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Abstract

Introduction

Protocol

Representative Results

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Materials

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Medicine

Whole-Mount Immunofluorescence Staining, Confocal Imaging and 3D Reconstruction of the Sinoatrial and Atrioventricular Node in the Mouse

Published: December 22nd, 2020

DOI:

10.3791/62058

1University Hospital Munich, Department of Medicine I, Ludwig Maximilians University (LMU) Munich, 2Institute of Surgical Research at the Walter Brendel Center of Experimental Medicine, University Hospital Munich, Ludwig Maximilians University (LMU) Munich, 3German Center for Cardiovascular Research (DZHK), Partner Site Munich, Munich Heart Alliance

ERRATUM NOTICE

Important: There has been an erratum issued for this article. Read more …

We provide a step-by-step protocol for whole-mount immunofluorescence staining of the sinoatrial node (SAN) and atrioventricular node (AVN) in murine hearts.

The electrical signal physiologically generated by pacemaker cells in the sinoatrial node (SAN) is conducted through the conduction system, which includes the atrioventricular node (AVN), to allow excitation and contraction of the whole heart. Any dysfunction of either SAN or AVN results in arrhythmias, indicating their fundamental role in electrophysiology and arrhythmogenesis. Mouse models are widely used in arrhythmia research, but the specific investigation of SAN and AVN remains challenging.

The SAN is located at the junction of the crista terminalis with the superior vena cava and AVN is located at the apex of the triangle of Koch, formed by the orifice of the coronary sinus, the tricuspid annulus, and the tendon of Todaro. However, due to the small size, visualization by conventional histology remains challenging and it does not allow the study of SAN and AVN within their 3D environment.

Here we describe a whole-mount immunofluorescence approach that allows the local visualization of labelled mouse SAN and AVN. Whole-mount immunofluorescence staining is intended for smaller sections of tissue without the need for manual sectioning. To this purpose, the mouse heart is dissected, with unwanted tissue removed, followed by fixation, permeabilization and blocking. Cells of the conduction system within SAN and AVN are then stained with an anti-HCN4 antibody. Confocal laser scanning microscopy and image processing allow differentiation between nodal cells and working cardiomyocytes, and to clearly localize SAN and AVN. Furthermore, additional antibodies can be combined to label other cell types as well, such as nerve fibers.

Compared to conventional immunohistology, whole-mount immunofluorescence staining preserves the anatomical integrity of the cardiac conduction system, thus allowing the investigation of AVN; especially so into their anatomy and interactions with the surrounding working myocardium and non-myocyte cells.

Arrhythmias are common diseases affecting millions of people, and are the cause of significant morbidity and mortality worldwide. Despite enormous advances in treatment and prevention, such as the development of cardiac pacemakers, treatment of arrhythmias remains challenging, primarily due to the very limited knowledge regarding underlying disease mechanisms1,2,3. A better understanding of both the normal electrophysiology and the pathophysiology of arrhythmias may help to develop novel, innovative and causal treatment strategies in the future. Additionally, to comprehensive....

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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 (ROB-55.2-2532.Vet_02-16-106, ROB-55.2-2532.Vet_02-19-86). C57BL6/J mice were purchased from Jackson Laboratory.

NOTE: Figure 1 shows the instruments needed for the experiment.

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By using the protocol outlined above, confocal microscopy imaging of both SAN and AVN can be reliably performed. Specific staining of the conduction system using fluorescent antibodies targeting HCN4 and staining of the working myocardium using fluorescent antibodies targeting Cx43 allows the clear identification of SAN (Figure 5, Video 1) and AVN (Figure 6, Video 2) within the intact anatom.......

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Cardiac anatomy has traditionally been studied using thin histological sections11. However, these methods do not preserve the three-dimensional structure of the conduction system and thus, only provides 2D information. The whole-mount immunofluorescence staining protocol described here allows to overcome these limitations and can be routinely used for SAN and AVN imaging.

In comparison to standard methods such as conventional immunohistochemistry that require paraffin-e.......

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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. Kääb), the Corona Foundation (S199/10079/2019 to S. Clauss), the SFB 914 (project Z01 to H. Ishikawa-Ankerhold and S. Massberg and project A10 to C. Schulz), the ERA-NET on Cardiovascular Diseases (ERA-CVD; 01KL1910 to S. Clauss) and the Heinrich-and-Lotte-Mühlfenzl Stiftung (to S. Clauss). The funders had no role in manuscript preparation.

