This research is supported by The Netherlands Organization for Scientific Research (NWO) (VENI 016.146.079) and a LUMC Research fellowship both to AMS, and LUMC Bontius Stichting (MJG).

All experiments with human tissue specimens were approved by the ethics committee of the Leiden University Medical Center and conforms to the Declaration of Helsinki. All steps are performed with sterile equipment in a cell culture flow cabinet.
1. Preparations
<ol>
	<li>Prepare EPDC medium by mixing Dulbecco&#39;s modified Eagle&#39;s medium (DMEM low- glucose) and Medium 199 (M199) in a 1:1 ratio. Add 10% heat inactivated fetal bovine serum (FBS, heat inactivated for 25 min at 56 &#176;C) and supplement with 100 U/mL penicillin and 100 mg/mL streptomycin. Pre-warm the EPDC medium in a 37 &#176;C water bath.</li>
	<li>Pre-warm Trypsin 0.25%/EDTA (1:1) in a 37 &#176;C water bath.</li>
	<li>Coat wells with gelatin. Add 0.1% gelatin/PBS to each well and incubate the plates for at least 15 min at 37 &#176;C. Guidelines for the required cell culture plate are summarized in Table 1. Carefully remove all fluid before plating cells.</li>
	<li>Prepare a stock solution of 10 mM SB431542 (SB), diluted in DMSO (CAUTION). Make 50 &#181;L aliquots in conical bottom polypropylene centrifuge tubes, like Eppendorf tubes, and store them at -20 &#176;C. Note that SB aliquots can be thawed only once.</li>
</ol>
2. Retrieval and Storage of Adult and Fetal Heart Specimens
<ol>
	<li>Store human adult auricles directly upon removal during surgery in a 50-mL tube with 15 mL high-glucose DMEM containing 10% FBS, 100 U/mL penicillin, and 100 mg/mL streptomycin at 4 &#176;C. Samples are generally 3 - 5 cm in size and can be stored up to 48 h after dissection.</li>
	<li>Store fetal hearts obtained from elective abortion material in EPDC medium at 4 &#176;C up to 24 h after isolation. For this protocol, use samples with a gestational age between 12 - 22 weeks. Note that the whole heart can be used for isolation of the epicardium.</li>
</ol>
3. Isolation of the Epicardial Layer
<ol>
	<li>In the laminar flow cabinet, prepare a 100-mm cell-culture dish with PBS and place a separate droplet (~200 &#181;L) of PBS in the lid. Fill a 15-mL tube with 5 mL pre-warmed EPDC medium.</li>
	<li>Place the tissue in the cell-culture dish filled with PBS. Make sure that the tissue is moistened frequently during the procedure.</li>
	<li>Using a stereomicroscope, remove as much of the epicardial layer from the tissue sample as possible by peeling it off using forceps. 
	Note: The epicardium can be recognized as a very thin, transparent layer tightly adhered to the outside of the heart (Figure 1A). Try to avoid contamination with epicardial adipose tissue and blood vessels since this will hamper the isolation.</li>
	<li>Collect pieces of epicardial tissue in the droplet of PBS on the lid.</li>
	<li>Cut the epicardial tissue into small pieces (0.5 mm3) using a scalpel (Figure 1B), or using the sharp tips of small forceps.Note that the pieces should be able to pass a P1,000 pipet tip (step 3.6).</li>
	<li>Add 1 mL of trypsin to the epicardial tissue and collect the pieces and trypsin with a P1,000 pipet tip. Transfer the tissue into a 1.5-mL conical centrifuge tube (Figure 1C).</li>
	<li>Incubate the tube in a 37 &#176;C water bath for 10 min, while shaking at ~60 rpm.</li>
	<li>Remove the tube from the water bath, and clean the outside of the tube with 70% ethanol.</li>
	<li>Allow the tissue to sink to the bottom of the tube (Figure 1D) and carefully transfer the supernatant containing epicardial cells to the 15-mL tube containing 5 mL EPDC medium to inactivate the trypsin.</li>
	<li>Replenish the remaining tissue in the conical centrifuge tube with 1 mL trypsin, and mix by gently pipetting up and down.</li>
	<li>Repeat step 3.7 to 3.10 two times. At the final step, after a total of 30 min of trypsin incubation, transfer both the supernatant and the remaining epicardial tissue into the tube containing EPDC medium.</li>
	<li>When all cells are collected in EPDC medium, gently pass the suspension through a 10-mL syringe with a 19-gauge needle into a new 15-mL tube to mechanically dissociate the cells (Figure 1E). 
