Circadian clock genes REV-ERBα regulates the secretion of IL-1β in deciduous tooth pulp stem cells by regulating autophagy in the process of physiological root resorption of deciduous teeth

Physiological root resorption is a common occurrence during the development of deciduous teeth in children. Previous research has shown that the regulation of the inflammatory microenvironment through autophagy in DDPSCs is a significant factor in this process. However, it remains unclear why there are variations in the autophagic status of DDPSCs at different stages of physiological root resorption. To address this gap in knowledge, this study examines the relationship between the circadian clock of DDPSCs, the autophagic status, and the periodicity of masticatory behavior. Samples were collected from deciduous teeth at various stages of physiological root resorption, and DDPSCs were isolated and cultured for analysis. The results indicate that the circadian rhythm of important autophagy genes, such as Beclin-1 and LC3, and the clock gene REV-ERBα in DDPSCs, disappears under mechanical stress. Additionally, the study found that REV-ERBα can regulate Beclin-1 and LC3. Evidence suggests that mechanical stress is a trigger for the regulation of autophagy via REV-ERBα. Overall, this study highlights the importance of mechanical stress in regulating autophagy of DDPSCs via REV-ERBα, which affects the formation of the inflammatory microenvironment and plays a critical role in physiological root resorption in deciduous teeth.

Nasal solitary chemosensory cells govern daily rhythm in mouse model of allergic rhinitis

BACKGROUND

While the daily rhythm of allergic rhinitis (AR) has long been recognized, the molecular mechanism underlying this phenomenon remains enigmatic.

OBJECTIVE

We aim to investigate the role of circadian clock in AR development and to clarify the mechanism by which the daily rhythm of AR is generated.

METHODS

AR was induced in mice using the ovalbumin method. Toluidine blue staining, LC-MS/MS analysis, qPCR, and immunoblotting were performed with AR and control mice.

RESULTS

Ovalbumin-induced AR is diurnally rhythmic and associated with clock gene disruption in nasal mucosa. In particular, Rev-erbα is generally down-regulated, and its rhythm retained but with a near 12-h phase shift. Furthermore, global knockout of the core clock gene Bmal1 or Rev-erbα increases the susceptibility of mice to AR and blunts AR rhythmicity. Importantly, nasal SCCs (solitary chemosensory cells) are rhythmically activated, and inhibition of the SCC pathway leads to attenuated AR and a loss of its rhythm. Moreover, rhythmic activation of SCCs is accounted for by diurnal expression of ChAT (an enzyme responsible for the synthesis of acetylcholine) and temporal generation of the neurotransmitter acetylcholine. Mechanistically, REV-ERBα trans-represses Chat through direct binding to a specific response element, generating a diurnal oscillation in this target gene.

CONCLUSION

These findings identify SCCs, under the control of REV-ERBα, as a driver of AR rhythmicity, and suggest targeting SCCs as a new avenue for AR management.

REV-ERBα negatively regulates NLRP6 transcription and reduces the severity of Salmonella infection in mice

Non-typhoidal Salmonella infection is among the most frequent foodborne diseases threatening human health worldwide. The host circadian clock orchestrates daily rhythms to adapt to environmental changes, including coordinating immune function in response to potential infections. However, the molecular mechanisms underlying the interplay between the circadian clock and the immune system in modulating infection processes are incompletely understood. Here, we demonstrate that NLRP6, a novel nucleotide-oligomerization domain (NOD)-like receptor (NLR) family member highly expressed in the intestine, is closely associated with the differential day-night response to Salmonella infection. The core clock component REV-ERBα negatively regulates NLRP6 transcription, leading to the rhythmic expression of NLRP6 and the secretion of IL-18 in intestinal epithelial cells, playing a crucial role in mediating the differential day-night response to Salmonella infection. Activating REV-ERBα with agonist SR9009 in wild-type mice attenuated the severity of infection by decreasing the NLRP6 level in intestinal epithelial cells. Our findings provide new insights into the association between the host circadian clock and the immune response to enteric infections by revealing the regulation of Salmonella infection via the inhibitory effect of REV-ERBα on NLRP6 transcription. Targeting REV-ERBα to modulate NLRP6 activation may be a potential therapeutic strategy for bacterial infections.

The Molecular Circadian Clock Is a Target of Anti-cancer Translation Inhibitors

Circadian-paced biological processes are key to physiology and required for metabolic, immunologic, and cardiovascular homeostasis. Core circadian clock components are transcription factors whose half-life is precisely regulated, thereby controlling the intrinsic cellular circadian clock. Genetic disruption of molecular clock components generally leads to marked pathological events phenotypically affecting behavior and multiple aspects of physiology. Using a transcriptional signature similarity approach, we identified anti-cancer protein synthesis inhibitors as potent modulators of the cardiomyocyte molecular clock. Eukaryotic protein translation inhibitors, ranging from translation initiation (rocaglates, 4-EGI1, etc.) to ribosomal elongation inhibitors (homoharringtonine, puromycin, etc.), were found to potently ablate protein abundance of REV-ERBα, a repressive nuclear receptor and component of the molecular clock. These inhibitory effects were observed both in vitro and in vivo and could be extended to PER2, another component of the molecular clock. Taken together, our observations suggest that the activity spectrum of protein synthesis inhibitors, whose clinical use is contemplated not only in cancers but also in viral infections, must be extended to circadian rhythm disruption, with potential beneficial or iatrogenic effects upon acute or prolonged administration.

Targeting NR1D1 in organ injury: challenges and prospects

Nuclear receptor subfamily 1, group D, member 1 (NR1D1, also known as REV-ERBα) belongs to the nuclear receptor (NR) family, and is a heme-binding component of the circadian clock that consolidates circadian oscillators. In addition to repressing the transcription of multiple clock genes associated with circadian rhythms, NR1D1 has a wide range of downstream target genes that are intimately involved in many physiopathological processes, including autophagy, immunity, inflammation, metabolism and aging in multiple organs. This review focuses on the pivotal role of NR1D1 as a key transcription factor in the gene regulatory network, with particular emphasis on the milestones of the latest discoveries of NR1D1 ligands. NR1D1 is considered as a promising drug target for treating diverse diseases and may contribute to research on innovative biomarkers and therapeutic targets for organ injury-related diseases. Further research on NR1D1 ligands in prospective human trials may pave the way for their clinical application in many organ injury-related disorders.

The cross-talk between leptin and circadian rhythm signaling proteins in physiological processes: a systematic review

BACKGROUND

Today, modern lifestyles and disrupted sleep patterns cause circadian clock rhythm impairments that are associated with altered leptin levels, which subsequently affect a wide range of physiological processes and have significant health burdens on societies. Nevertheless, there has been no systematic review of circadian clock genes and proteins, leptin, and related signaling pathways.

METHODS

Accordingly, we systematically reviewed circadian clock proteins, leptin, and molecular mechanisms between them by searching Pubmed, Scopus, ProQuest, Web of Sciences, and Google Scholar until September 2022. After considering the inclusion and exclusion criteria, 20 animal studies were selected. The risk of bias was assessed in each study.

RESULTS

The results clarified the reciprocal interconnected relationship between circadian clock genes and leptin. Circadian clock genes regulate leptin expression and signaling via different mechanisms, such as CLOCK-BMAL1 heterodimers, which increase the expression of PPARs. PPARs induce the expression of C/EBPα, a key factor in upregulating leptin expression. CLOCK-BMAL1 also induces the expression of Per1 and Rev-erb genes. PER1 activates mTORC1 and mTORC1 enhances the expression of C/EBPα. In addition, REV-ERBs activate the leptin signaling pathway. Also, leptin controls the expression of circadian clock genes by triggering the AMPK and ERK/MAPK signaling pathways, which regulate the activity of PPARs. Moreover, the roles of these molecular mechanisms are elucidated in different physiological processes and organs.

