Name: magnetic adjustment of afterload in engineered heart tissues
Uploaded: 2020-05-05T13:30:00
Description: Watch this Scientific Journal Video about Magnetic Adjustment of Afterload in Engineered Heart Tissues at JoVE.com

The authors thank Jutta Starbatty for her support in tissue culture work, Axel Kirchhof for photography, Alice Casagrande Cesconetto for editing work, and a special thanks to B&#252;lent Aksehirlioglu for technical support in the development of this device. B.B. was supported by a DZHK (German Centre for Cardiovascular Research) Scholar Grant, M.L.R. by a Whitaker International Postdoctoral Scholar Grant and M.N.H. by funds from the DZHK.

1. Preparation of the Afterload Tuning Platform
NOTE: The steps involved in this portion of the protocol are not time-sensitive.
<ol>
	<li>Manufacturing the magnetically responsive silicone racks 
	NOTE: These racks serve as the culture platform for EHTs. Each EHT is suspended between two silicone posts, which impart afterload to the tissue. The degree of afterload is directly related to the stiffness of these posts. To enable magnetic afterload tuning,...

<ol>
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H., Downing, S. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Afterload+as+a+primary+determinat+of+ventricular+performance.">Afterload as a primary determinat of ventricular performance.</a> The American Journal of Physiology. 204, 604-610 (1963).</li><li>Hirt, M. N., 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=Increased+afterload+induces+pathological+cardiac+hypertrophy:+a+new+in+vitro+model.">Increased afterload induces pathological cardiac hypertrophy: a new in vitro model.</a> Basic Research in Cardiology. 107 (6), 307 (2012).</li><li>Hirt, M. 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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=Molecular+basis+of+physiological+heart+growth:+fundamental+concepts+and+new+players.">Molecular basis of physiological heart growth: fundamental concepts and new players.</a> Nature Reviews Molecular Cell Biology. 14 (1), 38-48 (2013).</li><li>Stenzig, 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=DNA+methylation+in+an+engineered+heart+tissue+model+of+cardiac+hypertrophy:+common+signatures+and+effects+of+DNA+methylation+inhibitors.">DNA methylation in an engineered heart tissue model of cardiac hypertrophy: common signatures and effects of DNA methylation inhibitors.</a> Basic Research in Cardiology. 111 (1), 9 (2016).</li><li>Werner, T. R., Kunze, A. C., Stenzig, J., Eschenhagen, T., Hirt, M. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Blockade+of+miR-140-3p+prevents+functional+deterioration+in+afterload-enhanced+engineered+heart+tissue.">Blockade of miR-140-3p prevents functional deterioration in afterload-enhanced engineered heart tissue.</a> Scientific Reports. 9 (1), 11494 (2019).</li><li>Leonard, A., 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=Afterload+promotes+maturation+of+human+induced+pluripotent+stem+cell+derived+cardiomyocytes+in+engineered+heart+tissues.">Afterload promotes maturation of human induced pluripotent stem cell derived cardiomyocytes in engineered heart tissues.</a> Journal of Molecular and Cellular Cardiology. 118, 147-158 (2018).</li><li>Rodriguez, M. L., Werner, T. R., Becker, B., Eschenhagen, T., Hirt, M. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Magnetics-Based+Approach+for+Fine-Tuning+Afterload+in+Engineered+Heart+Tissues.">Magnetics-Based Approach for Fine-Tuning Afterload in Engineered Heart Tissues.</a> ACS Biomaterials Science &amp; Engineering. 5 (7), 3663-3675 (2019).</li><li>Mannhardt, I., 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=Automated+Contraction+Analysis+of+Human+Engineered+Heart+Tissue+for+Cardiac+Drug+Safety+Screening.">Automated Contraction Analysis of Human Engineered Heart Tissue for Cardiac Drug Safety Screening.</a> Journal of Visualized Experiments: JoVE. (122), e55461 (2017).</li></ol>

The protocol outlined herein describes a new technique for magnetically altering afterload in engineered heart tissues. This technique relies upon the use of a piezoelectric stage to translate a plate of strong magnets towards and away from magnetically responsive racks of silicone posts. The closer the two sets of magnets, the stronger the afterload experienced by the EHTs cultured on them.
There are several steps that are critical to the successful production and use of this system. While fa...

