The authors would like to express gratitude to Thao Nguyen and Atsushi Nakano from UCLA for providing the mice sample to image. This study was supported by grants NIH HL118650 (to Tzung K. Hsiai), HL083015 (to Tzung K. Hsiai), HD069305 (to N. C. Chi and Tzung K. Hsiai.), HL111437 (to Tzung K. Hsiai and N. C. Chi), HL129727 (to Tzung K. Hsiai), and University of Texas System STARS funding (to Juhyun Lee).

All the procedures involving the use of animals have been approved by the Institutional Review Committees (IACUC) at the University of California, Los Angeles, California.
1. Imaging System Setup
Note: See Figure 1 and Figure 2.
<ol>
	<li>Retrieve a continuous wave (CW) laser with 3 wavelengths: 405 nm, 473 nm, and 532 nm. Place 2 mirrors (M1 and M2) 150 mm apart and align them with their mirror planes at 45&#176; to the beam. 
	Note: This step is performed to redirect the laser away from the dual-sided illumination setup. The resulting beam will be in the same direction as the initial beam.</li>
	<li>Pass the beam through a 25-mm diameter iris diaphragm/pinhole (PH), a 50-mm diameter neutral density filter (NDF) with an optical density range of 0 - 4.0, a beam expander (BE), a 30 mm slit (S) with the width of ~0 - 6 mm, and a mirror (M3), all positioned 150 mm from each other. Place the mirror with its mirror plane at 45&#176; to the beam.</li>
	<li>Pass the beam through a 50:50 beam splitter placed 150 mm from M3. Place a mirror (M6) 150 mm from the beam splitter and align it so that its mirror plane is at 45&#176; to the beam that is emitted in the forward direction. Use the reflected beam to form one side of the dual-illumination light sheet.</li>
	<li>Place a mirror (M4) 150 mm from the beam splitter and align it so that its mirror plane is at 45&#176; to the beam that was emitted at a 90&#176; angle from the beam splitter. Place a second mirror (M5) 150 mm from M4 and align it so that its mirror plane is at 45&#176; to the beam reflected from M6. Use the beam emitted from M5 to form the second side of the dual-illumination light sheet.</li>
	<li>Set up the dual-sided illumination system in a symmetric fashion (see Figure 1). Place one cylindrical lens (CL1) [diameter (d) = 1 in; focal length (f) = 50 mm] 150 mm in line with the beam emitted from M5 on one side and another identical cylindrical lens (CL2) 150 mm in line with the beam emitted from M6 on the other side of the dual-illumination setup. Place 2 mirrors (M7 and M8) each in line with the cylindrical lenses at distances of 50 mm to reflect the beam at 90&#176;.</li>
	<li>Form an achromatic doublet from a pair of lenses. Place the first lens, L1 (d = 1 in; f = 100 mm), 100 mm from M7, and the second lens, L2 (d = 1 in; f = 60 mm), 160 mm from L1. Repeat this on the other side of the dual-illumination with identical lenses (L3, L4) placed the same distance from M8.</li>
	<li>Place mirrors, M9 and M10, 60 mm from lenses L2 and L4, respectively, and in line with the beam. Place the illumination objectives, OL1 and OL2 (d = 2 in; f = 150 mm), 150 mm from M9 and M10 and in line with the beam. The beam emitted from the objectives forms the light sheet for imaging the samples.</li>
	<li>Use a 3-D printer to print the sample holder from acrylonitrile butadiene styrene (ABS). Embed a piece of cover glass [refractive index (RI) = 1.4745] on each side of the chamber, perpendicular to the illumination beam, to minimize refractive index mismatching. Evenly place the chamber in between the beams emitted from the objective lenses.</li>
	<li>Install a stereo microscope with a 1X magnification objective and a scientific complementary metal oxide semiconductor (sCMOS) camera perpendicular to the illumination plane (see Figure 2).</li>
</ol>
2. Imaging System Calibration
<ol>
	<li>Retrieve fluorescent polystyrene beads that are 0.53 &#956;m in diameter.</li>
	<li>Prepare the fluorescent bead sample by diluting the bead solution in a refractive index matching solution (RIMS) with 1% low-melt pointing agarose to 1:150,000. Cut a piece of borosilicate glass tubing with an inner diameter of 12 mm and an outer diameter of 18 mm to a length of 30 mm. 
	Note: The borosilicate glass tubing is used to match the refractive index (1.47).</li>
	<li>Mix the diluted bead sample with 1% agarose and pipette the bead/agarose solution into the borosilicate tubing. Allow the agarose to solidify at room temperature (23 &#176;C).</li>
	<li>Fill the ABS chamber (from step 1.7) with a 99.5% glycerol solution. Place the borosilicate glass tubing containing the beads inside the chamber. Place the ABS chamber in the imaging system so that it is in the center of the Gaussian beam created by the dual illumination system.</li>
	<li>Attach a 3-D motorized translational stage to the borosilicate glass tubing to control the movement and orientation of the sample within the ABS chamber (see Supplemental Figure 1).</li>
	<li>Acquire images using the sCMOS camera at a rate of 30 frames per second (fps). Using the motor controller, move the sample 1 mm in the lateral direction and acquire images at each 1-mm increment using the sCMOS camera. Continue until the entire sample has been imaged.</li>
	<li>Stack the acquired images using a visualization software (see Table of Materials). Measure the point spread function (PSF) of the system using these bead images. Use this PSF for deconvolution during the image processing in later steps.</li>
</ol>
3. Sample Preparation
<ol>
	<li>Dissect hearts from a wild type P1 mouse and from a double heterozygous sarcolipin-Cre knockin mouse with the Rosa26-YFP gene (SlnCre/+; R26YFP reporter/+) at P7. 
	Note: Euthanasia was performed using pentobarbital and the technique described by Robbins et al.10. The dissection was performed according to the technique described by the National Heart, Lung, and Blood Institute (NHLBI)10,11.</li>
	<li>Perform a chemical clearing of the murine hearts as described by Kevin Sung et al.12. 
	Note: The following steps should be performed in a fume hood since the chemicals being used are toxic.
	<ol>
		<li>Rinse the hearts in 1x phosphate-buffered saline (PBS) 3x for 10 min. After rinsing, place the hearts in a 4% paraformaldehyde solution and incubate these samples at 4 &#176;C overnight.</li>
		<li>Place the samples in a 4% acrylamide solution containing 0.5% w/v of 2,2&#8217;-Azobis dihydrochloride. Allow the samples to incubate at 4 &#176;C overnight. After the overnight incubation, remove the samples and incubate them at 37 &#176;C for 2 - 3 h.</li>
		<li>Rinse the samples with PBS and then place them in a solution of 8% w/v sodium dodecyl sulfate and 1.25% w/v boric acid. Incubate the samples at 37 &#176;C until they are clear. This can take several hours depending on the thickness of the sample. After clearing, remove the samples and place them in 1x phosphate-buffered saline for 1 day.</li>
		<li>Prepare a refractive index matching solution with 40 g of nonionic density gradient medium (see Table of Materials) in 30 mL of 0.02 M phosphate buffer (PB), 0.1% Tween-20, and 0.01% sodium azide. Bring the solution to a pH of 7.5 with sodium hydroxide.</li>
	</ol>
	</li>
	<li>Place the cleared sample in RIMS with a refractive index of 1.46 - 1.48 and 1% agarose. Insert the sample into borosilicate glass tubing and allow the agarose to solidify at room temperature (23 &#176;C).</li>
	<li>Attach a 3-D motorized translational stage to the borosilicate glass tubing to control the movement and orientation of the sample within the 3-D printed ABS chamber (see Supplemental Figure 1).</li>
</ol>
4. Adult Heart Imaging
<ol>
	<li>Inject 8.7 x 1012 viruses of type adeno-associated virus vector 9 (AAV9) containing a cardiac-specific troponin T promoter (cTnT) and green fluorescent protein (GFP) in a 100-&#956;L volume into the tail vein of a 2-month wild type (C57BL/6) mouse. 
	Note: The AAV9 was developed according to the technique described by Yuan et al.13. This causes GFP to bind to the renal outer medullary potassium channel (ROMK) producing AAV9-cTnT-ROMK-GFP (see Table of Materials).</li>
	<li>Dissect the adult mouse hearts at 7.5 months of age according to the technique described by the NHLBI11. Prepare the samples using steps 3.1 - 3.3.</li>
	<li>Connect the motor controller to the motor actuator. Attach the actuator to the borosilicate glass tubing to control the movement and orientation of the sample within the 3-D printed ABS chamber.</li>
	<li>Position the sample so that it is in the center of the Gaussian beam created by the dual illumination system. Acquire images using the sCMOS camera at a rate of 100 fps.</li>
	<li>Using the motor controller, move the sample 1 mm in the axial direction and acquire images at each 1-mm increment with the sCMOS camera. Continue until the entire sample has been imaged. 
	Note: The system is controlled by a custom-developed instrument-control software.</li>
	<li>Stack the acquired images using a visualization software (see Table of Materials). Develop 3-D images using these image stacks and the visualization software14. Deconvolve the PSF from step 2.6 with the acquired image stack. Set a pixel threshold intensity value to observe the contours of the heart and add pseudo-color to the images based on this gray-scale intensity.</li>
</ol>

