DHA Inhibited AGEs-Induced Retinal Microglia Activation Via Suppression of the PPARγ/NFκB Pathway and Reduction of Signal Transducers in the AGEs/RAGE Axis Recruitment into Lipid Rafts

Recent studies revealed that dietary intake of docosahexaenoic acid (DHA) prevented diabetic retinopathy (DR), but the underlying mechanism was not fully understood. Retinal microglia are a specialized population of macrophages in retina. Considerable evidence has shown that microglia activation may trigger neuronal death and vascular dysfunction in DR. The aim of this study was to investigate the effects of DHA on advanced glycation end products (AGEs)-induced microglia activation using an in vitro microglia culture system, and concurrently to explore the mediating mechanisms. DHA inhibited AGEs-induced microglia activation and tumor necrosis factor alpha (TNF alpha) secretion. These effects of DHA were directly linked with suppression of nuclear factor-kappa B (NF kappa B) activity, as evident by the reduction of p-I kappa B alpha expression, p-NF kappa B p65 nucleus translocation, NF kappa B DNA binding activity, and the regulation of gene transcription (TNF alpha, IL-1 beta, ICAM-1, and RAGE mRNA). Furthermore, DHA significantly increased phosphorylation of peroxisome proliferator-activated receptor-gamma (PPAR gamma), and combined with PPAR gamma stealth RNAi oligonucleotide, we confirmed that DHA inhibition of AGEs-induced microglia activation was partially through the PPAR gamma/NF kappa B pathway. Moreover, although AGEs incubation dramatically elevated expression of the cell surface receptor for AGEs (RAGE), DHA significantly inhibited RAGE and Src recruitment into lipid rafts. The AGEs-RAGE axis downstream signal transducers increased mitogen-activated protein kinase (p38 and JNK) phosphorylation. Taken together, DHA might inhibit AGEs-induced microglia activation via suppression of the PPAR gamma/NF kappa B pathway, and reduction of RAGE and AGEs/RAGE transducer recruitment into lipid rafts. These results provide a novel potential mechanism for the anti-inflammatory effects of DHA in DR prevention.