Name: lucifer yellow - a robust paracellular permeability marker in a cell model of the human blood-brain barrier
Uploaded: 2019-08-19T13:00:00
Description: Watch this Scientific Journal Video about Lucifer Yellow - A Robust Paracellular Permeability Marker in a Cell Model of the Human Blood-brain Barrier at JoVE.com

The authors are thankful for the financial support from the 2017 New Investigator Award from the American Association of Pharmacy, a Hunkele Dreaded Disease award from Duquesne University and the School of Pharmacy start-up funds for the Manickam laboratory. We would like to thank the Leak laboratory (Duquesne University) for western blotting assistance and allowing use of their Odyssey 16-bit imager. We would also like to include a special note of appreciation for Kandarp Dave (Manickam laboratory) for help with western blotting.

1.General hCMEC/D3 cell culture
<ol>
	<li>Resuscitation of frozen cells 
	NOTE: All cell culture maintenance and experiments were performed inside a sterile biosafety hood. Culture media, supplements and reagents were either purchased as sterile products or sterilized via filtration using a 0.22 &#181;m membrane filter to prevent microbial contamination.
	<ol>
		<li>Add 8.5 mL of collagen solution (0.15mg/mL) in a tissue culture flask (75 cm2&#160;growth area; referred henceforth as T75...

<ol>
	<li>Abbott, N. J., Patabendige, A. A., Dolman, D. E., Yusof, S. R., Begley, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structure+and+function+of+the+blood-brain+barrier.">Structure and function of the blood-brain barrier.</a> Neurobiology Of Disease. 37 (1), 13-25 (2010).</li><li>Griep, L. 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=BBB+on+chip:+microfluidic+platform+to+mechanically+and+biochemically+modulate+blood-brain+barrier+function.">BBB on chip: microfluidic platform to mechanically and biochemically modulate blood-brain barrier function.</a> Biomedical Microdevices. 15 (1), 145-150 (2013).</li><li>Camos, S., Mallolas, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Experimental+models+for+assaying+microvascular+endothelial+cell+pathophysiology+in+stroke.">Experimental models for assaying microvascular endothelial cell pathophysiology in stroke.</a> Molecules. 15 (12), 9104-9134 (2010).</li><li>Cucullo, L., 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=Immortalized+human+brain+endothelial+cells+and+flow-based+vascular+modeling:+a+marriage+of+convenience+for+rational+neurovascular+studies.">Immortalized human brain endothelial cells and flow-based vascular modeling: a marriage of convenience for rational neurovascular studies.</a> Journal of Cerebral Blood Flow &amp; Metabolism. 28 (2), 312-328 (2008).</li><li>Wolff, A., Antfolk, M., Brodin, B., Tenje, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+Blood-Brain+Barrier+Models-An+Overview+of+Established+Models+and+New+Microfluidic+Approaches.">In vitro Blood-Brain Barrier Models-An Overview of Established Models and New Microfluidic Approaches.</a> Journal of Pharmaceutical Sciences. 104 (9), 2727-2746 (2015).</li><li>Weksler, B., Romero, I. 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A., Couraud, P. O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+hCMEC/D3+cell+line+as+a+model+of+the+human+blood+brain+barrier.">The hCMEC/D3 cell line as a model of the human blood brain barrier.</a> Fluids and Barriers of the CNS. 10 (1), 16 (2013).</li><li>Llombart, V., 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=Characterization+of+secretomes+from+a+human+blood+brain+barrier+endothelial+cells+in-vitro+model+after+ischemia+by+stable+isotope+labeling+with+aminoacids+in+cell+culture+(SILAC).">Characterization of secretomes from a human blood brain barrier endothelial cells in-vitro model after ischemia by stable isotope labeling with aminoacids in cell culture (SILAC).</a> Journal of Proteomics. 133, 100-112 (2016).</li><li>Weksler, B. 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J., Abbott, N. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> The Blood-Brain Barrier. , 307-324 (2003).</li><li>Deli, M. A., &#193;brah&#225;m, C. S., Kataoka, Y., Niwa, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Permeability+Studies+on+In+vitro+Blood&#8211;Brain+Barrier+Models:+Physiology,+Pathology,+and+Pharmacology.">Permeability Studies on In vitro Blood&#8211;Brain Barrier Models: Physiology, Pathology, and Pharmacology.</a> Cellular and Molecular Neurobiology. 25 (1), 59-127 (2005).</li><li>Ren, T. B., 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=A+General+Method+To+Increase+Stokes+Shift+by+Introducing+Alternating+Vibronic+Structures.">A General Method To Increase Stokes Shift by Introducing Alternating Vibronic Structures.</a> Journal of the American Chemical Society. 140 (24), 7716-7722 (2018).</li><li>Pack, D. W., Hoffman, A. S., Pun, S., Stayton, P. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Design+and+development+of+polymers+for+gene+delivery.">Design and development of polymers for gene delivery.</a> Nature Reviews Drug Discovery. 4 (7), 581-593 (2005).</li><li>Oupick&#253;, D., Kon&#225;k, C., Ulbrich, K., Wolfert, M. A., Seymour, L. 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E., Artursson, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+of+drug+permeability+and+prediction+of+drug+absorption+in+Caco-2+monolayers.">Determination of drug permeability and prediction of drug absorption in Caco-2 monolayers.</a> Nature Protocols. 2 (9), 2111-2119 (2007).</li><li>Balda, M. S., Anderson, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Two+classes+of+tight+junctions+are+revealed+by+ZO-1+isoforms.">Two classes of tight junctions are revealed by ZO-1 isoforms.</a> The American Physiological Society. , (1992).</li><li>Brown, R. C., Davis, T. 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A key role of the BBB is to prevent the exchange of non-essential ions and toxic substances between the systemic circulation and the brain to maintain hemostasis of neural microenvironment. One of the characteristic features of the BBB is the ability of the capillary endothelial cells to form tight junctions (TJs) that effectively seal the paracellular route of transport. We demonstrated a LY Papp assay as a quantitative method to determine the apparent kinetics of TJ barrier formation in cultured hCMEC/D3 mon...

