Name: high efficiency differentiation of human pluripotent stem cells to cardiomyocytes and characterization by flow cytometry
Uploaded: 2014-09-23T15:00:00
Description: Watch this Scientific Journal Video about High Efficiency Differentiation of Human Pluripotent Stem Cells to Cardiomyocytes and Characterization by Flow Cytometry at JoVE.com

This research was supported by NIH 4R00HL094708-03, MCW Research Affairs Committee New Faculty Award, and the Kern foundation (startup funds) at the Medical College of Wisconsin (RLG); Research Grants Council of Hong Kong Theme-based Research Scheme T13-706/11 (KRB); U01 HL099776, CIRM TR3-05556, CIRM DR2A-05394, and AHA Established Investigator Award (JCW); AHA Postdoctoral Fellowship 12POST12050254 (PWB). We thank Hope Campbell at the Flow Cytometry Core of the Blood Research Institute of Wisconsin for assistance with data collection and careful review of the manuscript.

1. Solution and Media Preparation
<ol>
	<li>hESC Qualified Matrix Coating Stock Solution
	<ol>
		<li>Slowly thaw hESC qualified matrix (5 ml) on ice at 4 &#186;C overnight. Dispense aliquots into pre-chilled, 1.5 ml sterile microcentrifuge tubes and immediately store at -20 &#186;C. 
		NOTE: The volume of the aliquot will vary based on lot and typically ranges 270-350 &#181;l. Manufacturer provides details regarding volume of aliquot required to achieve a 1x concentration upon dilution into 25 ml as described in s...

Critical to the success of the differentiation protocol is the use of high quality cultures of hPSCs that have been passaged at the single cell level for at least five passages prior to the start of differentiation. Similar differentiation efficiencies are routinely observed among various hPSC lines if they are 100% confluent at the start of differentiation, independent of cell line. Suboptimal efficiency is observed if the confluence of cells at the start of differentiation is &#8804;95% or &#62;100%. Therefore, seeding...

