Regulation of TIGR/MYOC gene expression in human trabecular meshwork cells

Glucocorticoid (GC) treatment of human trabecular meshwork (HTM) cells prod uces delayed, progressive cellular and extracellular protein/glycoprotein i nductions with characteristics matching those for intraocular pressure elev ation with corticosteroid eyedrops. The cloning of the Trabecular Meshwork Inducible Glucocorticoid Response (TIGR) gene from this system has suggeste d possible environmental and genetic influences in relation to glaucoma mec hanisms. As reported here, the major GC-induced increase of TIGR expression in HTM cells is reduced approximately 4-fold by basic fibroblast growth fa ctor (bFGF, 100-1000 pM), with a somewhat smaller inhibition noted with the thyroid hormone triiodothyronine (T-3, 100 nM). Such endogenous 'protectiv e' factors could help balance stimulatory effects on TIGR gene expression f rom 'stress' and/or mechanical perturbations in the trabecular meshwork. TI GR coding region mutations affecting the gene's olfactomedin (OLF) homology domain may also perturb biosynthetic pathways and cellular homeostatic fun ctions. Our recent studies have shown the OLF domain corresponds to a major translocational 'pause', an area where critical processes for normal TIGR biogenesis are expected to take place. Observations that Glu323Lys (and oth er mutations early in the OLF domain) altered the pattern of paused protein intermediates provide possible clues to previously unexplained pathogeneti c mechanisms. HTM cell transfection studies using TIGR-green fluorescent pr otein (GFP) fusions showed increased and altered distribution of the expres sed protein with constructs missing the OLF domain, an effect also found wi th the Pro370 Leu mutation for early-onset glaucoma. The data suggest an ac tivation of stress/apoptotic pathways in HTM cells as a potential mechanism for environmental/genetic interactions in glaucoma pathogenesis.