Name: ex vivo corneal organ culture model for wound healing studies
Uploaded: 2019-02-15T12:30:00
Description: Watch this Scientific Journal Video about Ex Vivo Corneal Organ Culture Model for Wound Healing Studies at JoVE.com

This work was supported by NIH-NEI R01 EY024942, Research to Prevent Blindness, Upstate Medical University Unrestricted Research Funds, and Lions District 20-Y. Microscopy and image analysis of paraffin sections were performed at the Microscopy CORE and histological slide preparation was performed at the Biorepository and Pathology CORE at the Icahn School of Medicine at Mount Sinai.

1. Organ Culture
<ol>
	<li>Preparations
	<ol>
		<li>Prepare agar solution as follows. In a small flask, prepare 1% agar and 1 mg/mL bovine collagen in DMEM-F12 up to 20 mL. Bring to boil on a hot plate. Put the solution into a 50 mL conical tube. Place tube in a water bath on a hot plate to keep the solution from solidifying.</li>
		<li>Prepare supplemented serum-free media (SSFM) as per the composition provided in the Table of Materials. 
		NOTE: The necessary am...

This protocol describes a model for studying wound healing in a natural stratified 3D environment. Use of organ culture as an intermediate between cell culture and in vivo studies significantly reduces costs as well as reducing procedures on live animals. Other 3D models have been of great benefit to the field including self-synthesizing collagen gels made from primary human corneal fibroblasts2 or these same cells embedded in gels made from animal-derived collagens31. The ...