Blood-brain barrier (BBB) is the protective barrier limiting the influx of plasma components into the brain tissue and consists of brain endothelial cells along with supporting cells such as pericytes. The major role of BBB is to serve as a barrier that seals the space between peripheral blood and central nervous system (CNS) to maintain hemostasis of the neural microenvironment1,2. The brain capillary endothelial cells effectively seal the paracellular pathway via formation of intercellular tight junctions (TJs)1. This protective barrier allows glucose and selected nutrients to enter the brain while it prevents the majority of ions, toxic substances and drugs from passing through this tight barrier. Apart from its protective role, the natural barrier function of the BBB poses a severe challenge in the development of drug delivery systems targeting the CNS.
In vitro cell culture models of the BBB are helpful tools to study its biology and to understand the effects of drug treatment on TJ barrier integrity. We used the human cerebral microvascular endothelial cell line (hCMEC/D3) as an in vitro model since it is an accepted model of human brain endothelium3 and recapitulates many functions of the human BBB. hCMEC/D3is one of the most commonly used cell lines for modeling the BBB in vitro4,5,6,7,8,9. Despite its comparatively low values of transendothelial electrical resistance (TEER), a measure of barrier tightness, this cell line retains most of the morphological and functional properties of brain endothelial cells, even as a monoculture in the absence of cocultured glial cells6,7. The hCMEC/D3 cell line expresses multiple BBB markers including active transporters and receptors until approximately passage 35 without undergoing dedifferentiation to unstable phenotypes6,7,9,10,11. The most striking characteristic of hCMEC/D3 cell line as an in vitro BBB model is its ability to form TJs5,9,11,12. It should be noted that although stem cell-derived BBB models showed higher permeability in many studies compared with hCMEC/D3 cell line and they do express some BBB markers, they are yet to evolve as the most common BBB cell model13. Importantly, stem-cell derived BBB models remain to be characterized with respect to maximum passage numbers that allow the cells to maintain stable BBB phenotypes14.
Three primary methods are commonly used to determine the TJ barrier integrity, including the measurement of TEER, measurement of apparent permeability coefficient (Papp) of small hydrophilic tracer molecules such as sucrose, inulin, Lucifer Yellow, etc. and immunostaining of known molecular markers of TJs such as claudin-5, ZO-1, occludin, etc.5. TEER is a relatively simple and quantitative method that measures the electrical resistance across the cell monolayers cultured on a porous membrane substrate5. However, TEER values can be influenced by experimental variables such as composition of the culture medium and the type of measurement instrument. A likely combination of these factors leads to a broad distribution of TEER values ranging from 2 to 1150 &#937; cm2 in the hCMEC/D3 cell line cultured for 2-21 days13. Immunostaining is a visual method to determine the presence of TJ proteins by labelling the targeted protein using antibodies. However, immunostaining involves a series of experimental steps, including the need to fix/permeabilize cells that may result in experimental artifacts and the fluorescent signals may fade over time. The above factors may lead to subjective errors affecting data quality.
The primary focus of this work is to present a LY-based apparent permeability assay determine the kinetics of a confluent monolayer formation in cultured hCMEC/D3 cells. Although other advanced in vitro BBB systems, such as co-culture systems, microfluidic systems, are physiologically more relevant mimics with significantly improved barrier function15,16,17, the hCMEC/D3 transwell setup is a simple and reliable model to estimate the kinetics of TJ formation and rapidly screen the effect of different drug formulations on barrier function. In general, Papp values are consistent for various hydrophilic solutes in hCMEC/D3 monolayers. For example, the reported Papp values for various low molecular mass solutes (such as sucrose, mannitol, LY, etc.) in different in vitro&#160;BBB models are in the order of 10-4 cm/min5,18,19,20. In our experimental setup, the brain endothelial cells are seeded on a collagen-coated microporous membrane for cell attachment and monolayer formation to mimic the in vivo barrier. The LY added in the apical side is expected to traverse the intercellular tight junctions and accumulate in the basolateral side. Greater concentrations of LY in the basolateral side indicate an immature, not-fully functional barrier while lower concentrations reflect restricted transport due to the presence of functional TJs resulting in a mature barrier.
LY is a hydrophilic dye with distinct excitation/emission peaks and avoids the need to radiolabel tracer molecules such as sucrose, mannitol or inulin. Thus, the fluorescence values of LY can be used to directly calculate its paracellular permeability across the BBB monolayers. Also, compared to many commercially available dyes used in biomedical fields that suffer from small Stokes shifts such as fluorescein21, the Stokes shift of LY is about 108 nm with sufficient spectral separation, thus allowing LY fluorescence data as a robust readout to determine paracellular permeability. We used Western blotting as an orthogonal technique to demonstrate changes in expression of the tight junction marker protein, ZO-1, over culture time. ZO-1 expression detected via Western blotting is used to supplement the LY Papp data and in combination, these data suggest that the observed changes in LY Papp values is reflective of the formation of a monolayer with gradual increase in expression of the tight junction marker, ZO-1.
As pointed out earlier, the central focus of this work is to demonstrate a LY assay as a simple technique to monitor the formation of a confluent monolayer with functional tight junctions. However, to demonstrate an additional utility of the developed assay, we measured the LY Papp in DNA nanoparticle-transfected hCMEC/D3 monolayers. Nucleic acids can be condensed into polyelectrolyte nanoparticles with a diameter of 100-200 nm via electrostatic interaction between the positively charged groups of polymers and the negatively charged phosphate groups of nucleic acids22,23. We refer to these complexes as DNA nanoparticles (DNA NPs) in our work. While our intention is to transfect cells and express the desired protein, we must ensure that the barrier properties of the hCMEC/D3 monolayers are not compromised. Our data suggests that a standard 4 h luciferase gene transfection regime does not measurably change the LY permeability demonstrating the utility of the LY Papp assay to determine changes in TJ barrier integrity.