Afterload is the systolic load on the ventricle after it has begun to eject blood1. During cardiac development, an appropriate afterload is of critical importance for cardiomyocyte maturation2. In adulthood, low levels of ventricular afterload (e.g., in bedridden patients with high-level spinal cord injury3 or in very special cases like spaceflight4) can result in hypotrophy of the heart. Conversely, high afterload can lead to cardiac hypertrophy5. While cardiac hypertrophy in endurance athletes or pregnant women is considered beneficial and physiological, hypertrophy associated with long-term arterial hypertension or severe aortic valve stenosis is detrimental as it predisposes one to cardiac arrhythmias and heart failure6. Although the 5-year mortality rate for heart failure patients has reduced from ~70% in the 1980s6 to 40&#8211;50%7 presently, there is still a great need for new therapeutic treatment options for this highly prevalent condition (currently 2.2% of the population in the Western world)8.
In order to investigate the molecular mechanisms of pathological cardiac hypertrophy and to test preventive or therapeutic strategies for treating this disease, in vivo models of afterload have been developed9,10,11,12. While these models have offered beneficial insights into the effects of afterload on ventricular performance, they do not allow for fine control over afterload magnitude. Alternatively, in vitro studies of afterload performed on excised hearts and muscle preparations allow for finer control over tissue loading, but these models are not conducive to longitudinal studies13,14,15.
To overcome these issues, we developed an in vitro model of elevated afterload in engineered heart tissues (EHTs)16,17. This model is a 3-dimensional culture format for rat heart cells embedded in a fibrin matrix suspended between flexible hollow silicone posts. These tissues beat spontaneously (against the resistance of the silicone posts) and perform auxotonic work. We have increased afterload applied to EHTs by a factor of 12 in previous experiments by the insertion of rigid metal braces into the hollow silicone posts for one week. This led to a multitude of changes, characteristic of pathological cardiac hypertrophy18,19,20: cardiomyocyte hypertrophy, partial necroptosis, a decline in contractile force, the impairment of tissue relaxation, reactivation of the fetal gene program, a metabolic shift from fatty acid oxidation to anaerobic glycolysis, and an increase in fibrosis. Though this procedure has been successfully employed in several studies17,21,22, it has some disadvantages. There are only two states, low or very high (12-fold) afterload, and the procedure requires manual handling of the EHTs, which limits its temporal flexibility and poses the risk of contamination.
Recently, Leonard et al. used a similar technique to modulate afterload in EHTs cultured on silicone posts23. Braces of varying lengths were placed around the outside of the posts to restrict their bending motion. The authors of this study reported that a singular small-to-medium increase in load enhanced force development and maturation of human iPS-derived EHTs, while higher loads resulted in a pathological state. However, similar to our own system, this technique only allows for singular increases in afterload, the magnitude of which is dictated by the length of the braces. As such, fine alterations in afterload, modifications in afterload over time, and precise loading regimens are not possible with these techniques.
Here, we provide the protocol for a system that can be used to modulate post-resistance, i.e., afterload of EHTs magnetically24. This platform facilitates the fine-tuning of afterload, enables user-defined afterload regimens, and ensures EHT sterility.

<table>
	<tbody>
		<tr>
			<td>Cylindrical plate magnets</td>
			<td>HKCM</td>
			<td>9962-55184</td>
			<td>h = 14 mm, d = 13 mm</td>
		</tr>
		<tr>
			<td>Cylindrical post magnets</td>
			<td>HKCM</td>
			<td>9962-63571</td>
			<td>h = 2 mm, d = 0.5 mm</td>
		</tr>
		<tr>
			<td>Dental wire</td>
			<td>Ormco</td>
			<td>266-1316</td>
			<td>d = 0.016 inches (0.406 mm)</td>
		</tr>
		<tr>
			<td>GraphPad</td>
			<td>GraphPad Software, La Jolla, California, USA</td>
			<td>version 6.00 for Windows</td>
			<td></td>
		</tr>
		<tr>
			<td>Motion control software for piezo motor</td>
			<td>Micronix USA</td>
			<td></td>
			<td>free download on manufacturer homepage</td>
		</tr>
		<tr>
			<td>Motion controller for piezo motor</td>
			<td>Micronix USA</td>
			<td>MMC-100-01000</td>
			<td></td>
		</tr>
		<tr>
			<td>Optical contractility analysis platform</td>
			<td>EHT technologies</td>
			<td>A0001</td>
			<td></td>
		</tr>
		<tr>
			<td>Piezoelectric linear motor</td>
			<td>Micronix USA</td>
			<td>PPS-20-15206</td>
			<td>fitted with linear optical encoder, incubator-environment compatible</td>
		</tr>
		<tr>
			<td>Styrene Rod</td>
			<td>Plastruct</td>
			<td>MR-15</td>
			<td>d= 0.015 inches (0.381 mm)</td>
		</tr>
		<tr>
			<td>USB camera</td>
			<td>Reichelt Elektronik</td>
			<td>REFLECTA 66142</td>
			<td></td>
		</tr>
	</tbody>
</table>

