Abstract
Purpose :
Clinical studies support a role for the stress response protein regulated in DNA damage 1 (REDD1) in diabetes-induced visual dysfunction. REDD1 was recently shown to directly promote inflammatory signaling in myeloid cells. Retinal inflammation is a significant contributor to the development and progression of diabetic retinopathy (DR). Thus, we investigated the role of REDD1 in development of retinal inflammation in diabetes.
Methods :
REDD1+/+ and REDD1-/- mice were administered streptozotocin to induce diabetes. Retinas were isolated after 16 weeks of diabetes and analyzed for protein and RNA expression by western blot and qPCR, respectively. Macrophages were visualized in retinal sections by immunofluorescence. Activity of the transcription factor nuclear factor-kappa B (NF-κB) was measured by luciferase assay. Similar analyses were performed on wild-type and REDD1 knockout human MIO-M1 retinal cell cultures after exposure to hyperglycemic conditions, inflammatory cytokines, or genetic REDD1 induction.
Results :
Enhanced REDD1 expression was observed in the retina of diabetic REDD1+/+ mice in association with increased pro-inflammatory gene expression and macrophage infiltration of the inner retina. Compared to diabetic REDD1+/+ mice, inflammatory markers and macrophage infiltration were attenuated in the retina of diabetic REDD1-/- mice. In retinal cell cultures, REDD1 deletion prevented hyperglycemia- and TNFα-induced pro-inflammatory gene expression. REDD1 was not sufficient to promote inflammation, but rather sustained activation of NF-κB in cells exposed to either hyperglycemic conditions or TNFα. In REDD1-deficient cells, GSK3β phosphorylation and Nrf2 activation was observed in association with NF-κB suppression. Consistent with prior studies, REDD1 deletion prevented the development of oxidative stress in cells exposed to hyperglycemic conditions, and Nrf2 knockdown prevented the effect. However, Nrf2 knockdown was not sufficient to restore NF-κB signaling in REDD1-deficient cells exposed to hyperglycemic conditions. In contrast, inhibition of GSK3β suppressed NF-κB activation in cells exposed to hyperglycemic conditions.
Conclusions :
The findings provide new insight into how diabetes promotes retinal inflammation and support that REDD1 acts independently of Nrf2 to suppress inflammatory signaling via GSK3β-dependent activation of NF-κB.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.