CONCLUSIONS

Crosstalk between circadian clock genes and leptin and their affecting elements should be considered in the selection of new therapeutic targets for related disorders, especially obesity and metabolic impairments.

Presenilin 2 N141I Mutation Induces Hyperimmunity by Immune Cell-specific Suppression of REV-ERBα without Altering Central Circadian Rhythm

Circadian rhythm is a 24-hour cycle of behavioral and physiological changes. Disrupted sleep-wake patterns and circadian dysfunction are common in patients of Alzheimer Disease (AD) and are closely related with neuroinflammation. However, it is not well known how circadian rhythm of immune cells is altered during the progress of AD. Previously, we found presenilin 2 (Psen2) N141I mutation, one of familial AD (FAD) risk genes, induces hyperimmunity through the epigenetic repression of REV-ERBα expression in microglia and bone marrow-derived macrophage (BMDM) cells. Here, we investigated whether repression of REV-ERBα is associated with dysfunction of immune cell-endogenous or central circadian rhythm by analyses of clock genes expression and cytokine secretion, bioluminescence recording of rhythmic PER2::LUC expression, and monitoring of animal behavioral rhythm. Psen2 N141I mutation down-regulated REV-ERBα and induced selective over-production of IL-6 (a well-known clock-dependent cytokine) following the treatment of toll-like receptor (TLR) ligands in microglia, astrocytes, and BMDM. Psen2 N141I mutation also lowered amplitude of intrinsic daily oscillation in these immune cells representatives of brain and periphery. Of interest, however, the period of daily rhythm remained intact in immune cells. Furthermore, analyses of the central clock and animal behavioral rhythms revealed that central clock remained normal without down-regulation of REV-ERBα. These results suggest that Psen2 N141I mutation induces hyperimmunity mainly through the suppression of REV-ERBα in immune cells, which have lowered amplitude but normal period of rhythmic oscillation. Furthermore, our data reveal that central circadian clock is not affected by Psen2 N141I mutation.

Time-dependent effect of REV-ERBα agonist SR9009 on nonalcoholic steatohepatitis and gut microbiota in mice

The circadian clock is involved in the pathogenesis of nonalcoholic steatohepatitis (NASH), and the target pathways of many NASH candidate drugs are controlled by the circadian clock. However, the application of chronopharmacology in NASH is little considered currently. Here, the time-dependent effect of REV-ERBα agonist SR9009 on diet-induced NASH and microbiota was investigated. C57BL/6J mice were fed a high-cholesterol and high-fat diet (CL) for 12 weeks to induce NASH and then treated with SR9009 either at Zeitgeber time 0 (ZT0) or ZT12 for another 6 weeks. Pharmacological activation of REV-ERBα by SR9009 alleviated hepatic steatosis, insulin resistance, liver inflammation, and fibrosis in CL diet-induced NASH mice. These effects were accompanied by improved gut barrier function and altered microbial composition and function in NASH mice, and the effect tended to be stronger when SR9009 was injected at ZT0. Moreover, SR9009 treatment at different time points resulted in a marked difference in the composition of the microbiota, with a stronger effect on the enrichment of beneficial bacteria and the diminishment of harmful bacteria when SR9009 was administrated at ZT0. Therefore, the time-dependent effect of REV-ERBα agonist on NASH was partly associated with the microbiota, highlighting the potential role of microbiota in the chronopharmacology of NASH and the possibility of discovering new therapeutic strategies for NASH.

Regulation of BCRP expression and sulfasalazine pharmacokinetics by the nuclear receptor REV-ERBα

BCRP (breast cancer resistance protein) is a crucial efflux transporter involved in the regulation of the pharmacokinetics and pharmacodynamics of a wide range of drugs. Herein, we aimed to investigate a potential role for the nuclear receptor REV-ERBα in the regulation of BCRP expression and sulfasalazine (a BCRP probe substrate) pharmacokinetics.Regulation of BCRP expression by REV-ERBα was assessed using Rev-erbα^-/- mice and AML12 and CT26 cells. Pharmacokinetic analysis was performed with Rev-erbα^-/- and wild-type mice after sulfasalazine administration.We found that the expression levels of BCRP mRNA and protein were downregulated in the liver and small intestine of Rev-erbα-dificient mice. In line with this, Rev-erbα ablation increased the systemic exposures of oral sulfasalazine.Positive regulation of BCRP expression and function by REV-ERBα was furtherly confirmed in AML12 and CT26 cells. Moreover, indirect regulation of Bcrp expression by REV-ERBα was potentially mediated by a negative transcription factor DEC2, which is a downstream target of REV-ERBα.In conclusion, REV-ERBα positively regulates BCRP expression in mice, thereby affecting sulfasalazine pharmacokinetics.

The nuclear receptor REV-ERBα integrates circadian clock and energy metabolism

The physiological processes of mammals show rhythmic changes in a 24-h cycle. Circadian rhythms are under the subtle control of the autonomous circadian clock, and dysregulation of the circadian system can lead to health problems such as metabolic disorders. REV-ERBα, a member of the nuclear receptor superfamily, is an important component of the mammalian circadian clock. REV-ERBα regulates various physiological processes, including the regulation of metabolism, inflammation and immunity as well as the circadian rhythm, making it a potential therapeutic target for metabolic syndrome, inflammatory diseases and cancers. In recent years, an array of new REV-ERBα ligands have been discovered, most of which have potential applications in the treatment of diseases. In this review, we focus on the regulatory role of nuclear receptor REV-ERBα in energy metabolism and inflammation, in order to provide new strategies for the therapy of metabolic syndrome and its related diseases.

Circadian Rhythm Regulator REV-ERBα Attenuates Neuroapoptosis in Early Brain Injury After Experimental Subarachnoid Hemorrhage in Rats

Subarachnoid hemorrhage (SAH) is associated with circadian rhythm abnormalities, in which REV-ERBα plays a major regulatory role. Our ambition was to investigate the capacity of REV-ERBα to inhibit neuronal neuroapoptosis induced by early brain injury (EBI) after SAH. The endovascular perforation model was used to produce experimental SAH in Sprague-Dawley rats. Specific small-interfering RNA was used to downregulate the expression REV-ERBα while SR9009 was used to upregulate the expression before assessments. Short- and long-term neurobehavior assessments, immunofluorescence staining, TUNEL staining, Nissl staining, brain water content, and Western blot were performed. The expression level of endogenous REVERBα tended to increase and then decrease after SAH and peaked at 48 h. REV-ERBα upregulation diminished neuronal apoptosis and enhanced neurological function deficits. Meanwhile, REV-ERBα downregulation aggravated the damage. Furthermore, the levels of downstream proteins of REV-ERBα (i.e., brain and muscle ARNT-like 1 (BMAL1) and circadian locomotor output cycles kaput (CLOCK)) changed accordingly with REV-ERBα regulation. REV-ERBα may attenuate neuronal apoptosis in EBI after SAH through the BMAL1/CLOCK pathway.

Fluoxetine Decreases Phagocytic Function via REV-ERBα in Microglia

Although fluoxetine (FLX) is a commonly used drug in psychiatric disorders, such as major depressive disorder, anxiety disorder, panic disorder, and obsessive-compulsive disorder, the mechanism by which FLX exerts its therapeutic effect is not completely understood. In this study, we aimed to determine the possible mechanism by which FLX focuses on microglial phagocytosis. FLX reduced phagocytic function in BV2 cells and increased REV-ERBα without affecting other microglia-related genes, such as inflammation and phagocytosis. Although FLX did not change BMAL1 protein levels, it restricted the nucleocytoplasmic transport (NCT) of BMAL1, leading to its cytosolic accumulation. REV-ERBα antagonist SR8278 rescued the decreased phagocytic activity and restricted NCT of BMAL1. We also found that REV-ERBα mediates the effect of FLX via the inhibition of phospho-ERK (pERK). The ERK inhibitor FR180204 was sufficient to reduce phagocytic function in BV2 cells and restrict the NCT of BMAL1. These results were recapitulated in the primary microglia. In conclusion, we propose that FLX decreases phagocytic function and restricts BMAL1 NCT via REV-ERBα. In addition, ERK inhibition mimics the effects of FLX on microglia.

