Name: refined clarity-based tissue clearing for three-dimensional fibroblast organization in healthy and injured mouse hearts
Uploaded: 2021-05-16T14:00:00
Description: Watch this Scientific Journal Video about Refined CLARITY-Based Tissue Clearing for Three-Dimensional Fibroblast Organization in Healthy and Injured Mouse Hearts at JoVE.com

The authors would like to acknowledge the CCHMC Confocal Imaging Core for their assistance and guidance in development of this model, as well as Matt Batie from Clinical Engineering for the design of all 3D printed parts. Demetria Fischesser was supported by a training grant from the National Institutes of Health, (NHLBI, T32 HL125204) and Jeffery D. Molkentin was supported by the Howard Hughes Medical Institute.

All experiments involving mice were approved by the Institutional Animal Care and Use Committee (IACUC) at Cincinnati Children&#8217;s Hospital Medical Center. The institution is also AAALAC (American Association for Accreditation of Laboratory Animal Care) certified. Mice were euthanized via cervical dislocation, and mice undergoing survival surgical procedures were given pain relief (see below). All methods used for pain management and euthanasia are based on recommendations of the Panel on Euthanasia of the American V...

<ol>
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This article presents a refined method for tissue clearing that allows for visualization of cardiac fibroblasts in vivo, both at baseline and following injury, to characterize and better understand fibroblasts in the mouse heart. This enhanced protocol addresses limitations in existing tissue clearing protocols that have attempted to identify specific cell types in the adult or neonatal heart12,13,14,<sup class="xref"...

Although cardiomyocytes comprise the greatest volume fraction in the heart, cardiac fibroblasts are more plentiful and are critically involved in regulating the baseline structural and reparative features of this organ. Cardiac fibroblasts are highly mobile, mechanically responsive, and phenotypically ranging depending on the extent of their activation. Cardiac fibroblasts are necessary to maintain normal levels of extracellular matrix (ECM), and too little or too much ECM production by these cells can lead to disease1,2,3. Given their importance in disease, cardiac fibroblasts have become an increasingly important topic of investigation towards identifying novel treatment strategies, especially in attempting to limit excessive fibrosis4,5,6,7. Upon injury, fibroblasts activate and differentiate into a more synthetic cell type known as a myofibroblast, which can be proliferative and secrete abundant ECM, as well as have contractile activity that helps remodel the ventricles.
While cardiac fibroblasts have been extensively evaluated for their properties in 2-D cultures6,8,9,10, much less is understood of their properties and dynamics in the 3-D living heart, either at baseline or with disease stimulation. Here, a refined method has been described to tissue clear the adult mouse heart while maintaining the fluorescence of fibroblasts labeled with a Rosa26-loxP-eGFP x Tcf21-MerCreMer genetic reporter system. Within the heart, Tcf21 is a relatively specific marker of quiescent fibroblasts4. After tamoxifen is given to activate the inducible MerCreMer protein, essentially all quiescent fibroblasts will permanently express enhanced green fluorescent protein (eGFP) from the Rosa26 locus, which allows for their tracking in vivo.
Numerous well-established tissue clearing protocols exist, some of which have been applied to the heart11,12,13,14,15,16,17. However, many of the reagents used in different tissue clearing protocols have been found to quench endogenous fluorescence signals18. Additionally, the adult heart is difficult to clear due to abundant heme group-containing proteins that generate autofluorescence19. Therefore, the goal of this protocol was to preserve fibroblast marker fluorescence with the simultaneous inhibition of heme autofluorescence in the injured adult heart for optimal 3-D visualization in vivo12,13,14,16,17,20.
Previous studies attempting to examine the cardiac fibroblast in vivo employed perfused antibodies to label these cells, although such studies were limited by antibody penetration and cardiac vascular structure14,16,17,20. Although Salamon et al. have shown tissue clearing with maintenance of topical neuronal fluorescence in the neonatal heart, and Nehrhoff et al. have shown maintenance of fluorescence marking myeloid cells, maintenance of endogenous fluorescence through the entire ventricular wall has not yet been demonstrated, including the visualization of adult cardiac fibroblasts at baseline or following injury13,20. This tissue clearing protocol refines a mixture of previous protocols based on the CLARITY method (clear lipid-exchanged acrylamide-hybridized rigid Imaging/immunostaining/in situ-hybridization-compatible tissue hydrogel) and PEGASOS (polyethylene glycol (PEG)-associated solvent system). This refined protocol permitted a more robust examination of cardiac fibroblasts in the mouse heart at baseline and of how they respond to different types of injury. The protocol is straightforward and reproducible and will help characterize the behavior of cardiac fibroblasts in vivo.

