Involvement of FoxO1 in the effects of follicle-stimulating hormone on inhibition of apoptosis in mouse granulosa cells.

M Shen,Y Teng,B Li,H Liu,Z Liu,S-C Sun,Y Tang,J Zhang

doi:10.1038/cddis.2014.400

Abstract

In mammalian ovaries, follicular atresia occurs periodically and destroys almost all the follicles in the ovary. Follicle-stimulating hormone (FSH) acts as the primary survival factor during follicular atresia by preventing apoptosis in granulosa cells. FoxO1 is a critical factor in promoting follicular atresia and granulosa cell apoptosis. FSH inhibits the induction of FoxO1. In this report, we investigated the role of FSH-FoxO1 pathway in mouse follicular atresia. FSH dampened stress-induced apoptosis and the expression of FoxO1 and pro-apoptosis genes in mouse granulosa cells (MGCs). In contrast, overexpression of FoxO1 inhibited the viability of MGCs and induced the expression of endogenous FoxO1. The signaling cascades involved in regulating FoxO1 activity upon FSH treatment were identified using FSH signaling antagonists. Blocking protein kinase A (PKA), phosphatidylinositol-3 kinase (PI3K) or protein kinase B (AKT) restored the upregulation of FoxO1 and apoptotic signals, which was suppressed by FSH. Moreover, inhibition of PKA or PI3K impaired FSH-induced AKT activity, but inactivation of PI3K or AKT had little effect on PKA activity in the presence of FSH. Correspondingly, constitutive activation of FoxO1 (all three AKT sites were replaced by alanines) also promoted MGC apoptosis despite FSH administration. Furthermore, both luciferase reporter assays and chromatin immunoprecipitation assays showed that FoxO1 directly bound to a FoxO-recognized element site within the FoxO1 promoter and contributed to the regulation of FoxO1 expression in response to FSH. Taken together, we propose a novel model in which FSH downregulates FoxO1-dependent apoptosis in MGCs by coordinating the PKA–PI3K–AKT–FoxO1 axis and FoxO1–FoxO1 positive feedback.

Highlights

( known as premature menopause), leading to infertility in women.[2,3] Previous studies have demonstrated a close relationship between follicular atresia and granulosa cell apoptosis in which DNA fragmentation, activation of caspases and upregulation of pro-apoptotic gene expression are seen.[4]
Our results suggested a primary role for FoxO1 inhibition of FSHinduced mouse granulosa cells (MGCs) survival through coordination of the protein kinase A (PKA)– phosphatidylinositol-3 kinase (PI3K)–AKT–FoxO1 axis and FoxO1–FoxO1 positive feedback
Using hematoxylin and eosin (H&E) staining, we detected the effects of follicle-stimulating hormone (FSH) on follicular atresia under the same conditions

Summary

Introduction

( known as premature menopause), leading to infertility in women.[2,3] Previous studies have demonstrated a close relationship between follicular atresia and granulosa cell apoptosis in which DNA fragmentation, activation of caspases and upregulation of pro-apoptotic gene expression are seen.[4]. A recent study in the ovary suggests a potential function for FoxO1 in follicular development.[22] An immunohistochemical assay demonstrated the centralization and nuclear distribution of FoxO1 staining in rat granulosa cells from atretic follicles.[23] FoxO1 inhibits proliferation and steroidogenesis in mouse granulosa cells (MGCs), which may further induce apoptosis and follicular atresia. FSH upregulates the expression of genes involved in cell proliferation and estrogen production, promotes follicular growth, and decreases granulosa cell apoptosis.[24] The opposing activities of FoxO1 and FSH on follicular development and granulosa cell survival imply a reciprocal inhibition between these two factors in the ovary. Our results suggested a primary role for FoxO1 inhibition of FSHinduced MGC survival through coordination of the PKA– phosphatidylinositol-3 kinase (PI3K)–AKT–FoxO1 axis and FoxO1–FoxO1 positive feedback

Methods

Results

Conclusion