Basal metallothionein-I/II protects against NMDA-mediated oxidative injury in cortical neuron/astrocyte cultures

Abstract

N-methyl- d-aspartate (NMDA) receptor overactivation-mediated oxidative stress has been proposed to contribute to brain injury. Metallothionein-I/II (MT-I/II), a member of cysteine-rich metalloproteins, has been found to express in the central nervous system primarily in cortical tissues and be upregulated following brain injury. To address the role of MT-I/II on NMDA-mediated oxidative injury, we established primary cortical neuron/astrocyte cultures from neonatal MT-I/II deficient (MT −/−) and wild type (MT +/+) mice to test whether basal MT-I/II protects cortical cultures against NMDA-mediated injury. We found that MT-I/II expression was increased by NMDA in MT +/+ cultures but was not detectable in MT −/− cultures. NMDA concentration-dependently induced oxidative injury in both MT +/+ and MT −/− cultures as evidenced by decrease of cell viability, increases of lipid peroxidation and DNA damage. However, these toxic effects were greater in MT −/− than MT +/+ cultures. NMDA significantly increased reactive oxygen species (ROS) generation and disrupted mitochondrial membrane potential in neurons in MT +/+ cultures, and these effects were exaggerated in MT −/− cultures. Our findings clearly show that basal MT-I/II provides protection against NMDA-mediated oxidative injury in cortical neuron/astrocyte cultures, and suggest that the protective effects are possibly associated with inhibition of ROS generation and preservation of mitochondrial membrane potential.