Pathophysiologically Relevant Levels of Hydrogen Peroxide Induce Glutamate-Independent Neurodegeneration That Involves Activation of Transient Receptor Potential Melastatin 7 Channels

Stroke/brain ischemia is a leading cause of death and long-term disabilities. Increased oxidative stress plays an important role in the pathology of brain ischemia. Hydrogen peroxide (H2O2) is a major oxidant known to cause neuronal injury; however, the detailed mechanism remains unclear. Previous studies have suggested that H2O2-induced injury is associated with increased intracellular Ca2+, mediated by glutamate receptors or voltage-gated Ca2+ channels. Here, we demonstrate that, at concentrations relevant to stroke, H2O2 induces a Ca2+-dependent injury of mouse cortical neurons in the absence of activation of these receptors/channels. With the culture medium containing blockers of glutamate receptors and voltage-gated Ca2+ channels, brief exposure of neurons to H2O2 induced a dose-dependent injury. Reducing [Ca2+](e) inhibited whereas increasing [Ca2+](e) potentiated the H2O2 injury. Fluorescent Ca2+ imaging confirmed the increase of [Ca2+](i) by H2O2 in the presence of the blockers of glutamate receptors and voltage-gated Ca2+ channels. Addition of 2-aminoethoxydiphenyl borate, an inhibitor of transient receptor potential melastatin 7 (TRPM7) channels, or the use of TRPM7-small interference RNA, protected the neurons from H2O2 injury. In contrast, overexpressing TRPM7 channels in human embryonic kidney 293 cells increased H2O2 injury. Our findings indicate that H2O2 can induce Ca2+ toxicity independent of glutamate receptors and voltage-gated Ca2+ channels. Activation of TRPM7 channels is involved in such toxicity. Antioxid. Redox Signal. 14, 1815-1827.