This work was supported, in part, by the US Department of Veterans Affairs Biomedical Laboratory R&#38;D Service (I01 BX003482) and by institutional funds to M.L.R.

1. Experimental preparation/plating
<ol>
	<li>Maintain CMs and ECs according to the manufacturer&#39;s instructions.
	<ol>
		<li>Thaw both cell lines when they arrive from vendors. Plate in T25 flasks after being washed with fresh media. It is recommended to purchase each cell culture media from the same vendors the cells were purchased from. The next day, refresh the cells with media and use when confluent.</li>
		<li>Maintain the cell culture incubator at 37 &#176;C with 21% O2, 5% CO2, 74% N2 and keep it humidified. 
		NOTE: The Mouse Primary Coronary Artery Endothelial Cells used in this protocol are isolated from coronary arteries of C57BL/6 mice, and Adult Mouse Cardiomyocytes are isolated from adult C57BL/6J mouse hearts and commercially obtained (see Table of Materials).</li>
	</ol>
	</li>
	<li>Plate CMs under sterile conditions onto the bottom of 24-well plates (inferior layer). 24 h later, plate ECs into the insert (or superior portion) of the co-culture well. 24 h after EC plating, place EC inserts onto CM plate bases, starting the co-culture period. Allow the cells to co-culture for at least 12-24 h before use. These steps are described in detail below.
	<ol>
		<li>Estimate CM cell line confluency under a light microscope. When cells appear to be 90%-100% confluent in culture flasks, proceed with experimental plating.</li>
		<li>Remove the media from the flasks containing confluent cell cultures and trypsinize with 3-5 mL of Trypsin/Ethylenediaminetetraacetic acid (EDTA) for T25 flasks. Agitate the flask gently, incubate at 37 &#176;C for 2-5 min, and then assess the enzymatic progress under a light microscope. Once the cells start to round up, use a cell scraper to detach the cells from the surface.</li>
		<li>After detachment, inactivate the trypsin solution by adding the trypsin/cell solution to a 50 mL tube containing 10 mL of media for T25 flasks. Centrifuge the cell suspension at 120 x g for 2 min to obtain a soft cell pellet. Remove the supernatant and resuspend the pellet in 5 mL of media.</li>
		<li>To perform cell counting and confirm cell viability, mix an aliquot of 10&#160;&#181;L of resuspended cells and 10&#160;&#181;L of trypan blue dye. Count the living cells using a cell counter. Dilute the cells with fresh regular media to achieve the desired seeding densities. Volumes are calculated depending on the desired seed density and cell concentration of stock solutions. All plating should be performed under sterile conditions.</li>
		<li>Plate CMs at seeding densities of 300,000 per well onto the bottom of a 24-well plate pre-coated with extracellular matrix. Maintain the cells at 37 &#176;C with 21% O2 and 5% CO2 overnight.</li>
		<li>After 24 h, plate ECs into inserts at an optimal plating density of 100,000 per insert (culture area is 33.6 mm2), (Figure 1). After 24 h of EC plating, place EC inserts inside the CM wells, initiating co-culture. Allow cells to co-culture for 12-24 h before performing the experiments.</li>
		<li>Ensure that, by the time experiments are performed, both CMs and ECs have reached 80%-90% confluency.</li>
	</ol>
	</li>
</ol>
2. Hypoxia/reoxygenation to simulate ischemia/reperfusion injury&#160;&#160;In Vitro
NOTE: The following steps need to be performed as described, do not pause in-between.
<ol>
	<li>Prepare the hypoxic media by pouring ~25 mL of media in a 50 mL conical tube. Air-seal the top with a silicone membrane and use a sterilized pipette to punch a hole. Create another hole, this time leaving the pipette submerged approximately 2/3 into the media.</li>
	<li>Flush the media with hypoxic gas (0.0125% O2, 5% CO2, 94.99% N2) for 5 min at a flow rate of 30 L/min. This minimizes O2 dissolved in the media when hypoxia starts (step 2.5).</li>
	<li>Discard the media of the 24-well plates or culture inserts containing attached cells and wash with 100 &#181;L/well of 10% Phosphate Buffered Saline (PBS) very gently. Afterwards, add 500 &#181;L of the freshly prepared hypoxic media to each well of the plates or inserts. 
	NOTE: Hypoxia in the media is interrupted as briefly as possible during this step before true hypoxia for cells and media starts in step 2.5.
	<ol>
		<li>In the normoxic control group, replace the original media with fresh normal media containing glucose and serum.</li>
	</ol>
	</li>
	<li>Humidify the hypoxia chamber by placing a Petri-dish filled with sterile water within the chamber. Next, place the plates comprising the hypoxic groups into the chamber.</li>
	<li>Flush the hypoxia chamber with hypoxic gas (0.0125% O2, 5% CO2, 94.99% N2) for 5 min at a flow of 30 L/min. Place the chamber in the 37 &#176;C incubator for 24 h.</li>
	<li>After hypoxia, cultivate CMs and ECs under normal conditions. To do so, discard the old media of the plates/inserts, replace it with normal media (containing glucose and serum; 500 &#181;L of each well/insert) and store it in the incubator under normal culture conditions (21% O2, 5% CO2, 74% N2, 37 &#176;C) for 2 h to mimic reperfusion.</li>
	<li>To control for any effects of media replacement, change the media of normoxic cells at the same time as the hypoxic media is changed. 
	NOTE: Figure 2 provides a schematic overview of this protocol.</li>
</ol>
3. Endpoint assessment
<ol>
	<li>Transfer the cell culture media from the 24-well plate into a 96-well plate. Use 200 &#181;L of media from each well of the 24-well plate and equally distribute into four wells of the 96-well plate, accordingly. Use one plate each for normoxia versus hypoxia versus HR.</li>
	<li>Determine the degree of cellular injury, e.g., by measuring absorbance for LDH using a cytotoxicity assay kit following the manufacturer&#39;s instructions. Perform the assay in a 96-well plate as instructed in the assay protocol.</li>
</ol>
4. Statistics
<ol>
	<li>Display the parametric data as mean/standard deviation and non-parametric data as box plots with median/interquartile range. Adequate parametric versus non-parametric multiple comparisons tests with acceptable post-hoc tests to decrease the chance for a type-1 error should be performed. Significance is typically set at an alpha of 0.05 (two-tailed).</li>
	<li>For all the experiments carried out in the current study, perform at least three well replicates within one experiment. There were three to six repetitions of each experiment used for statistical analysis.</li>
</ol>

