Solving the puzzle of pluripotent stem cell-derived cardiomyocyte maturation: piece by piece

Microstripe pattern substrate consisting of alternating planar and nanoprotrusive regions improved hiPSC-derived cardiomyocytes' unidirectional alignment and functional properties

The alignment of each cell in human myocardium is considered critical for the efficient movement of cardiac tissue. We investigated 96-well microstripe-patterned plates to align human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes (CMs), which resemble fetal myocardium. The aligned CMs (ACMs) cultured on the microstripe-patterned plates exhibited pathology, motor function, gene expression, and drug response that more closely resembled those of adult cells than did unaligned CMs cultured on a flat plate (FCMs). We used these ACMs to evaluate drug side effects and efficacy, and to determine whether these were similar to adult-like responses. When CMs from patients with hypertrophic cardiomyopathy (HCMs) were seeded and cultured on the microstripe-patterned plates or layered on top of the ACMs, both sets of HCMs showed increased heart rate and synchronized contractions, indicating improved cardiac function. It is suggested that the ACMs could be used for drug screening as cells representative of adult-like CMs and be transplanted in the form of a cell sheet for regenerative treatment of heart failure.

Strategies and Challenges to Improve Cellular Programming-Based Approaches for Heart Regeneration Therapy

Limited adult cardiac cell proliferation after cardiovascular disease, such as heart failure, hampers regeneration, resulting in a major loss of cardiomyocytes (CMs) at the site of injury. Recent studies in cellular reprogramming approaches have provided the opportunity to improve upon previous techniques used to regenerate damaged heart. Using these approaches, new CMs can be regenerated from differentiation of iPSCs (similar to embryonic stem cells), the direct reprogramming of fibroblasts [induced cardiomyocytes (iCMs)], or induced cardiac progenitors. Although these CMs have been shown to functionally repair infarcted heart, advancements in technology are still in the early stages of development in research laboratories. In this review, reprogramming-based approaches for generating CMs are briefly introduced and reviewed, and the challenges (including low efficiency, functional maturity, and safety issues) that hinder further translation of these approaches into a clinical setting are discussed. The creative and combined optimal methods to address these challenges are also summarized, with optimism that further investigation into tissue engineering, cardiac development signaling, and epigenetic mechanisms will help to establish methods that improve cell-reprogramming approaches for heart regeneration.

Programmed Cell Death-1: Programmed Cell Death-Ligand 1 Interaction Protects Human Cardiomyocytes Against T-Cell Mediated Inflammation and Apoptosis Response In Vitro

Aim: Immunological checkpoint therapy is considered a powerful method for cancer therapy and acts by re-activating autologous T cells to kill the cancer cell. Myocarditis cases have been reported in cancer patients after immunological therapy; for example, nivolumab treatment is a monoclonal antibody that blocks programmed cell death-1/programmed cell death ligand-1 ligand interaction. This project provided insight into the inflammatory response as a benchmark to investigate the potential cardiotoxic effect of T cell response to the programmed cell death-1 (PD-1)/programmed cell death ligand-1 (PD-L1) axis in regulating cardiomyocyte injury in vitro. Methods and Results: We investigated cardiomyopathy resulted from the PD-1/PD-L1 axis blockade using the anti-PD-1 antibody in Rockefeller University embryonic stem cells-derived cardiomyocytes (RUES2-CMs) and a melanoma tumor-bearing murine model. We found that nivolumab alone did not induce inflammatory-related proteins, including PD-L1 expression, and did not induce apoptosis, which was contrary to doxorubicin, a cardiotoxic chemotherapy drug. However, nivolumab was able to exacerbate the immune response by increasing cytokine and inflammatory gene expression in RUES2-CMs when co-cultured with CD4⁺ T lymphocytes and induced apoptosis. This effect was not observed when RUES2-CMs were co-cultured with CD8⁺ T lymphocytes. The in vivo model showed that the heart function of tumor-bearing mice was decreased after treatment with anti-PD-1 antibody and demonstrated a dilated left ventricle histological examination. The dilated left ventricle was associated with an infiltration of CD4⁺ and CD8⁺ T lymphocytes into the myocardium. PD-L1 and inflammatory-associated gene expression were significantly increased in anti-PD-1-treated tumor-bearing mice. Cleaved caspase-3 and mouse plasma cardiac troponin I expressions were increased significantly. Conclusion: PD-L1 expression on cardiomyocytes suppressed T-cell function. Blockade of PD-1 by nivolumab enhanced cardiomyocyte inflammation and apoptosis through the enhancement of T-cell response towards cardiomyocytes.

