Abstract
Peroxynitrite-mediated damage has been linked to numerous neurological and neurodegenerative diseases, including stroke, Alzheimer's and Parkinson's Diseases, amyotrophic lateral sclerosis and multiple sclerosis. Studies on the toxic effects of peroxynitrite in neurons have focused primarily on adverse effects resulting from the nitration of cellular proteins as the principal mode of toxicity while the consequences of the modulation of kinase pathways by peroxynitrite have received relatively less attention. Our results show that treatment of primary rat neurons with the peroxynitrite donor, SIN-1, leads to decreases in glutathione (GSH) levels and cell viability via a novel extracellular-signal-related kinase (ERK)/c-Myc phosphorylation pathway and a reduction in the nuclear expression of NF-E2-related factor-2 (Nrf2) that down-regulate the expression of glutamate cysteine ligase, the rate limiting enzyme for GSH synthesis. The flavonoid fisetin protects against the SIN-1-mediated alterations in ERK/c-Myc phosphorylation, nuclear Nrf2 levels, glutamate cysteine ligase levels, GSH concentration and cell viability. We also show that inhibition of mitogen-activated protein kinase kinase or Raf kinase can increase GSH levels in unstressed primary rat neurons through the same ERK/c-Myc phosphorylation pathway. Together, these results demonstrate that distinct signaling pathways modulate GSH metabolism in unstressed and stressed cortical neurons.