DYNAMIC CHANGES IN SEGMENTAL OUTFLOW ARE LOST WITH AGE IN MICE

Abstract

Purpose : Aqueous humour drainage through the trabecular meshwork (TM) is spatially non-uniform or segmental, with regions of higher and lower local filtration around the TM circumference. By regulating filtration through the TM, segmental outflow likely contributes to outflow resistance generation, but we know little about the factors controlling segmental outflow. In this project, we explore whether segmental outflow patterns change over time in living mice and whether these changes are affected by age.

Methods : Fluorescent tracer microspheres (0.2 µm; 10⁸ µl^-1) were delivered intracamerally to label segmental outflow patterns in male C57BL/6J mice (4 or 8 months old). We used two distinct tracer colours delivered simultaneously or with a delay of 2, 7 or 14 days in young mice, while in older mice the delay was fixed at 14 days. Microspheres were perfused into the anterior chamber for 10 min at 15 mmHg under isoflurane anaesthesia. Mice were euthanised 48 hrs after the second tracer injection. Eyes were enucleated, immersion fixed, and prepared for en face fluorescence imaging of the TM. We analysed the spatial colocalization of the two tracer patterns using linear regression analysis, calculating the Pearson’s correlation coefficient (r).

Results : In young mice, the two tracer colours were highly correlated when delivered simultaneously (r = 0.91 [0.83, 0.99]; mean [95% CI], n = 5 eyes). However, the correlation was lost over time (Figure), such that by 14 days the correlation was undetectable (r = 0.06 [-0.14, 0.26]; n = 6, p < 0.0001). In older mice, the correlation between the two tracer colours was maintained for at least 14 days (r = 0.71 [0.60, 0.82], n = 6; p < 0.0001).

Conclusions : These data reveal that segmental outflow patterns are dynamic in young mice, changing over a timescale of several days, but relatively static in older mice. This demonstrates that the locations of active filtration are continuously moving about within the trabecular meshwork in young individuals, but this dynamic process slows with age. It will be important to identify what factors contribute to the time-dependent changes in segmental outflow and whether loss of this time-dependence coincides with TM dysfunction.

This is a 2020 ARVO Annual Meeting abstract.

 

The correlation coefficient represents the spatial colocalisation between segmental outflow patterns in the TM labelled by two tracer colours separated by a time delay. The correlation decays over 14 days in young mice, but not in older mice.