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 proinflammatory 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 proinflammatory 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 (Pl₃K) 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.