In Vivo Imaging of Reactive Oxygen Species in a Murine Wound Model
Summary
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.
Abstract
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.
Introduction
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.
Protocol
Representative Results
Discussion
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<…
Divulgaciones
The authors have nothing to disclose.
Acknowledgements
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 "Pathway to Stop Diabetes" to D.C. [grant number 1-16-ACE-08] and the NYU Applied Research Support Fund to P.R.
Materials
| BKS.Cg-Dock7m+/+ Leprdb/J mice | Jackson Laboratories | 000642 | |
| 13 cm x 18 cm Silicone sheet (0.6 mm) | Sigma Aldrich | 665581 | |
| 3M Tegaderm Transparent Film Dressings | 3M | 88-1626W | |
| Lipofectamine 2000 Transfection Reagent | Life Technologies | 11668027 | |
| Keap1 Stealth siRNA | Thermofisher Scientific | 1299001 | |
| Silencer negative control | Thermofisher Scientific | AM4635 | |
| Opti-MEM Reduced Serum | ThermoFisher Scientific | 11058021 | |
| DPBS | ThermoFisher Scientific | 14040133 | |
| Methyl-cellulose | Sigma Aldrich | 9004-67-5 | |
| L-012 | Wako Chemicals | 120-04891 | |
| IVIS Lumina III XR In Vivo Imaging System | PerkinElmer |
Referencias
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