Puerariae lobatae radix protects against UVB-induced skin aging via antagonism of REV-ERBα in mice

Puerariae lobatae radix (PLR) is a wildly used herbal medicine. Here we aimed to assess the PLR efficacy against UVB (ultraviolet-B)-induced skin aging and to determine the mechanisms thereof. We found a significant protective effect of PLR (topical application) on UVB-induced skin aging in mice, as evidenced by reduced skin wrinkles, epidermal thickness, and MDA (malondialdehyde) content as well as increased levels of HYP (hydroxyproline) and SOD (superoxide dismutase) in the skin. In the meantime, Mmp-1, p21 and p53 levels were decreased in the skin of PLR-treated mice. Anti-aging effects of PLR were also confirmed in L929 cells. Furthermore, PLR up-regulated skin expression of BMAL1, which is a known regulator of aging by promoting Nrf2 and antioxidant enzymes. Consistently, Nrf2 and several genes (i.e., Prdx6, Sod1, and Sod2) encoding antioxidant enzymes in the skin were increased in PLR-treated mice. Moreover, based on Gal4 chimeric assay, Bmal1 reporter gene and expression assays, we identified PLR as an antagonist of REV-ERBα that can increase Bmal1 expression. Intriguingly, loss of Rev-erbα protected mice against UVB-induced skin aging and abrogated the protective effect of PLR. In conclusion, PLR acts as an antagonist of REV-ERBα and promotes the expression of BMAL1 to protect against skin aging in mice.

The nuclear receptor REV-ERBα regulates CYP2E1 expression and acetaminophen hepatotoxicity

CYP2E1 plays an important role in drug metabolism and drug-induced hepatotoxicity. Here, we aimed to investigate a potential role for the nuclear receptor REV-ERBα in regulation of CYP2E1 expression and acetaminophen (APAP)-induced hepatotoxicity, and to determine the underlying mechanisms.Regulatory effects of REV-ERBα on CYP2E1 expression were assessed in vivo (using Rev-erbα^-/- mice) and in vitro (using AML12 and HepG2 cells). In vitro microsomal CYP2E1 activity was probed using its specific substrate p-nitrophenol. Pharmacokinetic and acute toxicities studies were performed with Rev-erbα^-/- and wild-type mice after APAP administration.We found that Rev-erbα ablation led to decreases in hepatic CYP2E1 expression and activity in mice. In line with this, APAP-induced hepatotoxicity was attenuated in Rev-erbα-deficient mice. The attenuated toxicity was due to down-regulation of APAP metabolism mediated by CYP2E1, which was evidenced by a decrease in formation of the toxic intermediate metabolite NAPQI (i.e., reduced APAP-Cysteine and APAP-N-acetylcysteine levels). Furthermore, positive regulation of CYP2E1 expression by REV-ERBα was confirmed in both AML12 and HepG2 cells. Based on luciferase reporter assays, it was found that REV-ERBα regulated Cyp2e1 transcription and expression through repression of DEC2.In conclusion, REV-ERBα positively regulates CYP2E1 expression in mice, thereby affecting APAP metabolism and hepatotoxicity.

BMAL1 regulates Propionibacterium acnes-induced skin inflammation via REV-ERBα in mice

Acne vulgaris is a common skin disease, affecting over 80% of adolescents. Inflammation is known to play a central role in acne development. Here, we aimed to investigate the role of the central clock gene Bmal1 in acne-associated inflammation in mice. To this end, mice were injected intradermally with Propionibacterium acnes (P. acnes) to induce acne-associated skin inflammation. We found that Bmal1 and its target genes Rev-erbα, Dbp, Per1 and Cry2 were down-regulated in the skin of P. acnes-treated mice, suggesting a role of Bmal1 in the condition of acne. Supporting this, Bmal1-deleted or jet-lagged mice showed exacerbated P. acnes-induced inflammation in the skin. Regulation of P. acnes-induced inflammation by Bmal1 was further confirmed in RAW264.7 cells and primary mouse keratinocytes. Transcriptomic and protein expression analyses suggested that Bmal1 regulated P. acnes-induced inflammation via the NF-κB/NLRP3 axis, which is known to be repressed by REV-ERBα (a direct target of BMAL1). Moreover, loss of Rev-erbα in mice exacerbated P. acnes-induced inflammation. In addition, Rev-erbα silencing attenuated the inhibitory effects of Bmal1 on P. acnes-induced inflammation. Bmal1 knockdown failed to modulate P. acnes-induced inflammation in Rev-erbα-silenced cells. It was thus proposed that Bmal1 restrained P. acnes-induced skin inflammation via its target REV-ERBα, which acts on the NF-κB/NLRP3 axis to repress inflammation. In conclusion, Bmal1 disruption is identified as a potential pathological factor of acne-associated inflammation. The findings increase our understanding of the crosstalk between skin clock and acne and suggest targeting circadian rhythms as a promising approach for management of acne.

Downregulation of REV-ERBα is associated with the progression of lung adenocarcinoma

Background

The nuclear receptor REV-ERBα (nuclear receptor subfamily 1, Group D member 1, NR1D1) is one of the essential components of the circadian clock which modulates cell proliferation, glucose metabolism, inflammation, and many other biological processes. Modulation of these processes are also relevant to cancer development. Previous studies have suggested that activation of REV-ERBα correlates with cancer cell senescence and death, but how REV-ERBα play roles in tumor progression require further elucidation.

Methods

We investigated the expression of REV-ERBα in clinical samples by immunohistochemistry (IHC). REV-ERBα is downregulated by shorth hairpin RNA (shRNA). The gene expression level of each group was detected by Western blot analysis. The effects of REV-ERBα downregulation on apoptosis and cell cycles was assessed by flow cytometry assay. A549 cell growth curve under different treatments measured by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay. Cell invasion ability under different treatments was measured by Transwell assay. Immunostaining analysis was also used for evaluating the effects of downregulation of REV-ERBα on nuclear factor-κB (NF-κB).

Results

Compared to 81.8% (54/66) of samples exhibiting a lower expression level of REV-ERBα in cancer tissue than in paired normal tissue, only 18.2% (12/66) were higher or equally expressed in lung cancer tissue. Furthermore, downregulation of REV-ERBα by RNA interference can significantly enhance the transcription of nuclear factor-κB (NF-κB), while the expression of p53 remained the same. Downregulation of REV-ERBα was also shown to stimulate the invasion and promote the proliferation of lung adenocarcinoma cell line A549.

Conclusions

Our findings suggest that tumorigenesis and progression of lung carcinoma is relevant to downregulation or inhibition of REV-ERBα. This pathophysiological process also correlates with regulation of the NF-κB signaling pathway, indicating that REV-ERBα is a potential target of lung cancer therapy.

