Granulosa Cell-Secreted KITL Is Involved in Maintaining Zinc Homeostasis in the Oocytes of Neonatal Mouse Ovaries.

Proto-oncogenic receptor tyrosine kinase (KIT) ligand (KITL) secreted by granulosa cells and its receptor KIT on oocytes are crucial for primordial follicle formation and activation, and follicular development. In the present study, ZnSO(4) decreased the number of primordial and growing follicles in cultured neonatal mouse ovaries when KITL-KIT signaling was inhibited by ISCK03. ZnSO(4) also significantly increased the mRNA and protein levels of Zrt/Irt-like protein 6 (ZIP6, a zinc importer) and zinc levels in the oocytes of cultured neonatal mouse ovaries in the presence of ISCK03, suggesting that the increase in ZIP6 levels results in zinc overload in the oocytes of cultured neonatal mouse ovaries. Further experiments indicated that zinc overload resulted in oocyte apoptosis in cultured neonatal mouse ovaries via oxidative stress-driven dual mechanisms: irreversible DNA damage in the nucleus and autophagic flux blockade in the cytoplasm of oocytes. Moreover, the intraperitoneal injection of ZnSO(4) and ISCK03 significantly increased ZIP6 expression, DNA damage, autophagic flux blockade, and apoptosis of oocytes in neonatal mice. Taken together, these findings indicate that granulosa cell-secreted KITL is involved in maintaining zinc homeostasis in the oocytes of neonatal mouse ovaries. This study not only reveals a novel function of granulosa cells in supporting oocyte homeostasis, but also provides a theoretical basis for identifying individuals susceptible to zinc dyshomeostasis caused by the impaired KITL-KIT signaling.