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Inas F Aboobakar, Jin Liang, Michael A Hauser, R Rand Allingham, W Daniel Stamer; Cyclic mechanical stress alters LOXL1 gene expression in trabecular meshwork and Schlemm’s canal cells. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):3540.
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© ARVO (1962-2015); The Authors (2016-present)
Genetic variants in the LOXL1 gene are strongly associated with risk for developing exfoliation syndrome (XFS), a systemic fibrillopathy. Ocular hypertension resulting from XFS commonly leads to exfoliation glaucoma (XFG). However, the mechanism for ocular hypertension in XFS is poorly understood. Tissues of the conventional aqueous outflow tract reside in a mechanically demanding environment. They undergo periods of stretch and relaxation in response to dynamic changes in intraocular pressure, which leads to altered gene expression, increased extracellular matrix (ECM) turnover, and tissue remodeling. Here, we test the hypothesis that cyclic mechanical stress (CMS) alters expression of LOXL1, an ECM cross-linking enzyme.
A Flexercell system was used to apply CMS (15% at 1Hz) to primary cultures of human trabecular meshwork (HTM) and Schlemm’s canal (SC) cells. Two SC and four HTM cell strains from non-glaucomatous donors were tested. A control plate was placed in the Flexercell apparatus but was not subjected to stretch. Total RNA was collected after 24 hours of CMS and quantitative real-time PCR was used to measure changes in LOXL1 gene expression. Data were normalized relative to 36b4 gene expression. Changes in IL-6 gene expression and ERK phosphorylation status were also monitored, serving as positive controls for cellular responses to CMS.
LOXL1 expression decreased 1.5-fold after 24 hours of CMS in HTM cells (n=4, p<0.02). Interestingly, SC cells demonstrated a 2.2-fold increase in LOXL1 expression with CMS (n=2, p<0.05). IL-6 expression increased 3.3-fold in HTM cells (p<0.01) and 4-fold in SC cells (p<0.05) in response to CMS, consistent with previously published data. Additionally, cell lysates showed decreased ERK phosphorylation in stretch samples compared to controls, further indicating induction of cellular changes in response to CMS.
These data suggest that CMS differentially affects LOXL1 gene expression in HTM and SC cells, two major cell types of the conventional outflow tract. Mechanically-induced alterations in LOXL1 expression may play an important role in normal repair functions of conventional outflow tissues. The hypothesis that perturbations of this system produced by LOXL1 genetic variants underlie the pathobiology of ocular hypertension, XFG, and the systemic manifestations of XFS deserves further investigation.
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