Effects of dexamethasone on trabecular meshwork stiffness in mice

Abstract

Purpose : Treatment with dexamethasone (DEX) can increase intraocular pressure (IOP) and may lead to the development of steroid-induced glaucoma. Previous studies demonstrated that DEX treatment increased the stiffness of cultured trabecular meshwork (TM) cells along with their extracellular matrix; however, whether the increased TM stiffness is a contributor to elevated IOP remains unknown. Our goal was to study the correlation between IOP and TM stiffness in DEX-treated mice.

Methods : C57BL/6J mice (n=13; ages: 8-14 weeks) were divided into DEX-treated (DEX mice; n=10) and vehicle-treated (control mice; n=3) groups. Custom nano-sized polymers (NPs) which incorporated either DEX or vehicle were injected into the subconjunctival space of the right eye for DEX and control mice respectively at day 0, and again at day 13. IOP was recorded approximately weekly using tonometry (Tonolab), up to day 20-40. Both eyes were then enucleated, snap-frozen, sagittally cryosectioned and TM stiffness measured using atomic force microscopy (AFM) on thawed cyosections, in a masked manner.

Results : In control mice, no significant differences in either IOP or TM stiffness were observed between the two eyes. In DEX mice, 70% of animals had elevated IOP in the DEX-treated eye on the day of sacrifice. Three DEX mice had significantly increased TM stiffness in the treated eyes vs. their contralateral eyes (Figure 1; Benjamini-Hochberg correction performed). Further, IOP and TM stiffness were highly correlated (R²=0.99) in those mice, but this did not reach statistical significance (P=0.07) due to small sample size.

Conclusions : DEX treatment increases TM stiffness in some, but not all, mice. There is a correlation between TM stiffness and IOP in mice with higher TM stiffness. Further studies are underway to measure DEX concentrations OU after treatment and to identify mechanisms underlying the biomechanical response of TM to DEX.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.

 

Figure 1: Boxplot of compressive modulus of TM in DEX-treated mice (n=10). For each box, the central mark is the median, the edges of the box are the 25th and 75th percentiles, and whiskers extend to the most extreme data points not considered outliers. R: right eye; L: left eye. All mice were DEX treated in the right eyes; contralateral eyes served as controls. Blue dashed line is the mean TM stiffness of control mice with 95% confidence interval indicated as blue band. * corrected p-value<0.05.