Name: isolation and culture of resident cardiac macrophages from the murine sinoatrial and atrioventricular node
Uploaded: 2021-05-07T13:00:00
Description: Watch this Scientific Journal Video about Isolation and Culture of Resident Cardiac Macrophages from the Murine Sinoatrial and Atrioventricular Node at JoVE.com

This work was supported by the China Scholarship Council (CSC, to R. Xia), the German Centre for Cardiovascular Research (DZHK; 81X2600255 to S. Clauss, 81Z0600206 to S. K&#228;&#228;b, 81Z0600204 to C.S.), the Corona Foundation (S199/10079/2019 to S. Clauss), the SFB 914 (project Z01 to S. Massberg), the ERA-NET on Cardiovascular Diseases (ERA-CVD; 01KL1910 to S. Clauss) and the Heinrich-and-Lotte-M&#252;hlfenzl Stiftung (to S. Clauss). The funders had no role in manuscript preparation.

Animal care and all experimental procedures were conducted in accordance with the guidelines of the Animal Care and Ethics committee of the University of Munich and all the procedures undertaken on mice were approved by the Government of Bavaria, Munich, Germany. C57BL6/J mice were commercially obtained.
1. Preparations
<ol>
	<li>Prepare Cell sorting buffer (Table 1) and store at 4 &#176;C. 
	NOTE: During the whole experimental procedure, the cell sorting buffer should ...

<ol>
	<li>Nikolaidou, T., Aslanidi, O. V., Zhang, H., Efimov, I. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structure-function+relationship+in+the+sinus+and+atrioventricular+nodes.">Structure-function relationship in the sinus and atrioventricular nodes.</a> Pediatric Cardiology. 33 (6), 890-899 (2012).</li><li>Clauss, 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=Animal+models+of+arrhythmia:+classic+electrophysiology+to+genetically+modified+large+animals.">Animal models of arrhythmia: classic electrophysiology to genetically modified large animals.</a> Nature Review Cardiology. 16 (8), 457-475 (2019).</li><li>Hulsmans, 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=Macrophages+Facilitate+Electrical+Conduction+in+the+Heart.">Macrophages Facilitate Electrical Conduction in the Heart.</a> Cell. 169 (3), 510-522 (2017).</li><li>Rosas, 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+transcription+factor+Gata6+links+tissue+macrophage+phenotype+and+proliferative+renewal.">The transcription factor Gata6 links tissue macrophage phenotype and proliferative renewal.</a> Science. 344 (6184), 645-648 (2014).</li><li>Schulz, 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=A+lineage+of+myeloid+cells+independent+of+Myb+and+hematopoietic+stem+cells.">A lineage of myeloid cells independent of Myb and hematopoietic stem cells.</a> Science. 336 (6077), 86-90 (2012).</li><li>Epelman, 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=Embryonic+and+adult-derived+resident+cardiac+macrophages+are+maintained+through+distinct+mechanisms+at+steady+state+and+during+inflammation.">Embryonic and adult-derived resident cardiac macrophages are maintained through distinct mechanisms at steady state and during inflammation.</a> Immunity. 40 (1), 91-104 (2014).</li><li>Gordon, S., Pluddemann, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tissue+macrophages:+heterogeneity+and+functions.">Tissue macrophages: heterogeneity and functions.</a> BMC Biology. 15 (1), 53 (2017).</li><li>Bajpai, 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=The+human+heart+contains+distinct+macrophage+subsets+with+divergent+origins+and+functions.">The human heart contains distinct macrophage subsets with divergent origins and functions.</a> Nature Medicine. 24 (8), 1234-1245 (2018).</li><li>Davies, L. C., Jenkins, S. J., Allen, J. E., Taylor, P. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tissue-resident+macrophages.">Tissue-resident macrophages.</a> Nature Immunology. 14 (10), 986-995 (2013).</li><li>Xia, 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=Whole-mount+immunofluorescence+staining,+confocal+imaging+and+3D+reconstruction+of+the+sinoatrial+and+atrioventricular+node+in+the+mouse.">Whole-mount immunofluorescence staining, confocal imaging and 3D reconstruction of the sinoatrial and atrioventricular node in the mouse.</a> Journal of Visualized Experiments. (166), e62058 (2020).</li><li>van Weerd, J. H., Christoffels, V. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+formation+and+function+of+the+cardiac+conduction+system.">The formation and function of the cardiac conduction system.</a> Development. 143 (2), 197-210 (2016).</li><li>Ye Sheng, 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=Isolation+and+characterization+of+atrioventricular+nodal+cells+from+neonate+rabbit+heart.">Isolation and characterization of atrioventricular nodal cells from neonate rabbit heart.</a> Circulation: Arrhythmia and Electrophysiology. 4 (6), 936-946 (2011).</li><li>Murray, P. J., Wynn, T. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Protective+and+pathogenic+functions+of+macrophage+subsets.">Protective and pathogenic functions of macrophage subsets.</a> Nature Reviews Immunology. 11 (11), 723-737 (2011).</li><li>Pinto, A. 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=Revisiting+cardiac+cellular+composition.">Revisiting cardiac cellular composition.</a> Circulation Research. 118 (3), 400-409 (2016).</li><li>Bajpai, 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=Tissue+resident+CCR2-+and+CCR2++cardiac+macrophages+differentially+orchestrate+monocyte+recruitment+and+fate+specification+following+myocardial+injury.">Tissue resident CCR2- and CCR2+ cardiac macrophages differentially orchestrate monocyte recruitment and fate specification following myocardial injury.</a> Circulation Research. 124 (2), 263-278 (2019).</li><li>Honold, L., Nahrendorf, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Resident+and+monocyte-derived+macrophages+in+cardiovascular+disease.">Resident and monocyte-derived macrophages in cardiovascular disease.</a> Circulation Research. 122 (1), 113-127 (2018).</li><li>Leid, 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=Primitive+embryonic+macrophages+are+required+for+coronary+development+and+maturation.">Primitive embryonic macrophages are required for coronary development and maturation.</a> Circulation Research. 118 (10), 1498-1511 (2016).</li></ol>

