Name: an acute retinal model for evaluating blood retinal barrier breach and potential drugs for treatment
Uploaded: 2016-09-13T15:00:00.000+00:00
Duration: 9 min 33 s
Description: Watch this Scientific Journal Video about An Acute Retinal Model for Evaluating Blood Retinal Barrier Breach and Potential Drugs for Treatment at JoVE.com

Bringhurst Meats (Berlin, NJ) is acknowledged for their genuine help in providing the swine eyeballs.

All protocols were carried out in compliance with the policies of the Institutional Animal Care and Use Committee where applicable.
1. Preparation
<ol>
	<li>Prepare the stabilization media with 75% Dulbecco&#39;s Modified Eagle Medium (DMEM), 25% Hanks&#39; Balanced Salt Solution (HBSS). Mix well, aliquot and store at -20 &#176;C until use.</li>
	<li>Prepare the Phosphate Buffered Saline (PBS) and sterilize by autoclaving. Store the solution at room temperature. Warm the PBS to 37 &#176;C before the experiment (5 ml per well).</li>
	<li>Prepare 10%, 20% and 30% sucrose in PBS. Filter all the solutions individually over separate 0.22 &#956;m filters for sterilization. Save the solutions at 4 &#176;C.</li>
	<li>Prepare the histamine stock solution in PBS to a concentration of 90 mM. Sterilize the solution by filtering over a 0.22 &#181;M filter. Aliquot and save the solution at -80 &#176;C. Avoid multiple freeze-and-thaw cycles.</li>
	<li>Make fresh 4% paraformaldehyde (PFA) in PBS before the experiment. Place it on ice. 
	Caution: Keep PFA in a fume hood and wear appropriate protective equipment.</li>
	<li>Thaw the stabilization medium (20 ml per retina). Add Penicillin-Streptomycin to a final concentration of 100 U/ml. Warm part of the medium (15 ml per retina) to 37 &#176;C in incubator before the experiment. Leave the rest of the medium on ice.</li>
	<li>Place the HBSS (10 ml per retina) on ice.</li>
</ol>
2. Retinal Organotypic Culture
<ol>
	<li>Transfer the samples to a tissue culture hood. Open the eyecup by cutting around the lens. Using a brush, gently remove the vitreous humor without pulling on the retina. Gently detach the retina from the cut edge with a brush to expose the optic disc. Severe the optic nerve with a razor and release the retina.</li>
	<li>Transfer the retina into a Petri dish and carefully rinse the retina once using cold HBSS. Place the sample in HBSS on ice. Dissect as many retinas out as needed by repeating Step 2.1 and this step.</li>
	<li>Cut the retina in half symmetrically with a razor. Gently transfer samples to a 6-well plate with 3 ml of stabilization media per well. Allow equilibration for 30 min at 37 &#176;C in an incubator with the atmosphere containing 5% CO2.</li>
	<li>Prepare the following reagents during the incubation at Step 2.3: Dilute the histamine stock solution to the desired concentration (450 &#956;M) in warm medium. Dissolve LXA4 (stored under Argon) into the medium to a final concentration of 250 ng/ml. 
	NOTE: When measuring the effect of LXA4, one half from a single retina is used for histamine alone, while the other half is used for histamine with LXA4.</li>
	<li>Aspirate the stabilization medium carefully and add the prepared medium to each well (3 ml per well). Incubate the samples at 37 &#176;C for 1 hr in an incubator with the atmosphere containing 5% CO2.</li>
	<li>Rinse the samples once in warm, sterile PBS.</li>
</ol>
3. Prepare the Samples for Immunostaining
<ol>
	<li>Aspirate PBS from the plates. Add 4% PFA (3 ml per well) and incubate for 15 min at room temperature.</li>
	<li>Quickly aspirate the PFA. Rinse the samples once using PBS. Transfer the samples to 10% sucrose (5 ml per well) and incubate for 2 to 4 hr at 4 &#176;C.</li>
	<li>Transfer the samples to a 30% sucrose (5 ml per well) and incubate overnight at 4 &#176;C. Mix one part of the commercial freezing medium with two parts of 20% sucrose to make the working freezing medium. Leave it at 4 &#176;C overnight or longer until the air bubbles disappear.</li>
	<li>Transfer the samples to the working freezing medium and allow equilibration for 5 min at room temperature. Trim each retina into rectangles (roughly 3 mm by 5 mm).</li>
	<li>Carefully transfer the samples into the working freezing media contained in a cylindrical container (about 1 cm radius x 2 cm height) devised from aluminum foil. Ensure that the retinal slices are vertical (oriented to provide a cross-section of the retina upon sectioning) and freeze them in liquid nitrogen. Save the blocks at -80 &#176;C until use.</li>
	<li>Section each block on a cryostat into 14 &#956;m thick slices and mount the sections on glass slides. Store the slides at -80 &#176;C until use.</li>
</ol>
4. Immunostaining
<ol>
	<li>Wash the sections with 5% sucrose phosphate buffer (SPB, 5% sucrose in PBS, pH 7.4) once. Block the non-specific binding sites by incubating the sections in blocking buffer (5% SPB with 10% normal goat serum and 0.5% Triton X-100) for 1 hr at room temperature.</li>
	<li>Incubate the sections (on slides) with the appropriate primary antibody (GFAP or MAP2, diluted at 1:500 in blocking buffer) for 1 hr. Aspirate the solution. Wash three times in 5% SPB. For staining the endogenous IgG, skip this step.</li>
	<li>Incubate the sections with the corresponding secondary antibodies (Cyanine3/FITC conjugated donkey anti-mouse/anti-rabbit IgG, diluted at 1:800 in the blocking buffer) for 1 hr.</li>
	<li>Wash the sections thoroughly with 5% SPB three times. Prepare the samples for microscopy by mounting them in mounting medium containing DAPI and covering with coverslips.</li>
	<li>Using a laser confocal microscope, capture images through a 20X lens under identical parameters such as laser intensity, gain value, dwell time, etc. across groups. Set the excitation/emission wavelengths for the blue channel (to detect DAPI) as 408/447 nm, for the red channel (to detect Cyanine3) as 561/785 nm and for the green channel (to detect FITC) as 488/525 nm.</li>
</ol>
5. Image Analysis
<ol>
	<li>Quantify percentage of leaky blood vessels according to the following criteria12: Include only blood vessels with endothelial cell nuclei within the plane of section in the count; consider a blood vessel leaky if it shows a gradient of immunostaining surrounding the vessel.</li>
	<li>To determine the expression level, select regions of interest and measure the mean grey value using the image analysis software.</li>
	<li>To measure the width of the process, choose an area of the section where the processes are distinct (the outer nuclear layer, ONL, for example). Then choose an optical field where such processes are visible and continuous. Set the scale bar according to the microscopic setting, draw a line across the process and perform the measurement.</li>
	<li>To analyze the continuity of the process, select regions of interest, apply the filter called variance which enhances the edges in the image by replacing each pixel with its neighborhood variance, automatically adjust the contrast and brightness, count the lines and normalize the count by the area.</li>
	<li>Calculate statistical significances using a two-tailed Student&#39;s t-test. *, P &#60; 0.05; **, P &#60; 0.01; ***, P &#60; 0.001. Plot the result as Mean &#177; SEM.</li>
</ol>

