BACKGROUND:Discovering determinants of cardiomyocyte maturity is critical for deeply understanding the maintenance of differentiated states and potentially reawakening endogenous regenerative programs in adult mammalian hearts as a therapeutic strategy. Forced dedifferentiation paired with oncogene expression is sufficient to drive cardiac regeneration, but elucidation of endogenous developmental regulators of the switch between regenerative and mature cardiomyocyte cell states is necessary for optimal design of regenerative approaches for heart disease. MBNL1 (muscleblind-like 1) regulates fibroblast, thymocyte, and erythroid differentiation and proliferation. Hence, we examined whether MBNL1 promotes and maintains mature cardiomyocyte states while antagonizing cardiomyocyte proliferation.METHODS:MBNL1 gain- and loss-of-function mouse models were studied at several developmental time points and in surgical models of heart regeneration. Multi-omics approaches were combined with biochemical, histological, and in vitro assays to determine the mechanisms through which MBNL1 exerts its effects.RESULTS:MBNL1 is coexpressed with a maturation-association genetic program in the heart and is regulated by the MEIS1/calcineurin signaling axis. Targeted MBNL1 overexpression early in development prematurely transitioned cardiomyocytes to hypertrophic growth, hypoplasia, and dysfunction, whereas loss of MBNL1 function increased cardiomyocyte cell cycle entry and proliferation through altered cell cycle inhibitor transcript stability. Moreover, MBNL1-dependent stabilization of estrogen-related receptor signaling was essential for maintaining cardiomyocyte maturity in adult myocytes. In accordance with these data, modulating MBNL1 dose tuned the temporal window of neonatal cardiac regeneration, where increased MBNL1 expression arrested myocyte proliferation and regeneration and MBNL1 deletion promoted regenerative states with prolonged myocyte proliferation. However, MBNL1 deficiency was insufficient to promote regeneration in the adult heart because of cell cycle checkpoint activation.CONCLUSIONS:Here, MBNL1 was identified as an essential regulator of cardiomyocyte differentiated states, their developmental switch from hyperplastic to hypertrophic growth, and their regenerative potential through controlling an entire maturation program by stabilizing adult myocyte mRNAs during postnatal development and throughout adulthood. Targeting loss of cardiomyocyte maturity and downregulation of cell cycle inhibitors through MBNL1 deletion was not sufficient to promote adult regeneration.

中文翻译：

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MBNL1 调节再生心脏状态和分化心脏状态之间的程序化产后切换

背景：发现心肌细胞成熟的决定因素对于深入了解成年哺乳动物心脏中分化状态的维持和潜在的重新唤醒内源性再生程序作为治疗策略至关重要。强制去分化与癌基因表达相结合足以驱动心脏再生，但阐明再生和成熟心肌细胞状态之间转换的内源性发育调节因子对于心脏病再生方法的优化设计是必要的。MBNL1（肌盲样 1）调节成纤维细胞、胸腺细胞和红细胞分化和增殖。因此，我们检查了MBNL1是否在拮抗心肌细胞增殖的同时促进和维持成熟的心肌细胞状态。方法：在多个发育时间点和心脏再生手术模型中研究了MBNL1功能获得和丧失的小鼠模型。多组学方法与生化、组织学和体外测定相结合，以确定 MBNL1 发挥作用的机制。 结果：MBNL1 与心脏中的成熟相关遗传程序共表达，并受 MEIS1/钙调磷酸酶信号传导调节轴。发育早期的靶向MBNL1过表达会使心肌细胞过早转变为肥大生长、发育不全和功能障碍，而MBNL1功能的丧失则通过改变细胞周期抑制剂转录稳定性来增加心肌细胞细胞周期的进入和增殖。此外，MBNL1 依赖性雌激素相关受体信号传导的稳定性对于维持成年心肌细胞的心肌细胞成熟至关重要。根据这些数据，调节MBNL1剂量调整了新生儿心脏再生的时间窗口，其中增加的MBNL1表达抑制了心肌细胞的增殖和再生，而MBNL1的缺失则促进了再生状态并延长了心肌细胞的增殖。然而，由于细胞周期检查点激活，MBNL1 缺乏不足以促进成年心脏的再生。结论：在这里，MBNL1 被确定为心肌细胞分化状态、心肌细胞从增生性生长到肥大性生长的发育转变以及其再生潜力的重要调节因子。通过在出生后发育和整个成年期稳定成体肌细胞 mRNA 来控制整个成熟程序。通过删除 MBNL1 来靶向心肌细胞成熟度的丧失和细胞周期抑制剂的下调不足以促进成体再生。