Name: oxygen-induced retinopathy model for ischemic retinal diseases in rodents
Uploaded: 2020-09-16T14:30:00
Description: Watch this Scientific Journal Video about Oxygen-Induced Retinopathy Model for Ischemic Retinal Diseases in Rodents at JoVE.com

We thank Marianne Karlsberg, Anne Mari Haapaniemi, P&#228;ivi Partanen and Anne Kankkunen for excellent technical support. This work was funded by the Academy of Finland, P&#228;ivikki and Sakari Sohlberg Foundation, Tampere Tuberculosis Foundation, Finnish Medical Foundation, Pirkanmaa Hospital District Research Foundation and the Tampere University Hospital Research Fund.

The protocol described here has been approved by the National Animal Ethics Committee of Finland (protocol number ESAVI/9520/2020 and ESAVI/6421/04.10.07/2017).
1. Experimental animals and mouse OIR model induction
NOTE: Use time-mated animals, e.g., commonly used C57BL/6J mice, to get pups born on the same day. Use fostering dams, e.g., 129 strain (129S1/SvImJ or 129S3/SvIM) lactating dams, to nurse the pups during and after the induction of hyperoxia. Alternatively,...

The severity of disease phenotype is dependent on both the strain and even vendor in both mouse and rat OIR models23. This suggests that there is a wide genotypic variability in the pathology development. In general, pigmented rodents develop more severe phenotype than the albino ones. For example, the retinal vasculature of albino BALB/c revascularizes rapidly after hyperoxia and does not develop NV at all24. Similarly, in rats, pigmented Brown Norway rats show more severe...

Reliable and reproducible experimental models are needed to study the pathology behind angiogenic eye diseases and to develop novel therapeutics to these devastating diseases. Pathological angiogenesis is the hallmark for wet age-related macular degeneration (AMD) and for many ischemic retinal diseases among them retinopathy of prematurity (ROP), proliferative diabetic retinopathy (PDR) and retinal vein occlusion (RVO)1,2,3,4. Human and rodent retinas follow a similar pattern of development, as both human and rodent retina are among the last tissues that are vascularized. Before the retinal vasculature has completely developed, retina receives its nutrient supply from hyaloid vasculature, which, in turn, regresses when the retinal vasculature starts to develop1,2. In human, retinal vascular development is completed before birth, whereas in rodents the growth of retinal vasculature occurs after birth. Since the retinal vascular development occurs postnatally in rodents, it provides an ideal model system to study the angiogenesis2,3. The newborn rodents have an avascular retina that develops gradually until complete vascular retina development is achieved by the end of third postnatal week4. The growing blood vessels of neonatal mouse are plastic, and they undergo regression during hyperoxia stimulus5.
ROP is the leading cause for childhood blindness in Western countries, as it affects almost 70% of the premature infants with birthweight under 1,250 g6,7. ROP occurs in premature infants who are born before retinal vessels complete&#160;their normal growth. ROP progresses in two phases: in Phase I, preterm birth delays the retinal vascular growth where after in phase II, the unfinished vascularization of the developing retina causes hypoxia, which induces the expression of angiogenic growth factors that stimulate new and abnormal blood vessel growth8. The OIR model has been a widely used model to study the pathophysiology of ROP and other ischemic retinopathies as well as to test novel drug candidates2,3,9. It is widely considered as a reproducible model for carrying out proof-of-concept studies for potential antiangiogenic drugs for ocular as well as non-ocular diseases. The two rodent models i.e., mouse and rat OIR differ in their model induction and disease phenotype. The rat model mimics ROP phenotype more accurately, but the mouse model provides a more robust, fast and reproducible model for retinal neovascularization (NV). In the mouse model, NV develops to the central retina. This pathological read-out is important in pharmacologic efficacy studies for many ischemic retinopathies, such as PDR, RV and exudative AMD as well as for non-ocular, angiogenic diseases such as cancer. Moreover, availability of genetically manipulated (transgenic and knockout) mice makes the mouse OIR model a more popular option. However, neither mouse nor rat OIR model creates retinal fibrosis, which is typical in human diseases.
The understanding that high oxygen levels contribute to the development of ROP in 1950s10,11 led to the development of animal models. The first studies about the effect of oxygen on&#160;retinal vasculature were done in 195012,13,14 and until the 1990s there were many refinements to the OIR model. The research by Smith et al. in 1994 set a standard for the&#160;current mouse OIR model that separates hyaloidopathy from retinopathy15. A wide adoption of the method to quantify vaso-obliteration and pathological NV by Connor et al. (2009) further increased its popularity16. In this model, mice are placed at 75% oxygen (O2) for 5 days at P7, followed by 5 days in normoxic conditions. Hyperoxia from P7 to P12 causes retinal vasculature to regress in central retina. Upon return to normoxic conditions, avascular retina becomes hypoxic (Figure 1A). Due to the hypoxic stimuli of the avascular central retina, some of the retinal blood vessels sprout towards the vitreous, forming preretinal NV, called preretinal tufts2,3. These tufts are immature, and hyperpermeable. The amount of NV peaks at P17, after which it regresses. The retina is fully revascularized and NV is fully regressed by P23 - P25 (Figure 2A)2,3.
The rat OIR model (using varying levels of O2) was first described in the 1990s showing that varying O2 levels at 80% and 40% cause more pronounced NV than under 80% O2 constant exposure17. Later it was discovered that the intermittent hypoxia model, where O2 is cycled from hyperoxia (50%) to hypoxia (10-12 %), causes even more NV than the 80/40% O2 model18. In the 50/10% model, rat pups are exposed to 50% for 24 hours, followed by 24 hours in 10% O2. These cycles are continued until P14, when the rat pups are returned to normoxic conditions (Figure 1B). As in human ROP patients, in the rat model the avascular areas develop to the periphery of retina because of immature retinal vascular plexus (Figure 3).
In both models, the main parameters that are usually quantified are the size of AVA and NV. These parameters are typically analyzed from retinal flat mounts where the endothelial cells are labeled4,16. Previously the amount of preretinal NV was evaluated from retinal cross sections by counting blood vessel or vascular cell nuclei extending to vitreous above the inner limiting membrane. The major limitation of this approach is that it is not possible to quantify the AVAs.