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W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Clarifying+tissue+clearing.">Clarifying tissue clearing.</a> Cell. 162 (2), 246-257 (2015).</li><li>Lee, 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=4-Dimensional+light-sheet+microscopy+to+elucidate+shear+stress+modulation+of+cardiac+trabeculation.">4-Dimensional light-sheet microscopy to elucidate shear stress modulation of cardiac trabeculation.</a> Journal of Clinical Investigation. 126 (5), 1679-1690 (2016).</li><li>Huisken, J., Swoger, J., Del Bene, F., Wittbrodt, J., Stelzer, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+sectioning+deep+inside+live+embryos+by+selective+plane+illumination+microscopy.">Optical sectioning deep inside live embryos by selective plane illumination microscopy.</a> Science. 305 (5686), 1007-1009 (2004).</li><li>Huisken, J., Stainier, D. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Selective+plane+illumination+microscopy+techniques+in+developmental+biology.">Selective plane illumination microscopy techniques in developmental biology.</a> Development. 136 (12), 1963-1975 (2009).</li><li>Bakkers, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Zebrafish+as+a+model+to+study+cardiac+development+and+human+cardiac+disease.">Zebrafish as a model to study cardiac development and human cardiac disease.</a> Cardiovascular Research. 91 (2), 279-288 (2011).</li><li>High, F. A., Epstein, J. 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The authors have nothing to disclose.

