Growth of Engineered Human Myocardium With Mechanical Loading and Vascular Coculture

Abstract

Rationale The developing heart requires both mechanical load and vascularization to reach its proper size, yet the regulation of human heart growth by these processes is poorly understood. Objective We seek to elucidate the responses of immature human myocardium to mechanical load and vascularization using tissue engineering approaches. Methods and Results Using human embryonic stem cell and human induced pluripotent stem cell-derived cardiomyocytes in a three dimensional collagen matrix, we show that uniaxial mechanical stress conditioning promotes 2-fold increases in cardiomyocyte and matrix fiber alignment and enhances myofibrillogenesis and sarcomeric banding. Furthermore, cyclic strain markedly increases cardiomyocyte hypertrophy (2.2-fold) and proliferation rates (21%) vs. unstrained constructs. Addition of endothelial cells enhances cardiomyocyte proliferation under all stress conditions (14% to 19%), and addition of stromal supporting cells enhances formation of vessel-like structures by ~10-fold. Furthermore, these optimized human cardiac tissue constructs generate Starling curves, increasing their active force in response to increased resting length. When transplanted onto hearts of athymic rats, the human myocardium survives and forms grafts closely apposed to host myocardium. The grafts contain human microvessels that are perfused by the host coronary circulation. Conclusions Our results indicate that both mechanical load and vascular cell co-culture control cardiomyocyte proliferation, and that mechanical load further controls the hypertrophy and architecture of engineered human myocardium. Such constructs may be useful for studying human cardiac development as well as for regenerative therapy.

Hydrogels for cardiac tissue engineering

“…82 In another study, it was demonstrated that uniaxial mechanical loading promoted the cardiomyocyte differentiation of human ESCs within 3D collagen hydrogels. 83 It was found that the application of mechanical stimulation enhanced cardiomyocyte alignment, hypertrophy, proliferation as well as the formation of sarcomeric bands. To further improve the function of engineered cardiac tissue construct, ECs and stromal cells were co-cultured with ESC-derived cardiomyocytes to form a tissue construct containing highly vascularized networks.…”

Engineered Cardiac Tissues Generated from Immature Cardiac and Stem Cell-Derived Cells: Multiple Approaches and Outcomes

“…A variety of stem cell sources (embryonic stem cells, induced pluripotent stem cells, cardiac stem cells, adipose stem cells, etc.) have also been used to generate immature CM using a variety of CM lineage specification and selection protocols [10][11][12][13][14]. Not surprisingly, stem cell populations can be rapidly expanded in vitro along with the induction of cardiac lineages; however, their functional maturation remains a major technical challenge [15][16][17].…”

“…Because human cells are required for clinical translation, the optimization of protocols that can generate large quantities of functional human CM is a high priority for cardiac repair strategies. Further, there may be advantages to generating ECTs that contain both cardiac and vascular lineage cells to accelerate angiogenesis and vascular perfusion of implanted ECTs [11][12][13]. …”

“…The constructs used for cardiac tissue repair include the implantation of multicellular cardiospheres [18], various formulations of 2D cellular sheets [19][20][21][22], and various formulations of 3D tissues [5][6][7][8]13]. The composition of the noncellular constituents varies from minimal constituents for cardiosphere clusters to a range of ECM components [23,24] and growth factors [25][26][27] selected for their ability to facilitate CM survival and functional maturation.…”

Engineering Cardiovascular Regeneration

“…The incorporation of cells into a hydrogel is one of the oldest ideas in tissue engineering, which was introduced 35 years ago [93] and was applied to generate the first engineered cardiac tissues [94]. The most commonly used hydrogels are based on collagen I [87], Matrigel [95], fibrin [88, 89••, 96], and mixtures thereof. The principle is always similar: cells are mixed with the hydrogel and filled into a casting mold that determines the shape of the engineered tissue.…”