Period 2 Regulates CYP2B10 Expression and Activity in Mouse Liver

CYP2B10 is responsible for metabolism and detoxification of many clinical drugs. Here, we aimed to investigate a potential role of Period 2 (PER2) in regulating expression of hepatic CYP2B10. Regulatory effects of PER2 on hepatic expression of CYP2B10 and other enzymes were determined using Per2-deficient mice with exons 4-6 deleted (named Per2^Del4-6 mice). In vitro and in vivo metabolic activities of CYP2B10 were probed using cyclophosphamide (CPA) as a specific substrate. Regulatory mechanism was investigated using luciferase reporter assays. Genotyping and Western blotting demonstrated loss of wild-type Per2 transcript and markedly reduced PER2 protein in Per2^Del4-6 mice. Hepatic expression of a plenty of drug-metabolizing genes (including Cyp2a4/2a5, Cyp2b10, Ugt1a1, Ugt1a9, Ugt2b36, Sult1a1 and Sult1e1) were altered (and majority were down-regulated) in Per2^Del4-6 mice. Of note, Cyp2b10, Ugt1a9 and Sult1a1 were three genes considerably affected with reduced expression. Decreased expression of CYP2B10 was translated to reduced metabolism and altered pharmacokinetics of CPA as well as attenuated CPA hepatotoxicity in Per2^Del4-6 mice. Positive regulation of CYP2B10 by PER2 was further confirmed in both Hepa-1c1c7 and AML-12 cells. Based on luciferase reporter assays, it was shown that PER2 regulated Cyp2b10 transcription in a REV-ERBα-dependent manner. REV-ERBα was negatively regulated by PER2 (increased REV-ERBα expression in Per2^Del4-6 mice) and itself was also a repressor of CYP2B10. In conclusion, PER2 positively regulates CYP2B10 expression and activity in mouse liver through inhibiting its repressor REV-ERBα.

Dietary Conjugated Linoleic Acid Modulates the Hepatic Circadian Clock Program via PPARα/REV-ERBα-Mediated Chromatin Modification in Mice

Scope: Disruptions of circadian rhythm cause metabolic disorders and are closely related to dietary factors. In this study, we investigated the interplays between the dietary conjugated linoleic acid (CLA)-induced hepatic steatosis and the circadian clock regulation, in association with lipid homeostasis. Methods and Results: Exposure of mice to 1.5% dietary CLA for 28 days caused insulin resistance, enlarged livers, caused hepatic steatosis, and increased triglyceride levels. Transcriptional profiling showed that hepatic circadian clock genes were significantly downregulated with increased expression of the negative transcription factor, REV-ERBα. We uncovered that the nuclear receptor (NR) PPARα, as a major target of dietary CLA, drives REV-ERBα expression via its binding to key genes of the circadian clock, including Cry1 and Clock, and the recruitment of histone marks and cofactors. The PPARα or REV-ERBα inhibition blocked the physical connection of this NR pair, reduced the cobinding of PPARα and REV-ERBα to the genomic DNA response element, and abolished histone modifications in the CLA-hepatocytes. In addition, we demonstrated that CLA promotes PPARα driving REV-ERBα transcriptional activity by directly binding to the PPAR response element (PPRE) at the Nr1d1 gene. Conclusions: Our results add a layer to the understanding of the peripheral clock feedback loop, which involves the PPARα-REV-ERBα, and provide guidance for nutrients optimization in circadian physiology.

Involvement of REV-ERBα dysregulation and ferroptosis in aristolochic acid I-induced renal injury

The molecular events underlying aristolochic acid (AA) nephropathy are poorly understood, and specific therapies for treatment of AA nephropathy are still lacking. Here we aimed to investigate a potential role of REV-ERBα and ferroptosis in renal injury induced by aristolochic acid I (AAI), a typical AA. The regulatory effects of REV-ERBα on AAI-induced renal injury were determined using kidney-specific Rev-erbα knockout mice. Ferroptosis was assessed based on measurements of iron, GSH, and GPX4. Targeted antagonism of REV-ERBα to alleviate AAI-induced renal injury and ferroptosis was assessed using the small molecule antagonist SR8278. mRNAs and proteins were quantified by qPCR and Western blotting, respectively. We first showed that REV-ERBα was upregulated and its target BMAL1 was downregulated in the kidney of mice with AAI nephropathy. Upregulation of REV-ERBα protein was confirmed in aristolactam I (ALI, a nephrotoxic metabolite of AAI)-treated mRTECs. We also observed enhanced ferroptosis (known to be regulated by REV-ERBα) in mice with AAI nephropathy and in ALI-treated mRTECs. Kidney-specific knockout of Rev-erbα reduced the sensitivity of mice to AAI-induced ferroptosis and renal injury. Furthermore, knockdown of Rev-erbα by siRNA or SR8278 (a REV-ERBα antagonist) treatment attenuated ALI-induced ferroptosis in mRTECs. Moreover, REV-ERBα antagonism by SR8278 alleviated ferroptosis and renal injury caused by AAI in mice. In conclusion, we identify REV-ERBα as a regulator of AAI-induced renal injury via promoting ferroptosis. Targeting REV-ERBα may represent a promising approach for management of AAI nephropathy.

REV-ERBα agonist SR9009 suppresses IL-1β production in macrophages through BMAL1-dependent inhibition of inflammasome

The circadian clock plays an important role in adapting organisms to the daily light/dark cycling environment. Recent research findings reveal the involvement of the circadian clock not only in physiological functions but also in regulating inflammatory responses under pathological situations. Previous studies showed that the time-of-day variance of leucocyte circulation and pro-inflammatory cytokines secretion could be directly regulated by the clock-related proteins, including BMAL1 and REV-ERBα in a 24-hour oscillation pattern. To investigate the molecular mechanism behind the regulation of inflammation by the core clock components, we focus on the inflammatory responses in macrophages. Using bone marrow-derived macrophages from wild type and myeloid selective BMAL1-knockout mice, we found that the production of inflammatory cytokines, particularly IL-1β, was dependent on the timing of the lipopolysaccharide (LPS) stimulation in macrophages. Pharmacological activation of REV-ERBα with SR9009 significantly suppressed the LPS-induced inflammation in vitro and in vivo. Particularly, the effect of SR9009 on inhibiting NLRP3-mediated IL-1β and IL-18 production in macrophages was dependent on BMAL1 expression. Further analysis of the metabolic activity in LPS-treated mice showed that knockout of BMAL1 in macrophages exacerbated the hypometabolic state and delayed the recovery from LPS-induced endotoxemia even in the presence of SR9009. These results demonstrated an anti-inflammatory role of REV-ERBα in endotoxin-induced inflammation, during which the secretion of IL-1β through the NLRP3 inflammasome pathway inhibited by SR9009 was regulated by BMAL1.

Translational Regulation of Clock Genes BMAL1 and REV-ERBα by Polyamines

Polyamines stimulate the synthesis of specific proteins at the level of translation, and the genes encoding these proteins are termed as the "polyamine modulon". The circadian clock generates daily rhythms in mammalian physiology and behavior. We investigated the role of polyamines in the circadian rhythm using control and polyamine-reduced NIH3T3 cells. The intracellular polyamines exhibited a rhythm with a period of about 24 h. In the polyamine-reduced NIH3T3 cells, the circadian period of circadian clock genes was lengthened and the synthesis of BMAL1 and REV-ERBα was significantly reduced at the translation level. Thus, the mechanism of polyamine stimulation of these protein syntheses was analyzed using NIH3T3 cells transiently transfected with genes encoding enhanced green fluorescent protein (EGFP) fusion mRNA with normal or mutated 5'-untranslated region (5'-UTR) of Bmal1 or Rev-erbα mRNA. It was found that polyamines stimulated BMAL1 and REV-ERBα synthesis through the enhancement of ribosomal shunting during the ribosome shunting within the 5'-UTR of mRNAs. Accordingly, the genes encoding Bmal1 and Rev-erbα were identified as the members of "polyamine modulon", and these two proteins are significantly involved in the circadian rhythm control.

