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Denise M Inman, Lucy Coughlin; The role of Nrf2 transcription factor in ganglion cell survival in glaucoma. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2424.
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© ARVO (1962-2015); The Authors (2016-present)
Oxidative stress contributes to neurodegeneration in glaucoma, as determined by the accumulation of lipids, proteins and nucleic acid altered by reactive oxygen species in the retina. The Nrf2-antioxidant response element (ARE) system is a key regulator of antioxidant levels; therefore, its control is crucial to eliminating glaucoma-associated oxidative stress. We sought to determine the degree to which the Nrf2-ARE contributes to RGC survival by subjecting wildtype and Nrf2-knockout (Nrf2-/-) mice to acute glaucoma injury.
Baseline, post-injection and weekly intraocular pressure (IOP) was measured in wildtype and Nrf2-/- mice using the TonoLab rebound tonometer. Mice were subjected to a 1µL injection of 10µm polystyrene beads into the anterior chamber to induce glaucoma through blockage of aqueous humor outflow. Twice weekly, mouse visual acuity was determined using the OptoMotry system that tracks optokinetic response. At 3 weeks post-injection, mice received an injection of FluoroGold in each lobe of the superior colliculus to retrogradely label retinal ganglion cells. Mice were sacrificed at 4 weeks and tissue processed for protein, RNA, or to determine the number of surviving retinal ganglion cells in wholemount retina. Laser capture microdissection then quantitative PCR (qPCR) of ganglion cell layer and inner nuclear layer was undertaken to monitor genes involved in antioxidant response.
Wildtype and Nrf2-/- mice, when subjected to the bead occlusion model, had similar IOP increase. Despite equivalent IOP increase, Nrf2-/- retina underwent a 36 percent decrease in RGC survival compared to wildtype. Visual acuity in the Nrf2-/- at baseline was 0.4 cycles/degree, but fell to 0.26 cycles/degree one day post-surgery and never recovered. Glutathione levels in Nrf2-/- mice were significantly lower than wildtype. Quantitative PCR analysis showed decreased expression of glutathione peroxidase-4 and peroxiredoxin-2 in Nrf2-/- ganglion cell layer compared to wildtype. There were also signs of increased glial activation in Nrf2-/- retina.
Compromised antioxidant response is detrimental to ganglion cell survival in glaucoma. The magnitude of ganglion cell loss in Nrf2-/- versus control suggests that antioxidant mechanisms play a role in glaucoma pathogenesis, and improving antioxidant response may prove protective.
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