REDD1 redox modification acts as a molecular sensor in retinal disease

Abstract

Purpose : We previously demonstrated that an increased abundance of the stress response protein Regulated in Development and DNA damage 1 (REDD1, also known as RTP801/DDIT4) in the retina contributes to the development of retinal pathology and impaired visual function in mice. Mechanistically, REDD1 promotes oxidative stress and chronic immune signaling. Studies here investigated the molecular mechanisms that cause REDD1 upregulation in the context of retinal disease.

Methods : Mice were administered either streptozotocin (STZ) to model diabetes or sodium iodate (NaIO₃) to model geographic atrophy by intraperitoneal injection. Complementary studies were performed in MIO-M1 or ARPE-19 cell cultures exposed to hyperglycemic conditions or oxidant stress. Mass spectroscopy was used to identify novel post-translational modifications. Discrete molecular dynamics (DMD) simulation was used to examine protein structure and an artificial intelligence (AI) neural network was used to evaluate protein-ligand binding.

Results : Following administration of STZ or NaIO_3, REDD1 protein abundance was increased in the retina without a change in REDD1 mRNA expression. In retinal cells in culture, the normally rapid degradation of REDD1 protein was blocked by an increase in reactive oxygen species (ROS). Exposure to oxidants resulted in formation of a cross-strand disulfide bridge in REDD1 at C150/C157 that suppressed proteasome-independent REDD1 degradation. DMD simulations of REDD1 with and without the disulfide revealed allosteric regulation of residues that controlled the lysosomal proteolysis of REDD1. Genetic disruption of REDD1 allostery prevented the suppressive effect of disulfide bond formation on REDD1 degradation and reduced signaling downstream of REDD1. Small molecule compounds with high bioavailability and cell permeability that bind REDD1 at the site of allosteric regulation were identified.

Conclusions : The results reveal a new molecular redox switch in the REDD1 protein that is activated in the context of retinal disease. Genetic or small molecule inhibition of REDD1 protein allostery may represent a new clinically translatable therapeutic intervention.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.