	Note: Make sure to homogenize the suspension by pipetting up and down before passing the solution through the needle to prevent the needle getting obstructed.</li>
	<li>To further dissociate the cells, repeat step 3.12 with a 21-gauge needle.</li>
	<li>Place a 100-&#181;m cell strainer on top of a 50-mL tube and transfer the medium containing the epicardial cells onto the strainer using a 10-mL pipette to remove all remaining clumps (Figure 1F).</li>
	<li>Wash the strainer to collect residual cells by pipetting 5 mL EPDC medium onto the strainer.</li>
	<li>Pipet the cell suspension from the 50-mL tube into a 15-mL tube. Since cells sink to the bottom of the tube, shake the solution gently before pipetting. 
	Note: While this step is not necessary, a smaller tube aids visualization of the pellet after centrifugation.</li>
	<li>Centrifuge at 200 x g for 5 min at room temperature (Figure 1G).</li>
	<li>Remove the supernatant and resuspend the cell pellet (Figure 1H) in the required volume of EPDC medium (Table 1). 
	Note: For fetal EPDCs, directly use EPDC medium containing 10 &#181;M of the ALK5 kinase inhibitor&#160;(EPDC+SB). Adult cells can be plated without SB during the first passage.</li>
	<li>Plate the cell suspension on the gelatin coated culture plates (Figure 1I). The size of the well depends on the size of the epicardial tissue sample (Table 1). Note that low confluency will induce the occurrence of EMT.</li>
	<li>Place the cells in the incubator for at least 48 h at 37 &#176;C, 5% CO2 to allow the cells to attach to the culture plate.</li>
</ol>
4. Culture of EPDCs
<ol>
	<li>Replenish the EPDC+SB medium at least every 3 days.</li>
	<li>Inspect the cells at least every 3 days using the microscope. When the cells reach confluency, i.e., when the culture plate is fully covered with cells, passage the cells in a 1:2 surface ratio. Note that reaching confluency can take ~5 - 10 days.
	<ol>
		<li>Aspirate the medium using a pipet or an aspiration system with, e.g., a glass pipet.</li>
		<li>Wash the cells carefully by adding PBS to the cells. Gently swirl the plate and aspirate the PBS.</li>
		<li>Add trypsin to the plate. Gently rotate the plate to cover all cells with trypsin and incubate the plate for 1 min at 37 &#176;C. 
		NOTE: Use as little trypsin as possible (indication: 200 &#181;L per&#160;well of a 6 well plate)</li>
		<li>Tap the plate to mechanically detach the cells from the bottom of the plate. Use the microscope to visually check if cells have detached. If not, incubate the cell culture plate for an extra minute.</li>
		<li>Add the required volume of EPDC+SB medium to the cells, resuspend by pipetting up and down, and transfer the cell suspension to a new gelatin coated culture plate. 
		NOTE: In general, cells can be kept in a cobblestone morphology up to passage 8.</li>
	</ol>
	</li>
</ol>
5. Induction of EMT in EPDCs
<ol>
	<li>To induce EMT, dissociate the cells with trypsin and transfer the cells to new gelatin coated wells in a 1:2 surface ratio in EPDC+SB medium, as described in 4, and incubate for at least 24 h at 37 &#176;C, 5% CO2.</li>
	<li>Check if confluency is 50 - 70% and if EPDCs have a cobblestone morphology. 
	NOTE: Confluency affects the ability of EPDCs to undergo EMT.</li>
	<li>Aspirate the medium from the cells and wash the cells carefully with PBS (see step 4.2.1 - 4.2.2).</li>
	<li>Stimulate cells with 1 ng/mL TGF&#946;3 in EPDC medium and place them in an incubator at 37 &#176;C, 5% CO2 for 5 days. Note that during stimulation, the EPDC medium containing TGF&#946;3 does not have to be replenished.</li>
	<li>Monitor the cells daily. After 5 days, cells that underwent EMT are recognized by a spindle-shaped morphology (Figure 2A).</li>
	<li>Culture spindle-shaped EPDCs according to the method described in 4 without addition of SB or TGF&#946; to the EPDC medium. Note that in general, spindle-shaped EPDCs can be cultured up to passage 20.</li>
	<li>Validate the occurrence of EMT with immunofluorescent staining using antibodies against the mesenchymal markers &#945;SMA or Vimentin or by phalloidin to detect the formation of F-actin stress fibers (Figure 2B), or using qRT-PCR for EMT-related genes (e.g., WT1, Periostin, Col1A1, &#945;SMA, N-Cadherin, MMP3, Snail, Slug) (Figure 2C and Table 2).</li>
</ol>

