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.

<ol>
	<li>Zipes, D. P., Libby, P., Bonow, R. O., Mann, D. L., Tomaselli, G. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. 11th edn. , (2018).</li><li>McCain, M. L., Yuan, H., Pasqualini, F. S., Campbell, P. H., Parker, K. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Matrix+elasticity+regulates+the+optimal+cardiac+myocyte+shape+for+contractility.">Matrix elasticity regulates the optimal cardiac myocyte shape for contractility.</a> American Journal of Physiology- Heart and Circulatory Physiology. 306 (11), 1525-1539 (2014).</li><li>de Groot, P. C., van Dijk, A., Dijk, E., Hopman, M. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preserved+cardiac+function+after+chronic+spinal+cord+injury.">Preserved cardiac function after chronic spinal cord injury.</a> Archives of Physical Medicine and Rehabilitation. 87 (9), 1195-1200 (2006).</li><li>Perhonen, M. 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=Cardiac+atrophy+after+bed+rest+and+spaceflight.">Cardiac atrophy after bed rest and spaceflight.</a> Journal of Applied Physiology. 91 (2), 645-653 (2001).</li><li>Levy, D., Larson, M. G., Vasan, R. S., Kannel, W. B., Ho, K. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+progression+from+hypertension+to+congestive+heart+failure.">The progression from hypertension to congestive heart failure.</a> Journal of the American Medical Association. 275 (20), 1557-1562 (1996).</li><li>Levy, D., 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=Long-term+trends+in+the+incidence+of+and+survival+with+heart+failure.">Long-term trends in the incidence of and survival with heart failure.</a> The New England Journal of Medicine. 347 (18), 1397-1402 (2002).</li><li>Maggioni, A. P., 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=EURObservational+Research+Programme:+regional+differences+and+1-year+follow-up+results+of+the+Heart+Failure+Pilot+Survey+(ESC-HF+Pilot).">EURObservational Research Programme: regional differences and 1-year follow-up results of the Heart Failure Pilot Survey (ESC-HF Pilot).</a> European Journal of Heart Failure. 15 (7), 808-817 (2013).</li><li>Mozaffarian, D., 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+disease+and+stroke+statistics--2015+update:+a+report+from+the+American+Heart+Association.">Heart disease and stroke statistics--2015 update: a report from the American Heart Association.</a> Circulation. 131 (4), 29 (2015).</li><li>Klautz, R. J., Teitel, D. F., Steendijk, P., van Bel, F., Baan, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Interaction+between+afterload+and+contractility+in+the+newborn+heart:+evidence+of+homeometric+autoregulation+in+the+intact+circulation.">Interaction between afterload and contractility in the newborn heart: evidence of homeometric autoregulation in the intact circulation.</a> Journal of the American College of Cardiology. 25 (6), 1428-1435 (1995).</li><li>Liedtke, A. J., Pasternac, A., Sonnenblick, E. H., Gorlin, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Changes+in+canine+ventricular+dimensions+with+acute+changes+in+preload+and+afterload.">Changes in canine ventricular dimensions with acute changes in preload and afterload.</a> The American Journal of Physiology. 223 (4), 820-827 (1972).</li><li>Toischer, K., 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=Differential+cardiac+remodeling+in+preload+versus+afterload.">Differential cardiac remodeling in preload versus afterload.</a> Circulation. 122 (10), 993-1003 (2010).</li><li>Zhang, H., 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=Cellular+Hypertrophy+and+Increased+Susceptibility+to+Spontaneous+Calcium-Release+of+Rat+Left+Atrial+Myocytes+Due+to+Elevated+Afterload.">Cellular Hypertrophy and Increased Susceptibility to Spontaneous Calcium-Release of Rat Left Atrial Myocytes Due to Elevated Afterload.</a> PloS one. 10 (12), 0144309 (2015).</li><li>Hori, M., 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=Loading+sequence+is+a+major+determinant+of+afterload-dependent+relaxation+in+intact+canine+heart.">Loading sequence is a major determinant of afterload-dependent relaxation in intact canine heart.</a> The American Journal of Physiology. 249, 747-754 (1985).</li><li>Schotola, H., 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=The+contractile+adaption+to+preload+depends+on+the+amount+of+afterload.">The contractile adaption to preload depends on the amount of afterload.</a> ESC Heart Failure. 4 (4), 468-478 (2017).</li><li>Sonnenblick, E. 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. 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=Deciphering+the+microRNA+signature+of+pathological+cardiac+hypertrophy+by+engineered+heart+tissue-+and+sequencing-technology.">Deciphering the microRNA signature of pathological cardiac hypertrophy by engineered heart tissue- and sequencing-technology.</a> Journal of Molecular and Cellular Cardiology. 81, 1-9 (2015).</li><li>Dorn, G. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+fuzzy+logic+of+physiological+cardiac+hypertrophy.">The fuzzy logic of physiological cardiac hypertrophy.</a> Hypertension. 49 (5), 962-970 (2007).</li><li>Hill, J. A., Olson, E. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cardiac+plasticity.">Cardiac plasticity.</a> The New England Journal of Medicine. 358 (13), 1370-1380 (2008).</li><li>Maillet, M., van Berlo, J. H., Molkentin, J. 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>

