Stress Conditioning Controls Differentiation, Organization, and Maturation of Functional Bioengineered Human Cardiovascular Tissue

The regulation of heart growth through the interaction of cell types, matrix molecules, and mechanical cues is poorly understood, yet is necessary for the heart to reach its proper size and function. This body of work focuses on the directive cues necessary for differentiation, organization, and maturation of developing human cardiac tissue through proliferation, cellular and matrix alignment, hypertrophy, contractility, and force generation. Using mechanical stress conditioning and vascular cell co-culture in the context of tissue engineering approaches that utilize human cardiomyocytes within 3-dimensional scaffolds, we have been able to generate organized human myocardium in vitro and, further, to modulate cardiomyocyte differentiation, proliferation, and hypertrophy, as well as improve the maturation and contractile function of the engineered tissue as a whole. First, we found that stress conditioning and the presence of human endothelium both increased cardiomyocyte proliferation, and that stress conditioning and a 3-dimensional scaffold environment increased hypertrophy and cell alignment of cardiomyocytes, as well as cardiomyocyte differentiation from cardiovascular progenitor cells. We also observed that these vascularized engineered cardiac tissue constructs could be engrafted onto the heart in vivo and quickly perfused by host circulation through connection to the pre-formed human vascular networks within the constructs, indicating that these pre-vascularized cardiac tissues may have potential for therapeutic applications. Finally, as these bioengineered tissues are able to contract spontaneously and synchronously, we were able to observe and measure calcium transients as well as active twitch force production within the intact cardiac tissue constructs. Quantification of active force allowed us to determine Force/Length Relationships analogous to Frank-Starling Curves generated in the intact heart. Not only did these constructs become more contractile when stretched to greater lengths, as native myocardium does, but 14 days of stress pre-conditioning markedly potentiated this tissue-level response. The goal of these studies has been to characterize in vitro models of human cardiac development and to work towards human therapeutics using organized, vascularized, contractile human cardiac tissue.