<table border="0" cellpadding="0" cellspacing="0" style="width:1035px;" width="1033">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:545px;">hCMEC/D3 cell line</td>
			<td style="width:195px;">Cedarlane Laboratories</td>
			<td style="width:123px;">102114.3C-P25</td>
			<td style="width:172px;">human cerebral microvascular endothelial cell line&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">gWizLuc</td>
			<td>Aldevron&#160;</td>
			<td>5000-5001</td>
			<td>Plasmid DNA encoding luciferase gene</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">lucifer yellow CH dilithium salt&#160;</td>
			<td>Invitrogen</td>
			<td>155267</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Transwell inserts with polyethylene terephthalate (PET) track-etched membranes</td>
			<td>Falcon</td>
			<td>353095</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Tissue culture flask&#160;</td>
			<td>Olympus Plastics</td>
			<td>25-207</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">24-well Flat Bottom&#160;</td>
			<td>Olympus Plastics</td>
			<td>25-107</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Black 96-Well Immuno Plates&#160;</td>
			<td>Thermo Scientific</td>
			<td>437111</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">S-MEM 1X</td>
			<td>Gibco</td>
			<td>1951695</td>
			<td>Spinner-minimum essential medium (S-MEM)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">EBM-2</td>
			<td>Clonetics</td>
			<td>CC-3156</td>
			<td>Endothelial cell basal medium-2(EBM-2)&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">phosphate-buffered saline 1X</td>
			<td>HyClone</td>
			<td>SH3025601</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Collagen Type I&#160;</td>
			<td>Discovery Labware, Inc.</td>
			<td>354236</td>
			<td></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;">Pierce BCA Protein Assay Kit&#160;</td>
			<td>Thermo Scientific</td>
			<td>23227</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Cell Culture Lysis 5X Reagent&#160;</td>
			<td>Promega</td>
			<td>E1531</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Beetle Luciferin, Potassium Salt&#160;</td>
			<td>Promega</td>
			<td>E1601</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:545px;">SpectraMax i3&#160;</td>
			<td style="width:195px;">Molecular Devices</td>
			<td style="width:123px;"></td>
			<td>Fluorescence Plate Reader</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:545px;">Trypan Blue Solution, 0.4%</td>
			<td style="width:195px;">Gibco</td>
			<td style="width:123px;">15250061</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:545px;">ZO-1 Polyclonal Antibody&#160;</td>
			<td style="width:195px;">ThermoFisher</td>
			<td style="width:123px;">61-7300</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:545px;">anti-GAPDH antibody</td>
			<td style="width:195px;">abcam</td>
			<td style="width:123px;">ab8245</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:545px;">Alexa Fluor680-conjugated AffiniPure Donkey Anti-Mouse LgG(H+L)</td>
			<td style="width:195px;">Jackson ImmunoResearch Inc</td>
			<td style="width:123px;">128817</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:545px;">12-well, Flat Bottom</td>
			<td style="width:195px;">Olympus Plastics</td>
			<td style="width:123px;">25-106</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:545px;">RIPA buffer (5X)</td>
			<td style="width:195px;">Alfa Aesar</td>
			<td style="width:123px;">J62524</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:545px;">Aprotinin</td>
			<td style="width:195px;">Fisher BioReagents</td>
			<td style="width:123px;">BP2503-10</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:545px;">Odyssey CLx imager</td>
			<td style="width:195px;">LI-COR Biosciences</td>
			<td style="width:123px;"></td>
			<td>for scanning western blot membranes</td>
		</tr>
	</tbody>
</table>

lucifer yellow - a robust paracellular permeability marker in a cell model of the human blood-brain barrier