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The authors have nothing to disclose.

In this report, we present a powerful ex vivo acute retinal model of BRB dysfunction using the swine retina. This model system does not require special instruments and can be easily adapted under most laboratory settings. However, to obtain a successful result, several steps require close attention. After obtaining the eyeballs from the source, they must be kept at 4 &#176;C or on ice and processed as soon as possible. When the effect of a treatment is being analyzed, two halves of the same retina must be used - one half to detect changes solely due to experimental procedures (baseline) and the other to detect the effect of the treatment. This approach also allows corrections for animal variations such as age, sex and health. 
This protocol can be successfully applied to retina from various species, such as M. musculus and B. Taurus (data not shown). Using commercial swine eyeballs is a significant cost-saving factor compared to maintaining the animals. Furthermore, in this study, the incubation time with histamine is only 60 minutes. This short incubation time provides the advantage of teasing out the early responses. It is noted that the study was carried out over different durations (20 min to 120 min) and different histamine concentrations (up to 700 &#956;M). Effects are observable at 30 min and at 225 &#956;M histamine. For illustrative purposes, the result obtained at 60 min with 450 &#956;M histamine is presented. In its present form, the following are the limitations of the model: (1) use of commercially obtained eyeballs increases the variability (but significantly cuts down on the cost); (2) the short incubation time may not allow complete manifestation of the response to the treatment - for example, those that require de novo protein synthesis. Modifications may help including longer incubation periods that could enable monitoring delayed responses.
LXA4 is chosen as the drug to investigate possible protection against the histamine-induced BRB damage. LXA4 is an endogenous compound that plays a key role in inflammatory events. It is produced in response to stress in vivo and has a short half life23. To mimic these conditions, a single addition of LXA4 was carried out along with histamine. This model system could also be used to further investigate if a prior treatment with LXA4 (or any other drug) would yield protection as well as to evaluate the duration of the protective treatment.
To the best of our knowledge, this is the first report of a retinal culture system with an experimentally-induced BRB breach. Evidently, exogenous perturbations other than histamine, such as lipopolysaccharides (LPS)24 and vascular endothelial growth factor (VEGF)25, can also be utilized to induce BRB breach. The effects of those perturbations and their potential treatments can be investigated on different cell types such as endothelial, M&#252;ller glial and neuronal cells in the presented model. Analyses may be performed on the entire retina or on one or more specific layers. Available cell-specific markers for retinal cells and synaptic layers allow an efficient detection of the responses via a large combination of parameters. Thus, we have established a retinal culture system for the rapid screening of products that protect against BRB dysfunction.

