The role of mechanical forces in cardiomyocyte differentiation in 3D culture

Heart disease is the leading cause of death in many developing and industrialized countries. The loss of cardiomyocyte (CM) proliferation in the post-natal myocardium is the major barrier to myocardial regeneration, which leads to a loss of functional myocytes and thus contractile function after injury. While significant advances in cardiac tissue engineering as an alternative strategy for treatment have been made in the recent years, the application for repair of the injured myocardium remains to be realized. However, tissue engineering as an in vitro model system for characterizing functional properties of cardiac tissue can be used as a powerful tool now. The overall goal of this doctoral thesis was to determine the role of mechanical strain on CM differentiation within a 3D engineered tissue to use as a system for evaluation of strategies for enhancing directed CM differentiation and tissue contractile properties. Substantial progress towards this goal was made by a combination of testing new strategies for monitoring differential CM differentiation and contractile function, such as using MDSCs in a 3D collagen gel bioreactor to induce CM differentiation and applying mechanical strain to determine the responsive cell type, and by developing new tools and methods for characterizing CM differentiation and cell morphology changes. Our in vitro engineered cardiac tissue from fetal/developing native cardiac cells maintained CM proliferative activity and contractile properties similar to the native myocardium which increased in response to mechanical stretch. The implanted graft maintained CM proliferative activity in vivo, survived as a donor myocardial tissue, and contributed to the cardiac functional recovery of injured myocardium better than a graft with post-natal cardiac cells. Skeletal muscle derived stem cell (MDSC) aggregate formation and 3D collagen gel bioreactor (3DGB) culture (MDSC-3DGB) triggered differentiation of cells with an immature functioning CM phenotype in vitro. In addition, mechanical strain directed cell morphology changes were significant factors in directing CM differentiation from MDSCs within MDSC-3DGB. In conclusion, our 3D collagen gel bioreactor culture, with capabilities for spatial and temporal monitoring, represents a powerful model for elucidating the role of specific environmental factors and their underlying mechanisms on directed cell proliferation and differentiation