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Hongman Song, Ronald A Bush, Yong Zeng, Camasamudram Vijayasarathy, Dario Marangoni, Paul A Sieving; Constitutively Active RAC1 Causes Photoreceptor Degeneration through NADPH Oxidase-Mediated Oxidative Stress. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5451.
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Conditional knockout of RAC1, a component of NADPH oxidase (Nox), in mouse retina reduces its susceptibility to light-induced degeneration. One effect of expression of constitutively active (CA) RAC1 in rod photoreceptors of transgenic (Tg) CA RAC1 mice is extensive photoreceptor cell death in adult animals. The current study tests whether Nox-induced oxidative stress contributes to this degeneration.
The retinas of Tg CA RAC1 and wild-type (WT) control mice were examined by H and E staining and TUNEL assay at three different ages to evaluate photoreceptor cell loss and apoptosis. Another group of Tg CA RAC1 mice were given daily intraperitonal (IP) injection of a Nox inhibitor, apocynin (10 mg/kg), or control vehicle for up to 12 weeks. ONL cell counts and retinal function (ERG) of apocynin and vehicle injected Tg CA RAC1 mice were compared at the end of the dosing period. Superoxide production and oxidative damage were assessed with hydroethidine (oxidative fluorescence dye for superoxide detection) and ELISA (for measurement of protein carbonyl content), respectively.
The Tg CA RAC1 retinas had significantly fewer photoreceptor cells compared with WT littermates from postnatal week 3 (Pw3) to week 12 (Pw12) and had a greater number of apoptotic cells in the ONL at all three ages examined than WT control retinas, which had nearly no TUNEL-positive cells in any layers. Tg CA RAC1 retinas had an increase in accumulation of superoxide radicals and protein carbonyl content, indicating increased oxidative stress. Preliminary data indicate that apocynin-treated Tg CA RAC1 mice had significantly more photoreceptor cells, larger rod a- and b-wave amplitudes, and reduced accumulation of superoxide radicals and oxidative damage in the retina.
CA RAC1 promoted rod photoreceptor degeneration and oxidative damage. Apocynin, an inhibitor of Nox, protected rods from degeneration and reduced oxidative damage. This indicates that photoreceptor degeneration in Tg CA RAC1 retinas occurs, at least partially, through Nox-induced oxidative stress. Combined with our previous study showing that RAC1 depletion protects photoreceptors from photo-oxidative stress, these results support the investigation of RAC1 as a potential therapeutic target in retinal neurodegeneration caused by oxidative damage.
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