Cyclin A2 Induces Human Adult Cardiomyocyte Cytokinesis and Elicits Cardiomyocyte Reprogramming and Dedifferentiation

Cyclin A2 (CCNA2), a master cell cycle regulator, is silenced in postnatal mammalian cardiomyocytes. We have previously demonstrated its ability to promote cardiac repair in small and large animals when delivered to the heart via a viral vector. However, the effect of CCNA2 gene delivery on cytokinesis in isolated cardiomyocytes from adult human hearts has not been explored. We designed a human gene therapy vector featuring a replication-deficient adenovirus encoding human CCNA2 driven by the cardiac Troponin T promoter to enable the expression of CCNA2 in freshly isolated human cardiomyocytes. Time-lapse live imaging of adult human primary cardiomyocytes from a 21-year-old male, a 41-year-old female, and a 55-year-old male demonstrated the induction of complete cytokinesis in human adult cardiomyocytes with preservation of sarcomere integrity in the resulting daughter cells with active calcium mobilization in redifferentiated cardiomyocytes. To elucidate the transcriptional mechanisms underlying this response, we conducted single-nucleus transcriptomics analysis of hearts isolated from adult transgenic mice that constitutively express CCNA2 in cardiomyocytes (CCNA2-Tg) and non- transgenic mice (nTg). This revealed a cardiomyocyte subpopulation enriched with cytokinesis, proliferative, and reprogramming genes in hearts obtained from CCNA2-Tg mice as compared to41nTg mice. Ultra-deep bulk RNA sequencing of human adult and fetal hearts identified key reprogramming genes relevant to understanding the mechanisms of CCNA2-induced effects observed in our experimental models. These findings provide a promising path for the clinical development of CCNA2-based cardiac regenerative therapy.