Tani Hidenori

Human induced pluripotent stem cells (hiPSCs) have emerged as a promising platform for elucidating disease mechanisms and developing new drugs. Over the past 2 decades, it has become possible to efficiently generate large quantities of cardiomyocytes (CMs) from hiPSCs, thereby enabling the reproduction of disease-specific characteristics in culture dishes. Although this technology has the potential to substantially enhance the efficiency of drug discovery and understanding of disease, the immaturity of hiPSC-derived CMs (hiPSC-CMs) has been a major barrier to their widespread adoption. This review discusses the recent advances that address these challenges and explores the potential of hiPSCs to advance disease modeling, elucidate disease mechanisms, and accelerate drug discovery.

Human pluripotent stem cell-derived cardiomyocyte (hPSC-CM) differentiation can improve using chemical compounds which mimic early heart development. However, variations in hPSC-CM differentiation efficiency and its poor reproducibility have remained a challenge. Here, we report a unique metabolic method to promote hPSC-CM differentiation that involves marked suppression of the mitochondrial oxidative phosphorylation from the mesendoderm to the cardiac mesoderm, which is regulated by PHGDH, a rate-limiting enzyme in the serine synthesis pathway. Mechanistically, PHGDH inhibition impairs mitochondrial respiration by blocking the electron transport chain, resulting in elevated ROS levels and promoting the cardiomyocyte lineage specification by disrupting the cardiopharyngeal mesoderm lineage differentiation. Additionally, antioxidant supplementation can scavenge ROS and eliminate the effects of PHGDH inhibition. Collectively, our findings show that serine synthesis pathway can regulate cardiomyocyte lineage specification and have implications in providing a cellular source for transplantation and elucidating the potential mechanisms of heart development and pathogenesis of heart disease.

Three-dimensional cultures mimic in vivo environments better than two-dimensional cultures and are often used in drug discovery research. Herein, we present a protocol for producing homogeneous induced pluripotent stem cell (iPSC) spheroids and microtissues using the suction technique. We describe steps for preparing the suction device, preparing and seeding cells, and suction sedimentation of cells. We then detail procedures for self-assembly and evaluation of spheroids. For complete details on the use and execution of this protocol, please refer to Moriwaki et al.1.

Recently human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) have become an attractive platform to evaluate drug responses for cardiotoxicity testing and disease modeling. Moreover, three-dimensional (3D) cardiac models, such as engineered heart tissues (EHTs) developed by bioengineering approaches, and cardiac spheroids (CSs) formed by spherical aggregation of hPSC-CMs, have been established as useful tools for drug discovery and transplantation. These 3D models overcome many of the shortcomings of conventional 2D hPSC-CMs, such as immaturity of the cells. Cardiac organoids (COs), like other organs, have also been studied to reproduce structures that resemble a heart in vivo more closely and optimize various culture conditions. Heart-on-a-chip (HoC) developed by a microfluidic chip-based technology that enables real-time monitoring of contraction and electrical activity, provides multifaceted information that is essential for capturing natural tissue development in vivo. Recently, 3D experimental systems have been developed to study organ interactions in vitro. This review aims to discuss the developments and advancements of hPSC-CMs and 3D cardiac tissues.

There are high expectations regarding heart regeneration for refractory heart failure (HF). Transplantation of human pluripotent stem cell (hPSC)-derived cardiomyocytes (CMs) is expected to replace CMs lost due to HF, and various studies have been conducted to apply this therapy clinically. Though issues such as arrhythmias and immune rejection remain, the mass production of purified hPSC-derived CMs, their efficient transplantation, and methods to improve their engraftment pushed up the transplantation of hPSC-derived CMs to the clinical stage. In contrast, a direct cardiac reprogramming method has been developed, where cardiac fibroblasts are directly converted into CM-like cells without undergoing PSCs by overexpressing reprogramming factors. Although many challenges still remain in the clinical application of direct cardiac reprogramming, this can be a novel treatment which overcomes issues of transplantation of hPSC-derived CMs.