dc.description.abstract | 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.
(Invest Ophthalmol Vis Sci. 2001;42:1769–1780) | en_US |