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The circadian rhythm is a widespread physiological phenomenon present in almost all forms of life and is constituted by a system of interlocked transcriptional/translational feedback loops (TTFLs). External zeitgebers regulate biological rhythms through the direct or indirect regulation of circadian genes. Oxidative stress is involved in many diseases and injuries, such as ageing, diabetes, Alzheimer's disease, and cancer. Despite an increasing number of studies on circadian rhythm disorders caused by oxidative stress, little is known about the effects of oxidants on clock gene expression and the underlying mechanism. In this study, we found that the protein expression of circadian genes Clock, Bmal1, Per1/2, and Cry1/2 in NIH3T3 cells was upregulated by hydrogen peroxide (H2O2), an important mediator of oxidative stress. In addition, H2O2 modulated the circadian rhythm of Bmal1-luciferase via RORα, REV-ERBα (NR1D1), and REV-ERBβ (NR1D2). Further studies showed that H2O2 regulated biological rhythm by PRX2-STAT3-REV-ERBα/β pathway. These findings provide an accessory loop-related mechanism by which non-transcriptional oscillation interplays with TTFLs.
The circadian clock regulates behavioural and physiological processes in a 24-h cycle. The nuclear receptors REV-ERBα and REV-ERBβ are involved in the cell-autonomous circadian transcriptional/translational feedback loops as transcriptional repressors. A number of studies have also demonstrated a pivotal role of REV-ERBs in regulation of metabolic, neuronal, and inflammatory functions including bile acid metabolism, lipid metabolism, and production of inflammatory cytokines. Given the multifunctional role of REV-ERBs, it is important to elucidate the mechanism through which REV-ERBs exert their functions. To this end, we established a Rev-erbα/Rev-erbβ double-knockout mouse embryonic stem (ES) cell model and analyzed the circadian clock and clock-controlled output gene expressions. A comprehensive mRNA-seq analysis revealed that the double knockout of both Rev-erbα and Rev-erbβ does not abrogate expression rhythms of E-box-regulated core clock genes but drastically changes a diverse set of other rhythmically-expressed output genes. Of note, REV-ERBα/β deficiency does not compromise circadian expression rhythms of PER2, while REV-ERB target genes, Bmal1 and Npas2, are significantly upregulated. This study highlight the relevance of REV-ERBs as pivotal output mediators of the mammalian circadian clock.
REV-ERBα is a nuclear heme receptor, transcriptional repressor and critical component of the molecular clock that drives daily rhythms of metabolism. Evidence reveals that REV-ERBα also plays an important regulatory role in clock-dependent lung physiology and inflammatory responses. We hypothesize that cigarette smoke (CS) exposure influences REV-ERBα abundance in the lungs, facilitating a pro-inflammatory phenotype. To determine the impact of REV-ERBα activation in the CS-induced inflammatory response we treated primary human small airway epithelial cells (SAECs) with CS extract (CSE) or lipopolysaccharide (LPS) in the absence or presence of pre-treatment with the REV-ERBα agonist GSK 4112. We also exposed adult C57BL/6J (WT) and Rev-erbα global KO mice to CS (10 and 30 days) and measured pro-inflammatory cytokine release. Our data reveal that pre-treatment with GSK 4112 reduced CSE/LPS induced pro-inflammatory cytokines release from both SAECs and mouse lung fibroblasts (MLFs). Furthermore, REV-ERBα KO mice show a greater inflammatory response to 10 and 30 days of CS, including increased neutrophil lung influx, pro-inflammatory cytokine (IL-6, MCP-1 and KC) release, and pro-senescence marker (p16) when compared to WT mice. These data demonstrate that REV-ERBα is a critical regulator of CS-induced lung inflammatory responses.
REV-ERBα and its paralog, REV-ERBβ, encoded by NR1D1 and NR1D2 genes, are key nuclear receptors that link the circadian timing system and metabolic homeostasis. Since heme is an endogenous ligand, REV-ERBs have been considered key components of the circadian molecular clock and can be pharmacologically targeted to treat various circadian rhythm-related diseases, such as cardiometabolic, inflammatory, and neuropsychiatric diseases, as well as cancer. REV-ERBs are believed to be functionally redundant and compensatory, although they often affect the expression of gene subsets in an isoform-specific manner. Therefore, this study aimed to identify the redundant and distinct roles of each isoform in controlling its target genes by comparing the transcriptome profiles of a panel of mutant U2OS human osteosarcoma cells in which either NR1D1 or NR1D2 was ablated. Indeed, our transcriptomic analyses revealed that most REV-ERB-regulated genes are controlled by redundant or even additive actions. However, the RNA expression profiles of each single mutant cell line also provide strong evidence for isoform-dependent actions. For example, REV-ERBα is more responsible for regulating the NF-κΒ signaling pathway, whereas a group of extracellular matrix components requires REV-ERBβ to maintain their expression. We found that REV-ERBs have isoform-selective functions in the regulation of certain circadian output pathways despite their overlapping roles in the circadian molecular clock. Thus, the development of isoform-selective REV-ERB modulators can help treat metabolic disturbances and certain types of cancer.
