Background: The inability of the adult mammalian heart to regenerate following injury represents a major barrier in cardiovascular medicine. In contrast, the neonatal mammalian heart retains a transient capacity for regeneration, which is lost shortly after birth. Defining the molecular mechanisms that govern regenerative capacity in the neonatal period remains a central goal in cardiac biology. Here, we assemble a transcriptomic framework of multiple cardiac cell populations during postnatal development and following injury, which enables comparative analyses of the regenerative (neonatal) versus nonregenerative (adult) state for the first time.

Methods: Cardiomyocytes, fibroblasts, leukocytes, and endothelial cells from infarcted and noninfarcted neonatal (P1) and adult (P56) mouse hearts were isolated by enzymatic dissociation and fluorescence-activated cell sorting at day 3 following surgery. RNA sequencing was performed on these cell populations to generate the transcriptome of the major cardiac cell populations during cardiac development, repair, and regeneration. To complement our transcriptomic data, we also surveyed the epigenetic landscape of cardiomyocytes during postnatal maturation by performing deep sequencing of accessible chromatin regions by using the Assay for Transposase-Accessible Chromatin from purified mouse cardiomyocyte nuclei (P1, P14, and P56).

Results: Profiling of cardiomyocyte and nonmyocyte transcriptional programs uncovered several injury-responsive genes across regenerative and nonregenerative time points. However, the majority of transcriptional changes in all cardiac cell types resulted from developmental maturation from neonatal stages to adulthood rather than activation of a distinct regeneration-specific gene program. Furthermore, adult leukocytes and fibroblasts were characterized by the expression of a proliferative gene expression network following infarction, which mirrored the neonatal state. In contrast, cardiomyocytes failed to reactivate the neonatal proliferative network following infarction, which was associated with loss of chromatin accessibility around cell cycle genes during postnatal maturation.

Conclusions: This work provides a comprehensive framework and transcriptional resource of multiple cardiac cell populations during cardiac development, repair, and regeneration. Our findings define a regulatory program underpinning the neonatal regenerative state and identify alterations in the chromatin landscape that could limit reinduction of the regenerative program in adult cardiomyocytes.

中文翻译：

---

哺乳动物心脏再生的多细胞转录分析

背景：成年哺乳动物心脏在受伤后无法再生，这是心血管医学的主要障碍。相反，新生的哺乳动物心脏保留了短暂的再生能力，该能力在出生后不久就会丧失。定义控制新生儿再生能力的分子机制仍然是心脏生物学的主要目标。在这里，我们组装了出生后发育过程中和受伤后多个心脏细胞群体的转录组框架，这使得首次能够比较分析再生（新生儿）与非再生（成人）状态。

方法：在手术后第3天，通过酶解和荧光激活细胞分选法分离来自梗塞和未梗塞的新生（P1）和成年（P56）小鼠心脏的心肌细胞，成纤维细胞，白细胞和内皮细胞。在心脏发育，修复和再生过程中，对这些细胞群体进行RNA测序，以生成主要心脏细胞群体的转录组。为了补充我们的转录组数据，我们还通过使用来自纯化小鼠心肌细胞核的转座酶可及染色质测定法（P1，P14和P56）对可及染色质区域进行了深度测序，从而调查了出生后成熟期间心肌细胞的表观遗传学景观。

结果：心肌细胞和非肌细胞转录程序的分析揭示了跨再生和非再生时间点的几个损伤反应基因。但是，所有心脏细胞类型的大多数转录变化是由于从新生儿阶段到成年期的发育成熟，而不是激活了独特的再生特异性基因程序。此外，成年白细胞和成纤维细胞的特征在于梗死后增殖基因表达网络的表达，这反映了新生儿的状态。相反，心肌细胞在梗塞后未能重新激活新生儿增殖网络，这与出生后成熟期间细胞周期基因周围的染色质可及性丧失有关。

结论：这项工作为心脏发育，修复和再生期间多个心脏细胞群体提供了一个全面的框架和转录资源。我们的研究结果确定了新生儿再生状态的基础调控程序，并确定了染色质景观的变化，这些变化可能会限制成年心肌细胞再生程序的还原。