<ol>
	<li>Hausenloy, D. J., 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=Ischaemic+conditioning+and+targeting+reperfusion+injury:+a+30+year+voyage+of+discovery.">Ischaemic conditioning and targeting reperfusion injury: a 30 year voyage of discovery.</a> Basic Research in Cardiology. 111 (6), 70 (2016).</li><li>Hausenloy, D. J., Yellon, D. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Myocardial+ischemia-reperfusion+injury:+a+neglected+therapeutic+target.">Myocardial ischemia-reperfusion injury: a neglected therapeutic target.</a> The Journal of Clinical Investigation. 123 (1), 92-100 (2013).</li><li>Gottlieb, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cell+death+pathways+in+acute+ischemia/reperfusion+injury.">Cell death pathways in acute ischemia/reperfusion injury.</a> Journal of Cardiovascular Pharmacology and Therapeutics. 16 (3-4), 233-238 (2011).</li><li>Colliva, A., Braga, L., Giacca, M., Zacchigna, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Endothelial+cell-cardiomyocyte+crosstalk+in+heart+development+and+disease.">Endothelial cell-cardiomyocyte crosstalk in heart development and disease.</a> The Journal of Physiology. 598 (14), 2923-2939 (2020).</li><li>Bogdanowicz, D. R., Lu, H. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Studying+cell-cell+communication+in+co-culture.">Studying cell-cell communication in co-culture.</a> Biotechnology Journal. 8 (4), 395-396 (2013).</li><li>Salzman, M. M., Bartos, J. A., Yannopoulos, D., Riess, M. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Poloxamer+188+protects+isolated+adult+mouse+cardiomyocytes+from+reoxygenation+injury.">Poloxamer 188 protects isolated adult mouse cardiomyocytes from reoxygenation injury.</a> Pharmacology Research &amp; Perspectives. 8 (6), 00639 (2020).</li><li>Kalogeris, T., Baines, C. P., Krenz, M., Korthuis, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cell+biology+of+ischemia/reperfusion+injury.">Cell biology of ischemia/reperfusion injury.</a> International Review of Cell and Molecular Biology. 298, 229-317 (2012).</li><li>Martindale, J. J., Metzger, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Uncoupling+of+increased+cellular+oxidative+stress+and+myocardial+ischemia+reperfusion+injury+by+directed+sarcolemma+stabilization.">Uncoupling of increased cellular oxidative stress and myocardial ischemia reperfusion injury by directed sarcolemma stabilization.</a> Journal of Molecular and Cellular Cardiology. 67, 26-37 (2014).</li><li>vander Meer, A. D., Orlova, V. V., ten Dijke, P., vanden Berg, A., Mummery, C. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Three-dimensional+co-cultures+of+human+endothelial+cells+and+embryonic+stem+cell-derived+pericytes+inside+a+microfluidic+device.">Three-dimensional co-cultures of human endothelial cells and embryonic stem cell-derived pericytes inside a microfluidic device.</a> Lab on a Chip. 13, 3562-3568 (2013).</li><li>Bidarra, S. J., 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=Phenotypic+and+proliferative+modulation+of+human+mesenchymal+stem+cells+via+crosstalk+with+endothelial+cells.">Phenotypic and proliferative modulation of human mesenchymal stem cells via crosstalk with endothelial cells.</a> Stem Cell Research. 7, 186-197 (2011).</li><li>Campbell, J. J., Davidenko, N., Caffarel, M. M., Cameron, R. E., Watson, C. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+multifunctional+3D+co-culture+system+for+studies+of+mammary+tissue+morphogenesis+and+stem+cell+biology.">A multifunctional 3D co-culture system for studies of mammary tissue morphogenesis and stem cell biology.</a> PloS One. 6, 25661 (2011).</li><li>Mehes, E., Mones, E., Nemeth, V., Vicsek, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Collective+motion+of+cells+mediates+segregation+and+pattern+formation+in+co-cultures.">Collective motion of cells mediates segregation and pattern formation in co-cultures.</a> PloS One. 7, 31711 (2012).</li><li>Miki, Y., 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+advantages+of+co-culture+over+mono+cell+culture+in+simulating+in+vivo+environment.">The advantages of co-culture over mono cell culture in simulating in vivo environment.</a> The Journal of Steroid Biochemistry and Molecular Biology. 131 (3-5), 68-75 (2012).</li><li>Moraes, C., Mehta, G., Lesher-Perez, S. C., Takayama, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Organs-on-a-chip:+a+focus+on+compartmentalized+microdevices.">Organs-on-a-chip: a focus on compartmentalized microdevices.</a> Annals of Biomedical Engineering. 40 (6), 1211-1227 (2012).</li><li>Campbell, J., Davidenko, N., Caffarel, M., Cameron, R., Watson, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+multifunctional+3D+co-culture+system+for+studies+of+mammary+tissue+morphogenesis+and+stem+cell+biology.">A multifunctional 3D co-culture system for studies of mammary tissue morphogenesis and stem cell biology.</a> PLoS One. 6, 25661 (2011).</li><li>Wu, M. H., Huang, S. B., Lee, G. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microfluidic+cell+culture+systems+for+drug+research.">Microfluidic cell culture systems for drug research.</a> Lab on a Chip. 10, 939-956 (2010).</li></ol>

