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Renata A. Puertas, Marcus Koch, Rudolf Fuchshofer, Walter Paper, Ahmed Elkarmouty, Keith Barton, Ernst Tamm; Myocilin Expression in Uveitic, Fuchs Heterochromic Iridocyclitis and Non-Uveitic Trabecular Meshwork and Aqueous Humor. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4648.
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To compare the concentration of myocilin in aqueous humour (AH), and mRNA expression in TM in 3 groups of patients: Fuchs Heterochromic Cyclitis (FHC), other types of uveitic glaucoma (± steroid response), and primary open angle glaucoma (POAG).
Thirty-nine patients who were due to undergo trabeculectomy surgery at one institution were recruited, consented according to the Declaration of Helsinki, and divided into the following groups:A. 9 FHC,B. 16 Uveitic Glaucoma (without FHC) with or without significant steroid exposure,C. 14 POAG.A sample of AH was collected at the beginning of surgery. During the procedure a 2x1mm TM block was excised. AH samples were processed by SDS-PAGE and Western Blot (WB) analysis using anti-myocilin antibodies (Santa Cruz Biotechnology, 1:2000). For normalization of myocilin bands, blotted membranes were stained with Coomassie and digitized. The intensity of the albumin signal was determined using appropriate software and used to normalize the signal intensity of the myocilin band. RNA was isolated from TM samples, cDNA prepared and quantitative real time RT-PCR performed with primers specific for myocilin and GAPDH and GNB2L as housekeeping genes. Mean expression levels were compared using Student’s t-test.
There was no significant difference between groups B and C in WB analysis of the AH. Nevertheless, there was a trend towards higher values in group B. Interestingly, group A showed significantly higher values of myocilin in AH than those in group B (p<0.04). When groups A and C were compared, this remained true (p<0.003). Again, no significant differences were observed between groups B and C in RT-PCR of the TM samples. However, significant differences were found between groups A and B (p<0.05), and A and C (p < 0.05).
We have not found specific evidence of a pathogenic role for myocilin in patients with non-FHC uveitic glaucoma, as expression levels are similar to POAG. We would speculate that the high levels of myocilin in AH of FHC patients are likely released from affected iris tissues, as the iris is often profoundly affected by FHC. The increased myocilin mRNA expression in TM specimens may indicate either a pathogenic process in the TM outflow pathways or a higher sensitivity to steroid treatment than is observed in other types of uveitic glaucoma or POAG.
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