The generation of cardiomyocytes from hPSCs, including hESC and hiPSC, can function as an in vitro model of very early human cardiac developmental processes, providing insight into stages not otherwise accessible for mechanistic studies. This model system provides unique opportunities to study the molecular pathways that control cardiac lineage commitment and cell fate specification. In recent years, the ability to efficiently generate cardiomyogenic cells from hPSCs has greatly improved1-15. However, among protocols there is cell line variation with respect to the efficiency in generating cardiomyogenic cells and timing at which the cells express chamber-specific markers (e.g., ventricle and atria). Ideally, for future applications of this model system, more homogeneous populations of functionally defined cells are desired. In contrast to previous methods, the cardiomyocyte differentiation protocol described here does not require cell aggregation or the addition of Activin A or Bone morphogenetic protein 4(BMP4) and robustly generates cultures highly positive for TNNI3, TNNT2, IRX4, MLC2v, and MLC2a by day 10 cells across all hESC and hiPSC lines tested to date. The strategy is technically simple to implement, especially compared to three-dimensional cultures, mass culture, or embryoid body based strategies4-9, and was recently defined in a study that describes a small molecule with selective toxicity to hPSCs (Boheler et al.)65. Features of this protocol include differentiation of hPSCs in monolayer culture using a single layer of a hESC qualified matrix (Matrigel), fully defined media using small molecules to modulate Wnt signaling (similar, yet distinct from1,2,7,13), and optimized flow cytometry staining methods for evaluation of differentiation efficiency and cell identity. In summary, advantages of this protocol compared to previous reports include its cost-effectiveness, reproducibility, and its high efficiency for generating cardiomyocytes among multiple hPSC lines, including hESC and hiPSC lines.
Flow cytometry is a powerful analytical tool for assessing the quality of cells in culture and determining subpopulation homogeneity, and with proper experimental design, can provide quantitative measurements. As with all antibody-based strategies, accurate interpretation of experimental results requires that elements of the assay design including antibody concentration and fixation and permeabilization conditions (when targeting intracellular antigens) are carefully tested for each antibody as sub-optimal conditions significantly affect efficiency of antibody binding, and therefore, interpretation of results. Importantly, if quantitation is required, monoclonal antibodies are essential, as polyclonal antibodies can recognize multiple epitopes and are prone to batch-to-batch variation. Currently, a variety of antibodies (polyclonal and monoclonal) and staining protocols have been described for the assessment of in vitro differentiation, making it difficult to compare efficiency of cardiomyogenesis among protocols1,2,9,11. For that reason, monoclonal antibodies are used when available for all flow cytometry analyses. Going forward, it is expected that standardization of these staining protocols, especially with regards to quantitation, should better permit comparison among differentiation strategies.
The choice of markers, and their corresponding antibodies, used to assess purity of in vitro cardiomyogenesis varies among reports. TNNT2 has been considered an indicator of cells committed to the cardiomyogenic fate and is routinely used to assess efficiency of cardiac differentiation protocols. However, TNNT2 is also expressed in skeletal muscle during early chick and rat development16,17 and it is present in human smooth muscle18. Thus, TNNT2 is not necessarily a specific marker of human cardiomyogenesis in vitro. MLC2v and MLC2a are routinely used as surrogate markers of ventricular and atrial subtypes, respectively. However, challenges with relying on MLC2v and MLC2a to determine cardiomyocyte subtype in the context of in vitro differentiation arise from the fact that these gene products may not be restricted to a specific chamber throughout cardiac development, from heart tube through adult. In the rodent looped heart, MLC2a mRNA is predominant in the atrial/inflow tract area and MLC2v mRNA is predominant in the ventricular/outflow tract regions. In the looped heart, co-expression of MLC2a and MLC2v mRNAs are observed in the inflow tract, atrioventricular canal, and the outflow tract19,20. By 3 days after birth, MLC2v mRNA is restricted to the ventricle and by 10 days after birth, MLC2a is restricted to the atria in the neonatal rat heart19. Therefore, interpretation of data regarding cardiomyogenesis efficiency and subtype identity must not only consider the presence and quantity of reference marker levels, but must consider the developmental stage(s) to which the timepoints of differentiation that are analyzed correspond. This is especially important considering that the maturation stage of cardiomyogenic cells generated by in vitro differentiation of hPSCs resembles most closely those of embryonic/fetal development21-25. Thus, relying on a marker&#8217;s spatial expression in the postnatal heart may not be appropriate for the assessment of hPSC-derived cells, at least in some cases.
In an effort to facilitate the development of more specific criteria for defining cardiomyocyte identity in vitro, TNNI3 is considered to be a valuable marker for evaluating cardiomyogenesis in vitro as it is restricted to cardiac muscle throughout embryogenesis in chick and zebrafish15,20 and is absent in human fetal skeletal muscle26. While TNNI1 is present in human fetal heart, TNNI3 is the only TNNI isoform present in normal adult heart27,28. Regarding cardiomyocyte subtype identity, IRX429-31 is an informative marker of cells with a ventricular fate. At the protein level, IRX4 has recently been shown to be restricted to the ventricle from linear heart tube through neonatal stages in the mouse32. Accordingly, optimized staining protocols for the analysis of TNNI3 and IRX4 by flow cytometry are described. To our knowledge, this is the first description of a method for efficient antibody-based staining and analysis of IRX4 levels in human cardiomyocytes by flow cytometry.