The authors declare no conflicts of interest.

Critical steps in the protocol 
Cell co-culture models have been used to study cellular mechanisms of cardioprotection. How to create two separate layers with a meaningful distance between them is, thus, crucial for the development of a suitable co-culture model. A challenge in studying simulated IR, i.e., HR, injury is that not only ischemia (hypoxia) itself but also reperfusion (reoxygenation) aggravates cellular dysfunction. Therefore, a realistic model needs to reflect these characteristics by, ...

Ischemic heart disease is the leading cause of death and disability worldwide1,2. However, the treatment process of reperfusion can itself cause cardiomyocyte death, known as myocardial ischemia/reperfusion (IR) injury, for which there is still no effective remedy3. Endothelial cells (ECs) have been suggested to protect cardiomyocytes (CMs) through the secretion of paracrine signals, as well as cell-to-cell interactions4.
Cell co-culture models have been used extensively to investigate the role of autocrine and/or paracrine cell-cell interactions on cell function and differentiation. Among co-culture models, mixed co-culture is the simplest, where two different types of cells are in direct contact within a single culture compartment at a desired cell ratio5. However, separate treatments between cell types and downstream analysis of a single cell type are not readily feasible given the mixed population.
Previous studies indicated that hypoxic and ischemic insults cause significant damage to the integrity of cell membrane as measured by the release of lactate dehydrogenase (LDH). This injury is worsened upon reoxygenation, mimicking reperfusion injury6,7,8. The goal of the current protocol was to test the hypotheses that the presence of ECs can dose-dependently attenuate cell membrane leakage of CMs caused by hypoxia and reoxygenation (HR) and that the protective effect of ECs can be optimized by varying the contact distance between the two cell lines. Thus, we employed three types of cell culture inserts and Mouse Primary Coronary Artery Endothelial Cells and Adult Mouse Cardiomyocytes. The inserts, branded by Corning, Merck Millipore, and Greiner Bio-One allowed us to create three different cell culture crosstalk conditions with inter-cell line distances of 0.5, 1.0, and 2.0 mm, respectively. 100,000 ECs were plated per insert in each case.
In addition, in order to determine whether the density of ECs in co-culture contributes to HR injury attenuation in this model, we studied the dose-response relationship between EC concentration and LDH release by CMs. ECs were plated at 25,000, 50,000 and 100,000 per insert, respectively, in the 2.0 mm insert.
This report provides a step-by-step approach for investigators to use this important model to their advantage.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr >
			<td >Adult Mouse Cardiomyocytes (CMs)</td>
			<td >Celprogen Inc</td>
			<td >11041-14</td>
			<td >Isolated from adult C57BL/6J mouse cardiac tissue</td>
		</tr>
		<tr >
			<td >Automated Cell Counter Countess II</td>
			<td>Invitrogen</td>
			<td>A27977</td>
			<td>Cell counting for calculating cell numbers</td>
		</tr>
		<tr >
			<td >Bio-Safety Cabinet</td>
			<td>Nuaire</td>
			<td>NU425400</td>
			<td>Cell culture sterile hood</td>
		</tr>
		<tr >
			<td >Cell Culture Freezing Medium</td>
			<td>Cell Biologics Inc</td>
			<td>6916</td>
			<td>Used for cell freezing for long term cell line storage</td>
		</tr>
		<tr >
			<td >Cell Culture Incubator</td>
			<td>Nuaire</td>
			<td>Nu-5500</td>
			<td>To provide normal cell living condition (21%O2, 5%CO2, 74%N2, 37&#176;C, humidified)</td>
		</tr>
		<tr >
			<td >Cell Culture Incubator Gas Tank</td>
			<td>A-L Compressed Gases</td>
			<td>UN1013</td>
			<td>Gas needed for cell culture incubator&#160;</td>
		</tr>
		<tr >
			<td >Cell Culture Inserts A (0.5 mm)</td>
			<td>Corning Inc</td>
			<td>353095</td>
			<td>Used for EC-CM co-culture</td>
		</tr>
		<tr >
			<td >Cell Culture Inserts B (1.0 mm)</td>
			<td>Millicell Millipore</td>
			<td>PIHP01250</td>
			<td>Used for EC-CM co-culture</td>
		</tr>
		<tr >
			<td >Cell Culture Inserts C (2.0 mm)</td>
			<td>Greiner Bio-One</td>
			<td>662640</td>
			<td>Used for EC-CM co-culture</td>
		</tr>
		<tr >
			<td >Centrifuge</td>
			<td>Anstel Enterprises Inc</td>
			<td>4235</td>
			<td>For cell culture plating and passaging</td>
		</tr>
		<tr >
