Abstract
Purpose: :
Previous studies showed a marked elastosis of the lamina cribrosa (LC) in eyes with pseudoexfoliation (PEX) glaucoma suggesting an abnormal regulation of elastin metabolism. To provide a more detailed analysis of the LC elastic fiber system, we investigated the expression of elastic fiber components and related cross-linking enzymes in LC tissue and cells of eyes with and without PEX syndrome.
Methods: :
Protein and mRNA expression of elastic fiber components (elastin, tropoelastin, fibrillin-1/2, emilin-1, MFAP-1/2/5, LTBP-1/2/3/4, fibulin1/2/3/4/5/6), lysyl oxidase (LOX) and lysyl oxidase-like proteins (LOXL1, LOXL2) were assessed by quantitative real-time PCR, Western blot, and immunohistochemistry in posterior segment tissues (choroid, retina, sclera, optic nerve) and cultivated LC cells and astrocytes obtained from donor eyes with PEX syndrome (n=12) and age-matched normal eyes (n=15). Additionally, elastin content was evaluated by desmosine immunoassay.
Results: :
Compared to all other posterior segment tissues, highest levels of LOXL1 mRNA and protein were measured in normal LC tissue, whereas LOX and LOXL2 were not detected. High expression levels were also found for fibrillin-1 and fibulin-4 followed by tropoelastin. By immunolabeling, normal LC plates revealed a complex elastic network consisting of elastin-containing fibers and distinct subspecies of elastic microbrillar bundles with fibrillin-1 and fibulin-4 as major components, in close association with LOXL1-positive cells. Occasionally, LOXL1 was seen to colocalize with tropoelastin in fibrillar structures. LC tissue of PEX eyes revealed a disorganized elastic fiber system and a significant site-specific downregulation of LOXL1 (5-fold), elastin (12-fold), fibrillin-1 (9-fold), and fibulin-4 (3-fold) mRNA and protein as well as reduced elastin cross-links, whereas collagen expression was not different from controls. Synthesis and secretion of LOXL1 and elastic proteins by LC cells and astrocytes in vitro could be increased by various stimuli including TGF-ß1.
Conclusions: :
Elastinopathy resulting from LOXL1 deficiency may have adverse effects on biomechanical properties of the LC and may predispose to glaucoma development in eyes with PEX syndrome. Future strategies may target stimulation of LOXL1 and reinforcement of elastic fiber networks in LC tissue.
Keywords: lamina cribrosa • extracellular matrix • astrocytes: optic nerve head