The blood-brain barrier BBB consists of endothelial cells that form a barrier between the systemic circulation and the brain to prevent the exchange of non-essential ions and toxic substances. Tight junctions (TJ) effectively seal the paracellular space in the monolayers resulting in an intact barrier. This study describes a LY-based fluorescence assay that can be used to determine its apparent permeability coefficient (Papp) and in turn can be used to determine the kinetics of the formation of confluent monolayers and the resulting tight junction barrier integrity in hCMEC/D3 monolayers. We further demonstrate an additional utility of this assay to determine TJ functional integrity in transfected cells. Our data from the LY Papp assay shows that the hCMEC/D3 cells seeded in a transwell setup effectively limit LY paracellular transport 7 days-post culture. As an additional utility of the presented assay, we also demonstrate that the DNA nanoparticle transfection does not alter LY paracellular transport in hCMEC/D3 monolayers.

First, we determined the effect of culturing time on LY permeability to determine the apparent kinetics of TJ formation. The mean LY Papp values from day 1 to 10-post seeding are shown in Figure 2a. On day 1, the mean Papp was 4.25 x 10-4&#160;cm/min and slightly dropped to 3.32 x 10-4&#160;cm/min on day 2. The mean Papp value slightly increased to 3.93 x 10-4&#160;cm/min on day 3 and fluctuate...

Watch this Scientific Journal Video about Lucifer Yellow - A Robust Paracellular Permeability Marker in a Cell Model of the Human Blood-brain Barrier at JoVE.com

Lucifer Yellow - A Robust Paracellular Permeability Marker in a Cell Model of the Human Blood-brain Barrier

We present a fluorescence assay to demonstrate that Lucifer Yellow (LY) is a robust marker to determine the apparent paracellular permeability of hCMEC/D3 cell monolayers, an in vitro model of the human blood-brain barrier. We used this assay to determine the kinetics of a confluent monolayer formation in cultured hCMEC/D3 cells.

The blood-brain barrier BBB consists of endothelial cells that form a barrier between the systemic circulation and the brain to prevent the exchange of ...

This protocol is a robust technique to determine the functional integrity of intercellular tight junctions in a cell model of the human blood-brain barrier. This is a simple and fairly inexpensive protocol that allows calculating the apparent permeability in a shorter time period instead of running a longer kinetic assay. This method can also be used to determine the functional integrity of tight junctions in brain endothelial cells transfected with polymer DNA nanoparticles.To begin cell plating, place tissue culture inserts with microporous membranes into a 24-well culture plate. Add 400 microliters of 0.15-milligrams-per-milliliter collagen type one in each tissue culture insert. Then incubate for one hour in a 37 degree Celsius, 5%carbon dioxide incubator.Rock the 24-well plate gently to allow even spreading of the collagen solution over the microporous membrane in the tissue culture inserts. After an hour, remove the collagen solution and gently wash the microporous membrane with 0.4 milliliters of 1X PBS buffer. Now, plate hCMEC/D3 cells with a density of 50, 000 cells per square centimeter in the cell inserts.Place the 24-well plate with tissue culture setup in the incubator to allow cell attachment and proliferation. Incubate the plate for seven days to allow the cells to reach 100%confluency. Remove the growth medium every other day and transfer 0.5 milliliters of pre-warmed fresh media into the tissue culture inserts.Repeat the plating procedure for Western blotting to determine changes in ZO-1 expression for DNA nanoparticle transfection, and for the ATP assay to determine cell viability in transfected cells. For determining Lucifer Yellow apparent permeability, on each day post-seeding, remove the growth medium and add 1.5 milliliters of pre-warmed transport buffer to the basolateral side of the well. Now add 58.3 microliters of 20-micromolar Lucifer Yellow solution to the apical side of each trans-well insert.Save 50 microliters of the solution for fluorescence measurements. After completely removing residual PBS buffer from the apical side, add Lucifer Yellow solution as quickly as possible to avoid drying the cells. Ensure accurate volumes of Lucifer Yellow solution in the apical side.Make sure to add the same and accurate volume of Lucifer Yellow solution in all inserts. Work quickly to avoid drying the cells. Incubate the cells in a rotary plate shaker at 100 RPM and 37 degrees Celsius for 60 minutes.Then remove 30 microliters of the Lucifer Yellow sample from each apical compartment. Transfer the 20-micromolar Lucifer Yellow solution and the apical side samples to pre-labeled tubes. Now dilute the sample tenfold using transport buffer.Remove 500 microliters from each basolateral compartment, and transfer the sample to pre-labeled tubes. Prepare a series of Lucifer Yellow standards for the standard curve. Add 100 microliters of each standard apical and basolateral sample to each well of a black 96-well plate in duplicate.Use a fluorescence microplate reader to measure the Lucifer Yellow fluorescence intensity and calculate the apparent permeability, as described in the manuscript text. The effect of culturing time on Lucifer Yellow permeability was used to determine the apparent kinetics of tight junction formation. The apparent permeability values significantly decreased on day seven compared with day one, suggesting that the barrier became tighter.The apparent permeability values then stabilized until day 10. This implied the barrier formation was complete and functional, resulting in decreased Lucifer Yellow paracellular transport. Western blotting was used to detect changes in the expression of the tight junction protein ZO-1 over time.The two bands represent the two ZO-1 isoforms. Densitometry analysis revealed that the pixel value of ZO-1 increased from days three through seven post-seeding, suggesting that the tight junction protein ZO-1 formed continually from days three through seven. After calcium depletion treatment on day seven post-seeding, the band of ZO-1 was almost undetectable, indicating that ZO-1 was unable to form in the absence of calcium ions.As shown in the results, Western blotting of ZO-1 protein can be performed to determine changes in the expression level of tight junction proteins, complementing the Lucifer Yellow-based functional activity data. We also discovered that the functional activity of tight junctions in human brain endothelial cells was not affected by DNA nanoparticle transfection.

