This work was funded in part by the National Natural Science Foundation of China (81970265, 81900281,81700288), the China Postdoctoral Science Foundation (2019M651904); and the National Key Research and Development Program of China (2016YFC1101001, 2017YFC1308105).

Information regarding commercial reagents and instruments are listed in the Table of Materials.
The AC16 human cardiomyocyte cell line was derived from the fusion of primary cells from adult ventricular heart tissue with SV40-transformed human fibroblasts17, which were purchased from BLUEFBIO (Shanghai, China). The cell line develops many biochemical and morphological features characteristic of cardiomyocytes. In addition, the cell line is widely used t...

<ol>
	<li>Kim, B. S., 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=Myocardial+Ischemia+Induces+SDF-1alpha+Release+in+Cardiac+Surgery+Patients.">Myocardial Ischemia Induces SDF-1alpha Release in Cardiac Surgery Patients.</a> Journal of Cardiovascular Translational Research. 9 (3), 230-238 (2016).</li><li>Klein, P., 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=Less+invasive+ventricular+reconstruction+for+ischaemic+heart+failure.">Less invasive ventricular reconstruction for ischaemic heart failure.</a> EUROPEAN JOURNAL OF HEART FAILURE. 21 (12), 1638-1650 (2019).</li><li>Otto, K. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Therapeutic+hypothermia+applicable+to+cardiac+surgery.">Therapeutic hypothermia applicable to cardiac surgery.</a> VETERINARY ANAESTHESIA AND ANALGESIA. 42 (6), 559-569 (2015).</li><li>Wang, X., 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=Safety+of+Hypothermic+Circulatory+Arrest+During+Unilateral+Antegrade+Cerebral+Perfusion+for+Aortic+Arch+Surgery.">Safety of Hypothermic Circulatory Arrest During Unilateral Antegrade Cerebral Perfusion for Aortic Arch Surgery.</a> CANADIAN JOURNAL OF CARDIOLOGY. 35 (11), 1483-1490 (2019).</li><li>Leshnower, B. G., 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=Moderate+Versus+Deep+Hypothermia+With+Unilateral+Selective+Antegrade+Cerebral+Perfusion+for+Acute+Type+A+Dissection.">Moderate Versus Deep Hypothermia With Unilateral Selective Antegrade Cerebral Perfusion for Acute Type A Dissection.</a> ANNALS OF THORACIC SURGERY. 100 (5), 1563-1568 (2015).</li><li>Vallabhajosyula, P., 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=Moderate+versus+deep+hypothermic+circulatory+arrest+for+elective+aortic+transverse+hemiarch+reconstruction.">Moderate versus deep hypothermic circulatory arrest for elective aortic transverse hemiarch reconstruction.</a> ANNALS OF THORACIC SURGERY. 99 (5), 1511-1517 (2015).</li><li>Keeling, W. B., 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=Safety+of+Moderate+Hypothermia+With+Antegrade+Cerebral+Perfusion+in+Total+Aortic+Arch+Replacement.">Safety of Moderate Hypothermia With Antegrade Cerebral Perfusion in Total Aortic Arch Replacement.</a> ANNALS OF THORACIC SURGERY. 105 (1), 54-61 (2018).</li><li>Yan, T. D., 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=Consensus+on+hypothermia+in+aortic+arch+surgery.">Consensus on hypothermia in aortic arch surgery.</a> Annals of Cardiothoracic Surgery. 2 (2), 163-168 (2013).</li><li>Zhou, J., Empey, P. E., Bies, R. R., Kochanek, P. M., Poloyac, S. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cardiac+arrest+and+therapeutic+hypothermia+decrease+isoform-specific+cytochrome+P450+drug+metabolism.">Cardiac arrest and therapeutic hypothermia decrease isoform-specific cytochrome P450 drug metabolism.</a> DRUG METABOLISM AND DISPOSITION. 39 (12), 2209-2218 (2011).</li><li>Sharp, W. W., 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=Inhibition+of+the+mitochondrial+fission+protein+dynamin-related+protein+1+improves+survival+in+a+murine+cardiac+arrest+model.">Inhibition of the mitochondrial fission protein dynamin-related protein 1 improves survival in a murine cardiac arrest model.</a> CRITICAL CARE MEDICINE. 43 (2), 38-47 (2015).