Scarring in the cornea resulting from injury, trauma, or infection can lead to debilitating opacities and permanent vision loss. Thus, there is a critical need to identify pathways that can be targeted for therapeutic intervention. Current treatment options are limited and consist primarily of corneal transplantations, which are not accessible to patients across the world. Both human (Figure 1) and animal corneas can be utilized for 2D and 3D cell culture studies1,2. Human cadaver corneas not suitable for transplant can be obtained from eye banks or centralized tissue banks (National Disease Research Interchange (NDRI)), and animal eyes can be obtained from an abattoir. Primary corneal epithelial cells, stromal fibroblasts, and more recently, endothelial cells, can be isolated and cultured from these tissues for wound healing and toxicology studies3,4,5. In addition to the importance of understanding the molecular basis of blinding eye disease, the accessibility of tissue and the ability to culture primary cells has made the cornea an important model system for study. The cornea is ideal for testing the effects of agents on scarring as the normal cornea is transparent and certain types of wounds create opacities or fibrotic scars (reviewed in6). Several in vivo corneal wound healing models have also been extensively utilized for scarring studies1. Less utilized has been the ex vivo corneal wound healing model7,8 that is describe in detail here. The goal of this method is to quantify scarring outcomes characterized by fibrotic makers in a 3D multicellular corneal ex vivo model system.
Corneal epithelial wounding that does not breach the epithelial basement membrane normally closes within 24-72 h9. Soon after wounding, the cells at the edge of the epithelium start spreading and migrating into the epithelial free surface, to reestablish epithelial barrier function. This activity is sequentially followed by activation of corneal basal cell proliferation first and, in a later stage, of precursor cells located at the outer limbal zone to achieve recovery of epithelial cell mass10,11. These wounds often heal without scarring. However, a wound that penetrates the basement membrane into the stroma often results in scar formation1. After corneal stromal wounding, the stroma is populated with cells of multiple origins including differentiated resident stromal cells as well as bone marrow-derived fibrocytes12,13,14. Fibrotic scarring is characterized by the persistence of myofibroblasts in a healing wound. These pathological myofibroblasts demonstrate increased adhesion through the accumulation of integrins in focal adhesions, contractile &#945;-smooth muscle actin (&#945;-SMA) stress fibers, and local activation of extracellular matrix (ECM)-sequestered latent-transforming growth factor-beta (TGF&#946;). The differentiation of epithelial-derived cells, known as epithelial to mesenchymal transition (EMT), may also contribute to scar formation6.
There is a delicate balance between cell differentiation and apoptosis after wounding. Because of the breach in the basement membrane, growth factors such as platelet-derived growth factor (PDGF) and TGF&#946; from tears and the epithelium bathe the stroma, inducing myofibroblast differentiation, a sustained autocrine loop of TGF&#946;&#160;activation, and the secretion of disorganized fibrotic ECM15,16. The persistence of myofibroblasts in the healed wound promotes haze and scarring in the cornea (Figure 2). However, in regeneratively healed wound although myofibroblasts develop, they apoptose and thus are absent or significantly reduced in number in the healed tissue (reviewed in reference6,10). Thus, research on fibrotic scarring has focused at least in part on targeting molecules that prevent excessive myofibroblast development or myofibroblast persistence17,18. Because myofibroblast persistence characterizes both scarring and fibrotic disease in all tissues19, the cornea may be useful as a model system to study general cellular mechanisms of fibrosis.
In our model system, the cornea is wounded with a cylindrical blade called a trephine while still in the globe. Human and pig corneas can be wounded with either a 6 or 7 mm trephine; for rabbit corneas a 6 mm trephine is preferred. The pig cornea is similar in size to the human cornea. Because they are cost effective and readily available in large numbers, pig corneas are routinely used for organ culture. Furthermore, antibodies and siRNAs made to react with human have consistently cross-reacted with pig7. After wounding, corneas are cut from the globe with the limbus intact and mounted on an agar/collagen base. The corneas are cultured in serum-free media plus stabilized vitamin C to simulate fibroblast proliferation and ECM deposition20. Neither the addition of serum nor growth factors are needed to induce myofibroblast formation7. Corneas are routinely fixed and processed for histology after two weeks of culture. For gene knockdown, or to test the effects of an agent on wound healing, the wound can be treated with siRNA in the wound after wounding7 or a soluble agent can be added to the media, respectively8.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>PBS</td>
			<td>Gibco</td>
			<td>10-010-023</td>
			<td></td>
		</tr>
		<tr>
			<td>Pen Strep&#160;</td>
			<td>MP Biomedicals</td>
			<td>91670049</td>
			<td></td>
		</tr>
		<tr>
			<td>Bovine Collagen Solution</td>
			<td>Advance Biomatrix</td>
			<td>5005</td>
			<td></td>
		</tr>
		<tr>
			<td>Pig eyes with lids attached&#160;</td>
			<td>Pel-freeze, Arkansas</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>6.0 mm trephine&#160;</td>
			<td>Katena</td>
			<td>K28014</td>
