Name: surgery and sample processing for correlative imaging of the murine pulmonary valve
Uploaded: 2021-08-05T14:00:00
Description: Watch this Scientific Journal Video about Surgery and Sample Processing for Correlative Imaging of the Murine Pulmonary Valve at JoVE.com

This work is supported, in part, by R01HL139796 and R01HL128847 grants to CKB and RO1DE028297 and CBET1608058 for DWM.

The use of animals in this study was in accordance with Nationwide Children&#39;s Hospital institutional animal care and use committee under protocol AR13-00030.
1. Pulmonary valve excision
<ol>
	<li>Autoclave the necessary tools needed for the mouse dissection. This includes fine scissors, micro forceps, micro vascular clamps, clamp applying forceps, microneedle holders, spring scissors, and retractors.</li>
	<li>Acclimate all mice for a minimum of 2 weeks before the operation. Remove C57BL...

<ol>
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D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+aortic+valve+microstructure:+Effects+of+transvalvular+pressure.">The aortic valve microstructure: Effects of transvalvular pressure.</a> Journal of Biomedical Materials Research. 41 (1), 131-141 (1998).</li><li>Ayoub, 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=Heart+valve+biomechanics+and+underlying+mechanobiology.">Heart valve biomechanics and underlying mechanobiology.</a> Comprehensive Physiology. 6 (4), 1743-1780 (2016).</li><li>Stella, J. A., Liao, J., Sacks, M. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Time-dependent+biaxial+mechanical+behavior+of+the+aortic+heart+valve+leaflet.">Time-dependent biaxial mechanical behavior of the aortic heart valve leaflet.</a> Journal of Biomechanics. 40 (14), 3169-3177 (2007).</li><li>Korn, E. D., Weisman, R. A. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=loss+of+lipids+during+preparation+of+amoebae+for+electron+microscopy.">loss of lipids during preparation of amoebae for electron microscopy.</a> Biochimica et Biophysica Acta (BBA)/Lipids and Lipid Metabolism. 116 (2), 309-316 (1966).</li><li>Tapia, J. 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=High-contrast+en+bloc+staining+of+neuronal+tissue+for+field+emission+scanning+electron+microscopy.">High-contrast en bloc staining of neuronal tissue for field emission scanning electron microscopy.</a> Nature Protocols. 7 (2), 193-206 (2012).</li><li>Hinton, R. 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=Mouse+heart+valve+structure+and+function:+Echocardiographic+and+morphometric+analyses+from+the+fetus+through+the+aged+adult.">Mouse heart valve structure and function: Echocardiographic and morphometric analyses from the fetus through the aged adult.</a> American Journal of Physiology - Heart and Circulatory Physiology. 294 (6), 2480-2488 (2008).</li><li>Denk, W., Horstmann, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Serial+block-face+scanning+electron+microscopy+to+reconstruct+three-dimensional+tissue+nanostructure.">Serial block-face scanning electron microscopy to reconstruct three-dimensional tissue nanostructure.</a> Plos Biology. 2 (11), 1900-1909 (2004).</li><li>Lincoln, J., Florer, J. B., Deutsch, G. H., Wenstrup, R. J., Yutzey, K. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=ColVa1+and+ColXIa1+are+required+for+myocardial+morphogenesis+and+heart+valve+development.">ColVa1 and ColXIa1 are required for myocardial morphogenesis and heart valve development.</a> Developmental Dynamics. 235 (12), 3295-3305 (2006).</li><li>Hamatani, 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=Pathological+investigation+of+congenital+bicuspid+aortic+valve+stenosis,+compared+with+atherosclerotic+tricuspid+aortic+valve+stenosis+and+congenital+bicuspid+aortic+valve+regurgitation.">Pathological investigation of congenital bicuspid aortic valve stenosis, compared with atherosclerotic tricuspid aortic valve stenosis and congenital bicuspid aortic valve regurgitation.</a> PLoS One. 11 (8), (2016).</li></ol>

Removal of the ventricles serves two purposes. First, exposing the ventricle side to the atmospheric pressure, thereby only needing to apply a transvalvular pressure from the arterial side of the pulmonary valve to close, and second, providing a stable base to prevent twisting of the pulmonary trunk. During pressurization, the pulmonary trunk distends radially and inferiorly, making it prone to twisting, causing the collapse of the pulmonary trunk. Preloading the pulmonary valve with a saline solution offers an additiona...

