Comparative single-cell profiling reveals distinct cardiac resident macrophages essential for zebrafish heart regeneration

Zebrafish exhibit a robust ability to regenerate their hearts following injury, and the immune system plays a key role in this process. We previously showed that delaying macrophage recruitment by clodronate liposome (CL) treatment compromises neutrophil resolution and heart regeneration, even when the infiltrating macrophage number was restored within the first-week post injury (Lai et al., 2017). Here, we examined the molecular mechanisms underlying the cardiac repair of regenerative PBS-control hearts vs. non-regenerative CL-treated hearts. Bulk transcriptomic analyses revealed that CL-treated hearts exhibited disrupted inflammatory resolution and energy metabolism during cardiac repair. Temporal single-cell profiling of inflammatory cells in regenerative vs. non-regenerative conditions further identified heterogenous macrophages and neutrophils with distinct infiltration dynamics, gene expression, and cellular crosstalk. Among them, two residential macrophage subpopulations were enriched in regenerative hearts and barely recovered in non-regenerative hearts. Early CL treatment at 8 days or even 1 month before cryoinjury led to the depletion of resident macrophages without affecting the circulating macrophage recruitment to the injured area. Strikingly, these resident macrophage-deficient zebrafish still exhibited compromised neovascularization and scar resolution. Our results characterized the inflammatory cells of the zebrafish injured hearts and identified key resident macrophage subpopulations prerequisite for successful heart regeneration.