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William Phillip Miller, Allyson Lee Toro, Alistair J Barber, Michael D. Dennis; Keap1-independent suppression of the Nrf2 antioxidant response in the retina of diabetic mice. Invest. Ophthalmol. Vis. Sci. 2020;61(7):745.
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Oxidative stress is a crucial factor implicated in the development and progression of diabetic retinopathy (DR). The transcription factor nuclear factor erythroid-2-related factor 2 (Nrf2) promotes the expression of an array of antioxidant gene products in response to oxidative stress. However, evidence from both postmortem retinas and preclinical diabetes models supports that there is a failure to properly upregulate Nrf2 activity to sufficiently prevent oxidative stress in DR. The hypothesis here is that diabetes-induced expression of the stress response protein REDD1 inhibits proper upregulation of Nrf2 activity.
Wild-type and REDD1-deficient mice were administered streptozotocin to induce diabetes. Western blotting and qPCR were used to analyze retinal homogenates. Similar analyses were performed on lysates from human MIO-M1 retinal Müller and HEK293 cell cultures. Nrf2 variants were generated by site-directed mutagenesis.
Diabetes increased oxidative stress, suppressed Nrf2 activity, and enhanced REDD1 expression in the retina. In the retina of REDD1-deficient mice, Nrf2-activity was increased and oxidative stress associated with diabetes was attenuated as compared to wild-type mice. In human Müller MIO-M1 retinal cells in culture, REDD1 deletion by CRISPR enhanced Nrf2 protein expression, nuclear localization, and Nrf2 activity. REDD1 decreased the stability of Nrf2, and proteasome inhbition was sufficient to prevent the effect. Remarkably, we found that the suppressive effect of REDD1 on Nrf2 stability was independent of Keap1, which is typically thought of as mediating Nrf2 degradation by the proteasome.
Overall, the findings provide new insight into the molecular basis for the insufficient antioxidant response in DR. The results suggest that an alternative strategy to the current Nrf2 activators that prevent Keap1-dependent degradation may be beneficial in preventing diabetes-induced oxidative damage.
This is a 2020 ARVO Annual Meeting abstract.
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