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R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterisation+of+the+human+embryonic+and+foetal+epicardium+during+heart+development.">Characterisation of the human embryonic and foetal epicardium during heart development.</a> Development. 142 (21), 3630-3636 (2015).</li><li>Zhou, B., Ma, Q., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Epicardial+progenitors+contribute+to+the+cardiomyocyte+lineage+in+the+developing+heart.">Epicardial progenitors contribute to the cardiomyocyte lineage in the developing heart.</a> Nature. 454 (7200), 109-113 (2008).</li><li>Smits, A., Riley, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Epicardium-Derived+Heart+Repair.">Epicardium-Derived Heart Repair.</a> Journal of Developmental Biology. 2 (2), 84-100 (2014).</li><li>Chen, T. H. P., Chang, T. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Epicardial+Induction+of+Fetal+Cardiomyocyte+Proliferation+via+a+Retinoic+Acid-Inducible+Trophic+Factor.">Epicardial Induction of Fetal Cardiomyocyte Proliferation via a Retinoic Acid-Inducible Trophic Factor.</a> Developmental Biology. 250 (1), 198-207 (2002).</li><li>Pennisi, D. J., Ballard, V. L. T., Mikawa, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Epicardium+is+required+for+the+full+rate+of+myocyte+proliferation+and+levels+of+expression+of+myocyte+mitogenic+factors+FGF2+and+its+receptor,+FGFR-1,+but+not+for+transmural+myocardial+patterning+in+the+embryonic+chick+heart.">Epicardium is required for the full rate of myocyte proliferation and levels of expression of myocyte mitogenic factors FGF2 and its receptor, FGFR-1, but not for transmural myocardial patterning in the embryonic chick heart.</a> Developmental Dynamics. 228 (2), 161-172 (2003).</li><li>Lavine, K. 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B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Erythropoietin+and+retinoic+acid,+secreted+from+the+epicardium,+are+required+for+cardiac+myocyte+proliferation.">Erythropoietin and retinoic acid, secreted from the epicardium, are required for cardiac myocyte proliferation.</a> Developmental biology. 255 (2), 334-349 (2003).</li><li>M&#228;nner, J., Schlueter, J., Brand, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Experimental+analyses+of+the+function+of+the+proepicardium+using+a+new+microsurgical+procedure+to+induce+loss-of-proepicardial-function+in+chick+embryos.">Experimental analyses of the function of the proepicardium using a new microsurgical procedure to induce loss-of-proepicardial-function in chick embryos.</a> Developmental Dynamics. 233 (4), 1454-1463 (2005).</li><li>Weeke-Klimp, A., Bax, N. A. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Epicardium-derived+cells+enhance+proliferation,+cellular+maturation+and+alignment+of+cardiomyocytes.">Epicardium-derived cells enhance proliferation, cellular maturation and alignment of cardiomyocytes.</a> Journal of Molecular and Cellular Cardiology. 49 (4), 606-616 (2010).</li><li>Eralp, I., Lie-Venema, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Coronary+Artery+and+Orifice+Development+Is+Associated+With+Proper+Timing+of+Epicardial+Outgrowth+and+Correlated+Fas+Ligand+Associated+Apoptosis+Patterns.">Coronary Artery and Orifice Development Is Associated With Proper Timing of Epicardial Outgrowth and Correlated Fas Ligand Associated Apoptosis Patterns.</a> Circulation Research. 96 (5), (2005).</li><li>Kelder, T. P., Duim, S. N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+epicardium+as+modulator+of+the+cardiac+autonomic+response+during+early+development.">The epicardium as modulator of the cardiac autonomic response during early development.</a> Journal of Molecular and Cellular Cardiology. 89, 251-259 (2015).</li><li>van Wijk, B., Gunst, Q. D., Moorman, A. F. M., van den Hoff, M. J. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cardiac+regeneration+from+activated+epicardium.">Cardiac regeneration from activated epicardium.</a> PloS one. 7 (9), e44692 (2012).</li><li>Zhou, B., Honor, L. 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O., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modified+mRNA+directs+the+fate+of+heart+progenitor+cells+and+induces+vascular+regeneration+after+myocardial+infarction.">Modified mRNA directs the fate of heart progenitor cells and induces vascular regeneration after myocardial infarction.</a> Nature Biotechnology. 31 (10), 898-907 (2013).</li><li>Moerkamp, A. T., Lodder, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Human+fetal+and+adult+epicardial-derived+cells:+a+novel+model+to+study+their+activation.">Human fetal and adult epicardial-derived cells: a novel model to study their activation.</a> Stem Cell Research &amp; Therapy. 7 (1), 1-12 (2016).</li><li>Clunie-O'Connor, C., Smits, A. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Derivation+of+Primary+Human+Epicardium-Derived+Cells.">The Derivation of Primary Human Epicardium-Derived Cells.</a> Current Protocols in Stem Cell Biology. 35, 2C.5.1-2C.5.12 (2015).</li><li>Van Tuyn, J., Atsma, D. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Epicardial+Cells+of+Human+Adults+Can+Undergo+an+Epithelial-to-+Mesenchymal+Transition+and+Obtain+Characteristics+of+Smooth+Muscle+Cells+In+Vitro.">Epicardial Cells of Human Adults Can Undergo an Epithelial-to- Mesenchymal Transition and Obtain Characteristics of Smooth Muscle Cells In Vitro.</a> Stem Cells. 25 (2), 271-278 (2007).</li><li>Bax, N. A. M., van Oorschot, A. A. 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The authors have nothing to disclose.

