Interleukin-1β enhances nucleotide-induced and α-secretase- dependent amyloid precursor protein processing in rat primary cortical neurons via up-regulation of the P2Y₂ receptor

The heterologous expression and activation of the human P2Y₂ nucleotide receptor (P2Y₂R) in human 1321N1 astrocytoma cells stimulates α-secretase-dependent cleavage of the amyloid precursor protein (APP), causing extracellular release of the non-amyloidogenic protein secreted amyloid precursor protein (sAPPα). To determine whether a similar response occurs in a neuronal cell, we analyzed whether P2Y₂R-mediated production of sAPPα occurs in rat primary cortical neurons (rPCNs). In rPCNs, P2Y₂R mRNA and receptor activity were virtually absent in quiescent cells, whereas overnight treatment with the pro-inflammatory cytokine interleukin-1β (IL-1β) up-regulated both P2Y₂R mRNA expression and receptor activity by four-fold. The up-regulation of the P2Y ₂R was abrogated by pre-incubation with Bay 11-7085, an IκB-α phosphorylation inhibitor, which suggests that P2Y ₂R mRNA transcript levels are regulated through nuclear factor-κ-B (NFκB) signaling. Furthermore, the P2Y₂R agonist Uridine-5′-triphosphate (UTP) enhanced the release of sAPPα in rPCNs treated with IL-1β or transfected with P2Y₂R cDNA. UTP-induced release of sAPPα from rPCNs was completely inhibited by pre-treatment of the cells with the metalloproteinase inhibitor TACE inhibitor (TAPI-2) or the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002, and was partially inhibited by the MAPK/extracellular signal-regulated kinase inhibitor U0126 and the protein kinase C inhibitor GF109203. These data suggest that P2Y₂R-mediated release of sAPPα from cortical neurons is directly dependent on a disintegrin and metalloproteinase (ADAM) 10/17 and PI3K activity, whereas extracellular signal-regulated kinase 1/2 and PI3K activity may indirectly regulate APP processing. These results demonstrate that elevated levels of pro-inflammatory cytokines associated with neurodegenerative diseases, such as IL-1β, can enhance non-amyloidogenic APP processing through up-regulation of the P2Y₂R in neurons.