REDD1-dependent GSK3β dephosphorylation promotes NF-KB activation and macrophage infiltration in the retina of diabetic mice

Increasing evidence supports a role for inflammation in the early development and progression of retinal complications caused by diabetes. We recently demonstrated that the stress response protein regulated in development and DNA damage response 1 (REDD1) promotes diabetes -induced retinal inflammation by sustaining canonical activation of nuclear transcription factor, NF -KB. The studies here were designed to identify signaling events whereby REDD1 promotes NF -KB activation in the retina of diabetic mice. We observed increased REDD1 expression in the retina of mice after 16 weeks of streptozotocin (STZ)-induced diabetes and found that REDD1 was essential for diabetes to suppress inhibitory phosphorylation of glycogen synthase kinase 3P (GSK3P) at S9. In human retinal MIO-M1 Muller cell cultures, REDD1 deletion prevented dephosphorylation of GSK3P and increased NF -KB activation in response to hyperglycemic conditions. Expression of a constitutively active GSK3P variant restored NF -KB activation in cells deficient for REDD1. In cells exposed to hyperglycemic conditions, GSK3P knockdown inhibited NF -KB activation and proinflammatory cytokine expression by preventing inhibitor of KB kinase complex autophosphorylation and inhibitor of KB degradation. In both the retina of STZdiabetic mice and in Muller cells exposed to hyperglycemic conditions, GSK3 inhibition reduced NF -KB activity and prevented an increase in proinflammatory cytokine expression. In contrast with STZ-diabetic mice receiving a vehicle control, macrophage infiltration was not observed in the retina of STZdiabetic mice treated with GSK3 inhibitor. Collectively, the findings support a model wherein diabetes enhances REDD1dependent activation of GSK3P to promote canonical NF -KB signaling and the development of retinal inflammation.