			<td >CMs Cell Culture Flasks T25</td>
			<td>Celprogen Inc</td>
			<td>E11041-14</td>
			<td>Used for CMs regular culture, coated by manufacturer</td>
		</tr>
		<tr >
			<td >CMs Cell Culture Medium Complete</td>
			<td>Celprogen Inc</td>
			<td>M11041-14S</td>
			<td>CMs culture complete medium</td>
		</tr>
		<tr >
			<td >CMs Cell Culture Medium Complete Phenol free</td>
			<td>Celprogen Inc</td>
			<td>M11041-14PN</td>
			<td>CMs culture medium without phenol red used during LDH measurement</td>
		</tr>
		<tr >
			<td >CMs Cell Culture Plates 96 well</td>
			<td>Celprogen Inc</td>
			<td>E11041-14-96well</td>
			<td>Used for experiments of LDH measurement, coated by manufacturer</td>
		</tr>
		<tr >
			<td >CMs Hypoxia Cell Culture Medium</td>
			<td>Celprogen Inc</td>
			<td>M11041-14GFPN</td>
			<td>CMs cell culture under hypoxic condition (glucose- and serum-free)</td>
		</tr>
		<tr >
			<td >Countess cell counting chamber slides</td>
			<td>Invitrogen</td>
			<td>C10283</td>
			<td>Counting slides used for cell counter</td>
		</tr>
		<tr >
			<td >Cyquant LDH Cytotoxicity Kit</td>
			<td>Thermo Scientific&#160;</td>
			<td>C20301</td>
			<td>LDH measurement kit</td>
		</tr>
		<tr >
			<td >ECs Cell Culture Flasks T25</td>
			<td>Fisher Scientific&#160;</td>
			<td>FB012935</td>
			<td>Used for ECs regular culture</td>
		</tr>
		<tr >
			<td >ECs Cell Culture Medium Complete</td>
			<td>Cell Biologics Inc</td>
			<td>M1168</td>
			<td>ECs culture complete medium</td>
		</tr>
		<tr >
			<td >ECs Cell Culture Medium Complete Phenol free</td>
			<td>Cell Biologics Inc</td>
			<td>M1168PF</td>
			<td>ECs culture medium without phenol red used during LDH measurement</td>
		</tr>
		<tr >
			<td >ECs Cell Culture Plates 96 well</td>
			<td>Fisher Scientific (Costar)</td>
			<td>3370</td>
			<td>Used for experiments of LDH measurement</td>
		</tr>
		<tr >
			<td >ECs Culture Gelatin-Based Coating Solution</td>
			<td>Cell Biologics Inc</td>
			<td>6950</td>
			<td>Used for coating flasks and plates for ECs</td>
		</tr>
		<tr >
			<td >ECs Hypoxia Cell Culture Medium</td>
			<td>Cell Biologics Inc</td>
			<td>GPF1168</td>
			<td>ECs cell culture under hypoxic condition (glucose- and serum-free)</td>
		</tr>
		<tr >
			<td >Fetal Bovine Serum (FBS)</td>
			<td>Fisher Scientific</td>
			<td>MT35011CV</td>
			<td>FBS-HI USDA-approved for cell culture and maintenance</td>
		</tr>
		<tr >
			<td >Hypoxia Chamber</td>
			<td>StemCell Technologies</td>
			<td>27310</td>
			<td>To create a hypoxic condition with 0.01%O2 environment</td>
		</tr>
		<tr >
			<td >Hypoxia Chamber Flow Meter</td>
			<td>StemCell Technologies</td>
			<td>27311</td>
			<td>To connect with hypoxic gas tank for a consistent gas flow speed</td>
		</tr>
		<tr >
			<td >Hypoxic Gas Tank (0.01%O2 Cylinder)</td>
			<td>A-L Compressed Gases</td>
			<td>UN1956</td>
			<td>Used to flush hypoxic medium and chamber (0.01%O2/5%CO2/94.99N2)</td>
		</tr>
		<tr >
			<td >Microscope&#160;</td>
			<td>Nikon</td>
			<td>TMS</td>
			<td>To observe cell condition</td>
		</tr>
		<tr >
			<td >Mouse Primary Coronary Artery Endothelial Cells (ECs)</td>
			<td>Cell Biologics Inc</td>
			<td>C57-6093</td>
			<td>Isolated from coronary artery of C57BL/6 mice</td>
		</tr>
		<tr >
			<td >NUNC 15ML CONICL Tubes</td>
			<td>Fisher Scientific</td>
			<td>12565269</td>
			<td>For cell culture process, experiments, solution preparation etc.</td>
		</tr>
		<tr >
			<td >NUNC 50ML CONICL Tubes</td>
			<td>Fisher Scientific</td>
			<td>12565271</td>
			<td>For cell culture process, experiments, solution preparation etc.</td>
		</tr>
		<tr >
			<td >Phosphate Buffered Saline (PBS)</td>
			<td>Sigma-Aldrich</td>
			<td>D8662</td>
			<td>Used for cell washing during culture or experiments</td>
		</tr>
		<tr >
			<td >Plate Reader</td>
			<td>BioTek Instrument</td>
			<td>11120533</td>
			<td>Colorimetric or fluorometric plate reading</td>
		</tr>
		<tr >
			<td >Reaction 96 Well Palte (clear no lid)</td>
			<td>Fisher Scientific</td>
			<td>12565226</td>
			<td>Used for LDH measurement plate reading</td>
		</tr>
		<tr >
			<td >Trypsin/EDTA for CMs</td>
			<td>Celprogen Inc</td>
			<td>T1509-014</td>
			<td>1 x sterile filtered and tissue culture tested</td>
		</tr>
		<tr >
			<td >Trypsin/EDTA for ECs</td>
			<td>Cell Biologics Inc</td>
			<td>6914/0619</td>
			<td>0.25%, cell cuture-tested</td>
		</tr>
	</tbody>
</table>

development of a cell co-culture model to mimic cardiac ischemia/reperfusion in vitro

