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Vidhya R Rao, Alexandra D. Hegel, Jamie C. Floss, Jonathan Lautz, Vicki Husak, Evan B Stubbs, Simon Kaja; Elevated hydrostatic pressure increases the sensitivity of optic nerve head astrocytes to an oxidative challenge. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4605.
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© ARVO (1962-2015); The Authors (2016-present)
Primary open angle glaucoma (POAG) is often associated with elevated intraocular pressure (IOP), manifesting in a pathological triad of optic nerve head remodeling, damage to the optic nerve, and retinal ganglion cell loss. Optic nerve head astrocytes (ONHAs), the primary cell type in the optic nerve head, undergo significant pathological changes in POAG. Increased levels of oxidative stress, secondary to elevated IOP, are strongly implicated in the pathophysiology of POAG. Here, the cellular and molecular consequence of elevated hydrostatic pressure on cultured ONHAs responses to an oxidative challenge was investigated.
Primary adult rat ONHAs were exposed to ambient or elevated hydrostatic pressure (25-30mm Hg above ambient pressure) for 16h using a custom-built cell culture pressure chamber. Cells were subsequently challenged with chemically-induced oxidative stress using tert-butylhydroperoxide (tBHP; 0-500 µM for 5h). In some cases, ONHA cultures were pre-treated with the antioxidant Trolox (100 µM). Cell viability was measured using plate reader-based MTT or lactate dehydrogenase (LDH) release assays; levels of oxidative stress were quantified using the fluorescent indicator, CellROX®.
ONHA cultures exposed to elevated hydrostatic pressure exhibited a marked increase in the level of reactive oxygen species as quantified by CellROX® fluorescent staining, but did not significantly alter cell viability (n=3, p=0.65). Compared to ambient control cultures, ONHA cultures exposed to elevated hydrostatic pressure exhibited a significant increase in sensitivity to a subsequent oxidative challenge [LD50 for tBHP were 179 ± 2 µM (ambient) vs. 84 ± 1 µM (elevated pressure); n=3; P<0.01 in the MTT assay and 145 ± 5 (ambient) vs. 67 ± 6 µM (elevated pressure); n=3; P<0.01 in the LDH assay]. By comparison, Trolox shifted the LD50 to a similar extent under both ambient (D = 50 ± 2 µM; n=3, P<0.01) and hydrostatic pressure (D = 48 ± 2 µM; n=3, P<0.01).
Short-term exposure to elevated hydrostatic pressure increases the levels of ROS in cultured ONHAs without affecting cell viability, but causing a significant increase in the sensitivity of ONHAs toward a subsequent oxidative challenge. These data suggest that even modest exposure to elevated IOP in POAG may significantly alter the oxidation response of ONHAs.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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