ToxSci Advance Access published online on August 28, 2008
Toxicological Sciences, doi:10.1093/toxsci/kfn186
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Crosstalk between the Akt and NF
B signaling pathways inhibits MEHP-induced germ cell apoptosis
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* The Center for Environmental Studies
Department of Pathology and Laboratory Medicine, Brown University, Providence, Rhode Island, 02912
1 To whom correspondence should be addressed: Mary L. Hixon, Ph.D., GE505, Department of Pathology and Laboratory Medicine, Brown University; Providence, Rhode Island 02912, Phone: 401-863-6112; Fax 401-863-9008; e-mail: Mary_Hixon{at}Brown.edu
Received June 3, 2008; revision received August 22, 2008; accepted August 25, 2008
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Abstract |
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Phthalates are ubiquitous contaminants that target the testis during in utero and postnatal development. The PI3K/Akt and NF
B signaling pathways have been implicated in germ cell survival following testicular injury. Here we observe that Akt kinase activity increases in the testes of postnatal day 28 wild-type mice following exposure to 500 mg/kg MEHP, and that loss of Akt1 results in the premature onset of germ cell apoptosis. To further determine the basis for this sensitivity, we investigated the potential for crosstalk between the PI3K/Akt and NF-B signaling pathways. We found a two-fold increase in Akt1-dependent phosphorylation of the IB
subunit following exposure to 500 mg/kg MEHP and decreased levels of the total IB protein. Examination of the expression of the NF-B subunits, p50 and p65, in Akt1 wild type testes following MEHP exposure revealed a 2-fold increase in p50 mRNA at 6 hours. Interestingly, in Akt1-deficient testes, basal expression of both the p50 and p65 subunits was elevated 1.6- and 4- fold, respectively. This was due, at least in part, to increased levels of oxidative stress as measured by both superoxide anion formation and increased expression of SMAC/DIABLO, a pro-apoptotic mitochondrial protein. In wild type testes, MEHP induced Akt1-dependent transcription of the anti-apoptotic mitochondrial target gene, Bcl-xL. Together, these results indicate that Akt1 plays a role in the initial protection of germ cells following MEHP-induced germ cell apoptosis and that this response is partially mediated by crosstalk with the NF-B signaling pathway and an increased sensitivity to oxidative stress.
Key Words: Akt1; NF-B; germ cell; Sertoli cell; phthalates; MEHP; oxidative stress.