Co-induction of p75NTR and p75NTR-associated death executor in neurons after zinc exposure in cortical culture or transient ischemia in the rat

Abstract

Recently, a 22 kDa protein termed p75NTR-associated death executor (NADE) was discovered to be a necessary factor for p75NTR-mediated apoptosis in certain cells. However, the possible role for p75NTR/NADE in pathological neuronal death has yet been undetermined. In the present study, we have examined this possibility in vivo and in vitro. Exposure of cortical cultures to zinc induced both p75NTR and NADE in neurons, whereas exposure to NMDA, ionomycin, iron, or H2O2 induced neither. In addition, zinc exposure increased neuronal NGF expression and its release into the medium. A function-blocking antibody of p75NTR (REX) inhibited association between p75NTR and NADE as well as neuronal death induced by zinc. Conversely, NGF augmented zinc-induced neuronal death. Caspase inhibitors reduced zinc-induced neuronal death, indicating that caspases were involved. Because reduction of NADE expression with cycloheximide or NADE antisense oligonucleotides attenuated zinc-induced neuronal death, NADE appears to contribute to p75NTR-induced cortical neuronal death as shown in other cells. Because zinc neurotoxicity may be a key mechanism of neuronal death after transient forebrain ischemia, we next examined this model. After ischemia, p75NTR and NADE were induced in degenerating rat hippocampal CA1 neurons. There was a close correlation between zinc accumulation and p75NTR/NADE induction. Suggesting the role of zinc here, injection of a metal chelator, CaEDTA, into the lateral ventricle completely blocked the induction of p75NTR and NADE. Our results suggest that coinduction of p75NTR and NADE plays a role in zinc-triggered neuronal death in vitro and in vivo.