REV-ERBα Agonist GSK4112 attenuates Fas-induced Acute Hepatic Damage in Mice

Fas-induced apoptosis is a central mechanism of hepatocyte damage during acute and chronic hepatic disorders. Increasing evidence suggests that circadian clock plays critical roles in the regulation of cell fates. In the present study, the potential significance of REV-ERBα, a core ingredient of circadian clock, in Fas-induced acute liver injury has been investigated. The anti-Fas antibody Jo2 was injected intraperitoneally in mice to induce acute liver injury and the REV-ERBα agonist GSK4112 was administered. The results indicated that treatment of GSK4112 decreased the level of plasma ALT and AST, attenuated the liver histological changes, and promoted the survival rate in Jo2-insulted mice. Treatment with GSK4112 also downregulated the activities of caspase-3 and caspase-8, suppressed hepatocyte apoptosis. In addition, treatment with GSK4112 decreased the level of Fas and enhanced the phosphorylation of Akt. In conclusion, treatment with GSK4112 alleviated Fas-induced apoptotic liver damage in mice, suggesting that REV-ERBα agonist might have potential value in pharmacological intervention of Fas-associated liver injury.

Cold-induced chromatin compaction and nuclear retention of clock mRNAs resets the circadian rhythm

Cooling patients to sub‐physiological temperatures is an integral part of modern medicine. We show that cold exposure induces temperature‐specific changes to the higher‐order chromatin and gene expression profiles of human cells. These changes are particularly dramatic at 18°C, a temperature synonymous with that experienced by patients undergoing controlled deep hypothermia during surgery. Cells exposed to 18°C exhibit largely nuclear‐restricted transcriptome changes. These include the nuclear accumulation of mRNAs encoding components of the negative limbs of the core circadian clock, most notably REV‐ERBα. This response is accompanied by compaction of higher‐order chromatin and hindrance of mRNPs from engaging nuclear pores. Rewarming reverses chromatin compaction and releases the transcripts into the cytoplasm, triggering a pulse of negative limb gene proteins that reset the circadian clock. We show that cold‐induced upregulation of REV‐ERBα is sufficient to trigger this reset. Our findings uncover principles of the cellular cold response that must be considered for current and future applications involving therapeutic deep hypothermia.

Moxibustion benignantly regulates circadian rhythm of REV-ERBα in RA rats

The key clinical symptoms and previous findings of RA show a circadian variation, with more prominent joint swelling, stiffness, and pain occurring in the early morning. Moxibustion is able to relieve RA in various pass ways, however, there is no verifying study results for the pathological rhythm of RA. Therefore, we conducted this work to verify whether moxibustion could adjust RA circadian rhythm according to regulate core clock genes. Based on these previous findings that circadian timekeeping is disturbed in RA at molecular level, the aim of this study was to observe the influence of moxibustion on expression level and circadian rhythm of REV-ERBα at different tissues of RA rats. Furthermore, the expression level of core clock genes closely related to RA were evaluated by RT-PCR. 96 SD rats were randomly assigned as 1:1:1:1 ratio to 4 groups for normal control group, RA model group, 5-7 am moxibustion group, and 5-7 pm moxibustion group. RT-PCR was used to measure the relatively expression quantity of REV-ERBα, CLOCK, BMAL1, and PER2 in hypothalamus, hippocampus, and adrenal gland. In RA rats, the expression level of REV-ERBα mRNA were up-regulated in different tissues, and moxibustion potentially up-regulated them in different degrees. In untreated RA rats, the circadian rhythm of REV-ERBα mRNA in hippocampus and adrenal gland both disappeared (P>0.05) and moxibustion was able to recover them (P<0.05). The expression level of CLOCK and PER2 mRNA in hippocampus and adrenal gland were down-regulated significantly (P<0.05) in RA model rats, while moxibustion up-regulated both of them in hippocampus (P<0.05). These results suggested together that moxibustion can benign regulate circadian rhythm of REV-ERBα in different tissues of RA rats. It was revealed that moxibustion not only recovered the losing diurnal oscillation of REV-ERBα in hippocampus and adrenal gland, but also adjusted the circadian rhythm of REV-ERBα in hypothalamus, hippocampus, and adrenal gland to close the normal circadian pattern.

Central administration of REV-ERBα agonist promotes opposite responses on energy balance in fasted and fed states

The REV-ERBα receptor has a recognised role in the regulation of the circadian rhythm system. However, recent evidence suggests that it also contributes to energy balance regulation. Both expression and function of REV-ERBα can be influenced by the energy status of the body. Considering the possibility of the involvement of REV-ERBα in the regulation of energy balance, which is critically regulated by the hypothalamus, and based on the impact of intermittent fasting, the present study evaluated the effects of central administration of REV-ERBα agonist on energy balance in rats exposed to 24 hours of fasting or ad lib. feeding conditions. Initially, 24-hour fasted rats received an acute i.c.v. administration of agonist at doses of 1, 5, 10 or 15 μg per rat and feed efficiency was evaluated. Because 10 μg was a sufficient dose to affect feed efficiency, subsequent experiments used this dose to assess effects of agonist on the following parameters: energy expenditure induced by physical activity and locomotor activity, time spent in physical activity over 24 hours, and glucose and insulin tolerance. In fasted rats, the agonist promoted increased food intake and feed efficiency, with a greater body weight gain associated with less time spent in locomotor activity, suggesting a reduction in energy expenditure induced by physical activity. Furthermore, a reduction in glucose tolerance was noted. By contrast, free-fed rats exhibited reduced food intake and feed efficiency with decreased body weight gain along with an increase in locomotor activity and physical activity-dependent energy expenditure. Thus, i.c.v. administration of REV-ERBα agonist regulates energy balance depending on the energy status of the organism; that is, it promotes a positive energy balance in the fasted state and a negative energy balance in the fed state. These results may be useful in understanding the underlying mechanisms of energy balance disorders and intermittent fasting for body weight control.

Circadian Clock Regulation of Hepatic Energy Metabolism Regulatory Circuits

The liver is a critical organ of energy metabolism. At least 10% of the liver transcriptome demonstrates rhythmic expression, implying that the circadian clock regulates large programmes of hepatic genes. Here, we review the mechanisms by which this rhythmic regulation is conferred, with a particular focus on the transcription factors whose actions combine to impart liver- and time-specificity to metabolic gene expression.

Rev-erbα activation down-regulates hepatic Pck1 enzyme to lower plasma glucose in mice

REV-ERBα (NR1D1) is a nuclear heme receptor that controls many cellular processes including cell differentiation, lipid metabolism, and inflammatory responses. Although REV-ERBα has been also implicated in regulation of glucose homeostasis, the mechanism for this regulation remains unclear. Here we investigate a potential role of REV-ERBα in regulation of PCK1 (phosphoenolpyruvate carboxykinase 1), a rate-limiting enzyme in gluconeogenesis. Hepatoma cells (Hepa-1c1c7 and HepG2 cells), wild-type mice and streptozotocin-induced diabetic mice were treated with SR9009, a specific REV-ERBα agonist. The relative mRNA and protein levels of enzymes in the cells or mouse livers were determined by qPCR and Western blotting, respectively. The fasting plasma glucose test was performed to determine the effects of Rev-erbα on glucose homeostasis. Transcriptional regulation of Pck1 by Rev-erbα was investigated using a combination of luciferase reporter, mobility shift, and chromatin immunoprecipitation (ChIP) assays. SR9009 treatment significantly decreased the mRNA level of Pck1 in mouse hepatoma Hepa-1c1c7 cells, whereas other major enzymes involved in gluconeogenesis (pyruvate carboxylase, glucose-6-phosphatase, fructose bisphosphatase and Pck2) and in glycolysis (phosphofructokinase and hexokinase-1) were unaffected. Consistent with the mRNA change, the protein level of Pck1 was down-regulated. Similarly, a repressive action of REV-ERBα on PCK1 expression was observed in human HepG2 hepatoma cells. SR9009 administration to wild-type or diabetic mice significantly reduced the level of fasting plasma glucose. This coincided with decreased mRNA and protein levels of Pck1 in the liver. In addition, the diabetic mice showed an improvement in glucose tolerability after SR9009 treatment. Promoter analysis, mobility shift, and ChIP assays revealed that Rev-erbα trans-repressed Pck1 through direct binding to -325 to -320 bp region (a RevRE site) in the gene promoter. In conclusion, Rev-erbα activation down-regulates hepatic Pck1 to lower plasma glucose.