</li><li>Zhu, W. S., 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=Hsp90aa1:+a+novel+target+gene+of+miR-1+in+cardiac+ischemia/reperfusion+injury.">Hsp90aa1: a novel target gene of miR-1 in cardiac ischemia/reperfusion injury.</a> Sci Rep. 6, 24498 (2016).</li><li>Castedo, 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=Influence+of+hypothermia+on+right+atrial+cardiomyocyte+apoptosis+in+patients+undergoing+aortic+valve+replacement.">Influence of hypothermia on right atrial cardiomyocyte apoptosis in patients undergoing aortic valve replacement.</a> Journal of Cardiothoracic Surgery. 2, 7 (2007).</li><li>Krech, 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=Moderate+therapeutic+hypothermia+induces+multimodal+protective+effects+in+oxygen-glucose+deprivation/reperfusion+injured+cardiomyocytes.">Moderate therapeutic hypothermia induces multimodal protective effects in oxygen-glucose deprivation/reperfusion injured cardiomyocytes.</a> Mitochondrion. 35, 1-10 (2017).</li><li>Cooper, W. A., 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=Hypothermic+circulatory+arrest+causes+multisystem+vascular+endothelial+dysfunction+and+apoptosis.">Hypothermic circulatory arrest causes multisystem vascular endothelial dysfunction and apoptosis.</a> ANNALS OF THORACIC SURGERY. 69 (3), 696-702 (2000).</li><li>Kajimoto, 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=Selective+cerebral+perfusion+prevents+abnormalities+in+glutamate+cycling+and+neuronal+apoptosis+in+a+model+of+infant+deep+hypothermic+circulatory+arrest+and+reperfusion.">Selective cerebral perfusion prevents abnormalities in glutamate cycling and neuronal apoptosis in a model of infant deep hypothermic circulatory arrest and reperfusion.</a> JOURNAL OF CEREBRAL BLOOD FLOW AND METABOLISM. 36 (11), 1992-2004 (2016).</li><li>Liu, 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=Deep+Hypothermic+Circulatory+Arrest+Does+Not+Show+Better+Protection+for+Vital+Organs+Compared+with+Moderate+Hypothermic+Circulatory+Arrest+in+Pig+Model.">Deep Hypothermic Circulatory Arrest Does Not Show Better Protection for Vital Organs Compared with Moderate Hypothermic Circulatory Arrest in Pig Model.</a> Biomed Research International. 2019, 1420216 (2019).</li><li>Davidson, M. 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=Novel+cell+lines+derived+from+adult+human+ventricular+cardiomyocytes.">Novel cell lines derived from adult human ventricular cardiomyocytes.</a> JOURNAL OF MOLECULAR AND CELLULAR CARDIOLOGY. 39 (1), 133-147 (2005).</li><li>Khan, K., Makhoul, G., Yu, B., Schwertani, A., Cecere, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+cytoprotective+impact+of+yes-associated+protein+1+after+ischemia-reperfusion+injury+in+AC16+human+cardiomyocytes.">The cytoprotective impact of yes-associated protein 1 after ischemia-reperfusion injury in AC16 human cardiomyocytes.</a> EXPERIMENTAL BIOLOGY AND MEDICINE. 244 (10), 802-812 (2019).</li><li>Pan, J. A., 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=miR-146a+attenuates+apoptosis+and+modulates+autophagy+by+targeting+TAF9b/P53+pathway+in+doxorubicin-induced+cardiotoxicity.">miR-146a attenuates apoptosis and modulates autophagy by targeting TAF9b/P53 pathway in doxorubicin-induced cardiotoxicity.</a> Cell Death Discovery. 10 (9), 668 (2019).</li><li>Schmitt, K. R., 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=S100B+modulates+IL-6+release+and+cytotoxicity+from+hypothermic+brain+cells+and+inhibits+hypothermia-induced+axonal+outgrowth.">S100B modulates IL-6 release and cytotoxicity from hypothermic brain cells and inhibits hypothermia-induced axonal outgrowth.</a> NEUROSCIENCE RESEARCH. 59 (1), 68-73 (2007).</li><li>Tong, G., 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=Deep+hypothermia+therapy+attenuates+LPS-induced+microglia+neuroinflammation+via+the+STAT3+pathway.">Deep hypothermia therapy attenuates LPS-induced microglia neuroinflammation via the STAT3 pathway.</a> Neuroscience. 358, 201-210 (2017).