Bromodomain containing 9 (BRD9) regulates macrophage inflammatory responses and modulates glucocorticoids receptor activity [RNA-seq]. Bromodomain containing 9 (BRD9) regulates macrophage inflammatory responses and modulates glucocorticoids receptor activity [RNA-seq]

In macrophages, homeostatic and immune signals induce distinct sets of transcriptional responses, defining the cellular identity and function. The activity of lineage specific and signal induced transcription factors are regulated by chromatin accessibility and other epigenetic modulators. Glucocorticoids are potent anti-inflammatory drugs. Acting through the glucocorticoid receptor (GR), glucocorticoids directly repress inflammatory responses at transcriptional and epigenetic levels in macrophages. In this study, we identified bromodomain containing 9 (BRD9), a component of SWI/SNF chromatin remodeling complex, as a novel modulator for glucocorticoids responses in macrophages. Inhibition, degradation, or genetic depletion of BRD9 in bone marrow derived macrophages (BMDM), significantly compromised their responses to inflammatory stimuli, such as liposaccharides (LPS), and interferons. A large portion of BRD9-regulated genes are also known to be regulated by dexamethasone, a synthetic glucocorticoid. Importantly, pharmacologic inhibition of BRD9 is able to further potentiate the anti-inflammatory responses of dexamethasone, by further repressing the GR downstream targets. Mechanistically, BRD9 co-localized with a subset of GR binding sites. Depletion of BRD9 enhanced GR occupancy at a subset of its targets. Enhanced occupancy of GR at these sites is associated with further repression of inflammation-related genes. Collectively, these findings establish BRD9 as a key modulator of macrophage inflammatory responses, revealing the therapeutic potential of BRD9 inhibitors as modulators for glucocorticoids action. Overall design: RNA-seq of primary bone marrow-derived macrophages (BMDMs).

在巨噬细胞中，稳态信号与免疫信号可诱导截然不同的转录应答程序，进而定义细胞的身份与功能。谱系特异性转录因子与信号诱导型转录因子的活性，均受染色质开放性与其他表观遗传调控因子的调控。糖皮质激素是强效抗炎药物，通过糖皮质激素受体（glucocorticoid receptor, GR）发挥作用，可在巨噬细胞内直接从转录与表观遗传层面抑制炎症应答。本研究中，我们鉴定出含溴结构域蛋白9（bromodomain containing 9, BRD9）——SWI/SNF染色质重塑复合物的组分之一——作为巨噬细胞内糖皮质激素应答的新型调控因子。在骨髓来源巨噬细胞（bone marrow derived macrophages, BMDM）中，抑制、降解或基因敲除BRD9，会显著削弱细胞对脂多糖（liposaccharides, LPS）与干扰素等炎症刺激的应答能力。受BRD9调控的基因中，有很大一部分同时可被合成糖皮质激素地塞米松（dexamethasone）调控。尤为重要的是，通过药理学手段抑制BRD9，可通过进一步抑制GR下游靶基因，进一步增强地塞米松的抗炎应答效果。从机制层面来看，BRD9可与部分GR结合位点共定位；敲除BRD9会增强GR在部分靶位点上的结合占有率；这类受体结合占有率的提升，与炎症相关基因的进一步抑制存在关联。综上，本研究结果证实BRD9是巨噬细胞炎症应答的关键调控因子，同时揭示了BRD9抑制剂作为糖皮质激素作用调控剂的治疗潜力。实验整体设计：原代骨髓来源巨噬细胞（BMDMs）的RNA测序（RNA-seq）。