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>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 ...

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

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5.8K Views.  University Medical Center Hamburg-Eppendorf. This protocol provides detailed methods describing the fabrication and implementation of a magnetics-based afterload tuning platform for engineered heart tissues.

Video: Magnetic Adjustment of Afterload in Engineered Heart Tissues

Analysis of Cardiomyocyte Development using Immunofluorescence in Embryonic Mouse Heart

During heart development, the generation of myocardial-specific structural and functional units including sarcomeres, contractile myofibrils, intercalated discs, and costameres requires the coordinated assembly of multiple components in time and space. Disruption in assembly of these components leads to developmental heart defects. Immunofluorescent staining techniques are used commonly in cultured cardiomyocytes to probe myofibril maturation, but this ex vivo approach is limited by the extent to which myocytes will fully differentiate in culture, lack of normal in vivo mechanical inputs, and absence of endocardial cues. Application of immunofluorescence techniques to the study of developing mouse heart is desirable but more technically challenging, and methods often lack sufficient sensitivity and resolution to visualize sarcomeres in the early stages of heart development. Here, we describe a robust and reproducible method to co-immunostain multiple proteins or to co-visualize a fluorescent protein with immunofluorescent staining in the embryonic mouse heart and use this method to analyze developing myofibrils, intercalated discs, and costameres. This method can be further applied to assess cardiomyocyte structural changes caused by mutations that lead to developmental heart defects.

Mutations that lead to congenital heart defects benefit from in vivo investigation of cardiac structure during development, but high-resolution structural studies in the mouse embryonic heart are technically challenging. Here we present a robust immunofluorescence and image analysis method to assess cardiomyocyte-specific structures in the developing mouse heart.

During heart development, the generation of myocardial-specific structural and functional units including sarcomeres, contractile myofibrils, intercalated ...

Epigenetic Regulation of Cardiac Differentiation of Embryonic Stem Cells and Tissues

Specific gene transcription is a key biological process that underlies cell fate decision during embryonic development. The biological process is mediated by transcription factors which bind genomic regulatory regions including enhancers and promoters of cardiac constitutive genes. DNA is wrapped around histones that are subjected to chemical modifications. Modifications of histones further lead to repressed, activated or poised gene transcription, thus bringing another level of fine tuning regulation of gene transcription. Embryonic Stem cells (ES cells) recapitulate within embryoid bodies (i.e., cell aggregates) or in 2D culture the early steps of cardiac development. They provide in principle enough material for chromatin immunoprecipitation (ChIP), a technology broadly used to identify gene regulatory regions. Furthermore, human ES cells represent a human cell model of cardiogenesis. At later stages of development, mouse embryonic tissues allow for investigating specific epigenetic landscapes required for determination of cell identity. Herein, we describe protocols of ChIP, sequential ChIP followed by PCR or ChIP-sequencing using ES cells, embryoid bodies and cardiac specific embryonic regions. These protocols allow to investigating the epigenetic regulation of cardiac gene transcription.

