Title: Quantitative Evaluation of Cardiac Cell Interactions and Responses to Cyclic Strain
Abstract: The ventricular myocardium consists of multiple laminar sheets of two-dimensional cardiac tissues, which (by volume) are primarily composed of highly aligned cardiomyocytes. The other predominant cell-type in the myocardium is the cardiac fibroblast, which occupies space between layers of the myocardium and between cardiomyocytes, orienting along the prevailing direction of the cardiomyocytes. While the importance of cardiomyocyte organization and alignment on proper cardiac function is well established, structural organization of cardiac fibroblasts is comparatively poorly understood. Although cross talk between cardiomyocytes and cardiac fibroblasts contributes to proper heart function, as well as structural and electrical remodeling of the myocardium, the intricate interspersion of the two cell-types makes it difficult to investigate their functional interactions. In order to recapitulate the healthy myocardium in tissue engineering and understand how the dynamic strain environment of the heart influences pathology, the interactions and behavior of the two cell-types must be understood in this environment. Counter to what is observed in healthy myocardium where both cell-types are present, in isolated cultures that are exposed to cyclic strain, fibroblasts orient perpendicular to the strain direction while cardiomyocytes orient parallel. Therefore, in order to model both healthy and diseased myocardium, cyclic strain was applied to both cardiomyocyte dominant and fibroblast dominant co-cultures. Quantification of the response of cardiomyocytes and fibroblasts to cyclic strain under different co-culture conditions required developing an image analysis pipeline that automatically identifies and segments the cell-types and then measures the cell-type specific organization relative to the stretch direction. Quantitative evaluation of cardiac cell interactions and responses to cyclic strain will provide insight into how to mimic the dynamic mechanical environment of the heart in engineered tissue, as well as provide valuable information about the cardiac remodeling response in the diseased heart