Mechanism of okadaic acid-induced neuronal death and the effect of estrogens.
Serine/threonine protein phosphatases are important mediators of general cellular function as well as neurodegenerative processes. We have previously shown inhibition of protein phosphatases to be as neurotoxic as glutamate-induced neuronal death but resistant to neuroprotection by estrogens. In this study, the mechanism by which phosphatase inhibition via okadaic acid (OA) induced neurotoxicity is explored. Neurons were exposed to OA or glutamate in the presence or absence of various protein kinases inhibitors, and/or one of four estrogens. Both OA and glutamate induced cell death via increased reactive oxygen species, protein carbonylation, lipid peroxidation, caspase-3 activity, and mitochondrial dysfunction. All estrogens attenuated glutamate-mediated responses, but not OA-induced responses. In addition, inhibition of protein kinase C and mitogen-activated protein kinase pathway was neuroprotective against glutamate but not OA toxicity. Interestingly, inhibition of mitogen-activated protein kinase pathway with PD98096 or U0126 caused a decrease in reactive oxygen species production suggesting that activation of ERK1/2 could further exacerbate the oxidative stress caused by glutamate-induced toxicity; however, these inhibitors had no effect on OA-induced toxicity. Collectively, these results indicate that both glutamate and OA neurotoxicities are mediated by persistent activation of ERK1/2 and/or protein kinase C and a resulting oxidative stress, and that protein phosphatase activity is an important and necessary aspect of estrogen-mediated neuroprotection.
Yi
Kun Don
KD
Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX 76107, USA.
Covey
Douglas F
DF
Simpkins
James W
JW
D000818:Animals; D053148:Caspase 3 / Q000378:metabolism; D053179:Caspase 7 / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects*; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000187:drug effects; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004967:Estrogens / Q000494:pharmacology*; D005260:Female; D018698:Glutamic Acid / Q000633:toxicity; D015227:Lipid Peroxidation / Q000187:drug effects; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D009474:Neurons / Q000187:drug effects*; D018696:Neuroprotective Agents; D019319:Okadaic Acid / Q000633:toxicity*; D011247:Pregnancy; D050050:Protein Carbonylation / Q000187:drug effects; D051381:Rats; D017382:Reactive Oxygen Species; D013778:Tetrazolium Salts; D013844:Thiazoles
D004791:Enzyme Inhibitors; D004967:Estrogens; D018696:Neuroprotective Agents; D017382:Reactive Oxygen Species; D013778:Tetrazolium Salts; D013844:Thiazoles; D019319:Okadaic Acid; D018698:Glutamic Acid; D020928:Mitogen-Activated Protein Kinases; D053148:Caspase 3; D053179:Caspase 7; C022616:thiazolyl blue