Upregulation of the stress response protein REDD1 (regulated in development and DNA damage response 1) has been implicated in diabetes-induced retinal defects in both preclinical models and diabetic patients. In fact, intravitreal administration of a siRNA targeting the REDD1 mRNA has demonstrated promise for improving visual function in patients with diabetic macular edema. However, the mechanism responsible for increased retinal REDD1 protein content in the context of diabetes has never been established. Herein, we investigated the hypothesis that diabetes promotes REDD1 expression by reducing the rate of REDD1 degradation. In the retina of streptozotocin-induced diabetic mice, REDD1 protein content was increased in the absence of a change in REDD1 mRNA. When diabetic mice were administered antioxidants, neither oxidative stress nor REDD1 expression were increased in the retina. In human MIO-M1 retinal Müller cells, the rate of REDD1 degradation was reduced upon exposure to hyperglycemic conditions. Antioxidant addition to culture medium prevented both the increase in oxidative stress and REDD1 stability in cells exposed to hyperglycemic conditions. Surprisingly, the suppressive effect of oxidative stress on REDD1 degradation was independent of the ubiquitin-proteasome pathway. Rather, REDD1 was rapidly degraded upon activation of chaperone-mediated autophagy (CMA) and exposure to hyperglycemic conditions prevented the suppressive effect of CMA activation on REDD1 expression. Additional mechanistic details of this new regulatory pathway will be presented. Overall, the findings provide evidence that diabetes promotes retinal REDD1 protein content via a post-transcriptional effect and potentially identifies superior therapeutic targets for preventing the pathological increase in REDD1.
W. P. Miller: None. A. Toro: None. S. Sunilkumar: None. J. Giordano: None. M. D. Dennis: None.
American Diabetes Association/Pathway to Stop Diabetes (1-14-INI-04 to M.D.D.); National Institutes of Health (R01EY029702 to M.D.D.), (F31EY031199-01 to W.P.M.)