Transcriptional reprogramming of cardiac stromal cells post cardiac cryo-injury in Zebrafish

Injury induced fibrosis and scar formation are a leading cause 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 only show 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, il11ra mutant zebrafish fail to regenerate cardiac tissue post injury but induce a mammalian like scarring response. To better understand the mechanisms involved in regenerative reprogramming and scar formation, we now established scRNAseq data of cardiac stromal cells in response of zebrafish heart injury in wild type and il11ra loss of function mutants at different time points post injury. The combination of these datasets allows us to identify Il-11 dependent gene programs during cardiac regeneration and scar formation. We find that cardiac fibroblasts and endothelial cells rapidly undergo dedifferentiation including the transcriptional silencing of mature marker genes like vsg1, ogna, mfap5, col18a1b within the first 24 hours post injury while inducing a regeneration specific gene set including fn1b, hspd1, rspo3, crlf1a etc. In contrast, cardiac stromal cells isolated from interleukin-11 mutants fail to undergo this response hence directly committing towards a fibrogenic gene program. High level of pro-fibrotic markers expression such as acta2, peristotin-b, col1a1 and elastin-b in mutant confirm this fibrotic event as early as 24hpci, which gets more pronounced over time. Together, our data suggests IL11/Stat3 signaling to act on top of the known hierarchy of scar free regeneration by driving cellular reprogramming, a phenomenon including dedifferentiation and the activation of a cell type specific regenerative gene program.