The success of cardiac cell grafts for repair of infarcts or congestive heart failure has been moderate to date. While graft cells may survive transplantation, their contribution to conduction and force generation is neither well-defined nor understood. Also, there is concern that the stem cells could negatively impact some aspects of heart function and lead to disturbances of heart rhythm. In light of this, we proposed to develop a model to study the detailed interaction of stem cells and healthy heart tissue in the laboratory, focusing on two main thrusts.
The first part of this project had seen the successful development of a platform to better understand the transition that stem cells make as they mature into heart cells, a process known as differentiation. Using arrays of microelectrodes, recording of electrical activity from maturing stem cells was demonstrated. Impact of electrical stimulation on the differentiation process had been probed. Investigation of the interaction between stem cells and heart cells had also been initiated. The second part focused mainly on the latter aspect – functional coupling of stem cells in the heart tissue. New analysis tools for the quantification of the conduction of the electrical activity across a heart tissue were developed. Studies with mixed co-cultures of cardiac cells and fibroblasts revealed a high sensitivity of the conduction properties to the presence of non-conductive cells (fibroblasts), and provide a model for assessing conduction in stem cell grafts of varying homogeneity. Co-cultures of heart cells (host) and stem cells (graft), first grown separately then allowed them to merge, highlighted issues of conduction mismatch at the interface between the host and graft tissue, as well as the dependence of this conduction on the maturity and purity of the grafts used. Most importantly, these studies demonstrated the value of the model developed under this grant for the investigation of electrical coupling and conduction in stem cell grafts, issues that are vital to the safe, effective and successful use of stem cell therapy.