In this manuscript, we describe a protocol for the enrichment of cardiac resident macrophages specifically from the SAN and AVN regions at high purity.
Macrophages are divided into subpopulations based on their anatomical location and functional phenotype. They can also switch from one functional phenotype to another in response to variable microenvironmental signals13. Compared to other organs such as bone marrow and liver, cardiac tissue contains a lower percentage of...

An erratum was issued for: <a href="https://www.jove.com/t/62236">Isolation and Culture of Resident Cardiac Macrophages from the Murine Sinoatrial and Atrioventricular Node</a>. The Authors section was updated from:
Ruibing Xia123 
Simone Loy1 
Stefan K&#228;&#228;b13 
Anna Titova1 
Christian Schulz123 
Steffen Massberg123 
Sebastian Clauss123 
1University Hospital Munich, Department of Medicine I Ludwig-Maximilian-Unversity Munich (LMU) 
2Walter Brendel Center of Experimental Medicine (WBex) LMU Munich 
3German Center for Cardiovascular Research (DZHK), Partner Site Munich, Munich Heart Alliance (MHA)
to:
Ruibing Xia123 
Simone Loy1 
Stefan K&#228;&#228;b13 
Anna Titova1 
Christian Schulz123 
Steffen Massberg123 
Sebastian Clauss123 
1University Hospital Munich, Department of Medicine I Ludwig-Maximilian-University Munich (LMU) 
2Insitute of Surgical Research at the Walter Brendel Center of Experimental Medicine, University Hospital Munich, Ludwig-Maximilians-University (LMU) 
3German Center for Cardiovascular Research (DZHK), Partner Site Munich, Munich Heart Alliance (MHA)

An erratum was issued for:&#160;<a href="https://www.jove.com/t/62236">Isolation and Culture of Resident Cardiac Macrophages from the Murine Sinoatrial and Atrioventricular Node</a>. The Authors section was updated.

