The role of VEGF on outflow facility in mice with glucocorticoid-induced ocular hypertension

Abstract

Purpose : Glucocorticoid (GC) therapy causes ocular hypertension by reducing outflow facility (C), but it remains unclear exactly how GCs impair outflow. Our prior work has shown that VEGF regulates outflow within the trabecular outflow pathway, with VEGF₁₆₅a and VEGF-D increasing C and VEGF₁₆₅b decreasing C in naïve mice (Overby, D., ARVO Abstract #3542, 2015). We hypothesize that GCs disrupt the normal VEGF response to contribute to outflow dysfunction. To test this hypothesis, we measured C in mice treated with low or high doses of dexamethasone (DEX).

Methods : Two cohorts of C57BL/6J mice (12 weeks) were treated with low DEX (0.1 mg/kg/d, n = 15) or high DEX (2 mg/kg/d, n = 20), delivered systemically via an osmotic mini-pump for 4 weeks. Intraocular pressure (IOP) was measured once a week via rebound tonometry under isoflurane anaesthesia. After 4 weeks, paired eyes were enucleated and perfused with 13 nM VEGF₁₆₅a, 13 nM VEGF₁₆₅b or 77 nM VEGF-D versus vehicle using the iPerfusion system. Statistical significance was determined with a two-tailed paired t-test (IOP) or a weighted t-test (C). All experiments were conducted in compliance with the ”ARVO Statement for the Use of Animals in Ophthalmic and Visual Research".

Results : For low DEX, IOP increased from 11.0 ± 1.6 to 13.3 ± 1.6 mmHg (mean ± 2SD, n = 15, P = 3x10^-5), and for high DEX, IOP increased from 12.5 ± 5.2 to 14.7 ± 6.0 mmHg (n = 18, P = 0.01). There was no significant difference in IOP elevation between cohorts (P = 0.91). VEGF₁₆₅a had no clear effect on C in mice treated with low DEX (-32% (0.68 ^x/ 1.62, proportional change, 95% confidence interval), n = 5 pairs, p = 0.09) or high DEX (-5% (0.95 ^x/ 1.49), n = 4 pairs, P = 0.70). VEGF-D had no apparent effect on C with high DEX (-14% (0.86 ^x/ 1.42), n = 6 pairs, P = 0.32). VEGF₁₆₅b increased C with low DEX (+104% (2.04 ^x/ 1.81), n = 4 pairs, P = 0.03).

Conclusions : DEX eliminated the effect of VEGF₁₆₅a and VEGF-D that increase C in naïve mice, and DEX reversed the effect of VEGF₁₆₅b that decreases C in naïve mice. GC therapy can thereby alter VEGF signaling in the trabecular outflow pathway, potentially contributing to outflow dysfunction and ocular hypertension.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.