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Here, we describe an easy-to-use methodology to generate 3D self-assembled cardiac microtissue arrays composed of pre-differentiated human-induced pluripotent stem cell-derived cardiomyocytes, cardiac fibroblasts, and endothelial cells. This user-friendly and low cell requiring technique to generate cardiac microtissues can be implemented for disease modeling and early stages of drug development.
Generation of human cardiomyocytes (CMs), cardiac fibroblasts (CFs), and endothelial cells (ECs) from induced pluripotent stem cells (iPSCs) has provided a unique opportunity to study the complex interplay among different cardiovascular cell types that drives tissue development and disease. In the area of cardiac tissue models, several sophisticated three-dimensional (3D) approaches use induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) to mimic physiological relevance and native tissue environment with a combination of extracellular matrices and crosslinkers. However, these systems are complex to fabricate without microfabrication expertise and require several weeks to self-assemble. Most importantly, many of these systems lack vascular cells and cardiac fibroblasts that make up over 60% of the nonmyocytes in the human heart. Here we describe the derivation of all three cardiac cell types from iPSCs to fabricate cardiac microtissues. This facile replica molding technique allows cardiac microtissue culture in standard multi-well cell culture plates for several weeks. The platform allows user-defined control over microtissue sizes based on initial seeding density and requires less than 3 days for self-assembly to achieve observable cardiac microtissue contractions. Furthermore, the cardiac microtissues can be easily digested while maintaining high cell viability for single-cell interrogation with the use of flow cytometry and single-cell RNA sequencing (scRNA-seq). We envision that this in vitro model of cardiac microtissues will help accelerate validation studies in drug discovery and disease modeling.
Drug discovery and disease modeling in the field of cardiovascular research face several challenges due to a lack of clinically relevant samples and inadequate translational tools1. Highly complex pre-clinical models or oversimplified in vitro single-cell models do not exhibit pathophysiological conditions in a reproducible manner. Therefore, several miniaturized tissue-engineered platforms have evolved to help bridge the gap, with the goal of achieving a balance between ease of application in a high-throughput manner and faithful recapitulation of tissue function2,3. With the advent of induced pluripotent stem cell (iPSC) technology, tissue engineering tools can be applied to patient-specific cells with or without underlying cardiovascular disease state to answer research questions4,5,6. Such tissue engineered models with cellular composition similar to the heart tissue could be utilized in drug development efforts to test for cardiotoxicity and dysfunction induced by pathological changes in behavior of one or multiple cell types.
Self-assembled microtissues or organoids derived from human iPSCs are three-dimensional (3D) structures that are miniature tissue-like assemblies exhibiting functional similarities to their in vivo counterparts. There are several different approaches that allow formation of organoids in situ via directed differentiation of iPSCs or through the formation of embryoid bodies4. The resulting organoids are an indispensable tool to study morphogenetic processes that drive organogenesis. However, the presence of a variety of cell populations and differences in self-organization can lead to variability in outcomes between different organoids5. Alternatively, pre-differentiated cells that are self-assembled into microtissues with tissue-specific cell types to study local cell-cell interactions are excellent models, where it is feasible to isolate the self-assembled components. Particularly in human cardiac research, development of 3D cardiac microtissues with multicellular components has proven to be challenging when cells are derived from different patient lines or commercial sources.
To improve our mechanistic understanding of cell behaviors in a physiologically relevant, personalized, in vitro model, ideally all component cell types should be derived from the same patient line. In the context of a human heart, a truly representative cardiac in vitro model would capture the crosstalk among predominant cell types, namely, cardiomyocytes (CMs), endothelial cells (ECs), and cardiac fibroblasts (CFs)6,7. The faithful recapitulation of a myocardium not only requires biophysical stretch and electrophysiological stimulation, but also cell-cell signaling that arise from supporting cell types such as ECs and CFs8. CFs are involved in the synthesis of extracellular matrix and maintaining tissue structure; and in a pathological state, CFs can induce fibrosis and alter electrical conduction in the CMs9. Similarly, ECs can regulate contractile properties of CMs through paracrine signaling and supplying vital metabolic demands10. Hence, there is a need for human cardiac microtissues composed of all three major cell types to allow physiologically relevant high-throughput experiments to be conducted.
Here, we describe a bottom-up approach in fabrication of cardiac microtissues by derivation of human iPSC-derived cardiomyocytes (iPSC-CMs), iPSC-derived endothelial cells (iPSC-ECs), and iPSC-derived cardiac fibroblasts (iPSC-CFs) and their 3D culture in uniform cardiac microtissue arrays. This facile method of generating spontaneously beating cardiac microtissues can be utilized for disease modeling and rapid testing of drugs for functional and mechanistic understanding of heart physiology. Furthermore, such multicellular cardiac microtissue platforms could be exploited with genome editing techniques to emulate cardiac disease progression over time under chronic or acute culture conditions.
1. Medium, reagent, culture plate preparation
2. Cardiac differentiation and purification
NOTE: All iPSCs should be maintained at ~75% to 80% confluency prior to cardiomyocyte differentiation. iPSCs used for this protocol were derived from peripheral blood mononuclear cells (PBMCs) using Sendai virus reprogramming performed at the Stanford Cardiovascular Institute (SCVI) Biobank.