magnetic adjustment of afterload in engineered heart tissues

Afterload is known to drive the development of both physiological and pathological cardiac states. As such, studying the outcomes of altered afterload states could yield important insights into the mechanisms controlling these critical processes. However, an experimental technique for precisely fine-tuning afterload in heart tissue over time is currently lacking. Here, a newly developed magnetics-based technique for achieving this control in engineered heart tissues (EHTs) is described. In order to produce magnetically responsive EHTs (MR-EHTs), the tissues are mounted on hollow silicone posts, some of which contain small permanent magnets. A second set of permanent magnets is press-fit into an acrylic plate such that they are oriented with the same polarity and are axially-aligned with the post magnets. To adjust afterload, this plate of magnets is translated toward (higher afterload) or away (lower afterload) from the post magnets using a piezoelectric stage fitted with an encoder. The motion control software used to adjust stage positioning allows for the development of user-defined afterload regimens while the encoder ensures that the stage corrects for any inconsistencies in its location. This work describes the fabrication, calibration, and implementation of this system to enable the development of similar platforms in other labs around the world. Representative results from two separate experiments are included to exemplify the range of different studies that can be performed using this system.

Magnet post stiffness quantification 
A horizontally oriented magnetically responsive silicone post was mounted in a fixed position, and an axially aligned calibration magnet was placed at several defined distances (&#8220;magnet spacings&#8221;) from this post. Test loads of known weight were suspended from the end of the silicone post, causing the post to bend. This deflection was quantified optically. A linear relationship between the gravitational force of the test load and resulting post deflec...

Watch this Scientific Journal Video about Magnetic Adjustment of Afterload in Engineered Heart Tissues at JoVE.com

Magnetic Adjustment of Afterload in Engineered Heart Tissues

This protocol provides detailed methods describing the fabrication and implementation of a magnetics-based afterload tuning platform for engineered heart tissues.

Afterload is known to drive the development of both physiological and pathological cardiac states. As such, studying the outcomes of altered afterload ...

