Lysyl Oxidase-Like 1 (LOXL1) and Elastic Microfibrils Are Regulated by Pathogenetic Factors Involved in Pseudoexfoliation Syndrome

Abstract

Purpose: : Genetic variation in the lysyl oxidase-like 1 (LOXL1) gene has been identified as the principal genetic risk factor for pseudoexfoliation (PEX) syndrome and glaucoma. However, additional genetic and/or external factors are required for the phenotypic manifestation of PEX syndrome. The aim of this study was to analyze the effect of various PEX-associated fibrogenic stimuli on the expression of LOXL1 and elastic microfibrillar components in vitro.

Methods: : Cultured human Tenon’s capsule fibroblasts obtained from patients with PEX syndrome were exposed to stimuli, such as TGF-ß1 (0.1-10 ng/ml), IL-6 (1-50 ng/ml), homocysteine (1-500 µM), oxidative stress (25-500 µM H₂O₂) or hypoxia (3% oxygen) for up to 48h. The mRNA expression and protein secretion of both LOXL1 and elastic microfibrillar components (fibrillin-1, -2, latent transforming growth factor binding protein (LTBP) -1, -2, and fibulin-1, -2) were analyzed using quantitative real-time PCR and Western blot analysis of cell culture supernatants.

Results: : Pathogenetic stimuli, which are known to be involved in the PEX process, were found to regulate both mRNA and protein expression of LOXL1 as well as elastic fiber components in human Tenon’s capsule fibroblasts in a time and dose dependent manner. As compared to controls, the mRNA expression and secretion of LOXL1 was significantly upregulated by TGF-ß1 (up to 3-fold; p<0.01), oxidative stress (up to 4-fold; p<0.005), and hypoxia (up to 6-fold; p<0.001), whereas homocysteine and IL-6 had no effect. Fibrillin-1, LTBP-1 and LTBP-2, the main elastic components of PEX material, were upregulated in parallel with LOXL1 on the mRNA and protein level in response to TGF-ß1 and oxidative stress (up to 3-fold; p<0.001). In contrast, hypoxia and IL-6 did not affect the mRNA or protein expression of elastic microfibrillar components.

Conclusions: : Our data suggest that the abnormal matrix process characteristic of PEX syndrome may be activated by certain fibrogenic stimuli, such as TGF-ß1, oxidative stress, and hypoxia, all of them being present in PEX eyes, and in the background of a specific LOXL1 genotype, may lead to the formation and aggregation of the elastotic PEX material.

Keywords: extracellular matrix • pathology: human • proteins encoded by disease genes