Project description:Canonical roles for macrophages in mediating the fibrotic response after a heart attack (myocardial infarction) include turnover of the extracellular matrix and activation of cardiac fibroblasts to initiate collagen deposition. Here we reveal through studying the functional kinetics of fibrosis during zebrafish heart regeneration and mouse heart repair that macrophages can directly contribute collagen to the forming scar. Unbiased transcriptomics revealed an up-regulation of collagen isoforms in both zebrafish and mouse macrophages following injury. Adoptive transfer of macrophages from collagen-tagged transgenic zebrafish and splenic monocyte-derived macrophages from adult mouse GFPtpz-collagen donors, enhanced scar formation and induced fibrosis, respectively, via cell autonomous production of collagen. In zebrafish, macrophage-specific targeting of collagen 4a binding protein and cognate collagen 4a1 followed by transfer led to significantly reduced scarring in cryo-injured hosts. These findings contrast with the current model of scarring whereby collagen deposition is exclusively attributed to myofibroblasts, and implicate macrophages as direct contributors to fibrosis during heart repair.
Project description:The adult mammalian heart heals after myocardial infarction (MI) by deposition of scar tissue, leading to downstream arrhythmia, remodelling and heart failure1. In contrast, adult zebrafish and neonatal mouse hearts are capable of regenerating after injury. Macrophages are key mediators of tissue repair and appear to be required for both regeneration and healing by scar formation, but the mechanisms underlying these distinct roles are poorly understood2-4. Here we investigated how macrophages differentially influence the mode of repair by determining their responses in scar-free versus scar-induced healing, comparing ventricular resection with cryo-injured adult zebrafish hearts and neonatal versus adult mouse hearts after MI. Unbiased transcriptomics revealed molecular programmes implicating macrophages in the initiation and resolution of inflammation to dictate the kinetics of scarring during zebrafish regeneration and the activation of direct and indirect pathways to drive fibrosis in the adult mouse heart. Most notably we observed up-regulation of collagen isoforms in both zebrafish and mouse macrophages following injury. Adoptive transfer of macrophages, from resected zebrafish hearts into cryo-injured hosts and splenic monocyte-derived macrophages from adult mouse donors into neonatal hearts, enhanced scar formation and induced fibrosis, respectively, via cell autonomous production of collagen. In zebrafish, macrophage-specific targeting of collagen 4a binding protein and cognate collagen 4a1 followed by transfer led to significantly reduced scarring in cryo-injured hosts, as further evidence of a direct macrophage contribution to collagen deposition and scar formation. These findings contrast with the current model of scarring, whereby collagen is laid down exclusively by myofibroblasts, and implicate macrophages as critical regulators of heart repair.
Project description:Fibroblasts are activated to repair the heart following injury. Fibroblast activation in the mammalian heart leads to a permanent fibrotic scar that impairs cardiac function. In other organisms, such as zebrafish, cardiac injury is followed by transient fibrosis and scar-free regeneration. The mechanisms that drive scarring versus scar-free regeneration are not well understood. Here, we show that the homeobox-containing transcription factor Prrx1b is required for scar-free regeneration of the zebrafish heart as the loss of Prrx1b results in excessive fibrosis and impaired cardiomyocyte proliferation. Through lineage tracing and single-cell RNA sequencing we find that Prrx1b is activated in epicardial-derived cells where it restricts TGFβ ligand expression and collagen production. Furthermore, through combined in vitro experiments in human fetal epicardial-derived cells and in vivo rescue experiments in zebrafish, we conclude that Prrx1 stimulates Nrg1 expression and promotes cardiomyocyte proliferation. Collectively, these results indicate that Prrx1 is a key transcription factor that balances fibrosis and regeneration in the injured zebrafish heart.
Project description:Amputation of heart tissue followed by regeneration of the heart. Samples were taken at 0 hpa (hours post-amputation), 6 hpa, 12 hpa, 24 hpa, 3 dpa and 5 dpa.