Here we describe a detailed protocol to isolate and culture primary epicardial cells derived from human adult and fetal hearts. Extensive characterization of these cells has been previously published17. We have shown that both cell types can be maintained as epithelial cobblestone-like cells when cultured with the ALK5 kinase inhibitor SB431542. EMT is an integral part of epicardial activation in vivo during both development and the post-injury response. EMT can be studied using this meth...

The epicardium, a single-cell epithelial layer that envelopes the heart, is of vital importance for cardiac development and repair (reviewed in Smits et al.1). Developmentally, the epicardium arises from the proepicardial organ, a small structure located at the base of the developing heart. Around developmental day E9.5 in mouse, and 4 weeks post-conception in human, cells start to migrate from this cauliflower structure and cover the developing myocardium2. Once a single epithelial cell layer is formed, a portion of the epicardial cells undergoes&#160;epithelial to mesenchymal transition (EMT). During EMT, cells lose their epithelial characteristics, such as cell-cell adhesions, and obtain a mesenchymal phenotype which gives them the capacity to migrate into the developing myocardium. The formed epicardial derived cells (EPDCs) can differentiate into several cardiac cell types including fibroblasts, smooth muscle cells, and potentially cardiomyocytes and endothelial cells3, although differentiation of the latter two cell populations remains subject to debate (reviewed in Smits et al.4). Furthermore, the epicardium provides instructive paracrine signals to the myocardium to regulate its growth and vascularization5,6,7,8. Multiple studies have demonstrated that impaired epicardial formation leads to developmental defects in cardiac muscle9,10, vasculature11, and conduction system12, emphasizing the essential contribution of the epicardium to the formation of the heart.
Although in the adult heart the epicardium is present as a dormant layer, it becomes reactivated upon ischemia13. Epicardial reactivation post-injury recapitulates several of the processes described for cardiac development, including proliferation and EMT14, albeit less efficiently. Interestingly, although the exact mechanism is not fully understood, the epicardial contribution to repair can be improved by treatment with, e.g., Thymosin &#946;415 or modified VEGF-A mRNA16, resulting in ameliorated cardiac function after myocardial infarction. The epicardium is therefore considered an interesting cell source to enhance endogenous repair of the injured heart.
Mechanisms of cardiac development are often recapitulated during injury, although in a less efficient manner. In search of epicardial activators, it is paramount that we can determine and compare the full capacity of the fetal and adult epicardium. Moreover, from a therapeutic point of view, it is important that, in addition to animal experiments, we extend knowledge regarding the response of the human epicardium. Here, we describe a method to isolate and culture human adult and fetal epicardial derived cells (EPDCs) in an epithelial-cell-like morphology and to induce EMT. With this model, we aim to explore and compare adult and fetal epicardial cell behavior.
The main advantage of this protocol is the use of human epicardial material, which has not been thoroughly studied. Importantly, the described isolation and cell culture protocol provides a single uniform method to derive both fetal and adult cobble EPDCs, enabling a direct comparison between these two cell sources. Additionally, since the epicardium is isolated based on its location, it is ensured that the cells are actually epicardially derived17.
While human EPDC isolation methods have been established previously, these mostly rely on outgrowth protocols where pieces of cardiac or epicardial tissue are plated onto a cell culture dish18,19. This approach thereby selects specifically for cells that partially lose their epithelial phenotype in order to migrate, and that are more prone to undergo spontaneous EMT. In the current protocol, the epicardium is first processed into a single cell solution which allows the isolated EPDCs to maintain their epithelial state. This method therefore provides a solid in vitro model to study epicardial EMT.

<table><tbody><tr><td>Dulbecco&amp;rsquo;s modified Eagle&amp;rsquo;s medium + GlutaMAX</td><td>Gibco</td><td>21885-025</td><td></td></tr><tr><td>Medium 199&amp;nbsp;</td><td>Gibco</td><td>31150-022</td><td></td></tr><tr><td>Fetal Bovine Serum&amp;nbsp;</td><td>Gibco</td><td>10270-106</td><td></td></tr><tr><td>Trypsin 0.25%</td><td>Invitrogen</td><td>25200-056</td><td></td></tr><tr><td>Penicillin G sodium salt</td><td>Roth</td><td>HP48</td><td></td></tr><tr><td>Streptomycin sulphate</td><td>Roth</td><td>HP66</td><td></td></tr><tr><td>Trypsin 1:250 from bovine pancreas</td><td>Serva</td><td>37289</td><td></td></tr><tr><td>EDTA</td><td>Sigma</td><td>E4884</td><td></td></tr><tr><td>Gelatin from porcine skin</td><td>Sigma-Aldrich</td><td>G1890</td><td></td></tr><tr><td>Culture plates 6 well</td><td>Greiner bio-one</td><td>657160</td><td></td></tr><tr><td>Culture plates 12 well</td><td>Corning</td><td>3512</td><td></td></tr><tr><td>Culture plates 24 well</td><td>Greiner bio-one</td><td>662160</td><td></td></tr><tr><td>SB 431542</td><td>Tocris</td><td>1614</td><td></td></tr><tr><td>Dimethyl Sulfoxide (DMSO)</td><td>Merck</td><td>102931</td><td></td></tr><tr><td>100-1000&amp;micro;L Filtered Pipet Tips</td><td>Corning</td><td>4809</td><td></td></tr><tr><td>10-ml pipet</td><td>Greiner bio-one</td><td>607180</td><td></td></tr><tr><td>5-ml pipet</td><td>Greiner bio-one</td><td>606180</td><td></td></tr><tr><td>Cell culture dish 100/20 mm</td><td>Greiner bio-one</td><td>664160</td><td></td></tr><tr><td>PBS</td><td>Gibco</td><td>10010056</td><td>Or home-made and sterilized</td></tr><tr><td>Eppendorf tubes 1.5 mL</td><td>Eppendorf</td><td>0030120086</td><td></td></tr><tr><td>15-ml centrifuge tubes</td><td>Greiner bio-one</td><td>188271</td><td></td></tr><tr><td>50-ml centrifuge tubes</td><td>Greiner bio-one</td><td>227261</td><td></td></tr><tr><td>10 mL Syringe</td><td>Becton Dickinson</td><td>305959</td><td></td></tr><tr><td>Needles 19 Gauge</td><td>Becton Dickinson</td><td>301700</td><td></td></tr><tr><td>Needles 21 Gauge</td><td>Becton Dickinson</td><td>304432</td><td></td></tr><tr><td>EASYstrainer Cell Sieves, 100 &amp;micro;m</td><td>Greiner bio-one</td><td>542000</td><td></td></tr><tr><td>TGF&amp;beta;3&amp;nbsp;</td><td>R&amp;amp;D systems</td><td>243-B3</td><td></td></tr><tr><td>Monoclonal Anti-Actin, &amp;alpha;-Smooth Muscle</td><td>Sigma</td><td>A2547&amp;nbsp;</td><td></td></tr><tr><td>Anti-Mouse Alexa Fluor 555</td><td>Invitrogen</td><td>A31570</td><td></td></tr><tr><td>Alexa Fluor 488 Phalloidin</td><td>Invitrogen</td><td>A12379</td><td></td></tr><tr><td>&lt;strong&gt;Equipment&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>&lt;strong&gt;Name&lt;/strong&gt;</td><td>&lt;strong&gt;Company&lt;/strong&gt;</td><td>&lt;strong&gt;Catalog Number&lt;/strong&gt;</td><td>&lt;strong&gt;Comments&lt;/strong&gt;</td></tr><tr><td>Pipet P1,000</td><td>Gilson</td><td>F123602</td><td></td></tr><tr><td>Pipet controller</td><td>Integra</td><td>155 015</td><td></td></tr><tr><td>Stereomicroscope</td><td>Leica</td><td>M80</td><td></td></tr><tr><td>Inverted Light Microscope</td><td>Olympus</td><td>CK2</td><td></td></tr><tr><td>Centrifuge</td><td>Eppendorf</td><td>5702</td><td></td></tr><tr><td>Waterbath</td><td>GFL</td><td>1083</td><td></td></tr></tbody></table>