lucifer-yellow-robust-paracellular-permeability-marker-cell-model

Research

JoVE Journal

Bioengineering

Creating Two-Dimensional Patterned Substrates for Protein and Cell Confinement

Microcontact printing provides a rapid, highly reproducible method for the creation of well-defined patterned substrates.1 While microcontact printing can be employed to directly print a large number of molecules, including proteins,2 DNA,3 and silanes,4 the formation of self-assembled monolayers (SAMs) from long chain alkane thiols on gold provides a simple way to confine proteins and cells to specific patterns containing adhesive and resistant regions. This confinement can be used to control cell morphology and is useful for examining a variety of questions in protein and cell biology. Here, we describe a general method for the creation of well-defined protein patterns for cellular studies.5 This process involves three steps: the production of a patterned master using photolithography, the creation of a PDMS stamp, and microcontact printing of a gold-coated substrate. Once patterned, these cell culture substrates are capable of confining proteins and/or cells (primary cells or cell lines) to the pattern.
The use of self-assembled monolayer chemistry allows for precise control over the patterned protein/cell adhesive regions and non-adhesive regions; this cannot be achieved using direct protein stamping. Hexadecanethiol, the long chain alkane thiol used in the microcontact printing step, produces a hydrophobic surface that readily adsorbs protein from solution. The glycol-terminated thiol, used for backfilling the non-printed regions of the substrate, creates a monolayer that is resistant to protein adsorption and therefore cell growth.6 These thiol monomers produce highly structured monolayers that precisely define regions of the substrate that can support protein adsorption and cell growth. As a result, these substrates are useful for a wide variety of applications from the study of intercellular behavior7 to the creation of microelectronics.8
While other types of monolayer chemistry have been used for cell culture studies, including work from our group using trichlorosilanes to create patterns directly on glass substrates,9 patterned monolayers formed from alkane thiols on gold are straight-forward to prepare. Moreover, the monomers used for monolayer preparation are commercially available, stable, and do not require storage or handling under inert atmosphere. Patterned substrates prepared from alkane thiols can also be recycled and reused several times, maintaining cell confinement.10

Self-assembled monolayers (SAMs) formed from long chain alkane thiols on gold provide well-defined substrates for the formation of protein patterns and cell confinement. Microcontact printing of hexadecanethiol using a polydimethylsiloxane (PDMS) stamp followed by backfilling with a glycol-terminated alkane thiol monomer produces a pattern where protein and cells adsorb only to the stamped hexadecanethiol region.

Microcontact printing provides a rapid, highly reproducible method for the creation of well-defined patterned substrates.1  While microcontact printing ...

Rotating Cell Culture Systems for Human Cell Culture: Human Trophoblast Cells as a Model