A fine tuning regulation of gene transcription underlies embryonic cell fate decision. Herein, we describe chromatin immunoprecipitation assays used to investigate epigenetic regulation of both cardiac differentiation of stem cells and cardiac development of mouse embryos.

Specific gene transcription is a key biological process that underlies cell fate decision during embryonic development. The biological process is mediated ...

Nanoparticle-mediated siRNA Gene-silencing in Adult Zebrafish Heart

Mammals have a very limited capacity to regenerate the heart after myocardial infarction. On the other hand, the adult zebrafish regenerates its heart after apex resection or cryoinjury, making it an important model organism for heart regeneration study. However, the lack of loss-of-function methods for adult organs has restricted insights into the mechanisms underlying heart regeneration. RNA interference via different delivery systems is a powerful tool for silencing genes in mammalian cells and model organisms. We have previously reported that siRNA-encapsulated nanoparticles successfully enter cells and result in a remarkable gene-specific knockdown in the regenerating adult zebrafish heart. Here, we present a simple, rapid, and efficient protocol for the dendrimer-mediated siRNA delivery and gene-silencing in the regenerating adult zebrafish heart. This method provides an alternative approach for determining gene functions in adult organs in zebrafish and can be extended to other model organisms as well.

It remains a major challenge to develop conditional gene-knockout or effective gene-knockdown in adult zebrafish organs. Here we report a protocol for performing nanoparticle-mediated siRNA gene-silencing in adult zebrafish heart, thus providing a new loss-of-function method for studying adult organs in zebrafish and other model organisms.

Mammals have a very limited capacity to regenerate the heart after myocardial infarction. On the other hand, the adult zebrafish regenerates its heart ...

Microinjection-based System for In Vivo Implantation of Embryonic Cardiomyocytes in the Avian Embryo

Interpreting the relative impact of cell autonomous patterning versus extrinsic microenvironmental influence on cell lineage determination represents a general challenge in developmental biology research. In the embryonic heart, this can be particularly difficult as regional differences in the expression of transcriptional regulators, paracrine/juxtacrine signaling cues, and hemodynamic force are all known to influence cardiomyocyte maturation. A simplified method to alter a developing cardiomyocyte's molecular and biomechanical microenvironment would, therefore, serve as a powerful technique to examine how local conditions influence cell fate and function. To address this, we have optimized a method to physically transplant juvenile cardiomyocytes into ectopic locations in the heart or the surrounding embryonic tissue. This allows us to examine how microenvironmental conditions influence cardiomyocyte fate transitions at single cell resolution within the intact embryo. Here, we describe a protocol in which embryonic myocytes can be isolated from a variety of cardiac sub-domains, dissociated, fluorescently labeled, and microinjected into host embryos with high precision. Cells can then be directly analyzed in situ using a variety of imaging and histological techniques. This protocol is a powerful alternative to traditional grafting experiments that can be prohibitively difficult in a moving tissue such as the heart. The general outline of this method can also be adapted to a variety of donor tissues and host environments, and its ease of use, low cost, and speed make it a potentially useful application for a variety of developmental studies.

In this method, embryonic cardiac tissues are surgically microdissected, dissociated, fluorescently labeled, and implanted into host embryonic tissues. This provides a platform for studying the individual or tissue level developmental organization under ectopic hemodynamic conditions, and/or altered paracrine/juxtacrine environments.

Interpreting the relative impact of cell autonomous patterning versus extrinsic microenvironmental influence on cell lineage determination represents a ...