Erratum: Isolation and Culture of Resident Cardiac Macrophages from the Murine Sinoatrial and Atrioventricular Node

The sinoatrial node (SAN) physiologically initiates the electrical impulse and is, therefore, the primary pacemaker of the heart. The atrioventricular node (AVN) conducts the electrical impulse from the atria to the ventricles and also acts as a subsidiary pacemaker1. In general, generation and conduction of electrical impulses is a complex process that can be modulated by various factors2, including resident macrophage in SAN/AVN regions. A recent study by Hulsmans et al. demonstrates a specific population of cardiac resident macrophages which are enriched in the AVN and function as key players in keeping a steady heartbeat3. They found that macrophages are electrically coupled to the cardiomyocytes and could change the electrical properties of coupled cardiomyocytes. The authors also note that such conducting cells interleaving with macrophages are also present in other components of the cardiac conduction system, such as the SAN.
Currently, it is not fully known if the phenotype of resident cardiac macrophages differs between the cardiac regions. However, it has been shown that the tissue microenvironment can affect transcription and proliferative renewal of tissue macrophages4. Furthermore, since the cardiomyocyte phenotype has been demonstrated to be different between regions, the functional effects of macrophages on cardiomyocytes may also be region-specific, even if the macrophage phenotype itself may be the same. Therefore, further studies on specific cardiac regions are needed.
Recent studies have demonstrated that, at steady state, the tissue resident macrophages are established prenatally, arising independently of definitive hematopoiesis, and persist into adulthood5. However, after macrophage depletion or during cardiac inflammation, Ly6chi monocytes contribute to replenish cardiac macrophage population6. Studies involving genetic lineage tracing, parabiosis, fate mapping, and cell tracking showed the coexistence of a variety of tissue resident macrophages populations in organs and tissues, and, also, different cellular behavior of macrophage subsets that are potentially associated with their ontogeny7,8,9.
Characterization of resident cardiac macrophages has benefited from the use of magnetic activated cell sorting (MACS) and fluorescent activated cell sorting. These methods are particularly useful for isolating specific cell populations from multiple tissue fractions by labeling them with their cell surface markers. This not only leads to a higher purity of the isolated immune cell type, but also allows for phenotypic analysis. Here, we present a protocol including magnetic beads-coated cells followed with fluorescent activated cell sorting for the enrichment of cardiac resident macrophages specifically isolated from the SAN and AVN region.
To explore the characteristics of cardiac resident macrophages in conduction system and their function for cardiac conduction and arrhythmogenesis, precise localization and dissection of SAN and AVN are critical. For microdissection of SAN and AVN, anatomical landmarks are used for the region identification10. In brief, SAN is located at the junction of the superior vena cava and right atrium. AVN is located within the triangle of Koch, which is anteriorly bordered by the septal leaflet of the tricuspid valve, and posteriorly by the tendon of Todaro11. We also provide an accurate microdissection procedure of SAN and AVN in mice which is confirmed by histology and immunofluorescence staining.
