Phenotypic Characterization of the LOXL1 Null Mouse

Abstract

Purpose: : LOXL1 SNPs have been shown to be significantly associated with pseudoexfoliation syndrome and pseudoexfoliation glaucoma in humans. Two of the associated SNPs are missense changes which could contribute to disease through a gain of function mechanism or could result in a loss of function of the LOXL1 protein. The purpose of this study is to evaluate the phenotype of the LOXL1 knockout (null) mouse to help define the pathogenic mechanism disease.

Methods: : Twenty LOXL1 null mice (ages 3-8 months) and 20 control mice (DBA/2J) were used for this study. Intraocular pressure (rebound tonometer), iris fluorescein angiography and anterior segment histology were evaluated. Fluorescein angiography was performed by injecting 50ul of 1% fluorescein into the femoral artery and recording images using the Imagenet Digital Angiography System (Topcon TRC 50 IX retinal camera and Imagenet 2000 system; Topcon America Corp, Paramus NJ). For histology, eyes were enucleated after mice were sacrificed and fixed in mixed aldehyde fixative. The eyes were processed for embedding in Epon.

Results: : Intraocular pressure measurements were within the normal range (16.5 mmHg +2) for all mice evaluated, including mice aged to 1 year. Iris fluorescein angiography did not reveal differences in vessel contour between null and control mice, but did demonstrate an increased diffusion of fluorescein into the anterior chamber of the null mice compared with age-matched controls, suggesting a compromise of the blood aqueous barrier in the null mice. Anterior segment histology demonstrated a pronounced vesiculation of the anterior lens capsule in the null mice. The location of the lesion is in direct apposition to the back of the iris. Light microscopic examination of the iris, trabecular meshwork and ciliary body did not show any significant differences between null mice and controls.

Conclusions: : These results indicate that the LOXL1 null mouse has some, but not all, of the phenotypic features found in humans affected with pseudoexfoliation syndrome, suggesting that a loss of LOXL1 protein can contribute to the human condition. Certain aspects of the clinical phenotype present in humans, including increased intraocular pressure, are not apparent in the LOXL1 null mouse suggesting that other factors may also contribute to this disease.

Keywords: genetics • iris • trabecular meshwork