<table>
	<tbody>
		<tr>
			<td>4-0 braided silk</td>
			<td>Ethicon</td>
			<td>K871H</td>
			<td></td>
		</tr>
		<tr>
			<td>8-0 prolene</td>
			<td>Ethicon</td>
			<td>8730H</td>
			<td></td>
		</tr>
		<tr>
			<td>40% Acrylamide Solution</td>
			<td>Bio-Rad</td>
			<td>1610140</td>
			<td></td>
		</tr>
		<tr>
			<td>Angiotensin II</td>
			<td>Sigma</td>
			<td>A9525-50G</td>
			<td></td>
		</tr>
		<tr>
			<td>Artificial Tear Ointment</td>
			<td>Covetrus</td>
			<td>048272</td>
			<td></td>
		</tr>
		<tr>
			<td>DABCO (1,4-diazabicyclo[2.2. 2]octane)</td>
			<td>Millipore Sigma</td>
			<td>D27802-25G</td>
			<td></td>
		</tr>
		<tr>
			<td>GLUture topical tissue adhesive</td>
			<td>World Precision Instruments</td>
			<td>503763</td>
			<td></td>
		</tr>
		<tr>
			<td>Heparin</td>
			<td>Sigma</td>
			<td>H0777</td>
			<td></td>
		</tr>
		<tr>
			<td>Imaris Start Analysis Software</td>
			<td>Oxford Instruments</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Micro-osmotic pumps</td>
			<td>Alzet</td>
			<td>Model 1002</td>
			<td></td>
		</tr>
		<tr>
			<td>Nikon Elements Analysis Software</td>
			<td>Nikon</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Nikon A1R HD upright microscope</td>
			<td>Nikon</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Normal autoclaved chow</td>
			<td>Labdiet</td>
			<td>5010</td>
			<td></td>
		</tr>
		<tr>
			<td>Nycodenz, 5- (N-2, 3-dihydroxypropylacetamido)-2, 4, 6-tri-iodo-N, 
			N&#39;-bis (2, 3 dihydroxypropyl) isophthalamide</td>
			<td>CosmoBio</td>
			<td>AXS-1002424</td>
			<td></td>
		</tr>
		<tr>
			<td>Paraformaldehyde</td>
			<td>Electron Microscopy Sciences</td>
			<td>15710</td>
			<td></td>
		</tr>
		<tr>
			<td>Phenylephrine Hydrochloride</td>
			<td>Sigma</td>
			<td>P6126-10G</td>
			<td></td>
		</tr>
		<tr>
			<td>Photoinitiator</td>
			<td>Wako Chemicals</td>
			<td>VA-044</td>
			<td></td>
		</tr>
		<tr>
			<td>Rosa26-nLacZ [FVB.Cg-Gt(ROSA)26Sortm1 (CAG-lacZ,-EGFP)Glh/J]</td>
			<td>Jackson Laboratories</td>
			<td>Jax Stock No:012429</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Azide</td>
			<td>Sigma Aldrich</td>
			<td>S2002-5G</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Chloride solution</td>
			<td>Hospira, Inc.</td>
			<td>NDC 0409-4888-10</td>
			<td></td>
		</tr>
		<tr>
			<td>Tamoxifen</td>
			<td>Sigma Aldrich</td>
			<td>T5648</td>
			<td></td>
		</tr>
		<tr>
			<td>Tamoxifen food</td>
			<td>Envigo</td>
			<td>TD.130860</td>
			<td></td>
		</tr>
		<tr>
			<td>Tween-20</td>
			<td>Thermo Fisher Scientific</td>
			<td>BP337-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Quadrol, N,N,N&#8242;,N&#8242;-Tetrakis(2-Hydroxypropyl)ethylenediamine, decolorizing agent</td>
			<td>Millipore Sigma</td>
			<td>122262-1L</td>
			<td></td>
		</tr>
		<tr>
			<td>X-Clarity electrophoretic clearing chamber</td>
			<td>Logos Biosystems</td>
			<td>C30001</td>
			<td></td>
		</tr>
		<tr>
			<td>X-Clarity electrophoretic clearing solution</td>
			<td>Logos Biosystems</td>
			<td>C13001</td>
			<td></td>
		</tr>
		<tr>
			<td>X-Clarity electrophoresis tissue basket</td>
			<td>Logos Biosystems</td>
			<td>C12001</td>
			<td></td>
		</tr>
		<tr>
			<td>X-Clarity electrophoresis tissue basket holder</td>
			<td>Logos Biosystems</td>
			<td>C12002</td>
			<td></td>
		</tr>
	</tbody>
</table>

refined clarity-based tissue clearing for three-dimensional fibroblast organization in healthy and injured mouse hearts

