Gene Expression Profiling Of Human Trabecular Meshwork In Glaucoma Patients With Or Without Myocilin Mutations

Abstract

Purpose: : To identify genes differentially expressed in human trabecular meshwork (HTM) in patients with primary open-angle glaucoma (POAG), with or without myocilin mutations, compared with non-glaucomatous controls.

Methods: : Surgical HTM samples were obtained from 15 patients undergoing trabeculectomy. Non-glaucomatous control tissue was obtained from 13 donor human eyes. The HTM was dissected in a manner similar to the approach used in trabeculectomy surgery. Total RNA was labeled and hybridized to HumanWG-6 BeadChip. The expression data was applied with quantile normalization prior to analyses using linear model of limma in Biocondutor. Pathway analyses were performed with DAVID Bioinformatics Resources and Ingenuity Pathway Analysis.

Results: : One POAG case had a heterozygous Q368X myocilin mutation (designated as MYOCcase). For the MYOCcase and 6 controls, expression data was available from both left and right eyes. We used the average of the expression value from both eyes for analysis. The analyses were done in the following manner: 1) MYOCcase vs 14 non-MYOC cases; 2) MYOCcase vs 13 controls; 3) 14 non-MYOC cases vs 13 controls. Myocilin expression was not different in all comparisons. In the first comparison between cases, we identified 35 differentially expressed genes, including two non-protein-coding RNAs. Pathway analysis indicated that there was an enrichment of genes related to DNA binding, acetylation, alternative splicing, and organelle lumen such as ER. The second comparison identified more than 200 genes with differential expression related to the MYOCcase compared with controls. Pathway analysis indicated enrichment of genes associated with the enzyme linked receptor protein signaling pathway, signal peptides, glycoproteins, serine/threonine and tyrosine kinase signaling pathways, and secretion. Since myocilin has been shown to be constituent of exosomes, we identified 11 components of TM exosomes with differential expression caused by myocilin mutation. The third comparison identified over 100 differentially expressed genes, which are enriched in actin cytoskeleton organization, regulation of apoptosis, and NF-kB cascade. Three genes are involved in Rho-kinase pathways, suggesting the importance of this pathway in POAG.

Conclusions: : This is the first study to describe gene expression profiles in HTM of a case with a well described myocilin mutation. Our findings lend support to the notion that myocilin mutations may increase ER stress as well as evidence that myocilin mutations may exert their pathophysiological effect by altering exosome function in POAG. We also provide evidence that Rho-kinase pathways may be involved in POAG pathogenesis.

Keywords: gene/expression • mutations • trabecular meshwork