Synergistic Effect of Cardio-Stemin and YAP5SA Promotes Cardiomyocyte Regeneration in vivo

Cardiovascular diseases are the leading cause of death worldwide. The fundamental goal of rescuing heart disease caused by loss or dysfunction of cardiomyocyte is to regain beating cardiomyocytes after injury. In this dissertation, we elucidated the synergistic effect of Stemin and YAP5SA in cardiomyocyte proliferation. More specifically, we focused on the potential of Stemin synergistically work with YAP5SA, inhibiting interactions between SRF and cardiac specific cofactors to inhibit SRF dependent cardiomyocyte differentiation, and promoting cell proliferation. Co-expression of Stemin and YAP5SA promoted EdU incorporation in both neonatal and adult cardiomyocyte. Adult cardiomyocytes were brought back into a putatively more primitive, fetal-like state for cell replication. Bioinformatic analysis revealed the upregulation of multiple cell cycle gene clusters with co-expression of Stemin and YAP5SA, while gene clusters associated with cardiomyocyte differentiation (GO: 0055007), sarcomeric assembly and cardiac muscle contraction (GO: 0060048) were profoundly downregulated. We also performed ATAC-seq in mRNA treated neonatal cardiomyocytes, which suggested a substantial increase of accessible chromatin region in mRNA treatment groups compared to the controls, indicating that Stemin and YAP5SA treatment may induce a global epigenetic change, which showed consistency with the RNA-seq results. We tested the treatment combination in vivo by injecting Stemin and YAP5SA mRNA directly into the left ventricles of adult mice after myocardial infarction. We were able to detect EdU incorporation around the needle tracts in the mRNA treatment groups, indicating promoted cell proliferation in response to Stemin and YAP5SA mRNA injection. Picrosirius Red staining also suggested reduced fibrosis. We further illustrated the improvement in mouse cardiac function in long-term experiments by echocardiography, demonstrating an ameliorated cardiac function by Stemin and YAP5SA mRNA co-injection. In conclusion, here we described a combination of factors that effectively induce cardiomyocyte proliferation both in vitro and in vivo. We revealed that the introduction of Stemin and YAP5SA synergistically promotes cardiomyocyte proliferation by inhibiting SRF dependent cardiomyocyte differentiation, thus pushing cardiomyocyte into a more primitive, stem cell-like stage to foster cell replication. Our findings suggested that inducing tissue renewal by Stemin and YAP5SA mRNA may be a useful strategy to treat degenerative human disease such as myocardial infarction.