Regulation of Smad2/3 Nuclear Exclusion by Follicle-Stimulating Hormone (FSH) in Chicken Follicular Granulosa Cells and Its Effect on FOXO3/4.

Abstract

Background: This study aims to investigate the regulation of small mothers against decapentaplegic 2 and 3 (Smad2/3) protein phosphorylation and nuclear exclusion in follicular granulosa cells (GCs) by chicken follicle-stimulating hormone (FSH) through the phosphatidylinositol 3-kinase (PI3K) signaling pathway, as well as the effect of Smad2/3 proteins on forkhead box O 3 and 4 (FoxO3/4). This lays the foundation for exploring the regulatory functions of signaling pathways closely related to follicular growth and development, as well as the molecular mechanisms of subcellular localization and nuclear exclusion of various effector factors (including transcription factors).

Methods: In this study, we used granulosa cells from 6-8 mm prehierachical follicles of chickens and performed immunofluorescence, quantitative real-time PCR (RT-qPCR), and Western blotting analysis to detect the phosphorylation and nuclear exclusion of Smad2/3 induced by FSH, as well as the regulatory effect of Smad2/3 on FOXO3/4 proteins.

Results: The results showed that 10 ng/mL FSH and 50 μg/mL PI3K activator significantly reduced the phosphorylation level of Smad2/3 (p < 0.05), while no nuclear exclusion was observed. On the other hand, 16 nM/mL PI3K inhibitor and 50 μg/mL alkaline phosphatase significantly increased the phosphorylation level of Smad2/3 (p < 0.05). Overexpression of Smad2/3 increased the phosphorylation level of FOXO3/4 (p < 0.05); Smad2/3 interference resulted in a decrease in FOXO3/4 phosphorylation levels (p < 0.05).

Conclusions: FSH can inhibit Smad2/3 phosphorylation and retain it in the nucleus through the PI3K signaling pathway. Smad2/3 and FOXO3/4 act as downstream effectors of the PI3K signaling pathway, and Smad2/3 can promote the phosphorylation of FOXO3/4.