Cardiovascular disease is the most prevalent cause of mortality worldwide and is often marked by heightened cardiac fibrosis that can lead to increased ventricular stiffness with altered cardiac function. This increase in cardiac ventricular fibrosis is due to activation of resident fibroblasts, although how these cells operate within the 3-dimensional (3-D) heart, at baseline or after activation, is not well understood. To examine how fibroblasts contribute to heart disease and their dynamics in the 3-D heart, a refined CLARITY-based tissue clearing and imaging method was developed that shows fluorescently labeled cardiac fibroblasts within the entire mouse heart. Tissue resident fibroblasts were genetically labeled using Rosa26-loxP-eGFP florescent reporter mice crossed with the cardiac fibroblast expressing Tcf21-MerCreMer knock-in line. This technique was used to observe fibroblast localization dynamics throughout the entire adult left ventricle in healthy mice and in fibrotic mouse models of heart disease. Interestingly, in one injury model, unique patterns of cardiac fibroblasts were observed in the injured mouse heart that followed bands of wrapped fibers in the contractile direction. In ischemic injury models, fibroblast death occurred, followed by repopulation from the infarct border zone. Collectively, this refined cardiac tissue clarifying technique and digitized imaging system allows for 3-D visualization of cardiac fibroblasts in the heart without the limitations of antibody penetration failure or previous issues surrounding lost fluorescence due to tissue processing.

Cardiac fibroblasts are essential for baseline function of the heart as well as for response to cardiac injury. Previous attempts to understand the arrangement and morphology of these cells have been conducted largely in 2-D settings. However, a refined cardiac tissue clearing (Figure 2) and 3-D imaging technique has been published, which allows for the advanced, more detailed visualization of cardiac fibroblasts. With this imaging technique, fibroblasts were found to be densely packed and h...

Watch this Scientific Journal Video about Refined CLARITY-Based Tissue Clearing for Three-Dimensional Fibroblast Organization in Healthy and Injured Mouse Hearts at JoVE.com

Refined CLARITY-Based Tissue Clearing for Three-Dimensional Fibroblast Organization in Healthy and Injured Mouse Hearts

A refined method of tissue clearing was developed and applied to the adult mouse heart. This method was designed to clear dense, autofluorescent cardiac tissue, while maintaining labeled fibroblast fluorescence attributed to a genetic reporter strategy.

Cardiovascular disease is the most prevalent cause of mortality worldwide and is often marked by heightened cardiac fibrosis that can lead to increased ...

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Heterotypic Three-dimensional In Vitro Modeling of Stromal-Epithelial Interactions During Ovarian Cancer Initiation and Progression

Heterotypic Three-dimensional In Vitro Modeling of Stromal-Epithelial Interactions During Ovarian Cancer Initiation and Progression

Epithelial ovarian cancers (EOCs) are the leading cause of death from gynecological malignancy in Western societies. Despite advances in surgical ...

A Three-dimensional Tissue Culture Model to Study Primary Human Bone Marrow and its Malignancies

Tissue culture has been an invaluable tool to study many aspects of cell function, from normal development to disease. Conventional cell culture methods ...

Three-dimensional Co-culture Model for Tumor-stromal Interaction

Cancer progression (initiation, growth, invasion and metastasis) occurs through interactions between malignant cells and the surrounding tumor stromal ...

Three-Dimensional (3D) Tumor Spheroid Invasion Assay

Three-Dimensional 3D Tumor Spheroid Invasion Assay

Invasion of surrounding normal tissues is generally considered to be a key hallmark of malignant (as opposed to benign) tumors. For some cancers in ...

Three-dimensional Alginate-bead Culture of Human Pituitary Adenoma Cells

A three-dimensional culture method is described in which primary pituitary adenoma cells are grown in alginate beads. Alginate is a polymer derived from ...

Oral Biofilm Sampling for Microbiome Analysis in Healthy Children

Oral biofilm and its molecular analysis provide a basis for investigating various dental research and clinical questions. Knowledge of biofilm composition ...

Optical Clearing and Imaging of Immunolabeled Kidney Tissue

Optical clearing techniques render tissue transparent by equilibrating the refractive index throughout a sample for subsequent three-dimensional (3-D) ...

On-Site Sampling and Extraction of Brain Tumors for Metabolomics and Lipidomics Analysis

Despite the variety of tools available for cancer diagnosis and classification, methods that enable fast and simple characterization of tumors are still ...

Advanced Cardiac Rhythm Management by Applying Optogenetic Multi-Site Photostimulation in Murine Hearts

Ventricular tachyarrhythmias are a major cause of mortality and morbidity worldwide. Electrical defibrillation using high-energy electric shocks is ...

Three-Dimensional Collagen Matrix Scaffold Implantation as a Liver Regeneration Strategy

Liver diseases are the leading cause of death worldwide. Excessive alcohol consumption, a high-fat diet, and hepatitis C virus infection promote fibrosis, ...