Methylmercury alters the activities of Hsp90 client proteins, prostaglandin E synthase/p23 (PGES/23) and nNOS.
Methylmercury (MeHg) is a persistent pollutant with known neurotoxic effects. We have previously shown that astrocytes accumulate MeHg and play a prominent role in mediating MeHg toxicity in the central nervous system (CNS) by altering glutamate signaling, generating oxidative stress, depleting glutathione (GSH) and initiating lipid peroxidation. Interestingly, all of these pathways can be regulated by the constitutively expressed, 90-kDa heat shock protein, Hsp90. As Hsp90 function is regulated by oxidative stress, we hypothesized that MeHg disrupts Hsp90-client protein functions. Astrocytes were treated with MeHg and expression of Hsp90, as well as the abundance of complexes of Hsp90-neuronal nitric oxide synthase (nNOS) and Hsp90-prostaglandin E synthase/p23 (PGES/p23) were assessed. MeHg exposure decreased Hsp90 protein expression following 12 h of treatment while shorter exposures had no effect on Hsp90 protein expression. Interestingly, following 1 or 6 h of MeHg exposure, Hsp90 binding to PGES/p23 or nNOS was significantly increased, resulting in increased prostaglandin E2 (PGE2) synthesis from MeHg-treated astrocytes. These effects were attenuated by the Hsp90 antagonist, geldanmycin. NOS activity was increased following MeHg treatment while cGMP formation was decreased. This was accompanied by an increase in •O2- and H2O2 levels, suggesting that MeHg uncouples NO formation from NO-dependent signaling and increases oxidative stress. Altogether, our data demonstrates that Hsp90 interactions with client proteins are increased following MeHg exposure, but over time Hsp90 levels decline, contributing to oxidative stress and MeHg-dependent excitotoxicity.
Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York, United States of America.
Samuel
S
Caito
Department of Pediatrics, Vanderbilt University School of Medicine, Nashville, Tennessee, United States of America.
Heng
H
Zeng
Department of Pediatrics and Obstetrics & Gynecology and Women's Health, Albert Einstein College of Medicine of Yeshiva University and Children's Hospital at Montefiore, Bronx, New York, United States of America.
Judy L
JL
Aschner
Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York, United States of America; Department of Pediatrics, Vanderbilt University School of Medicine, Nashville, Tennessee, United States of America; Department of Pediatrics and Obstetrics & Gynecology and Women's Health, Albert Einstein College of Medicine of Yeshiva University and Children's Hospital at Montefiore, Bronx, New York, United States of America; The Kennedy Center, Albert Einstein College of Medicine, Bronx, New York, United States of America.
Michael
M
Aschner
D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism*; D019746:Intramolecular Oxidoreductases / Q000378:metabolism*; D008767:Methylmercury Compounds / Q000633:toxicity*; D052248:Nitric Oxide Synthase Type I / Q000378:metabolism*; D000071876:Prostaglandin-E Synthases; D051381:Rats; D017207:Rats, Sprague-Dawley
D018841:HSP90 Heat-Shock Proteins; D008767:Methylmercury Compounds; D052248:Nitric Oxide Synthase Type I; D019746:Intramolecular Oxidoreductases; D000071876:Prostaglandin-E Synthases