High-throughput longitudinal electrophysiology screening of mature chamber-specific hiPSC-CMs using optical mapping

Metabolic changes of human induced pluripotent stem cell-derived cardiomyocytes and teratomas after transplantation

Cardiac regenerative therapy using human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) has been applied in clinical settings. Herein, we aimed to investigate the in vivo metabolic profiles of hiPSC-CM grafts. RNA sequencing and imaging mass spectrometry were performed in the present study, which revealed that hiPSC-CM grafts matured metabolically over time after transplantation. Glycolysis, which was active in the hiPSC-CM grafts immediately after transplantation, shifted to fatty acid oxidation. Additionally, we examined the metabolic profile of teratomas that may form when non-CMs, including undifferentiated human induced pluripotent stem cells (hiPSCs), remain in transplanted cells. The upregulated gene expression of amino acid transporters and the high accumulation of amino acids, such as methionine and aromatic amino acids, were observed in the teratomas. We show that subcutaneous teratomas derived from undifferentiated hiPSCs can be detected in vivo using positron emission tomography with [18F]fluorophenylalanine ([18F]fPhe). These results provided insights into the clinical application of cardiac regenerative therapy.

Microphysiological systems to advance human pathophysiology and translational medicine

Microphysiological systems (MPS) or "organ-on-a-chip" models are sophisticated tools that harness techniques from cell biology, tissue engineering, and microengineering to recapitulate human physiology. Typically, MPS are biofabricated three-dimensional (3-D) tissue constructs integrated into platforms designed to mimic the tissue microenvironment and provide functional outputs. Over the past decade, researchers have endeavored to manufacture high-throughput, high-fidelity MPS models of all major human organs. By incorporating patient-derived cells, researchers have produced biomimetic models of tissues with disease-linked genetic mutations capable of exhibiting patient heterogeneity. This work has demonstrated that MPS more closely model organotypic function and pathophysiology than traditional two-dimensional (2-D) culture systems. Moreover, investigators have shown that human MPS are better predictors of drug efficacy and toxicity than animal models. Thus, MPS have emerged as a promising candidate to improve the efficacy and safety of preclinical trials. In this mini-review, we provide an overview of current advances in MPS models, their applications in mechanistic research, and relevance to drug screening. Finally, we discuss current investments in MPS development by the United States federal government and research institutions around the world to advance translational medicine.

Bipolar Patient-Specific In Vitro Diagnostic Test Reveals Underlying Cardiac Arrhythmia Phenotype Caused by Calcium Channel Genetic Risk Factor

A common genetic risk factor for bipolar disorder is CACNA1C, a gene that is also critical for cardiac rhythm. The impact of CACNA1C mutations on bipolar patient cardiac rhythm is unknown. Here, we report the cardiac electrophysiological implications of a bipolar disorder-associated genetic risk factor in CACNA1C using patient induced pluripotent stem cell-derived cardiomyocytes. Results indicate that the CACNA1C bipolar disorder-related mutation causes cardiac electrical impulse conduction slowing mediated by impaired intercellular coupling via connexin 43 gap junctions. In vitro gene therapy to restore connexin 43 expression increased cardiac electrical impulse conduction velocity and protected against thioridazine-induced QT prolongation. Patients positive for bipolar disorder CACNA1C genetic risk factors may have elevated proarrhythmic risk for adverse events in response to psychiatric medications that slow conduction or prolong the QT interval. This in vitro diagnostic tool enables cardiac testing specific to patients with psychiatric disorders to determine their sensitivity to off-target effects of psychiatric medications.