A growing body of evidence supports the existence of blood retinal barrier (BRB)1-5 and its similarity to the blood brain barrier (BBB)6,7. Compromise of the BBB has been tightly linked causally or as a diagnostic marker to chronic neurodegenerative diseases such as Alzheimer&#39;s disease (AD)8,9 and acute conditions such as delirium10. Mechanistic insights into these pathologies and discoveries for potential drug targets are generally hampered by the limited accessibility and network intricacy of the brain. Alternatives such as in vivo imaging11, brain organotypic culture12, primary cell cultures13,14 and co-culture systems15 have been generated. However, most of these models require special instruments, long experimental periods or multiple markers to identify cells. Functional and structural similarities between BBB and BRB as well as a correlation between the dysfunctions of the two have been argued16-19. In addition, easier access, well-defined cell types and a layered structure have allowed the well-characterized retina as a window to the brain. The structural and functional identities of the BBB and BRB remain to be compared in detail. However, retinal pathologies, especially the BRB breach, have also been tightly associated with the progression of various diseases, including diabetes18-19 and AD21,22. Thus, it is of interest to establish a BRB dysfunction system not only to delineate the mechanism but also to screen potential drugs. In this report, a protocol enabling BRB dysfunction using a simple acute retinal culture is developed and presented.
Increased BBB permeability and AD-like pathological changes have been established in a brain organotypic culture incubated with histamine, a pro-inflammatory mediator12. Therefore, in the presented system, histamine was applied to the ex vivo retinal culture to induce BRB dysfunction. Retinas from several species, such as Mus musculus and Bos Taurus, have been tested. Due to their commercial availability and resemblance to human tissue, fresh swine eyeballs were utilized to provide the data reported here. After incubating with histamine and/or other drugs, the retinas were processed for evaluation by immunostaining for several proteins12, such as Immunoglobulin G (IgG), one of the major components of the blood; glial fibrillary acidic protein (GFAP), a well-known marker for glial activation; and microtubule-associated protein 2 (MAP2), a neuron-specific cytoskeletal protein essential for microtubule assembly. Furthermore, the layered structure of the retina allows a detailed analysis of the processes of M&#252;ller cells and ganglion cells, such as changes in their width and continuity. Thus several additional parameters are available to assess the consequences of the BRB breach at an early stage and to evaluate the reversal effects of potential treatments as well.
In this protocol, potential reversal effects of screened drugs are evaluated from three perspectives: the leakage of blood vessels (BVs), the activation of glial cells and the damage-response of neuronal cells. Several quantification methods are utilized, for instance, the expression level shown by intensity of the immunostaining, width measurement of a process and continuity of neuronal processes shown by an enhancement filter. To better illustrate the method and to help interpret results, lipoxin A4 (LXA4), a compound endogenously synthesized in response to inflammatory injury and attenuating endothelial dysfunction23, has been chosen for demonstration purposes.

<table><tbody><tr><td>DMEM</td><td>Life Technologies&amp;nbsp;</td><td>11965-092</td><td></td></tr><tr><td>HBSS</td><td>Life Technologies&amp;nbsp;</td><td>14170-112</td><td></td></tr><tr><td>Sucrose</td><td>J.T.Baker</td><td>4072-05</td><td></td></tr><tr><td>Histamine&amp;nbsp;</td><td>Sigma</td><td>H7125-1G</td><td></td></tr><tr><td>Penicillin-Streptomycin&amp;nbsp;</td><td>Invitrogen</td><td></td><td></td></tr><tr><td>PFA</td><td>Electron Microscopy Sciences</td><td>15710</td><td></td></tr><tr><td>Freezing Media&amp;nbsp;</td><td>Triangle Biomedical Sciences</td><td>TFM-5</td><td></td></tr><tr><td>Normal Goat Serum&amp;nbsp;</td><td>Rockland</td><td>D104-00-0050</td><td></td></tr><tr><td>Triton X-100</td><td>Sigma</td><td>T8787</td><td></td></tr><tr><td>GFAP Antibody</td><td>Millipore</td><td>AB5804</td><td></td></tr><tr><td>MAP2 Antibody</td><td>EMD Millipore</td><td>MAB3418</td><td></td></tr><tr><td>FITC conjugated Donkey anti-rabbit IgG</td><td>Jackson ImmunoResearch Laboratories, Inc.</td><td>711-095-152</td><td></td></tr><tr><td>Cy3 conjugated Donkey anti-mouse IgG</td><td>Jackson ImmunoResearch Laboratories, Inc.</td><td>715-165-150</td><td></td></tr><tr><td>mounting medium containing DAPI</td><td>Vector Laboratories, Inc.</td><td>H-1200</td><td></td></tr><tr><td>Laser Confocal Microscope</td><td>Nikon</td><td>Eclipse Ti microscope</td><td></td></tr><tr><td>ImageJ</td><td>National Institutes of Health</td><td>1.45s</td><td></td></tr></tbody></table>

an acute retinal model for evaluating blood retinal barrier breach and potential drugs for treatment