The LSFM system and technique described here utilizes a dual-sided illumination beam combined with an optical clearing to image the mouse heart at post-natal and adult stages of its development. A traditional single illumination beam suffers from photon scattering and absorption through thicker and larger tissue samples1,3. The dual-sided beams provide a more even illumination of the sample, thereby minimizing the effect of striping and other artifacts that are o...

Light-sheet fluorescence microscopy was a technique first developed in 1903 and is used today as a method to study gene expression and also to produce 3-D or 4-D models of tissue samples1,2,3. This imaging method uses a thin sheet of light to illuminate a single plane of a sample so that only that plane is captured by the detector. The sample can then be moved in the axial-direction to capture each layer, one section at a time, and render a 3-D model after the post-processing of the acquired images4. However, due to the absorption and scattering of photons, LSFM has been limited to samples that are either a few microns thick or are optically transparent1.
The limitations of LSFM have led to extensive studies of organisms that have tissues that are optically transparent, such as the zebrafish. Studies involving cardiac development and differentiation are often conducted on zebrafish since there are conserved genes between humans and zebrafish5,6. Although these studies have led to advances in cardiac research related to cardiomyopathies6,7, there is still a need to conduct similar research on higher-level organisms such as mammals.
Mammalian cardiac tissue presents a challenge due to the thickness and opacity of the tissue, the absorption due to hemoglobin in red blood cells, and the striping that occurs due to single-sided illumination of the sample under traditional LSFM methods1,8. To compensate for these limitations, we proposed to use dual-sided illumination and a simplified version of the CLARITY technique9 combined with a refractive index matching solution (RIMS). Therefore, this system allows for the imaging of a sample that is greater than 10 x 10 x 10 mm3 while maintaining a good quality resolution in the axial and lateral planes8.
This system was first calibrated using fluorescent beads arranged in different configurations within the glass tubing. Then, the system was used to image post-natal and adult murine hearts. First, the post-natal mouse heart was imaged at 7 days (P7) to reveal the ventricular cavity, the thickness of the ventricular wall, the valve structures, and the presence of trabeculation. Secondly, a study was conducted to identify cells that would differentiate into cardiomyocytes by using a post-natal mouse heart at 1 day (P1) with Cre-labeled cardiomyocytes and yellow fluorescent protein (YFP). Finally, adult mice at 7.5 months were imaged to observe the presence of renal outer medullary potassium (ROMK) channels after gene therapy8.

