Abstract
Purpose :
The impact of glaucoma on the retinal capillary plexi (RCP) and its relationship to retinal ganglion cell (RGC) injury is not well understood. In this project, we studied microvascular injury in mice exposed to elevated IOP with the microbead model.
Methods :
We used microbead injection in one eye of seven 12-week-old wild-type mice to induce IOP elevation. IOP was measured prior to injection and then 3 times per week. After 2 weeks, we immunostained retinas with CD31 (endothelium), Collagen IV (vascular basement membrane), and RBPMS (RGCs) and performed z-stack confocal microscopy. We performed Sholl analysis to quantify the number of intersections in the retinal capillary network. Using ImageJ we quantified RGC density and processed the confocal images to separate the three RCP into distinct images. We then established a novel, optimized image workflow to semi-automatically quantify the vascular anatomy using Angiotool (NIH, open-source). This provided topographical vascular features as well as spatial dimensions for the vascular network.
Results :
IOP elevation of 1-4 mmHg above baseline was achieved throughout the study. IOP elevation to this level and duration did not cause RGC loss. Sholl analysis showed a 15% ± 3.50% reduction (p ≤ 0.01) in the total number of capillary intersections at a distance of 1500μm from the optic nerve head. We also identified a plexus-selective phenotype. There was a significant reduction in the number of capillary junctions/mm2 for both CD31 (26% ± 5.91%, p ≤ 0.01) and Collagen IV (26% ± 5.77%, p ≤ 0.01) in the intermediate retinal capillary plexus (IRCP). Furthermore, the total capillary vessel length/mm2 was reduced for both CD31 (12% ± 2.04%, p ≤ 0.01) and Collagen IV (12% ± 2.55%, p ≤ 0.001) in the IRCP. There was also a decrease in the IRCP vessel area for CD31 (19% ± 2.09%, p ≤ 0.01). No differences between control and bead injected eyes were detected for the superficial or deep RCP.
Conclusions :
We have discovered a novel vascular phenotype in which the IRCP is rapidly sensitive to the effects of IOP elevation. This vascular phenotype is not detected in other retinal plexi and precedes RGC loss. This study advances our knowledge of microvascular deficits during glaucomatous pathology.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.