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Abbot F. Clark, H. Thomas Steely, Jaime E. Dickerson, Sherry English-Wright, Karen Stropki, Mitchell D. McCartney, Nasreen Jacobson, Allan R. Shepard, John I. Clark, Hiroyuki Matsushima, Elaine R. Peskind, James B. Leverenz, Charles W. Wilkinson, Ruth E. Swiderski, John H. Fingert, Val C. Sheffield, Edwin M. Stone; Glucocorticoid Induction of the Glaucoma Gene MYOC in Human and Monkey Trabecular Meshwork Cells and Tissues. Invest. Ophthalmol. Vis. Sci. 2001;42(8):1769-1780. doi: https://doi.org/.
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purpose. To examine the intracellular and extracellular expression of myocilin
in the human and primate trabecular meshwork (TM) in the presence and
absence of glucocorticoids.
methods. Myocilin expression was examined in cultured human TM cells by Northern
blot analysis and myocilin antibody–mediated immunoprecipitation.
Myocilin expression was quantified using high-resolution
two-dimensional polyacrylamide 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 pigtailed monkeys treated orally
for 1 year with cortisone acetate. Immunofluorescence 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 myocilin
mRNA, a tetrad of cell-associated proteins, and 8 to 20 secreted
proteins (molecular mass [Mr] 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. Western immunoblot analysis using
anti-myocilin peptide antibodies identified these proteins as encoded
by the MYOC gene. There was significant induction of the
myocilin proteins in three perfusion-cultured human eyes, in which
DEX-induced elevated intraocular pressure developed. Monkeys treated 1
year with cortisol acetate showed steroid glaucoma-like morphologic
changes in the TM that correlated with the induction of myocilin in the
TM. Immunofluorescence analysis of cultured TM cells localized myocilin
intracellularly in discrete perinuclear and cytoplasmic vesicular
deposits as well as extracellularly on the cell surface associated with
the extracellular matrix. In several DEX-treated TM cell lines, there
were significant levels of myocilin secreted into the media. Enzymatic
deglycosylation of proteins in the TM media converted the higher
molecular weight isoforms of myocilin (∼57 kDa) to the lower
molecular weight isoforms (∼55 kDa).
conclusions. Although the function of myocilin is unknown, induction of these TM
proteins was found in eyes in which glucocorticoid-induced ocular
hypertension developed. Therefore, myocilin may play an important
pathogenic role in ocular hypertension in addition to its role in
certain forms of POAG.
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