The pulmonary valve (PV) serves to ensure unidirectional blood flow between the right ventricle and the pulmonary artery. Pulmonary valve malformations are associated with several forms of congenital heart disease. The current treatment for congenital heart valve disease (HVD) is valvular repair or valve replacement, which can necessitate multiple invasive surgeries throughout a patient&#39;s lifetime1. It has been widely accepted that the function of the heart valve is derived from its structure, often referred to as the structure-function correlate. More specifically, the geometric and biomechanical properties of the heart dictate its function. The mechanical properties, in turn, are determined by the composition and organization of the ECM. By developing a method for determining the biomechanical properties of murine heart valves, transgenic animal models can be used to interrogate the role of the ECM on heart valve function and dysfunction2,3,4,5.
The murine animal model has long been regarded as the standard for molecular studies because transgenic models are more readily available in mice compared to other species. Murine transgenic models provide a versatile platform for researching heart valve-related diseases6. However, the surgical expertise and instrumentation requirements to characterize both the geometry and ECM organization have been a major hurdle in progressing HVD research. Hstological data in literature provides a picture into murine heart valve extracellular matrix content, but only in the form of 2D images, and are unable to describe its 3D architecture7,8. Additionally, the heart valve is both spatially and temporally heterogeneous, making it difficult to draw conclusions across experiments regarding ECM organization if the sampling and conformation are not fixed. Conventional 3D characterization methods, such as MRI or 3D echocardiography, do not provide the resolution necessary to resolve ECM components9,10.
This work details a fully correlative workflow where the temporal heterogeneity due to the cardiac cycle was addressed by fixing the conformation of the murine PV with hydrostatic transvalvular pressure. The spatial heterogeneity was controlled precisely by sampling regions of interest and registering data sets from different imaging modalities, specifically &#181;CT and serial block face scanning electron microscopy, across different length scales. This method of scouting with &#181;CT for guiding downstream sampling has been proposed previously, but because the pulmonary valve exhibits temporal variation, an additional level of control was needed on the surgical level11.
In vivo studies describing murine heart valve biomechanics are sparse and, instead, rely on computational models when describing the deformation behavior. It is of critical importance that local extracellular data on the nanometer length scale be related to the geometry and location of the heart valve. This, in turn, provides quantifiable, spatially mapped distributions of mechanically contributing ECM proteins, which can be used to reinforce existing biomechanical heart valve models12,13,14.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>25% glutaraldehyde (aq)</td>
			<td>EMS</td>
			<td>16210</td>
			<td>Primary fixative component</td>
		</tr>
		<tr>
			<td>0.9% sodium chloride injection</td>
			<td>Hospira Inc.</td>
			<td>NDC 0409-4888-10</td>
			<td></td>
		</tr>
		<tr>
			<td>1 mL syringe</td>
			<td>BD</td>
			<td>309659</td>
			<td></td>
		</tr>
		<tr>
			<td>10 mL syringe</td>
			<td>BD</td>
			<td>309604</td>
			<td></td>
		</tr>
		<tr>
			<td>200 proof ethanol</td>
			<td>EMS</td>
			<td>15055</td>
			<td></td>
		</tr>
		<tr>
			<td>22G needle</td>
			<td>BD</td>
			<td>305156</td>
			<td></td>
		</tr>
		<tr>
			<td>3 mL syringe</td>
			<td>BD</td>
			<td>309657</td>
			<td></td>
		</tr>
		<tr>
			<td>3-way stopcock</td>
			<td>Smiths Medical ASD, Inc.</td>
			<td>MX5311L</td>
			<td></td>
		</tr>
		<tr>
			<td>4% osmium tetroxide</td>
			<td>EMS</td>
			<td>19150</td>
			<td>Staining component</td>
		</tr>
		<tr>
			<td>4% paraformaldehyde (aq)</td>
			<td>EMS</td>
			<td>157-4-100</td>
			<td>Primary fixative component</td>
		</tr>
		<tr>