Isolated resident macrophages could be used for further experiments such as RNA sequencing or could be recovered and cultivated for more than two weeks allowing various in vitro experiments. Therefore, our protocol describes a highly valuable procedure for the immuno-rhythmologist. Table 1 shows the composition of all the solutions needed, Figure 1 shows the microdissection landmarks for SAN and AVN. Figure 2 is schematic illustration of SAN and AVN localization. Figure 3 shows the histological staining of SAN and AVN (Masson&#39;s trichrome and immunofluorescence staining). Figure 4 shows a step-by-step gating strategy to isolate cardiac resident macrophages by fluorescence-activated cell sorting.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td colspan="4">Anesthesia</td>
		</tr>
		<tr>
			<td>Isoflurane vaporizer system</td>
			<td>Hugo Sachs Elektronik</td>
			<td>34-0458, 34-1030, 73-4911, 34-0415, 73-4910</td>
			<td>Includes an induction chamber, a gas evacuation unit and charcoal filters</td>
		</tr>
		<tr>
			<td>Modified Bain circuit</td>
			<td>Hugo Sachs Elektronik</td>
			<td>73-4860</td>
			<td>Includes an anesthesia mask for mice</td>
		</tr>
		<tr>
			<td>Surgical Platform</td>
			<td>Kent scientific</td>
			<td>SURGI-M</td>
			<td></td>
		</tr>
		<tr>
			<td colspan="4">In vivo instrumentation</td>
		</tr>
		<tr>
			<td>Fine forceps</td>
			<td>Fine Science Tools</td>
			<td>11295-51</td>
			<td></td>
		</tr>
		<tr>
			<td>Iris scissors</td>
			<td>Fine Science Tools</td>
			<td>14084-08</td>
			<td></td>
		</tr>
		<tr>
			<td>Spring scissors</td>
			<td>Fine Science Tools</td>
			<td>91500-09</td>
			<td></td>
		</tr>
		<tr>
			<td>Tissue forceps</td>
			<td>Fine Science Tools</td>
			<td>11051-10</td>
			<td></td>
		</tr>
		<tr>
			<td>Tissue pins</td>
			<td>Fine Science Tools</td>
			<td>26007-01</td>
			<td>Could use 27G needles as a substitute</td>
		</tr>
		<tr>
			<td colspan="4">General lab instruments</td>
		</tr>
		<tr>
			<td>Orbital shaker</td>
			<td>Sunlab</td>
			<td>D-8040</td>
			<td></td>
		</tr>
		<tr>
			<td>Pipette,volume 10ul, 100ul, 1000ul</td>
			<td>Eppendorf</td>
			<td>Z683884-1EA</td>
			<td></td>
		</tr>
		<tr>
			<td>Magnetic stirrer</td>
			<td>IKA</td>
			<td>RH basic</td>
			<td></td>
		</tr>
		<tr>
			<td colspan="4">Microscopes</td>
		</tr>
		<tr>
			<td>Dissection stereo- zoom microscope</td>
			<td>vwr</td>
			<td>10836-004</td>
			<td></td>
		</tr>
		<tr>
			<td>Leica microscope</td>
			<td>Leica microsystems</td>
			<td>Leica DM6</td>
			<td></td>
		</tr>
		<tr>
			<td colspan="4">Flow cytometry machine</td>
		</tr>
		<tr>
			<td>Beckman Coulter</td>
			<td>Beckman coulter</td>
			<td>MoFlo Astrios</td>
			<td></td>
		</tr>
		<tr>
			<td colspan="4">Software</td>
		</tr>
		<tr>
			<td>FlowJo v10</td>
			<td>FlowJo</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td colspan="4">General Lab Material</td>
		</tr>
		<tr>
			<td>0.2 &#181;m syringe filter</td>
			<td>sartorius</td>
			<td>17597</td>
			<td></td>
		</tr>
		<tr>
			<td>100 mm petri dish</td>
			<td>Falcon</td>
			<td>351029</td>
			<td></td>
		</tr>
		<tr>