N-cadherin overexpression enhances the reparative potency of human-induced pluripotent stem cell-derived cardiac myocytes in infarcted mouse hearts

AIMS

In regenerative medicine, cellular cardiomyoplasty is one of the promising options for treating myocardial infarction (MI); however, the efficacy of such treatment has shown to be limited due to poor survival and/or functional integration of implanted cells. Within the heart, the adhesion between cardiac myocytes (CMs) is mediated by N-cadherin (CDH2) and is critical for the heart to function as an electromechanical syncytium. In this study, we have investigated whether the reparative potency of human-induced pluripotent stem cell-derived cardiac myocytes (hiPSC-CMs) can be enhanced through CDH2 overexpression.

METHODS AND RESULTS

CDH2-hiPSC-CMs and control wild-type (WT)-hiPSC-CMs were cultured in myogenic differentiation medium for 28 days. Using a mouse MI model, the cell survival/engraftment rate, infarct size, and cardiac functions were evaluated post-MI, at Day 7 or Day 28. In vitro, conduction velocities were significantly greater in CDH2-hiPSC-CMs than in WT-hiPSC-CMs. While, in vivo, measurements of cardiac functions: left ventricular (LV) ejection fraction, reduction in infarct size, and the cell engraftment rate were significantly higher in CDH2-hiPSC-CMs treated MI group than in WT-hiPSC-CMs treated MI group. Mechanistically, paracrine activation of ERK signal transduction pathway by CDH2-hiPSC-CMs, significantly induced neo-vasculogenesis, resulting in a higher survival of implanted cells.

CONCLUSION

Collectively, these data suggest that CDH2 overexpression enhances not only the survival/engraftment of cultured CDH2-hiPSC-CMs, but also the functional integration of these cells, consequently, the augmentation of the reparative properties of implanted CDH2-hiPSC-CMs in the failing hearts.

Fatty Acid-Treated Induced Pluripotent Stem Cell-Derived Human Cardiomyocytes Exhibit Adult Cardiomyocyte-Like Energy Metabolism Phenotypes

Human induced pluripotent stem cell (iPSC)-derived cardiomyocytes (CMs) (iPSC-CMs) are a promising cell source for myocardial regeneration, disease modeling and drug assessment. However, iPSC-CMs exhibit immature fetal CM-like characteristics that are different from adult CMs in several aspects, including cellular structure and metabolism. As an example, glycolysis is a major energy source for immature CMs. As CMs mature, the mitochondrial oxidative capacity increases, with fatty acid β-oxidation becoming a key energy source to meet the heart’s high energy demand. The immaturity of iPSC-CMs thereby limits their applications. The aim of this study was to investigate whether the energy substrate fatty acid-treated iPSC-CMs exhibit adult CM-like metabolic properties. After 20 days of differentiation from human iPSCs, iPSC-CMs were sequentially cultured with CM purification medium (lactate+/glucose-) for 7 days and maturation medium (fatty acids+/glucose-) for 3–7 days by mimicking the adult CM’s preference of utilizing fatty acids as a major metabolic substrate. The purity and maturity of iPSC-CMs were characterized via the analysis of: (1) Expression of CM-specific markers (e.g., troponin T, and sodium and potassium channels) using RT-qPCR, Western blot or immunofluorescence staining and electron microscopy imaging; and (2) cell energy metabolic profiles using the XF96 Extracellular Flux Analyzer. iPSCs-CMs (98% purity) cultured in maturation medium exhibited enhanced elongation, increased mitochondrial numbers with more aligned Z-lines, and increased expression of matured CM-related genes, suggesting that fatty acid-contained medium promotes iPSC-CMs to undergo maturation. In addition, the oxygen consumption rate (OCR) linked to basal respiration, ATP production, and maximal respiration and spare respiratory capacity (representing mitochondrial function) was increased in matured iPSC-CMs. Mature iPSC-CMs also displayed a larger change in basal and maximum respirations due to the utilization of exogenous fatty acids (palmitate) compared with non-matured control iPSC-CMs. Etomoxir (a carnitine palmitoyltransferase 1 inhibitor) but not 2-deoxyglucose (an inhibitor of glycolysis) abolished the palmitate pretreatment-mediated OCR increases in mature iPSC-CMs. Collectively, our data demonstrate for the first time that fatty acid treatment promotes metabolic maturation of iPSC-CMs (as evidenced by enhanced mitochondrial oxidative function and strong capacity of utilizing fatty acids as energy source). These matured iPSC-CMs might be a promising human CM source for broad biomedical application.

