Evaluation of Norrin-Based Treatment on Improved Vascular Growth in a Mouse OIR Protocol Modified to Avoid Pulmonary Stress in Adult Dams

Document Type

Conference Proceeding

Publication Date

6-2026

Publication Title

Investigative Ophthalmology and Visual Science

Abstract

Purpose : The mouse oxygen-induced retinopathy (OIR) model is used to evaluate mechanisms of retinal neovascularization and to test interventions that accelerate vascular regrowth in vivo. While 75% oxygen from P7-P12 is tolerated by neonatal mice, the adult dams can develop pulmonary stress and must be replaced with surrogate dams. High oxygen promotes a shift to pro-inflammatory Streptococci in the lungs of adult mice, so we modified the protocol to remove dams for 1.25 hrs/day to room air, leaving litters in 75% oxygen. This process was used to evaluate Norrin's effects on neovascular regrowth compared to previous results with the traditional model

Methods : Litters were subjected to a modified OIR protocol: 75% oxygen from P7–P12, dams cycled to room air for 1.25 hrs/day. P13 mice received an intravitreal injection of Norrin (200 ng, OD) or Vehicle. P17 retinas were harvested and the microvasculature was labeled with Isolectin-B4-Alexa594. Retinas were flat mounted and imaged by confocal microscopy (5x5 tile stitching). GIMP software was used to measure the fractional avascular area. Results for OD retinas were normalized to OS retinas.

Results : Use of the modified OIR protocol for seven experiments with 3 litters per experiment have resulted in no pulmonary stress in any dams. The average weights of littermates were closer to normal room air littermates, indicating healthier lactating dams in high oxygen. No surrogate dams were required. Use of the modified protocol to test the effects of a research grade Norrin (RnD systems) found that Vehicle injection reduced avascular area by 10% compared to the non-injected eyes (0.900 ± 0.274, N=11). Norrin injection reduced the avascular area an additional 26% compared to Vehicle (0.644 ± 0.259, N=10, P=0.020). Testing of 200 ng Noregen (NorrinK86P) resulted in the same magnitude of effect.

Conclusions : The reduction of avascular area reported previously using Norrin in the traditional OIR protocol was reproduced using the modified protocol. On average the weights of neonatal mice were like room air litters with improved feeding by healthier dams. This also resulted in more usable mice for analysis. We conclude that researchers can consider cycling dams to room air for a short period each day when using the OIR model.

Volume

67

Issue

7

First Page

544

Comments

Association for Research in Vision and Ophthalmology, May 3-7, 2026, Denver, CO

Last Page

544

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