Cross-talk between the Akt and NF-kappaB signaling pathways inhibits MEHP-induced germ cell apoptosis.
Phthalates are ubiquitous contaminants that target the testis during in utero and postnatal development. The PI3K/Akt and nuclear factor kappa B (NF-kappaB) 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 mono-(2-ethylhexyl) phthalate (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 cross-talk between the PI3K/Akt and NF-kappaB signaling pathways. We found a twofold increase in Akt1-dependent phosphorylation of the I kappaB alpha subunit following exposure to 500 mg/kg MEHP and decreased levels of the total I kappaB alpha protein. Examination of the expression of the NF-kappaB subunits, p50 and p65, in Akt1 wild-type testes following MEHP exposure revealed a twofold increase in p50 mRNA at 6 h. 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 proapoptotic mitochondrial protein. In wild-type testes, MEHP-induced Akt1-dependent transcription of the antiapoptotic 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 cross-talk with the NF-kappaB signaling pathway and an increased sensitivity to oxidative stress.
Rogers
Rachel
R
The Center for Environmental Studies, Department of Pathology and Laboratory Medicine, Brown University, Providence, Rhode Island 02912, USA.
Ouellet
Gregory
G
Brown
Caitlin
C
Moyer
Ben
B
Rasoulpour
Teresa
T
Hixon
Mary
M