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Katalin Csiszar, Rozalia Laczko, Kornelia Molnarne Szauter, Robert Ritch; LOXL-1-Associated Pathomechanisms in Exfoliation Syndrome. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6319.
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Strong genetic linkage has been consistently demonstrated in populations world-wide for LOXL1 gene alleles that predispose to a high risk for exfoliation syndrome (XFS) and exfoliation glaucoma (XFG). In this study we aimed to determine ocular epithelia-specific LOXL1 functions and the mechanism by which LOXL1 risk alleles may contribute to XFS/XFG pathology.
An epithelial cell model was used to determine LOXL1 synthesis, processing, activation, nuclear and extracellular matrix (ECM) localization, and LOXL1 functional parameters. A LOXL1 risk-allele overexpressing cell system and immune-detection were applied to monitor cell phenotype changes and E-cadherin levels. LOXL1-Snail interactions were tested with co-immune precipitation using whole cell lysates and Snail or LOXL1-specific antibodies.
In epithelial cells, high levels of LOXL1 were produced, localized within the nuclei, and secreted into the media. The secreted LOXL1 appeared in various processed forms of molecular masses between 42 and 55 kD of which the 42 kD form proved specific for epithelial cell types. In ARPE-19 retinal epithelial cells, the 42 kD form was highly abundant, while this was not a feature in HEK293 kidney epithelial cells. LOXL1 risk-allele overexpression in HEK293 cells resulted in high levels of active LOXL1 that did not visibly alter morphology or migration, however, significantly reduced E-cadherin expression. Immune-precipitation experiments identified interaction of LOXL1 with the transcription regulator Snail. In LOXL1 overexpressing HEK293 cells, Snail interacted with the full-length LOXL1, an interaction that was not detectable in native HEK293 cells or in vector transfected cells. In contrast, interaction of LOXL1 with Snail occurred in native ARPE-19 cells. Furthermore, this interaction involved the processed and epithelia-specific 42 kD LOXL1. In functional tests, the activity of LOXL1 did not prove critical in Snail-mediated LOXL1 functions in ARPE-19 cells as inhibition of LOXL1 activity using BAPN or catalase-mediated depletion of H2O2, a byproduct of LOXL1 activity, did not significantly alter E-cadherin levels.
In XFS/XFG, LOXL1-associated epithelial pathology appears to involve both altered ECM cross-linking activity and cellular mechanisms with a significant role for LOXL1 in direct interactions with Snail, a transcriptional regulator of epithelial to mesenchymal transition, resulting in reduced E-cadherin expression, compromised epithelial cell adhesion, and a potential shift towards fibrogenic cell phenotypes.
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