<table border="0" cellpadding="0" cellspacing="0" style="width:967px;" width="967">
	<tbody>
		<tr height="40">
			<td height="40" style="height:40px;width:247px;">CW Laser</td>
			<td style="width:136px;">Laserglow Technologies</td>
			<td style="width:393px;">LMM-GBV1-PF3-00300-05</td>
			<td style="width:191px;">Excitation of fluorophores</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:247px;">Neutral density filter</td>
			<td style="width:136px;">Thorlabs</td>
			<td style="width:393px;">NDC-50C-4M</td>
			<td style="width:191px;">Controls amount of light entering system</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:247px;">Achromatic beam expander</td>
			<td style="width:136px;">Thorlabs</td>
			<td style="width:393px;">GBE05-A</td>
			<td style="width:191px;">Expands the beam of light</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:247px;">Mechanical slit</td>
			<td style="width:136px;">Thorlabs</td>
			<td style="width:393px;">VA100C</td>
			<td style="width:191px;">Controls width of beam</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:247px;">Beam splitter</td>
			<td style="width:136px;">Thorlabs</td>
			<td style="width:393px;">BS013</td>
			<td style="width:191px;">Forms dual-illumination beam</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:247px;">Stereo microscope with 1X objective lense</td>
			<td style="width:136px;">Olympus</td>
			<td style="width:393px;">MVX10</td>
			<td style="width:191px;">Used for observation of sample</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:247px;">ORCA-Flash4.0 LT sCMOS camera</td>
			<td style="width:136px;">Hamamatsu Photonics</td>
			<td style="width:393px;">C11440-42U</td>
			<td style="width:191px;">Used to capture Images</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:247px;">Acrylonitrile butadiene styrene (ABS)</td>
			<td style="width:136px;">Stratasys</td>
			<td style="width:393px;">uPrint</td>
			<td style="width:191px;">Material used to 3-D print a sample holder</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:247px;">Fluorescent polystyrene beads</td>
			<td style="width:136px;">Spherotech Inc</td>
			<td style="width:393px;">PP-05-10</td>
			<td style="width:191px;">Used for imaging system calibration</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:247px;">Borosilicate glass tubing</td>
			<td style="width:136px;">Corning</td>
			<td style="width:393px;">Pyrex 7740</td>
			<td style="width:191px;">Tubing for sample embedding</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:247px;">Glycerol</td>
			<td style="width:136px;">Fisher Scientific</td>
			<td style="width:393px;">BP229-4</td>
			<td style="width:191px;">Fill for sample chamber</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:247px;">Phosphate-buffered saline</td>
			<td style="width:136px;">Fisher Scientific</td>
			<td style="width:393px;">BP39920</td>
			<td style="width:191px;">Rinse solution for mouse hearts</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:247px;">Paraformaldehyde</td>
			<td style="width:136px;">Electron microscopy sciences</td>
			<td style="width:393px;">RT-15700</td>
			<td style="width:191px;">First incubation solution</td>
		</tr>
		<tr height="80">
			<td height="80" style="height:80px;width:247px;">Acrylamide</td>
			<td style="width:136px;">Wako Chemicals</td>
			<td style="width:393px;">AAL-107</td>
			<td style="width:191px;">Mixed with 2,2&#39;-Azobis dihydrochloride for second incubation solution for mouse hearts</td>
		</tr>
		<tr height="60">
			<td height="60" style="height:60px;width:247px;">2,2&#39;-Azobis dihydrochloride</td>
			<td style="width:136px;">Wako Chemicals</td>
			<td style="width:393px;">VA-044</td>
			<td style="width:191px;">Mixed with Acrylamide for second incubation solution for mouse hearts</td>
		</tr>
		<tr height="60">
			<td height="60" style="height:60px;width:247px;">Sodium dodecyl sulfate&#160;</td>
			<td style="width:136px;">Sigma Aldrich</td>
			<td style="width:393px;">71725</td>
			<td style="width:191px;">Mixed with Boric acid for third incubtion solution for mouse hearts</td>
		</tr>
		<tr height="60">
			<td height="60" style="height:60px;width:247px;">Boric acid</td>
			<td style="width:136px;">Fischer Scientific</td>
			<td style="width:393px;">A74-1</td>
			<td style="width:191px;">Mixed with Sodium dodecyl sulfate for third incubtion solution for mouse hearts</td>
		</tr>
		<tr height="80">
			<td height="80" style="height:80px;width:247px;">Sigma D2158</td>
			<td style="width:136px;">Sigma Aldrich</td>
			<td style="width:393px;">D2158</td>
			<td style="width:191px;">Mixed with PB, Tween-20, and Sodium azide as a refractive index matching solution</td>
		</tr>
		<tr height="80">
			<td height="80" style="height:80px;width:247px;">Tween-20</td>
			<td style="width:136px;">Sigma Aldrich</td>
			<td>11332465001</td>
			<td style="width:191px;">Mixed with Sigma D2158, PB, and Sodium azide as a refractive index matching solution</td>
		</tr>
		<tr height="60">
			<td height="60" style="height:60px;width:247px;">Sodium azide</td>
			<td style="width:136px;">Sigma Aldrich</td>
			<td>S2002</td>
			<td style="width:191px;">Mixed with Sigma D2158, PB, and Tween-20 as a refractive index matching solution</td>
		</tr>
		<tr height="60">
			<td height="60" style="height:60px;width:247px;">Adeno-associated virus vector 9 with a cardiac-specific Troponin T promoter tagged with GFP</td>
			<td style="width:136px;">Vector Biolabs</td>
			<td style="width:393px;">VB2045</td>
			<td style="width:191px;">Expresses GFP when bound to ROMK</td>
		</tr>
		<tr height="60">
			<td height="60" style="height:60px;width:247px;">DC Servo Motor Actuator</td>
			<td style="width:136px;">Thorlabs</td>
			<td style="width:393px;">Z825B</td>
			<td style="width:191px;">Used for movement of sample in axial direction within light sheet</td>
		</tr>
		<tr height="60">
			<td height="60" style="height:60px;width:247px;">K-Cube Brushed DC Servo Motor Controller</td>
			<td style="width:136px;">Thorlabs</td>
			<td style="width:393px;">KDC101</td>
			<td style="width:191px;">Connects to motor actuator and controls movement of the actuator</td>
		</tr>
		<tr height="60">
			<td height="60" style="height:60px;width:247px;">Amira</td>
			<td style="width:136px;">FEI Software</td>
			<td style="width:393px;">N/A</td>
			<td style="width:191px;">Visualization software for producing 2-D and 3-D images</td>
		</tr>
	</tbody>
</table>

light-sheet fluorescence microscopy for the study of the murine heart

Light-sheet fluorescence microscopy has been widely used for rapid image acquisition with a high axial resolution from micrometer to millimeter scale. Traditional light-sheet techniques involve the use of a single illumination beam directed orthogonally at sample tissue. Images of large samples that are produced using a single illumination beam contain stripes or artifacts and suffer from a reduced resolution due to the scattering and absorption of light by the tissue. This study uses a dual-sided illumination beam and a simplified CLARITY optical clearing technique for the murine heart. These techniques allow for deeper imaging by removing lipids from the heart and produce a large field of imaging, greater than 10 x 10 x 10 mm3. As a result, this strategy enables us to quantify the ventricular dimensions, track the cardiac lineage, and localize the spatial distribution of cardiac-specific proteins and ion-channels from the post-natal to adult mouse hearts with sufficient contrast and resolution.