The nuclear receptors REV-ERBα and REV-ERBβ have been demonstrated to be core members of the circadian clock and participate in the regulation of a diverse set of metabolic functions. Due to their overlapping tissue expression patterns and gene expression profiles, REV-ERBβ is thought to be redundant to REV-ERBα. Recent work has highlighted REV-ERBα's role in the regulation of skeletal muscle oxidative capacity and mitochondrial biogenesis. Considering the similarity between the REV-ERBs and the hypothesized overlap in function, we sought to determine whether REV-ERBβ-deficiency presented with a similar skeletal muscle phenotype as REV-ERBα-deficiency. Ectopic overexpression in C2C12 cells demonstrated that REV-ERBβ drives mitochondrial biogenesis and the expression of genes involved in fatty acid oxidation. Intriguingly, knock down of REV-ERBβ in C2C12 cultures also resulted in mitochondrial biogenesis and increased expression of genes involved in fatty acid β-oxidation. To determine whether these effects occurred in vivo, we examined REV-ERBβ-deficient mice and observed a similar increase in expression of genes involved in mitochondrial biogenesis and fatty acid β-oxidation. Consistent with these results, REV-ERBβ-deficient mice exhibited an altered metabolic phenotype compared to wild-type littermate controls when measured by indirect calorimetry. This likely compensated for the increased food consumption that occurred, possibly aiding in the maintenance of their weight over time. Since feeding behaviors are a direct circadian output, this study suggests that REV-ERBβ may have more subtle effects on circadian behaviors than originally identified. Furthermore, these data implicate REV-ERBβ in the control of skeletal muscle metabolism and energy expenditure and suggest that development of REV-ERBα versus REV-ERBβ selective ligands may have therapeutic utility in the treatment of metabolic syndrome.
REV-ERB agonists have shown antifibrotic effects in the heart and other organs. The function of REV-ERB in the cardiac fibroblasts remains unstudied. Here, we characterize the functional difference of REV-ERB in mouse embryonic fibroblasts and cardiac fibroblasts using genetic deletion of REV-ERBα and ß in vitro. We show that REV-ERB α/β double deleted cardiac fibroblasts have reduced viability and proliferation, but increased migration and myofibroblasts activation. Thus, REV-ERB α/β has essential cell-autonomous role in cardiac fibroblasts in maintaining them in a healthy, quiescent state. We also show that existing REV-ERB agonist SR9009 strongly suppresses cardiac fibroblasts activation but in a REV-ERB-independent manner highlighting the need to develop novel REV-ERB agonists for treating cardiac fibrosis.
RORγt is well recognized as the lineage-defining transcription factor for T helper 17 (TH17) cell development. However, the cell-intrinsic mechanisms that negatively regulate TH17 cell development and autoimmunity remain poorly understood. Here, we demonstrate that the transcriptional repressor REV-ERBα is exclusively expressed in TH17 cells, competes with RORγt for their shared DNA consensus sequence, and negatively regulates TH17 cell development via repression of genes traditionally characterized as RORγt dependent, including Il17a. Deletion of REV-ERBα enhanced TH17-mediated pro-inflammatory cytokine expression, exacerbating experimental autoimmune encephalomyelitis (EAE) and colitis. Treatment with REV-ERB-specific synthetic ligands, which have similar phenotypic properties as RORγ modulators, suppressed TH17 cell development, was effective in colitis intervention studies, and significantly decreased the onset, severity, and relapse rate in several models of EAE without affecting thymic cellularity. Our results establish that REV-ERBα negatively regulates pro-inflammatory TH17 responses in vivo and identifies the REV-ERBs as potential targets for the treatment of TH17-mediated autoimmune diseases.