the isolation and culture of primary epicardial cells derived from human adult and fetal heart specimens

The epicardium, an epithelial cell layer covering the myocardium, has an essential role during cardiac development, as well as in the repair response of the heart after ischemic injury. When activated, epicardial cells undergo a process known as epithelial to mesenchymal transition (EMT) to provide cells to the regenerating myocardium. Furthermore, the epicardium contributes via secretion of essential paracrine factors. To fully appreciate the regenerative potential of the epicardium, a human cell model is required. Here we outline a novel cell culture model to derive primary epicardial derived cells (EPDCs) from human adult and fetal cardiac tissue. To isolate EPDCs, the epicardium is dissected from the outside of the heart specimen and processed into a single cell suspension. Next, EPDCs are plated and cultured in EPDC medium containing the ALK 5-kinase inhibitor SB431542 to maintain their epithelial phenotype. EMT is induced by stimulation with TGF&#946;. This method enables, for the first time, the study of the process of human epicardial EMT in a controlled setting, and facilitates gaining more insight in the secretome of EPDCs that may aid heart regeneration. Furthermore, this uniform approach allows for direct comparison of human adult and fetal epicardial behavior.

Here, we outline a straightforward protocol to isolate EPDCs from human adult and fetal cardiac tissue (Figure 1). This protocol takes advantage of the easily accessible location of the epicardium on the outside of the heart (Figure 1A). Staining of the heart auricle after dissection demonstrates that the WT1+ epicardium is removed while the underlying subepicardial extracellular matrix and myocardial tissue remain intact (<stron...

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The Isolation and Culture of Primary Epicardial Cells Derived from Human Adult and Fetal Heart Specimens

The epicardium plays a crucial role in the development and repair of the heart by providing cells and growth factors to the myocardial wall. Here, we describe a method to culture human primary epicardial cells that enables the study and comparison of their developmental and adult characteristics.

The epicardium, an epithelial cell layer covering the myocardium, has an essential role during cardiac development, as well as in the repair response of ...

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Research

JoVE Journal

Developmental Biology

7.7K Views.  Leiden University Medical Center. The epicardium plays a crucial role in the development and repair of the heart by providing cells and growth factors to the myocardial wall. Here, we describe a method to culture human primary epicardial cells that enables the study and comparison of their developmental and adult characteristics.

Video: The Isolation and Culture of Primary Epicardial Cells Derived from Human Adult and Fetal Heart Specimens

Epicardial Outgrowth Culture Assay and Ex Vivo Assessment of Epicardial-derived Cell Migration

A single layer of epicardial cells lines the heart, providing paracrine factors that stimulate cardiomyocyte proliferation and directly contributing cardiovascular progenitors during development and disease. While a number of factors have been implicated in epicardium-derived cell (EPDC) mobilization, the mechanisms governing their subsequent migration and differentiation are poorly understood. Here, we present in vitro and ex vivo strategies to study EPDC motility and differentiation. First, we describe a method of obtaining primary epicardial cells by outgrowth culture from the embryonic mouse heart. We also introduce a detailed protocol to assess three-dimensional migration of labeled EPDC in an organ culture system. We provide evidence using these techniques that genetic deletion of myocardin-related transcription factors in the epicardium attenuates EPDC migration. This approach serves as a platform to evaluate candidate modifiers of EPDC biology and could be used to develop genetic or chemical screens to identify novel regulators of EPDC mobilization that might be useful for cardiac repair.

