Changing epigenetic landscape contributes to regenerative reprogramming post cardiac injury in zebrafish

M. Rana (Gießen)¹, M. Bentsen (Bad Nauheim)², S. Allanki (Bad Nauheim)³, N. Ahmed (Gießen)¹, D. Stainier (Gießen)⁴, M. looso (Bad Nauheim)², S. Reischauer (Gießen)^5
1medical clinic and campus Kerckhoff, Justus Liebig University experimental cardiology Gießen, Deutschland; ²Bioinformatics Core Unit (BCU), Max Planck Institute for Heart and Lung Research Bad Nauheim, Deutschland; ³Max Planck Institute for Heart and Lung Research department of developmental genetics Bad Nauheim, Deutschland; ⁴cardiopulmonary institute, UGMLC Gießen, Deutschland; ⁵Justus Liebig university Giessen Internal medicine I - Department of Cardiology Gießen, Deutschland

Unlike the adult human heart, which forms non-functional scar tissue after injury, the adult zebrafish heart can regenerate functional cardiac muscle with minimal scarring.  Effective cardiac regeneration depends on the orchestrated and precise integration of various cell types, where their interactions prompt the temporary activation of regenerative cell states. To gain a deeper understanding of the specific extracellular signals and intrinsic epigenetic frameworks that trigger these transient functional cell states, we characterized the chromatin landscapes of cardiac stromal cell populations within the regenerating heart from wildtype and mammalian like scar inducing, non-regenerative interleukin-11receptor (il11ra) deficient hearts at single-cell resolution. Our data reveals cis-regulatory elements and trans-regulatory factors that drive cell-specific gene expression patterns. Notably, we identified cell type specific Interleukin-11 dependent and independent chromatin remodelling of regulatory elements as early as 24hrs post injury and 96 hrs post injury. Our analysis reveals regeneration specific interleukin-11 dependent remodelling of elements in proximity to il11a, aldh1a2, lepb which are known regulators of cardiac regeneration in zebrafish. Moreover, we identified elements with higher accessibility in fibrotic il11ra mutant hearts linked to genes acvr1l and sox9b which are responsible for fibrosis in mammals. In addition, motif enrichment analysis revealed enrichment for Stat transcription factors binding sites which act downstream of il11ra in regenerating stromal cells when compared to our fibrotic model which shows an enrichment of egr1, a known key regulator of fibrosis in mammals.  Our findings thus underscore the critical early role played by endocardial cells (EndoCs) and epicardial-derived cells (EPDCs) in the cardiac regeneration process in zebrafish, and provides key insights into how these animals escape a fibrotic response.