Research Paper Volume 13, Issue 1 pp 1096—1119

The endothelial nitric oxide synthase/cyclic guanosine monophosphate/protein kinase G pathway activates primordial follicles

Peikun Zhao1, , Zidai Song1, , Yan Wang1, , Han Cai2, , Xiaoyan Du1, , Changlong Li1, , Jianyi Lv1, , Xin Liu1, , Meng Guo1, , Zhenwen Chen1, ,

  • 1 Beijing Key Laboratory of Cancer Invasion and Metastasis Research, School of Basic Medical Sciences, Capital Medical University, Beijing, People’s Republic of China
  • 2 Fujian Provincial Key Laboratory of Reproductive Health Research, Medical College of Xiamen University, Xiamen, Fujian, China

Received: May 2, 2020       Accepted: October 20, 2020       Published: December 3, 2020
How to Cite

Copyright: © 2020 Zhao et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.


In mammals, the well-organized activation of quiescent primordial follicles is pivotal for female reproductive reserve. In the present study, we examined the mechanisms underlying primordial follicle activation in mice. We found that endothelial nitric oxide synthase (eNOS) and its downstream effectors, cyclic guanosine monophosphate (cGMP) and cGMP-dependent protein kinase G (PKG), were expressed in pre-granulosa cells and promoted primordial follicle activation, oocyte growth and granulosa cell proliferation in neonatal ovaries. Mammalian target of rapamycin (mTOR) colocalized with PKG in pre-granulosa cells and was essential for eNOS/cGMP/PKG pathway-induced primordial follicle activation. The eNOS/cGMP/PKG pathway was found to stabilize mTOR protein. The mRNA levels of F-box and WD repeat domain containing 7 (FBXW7), an E3 ubiquitin ligase, correlated negatively with mTOR protein levels in neonatal ovaries. FBXW7 bound to and destabilized mTOR protein in pre-granulosa cells in a ubiquitin/proteasome-dependent manner. However, agonists of the eNOS/cGMP/PKG pathway reduced FBXW7 mRNA levels. FBXW7 overexpression suppressed primordial follicle activation and prevented the eNOS/cGMP/PKG pathway from activating primordial follicles and stabilizing mTOR protein. These findings demonstrate that the eNOS/cGMP/PKG pathway activates primordial follicles by suppressing FBXW7-induced ubiquitination of mTOR in mice.


PF: primordial follicle; GF: growing follicle; preGC: pre-granulosa cell; dpp: days post-partum; POI: primary ovarian insufficiency; eNOS: endothelial nitric oxide synthase; iNOS: inducible nitric oxide synthase; nNOS: neuronal nitric oxide synthase; NO: nitric oxide; sGC: soluble guanylate cyclase; cGMP: cyclic guanosine monophosphate; PKG: cGMP-dependent protein kinase G; mTOR: mammalian target of rapamycin; FBXW7: F-box and WD repeat domain containing 7; FOXO3a: forkhead box O3a; MSY2: the germline marker Y box protein 2; rpS6: ribosomal protein S6; cAMP: cyclic adenosine monophosphate; NFκB: nuclear factor κB; Mcl-1: the Bcl-2 family member myeloid cell leukemia sequence 1.