Ischemic heart disease is the leading cause of death and disability worldwide. Reperfusion causes additional injury beyond ischemia. Endothelial cells (ECs) can protect cardiomyocytes (CMs) from reperfusion injury through cell-cell interactions. Co-cultures can help investigate the role of cell-cell interactions. A mixed co-culture is the simplest approach but is limited as isolated treatments and downstream analyses of single cell types are not feasible. To investigate whether ECs can dose-dependently attenuate CM cell damage and whether this protection can be further optimized by varying the contact distance between the two cell lines, we used Mouse Primary Coronary Artery Endothelial Cells and Adult Mouse Cardiomyocytes to test three types of cell culture inserts which varied in their inter-cell layer distance at 0.5, 1.0, and 2.0 mm, respectively. In CMs-only, cellular injury as assessed by lactate dehydrogenase (LDH) release increased significantly during hypoxia and further upon reoxygenation when the distance was 2.0 mm compared to 0.5 and 1.0 mm. When ECs and CMs were in nearly direct contact (0.5 mm), there was only a mild attenuation of the reoxygenation injury of CMs following hypoxia. This attenuation was significantly increased when the spatial distance was 1.0 mm. With 2.0 mm distance, ECs attenuated CM injury during both hypoxia and hypoxia/reoxygenation, indicating that sufficient culture distancing is necessary for ECs to crosstalk with CMs, so that secreted signal molecules can circulate and fully stimulate protective pathways. Our findings suggest, for the first time, that optimizing the EC/CM co-culture spatial environment is necessary to provide a favorable in vitro model for testing the role of ECs in CM-protection against simulated ischemia/reperfusion injury. The goal of this report is to provide a step-by-step approach for investigators to use this important model to their advantage.

All three types of inserts (A, B, C) used in this experiment have the same pore size of 0.4 &#181;m. The only difference among them is the insert-to-base height, which allows distances between the two co-cultured cell layers to be 0.5, 1.0 and 2.0 mm, respectively, (Figure 3) and that they are from different vendors (for details see Table of Materials).
To establish an in vitro co-culture model with separate layers of two cell lines under...

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Development of a Cell Co-Culture Model to Mimic Cardiac Ischemia/Reperfusion In Vitro

Spatial distance is a key parameter in assessing hypoxia/reoxygenation injury in a co-culture model of separate endothelial and cardiomyocyte cell layers, suggesting, for the first time, that optimizing the co-culture spatial environment is necessary to provide a favorable in vitro model for testing the role of endothelial cells in cardiomyocyte protection.

Development of a Cell Co-Culture Model to Mimic Cardiac Ischemia/Reperfusion In Vitro

Ischemic heart disease is the leading cause of death and disability worldwide. Reperfusion causes additional injury beyond ischemia. Endothelial cells ...

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3.5K Views.  Vanderbilt University Medical Center. Spatial distance is a key parameter in assessing hypoxia/reoxygenation injury in a co-culture model of separate endothelial and cardiomyocyte cell layers, suggesting, for the first time, that optimizing the co-culture spatial environment is necessary to provide a favorable in vitro model for testing the role of endothelial cells in cardiomyocyte protection.

Video: Development of a Cell Co-Culture Model to Mimic Cardiac Ischemia/Reperfusion In Vitro

A Neuronal and Astrocyte Co-Culture Assay for High Content Analysis of Neurotoxicity

High Content Analysis (HCA) assays combine cells and detection reagents with automated imaging and powerful image analysis algorithms, allowing measurement of multiple cellular phenotypes within a single assay. In this study, we utilized HCA to develop a novel assay for neurotoxicity. Neurotoxicity assessment represents an important part of drug safety evaluation, as well as being a significant focus of environmental protection efforts. Additionally, neurotoxicity is also a well-accepted in vitro marker of the development of neurodegenerative diseases such as Alzheimer's and Parkinson's diseases. Recently, the application of HCA to neuronal screening has been reported. By labeling neuronal cells with &beta;III-tubulin, HCA assays can provide high-throughput, non-subjective, quantitative measurements of parameters such as neuronal number, neurite count and neurite length, all of which can indicate neurotoxic effects. However, the role of astrocytes remains unexplored in these models. Astrocytes have an integral role in the maintenance of central nervous system (CNS) homeostasis, and are associated with both neuroprotection and neurodegradation when they are activated in response to toxic substances or disease states. GFAP is an intermediate filament protein expressed predominantly in the astrocytes of the CNS. Astrocytic activation (gliosis) leads to the upregulation of GFAP, commonly accompanied by astrocyte proliferation and hypertrophy. This process of reactive gliosis has been proposed as an early marker of damage to the nervous system. The traditional method for GFAP quantitation is by immunoassay. This approach is limited by an inability to provide information on cellular localization, morphology and cell number. We determined that HCA could be used to overcome these limitations and to simultaneously measure multiple features associated with gliosis - changes in GFAP expression, astrocyte hypertrophy, and astrocyte proliferation - within a single assay. In co-culture studies, astrocytes have been shown to protect neurons against several types of toxic insult and to critically influence neuronal survival. Recent studies have suggested that the use of astrocytes in an in vitro neurotoxicity test system may prove more relevant to human CNS structure and function than neuronal cells alone. Accordingly, we have developed an HCA assay for co-culture of neurons and astrocytes, comprised of protocols and validated, target-specific detection reagents for profiling &beta;III-tubulin and glial fibrillary acidic protein (GFAP). This assay enables simultaneous analysis of neurotoxicity, neurite outgrowth, gliosis, neuronal and astrocytic morphology and neuronal and astrocytic development in a wide variety of cellular models, representing a novel, non-subjective, high-throughput assay for neurotoxicity assessment. The assay holds great potential for enhanced detection of neurotoxicity and improved productivity in neuroscience research and drug discovery.

