VEGF expression is elevated in high-flow regions of mouse trabecular meshwork.

Abstract

Purpose : Aqueous humour drainage through the trabecular meshwork (TM) is non-uniform or segmental, with some regions of the TM exhibiting greater local filtration than others. We have recently shown that segmental outflow patterns are dynamic¹, redistributing over a time scale of a few days in living mice. This redistribution implies some regulatory mechanism governing segmental outflow. We hypothesise that VEGF, which modulates outflow resistance², controls the distribution segmental outflow. We test this hypothesis by comparing VEGF expression in high, medium, and low-flow regions of segmental outflow.

Methods : Segmental outflow patterns were labelled in one live C57BL/6J mouse (N = 1 eye) by intracameral injection of fluorescent tracer microparticles (0.2 µm; 10¹¹ particles/ml) under anaesthesia. After 6 hours, the eye was enucleated following humane culling and fixed overnight in 4% PFA. The anterior segment was dissected and immunolabelled for VEGF-A. Sagittal 100 µm cryosections through the iridocorneal angle were imaged by confocal microscopy around the TM circumference (N = 27 cryosections). From each cryosection, 15 consecutive confocal slices (0.5 µm; 40x) were selected for analysis. A polygon was drawn to include all tracer fluorescence within the TM and to create a 3D mask. We calculated the average intensity of tracer and VEGF-A immunolabelling within the mask for each cryosection. We lumped data from the highest, middle and lowest thirds of tracer intensity and compared VEGF-A labelling between these groups using one-way ANOVA with a post-hoc Tukey test.

Results : The intensity of VEGF-A immunolabelling was significantly different between high, medium and low-flow regions of the TM (p = 0.018). VEGF-A labelling was 4.7-fold greater in high-flow regions, and 2.4-fold greater in medium-flow regions, relative to low-flow regions of the TM (p < 0.03).

Conclusions : VEGF-A expression in the TM appears to coincide with the distribution of segmental outflow. As VEGF-A is known to increase outflow facility², this raises the possibility that VEGF expression by TM cells is acting as a paracrine regulator of local outflow conductivity to control segmental outflow.

1. Reina-Torres, E., et al. (2022) Exp Eye Res
2. Reina-Torres, E., et al. (2017) IOVS

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.

 

VEGF-A expression from regions of the TM corresponding to the upper, medium and lower thirds of tracer intensity (N=27 sections from 1 eye). Boxes show mean and 95% CI.