Regulation of heart regeneration by LSD1 through suppressing CEND1

<b>Rationale:</b> Improving heart regeneration through reactivating cardiomyocyte proliferation holds a great potential for repairing diseased hearts. We recently reported that LSD1-dependent epigenetic repression of Cend1 transcription is prerequisite for cardiomyocyte proliferation and mouse heart development. This study interrogates the potential role of this LSD1-CEND1 axis in heart regeneration and repair. <b>Methods:</b> The cardiomyocyte-specific Lsd1 knockout or overexpression mice, Cend1 null mice and cardiomyocyte-specific Cend1 overexpression mice were used to determine the role of LSD1-CEND1 axis in heart regeneration after experimental injuries. Neonatal and adult mice were subjected to apical resection or left anterior descending coronary artery ligation, respectively, to establish cardiac injury models. Echocardiography and Masson staining were employed to assess cardiac function and histopathology, respectively. The molecular changes were determined using RNA sequencing, quantitative RT-PCR, Western blotting and immunostaining. <b>Results:</b> Cardiomyocyte-specific deletion impeded neonatal heart regeneration, while overexpression of Lsd1 had the opposite effect. RNA sequencing revealed that Cend1, a crucial suppressor of cardiomyocyte cycling, was the most significantly elevated gene induced by Lsd1 loss during heart regeneration. Cardiomyocyte-specific Cend1 overexpression hindered neonatal heart regeneration, while Cend1 loss in nullizygous mice had the opposite effect. Cend1 deletion resulted in gene expression alterations associated with enhanced cardiomyocyte proliferation, neovascularization, and macrophage activation. Furthermore, the cardiac regeneration defect caused by Lsd1 loss was not observed when experiments were performed with mice that were nullizyogus for Cend1. Moreover, we found that either Lsd1 overexpression or Cend1 deletion could promote heart regeneration and repair, and improve cardiac function following experimental myocardial infraction in adult mice. <b>Conclusion:</b> Our results demonstrate that LSD1-dependent suppression of CEND1 is crucial for heart regeneration in neonatal and adult mice after experimental injury. These findings suggest LSD1 activation and CEND1 inhibition as promising therapeutic strategies to enhance endogenous cardiac repair in humans.