This article describes a novel protocol and reagent set designed for sensitive measurement of neurotoxic effects of compounds and treatments on co-cultures of neurons and astrocytes using high content analysis. Results demonstrate that high content analysis represents an exciting novel technology for neurotoxicity assessment.

High Content Analysis (HCA) assays combine cells and detection reagents with automated imaging and powerful image analysis algorithms, allowing ...

Endothelial Cell Co-culture Mediates Maturation of Human Embryonic Stem Cell to Pancreatic Insulin Producing Cells in a Directed Differentiation Approach

Embryonic stem cells (ESC) have two main characteristics: they can be indefinitely propagated in vitro in an undifferentiated state and they are pluripotent, thus having the potential to differentiate into multiple lineages. Such properties make ESCs extremely attractive for cell based therapy and regenerative treatment applications 1. However for its full potential to be realized the cells have to be differentiated into mature and functional phenotypes, which is a daunting task. A promising approach in inducing cellular differentiation is to closely mimic the path of organogenesis in the in vitro setting. Pancreatic development is known to occur in specific stages 2, starting with endoderm, which can develop into several organs, including liver and pancreas. Endoderm induction can be achieved by modulation of the nodal pathway through addition of Activin A 3 in combination with several growth factors 4-7. Definitive endoderm cells then undergo pancreatic commitment by inhibition of sonic hedgehog inhibition, which can be achieved in vitro by addition of cyclopamine 8. Pancreatic maturation is mediated by several parallel events including inhibition of notch signaling; aggregation of pancreatic progenitors into 3-dimentional clusters; induction of vascularization; to name a few. By far the most successful in vitro maturation of ESC derived pancreatic progenitor cells have been achieved through inhibition of notch signaling by DAPT supplementation 9. Although successful, this results in low yield of the mature phenotype with reduced functionality. A less studied area is the effect of endothelial cell signaling in pancreatic maturation, which is increasingly being appreciated as an important contributing factor in in-vivo pancreatic islet maturation 10,11.
The current study explores such effect of endothelial cell signaling in maturation of human ESC derived pancreatic progenitor cells into insulin producing islet-like cells. We report a multi-stage directed differentiation protocol where the human ESCs are first induced towards endoderm by Activin A along with inhibition of PI3K pathway. Pancreatic specification of endoderm cells is achieved by inhibition of sonic hedgehog signaling by Cyclopamine along with retinoid induction by addition of Retinoic Acid. The final stage of maturation is induced by endothelial cell signaling achieved by a co-culture configuration. While several endothelial cells have been tested in the co-culture, herein we present our data with rat heart microvascular endothelial Cells (RHMVEC), primarily for the ease of analysis.

The current study describes a directed differentiation approach in inducing pancreatic differentiation of human embryonic stem cells. Of great significance is the finding that endothelial cell co-culture mediates maturation of human embryonic stem cell derived pancreatic progenitors into insulin expressing cells.

Embryonic stem cells (ESC) have two main characteristics: they can be indefinitely propagated in vitro in an undifferentiated state and they are ...

Blastomere Explants to Test for Cell Fate Commitment During Embryonic Development

Fate maps, constructed from lineage tracing all of the cells of an embryo, reveal which tissues descend from each cell of the embryo. Although fate maps are very useful for identifying the precursors of an organ and for elucidating the developmental path by which the descendant cells populate that organ in the normal embryo, they do not illustrate the full developmental potential of a precursor cell or identify the mechanisms by which its fate is determined. To test for cell fate commitment, one compares a cell's normal repertoire of descendants in the intact embryo (the fate map) with those expressed after an experimental manipulation. Is the cell's fate fixed (committed) regardless of the surrounding cellular environment, or is it influenced by external factors provided by its neighbors? Using the comprehensive fate maps of the Xenopus embryo, we describe how to identify, isolate and culture single cleavage stage precursors, called blastomeres. This approach allows one to assess whether these early cells are committed to the fate they acquire in their normal environment in the intact embryo, require interactions with their neighboring cells, or can be influenced to express alternate fates if exposed to other types of signals.

The fate of an individual embryonic cell can be influenced by inherited molecules and/or by signals from neighboring cells. Utilizing fate maps of the cleavage stage Xenopus embryo, single blastomeres can be identified for culture in isolation to assess the contributions of inherited molecules versus cell-cell interactions.

Fate maps, constructed from lineage tracing all of the cells of an embryo, reveal  which tissues descend from each cell of the embryo.  Although fate maps ...

