267 binding. STL1267 displayed Kis for REV-ERBα and REV-ERBβ of 253 ± 30 nM and 98 ± 14 nM, respectively. As expected, SR9009 displayed considerably lower potency than STL1267, with a Ki of 692 ± 209 nM for REV-ERBα and 2546 ± 127 nM for REV-ERBβ. Although developing an RLBA has been challenging due to the lack of high-affinity ligands that can be used as probes, our results demonstrate the feasibility of such an assay for both receptors, providing a robust assay with utility for ligand/drug discovery.

The intricate relationship between circadian rhythms and gastrointestinal peptides in obesity

There are different molecular pathways that regulate appetite, particularly the role of the hypothalamus, circadian rhythms, and gastrointestinal peptides. The hypothalamus integrates signals from orexigenic peptides like neuropeptide Y (NPY) and agouti-related protein (AgRP), which stimulate appetite, and anorexigenic peptides such as pro-opiomelanocortin (POMC) and cocaine- and amphetamine-regulated transcript (CART), which promote satiety. These signals are influenced by peripheral hormones like leptin, ghrelin, insulin, and cortisol, as well as gut peptides including glucagon-like peptide-1 (GLP-1), peptide YY (PYY), and cholecystokinin (CCK). The circadian rhythm, regulated by proteins like circadian locomotor output cycles kaput (CLOCK) and brain and muscle ARNT-like 1 (BMAL1), modulates the secretion of these peptides, aligning feeding behaviors with the sleep-wake cycle. In obesity, these regulatory systems are disrupted, leading to leptin resistance, increased ghrelin sensitivity, and altered gut peptide secretion. This results in heightened appetite and impaired satiety, contributing to overeating and metabolic dysfunction. Additionally, circadian disruptions further impair metabolic processes, exacerbating obesity. The present article underscores the importance of understanding the molecular interplay between circadian rhythms and gastrointestinal peptides, particularly in the context of obesity. While some molecular interactions, such as the regulation of GLP-1 and PYY by reverberation of circadian rhythm α (REV-ERBα) and retinoic acid-related orphan receptor α (RORα), are well-established, clinical studies are scarce. Future research is expected to explore these pathways in obesity management, especially with the rise of incretin-based treatments like semaglutide. A deeper understanding of hypothalamic molecular mechanisms could lead to novel pharmacological and non-pharmacological therapies for obesity.

Light Exposure, Physical Activity, and Indigeneity Modulate Seasonal Variation in NR1D1 (REV-ERBα) Expression

Nuclear receptor subfamily 1 group D member 1 (NR1D1 or REV-ERBα) is a crucial element of the circadian clock's transcriptional and translational feedback loop. Understanding its expression in humans is critical for elucidating its role in circadian rhythms and metabolic processes, and in finding potential links to various pathologies. In a longitudinal survey, we examined REV-ERBα expression at 08:00 using a real-time polymerase chain reaction (qRT-PCR) in blood mononuclear cells from Arctic native and non-native residents during equinoxes and solstices. REV-ERBα expression exhibited a pronounced seasonality, peaking at the summer solstice, and reaching a nadir at the winter solstice in both natives and non-natives, with a relatively higher summer peak in natives. After adjusting for age, sex, and body mass index, the amount and timing of light exposure, the amount of physical activity, and indigeneity emerged as significant predictors of REV-ERBα expression.

Grape Seed Proanthocyanidin Extract Attenuates Cafeteria-Diet-Induced Liver Metabolic Disturbances in Rats: Influence of Photoperiod

This study investigated the influence of photoperiod (day length) on the efficacy of grape seed proanthocyanidin extract (GSPE) in mitigating metabolic disorders in obese rats fed a cafeteria diet. Rats were exposed to standard (L12), long (L18), or short (L6) photoperiods and treated with GSPE or vehicle. In the standard photoperiod, GSPE reduced body weight gain (50.5%), total cholesterol (37%), and triglycerides (34.8%), while increasing the expression of hepatic metabolic genes. In the long photoperiod, GSPE tended to decrease body weight gain, increased testosterone levels (68.3%), decreased liver weight (12.4%), and decreased reverse serum amino acids. In the short photoperiod, GSPE reduced glycemia (~10%) and lowered triglyceride levels (38.5%), with effects modified by diet. The standard photoperiod showed the greatest efficacy against metabolic syndrome-associated diseases. The study showed how day length affects GSPE's benefits and underscores considering biological rhythms in metabolic disease therapies.