Pharmacological activation of REV-ERBα represses LPS-induced microglial activation through the NF-κB pathway

REV-ERBα, the NR1D1 (nuclear receptor subfamily 1, group D, member 1) gene product, is a dominant transcriptional silencer that represses the expression of genes involved in numerous physiological functions, including circadian rhythm, inflammation, and metabolism, and plays a crucial role in maintaining immune functions. Microglia-mediated neuroinflammation is tightly associated with various neurodegenerative diseases and psychiatric disorders. However, the role of REV-ERBα in neuroinflammation is largely unclear. In this study, we investigated whether and how pharmacological activation of REV-ERBα affected lipopolysaccharide (LPS)-induced neuroinflammation in mouse microglia in vitro and in vivo. In BV2 cells or primary mouse cultured microglia, application of REV-ERBα agonist GSK4112 or SR9011 dose-dependently suppressed LPS-induced microglial activation through the nuclear factor kappa B (NF-κB) pathway. In BV2 cells, pretreatment with GSK4112 inhibited LPS-induced phosphorylation of the inhibitor of NF-κB alpha (IκBα) kinase (IκK), thus restraining the phosphorylation and degradation of IκBα, and blocked the nuclear translocation of p65, a NF-κB subunit, thereby suppressing the expression and secretion of the proinflammatory cytokines, such as interleukin 6 (IL-6) and tumor necrosis factor α (TNFα). Moreover, REV-ERBα agonist-induced inhibition on neuroinflammation protected neurons from microglial activation-induced damage, which were also demonstrated in mice with their ventral midbrain microinjected with GSK4112, and then stimulated with LPS. Our results reveal that enhanced REV-ERBα activity suppresses microglial activation through the NF-κB pathway in the central nervous system.

Combinatorial regulation of hepatic cytoplasmic signaling and nuclear transcriptional events by the OGT/REV-ERBα complex

The nuclear receptor REV-ERBα integrates the circadian clock with hepatic glucose and lipid metabolism by nucleating transcriptional comodulators at genomic regulatory regions. An interactomic approach identified O-GlcNAc transferase (OGT) as a REV-ERBα-interacting protein. By shielding cytoplasmic OGT from proteasomal degradation and favoring OGT activity in the nucleus, REV-ERBα cyclically increased O-GlcNAcylation of multiple cytoplasmic and nuclear proteins as a function of its rhythmically regulated expression, while REV-ERBα ligands mostly affected cytoplasmic OGT activity. We illustrate this finding by showing that REV-ERBα controls OGT-dependent activities of the cytoplasmic protein kinase AKT, an essential relay in insulin signaling, and of ten-of-eleven translocation (TET) enzymes in the nucleus. AKT phosphorylation was inversely correlated to REV-ERBα expression. REV-ERBα enhanced TET activity and DNA hydroxymethylated cytosine (5hmC) levels in the vicinity of REV-ERBα genomic binding sites. As an example, we show that the REV-ERBα/OGT complex modulates SREBP-1c gene expression throughout the fasting/feeding periods by first repressing AKT phosphorylation and by epigenomically priming the Srebf1 promoter for a further rapid response to insulin. Conclusion: REV-ERBα regulates cytoplasmic and nuclear OGT-controlled processes that integrate at the hepatic SREBF1 locus to control basal and insulin-induced expression of the temporally and nutritionally regulated lipogenic SREBP-1c transcript.

Abrogation of the Circadian Nuclear Receptor REV-ERBα Exacerbates 6-Hydroxydopamine-Induced Dopaminergic Neurodegeneration

Parkinson's disease (PD) is a neurodegenerative disease characterized by progressive degeneration of dopaminergic (DAergic) neurons, particularly in the substantia nigra (SN). Although circadian dysfunction has been suggested as one of the pathophysiological risk factors for PD, the exact molecular link between the circadian clock and PD remains largely unclear. We have recently demonstrated that REV-ERBα, a circadian nuclear receptor, serves as a key molecular link between the circadian and DAergic systems. It competitively cooperates with NURR1, another nuclear receptor required for the optimal development and function of DA neurons, to control DAergic gene transcription. Considering our previous findings, we hypothesize that REV-ERBα may have a role in the onset and/or progression of PD. In the present study, we therefore aimed to elucidate whether genetic abrogation of REV-ERBα affects PD-related phenotypes in a mouse model of PD produced by a unilateral injection of 6-hydroxydopamine (6-OHDA) into the dorsal striatum. REV-ERBα deficiency significantly exacerbated 6-OHDA-induced motor deficits as well as DAergic neuronal loss in the vertebral midbrain including the SN and the ventral tegmental area. The exacerbated DAergic degeneration likely involves neuroinflammation-mediated neurotoxicity. The Rev-erbα knockout mice showed prolonged microglial activation in the SN along with the overproduction of interleukin 1β, a pro-inflammatory cytokine, in response to 6-OHDA. In conclusion, the present study demonstrates for the first time that genetic abrogation of REV-ERBα can increase vulnerability of DAergic neurons to neurotoxic insults, such as 6-OHDA, thereby implying that its normal function may be beneficial for maintaining DAergic neuron populations during PD progression.

Gene expression profiling of the SCN in young and old rhesus macaques

In mammals, the suprachiasmatic nucleus (SCN) is the location of a master circadian pacemaker. It receives photic signals from the environment via the retinal hypothalamic tract, which play a key role in synchronizing the body's endogenously generated circadian rhythms with the 24-h rhythm of the environment. Therefore, it is plausible that age-related changes within the SCN contribute to the etiology of perturbed activity-rest cycles that become prevalent in humans during aging. To test this hypothesis, we used gene arrays and quantitative RT-PCR to profile age-related gene expression changes within the SCN of male rhesus macaques - a pragmatic translational animal model of human aging, which similarly displays an age-related attenuation of daytime activity levels. As expected, the SCN showed high expression of arginine vasopressin, vasoactive intestinal polypeptide, calbindin and nuclear receptor subfamily 1, group D, member 1 (NR1D1) (also known as reverse strand of ERBA (REV-ERBα), both at the mRNA and protein level. However, no obvious difference was detected between the SCNs of young (7-12 years) and old animals (21-26 years), in terms of the expression of core clock genes or genes associated with SCN signaling and neurotransmission. These data demonstrate the resilience of the primate SCN to normal aging, at least at the transcriptional level and, at least in males, suggest that age-related disruption of activity-rest cycles in humans may instead stem from changes within other components of the circadian system, such as desynchronization of subordinate oscillators in other parts of the body.

Development and implementation of a cell-based assay to discover agonists of the nuclear receptor REV-ERBα

The nuclear receptors are transcription factors involved in the regulation of a variety of physiological processes whose activity can be modulated by binding to relevant small molecule ligands. Their dysfunction has been shown to play a role in disease states such as diabetes, cancer, inflammatory diseases, and hormonal resistance ailments, which makes them interesting targets for drug discovery. The nuclear receptor REV-ERBα is involved in regulating the circadian rhythm and metabolism. Its natural ligand is heme and there is significant interest in identifying novel synthetic modulators to serve as tools to characterize its function and to serve as drugs in treating metabolic disorders. To do so, we established a mammalian cell-based two-hybrid assay system capable of measuring the interaction between REV-ERBα and its co-repressor, nuclear co-repressor 1. This assay was validated to industry standard criteria and was used to screen a subset of the LOPAC^®1280 library and 29568 compounds from a diverse compound library. Profiling of the primary hits in a panel of counter and selectivity assays confirmed that REV-ERBα activity can be modulated pharmacologically and chemical scaffolds have been identified for optimization.