Considerations for an In Vitro, Cell-Based Testing Platform for Detection of Drug-Induced Inotropic Effects in Early Drug Development. Part 2: Designing and Fabricating Microsystems for Assaying Cardiac Contractility With Physiological Relevance Using Human iPSC-Cardiomyocytes

Contractility of the myocardium engines the pumping function of the heart and is enabled by the collective contractile activity of its muscle cells: cardiomyocytes. The effects of drugs on the contractility of human cardiomyocytes in vitro can provide mechanistic insight that can support the prediction of clinical cardiac drug effects early in drug development. Cardiomyocytes differentiated from human-induced pluripotent stem cells have high potential for overcoming the current limitations of contractility assays because they attach easily to extracellular materials and last long in culture, while having human- and patient-specific properties. Under these conditions, contractility measurements can be non-destructive and minimally invasive, which allow assaying sub-chronic effects of drugs. For this purpose, the function of cardiomyocytes in vitro must reflect physiological settings, which is not observed in cultured cardiomyocytes derived from induced pluripotent stem cells because of the fetal-like properties of their contractile machinery. Primary cardiomyocytes or tissues of human origin fully represent physiological cellular properties, but are not easily available, do not last long in culture, and do not attach easily to force sensors or mechanical actuators. Microengineered cellular systems with a more mature contractile function have been developed in the last 5 years to overcome this limitation of stem cell-derived cardiomyocytes, while simultaneously measuring contractile endpoints with integrated force sensors/actuators and image-based techniques. Known effects of engineered microenvironments on the maturity of cardiomyocyte contractility have also been discovered in the development of these systems. Based on these discoveries, we review here design criteria of microengineered platforms of cardiomyocytes derived from pluripotent stem cells for measuring contractility with higher physiological relevance. These criteria involve the use of electromechanical, chemical and morphological cues, co-culture of different cell types, and three-dimensional cellular microenvironments. We further discuss the use and the current challenges for developing and improving these novel technologies for predicting clinical effects of drugs based on contractility measurements with cardiomyocytes differentiated from induced pluripotent stem cells. Future research should establish contexts of use in drug development for novel contractility assays with stem cell-derived cardiomyocytes.

CRISPR/Cas9-mediated genome editing in human stem cell-derived cardiomyocytes: Applications for cardiovascular disease modelling and cardiotoxicity screening

Cardiovascular diseases (CVDs) are leading causes of death worldwide, and drug-induced cardiotoxicity is among the most common cause of drug withdrawal from the market. Improved models of cardiac tissue are needed to study the mechanisms of CVDs and drug-induced cardiotoxicity. Human pluripotent stem cell-derived cardiomyocytes (hPSC-CM) have provided a major advance to our ability to study these conditions. Combined with efficient genome editing technologies, such as CRISPR/Cas9, we now have the ability to study with greater resolution the genetic causes and underlying mechanisms of inherited and drug-induced cardiotoxicity, and to investigate new treatments. Here, we review recent advances in the use of hPSC-CMs and CRISPR/Cas9-mediated genome editing to study cardiotoxicity and model CVD.