Name: in vivo imaging of reactive oxygen species in a murine wound model
Uploaded: 2018-11-17T13:00:00
Description: Watch this Scientific Journal Video about In Vivo Imaging of Reactive Oxygen Species in a Murine Wound Model at JoVE.com

We are grateful to the Preclinical Imaging Core at the NYU School of Medicine, with special thanks to Orlando Aristizabal and Youssef Zaim Wadghiri. The core is a shared resource partially supported by the Laura and Isaac Perlmutter Cancer Center Support Grant NIH/NCI 5P30CA016087 and NIBIB Biomedical Technology Resource Center Grant NIH P41 EB017183. This work was supported by the American Diabetes Association &#34;Pathway to Stop Diabetes&#34; to D.C. [grant number 1-16-ACE-08] and the NYU Applied Research Support Fund to P.R.

All methods described here have been approved by the Institutional Animal Care and Use Committee of New York University School of Medicine. All mice are housed behind a barrier and all personnel wear appropriate personal protective equipment.
1. Day 0: Preparation of Murine Model of Excisional Wound Healing
<ol>
	<li>Anesthetize diabetic (Leprdb/db) mice, aged 8&#8211;12 weeks, with inhalational 2% isoflurane. Confirm that each mouse has been properly anesthetized using the foot p...

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Common techniques for measuring ROS have been limited by complex protocols requiring tissue extraction or similarly invasive techniques. In recent years, measurements of oxidative stress have been reported on the basis of innovative imaging modalities, thereby allowing for spatiotemporal assessments9,10,11. L-012 has several advantages as a chemiluminescent probe relative to luminol, lucigenin, and MCLA1<...

Oxygen metabolites generated through inflammatory processes contribute to various signaling cascades as well as destructive alteration of cellular components1. Utilizing sensitive and specific techniques to measure ROS is critical for studying inflammatory processes and characterizing the effects of oxidative stress. In vivo imaging is valuable because of its ability to provide dynamic spatial and temporal data in living tissue. L-012 is a synthetic chemiluminescent probe that is highly sensitive for superoxide anions and produces a higher light intensity than other fluorescent probes in cells, tissues, and whole blood1,2,3,4. It has been successfully employed for in vivo imaging in murine models to study several inflammatory diseases, including arthritis and colitis5,6. It has yet to be employed in an established cutaneous wound healing model. Measurement of ROS generated is equally relevant to assess the progression of wound healing under different conditions. The sensitivity and noninvasive nature of this method makes it a promising technique for studying wound healing across murine models.
Nrf2 is a major driver of the antioxidant response and a transcriptional factor with specificity for the antioxidant response element (ARE) common to the promoter regions of several antioxidant enzymes8. In the absence of oxidative stress, Nrf2 is sequestered in the cytoplasm by Keap1, which subsequently causes its ubiquitination and degradation. Imbalance of the Nrf2/Keap1 pathway has been implicated in inappropriate redox homeostasis and delayed wound healing in the setting of increased oxidative stress9. We have previously shown that suppression of Keap1 stimulates increased Nrf2 activity and promotes rescue of pathologic cutaneous wound healing in diabetic wounds9.
Here we describe a protocol that utilizes L-012-assisted bioluminescence imaging to measure ROS levels in an excisional cutaneous wound healing model, which is critical for highlighting the association between ROS and wound healing. This technique demonstrates real-time changes in oxidative burden within wounds and immediate periphery. Furthermore, this method allows for rapid assessment of interventions and mechanisms that affect redox handling. Here we use a model of Keap1 knockdown for the restoration of redox homeostasis to evaluate the applicability of our strategy. Because our technique is non-invasive and wounds are undisturbed, the same animal can be used for further confirmatory analyses on the basis of histology or cell lysates.

