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Diabetic nephropathy (DN) is the leading cause of end-stage renal disease and effective treatment modalities that fully address its molecular etiology are lacking. Prior studies support that the stress response protein REDD1 (Regulated in Development and DNA Damage 1) contributes to the development of diabetic complications. This study investigated a potential role for REDD1 expression in podocytes in diabetes-induced podocyte loss and compromised glomerular filtration. Podocyte-specific REDD1 deletion protected against renal injury, as evidenced by reduced albuminuria, glomerular hypertrophy, and mesangial matrix deposition in streptozotocin (STZ)-induced diabetic mice. Podocyte-specific REDD1 expression was required for diabetes-induced reduction in slit diaphragm (SD) proteins podocin and nephrin. Notably, podocyte-specific REDD1 deletion protected against podocytopenia and preserved glomerular basement membrane and foot process architecture in diabetic mice. In the kidneys of diabetic mice and in human podocyte cultures exposed to hyperglycemic conditions, REDD1 was necessary for increased expression of the transient receptor potential canonical 6 (TRPC6) channel. More specifically, REDD1 promoted NF-κB-dependent transcription of TRPC6, intracellular calcium entry, and cytoskeletal remodeling under hyperglycemic conditions. Overall, the findings provide new insight into the role of podocyte-specific REDD1 expression in renal pathology and support the possibility that therapeutics targeting REDD1 in podocytes could be beneficial for DN., (© 2024 by the American Diabetes Association.)

The stress response protein regulated in development and DNA damage response 1 (REDD1) has been implicated in visual deficits in patients with diabetes. The aim here was to investigate the mechanism responsible for the increase in retinal REDD1 protein content that is observed with diabetes. We found that REDD1 protein expression was increased in the retina of streptozotocin-induced diabetic mice in the absence of a change in REDD1 mRNA abundance or ribosome association. Oral antioxidant supplementation reduced retinal oxidative stress and suppressed REDD1 protein expression in the retina of diabetic mice. In human retinal Müller cell cultures, hyperglycemic conditions increased oxidative stress, enhanced REDD1 expression, and inhibited REDD1 degradation independently of the proteasome. Hyperglycemic conditions promoted a redox-sensitive cross-strand disulfide bond in REDD1 at C150/C157 that was required for reduced REDD1 degradation. Discrete molecular dynamics simulations of REDD1 structure revealed allosteric regulation of a degron upon formation of the disulfide bond that disrupted lysosomal proteolysis of REDD1. REDD1 acetylation at K129 was required for REDD1 recognition by the cytosolic chaperone HSC70 and degradation by chaperone-mediated autophagy. Disruption of REDD1 allostery upon C150/C157 disulfide bond formation prevented the suppressive effect of hyperglycemic conditions on REDD1 degradation and reduced oxidative stress in cells exposed to hyperglycemic conditions. The results reveal redox regulation of REDD1 and demonstrate the role of a REDD1 disulfide switch in development of oxidative stress., (© 2022 by the American Diabetes Association.)

Chronic hyperglycemia contributes to development of diabetic kidney disease by promoting glomerular injury. In this study, we evaluated the hypothesis that hyperglycemic conditions promote expression of the stress response protein regulated in development and DNA damage response 1 (REDD1) in the kidney in a manner that contributes to the development of oxidative stress and renal injury. After 16 weeks of streptozotocin-induced diabetes, albuminuria and renal hypertrophy were observed in wild-type (WT) mice coincident with increased renal REDD1 expression. In contrast, diabetic REDD1 knockout (KO) mice did not exhibit impaired renal physiology. Histopathologic examination revealed that glomerular damage including mesangial expansion, matrix deposition, and podocytopenia in the kidneys of diabetic WT mice was reduced or absent in diabetic REDD1 KO mice. In cultured human podocytes, exposure to hyperglycemic conditions enhanced REDD1 expression, increased reactive oxygen species (ROS) levels, and promoted cell death. In both the kidney of diabetic mice and in podocyte cultures exposed to hyperglycemic conditions, REDD1 deletion reduced ROS and prevented podocyte loss. Benefits of REDD1 deletion were recapitulated by pharmacological GSK3β suppression, supporting a role for REDD1-dependent GSK3β activation in diabetes-induced oxidative stress and renal defects. The results support a role for REDD1 in diabetes-induced renal complications., (© 2022 by the American Diabetes Association.)

Clinical studies support a role for the protein regulated in development and DNA damage response 1 (REDD1) in ischemic retinal complications. To better understand how REDD1 contributes to retinal pathology, we examined human single-cell sequencing data sets and found specificity of REDD1 expression that was consistent with markers of retinal Müller glia. Thus, we investigated the hypothesis that REDD1 expression specifically in Müller glia contributes to diabetes-induced retinal pathology. The retina of Müller glia-specific REDD1 knockout (REDD1-mgKO) mice exhibited dramatic attenuation of REDD1 transcript and protein expression. In the retina of streptozotocin-induced diabetic control mice, REDD1 protein expression was enhanced coincident with an increase in oxidative stress. In the retina of diabetic REDD1-mgKO mice, there was no increase in REDD1 protein expression, and oxidative stress was reduced compared with diabetic control mice. In both Müller glia within the retina of diabetic mice and human Müller cell cultures exposed to hyperglycemic conditions, REDD1 was necessary for increased expression of the gliosis marker glial fibrillary acidic protein. The effect of REDD1 deletion in preventing gliosis was associated with suppression of oxidative stress and required the antioxidant transcription factor nuclear factor erythroid-2-related factor 2 (Nrf2). In contrast to diabetic control mice, diabetic REDD1-mgKO mice did not exhibit retinal thinning, increased markers of neurodegeneration within the retinal ganglion cell layer, or deficits in visual function. Overall, the findings support a key role for Müller glial REDD1 in the failed adaptive response of the retina to diabetes that includes gliosis, neurodegeneration, and impaired vision., (© 2022 by the American Diabetes Association.)