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Name Company Catalog Number Comments
Anesthesia
Isoflurane vaporizer system  Hugo Sachs Elektronik 34-0458, 34-1030, 73-4911, 34-0415, 73-4910 Includes an induction chamber, a gas evacuation unit and charcoal filters
Modified Bain circuit Hugo Sachs Elektronik 73-4860 Includes an anesthesia mask for mice
Surgical Platform Kent Scientific SURGI-M
In vivo instrumentation
Fine forceps Fine Science Tools 11295-51
Iris scissors Fine Science Tools 14084-08
Spring scissors Fine Science Tools 91500-09
Tissue forceps Fine Science Tools 11051-10
Tissue pins Fine Science Tools 26007-01 Could use 27G needles as a substitute
General lab instruments
Orbital shaker Sunlab D-8040
Magnetic stirrer IKA  RH basic
Pipette,volume 10 µL, 100 µL, 1000 µL Eppendorf Z683884-1EA
Microscopes
Dissection stereo- zoom microscope  VWR 10836-004
Laser Scanning Confocal microscope Zeiss LSM 800
Software
Imaris 8.4.2 Oxford instruments
ZEN 2.3 SP1 black Zeiss
General Lab Material
0.2 µm syringe filter Sartorius 17597
100 mm petri dish Falcon 351029
27G needle BD Microlance 3 300635
50 ml Polypropylene conical Tube Falcon 352070
5ml Syringe Braun 4606108V
Cover slips Thermo Scientific 7632160
Eppendorf Tubes Eppendorf 30121872
Chemicals
0.5 M EDTA Sigma 20-158 Components of TEA
16% Formaldehyde Solution Thermo Scientific  28908 use as a 4% solution 
Acetic acid Merck 100063 Components of TEA
Agarose Biozym 850070
Bovine Serum Albumin Sigma A2153-100G
DPBS (1X) Dulbecco's Phosphate Buffered Saline Gibco 14190-094
Normal goat serum Sigma NS02L
Sucrose Sigma S1888-1kg
Tris-base Roche TRIS-RO Components of TEA
Triton X-100 Sigma T8787-250ml Diluted to 1% in PBS
Tween 20 Sigma P2287-500ml
Drugs
Fentanyl 0.5 mg/10 mL Braun Melsungen
Isoflurane 1 mL/mL Cp-pharma 31303
Oxygen 5 L Linde 2020175 Includes a pressure regulator
Antibodies
Goat anti-Rabbit IgG Alexa Fluor 488  Cell Signaling Technology #4412 diluted to 1:200
Goat anti-Rat IgG Alexa Fluor 647 Invitrogen #A-21247 diluted to 1:200
Hoechst 33342, Trihydrochloride, Trihydrate (DAPI) Invitrogen H3570 diluted to 1:1000
Rabbit Anti-Connexin-43 Sigma C6219 diluted to 1:200
Rat anti-HCN4 (SHG 1E5) Invitrogen MA3-903 diluted to 1:200
Other
Plastic ring Self-designed and 3D printed
Plasticine Cernit 49655005
Silikonpasten, Baysilone VWR 291-1220
Animals
Mouse, C57BL/6 The Jackson Laboratory

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Erratum

Erratum: Whole-Mount Immunofluorescence Staining, Confocal Imaging and 3D Reconstruction of the Sinoatrial and Atrioventricular Node in the Mouse

An erratum was issued for: Whole-Mount Immunofluorescence Staining, Confocal Imaging and 3D Reconstruction of the Sinoatrial and Atrioventricular Node in the Mouse. The Authors section was updated from:

Ruibing Xia1,2,3
Julia Vlcek1,2
Julia Bauer1,2,3
Stefan Kääb1,3
Hellen Ishikawa-Ankerhold1,2
Dominic Adam van den Heuvel1,2
Christian Schulz1,2,3
Steffen Massberg1,2,3
Sebastian Clauss1,2,3
1University Hospital Munich, Department of Medicine I, Ludwig Maximilian University Munich
2Walter Brendel Center of Experimental Medicine, Ludwig Maximilian University Munich
3German Center for Cardiovascular Research (DZHK), Partner Site Munich, Munich Heart Alliance

to:

Ruibing Xia1,2,3
Julia Vlcek1,2
Julia Bauer1,2,3
Stefan Kääb1,3
Hellen Ishikawa-Ankerhold1,2
Dominic Adam van den Heuvel1,2
Christian Schulz1,2,3
Steffen Massberg1,2,3
Sebastian Clauss1,2,3
1University Hospital Munich, Department of Medicine I, Ludwig Maximilians University (LMU) Munich
2Institute of Surgical Research at the Walter Brendel Center of Experimental Medicine, University Hospital Munich, Ludwig Maximilians University (LMU) Munich
3German Center for Cardiovascular Research (DZHK), Partner Site Munich, Munich Heart Alliance

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