The study of human embryonic stem cells (hESC) has unleashed new avenues
in the fields of developmental biology and regenerative medicine. Derivation of
functional cardiac myocytes from hESC allows elucidation of the mechanisms
involved in cardiac differentiation and maturation. One of the most attractive
potential applications of hESC derived cardiomyocytes may be their use as a
cell source for cell replacement therapy. Beyond the potential use for
myocardial regeneration, the unique capability to reproducibly generate human
cardiac tissue can potentially be employed for screening and predicting the
adverse effects of drugs, developing novel anti-arrhythmic drugs and allowing
better understanding of the delicate mechanism of cardiomyocyte interaction
with adjacent cells. In the present work, we studied the potential cues
underlying hESCs differentiation to the cardiac lineage. Initially we
demonstrated that the microenvironment of the neonatal, uninjured and injured
adult rat heart does not provide the instructing signals allowing hESC
differentiation to the cardiac lineage. Moreover, transplantation of undifferentiated
cells results in the formation of teratomas. Hence, to allow cell
transplantation we hypothesized that cells must be initially differentiated
ex-vivo to the cardiac lineage. To this end we evaluated both a spontaneous
differentiation system as well as directed system based on manipulation of the
non-canonical Wnt signaling pathway. We then took advantage of the established
in vitro cardiomyocyte differentiation system to assess the potential of the
hESCs technology to serve as an in-vitro drug screening system. We next
examined the fate of the transplanted hESC derived cardiomyocytes and
demonstrated that the cells survived, integrated, and proliferated to a certain
degree following engraftment to the adult rat myocardium. Moreover,
transplantation of hESC derived cardiomyocytes to the infarcted rat myocardium
was shown to favorably affect the remodeling process when compared to
transplantation of non-cardiac cells or saline injection. Since cardiomyocyte
cell transplantation is hampered by the limited long-term survival of the donor
cell, we attempted to develop an alternating myocardial regenerative strategy.
This approach aimed at engineering a three-dimensional vascularized cardiac
tissue by seeding a cell mixture of hESC derived cardiomyocytes, endothelial
cells, and embryonic fibroblasts on a polymeric scaffold. Our results stress
the importance of the embryonic fibroblasts for the vascularization process
within the cardiac muscle tissue-construct. In summary, our results stress the potential of unique hESCs
differentiation system for cardiovascular developmental biology, drug screening
and target validation, and for the emerging field of regenerative medicine.