The field of human trophoblast research aids in understanding the complex environment established during placentation. Due to the nature of these studies, human in vivo experimentation is impossible. A combination of primary cultures, explant cultures and trophoblast cell lines1 support our understanding of invasion of the uterine wall2 and remodeling of uterine spiral arteries3,4 by extravillous trophoblast cells (EVTs), which is required for successful establishment of pregnancy. Despite the wealth of knowledge gleaned from such models, it is accepted that in vitro cell culture models using EVT-like cell lines display altered cellular properties when compared to their in vivo counterparts5,6. Cells cultured in the rotating cell culture system (RCCS) display morphological, phenotypic, and functional properties of EVT-like cell lines that more closely mimic differentiating in utero EVTs, with increased expression of genes mediating invasion (e.g. matrix metalloproteinases (MMPs)) and trophoblast differentiation7,8,9. The Saint Georges Hospital Placental cell Line-4 (SGHPL-4) (kindly donated by Dr. Guy Whitley and Dr. Judith Cartwright) is an EVT-like cell line that was used for testing in the RCCS.
The design of the RCCS culture vessel is based on the principle that organs and tissues function in a three-dimensional (3-D) environment. Due to the dynamic culture conditions in the vessel, including conditions of physiologically relevant shear, cells grown in three dimensions form aggregates based on natural cellular affinities and differentiate into organotypic tissue-like assemblies10,11,12 . The maintenance of a fluid orbit provides a low-shear, low-turbulence environment similar to conditions found in vivo. Sedimentation of the cultured cells is countered by adjusting the rotation speed of the RCCS to ensure a constant free-fall of cells. Gas exchange occurs through a permeable hydrophobic membrane located on the back of the bioreactor. Like their parental tissue in vivo, RCCS-grown cells are able to respond to chemical and molecular gradients in three dimensions (i.e. at their apical, basal, and lateral surfaces) because they are cultured on the surface of porous microcarrier beads. When grown as two-dimensional monolayers on impermeable surfaces like plastic, cells are deprived of this important communication at their basal surface. Consequently, the spatial constraints imposed by the environment profoundly affect how cells sense and decode signals from the surrounding microenvironment, thus implying an important role for the 3-D milieu13.
We have used the RCCS to engineer biologically meaningful 3-D models of various human epithelial tissues7,14,15,16. Indeed, many previous reports have demonstrated that cells cultured in the RCCS can assume physiologically relevant phenotypes that have not been possible with other models10,17-21. In summary, culture in the RCCS represents an easy, reproducible, high-throughput platform that provides large numbers of differentiated cells that are amenable to a variety of experimental manipulations. 
In the following protocol, using EVTs as an example, we clearly describe the steps required to three-dimensionally culture adherent cells in the RCCS.

Traditional, two dimensional cell culture techniques often result in altered characteristics with respect to differentiation markers, cytokines and growth factors. Three-dimensional cell culture in the rotating cell culture system (RCCS) reestablishes expression of many of these factors as shown here with an extravillous trophoblast cell line.

The field of human trophoblast research aids in  understanding the complex environment established during placentation. Due to the  nature of these ...

Improved Method for the Preparation of a Human Cell-based, Contact Model of the Blood-Brain Barrier

The blood-brain barrier (BBB) comprises impermeable but adaptable brain capillaries which tightly control the brain environment. Failure of the BBB has been implied in the etiology of many brain pathologies, creating a need for development of human in vitro BBB models to assist in clinically-relevant research. Among the numerous BBB models thus far described, a static (without flow), contact BBB model, where astrocytes and brain endothelial cells (BECs) are cocultured on the opposite sides of a porous membrane, emerged as a simplified yet authentic system to simulate the BBB with high throughput screening capacity. Nevertheless the generation of such model presents few technical challenges. Here, we describe a protocol for preparation of a contact human BBB model utilizing a novel combination of primary human BECs and immortalized human astrocytes. Specifically, we detail an innovative method for cell-seeding on inverted inserts as well as specify insert staining techniques and exemplify how we use our model for BBB-related research.

Establishment of human models of the blood-brain barrier (BBB) can benefit research into brain conditions associated with BBB failure. We describe here an improved technique for preparation of a contact BBB model, which permits coculturing of human astrocytes and brain endothelial cells on the opposite sides of a porous membrane.

The blood-brain barrier (BBB) comprises impermeable but adaptable brain capillaries which tightly control the brain environment. Failure of the BBB has ...

Cell Squeezing as a Robust, Microfluidic Intracellular Delivery Platform

Rapid mechanical deformation of cells has emerged as a promising, vector-free method for intracellular delivery of macromolecules and nanomaterials. This technology has shown potential in addressing previously challenging applications; including, delivery to primary immune cells, cell reprogramming, carbon nanotube, and quantum dot delivery. This vector-free microfluidic platform relies on mechanical disruption of the cell membrane to facilitate cytosolic delivery of the target material. Herein, we describe the detailed method of use for these microfluidic devices including, device assembly, cell preparation, and system operation. This delivery approach requires a brief optimization of device type and operating conditions for previously unreported applications. The provided instructions are generalizable to most cell types and delivery materials as this system does not require specialized buffers or chemical modification/conjugation steps. This work also provides recommendations on how to improve device performance and trouble-shoot potential issues related to clogging, low delivery efficiencies, and cell viability.

Rapid mechanical deformation of cells has emerged as a promising, vector-free method for intracellular delivery of macromolecules and nanomaterials. This protocol provides detailed steps on how to use the system for a broad range of applications.

Rapid mechanical deformation of cells has emerged as a promising, vector-free method for intracellular delivery of macromolecules and nanomaterials. This ...

