Dynamic compensation occurs in the aqueous outflow pathway in non-human primates with experimental glaucoma

Abstract

Purpose : Retinal and optic nerve changes in non-human primates (NHPs) with laser-induced experimental glaucoma (EG) are known, but aqueous outflow pathway changes are understudied. This investigation reports biomechanical, proteomic, and ultrastructural features of unlasered trabecular meshwork (TM) in NHPs with EG.

Methods : Enucleated globes were analyzed from 16 adult female Macaca fascicularis with EG OD, previously used in preclinical study of hypotensive drugs. Globes were included from animals with EG for >3 years, drug washout ≥3 months prior to collection, and prior serial measurement of retinal nerve fiber layer thickness (RNFLT) with optical coherence tomography (SD-OCT). Unlasered TM from EG eyes and site-matched TM from fellow globes (OS, controls) were dissected for: measurement of elastic modulus (EM) with atomic force microscopy (AFM), proteomic analysis, and confocal light and transmission electron microscopy (TEM).

Results : Between EG eyes and controls, RNFLT differed by >10% in n=11 animals (Set 1), and by ≤5% in n=5 animals (Set 2). Mean EM in n=8 animals (Set 1: n=6, Set 2: n=2) was ~6-fold lower in EG eyes (Set 1: 0.464±0.036 kPa, Set 2: 0.151±0.014 kPa) than controls (Set 1: 3.31±0.32 kPa, Set 2: 2.63±0.14 kPa). There was no correlation between EM and in vivo intraocular pressure (IOP) or RNFLT. Proteomic analysis of TM from n=7 animals (Set 1: n=5, Set 2: n=2) yielded significant differences in expression of 11 matricellular proteins. Microscopy of n=3 animals (Set 1) showed TM thinning in EG eyes compared to controls (mean 53.7±3.1 vs. 127.4±24.0 μm, respectively;p=0.03). On TEM, fewer giant vacuoles were seen in EG eyes than controls (mean 11±8 vs. 47±9/mm, respectively;p<0.01); and narrowing and inner wall endothelial cell loss was observed in Schlemm’s canal of EG eyes.

Conclusions : Marked RNFL thinning may not be observed in all animals with EG despite elevated IOP. In EG eyes, unlasered TM is invariably and maximally softened, with downregulation of structural and metabolic proteins. TM is also comparatively thinned and acellular in EG eyes. Dynamic compensation of TM in EG eyes suggests a response lacking in human patients with POAG. Despite in vivo findings that support its use in neuroprotective investigations, compensatory aqueous outflow pathway changes in NHPs with laser-induced EG may limit this model’s utility in studies of therapies that target the TM.

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