Systemic insulin sensitivity shows a diurnal rhythm with a peak upon waking1,2. The molecular mechanism that underlies this temporal pattern is unclear. Here we show that the nuclear receptors REV-ERB-α and REV-ERB-β (referred to here as 'REV-ERB') in the GABAergic (γ-aminobutyric acid-producing) neurons in the suprachiasmatic nucleus (SCN) (SCNGABA neurons) control the diurnal rhythm of insulin-mediated suppression of hepatic glucose production in mice, without affecting diurnal eating or locomotor behaviours during regular light-dark cycles. REV-ERB regulates the rhythmic expression of genes that are involved in neurotransmission in the SCN, and modulates the oscillatory firing activity of SCNGABA neurons. Chemogenetic stimulation of SCNGABA neurons at waking leads to glucose intolerance, whereas restoration of the temporal pattern of either SCNGABA neuron firing or REV-ERB expression rescues the time-dependent glucose metabolic phenotype caused by REV-ERB depletion. In individuals with diabetes, an increased level of blood glucose after waking is a defining feature of the 'extended dawn phenomenon'3,4. Patients with type 2 diabetes with the extended dawn phenomenon exhibit a differential temporal pattern of expression of REV-ERB genes compared to patients with type 2 diabetes who do not have the extended dawn phenomenon. These findings provide mechanistic insights into how the central circadian clock regulates the diurnal rhythm of hepatic insulin sensitivity, with implications for our understanding of the extended dawn phenomenon in type 2 diabetes.
The main function attributed to the Rev proteins of immunodeficiency viruses is the shuttling of viral RNAs containing the Rev responsive element (RRE) via the CRM-1 export pathway from the nucleus to the cytoplasm. This restricts expression of structural proteins to the late phase of the lentiviral replication cycle. Using Rev-independent gag-pol expression plasmids of HIV-1 and simian immunodeficiency virus and lentiviral vector constructs, we have observed that HIV-1 and simian immunodeficiency virus Rev enhanced RNA encapsidation 20- to 70-fold, correlating well with the effect of Rev on vector titers. In contrast, cytoplasmic vector RNA levels were only marginally affected by Rev. Binding of Rev to the RRE or to a heterologous RNA element was required for Rev-mediated enhancement of RNA encapsidation. In addition to specific interactions of nucleocapsid with the packaging signal at the 5' end of the genome, the Rev/RRE system provides a second mechanism contributing to preferential encapsidation of genomic lentiviral RNA.
In mammals, many aspects of behavior and physiology, and in particular cellular metabolism, are coordinated by the circadian timing system. Molecular clocks are thought to rely on negative feedback loops in clock gene expression that engender oscillations in the accumulation of transcriptional regulatory proteins, such as the orphan receptor REV-ERBalpha. Circadian transcription factors then drive daily rhythms in the expression of clock-controlled output genes, for example genes encoding enzymes and regulators of cellular metabolism. To gain insight into clock output functions of REV-ERBalpha, we carried out genome-wide transcriptome profiling experiments with liver RNA from wild-type mice, Rev-erbalpha knock-out mice, or REV-ERBalpha overexpressing mice. On the basis of these genetic loss- and gain-of-function experiments, we concluded that REV-ERBalpha participates in the circadian modulation of sterol regulatory element-binding protein (SREBP) activity, and thereby in the daily expression of SREBP target genes involved in cholesterol and lipid metabolism. This control is exerted via the cyclic transcription of Insig2, encoding a trans-membrane protein that sequesters SREBP proteins to the endoplasmic reticulum membranes and thereby interferes with the proteolytic activation of SREBPs in Golgi membranes. REV-ERBalpha also participates in the cyclic expression of cholesterol-7alpha-hydroxylase (CYP7A1), the rate-limiting enzyme in converting cholesterol to bile acids. Our findings suggest that this control acts via the stimulation of LXR nuclear receptors by cyclically produced oxysterols. In conclusion, our study suggests that rhythmic cholesterol and bile acid metabolism is not just driven by alternating feeding-fasting cycles, but also by REV-ERBalpha, a component of the circadian clockwork circuitry.
Foraging is costly in terms of time and energy. An endogenous food-entrainable system allows anticipation of predictable changes of food resources in nature. Yet the molecular mechanism that controls food anticipation in mammals remains elusive. Here we report that deletion of the clock component Rev-erbα impairs food entrainment in mice. Rev-erbα global knockout (GKO) mice subjected to restricted feeding showed reduced elevations of locomotor activity and body temperature prior to mealtime, regardless of the lighting conditions. The failure to properly anticipate food arrival was accompanied by a lack of phase-adjustment to mealtime of the clock protein PERIOD2 in the cerebellum, and by diminished expression of phosphorylated ERK 1/2 (p-ERK) during mealtime in the mediobasal hypothalamus and cerebellum. Furthermore, brain-specific knockout (BKO) mice for Rev-erbα display a defective suprachiasmatic clock, as evidenced by blunted daily activity under a light-dark cycle, altered free-running rhythm in constant darkness and impaired clock gene expression. Notably, brain deletion of Rev-erbα totally prevented food-anticipatory behaviour and thermogenesis. In response to restricted feeding, brain deletion of Rev-erbα impaired changes in clock gene expression in the hippocampus and cerebellum, but not in the liver. Our findings indicate that Rev-erbα is required for neural network-based prediction of food availability.