Epicardial Outgrowth Culture Assay and Ex Vivo Assessment of Epicardial-derived Cell Migration

Here, we describe methods for isolating primary mouse epicardial cells by an outgrowth culture assay and assessing the functional migration of epicardial-derived cells (EPDC) using an ex vivo heart culture system. These protocols are suitable for identifying genetic and chemical modulators of epicardial epithelial-to-mesenchymal transition (EMT) and motility.

A single layer of epicardial cells lines the heart, providing paracrine factors that stimulate cardiomyocyte proliferation and directly contributing ...

Isolation of Perivascular Multipotent Precursor Cell Populations from Human Cardiac Tissue

Multipotent mesenchymal stem/stromal cells (MSC) were conventionally isolated, through their plastic adherence, from primary tissue digests whilst their anatomical tissue location remained unclear. The recent discovery of defined perivascular and MSC cell marker expression by perivascular cells in multiple tissues by our group and other researchers has provided an opportunity to prospectively isolate and purify specific homogenous subpopulations of multipotent perivascular precursor cells. We have previously demonstrated the use of fluorescent activated cell sorting (FACS) to purify microvascular CD146+CD34- pericytes and vascular CD34+CD146- adventitial cells from human skeletal muscle. Herein we describe a method to simultaneously isolate these two perivascular cell subsets from human myocardium by FACS, based on the expression of a defined set of cell surface markers for positive and negative selections. This method thus makes available two specific subpopulations of multipotent cardiac MSC-like precursor cells for use in basic research and/or therapeutic investigations.

Human cardiac tissue harbours multipotent perivascular precursor cell populations that may be suitable for myocardial regeneration. The technique described here allows for the simultaneous isolation and purification of two multipotent stromal cell populations associated with native blood vessels, i.e. CD146+CD34- pericytes and CD34+CD146- adventitial cells, from the human myocardium.

Multipotent mesenchymal stem/stromal cells (MSC) were conventionally isolated, through their plastic adherence, from primary tissue digests whilst their ...

In Vitro Culture of Epicardial Cells From Mouse Embryonic Heart

During embryogenesis, the epicardial contribution to coronary vasculature development has been very well established. Cells derived from the epicardium differentiate into smooth muscle cells, fibroblasts and endothelial cells that contribute to the formation of coronary vessels. Here we have established an in vitro culture method for embryonic epicardial cells. Using genetic labelling, we have demonstrated that the majority of the migrating cells in our explant culture are of epicardial origin. Epicardial explant cells also retain the expression of epicardial markers (Wt1 and Tbx18). Furthermore, we provide evidence that epicardial explant cells undergo epithelial to mesenchymal transition (EMT), migrate and differentiate into smooth muscle cells after Transforming growth factor beta 1 (TGF-&#946;1) treatment in a manner indistinguishable from that of epicardial cells in vivo. In conclusion, we provide a novel method for the culture of embryonic epicardial cells, which will help to explore the role of specific genes in epicardial cell biology.

In Vitro Culture of Epicardial Cells From Mouse Embryonic Heart

The epicardium is an essential source of multipotent cardiovascular progenitor cells and paracrine factors that are required for cardiovascular development and regeneration. We describe here a method to culture mouse embryonic epicardial cells.

During embryogenesis, the epicardial contribution to coronary vasculature development has been very well established. Cells derived from the epicardium ...

Engineering

Isolation and Functional Characterization of Human Ventricular Cardiomyocytes from Fresh Surgical Samples

Cardiomyocytes from diseased hearts are subjected to complex remodeling processes involving changes in cell structure, excitation contraction coupling and membrane ion currents. Those changes are likely&#160;to be responsible for the increased arrhythmogenic risk and the contractile alterations leading to systolic and diastolic dysfunction in cardiac patients. However, most information on the alterations of myocyte function in cardiac diseases has come from animal models.
Here we describe and validate a protocol to isolate viable myocytes from small surgical samples of ventricular myocardium from patients undergoing cardiac surgery operations. The protocol is described in detail. Electrophysiological and intracellular calcium measurements are reported to demonstrate the feasibility of a number of single cell measurements in human ventricular cardiomyocytes obtained with this method.
The protocol reported here can be useful for future investigations of the cellular and molecular basis of functional alterations of the human heart in the presence of different cardiac diseases. Further, this method can be used to identify novel therapeutic targets at cellular level and to test the effectiveness of new compounds on human cardiomyocytes, with direct translational value.

Current knowledge on the cellular basis of cardiac diseases mostly relies on studies on animal models. Here we describe and validate a novel method to obtain single viable cardiomyocytes from small surgical samples of human ventricular myocardium. Human ventricular myocytes can be used for electrophysiological studies and drug testing.

Cardiomyocytes from diseased hearts are subjected to complex remodeling processes involving changes in cell structure, excitation contraction coupling and ...

Medicine

Isolation of Endocardial and Coronary Endothelial Cells from the Ventricular Free Wall of the Rat Heart

It has been shown that endocardial endothelial cells (EECs) and coronary endothelial cells (CECs) differ in origin, development, markers, and functions. Consequently, these two cell populations play unique roles in cardiac diseases. Current studies involving isolated endothelial cells investigate cell populations consisting of both EECs and CECs. This protocol outlines a method to independently isolate these two cell populations for cell-specific characterization. Following the collection of the left and right ventricular free wall, endothelial cells from the outer surface and inner surface are separately liberated using a digestion buffer solution. The sequential digestion of the outer surface and the inner endocardial layer retained separation of the two endothelial cell populations. The separate isolation of EECs and CECs is further verified through the identification of markers specific to each population. Based on previously published single cell RNA profiling in the mouse heart, the Npr3, Hapln1, and Cdh11 gene expression is unique to EECs; while Fabp4, Mgll, and Cd36 gene expression is unique to CECs. qPCR data revealed enriched expression of these characteristic markers in their respective samples, indicating successful EEC and CEC isolation, as well as maintenance of cell phenotype, enabling further cell-specific functional analysis.