OptoDyCE-plate as an affordable high throughput imager for all optical cardiac electrophysiology

We present a simple low-cost system for comprehensive functional characterization of cardiac function under spontaneous and paced conditions, in standard 96 and 384-well plates. This full-plate actuator/imager, OptoDyCE-plate, uses optogenetic stimulation and optical readouts of voltage and calcium (parallel recordings from up to 100 wells in 384-well plates are demonstrated). The system is validated with syncytia of human induced pluripotent stem cell derived cardiomyocytes, iPSC-CMs, grown as monolayers, or in quasi-3D isotropic and anisotropic constructs using electrospun matrices, in 96 and 384-well format. Genetic modifications, e.g. interference CRISPR (CRISPRi), and nine compounds of acute and chronic action were tested, including five histone deacetylase inhibitors (HDACis). Their effects on voltage and calcium were compared across growth conditions and pacing rates. We also demonstrated optogenetic point pacing via cell spheroids to study conduction in 96-well format, as well as temporal multiplexing to register voltage and calcium simultaneously on a single camera. Opto-DyCE-plate showed excellent performance even in the small samples in 384-well plates. Anisotropic structured constructs may provide some benefits in drug testing, although drug responses were consistent across tested configurations. Differential voltage vs. calcium responses were seen for some drugs, especially for non-traditional modulators of cardiac function, e.g. HDACi, and pacing rate was a powerful modulator of drug response, highlighting the need for comprehensive multiparametric assessment, as offered by OptoDyCE-plate. Increasing throughput and speed and reducing cost of screening can help stratify potential compounds early in the drug development process and accelerate the development of safer drugs.

OptoDyCE-plate as an affordable high throughput imager for all optical cardiac electrophysiology

We present a simple low-cost system for comprehensive functional characterization of cardiac function under spontaneous and paced conditions, in standard 96 and 384-well plates. This full-plate actuator/imager, OptoDyCE-plate, uses optogenetic stimulation and optical readouts of voltage and calcium from all wells in parallel. The system is validated with syncytia of human induced pluripotent stem cell derived cardiomyocytes, iPSC-CMs, grown as monolayers, or in quasi-3D isotropic and anisotropic constructs using electrospun matrices, in 96 and 394-well format. Genetic modifications, e.g. interference CRISPR (CRISPRi), and nine compounds of acute and chronic action were tested, including five histone deacetylase inhibitors (HDACis). Their effects on voltage and calcium were compared across growth conditions and pacing rates. We also demonstrated deployment of optogenetic cell spheroids for point pacing to study conduction in 96-well format, and the use of temporal multiplexing to register voltage and calcium simultaneously on a single camera in this stand-alone platform. Opto-DyCE-plate showed excellent performance even in the small samples in 384-well plates, in the various configurations. Anisotropic structured constructs may provide some benefits in drug testing, although drug responses were consistent across tested configurations. Differential voltage vs. calcium responses were seen for some drugs, especially for non-traditional modulators of cardiac function, e.g. HDACi, and pacing rate was a powerful modulator of drug response, highlighting the need for comprehensive multiparametric assessment, as offered by OptoDyCE-plate. Increasing throughput and speed and reducing cost of screening can help stratify potential compounds early in the drug development process and accelerate the development of safer drugs.

Optical Mapping of Cardiomyocytes in Monolayer Derived from Induced Pluripotent Stem Cells

Optical mapping is a powerful imaging technique widely adopted to measure membrane potential changes and intracellular Ca2+ variations in excitable tissues using voltage-sensitive dyes and Ca2+ indicators, respectively. This powerful tool has rapidly become indispensable in the field of cardiac electrophysiology for studying depolarization wave propagation, estimating the conduction velocity of electrical impulses, and measuring Ca2+ dynamics in cardiac cells and tissues. In addition, mapping these electrophysiological parameters is important for understanding cardiac arrhythmia mechanisms. In this review, we delve into the fundamentals of cardiac optical mapping technology and its applications when applied to hiPSC-derived cardiomyocytes and discuss related advantages and challenges. We also provide a detailed description of the processing and analysis of optical mapping data, which is a crucial step in the study of cardiac diseases and arrhythmia mechanisms for extracting and comparing relevant electrophysiological parameters.