A low-cost, easy-to-use and powerful model system is established to evaluate potential treatments that could ameliorate blood retinal barrier breach. An inflammatory factor, histamine, is demonstrated to compromise vessel integrity in the cultured retina through positive staining of IgG outside of the blood vessels. The effects of histamine itself and those of candidate drugs for potential treatments, such as lipoxin A4, are assessed using three parameters: blood vessel leakage via IgG immunostaining, activation of M&#252;ller cells via GFAP staining and change in neuronal dendrites through staining for MAP2. Furthermore, the layered organization of the retina allows a detailed analysis of the processes of M&#252;ller and ganglion cells, such as changes in width and continuity. While the data presented is with swine retinal culture, the system is applicable to multiple species. Thus, the model provides a reliable tool to investigate the early effects of compromised retinal vessel integrity on different cell types and also to evaluate potential drug candidates for treatment.

We present a low-cost, time-efficient and easy-to-use system to evaluate potential treatments that could protect against the BRB breach induced by histamine. IgG is constrained within the vessels in control retina (Figure 1A), but leaks out of the blood vessels upon histamine exposure (Figure 1B), confirming that the model is successfully established.
LXA4 was chosen to demonstrate the screening for drugs against BRB breach in the presented system. BRB dysfunction is attenuated upon treatment with LXA4 (Figure 1D), which has no significant effect by itself (Figure 1C). The reversal is quantitated as a percentage of the leaked blood vessels and the result is significant (Figure 1E). Two other retinal cell types, M&#252;ller glial cells (Figure 2) and ganglion cells (Figure 3), are further assessed. LXA4 treatment reverses the decrease in the width of the M&#252;ller glial cell processes (Figure 2E) shown through GFAP staining (Figure 2, A-D) but has no significant effects on the continuity of the dendritic processes in ganglion cells (Figure 3G), shown by MAP2 staining (Figure 3, A-E). It is also noted that no significant change in the expression level of either proteins is detected.
<img alt="Figure 1" src="/files/ftp_upload/54619/54619fig1.jpg" /> 
Figure 1: The Blood Retinal Barrier is Compromised upon Histamine Exposure and Rescued by LXA4 Treatment. IgG immunostaining (red) is presented from retina which was untreated (A), damage-induced with histamine only (B), treated with LXA4 only (C), or exposed to both histamine and LXA4 (D). In control (A) and LXA4 treated (C) groups, IgG is restricted within the blood vessels (BVs) while in the histamine group (B), IgG is detected out of the BVs where it forms leakage clouds indicated by dotted circles. Further addition of LXA4 rescues the vessel dysfunction (D). Scale bar, 20 &#956;m. (E) Quantitative measurement of the leaky BVs across the tested groups. Statistical significance is determined by a two-tailed Student&#39;s t-test. *, P &#60; 0.05; **, P &#60; 0.01; ***, P &#60; 0.001. Mean &#177; SEM (n = 18) is plotted in the graph. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54619/54619fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/54619/54619fig2.jpg" /> 
Figure 2: M&#252;ller Cell Processes are Compromised by Histamine and Rescued by LXA4 Treatment. Immunostaining for GFAP is presented from retina which was untreated (A), damage-induced with histamine only (B) treated with LXA4 only (C) or exposed to both histamine and LXA4 (D). Positive staining is obtained in the processes of M&#252;ller cells across the retina and around the BVs. Scale bar, 20 &#956;m. (E) The width of the M&#252;ller cell processes from all groups are presented. About 30 individual processes were measured per group. Statistical significance is determined by a two-tailed Student&#39;s t-test. *, P &#60; 0.05; **, P &#60; 0.01; ***, P &#60; 0.001. Mean &#177; SEM (n = 30) is plotted in the graph. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54619/54619fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/54619/54619fig3.jpg" /> 
Figure 3: The Continuity of Ganglion Cell Processes is not Affected by LXA4. (A) Immunostaining against MAP2 is presented from retina which was untreated (A), damage-induced with histamine only (B) treated with LXA4 only (C) or exposed to both histamine and LXA4 (D). Positive staining is obtained in the processes and cell bodies of ganglion cells. A sample image of MAP2 staining (E) together with its corresponding filter-enhanced image (F) is presented. The continuous processes are indicated by arrowheads. Scale bar, 20 &#956;m. (G) The density of the continuous, MAP2-positive ganglion cell processes from all groups are presented. Statistical significance is determined by a two-tailed Student&#39;s t-test. *, P &#60; 0.05; **, P &#60; 0.01; ***, P &#60; 0.001. Mean &#177; SEM (n= 18) is plotted in the graph. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54619/54619fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about An Acute Retinal Model for Evaluating Blood Retinal Barrier Breach and Potential Drugs for Treatment at JoVE.com

An Acute Retinal Model for Evaluating Blood Retinal Barrier Breach and Potential Drugs for Treatment

A low-cost, easy-to-use and powerful system is established to evaluate potential treatments that could ameliorate blood retinal barrier breach induced by histamine. Blood vessel leakage, M&#252;ller cell activation and the continuity of neuronal processes are utilized to assess the damage response and its reversal with a potential drug, lipoxin A4.

