ABSTRACT
Amyloid beta (Abeta) is a main component of senile plaques in Alzheimer's disease and induces neuronal cell death. Reactive oxygen species (ROS), nitric oxide and endoplasmic reticulum (ER) stress have been implicated in Abeta-induced neurotoxicity. We have reported that apoptosis signal-regulating kinase 1 (ASK1) is required for ROS- and ER stress-induced JNK activation and apoptosis. Here we show the involvement of ASK1 in Abeta-induced neuronal cell death. Abeta activated ASK1 mainly through production of ROS but not through ER stress in cultured neuronal cells. Importantly, ASK1-/- neurons were defective in Abeta-induced JNK activation and cell death. These results indicate that ROS-mediated ASK1 activation is a key mechanism for Abeta-induced neurotoxicity, which plays a central role in Alzheimer's disease.
Subject(s)
Amyloid beta-Peptides/pharmacology , MAP Kinase Kinase Kinase 5/metabolism , Neurons/drug effects , Reactive Oxygen Species/metabolism , Alzheimer Disease/etiology , Animals , Cell Death/drug effects , Endoplasmic Reticulum/enzymology , Endoplasmic Reticulum/metabolism , Enzyme Activation/drug effects , JNK Mitogen-Activated Protein Kinases/metabolism , MAP Kinase Kinase Kinase 5/genetics , Membrane Proteins/metabolism , Mice , Mice, Inbred C57BL , Mice, Knockout , Neurons/cytology , Neurons/metabolism , Nitrogen Oxides/metabolism , PC12 Cells , Peptide Fragments/pharmacology , Protein Serine-Threonine Kinases/metabolism , Rats , eIF-2 Kinase/metabolismABSTRACT
alphaB-Crystallin, a member of the small heat shock protein (HSP) family, accumulates in reactive astrocytes in a variety of pathological conditions. We previously reported the upregulation of alphaB-crystallin in response to high extracellular potassium concentration. In the present study, we investigated the regulatory mechanism of alphaB-crystallin expression by KCl. When human glioma U-251MG cells were exposed to continuous KCl treatment, induction of alphaB-crystallin mRNA was observed after 8 h and persisted for a few days. Functional promoter analysis using deletion and mutation constructs revealed that the proximal heat shock element (HSE-P), which contributes to heat shock induction in HeLa cells, is essential for transcriptional activation of the alphaB-crystallin gene by KCl in U-251MG cells. Gel mobility shift and antibody supershift assays showed that KCl induces the HSE-binding activity of heat shock factor (HSF) 2, while heat shock induces that of HSF1. This is the first demonstration that HSF2 can be activated by KCl and is involved in the upregulation of alphaB-crystallin gene expression in glial cells.
