Single-cell chromatin accessibility landscape of cardiac non-myocytes identifies tissue repair program 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 conduct single-cell ATAC sequencing 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, exhibit the most dynamic chromatin remodeling upon injury. Furthermore, we reveal CEBPD and AP-1 family transcriptional factors as pivotal trans-regulators orchestrating these alterations, governing beneficial fibroblast activation and endothelial cell angiogenesis crucial for cardiac regeneration, respectively. 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.