The technique described here used a dual-sided illumination beam combined with an optical clearing of mouse heart tissue samples to achieve a deeper imaging depth and a larger imaging volume with sufficient imaging resolution (Figure 1). To calibrate the system, fluorescent beads were placed inside the glass tubing and within the imaging system. The beads were then imaged and visualized in the x-y plane, y-z plane, and in the x-z plane, to obtain the point sp...

Watch this Scientific Journal Video about Light-sheet Fluorescence Microscopy for the Study of the Murine Heart at JoVE.com

Light-sheet Fluorescence Microscopy for the Study of the Murine Heart

This study uses a dual-sided illumination light-sheet fluorescence microscopy (LSFM) technique combined with optical clearing to study the murine heart.

Light-sheet fluorescence microscopy has been widely used for rapid image acquisition with a high axial resolution from micrometer to millimeter scale. ...

light-sheet-fluorescence-microscopy-for-the-study-of-the-murine-heart

Research

JoVE Journal

Bioengineering

9.2K Views.  University of California Los Angeles. This study uses a dual-sided illumination light-sheet fluorescence microscopy (LSFM) technique combined with optical clearing to study the murine heart.

Video: Light-sheet Fluorescence Microscopy for the Study of the Murine Heart

Design of a Cyclic Pressure Bioreactor for the Ex Vivo Study of Aortic Heart Valves

The aortic valve, located between the left ventricle and the aorta, allows for unidirectional blood flow, preventing backflow into the ventricle. Aortic valve leaflets are composed of interstitial cells suspended within an extracellular matrix (ECM) and are lined with an endothelial cell monolayer. The valve withstands a harsh, dynamic environment and is constantly exposed to shear, flexion, tension, and compression. Research has shown calcific lesions in diseased valves occur in areas of high mechanical stress as a result of endothelial disruption or interstitial matrix damage1-3. Hence, it is not surprising that epidemiological studies have shown high blood pressure to be a leading risk factor in the onset of aortic valve disease4. 
The only treatment option currently available for valve disease is surgical replacement of the diseased valve with a bioprosthetic or mechanical valve5. Improved understanding of valve biology in response to physical stresses would help elucidate the mechanisms of valve pathogenesis. In turn, this could help in the development of non-invasive therapies such as pharmaceutical intervention or prevention. Several bioreactors have been previously developed to study the mechanobiology of native or engineered heart valves6-9. Pulsatile bioreactors have also been developed to study a range of tissues including cartilage10, bone11 and bladder12. The aim of this work was to develop a cyclic pressure system that could be used to elucidate the biological response of aortic valve leaflets to increased pressure loads. 
The system consisted of an acrylic chamber in which to place samples and produce cyclic pressure, viton diaphragm solenoid valves to control the timing of the pressure cycle, and a computer to control electrical devices. The pressure was monitored using a pressure transducer, and the signal was conditioned using a load cell conditioner. A LabVIEW program regulated the pressure using an analog device to pump compressed air into the system at the appropriate rate. The system mimicked the dynamic transvalvular pressure levels associated with the aortic valve; a saw tooth wave produced a gradual increase in pressure, typical of the transvalvular pressure gradient that is present across the valve during diastole, followed by a sharp pressure drop depicting valve opening in systole. The LabVIEW program allowed users to control the magnitude and frequency of cyclic pressure. The system was able to subject tissue samples to physiological and pathological pressure conditions. This device can be used to increase our understanding of how heart valves respond to changes in the local mechanical environment.

Design of a Cyclic Pressure Bioreactor for the Ex Vivo Study of Aortic Heart Valves

A cyclic pressure bioreactor capable of subjecting heart valve tissue to physiological and pathological pressure conditions has been designed. A LabVIEW program allows users to control pressure magnitude, amplitude and frequency. This device can be used to study the mechanobiology of heart valve tissue or isolated cells.

The aortic valve, located between the left ventricle and the aorta, allows for unidirectional blood flow, preventing backflow into the ventricle. Aortic ...

