染色质重塑相关蛋白EZH2调控心房肌细胞钙稳态与成纤维细胞分化在衰老伴发房颤中的作用和机制研究

Atrial fibrillation is the most common arrhythmia associated with aging. Chromatin remodeling plays an important role in this process, in which the histone methyltransferase EZH2 affects chromatin remodeling by methylation histone H3K27. However, how EZH2 affects atrial fibrillation associated with aging has not been clarified. Our latest study shows that EZH2 inhibitor GSK126 reduce Ang-II-induced atrial fibrosis and the susceptibility to atrial fibrillation. Our pilot study further found that: 1) EZH2 expression in the atria of elderly patients with atrial fibrillation was significantly higher than that of patients with sinus rhythm, and its expression was positively correlated with the extent of atrial fibrosis; 2) In aged mouse atrial myocytes, EZH2 affects calcium homeostasis by up-regulating the L-type calcium channel CACNA1C subunit and down-regulating the sodium-calcium exchanger SLC8A1 gene expressions; 3) In senescent atrial fibroblasts, silencing of EZH2 can up-regulate PPAR-γ but down-regulate MMP9 and other key cell differentiation factors. We are the first to propose the hypothesis that EZH2, which is up-regulated by aging, increases the susceptibility to atrial fibrillation by regulating the calcium homeostasis (electrical remodeling) and atrial fibroblasts differentiation (structural remodeling). This study aims to elucidate the role of EZH2 in the pathogenesis of atrial fibrillation associated with aging at various levels, such as molecules, cells, and aging mice, thus providing a new therapeutic target for atrial fibrillation.

房颤是衰老伴发的最常见心律失常。染色质重塑在此过程中起重要作用，其中组蛋白甲基化转移酶EZH2通过甲基化组蛋白H3K27来影响染色质重塑。但EZH2如何影响衰老伴发房颤未见报道。我们最新研究表明，EZH2抑制剂GSK126降低Ang-II引起的心房纤维化及房颤诱发易感性。预实验进一步发现：1）老龄房颤患者心房肌中EZH2表达明显高于窦律患者，且其表达与心房纤维化程度呈正相关；2）老年小鼠心房肌细胞中，EZH2通过上调L型钙通道CACNA1C亚基和下调钠-钙交换体SLC8A1的表达而影响钙稳态；3）衰老心房成纤维细胞中，EZH2沉默可上调PPAR-γ和下调MMP9等关键细胞分化因子。我们率先提出衰老上调的EZH2通过对心房肌细胞钙稳态（电重构）和心房成纤维细胞分化（结构重构）的调控增加房颤易感性这一假说，拟在分子、细胞、衰老动物等多水平上阐明EZH2在衰老伴发房颤的作用，为其治疗提供新靶标。

心房颤动是目前临床上最常见的心律失常，主要表现为心律绝对不规则，患者多出现心悸、头晕等不适，严重者可出现晕厥，甚至猝死。房颤可引起严重的并发症，如心衰，卒中等。随着年龄的进展，房颤的发病及患病人数逐年上升，年龄为房颤发生发展的主要独立危险因素。表观遗传学是在DNA 碱基序列不变前提下引起基因表达或细胞表型变化的一种遗传，包括DNA 甲基化、染色体重塑和非编码RNA 调控等，其中染色质重塑是调节真核基因表达的重要机制，是基因表达在表观遗传水平上调控的主要方式。染色质重塑在衰老引起的房颤中扮演着重要的角色，本课题组发现组蛋白甲基化转移酶EZH2通过甲基化组蛋白H3K27调控染色质重塑，促进房颤的发生。在房颤病人及AngII小鼠房颤模型和快速刺激诱发房颤的狗的模型中均发现EZH2的升高，并且介导H3K27me3，并通过TGF-β-Smad信号通路刺激成纤维细胞分化，使心房肌细胞纤维化加重，导致结构重构，增加房颤的诱发率，而应用EZH2抑制剂GSK126抑制EZH2的表达后，心房肌纤维化程度明显减轻。同时，在体外进行心房成纤维细胞连续传代（P5）构建成纤维细胞衰老模型中，我们则发现EZH2表达下调，且其同样调控H3K27me3，而后者可直接富集在CDKN2A and Timp4基因的启动子区域,并直接引起Timp4-MMP8信号通路紊乱，从而促进细胞外基质紊乱，纤维化增加。本课题在多种动物和细胞模型中证实EZH2在心房电重构和结构重构中发挥重要作用，并进一步阐明EZH2通过参与不同的信号通路如TGFβ-Smad通路和TIMP4-MMP8信号通路等发挥上述作用，为房颤的治疗及预防提供潜在分子靶点。