Continuous gibberellin A3 exposure from weaning to sexual maturity induces ovarian granulosa cell apoptosis by activating Fas-mediated death receptor signaling pathways and changing methylation patterns on caspase-3 gene promoters

Abstract

Information on the effects of gibberellic acid (gibberellin A3, GA3) on ovarian follicle development is limited. In our present study, 21-day-old female Wistar rats were exposed to GA3 by gavage (25, 50, and 100 mg/kg body weight, once per day) for eight weeks to evaluate the influence of GA3 on ovarian follicle development. After treatment, significant (P < 0.05) increases (to 40.17 % and 44.5 %, respectively) in atretic follicle proportions and significant decreases (to 19.49 % and 17.86 %, respectively) in corpus luteum proportions were observed in the 50 and 100 mg/kg treatment groups compared to the control group. Significant (P < 0.05) increases (to 31.3 % and 42.0 %, respectively) in follicle apoptosis were observed in the 50 and 100 mg/kg treatment groups by transmission electron microscopy and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assays. Significantly increased expression of caspase-3, caspase-8, caspase-9 and Fas was observed by real-time PCR and Western blotting. Bisulfite sequencing PCR (BSP) revealed obviously decreased total methylation percentages of the caspase-3 promoter region in the two treatment groups. Real-time quantitative PCR also showed significantly decreased mRNA expression of DNA methyltransferase (Dnmt) 3a and Dnmt3b. Further in vitro studies showed that a DNA methylation inhibitor could enhance the GA3-induced increase in the mRNA expression of caspase-3. Overall, our present study indicates that GA3 administration from weaning until sexual maturity can affect ovarian follicle development by inducing apoptosis and suggests that signaling through the Fas-mediated apoptotic pathway may be an important underlying mechanism of this apoptosis. In addition, GA3-induced aberrant DNA methylation patterns might be partly responsible for upregulation of caspase-3 gene expression.