1Justus-Liebig-University Giessen, Medical Clinic I Cardiology & Angiology Gießen, Deutschland; 2Max Planck Institute for Heart and Lung Research Bioinformatics and Deep Sequencing Platform Bad Nauheim, Deutschland; 3Max Planck Institute for Heart and Lung Research Developmental Genetics Bad Nauheim, Deutschland; 4Universitätsklinikum Gießen und Marburg GmbH Medizinische Klinik I - Kardiologie und Angiologie Gießen, Deutschland; 5Justus-Liebig-University Giessen, Medical Clinic I Cardiology & Angiology Giessen, Deutschland
Background: Injury-induced fibrosis and scar formation are leading causes of heart failure and morbidity worldwide. Zebrafish, unlike mammals, have the ability to regenerate heart tissue even after severe myocardial lesions. Notably, epicardial-derived cells (EPDCs) and endocardial cells (EndoCs), which are major contributors to fibrotic remodeling in mammals, show only transient matrix secretion and minor differentiation of scar-forming myofibroblasts in zebrafish. In a previous study, we identified IL11/Stat3 signaling at the center of the injury response-limiting scar formation while controlling the activation of regeneration-specific gene programs. Consequently, interleukin-11 receptor (il11ra) mutant zebrafish fail to regenerate cardiac tissue post injury but induce a mammalian-like scarring response. The aim of this investigation was to better understand the mechanisms involved in regenerative reprogramming and scar formation.
Methods: We obtained scRNAseq data from cardiac stromal cells in response to zebrafish heart injury in wild-type and il11ra loss-of-function mutants at different timepoints cardiac post-injury. The combination of these datasets allowed us to analyze IL-11-dependent gene programs during cardiac regeneration and scar formation.
Results: We found that cardiac fibroblast and endothelial cells rapidly undergo dedifferentiation, including the transcriptional silencing of mature marker genes like vsg1, ogna, mfap5, and col18a1b, within the first 24 hours post-injury while inducing a regeneration-specific gene set including fn1b, hspd1, rspo3, and crlf1a, among others. In contrast, cardiac stromal cells isolated from mutants failed to undergo this response while directly committing towards a fibrogenic gene program. A high level of expression of pro-fibrotic markers such as acta2, peristotin-b, col1a1, and elastin-b in the mutants, which became more pronounced over time, confirmed this fibrotic event as early as 24 hours post cryoinjury.
Conclusions: Together, our data suggest IL11/Stat3 signaling acts on top of the known hierarchy of scar-free regeneration by driving cellular reprogramming, a process also observed in other models of scar-free regeneration during blastema formation.