Cyclic AMP inhibition of tumor necrosis factor α production induced by amyloidogenic C-terminal peptide of Alzheimer's amyloid precursor protein in macrophages: Involvement of multiple intracellular pathways and cyclic AMP response element binding protein

Abstract

In the present study, we focused on the molecular events involved in tumor necrosis factor-α (TNF-α) production in response to the amyloidogenic 105-amino acid carboxyl-terminal fragment (CT105) of amyloid precursor protein, a candidate alternative toxic element in Alzheimer's disease pathology, and the mechanisms by which cyclic AMP regulates the relating inflammatory signal cascades. CT105 at nanomolar concentrations strongly activated multiple signaling pathways involving tyrosine kinase-dependent extracellular signal-regulated kinase and p38 mitogen-activated protein kinases. Moreover, phosphatidylinositol 3-kinase/Akt signal was required for excess TNF-α production in human macrophages derived from THP-1 cells. Interferon-γ significantly potentiated the induction of the CT105-mediated signal cascade. These multiple signaling pathways in turn converged, at least in part, at the nuclear transcription factor known as cAMP response element binding protein (CREB), which acts on the TNF-α gene promoter through the cAMP response element. The cell-permeable cAMP analog dibutyryl cAMP partially and almost simultaneously suppressed all of these CT105-induced signaling pathways through excessive CREB phosphorylation, which led to decreased CREB DNA binding activity and reduced TNF-α expression. Furthermore, dibutyryl cAMP decreased the interaction of the p65 nuclear factor-KB with CREB binding protein, thus further inhibiting CT105-mediated TNF-α expression. Collectively, the detailed molecular mechanisms of amyloidogenic CT-induced TNF-α production as negatively regulated by cAMP may advance the possibility of targeted treatment in Alzheimer's disease.