Intravital Microscopy of the Microcirculation in the Mouse Cremaster Muscle for the Analysis of Peripheral Stem Cell Migration

In the era of intravascular cell application protocols in the context of regenerative cell therapy, the underlying mechanisms of stem cell migration to nonmarrow tissue have not been completely clarified. We describe here the technique of intravital microscopy applied to the mouse cremaster microcirculation for analysis of peripheral bone marrow stem cell migration in vivo. Intravital microscopy of the M. cremaster has been previously introduced in the field of inflammatory research for direct observation of leucocyte interaction with the vascular endothelium. Since sufficient peripheral stem and progenitor cell migration includes similar initial steps of rolling along and firm adhesion at the endothelial lining it is conceivable to apply the M. cremaster model for the observation and quantification of the interaction of intravasculary administered stem cells with the endothelium. As various chemical components can be selectively applied to the target tissue by simple superfusion techniques, it is possible to establish essential microenvironmental preconditions, for initial stem cell recruitment to take place in a living organism outside the bone marrow.

Intravital microscopy of the mouse M. cremaster microcirculation offers a unique and well-standardized in vivo model for the analysis of peripheral bone marrow stem cell migration.

In the era of intravascular cell application protocols in the context of regenerative cell therapy, the underlying mechanisms of stem cell migration to ...

An Anoxia-starvation Model for Ischemia/Reperfusion in C. elegans

Protocols for anoxia/starvation in the genetic model organism C. elegans simulate ischemia/reperfusion. Worms are separated from bacterial food and placed under anoxia for 20 hr&#160;(simulated ischemia), and subsequently moved to a normal atmosphere with food (simulated reperfusion). This experimental paradigm results in increased death and neuronal damage, and techniques are presented to assess organism viability, alterations to the morphology of touch neuron processes, as well as touch sensitivity, which represents the behavioral output of neuronal function. Finally, a method for constructing hypoxic incubators using common kitchen storage containers is described. The addition of a mass flow control unit allows for alterations to be made to the gas mixture in the custom incubators, and a circulating water bath allows for both temperature control and makes it easy to identify leaks. This method provides a low cost alternative to commercially available units.

An Anoxia-starvation Model for Ischemia/Reperfusion in C. elegans

A protocol is described that uses anoxia/starvation in C. elegans to model ischemia/reperfusion. Functional outcomes include increased mortality, visible abnormalities in GFP-labeled neuronal processes, and impaired behavioral responses that require neuronal function.

Protocols for anoxia/starvation in the genetic model organism C. elegans simulate ischemia/reperfusion. Worms are separated from bacterial food and placed ...

Isolation and Culture of Adult Mouse Cardiomyocytes for Cell Signaling and in vitro Cardiac Hypertrophy

Technological advances have made genetically modified mice, including transgenic and gene knockout mice, an essential tool in many research fields. Adult cardiomyocytes are widely accepted as a good model for cardiac cellular physiology and pathophysiology, as well as for pharmaceutical intervention. Genetically modified mice preclude the need for complicated cardiomyocyte infection processes to generate the desired genotype, which are inefficient due to cardiomyocytes&#8217; terminal differentiation. Isolation and culture of high quantity and quality functional cardiomyocytes will dramatically benefit cardiovascular research and provide an important tool for cell signaling transduction research and drug development. Here, we describe a well-established method for isolation of adult mouse cardiomyocytes that can be implemented with little training. The mouse heart is excised and cannulated to an isolated heart system, then perfused with a calcium-free and high potassium buffer followed by type II collagenase digestion in Langendorff retrograde perfusion mode. This protocol yields a consistent result for the collection of functional adult mouse cardiomyocytes from a variety of genetically modified mice.

Isolation and Culture of Adult Mouse Cardiomyocytes for Cell Signaling and in vitro Cardiac Hypertrophy

We describe a reliable method for isolation of adult mouse cardiomyocytes. This protocol yields a consistent result for the culture of functional adult cardiomyocytes from a variety of genetically modified mice.

Technological advances have made genetically modified mice, including transgenic and gene knockout mice, an essential tool in many research fields. Adult ...

Validation of a Mouse Model to Disrupt LINC Complexes in a Cell-specific Manner

Nuclear migration and anchorage within developing and adult tissues relies heavily upon large macromolecular protein assemblies called LInkers of the Nucleoskeleton and Cytoskeleton (LINC complexes). These protein scaffolds span the nuclear envelope and connect the interior of the nucleus to components of the surrounding cytoplasmic cytoskeleton. LINC complexes consist of two evolutionary-conserved protein families, Sun proteins and Nesprins that harbor C-terminal molecular signature motifs called the SUN and KASH domains, respectively. Sun proteins are transmembrane proteins of the inner nuclear membrane whose N-terminal nucleoplasmic domain interacts with the nuclear lamina while their C-terminal SUN domains protrudes into the perinuclear space and interacts with the KASH domain of Nesprins. Canonical Nesprin isoforms have a variable sized N-terminus that projects into the cytoplasm and interacts with components of the cytoskeleton. This protocol describes the validation of a dominant-negative transgenic mouse strategy that disrupts endogenous SUN/KASH interactions in a cell-type specific manner. Our approach is based on the Cre/Lox system that bypasses many drawbacks such as perinatal lethality and cell nonautonomous phenotypes that are associated with germline models of LINC complex inactivation. For this reason, this model provides a useful tool to understand the role of LINC complexes during development and homeostasis in a wide array of tissues.

Nuclear envelope proteins play a central role in many basic biological processes and have been implicated in a variety of human diseases. This protocol describes a new Cre/Lox-based mouse model that allows for the spatiotemporal control of LINC complexes disruption.

