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      Bmal1 regulates inflammatory responses in macrophages by modulating enhancer RNA transcription

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          Abstract

          Bmal1 (encoded by Arntl gene) is a core circadian clock gene that regulates various genes involved in circadian rhythm. Although Bmal1 is expressed rhythmically in macrophages, the role of Bmal1 in the regulation of their cellular function remains insufficiently understood. Here, we report that Bmal1 regulates time-dependent inflammatory responses following Toll-like receptor 4 (TLR4) activation by modulating enhancer activity. Global transcriptome analysis indicated that deletion of Arntl perturbed the time-dependent inflammatory responses elicited by TLR4 activation by Kdo2-lipid A (KLA). Although the recruitment of NF-κB p65 was unaffected, the acetylation status of lysine 27 of histone 3, which correlates positively with enhancer activity, was globally increased at PU.1-containing enhancers in Arntl −/− macrophages as compared to wild-type cells. Expression of Nr1d1 and Nr1d2, encoding RevErb transcription factors, which repress enhancer RNA expression, was significantly decreased in Arntl −/− macrophages. Moreover, the level of H3K27 acetylation was increased by Arntl deletion at RevErb-dependent eRNA-expressing enhancers. These results suggest that Bmal1 controls KLA-responsive enhancers, in part by regulating RevErb-directed eRNA transcription. Taken together, the results of this study show that the clock transcription factor network containing Bmal1 controls the inflammatory responses of macrophages by regulating the epigenetic states of enhancers.

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          Most cited references 21

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          Molecular components of the mammalian circadian clock.

          Circadian rhythms are approximately 24-h oscillations in behavior and physiology, which are internally generated and function to anticipate the environmental changes associated with the solar day. A conserved transcriptional-translational autoregulatory loop generates molecular oscillations of 'clock genes' at the cellular level. In mammals, the circadian system is organized in a hierarchical manner, in which a master pacemaker in the suprachiasmatic nucleus (SCN) regulates downstream oscillators in peripheral tissues. Recent findings have revealed that the clock is cell-autonomous and self-sustained not only in a central pacemaker, the SCN, but also in peripheral tissues and in dissociated cultured cells. It is becoming evident that specific contribution of each clock component and interactions among the components vary in a tissue-specific manner. Here, we review the general mechanisms of the circadian clockwork, describe recent findings that elucidate tissue-specific expression patterns of the clock genes and address the importance of circadian regulation in peripheral tissues for an organism's overall well-being.
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            Transcriptional architecture and chromatin landscape of the core circadian clock in mammals.

            The mammalian circadian clock involves a transcriptional feed back loop in which CLOCK and BMAL1 activate the Period and Cryptochrome genes, which then feedback and repress their own transcription. We have interrogated the transcriptional architecture of the circadian transcriptional regulatory loop on a genome scale in mouse liver and find a stereotyped, time-dependent pattern of transcription factor binding, RNA polymerase II (RNAPII) recruitment, RNA expression, and chromatin states. We find that the circadian transcriptional cycle of the clock consists of three distinct phases: a poised state, a coordinated de novo transcriptional activation state, and a repressed state. Only 22% of messenger RNA (mRNA) cycling genes are driven by de novo transcription, suggesting that both transcriptional and posttranscriptional mechanisms underlie the mammalian circadian clock. We also find that circadian modulation of RNAPII recruitment and chromatin remodeling occurs on a genome-wide scale far greater than that seen previously by gene expression profiling.
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              Disruption of the Clock Components CLOCK and BMAL1 Leads to Hypoinsulinemia and Diabetes

              The molecular clock maintains energy constancy by producing circadian oscillations of rate-limiting enzymes involved in tissue metabolism across the day and night1–3. During periods of feeding, pancreatic islets secrete insulin to maintain glucose homeostasis, and while rhythmic control of insulin release is recognized to be dysregulated in humans with diabetes4, it is not known how the circadian clock may affect this process. Here we show that pancreatic islets possess self-sustained circadian gene and protein oscillations of the transcription factors CLOCK and BMAL1. The phase of oscillation of islet genes involved in growth, glucose metabolism, and insulin signaling is delayed in circadian mutant mice, and both Clock 5,6 and Bmal1 7 mutants exhibit impaired glucose tolerance, reduced insulin secretion, and defects in size and proliferation of pancreatic islets that worsen with age. Clock disruption leads to transcriptome-wide alterations in the expression of islet genes involved in growth, survival, and synaptic vesicle assembly. Remarkably, conditional ablation of the pancreatic clock causes diabetes mellitus due to defective β-cell function at the very latest stage of stimulus-secretion coupling. These results demonstrate a role for the β-cell clock in coordinating insulin secretion with the sleep-wake cycle, and reveal that ablation of the pancreatic clock can trigger onset of diabetes mellitus.
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                Author and article information

                Contributors
                yuooisih-circ@umin.ac.jp
                manabetky@umin.ac.jp
                Journal
                Sci Rep
                Sci Rep
                Scientific Reports
                Nature Publishing Group UK (London )
                2045-2322
                1 August 2017
                1 August 2017
                2017
                : 7
                Affiliations
                [1 ]ISNI 0000 0001 1014 9130, GRID grid.265073.5, Department of Cellular and Molecular Medicine, Medical Research Institute, , Tokyo Medical and Dental University, ; Tokyo, Japan
                [2 ]ISNI 0000 0000 8902 2273, GRID grid.174567.6, Department of Cardiovascular Medicine, , Nagasaki University Graduate School of Biomedical Sciences, ; Nagasaki, Japan
                [3 ]ISNI 0000 0004 0370 1101, GRID grid.136304.3, Department of Cellular and Molecular Medicine, Graduate School of Medicine, , Chiba University, ; Chiba, Japan
                [4 ]ISNI 0000 0001 2149 8846, GRID grid.260969.2, Department of Health Science, School of Pharmacology, , Nihon University, ; Tokyo, Japan
                [5 ]ISNI 0000 0004 0372 2033, GRID grid.258799.8, Department of System Biology, Graduate School of Pharmaceutical Sciences, , Kyoto University, ; Kyoto, Japan
                [6 ]ISNI 0000 0004 0370 1101, GRID grid.136304.3, Department of Disease Biology and Molecular Medicine, Graduate School of Medicine, , Chiba University, ; Chiba, Japan
                Article
                7100
                10.1038/s41598-017-07100-3
                5539165
                28765524
                © The Author(s) 2017

                Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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