Background:Establishment of the myocardial wall requires proper growth cues from nonmyocardial tissues. During heart development, the epicardium and epicardium-derived cells instruct myocardial growth by secreting essential factors including FGF (fibroblast growth factor) 9 and IGF (insulin-like growth factor) 2. However, it is poorly understood how the epicardial secreted factors are regulated, in particular by chromatin modifications for myocardial formation. The current study is to investigate whether and how HDAC (histone deacetylase) 3 in the developing epicardium regulates myocardial growth.Methods:Various cellular and mouse models in conjunction with biochemical and molecular tools were employed to study the role of HDAC3 in the developing epicardium.Results:We deleted Hdac3 in the developing murine epicardium, and mutant hearts showed ventricular myocardial wall hypoplasia with reduction of epicardium-derived cells. The cultured embryonic cardiomyocytes with supernatants from Hdac3 knockout (KO) mouse epicardial cells also showed decreased proliferation. Genome-wide transcriptomic analysis revealed that Fgf9 and Igf2 were significantly downregulated in Hdac3 KO mouse epicardial cells. We further found that Fgf9 and Igf2 expression is dependent on HDAC3 deacetylase activity. The supplementation of FGF9 or IGF2 can rescue the myocardial proliferation defects treated by Hdac3 KO supernatant. Mechanistically, we identified that microRNA (miR)-322 and miR-503 were upregulated in Hdac3 KO mouse epicardial cells and Hdac3 epicardial KO hearts. Overexpression of miR-322 or miR-503 repressed FGF9 and IGF2 expression, while knockdown of miR-322 or miR-503 restored FGF9 and IGF2 expression in Hdac3 KO mouse epicardial cells.Conclusions:Our findings reveal a critical signaling pathway in which epicardial HDAC3 promotes compact myocardial growth by stimulating FGF9 and IGF2 through repressing miR-322 or miR-503, providing novel insights in elucidating the etiology of congenital heart defects and conceptual strategies to promote myocardial regeneration.

中文翻译：

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心外膜 HDAC3 通过新型 MicroRNA 途径促进心肌生长

背景：心肌壁的建立需要来自非心肌组织的适当生长线索。在心脏发育过程中，心外膜和心外膜衍生细胞通过分泌 FGF（成纤维细胞生长因子）9 和 IGF（胰岛素样生长因子）2 等必需因子来指导心肌生长。然而，人们对心外膜分泌因子的调节机制知之甚少。 ，特别是通过染色质修饰促进心肌形成。目前的研究是探讨心外膜发育中的HDAC（组蛋白脱乙酰酶）3是否以及如何调节心肌生长。方法：采用各种细胞和小鼠模型结合生化和分子工具来研究HDAC3在心外膜发育中的作用。结果：我们在发育中的小鼠心外膜中删除了Hdac3，突变心脏表现出心室心肌壁发育不全，心外膜来源的细胞减少。用Hdac3敲除 (KO) 小鼠心外膜细胞上清液培养的胚胎心肌细胞也显示增殖减少。全基因组转录组分析显示，Hdac3 KO 小鼠心外膜细胞中Fgf9和Igf2显着下调。我们进一步发现Fgf9和Igf2的表达依赖于HDAC3脱乙酰酶活性。补充FGF9或IGF2可以挽救Hdac3 KO上清液治疗的心肌增殖缺陷。从机制上讲，我们发现 microRNA (miR)-322 和 miR-503 在Hdac3 KO 小鼠心外膜细胞和Hdac3心外膜 KO 心脏中上调。在Hdac3 KO 小鼠心外膜细胞中，miR-322 或 miR-503 的过表达抑制了 FGF9 和 IGF2 的表达，而 miR-322 或 miR-503 的敲低则恢复了 FGF9 和 IGF2 的表达。结论：我们的研究结果揭示了心外膜 HDAC3 参与其中的一个关键信号通路。通过抑制 miR-322 或 miR-503 刺激 FGF9 和 IGF2 来促进致密心肌生长，为阐明先天性心脏缺陷的病因和促进心肌再生的概念策略提供了新的见解。