Bmal1 regulates inflammatory responses in macrophages by modulating enhancer RNA transcription

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.