Cardiomyocyte Cell Cycle, Renewal and Isolation

Heart disease results from the loss of cardiomyocytes following myocardial damage and is a leading cause of death worldwide. Stimulating the endogenous regeneration of cardiomyocytes or isolating them from in vitro culture is an attractive therapeutic strategy. In paper I, the focus is on the cellular growth patterns of murine cardiomyocytes under steady-state conditions. The turnover of cardiomyocytes was accurately established and key gene expression patterns associated with developmentally distinct periods of cardiomyocyte growth and turnover were identified. There was no significant generation of cardiomyocytes in the adult mouse heart. In paper II, the focus is on turnover of human cardiomyocytes . Taking advantage of the integration of 14C generated by nuclear bomb tests during the Cold War into DNA, we were able to accurately establish the age of cardiomyocytes in humans. Through mathematical modeling it was established that cardiomyocytes are renewed at a rate of approximately 1% per year at the age of 20 and 0.4% at the age of 75. In papers III and IV, the focus was the development of isolation strategies for embryonic (paper III & IV) and more mature cardiomyocytes (paper IV). We establish a non-genetic FACS based technique utilizing the surface marker VCAM-1, facilitating the enrichment of embryonic cardiomyocytes (paper III). Additional surface markers are assayed for their potential to isolate cardiomyocytes from other time-points in paper IV.
This thesis provides new knowledge in the field of cardiomyocyte kinetics and mitotic activity. In addition we have identified key genes involved in cell cycle control in cardiomyocytes, which are potential candidates for therapeutic manipulation. We have also established a non-genetic FACS based purification method for embryonic cardiomyocytes. Any potential cellular therapy for heart disease involving cardiomyocytes would require the elimination of contaminating non-myocyte cells. A strategy that facilitates a non-genetic method of isolating embryonic cardiomyocytes would also be a powerful tool for the study of such cells.