Nuclear migration and anchorage within developing and adult tissues relies heavily upon large macromolecular protein assemblies called LInkers of the ...

Development of an Insert Co-culture System of Two Cellular Types in the Absence of Cell-Cell Contact

The role of secreted soluble factors in the modification of cellular responses is a recurrent theme in the study of all tissues and systems. In an attempt to make straightforward the very complex relationships between the several cellular subtypes that compose multicellular organisms, in vitro techniques have been developed to help researchers acquire a detailed understanding of single cell populations. One of these techniques uses inserts with a permeable membrane allowing secreted soluble factors to diffuse. Thus, a population of cells grown in inserts can be co-cultured in a well or dish containing a different cell type for evaluating cellular changes following paracrine signaling in the absence of cell-cell contact. Such insert co-culture systems offer various advantages over other co-culture techniques, namely bidirectional signaling, conserved cell polarity and population-specific detection of cellular changes. In addition to being utilized in the field of inflammation, cancer, angiogenesis and differentiation, these co-culture systems are of prime importance in the study of the intricate relationships that exist between the different cellular subtypes present in the central nervous system, particularly in the context of neuroinflammation. This article offers general methodological guidelines in order to set up an experiment in order to evaluating cellular changes mediated by secreted soluble factors using an insert co-culture system. Moreover, a specific protocol to measure the neuroinflammatory effects of cytokines secreted by lipopolysaccharide-activated N9 microglia on neuronal PC12 cells will be detailed, offering a concrete understanding of insert co-culture methodology.

In multicellular organisms, secreted soluble factors elicit responses from different cell types as a result of paracrine signaling. Insert co-culture systems offer a simple way to assess the changes mediated by secreted soluble factors in the absence of cell-cell contact.

The role of secreted soluble factors in the modification of cellular responses is a recurrent theme in the study of all tissues and systems. In an attempt ...

G Protein-selective GPCR Conformations Measured Using FRET Sensors in a Live Cell Suspension Fluorometer Assay

F&#1255;rster resonance energy transfer (FRET)-based studies have become increasingly common in the investigation of GPCR signaling. Our research group developed an intra-molecular FRET sensor to detect the interaction between G&#945; subunits and GPCRs in live cells following agonist stimulation. Here, we detail the protocol for detecting changes in FRET between the &#946;2-adrenergic receptor and the G&#945;s C-terminus peptide upon treatment with 100 &#181;M isoproterenol hydrochloride as previously characterized1. Our FRET sensor is a single polypeptide consisting serially of a full-length GPCR, a FRET acceptor fluorophore (mCitrine), an ER/K SPASM (systematic protein affinity strength modulation) linker, a FRET donor fluorophore (mCerulean), and a G&#945; C-terminal peptide. This protocol will detail cell preparation, transfection conditions, equipment setup, assay execution, and data analysis. This experimental design detects small changes in FRET indicative of protein-protein interactions, and can also be used to compare the strength of interaction across ligands and GPCR-G protein pairings. To enhance the signal-to-noise in our measurements, this protocol requires heightened precision in all steps, and is presented here to enable reproducible execution.

Simple methods to detect the selective activation of G proteins by G protein-coupled receptors remain an outstanding challenge in cell signaling. Here, F&#1255;rster resonance energy transfer (FRET) biosensors have been developed by pairwise tethering a GPCR to G protein peptides to probe conformational changes at controlled concentrations in live cells.

F&#1255;rster resonance energy transfer (FRET)-based studies have become increasingly common in the investigation of GPCR signaling. Our research group ...

Mass Spectrometry Analysis to Identify Ubiquitylation of EYFP-tagged CENP-A (EYFP-CENP-A)

Studying the structure and the dynamics of kinetochores and centromeres is important in understanding chromosomal instability (CIN) and cancer progression. How the chromosomal location and function of a centromere (i.e., centromere identity) are determined and participate in accurate chromosome segregation is a fundamental question. CENP-A is proposed to be the non-DNA indicator (epigenetic mark) of centromere identity, and CENP-A ubiquitylation is required for CENP-A deposition at the centromere, inherited through dimerization between cell division, and indispensable to cell viability.
Here we describe mass spectrometry analysis to identify ubiquitylation of EYFP-CENP-A K124R mutant suggesting that ubiquitylation at a different lysine is induced because of the EYFP tagging in the CENP-A K124R mutant protein. Lysine 306 (K306) ubiquitylation in EYFP-CENP-A K124R was successfully identified, which corresponds to lysine 56 (K56) in CENP-A through mass spectrometry analysis. A caveat is discussed in the use of GFP/EYFP or the tagging of high molecular weight protein as a tool to analyze the function of a protein. Current technical limit is also discussed for the detection of ubiquitylated bands, identification of site-specific ubiquitylation(s), and visualization of ubiquitylation in living cells or a specific single cell during the whole cell cycle.
The method of mass spectrometry analysis presented here can be applied to human CENP-A protein with different tags and other centromere-kinetochore proteins. These combinatory methods consisting of several assays/analyses could be recommended for researchers who are interested in identifying functional roles of ubiquitylation.

Mass Spectrometry Analysis to Identify Ubiquitylation of EYFP-tagged CENP-A EYFP-CENP-A

CENP-A ubiquitylation is an important requirement for CENP-A deposition at the centromere, inherited through dimerization between cell division, and indispensable to cell viability. Here we describe mass spectrometry analysis to identify ubiquitylation of EYFP-tagged CENP-A (EYFP-CENP-A) protein.