Macrophage Inflammatory Protein 2 Inhibits β-Amyloid Peptide (1-42)-Mediated Hippocampal Neuronal Apoptosis through Activation of Mitogen-Activated Protein Kinase and Phosphatidylinositol 3-Kinase Signaling Pathways

Abstract

beta-Amyloid peptide accumulation in senile plaques in the brains of patients with Alzheimer's disease has been considered as a major cause of neuronal death. The present study demonstrated that the CXCR2 ligands macrophage inflammatory protein 2 (MIP-2), CXCL1, and CXCL8, protected hippocampal neurons against beta-amyloid (1-42) induced death. MIP-2-activated extracellular signal-regulated kinase (ERK)1/2 and Akt and both the mitogen-activated protein kinase kinase 1 (MEK1) and phosphatidylinositol 3-kinase (PI3K) inhibitors 2'-amino-3'-methoxyflavone (PD98059) and wortmannin reduced the neuroprotective effect of MIP-2. MIP-2 induced weak phosphorylation of ribosomal S6 kinase (RSK) 1 but remarkable phosphorylation and nuclear translocation of RSK2. MIP-2-induced phosphorylation of RSK2 was inhibited by PD98059 but not by wortmannin. MIP-2 treatment of the neuronal cells resulted in phosphorylation of Bad at both the Ser-112 and Ser-136. The phosphorylation at Ser-112 was blocked by PD98059, whereas the phosphorylation at Ser-136 was blocked by wortmannin. The transcription factor cyclic AMP response element binding protein (CREB) was phosphorylated by MIP-2 stimulation of the neuronal cells. MIP-2-induced CREB phosphorylation was reduced by both PD98059 and wortmannin. These data demonstrate that both MEK1-ERK1/2 and PI3K-Akt signaling pathways are involved in CXCR2-mediated neuroprotection and that multiple downstream signaling events, including RSKs, Bad, and CREB, are activated in this process.