Single-cell analysis reveals the epigenetic remodeling and key effectors of non-cardiomyocytes during heart regeneration.

The restricted regenerative potential of adult hearts poses a significant barrier to effective repair following injury. In contrast to numerous vertebrates, mammalian hearts exhibit only transient neonatal renewal capacity during the initial days of life. Beyond cardiomyocytes, understanding the diverse compositions of non-cardiomyocytes (non-CMs) is imperative for maintaining heart microenvironment homeostasis during neonatal heart regeneration. Here, we conducted single-cell ATAC sequencing (scATAC-seq) on neonatal hearts at varying time points post-apical resection to profile the epigenetic landscape. Intriguingly, fibroblasts and endothelial cells, as the most abundant populations in the heart, exhibited the most dynamic chromatin remodeling as the heart loses its regenerative potential. Our application of scATAC-seq unveiled key regulatory elements such as Cebpd in fibroblast activation and proliferation, while highlighting the essential role of AP-1 in endothelial cell angiogenesis, migration, and proliferation. Additionally, we uncovered active engagement of regulatory elements identified by non-CMs in regulating the behavior of cardiomyocytes, inhibition of which impaired cardiac function post-injury. Collectively, our study delineates the cellular identity of non-CMs at the epigenome level using single-cell approaches, offering insights into cell-type-targeted interventions for heart regeneration.