Patient-specific Modeling of the Heart: Estimation of Ventricular Fiber Orientations

Patient-specific simulations of heart (dys)function aimed at personalizing cardiac therapy are hampered by the absence of in vivo imaging technology for clinically acquiring myocardial fiber orientations. The objective of this project was to develop a methodology to estimate cardiac fiber orientations from in vivo images of patient heart geometries. An accurate representation of ventricular geometry and fiber orientations was reconstructed, respectively, from high-resolution ex vivo structural magnetic resonance (MR) and diffusion tensor (DT) MR images of a normal human heart, referred to as the atlas. Ventricular geometry of a patient heart was extracted, via semiautomatic segmentation, from an in vivo computed tomography (CT) image. Using image transformation algorithms, the atlas ventricular geometry was deformed to match that of the patient. Finally, the deformation field was applied to the atlas fiber orientations to obtain an estimate of patient fiber orientations. The accuracy of the fiber estimates was assessed using six normal and three failing canine hearts. The mean absolute difference between inclination angles of acquired and estimated fiber orientations was 15.4 &deg;. Computational simulations of ventricular activation maps and pseudo-ECGs in sinus rhythm and ventricular tachycardia indicated that there are no significant differences between estimated and acquired fiber orientations at a clinically observable level.The new insights obtained from the project will pave the way for the development of patient-specific models of the heart that can aid physicians in personalized diagnosis and decisions regarding electrophysiological interventions.

A methodology to estimate ventricular fiber orientations from in vivo images of patient heart geometries for personalized modeling is described. Validation of the methodology performed using normal and failing canine hearts demonstrate that that there are no significant differences between estimated and acquired fiber orientations at a clinically observable level.

Patient-specific  simulations of heart (dys)function aimed at personalizing cardiac therapy are hampered  by the absence of in vivo imaging technology for ...

Creating Adhesive and Soluble Gradients for Imaging Cell Migration with Fluorescence Microscopy

Cells can sense and migrate towards higher concentrations of adhesive cues such as the glycoproteins of the extracellular matrix and soluble cues such as growth factors. Here, we outline a method to create opposing gradients of adhesive and soluble cues in a microfluidic chamber, which is compatible with live cell imaging. A copolymer of poly-L-lysine and polyethylene glycol (PLL-PEG) is employed to passivate glass coverslips and prevent non-specific adsorption of biomolecules and cells. Next, microcontact printing or dip pen lithography are used to create tracks of streptavidin on the passivated surfaces to serve as anchoring points for the biotinylated peptide arginine-glycine-aspartic acid (RGD) as the adhesive cue. A microfluidic device is placed onto the modified surface and used to create the gradient of adhesive cues (100% RGD to 0% RGD) on the streptavidin tracks. Finally, the same microfluidic device is used to create a gradient of a chemoattractant such as fetal bovine serum (FBS), as the soluble cue in the opposite direction of the gradient of adhesive cues.

A method for the assembly of adhesive and soluble gradients in a microscopy chamber for live cell migration studies is described. The engineered environment combines antifouling surfaces and adhesive tracks with solution gradients and therefore allows one to determine the relative importance of guidance cues.

Cells can sense and migrate towards higher concentrations of adhesive cues such as the glycoproteins of the extracellular matrix and soluble cues such as ...

3D Orbital Tracking in a Modified Two-photon Microscope: An Application to the Tracking of Intracellular Vesicles

The objective of this video protocol is to discuss how to perform and analyze a three-dimensional fluorescent orbital particle tracking experiment using a modified two-photon microscope1. As opposed to conventional approaches (raster scan or wide field based on a stack of frames), the 3D orbital tracking allows to localize and follow with a high spatial (10 nm accuracy) and temporal resolution (50 Hz frequency response) the 3D displacement of a moving fluorescent particle on length-scales of hundreds of microns2. The method is based on a feedback algorithm that controls the hardware of a two-photon laser scanning microscope in order to perform a circular orbit around the object to be tracked: the feedback mechanism will maintain the fluorescent object in the center by controlling the displacement of the scanning beam3-5. To demonstrate the advantages of this technique, we followed a fast moving organelle, the lysosome, within a living cell6,7. Cells were plated according to standard protocols, and stained using a commercially lysosome dye. We discuss briefly the hardware configuration and in more detail the control software, to perform a 3D orbital tracking experiment inside living cells. We discuss in detail the parameters required in order to control the scanning microscope and enable the motion of the beam in a closed orbit around the particle. We conclude by demonstrating how this method can be effectively used to track the fast motion of a labeled lysosome along microtubules in 3D within a live cell. Lysosomes can move with speeds in the range of 0.4-0.5 &#181;m/sec, typically displaying a directed motion along the microtubule network8.

In this video protocol we track - at high speed and in three dimensions - fluorescently labeled lysosomes within living cells, using the orbital tracking method in a modified two-photon microscope.

The objective of this video protocol is to discuss how to perform and analyze a three-dimensional fluorescent orbital particle tracking experiment using a ...

