3D aggregate culture improves metabolic maturation of human pluripotent stem cell derived cardiomyocytes

Current methods for the maturation of induced pluripotent stem cell-derived cardiomyocytes

Induced pluripotent stem cells (iPSCs) were first generated by Yamanaka and colleagues over a decade ago. Since then, iPSCs have been successfully differentiated into many distinct cell types, enabling tissue-, disease-, and patient-specific in vitro modelling. Cardiovascular disease is the greatest cause of mortality worldwide but encompasses rarer disorders of conduction and myocardial function for which a cellular model of study is ideal. Although methods to differentiate iPSCs into beating cardiomyocytes (iPSC-CMs) have recently been adequately optimized and commercialized, the resulting cells remain largely immature with regards to their structure and function, demonstrating fetal gene expression, disorganized morphology, reliance on predominantly glycolytic metabolism and contractile characteristics that differ from those of adult cardiomyocytes. As such, disease modelling using iPSC-CMs may be inaccurate and of limited utility. However, this limitation is widely recognized, and numerous groups have made substantial progress in addressing this problem. This review highlights successful methods that have been developed for the maturation of human iPSC-CMs using small molecules, environmental manipulation and 3-dimensional (3D) growth approaches.

Regulation of cardiomyocyte maturation during critical perinatal window

A primary limitation in the use of pluripotent stem cell-derived cardiomyocytes (PSC-CMs) for both patient health and scientific investigation is the failure of these cells to achieve full functional maturity. In vivo, cardiomyocytes undergo numerous adaptive structural, functional and metabolic changes during maturation. By contrast, PSC-CMs fail to fully undergo these developmental processes, instead remaining arrested at an embryonic stage of maturation. There is thus a significant need to understand the biological processes underlying proper CM maturation in vivo. Here, we discuss what is known regarding the initiation and coordination of CM maturation. We postulate that there is a critical perinatal window, ranging from embryonic day 18.5 to postnatal day 14 in mice, in which the maturation process is exquisitely sensitive to perturbation. While the initiation mechanisms of this process are unknown, it is increasingly clear that maturation proceeds through interconnected regulatory circuits that feed into one another to coordinate concomitant structural, functional and metabolic CM maturation. We highlight PGC1α, SRF and the MEF2 family as transcription factors that may potentially mediate this cross-talk. We lastly discuss several emerging technologies that will facilitate future studies into the mechanisms of CM maturation. Further study will not only produce a better understanding of its key processes, but provide practical insights into developing a robust strategy to produce mature PSC-CMs.

Oxygen transporter for the hypoxic transplantation site

Cell transplantation is a promising treatment for complementing lost function by replacing new cells with a desired function, e.g. pancreatic islet transplantation for diabetics. To prevent cell obliteration, oxygen supply is critical after transplantation, especially until the graft is sufficiently re-vascularized. To supply oxygen during this period, we developed a chemical-/electrical-free implantable oxygen transporter that delivers oxygen to the hypoxic graft site from ambient air by diffusion potential. This device is simply structured using a biocompatible silicone-based body that holds islets, connected to a tube that opens outside the body. In computational simulations, the oxygen transporter increased the oxygen level to >120 mmHg within grafts; in contrast, a control device that did not transport oxygen showed <6.5 mmHg. In vitro experiments demonstrated similar results. To test the effectiveness of the oxygen transporter in vivo, we transplanted pancreatic islets, which are susceptible to hypoxia, subcutaneously into diabetic rats. Islets transplanted using the oxygen transporter showed improved graft viability and cellular function over the control device. These results indicate that our oxygen transporter, which is safe and easily fabricated, effectively supplies oxygen locally. Such a device would be suitable for multiple clinical applications, including cell transplantations that require changing a hypoxic microenvironment into an oxygen-rich site.