In Vitro Generation of Heart Field-specific Cardiac Progenitor Cells

Pluripotent stem cells offer great potential for understanding heart development and disease and for regenerative medicine. While recent advances in developmental cardiology have led to generating cardiac cells from pluripotent stem cells, it is unclear if the two cardiac fields - the first and second heart fields (FHF and SHF) &#8212; are induced in pluripotent stem cells systems. To address this, we generated a protocol for in vitro specification and isolation of heart field-specific cardiac progenitor cells. We used embryonic stem cells lines carrying Hcn4-GFP and Tbx1-Cre; Rosa-RFP reporters of the FHF and the SHF, respectively, and live cell immunostaining of the cell membrane protein Cxcr4, a SHF marker. With this approach, we generated progenitor cells which recapitulate the functional properties and transcriptome of their in vivo counterparts. Our protocol can be utilized to study early specification and segregation of the two heart fields and to generate chamber-specific cardiac cells for heart disease modelling. Since this is an in vitro organoid system, it may not provide precise anatomical information. However, this system overcomes the poor accessibility of gastrulation-stage embryos and can be upscaled for high-throughput screens.

The purpose of this method is to generate heart field-specific cardiac progenitor cells in vitro in order to study the progenitor cell specification and functional properties, and to generate chamber specific cardiac cells for heart disease modelling.

Pluripotent stem cells offer great potential for understanding heart development and disease and for regenerative medicine. While recent advances in ...

Analysis of Congenital Heart Defects in Mouse Embryos Using Qualitative and Quantitative Histological Methods

Congenital heart defects (CHD) are the most common type of birth defect in humans, affecting up to 1% of all live births. However, the underlying causes for CHD are still poorly understood. The developing mouse constitutes a valuable model for the study of CHD, because cardiac developmental programs between mice and humans are highly conserved. The protocol describes in detail how to produce mouse embryos of the desired gestational stage, methods to isolate and preserve the heart for downstream processing, quantitative methods to identify common types of CHD by histology (e.g., ventricular septal defects, atrial septal defects, patent ductus arteriosus), and quantitative histomorphometry methods to measure common muscular compaction phenotypes. These methods articulate all the steps involved in sample preparation, collection, and analysis, allowing scientists to correctly and reproducibly measure CHD.

In this protocol, we describe procedures to qualitatively and quantitatively analyze developmental phenotypes in mice associated with congenital heart defects.

Congenital heart defects (CHD) are the most common type of birth defect in humans, affecting up to 1% of all live births. However, the underlying causes ...

Fluorescent Immunolocalization of Arabinogalactan Proteins and Pectins in the Cell Wall of Plant Tissues

Plant development involves constant adjustments of the cell wall composition and structure in response to both internal and external stimuli. Cell walls are composed of cellulose and non-cellulosic polysaccharides together with proteins, phenolic compounds and water. 90% of the cell wall is composed of&#160;polysaccharides (e.g., pectins) and arabinogalactan proteins (AGPs). The fluorescent immunolocalization of specific glycan epitopes in plant histological sections remains a key tool to uncover remodeling of wall polysaccharide networks, structure and components.
Here, we report an optimized fluorescent immunolocalization procedure to detect glycan epitopes from AGPs and pectins in plant tissues. Paraformaldehyde/glutaraldehyde fixation was used along with LR-White embedding of the plant samples, allowing for a better preservation of the tissue structure and composition. Thin sections of the embedded samples obtained with an ultra-microtome were used for immunolocalization with specific antibodies. This technique offers great resolution, high specificity, and the chance to detect multiple glycan epitopes in the same sample. This technique allows subcellular localization of glycans and detects their level of accumulation in the cell wall. It also permits the determination of spatio-temporal patterns of AGP and pectin distribution during developmental processes. The use of this tool may ultimately guide research directions and link glycans to specific functions in plants. Furthermore, the information obtained can complement biochemical and gene expression studies.