			<td></td>
		</tr>
		<tr>
			<td>Surgical Blade&#160;</td>
			<td>Personna</td>
			<td>0.009</td>
			<td></td>
		</tr>
		<tr>
			<td>Small scissor</td>
			<td>Fisher</td>
			<td>895110</td>
			<td></td>
		</tr>
		<tr>
			<td>Forceps</td>
			<td>Fisher</td>
			<td>08953-F</td>
			<td></td>
		</tr>
		<tr>
			<td>Kim Wipes&#160;</td>
			<td>Kimberly-Clark&#8482; 34120</td>
			<td>06-666</td>
			<td></td>
		</tr>
		<tr>
			<td>60 mm cell culture dishes&#160;</td>
			<td>Falcon</td>
			<td>08-772B</td>
			<td></td>
		</tr>
		<tr>
			<td>Supplemented Serum- Free media (SSFM)</td>
			<td></td>
			<td></td>
			<td>Add all of the following components to DMEM/F-12:&#160; ITS, RPMI, Glutathione, L-Glutamine, MEM Non essential amino acids, MEM Sodium Pyruvate, ABAM, Gentamicin, Vitamin C.&#160;</td>
		</tr>
		<tr>
			<td>DMEM/F-12</td>
			<td>Gibco</td>
			<td>11330</td>
			<td></td>
		</tr>
		<tr>
			<td>ITS Liquid Media Supplement&#160;</td>
			<td>Sigma</td>
			<td>I3146</td>
			<td>100X</td>
		</tr>
		<tr>
			<td>RPMI 1640 Vitamins Solution&#160;</td>
			<td>Sigma</td>
			<td>R7256</td>
			<td>100X</td>
		</tr>
		<tr>
			<td>Glutathione</td>
			<td>Sigma</td>
			<td>G6013</td>
			<td>Use at 1 &#181;g/mL. Freeze aliquots; do not reuse after thawing.</td>
		</tr>
		<tr>
			<td>1% L-glutamine solution&#160;</td>
			<td>Gibco</td>
			<td>25030-081</td>
			<td>100X</td>
		</tr>
		<tr>
			<td>MEM Non-essential amino acids solution&#160;</td>
			<td>Gibco</td>
			<td>11140</td>
			<td>100X</td>
		</tr>
		<tr>
			<td>MEM Sodium pyruvate solution&#160;</td>
			<td>Gibco</td>
			<td>11360</td>
			<td>1 M Stocks (1000X) and freeze in single use aliquits.&#160; Use from freezer each time media is made.</td>
		</tr>
		<tr>
			<td>ABAM&#160;</td>
			<td>Sigma</td>
			<td>A7292</td>
			<td>100X</td>
		</tr>
		<tr>
			<td>Gentamicin&#160;</td>
			<td>Sigma</td>
			<td>30-005-CR</td>
			<td>200X</td>
		</tr>
		<tr>
			<td>Vitamin C&#160;</td>
			<td>Wako</td>
			<td>070-0483</td>
			<td>2-0-aD Glucopyranosyl-Ascorbic Acid. 1 mM stocks (1000x)</td>
		</tr>
		<tr>
			<td>10% Iodine&#160;</td>
			<td>Fisher Chemical</td>
			<td>SI86-1</td>
			<td></td>
		</tr>
		<tr>
			<td>Tissue Path Cassettes&#160;</td>
			<td>Fisher</td>
			<td>22-272416</td>
			<td></td>
		</tr>
		<tr>
			<td>Normal Goat Serum (NGS)</td>
			<td>Jackson Immuno Research</td>
			<td>005-000-121</td>
			<td>We use 3% NGS</td>
		</tr>
		<tr>
			<td>Mounting Media&#160;</td>
			<td>Thermo Scientific</td>
			<td>TA-030-FM</td>
			<td></td>
		</tr>
		<tr>
			<td>Safe Clear&#160;</td>
			<td>Fisher</td>
			<td>314-629</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethyl Alcohol</td>
			<td>Ultra Pure</td>
			<td>200CSGP</td>
			<td>200 Proof, diluted at 100%, 70%, 50%)&#160;</td>
		</tr>
		<tr>
			<td>Sodium citrate&#160;</td>
			<td>Fisher</td>
			<td>BP327</td>
			<td>10mM, pH 6.4</td>
		</tr>
		<tr>
			<td>Hematoxylin</td>
			<td>EMD Millipore</td>
			<td>M10742500</td>
			<td></td>
		</tr>
		<tr>
			<td>Bluing agent&#160;</td>
			<td>Ricca Chemical Company</td>
			<td>220-106</td>
			<td></td>
		</tr>
		<tr>
			<td>1% Triton X-100</td>
			<td>Fisher</td>
			<td>9002-93-1</td>
			<td>Diluted in PBS</td>
		</tr>
		<tr>
			<td>0.1% Tween 20&#160;</td>
			<td>Fisher</td>
			<td>BP337</td>
			<td>Diluted in PBS</td>
		</tr>
		<tr>
			<td>3% Hydrogen Peroxide&#160;</td>
			<td>Fisher</td>
			<td>H324</td>
			<td></td>
		</tr>
		<tr>
			<td>DAB Kit&#160;</td>
			<td>Vector Laboratories</td>
			<td>SK-4100</td>
			<td></td>
		</tr>
		<tr>
			<td>Agar&#160;</td>
			<td>Fisher&#160;</td>
			<td>BP1423-500</td>
			<td>Agar solution: prepare 1% agar and 1 mg/mL bovine collagen in DMEM-F12 up to 20 mL</td>
		</tr>
		<tr>
			<td>Parafilm</td>
			<td>Bermis</td>
			<td>13-374-12</td>
			<td></td>
		</tr>
		<tr>
			<td>Moist Chamber</td>
			<td></td>
			<td></td>
			<td>Use any chamber, cover it with wet Wipe Tissue and then put a layer of Parafilm over it.</td>
		</tr>
		<tr>
			<td>Lipofectamine 2000</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Qiagen RNAprotect Cell Reagent</td>
			<td>Qiagen</td>
			<td>&#160;76104</td>
			<td></td>
		</tr>
		<tr>
			<td>Ambion PureLink RNA Mini Kit</td>
			<td>Thermo Scientific</td>
			<td>12183018A</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-Fibronectin-EDA Antibody</td>
			<td>Sigma</td>
			<td>F6140</td>
			<td>1:200 Diluted in&#160; 3% normal goat serum</td>
		</tr>
		<tr>
			<td>Anti-alpha smooth muscle actin Antibody</td>
			<td>Sigma</td>
			<td>A2547 or C6198 (cy3 conjugated)</td>
			<td>1:200 Diluted in 3% normal goat serum</td>
		</tr>
		<tr>
			<td>Permafluor&#160;</td>
			<td>Thermo Scientific</td>
			<td>TA-030-FM</td>
			<td></td>
		</tr>
		<tr>
			<td>DAPI&#160;</td>
			<td>Invitrogen</td>
			<td>P36931</td>
			<td></td>
		</tr>
		<tr>
			<td>Gt anti -MS IgG (H+L) Secondary Antibody, HRP&#160;</td>
			<td>Invitrogen</td>
			<td>62-6520</td>
			<td>1:100 diluted in 3% normal goat serum (for a-SMA, DAB staining)</td>
		</tr>
		<tr>
			<td>Gt anti -MS IgM (H+L) Secondary Antibody, HRP&#160;</td>
			<td>Thermo Scientific</td>
			<td>PA1-85999</td>
			<td>1:100 diluted in 3% normal goat serum (for FN-EDA, DAB staining)</td>
		</tr>
		<tr>
			<td>Gt anti -MS IgG (H+L) Secondary Antibody, Cy3&#160;</td>
			<td>Jackson Immuno Research</td>
			<td>115-165-146</td>
			<td>1:200 Diluted in&#160; 3% normal goat serum (for a-SMA, Fluorescence staining)</td>
		</tr>
		<tr>
			<td>&#160;Zeiss Axioplan2&#160;</td>
			<td>Zeiss</td>
			<td></td>
			<td>Microscope</td>
		</tr>
		<tr>
			<td>SPOT-2</td>
			<td colspan="2">Diagnostic Instruments, Sterling Heights, Michigan</td>
			<td>CCD camera</td>
		</tr>
	</tbody>
</table>