Differential Expression of Circadian Clock Genes in the Bovine Neuroendocrine Adrenal System

Knowledge of circadian rhythm clock gene expression outside the suprachiasmatic nucleus is increasing. The purpose of this study was to determine whether expression of circadian clock genes differed within or among the bovine stress axis tissues (e.g., amygdala, hypothalamus, pituitary, adrenal cortex, and adrenal medulla). Tissues were obtained at an abattoir from eight mature nonpregnant Brahman cows that had been maintained in the same pasture and nutritional conditions. Sample tissues were stored in RNase-free sterile cryovials at -80 °C until the total RNA was extracted, quantified, assessed, and sequenced (NovaSeq 6000 system; paired-end 150 bp cycles). The trimmed reads were then mapped to a Bos taurus (B. taurus) reference genome (Umd3.1). Further analysis used the edgeR package. Raw gene count tables were read into RStudio, and low-expression genes were filtered out using the criteria of three minimum reads per gene in at least five samples. Normalization factors were then calculated using the trimmed mean of M values method to produce normalized gene counts within each sample tissue. The normalized gene counts important for a circadian rhythm were analyzed within and between each tissue of the stress axis using the GLM and CORR procedures of the Statistical Analysis System (SAS). The relative expression profiles of circadian clock genes differed (p < 0.01) within each tissue, with neuronal PAS domain protein 2 (NPAS2) having greater expression in the amygdala (p < 0.01) and period circadian regulator (PER1) having greater expression in all other tissues (p < 0.01). The expression among tissues also differed (p < 0.01) for individual circadian clock genes, with circadian locomotor output cycles protein kaput (CLOCK) expression being greater within the adrenal tissues and nuclear receptor subfamily 1 group D member 1 (NR1D1) expression being greater within the other tissues (p < 0.01). Overall, the results indicate that within each tissue, the various circadian clock genes were differentially expressed, in addition to being differentially expressed among the stress tissues of mature Brahman cows. Future use of these findings may assist in improving livestock husbandry and welfare by understanding interactions of the environment, stress responsiveness, and peripheral circadian rhythms.

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.

Nuclear Receptor NR1D1 Regulates Abdominal Aortic Aneurysm Development by Targeting the Mitochondrial Tricarboxylic Acid Cycle Enzyme Aconitase-2

BACKGROUND

Metabolic disorder increases the risk of abdominal aortic aneurysm (AAA). NRs (nuclear receptors) have been increasingly recognized as important regulators of cell metabolism. However, the role of NRs in AAA development remains largely unknown.

METHODS

We analyzed the expression profile of the NR superfamily in AAA tissues and identified NR1D1 (NR subfamily 1 group D member 1) as the most highly upregulated NR in AAA tissues. To examine the role of NR1D1 in AAA formation, we used vascular smooth muscle cell (VSMC)-specific, endothelial cell-specific, and myeloid cell-specific conditional Nr1d1 knockout mice in both AngII (angiotensin II)- and CaPO4-induced AAA models.

RESULTS

Nr1d1 gene expression exhibited the highest fold change among all 49 NRs in AAA tissues, and NR1D1 protein was upregulated in both human and murine VSMCs from AAA tissues. The knockout of Nr1d1 in VSMCs but not endothelial cells and myeloid cells inhibited AAA formation in both AngII- and CaPO4-induced AAA models. Mechanistic studies identified ACO2 (aconitase-2), a key enzyme of the mitochondrial tricarboxylic acid cycle, as a direct target trans-repressed by NR1D1 that mediated the regulatory effects of NR1D1 on mitochondrial metabolism. NR1D1 deficiency restored the ACO2 dysregulation and mitochondrial dysfunction at the early stage of AngII infusion before AAA formation. Supplementation with αKG (α-ketoglutarate, a downstream metabolite of ACO2) was beneficial in preventing and treating AAA in mice in a manner that required NR1D1 in VSMCs.