Single Molecule Fluorescence Microscopy on Planar Supported Bilayers

In the course of a single decade single molecule microscopy has changed from being a secluded domain shared merely by physicists with a strong background in optics and laser physics to a discipline that is now enjoying vivid attention by life-scientists of all venues 1. This is because single molecule imaging has the unique potential to reveal protein behavior in situ in living cells and uncover cellular organization with unprecedented resolution below the diffraction limit of visible light 2. Glass-supported planar lipid bilayers (SLBs) are a powerful tool to bring cells otherwise growing in suspension in close enough proximity to the glass slide so that they can be readily imaged in noise-reduced Total Internal Reflection illumination mode 3,4. They are very useful to study the protein dynamics in plasma membrane-associated events as diverse as cell-cell contact formation, endocytosis, exocytosis and immune recognition. Simple procedures are presented how to generate highly mobile protein-functionalized SLBs in a reproducible manner, how to determine protein mobility within and how to measure protein densities with the use of single molecule detection. It is shown how to construct a cost-efficient single molecule microscopy system with TIRF illumination capabilities and how to operate it in the experiment.

Preparation of protein-functionalized planar glass-supported lipid bilayers, determination of protein mobility within and measurement of protein densities is shown here. A roadmap to building a noise-reduced Total Internal Reflection microscope is outlined, which allows visualizing single bilayer-resident fluorochromes with high spatiotemporal resolution.

In the course of a single decade single molecule microscopy has changed from being a secluded domain shared merely by physicists with a strong background ...

Light-sheet Fluorescence Microscopy to Capture 4-Dimensional Images of the Effects of Modulating Shear Stress on the Developing Zebrafish Heart

The hemodynamic forces experienced by the heart influence cardiac development, especially trabeculation, which forms a network of branching outgrowths from the myocardium. Genetic program defects in the Notch signaling cascade are involved in ventricular defects such as Left Ventricular Non-Compaction Cardiomyopathy or Hypoplastic Left Heart Syndrome. Using this protocol, it can be determined that shear stress driven trabeculation and Notch signaling are related to one another. Using Light-sheet Fluorescence Microscopy, visualization of the developing zebrafish heart was possible. In this manuscript, it was assessed whether hemodynamic forces modulate the initiation of trabeculation via Notch signaling and thus, influence contractile function occurs. For qualitative and quantitative shear stress analysis, 4-D (3-D+time) images were acquired during zebrafish cardiac morphogenesis, and integrated light-sheet fluorescence microscopy with 4-D synchronization captured the ventricular motion. Blood viscosity was reduced via gata1a-morpholino oligonucleotides (MO) micro-injection to decrease shear stress, thereby, down-regulating Notch signaling and attenuating trabeculation. Co-injection of Nrg1 mRNA with gata1a MO rescued Notch-related genes to restore trabeculation. To confirm shear stress driven Notch signaling influences trabeculation, cardiomyocyte contraction was further arrested via tnnt2a-MO to reduce hemodynamic forces, thereby, down-regulating Notch target genes to develop a non-trabeculated myocardium. Finally, corroboration of the expression patterns of shear stress-responsive Notch genes was conducted by subjecting endothelial cells to pulsatile flow. Thus, the 4-D light-sheet microscopy uncovered hemodynamic forces underlying Notch signaling and trabeculation with clinical relevance to non-compaction cardiomyopathy.

Here, we present a protocol to visualize developing hearts in zebrafish in 4-Dimensions (4-D). 4-D imaging, via light-sheet fluorescence microscopy (LSFM), takes 3-Dimensional (3-D) images over time, to reconstruct developing hearts. We show qualitatively and quantitatively that shear stress activates endocardial Notch signaling during chamber development, which promotes cardiac trabeculation.

The hemodynamic forces experienced by the heart influence cardiac development, especially trabeculation, which forms a network of branching outgrowths ...

Intra-cardiac Side-Firing Light Catheter for Monitoring Cellular Metabolism using Transmural Absorbance Spectroscopy of Perfused Mammalian Hearts

Absorbance spectroscopy of cardiac muscle provides non-destructive assessment of cytosolic and mitochondrial oxygenation via myoglobin and cytochrome absorbance respectively. In addition, numerous aspects of the mitochondrial metabolic status such as membrane potential and substrate entry can also be estimated. To perform cardiac wall transmission optical spectroscopy, a commercially available side-firing optical fiber catheter is placed in the left ventricle of the isolated perfused heart as a light source. Light passing through the heart wall is collected with an external optical fiber to perform optical spectroscopy of the heart in near real- time. The transmission approach avoids numerous surface scattering interference occurring in widely used reflection approaches. Changes in transmural absorbance spectra were deconvolved using a library of chromophore reference spectra, providing quantitative measures of all the known cardiac chromophores simultaneously. This spectral deconvolution approach eliminated intrinsic errors that may result from using common dual wavelength methods applied to overlapping absorbance spectra, as well as provided a quantitative evaluation of the goodness of fit. A custom program was designed for data acquisition and analysis, which permitted the investigator to monitor the metabolic state of the preparation during the experiment. These relatively simple additions to the standard heart perfusion system provide a unique insight into the metabolic state of the heart wall in addition to conventional measures of contraction, perfusion, and substrate/oxygen extraction.

Here we introduce a method for using an intra-ventricle optical catheter in perfused hearts to perform absorbance spectroscopy across the heart wall. The data obtained provides robust information on tissue oxygen tension as well as substrate utilization and membrane potential simultaneously with cardiac performance measures in this ubiquitous preparation.