Moving to the Rhythm with Clock (Circadian) Genes, Autophagy, mTOR, and SIRT1 in Degenerative Disease and Cancer

BACKGROUND

The mammalian circadian clock and its associated clock genes are increasingly been recognized as critical components for a number of physiological and disease processes that extend beyond hormone release, thermal regulation, and sleep-wake cycles. New evidence suggests that clinical behavior disruptions that involve prolonged shift work and even space travel may negatively impact circadian rhythm and lead to multi-system disease.

METHODS

In light of the significant role circadian rhythm can hold over the body's normal physiology as well as disease processes, we examined and discussed the impact circadian rhythm and clock genes hold over lifespan, neurodegenerative disorders, and tumorigenesis.

RESULTS

In experimental models, lifespan is significantly reduced with the introduction of arrhythmic mutants and leads to an increase in oxidative stress exposure. Interestingly, patients with Alzheimer's disease and Parkinson's disease may suffer disease onset or progression as a result of alterations in the DNA methylation of clock genes as well as prolonged pharmacological treatment for these disorders that may lead to impairment of circadian rhythm function. Tumorigenesis also can occur with the loss of a maintained circadian rhythm and lead to an increased risk for nasopharyngeal carcinoma, breast cancer, and metastatic colorectal cancer. Interestingly, the circadian clock system relies upon the regulation of the critical pathways of autophagy, the mechanistic target of rapamycin (mTOR), AMP activated protein kinase (AMPK), and silent mating type information regulation 2 homolog 1 (Saccharomyces cerevisiae) (SIRT1) as well as proliferative mechanisms that involve the wingless pathway of Wnt/β-catenin pathway to foster cell survival during injury and block tumor cell growth.

CONCLUSION

Future targeting of the pathways of autophagy, mTOR, SIRT1, and Wnt that control mammalian circadian rhythm may hold the key for the development of novel and effective therapies against aging- related disorders, neurodegenerative disease, and tumorigenesis.

Novel Treatment Strategies for the Nervous System: Circadian Clock Genes, Non-coding RNAs, and Forkhead Transcription Factors

BACKGROUND

With the global increase in lifespan expectancy, neurodegenerative disorders continue to affect an ever-increasing number of individuals throughout the world. New treatment strategies for neurodegenerative diseases are desperately required given the lack of current treatment modalities.

METHODS

Here, we examine novel strategies for neurodegenerative disorders that include circadian clock genes, non-coding Ribonucleic Acids (RNAs), and the mammalian forkhead transcription factors of the O class (FoxOs).

RESULTS

Circadian clock genes, non-coding RNAs, and FoxOs offer exciting prospects to potentially limit or remove the significant disability and death associated with neurodegenerative disorders. Each of these pathways has an intimate relationship with the programmed death pathways of autophagy and apoptosis and share a common link to the silent mating type information regulation 2 homolog 1 (Saccharomyces cerevisiae) (SIRT1) and the mechanistic target of rapamycin (mTOR). Circadian clock genes are necessary to modulate autophagy, limit cognitive loss, and prevent neuronal injury. Non-coding RNAs can control neuronal stem cell development and neuronal differentiation and offer protection against vascular disease such as atherosclerosis. FoxOs provide exciting prospects to block neuronal apoptotic death and to activate pathways of autophagy to remove toxic accumulations in neurons that can lead to neurodegenerative disorders.

CONCLUSION

Continued work with circadian clock genes, non-coding RNAs, and FoxOs can offer new prospects and hope for the development of vital strategies for the treatment of neurodegenerative diseases. These innovative investigative avenues have the potential to significantly limit disability and death from these devastating disorders.

The nuclear receptor and clock gene REV-ERBα regulates cigarette smoke-induced lung inflammation

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.

Implications of Circadian Rhythm in Dopamine and Mood Regulation

Mammalian physiology and behavior are regulated by an internal time-keeping system, referred to as circadian rhythm. The circadian timing system has a hierarchical organization composed of the master clock in the suprachiasmatic nucleus (SCN) and local clocks in extra-SCN brain regions and peripheral organs. The circadian clock molecular mechanism involves a network of transcription-translation feedback loops. In addition to the clinical association between circadian rhythm disruption and mood disorders, recent studies have suggested a molecular link between mood regulation and circadian rhythm. Specifically, genetic deletion of the circadian nuclear receptor Rev-erbα induces mania-like behavior caused by increased midbrain dopaminergic (DAergic) tone at dusk. The association between circadian rhythm and emotion-related behaviors can be applied to pathological conditions, including neurodegenerative diseases. In Parkinson's disease (PD), DAergic neurons in the substantia nigra pars compacta progressively degenerate leading to motor dysfunction. Patients with PD also exhibit non-motor symptoms, including sleep disorder and neuropsychiatric disorders. Thus, it is important to understand the mechanisms that link the molecular circadian clock and brain machinery in the regulation of emotional behaviors and related midbrain DAergic neuronal circuits in healthy and pathological states. This review summarizes the current literature regarding the association between circadian rhythm and mood regulation from a chronobiological perspective, and may provide insight into therapeutic approaches to target psychiatric symptoms in neurodegenerative diseases involving circadian rhythm dysfunction.

Mildly Increased Mechanical Nociceptive Sensitivity in REV-ERBα Knock-out Mice

Nociception is one of the most complex senses that is affected not only by external stimulation but also internal conditions. Previous studies have suggested that circadian rhythm is important in modulating nociception. REV-ERBα knock-out (KO) mice have disrupted circadian rhythm and altered mood-related phenotypes. In this study, we examined the role of REV-ERBα in inflammatory nociception. We found that the nociceptive sensitivity of KO mice was partially enhanced in mechanical nociception. However, this partial alteration was independent of the circadian rhythm. Taken together, deletion of REV-ERBα induced a mild change in mechanical nociceptive sensitivity but this alteration was not dependent on the circadian rhythm.

REV-ERBα influences the stability and nuclear localization of the glucocorticoid receptor

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.

Disruption of Sirtuin 1-Mediated Control of Circadian Molecular Clock and Inflammation in Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is the fourth most common cause of death, and it is characterized by abnormal inflammation and lung function decline. Although the circadian molecular clock regulates inflammatory responses, there is no information available regarding the impact of COPD on lung molecular clock function and its regulation by sirtuin 1 (SIRT1). We hypothesize that the molecular clock in the lungs is disrupted, leading to increased inflammatory responses in smokers and patients with COPD and its regulation by SIRT1. Lung tissues, peripheral blood mononuclear cells (PBMCs), and sputum cells were obtained from nonsmokers, smokers, and patients with COPD for measurement of core molecular clock proteins (BMAL1, CLOCK, PER1, PER2, and CRY1), clock-associated nuclear receptors (REV-ERBα, REV-ERBβ, and RORα), and SIRT1 by immunohistochemistry, immunofluorescence, and immunoblot. PBMCs were treated with the SIRT1 activator SRT1720 followed by LPS treatment, and supernatant was collected at 6-hour intervals. Levels of IL-8, IL-6, and TNF-α released from PBMCs were determined by ELISA. Expression of BMAL1, PER2, CRY1, and REV-ERBα was reduced in PBMCs, sputum cells, and lung tissues from smokers and patients with COPD when compared with nonsmokers. SRT1720 treatment attenuated LPS-mediated reduction of BMAL1 and REV-ERBα in PBMCs from nonsmokers. Additionally, LPS differentially affected the timing and amplitude of cytokine (IL-8, IL-6, and TNF-α) release from PBMCs in nonsmokers, smokers, and patients with COPD. Moreover, SRT1720 was able to inhibit LPS-induced cytokine release from cultured PBMCs. In conclusion, disruption of the molecular clock due to SIRT1 reduction contributes to abnormal inflammatory response in smokers and patients with COPD.

