Purpose: To identify myocilin (TIGR/MYOC) properties that are specific to the human trabecular meshwork (HTM). To search for genes highly expressed in dexamethasone (DEX)-induced HTM cells that are barely expressed or absent in DEX-induced cells from other tissues.
Methods: TIGR/MYOC induction by DEX (10(-7) M for 8-10 days) was analyzed by Northern and Western blot analyses in HTM, human umbilical vein endothelial cells, HeLa cells, and human embryonic skeletal muscle cells and optic nerve head (ONH) astrocytes at confluence. Processing and secretion were analyzed after the cells were infected with adenoviruses overexpressing wild-type and mutant forms of TIGR/MYOC. Affymetrix U95Av2 GeneChips (n = 6) and software were used to compare paired expression profiles of HTM, HTM-DEX, ONH astrocytes, and ONH astrocytes-DEX. Identification of HTM-DEX-specific genes (compared with ONH astrocytes-DEX) was performed by selecting genes with the highest fold change values (>/=20). Genes with fold change values of four or more were matched with loci linked to glaucoma, by using gene databases.
Results: TIGR/MYOC induction by DEX occurred only in HTM cells. Secretory and glycosylation characteristics remained the same across cell types. Expression profile analysis revealed multiple genes differentially upregulated in HTM-DEX including, in addition to TIGR/MYOC, a serine protease inhibitor (alpha1-antichymotrypsin), a neuroprotective factor (pigment epithelium-derived factor), an antiangiogenesis factor (cornea-derived transcript 6), and a prostaglandin synthase (prostaglandin D(2) synthase). Fifteen of the 249 genes with fold change values of four or more mapped to glaucoma-linked loci.
Conclusions: The induction of TIGR/MYOC by DEX is HTM-specific, whereas its secretory and glycosylation characteristics are ubiquitous. The known functions of HTM-DEX-specific genes reveal the presence of protective and damaging mechanisms for regulation of IOP during DEX treatment. Besides TIGR/MYOC, other HTM-DEX-specific genes may be good candidates for linkage to glaucoma.