500-P: Disruption of REDD1 Protein Allostery as a Therapeutic for Diabetic Retinopathy

Introduction & Objective: Increased abundance of the protein Regulated in Development and DNA damage 1 (REDD1, also known as RTP801/DDIT4) in cells of the retina is required for retinal pathology and visual function deficits in diabetic mice. Indeed, an RNA-based therapeutic designed to reduce REDD1 modestly improved visual acuity in patients with diabetic macular edema. Studies here investigated the cause of REDD1 upregulation in the context of diabetes.

Methods: Mice were administered low dose streptozotocin (STZ) to model diabetes and treated with either the SGLT-2 inhibitor dapagliflozin or the antioxidant N-acetyl cysteine. Complementary studies were performed in human MIO-M1 cells exposed to hyperglycemic conditions. Discrete molecular dynamics (DMD) and an artificial intelligence (AI) neural network were used to examine REDD1 structure and ligand binding.

Results: Hyperglycemia and an increase in reactive oxygen species were required for increased REDD1 protein abundance in the retina of diabetic mice, which was observed without a change in REDD1 mRNA expression. Hyperglycemic conditions promoted formation of a cross-strand disulfide bond in REDD1 at C150/C157 that suppressed its normally rapid degradation. DMD revealed allosteric regulation of residues upon formation of the redox-sensitive disulfide bridge that controlled REDD1 proteolysis. Genetic disruption of REDD1 allostery prevented the suppressive effect of disulfide bond formation on REDD1 degradation. Ligands with high bioavailability and cell permeability that bind REDD1 at the site of allosteric regulation were identified.

Conclusions: The results reveal a new molecular switch in the REDD1 protein that is activated by diabetes and suggest that the prior clinical trials designed to reduce REDD1 synthesis were undermined by diabetes-induced blockade of REDD1 degradation. Genetic or small molecule inhibition of REDD1 protein allostery may represent a new clinically translatable therapeutic intervention.