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			<td height="20" style="height:20px;width:265px;">BKS.Cg-Dock7m+/+ Leprdb/J mice</td>
			<td style="width:164px;">Jackson Laboratories</td>
			<td style="width:111px;">000642</td>
			<td style="width:79px;"></td>
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			<td height="20" style="height:20px;">13 cm x 18 cm Silicone sheet (0.6 mm)</td>
			<td>Sigma Aldrich&#160;</td>
			<td>665581</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">3M Tegaderm Transparent Film Dressings</td>
			<td>3M</td>
			<td>88-1626W</td>
			<td></td>
		</tr>
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			<td height="20" style="height:20px;">Lipofectamine 2000 Transfection Reagent</td>
			<td>Life Technologies&#160;</td>
			<td>11668027</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Keap1 Stealth siRNA</td>
			<td>Thermofisher Scientific</td>
			<td>1299001</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Silencer negative control&#160;</td>
			<td>Thermofisher Scientific&#160;</td>
			<td>AM4635</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Opti-MEM Reduced Serum</td>
			<td>ThermoFisher Scientific</td>
			<td>11058021</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">DPBS</td>
			<td>ThermoFisher Scientific</td>
			<td>14040133</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Methyl-cellulose&#160;</td>
			<td>Sigma Aldrich</td>
			<td>9004-67-5</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">L-012</td>
			<td>Wako Chemicals</td>
			<td>120-04891</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">IVIS Lumina III XR In Vivo Imaging System&#160;</td>
			<td>PerkinElmer</td>
			<td></td>
			<td></td>
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in vivo imaging of reactive oxygen species in a murine wound model

The generation of reactive oxygen species (ROS) is a hallmark of inflammatory processes, but in excess, oxidative stress is widely implicated in various pathologies such as cancer, atherosclerosis and diabetes. We have previously shown that dysfunction of the Nuclear factor (erythroid-derived 2)-like 2 (Nrf2)/ Kelch-like erythroid cell-derived protein 1 (Keap1) signaling pathway leads to extreme ROS imbalance during cutaneous wound healing in diabetes. Since ROS levels are an important indicator of progression of wound healing, specific and accurate quantification techniques are valuable. Several in vitro assays to measure ROS in cells and tissues have been described; however, they only provide a single cumulative measurement per sample. More recently, the development of protein-based indicators and imaging modalities have allowed for unique spatiotemporal analyses. L-012 (C13H8ClN4NaO2) is a luminol derivative that can be used for both in vivo and in vitro chemiluminescent detection of ROS generated by NAPDH oxidase. L-012 emits a stronger signal than other fluorescent probes and has been shown to be both sensitive and reliable for detecting ROS. The time lapse applicability of L-012-facilitated imaging provides valuable information about inflammatory processes while reducing the need for sacrifice and overall reducing the number of study animals. Here, we describe a protocol utilizing L-012-facilitated in vivo imaging to quantify oxidative stress in a model of excisional wound healing using diabetic mice with locally dysfunctional Nrf2/Keap1.

Three days after creating bilateral wounds according to an established excisional wound model (Figure 1A), diabetic mice are positioned in the imaging chamber. An initial photograph and a measure of bioluminescence are taken before injection of L-012 to account for background signal (Figure 1B). Following intraperitoneal injection with the L-012 solution, the mice are repositioned in the chamber and bioluminescence is visualized ...

Watch this Scientific Journal Video about In Vivo Imaging of Reactive Oxygen Species in a Murine Wound Model at JoVE.com

In Vivo Imaging of Reactive Oxygen Species in a Murine Wound Model

We describe a non-invasive in vivo imaging protocol that is streamlined and cost-effective, utilizing L-012, a chemiluminescent luminol-analog, to visualize and quantify reactive oxygen species (ROS) generated in a mouse excisional wound model.

In Vivo Imaging of Reactive Oxygen Species in a Murine Wound Model

The generation of reactive oxygen species (ROS) is a hallmark of inflammatory processes, but in excess, oxidative stress is widely implicated in various ...

