Glucocorticoid induction of the glaucoma gene MYOC in human and monkey trabecular meshwork cells and tissues

PURPOSE. TO examine the intracellular and extracellular expression of myoci lin in the human and primate trabecular meshwork (TM) in the presence and a bsence of glucocorticoids. METHODS. Myocilin expression was examined in cultured human TM cells by Nor thern blot analysis and myocilin antibody-mediated immunoprecipitation. Myo cilin expression was quantified using high-resolution two-dimensional polya crylamide gel electrophoresis of radiolabeled proteins from human TM cells, TM tissue explants, and perfused human anterior segments cultured with and without dexamethasone (DEX) for 14 to 21 days, as well as TM tissue from p igtailed monkeys treated orally for 1 year with cortisone acetate. Immunofl uorescence with anti-myocilin antibodies was used to localize cellular and extracellular expression of myocilin in cultured human TM cells. RESULTS. Glucocorticoid treatment caused a significant induction of myocili n mRNA, a tetrad of cell-associated proteins, and 8 to 20 secreted proteins (molecular mass [M-t] 56 and 59 kDa and isoelectric point [pI] 5.2 and 5.3 ) in some, but not all the cultured human TM cells and explanted tissues. W estern immunoblot analysis using anti-myocilin peptide antibodies identifie d these proteins as encoded by the MYOC gene. There was significant inducti on of the myocilin proteins in three perfusion-cultured human eyes, in whic h DM-induced elevated intraocular pressure developed. Monkeys treated 1 yea r with cortisol acetate showed steroid glaucoma-like morphologic changes in the TM that correlated with the induction of myocilin in the TM. Immunoflu orescence analysis of cultured TM cells localized myocilin intracellularly in discrete perinuclear and cytoplasmic vesicular deposits as well as extra cellularly on the cell surface associated with the extracellular matrix. In several DEX-treated TM cell lines, there were significant levels of myocil in secreted into the media. Enzymatic deglycosylation of proteins in the TM media converted the higher molecular weight isoforms of myocilin (similar to 57 kDa) to the lower molecular weight isoforms (similar to 55 kDa). CONCLUSIONS. Although the function of myocilin is unknown, induction of the se TM proteins was found in eyes in which glucocorticoid-induced ocular hyp ertension developed. Therefore, myocilin may play an important pathogenic r ole in ocular hypertension in addition to its role in certain forms of POAG .