CONCLUSIONS

Our data define a previously unrecognized role of nuclear receptor NR1D1 in AAA pathogenesis and an undescribed NR1D1-ACO2 axis involved in regulating mitochondrial metabolism in VSMCs. It is important that our findings suggest αKG supplementation as an effective therapeutic approach for AAA treatment.

Role of Circadian Transcription Factor Rev-Erb in Metabolism and Tissue Fibrosis

Circadian rhythms significantly affect metabolism, and their disruption leads to cardiometabolic diseases and fibrosis. The clock repressor Rev-Erb is mainly expressed in the liver, heart, lung, adipose tissue, skeletal muscles, and brain, recognized as a master regulator of metabolism, mitochondrial biogenesis, inflammatory response, and fibrosis. Fibrosis is the response of the body to injuries and chronic inflammation with the accumulation of extracellular matrix in tissues. Activation of myofibroblasts is a key factor in the development of organ fibrosis, initiated by hormones, growth factors, inflammatory cytokines, and mechanical stress. This review summarizes the importance of Rev-Erb in ECM remodeling and tissue fibrosis. In the heart, Rev-Erb activation has been shown to alleviate hypertrophy and increase exercise capacity. In the lung, Rev-Erb agonist reduced pulmonary fibrosis by suppressing fibroblast differentiation. In the liver, Rev-Erb inhibited inflammation and fibrosis by diminishing NF-κB activity. In adipose tissue, Rev- Erb agonists reduced fat mass. In summary, the results of multiple studies in preclinical models demonstrate that Rev-Erb is an attractive target for positively influencing dysregulated metabolism, inflammation, and fibrosis, but more specific tools and studies would be needed to increase the information base for the therapeutic potential of these substances interfering with the molecular clock.

Excessive fat expenditure in cachexia is associated with dysregulated circadian rhythm: a review

Cachexia is a progressive metabolic disorder characterized by the excessive depletion of adipose tissue. This hypermetabolic condition has catastrophic impacts on the survival and quality of life for patients suffering from critical illness. However, efficient therapies to prevent adipose expenditure have not been discovered. It has been established that the circadian clock plays an important role in modulating fat metabolic processes. Recently, an increasing number of studies had provided evidence showing that disrupted circadian rhythm leads to insulin resistance and obesity; however, studies analyzing the relationship between circadian misalignment and adipose tissue expenditure in cachexia are scarce. In the present review, we cover the involvement of the circadian clocks in the regulation of adipogenesis, lipid metabolism and thermogenesis as well as inflammation in white and brown adipose tissue. According to the present review, we conclude that circadian clock disruption is associated with lipid metabolism imbalance and elevated adipose tissue inflammation. Moreover, under cachexia conditions, lipid synthesis and storage processes lost rhythm and decreased, while lipolysis and thermogenesis activities remained high for 24 h. Therefore, disordered circadian clock may be responsible for fat expenditure in cachexia by adversely influencing lipid synthesis/ storage/lipolysis/utilization. Further study needs to be performed to explore the direct interaction between circadian clock and fat expenditure in cachexia, it will likely provide potential efficient drugs for the treatment of fat expenditure in cachexia.