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			<td height="34" style="height:34px;width:431px;">Name of Reagent / Equipment</td>
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		<tr height="17">
			<td height="17" style="height:17px;width:431px;">BD Matrigel, hESC-qualified matrix</td>
			<td style="width:152px;">BD Biosciences</td>
			<td style="width:111px;">354277</td>
			<td></td>
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			<td height="17" style="height:17px;width:431px;">Accutase cell detachment solution</td>
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			<td style="width:111px;">7920</td>
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		<tr height="34">
			<td height="34" style="height:34px;width:431px;">Dubelcco&#39;s phosphate buffered saline (DPBS), no calcium, no magnesium</td>
			<td style="width:152px;">Life Technologies</td>
			<td style="width:111px;">14190-136</td>
			<td></td>
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		<tr height="17">
			<td height="17" style="height:17px;width:431px;">Dimethyl sulfoxide (DMSO, Hybri-Max, sterile-filtered)</td>
			<td style="width:152px;">Sigma Aldrich</td>
			<td style="width:111px;">D2650</td>
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		<tr height="17">
			<td height="17" style="height:17px;width:431px;">Sodium bicarbonate</td>
			<td style="width:152px;">Sigma Aldrich</td>
			<td style="width:111px;">53817</td>
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			<td height="17" style="height:17px;width:431px;">Citric acid</td>
			<td style="width:152px;">Sigma Aldrich</td>
			<td style="width:111px;">C2404-100G</td>
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		<tr height="17">
			<td height="17" style="height:17px;width:431px;">Y-27632 dihydrochloride selective p160ROCK inhibitor</td>
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			<td style="width:111px;">1254</td>
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			<td height="17" style="height:17px;width:431px;">L-ascorbic acid-2-phosphate sesquimagnesium salt hydrate</td>
			<td style="width:152px;">Sigma Aldrich</td>
			<td style="width:111px;">A8960-5G</td>
			<td></td>
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			<td height="17" style="height:17px;width:431px;">Sodium selenite</td>
			<td style="width:152px;">Sigma Aldrich</td>
			<td style="width:111px;">S5261-10G</td>
			<td></td>
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		<tr height="17">
			<td height="17" style="height:17px;width:431px;">Transferrin (Optiferrin &#8211; Defined, Animal-free, Recombinant Human)</td>
			<td style="width:152px;">Invitria</td>
			<td style="width:111px;">777TRF029</td>
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			<td height="17" style="height:17px;width:431px;">Fibroblast growth factor 2 (FGF2)</td>
			<td style="width:152px;">R&#38;D Systems</td>
			<td style="width:111px;">4144-TC-01M</td>
			<td></td>
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		<tr height="17">
			<td height="17" style="height:17px;width:431px;">Transforming growth factor beta 1 (TGF&#946;1)</td>
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			<td style="width:111px;">100-21</td>
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			<td style="width:111px;">11330-032</td>
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			<td height="17" style="height:17px;width:431px;">IWR-1</td>
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			<td style="width:111px;">I0161</td>
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			<td height="17" style="height:17px;width:431px;">RPMI 1640 with L-Glutamine</td>
			<td style="width:152px;">Life Technologies</td>
			<td style="width:111px;">11875-093</td>
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			<td style="width:152px;">Life Technologies</td>
			<td style="width:111px;">A1895601</td>
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			<td height="17" style="height:17px;">B-27 Supplement (with Insulin)</td>
			<td style="width:152px;">Life Technologies</td>
			<td style="width:111px;">17504-044</td>
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			<td style="width:152px;">Life Technologies</td>
			<td style="width:111px;">10437</td>
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			<td height="17" style="height:17px;width:431px;"></td>
			<td style="width:152px;"></td>
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			<td height="17" style="height:17px;width:431px;">Phosphate buffered saline (10X)</td>
			<td style="width:152px;">Quality Biological Inc.</td>
			<td style="width:111px;">119-069-151</td>
			<td></td>
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		<tr height="19">
			<td height="19" style="height:19px;width:431px;">Hank&#39;s balanced salt solution without Ca2+ and Mg2+</td>
			<td style="width:152px;">Life Technologies</td>
			<td style="width:111px;">14175-095</td>
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			<td height="17" style="height:17px;width:431px;">BD Cytofix</td>
			<td style="width:152px;">BD Biosciences</td>
			<td style="width:111px;">554655</td>
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			<td style="width:152px;">BD Biosciences</td>
			<td style="width:111px;">558050</td>
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			<td style="width:152px;"></td>
			<td style="width:111px;"></td>
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		<tr height="17">
			<td height="17" style="height:17px;width:431px;">5 ml round bottom polystyrene tube (without cap)</td>
			<td style="width:152px;">Corning</td>
			<td style="width:111px;">352008</td>
			<td>for preparation of cells for flow cytometry</td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;width:431px;">5 ml round bottom polystyrene tube (with 35 &#181;M cell strainer snap cap)</td>
			<td style="width:152px;">Corning</td>
			<td style="width:111px;">352235</td>
			<td>for preparation of cells for flow cytometry</td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;width:431px;">2 ml rubber bulbs</td>
			<td style="width:152px;">Fischer Scientific</td>
			<td style="width:111px;">03-448-24</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;width:431px;">9&#34; borosilicate unplugged glass Pasteur pipets</td>
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			<td style="width:111px;">P-2904-2</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;width:431px;">0.65 mL microcentrifuge tubes, graduated, green</td>
			<td style="width:152px;">GeneMate</td>
			<td style="width:111px;">C-3259-G</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;width:431px;">1.5 mL microcentrifuge tubes, graduated, red</td>
			<td style="width:152px;">GeneMate</td>
