Role for Arg1 and Arg2 in Age-related Intraocular Pressure Homeostasis

Abstract

Purpose : Elevated intraocular pressure (IOP) is the major risk factor and treatment target of primary open-angle glaucoma (POAG). Exogenous nitric oxide (NO) increases outflow facility and lowers IOP. Since endogenous NO production is limited in part by altered activation of arginase with aging, we aimed to investigate the expression of arginases (Arg1 & Arg2) in the conventional outflow tissues and their potential role in IOP regulation over time.

Methods : Remnant human corneal rims after transplantation were fixed and embedded in paraffin for histological sections. Outflow tissues were incubated with antibodies against ARG1 or ARG2 followed by the secondary antibody for immunofluorescence-based protein expression analysis. The expression of ARG1 and ARG2 was also examined in primary human trabecular meshwork (TM) cells with or without cyclic stretch for 24 hours (n=5) using droplet digital PCR. IOP in three groups of littermate mice, wild type (C57BL6, n=40), Arg1^+/- (n=34), and Arg2^-/- (n=134) was measured using rebound tonometery once per week in both eyes from 24 weeks to death (up to 108 weeks). The IOPs of age-matched mice were compared using student t-test with a significance threshold of p<0.05. The images of anterior chamber and the iridocorneal angle were taken in mice older than one year using a Leica Envision SD-OCT R2200 system.

Results : ARG1 and ARG2 proteins are expressed in human conventional outflow tissues. In TM cells, the expression of ARG1/ARG2 did not change significantly in response to the mechanical stretch. In mice, the mean weekly IOP measurements were comparable among three groups until 45 weeks of age. While IOP levels of wild type mice progressively decreased from 13 mmHg to 12 mmHg at 50 weeks, and to 11 mmHg after 95 weeks, IOP of Arg1^+/- and Arg2^-/- mice was stable at 13 mmHg until up to 108 weeks. An open iridocorneal angle was confirmed in the old mice of all genotypes using SD-OCT imaging and histological morphological analysis.

Conclusions : ARG1 and ARG2 are expressed in the outflow tissues and cells. Partial loss of Arg1 or complete loss of Arg2 in mice abolished the age-related IOP decrease in aged wild type mice, suggesting their role in age-related IOP homeostasis.

This is a 2021 ARVO Annual Meeting abstract.