In Vitro Permeation of FITC-loaded Ferritins Across a Rat Blood-brain Barrier: a Model to Study the Delivery of Nanoformulated Molecules

Brain microvascular endothelial cells, supported by pericytes and astrocytes endfeet, are responsible for the low permeation of large hydrosoluble drugs through the blood-brain barrier (BBB), causing difficulties for effective pharmacological therapies. In recent years, different strategies for promoting brain targeting have aimed to improve drug delivery and activity at this site, including innovative nanosystems for drug delivery across the BBB. In this context, an in vitro approach based on a simplified cellular model of the BBB provides a useful tool to investigate the effect of nanoformulations on the trans-BBB permeation of molecules. This study describes the development of a double-layer BBB, consisting of co-cultured commercially available primary rat brain microvascular endothelial cells and astrocytes. A multiparametric approach for the validation of the model, based on the measurement of the transendothelial electrical resistance and the apparent permeability of a high molecular weight dextran, is also described. As proof of concept for the employment of this BBB model to study the effect of different nanoformulations on the translocation of fluorescent molecules across the barrier, we describe the use of fluorescein isothiocyanate (FITC), loaded into ferritin nanoparticles. The ability of ferritins to improve the trans-BBB permeation of FITC was demonstrated by flux measurements and confocal microscopy analyses. The results suggest this is a useful system for validating nanosystems for delivery of drugs across the BBB.

In Vitro Permeation of FITC-loaded Ferritins Across a Rat Blood-brain Barrier: a Model to Study the Delivery of Nanoformulated Molecules

A method to establish an in vitro model of blood-brain barrier based on a co-culture of rat brain microvascular endothelial cells and astrocytes is described and validated. This system proved to be a valid tool to study the effect of nanoformulation on the trans-barrier permeation of fluorescent molecules.

Brain microvascular endothelial cells, supported by pericytes and astrocytes endfeet, are responsible for the low permeation of large hydrosoluble drugs ...

A Method for Determination and Simulation of Permeability and Diffusion in a 3D Tissue Model in a Membrane Insert System for Multi-well Plates

In vitro cultivated skin models have become increasingly relevant for pharmaceutical and cosmetic applications, and are also used in drug development as well as substance testing. These models are mostly cultivated in membrane-insert systems, their permeability toward different substances being an essential factor. Typically, applied methods for determination of these parameters usually require large sample sizes (e.g., Franz diffusion cell) or laborious equipment (e.g., fluorescence recovery after photobleaching (FRAP)). This study presents a method for determining permeability coefficients directly in membrane-insert systems with diameter sizes of 4.26 mm and 12.2 mm (cultivation area). The method was validated with agarose and collagen gels as well as a collagen cell model representing skin models. The permeation processes of substances with different molecular sizes and permeation through different cell models (consisting of collagen gel, fibroblast, and HaCaT) were accurately described.
Moreover, to support the above experimental method, a simulation was established. The simulation fits the experimental data well for substances with small molecular size, up to 14 x 10-10 m Stokes radius (4,000 MW), and is therefore a promising tool to describe the system. Furthermore, the simulation can considerably reduce experimental efforts and is robust enough to be extended or adapted to more complex setups.

A method for determination of permeability in a membrane insert system for multi-well plates and in silico parameter optimization for the calculation of diffusion coefficients using simulation are presented.

In vitro cultivated skin models have become increasingly relevant for pharmaceutical and cosmetic applications, and are also used in drug development as ...

A Human 3D Extracellular Matrix-Adipocyte Culture Model for Studying Matrix-Cell Metabolic Crosstalk

The extracellular matrix (ECM) plays a central role in regulating tissue homeostasis, engaging in crosstalk with cells and regulating multiple aspects of cellular function. The ECM plays a particularly important role in adipose tissue function in obesity, and alterations in adipose tissue ECM deposition and composition are associated with metabolic disease in mice and humans. Tractable in vitro models that permit dissection of the roles of the ECM and cells in contributing to global tissue phenotype are sparse. We describe a novel 3D in vitro model of human ECM-adipocyte culture that permits study of the specific roles of the ECM and adipocytes in regulating adipose tissue metabolic phenotype. Human adipose tissue is decellularized to isolate ECM, which is subsequently repopulated with preadipocytes that are then differentiated within the ECM into mature adipocytes. This method creates ECM-adipocyte constructs that are metabolically active and retain characteristics of the tissues and patients from which they are derived. We have used this system to demonstrate disease-specific ECM-adipocyte crosstalk in human adipose tissue. This culture model provides a tool for dissecting the roles of the ECM and adipocytes in contributing to global adipose tissue metabolic phenotype and permits study of the role of the ECM in regulating adipose tissue homeostasis.

We describe a 3D human extracellular matrix-adipocyte in vitro culture system that permits dissection of the roles of the matrix and adipocytes in contributing to adipose tissue metabolic phenotype.

The extracellular matrix (ECM) plays a central role in regulating tissue homeostasis, engaging in crosstalk with cells and regulating multiple aspects of ...