ex vivo corneal organ culture model for wound healing studies

The cornea has been used extensively as a model system to study wound healing. The ability to generate and utilize primary mammalian cells in two dimensional (2D) and three dimensional (3D) culture has generated a wealth of information not only about corneal biology but also about wound healing, myofibroblast biology, and scarring in general. The goal of the protocol is an assay system for quantifying myofibroblast development, which characterizes scarring. We demonstrate a corneal organ culture ex vivo model using pig eyes. In this anterior keratectomy wound, corneas still in the globe are wounded with a circular blade called a trephine. A plug of approximately 1/3 of the anterior cornea is removed including the epithelium, the basement membrane, and the anterior part of the stroma. After wounding, corneas are cut from the globe, mounted on a collagen/agar base, and cultured for two weeks in supplemented-serum free medium with stabilized vitamin C to augment cell proliferation and extracellular matrix secretion by resident fibroblasts. Activation of myofibroblasts in the anterior stroma is evident in the healed cornea. This model can be used to assay wound closure, the development of myofibroblasts and fibrotic markers, and for toxicology studies. In addition, the effects of small molecule inhibitors as well as lipid-mediated siRNA transfection for gene knockdown can be tested in this system.

Immunohistochemistry is the primary assay utilized to analyze the success of the ex vivo wound healing experiment. Figure 4 depicts the epithelium and anterior stroma in control tissue (Figure 4A, 4B). Six hours after wounding, the epithelium was absent (Figure 4C, 4D). Six days after wounding as expected, the epithelium had regrown (Figure 4E</s...

Watch this Scientific Journal Video about Ex Vivo Corneal Organ Culture Model for Wound Healing Studies at JoVE.com

Ex Vivo Corneal Organ Culture Model for Wound Healing Studies

A protocol for an ex vivo corneal organ culture model useful for wound healing studies is described. This model system can be used to assess the effects of agents to promote regenerative healing or drug toxicity in an organized 3D multicellular environment.

The cornea has been used extensively as a model system to study wound healing. The ability to generate and utilize primary mammalian cells in two ...