</li><li>Yu, Z. P., 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=Troxerutin+attenuates+oxygenglucose+deprivation+and+reoxygenationinduced+oxidative+stress+and+inflammation+by+enhancing+the+PI3K/AKT/HIF1alpha+signaling+pathway+in+H9C2+cardiomyocytes.">Troxerutin attenuates oxygenglucose deprivation and reoxygenationinduced oxidative stress and inflammation by enhancing the PI3K/AKT/HIF1alpha signaling pathway in H9C2 cardiomyocytes.</a> Molecular Medicine Reports. 22 (2), 1351-1361 (2020).</li><li>Drescher, C., Diestel, A., Wollersheim, S., Berger, F., Schmitt, K. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=How+does+hypothermia+protect+cardiomyocytes+during+cardioplegic+ischemia.">How does hypothermia protect cardiomyocytes during cardioplegic ischemia.</a> European journal of cardiothoracic surgery. 40 (2), 352-359 (2011).</li><li>Diestel, A., Drescher, C., Miera, O., Berger, F., Schmitt, K. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hypothermia+protects+H9c2+cardiomyocytes+from+H2O2+induced+apoptosis.">Hypothermia protects H9c2 cardiomyocytes from H2O2 induced apoptosis.</a> Cryobiology. 62 (1), 53-61 (2011).</li><li>Zhang, 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=HIF-1alpha/BNIP3+signaling+pathway-induced-autophagy+plays+protective+role+during+myocardial+ischemia-reperfusion+injury.">HIF-1alpha/BNIP3 signaling pathway-induced-autophagy plays protective role during myocardial ischemia-reperfusion injury.</a> BIOMEDICINE &amp; PHARMACOTHERAPY. 120, 109464 (2019).</li><li>An, W., 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=Exogenous+IL-19+attenuates+acute+ischaemic+injury+and+improves+survival+in+male+mice+with+myocardial+infarction.">Exogenous IL-19 attenuates acute ischaemic injury and improves survival in male mice with myocardial infarction.</a> BRITISH JOURNAL OF PHARMACOLOGY. 176 (5), 699-710 (2019).</li><li>Han, Y. S., Schaible, N., Tveita, T., Sieck, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Discontinued+stimulation+of+cardiomyocytes+provides+protection+against+hypothermia-rewarming-induced+disruption+of+excitation-contraction+coupling.">Discontinued stimulation of cardiomyocytes provides protection against hypothermia-rewarming-induced disruption of excitation-contraction coupling.</a> EXPERIMENTAL PHYSIOLOGY. 103 (6), 819-826 (2018).</li><li>Yarbrough, W. 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=Caspase+inhibition+attenuates+contractile+dysfunction+following+cardioplegic+arrest+and+rewarming+in+the+setting+of+left+ventricular+failure.">Caspase inhibition attenuates contractile dysfunction following cardioplegic arrest and rewarming in the setting of left ventricular failure.</a> Journal of cardiovascular pharmacology. 44 (6), 645-650 (2004).</li><li>Egorov, Y. V., Glukhov, A. V., Efimov, I. R., Rosenshtraukh, L. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hypothermia-induced+spatially+discordant+action+potential+duration+alternans+and+arrhythmogenesis+in+nonhibernating+versus+hibernating+mammals.">Hypothermia-induced spatially discordant action potential duration alternans and arrhythmogenesis in nonhibernating versus hibernating mammals.</a> AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY. 303 (8), 1035-1046 (2012).</li><li>Bobi, 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=Moderate+Hypothermia+Modifies+Coronary+Hemodynamics+and+Endothelium-Dependent+Vasodilation+in+a+Porcine+Model+of+Temperature+Management.">Moderate Hypothermia Modifies Coronary Hemodynamics and Endothelium-Dependent Vasodilation in a Porcine Model of Temperature Management.</a> Journal of the American Heart Association. 9 (3), 014035 (2020).</li><li>Dietrichs, E. S., Tveita, T., Myles, R., Smith, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+novel+ECG-biomarker+for+cardiac+arrest+during+hypothermia.">A novel ECG-biomarker for cardiac arrest during hypothermia.</a> Scandinavian Journal of Trauma Resuscitation &amp; Emergency Medicine. 28 (1), 27 (2020).</li></ol>