			<td>27G needle</td>
			<td>BD Microlance 3</td>
			<td>300635</td>
			<td></td>
		</tr>
		<tr>
			<td>50 ml Polypropylene conical Tube</td>
			<td>FALCON</td>
			<td>352070</td>
			<td></td>
		</tr>
		<tr>
			<td>Cover slips</td>
			<td>Thermo scientific</td>
			<td>7632160</td>
			<td></td>
		</tr>
		<tr>
			<td>Eppendorf Tubes</td>
			<td>Eppendorf</td>
			<td>30121872</td>
			<td></td>
		</tr>
		<tr>
			<td>5ml Syringe</td>
			<td>Braun</td>
			<td>4606108V</td>
			<td></td>
		</tr>
		<tr>
			<td colspan="4">Chemicals</td>
		</tr>
		<tr>
			<td>0.5 M EDTA</td>
			<td>Sigma</td>
			<td>20-158</td>
			<td></td>
		</tr>
		<tr>
			<td>Acetic acid</td>
			<td>Merck</td>
			<td>100063</td>
			<td>Component of TEA</td>
		</tr>
		<tr>
			<td>Agarose</td>
			<td>Biozym</td>
			<td>850070</td>
			<td></td>
		</tr>
		<tr>
			<td>Bovine Serum Albumin</td>
			<td>Sigma</td>
			<td>A2153-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>Collagenase I</td>
			<td>Worthington Biochemical</td>
			<td>LS004196</td>
			<td></td>
		</tr>
		<tr>
			<td>Collagenase XI</td>
			<td>Sigma</td>
			<td>C7657</td>
			<td></td>
		</tr>
		<tr>
			<td>DNase I</td>
			<td>Sigma</td>
			<td>D4527</td>
			<td></td>
		</tr>
		<tr>
			<td>Hyaluronidase</td>
			<td>Sigma</td>
			<td>H3506</td>
			<td></td>
		</tr>
		<tr>
			<td>HEPES buffer</td>
			<td>Sigma</td>
			<td>H4034</td>
			<td></td>
		</tr>
		<tr>
			<td>Bovine Serum Albumin</td>
			<td>Sigma</td>
			<td>A2153-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>DPBS (1X) Dulbecco&#39;s Phosphate Buffered Saline</td>
			<td>Gibco</td>
			<td>14190-094</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal bovine serum</td>
			<td>Sigma</td>
			<td>F2442-500ml</td>
			<td></td>
		</tr>
		<tr>
			<td>Penicillin &#8722; Streptomycin</td>
			<td>Sigma</td>
			<td>P4083</td>
			<td></td>
		</tr>
		<tr>
			<td>DMEM</td>
			<td>Gibco</td>
			<td>41966029</td>
			<td></td>
		</tr>
		<tr>
			<td colspan="4">Drugs</td>
		</tr>
		<tr>
			<td>Fentanyl 0.5&#160;mg/10&#160;ml</td>
			<td>Braun Melsungen</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Isoflurane 1 ml/ml</td>
			<td>Cp-pharma</td>
			<td>31303</td>
			<td></td>
		</tr>
		<tr>
			<td>Oxygen 5L</td>
			<td>Linde</td>
			<td>2020175</td>
			<td>Includes a pressure regulator</td>
		</tr>
		<tr>
			<td colspan="4">Antibodies</td>
		</tr>
		<tr>
			<td>Anti-mouse Ly6C FITC (clone HK1.4)</td>
			<td>BioLegend</td>
			<td>Cat# 128006</td>
			<td>diluted to 1:100</td>
		</tr>
		<tr>
			<td>Anti-mouse F4/80 PE/Cy7(clone BM8)</td>
			<td>BioLegend</td>
			<td>Cat# 123114</td>
			<td>diluted to 1:100</td>
		</tr>
		<tr>
			<td>Anti-mouse CD64 APC (clone X54-5/7.1)</td>
			<td>BioLegend</td>
			<td>Cat# 139306</td>
			<td>diluted to 1:100</td>
		</tr>
		<tr>
			<td>Anti-mouse CD11b APC/Cy7(clone M1/70)</td>
			<td>BioLegend</td>
			<td>Cat# 101226</td>
			<td>diluted to 1:100</td>
		</tr>
		<tr>
			<td>Anti-mouse CD45 PE (clone 30-F11)</td>
			<td>BioLegend</td>
			<td>Cat# 103106</td>
			<td>diluted to 1:100</td>
		</tr>
		<tr>
			<td>Hoechst 33342, Trihydrochloride, Trihydrate (DAPI)</td>
			<td>Invitrogen</td>
			<td>H3570</td>
			<td>diluted to 1:1000</td>
		</tr>
		<tr>
			<td colspan="4">Animals</td>
		</tr>
		<tr>
			<td>Mouse, C57BL/6</td>
			<td>Charles River Laboratories</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