A low-cost, easy-to-use and powerful model system is established to evaluate potential treatments that could ameliorate blood retinal barrier breach. An ...

an-acute-retinal-model-for-evaluating-blood-retinal-barrier-breach

Nanyang Technological University

Research

JoVE Journal

Medicine

7.1K Views.  Rowan University.  Een low-cost, is makkelijk te gebruiken en krachtige systeem opgezet om potentiële behandelingen die bloed retinale barrière schending geïnduceerd door histamine kon verbeteren evalueren. Bloedvat lekkage Müller celactivering en de continuïteit van neuronale processen worden gebruikt om de schadereactie en de omkering van een potentieel geneesmiddel, lipoxine A4 beoordelen. 

Video: An Acute Retinal Model for Evaluating Blood Retinal Barrier Breach and Potential Drugs for Treatment

Experimental Models for Study of Retinal Pigment Epithelial Physiology and Pathophysiology

We have developed a cell culture procedure that can produce large quantities of confluent monolayers of primary human fetal retinal pigment epithelium (hfRPE) cultures with morphological, physiological and genetic characteristics of native human RPE. These hfRPE cell cultures exhibit heavy pigmentation, and electron microscopy show extensive apical membrane microvilli. The junctional complexes were identified with immunofluorescence labeling of various tight junction proteins. Epithelial polarity and function of these easily reproducible primary cultures closely resemble previously studied mammalian models of native RPE, including human. These results were extended by the development of therapeutic interventions in several animal models of human eye disease. We have focused on strategies for the removal of abnormal fluid accumulation in the retina or subretinal space. The extracellular subretinal space separates the photoreceptor outer segments and the apical membrane of the RPE and is critical for maintenance of retinal attachments and a whole host of RPE/retina interactions.

We provide a reproducible method for culturing confluent monolayers of human fetal retinal pigment epithelial cells (hfRPE) cells that exhibit morphology, physiology, polarity, and protein and gene expression patterns of adult native tissue. This work has been extended to an animal model of several eye diseases.

We have developed a cell culture procedure that can produce large quantities of confluent monolayers of primary human fetal retinal pigment epithelium ...

Neuroscience

Rat Model of Blood-brain Barrier Disruption to Allow Targeted Neurovascular Therapeutics

Endothelial cells with tight junctions along with the basement membrane and astrocyte end feet surround cerebral blood vessels to form the blood-brain barrier1. The barrier selectively excludes molecules from crossing between the blood and the brain based upon their size and charge. This function can impede the delivery of therapeutics for neurological disorders. A number of chemotherapeutic drugs, for example, will not effectively cross the blood-brain barrier to reach tumor cells2. Thus, improving the delivery of drugs across the blood-brain barrier is an area of interest.
The most prevalent methods for enhancing the delivery of drugs to the brain are direct cerebral infusion and blood-brain barrier disruption3. Direct intracerebral infusion guarantees that therapies reach the brain; however, this method has a limited ability to disperse the drug4. Blood-brain barrier disruption (BBBD) allows drugs to flow directly from the circulatory system into the brain and thus more effectively reach dispersed tumor cells. Three methods of barrier disruption include osmotic barrier disruption, pharmacological barrier disruption, and focused ultrasound with microbubbles. Osmotic disruption, pioneered by Neuwelt, uses a hypertonic solution of 25% mannitol that dehydrates the cells of the blood-brain barrier causing them to shrink and disrupt their tight junctions. Barrier disruption can also be accomplished pharmacologically with vasoactive compounds such as histamine5 and bradykinin6. This method, however, is selective primarily for the brain-tumor barrier7. Additionally, RMP-7, an analog of the peptide bradykinin, was found to be inferior when compared head-to-head with osmotic BBBD with 25% mannitol8. Another method, focused ultrasound (FUS) in conjunction with microbubble ultrasound contrast agents, has also been shown to reversibly open the blood-brain barrier9. In comparison to FUS, though, 25% mannitol has a longer history of safety in human patients that makes it a proven tool for translational research10-12.
In order to accomplish BBBD, mannitol must be delivered at a high rate directly into the brain's arterial circulation. In humans, an endovascular catheter is guided to the brain where rapid, direct flow can be accomplished. This protocol models human BBBD as closely as possible. Following a cut-down to the bifurcation of the common carotid artery, a catheter is inserted retrograde into the ECA and used to deliver mannitol directly into the internal carotid artery (ICA) circulation. Propofol and N2O anesthesia are used for their ability to maximize the effectiveness of barrier disruption13. If executed properly, this procedure has the ability to safely, effectively, and reversibly open the blood-brain barrier and improve the delivery of drugs that do not ordinarily reach the brain 8,13,14.