The complexities of intact animals, including the interactions between different types of cells, often prevent detailed studies of specific components of I/R injury. Therefore, it is necessary to establish an in vitro cell model that can accurately reflect the molecular changes after ischemia in vivo. Research on OGD models has been previously reported13,22, and many sophisticated methods have been established23,<sup class="xref...

Ischemia/reperfusion-derived myocardial dysfunction is a common clinical scenario in patients after cardiac surgery1,2. During nonpulsatile low flow perfusion and periods of total circulatory arrest, damage involving all types of heart cells still occurs. In particular, the sensitivity of cardiomyocytes to ischemic injury is higher than that of other cell populations. At present, therapeutic hypothermia (TH) affords substantial protection against an expected ischemic insult in patients undergoing cardiac surgery3,4. TH is defined as a core body temperature of 14-34 &#176;C, although no consensus exists regarding a definition of cooling during cardiac surgery5,6,7. In 2013, an international panel of experts proposed a standardized reporting system to classify various temperature ranges of systemic hypothermic circulatory arrest8. Based on electroencephalography and metabolism studies of the brain, they divided hypothermia into four levels: profound hypothermia (&#8804; 14 &#176;C), deep hypothermia (14.1-20 &#176;C), moderate hypothermia (20.1-28 &#176;C), and mild hypothermia (28.1-34 &#176;C). The expert consensus provided a clear and uniform classification, allowing studies to be more comparable and provide more clinically relevant outcomes. This protection afforded by TH is based on its capacity to reduce the metabolic activity of cells, further limiting their rate of high-energy phosphates consumption9,10. However, the role of TH in myocardial protection is controversial and may have multiple effects depending on the degree of hypothermia.
Myocardial I/R is well known to be accompanied by increased cell apoptisis11. Recent reports have observed that programmed cardiomyocyte death increases during open-heart surgery, and may coincide with necrosis, thereby increasing the number of dead myocardial cells12. Therefore, reducing cardiomyocyte apoptosis is a useful therapeutic approach in clinical practice. In the mouse atrial HL-1 cardiomyocyte model, therapeutic hypothermia was shown to reduce the mitochondrial release of cytochrome c and apoptosis-inducing factor (AIF) during reperfusion13. However, the effect of temperature in regulating apoptosis is controversial and appears to depend on the degree of hypothermia. Cooper and colleagues observed that compared to a normothermic cardiopulmonary bypass control group, the apoptosis rate of myocardial tissue from pigs with the deep hypothermic circulatory arrest was increased14. In addition, the results of some studies have suggested that deep hypothermia may activate the apoptosis pathway, while less aggressive hypothermia appears to inhibit the pathway12,15,16. The reason for this result may be due to confounding effects associated with ischemic injury and a lack of understanding of the mechanisms by which temperature affects myocardial tissue. Therefore, the temperature limits at which apoptosis is enhanced or attenuated should be accurately defined.
To gain a better understanding of the mechanisms associated with the efficacy of hypothermia and provide a rational basis for its implementation in humans, it is essential to identify a culture condition similar to in vivo conditions that can produce damage similar to that observed for the clinical condition in a reproducible manner. An essential step towards achieving this goal is to establish the optimal conditions for inducing cardiomyocyte apoptosis. Accordingly, in the present study, we explored the methodological details regarding oxygen-glucose deprivation experiments with cultured cells, a facile in vitro model of ischemia-reperfusion. Furthermore, we evaluated the effect of different hypoxic-ischemic times on cardiomyocyte apoptosis, and verified our hypothesis regarding the effect of different temperature conditions on cell apoptosis in vitro.

