Activation of a transient progenitor state in the epicardium is required for zebrafish heart regeneration

Abstract

The epicardium, a mesothelial cell tissue that encompasses vertebrate hearts, supports heart regeneration after injury through paracrine effects and as a source of multipotent progenitors. However, the progenitor state in the adult epicardium has yet to be defined. Through single-cell RNA-sequencing of isolated epicardial cells from uninjured and regenerating adult zebrafish hearts, we define the epithelial and mesenchymal subsets of the epicardium. We further identify a transiently activated epicardial progenitor cell (aEPC) subpopulation marked by ptx3a and col12a1b expression. Upon cardiac injury, aEPCs emerge from the epithelial epicardium, migrate to enclose the wound, undergo epithelial-mesenchymal transition (EMT), and differentiate into mural cells and pdgfra+hapln1a+ mesenchymal epicardial cells. These EMT and differentiation processes are regulated by the Tgfβ pathway. Conditional ablation of aEPCs blocks heart regeneration through reduced nrg1 expression and mesenchymal cell number. Our findings identify a transient progenitor population of the adult epicardium that is indispensable for heart regeneration and highlight it as a potential target for enhancing cardiac repair.

ptx3a+ fibroblast/epicardial cells provide a transient macrophage niche to promote heart regeneration

“… 38 After further examination of gene expression, we identified in these cells significant enrichment of the inflammatory response regulator ptx3a ( Figure S1C ), 39 a gene recently reported to label a transient Fb/Epi subtype during heart regeneration. 40 We examined ptx3a expression in zebrafish and observed no signals in uninjured hearts but in situ signals exclusively localized to the injury site at 7 dpa ( Figure S1D ). We then employed ptx3a regulatory sequences to create a ptx3a:EGFP BAC transgenic fluorescence reporter and visualized EGFP + cells in the injury site at 3 and 7 dpa and EGFP + fluorescence is returned to undetectable levels at 30 dpa ( Figure 3A ), which recapitulates endogenous ptx3a expression.…”

Foxm1 regulates cardiomyocyte proliferation in adult zebrafish after cardiac injury

“…1 G-J). Semi-qualitative analysis of the fibrotic area was performed to indicate the increased severity of the damage as shown in previous studies ( Bise et al, 2020 ; She et al, 2020 ; Sun et al, 2022 ; Xia et al, 2022 ). Acid fuchsin orange G (AFOG) staining revealed fibrotic tissue in foxm1 m/m ( Fig.…”

Cross-species single-cell comparison of systemic and cardiac inflammatory responses after cardiac injury

“…Heart ventricles were collected from adult hearts either with cryoinjury or uninjured control fish. Briefly, ventricles were collected as described previously 45, 46 . Ventricles were placed in the ice-cold PBS buffer with 1% BSA.…”