Name: Magnetic Adjustment of Afterload in Engineered Heart Tissues (Video) | JoVE Journal
Uploaded: 2020-05-05T13:30:00.000+00:00
Duration: 9 min 40 s
Description: Learn magnetic afterload tuning for engineered heart tissues using magnetically responsive silicone racks and fixed polarity magnets. This non-invasive method enables customizable mechanical stimuli studies over prolonged culture periods.

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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.

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</ol>

TE and MNH are co-founders of EHT Technologies GmbH. All other authors have nothing to disclose.

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>&lt;strong&gt;MMC-100-01000&lt;/strong&gt;</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

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 (“magnet spacings”) 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 deflection was obser...

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 ...

magnetic-adjustment-of-afterload-in-engineered-heart-tissues

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Learn magnetic afterload tuning for engineered heart tissues using magnetically responsive silicone racks and fixed polarity magnets. This non-invasive method enables customizable mechanical stimuli studies over prolonged culture periods.

Magnetic Adjustment of Afterload in Engineered Heart Tissues

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