This protocol describes in detail how the plant material for immunolocalization of Arabinogalactan proteins and pectins is fixed, embedded in a hydrophilic acrylic resin, sectioned and mounted on glass slides. We show cell wall related epitopes will be detected with specific antibodies.

Plant development involves constant adjustments of the cell wall composition and structure in response to both internal and external stimuli. Cell walls ...

Modeling Paracrine Noncanonical Wnt Signaling In Vitro

Noncanonical Wnt signaling regulates intracellular actin filament organization and polarized migration of progenitor cells during embryogenesis. This process requires complex and coordinated paracrine interactions between signal-sending and signal-receiving cells. Given that these interactions can occur between various types of cells from different lineages, in vivo evaluation of cell-specific defects can be challenging. The present study describes a highly reproducible method to evaluate paracrine noncanonical Wnt signaling in vitro. This protocol was designed with the ability to (1) conduct functional and molecular assessments of noncanonical Wnt signaling between any two cell types of interest; (2) dissect the role of signal-sending versus signal-receiving molecules in the noncanonical Wnt signaling pathway; and (3) perform phenotypic rescue experiments with standard molecular or pharmacologic approaches.
This protocol was used to evaluate neural crest cell (NCC)-mediated noncanonical Wnt signaling in myoblasts. The presence of NCCs is associated with an increased number of phalloidin-positive cytoplasmic filopodia and lamellipodia in myoblasts and improved myoblast migration in a wound-healing assay. The Wnt5a-ROR2 axis was identified as a crucial noncanonical Wnt signaling pathway between NCC and second heart field (SHF) cardiomyoblast progenitors. In conclusion, this is a highly tractable protocol to study paracrine noncanonical Wnt signaling mechanisms in vitro.

Modeling Paracrine Noncanonical Wnt Signaling In Vitro

The present study outlines a highly reproducible and tractable method to study paracrine noncanonical Wnt signaling events in vitro. This protocol was applied to evaluate the impact of paracrine Wnt5a signaling in murine neural crest cells and myoblasts.

Noncanonical Wnt signaling regulates intracellular actin filament organization and polarized migration of progenitor cells during embryogenesis. This ...

A Pipeline to Characterize Structural Heart Defects in the Fetal Mouse

Congenital heart diseases (CHDs) are major causes of infant death in the United States. In the 1980s and earlier, most patients with moderate or severe CHD died before adulthood, with the maximum mortality during the first week of life. Remarkable advances in surgical techniques, diagnostic approaches, and medical management have led to marked improvements in outcomes. To address the critical research needs of understanding congenital heart defects, murine models have provided an ideal research platform, as they have very similar heart anatomy to humans and short gestation rates. The combination of genetic engineering with high-throughput phenotyping tools has allowed for the replication and diagnosis of structural heart defects to further elucidate the molecular pathways behind CHDs. The use of noninvasive fetal echocardiography to screen the cardiac phenotypes in mouse models coupled with the high fidelity of Episcopic fluorescence image capture (EFIC) using Episcopic confocal microscopy (ECM) histopathology with three-dimensional (3D) reconstructions enables a detailed view into the anatomy of various congenital heart defects. This protocol outlines a complete workflow of these methods to obtain an accurate diagnosis of murine congenital heart defects. Applying this phenotyping protocol to model organisms will allow for accurate CHD diagnosis, yielding insights into the mechanisms of CHD. Identifying the underlying mechanisms of CHD provide opportunities for potential therapies and interventions.

This article details murine congenital heart disease (CHD) diagnostic methods using fetal echocardiography, necropsy, and Episcopic fluorescence image capture (EFIC) using Episcopic confocal microscopy (ECM) followed by three-dimensional (3D) reconstruction.

Congenital heart diseases (CHDs) are major causes of infant death in the United States. In the 1980s and earlier, most patients with moderate or severe ...