This system can be used to expose engineered heart tissues to varying regimens of afterload, in order to study the effects of these stimuli on tissue force development, remodeling and maturation. Our technique allows one to precisely subject beating tissues to a broad range of customizable afterload routines over prolonged periods of culture without even needing to open the cell culture plate. Our method could be modified to control afterload in other muscle tissue culture system, such as skeletal muscle, smooth muscle or excised papillary muscle.Since our systems approach is rather unique and features technical aspects that many scientists are not familiar with, visual demonstration may aid in recreating our setup. To manufacture the magnetically responsive silicone racks, acquire the 24 well plate can paddle racks of silicone posts described in the text protocol. Using a fixed polarity, lubricate the magnets with water and insert them one at a time into the outermost posts of the silicone racks.Use a blended piece of stainless steel dental wire to carefully push them to the bottom of the hollow post cavity. Up to five magnets can be stacked in each post. Use round nose pliers to bend stainless steel dental wire into braces 11.25 millimeters wide and 15 millimeters long.To ensure the correct dimensions are achieved, one can use a self made jig to aid in the wire bending, then use wire cutters to cut the braces and the file to smooth the cutting surface. Lubricate the braces or posts with water and insert them into the silicone rack fixing the second and third to the outermost post in the process. Begin preparing the afterload the tuning device as described in the text protocol, attach to the magnet holder to the piezoelectric stage using a non magnetic material, this can be achieved using an L shaped piece of aluminum.To enable visual analysis of the tissues, install a light source within the afterload tuning device. Here an array of LEDs was employed to illuminate the engineer to heart tissues from below. To calibrate the afterload tuning system, mount one of the silicone racks and vertically using non magnetic materials, such that the magnetically responsive silicone posts are oriented horizontally.Now mount one of the plate magnets on a horizontally traveling linear stage such that it is axially aligned with the magnetically responsive post. Position the calibration magnet a defined distance from magnetically responsive silicone post using the horizontal stage. Place a camera to the side of this setup in order to be able to optically record the posts deflection under the influence of the test loads.Make sure that there is enough space below the post for the attached loads to hang freely. Take a picture of the post in the absence of any weights to use as a reference for the posts neutral position. Without changing the camera's perspective, attach one of the loads to the very end of the silicone post, then take a picture of the post bending under the influence of the weight.Now graph the deflection of the silicone post on the x-axis against the gravitational force of each test weight on the y-axis. This should yield a linear relationship between force and deflection. Plot a linear regression function passing through 00 and the acquire data.The slope of this function is the stiffness, k of the magnetically responsive silicone post at the tested magnet spacing. Repeat these steps at several spacings between dmax and a dmin. Here deflections at eight different magnet positions, ranging from about 31 millimeters to about five millimeters were analyzed.A lot of regression function through these values. For example, use nonlinear fit, one phase decay function in the analysis software. This regression function describes the relationship between magnet spacing and afterload.To prepare the afterload tuning device for experiments, connect the piezoelectric stage motor to the motion controller and connect the motion controller to the computer. Make sure the motion controller is also connected to a power source. Then start the motion controller platform software, connect the software to the piezo stage motor by selecting the port designated as the stage board during installation of the motion control software and then click the open port button.Go to the system panel, select open loop, in the loop drop down menu. Manually move the magnet plate to its highest position, the closest possible magnet spacing dmin. The magnet plate should make contact with the culture plate mount.Now go to the Motion Panel, like the zero button to reset the current position of the piezo stage to zero millimeters. Manually move the magnet blade to its lowest possible position, write down the encoder position to determine the range of motion for the piezoelectric stage motor. Set the travel limits in the system panel to values within the range of motion determined in the previous step.This prevents the magnet blade from bumping into the culture blade or the bottom of the afterload tuning device. Once again, move the magnet blade to its highest position and click the zero button. Go to the system panel and change the feedback loop mode to closed loop, doing this ensures that the stage will correct for any errors in its positioning.Click the save button in the store parameters box to store these settings in the system. Now place the 24 well culture plate containing engineered heart tissues on magnetically responsive silicone racks on the culture plate mount. To calculate the magnet spacing necessary to achieve a desired afterload, solve the nonlinear regression function determined earlier for d.Subtract dmin from the calculated magnet spacing, d. The result is the distance the magnet plate has to travel from its zero position to achieve the desired afterload. Type this value into the Target Position one input field in the Motion panel and click Go to adjust the engineered heart tissue's afterload to the calculated value.Control an MREHTs produced from rat hearts were cultured in the absence of magnetic afterload until a plateau in contractile force was reached. On this day, MREHTs and controlled EHTs had similar mean forces. Over the next week, the afterload exerted on MREHTs was incrementally increased from point nine one to six point eight five millinewton's per millimeter, while afterload for controlling EHTs remained constant.Mean contractile force increased with increasing afterload up to point nine five millinewton, which marks more than a three fold increase in force compared to the average value measured for controlled EHTs. Post deflection on the other hand decreased compared to control tissues. On the last day of culture the main deflection measured for MREHTs was only point one one millimeters, compared to point four eight millimeters for control EHT's.Rad EHTs on magnetically responsive silicone posts were cultured at a minimal afterload of point nine one millinewton per millimeter until a plateau and contractile force was reached. From this day onwards, MREHTs underwent a seven day afterload regimen which expose the EHTs to cycles of afterload alternating between point nine one and six point eight five millinewton per millimeter. The afterload of control EHT's was kept constant at point six zero millinewton per millimeter over the entire duration of culture.The observed differences were not statistically significant. Combined with optical contractility analysis, this method enables the real time measurement of short term contractile response to fluctuating magnitudes of afterload, which could be useful for investigating physiological muscle properties. Strong magnets may suddenly cling to each other, potentially causing injury to the user and damaging the magnets themselves, to avoid this, keep the magnet separated at a safe distance.

Research

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