			<td style="width:111px;">C-3260-R</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;width:431px;">TC20 automated cell counter</td>
			<td style="width:152px;">BioRad</td>
			<td>145-0102</td>
			<td></td>
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		<tr height="17">
			<td height="17" style="height:17px;width:431px;">Counting slides for TC20</td>
			<td style="width:152px;">BioRad</td>
			<td style="width:111px;">145-0011</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;width:431px;">6 well flat bottom tissue-culture treated plate</td>
			<td style="width:152px;">Corning</td>
			<td style="width:111px;">353046</td>
			<td></td>
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		<tr height="17">
			<td height="17" style="height:17px;width:431px;">20 mL syringes</td>
			<td style="width:152px;">BD Plastipak</td>
			<td style="width:111px;">300613</td>
			<td>For filter sterilization of aliquots</td>
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		<tr height="17">
			<td height="17" style="height:17px;width:431px;">Sterile syringe filters, 0.2 &#181;m polyethersulfone</td>
			<td style="width:152px;">VWR</td>
			<td style="width:111px;">28145-501</td>
			<td>For filter sterilization of aliquots</td>
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		<tr height="17">
			<td height="17" style="height:17px;width:431px;">250 mL filter system, 0.22 &#181;m polyethersulfone, sterilizing, low binding&#160;</td>
			<td style="width:152px;">Corning</td>
			<td style="width:111px;">431096</td>
			<td>For filter sterilization of bulk media&#160;</td>
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		<tr height="17">
			<td height="17" style="height:17px;width:431px;">500 mL filter system, 0.22 &#181;m polyethersulfone, sterilizing, low binding&#160;</td>
			<td style="width:152px;">Corning</td>
			<td style="width:111px;">431097</td>
			<td>For filter sterilization of bulk media&#160;</td>
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			<td style="width:111px;"></td>
			<td></td>
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		<tr height="17">
			<td height="17" style="height:17px;width:431px;">Anti-TNNI3 (clone: 284 (19C7))</td>
			<td style="width:152px;">Abcam</td>
			<td>ab19615</td>
			<td>Primary antibody</td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">Anti-TNNT2 (clone: 1C11)</td>
			<td>Thermo Scientific</td>
			<td>MA1-16687</td>
			<td>Primary antibody</td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">Anti-MYL2 (MLC2v, clone: 330G5)</td>
			<td>Synaptic Systems</td>
			<td>310111</td>
			<td>Primary antibody</td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">Anti-MYL7 (MLC2a, clone: 4E7)</td>
			<td>Abcam</td>
			<td>AB131661</td>
			<td>Primary antibody</td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">Anti-IRX4&#160;&#160;</td>
			<td>Bioss</td>
			<td>BS-9464R</td>
			<td>Primary antibody</td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;width:431px;">Alexa Fluor 488 Goat anti-mouse IgG1&#160;</td>
			<td style="width:152px;">Life Technologies</td>
			<td>A21121</td>
			<td>Secondary antibody</td>
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		<tr height="17">
			<td height="17" style="height:17px;width:431px;">Alexa Fluor 647 Goat anti-mouse IgG2a</td>
			<td style="width:152px;">Life Technologies</td>
			<td>A21241</td>
			<td>Secondary antibody</td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;width:431px;">Alexa Fluor 488 Goat anti-mouse IgG2b</td>
			<td style="width:152px;">Life Technologies</td>
			<td>A21141</td>
			<td>Secondary antibody</td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;width:431px;">Phycoerythrin(PE) Goat anti-rabbit IgG</td>
			<td style="width:152px;">R&#38;D Systems</td>
			<td style="width:111px;">F0110</td>
			<td>Secondary antibody</td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">Mouse IgG1</td>
			<td>BD Biosciences</td>
			<td>557273</td>
			<td>Isotype Control</td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">Mouse IgG2a</td>
			<td>eBiosciences</td>
			<td>16-4724-81</td>
			<td>Isotype Control</td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">Rabbit IgG-PE</td>
			<td>R&#38;D Systems</td>
			<td>IC105P</td>
			<td>Isotype Control</td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;width:431px;"></td>
			<td style="width:152px;"></td>
			<td style="width:111px;"></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:431px;">TaqMan Probesets for qRT-PCR</td>
			<td style="width:152px;"></td>
			<td style="width:111px;"></td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">ACTB</td>
			<td>Life Technologies</td>
			<td>Hs01060665</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">Brachyury T</td>
			<td>Life Technologies</td>
			<td>Hs00610080</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">CASQ2</td>
			<td>Life Technologies</td>
			<td>Hs00154286</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">IRX4</td>
			<td>Life Technologies</td>
			<td>Hs01100809</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">ISL1</td>
			<td>Life Technologies</td>
			<td>Hs00158126</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">MESP1</td>
			<td>Life Technologies</td>
			<td>Hs01001283</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">MYH11 (SMMHC)</td>
			<td>Life Technologies</td>
			<td>Hs00224610</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;width:431px;">MYH6</td>
			<td>Life Technologies</td>
			<td>Hs01101425</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">MYL2 (MLC2v)</td>
			<td>Life Technologies</td>
			<td>Hs00166405</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">MYL7 (MLC2a)</td>
			<td>Life Technologies</td>
			<td>Hs01085598</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">MYOG</td>
			<td>Life Technologies</td>
			<td>Hs01072232</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">NKX2.5</td>
			<td>Life Technologies</td>
			<td>Hs00231763</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">NPPA</td>
			<td>Life Technologies</td>
			<td>Hs01081097</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">POU5F1</td>
			<td>Life Technologies</td>
			<td>Hs04260367</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">SOX17</td>
			<td>Life Technologies</td>
			<td>HS00751752</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">TNNI1</td>
			<td>Life Technologies</td>
			<td>Hs00913333</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">TNNI2</td>
			<td>Life Technologies</td>
			<td>Hs00268536</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">TNNI3</td>
			<td>Life Technologies</td>
			<td>HS00165957</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">TNNT2</td>
			<td>Life Technologies</td>
			<td>Hs00165960</td>
			<td></td>
		</tr>
	</tbody>
</table>

