Promotion of ovarian follicle growth following mTOR activation: synergistic effects of AKT stimulators.

Yuan Cheng,Jaehong Kim,Xiao Xiao Li,Aaron J. Hsueh,Wei Yan

doi:10.1371/journal.pone.0117769

Abstract

Mammalian target of rapamycin (mTOR) is a serine/threonine kinase and mTOR signaling is important in regulating cell growth and proliferation. Recent studies using oocyte- and granulosa cell-specific deletion of mTOR inhibitor genes TSC1 or TSC2 demonstrated the important role of mTOR signaling in the promotion of ovarian follicle development. We now report that treatment of ovaries from juvenile mice with an mTOR activator MHY1485 stimulated mTOR, S6K1 and rpS6 phosphorylation. Culturing ovaries for 4 days with MHY1485 increased ovarian explant weights and follicle development. In vivo studies further demonstrated that pre-incubation of these ovaries with MHY1485 for 2 days, followed by allo-grafting into kidney capsules of adult ovariectomized hosts for 5 days, led to marked increases in graft weights and promotion of follicle development. Mature oocytes derived from MHY1485-activated ovarian grafts could be successfully fertilized, leading the delivery of healthy pups. We further treated ovaries with the mTOR activator together with AKT activators (PTEN inhibitor and phosphoinositol-3-kinase stimulator) before grafting and found additive enhancement of follicle growth. Our studies demonstrate the ability of an mTOR activator in promoting follicle growth, leading to a potential strategy to stimulate preantral follicle growth in infertile patients.

Highlights

Mammalian ovaries consist of follicles as basic functional units
MHY1485 treatment increased the phosphorylation of downstream S6K1 and ribosomal protein S6 (rpS6) proteins without affecting total S6K1 and rpS6 levels. These findings demonstrate the ability of MHY1485 to stimulate the Mammalian target of rapamycin (mTOR) signaling pathway in the ovary
Our studies demonstrated the ability of an mTOR activator to stimulate the phosphorylation of mTOR and downstream proteins, to enhance secondary follicle growth in ovarian explant cultures, and to promote the generation of antral/preovulatory follicles in allografts

Summary

Introduction

Mammalian ovaries consist of follicles as basic functional units. During initial recruitment of follicles, unknown intraovarian mechanisms stimulate or release a small number of dormant primordial follicles to initiate growth [1]. Once entering the growing pool, ovarian follicles mature through primary, secondary, and antral stages to become preovulatory follicles containing mature oocytes [2]. Mammalian target of rapamycin (mTOR) is a serine/threonine kinase conserved from flies to mammals and part of the multi-protein mTORC1 complexes. Under the influence of nutritional factors, stress, oxygen, energy and other signals, the rapamycin-sensitive mTORC1 complex positively regulates cell growth and proliferation by promoting diverse anabolic processes, including biosynthesis of proteins, lipids and organelles, and by limiting.

Methods

Results

Conclusion