3. Endothelial cell differentiation and MACS
4. Cardiac fibroblast differentiation
5. Casting of cardiac microtissue molds and cell seeding
6. Fixation and permeabilization of cells and cardiac microtissues for immunostaining
7. Digestion of cardiac microtissues and preparation of cells for flow cytometry
8. Performing contraction analyses of spontaneously beating cardiac microtissues
Immunostaining and flow cytometry characterization of iPSC-derived CMs, ECs, and CFs
To generate cardiac microtissues composed of iPSC-CMs, iPSC-ECs, and iPSC-CFs, all three cell types are differentiated and characterized individually. In vitro differentiation of iPSCs to iPSC-CMs has improved over the past several years. However, the yield and purity of iPSC-CMs differ from line to line. The current protocol yields over 75% pure iPSC-CMs that spontaneously start beating around day 9 (
To generate cardiac microtissues from pre-differentiated iPSC-CMs, iPSC-ECs, and iPSC-CFs, it is essential to obtain a highly pure culture for better control of cell numbers after contact-inhibited cell compaction within the cardiac microtissues. Recently, Giacomelli et. al.18 have demonstrated the fabrication of cardiac microtissues using iPSC-CMs, iPSC-ECs, and iPSC-CFs. Cardiac microtissues generated using the described method consist of ~5,000 cells (70% iPSC-CMs, 15% iPSC-ECs, and 15% iPSC-CF...
J.C.W. is a cofounder of Khloris Biosciences but has no competing interests, as the work presented here is completely independent. The other authors report no conflicts.
We thank Dr. Amanda Chase for her helpful feedback on the manuscript. Funding support was provided by the Tobacco-Related Disease Research Program (TRDRP) of the University of California, T29FT0380 (D.T.) and 27IR-0012 (J.C.W.); American Heart Association 20POST35210896 (H.K.) and 17MERIT33610009 (J.C.W.); and National Institutes of Health (NIH) R01 HL126527, R01 HL123968, R01 HL150693, R01 HL141851, and NIH UH3 TR002588 (J.C.W).
Name | Company | Catalog Number | Comments |
12-well plates | Fisher Scientific | 08-772-29 | |
3D micro-molds | Microtissues | 12-81 format | |
6-well plates | Fisher Scientific | 08-772-1B | |
AutoMACS Rinsing Solution | Thermo Fisher Scientific | NC9104697 | |
B27 Supplement minus Insulin | Life Technologies | A1895601 | |
B27 Supplement plus Insulin | Life Technologies | 17504-044 | |
BD Cytofix | BD Biosciences | 554655 | |
BD Matrigel, hESC-qualified matrix | BD Biosciences | 354277 | |
Cardiac Troponin T Antibody | Miltenyi | 130-120-403 | |
CD144 (VE-Cadherin) MicroBeads | Miltenyi | 130-097-857 | |
CD31 Antibody | Miltenyi | 130-110-670 | |
CD31 Microbeads | Miltenyi | 130-091-935 | |
CHIR-99021 | Selleckchem | S2924 | |
DDR2 | Santa Cruz Biotechnology | sc-81707 | |
Dead Cell Apoptosis Kit with Annexin V FITC and PI | Thermo Fisher Scientific | V13242 | |
Dispase I | Millipore Sigma | 4942086001 | |
DMEM, high glucose (4.5g/L) no glutamine medium | 11960044 | ||
DMEM/F-12 basal medium | Gibco | 11320033 | |
Dulbecco's phosphate buffered saline (DPBS), no calcium, no magnesium | Life Technologies | 14190-136 | |
EGM2 BulletKit | Lonza | CC-3124 | |
Fetal bovine serum | Life Technologies | 10437 | |
FibroLife Serum-Free Fibroblast LifeFactors Kit | LifeLIne Cell Technology | LS-1010 | |
Glucose free RPMI medium | Life Technologies | 11879-020 | |
Goat serum | Life Technologies | 16210-064 | |
Human FGF-basic | Thermo Fisher Scientific | 13256029 | |
Human VEGF-165 | PeproTech | 100-20 | |
IWR-1-endo | Selleckchem | S7086 | |
Liberase TL | Millipore Sigma | 5401020001 | |
LS Sorting Columns | Miltenyi | 130-042-401 | |
MACS BSA Stock solution | Miltenyi | 130-091-376 | |
MACS Rinsing Buffer | Miltenyi | 130-091-222 | |
MidiMACS Separator | Miltenyi | 130-042-302 | |
RPMI medium | Life Technologies | 11835055 | |
SB431542 | Selleckchem | S1067 | |
TO-PRO 3 | Thermo Fisher Scientific | R37170 | |
Triton X-100 | Millipore Sigma | X100-100ML | |
TrypLE Select 10X | Thermo Fisher Scientific | red | |
Vimentin Alexa Fluor® 488-conjugated Antibody | R&D Systems | IC2105G |
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