Name: nitroreductase/metronidazole-mediated ablation and a matlab platform (rpegen) for studying regeneration of the zebrafish retinal pigment epithelium
Uploaded: 2022-03-02T14:00:00
Description: Watch this Scientific Journal Video about Nitroreductase/Metronidazole-Mediated Ablation and a MATLAB Platform RpEGEN for Studying Regeneration of the Zebrafish Retinal Pigment Epithelium at JoVE.com

Work described herein was supported by the National Institutes of Health (RO1-EY29410 to J.M.G, and NIH CORE Grant P30-EY08098 to the Department of Ophthalmology); the UPMC Immune Transplant &#38; Therapy Center (to L.L.L. and J.M.G.); and the E. Ronald Salvitti Chair in Ophthalmology Research (to J.M.G.). Additional support was received from the Wiegand Fellowship in Ophthalmology (to L.L.L), the Eye &#38; Ear Foundation of Pittsburgh, and an unrestricted grant from Research to Prevent Blindness, New York, NY. Authors also wish to thank Amanda Platt for technical assistance and Dr. Hugh Hammer and the aquatics staff for excellent animal care support.

All methodologies outlined herein are compliant with the Institutional Animal Care and Use Committee (IACUC) of the University of Pittsburgh.
1. Preparation prior to zebrafish embryo collection
<ol>
	<li>Set embryo incubator to 28.5&#176;C.</li>
	<li>Prepare a 25x stock solution of the melanogenesis inhibitor, N-phenylthiourea (PTU)21,22. This stock solution is scaled from a common recipe22...

This protocol describes methodology to genetically ablate the RPE and study mechanisms of degeneration and regeneration in larval-aged zebrafish. This protocol has also been successfully performed in adult zebrafish3 but with less extensive characterization, which is why larvae are the focus here. Critical aspects of this part of the protocol (steps 1-4) include: 1) adding 1.5x PTU to embryos prior to the onset of melanogenesis, 2) dechorionating PTU-treated embryos on 2-3 dpf, 3) careful screenin...