<table>
	<tbody>
		<tr>
			<td>Annexin V-FITC cell apoptosis detection kit</td>
			<td>Bio-Technology,China</td>
			<td>C1062M</td>
			<td></td>
		</tr>
		<tr>
			<td>Cardiac myocyte growth supplement</td>
			<td>Sciencell,USA</td>
			<td>6252</td>
			<td></td>
		</tr>
		<tr>
			<td>Caspase 3 activity assay kit</td>
			<td>Bio-Technology,China</td>
			<td>C1115</td>
			<td></td>
		</tr>
		<tr>
			<td>Caspase 8 activity assay kit</td>
			<td>Bio-Technology,China</td>
			<td>C1151</td>
			<td></td>
		</tr>
		<tr>
			<td>DMEM, no glucose</td>
			<td>Gibco,USA</td>
			<td>11966025</td>
			<td></td>
		</tr>
		<tr>
			<td>Dulbecco&#39;s modified eagle medium</td>
			<td>Gibco,USA</td>
			<td>11960044</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal bovine serum</td>
			<td>Gibco,USA</td>
			<td>16140071</td>
			<td></td>
		</tr>
		<tr>
			<td>Flow cytometry</td>
			<td>CytoFLEX,USA</td>
			<td>B49007AF</td>
			<td></td>
		</tr>
		<tr>
			<td>Human myocardial cells</td>
			<td>BLUEFBIO,China</td>
			<td>BFN60808678</td>
			<td></td>
		</tr>
		<tr>
			<td>Mitochondrial membrane potential assay kit with JC-1</td>
			<td>Bio-Technology,China</td>
			<td>C2006</td>
			<td></td>
		</tr>
		<tr>
			<td>Penicillin/Streptomycin solution</td>
			<td>Gibco,USA</td>
			<td>10378016</td>
			<td></td>
		</tr>
		<tr>
			<td>Reactive oxygen species assay kit</td>
			<td>Bio-Technology,China</td>
			<td>S0033S</td>
			<td></td>
		</tr>
		<tr>
			<td>Three-gas incubator</td>
			<td>Memmert,Germany</td>
			<td>ICO50</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypsin-EDTA (0.25%)</td>
			<td>Gibco,USA</td>
			<td>25200056</td>
			<td></td>
		</tr>
	</tbody>
</table>

in vitro assessment of myocardial protection following hypothermia-preconditioning in a human cardiac myocytes model

Ischemia/reperfusion-derived myocardial dysfunction is a common clinical scenario in patients after cardiac surgery. In particular, the sensitivity of cardiomyocytes to ischemic injury is higher than that of other cell populations. At present, hypothermia affords considerable protection against an expected ischemic insult. However, investigations into complex hypothermia-induced molecular changes remain limited. Therefore, it is essential to identify a culture condition similar to in vivo conditions that can induce damage similar to that observed in the clinical condition in a reproducible manner. To mimic ischemia-like conditions in vitro, the cells in these models were treated by oxygen/glucose deprivation (OGD). In addition, we applied a standard time-temperature protocol used during cardiac surgery. Furthermore, we propose an approach to use a simple but comprehensive method for the quantitative analysis of myocardial injury. Apoptosis and expression levels of apoptosis-associated proteins were assessed by flow cytometry and using an ELISA kit. In this model, we tested a hypothesis regarding the effects of different temperature conditions on cardiomyocyte apoptosis in vitro. The reliability of this model depends on strict temperature control, controllable experimental procedures, and stable experimental results. Additionally, this model can be used to study the molecular mechanism of hypothermic cardioprotection, which may have important implications for the development of complementary therapies for use with hypothermia.

The effect of OGD exposure on the viability of HCMs was determined by CCK-8 assay. Compared with that observed in the control group, cell viability was significantly decreased in a time-dependent manner (Figure 2A). The apoptosis rates of HCMs at different times after reperfusion showed a specific trend, where from 0 to 16 h, the apoptosis rates gradually increased and reached the maximum rate at the 16 h time point (Figure 2B). As OGD for 12 h reduced cell acti...

Watch this Scientific Journal Video about In vitro Assessment of Myocardial Protection following Hypothermia-Preconditioning in a Human Cardiac Myocytes Model at JoVE.com

In vitro Assessment of Myocardial Protection following Hypothermia-Preconditioning in a Human Cardiac Myocytes Model

The distinct effects of different degrees of hypothermia on myocardial protection have not been thoroughly evaluated. The goal of the present study was to quantify the levels of cell death following different hypothermia treatments in a human cardiomyocyte-based model, laying the foundation for future in-depth molecular research.

Ischemia/reperfusion-derived myocardial dysfunction is a common clinical scenario in patients after cardiac surgery. In particular, the sensitivity of ...