isolation and culture of resident cardiac macrophages from the murine sinoatrial and atrioventricular node

Resident cardiac macrophages have been demonstrated to facilitate the electrical conduction in the heart. The physiologic heart rhythm is initiated by electrical impulses generated in sinoatrial node (SAN) and then conducted to ventricles via atrioventricular node (AVN). To further study the role of resident macrophages in cardiac conduction system, a proper isolation of resident macrophages from SAN and AVN is necessary, but it remains challenging. Here, we provide a protocol for the reliable microdissection of the SAN and AVN in murine hearts followed by the isolation and culture of resident macrophages.
Both, SAN which is located at the junction of the crista terminalis with the superior vena cava, and AVN which is located at the apex of the triangle of Koch, are identified and microdissected. Correct location is confirmed by histologic analysis of the tissue performed with Masson's trichrome stain and by anti-HCN4.
Microdissected tissues are then enzymatically digested to obtain single cell suspensions followed by the incubation with a specific panel of antibodies directed against cell-type specific surface markers. This allows to identify, count, or isolate different cell populations by fluorescent activated cell sorting. To differentiate cardiac resident macrophages from other immune cells in the myocardium, especially recruited monocyte-derived macrophages, a delicate devised gating strategy is needed. First, lymphoid lineage cells are detected and excluded from further analysis. Then, myeloid cells are identified with resident macrophages being determined by high expression of both CD45 and CD11b, and low expression of Ly6C. With cell sorting, isolated cardiac macrophages can then be cultivated in vitro over several days for further investigation. We, therefore, describe a protocol to isolate cardiac resident macrophages located within the cardiac conduction system. We discuss pitfalls in microdissecting and digesting SAN and AVN, and provide a gating strategy to reliably identify, count and sort cardiac macrophages by fluorescence-activated cell sorting.

We describe a practical procedure for the isolation of cardiac resident macrophages specifically from the SAN and AVN region. To confirm a correct dissection, Masson&#39;s Trichrome staining and immunofluorescent HCN4-staining is performed (Figure 3)12. With this protocol, we could collect approximately 60,000 macrophages from one whole heart. Figure 4 shows the gating strategy for sorting cardiac macrophages. Live resident cardiac macrop...

Watch this Scientific Journal Video about Isolation and Culture of Resident Cardiac Macrophages from the Murine Sinoatrial and Atrioventricular Node at JoVE.com

Isolation and Culture of Resident Cardiac Macrophages from the Murine Sinoatrial and Atrioventricular Node

The protocol presented here provides a step-by-step approach for the isolation of cardiac resident macrophages from the sinoatrial node (SAN) and atrioventricular node (AVN) region of mouse hearts.

Resident cardiac macrophages have been demonstrated to facilitate the electrical conduction in the heart. The physiologic heart rhythm is initiated by ...