This paper described a simple method for assaying wounding in a three-dimensional, multi-cellular organ culture model system. We do this by using pig eyes, but even if you are not familiar with eyes, you can do this assay. As an overview, we received porcine eyes, cut out the globes, make a circular wound in the cornea that goes through the epithelium and about one third of the stroma.We cut out the cornea, and mount it on an Agar base, and put this construct in the incubator. The tissue will fill in creating a scar in the cornea. You don't need to add any growth factors, or even serum.This is done in serum-free media. Although this is performed in the cornea, it can be used as a model system for fibrotic healing in general. As many of the cellular pathways that are activated during scarring are similar between systems.In a biosafety hood, use a straight edge surgical blade to remove the globe from the lid on an ethanol-cleaned chopping board, and remove the excess fatty tissue from each eye. Holding the cleaned globe posteriorly with forceps immediately dip the eye in PBS followed by three quick dips in 10%iodine, and two quick dips in PBS. Then wrap the eye circumferentially with a clean lab tissue to wrap with enough pressure to achieve a taut corneal surface without contacting the cornea.Using a six millimeter trephine, penetrate the epithelium in the anterior stroma at the center of the cornea without making a full thickness wound through the entire cornea, and rotate the trephine 180 degrees clockwise and counterclockwise five times while applying light pressure to deepen the wound. When the wound is deep enough to allow a tissue flap to be lifted with forceps, use a surgical blade to cut the flap parallel to the globe while continuing to lift the anterior cornea within the wound margin. When the entire flap has been removed, a circular wound should be located at the center of the cornea.To harvest the cornea grasp the eye with the lab tissue, and use a surgical blade to make a small incision one millimeter away from the edge of the cornea to include the limbus and tissue collection. Using small, sharp scissors continue the incision around the globe keeping a millimeter margin across the cornea to keep the limbus in tact. Then place the cornea, wound-side down, in a 60 millimeter, or 100 millimeter dish containing one milliliter of PBS.To mount the cornea, use two pairs of forceps to hold the cornea epithelial-side up to create a cup, and use a sterile transfer pipette to add warmed agar solution into the cornea until the cup is full. After the agar hardens, carefully place the cornea in a new 60 millimeter plate agar-side down and cover the plate with a lid. Then add four milliliters of supplemented serum-free medium to each plate of corneas maintaining the corneas at an air-liquid interface at the limbal border in a cell culture incubator at 37 degrees celsius in 5%carbon dioxide, and wetting the corneal surfaces once daily with one drop of supplemented serum-free medium from the conditioned medium in the dish to keep the tissues hydrated.For gene knockdown, mix five microliters of small interfering or siRNa with 50 microliters of reduced serum minimum essential medium and two microliters of transfection reagent. With 50 microliters of reduced serum medium per cornea. After five minutes, mix the two mixtures together, and add 200 microliters of reduced serum minimum medium to each siRNA mixture.Then pipette the siRNA solutions drop wise onto each wound. Then put the corneas into the incubator. After three hours, use the medium in each dish to wash the siRNA from the corneal surfaces, and replace the conditioned medium in each dish with fresh supplemented serum free medium plus antibiotics.Then return the corneal cultures to the cell culture incubator, and incubate for two weeks. Six hours after wounding, the corneal epithelium is absent. Six days after wounding, the epithelium regrows.Fluorescence amino staining with alpha smooth muscle actin reveals a gradient of active myofibroblasts along the wound margin from the anterior to posterior stroma. Immuno-histochemical staining for alpha smooth muscle actin reveals a dramatic increase in alpha smooth muscle actin protein expression in wounded plus control siRNA corneas. Compared to unwounded and target protein siRNA treated, wounded corneas.Similarly, fibronectin extra domain A is upregulated in siRNA treated wounded corneas compared to unwounded and target protein siRNA treated wounded corneas. Demonstrating a successful knock down of the target protein. Further, treatment of the wounded corneas with the toxin that nonspecifically targets the target protein prevents re-epithelialization and results in qualitative cell death, a disorganized matrix, and stromal vacuoles suggesting that the toxin does not promote healing at the concentration assayed.In conclusion, while attempting this procedure it's important to remember to keep the blade parallel to the tissue while cutting, so that it doesn't penetrate the globe. Different wounding techniques can be employed with this assay, including chemical burn or epithelial scrape. It can also be used for drug toxicity assays to determine if the epithelium heals and at what rate.This is a cost-savings ex vivo, organ culture model system that can precede your in vivo wound healing studies.

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