high efficiency differentiation of human pluripotent stem cells to cardiomyocytes and characterization by flow cytometry

There is an urgent need to develop approaches for repairing the damaged heart, discovering new therapeutic drugs that do not have toxic effects on the heart, and improving strategies to accurately model heart disease. The potential of exploiting human induced pluripotent stem cell (hiPSC) technology to generate cardiac muscle &#8220;in a dish&#8221; for these applications continues to generate high enthusiasm. In recent years, the ability to efficiently generate cardiomyogenic cells from human pluripotent stem cells (hPSCs) has greatly improved, offering us new opportunities to model very early stages of human cardiac development not otherwise accessible. In contrast to many previous methods, the cardiomyocyte differentiation protocol described here does not require cell aggregation or the addition of Activin A or BMP4 and robustly generates cultures of cells that are highly positive for cardiac troponin I and T (TNNI3, TNNT2), iroquois-class homeodomain protein IRX-4 (IRX4), myosin regulatory light chain 2, ventricular/cardiac muscle isoform (MLC2v) and myosin regulatory light chain 2, atrial isoform (MLC2a) by day 10 across all human embryonic stem cell (hESC) and hiPSC lines tested to date. Cells can be passaged and maintained for more than 90 days in culture. The strategy is technically simple to implement and cost-effective. Characterization of cardiomyocytes derived from pluripotent cells often includes the analysis of reference markers, both at the mRNA and protein level. For protein analysis, flow cytometry is a powerful analytical tool for assessing quality of cells in culture and determining subpopulation homogeneity. However, technical variation in sample preparation can significantly affect quality of flow cytometry data. Thus, standardization of staining protocols should facilitate comparisons among various differentiation strategies. Accordingly, optimized staining protocols for the analysis of IRX4, MLC2v, MLC2a, TNNI3, and TNNT2 by flow cytometry are described.

On day 0, cells are 100% confluent with compact morphology and minimal cell debris. On days 1-2, it is common to observe significant cell death (40-50%), but attached cells will retain compact morphology (Figure 1A). During this time, media is orange and turbid. Pink media indicates excessive cell death, and in this case, confirm with trypan blue and discontinue if cell death exceeds 70%. Cells will recover during days 3-4 and density will increase. During days 5-6, minimal cell death occurs and dense pa...

Watch this Scientific Journal Video about High Efficiency Differentiation of Human Pluripotent Stem Cells to Cardiomyocytes and Characterization by Flow Cytometry at JoVE.com

High Efficiency Differentiation of Human Pluripotent Stem Cells to Cardiomyocytes and Characterization by Flow Cytometry

The article describes the detailed methodology to efficiently differentiate human pluripotent stem cells into cardiomyocytes by selectively modulating the Wnt pathway, followed by flow cytometry analysis of reference markers to assess homogeneity and identity of the population.

There is an urgent need to develop approaches for repairing the damaged heart, discovering new therapeutic drugs that do not have toxic effects on the ...

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