The metallic compound promotes primordial follicle activation and ameliorates fertility deficits in aged mice

Abstract

Background: Aged women and premature ovarian insufficiency (POI) patients have residual dormant primordial follicles that are hard to be activated through a physiological process. However, there are no effective and safe drugs to help them. Methods: We used the in vitro culture model of newborn mouse ovaries to identify the drugs that promote primordial follicle activation and study its mechanisms. It was verified by in vivo injection model of newborn mice and in vitro culture model of human ovarian tissue. In addition, we used the aged mice as a low infertility model to verify the effects of primordial follicle activation, and fertility by drugs. Results: Eleven metallic compounds activated mouse primordial follicles, and the five most effective compounds were selected for further study. Thapsigargin (TG), CrCl₃, MnCl₂, FeCl₃ and ZnSO₄ increased the levels of the glycolysis-related proteins (glucose transporter type 4, GLUT4; hexokinase 1, HK1; pyruvate kinase M2, PKM2; phosphofructokinase, liver type, PFKL), phosphorylated mammalian target of rapamycin (p-mTOR) in cultured mouse ovaries. The compound-promoted p-mTOR levels could be completely blocked by 2-DG (the inhibitor of glycolysis). The compounds also increased the levels of phosphorylated protein kinase B (p-Akt). TG-, CrCl₃- and FeCl₃-promoted p-Akt levels, but not MnCl₂- and ZnSO₄- promoted p-Akt levels, could be completely blocked by ISCK03 (the inhibitor of proto-oncogenic receptor tyrosine kinase, KIT). The injection of newborn mice with the compounds also activated primordial follicles and increased the levels of the glycolysis-related proteins, p-mTOR, and p-Akt. The oral administration of the compounds in adolescent and aged mice promoted primordial follicle activation, and had no obvious side effect. Importantly, ZnSO₄ also increased ovulated oocytes, oocyte quality and offspring in aged mice. Furthermore, the compounds promoted human primordial follicle activation and increased the levels of the glycolysis-related proteins, p-mTOR, and p-Akt. Conclusion: The metallic compounds activate primordial follicles through the glycolysis-dependent mTOR pathway and/or the PI3K/Akt pathway, and the oral administration of ZnSO₄ enhances fertility in aged mice. We suggest that these metallic compounds may be oral drugs to ameliorate fertility deficits in aged women and POI patients.

Keywords: Akt; fertility; mTOR; metallic compounds; primordial follicle activation.