We describe a protocol for microdissection and subsequent isolation of cardiac resident microphages by fluorescence-activated cell sorting specifically from sinus and AV node in the mouse. With the precise microdissection of the sinus and the V node, followed by the combination of magnetic and fluorescence-activated cell sorting, we are able to specifically isolate resident macrophages from the sinus and the V node at high purity. Identification and isolation of cardiac resident macrophages from distinct regions in the heart allows to further study their phenotype and their region-specific impact on cardiac electrophysiology.After isolating the heart, perform the microdissection procedures in a dissection dish with ice cold one-time PBS under a dissecting microscope. Use cardiac anatomical landmarks such as aorta, pulmonary artery, coronary sinus, and left or right ventricle to determine the left-right and anterior-posterior of the heart. After the orientation is determined, position the heart with the front at the bottom of the dish to expose the posterior large veins.Cut along the groove between the ventricles and the atria to remove the majority of the ventricles. Keep the atrial part. Fix the heart to the dissection dish by inserting pins through the remaining part of the LV free wall and the LAA.Cut the remaining RV free wall upwards through the tricuspid valve and superior vena cava. Flip the RA and RV away and pin the RAA to expose the RA cavity intercaval region and atrial septum. For the microdissection of SAN, cut the heart along the interatrial septum parallel to the crista terminalis to separate the intercaval region to obtain the SAN sample.Put the sample in an empty 1.5 milliliter microcentrifuge tube on ice. For microdissection of AVN, pin the remaining parts of the heart through the tissue adjacent to the interatrial septum and interventricular septum to face the right atrial side of the interatrial septum up. Look at the right atrium on the endocardial surface for the triangle of Koch which will be bordered anteriorly by the hinge line of the septal leaflet of the tricuspid valve and posteriorly by the tendon of Todaro.The orifice of the coronary sinus is observed at the base. Mince the SAN and AVN tissue with scalpels. Then add 500 microliters of freshly prepared digestion buffer to each sample and wash all minced tissue from the wall of the microcentrifuge tube.Gently pipette to help digest the sample and homogenize the tissue on a vortex machine. After digestion, transfer the tissue suspension to a fresh 15 milliliter centrifuge tube by passing it through a 40 micrometer cell strainer. Rinse the cell strainer with an additional five milliliters of cell sorting buffer to stop the digestion.Remove the supernatant. After resuspending the cell pellet with 90 microliters of cell sorting buffer, add 10 microliters of CD45 microbeads per 10 million total cells to the cell suspension in a 15 milliliter centrifuge tube. Mix the samples well.During the time for incubating the cell suspension with microbeads and antibody mixture, prepare the magnetic separation set by attaching the magnetic column to a suitable magnetic separator and then placing a collection tube under the magnetic column. Prepare magnetic columns by rinsing with 500 microliters of cell sorting buffer added at the top of the column and allowing the buffer to pass through. Apply the cell suspension immediately onto the column, avoiding air bubbles, while the cell sorting buffer is passing through.Wash the column three times with 500 microliters of cell sorting buffer. Add one milliliter of cell sorting buffer onto the column. Remove the column from the magnetic separator and place it on a new collection tube.Immediately flush the column by firmly applying the plunger supplied with the column to obtain the flow-through containing the magnetically labeled cells. After applying the unstained sample and compensation tubes, adjust the voltages of each channel to align both the positive and negative peaks to the proper position of the axis. Set the gating strategy as described in the text manuscript using DAPI as a viability marker.Check the flow cytometry charts to confirm that the cell population of interest is properly shown on the charts. Collect the sorted cells into medium or buffer-based on the need of subsequent experiments. To confirm a correct dissection, identification of the SAN and AVN was done using immunofluorescent and Masson's trichrome staining.Immunofluorescent staining of HCN4 positive conduction system cells in the SAN and AVN, as well as Masson's trichrome staining of SAN and AVN is shown here. The gating strategy for cell sorting of resident cardiac macrophages helped to identify mononuclear cells by exclusion of doublets in the forward scatter area of the y-axis versus that of the x-axis. Dead cells were excluded by DAPI.Live cells were gated for CD45 positive leukocytes, then for CD11b positive myeloid cells. Cardiac macrophages were identified by the expression of both F4/80 and CD64, then stratified by lymphocyte antigen six expression. Freshly sorted cells were observed under brightfield microscopy.The cells were positive for CD45 when observed under the fluorophore PE channel. When observed under fluorophore APC size seven channel, the same view of the sorted cells showed CD11b positive cells. The fluorophore PE size seven channel was used to identify the F4/80 positive phenotype.And the triple positive cells were identified as cardiac resident macrophages. Isolated cardiac macrophages cultured in medium for up to six days are indicated with white arrows, while the black arrows indicate dead cells. Sorted macrophages can be used for further functional studies such as patch clamp experiments or expression studies such as RNA sequencing or proteomic studies.

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