This method can help answer key questions in the tissue repair and regeneration field about the associations among the cytoprotective pathways, oxidative stress, and the wound healing response. The main advantage of this powerful technique is that you can measure reactive oxygen species in a wound, in real-time, to determine their impact on tissue regeneration. Demonstrating the procedure with me will be Jennifer Kwong, a research assistant in my laboratory.Use a glucometer to measure the blood glucose of each anesthetized eight to 12 week old diabetic mouse. And use a hair trimmer and depilatory cream to remove the dorsal hair from the first animal. Use alcohol wipes two times to clean the exposed skin and drape the animal so that only the surgical area is exposed.When the alcohol has dried, use sterile 10 millimeter biopsy punches to create two, 10 millimeter full thickness wounds extending through the panniculus carnosus according to a well established excisional wound healing technique. Use a 0.5 millimeter thick silicone sheet with 10 millimeter circular cutouts to splint the wounds open and secure the stints with interrupted 4/0 silk sutures. Then place the mice on a heat pad with monitoring until full recovery, before returning to its individual cage, providing paper towels as additional nesting material for two weeks.The next day, apply either control nonsense small interfering RNA gel or experimental small interfering Keap1 gel to the top of the wound of each animal and wrap each torso with transparent film dressing to keep the gel in place while leaving the limbs free. On day three of the experiment, load a one millimeter syringe equipped with a 27-gauge needle with freshly prepared L-012 solution and wrap the syringe to protect the solution from light. To image the wounds, gently remove the transparent film dressing from each of the mice without disturbing the wounds and place the mice into the imaging chamber of a bioluminescence imaging system.Set the imaging system inflow and the induction chamber oxygen levels to one liter per minute and image the mice by bioluminescence and bright field at baseline. Next, wipe the abdomens with alcohol wipes then inject five milligrams of L-012 solution per 200 grams body weight, IP, into each mouse once the alcohol has dried. Injecting the L-012 solution without disturbing the wounds on the dorsal skin is critical, because any distortion will affect the wound healing trajectory and data interpretation.Ensure that the animal is securely in dorsal recumbency before the injection. Immediately following the injection, place the mice back into their respective locations in the imaging chamber and image the animals for one minute every four minutes over a 60 minute imaging period, defining the 10 millimeter wound as the region of interest for determining the level of reactive oxygen species. Then place the mice on a heat pad with monitoring until full recovery before returning the animals to their individual cages.Three days after creating bilateral wounds according to the established excisional wound model, no bioluminescence is observed prior to L-012 injection. Following intraperintoneal L-012 solution injection, bioluminescence is observed in the areas of the wound where reactive oxygen species are detected. Recording of the bioluminescence for one minute every four to five minutes over the course of 60 minutes demonstrates the bioluminescent saturation of the region of interest over time, with the optimal imaging time to reach complete L-012 saturation observed at about 50 minutes.The bioluminescence in each wound region of interest before and after L-012 injection into nonsense small interfering RNA treated or Keap1 small interfering RNA treated mice can then be calculated by dividing the total counts of light intensity by the area. Analysis of day 10 wound tissue sections to confirm the accuracy of reactive oxygen species level measurement by H&E staining reveals a reduced cellular infiltration into small interfering Keap1 treated wounds compared to small interfering nonsense treated tissues, indicating a reduced inflammatory morphology in the experimental gel-treated animals. Analysis of the immuno-reactivity of F4/80, a protein macrophage marker on wound tissue sections, indicates a reduced number of macrophages in small interfering Keap1 treated wounds compared to small interfering nonsense treated wounds, further underscoring the validity of this method.When attempting this procedure, make sure to confirm the L-012 is not expired and to stir the solution in a place protected from light. Following this procedure, targeted probes and immuno-assay based methods can be used to study the sub-cellular localization of reactive oxygen species and their correlates, enabling a rapid assessment of interventions and mechanisms that affect the redux stats of wounds.

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