The goal of the present study was to quantify the levels of cell death, following different hypothermia treatments in a human cardiomyocyte-based model. This model can be used to study the molecular mechanism of hypothermic cardioprotection, which may have important implications for the development of complimentary therapies for use with hypothermia. To culture the HCM cells, thaw the cryopreserved cells from liquid nitrogen in a 37-degree Celsius water bath and maintain them in a humidifier incubator under an atmosphere with 95%air and 5%carbon dioxide.Once the cells reach 60 to 70%confluence, aspirate the medium from the six-well plate and gently wash the cells three times with PBS. Add two milliliters of fresh sugar-free medium into each well and culture the cells at a constant temperature in a three-gas incubator under a mixture of 95%nitrogen, 5%carbon dioxide, and 0.1%oxygen at 37 degrees Celsius. For the time-temperature protocol, aspirate the medium from the six-well plate and add two milliliters of fresh sugar-free medium.Culture the cells in a tri-gas incubator for 12 hours to establish hypoxia. Set the temperature program starting with 10 hours of low temperature treatment, followed by a rewarming phase for two hours and 24 hours of normothermia. Remove three Petri dishes at every time point for analysis.After the low temperature treatment, aspirate the medium from the six-well plate and wash three times with PBS. Add two milliliters of fresh medium to each well, then maintain the cells at 37 degrees Celsius in a humidified incubator under an atmosphere with 95%air and 5%carbon dioxide. Add eight microliters of CCK-8 solution to each well of the plate and leave the plate for one hour in the incubator.After the incubation, measure the absorbance at 450 nanometers using a microplate reader. For apoptosis analysis, add five microliters of Annexin V-FITC to dye the cells. Then add 10 microliters of propidium iodide to the cell suspension.Gently mix the cells and incubate them for 20 minutes at room temperature in the dark. In the flow cytometry software, open two dot plot windows and select forward scattered light on the x-axis and side scattered light on the y-axis. Select the PE detection channel and FITC.Click Record to collect particles from the suspension in the blank sample tube, then gate the cell population for further analysis in the first dot plot. Next, place the single-stained samples on the tube support arm. Click Record to collect particles from the suspension and gate the cell population for further analysis.For mitochondrial assessment, add 0.5 milliliters of JC-1 working solution to each tube containing the trypsinized cells and incubate them in a 37 degrees Celsius incubator for 20 minutes. After incubation, centrifuge the cells at 600 times g for three minutes at four degrees Celsius and resuspend the HCMs in one milliliter of ice-cold staining buffer in a 1.5-milliliter centrifuge tube. Measure the fluorescence intensity of JC-1 by selecting the PE and FITC detection channels.For the reactive oxygen species assay, stain the cells and culture medium with 10 micromolar DCFDA and adjust the cell density to around one to 10 million cells. Incubate these cells for 30 minutes at 37 degrees Celsius, then analyze them on a flow cytometer. Add 40 microliters of buffer solution to the enzyme-labeled plate, then add 80 microliters of the sample.Then add 10 microliters of two millimolar acetyl DEVDp-nitroanilide and incubate the plate at 37 degrees Celsius for 120 minutes. Measure the A405 value on a microplate reader machine using the manufacturer's instructions. The temperature conditions in the time-temperature protocol were created and maintained using a tri-gas incubator, which allows for precise temperature regulation at three time points.The effect of oxygen and glucose deprivation, or OGD, on the viability of HCMs was determined using the CCK-8 assay. Compared with the control group, cell viability was significantly decreased in a time-dependent manner. The apoptosis rates of HCMs gradually increased between zero and 16 hours after reperfusion, then reached the maximum rate at the 16-hour time point.Compared with the OGD group, the percentage of viable cells was higher in the three groups treated with hypothermia. In addition, cells in the deep hypothermia group had the highest viability, 2.1-fold higher than that observed in the OGD group. Flow cytometry results confirmed that hypothermia prevented the apoptosis of HCMs under OGD conditions.Hypothermia treatment also decreased the intracellular ROS levels in HCMs. Mitochondrial membrane potential was detected with JC-1 staining. After OGD treatment, the red-to-green fluorescence ratio was decreased.Hypothermia significantly inhibited this OGD-induced effect. Moreover, a decrease of caspase-8 and caspase-3 was observed in the cells that were treated with hypothermia. The reliability of this model depends on strict temperature control, controllable experimental procedures, and stable experimental results.This method can be used to further explore the specific mechanism of hypothermic treatment on cell apoptosis and to study the molecular mechanism of hypothermic cardioprotection. It is of great significance for the development of hypothermic adjuvant therapy.

in-vitro-assessment-myocardial-protection-following-hypothermia

Research

JoVE Journal

Medicine

2.9K vistas.  Children's Hospital of Nanjing Medical University. The goal of the present study was to quantify the levels of cell death, following different hypothermia treatments in a human cardiomyocyte-based model. This model can be used to study the molecular mechanism of hypothermic cardioprotection, which may have important implications for the development of complimentary therapies for use with hypothermia. To culture the HCM cells, thaw the cryopreserved cells from liquid nitrogen in a 37-degree Celsius water bath and maintain them in a humidifier ...