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Matthias Zenkel, Jan-Peter Roth, Antonio Bergua, Friedrich E Kruse, Ursula Schlotzer-Schrehardt; LOXL1 is involved in the regulation of extracellular matrix-related genes in optic nerve head astrocytes. Invest. Ophthalmol. Vis. Sci. 2014;55(13):5706.
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Dysregulated expression of lysyl oxidase-like 1 (LOXL1), a pivotal cross-linking enzyme in elastic fiber homeostasis, has been previously shown to contribute to an elastinopathy of the lamina cribrosa in patients with pseudoexfoliation (PEX) syndrome and to represent a candidate risk factor for a PEX-specific risk of glaucoma development. To further analyze the role of LOXL1 in glaucomatous optic neuropathy, we investigated the effects of LOXL1 overexpression and knockdown on the expression of genes related to PEX-specific extracellular matrix metabolism in optic nerve head (ONH) astrocytes.
Human ONH astrocytes from four nomal donors were transiently transfected with a full-length LOXL1 vector construct (pCMV6-LOXL1) or LOXL1 siRNA; transfection with the empty vector or unrelated siRNA, respectively, served as controls. Gene expression profiles of LOXL1 overexpressing and LOXL1 deficient cells were compared using a custom PCR array including 84 PEX-relevant genes related to extracellular matrix synthesis and remodeling. Differentially expressed genes were identified using the Qiagen RT2 Profiler Data Analysis Software v3.5 and verified by specific real-time PCR assays.
Transfection of primary human ONH astrocytes with LOXL1 expression vectors and LOXL1 siRNA resulted in significantly increased (about 100-fold) and decreased (about 90%) expression levels of LOXL1, respectively, as compared to controls, which could be maintained for about one week. Overexpression of LOXL1 resulted in reduced expression levels of extracellular matrix genes, particularly elastin and collagen type III, together with a downregulation of transcription factors SP-1, ATF4, c-Jun and Snail at 72 hours post-transfection relative to the empty vector control. Although LOXL1 knockdown induced a compensatory upregulation of other LOX isoenzymes, it resulted in increased expression levels of elastin, MMP-1 and TIMP-4 together with a downregulation of transcription factor Smad3 at 48 -72 hours post-transfection compared to controls.
The findings indicate a direct effect of LOXL1 on the regulation of extracellular matrix synthesis and turnover and on TGF-β signaling. They further suggest that dysregulated LOXL1 expression by ONH astrocytes may be a crucial determinant of altered elastin metabolism in the lamina cribrosa of patients with PEX syndrome/glaucoma.
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