Little evidence for association of the glaucoma gene MYOC with open-angle glaucoma

Abstract

BACKGROUND/AIM To determine if overexpression of the glaucoma gene MYOC is involved in the development of open-angle glaucoma (OAG) and if its promoter variants are associated with glaucoma in the Korean population. METHODS Human trabecular meshwork cells were cultured in the presence of ophthalmic steroids such as fluorometholone, fluorometholone acetate, dexamethasone, prednisolone acetate and rimexolone. The cells were cultured at a hydrostatic pressure of 32 mm Hg above atmospheric pressure and induction of MYOC was evaluated by northern blot analysis. Genomic DNA was extracted from blood samples obtained from 74 normal controls and 168 unrelated Korean patients with OAG, including primary OAG, normal tension glaucoma and steroid-induced glaucoma. A 461 base pair (bp) DNA fragment of the MYOC promoter region was amplified using PCR and its genotype was analysed by directly sequencing the product. RESULTS The potencies of steroid eye drops in MYOC induction in vitro was the same regardless of their potential for elevating intraocular pressure in vivo. Hydrostatic pressure had no effect on MYOC induction. A dinucleotide repeat polymorphism and three single nucleotide polymorphisms were identified, but no obvious differences in the genotype distribution and allele frequency of the variants between the control group and any type of OAG were observed. CONCLUSION Our data suggest that MYOC overexpression is not a cause or an effect of intraocular pressure elevation and that MYOC itself is not associated with OAG.

Figure 1

Effect of hydrostatic pressure on morphology and induction of MYOC expression in cultured human trabecular meshwork (HTM) cells. (A) Phase-contrast images were photographed from cells cultured for 9 days in the absence (upper panel) or presence of a hydrostatic pressure of 32 mm Hg above atmospheric pressure (lower panel). (B) RNA was extracted from cells cultured in the absence (lane 1) or presence of hydrostatic pressure (lane 3), hybridised with ³²P-labelled MYOC cDNA, and subjected to autoradiography (upper panel). The same RNA was visualised by ethidium bromide staining (lower panel). Cells treated with 100 nM dexamethasone (DEX) (lane 2) served as a positive control.

Figure 2

Effect of ophthalmic steroids on the induction of MYOC expression in cultured human trabecular meshwork (HTM) cells. Confluent HTM cells were cultured for 9 days in the presence of each steroid eye drop at the indicated concentrations. All of the RNA was extracted from each cell, hybridised with ³²P-labelled MYOC cDNA, and subjected to autoradiography (upper panel). RNA was also stained with ethidium bromide as a loading control (lower panel).