Abstract
Purpose :
Glaucoma is an age-related neurovascular disease affecting primarily retinal ganglion cells (RGCs) but also several other inner retinal components. We have previously established that the intermediate retinal capillary plexus (IRCP) is uniquely sensitive to ocular hypertension (OHT) in young adult mice and shows reduced complexity prior to RGC loss. In this study, we extend our analysis to aged mice to determine the combined impact of age and OHT on RGC and vascular phenotypes.
Methods :
We injected 82-85 week-old wild type mice (n=3) with polystyrene microbeads in one eye to induce mild OHT. The fellow eye was the intra-animal control. After 2 weeks, retinas were stained with antibodies to RBPMS (RGC), CD31 (endothelium), and Collagen IV (COLIV; vascular basement membrane). Z-stack images at 10x and 20x were obtained with confocal microscopy. We used our published vascular analysis workflow (ImageJ; AngioTool) to assess the complexity and topographical features of the retinal capillary network and RGC numbers.
Results :
Mild OHT was established with an average increase of 2.5 mmHg (p ≤ 0.001) above baseline and the fellow eye. Every retina with OHT showed reduced RGC density when compared to its fellow eye (23% ± 10.98%). Vascular complexity was reduced (p ≤ 0.05) in OHT retinas compared to controls (Sholl analysis). For both CD31 and COLIV, retinal capillary branches, total percentage of capillary area, and capillary diameter were all reduced in the IRCP of OHT retinas (p ≤ 0.05 for all). For the same parameters, no differences were detected in the superficial or deep retinal capillary plexus. Finally, there was a marked increase in acellular capillaries (p ≤ 0.01) in the IRCP of OHT retinas. Additional experiments are ongoing to increase the number of aged eyes with OHT in the study.
Conclusions :
Two weeks of mild OHT induced in aged wild type mice shows an augmented version of the IRCP-specific phenotype we previously reported in young adult mice. However, unlike in young adult retinas, mild OHT in aged retinas consistently caused RGC loss (there is no RGC loss at this level of OHT in young adult mice). Our findings demonstrate a potentially important impact of mouse age on glaucoma phenotypes.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.