Zinc pre-treatment enhances NMDAR-mediated excitotoxicity in cultured cortical neurons from SOD1G93A mouse, a model of amyotrophic lateral sclerosis

Zn2+ is co-released at glutamatergic synapses throughout the central nervous system and acts as a neuromodulator for glutamatergic neurotransmission, as a key modulator of NMDA receptor functioning. Zn2+ is also implicated in the neurotoxicity associated with several models of acute brain injury and neurodegeneration. Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease affecting motor neurons in the spinal cord and cortex. In this study, we have investigated the modulatory role exerted by Zn2+ in NMDA-mediated neurotoxicity in either near-pure or mixed cortical cultured neurons obtained from either mice over-expressing the G93A mutant form of Cu/Zn superoxide dismutase (SOD1) human gene, a gene linked to familial ALS, or wild type (WT) mice. To that aim, SOD1G93A or WT cultures were exposed to either NMDA by itself or to Zn2+ prior to a toxic challenge with NMDA, and neuronal loss evaluated 24 h later. While we failed to observe any significant difference between NMDA and Zn2+/NMDA-mediated toxicity in mixed SOD1G93A or WT cortical cultures, different vulnerability to these toxic paradigms was found in near-pure neuronal cultures. In the WT near-pure neuronal cultures, a brief exposure to sublethal concentrations of Zn2+-enhanced NMDA receptor-mediated cell death, an effect that was far more pronounced in the SOD1G93A cultures. This increased excitotoxicity in SOD1G93A near-pure neuronal cultures appears to be mediated by a significant increase in NMDA-dependent rises of intraneuronal Ca2+ levels as well as enhanced production of cytosolic reactive oxygen species, while the injurious process seems to be unrelated to activation of nNOS or ERK1/2 pathways.This article is part of a Special Issue entitled ‘Trends in Neuropharmacology: In Memory of Erminio Costa’.

► Zinc pre-treatment enhances NMDA-mediated toxicity in SOD1G93A mutant cortical cultures.
► The enhanced toxicity is independent from nNOS and ERK1/2 phosphorylation.
► The downstream mechanisms are linked to intraneuronal Ca2+ rises as well as enhanced generation of reactive oxygen species.