Absorbance spectroscopy of cardiac muscle provides non-destructive assessment of cytosolic and mitochondrial oxygenation via myoglobin and cytochrome ...

Biaxial Mechanical Characterizations of Atrioventricular Heart Valves

Extensive biaxial mechanical testing of the atrioventricular heart valve leaflets can be utilized to derive&#160;optimal parameters used in constitutive models, which provide a mathematical representation of the mechanical function of those structures. This presented biaxial mechanical testing protocol involves (i) tissue acquisition, (ii) the preparation of tissue specimens, (iii) biaxial mechanical testing, and (iv) postprocessing of the acquired data. First, tissue acquisition requires obtaining porcine or ovine hearts from a local Food and Drug Administration-approved abattoir for later dissection to retrieve the valve leaflets. Second, tissue preparation requires using tissue specimen cutters on the leaflet tissue to extract a clear zone for testing. Third, biaxial mechanical testing of the leaflet specimen requires the use of a commercial biaxial mechanical tester, which consists of force-controlled, displacement-controlled, and stress-relaxation testing protocols to characterize the leaflet tissue&#39;s mechanical properties. Finally, post-processing requires the use of data image correlation techniques and force and displacement readings to summarize the tissue&#39;s mechanical behaviors in response to external loading. In general, results from biaxial testing demonstrate that the leaflet tissues yield a nonlinear, anisotropic mechanical response. The presented biaxial testing procedure is advantageous to other methods since the method presented here allows for a more comprehensive characterization of the valve leaflet tissue under one unified testing scheme, as opposed to separate testing protocols on different tissue specimens. The proposed testing method has its limitations in that shear stress is potentially present in the tissue sample. However, any potential shear is presumed negligible.

This protocol involves characterizations of atrioventricular valve leaflets with force-controlled, displacement-controlled, and stress-relaxation biaxial mechanical testing procedures. Results acquired with this protocol can be used for constitutive model development to simulate the mechanical behavior of functioning valves under a finite element simulation framework.

Extensive biaxial mechanical testing of the atrioventricular heart valve leaflets can be utilized to derive&#160;optimal parameters used in constitutive ...

A Quantitative Fluorescence Microscopy-based Single Liposome Assay for Detecting the Compositional Inhomogeneity Between Individual Liposomes

Most research employing liposomes as membrane model systems or drug delivery carriers relies on bulk read-out techniques and thus intrinsically assumes all liposomes of the ensemble to be identical. However, new experimental platforms able to observe liposomes at the single-particle level have made it possible to perform highly sophisticated and quantitative studies on protein-membrane interactions or drug carrier properties on individual liposomes, thus avoiding errors from ensemble averaging. Here we present a protocol for preparing, detecting, and analyzing single liposomes using a fluorescence-based microscopy assay, facilitating such single-particle measurements. The setup allows for imaging individual liposomes in a massive parallel manner and is employed to reveal intra-sample size and compositional inhomogeneities. Additionally, the protocol describes the advantages of studying liposomes at the single liposome level, the limitations of the assay, and the important features to be considered when modifying it to study other research questions.

This protocol describes the fabrication of liposomes and how these can be immobilized on a surface and imaged individually in a massive parallel manner using fluorescence microscopy. This allows for the quantification of the size and compositional inhomogeneity between single liposomes of the population.

Most research employing liposomes as membrane model systems or drug delivery carriers relies on bulk read-out techniques and thus intrinsically assumes ...

Transplantation of a 3D Bioprinted Patch in a Murine Model of Myocardial Infarction

Testing regenerative properties of 3D bioprinted cardiac patches in vivo using murine models of heart failure via permanent left anterior descending (LAD) ligation is a challenging procedure and has a high mortality rate due to its nature. We developed a method to consistently transplant bioprinted patches of cells and hydrogels onto the epicardium of an infarcted mouse heart to test their regenerative properties in a robust and feasible way. First, a deeply anesthetized mouse is carefully intubated and ventilated. Following left lateral thoracotomy (surgical opening of the chest), the exposed LAD is permanently ligated and the bioprinted patch transplanted onto the epicardium. The mouse quickly recovers from the procedure after chest closure. The advantages of this robust and quick approach include a predicted 28-day mortality rate of up to 30% (lower than the 44% reported by other studies using a similar model of permanent LAD ligation in mice). Moreover, the approach described in this protocol is versatile and could be adapted to test bioprinted patches using different cell types or hydrogels where high numbers of animals are needed to optimally power studies. Overall, we present this as an advantageous approach which may change preclinical testing in future studies for the field of cardiac regeneration and tissue engineering.

This protocol aims to transplant a 3D bioprinted patch onto the epicardium of infarcted mice modeling heart failure. It includes details regarding anesthesia, the surgical chest opening, permanent ligation of the left anterior descending (LAD) coronary artery and application of a bioprinted patch onto the infarcted area of the heart.

Testing regenerative properties of 3D bioprinted cardiac patches in vivo using murine models of heart failure via permanent left anterior descending (LAD) ...