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Here we describe and validate a method to consistently generate robust human induced pluripotent stem cell-derived cardiomyocytes and characterize their function. These techniques may help in developing mechanistic insight into signaling pathways, provide a platform for large-scale drug screening, and reliably model cardiac diseases.
Human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) provide a valuable human source for studying the basic science of calcium (Ca2+) handling and signaling pathways as well as high-throughput drug screening and toxicity assays. Herein, we provide a detailed description of the methodologies used to generate high-quality iPSC-CMs that can consistently reproduce molecular and functional characteristics across different cell lines. Additionally, a method is described to reliably assess their functional characterization through the evaluation of Ca2+ handling properties. Low oxygen (O2) conditions, lactate selection, and prolonged time in culture produce high-purity and high-quality ventricular-like cardiomyocytes. Similar to isolated adult rat cardiomyocytes (ARCMs), 3-month-old iPSC-CMs exhibit higher Ca2+ amplitude, faster rate of Ca2+ reuptake (decay-tau), and a positive lusitropic response to β-adrenergic stimulation compared to day 30 iPSC-CMs. The strategy is technically simple, cost-effective, and reproducible. It provides a robust platform to model cardiac disease and for the large-scale drug screening to target Ca2+ handling proteins.
Human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) are an attractive human-based platform to model a large variety of cardiac diseases in vitro1,2,3,4,5,6,7,8. Moreover, iPSC-CMs can be used for the prediction of patient responses to novel or existing drugs, to screen hit compounds, and develop new personalized drugs9,10. However, despite significant progress, several limitations and challenges need to be considered when using iPSC-CMs11. Consequently, methods to improve cardiac differentiation protocols, to enhance iPSC-CMs efficiency and maturation, and to generate specific cardiomyocyte subtypes (ventricular, atrial, and nodal) have been intensely studied and already led to numerous culture strategies to overcome these hurdles12,13,14,15.
Notwithstanding the robustness of these protocols, a major concern for the use of iPSC-CMs is the reproducibility of long and complex procedures to obtain high-quality cardiomyocytes that can ensure the same performance and reproducible results. Reproducibility is critical not only when comparing cell lines with different genetic backgrounds, but also when repeating cellular and molecular comparisons of the same cell line. Cell variability, such as well-to-well differences in iPSCs density, may affect cardiac differentiation, generating a low yield and poor-quality cardiomyocytes. These cells could still be used to perform experiments that do not require a pure population of CMs (e.g., when performing Ca2+ transient measurements). Indeed, when performing electrophysiological analysis, the non-CMs will not beat, neither spontaneously nor under electrical stimulation, so it will be easy to exclude them from the analysis. However, because of the poor quality, iPSC-CMs can show altered electrophysiological characteristics (e.g., irregular Ca2+ transient, low Ca2+ amplitude) which are not due to their genetic makeup. Therefore, especially when using iPSC-CMs to model cardiac disease, it is important not to confuse results from a poor-quality CM with the disease phenotype. Careful screening and exclusion processes are required prior to proceeding to electrophysiological studies.
This method includes optimized protocols to generate high-purity and high-quality cardiomyocytes and to assess their function by performing Ca2+ transient measurements using a calcium and contractility acquisition and analysis system. This technique is a simple, yet powerful, way to distinguish between high efficiency and low efficiency iPSC-CM preparations and provide a more physiologically relevant characterization of human iPSC-CMs.
The experiments using adult rat cardiomyocytes in this study were conducted with approved Institutional Animal Care and Use Committee (IACUC) protocols of Icahn School of Medicine at Mount Sinai. The adult rat cardiomyocytes were isolated from Sprague Dawley rat hearts by the Langendorff-based method as previously described16.
1. Preparation of Media
2. Preparation of Human Embryonic Stem Cell (hESC)-qualified Matrix Coated Plates and Coverslips
NOTE: Perform all the steps under a sterilized tissue culture hood.
3. Preparation of Small Molecules
NOTE: Reconstitute all small molecules and Wnt modulators in DMSO unless otherwise stated.
4. Maintenance and Passaging of iPSCs
NOTE: Perform all of the following steps under a sterile tissue culture hood.