<table>
	<tbody>
		<tr>
			<td>33 gauge, Small Hub RN Needle</td>
			<td>Hamilton Company</td>
			<td>7803-05, 10mm, 25&#176;, PS4</td>
			<td>For intravitreal injection</td>
		</tr>
		<tr>
			<td>Adobe Photoshop</td>
			<td>Adobe Inc.</td>
			<td></td>
			<td>For image analysis</td>
		</tr>
		<tr>
			<td>Air pump air100</td>
			<td>Eheim GmbH &#38; Co. KG.</td>
			<td>143207</td>
			<td>For inhalation anaesthesia</td>
		</tr>
		<tr>
			<td>Anaesthesia unit 410 AP</td>
			<td>Univentor Ltd.</td>
			<td>2360309</td>
			<td>For inhalation anaesthesia</td>
		</tr>
		<tr>
			<td>AnalaR NORMAPUR Soda lime</td>
			<td>VWR International Ltd</td>
			<td>22666.362</td>
			<td>For CO2 control during model induction</td>
		</tr>
		<tr>
			<td>Attane Vet 1000 mg/g</td>
			<td>VET MEDIC ANIMAL HEALTH OY</td>
			<td>vnr 17 05 79</td>
			<td>For inhalation anaesthesia</td>
		</tr>
		<tr>
			<td>Brush</td>
			<td></td>
			<td></td>
			<td>For preparation of flat mounts</td>
		</tr>
		<tr>
			<td>Carbon dioxide gas</td>
			<td></td>
			<td></td>
			<td>For sacrifice</td>
		</tr>
		<tr>
			<td>Celeris D430 ERG system</td>
			<td>Diagnosys LLC</td>
			<td>121</td>
			<td>For in vivo ERG</td>
		</tr>
		<tr>
			<td>Cell culture dishes</td>
			<td>Greiner Bio-One International GmbH</td>
			<td>664 160</td>
			<td>For preparation of flat mounts</td>
		</tr>
		<tr>
			<td>Cepetor Vet 1 mg/mL</td>
			<td>VET MEDIC ANIMAL HEALTH OY</td>
			<td>vnr 08 78 96</td>
			<td>For anaesthesia</td>
		</tr>
		<tr>
			<td>Cover slips</td>
			<td>Thermo Fisher Scientific</td>
			<td>15165452</td>
			<td>For preparation of flat mounts</td>
		</tr>
		<tr>
			<td>O2 Controlled InVivo Cabinet, Aninal Filtrarion System and Dehumidifier</td>
			<td>Coy Laboratory Products</td>
			<td></td>
			<td>Closed system for disease model induction, optional for semi-closed system</td>
		</tr>
		<tr>
			<td>E702 O2 sensor</td>
			<td>BioSphenix, Ltd.</td>
			<td>E207, 1801901</td>
			<td>For oxygen level measurement</td>
		</tr>
		<tr>
			<td>Envisu R2200 Spectral Domain Optical Coherence Tomograph (SD-OCT)</td>
			<td>Bioptigen, Inc.</td>
			<td>BPN000668</td>
			<td>For in vivo imaging</td>
		</tr>
		<tr>
			<td>Eye spears</td>
			<td>Beaver-Visitec International, Inc.</td>
			<td>0008685</td>
			<td>For intravitreal injection and in vivo imaging</td>
		</tr>
		<tr>
			<td>Flexilux 600LL Cold light source</td>
			<td>Mikron</td>
			<td>11140</td>
			<td>For intravitreal injection or tissue collection</td>
		</tr>
		<tr>
			<td>Fluorescein sodium salt</td>
			<td>Merck KGaA</td>
			<td>F6377-100G</td>
			<td>For in vivo imaging</td>
		</tr>
		<tr>
			<td>Gas Exhaust unit (+Double 3-way valve, mouse and rat face masks, UNOsorb filter)</td>
			<td>UNO Roestvaststaal BV</td>
			<td>GEX 17015249</td>
			<td>For inhalation anaesthesia</td>
		</tr>
		<tr>
			<td>Glass syringe, Model 65 RN</td>
			<td>Hamilton Company</td>
			<td>7633-01</td>
			<td>For intravitreal injection</td>
		</tr>
		<tr>
			<td>HRA2 Retina angiograph (FA)</td>
			<td>Heidelberg Engineering GmbH</td>
			<td>Spec-KT-05488</td>
			<td>For in vivo imaging</td>
		</tr>
		<tr>