Blood-brain barrier disruption aids the delivery of certain drugs to the brain. Mannitol delivered intra-arterially shrinks cells surrounding blood vessels in order to physically disrupt the barrier.

Endothelial cells with tight junctions along with the basement membrane and astrocyte end feet surround cerebral blood vessels to form the blood-brain ...

Using Adeno-associated Virus as a Tool to Study Retinal Barriers in Disease

M&#252;ller cells are the principal glial cells of the retina. Their end-feet form the limits of the retina at the outer and inner limiting membranes (ILM), and in conjunction with astrocytes, pericytes and endothelial cells they establish the blood-retinal barrier (BRB). BRB limits material transport between the bloodstream and the retina while the ILM acts as a basement membrane that defines histologically the border between the retina and the vitreous cavity. Labeling M&#252;ller cells is particularly relevant to study the physical state of the retinal barriers, as these cells are an integral part of the BRB and ILM. Both BRB and ILM are frequently altered in retinal disease and are responsible for disease symptoms.
There are several well-established methods to study the integrity of the BRB, such as the Evans blue assay or fluorescein angiography. However these methods do not provide information on the extent of BRB permeability to larger molecules, in nanometer range. Furthermore, they do not provide information on the state of other retinal barriers such as the ILM. To study BRB permeability alongside retinal ILM, we used an AAV based method that provides information on permeability of BRB to larger molecules while indicating the state of the ILM and extracellular matrix proteins in disease states. Two AAV variants are useful for such study: AAV5 and ShH10. AAV5&#160;has a natural tropism for photoreceptors but it cannot get across to the outer retina when administered into the vitreous when the ILM is intact (i.e., in wild-type retinas). ShH10 has a strong tropism towards glial cells and will selectively label M&#252;ller glia in both healthy and diseased retinas. ShH10 provides more efficient gene delivery in retinas where ILM is compromised. These viral tools coupled with immunohistochemistry and blood-DNA analysis shed light onto the state of retinal barriers in disease.

To investigate the blood-retinal barrier permeability and the inner limiting membrane integrity in animal models of retinal disease, we used several adeno-associated virus (AAV) variants as tools to label retinal neurons and glia. Virus mediated reporter gene expression is then used as an indicator of retinal barrier permeability.

M&#252;ller cells are the principal glial cells of the retina. Their end-feet form the limits of the retina at the outer and inner limiting membranes ...

Generating Retinal Degeneration to Investigate Cellular Repair Strategies in Xenopus

Generating Retinal Injury Models in Xenopus Tadpoles

Retinal neurodegenerative diseases are the leading causes of blindness. Among numerous therapeutic strategies being explored, stimulating self-repair recently emerged as particularly appealing. A cellular source of interest for retinal repair is the M&#252;ller glial cell, which harbors stem cell potential and an extraordinary regenerative capacity in anamniotes. This potential is, however, very limited in mammals. Studying the molecular mechanisms underlying retinal regeneration in animal models with regenerative capabilities should provide insights into how to unlock the latent ability of mammalian M&#252;ller cells to regenerate the retina. This is a key step for the development of therapeutic strategies in regenerative medicine. To this aim, we developed several retinal injury paradigms in Xenopus: a mechanical retinal injury, a transgenic line allowing for nitroreductase-mediated photoreceptor conditional ablation, a retinitis pigmentosa model based on CRISPR/Cas9-mediated rhodopsin knockout, and a cytotoxic model driven by intraocular CoCl2 injections. Highlighting their advantages and disadvantages, we describe here this series of protocols that generate various degenerative conditions and allow the study of retinal regeneration in Xenopus.

Author Spotlight: Exploring Retinal Regeneration Mechanisms in the Xenopus Frog 

We have developed several protocols to induce retinal damage or retinal degeneration in Xenopus laevis tadpoles. These models offer the possibility of studying retinal regeneration mechanisms.

Retinal neurodegenerative diseases are the leading causes of blindness. Among numerous therapeutic strategies being explored, stimulating self-repair ...