Inhibition of Rev-erbα ameliorates muscular dystrophy

Duchene muscular dystrophy leads to progressive muscle structural and functional decline due to chronic degenerative-regenerative cycles. Enhancing the regenerative capacity of dystrophic muscle provides potential therapeutic options. We previously demonstrated that the circadian clock repressor Rev-erbα inhibited myogenesis and Rev-erbα ablation enhanced muscle regeneration. Here we show that Rev-erbα deficiency in the dystrophin-deficient mdx mice promotes regenerative myogenic response to ameliorate muscle damage. Loss of Rev-erbα in mdx mice improved dystrophic pathology and muscle wasting. Rev-erbα-deficient dystrophic muscle exhibit augmented myogenic response, enhanced neo-myofiber formation and attenuated inflammatory response. In mdx myoblasts devoid of Rev-erbα, myogenic differentiation was augmented together with up-regulation of Wnt signaling and proliferative pathways, suggesting that loss of Rev-erbα inhibition of these processes contributed to the improvement in regenerative myogenesis. Collectively, our findings revealed that the loss of Rev-erbα function protects dystrophic muscle from injury by promoting myogenic repair, and inhibition of its activity may have therapeutic utilities for muscular dystrophy.

Pharmacological activation of REV-ERBα improves nonalcoholic steatohepatitis by regulating intestinal permeability

BACKGROUND AND OBJECTIVES

The gut-liver axis plays an important role in the pathogenesis of nonalcoholic steatohepatitis (NASH), and increased intestinal permeability causes transfer of endotoxin to the liver, which activates the immune response, ultimately leading to hepatic inflammation. Nuclear receptor Rev-erbα is a critical regulator of circadian rhythm, cellular metabolism, and inflammatory responses. However, the role and mechanism of Rev-erbα in gut barrier function and NASH remain unclear. In the present study, we investigated the involvement of Rev-erbα in the regulation of intestinal permeability and the treatment of NASH.

METHODS AND RESULTS

The expression of tight junction-related genes and Rev-erbs decreased in the jejunum, ileum and colon of mice with high cholesterol, high fat diet (CL)-induced NASH. Chromatin immunoprecipitation analysis indicated that REV-ERBα directly bound to the promoters of tight junction genes to regulate intestinal permeability. Pharmacological activation of REV-ERBα by SR9009 protected against lipopolysaccharide-induced increased intestinal permeability both in vitro and in vivo, and these effects were associated with the activation of autophagy and decreased apoptotic signaling of epithelial cells. In addition, the chronopharmacological effects of SR9009 were more potent at Zeitgeber time 0 (ZT0) than at ZT12, which was contrary to the rhythm of Rev-erbs in the gastrointestinal tract. The administration of SR9009 attenuated hepatic lipid accumulation, insulin resistance, inflammation, and fibrosis in mice with CL diet-induced NASH, which might be partly attributed to the enhancement of intestinal barrier function.

CONCLUSION

Chronopharmacological activation of REV-ERBα might be a potential strategy to treat intestinal barrier dysfunction-related disorders and NASH.

Nuclear Receptors in the Control of the NLRP3 Inflammasome Pathway

The innate immune system is the first line of defense specialized in the clearing of invaders whether foreign elements like microbes or self-elements that accumulate abnormally including cellular debris. Inflammasomes are master regulators of the innate immune system, especially in macrophages, and are key sensors involved in maintaining cellular health in response to cytolytic pathogens or stress signals. Inflammasomes are cytoplasmic complexes typically composed of a sensor molecule such as NOD-Like Receptors (NLRs), an adaptor protein including ASC and an effector protein such as caspase 1. Upon stimulation, inflammasome complex components associate to promote the cleavage of the pro-caspase 1 into active caspase-1 and the subsequent activation of pro-inflammatory cytokines including IL-18 and IL-1β. Deficiency or overactivation of such important sensors leads to critical diseases including Alzheimer diseases, chronic inflammatory diseases, cancers, acute liver diseases, and cardiometabolic diseases. Inflammasomes are tightly controlled by a two-step activation regulatory process consisting in a priming step, which activates the transcription of inflammasome components, and an activation step which leads to the inflammasome complex formation and the subsequent cleavage of pro-IL1 cytokines. Apart from the NF-κB pathway, nuclear receptors have recently been proposed as additional regulators of this pathway. This review will discuss the role of nuclear receptors in the control of the NLRP3 inflammasome and the putative beneficial effect of new modulators of inflammasomes in the treatment of inflammatory diseases including colitis, fulminant hepatitis, cardiac ischemia-reperfusion and brain diseases.