			<td>Absorbable hemostat</td>
			<td>Ethicon</td>
			<td>1961</td>
			<td></td>
		</tr>
		<tr>
			<td>Acetone</td>
			<td>EMS</td>
			<td>10012</td>
			<td></td>
		</tr>
		<tr>
			<td>Black polyamide monofilament suture, 10-0</td>
			<td>AROSurgical instruments Corporation</td>
			<td>TI38402</td>
			<td></td>
		</tr>
		<tr>
			<td>Black polyamide monofilament suture, 6-0</td>
			<td>AROSurgical instruments Corporation</td>
			<td>SN-1956</td>
			<td></td>
		</tr>
		<tr>
			<td>C57BL/6 mice</td>
			<td>Jackson Laboratories</td>
			<td>664</td>
			<td>Approximately 1 yo</td>
		</tr>
		<tr>
			<td>Calcium chloride</td>
			<td>Sigma-Aldrich</td>
			<td>10043-52-4</td>
			<td></td>
		</tr>
		<tr>
			<td>Clamp applying forcep</td>
			<td>FST</td>
			<td>00072-14</td>
			<td></td>
		</tr>
		<tr>
			<td>Cotton tip applicators</td>
			<td>Fisher Scientific</td>
			<td>23-400-118</td>
			<td></td>
		</tr>
		<tr>
			<td>DPBS</td>
			<td>Gibco</td>
			<td>14190-144</td>
			<td></td>
		</tr>
		<tr>
			<td>Dumont #5 forcep</td>
			<td>FST</td>
			<td>11251-20</td>
			<td></td>
		</tr>
		<tr>
			<td>Dumont #5/45 forceps</td>
			<td>FST</td>
			<td>11251-35</td>
			<td></td>
		</tr>
		<tr>
			<td>Dumont #7 fine forcep</td>
			<td>FST</td>
			<td>11274-20</td>
			<td></td>
		</tr>
		<tr>
			<td>Durcupan ACM resin</td>
			<td>EMS</td>
			<td>14040</td>
			<td>For embedding</td>
		</tr>
		<tr>
			<td>Fine scissor</td>
			<td>FST</td>
			<td>14028-10</td>
			<td></td>
		</tr>
		<tr>
			<td>Heliscan microCT</td>
			<td>Thermo Fisher Scientific</td>
			<td></td>
			<td>Micro-CT</td>
		</tr>
		<tr>
			<td>Ketamine hydrochloride injection</td>
			<td>Hospira Inc.</td>
			<td>NDC 0409-2053</td>
			<td></td>
		</tr>
		<tr>
			<td>L-aspartic acid</td>
			<td>Sigma-Aldrich</td>
			<td>56-84-8</td>
			<td>Staining component</td>
		</tr>
		<tr>
			<td>Lead nitrate</td>
			<td>EMS</td>
			<td>17900</td>
			<td>Staining component</td>
		</tr>
		<tr>
			<td>low-vacuum backscatter detector</td>
			<td>Thermo Fisher Scientific</td>
			<td>VSDBS</td>
			<td>SEM backscatter detector</td>
		</tr>
		<tr>
			<td>Micro-adson forcep</td>
			<td>FST</td>
			<td>11018-12</td>
			<td></td>
		</tr>
		<tr>
			<td>Millex-GP filter, 0.22 um, PES 33mm, non-sterile</td>
			<td>EMD Millipore</td>
			<td>SLGP033NS</td>
			<td></td>
		</tr>
		<tr>
			<td>Non-woven songes</td>
			<td>McKesson Corp.</td>
			<td>94442000</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium hexacyanoferrate(II) trihydrate</td>
			<td>Sigma-Aldrich</td>
			<td>14459-95-1</td>
			<td>Staining component</td>
		</tr>
		<tr>
			<td>Potassium hydroxide</td>
			<td>Sigma-Aldrich</td>
			<td>1310-58-3</td>
			<td></td>
		</tr>
		<tr>
			<td>Pressure monitor line</td>
			<td>Smiths Medical ASD, Inc.</td>
			<td>MX562</td>
			<td></td>
		</tr>
		<tr>
			<td>Saline solution (sterile 0.9% sodium chloride)</td>
			<td>Hospira Inc.</td>
			<td>NDC 0409-0138-22</td>
			<td></td>
		</tr>
		<tr>
			<td>Size 3 BEEM capsule</td>
			<td>EMS</td>
			<td>69910-01</td>
			<td>Embedding container</td>
		</tr>
		<tr>
			<td>Sodium cacodylate trihydrate</td>
			<td>Sigma-Aldrich</td>
			<td>6131-99-3</td>
			<td>Buffer</td>
		</tr>
		<tr>
			<td>Solibri retractors</td>
			<td>FST</td>
			<td>17000-04</td>
			<td></td>
		</tr>
		<tr>
			<td>Sputter, carbon and e-beam coater</td>
			<td>Leica</td>
			<td>EM ACE600</td>
			<td>Gold coater</td>
		</tr>
		<tr>
			<td>Surgical microscope</td>
			<td>Leica</td>
			<td>M80</td>
			<td></td>
		</tr>
		<tr>
			<td>Thiocarbohydrazide (TCH)</td>
			<td>EMS</td>
			<td>21900</td>
			<td>Staining component</td>
		</tr>
		<tr>
			<td>Tish needle holder/forcep</td>
			<td>Micrins</td>
			<td>MI1540</td>
			<td></td>
		</tr>
		<tr>
			<td>Trimmer</td>
			<td>Wahl</td>
			<td>9854-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Uranyl acetate</td>
			<td>EMS</td>
			<td>22400</td>
			<td>Staining component</td>
		</tr>
		<tr>
			<td>Volumescope scanning electron microscope</td>
			<td>Thermo Fisher Scientific</td>
			<td>VOLUMESCOPESEM</td>
			<td>Serial Block Face Scanning Electron Microscope</td>
		</tr>
		<tr>
			<td>Xylazine sterile solution</td>
			<td>Akorn Inc.</td>
			<td>NADA# 139-236</td>
			<td></td>
		</tr>
	</tbody>
</table>

