Data_Sheet_1_An Interplay Between MRTF-A and the Histone Acetyltransferase TIP60 Mediates Hypoxia-Reoxygenation Induced iNOS Transcription in Macrophages.PDF

Cardiac ischemia-reperfusion injury (IRI) represents a major pathophysiological event associated with permanent loss of heart function. Several inter-dependent processes contribute to cardiac IRI that include accumulation of reactive oxygen species (ROS), aberrant inflammatory response, and depletion of energy supply. Inducible nitric oxide synthase (iNOS) is a pro-inflammatory mediator and a major catalyst of ROS generation. In the present study we investigated the epigenetic mechanism whereby iNOS transcription is up-regulated in macrophages in the context of cardiac IRI. We report that germline deletion or systemic inhibition of myocardin-related transcription factor A (MRTF-A) in mice attenuated up-regulation of iNOS following cardiac IRI in the heart. In cultured macrophages, depletion or inhibition of MRTF-A suppressed iNOS induction by hypoxia-reoxygenation (HR). In contrast, MRTF-A over-expression potentiated activation of the iNOS promoter by HR. MRTF-A directly binds to the iNOS promoter in response to HR stimulation. MRTF-A binding to the iNOS promoter was synonymous with active histone modifications including trimethylated H3K4, acetylated H3K9, H3K27, and H4K16. Further analysis revealed that MRTF-A interacted with H4K16 acetyltransferase TIP60 to synergistically activate iNOS transcription. TIP60 depletion or inhibition achieved equivalent effects as MRTF-A depletion/inhibition in terms of iNOS repression. Of interest, TIP60 appeared to form a crosstalk with the H3K4 trimethyltransferase complex to promote iNOS trans-activation. In conclusion, we data suggest that the MRTF-A-TIP60 axis may play a critical role in iNOS transcription in macrophages and as such be considered as a potential target for the intervention of cardiac IRI.

心肌缺血再灌注损伤（IRI）是一种与心脏功能永久性丧失相关的重大病理生理事件。多种相互依赖的过程共同导致了心肌IRI的发生，包括活性氧（ROS）的积累、异常的炎症反应以及能量供应的耗竭。诱导型一氧化氮合酶（iNOS）是一种促炎性介质，是ROS生成的主要催化因子。在本研究中，我们探讨了iNOS在心肌IRI背景下在巨噬细胞中转录上调的表观遗传机制。我们报道，在心肌IRI后，通过小鼠的基因型删除或全身性抑制肌球蛋白相关转录因子A（MRTF-A），可以减轻心脏中iNOS的上调。在培养的巨噬细胞中，MRTF-A的耗竭或抑制可抑制由缺氧-复氧（HR）诱导的iNOS诱导。相反，MRTF-A的过表达增强了HR激活iNOS启动子。MRTF-A在HR刺激下直接与iNOS启动子结合。MRTF-A与iNOS启动子的结合与活跃的组蛋白修饰相关，包括三甲基化H3K4、乙酰化H3K9、H3K27和H4K16。进一步的分析显示，MRTF-A与乙酰转移酶TIP60相互作用，协同激活iNOS转录。TIP60的耗竭或抑制在抑制iNOS方面与MRTF-A的耗竭/抑制达到等效效果。有趣的是，TIP60似乎与H3K4三甲基转移酶复合物形成交叉对话，以促进iNOS的跨激活。综上所述，我们的数据表明MRTF-A-TIP60轴可能在巨噬细胞中的iNOS转录中发挥关键作用，因此可作为心肌IRI干预的潜在靶点。