Abstract P1019: CycleTrack , A Genetic Method To Trace Cardiomyocyte Renewal In Small And Large Animal Models

To what extent cardiac renewal occurs in adulthood and can be stimulated by therapeutic interventions is still a matter of investigation. In particular, over the last few years, significant effort has been made into awakening the endogenous regenerative potential of the adult mammalian heart after injury using different strategies. However, these studies are significantly hindered by the lack of tools to properly assess cardiomyocyte renewal over time. We have developed a genetic strategy, which we named CycleTrack, allowing a cumulative and accurate estimate of cardiomyocyte divisions in vivo. This method is based on the expression, in cardiomyocytes, of the Cre recombinase under the control of a 312-bp fragment of the Cyclin B2 promoter, which is specifically sensitive to cell proliferation. Replication-activated Cre acts on floxed GFP that is either present in the genome of transgenic mice or is exogenously delivered using Adeno-Associated Viral (AAV) vectors. As a result, cardiomyocytes traversing G2/M become irreversibly labeled. Using CycleTrack, we could monitor cardiomyocyte turnover in several physiological and pathological conditions. These included the measurement of the rate of proliferation of cardiomyocytes after apical resection in neonatal mice, the pro-regenerative effect of AAV9-mediated delivery of miRNA-199a and miRNA-590 after myocardial infarction in adult mice and the effect of pregnancy on myocardial hyperplasia. We also delivered the CycleTrack vectors into pig hearts to visualize cardiomyocyte turnover after myocardial infarction. Considering the large availability of Cre reporter mouse lines and the efficacy of AAVs to transfer genes into cardiomyocytes, we propose CycleTrack as a robust and straightforward tool to trace mitotic events for cardiac regeneration studies in small and large animal models.