Nuclear receptor REVERBα is a state-dependent regulator of liver energy metabolism

The circadian clock protein REVERBα is proposed to be a key regulator of liver metabolism. We now show that REVERBα action is critically dependent on metabolic state. Using transgenic mouse models, we show that the true role of REVERBα is to buffer against aberrant responses to metabolic perturbation, rather than confer rhythmic regulation to programs of lipid synthesis and storage, as has been thought previously. Thus, in the case of liver metabolism, the clock does not so much drive rhythmic processes, as provide protection against mistimed feeding cues. Understanding how the clock is coupled to metabolism is critical for understanding metabolic disease and the impacts of circadian disruptors such as shift work and 24-h lifestyles.

The nuclear receptor REVERBα is a core component of the circadian clock and proposed to be a dominant regulator of hepatic lipid metabolism. Using antibody-independent ChIP-sequencing of REVERBα in mouse liver, we reveal a high-confidence cistrome and define direct target genes. REVERBα-binding sites are highly enriched for consensus RORE or RevDR2 motifs and overlap with corepressor complex binding. We find no evidence for transcription factor tethering and DNA-binding domain-independent action. Moreover, hepatocyte-specific deletion of Reverbα drives only modest physiological and transcriptional dysregulation, with derepressed target gene enrichment limited to circadian processes. Thus, contrary to previous reports, hepatic REVERBα does not repress lipogenesis under basal conditions. REVERBα control of a more extensive transcriptional program is only revealed under conditions of metabolic perturbation (including mistimed feeding, which is a feature of the global Reverbα^−/− mouse). Repressive action of REVERBα in the liver therefore serves to buffer against metabolic challenge, rather than drive basal rhythmicity in metabolic activity.

Circadian redox rhythms in the regulation of neuronal excitability

Oxidation-reduction reactions are essential to life as the core mechanisms of energy transfer. A large body of evidence in recent years presents an extensive and complex network of interactions between the circadian and cellular redox systems. Recent advances show that cellular redox state undergoes a ~24-h (circadian) oscillation in most tissues and is conserved across the domains of life. In nucleated cells, the metabolic oscillation is dependent upon the circadian transcription-translation machinery and, vice versa, redox-active proteins and cofactors feed back into the molecular oscillator. In the suprachiasmatic nucleus (SCN), a hypothalamic region of the brain specialized for circadian timekeeping, redox oscillation was found to modulate neuronal membrane excitability. The SCN redox environment is relatively reduced in daytime when neuronal activity is highest and relatively oxidized in nighttime when activity is at its lowest. There is evidence that the redox environment directly modulates SCN K⁺ channels, tightly coupling metabolic rhythms to neuronal activity. Application of reducing or oxidizing agents produces rapid changes in membrane excitability in a time-of-day-dependent manner. We propose that this reciprocal interaction may not be unique to the SCN. In this review, we consider the evidence for circadian redox oscillation and its interdependencies with established circadian timekeeping mechanisms. Furthermore, we will investigate the effects of redox on ion-channel gating dynamics and membrane excitability. The susceptibility of many different ion channels to modulation by changes in the redox environment suggests that circadian redox rhythms may play a role in the regulation of all excitable cells.

Seasonality, morningness-eveningness, and sleep in common non - communicable medical conditions and chronic diseases in a population