Developmental Biology

A Mouse Model of Retinal Ischemia-Reperfusion Injury Through Elevation of Intraocular Pressure

Retinal ischemia-reperfusion (I/R) is a pathophysiological process contributing to cellular damage in multiple ocular conditions, including glaucoma, diabetic retinopathy, and retinal vascular occlusions. Rodent models of I/R injury are providing significant insights into mechanisms and treatment strategies for human I/R injury, especially with regard to neurodegenerative damage in the retinal neurovascular unit. Presented here is a protocol for inducing retinal I/R injury in mice through elevation of intraocular pressure (IOP). In this protocol, the ocular anterior chamber is cannulated with a needle, through which flows the drip of an elevated saline reservoir. Using this drip to raise IOP above systolic arterial blood pressure, a practitioner temporarily halts inner retinal blood flow (ischemia). When circulation is reinstated (reperfusion) by removal of the cannula, severe cellular damage ensues, resulting ultimately in retinal neurodegeneration. Recent studies demonstrate inflammation, vascular permeability, and capillary degeneration as additional elements of this model. Compared to alternative retinal I/R methodologies, such as retinal arterial ligation, retinal I/R injury by elevated IOP offers advantages in its&#160;anatomical specificity, experimental tractability, and technical accessibility, presenting itself as a valuable tool for examining neuronal pathogenesis and therapy in the retinal neurovascular unit.

This article describes a procedure for inducing retinal ischemia-reperfusion injury by elevated intraocular pressure in mice. Retinal ischemia-reperfusion injury by elevated intraocular pressure serves to model human pathologies characterized by compromised oxygen and nutrient delivery in the retina, enabling researchers to examine potential cellular mechanisms and treatments for human diseases of the retinal neurovascular unit.

Retinal ischemia-reperfusion (I/R) is a pathophysiological process contributing to cellular damage in multiple ocular conditions, including glaucoma, ...

In Vivo Vascular Injury Readouts in Mouse Retina to Promote Reproducibility

Advancements in ophthalmic imaging tools offer an unprecedented level of access to researchers working with animal models of neurovascular injury. To properly leverage this greater translatability, there is a need to devise reproducible methods of drawing quantitative data from these images. Optical coherence tomography (OCT) imaging can resolve retinal histology at micrometer resolution and reveal functional differences in vascular blood flow. Here, we delineate noninvasive vascular readouts that we use to characterize pathological damage post vascular insult in an optimized mouse model of retinal vein occlusion (RVO). These readouts include live imaging analysis of retinal morphology, disorganization of retinal inner layers (DRIL) measure of capillary ischemia, and fluorescein angiography measures of retinal edema and vascular density. These techniques correspond directly to those used to examine patients with retinal disease in the clinic. Standardizing these methods enables direct and reproducible comparison of animal models with clinical phenotypes of ophthalmic disease, increasing the translational power of vascular injury models.

In Vivo Vascular Injury Readouts in Mouse Retina to Promote Reproducibility

Here, we present three data analysis protocols for fluorescein angiography (FA) and optical coherence tomography (OCT) images in the study of Retinal Vein Occlusion (RVO).

Advancements in ophthalmic imaging tools offer an unprecedented level of access to researchers working with animal models of neurovascular injury. To ...

Retinal Pathophysiological Evaluation in a Rat Model

A posterior segment eye disease like diabetic retinopathy alters the physiology of the retina. Diabetic retinopathy is characterized by a retinal detachment, breakdown of the blood-retinal barrier (BRB), and retinal angiogenesis. An in vivo rat model is a valuable experimental tool to examine the changes in the structure and function of the retina. We propose three different experimental techniques in the rat model to identify morphological changes of retinal cells, retinal vasculature, and compromised BRB. Retinal histology is used to study the morphology of various retinal cells. Also, quantitative measurement is performed by retinal cell count and thickness measurement of different retinal layers. A BRB breakdown assay is used to determine the leakage of extraocular proteins from the plasma to vitreous tissue due to the breakdown of BRB. Fluorescence angiography is used to study angiogenesis and leakage of blood vessels by visualizing retinal vasculature using FITC-dextran dye.

Diabetic retinopathy is one of the leading causes of blindness. Histology, blood-retinal barrier breakdown assay, and fluorescence angiography are valuable techniques to understand the pathophysiology of the retina, which could further enhance the efficient drug screening against diabetic retinopathy.

A posterior segment eye disease like diabetic retinopathy alters the physiology of the retina. Diabetic retinopathy is characterized by a retinal ...

Endothelial Cell Transcytosis Assay as an In Vitro Model to Evaluate Inner Blood-Retinal Barrier Permeability

Dysfunction of the blood-retinal barrier (BRB) contributes to the pathophysiology of several vascular eye diseases, often resulting in retinal edema and subsequent vision loss. The inner blood-retinal barrier (iBRB) is mainly composed of retinal vascular endothelium with low permeability under physiological conditions. This feature of low permeability is tightly regulated and maintained by low rates of paracellular transport between adjacent retinal microvascular endothelial cells, as well as transcellular transport (transcytosis) through them. The assessment of retinal transcellular barrier permeability may provide fundamental insights into iBRB integrity in health and disease. In this study, we describe an endothelial cell (EC) transcytosis assay, as an in vitro model for evaluating iBRB permeability, using human retinal microvascular endothelial cells (HRMECs). This assay assesses the ability of HRMECs to transport transferrin and horseradish peroxidase (HRP) in receptor- and caveolae-mediated transcellular transport processes, respectively. Fully confluent HRMECs cultured on porous membrane were incubated with fluorescent-tagged transferrin (clathrin-dependent transcytosis) or HRP (caveolae-mediated transcytosis) to measure the levels of transferrin or HRP transferred to the bottom chamber, indicative of transcytosis levels across the EC monolayer. Wnt signaling, a known pathway regulating iBRB, was modulated to demonstrate the caveolae-mediated HRP-based transcytosis assay method. The EC transcytosis assay described here may provide a useful tool for investigating the molecular regulators of EC permeability and iBRB integrity in vascular pathologies and for screening drug delivery systems.