The methodology described herein details a protocol to genetically ablate the retinal pigment epithelium (RPE) utilizing larval zebrafish. The RPE extends over the back of the eye and resides between the stratified layers of the neural retina and the layer of vasculature constituting the choroid. Trophic support, absorption of phototoxic light, and maintenance of visual cycle proteins are only some of the critical functions the RPE performs that are essential for sustaining the health and integrity of these adjacent tissues1. Damage to mammalian RPE is reparable when lesions are small2; however, damage suffered by larger injuries or progressive degenerative disease is irreversible. In humans, RPE degenerative diseases (e.g.,&#160;age-related macular degeneration (AMD) and Stargardt disease) lead to permanent vision loss and, with few treatment options available, decreased patient&#160;quality of life. The limited ability for mammalian RPE to self-repair has created a knowledge gap in the field of RPE regenerative processes. Given the robust regenerative capacity of the zebrafish across many different tissue types, this protocol was developed to establish an in vivo vertebrate system to facilitate studies on intrinsically regenerating RPE and uncover mechanisms that drive that response. Using the ablation paradigm outlined here, the canonical Wnt signaling pathway3, the mTOR pathway4, and immune-related responses5 have been identified as critical mediators of RPE regeneration, likely with overlapping functions.
In this genetic ablation paradigm, Tg(rpe65a:nfsB-eGFP)3 zebrafish express the bacterial-derived nitroreductase (NTR/nfsB) gene6 fused to eGFP under control of the RPE enhancer element, rpe65a7. Ablation is achieved by adding the prodrug, metronidazole (MTZ), to system water housing zebrafish. Intracellular activation of MTZ by nitroreductase results in DNA crosslinking and apoptosis in NTR/nfsB-expressing cells8,9. This technology has been widely used in zebrafish to ablate cells of the retina10,11,12,13 and other tissues8. Together, these elements enable targeted expression (rpe65a) of an inducible cell ablation methodology (NTR/MTZ)8,9 and a fluorescent marker (eGFP) for visualization.
Other interesting in vivo models also exist that can be used to study the regenerative potential of the RPE14. These are broad and include RPE-to-retina transdifferentiation post-retinectomy in amphibians, in which RPE cells lost to retinal regrowth are replaced15,16; RPE restoration post-injury in the &#34;super healing&#34; MRL/MpJ mouse17; and exogenous stimulation of RPE proliferation in a rat model of spontaneous RPE and retinal degeneration18, among others. In vitro models, such as adult human RPE stem cells (RPESCs)19 have also been developed. These models are all valuable tools working to uncover the cellular processes related to RPE regeneration (e.g.,&#160;proliferation, differentiation, etc.); however, the zebrafish is unique in its capacity for intrinsic RPE repair post-ablation.
While the methodology here is written to focus on understanding the mechanisms driving RPE regeneration, the Tg(rpe65a:nfsB-eGFP) line and this genetic ablation protocol could be utilized to study other cellular processes such as RPE apoptosis, RPE degeneration, and the effect of RPE injury on adjacent retinal and vascular tissues. The ablation protocol can also be modified to include pharmacological manipulation, which is a convenient preliminary strategy to screen signaling pathways of interest. For example, blocking the canonical Wnt pathway using Inhibitor of Wnt Response-1 (IWR-1)20, has been shown to impair RPE regeneration3. This was repeated here to guide users through a pharmacological manipulation experiment and serve as proof-of-concept to validate a MATLAB script (RpEGEN) created to quantify RPE regeneration based on recovery of pigmentation. Like the transgenic line and ablation protocol, the RpEGEN scripts are adaptable and could be used to quantify other markers/cellular processes within the RPE.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Lab Material/Equipment</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>2-(4-Amidinophenyl)-6-indolecarbamidine dihydrochloride (DAPI)</td>
			<td>Millipore Sigma</td>
			<td>D9542</td>
			<td></td>
		</tr>
		<tr>
			<td>6-well plates</td>
			<td>Fisher Scientific</td>
			<td>07-200-83</td>
			<td></td>
		</tr>
		<tr>
			<td>Conical Polypropylene Centrifuge Tubes</td>
			<td>Fisher Scientific</td>
			<td>05-539-13</td>
			<td>Catalog number is for 50 mL tubes</td>
		</tr>
		<tr>
			<td>Diamond tip scribing pen</td>
			<td>Fisher Scientific</td>
			<td>50-254-51</td>
			<td>Manufactured by Electron Microscopy Sciences, items similar to this part number are adequate</td>
		</tr>
		<tr>
			<td>Dimethyl sulfoxide (DMSO) &#8805;99.7 %</td>
			<td>Fisher Scientific</td>
			<td>BP231</td>
			<td>Check instiutional chemical waste disposal requirements</td>
		</tr>
		<tr>
			<td>Embryo incubator (large)</td>
			<td>Fisher Scientific</td>
			<td>3720A</td>
			<td></td>
		</tr>
		<tr>
			<td>Embryo incubator (mini/tabletop)</td>
			<td>Labnet</td>
			<td>I5110A</td>
			<td></td>
		</tr>
		<tr>
			<td>Fluorescence stereo microscope</td>
			<td>Zeiss</td>
			<td>Axio Zoom.V16</td>
			<td>Or similar, with 488 nm excitation laser/filter</td>
		</tr>
		<tr>
			<td>Glass Pasteur pipette</td>
			<td>Fisher Scientific</td>
			<td>13-678-4</td>
			<td>Manufactured by Corning, non-sterile</td>
		</tr>
		<tr>
			<td>InSolution Wnt Antagonist I, IWR-1-endo</td>
			<td>Millipore Sigma</td>
			<td>5.04462</td>
			<td>Manufactured by Calbiochem; 25 mM in DMSO; check instiutional chemical waste disposal requirements</td>
		</tr>
		<tr>
			<td>Methylene blue (powder)</td>
			<td>Fisher Scientific</td>
			<td>BP117-100</td>
			<td>Also available as a premade aqeuous solution</td>
		</tr>
		<tr>
			<td>Metronidazole (MTZ)</td>
			<td>Millipore Sigma</td>
			<td>M3761</td>
			<td>Check instiutional chemical waste disposal requirements</td>
		</tr>
		<tr>
			<td>N-phenylthiourea (PTU)</td>
			<td>Millipore Sigma</td>
			<td>P7629</td>
			<td>Check instiutional chemical waste disposal requirements</td>
		</tr>
		<tr>
			<td>Paraformaldehyde (16 % w/v) methanol free</td>
			<td>Fisher Scientific</td>
			<td>AA433689M</td>
			<td>Chemical waste, proper disposal required</td>
		</tr>
		<tr>
			<td>Petri dishes</td>
			<td>Fisher Scientific</td>
			<td>FB0875712</td>
			<td>10 cm diameter</td>
		</tr>
		<tr>
			<td>Phosphate buffered saline (powder packets)</td>
			<td>Millipore Sigma</td>
			<td>P3813</td>
			<td>Used to make 10 X PBS stock</td>
		</tr>
		<tr>
			<td>Pronase</td>
			<td>Millipore Sigma</td>
			<td>PRON-RO</td>
			<td></td>
		</tr>
		<tr>
			<td>Shaking incubator</td>
			<td>Benchmark</td>
			<td>H2010</td>
			<td>Used for incubating MTZ for 1 hour at 37 degrees Celcius</td>
		</tr>
		<tr>
			<td>Stereo microscope</td>
			<td>Leica</td>
			<td>S9i</td>
			<td>Or similar, with transmitted light illumination</td>
		</tr>
		<tr>
			<td>Student Dumont #5 forceps</td>
			<td>Fine Science Tools</td>
			<td>91150-20</td>
			<td>Fine-tipped forceps for manual dechorionation</td>
		</tr>
		<tr>
			<td>Tabletop rotator/shaker</td>
			<td>Scilogex</td>
			<td>SK-D1807-E</td>
			<td></td>
		</tr>
		<tr>
			<td>Transfer pipette</td>
			<td>Millipore Sigma</td>
			<td>Z135003</td>
			<td>3.2 mL bulb draw, non-sterile</td>
		</tr>
		<tr>
			<td>Tricaine methanesulfonate (MS-222)</td>
			<td>Pentair</td>
			<td>TRS1, TRS2, TRS5</td>
			<td>Also available from Fisher Scientific (NC0342409)</td>
		</tr>
		<tr>
			<td>VECTASHIELD Antifade Mounting Medium with DAPI</td>
			<td>Vector Laboratories</td>
			<td>H-1200</td>
			<td></td>
		</tr>
		<tr>
			<td>Software Material</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>FIJI (Fiji is Just ImageJ)</td>
			<td>FIJI (Fiji is Just ImageJ)</td>
			<td>https://imagej.net/software/fiji/</td>
			<td>Version: 2.0.0-rc-69/1.52p; Build: 269a0ad53f; Plugin needed: Bio-Formats</td>
		</tr>
		<tr>
			<td>GRAMM examples and how-tos</td>
			<td>MathWorks</td>
			<td>https://www.mathworks.com/matlabcentral/fileexchange/54465-gramm-complete-data-visualization-toolbox-ggplot2-r-like.</td>
			<td></td>
		</tr>
		<tr>
			<td>MATLAB</td>
			<td>MathWorks</td>
			<td>https://www.mathworks.com/products/get-matlab.html</td>
			<td>Toolboxes needed to run RpEGEN: Image Processing Toolbox, Curve Fitting Toolbox, Statistics and Machine Learning Toolbox</td>
		</tr>
		<tr>
			<td>MATLAB support</td>
			<td>MathWorks</td>
			<td>https://www.mathworks.com/support.html</td>
			<td></td>
		</tr>
	</tbody>
</table>