The seasonal pattern for mood and behaviour, the behavioural trait of morningness-eveningness, and sleep are interconnected features, that may serve as etiological factors in the development or exacerbation of medical conditions. Methods: The study was based on a random sample of inhabitants aged 25 to 74 years living in Finland. As part of the national FINRISK 2012 study participants were invited (n=9905) and asked whether the doctor had diagnosed or treated them during the past 12 months for chronic diseases. Results: A total of 6424 participants filled in the first set of questionnaires and 5826 attended the physical health status examination, after which the second set of questionnaires were filled. Regression models were built in which each condition was explained by the seasonal, diurnal and sleep features, after controlling for a range of background factors. Of the chronic diseases, depressive disorder was associated with longer total sleep duration (p<.0001) and poor sleep quality (p<.0001). Of the measurements for health status assessment, none associated with sleep features, but systolic blood pressure yielded significant (p<.0001) associations with both seasonal and diurnal features at large. Conclusion: Sleep quality was the most sensitive probe in yielding associations with chronic diseases in this population-based study. The seasonal variations in mood and social activity, and the ease in getting up and tiredness in the morning were the most sensitive probes in yielding associations with blood pressure and waist circumference. Assessment of sleep quality, seasonal and diurnal features provides thus added value for health surveys of the general population.

Interplay between Metabolism and Epigenetics: A Nuclear Adaptation to Environmental Changes

The physiological identity of every cell is maintained by highly specific transcriptional networks that establish a coherent molecular program that is in tune with nutritional conditions. The regulation of cell-specific transcriptional networks is accomplished by an epigenetic program via chromatin-modifying enzymes, whose activity is directly dependent on metabolites such as acetyl-coenzyme A, S-adenosylmethionine, and NAD+, among others. Therefore, these nuclear activities are directly influenced by the nutritional status of the cell. In addition to nutritional availability, this highly collaborative program between epigenetic dynamics and metabolism is further interconnected with other environmental cues provided by the day-night cycles imposed by circadian rhythms. Herein, we review molecular pathways and their metabolites associated with epigenetic adaptations modulated by histone- and DNA-modifying enzymes and their responsiveness to the environment in the context of health and disease.

The heme-regulatory motif of nuclear receptor Rev-erbβ is a key mediator of heme and redox signaling in circadian rhythm maintenance and metabolism

Rev-erbβ is a heme-responsive transcription factor that regulates genes involved in circadian rhythm maintenance and metabolism, effectively bridging these critical cellular processes. Heme binding to Rev-erbβ indirectly facilitates its interaction with the nuclear receptor co-repressor (NCoR1), resulting in repression of Rev-erbβ target genes. Fe³⁺-heme binds in a 6-coordinate complex with axial His and Cys ligands, the latter provided by a heme-regulatory motif (HRM). Rev-erbβ was thought to be a heme sensor based on a weak K_d value for the Rev-erbβ·heme complex of 2 μm determined with isothermal titration calorimetry. However, our group demonstrated with UV-visible difference titrations that the K_d value is in the low nanomolar range, and the Fe³⁺-heme off-rate is on the order of 10^-6 s^-1 making Rev-erbβ ineffective as a sensor of Fe³⁺-heme. In this study, we dissected the kinetics of heme binding to Rev-erbβ and provided a K_d for Fe³⁺-heme of ∼0.1 nm Loss of the HRM axial thiolate via redox processes, including oxidation to a disulfide with a neighboring cysteine or dissociation upon reduction of Fe³⁺- to Fe²⁺-heme, decreased binding affinity by >20-fold. Furthermore, as measured in a co-immunoprecipitation assay, substitution of the His or Cys heme ligands in Rev-erbβ was accompanied by a significant loss of NCoR1 binding. These results demonstrate the importance of the Rev-erbβ HRM in regulating interactions with heme and NCoR1 and advance our understanding of how signaling through HRMs affects the major cellular processes of circadian rhythm maintenance and metabolism.

Clock Regulation of Metabolites Reveals Coupling between Transcription and Metabolism

The intricate connection between the circadian clock and metabolism remains poorly understood. We used high temporal resolution metabolite profiling to explore clock regulation of mouse liver and cell-autonomous metabolism. In liver, ∼50% of metabolites were circadian, with enrichment of nucleotide, amino acid, and methylation pathways. In U2 OS cells, 28% were circadian, including amino acids and NAD biosynthesis metabolites. Eighteen metabolites oscillated in both systems and a subset of these in primary hepatocytes. These 18 metabolites were enriched in methylation and amino acid pathways. To assess clock dependence of these rhythms, we used genetic perturbation. BMAL1 knockdown diminished metabolite rhythms, while CRY1 or CRY2 perturbation generally shortened or lengthened rhythms, respectively. Surprisingly, CRY1 knockdown induced 8 hr rhythms in amino acid, methylation, and vitamin metabolites, decoupling metabolite from transcriptional rhythms, with potential impact on nutrient sensing in vivo. These results provide the first comprehensive views of circadian liver and cell-autonomous metabolism.