The circadian clock regulates immune responses to microbes and affects pathogen replication, but the underlying molecular mechanisms are not well understood. Here we demonstrate that the circadian components BMAL1 and REV-ERBα influence several steps in the hepatitis C virus (HCV) life cycle, including particle entry into hepatocytes and RNA genome replication. Genetic knock out of Bmal1 and over-expression or activation of REV-ERB with synthetic agonists inhibits the replication of HCV and the related flaviruses dengue and Zika via perturbation of lipid signaling pathways. This study highlights a role for the circadian clock component REV-ERBα in regulating flavivirus replication.
Molecular clock REV-ERBα is central to regulating lung injuries, and decreased REV-ERBα abundance mediates sensitivity to pro-fibrotic insults and exacerbates fibrotic progression. In this study, we determine the role of REV-ERBα in fibrogenesis induced by bleomycin and Influenza A virus (IAV). Bleomycin exposure decreases the abundance of REV-ERBα, and mice dosed with bleomycin at night display exacerbated lung fibrogenesis. Rev-erbα agonist (SR9009) treatment prevents bleomycin induced collagen overexpression in mice. Rev-erbα global heterozygous (Rev-erbα Het) mice infected with IAV showed augmented levels of collagens and lysyl oxidases compared with WT-infected mice. Furthermore, Rev-erbα agonist (GSK4112) prevents collagen and lysyl oxidase overexpression induced by TGFβ in human lung fibroblasts, whereas the Rev-erbα antagonist exacerbates it. Overall, these results indicate that loss of REV-ERBα exacerbates the fibrotic responses by promoting collagen and lysyl oxidase expression, whereas Rev-erbα agonist prevents it. This study provides the potential of Rev-erbα agonists in the treatment of pulmonary fibrosis.
The nuclear receptor REV-ERB plays an important role in a range of physiological processes. REV-ERB behaves as a ligand-dependent transcriptional repressor and heme has been identified as a physiological agonist. Our current understanding of how ligands bind to and regulate transcriptional repression by REV-ERB is based on the structure of heme bound to REV-ERB. However, porphyrin (heme) analogues have been avoided as a source of synthetic agonists due to the wide range of heme binding proteins and potential pleotropic effects. How non-porphyrin synthetic agonists bind to and regulate REV-ERB has not yet been defined. Here, we characterize a high affinity synthetic REV-ERB agonist, STL1267, and describe its mechanism of binding to REV-ERB as well as the method by which it recruits transcriptional corepressor both of which are unique and distinct from that of heme-bound REV-ERB.
REV-ERBα (encoded by Nr1d1) is a nuclear receptor that is part of the circadian clock mechanism and regulates metabolism and inflammatory processes. The glucocorticoid receptor (GR, encoded by Nr3c1) influences similar processes, but is not part of the circadian clock, although glucocorticoid signaling affects resetting of the circadian clock in peripheral tissues. Because of their similar impact on physiological processes, we studied the interplay between these two nuclear receptors. We found that REV-ERBα binds to the C-terminal portion and GR to the N-terminal portion of HSP90α and HSP90β, a chaperone responsible for the activation of proteins to ensure survival of a cell. The presence of REV-ERBα influences the stability and nuclear localization of GR by an unknown mechanism, thereby affecting expression of GR target genes, such as IκBα (Nfkbia) and alcohol dehydrogenase 1 (Adh1). Our findings highlight an important interplay between two nuclear receptors that influence the transcriptional potential of each other. This indicates that the transcriptional landscape is strongly dependent on dynamic processes at the protein level.
The astrocyte brain-type fatty-acid binding protein (Fabp7) circadian gene expression is synchronized in the same temporal phase throughout mammalian brain. Cellular and molecular mechanisms that contribute to this coordinated expression are not completely understood, but likely involve the nuclear receptor Rev-erbα (NR1D1), a transcriptional repressor. We performed ChIP-seq on ventral tegmental area (VTA) and identified gene targets of Rev-erbα, including Fabp7. We confirmed that Rev-erbα binds to the Fabp7 promoter in multiple brain areas, including hippocampus, hypothalamus, and VTA, and showed that Fabp7 gene expression is upregulated in Rev-erbα knock-out mice. Compared to Fabp7 mRNA levels, Fabp3 and Fabp5 mRNA were unaffected by Rev-erbα depletion in hippocampus, suggesting that these effects are specific to Fabp7. To determine whether these effects of Rev-erbα depletion occur broadly throughout the brain, we also evaluated Fabp mRNA expression levels in multiple brain areas, including cerebellum, cortex, hypothalamus, striatum, and VTA in Rev-erbα knock-out mice. While small but significant changes in Fabp5 mRNA expression exist in some of these areas, the magnitude of these effects are minimal to that of Fabp7 mRNA expression, which was over 6-fold across all brain regions. These studies suggest that Rev-erbα is a transcriptional repressor of Fabp7 gene expression throughout mammalian brain.