surgery and sample processing for correlative imaging of the murine pulmonary valve

The underlying causes of heart valve related-disease (HVD) are elusive. Murine animal models provide an excellent tool for studying HVD, however, the surgical and instrumental expertise required to accurately quantify the structure and organization across multiple length scales have stunted its advancement. This work provides a detailed description of the murine dissection, en bloc staining, sample processing, and correlative imaging procedures for depicting the heart valve at different length scales. Hydrostatic transvalvular pressure was used to control the temporal heterogeneity by chemically fixing the heart valve conformation. Micro-computed tomography (&#181;CT) was used to confirm the geometry of the heart valve and provide a reference for the downstream sample processing needed for the serial block face scanning electron microscopy (SBF-SEM). High-resolution serial SEM images of the extracellular matrix (ECM) were taken and reconstructed to provide a local 3D representation of its organization. &#181;CT and SBF-SEM imaging methods were then correlated to overcome the spatial variation across the pulmonary valve. Though the work presented is exclusively on the pulmonary valve, this methodology could be adopted for describing the hierarchical organization in biological systems and is pivotal for the structural characterization across multiple length scales.

Anastomosis of the pulmonary artery to the pressurization tubing is shown in Figure 1A. Following the application of hydrostatic pressure, the pulmonary trunk distends radially (Figure 1B) indicating that the pulmonary valve leaflets are in a closed configuration. Pulmonary valve conformation was confirmed by &#181;CT. In this case, the leaflets were coapt (closed) and the annulus was circular (Figure 2A). Figur...

Watch this Scientific Journal Video about Surgery and Sample Processing for Correlative Imaging of the Murine Pulmonary Valve at JoVE.com

Surgery and Sample Processing for Correlative Imaging of the Murine Pulmonary Valve

Here, we describe a correlative workflow for the excision, pressurization, fixation, and imaging of the murine pulmonary valve to determine the gross conformation and local extracellular matrix structures.

The underlying causes of heart valve related-disease (HVD) are elusive. Murine animal models provide an excellent tool for studying HVD, however, the ...

