Abstract
Purpose :
Age-related macular degeneration (AMD) is a leading cause of blindness in developed countries. Few models exist for studying geographic atrophy (GA), the advanced form of dry AMD. We recently reported a rat model for acute RPE loss induced by subretinal injection of sodium iodate (NaIO3). In this study, we further characterize this model.
Methods :
Acute RPE loss was induced in rats (6-8 weeks old) by a 1µl subretinal NaIO3 or PBS (control) injection. At 3 weeks and 3 months post-injection, eyes were either fixed and cryopreserved or the retina and RPE/choroids were processed as flatmounts. Additional eyes were fixed and processed for transmission electron microscopy (TEM). Retinal flatmounts were stained with Glial markers. RPE/choroids were stained with RPE-65 with or without Griffonia Simplicifolia (GS) isolectin. Furthermore, cryosections were immunostained (Collagen I, IV, GS-isolectin, GFAP). Epithelial-mesenchymal transition (EMT) marker levels in both choroid and retina were analysed by RT-qPCR.
Results :
By injecting NaIO3 subretinally, we created a focal area of RPE loss surrounded by healthy RPE. Analysis of ultrathin sections at 3 months demonstrated the apparent expansion of atrophy from the original injection site. We identified a transition zone with less retinal thinning than that observed in the injection site. Within this transition zone and at the atrophic border, we noted RPE migration into retina, suggesting possible EMT. Flatmount analysis at 3 weeks provided further evidence for progression of atrophy and potential RPE EMT. RPE65 staining revealed multi-layered, multi-nucleated, enlarged and ghost RPE cells with a mottled appearance at the atrophic border. TEM analysis also revealed RPE undergoing degeneration, phagocytosis and complete loss. RT-qPCR showed an upregulation of S100a4 (fold change (fc) = 4.76) and the EMT marker Twist (fc = 3.57) in the RPE/choroids. We also expanded on our previous report of a subretinal glia within the atrophic area. Cross-section also demonstrated collagen while TEM revealed glial cell tight junctions in the subretinal space and in the choroid associated with choriocapillaris loss.
Conclusions :
The transition zone of the subretinal NaIO3 rat model supports its use for studying changes at the border in GA. Therefore, the subretinal NaIO3 model is a useful model for studying the expansion of atrophy in GA as well as the glial response to RPE loss.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.