In utero bisphenol A exposure disturbs germ cell cyst breakdown through the PI3k/Akt signaling pathway and BDNF expression

Abstract

Purpose: To determine the influence of the environmental endocrine disruptor bisphenol A (BPA) on germ cell cyst breakdown and explore the possible mechanisms regulating this activity.

Methods: BPA (2 μg/kg/d or 20 μg/kg/d) or tocopherol-stripped corn oil (vehicle control) was administered to pregnant mice by gavage at gestational day 11, and the offspring (prenatally treated mice) were sacrificed and ovariectomized at postnatal day (PND) 4 and PND22. Ovarian morphology was documented in the first filial (F1) generation female offspring, and the follicles were analyzed and classified morphologically on PND 4. To discover differentially expressed genes and associated target pathways, we used RNA-seq, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, and Gene Ontology (GO) analysis. The mRNA expression of key steroid hormone synthesis-related genes was evaluated by Q-PCR in forskolin-induced KGN cells. Western blotting (WB) and qRTPCR were used to determine the protein and gene expression levels of brain-derived neurotrophic factor (BDNF).

Results: BPA, a typical endocrine disrupting chemical (EDC), decreased the expression of the key steroid hormone synthesis-related genes P450scc and aromatase, while the expression of Star increased significantly and caused no significant difference in the expression of Cyp17a1 or HSD3β in forskolin-induced KGN cells. Moreover, we confirmed that in utero exposure to environmentally relevant concentrations of BPA (2 μg/kg/d and 20 μg/kg/d) could significantly disrupt germ cell cyst breakdown, leading to the generation of fewer primordial follicles than in the control group. The factors mediating the inhibitory effects included the PI3K-Akt signaling pathway and a significant downregulation of BDNF.

Conclusions: These findings indicate that in utero exposure to BPA at low doses, which are lower than recommended as 'safe' dosages, may influence the formation of primordial follicles by inhibiting the expression of steroid hormone synthesis-related genes and partly by regulating the BDNF-mediated PI3K/Akt pathway.

Keywords: Bisphenol A (BPA); Brain-derived neurotrophic factor; Ovarian function; PI3K/Akt; Primordial follicle pool; Steroidogenic enzyme.