			<td>Isolectin GS-IB4, Alexa Fluor 488 Conjugate</td>
			<td>Thermo Fisher Scientific</td>
			<td>I21411</td>
			<td>For labeling retinal vasculature on flat mounts</td>
		</tr>
		<tr>
			<td>Ketaminol Vet 50 mg/mL</td>
			<td>Intervet International B.V.</td>
			<td>vnr 51 14 85</td>
			<td>For anaesthesia</td>
		</tr>
		<tr>
			<td>Medicinal Oxygen gas</td>
			<td></td>
			<td></td>
			<td>For disease model induction</td>
		</tr>
		<tr>
			<td>Mice C57BL/6JRj</td>
			<td>Janvier Labs</td>
			<td></td>
			<td>Also other strains possible</td>
		</tr>
		<tr>
			<td>Microscope slides</td>
			<td>Thermo Fisher Scientific</td>
			<td>J1800AMNZ</td>
			<td>For preparation of flat mounts</td>
		</tr>
		<tr>
			<td>Minims Povidone Iodine 5% (unit)</td>
			<td>Bausch &#38; Lomb U.K Limited</td>
			<td>vnr 24 11 304</td>
			<td>For intravitreal injection</td>
		</tr>
		<tr>
			<td>Nitrogen gas</td>
			<td></td>
			<td></td>
			<td>For disease model induction (rat)</td>
		</tr>
		<tr>
			<td>Oftan Chlora 10 mg/g</td>
			<td>Santen Pharmaceutical Co., Ltd.</td>
			<td>vnr 55 01 11</td>
			<td>For intravitreal injection</td>
		</tr>
		<tr>
			<td>Oftan Metaoksedrin 100 mg/ml</td>
			<td>Santen Pharmaceutical Co., Ltd.</td>
			<td>vnr 55 03 43</td>
			<td>For in vivo ERG</td>
		</tr>
		<tr>
			<td>Oftan Obucain 4 mg/ml</td>
			<td>Santen Pharmaceutical Co., Ltd.</td>
			<td>vnr 55 03 50</td>
			<td>For intravitreal injection</td>
		</tr>
		<tr>
			<td>Oftan Tropicamid 5 mg/ml</td>
			<td>Santen Pharmaceutical Co., Ltd.</td>
			<td>vnr 04 12 36</td>
			<td>For in vivo imaging</td>
		</tr>
		<tr>
			<td>ProOx Model 110 O2 controller and animal chamber</td>
			<td>BioSphenix, Ltd.</td>
			<td>803</td>
			<td>For disease model induction, semi-closed system, optional for closed system</td>
		</tr>
		<tr>
			<td>ProOx Model P360 O2 controller and animal chamber</td>
			<td>BioSphenix, Ltd.</td>
			<td>538</td>
			<td>For disease model induction, semi-closed system, optional for closed system</td>
		</tr>
		<tr>
			<td>Rats CD(SD)</td>
			<td>Charles River Laboratories</td>
			<td></td>
			<td>Also other strains possible</td>
		</tr>
		<tr>
			<td>Revertor 5 mg/mL</td>
			<td>VET MEDIC ANIMAL HEALTH OY</td>
			<td>vnr 13 04 97</td>
			<td>For anaesthesia reversal</td>
		</tr>
		<tr>
			<td>Silica gel</td>
			<td></td>
			<td></td>
			<td>For humidity control during model induction</td>
		</tr>
		<tr>
			<td>Systane Ultra 10ml</td>
			<td>Alcon</td>
			<td>Tamro 2050250</td>
			<td>For hydration of the eye</td>
		</tr>
		<tr>
			<td>Systane Ultra unit 0.7ml</td>
			<td>Alcon</td>
			<td>Tamro 2064871</td>
			<td>For hydration of the eye</td>
		</tr>
		<tr>
			<td>Transfer pipette</td>
			<td>Thermo Fisher Scientific</td>
			<td>1343-9108</td>
			<td>For preparation of flat mounts</td>
		</tr>
		<tr>
			<td>VENTI-Line VL 180 PRIME Drying oven</td>
			<td>VWR</td>
			<td>VL180S 170301</td>
			<td>For drying silica gel</td>
		</tr>
		<tr>
			<td>VisiScope SZT350 Stereomicroscope</td>
			<td>VWR</td>
			<td>481067</td>
			<td>For intravitreal injection or tissue collection</td>
		</tr>
	</tbody>
</table>