Emerging functional roles of nuclear receptors in breast cancer

Nuclear receptors (NRs) have been targets of intensive drug development for decades due to their roles as key regulators of multiple developmental, physiological and disease processes. In breast cancer, expression of the estrogen and progesterone receptor remains clinically important in predicting prognosis and determining therapeutic strategies. More recently, there is growing evidence supporting the involvement of multiple nuclear receptors other than the estrogen and progesterone receptors, in the regulation of various processes important to the initiation and progression of breast cancer. We review new insights into the mechanisms of action of NRs made possible by recent advances in genomic technologies and focus on the emerging functional roles of NRs in breast cancer biology, including their involvement in circadian regulation, metabolic reprogramming and breast cancer migration and metastasis.

Nutrient-sensing nuclear receptors PPARα and FXR control liver energy balance

The nuclear receptors PPARα (encoded by NR1C1) and farnesoid X receptor (FXR, encoded by NR1H4) are activated in the liver in the fasted and fed state, respectively. PPARα activation induces fatty acid oxidation, while FXR controls bile acid homeostasis, but both nuclear receptors also regulate numerous other metabolic pathways relevant to liver energy balance. Here we review evidence that they function coordinately to control key nutrient pathways, including fatty acid oxidation and gluconeogenesis in the fasted state and lipogenesis and glycolysis in the fed state. We have also recently reported that these receptors have mutually antagonistic impacts on autophagy, which is induced by PPARα but suppressed by FXR. Secretion of multiple blood proteins is a major drain on liver energy and nutrient resources, and we present preliminary evidence that the liver secretome may be directly suppressed by PPARα, but induced by FXR. Finally, previous studies demonstrated a striking deficiency in bile acid levels in malnourished mice that is consistent with results in malnourished children. We present evidence that hepatic targets of PPARα and FXR are dysregulated in chronic undernutrition. We conclude that PPARα and FXR function coordinately to integrate liver energy balance.

Regulation of Mammalian Physiology by Interconnected Circadian and Feeding Rhythms

Circadian clocks are endogenous timekeeping systems that adapt in an anticipatory fashion the physiology and behavior of most living organisms. In mammals, the master pacemaker resides in the suprachiasmatic nucleus and entrains peripheral clocks using a wide range of signals that differentially schedule physiology and gene expression in a tissue-specific manner. The peripheral clocks, such as those found in the liver, are particularly sensitive to rhythmic external cues like feeding behavior, which modulate the phase and amplitude of rhythmic gene expression. Consequently, the liver clock temporally tunes the expression of many genes involved in metabolism and physiology. However, the circadian modulation of cellular functions also relies on multiple layers of posttranscriptional and posttranslational regulation. Strikingly, these additional regulatory events may happen independently of any transcriptional oscillations, showing that complex regulatory networks ultimately drive circadian output functions. These rhythmic events also integrate feeding-related cues and adapt various metabolic processes to food availability schedules. The importance of such temporal regulation of metabolism is illustrated by metabolic dysfunctions and diseases resulting from circadian clock disruption or inappropriate feeding patterns. Therefore, the study of circadian clocks and rhythmic feeding behavior should be of interest to further advance our understanding of the prevention and therapy of metabolic diseases.

Molecular Targets for Small-Molecule Modulators of Circadian Clocks

BACKGROUND

Circadian clocks are endogenous timing systems that regulate various aspects of mammalian metabolism, physiology and behavior. Traditional chronotherapy refers to the administration of drugs in a defined circadian time window to achieve optimal pharmacokinetic and therapeutic efficacies. In recent years, substantial efforts have been dedicated to developing novel small-molecule modulators of circadian clocks.