5. Cardiomyocyte Differentiation
6. Selection Procedure and iPSC-CM Dissociation
7. Preparation of iPSC-CMs for Flow Cytometry
8. Plating Cardiomyocytes onto Glass Coverslips
NOTE: Perform all steps in a sterile environment.
9. Fixing Cells
10. Immunofluorescence Staining
11. Assessment of Intracellular Ca2+ Transients
The protocol described in Figure 1A generated highly pure cardiomyocytes that acquire a ventricular/adult-like phenotype with time in culture. As assessed by immunofluorescence staining for the atrial and ventricular myosin regulatory light chain 2 isoforms (MLC2A and MLC2V, respectively), the majority of the cells generated by this protocol were MLC2A-positive at day 30 after induction of cardiac differentiation, while MLC2V was expressed in much lower amounts at the same t...
Critical steps for using human iPSC-CMs as experimental models are: 1) generating high-quality cardiomyocytes (CMs) that can ensure the consistent performance and reproducible results; 2) allowing the cells to mature in culture for at least 90 days to adequately assess their phenotype; 3) performing electrophysiological studies, e.g. calcium (Ca2+) transient measurements, to provide a physiologically relevant functional characterization of human iPSC-CMs. We developed a monolayer-based differentiation method t...
The authors have nothing to disclose.
This research was supported by AHA Scientist Development Grant 17SDG33700093 (F.S.); Mount Sinai KL2 Scholars Award for Clinical and Translational Research Career Development KL2TR001435 (F.S.); NIH R00 HL116645 and AHA 18TPA34170460 (C.K.).
Name | Company | Catalog Number | Comments |
Anti-Actin, α-Smooth Muscle antibody, Mouse monoclonal | Sigma Aldrich | A5228 | |
Alexa Fluor 488 goat anti mouse | Invitrogen | A11001 | |
Alexa Fluor 555 goat anti rabbit | Invitrogen | A21428 | |
B27 Supplement | Gibco | 17504-044 | |
B27(-) insulin Supplement | Gibco | A18956-01 | |
CHIR-99021 | Selleckchem | S2924 | |
DAPI nuclear stain | ThermoFisher | D1306 | |
DMEM/F12 (1:1) (1X) + L- Glutamine + 15mM Hepes | Gibco | 11330-032 | |
Double Ended Cell lifter, Flat blade and J-Hook | Celltreat | 229306 | |
Falcon Multiwell Tissue Culture Plate, 6 well | Corning | 353046 | |
Fluidic inline heater | Live Cell Instrument | IL-H-10 | |
Fura-2, AM | Invitrogen | F1221 | |
hESC-qualified matrix | Corning | 354277 | Matrigel Matrix |
hPSC media | Gibco | A33493-01 | StemFlex Basal Medium |
IWR-1 | Sigma Aldrich | I0161 | |
Live cell imaging chamber | Live Cell Instrument | EC-B25 | |
MLC-2A, Monoclonal Mouse Antibody | Synaptic Systems | 311011 | |
Myocyte calcium and contractility system | Ionoptix | ISW-400 | |
Myosin Light Chain 2 Antibody, Rabbit Polyclonal (MLC2V) | Proteintech | 10906-1-AP | |
Nalgene Rapid Flow Sterile Disposable Filter units with PES Membrane | ThermoFisher | 124-0045 | |
PBS with Calcium and Magnesium | Corning | 21-030-CV | |
PBS without Calcium and Magensium | Corning | 21-031-CV | |
Premium Glass Cover Slips | Lab Scientific | 7807 | |
RPMI medium 1640 (-) D-glucose (1X) | Gibco | 11879-020 | |
RPMI medium 1640 (1X) | Gibco | 11875-093 | |
Sodium L-lactate | Sigma Aldrich | L7022 | |
StemFlex Supplement | Gibco | A33492-01 | |
Thiazovivin | Tocris | 3845 | |
Trypsin-EDTA (0.25%) | ThermoFisher | 25200056 | |
Tyrode's solution | Boston Bioproducts | BSS-355w | Adjust pH at 7.2. Add 1.2mM Calcium Chloride |
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