oxygen-induced retinopathy model for ischemic retinal diseases in rodents

One of the commonly used models for ischemic retinopathies is the oxygen-induced retinopathy (OIR) model. Here we describe detailed protocols for the OIR model induction and its readouts in both mice and rats. Retinal neovascularization is induced in OIR by exposing rodent pups either to hyperoxia (mice) or alternating levels of hyperoxia and hypoxia (rats). The primary readouts of these models are the size of neovascular (NV) and avascular (AVA) areas in the retina. This preclinical in vivo model can be used to evaluate the efficacy of potential anti-angiogenic drugs or to address the role of specific genes in the retinal angiogenesis by using genetically manipulated animals. The model has some strain and vendor specific variation in the OIR induction which should be taken into consideration when designing the experiments.

The main outcome of the model is the vascular phenotype: the size of AVAs and the amount of NV. In the mouse OIR model, the vaso-obliteration occurs in the central retina (Figure 2A), while in the rat model it develops in the periphery, i.e., similar to human ROP22 (Figure 3A). This is because the superficial vascular plexus has already developed when mice are exposed to hyperoxia, whereas in the rat model the retina is avascular at the t...

Watch this Scientific Journal Video about Oxygen-Induced Retinopathy Model for Ischemic Retinal Diseases in Rodents at JoVE.com

Oxygen-Induced Retinopathy Model for Ischemic Retinal Diseases in Rodents

Oxygen-induced retinopathy (OIR) can be used to model ischemic retinal diseases such as retinopathy of prematurity and proliferative diabetic retinopathy and to serve as a model for proof-of-concept studies in evaluating antiangiogenic drugs for neovascular diseases. OIR induces robust and reproducible neovascularization in the retina that can be quantified.

One of the commonly used models for ischemic retinopathies is the oxygen-induced retinopathy (OIR) model. Here we describe detailed protocols for the OIR ...

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