Abstract 32: The Role of Cyclin A2 in Adult Human Cardiomyocyte Plasticity
The adult mammalian heart is known to have a very low abundance of progenitor cells which can take part in active cycling and regeneration after damage. Cardiomyocytes exit the cell cycle soon after birth coincident with the silencing of cyclin A2 (CCNA2). In our previous studies, we demonstrated that viral delivery of Ccna2 induces cardiac regeneration in infarcted hearts of small and large animal models. However, the molecular mechanism whereby Ccna2 induces cardiac regeneration and increase in cardiac function deserves further study. To explore further, we isolated adult mouse cardiomyocytes and induced Ccna2 expression by using adenovirus transfection and cultured them for 3 weeks. Co-expression of the mature cardiac marker troponin Tc with the immature cardiac marker non-muscle myosin IIB was observed. Additionally, expression of epithelial to mesenchymal transition markers (vimentin and FSP1) was observed. Also, decreased expression of mature cardiac markers α-MHC , ckmt2 and cTnT was noted. To study the factors responsible for human cardiomyocyte plasticity and cell division, we have optimized a novel method for culturing adult human cardiomyocytes in our laboratory. We cultured cardiomyocytes isolated from heart tissue obtained from a 55 yr old male patient. After transfection with CCNA2 adenovirus made for human use (cTnT promoter driving human CCNA2 cDNA), they were co-transfected with two more adenoviruses (1) cTnT-GFP to label cardiomyocytes (green) and (2) CMV-α-actinin-m-Cherry to label the sarcomere (red). Time lapse live epifluorescence microscopy was carried out for 70 hrs and time lapse movies were prepared (please refer the youtube link to see a representative time lapse movie https://youtu.be/OBrJGCq7YCA ). Movies were analyzed to calculate the cytokinesis index in samples transfected with (Test) and without (Null) CCNA2 adenoviruses. We observed a significantly higher cytokinesis index in CCNA2 samples versus Null. We are further investigating the role of cyclin A2 in dedifferentiation of adult human cardiomyocytes to generate immature or progenitor cardiac cells and their contractile status, which could be utilized for regeneration and functional restoration of damaged adult heart tissue.