HIV-1 replication is critically dependent upon controlled processing of its RNA and the activities provided by its encoded regulatory factors Tat and Rev. A screen of small molecule modulators of RNA processing identified several which inhibited virus gene expression, affecting both relative abundance of specific HIV-1 RNAs and the levels of Tat and Rev proteins.
REV-ERB ALPHA has been shown to link metabolism with circadian rhythms. We aimed to identify new polymorphisms in the promoter of REV-ERB ALPHA and tested whether these polymorphisms could be associated with obesity in the Spanish population. Of the 1197 subjects included in our study, 779 were obese (BMI 34.38±3.1 kg/m2) and 418 lean (BMI 23.27±1.5 kg/m2). In the obese group, 469 of the 779 had type 2 diabetes. Genomic DNA from all the subjects was obtained from peripheral blood cells and the genotyping in the REV-ERB ALPHA promoter was analyzed by High Resolution Melting. We found six polymorphisms in the REV-ERB ALPHA promoter and identified rs939347 as a SNP with the highest frequency in the total population. We did not find any association between rs939347 and type 2 diabetes (p = 0.101), but rs939347 was associated with obesity (p = 0.036) with the genotype AA exhibiting higher frequency in the obese (5.2% in total obese vs 2.4% in lean). This association was found only in men (p = 0.031; 6.5% AA-carriers in obese men vs 1.9% AA-carriers in lean men), with no association found in the female population (p = 0.505; 4.4% AA-carriers in obese women vs 2.7% AA-carriers in lean women). Our results suggest that the REV-ERB ALPHA rs939347 polymorphism could modulate body fat mass in men. The present work supports the role of REV-ERB ALPHA in the development of obesity as well as a potential target for the treatment of obesity.
The heart is a highly metabolic organ that uses multiple energy sources to meet its demand for ATP production. Diurnal feeding-fasting cycles result in substrate availability fluctuations which, together with increased energetic demand during the active period, impose a need for rhythmic cardiac metabolism. The nuclear receptors REV-ERBα and β are essential repressive components of the molecular circadian clock and major regulators of metabolism. To investigate their role in the heart, here we generated mice with cardiomyocyte (CM)-specific deletion of both Rev-erbs, which died prematurely due to dilated cardiomyopathy. Loss of Rev-erbs markedly downregulated fatty acid oxidation genes prior to overt pathology, which was mediated by induction of the transcriptional repressor E4BP4, a direct target of cardiac REV-ERBs. E4BP4 directly controls circadian expression of Nampt and its biosynthetic product NAD+ via distal cis-regulatory elements. Thus, REV-ERB-mediated E4BP4 repression is required for Nampt expression and NAD+ production by the salvage pathway. Together, these results highlight the indispensable role of circadian REV-ERBs in cardiac gene expression, metabolic homeostasis and function.
Duchenne muscular dystrophy (DMD) is a debilitating X-linked disorder that is fatal. DMD patients lack the expression of the structural protein dystrophin caused by mutations within the DMD gene. The absence of functional dystrophin protein results in excessive damage from normal muscle use due to the compromised structural integrity of the dystrophin associated glycoprotein complex. As a result, DMD patients exhibit ongoing cycles of muscle destruction and regeneration that promote inflammation, fibrosis, mitochondrial dysfunction, satellite cell (SC) exhaustion and loss of skeletal and cardiac muscle function. The nuclear receptor REV-ERB suppresses myoblast differentiation and recently we have demonstrated that the REV-ERB antagonist, SR8278, stimulates muscle regeneration after acute injury. Therefore, we decided to explore whether the REV-ERB antagonist SR8278 could slow the progression of muscular dystrophy. In mdx mice SR8278 increased lean mass and muscle function, and decreased muscle fibrosis and muscle protein degradation. Interestingly, we also found that SR8278 increased the SC pool through stimulation of Notch and Wnt signaling. These results suggest that REV-ERB is a potent target for the treatment of DMD.
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