Continuous cadmium exposure from weaning to maturity induces downregulation of ovarian follicle development-related SCF/c-kit gene expression and the corresponding changes of DNA methylation/microRNA pattern

Abstract

Cadmium (Cd) impairs ovary structure and function in mature animals. However, the influence of Cd on follicle development from weaning to maturity is obscure. In the current study, 21-day-old Wistar rats were administered Cd chloride at doses of 0, 0.5, 2.0 and 8.0mg/kg body weight once a day for eight weeks by gavage. After administration, a significant decrease in ovarian wet weight, ovarian/body weight ratios, and primordial follicles, in addition to an increase in atresic follicles, were observed. Transmission electron microscopy and TUNEL assay confirmed the increase of follicle apoptosis as Cd concentration increased. Real-time quantitative PCR and Western blotting showed a significantly decreased expression of follicle development-related factors, stem cell factor (SCF) and c-kit. Bisulfite sequencing suggested that the total methylation percentages of SCF/c-kit promoter region were not obvious change after Cd exposure. Real-time quantitative PCR revealed a significantly increased expression of miR-193, miR-221 and miR-222, which regulate c-kit, in the 2.0mg/kg and 8.0mg/kg treatment groups. Overall, this study proved that Cd administration from weaning to maturity could damage follicle development, suggesting that SCF/c-kit might play an important role in this effect. In addition, microRNAs might play a role in c-kit protein downregulation.