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Mechanism of Kemeng Fang's Inhibition of Podocyte Apoptosis in Rats with Membranous Nephropathy through the PI3K/AKT Signaling Pathway
Published on: August 23, 2024
Cross-talk between the Akt and NF-kappaB signaling pathways inhibits MEHP-induced germ cell apoptosis
Rachel Rogers1, Gregory Ouellet, Caitlin Brown
1The Center for Environmental Studies, Department of Pathology and Laboratory Medicine, Brown University, Providence, Rhode Island 02912, USA.
Abstract:
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.
Insights
Mono-(2-ethylhexyl) phthalate (MEHP) exposure increases testicular Akt kinase activity. Loss of Akt1 leads to premature germ cell apoptosis, indicating Akt1
Area of Science:
- Reproductive Toxicology
- Molecular Biology
- Cell Signaling
Background:
- Phthalates are widespread environmental contaminants impacting male reproductive development.
- The PI3K/Akt and NF-kappaB signaling pathways are crucial for germ cell survival after testicular damage.
Purpose of the Study:
- To investigate the role of Akt1 in protecting germ cells from mono-(2-ethylhexyl) phthalate (MEHP)-induced apoptosis.
- To explore the cross-talk between PI3K/Akt and NF-kappaB signaling pathways in response to MEHP exposure.
Main Methods:
- Assessed Akt kinase activity in wild-type mouse testes post-MEHP exposure.
- Utilized Akt1-deficient mice to evaluate germ cell apoptosis and signaling pathway alterations.
- Measured oxidative stress markers and expression of key apoptotic and anti-apoptotic proteins (e.g., I kappaB alpha, p50, p65, SMAC/DIABLO, Bcl-xL).
Main Results:
- MEHP exposure increased Akt kinase activity and Akt1-dependent phosphorylation of I kappaB alpha in wild-type testes.
- Akt1 deficiency resulted in elevated basal expression of NF-kappaB subunits (p50, p65) and increased oxidative stress.
- MEHP-induced Akt1 activation promoted transcription of the anti-apoptotic gene Bcl-xL.
Conclusions:
- Akt1 plays a protective role against MEHP-induced germ cell apoptosis in developing testes.
- This protective effect involves cross-talk with the NF-kappaB pathway and modulation of oxidative stress.
- Findings highlight Akt1 as a critical mediator in testicular response to phthalate exposure.