We present a protocol for the isolation of endocardial and coronary endothelial cells from rat hearts through sequential tissue digestion in a digestion buffer, cell collection from recurrent centrifuge cycles, and cell purification using anti-rat CD31 microbeads.

It has been shown that endocardial endothelial cells (EECs) and coronary endothelial cells (CECs) differ in origin, development, markers, and functions. ...

Isolating Primary Melanocyte-like Cells from the Mouse Heart

We identified a novel population of melanocyte-like cells (also known as cardiac melanocytes) in the hearts of mice and humans that contribute to atrial arrhythmia triggers in mice. To investigate the electrical and biological properties of cardiac melanocytes we developed a procedure to isolate them from mouse hearts that we derived from those designed to isolate neonatal murine cardiomyocytes. In order to obtain healthier cardiac melanocytes suitable for more extensive patch clamp or biochemical studies, we developed a refined procedure for isolating and plating cardiac melanocytes based on those originally designed to isolate cutaneous melanocytes. The refined procedure is demonstrated in this review and produces larger numbers of healthy melanocyte-like cells that can be plated as a pure population or with cardiomyocytes.

In this protocol, we identified a novel population of melanocyte-like cells (also known as cardiac melanocytes) in the hearts of mice and humans that contribute to atrial arrhythmia triggers in mice.&#160;

We identified a novel population of melanocyte-like cells (also known as cardiac melanocytes) in the hearts of mice and humans that contribute to atrial ...

Biology

Isolation of Human Atrial Myocytes for Simultaneous Measurements of Ca2+ Transients and Membrane Currents

The study of electrophysiological properties of cardiac ion channels with the patch-clamp technique and the exploration of cardiac cellular Ca2+ handling abnormalities requires isolated cardiomyocytes. In addition, the possibility to investigate myocytes from patients using these techniques is an invaluable requirement to elucidate the molecular basis of cardiac diseases such as atrial fibrillation (AF).1 Here we describe a method for isolation of human atrial myocytes which are suitable for both patch-clamp studies and simultaneous measurements of intracellular Ca2+ concentrations. First, right atrial appendages obtained from patients undergoing open heart surgery are chopped into small tissue chunks ("chunk method") and washed in Ca2+-free solution. Then the tissue chunks are digested in collagenase and protease containing solutions with 20 &mu;M Ca2+. Thereafter, the isolated myocytes are harvested by filtration and centrifugation of the tissue suspension. Finally, the Ca2+ concentration in the cell storage solution is adjusted stepwise to 0.2 mM. We briefly discuss the meaning of Ca2+ and Ca2+ buffering during the isolation process and also provide representative recordings of action potentials and membrane currents, both together with simultaneous Ca2+ transient measurements, performed in these isolated myocytes.

Isolation of Human Atrial Myocytes for Simultaneous Measurements of Ca2+ Transients and Membrane Currents

We describe the isolation of human atrial myocytes which can be used for intracellular Ca2+ measurements in combination with electrophysiological patch-clamp studies.

The study of  electrophysiological properties of cardiac ion channels with the patch-clamp  technique and the exploration of cardiac cellular Ca2+ ...

Isolation of Embryonic Ventricular Endothelial Cells

Cell culture has greatly enhanced our ability to assess individual populations of cells under myriad culture conditions. While immortalized cell lines offer significant advantages for their ease of use, these cell lines are unavailable for all potential cell types. By isolating primary cells from a specific region of interest, particularly from a transgenic mouse, more nuanced studies can be performed. The basic technique involves dissecting the organ or partial organ of interest (e.g. the heart or a specific region of the heart) and dissociating the organ to single cells. These cells are then incubated with magnetic beads conjugated to an antibody that recognizes the cell type of interest. The cells of interest can then be isolated with the use of a magnet, with a short trypsin incubation dissociating the cells from the beads. These isolated cells can then be cultured and analyzed as desired. This technique was originally designed for adult mouse organs but can be easily scaled down for use with embryonic organs, as demonstrated herein. Because our interest is in the developing coronary vasculature, we wanted to study this population of cells during specific embryonic stages. Thus, the original protocol had to be modified to be compatible with the small size of the embryonic ventricles and the low potential yield of endothelial cells at these developmental stages. Utilizing this scaled-down approach, we have assessed coronary plexus remodeling in transgenic embryonic ventricular endothelial cells.

Primary cell culture is a useful technique for analyzing specific populations of cells, particularly from transgenic mouse embryos at specific developmental stages. Herein, embryonic ventricles are dissected and dissociated, and antibody-conjugated beads recognize and separate out the endothelial cells for further analysis.

Cell culture has greatly enhanced our ability to assess individual populations of cells under myriad culture conditions. While immortalized cell lines ...