METHODS

Here, we review the recent progress in the identification of molecular targets of small-molecule clock modulators and their efficacies in clock-related disorders. Specifically, we examine the clock components and regulatory factors as possible molecular targets of small molecules, and we review several key clock-related disorders as promising venues for testing the preventive/therapeutic efficacies of these small molecules. Finally, we also discuss circadian regulation of drug metabolism.

RESULTS

Small molecules can modulate the period, phase and/or amplitude of the circadian cycle. Core clock proteins, nuclear hormone receptors, and clock-related kinases and other epigenetic regulators are promising molecular targets for small molecules. Through these targets small molecules exert protective effects against clock-related disorders including the metabolic syndrome, immune disorders, sleep disorders and cancer. Small molecules can also modulate circadian drug metabolism and response to existing therapeutics.

CONCLUSION

Small-molecule clock modulators target clock components or diverse cellular pathways that functionally impinge upon the clock. Target identification of new small-molecule modulators will deepen our understanding of key regulatory nodes in the circadian network. Studies of clock modulators will facilitate their therapeutic applications, alone or in combination, for clock-related diseases.

Targeting Time in Metabolic Therapeutics

One of the most predictable aspects of conscious life is the daily sleep-wake cycle, which is programmed by an internal clock that exerts broad effects on behavior and physiology. Studies of He et al. (2016) identify a small molecule clock modulator that improves metabolism, revealing that enhancing circadian function benefits health.

Evolving roles of circadian rhythms in liver homeostasis and pathology

Circadian clock in mammals is determined by a core oscillator in the suprachiasmatic nucleus (SCN) of the hypothalamus and synchronized peripheral clocks in other tissues. The coherent timing systems could sustain robust output of circadian rhythms in response to the entrainment controlled environmentally. Disparate approaches have discovered that clock genes and clock-controlled genes (CCGs) exist in nearly all mammalian cell types and are essential for establishing the mechanisms and complexity of internal time-keeping systems. Accumulating evidence demonstrates that the control of homeostasis and pathology in the liver involves intricate loops of transcriptional and post-translational regulation of clock genes expression. This review will focus on the recent advances with great importance concerning clock rhythms linking liver homeostasis and diseases. We particularly highlight what is currently known of the evolving insights into the mechanisms underlying circadian clock . Eventually , findings during recent years in the field might prompt new circadian-related chronotherapeutic strategies for the diagnosis and treatment of liver diseases by coupling these processes.

Clinical management of sleep disturbances in Alzheimer's disease: current and emerging strategies

Sleep and circadian disorders in Alzheimer's disease (AD) are more frequent than in the general population and appear early in the course of the disease. Quality of sleep and quality of life are parallel in these patients, and such disorders also represent a heavy burden for caregivers. Although alterations in melatonin and hypocretins (orexins) seem to play a key role in the origin of these disturbances, the etiology of these disorders is multifactorial, including many factors such as environment, behavior, treatments, and comorbidities, among others. A comprehensive evaluation of sleep in each patient is essential in the design of the treatment that includes nonpharmacological and pharmacological approaches. One particularly interesting point is the possibility of a role of sleep disorders in the pathogenesis of AD, raising the possibility that treating the sleep disorder may alter the course of the disease. In this review, we present an update on the role of sleep disorders in AD, the bidirectional influence of sleep problems and AD, and treatment options. Behavioral measures, bright light therapy (BLT), melatonin, and other drugs are likely well known and correctly managed by the physicians in charge of these patients. In spite of the multiple treatments used, evidence of efficacy is scarce and more randomized double-blind placebo-controlled studies are needed. Future directions for treatment are the establishment of BLT protocols and the development of drugs with new mechanisms of action, especially hypocretin receptor antagonists, melatonin receptor agonists, and molecules that modulate the circadian clock.