Signal transduction pathways in mouse microglia N‐11 cells activated by advanced glycation endproducts (AGEs)

Deposition of cross‐linked insoluble protein aggregates such as amyloid plaques is characteristic for Alzheimer's disease. Microglial activation by these extracullar deposits has been proposed to play a crucial role in functional degeneration as well as cell death of neurones. A sugar‐derived post‐translational modification of long‐lived proteins, advanced glycation endproducts (AGEs), activate specific signal transduction pathways, resulting in the up‐regulation of various pro‐inflammatory signals such as cytokines [interleukin‐6 (IL‐6), tumour necrosis factor‐alpha (TNF‐α)] and inducible nitric oxide synthase (iNOS). Our goal was to study AGE‐activated signal transduction pathways involved in the induction of pro‐inflammatory effectors in the murine microglial cell line N‐11. Chicken egg albumin‐AGE (CEA‐AGE), used as model AGE, induces nitric oxide (NO), TNF‐α and IL‐6 production. The AGE receptor, RAGE, and the transcription factor, nuclear factor kappa B (NF‐κB), appear to be involved in all pathways, since a neutralizing RAGE antibody and a peptide inhibiting NF‐κB translocation down‐regulated NO, TNF‐α and IL‐6 production. NO and TNF‐α, but not IL‐6 production appear to be regulated independently, since NOS inhibitors did not decrease TNF‐α secretion and a neutralizing TNF‐α antibody did not reduce NO production, while employment of NOS inhibitors reduced significantly the secretion of IL‐6. Inhibition of the MAP‐kinase‐kinase (MEK) and phosphatidylinositol 3‐kinase (PI3K) pathway, but not that of mitogen‐activated protein kinase‐p38 (MAPK‐p38), reduced NO, TNF‐α and IL‐6 significantly, suggesting that simultaneous activation of the first two pathways is necessary for the AGE‐induced induction of these pro‐inflammatory stimuli.