Isolation of Cardiomyocytes from Fixed Hearts for Immunocytochemistry and Ploidy Analysis

The adult mammalian heart is composed of various cell types including cardiomyocytes, endothelial cells and fibroblasts. Since it is difficult to reliably identify nuclei of cardiomyocytes on histological sections, many groups rely on isolating viable cardiomyocytes prior to fixation to perform immunostaining. However, these live cardiomyocyte isolation techniques require optimization to maximize the yield, viability and quality of the samples, with inherent fluctuations from sample to sample despite maximum optimization. Here, we report a reproducible protocol, involving fixation prior to enzymatic digestion of the heart, which leads to maximum yield while preserving the in vivo morphology of individual cardiomyocytes. We further developed an automated analysis platform to determine the number of nuclei and DNA content per nucleus for individual cardiomyocytes. After exposing the chest cavity, the heart was arrested in diastole by perfusion with 60 mM KCl in PBS. Next, the heart was fixed in 4% paraformaldehyde (PFA) solution, and then digested with 60 mg/mL collagenase solution. After digestions, cells were singularized by trituration, and the cardiomyocyte fraction was enriched via differential centrifugation. Isolated cardiomyocytes were stained for Troponin T and &#945;-actinin to assess purity of the obtained population. Furthermore, we developed an image analysis platform to determine cardiomyocyte nucleation and ploidy status following DAPI staining. Image based ploidy assessments led to consistent and reproducible results. Thus, with this protocol, it is possible to preserve native morphology of individual cardiomyocytes to allow immunocytochemistry and DNA content analysis while achieving maximum yield.

The goal of this work is to develop a method to reproducibly isolate cardiomyocytes from the adult heart and measure DNA content and nucleation.

The adult mammalian heart is composed of various cell types including cardiomyocytes, endothelial cells and fibroblasts. Since it is difficult to reliably ...

Isolation of Human Ventricular Cardiomyocytes from Vibratome-Cut Myocardial Slices

The isolation of ventricular cardiac myocytes from animal and human hearts is a fundamental method in cardiac research. Animal cardiomyocytes are commonly isolated by coronary perfusion with digestive enzymes. However, isolating human cardiomyocytes is challenging because human myocardial specimens usually do not allow for coronary perfusion, and alternative isolation protocols result in poor yields of viable cells. In addition, human myocardial specimens are rare and only regularly available at institutions with on-site cardiac surgery. This hampers the translation of findings from animal to human cardiomyocytes. Described here is a reliable protocol that enables efficient isolation of ventricular myocytes from human and animal myocardium. To increase the surface-to-volume ratio while minimizing cell damage, myocardial tissue slices 300 &#181;m thick are generated from myocardial specimens with a vibratome. Tissue slices are then digested with protease and collagenase. Rat myocardium was used to establish the protocol and quantify yields of viable, calcium-tolerant myocytes by flow-cytometric cell counting. Comparison with the commonly used tissue-chunk method showed significantly higher yields of rod-shaped cardiomyocytes (41.5 &#177; 11.9 vs. 7.89 &#177; 3.6%, p &#60; 0.05). The protocol was translated to failing and non-failing human myocardium, where yields were similar as in rat myocardium and, again, markedly higher than with the tissue-chunk method (45.0 &#177; 15.0 vs. 6.87 &#177; 5.23 cells/mg, p &#60; 0.05). Notably, with the protocol presented it is possible to isolate reasonable numbers of viable human cardiomyocytes (9&#8211;200 cells/mg) from minimal amounts of tissue (&#60;50 mg). Thus, the method is applicable to healthy and failing myocardium from both human and animal hearts. Furthermore, it is possible to isolate excitable and contractile myocytes from human tissue specimens stored for up to 36 h in cold cardioplegic solution, rendering the method particularly useful for laboratories at institutions without on-site cardiac surgery.

Presented is a protocol for the isolation of human and animal ventricular cardiomyocytes from vibratome-cut myocardial slices. High yields of calcium-tolerant cells (up to 200 cells/mg) can be obtained from small amounts of tissue (&#60;50 mg). The protocol is applicable to myocardium exposed to cold ischemia for up to 36 h.

The isolation of ventricular cardiac myocytes from animal and human hearts is a fundamental method in cardiac research. Animal cardiomyocytes are commonly ...

The Isolation and Culture of Primary Epicardial Cells Derived from Human Adult and Fetal Heart Specimens

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Epicardial Outgrowth Culture Assay and Ex Vivo Assessment of Epicardial-derived Cell Migration

Isolation of Perivascular Multipotent Precursor Cell Populations from Human Cardiac Tissue

In Vitro Culture of Epicardial Cells From Mouse Embryonic Heart

Isolation and Functional Characterization of Human Ventricular Cardiomyocytes from Fresh Surgical Samples

Isolation of Endocardial and Coronary Endothelial Cells from the Ventricular Free Wall of the Rat Heart

Isolating Primary Melanocyte-like Cells from the Mouse Heart

Isolation of Human Atrial Myocytes for Simultaneous Measurements of Ca²⁺ Transients and Membrane Currents

Isolation of Embryonic Ventricular Endothelial Cells

Isolation of Cardiomyocytes from Fixed Hearts for Immunocytochemistry and Ploidy Analysis

Isolation of Human Ventricular Cardiomyocytes from Vibratome-Cut Myocardial Slices