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Ernst R. Tamm, Paul Russell, David L. Epstein, Douglas H. Johnson, Joram Piatigorsky; Modulation of Myocilin/TIGR Expression in Human Trabecular Meshwork. Invest. Ophthalmol. Vis. Sci. 1999;40(11):2577-2582.
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purpose. To study factors that modulate myocilin/trabecular meshwork inducible
glucocorticoid response protein (TIGR) mRNA expression in human
trabecular meshwork (TM).
methods. mRNA from fresh TM of four human donors, from perfused anterior segment
organ cultured TM of three donors, and from four primary TM cell lines
of different donors was isolated. The full length cDNA of myocilin/TIGR
was cloned from TM mRNA using a polymerase chain reaction approach and
used as probe for northern blot analysis hybridization. Trabecular
meshwork cell cultures were treated with transforming growth factor
(TGF)-β1 (1 ng/ml), dexamethasone (10−7 M), and
mechanical stretch (10%).
results. mRNA for myocilin/TIGR could be readily detected by northern blot
analysis hybridization in 2 to 3 μg of total RNA from all fresh and
all organ-cultured TM samples. In contrast, no mRNA for myocilin/TIGR
could be detected in 20 μg of total RNA isolated from three different
primary TM cell lines. Only one TM cell line had a baseline expression
of myocilin/TIGR, which was 35- to 55-fold lower than that of fresh or
organ-cultured TM samples. Treatment of TM cell cultures with
dexamethasone for 1 day markedly increased expression of myocilin/TIGR
mRNA, an effect that was even more pronounced after 3 days of
treatment. Treatment with TGF-β1 for 24 hours had no effect; however,
after 3 and 12 days of treatment a 3.8- and 4-fold increase in
myocilin/TIGR mRNA expression was observed. Expression of myocilin/TIGR
mRNA was also increased after 10% mechanical stretch; however, in
contrast to the effects of TGF-β1, this effect was observed much
earlier (8–24 hours) after treatment.
conclusions. Dynamic mechanical stimuli maintain myocilin/TIGR expression in
TM in situ and lack of these stimuli in monolayer cell cultures might
be involved in downregulation of myocilin/TIGR
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