Endothelial Cell Transcytosis Assay as an In Vitro Model to Evaluate Inner Blood-Retinal Barrier Permeability

This protocol illustrates an in vitro endothelial cell transcytosis assay as a model to evaluate inner blood-retinal barrier permeability by measuring the ability of human retinal microvascular endothelial cells to transport horseradish peroxidase across cells in caveolae-mediated transcellular transport processes.

Dysfunction of the blood-retinal barrier (BRB) contributes to the pathophysiology of several vascular eye diseases, often resulting in retinal edema and ...

Novel Retina Protection Assay for Diabetic Retinopathy Pathogenesis Study

An Assay to Detect Protection of the Retinal Vasculature from Diabetes-Related Death in Mice

Diabetic retinopathy (DR) is a complex and progressive ocular disease characterized by two distinct phases in its pathogenesis. The first phase involves the loss of protection from diabetes-induced damage to the retina, while the second phase centers on the accumulation of this damage. Traditional assays primarily focus on evaluating capillary degeneration, which is indicative of the severity of damage, essentially addressing the second phase of DR. However, they only indirectly provide insights into whether the protective mechanisms of the retinal vasculature have been compromised. To address this limitation, a novel approach was developed to directly assess the retina's protective mechanisms - specifically, its resilience against diabetes-induced insults like oxidative stress and cytokines. This protection assay, although initially designed for diabetic retinopathy, holds the potential for broader applications in both physiological and pathological contexts. In summary, understanding the pathogenesis of diabetic retinopathy involves recognizing the dual phases of protection loss and damage accumulation, with this innovative protection assay offering a valuable tool for research and potentially extending to other medical conditions.

Author Spotlight: Understanding Retinal Vessel Resilience and Disease Progression

A protection assay was developed to monitor the retinal vasculature's resilience to death from diabetes/diabetic retinopathy-related insults such as oxidative stress and cytokines.

Diabetic retinopathy (DR) is a complex and progressive ocular disease characterized by two distinct phases in its pathogenesis. The first phase involves ...

Modeling and Analyzing Retinal Degeneration

LipidUNet-Machine Learning-Based Method of Characterization and Quantification of Lipid Deposits Using iPSC-Derived Retinal Pigment Epithelium

The retinal pigment epithelium (RPE) is a monolayer of hexagonal cells located at the back of the eye. It provides nourishment and support to photoreceptors and choroidal capillaries, performs phagocytosis of photoreceptor outer segments (POS), and secretes cytokines in a polarized manner for maintaining the homeostasis of the outer retina. Dysfunctional RPE, caused by mutations, aging, and environmental factors, results in the degeneration of other retinal layers and causes vision loss. A hallmark phenotypic feature of degenerating RPE is intra and sub-cellular lipid-rich deposits. These deposits are a common phenotype across different retinal degenerative diseases. To reproduce the lipid deposit phenotype of monogenic retinal degenerations in vitro, induced pluripotent stem cell-derived RPE (iRPE) was generated from patients&#39; fibroblasts. Cell lines generated from patients with Stargardt and Late-onset retinal degeneration (L-ORD) disease were fed with POS for 7 days to replicate RPE physiological function, which caused POS phagocytosis-induced pathology in these diseases. To generate a model for age-related macular degeneration (AMD), a polygenic disease associated with alternate complement activation, iRPE was challenged with alternate complement anaphylatoxins. The intra and sub-cellular lipid deposits were characterized using Nile Red, boron-dipyrromethene (BODIPY), and apolipoprotein E (APOE). To quantify the density of lipid deposits, a machine learning-based software, LipidUNet, was developed. The software was trained on maximum-intensity projection images of iRPE on culture surfaces. In the future, it will be trained to analyze three-dimensional (3D) images and quantify the volume of lipid droplets. The LipidUNet software will be a valuable resource for discovering drugs that decrease lipid accumulation in disease models.

Author Spotlight: Unraveling the Pathogenesis of Age-Related Macular Degeneration and Discovering Potential Therapies 

Degenerative eye diseases that affect the retinal pigment epithelium layer of the eye have monogenic and polygenic origins. Several disease models and a software application, LipidUNet, have been developed to study mechanisms of disease, as well as potential therapeutic interventions.

An Acute Retinal Model for Evaluating Blood Retinal Barrier Breach and Potential Drugs for Treatment

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