Chlorpyrifos induces apoptosis in rat cortical neurons that is regulated by a balance between p38 and ERK/JNK MAP kinases.
Chlorpyrifos, an acetylcholinesterase (AChE) inhibitor, is a widely used organophosphate pesticide. Recent concern has focused on its neurotoxicity that is not attributable to AChE inhibition. Here, we report that chlorpyrifos and chlorpyrifos-oxon, but not 3,5,6-trichloro-2-pyridinol (TCP; the breakdown product of chlorpyrifos and chlorpyrifos-oxon), induce apoptosis in primary cortical neurons cultured from embryonic day 17 or newborn rats. It is generally agreed that chlorpyrifos-oxon is approximately three orders of magnitude more potent than chlorpyrifos in inhibition of brain acetylcholinesterase activity. However, our data demonstrate that chlorpyrifos-oxon is only slightly more potent than chlorpyrifos in inducing apoptosis. This indicates that chlorpyrifos-induced apoptosis may occur independently of AChE inhibition, although AChE activity was not measured in this study. Furthermore, chlorpyrifos activates the ERK1/2 and p38 MAP kinases. Surprisingly, blocking ERK1/2 activation by the MEK inhibitor SL327 caused a small but statistically significant inhibition of apoptosis, while blocking p38 with SB202190 significantly accelerated apoptosis induced by chlorpyrifos. This suggests a pro- and anti-apoptotic role for ERK1/2 and p38, respectively. Although chlorpyrifos did not stimulate total JNK activity, it caused a sustained activation of a sub-pool of JNK in the nucleus and stimulated phosphorylation of c-Jun, a downstream target of JNK. Transient expression of a dominant negative c-Jun mutant inhibited chlorpyrifos-induced apoptosis, suggesting a role for JNK and JNK-mediated transcription in this cell death. Together, our data suggest apoptosis as a novel toxic endpoint of chlorpyrifos neurotoxicity in the brain that may be independent of AChE inhibition. Furthermore, activation of the ERK1/2 and JNK MAP kinases contributes to, while activation of the p38 MAP kinase counteracts chlorpyrifos-induced apoptosis in cortical neurons.
Caughlan
Anne
A
Toxicology Program in the Department of Environmental and Occupational Health Sciences, University of Washington, Seattle, Washington 98195-7234, USA.
Newhouse
Kathleen
K
Namgung
Uk
U
Xia
Zhengui
Z
D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D002467:Cell Nucleus / Q000187:drug effects / Q000648:ultrastructure; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology* / Q000187:drug effects; D004390:Chlorpyrifos / Q000031:analogs & derivatives* / Q000633:toxicity*; D004622:Embryo, Mammalian / Q000166:cytology / Q000502:physiology; D005260:Female; D006540:Herbicides / Q000633:toxicity; D007150:Immunohistochemistry; D007306:Insecticides / Q000633:toxicity*; D048031:JNK Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases / Q000235:genetics*; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics*; D009474:Neurons / Q000187:drug effects*; D011247:Pregnancy; D016755:Proto-Oncogene Proteins c-jun / Q000096:biosynthesis; D011728:Pyridones / Q000633:toxicity; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects; D013778:Tetrazolium Salts; D013844:Thiazoles; D014162:Transfection; D048051:p38 Mitogen-Activated Protein Kinases
D006540:Herbicides; D007306:Insecticides; D016755:Proto-Oncogene Proteins c-jun; D011728:Pyridones; D013778:Tetrazolium Salts; D013844:Thiazoles; C009618:O,O-diethyl O-3,5,6-trichloro-2-pyridyl phosphate; C012587:3,5,6-trichloro-2-pyridinol; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases; C022616:thiazolyl blue; D004390:Chlorpyrifos