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Heart regeneration is an unmet clinical need, hampered by limited renewal of adult cardiomyocytes and fibrotic scarring. Pluripotent stem cell-based strategies are emerging, but unravelling cellular dynamics of host–graft crosstalk remains elusive. Here, by combining lineage tracing and single-cell transcriptomics in injured non-human primate heart biomimics, we uncover the coordinated action modes of human progenitor-mediated muscle repair. Chemoattraction via CXCL12/CXCR4 directs cellular migration to injury sites. Activated fibroblast repulsion targets fibrosis by SLIT2/ROBO1 guidance in organizing cytoskeletal dynamics. Ultimately, differentiation and electromechanical integration lead to functional restoration of damaged heart muscle. In vivo transplantation into acutely and chronically injured porcine hearts illustrated CXCR4-dependent homing, de novo formation of heart muscle, scar-volume reduction and prevention of heart failure progression. Concurrent endothelial differentiation contributed to graft neovascularization. Our study demonstrates that inherent developmental programmes within cardiac progenitors are sequentially activated in disease, enabling the cells to sense and counteract acute and chronic injury.

Introduction:Larval zebrafish are used to study regenerative properties of cardiac muscle, and treatments that enhance this process. Cardiac injury models in zebrafish larva include cryoinjury, laser ablation, pharmacological treatment and cardiac dysfunction mutations. Effective in damaging cardiomyocytes, these models lack the critical element of tissue hypoxia, which induces molecular cascades within cardiac muscle.Methods and Results:We have developed a potentially more realistic model for studying cardiac arrest and recovery in larval zebrafish (Danio rerio) by using acute, severe hypoxic exposure. Exposure to PO2s of 6-9 mmHg induces loss of mobility followed by cardiac arrest within 120min in 5 days post fertilization (dpf) and 40min at 10dpf. Approximately 90% of 5dpf larvae survive acute hypoxic exposure, but survival fell to 30% by 10dpf. Heart beat resumed in surviving larvae and returned to air-saturated water at 4 min in 5dpf and 6-8 min at 8-10 dpf. Heart rate (HR), stroke volume (SV) and cardiac output (CO) in control 6-7dpf larvae before hypoxic exposure were 188?5bpm, 0.20?0.001nl and 35.5.3?2.2nl/min (n=35), respectively. In larvae with hypoxia-induced cardiac arrest, HR returned to control values by 24 h of recovery, but SV and CO remained ~50% depressed from control values at 24 h. Full restoration of cardiac performance was evident at 72h. Molecular markers (PCNA, PHH3, Ki67) indicate cardiomyocyte damage was associated with hypoxia-induced cardiac arrest, and that subsequent cardiomyocyte proliferation contributed to recovery of heart function.Conclusion:As an alternative to models employing mechanically or pharmacologically induced damage to the developing myocardium, the highly reproducible cardiac effects of acute hypoxia-induced cardiac arrest in the larval zebrafish represent an alternative, more realistic model, actually employing hypoxic damage, for studying cardiac tissue hypoxia injury and recovery of function.