nitroreductase/metronidazole-mediated ablation and a matlab platform (rpegen) for studying regeneration of the zebrafish retinal pigment epithelium

The retinal pigment epithelium (RPE) resides at the back of the eye and performs functions essential for maintaining the health and integrity of adjacent retinal and vascular tissues. At present, the limited reparative capacity of mammalian RPE, which is restricted to small injuries, has hindered progress to understanding in vivo RPE regenerative processes. Here, a detailed methodology is provided to facilitate the study of in vivo RPE repair utilizing the zebrafish, a&#160;vertebrate model capable of robust tissue regeneration. This protocol describes a transgenic nitroreductase/metronidazole (NTR/MTZ)-mediated injury paradigm (rpe65a:nfsB-eGFP), which results in ablation of the central two-thirds of the RPE after 24 h treatment with MTZ, with subsequent tissue recovery. Focus is placed on RPE ablations in larval zebrafish and methods for testing the effects of pharmacological compounds on RPE regeneration are also outlined. Generation and validation of RpEGEN, a MATLAB script created to automate quantification of RPE regeneration based on pigmentation, is also discussed. Beyond active RPE repair mechanisms, this protocol can be expanded to studies of RPE degeneration and injury responses as well as the effects of RPE damage on adjacent retinal and vascular tissues, among other cellular and molecular processes. This zebrafish system holds significant promise in identifying genes, networks, and processes that drive RPE regeneration and RPE disease-related mechanisms, with the long-term goal of applying this knowledge to mammalian systems and, ultimately, toward therapeutic development.

Inhibiting the canonical Wnt signaling pathway is known to significantly impair zebrafish RPE regeneration using the genetic ablation paradigm (rpe65a:nfsB-eGFP) and pharmacological manipulation methodology (IWR-1) described in the protocol3. This experiment was repeated here to validate an automated method for quantifying zebrafish RPE regeneration based on pigmentation. The results summarized below encompassed all steps of the protocol, from the day of fertilization (0 dpf) to quantific...

Watch this Scientific Journal Video about Nitroreductase/Metronidazole-Mediated Ablation and a MATLAB Platform RpEGEN for Studying Regeneration of the Zebrafish Retinal Pigment Epithelium at JoVE.com

Nitroreductase/Metronidazole-Mediated Ablation and a MATLAB Platform RpEGEN for Studying Regeneration of the Zebrafish Retinal Pigment Epithelium

This protocol describes the methodology to genetically ablate the retinal pigment epithelium (RPE) using a transgenic zebrafish model. Adapting the protocol to incorporate signaling pathway modulation using pharmacological compounds is extensively detailed. A MATLAB platform for quantifying RPE regeneration based on pigmentation was developed and is presented and discussed.

Nitroreductase/Metronidazole-Mediated Ablation and a MATLAB Platform (RpEGEN) for Studying Regeneration of the Zebrafish Retinal Pigment Epithelium

The retinal pigment epithelium (RPE) resides at the back of the eye and performs functions essential for maintaining the health and integrity of adjacent ...

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