This protocol is significant because it's designed to answer questions about the structure function correlate of the murine pulmonary valve, which is generally tricky because of its inherent heterogeneity. The controlled fixation and correlative imaging were used to capture the structure on multiple length scales. Local high-resolution images can then be mapped back to the precise anatomical location on the pulmonary valve.Demonstrating the procedure will be Dr.Tai Yi, the Director of Microsurgery in the Center of Regenerative Medicine at Nationwide Children's Hospital. Begin by autoclaving the tools needed for the mouse dissection, including fine scissors, microforceps, microvascular clamps, clamp applying forceps, microneedle holders, spring scissors, and retractors. After euthanizing an adult C57BL/6 mouse, place it in a dorsal recumbent position on a tray, secure its limbs with tape and perform the thoracotomy.Expose the heart by removing any excess adipose tissue and fascia, then remove the right atrium and perfuse the left ventricle with room temperature saline solution. Remove the entire heart by severing the superior vena cava, inferior vena cava, pulmonary artery, and aorta, and cut approximately two millimeters above the ventriculoatrial junction, which will serve as the conduit for pressurization. Remove the left and right ventricles to expose the chambers to atmospheric pressure, ensuring that the pulmonary trunk structure is unaffected by removing the ventricles.Anastomose pressurization tubing with the pulmonary artery, leaving approximately one millimeter distance between the sinotubular junction and the end of the tubing to accommodate for large movements of the leaflets and pulmonary trunk. Elevate the reservoir to an analogous physiological pressure and fill it with the saline solution. Test the flow-through system to ensure there are no blockages or air bubbles.Attach a stopcock to the anastomosed pulmonary valve and ensure adequate flow through the tubing by switching the outflow tract. Once the flow is sufficient, switch the outflow to the anastomosed pulmonary valve and ensure pressurization of the pulmonary trunk identified by trunk distension. After confirming the pressurization of the pulmonary trunk, gradually incorporate primary fixative solution until 25%of the reservoir capacity of the saline solution is purged.Place a fixative-soaked gauze over the tissue sample to prevent drying. Perfuse the fixative for three hours, refilling the reservoir to maintain a constant pressure. After perfusion, store the heart valve in the fixative solution at four degrees Celsius until use for up to one week.For staining, wash the fixed heart valve sample three times with cold 0.15 molar cacodylate buffer for five minutes and completely submerge the heart valve in a solution of 1.5 potassium ferrocyanide, 0.15 molar cacodylate, two millimolar calcium chloride, and 2%osmium tetroxide on ice for one hour. Wash the samples with room temperature double distilled water by placing them in a tube for five minutes with slight agitation. After three more washes, place the sample in filtered thiocarbohydrazide solution at room temperature.After 20 minutes, wash the sample three times with water as demonstrated earlier. Next, place the sample in 2%osmium tetroxide at room temperature. After 30 minutes, wash it with water three times for five minutes each and incubate the sample in 1%uranyl acetate overnight at four degrees Celsius.Meanwhile, prepare a solution of lead nitrate. On the following day, perform the washing step three times as demonstrated earlier, then incubate the heart valve tissue in lead aspartate solution at 60 degrees Celsius for 30 minutes. Wash the samples three more times, then perform a serial dehydration treatment on the heart valve tissues with freshly prepared 20, 50, 70, and 90%ethanol on ice for five minutes each, followed by two subsequent treatments with 100%ethanol.After dehydration, move the tissues to ice cold acetone, then place it in fresh acetone at room temperature for 10 minutes. For embedding, make the resin mixture according to the manufacturer's specifications. Place tissues in subsequent treatments of 25 to 75, 50 to 50 and 75 to 25 resin to acetone mixture for two hours each.Finally, place the tissues in 100%resin overnight. On the following day, place tissues in fresh 100%resin. After two hours, transfer the tissues to an embedding capsule, add fresh 100%resin and place it in a 60 degree Celsius oven for 48 hours to cure.The excised anastomosed pulmonary artery before and following the application of hydrostatic pressure is shown here. The pulmonary trunk distends radially indicating that the pulmonary valve leaflets are in a closed configuration. Microcomputed tomography confirmed the pulmonary valve confirmation.The leaflets were closed and the annulus was circular while varying degrees of inadequate pulmonary valve pressurization by either fixation or arterial collapse were observed. The micro CT volume rendering virtual cross-sections was correlated with optical images to confirm the slicing direction and location. High-resolution SBF SEM images were taken at a local region within a leaflet when the specimen block was at the desired location and orientation.Correlated images between the micro CT volume rendering virtual slice, low-resolution, and high-resolution SBF SEM images are shown here. In 3D representation of a segmented region of the pulmonary valve, extracellular components like endothelial cells, valvular interstitial cells, and extracellular fibers can be identified. When attempting this protocol, please keep in mind that performing the pressurization is critical and will ensure the yield to be as high as possible.

Research

JoVE Journal

Engineering

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