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Colleen M McDowell, Tasneem Putliwala Sharma; TLR4 signaling in the human trabecular meshwork and optic nerve head. Invest. Ophthalmol. Vis. Sci. 2018;59(9):4713.
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© ARVO (1962-2015); The Authors (2016-present)
The trabecular meshwork (TM) regulates aqueous humor outflow and intraocular pressure (IOP). Recently, we identified TGFβ2 and toll-like receptor 4 (TLR4) signaling crosstalk as a novel pathway involved in extracellular (ECM) regulation in the TM and ocular hypertension in mice. Here, we investigated TLR4 expression in normal and glaucomatous human TM and optic nerve head (ONH) sections, and set-up a human perfusion organ culture model to determine TGFβ2-TLR4 signaling crosstalk in human ocular hypertension and glaucoma.
Expression of TLR4 was determined by immunohistochemical analysis of TM in normal and glaucomatous human eyes (n=10/condition). Normal and glaucomatous ONH sections were analyzed for TLR4 and GFAP expression (n=4/condition). To study human ocular hypertension, anterior segments of paired human eyes were perfused at a constant flow (2.5uL/minute) for 4 days to acquire stable baseline IOPs. Elevated IOP was induced by constant perfusion of anterior segments (n=4 pairs) with TGFβ2 (5 ng/mL) in one eye and vehicle control in the paired eye for 4 days. In a duplicate set of experiments, after stable baseline IOP we treated one eye with TLR4 inhibitor TAK-242 (15 μM) and vehicle control in the paired eye (n=4 pairs, 4 days). Perfusate and TM tissue from each eye were collected and analyzed for FN and COL1 expression by western immunoblot analysis.
We observed increased expression of TLR4 in both the glaucomatous human TM and the glaucomatous human ONH compared to normal. Immunohistochemical staining for TLR4 was ranked none, mild, moderate, or high, in a masked manner. TGFβ2 increased IOP in human perfusion organ cultures >11 mmHg above baseline from days 1-4 post-treatment. TLR4 inhibitor TAK-242 had no significant effect on IOP alone. TGFβ2 increased FN and COL1 as evident by western blot analysis of TM and perfusate from perfusion experiments.
These studies identify TGFβ2 – TLR4 crosstalk as a novel pathway involved in ECM regulation in the TM and ocular hypertension. Future studies will determine the effect of TLR4 inhibition on TGFβ2 induced ocular hypertension in this model system. These data provide potential new targets to lower IOP and to further explore the molecular mechanisms involved in the development of glaucomatous TM damage.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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