Circadian clock-coupled lung cellular and molecular functions in chronic airway diseases

Airway diseases are associated with abnormal circadian rhythms of lung function, reflected in daily changes of airway caliber, airway resistance, respiratory symptoms, and abnormal immune-inflammatory responses. Circadian rhythms are generated at the cellular level by an autoregulatory feedback loop of interlocked transcription factors collectively referred to as clock genes. The molecular clock is altered by cigarette smoke, LPS, and bacterial and viral infections in mouse and human lungs and in patients with chronic airway diseases. Stress-mediated post-translational modification of molecular clock proteins, brain and muscle aryl hydrocarbon receptor nuclear translocator-like 1 (BMAL1) and PERIOD 2, is associated with a reduction in the activity/level of the deacetylase sirtuin 1 (SIRT1). Similarly, the levels of the nuclear receptor REV-ERBα and retinoic acid receptor-related orphan receptor α (ROR α), critical regulators of Bmal1 expression, are altered by environmental stresses. Molecular clock dysfunction is implicated in immune and inflammatory responses, DNA damage response, and cellular senescence. The molecular clock in the lung also regulates the timing of glucocorticoid sensitivity and phasic responsiveness to inflammation. Herein, we review our current understanding of clock-controlled cellular and molecular functions in the lungs, the impact of clock dysfunction in chronic airway disease, and the response of the pulmonary clock to different environmental perturbations. Furthermore, we discuss the evidence for candidate signaling pathways, such as the SIRT1-BMAL1-REV-ERBα axis, as novel targets for chronopharmacological management of chronic airway diseases.

α1B-Adrenergic receptor signaling controls circadian expression of Tnfrsf11b by regulating clock genes in osteoblasts

Circadian clocks are endogenous and biological oscillations that occur with a period of <24 h. In mammals, the central circadian pacemaker is localized in the suprachiasmatic nucleus (SCN) and is linked to peripheral tissues through neural and hormonal signals. In the present study, we investigated the physiological function of the molecular clock on bone remodeling. The results of loss-of-function and gain-of-function experiments both indicated that the rhythmic expression of Tnfrsf11b, which encodes osteoprotegerin (OPG), was regulated by Bmal1 in MC3T3-E1 cells. We also showed that REV-ERBα negatively regulated Tnfrsf11b as well as Bmal1 in MC3T3-E1 cells. We systematically investigated the relationship between the sympathetic nervous system and the circadian clock in osteoblasts. The administration of phenylephrine, a nonspecific α1-adrenergic receptor (AR) agonist, stimulated the expression of Tnfrsf11b, whereas the genetic ablation of α_1B-AR signaling led to the alteration of Tnfrsf11b expression concomitant with Bmal1 and Per2 in bone. Thus, this study demonstrated that the circadian regulation of Tnfrsf11b was regulated by the clock genes encoding REV-ERBα (Nr1d1) and Bmal1 (Bmal1, also known as Arntl), which are components of the core loop of the circadian clock in osteoblasts.

Summary: This study demonstrates that the circadian regulation of TNFRSF11B is regulated by the clock genes Nr1d1 and Arntl, which are components of the core loop of the circadian clock in osteoblasts, providing a molecular mechanism for the control of bone remodelling by circadian rhythms.

Circadian molecular clock in lung pathophysiology

Disrupted daily or circadian rhythms of lung function and inflammatory responses are common features of chronic airway diseases. At the molecular level these circadian rhythms depend on the activity of an autoregulatory feedback loop oscillator of clock gene transcription factors, including the BMAL1:CLOCK activator complex and the repressors PERIOD and CRYPTOCHROME. The key nuclear receptors and transcription factors REV-ERBα and RORα regulate Bmal1 expression and provide stability to the oscillator. Circadian clock dysfunction is implicated in both immune and inflammatory responses to environmental, inflammatory, and infectious agents. Molecular clock function is altered by exposomes, tobacco smoke, lipopolysaccharide, hyperoxia, allergens, bleomycin, as well as bacterial and viral infections. The deacetylase Sirtuin 1 (SIRT1) regulates the timing of the clock through acetylation of BMAL1 and PER2 and controls the clock-dependent functions, which can also be affected by environmental stressors. Environmental agents and redox modulation may alter the levels of REV-ERBα and RORα in lung tissue in association with a heightened DNA damage response, cellular senescence, and inflammation. A reciprocal relationship exists between the molecular clock and immune/inflammatory responses in the lungs. Molecular clock function in lung cells may be used as a biomarker of disease severity and exacerbations or for assessing the efficacy of chronotherapy for disease management. Here, we provide a comprehensive overview of clock-controlled cellular and molecular functions in the lungs and highlight the repercussions of clock disruption on the pathophysiology of chronic airway diseases and their exacerbations. Furthermore, we highlight the potential for the molecular clock as a novel chronopharmacological target for the management of lung pathophysiology.

Lost in translocation: the functions of the 18-kD translocator protein

Research spanning nearly four decades has assigned to the translocator protein (18 kDa) (TSPO) a critical role, among others, in the mitochondrial import of cholesterol, the subsequent steps of (neuro)steroid production, and systemic endocrine regulation, with implications for the pathophysiology of immune, inflammatory, neurodegenerative, and psychiatric as well as neoplastic diseases. Recent knockout studies in mice unexpectedly report normal or latent phenotypes, raising doubts about the protein's role in steroidogenesis and other previously postulated functions and challenging the validity of earlier data on the selectivity of TSPO-binding drugs. Here we provide a synthesis of the current debate from a structural and molecular biology perspective, discuss the limits of inference in loss-of-function (gene knockout) studies, and suggest new functions of TSPO.

A specific role for the REV-ERBα-controlled L-Type Voltage-Gated Calcium Channel CaV1.2 in resetting the circadian clock in the late night

Within the suprachiasmatic nucleus (SCN) of the hypothalamus, circadian timekeeping and resetting have been shown to be largely dependent on both membrane depolarization and intracellular second-messenger signaling. In both of these processes, voltage-gated calcium channels (VGCCs) mediate voltage-dependent calcium influx, which propagates neural impulses by stimulating vesicle fusion and instigates intracellular pathways resulting in clock gene expression. Through the cumulative actions of these processes, the phase of the internal clock is modified to match the light cycle of the external environment. To parse out the distinct roles of the L-type VGCCs, we analyzed mice deficient in Cav1.2 (Cacna1c) in brain tissue. We found that mice deficient in the Cav1.2 channel exhibited a significant reduction in their ability to phase-advance circadian behavior when subjected to a light pulse in the late night. Furthermore, the study revealed that the expression of Cav1.2 mRNA was rhythmic (peaking during the late night) and was regulated by the circadian clock component REV-ERBα. Finally, the induction of clock genes in both the early and late subjective night was affected by the loss of Cav1.2, with reductions in Per2 and Per1 in the early and late night, respectively. In sum, these results reveal a role of the L-type VGCC Cav1.2 in mediating both clock gene expression and phase advances in response to a light pulse in the late night.

The effects of the heme precursor 5-aminolevulinic acid (ALA) on REV-ERBα activation

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REV-ERBα has a key role in circadian rhythms and requires heme as its ligand.

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Heme precursor ALA exhibited increased nuclear heme level and activation of REV-ERBα.

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ALA inhibited REV-ERBα target genes including an essential component of the circadian oscillator.

The nuclear receptor, REV-ERBα, has a key role in circadian rhythms and requires heme as its ligand. The present study determined whether the heme precursor, 5-aminolevulinic acid (ALA), affects REV-ERBα and its target genes. When exposed to ALA, the human lung diploid cell line, WI-38, exhibited activation of REV-ERBα and repression of the transcription of REV-ERBα target genes, including BMAL1, an essential component of the circadian oscillator. Moreover, co-incubation of sodium ferrous citrate (SFC) and ALA also activated REV-ERBα and repressed the transcription of REV-ERBα target genes. These results indicate that ALA regulates human circadian rhythms via REV-ERBα.