Real-Time Intravital Multiphoton Microscopy to Visualize Focused Ultrasound and Microbubble Treatments to Increase Blood-Brain Barrier Permeability

The blood-brain barrier (BBB) is a key challenge for the successful delivery of drugs to the brain. Ultrasound exposure in the presence of microbubbles has emerged as an effective method to transiently and locally increase the permeability of the BBB, facilitating para- and transcellular transport of drugs across the BBB. Imaging the vasculature during ultrasound-microbubble treatment will provide valuable and novel insights on the mechanisms and dynamics of ultrasound-microbubble treatments in the brain.
Here, we present an experimental procedure for intravital multiphoton microscopy using a cranial window aligned with a ring transducer and a 20x objective lens. This set-up enables high spatial and temporal resolution imaging of the brain during ultrasound-microbubble treatments. Optical access to the brain is obtained via an open-skull cranial window. Briefly, a 3-4 mm diameter piece of the skull is removed, and the exposed area of the brain is sealed with a glass coverslip. A 0.82 MHz ring transducer, which is attached to a second glass coverslip, is mounted on top. Agarose (1% w/v) is used between the coverslip of the transducer and the coverslip covering the cranial window to prevent air bubbles, which impede ultrasound propagation. When sterile surgery procedures and anti-inflammatory measures are taken, ultrasound-microbubble treatments and imaging sessions can be performed repeatedly over several weeks. Fluorescent dextran conjugates are injected intravenously to visualize the vasculature and quantify ultrasound-microbubble induced effects (e.g., leakage kinetics, vascular changes). This paper describes the cranial window placement, ring transducer placement, imaging procedure, common troubleshooting steps, as well as advantages and limitations of the method.

This protocol describes the surgical and technical procedures that enable real-time in vivo multiphoton fluorescence imaging of the rodent brain during focused ultrasound and microbubble treatments to increase blood-brain barrier permeability.

The blood-brain barrier (BBB) is a key challenge for the successful delivery of drugs to the brain. Ultrasound exposure in the presence of microbubbles ...

Construction of a Human Aorta Smooth Muscle Cell Organ-On-A-Chip Model for Recapitulating Biomechanical Strain in the Aortic Wall

Conventional two-dimensional cell culture techniques and animal models have been used in the study of human thoracic aortic aneurysm and dissection (TAAD). However, human TAAD sometimes cannot be characterized by animal models. There is an apparent species gap between clinical human studies and animal experiments that may hinder the discovery of therapeutic drugs. In contrast, the conventional cell culture model is unable to simulate in vivo biomechanical stimuli. To this end, microfabrication and microfluidic techniques have developed greatly in recent years, providing novel techniques for establishing organoids-on-a-chip models that replicate the biomechanical microenvironment. In this study, a human aorta smooth muscle cell organ-on-a-chip (HASMC-OOC) model was developed to simulate the pathophysiological parameters of aortic biomechanics, including the amplitude and frequency of cyclic strain experienced by human aortic smooth muscle cells (HASMCs) that play a vital role in TAAD. In this model, the morphology of HASMCs became elongated in shape, aligned perpendicularly to the strain direction, and presented a more contractile phenotype under strain conditions than under static conventional conditions. This was consistent with the cell orientation and phenotype in native human aortic walls. Additionally, using bicuspid aortic valve-related TAAD (BAV-TAAD) and tricuspid aortic valve-related TAAD (TAV-TAAD) patient-derived primary HASMCs, we established BAV-TAAD and TAV-TAAD disease models, which replicate HASMC characteristics in TAAD. The HASMC-OOC model provides a novel in vitro platform that is complementary to animal models for further exploring the pathogenesis of TAAD and discovering therapeutic targets.

Here, we developed a human aorta smooth muscle cell organ-on-a-chip model to replicate the in vivo biomechanical strain of smooth muscle cells in the human aortic wall.

Conventional two-dimensional cell culture techniques and animal models have been used in the study of human thoracic aortic aneurysm and dissection ...

Disruption of the Blood-Spinal Cord Barrier Using Low-Intensity Focused Ultrasound in a Rat Model

Low-intensity focused ultrasound (LIFU) uses ultrasonic pulsations at lower intensities than ultrasound and is being tested as a reversible and precise neuromodulatory technology. Although LIFU-mediated blood-brain barrier (BBB) opening has been explored in detail, no standardized technique for blood-spinal cord barrier (BSCB) opening has been established to date. Therefore, this protocol presents a method for successful BSCB disruption using LIFU sonication in a rat model, including descriptions of animal preparation, microbubble administration, target selection&#160;and localization, as well as BSCB disruption visualization and confirmation. The approach reported here is particularly useful for researchers who need a fast and cost-effective method to test and confirm target localization and precise BSCB disruption in a small animal model with a focused ultrasound transducer, evaluate the BSCB efficacy of sonication parameters, or explore applications for LIFU at the spinal cord, such as drug delivery, immunomodulation, and neuromodulation. Optimizing this protocol for individual use is recommended, especially for advancing future preclinical, clinical, and translational work.

Disruption of the blood-spinal cord barrier (BSCB) can be successfully achieved with the intravenous administration of microbubbles and the application of low-intensity focused ultrasound (LIFU). This protocol details the opening of the BSCB using LIFU in a rodent model, including equipment setup, microbubble injection, target localization, and BSCB disruption visualization.

Low-intensity focused ultrasound (LIFU) uses ultrasonic pulsations at lower intensities than ultrasound and is being tested as a reversible and precise ...