BRD4 inhibition rewires cardiac macrophages toward a protective phenotype marked by low MHC class II expression. BRD4 inhibition rewires cardiac macrophages toward a protective phenotype marked by low MHC class II expression

Bromodomain and extra-terminal domain (BET) proteins, including BRD4, bind acetylated chromatin and co-activate gene transcription. A BET inhibitor, JQ1, prevents and reverses pathological cardiac remodeling in preclinical models of heart failure. However, the underlying cellular mechanisms by which JQ1 improves cardiac structure and function remain poorly defined. Here, we demonstrate that BRD4 knockdown reduced expression of genes encoding CC chemokines in cardiac fibroblasts, suggesting a role for this epigenetic reader in controlling fibroblast-immune cell crosstalk. Consistent with this, JQ1 dramatically suppressed recruitment of monocytes to the heart in response to stress. Normal mouse hearts were found to have approximately equivalent numbers of major histocompatibility complex (MHC-II)high and MHC-IIlow resident macrophages, while MHC-IIlow macrophages predominated following JQ1 treatment. Single-cell RNA-seq data confirmed that JQ1 treatment or BRD4 knockout in CX3CR1+ cells reduced MHC-II gene expression in cardiac macrophages, and studies with cultured macrophages further illustrated a cell autonomous role for BET proteins in controlling the MHC-II axis. Bulk RNA-seq analysis demonstrated that JQ1 blocked proinflammatory macrophage gene expression through a mechanism that likely involves repression of NF-kB signaling. JQ1 treatment reduced cardiac infarct size in mice subjected to ischemia/reperfusion. Our findings illustrate that BET inhibition affords a powerful pharmacological approach to manipulate monocyte-derived and resident macrophages in the heart. Such an approach has the potential to enhance the reparative phenotype of macrophages to promote wound healing and limit infarct expansion following myocardial ischemia. Overall design: To address the impact of BRD4 inhibition on resident macrophage phenotypes in the heart, transcriptomic profiling by bulk RNA-seq was performed using purified cardiac macrophages from mice treated with JQ1 or vehicle control for three days.

溴结构域与额外末端结构域（Bromodomain and extra-terminal domain, BET）蛋白（包括BRD4）可结合乙酰化染色质并共同激活基因转录。BET抑制剂JQ1可在心力衰竭的临床前模型中预防并逆转病理性心脏重构。然而，JQ1改善心脏结构与功能的潜在细胞机制仍未明确。本研究证实，BRD4敲低可降低心脏成纤维细胞中编码CC趋化因子的基因的表达，提示该表观遗传阅读器在调控成纤维细胞与免疫细胞串扰中发挥作用。与此一致，JQ1可显著抑制应激状态下单核细胞向心脏的招募。研究发现正常小鼠心脏中，主要组织相容性复合体（major histocompatibility complex, MHC）-II高表达与MHC-II低表达的驻留巨噬细胞数量大致相当，而JQ1处理后以MHC-II低表达巨噬细胞为主。单细胞RNA测序（single-cell RNA-seq）数据证实，在CX3CR1阳性细胞中进行JQ1处理或BRD4基因敲除，可降低心脏巨噬细胞的MHC-II基因表达；体外培养巨噬细胞的实验进一步表明，BET蛋白在调控MHC-II通路中具有细胞自主性作用。批量RNA测序（bulk RNA-seq）分析显示，JQ1可通过可能涉及抑制核因子κB（NF-κB）信号通路的机制，阻断促炎巨噬细胞的基因表达。JQ1处理可缩小缺血再灌注小鼠的心脏梗死面积。本研究结果表明，BET抑制是一种强大的药理学手段，可调控心脏中的单核细胞来源巨噬细胞与驻留巨噬细胞。该手段有望增强巨噬细胞的修复表型，从而促进心肌缺血后的伤口愈合并限制梗死扩展。实验整体设计：为探究BRD4抑制对心脏驻留巨噬细胞表型的影响，本研究对接受JQ1或溶剂对照处理3天的小鼠的纯化心脏巨噬细胞进行了批量RNA测序（bulk RNA-seq）转录组分析。